Best Practice & Research Clinical Anaesthesiology 28 (2014) 463e476
Contents lists available at ScienceDirect
Best Practice & Research Clinical Anaesthesiology journal homepage: www.elsevier.com/locate/bean
13
Impact of hemodynamic monitoring on clinical outcomes Emily A. Downs, MD, Resident a, James M. Isbell, MD, MSCI, Assistant Professor a, * a
Division of Thoracic and Cardiovascular Surgery, Department of Surgery, University of Virginia, Charlottesville, VA 22908, USA
Keywords: critical care hemodynamics/physiology monitoring, physiologic/methods outcome assessment perioperative care
In recent years, there has been a tremendous growth in available hemodynamic monitoring devices to support clinical decisionmaking in the operating room and intensive care unit. In addition to the “tried and true” heart rate and blood pressure monitors, there are several newer applications of existing technologies including arterial waveform analysis, intraoperative and bedside critical care echocardiography, esophageal Doppler, and tissue oximetry, among others. Several monitoring devices demonstrate positive effect on outcomes, especially when used in conjunction with specific goal-directed therapy protocols to achieve a desired clinical effect. Other devices remain in the validation stage, awaiting comprehensive comparison to established techniques. While these new technologies offer promising advances in intraoperative and critical care, they are often quite costly and many devices lack strong evidence for widespread adoption into clinical practice. In this review, we highlight the current data on clinical outcomes with the use of available hemodynamic monitoring devices. © 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. University of Virginia, P.O. Box 800679, Charlottesville, VA 22908, USA. Tel.: þ1 434 243 6443; Fax: þ1 434 244 9429. E-mail addresses: [email protected] (E.A. Downs), [email protected] (J.M. Isbell).
http://dx.doi.org/10.1016/j.bpa.2014.09.009 1521-6896/© 2014 Elsevier Ltd. All rights reserved.
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E.A. Downs, J.M. Isbell / Best Practice & Research Clinical Anaesthesiology 28 (2014) 463e476
Management of blood pressure Measurement of blood pressure is a historical standard for hemodynamic monitoring; the use of a simple fluid column to measure femoral arterial pressure in a horse constituted a very early monitoring device [1]. After numerous evolutionary steps, noninvasive blood pressure and arterial catheterization for continuous blood pressure monitoring remain in ubiquitous clinical use. The importance of maintaining adequate blood pressure is a well-accepted axiom. Fluid boluses and vasoactive agents are used routinely during surgery and postoperatively to maintain blood pressure and ensure that perfusion is adequate in the context of the physiologic stress of surgery. Conversely, maintaining blood pressure below specified thresholds is also sometimes important, such as to minimize myocardial oxygen demand or the risk of stroke. There is little published data describing ideal blood pressure parameters, and this is likely related to the heavy influence of anesthesiologist and surgeon experience and preference guiding intraoperative and postoperative blood pressure management. There have been recent efforts by Gawande et al. to delineate a scoring system for patients undergoing surgery to clarify a patient's condition and likelihood of major complications upon completion of a surgical procedure. This scoring system utilizes blood pressure as one of just three metrics. The surgical outcome score (referred to as the surgical Apgar score) uses lowest mean arterial pressure (MAP), estimated blood loss, and lowest heart rate during the procedure, with a clear increase in mortality for those receiving lower scores [2]. Regenbogen et al. examined records for 4119 patients undergoing general and vascular procedures and confirmed that the simple surgical Apgar score is predictive of both 30-day mortality and risk of postoperative complications [3]. These results underscore the importance of the fundamental hemodynamic parameters of intraoperative blood pressure and heart rate. Much of the scholarly work related to devices for monitoring of blood pressure is oriented toward validation or calibration of newer noninvasive blood pressure monitors as compared to the standard cuff pressure or arterial line measurement. There are several promising devices which use a variety of techniques to continuously measure blood pressure without the need for arterial catheterization, and each device has been found useful in some settings but compromised in others (e.g., critically ill patients, vasopressor use, awake/mobile patients as opposed to anesthetized patients, etc.). None of these devices has been studied with regard to their effects on outcomes. The importance of maintaining blood pressure within certain parameters is well understood in a general sense by anesthesiologists and surgeons, and the work of Gawande et al. and Regenbogen et al. confirms that intraoperative hypotension contributes to worsening outcomes when combined with bradycardia and blood loss as a surgical Apgar score. Newer generations of continuous, noninvasive blood pressure monitoring, while promising, have not been studied with respect to their impact on outcomes. Pulmonary artery catheterization Since the introduction of pulmonary artery catheterization by Swan et al., in 1970, this device has been used in a wide variety of clinical contexts. Pulmonary artery catheters (PACs) are utilized in critically ill patients with shock as well as in the preoperative, intraoperative, and postoperative settings. The device has been well studied with respect to clinical outcomes, both in retrospective analyses and in randomized controlled trials [4]. While some studies have shown benefit to pulmonary artery catheterization, several groups have found limited benefit with respect to the risk of complications from the device as well as misinterpretation of PAC data. The following sections will summarize the evidence behind PAC use in the intensive care unit (ICU) and in surgical populations. Pulmonary artery catheterization in the ICU PACs are used mainly in the ICU or in the operating room. Use of PACs in the medical ICU was examined by Mimoz et al. in a series of patients in a university hospital in France, with the goal of examining physicians' ability to predict hemodynamic profiles prior to PAC placement and follow subsequent clinical outcomes including change in therapy based on PAC measurements, complications
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from PAC, and mortality. The group found that physicians correctly predicted hemodynamic profiles in just 56% of the patients who received a PAC. They compared the group of patients who experienced a change in therapy based on PAC measurements and those who did not, and found a mortality benefit in those patients who did experience a change in therapy after pulmonary artery catheterization. The authors sought to study outcomes by following the manner PACs are often used in the ICU, namely as a method of guiding therapy when the patient's overall clinical picture is not completely clear from other hemodynamic indices [5]. After the Mimoz article was published in 1994, a group of five university hospitals published the results of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment (SUPPORT) investigators' work. This study examined decision-making processes and outcomes in ICU patients, with a particular focus on right heart catheterization in the first 24 h of an ICU stay. Outcomes included survival, length of stay, intensity of care, and cost of care. The group concluded that PAC use was associated with increased mortality and increased utilization of resources. This 1996 paper prompted editorials questioning whether clinicians should cease use of the PAC until additional studies were performed [6]. Another population in which PACs are frequently utilized is in the setting of severe congestive heart failure. Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE) study investigators sought to evaluate the use of PACs in patients with severe heart failure, examining outcomes including days alive and out of the hospital in the following 6 months. Their work was prompted by the controversy over PAC use, and the need to clarify utility of this device in specific populations. Patients from 26 heart failure centers in the USA and Canada were randomized to clinical assessment or clinical assessment plus PAC, and treated with vasodilators and diuretics (inotrope use was discouraged) to achieve relief from congestive symptoms. The authors found no difference in mortality or number of days out of the hospital. Like other investigators, the authors suggested that the PAC may be useful in some patients but routine use did not appear beneficial in comparison to the risks of invasive monitoring [7]. A 2006 study of PAC use in patients with severe trauma admitted to the ICU showed some potential benefit. Friese et al. performed a retrospective database analysis of patients in a national trauma database, adjusting for age, injury severity, and other factors. Of 53,312 patients in the database, 1933 were managed with a PAC. These patients were more likely to have more severe injuries and were older in age. Even after adjusting for a number of factors, the mortality rate was higher in the PAC group. However, the authors found improved outcomes with PAC use in patients who were older, had an arrival base deficit worse than 11, and an injury severity score between 25 and 75. They suggest that in the most severely injured patients or elderly patients with moderate shock, the PAC can provide useful guidance in resuscitation [8].
