_ _ _ _ _ _ _ _ _ _ _ _ _Editorial Regional Anesthesia: Testing Whether It Makes a Difference Mark P. Yeager, MD* Department of Anesthesiology, Dartmouth Medical School, Hanover, NH.
*Assistant
Professor of Anesthesiology and Medicine, Dartmouth Medical School Address reprint requests to Dr. Yeager at the Department of Anesthesiology, Dartmouth-Hitchcock Medical Center, 2 Maynard Street, Hanover, NH 03766, USA. Received for publication November 6, 1989; accepted for publication November 7, 1989. © 1990 Butterworth Publishers
Early practitioners of anesthesia had only a few clinical decisions to make. After they decided whether it was prudent to proceed with anesthesia induction at all, they chose one of the few agents available. Beyond these few preoperative decisions, the consequences of anesthesia were determined primarily by the physical skill with which it was administered. Although this skill is still important, its preeminence in determining the consequences of anesthesia has been tempered in recent years. Today, practicing anesthesiologists are confronted daily with a wide variety of important clinical decisions. They are involved in preoperative patient assessment, preoperative treatments designed to reduce operative morbidity, initiating and using various intraoperative physiologic monitors, and extending anesthetic management well into the postoperative period. Decisions reached in any of these important categories may have a profound effect on the course of the operation and on the course of postoperative events. Perhaps the most basic decision is made when choosing a particular anesthetic agent or technique for an operation. Here our choices are no longer so limited (they sometimes seem unlimited). And if choosing an anesthetic agent or technique is a basic decision, one might suppose that there would be a plethora of good clinical information that evaluates the important clinical effects of different agents and techniques. In fact, there is very little. There is a good deal of literature regarding the physiologic effects of a single agent or technique but very few comparisons. In this issue of The Journal of Clinical Anesthesia, Damask et al. present the results of a clinical study that compares the hemodynamic consequences of two different anesthetic techniques: lumbar epidural anesthesia and general endotracheal anesthesia. The study included patients undergoing lower extremity vascular reconstruction. Since one recent survey found that approximately 50% of practitioners use general anesthesia for vascular surgery and approximately 50% use regional anesthesia,' the techniques chosen for this study have clinical relevance. Also, since this patient population is known to have a high incidence of myocardial disease, especially coronary artery disease," the measured param-
J. Clin.
Anesth., vol. 2, March/April 1990
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Editorial
eters are relevant. Finally, the protocols that were used for managing patients randomized to either group are probably representative of current anesthesia practice in many operating rooms. The results of the study suggest that lumbar epidural anesthesia maintains better control of some determinants of myocardial performance and oxygen demand than does general anesthesia. Overall, these results are consistent with other studies that have examined some of the measured parameters in different clinical settings. 3-8 Shortly after induction, the rate pressure product (RPP) was decreased in both groups compared to their own preinduction values. During the operation, the two groups appeared to be remarkably similar with the exception of a persistently higher heart rate (HR), central venous pressure (CVP), and pulmonary capillary occlusion pressure (PCOP) in the general anesthesia group. These differences were significant at some, but not all, of the measurement times. At the conclusion of the case and in the recovery room, the intergroup differences again became apparent, with the general anesthesia group manifesting a significantly higher RPP than the epidural anesthesia group. The design of the study allows us to draw no conclusions regarding the etiology of the observed differences. The higher RPP in the general anesthesia group may well be a consequence of less control of the stress response to surgery. Certainly regional anesthesia has been repeatedly shown to provide more control of this response when compared with general anesthesia." Regional anesthesia and analgesia also result in an apparent lowering of adrenergic tone as assessed by blood catecholamine levels.v!? A direct effect of regional anesthesia on the arterial resistance and/or venous capacitance vessels also may be involved in lowering of the arterial pressure.v-" The lower HR in the lumbar epidural anesthesia group could be due to an increase in vagal tone (rather than a decrease in sympathetic tone);'! The relatively higher CVP and PCOP in the general anesthesia group may be due to the need for positive pressure ventilation in that group, as the authors point out. It also may be due to pooling of blood in the lower extremities- or in the mesenteric circulation of the patients who received epidural anesthesia. 