Pulmonary artery catheterization in surgical populations As a result of the controversy over PAC use, researchers have sought to demonstrate specific populations in which pulmonary artery catheterization may be useful. Tuman et al. followed up over 1000 cardiac surgery patients in a prospective, non-randomized study to elicit differences between PAC monitoring and central venous pressure (CVP) monitoring. They found no significant difference in length of ICU stay, occurrence of postoperative myocardial infarction, in-hospital death, or significant noncardiac complications [9]. Valentine et al. evaluated the routine use of PAC in aortic surgery, using a group of 120 patients who were admitted the evening prior to surgery and randomized to either placement of PAC in the ICU and fluid optimization, or admission to the ward without PAC. The researchers found that PAC patients received more intravenous (IV) fluids both preoperatively and postoperatively and had more intraoperative complications (18% in PAC group, 5% in controls, with p ¼ 0.02). Otherwise, no significant differences were seen [10]. Bender et al. similarly examined patients undergoing vascular surgery and randomized to PAC or no PAC with hemodynamic goals for pulmonary artery wedge pressure, cardiac index, and systemic vascular resistance. The PAC group received more IV fluids and there was no difference in complication rate, length of stay, mortality, or cost [11].
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Sandham et al. performed a randomized, controlled trial using the PAC to guide goal-directed therapy (GDT) in high-risk surgical patients. A total of 1994 patients considered high-risk due to age (60 or older) and American Society of Anesthesiologists (ASA) class (III or IV) were randomized to management with or without a PAC. The standard-care group was managed using typical ICU parameters and CVP measurement was allowed. The PAC group was managed with parameters for oxygen delivery, cardiac index, pulmonary capillary wedge pressure, heart rate, MAP, and hematocrit. The researchers found no benefit with PAC management in overall mortality, morbidity, or length of stay, and they also found no evidence of increased mortality in those randomized to PAC use [12]. Summary: Pulmonary artery catheterization The controversy surrounding PACs has led to numerous studies investigating the benefits and risks of this device in a variety of populations. While some benefit may be seen for patients with an unclear hemodynamic status, elderly trauma patients, and some select groups, most agree that routine use of PACs does not produce meaningful outcome benefit in mortality, morbidity, length of stay, or cost. Echocardiography Echocardiography is widely viewed as a useful diagnostic modality in patients in the operating room or the ICU. There is a significant body of work examining the feasibility and usefulness of echocardiography performed by intensivists, but only a few researchers have specifically studied the impact of echocardiography in the operative or critical care settings with respect to patient outcomes or cost-effectiveness. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) can be useful modalities when used in the appropriate setting. Impact of postoperative TTE or TEE on management Schmidlin et al. reviewed 301 TEE reports in patients after cardiac surgery. Their observational study found that in 73% of these cases, there was a therapeutic change made as a result of the TEE. These included change in fluid management, change in medications administered, resternotomy, or ability to defer a resternotomy by ruling out pathology. Patients undergoing postoperative TEE were found to have a higher mortality rate, but this was attributed to higher preoperative risk and increased complexity of operation [13]. Orme et al. examined the impact of both TEE and TTE on management of ICU patients. This group found that 51.2% of studies resulted in change in management. Of note, intensivists performed the majority of these echocardiograms (86.8%), and 72.4% were TTEs while 27.8% were TEEs. The authors pointed out that echocardiography can be useful when performed by non-cardiologists and that TTE continues to have a role in the ICU despite the increased difficulty in acquiring images in mechanically ventilated critically ill patients [14]. Intraoperative management with TEE Shillcutt et al. used echocardiography-derived parameters to guide hemodynamic management during noncardiac surgical procedures on patients with known left ventricular diastolic dysfunction. A variety of echocardiographic parameters were used to guide management of fluids and vasoactive agents, while the standard hemodynamic management group received therapies to maintain systolic blood pressure within 10e15% of the patient's baseline. Due to a limited number of patients, the feasibility of TEE examination and safety were the primary endpoints; secondary outcomes included fluids administered and 30-day postoperative complications (atrial fibrillation, congestive heart failure (CHF), myocardial infarction (MI), stroke, etc.). Patients monitored with TEE received less fluid intraoperatively. Measures of 30-day outcomes were not statistically significant but trended toward shorter hospital stay, lower incidence of CHF, and less atrial fibrillation in the patients managed with TEE parameters [15].
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Cost analysis of TTE and TEE in the ICU One difficulty in using TTE in critically ill patients is the lack of adequate acoustic windows in mechanically ventilated patients who may have dressings, lines, or other devices limiting access to the appropriate surface anatomy for echocardiographic exam. Cook et al. evaluated the failure rate of TTE in the surgical ICU setting and found that routine use of TTE with TEE as a secondary modality is not costeffective. The failure rate of TTE rises with patients receiving >15 cm H2O of positive end-expiratory pressure (PEEP), patients who have gained >10% body weight compared to admission weight, and those with chest tubes. The group found the lowest overall costs with TEE alone, and some cost-savings when TEE is used as the primary modality for patients at high-risk of TTE failure and TTE used for those at low risk of failure [16]. Summary: Echocardiography Echocardiography is a widely available modality that can be used in specific settings to answer questions about a patient's hemodynamic status. Use of TEE has shown initial success as an intraoperative monitoring device for patients with left ventricular diastolic dysfunction with a trend toward shorter hospital stay, lower incidence of CHF, and less atrial fibrillation postoperatively. In the setting of critically ill patients receiving high levels of PEEP and with significant increase in total fluid, use of TEE alone has been shown to be more cost-effective than trialing TTE prior to TEE in one study. Other than these studies, evidence is lacking in the use of TTE or TEE and impact on postoperative outcomes. Esophageal Doppler monitoring Esophageal Doppler monitoring (EDM) provides an assessment of stroke volume and cardiac output by measuring the Doppler signal of moving blood cells in the descending thoracic aorta. This is primarily used intraoperatively as it requires an intra-esophageal probe. To date, the device is used mainly in conjunction with goal-directed protocols to administer fluid and maximize stroke volume. EDM in patients undergoing femoral fracture fixation The earliest publication detailing EDM in surgical patients, by Sinclair et al., describes patients undergoing femoral fracture fixation. This relatively common procedure is performed on patients who are often frail with multiple comorbidities. Sinclair et al. published a randomized controlled trial of 40 patients undergoing fracture fixation with the control group receiving conventional fluid management and the intervention group receiving colloid fluid challenges to maintain maximal stroke volume as measured by EDM. The group found that patients receiving EDM experienced shorter time to being medically fit for discharge and a 39% reduction in-hospital stay compared to controls [17]. Venn et al. subsequently studied the same type of population, patients undergoing femoral fracture repair, and compared controls to EDM as well as a third group which received CVP monitoring. They found no difference in major morbidity or mortality, but did find shorter time to medical readiness for discharge in patients with CVP or EDM monitoring compared to controls. Both the CVP and EDM groups received more intraoperative fluids [18]. EDM in patients undergoing major abdominal/pelvic surgery or in trauma ICU Pillai et al. performed a prospective, randomized trial of patients undergoing radical cystectomy using EDM as compared to controls receiving fluids at the anesthesiologist's discretion. The researchers found that patients in the EDM group received more intraoperative fluids, and experienced decreased ileus and fewer infections. They did not demonstrate a reduction in length of stay, unlike the femoral fracture fixation studies [19]. Chytra et al. published the results of their randomized, controlled trial of 162 patients with multi-trauma. They also found that EDM patients received more colloid, and had fewer infectious complications. This paper did demonstrate shorter ICU and hospital stay for the trauma patients receiving EDM [20].
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EDM in patients undergoing abdominal surgery has led to numerous enhanced recovery programs (ERPs) due to encouraging results using EDM for fluid management in these patients. Gan et al. published the results of a randomized controlled trial of 100 patients undergoing major elective abdominal surgery and EDM monitoring. The control group experienced standard intraoperative care using fluids to maintain specified parameters for urine output, heart rate, blood pressure, and CVP while the EDM group received boluses to maintain maximum stroke volume. The EDM group received more intraoperative fluids and had a significantly shorter length of hospital stay (2 days shorter in the EDM group) [21]. This work was followed by Noblett et al. who studied patients undergoing elective colorectal surgery with similar control and EDM protocol groups. They found a shorter length of stay, shorter time to surgical fitness for discharge, and earlier diet tolerance. The control group had more complications requiring ICU admission. Interestingly, Noblett's control and EDM groups did not receive significantly different amounts of fluid during surgery or in the first 48 h after surgery [22]. Wakeling et al. randomized patients undergoing elective colorectal surgery to CVP (conventional) fluid management versus EDM protocol and also found significantly shorter length of stay by 1.5 days and shorter time to full diet in the EDM group, without significant difference in fluid administration [23]. Summary: EDM In summary, EDM with fluid administration protocol designed to maximize stroke volume intraoperatively has shown shorter length of stay in several studies, as well as improvements in diet tolerance in those undergoing abdominal surgery. This is made possible both in the setting of patients receiving more fluid than controls (as in femoral fracture fixation) and when the EDM patients receive a similar amount of fluid compared to controls. Arterial waveform analysis Several devices using analysis of arterial waveform to provide hemodynamic information are commercially available. PiCCO and LiDCO use thermodilution and lithium indicator dilution, respectively, to provide cardiac output measurements. These devices also use specific algorithms to estimate cardiac output from the arterial pressure waveform. The Vigileo FloTrac system uses the arterial waveform to calculate cardiac output, without requiring calibration. These devices have been studied with respect to outcomes mainly in conjunction with GDT protocols with promising results. Use of arterial waveform analysis in cardiac surgery patients Goepfert et al. published a 2007 paper describing goal-directed fluid management in cardiac surgery patients using PiCCO monitoring to optimize the global end-diastolic volume index (GEDVI). Forty patients undergoing coronary bypass grafting were prospectively studied and compared to historical controls. The group sought to maintain GEDVI above 640 mL/m [2], cardiac index above 2.5 L/min/m2, and MAP above 70 mmHg. The group was able to use fewer vasopressors, and the time for which patients were dependent on vasopressors was shorter in the intervention group. The GDT group also required shorter duration of mechanical ventilation, and patients were medically fit for ICU discharge sooner than the historical controls [24]. Kapoor et al. likewise studied cardiac surgery patients and used the FloTrac device to maintain specific parameters for CVP, and stroke volume variation (SVV). The study was fairly small, and showed trends toward shorter duration of mechanical ventilation, fewer days of inotrope use, and shorter ICU stay, but none of these reached statistical significance [25]. Arterial waveform analysis in patients undergoing major noncardiac surgery Jones et al. studied an ERP for patients undergoing open liver resection, using a comprehensive approach to patient education, pain management, and LiDCO-based GDT for fluid management in the first 6 h after surgery. The authors sought to determine whether this type of program could be successful in liver resection as promising results had already been demonstrated in colorectal resection. The group found that patients in the ERP experienced less time to medical fitness for discharge (3 vs. 6