12 Any or all of these physiologic events may have been operative in this study. We continue to learn about the effects of different anesthetic techniques on hemodynamic performance. In the future, as a consequence of studies such as this one, we hope to be able to predict with greater accuracy the favorable and unfavorable consequences of our decisions regarding choice of anesthetic agents and techniques. In the meantime, how should we incorporate information such as that reported here into our everyday practice? There are at least two answers to this question. The first answer depends on the goals of the anesthetic management plan for an individual patient. In the study reported by Damask et al., the notable difference between the two anesthetic techniques was a reduction in RPP in the epidural anesthesia group. Or was it an increase in RPP in the general anesthesia group? What's the difference? The difference depends on the patient. With a lower RPP, the determinants of myocardial oxygen demand will be lower. For the patient with clinically significant coronary artery disease, that finding may have an important advantage. Fortunately, or unfortunately, the determinants of myocardial oxygen demand are also the determinants of myocardial performance (stroke volume and cardiac output). The vascular surgical patient who receives an epidural anesthetic will often manifest a reduction in myocardial performance, compared with a patient who receives a gen68
J. Clin. Anesth., vol. 2, March/April 1990
Regional anesthesia: Yeager
eral anesthetic. 1.3 This fact may be important with regard to peripheral oxygen delivery." Which effect is clinically more important: a reduction in myocardial oxygen demand or a reduction in myocardial performance? Clearly, the answer requires a good deal ofjudgment and an appreciation of the unique physiology of each individual patient. The issue is further complicated by the fact that there are so many ways to manage hemodynamic variables in the surgical patient. The choice of anesthetic technique is just one of them. One could argue the benefit of choosing an anesthetic technique first as a means of managing hemodynamics. Alternately, one could argue that the choice of anesthetic technique is not as important as knowing how to manipulate hemodynamic variables by any of a variety of mechanisms using other vasoactive drugs. Possibly either approach will do, as long as the dictates of good anesthetic care and hemodynamic management are satisfied. The second answer is related, in a sense, to the constant evolution of our specialty. As the practice of anesthesiology matures, several themes become more apparent in our everyday practice. These themes include the postoperative nature of morbidity, the principle of kinetic matching, proactive management, and drug specificity. Serious morbidity (and vascular surgical patients are certainly at risk) is by and large a postoperative event. 13.14 Our intraoperative management has improved to the point where a patient who dies in the operating room because he or she "didn't take to anesthesia" is a modern-day rarity. We have learned repeatedly that serious morbidity, especially cardiovascular morbidity, occurs outside the operating room. If anesthesiologists are to have an impact on postoperative morbidity, they must be involved in postoperative care. Their involvement with critical care services and with postoperative pain services are examples of how this impact can be achieved. General anesthesia is usually terminated at the end of an operative procedure. Regional anesthesia may continue for a short time afterward. In marked contrast, the human physiologic response to major surgery begins with incision and continues for days into the postoperative period. IS Thus, although there are frequently reasons to use a short-acting drug in the operating room, the kinetics of such agents do not match those of the human response to surgical trauma. The results of Damask et al. tend to support this thesis. As soon as the general anesthetic was discontinued in the general anesthesia group, RPP increased significantly. In this group, the kinetics of the anesthetic intervention did not match the kinetics of the patients' response to the surgery. Prophylaxis is better than cure. Contemporary management of highrisk surgical patients supports this view. Prospective interventions designed to prevent an unfavorable perioperative event have a far more positive impact than interventions after the fact." Proactive management of the pain of surgery can be included in this category. We are beginning to learn why it is easier to control pain by anticipating a noxious stimulus than it is to control pain once it has been perceived."? . Finally, drug specificity seems to be a common goal. This goal is particularly obvious when one considers the new synthetic narcotics and nondepolarizing muscle relaxants currently on the market. One of their great advantages appears to be their lack of cardiovascular side effects, especially when compared with drugs such as morphine, curare, and pancuronium. Etomidate and adrenal suppression can be cited as an example of a potentially undesirable lack of drug specificity. Seen in this way, one of the advantages of regional anesthesia is the word regional. By virtue of