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days) and shorter length of stay (4 vs. 7 days). There were also fewer complications in the ERP group [26]. Pearse et al. used LiDCO monitoring in a more varied general surgery population in a randomized, controlled, partly blinded study. Patients undergoing high-risk general surgery were randomized to conventional management versus goal-directed therapy to maintain oxygen delivery index >600 mL/ min * m2, as measured by the LiDCO device. A member of the research team administered the treatments in the intervention group during the first 8 h after surgery; this included fluid boluses and dopexamine to maintain the desired oxygen delivery index. The team found that the GDT group experienced fewer complications (44% vs. 68%), with a shorter overall hospital length of stay (median 11 vs. 14 days) [27]. Both of these studies demonstrate promising outcomes despite providing GDT for a limited time (6 h in one case, 8 h in the other). In an effort to strengthen the evidence related to arterial waveform analysis and its use in GDT, Pearse and colleagues for the Optimisation of Peri-operative cardiovascular Management to Improve Surgical Outcome (OPTIMISE) trial performed a 17-center, prospective, randomized controlled trial of GDT in high-risk patients undergoing major abdominal surgery. The study enrolled 734 patients, the largest trial to date, and the investigators sought to perform a pragmatic effectiveness trial and minimized bias by blinding clinicians and, where possible, study staff as well. As in Pearse's prior work, the LiDCO arterial waveform monitor was utilized. Patients received standard perioperative care, and the intervention group additionally received 250 mL colloid boluses to maintain maximum stroke volume as well as a continuous infusion of dopexamine at a standard dose unless heart rate increases required dose reduction or discontinuation. This was compared to usual care, with recommendation to consider CVP target. Pearse and colleagues found that there was no statistically significant difference in outcomes, including composite measure of 30-day moderate or major postoperative complications, infectious complications, or mortality at 30 or 180 days. The study investigators performed an updated meta-analysis with 6595 patients, including the 734 in the OPTIMISE trial, and found that GDT using arterial waveform analysis is associated with a reduced complication rate. The investigators felt that these findings continue to support GDT guided by arterial waveform analysis [28]. Summary: Arterial waveform analysis Arterial waveform analysis, like other technologies used to guide goal-directed fluid management, demonstrates promise in reducing hospital length of stay and reducing complications as compared to conventional management. Bioimpedance and bioreactance Bioimpedance offers a truly noninvasive approach to measurement of cardiac output, and has generated interest in comprehensive monitoring. One example of its use is very early in resuscitation, as in trauma patients in the emergency department. Shoemaker et al. have published several papers describing noninvasive hemodynamic monitoring, including bioimpedance measurement of cardiac output. In a 2007 paper, the group describes predicting outcome and providing therapeutic support for trauma patients in the first hour after admission, using their mathematical algorithm taking into account several noninvasive parameters. As many as 185 consecutive patients were monitored, and the authors found that their system was able to accurately predict survivors versus non-survivors. While the study did not measure the effect on outcome of using noninvasive monitoring, including bioimpedance, the eventual goal of the work is to use such decision-support algorithms to impact treatments and outcomes in the critical time period after injury [29]. Until recently, other than Shoemaker's work the majority of studies using bioimpedance sought to validate the measure in comparison to other established devices (such as PAC) in a variety of clinical settings and patient populations. Waldron et al. embarked on a study to validate a noninvasive cardiac output monitoring device (NICOM) against EDM using a validated GDT protocol, and also evaluated postoperative outcomes when the NICOM was used to guide management. The group studied 100 patients undergoing elective colorectal surgery as part of an enhanced recovery after surgery program. All patients underwent both NICOM and EDM monitoring; the initial 50 patients' intraoperative fluid management was guided by EDM, while the subsequent 50 patients' management was guided by
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NICOM. The investigators found an absence of statistically significant disagreement between the two measurement techniques. Postoperative outcomes were similar between groups. The investigators concluded that in this population of patients undergoing elective colorectal surgery, the NICOM provides similar outcomes, with the advantages of greater ease of use, acquisition of more data points, and increased user-friendliness when compared to the EDM technique [30]. Gastric tonometry Interest in gastric tonometry began as clinicians noted the end-organ changes consistent with significant illness, with low gastric intramucosal pH (pHi) found to correlate with poor outcome. This led to studies utilizing gastric tonometry as a means of guiding resuscitation. Gomersall et al. prospectively studied the use of gastric tonometry in a randomized controlled trial of patients admitted from the emergency room to the ICU. All patients were managed with goal MAP, urine output, hemoglobin, and other standard parameters, with fluid resuscitation and inotropes used to achieve these goals. Intervention group patients were additionally managed to maintain goal pHi >7.35 with additional fluids or inotropes. The researchers found that the intervention group did not experience significant improvement in length of ICU stay, multiorgan dysfunction score, hospital mortality, or 30-day mortality. Lower pHi did, as in other studies, correlate with poorer outcome, but the interventions used to raise the pHi did not alter the overall outcome [31]. Palizas et al. subsequently compared gastric tonometry against cardiac index as resuscitation goals. The 2009 study randomized patients with septic shock to standard resuscitation with additional goals of either cardiac index >3.0 L/min/m2 or pHi >7.32. The group similarly failed to find an outcome benefit to using gastric tonometry as a resuscitation goal. Both studies indicate that pHi is a marker of prognosis, with lower pHi correlating with poorer outcomes. Guiding resuscitation based on pHi has not yet shown a meaningful clinical difference in the settings studied [32]. Photoplethysmography Pulse oximetry is widely used to monitor oxygen saturations using a noninvasive probe. Photoplethysmography makes use of the variations in the pulse oximetry waveform to gauge fluid responsiveness, as the waveform changes with respiration. Forget et al. studied 82 general surgery patients in a prospective, randomized controlled trial using pleth variability index (PVI, or the variation in the pulse oximeter plethysmogram) to guide fluid management. Colloid boluses were used to maintain PVI 65 mmHg. The PVI group demonstrated lower volume of fluid administered intraoperatively, and lactate levels were decreased intraoperatively and postoperatively. These results contrasted other goal-directed fluid management studies demonstrating increased fluid administration in the intervention group. The authors propose that the lower lactate levels in their PVI group indicate that this monitoring technique allows for tailoring of fluid administration to the patient population with improved perfusion despite less fluid administered [33]. Respiratory variation Systemic arterial waveform variation with respiration can be measured using a variety of hemodynamic metrics, and is used to gauge fluid responsiveness. The SVV, systolic pressure variation (SPV), and pulse pressure variation (PPV) can all be used to guide fluid management. The goal is to maximize stroke volume, with arterial waveform variation taking the place of more invasive measures, such as pulmonary artery catheterization. Buettner et al. used SPV to guide fluid resuscitation in 80 patients undergoing elective major abdominal surgery. The PiCCOplus monitor was used to determine SPV at 15-min intervals and fluid was administered accordingly with goal SPV
Contents lists available at ScienceDirect
Best Practice & Research Clinical Anaesthesiology journal homepage: www.elsevier.com/locate/bean
13
Impact of hemodynamic monitoring on clinical outcomes Emily A. Downs, MD, Resident a, James M. Isbell, MD, MSCI, Assistant Professor a, * a
Division of Thoracic and Cardiovascular Surgery, Department of Surgery, University of Virginia, Charlottesville, VA 22908, USA
Keywords: critical care hemodynamics/physiology monitoring, physiologic/methods outcome assessment perioperative care
In recent years, there has been a tremendous growth in available hemodynamic monitoring devices to support clinical decisionmaking in the operating room and intensive care unit. In addition to the “tried and true” heart rate and blood pressure monitors, there are several newer applications of existing technologies including arterial waveform analysis, intraoperative and bedside critical care echocardiography, esophageal Doppler, and tissue oximetry, among others. Several monitoring devices demonstrate positive effect on outcomes, especially when used in conjunction with specific goal-directed therapy protocols to achieve a desired clinical effect. Other devices remain in the validation stage, awaiting comprehensive comparison to established techniques. While these new technologies offer promising advances in intraoperative and critical care, they are often quite costly and many devices lack strong evidence for widespread adoption into clinical practice. In this review, we highlight the current data on clinical outcomes with the use of available hemodynamic monitoring devices. © 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. University of Virginia, P.O. Box 800679, Charlottesville, VA 22908, USA. Tel.: þ1 434 243 6443; Fax: þ1 434 244 9429. E-mail addresses: [email protected] (E.A. Downs), [email protected] (J.M. Isbell).
http://dx.doi.org/10.1016/j.bpa.2014.09.009 1521-6896/© 2014 Elsevier Ltd. All rights reserved.
464
E.A. Downs, J.M. Isbell / Best Practice & Research Clinical Anaesthesiology 28 (2014) 463e476
Management of blood pressure Measurement of blood pressure is a historical standard for hemodynamic monitoring; the use of a simple fluid column to measure femoral arterial pressure in a horse constituted a very early monitoring device [1]. After numerous evolutionary steps, noninvasive blood pressure and arterial catheterization for continuous blood pressure monitoring remain in ubiquitous clinical use. The importance of maintaining adequate blood pressure is a well-accepted axiom. Fluid boluses and vasoactive agents are used routinely during surgery and postoperatively to maintain blood pressure and ensure that perfusion is adequate in the context of the physiologic stress of surgery. Conversely, maintaining blood pressure below specified thresholds is also sometimes important, such as to minimize myocardial oxygen demand or the risk of stroke. There is little published data describing ideal blood pressure parameters, and this is likely related to the heavy influence of anesthesiologist and surgeon experience and preference guiding intraoperative and postoperative blood pressure management. There have been recent efforts by Gawande et al. to delineate a scoring system for patients undergoing surgery to clarify a patient's condition and likelihood of major complications upon completion of a surgical procedure. This scoring system utilizes blood pressure as one of just three metrics. The surgical outcome score (referred to as the surgical Apgar score) uses lowest mean arterial pressure (MAP), estimated blood loss, and lowest heart rate during the procedure, with a clear increase in mortality for those receiving lower scores [2]. Regenbogen et al. examined records for 4119 patients undergoing general and vascular procedures and confirmed that the simple surgical Apgar score is predictive of both 30-day mortality and risk of postoperative complications [3]. These results underscore the importance of the fundamental hemodynamic parameters of intraoperative blood pressure and heart rate. Much of the scholarly work related to devices for monitoring of blood pressure is oriented toward validation or calibration of newer noninvasive blood pressure monitors as compared to the standard cuff pressure or arterial line measurement. There are several promising devices which use a variety of techniques to continuously measure blood pressure without the need for arterial catheterization, and each device has been found useful in some settings but compromised in others (e.g., critically ill patients, vasopressor use, awake/mobile patients as opposed to anesthetized patients, etc.). None of these devices has been studied with regard to their effects on outcomes. The importance of maintaining blood pressure within certain parameters is well understood in a general sense by anesthesiologists and surgeons, and the work of Gawande et al. and Regenbogen et al. confirms that intraoperative hypotension contributes to worsening outcomes when combined with bradycardia and blood loss as a surgical Apgar score. Newer generations of continuous, noninvasive blood pressure monitoring, while promising, have not been studied with respect to their impact on outcomes. Pulmonary artery catheterization Since the introduction of pulmonary artery catheterization by Swan et al., in 1970, this device has been used in a wide variety of clinical contexts. Pulmonary artery catheters (PACs) are utilized in critically ill patients with shock as well as in the preoperative, intraoperative, and postoperative settings. The device has been well studied with respect to clinical outcomes, both in retrospective analyses and in randomized controlled trials [4]. While some studies have shown benefit to pulmonary artery catheterization, several groups have found limited benefit with respect to the risk of complications from the device as well as misinterpretation of PAC data. The following sections will summarize the evidence behind PAC use in the intensive care unit (ICU) and in surgical populations. Pulmonary artery catheterization in the ICU PACs are used mainly in the ICU or in the operating room. Use of PACs in the medical ICU was examined by Mimoz et al. in a series of patients in a university hospital in France, with the goal of examining physicians' ability to predict hemodynamic profiles prior to PAC placement and follow subsequent clinical outcomes including change in therapy based on PAC measurements, complications
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from PAC, and mortality. The group found that physicians correctly predicted hemodynamic profiles in just 56% of the patients who received a PAC. They compared the group of patients who experienced a change in therapy based on PAC measurements and those who did not, and found a mortality benefit in those patients who did experience a change in therapy after pulmonary artery catheterization. The authors sought to study outcomes by following the manner PACs are often used in the ICU, namely as a method of guiding therapy when the patient's overall clinical picture is not completely clear from other hemodynamic indices [5]. After the Mimoz article was published in 1994, a group of five university hospitals published the results of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment (SUPPORT) investigators' work. This study examined decision-making processes and outcomes in ICU patients, with a particular focus on right heart catheterization in the first 24 h of an ICU stay. Outcomes included survival, length of stay, intensity of care, and cost of care. The group concluded that PAC use was associated with increased mortality and increased utilization of resources. This 1996 paper prompted editorials questioning whether clinicians should cease use of the PAC until additional studies were performed [6]. Another population in which PACs are frequently utilized is in the setting of severe congestive heart failure. Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE) study investigators sought to evaluate the use of PACs in patients with severe heart failure, examining outcomes including days alive and out of the hospital in the following 6 months. Their work was prompted by the controversy over PAC use, and the need to clarify utility of this device in specific populations. Patients from 26 heart failure centers in the USA and Canada were randomized to clinical assessment or clinical assessment plus PAC, and treated with vasodilators and diuretics (inotrope use was discouraged) to achieve relief from congestive symptoms. The authors found no difference in mortality or number of days out of the hospital. Like other investigators, the authors suggested that the PAC may be useful in some patients but routine use did not appear beneficial in comparison to the risks of invasive monitoring [7]. A 2006 study of PAC use in patients with severe trauma admitted to the ICU showed some potential benefit. Friese et al. performed a retrospective database analysis of patients in a national trauma database, adjusting for age, injury severity, and other factors. Of 53,312 patients in the database, 1933 were managed with a PAC. These patients were more likely to have more severe injuries and were older in age. Even after adjusting for a number of factors, the mortality rate was higher in the PAC group. However, the authors found improved outcomes with PAC use in patients who were older, had an arrival base deficit worse than 11, and an injury severity score between 25 and 75. They suggest that in the most severely injured patients or elderly patients with moderate shock, the PAC can provide useful guidance in resuscitation [8].
Pulmonary artery catheterization in surgical populations As a result of the controversy over PAC use, researchers have sought to demonstrate specific populations in which pulmonary artery catheterization may be useful. Tuman et al. followed up over 1000 cardiac surgery patients in a prospective, non-randomized study to elicit differences between PAC monitoring and central venous pressure (CVP) monitoring. They found no significant difference in length of ICU stay, occurrence of postoperative myocardial infarction, in-hospital death, or significant noncardiac complications [9]. Valentine et al. evaluated the routine use of PAC in aortic surgery, using a group of 120 patients who were admitted the evening prior to surgery and randomized to either placement of PAC in the ICU and fluid optimization, or admission to the ward without PAC. The researchers found that PAC patients received more intravenous (IV) fluids both preoperatively and postoperatively and had more intraoperative complications (18% in PAC group, 5% in controls, with p ¼ 0.02). Otherwise, no significant differences were seen [10]. Bender et al. similarly examined patients undergoing vascular surgery and randomized to PAC or no PAC with hemodynamic goals for pulmonary artery wedge pressure, cardiac index, and systemic vascular resistance. The PAC group received more IV fluids and there was no difference in complication rate, length of stay, mortality, or cost [11].
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Sandham et al. performed a randomized, controlled trial using the PAC to guide goal-directed therapy (GDT) in high-risk surgical patients. A total of 1994 patients considered high-risk due to age (60 or older) and American Society of Anesthesiologists (ASA) class (III or IV) were randomized to management with or without a PAC. The standard-care group was managed using typical ICU parameters and CVP measurement was allowed. The PAC group was managed with parameters for oxygen delivery, cardiac index, pulmonary capillary wedge pressure, heart rate, MAP, and hematocrit. The researchers found no benefit with PAC management in overall mortality, morbidity, or length of stay, and they also found no evidence of increased mortality in those randomized to PAC use [12]. Summary: Pulmonary artery catheterization The controversy surrounding PACs has led to numerous studies investigating the benefits and risks of this device in a variety of populations. While some benefit may be seen for patients with an unclear hemodynamic status, elderly trauma patients, and some select groups, most agree that routine use of PACs does not produce meaningful outcome benefit in mortality, morbidity, length of stay, or cost. Echocardiography Echocardiography is widely viewed as a useful diagnostic modality in patients in the operating room or the ICU. There is a significant body of work examining the feasibility and usefulness of echocardiography performed by intensivists, but only a few researchers have specifically studied the impact of echocardiography in the operative or critical care settings with respect to patient outcomes or cost-effectiveness. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) can be useful modalities when used in the appropriate setting. Impact of postoperative TTE or TEE on management Schmidlin et al. reviewed 301 TEE reports in patients after cardiac surgery. Their observational study found that in 73% of these cases, there was a therapeutic change made as a result of the TEE. These included change in fluid management, change in medications administered, resternotomy, or ability to defer a resternotomy by ruling out pathology. Patients undergoing postoperative TEE were found to have a higher mortality rate, but this was attributed to higher preoperative risk and increased complexity of operation [13]. Orme et al. examined the impact of both TEE and TTE on management of ICU patients. This group found that 51.2% of studies resulted in change in management. Of note, intensivists performed the majority of these echocardiograms (86.8%), and 72.4% were TTEs while 27.8% were TEEs. The authors pointed out that echocardiography can be useful when performed by non-cardiologists and that TTE continues to have a role in the ICU despite the increased difficulty in acquiring images in mechanically ventilated critically ill patients [14]. Intraoperative management with TEE Shillcutt et al. used echocardiography-derived parameters to guide hemodynamic management during noncardiac surgical procedures on patients with known left ventricular diastolic dysfunction. A variety of echocardiographic parameters were used to guide management of fluids and vasoactive agents, while the standard hemodynamic management group received therapies to maintain systolic blood pressure within 10e15% of the patient's baseline. Due to a limited number of patients, the feasibility of TEE examination and safety were the primary endpoints; secondary outcomes included fluids administered and 30-day postoperative complications (atrial fibrillation, congestive heart failure (CHF), myocardial infarction (MI), stroke, etc.). Patients monitored with TEE received less fluid intraoperatively. Measures of 30-day outcomes were not statistically significant but trended toward shorter hospital stay, lower incidence of CHF, and less atrial fibrillation in the patients managed with TEE parameters [15].
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Cost analysis of TTE and TEE in the ICU One difficulty in using TTE in critically ill patients is the lack of adequate acoustic windows in mechanically ventilated patients who may have dressings, lines, or other devices limiting access to the appropriate surface anatomy for echocardiographic exam. Cook et al. evaluated the failure rate of TTE in the surgical ICU setting and found that routine use of TTE with TEE as a secondary modality is not costeffective. The failure rate of TTE rises with patients receiving >15 cm H2O of positive end-expiratory pressure (PEEP), patients who have gained >10% body weight compared to admission weight, and those with chest tubes. The group found the lowest overall costs with TEE alone, and some cost-savings when TEE is used as the primary modality for patients at high-risk of TTE failure and TTE used for those at low risk of failure [16]. Summary: Echocardiography Echocardiography is a widely available modality that can be used in specific settings to answer questions about a patient's hemodynamic status. Use of TEE has shown initial success as an intraoperative monitoring device for patients with left ventricular diastolic dysfunction with a trend toward shorter hospital stay, lower incidence of CHF, and less atrial fibrillation postoperatively. In the setting of critically ill patients receiving high levels of PEEP and with significant increase in total fluid, use of TEE alone has been shown to be more cost-effective than trialing TTE prior to TEE in one study. Other than these studies, evidence is lacking in the use of TTE or TEE and impact on postoperative outcomes. Esophageal Doppler monitoring Esophageal Doppler monitoring (EDM) provides an assessment of stroke volume and cardiac output by measuring the Doppler signal of moving blood cells in the descending thoracic aorta. This is primarily used intraoperatively as it requires an intra-esophageal probe. To date, the device is used mainly in conjunction with goal-directed protocols to administer fluid and maximize stroke volume. EDM in patients undergoing femoral fracture fixation The earliest publication detailing EDM in surgical patients, by Sinclair et al., describes patients undergoing femoral fracture fixation. This relatively common procedure is performed on patients who are often frail with multiple comorbidities. Sinclair et al. published a randomized controlled trial of 40 patients undergoing fracture fixation with the control group receiving conventional fluid management and the intervention group receiving colloid fluid challenges to maintain maximal stroke volume as measured by EDM. The group found that patients receiving EDM experienced shorter time to being medically fit for discharge and a 39% reduction in-hospital stay compared to controls [17]. Venn et al. subsequently studied the same type of population, patients undergoing femoral fracture repair, and compared controls to EDM as well as a third group which received CVP monitoring. They found no difference in major morbidity or mortality, but did find shorter time to medical readiness for discharge in patients with CVP or EDM monitoring compared to controls. Both the CVP and EDM groups received more intraoperative fluids [18]. EDM in patients undergoing major abdominal/pelvic surgery or in trauma ICU Pillai et al. performed a prospective, randomized trial of patients undergoing radical cystectomy using EDM as compared to controls receiving fluids at the anesthesiologist's discretion. The researchers found that patients in the EDM group received more intraoperative fluids, and experienced decreased ileus and fewer infections. They did not demonstrate a reduction in length of stay, unlike the femoral fracture fixation studies [19]. Chytra et al. published the results of their randomized, controlled trial of 162 patients with multi-trauma. They also found that EDM patients received more colloid, and had fewer infectious complications. This paper did demonstrate shorter ICU and hospital stay for the trauma patients receiving EDM [20].
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EDM in patients undergoing abdominal surgery has led to numerous enhanced recovery programs (ERPs) due to encouraging results using EDM for fluid management in these patients. Gan et al. published the results of a randomized controlled trial of 100 patients undergoing major elective abdominal surgery and EDM monitoring. The control group experienced standard intraoperative care using fluids to maintain specified parameters for urine output, heart rate, blood pressure, and CVP while the EDM group received boluses to maintain maximum stroke volume. The EDM group received more intraoperative fluids and had a significantly shorter length of hospital stay (2 days shorter in the EDM group) [21]. This work was followed by Noblett et al. who studied patients undergoing elective colorectal surgery with similar control and EDM protocol groups. They found a shorter length of stay, shorter time to surgical fitness for discharge, and earlier diet tolerance. The control group had more complications requiring ICU admission. Interestingly, Noblett's control and EDM groups did not receive significantly different amounts of fluid during surgery or in the first 48 h after surgery [22]. Wakeling et al. randomized patients undergoing elective colorectal surgery to CVP (conventional) fluid management versus EDM protocol and also found significantly shorter length of stay by 1.5 days and shorter time to full diet in the EDM group, without significant difference in fluid administration [23]. Summary: EDM In summary, EDM with fluid administration protocol designed to maximize stroke volume intraoperatively has shown shorter length of stay in several studies, as well as improvements in diet tolerance in those undergoing abdominal surgery. This is made possible both in the setting of patients receiving more fluid than controls (as in femoral fracture fixation) and when the EDM patients receive a similar amount of fluid compared to controls. Arterial waveform analysis Several devices using analysis of arterial waveform to provide hemodynamic information are commercially available. PiCCO and LiDCO use thermodilution and lithium indicator dilution, respectively, to provide cardiac output measurements. These devices also use specific algorithms to estimate cardiac output from the arterial pressure waveform. The Vigileo FloTrac system uses the arterial waveform to calculate cardiac output, without requiring calibration. These devices have been studied with respect to outcomes mainly in conjunction with GDT protocols with promising results. Use of arterial waveform analysis in cardiac surgery patients Goepfert et al. published a 2007 paper describing goal-directed fluid management in cardiac surgery patients using PiCCO monitoring to optimize the global end-diastolic volume index (GEDVI). Forty patients undergoing coronary bypass grafting were prospectively studied and compared to historical controls. The group sought to maintain GEDVI above 640 mL/m [2], cardiac index above 2.5 L/min/m2, and MAP above 70 mmHg. The group was able to use fewer vasopressors, and the time for which patients were dependent on vasopressors was shorter in the intervention group. The GDT group also required shorter duration of mechanical ventilation, and patients were medically fit for ICU discharge sooner than the historical controls [24]. Kapoor et al. likewise studied cardiac surgery patients and used the FloTrac device to maintain specific parameters for CVP, and stroke volume variation (SVV). The study was fairly small, and showed trends toward shorter duration of mechanical ventilation, fewer days of inotrope use, and shorter ICU stay, but none of these reached statistical significance [25]. Arterial waveform analysis in patients undergoing major noncardiac surgery Jones et al. studied an ERP for patients undergoing open liver resection, using a comprehensive approach to patient education, pain management, and LiDCO-based GDT for fluid management in the first 6 h after surgery. The authors sought to determine whether this type of program could be successful in liver resection as promising results had already been demonstrated in colorectal resection. The group found that patients in the ERP experienced less time to medical fitness for discharge (3 vs. 6
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days) and shorter length of stay (4 vs. 7 days). There were also fewer complications in the ERP group [26]. Pearse et al. used LiDCO monitoring in a more varied general surgery population in a randomized, controlled, partly blinded study. Patients undergoing high-risk general surgery were randomized to conventional management versus goal-directed therapy to maintain oxygen delivery index >600 mL/ min * m2, as measured by the LiDCO device. A member of the research team administered the treatments in the intervention group during the first 8 h after surgery; this included fluid boluses and dopexamine to maintain the desired oxygen delivery index. The team found that the GDT group experienced fewer complications (44% vs. 68%), with a shorter overall hospital length of stay (median 11 vs. 14 days) [27]. Both of these studies demonstrate promising outcomes despite providing GDT for a limited time (6 h in one case, 8 h in the other). In an effort to strengthen the evidence related to arterial waveform analysis and its use in GDT, Pearse and colleagues for the Optimisation of Peri-operative cardiovascular Management to Improve Surgical Outcome (OPTIMISE) trial performed a 17-center, prospective, randomized controlled trial of GDT in high-risk patients undergoing major abdominal surgery. The study enrolled 734 patients, the largest trial to date, and the investigators sought to perform a pragmatic effectiveness trial and minimized bias by blinding clinicians and, where possible, study staff as well. As in Pearse's prior work, the LiDCO arterial waveform monitor was utilized. Patients received standard perioperative care, and the intervention group additionally received 250 mL colloid boluses to maintain maximum stroke volume as well as a continuous infusion of dopexamine at a standard dose unless heart rate increases required dose reduction or discontinuation. This was compared to usual care, with recommendation to consider CVP target. Pearse and colleagues found that there was no statistically significant difference in outcomes, including composite measure of 30-day moderate or major postoperative complications, infectious complications, or mortality at 30 or 180 days. The study investigators performed an updated meta-analysis with 6595 patients, including the 734 in the OPTIMISE trial, and found that GDT using arterial waveform analysis is associated with a reduced complication rate. The investigators felt that these findings continue to support GDT guided by arterial waveform analysis [28]. Summary: Arterial waveform analysis Arterial waveform analysis, like other technologies used to guide goal-directed fluid management, demonstrates promise in reducing hospital length of stay and reducing complications as compared to conventional management. Bioimpedance and bioreactance Bioimpedance offers a truly noninvasive approach to measurement of cardiac output, and has generated interest in comprehensive monitoring. One example of its use is very early in resuscitation, as in trauma patients in the emergency department. Shoemaker et al. have published several papers describing noninvasive hemodynamic monitoring, including bioimpedance measurement of cardiac output. In a 2007 paper, the group describes predicting outcome and providing therapeutic support for trauma patients in the first hour after admission, using their mathematical algorithm taking into account several noninvasive parameters. As many as 185 consecutive patients were monitored, and the authors found that their system was able to accurately predict survivors versus non-survivors. While the study did not measure the effect on outcome of using noninvasive monitoring, including bioimpedance, the eventual goal of the work is to use such decision-support algorithms to impact treatments and outcomes in the critical time period after injury [29]. Until recently, other than Shoemaker's work the majority of studies using bioimpedance sought to validate the measure in comparison to other established devices (such as PAC) in a variety of clinical settings and patient populations. Waldron et al. embarked on a study to validate a noninvasive cardiac output monitoring device (NICOM) against EDM using a validated GDT protocol, and also evaluated postoperative outcomes when the NICOM was used to guide management. The group studied 100 patients undergoing elective colorectal surgery as part of an enhanced recovery after surgery program. All patients underwent both NICOM and EDM monitoring; the initial 50 patients' intraoperative fluid management was guided by EDM, while the subsequent 50 patients' management was guided by
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NICOM. The investigators found an absence of statistically significant disagreement between the two measurement techniques. Postoperative outcomes were similar between groups. The investigators concluded that in this population of patients undergoing elective colorectal surgery, the NICOM provides similar outcomes, with the advantages of greater ease of use, acquisition of more data points, and increased user-friendliness when compared to the EDM technique [30]. Gastric tonometry Interest in gastric tonometry began as clinicians noted the end-organ changes consistent with significant illness, with low gastric intramucosal pH (pHi) found to correlate with poor outcome. This led to studies utilizing gastric tonometry as a means of guiding resuscitation. Gomersall et al. prospectively studied the use of gastric tonometry in a randomized controlled trial of patients admitted from the emergency room to the ICU. All patients were managed with goal MAP, urine output, hemoglobin, and other standard parameters, with fluid resuscitation and inotropes used to achieve these goals. Intervention group patients were additionally managed to maintain goal pHi >7.35 with additional fluids or inotropes. The researchers found that the intervention group did not experience significant improvement in length of ICU stay, multiorgan dysfunction score, hospital mortality, or 30-day mortality. Lower pHi did, as in other studies, correlate with poorer outcome, but the interventions used to raise the pHi did not alter the overall outcome [31]. Palizas et al. subsequently compared gastric tonometry against cardiac index as resuscitation goals. The 2009 study randomized patients with septic shock to standard resuscitation with additional goals of either cardiac index >3.0 L/min/m2 or pHi >7.32. The group similarly failed to find an outcome benefit to using gastric tonometry as a resuscitation goal. Both studies indicate that pHi is a marker of prognosis, with lower pHi correlating with poorer outcomes. Guiding resuscitation based on pHi has not yet shown a meaningful clinical difference in the settings studied [32]. Photoplethysmography Pulse oximetry is widely used to monitor oxygen saturations using a noninvasive probe. Photoplethysmography makes use of the variations in the pulse oximetry waveform to gauge fluid responsiveness, as the waveform changes with respiration. Forget et al. studied 82 general surgery patients in a prospective, randomized controlled trial using pleth variability index (PVI, or the variation in the pulse oximeter plethysmogram) to guide fluid management. Colloid boluses were used to maintain PVI 65 mmHg. The PVI group demonstrated lower volume of fluid administered intraoperatively, and lactate levels were decreased intraoperatively and postoperatively. These results contrasted other goal-directed fluid management studies demonstrating increased fluid administration in the intervention group. The authors propose that the lower lactate levels in their PVI group indicate that this monitoring technique allows for tailoring of fluid administration to the patient population with improved perfusion despite less fluid administered [33]. Respiratory variation Systemic arterial waveform variation with respiration can be measured using a variety of hemodynamic metrics, and is used to gauge fluid responsiveness. The SVV, systolic pressure variation (SPV), and pulse pressure variation (PPV) can all be used to guide fluid management. The goal is to maximize stroke volume, with arterial waveform variation taking the place of more invasive measures, such as pulmonary artery catheterization. Buettner et al. used SPV to guide fluid resuscitation in 80 patients undergoing elective major abdominal surgery. The PiCCOplus monitor was used to determine SPV at 15-min intervals and fluid was administered accordingly with goal SPV
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