J. Clin.
Anesth., vol. 2, March/April 1990
69
Editorial
its mechanism of delivery, regional anesthesia has specificity of drug action (relative absence of systemic effects) as a largely built-in feature. Anesthetic management decisions do make a difference. But in order to detect the difference, one must first search for it. Before Mendelsohn's classic description of the acid aspiration syndrome, a decision to administer mask anesthesia rather than endotracheal anesthesia had little to do with the incidence of postoperative fever and pneumonia. In how many other ways do the anesthetic choices that we make every day affect the course of our patients' operation and recovery?
References 1. Bunt T], Manczuk M, Varley K: Continuous epidural anesthesia for aortic surgery: thoughts on peer review and safety. Surgery 1987;101:706-14. 2. Hertzer NR, Beven EG, Young Rj, et al: Coronary artery disease in peripheral vascular patient. A classification of 1000 coronary angiograms and results of surgical management. Ann Surg 1984; 199:223-33. 3. Lundbergj, Norgren L, Thomson D, et al: Hemodynamic effects of dopamine during thoracic epidural analgesia in man. Anesthesiology 1987;66:641-6. 4. Baron jF, Coriat P, Mundler 0, et al: Left ventricular global and regional function during lumbar epidural anesthesia in patients with and without angina pectoris. Influence of volume loading. Anesthesiology 1987;66:621-7. 5. Reiz S, Nath S, Ponten, et al: Effects of thoracic epidural block and the betal-adrenoreceptor agonist prenalterol in the cardiovascular response to infrarenal aortic cross clamping in man. Acta Anaesthiol Scand 1979;23:395-403. 6. LunnjK, Dannemiller F], Stanley TH: Cardiovascular responses to clamping the aorta during epidural and general anesthesia. Anesth Analg 1979;58: 372-6. 7. Wattwil M, Sundberg A, Arvill A, et al: Circulatory changes during high thoracic epidural anaesthesia-influence of sympathetic block and of systemic effect of the local anaesthetic. Acta Anaesthesiol Scand 1985;29:849-55. 8. Reinhart K, Foehring U, Kersting T, et al: Effects of thoracic epidural anaesthesia on systemic hemodynamic function and systemic oxygen supplydemand relationship. Anaesth Analg 1989;69:360-9. 9. Kehlet H: The endocrine responses to regional anesthesia. Int Anesthesiol Clin 1988;26: 182-6. 10. Breslow Mj, jordan DA, Christopherson R, et al: Epidural morphine decreases postoperative hypertension by attenuating sympathetic nervous system hyperactivity.JAMA 1989;261:3577-81. II. Baron jF, Decaux-jacolot A, Edouard A, et al: Influence of venous return on baroreflex control of heart rate during lumbar epidural anesthesia in humans. Anesthesiology 1986;64: 188-93. 12. Johansson K, Ahn H, Lindhagen j, et al: Effect of epidural anaesthesia on intestinal blood flow. Br J Surg 1988;75:73-6. 13. Diehl jT, Cali FR, Hertzer NR, et al: Complications of abdominal aortic reconstruction. Ann Surg 1983;197:49-56. 14. Rao TLK, jacobs KH, EI-Etr AA: Reinfarction following anesthesia in patients with myocardial infarction. Anesthesiology 1983;59:499-505. 15. Chernow B, Alexander HR, Smallridge RC, et al: Hormonal responses to graded surgical stress. Arch Intern Med 1987; 147: 1273-8. 16. Del Guercio LRM, CohnjD: Monitoring operative risk in the e1derly.JAMA 1980;243: 1350-5. 17. Armitage EN: Postoperative pain-prevention or relief? [Editorial]. Br J Anaesth 1989;63:136-7.
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J. Clin.
Anesth., vol. 2, March/April 1990
*Assistant
Professor of Anesthesiology and Medicine, Dartmouth Medical School Address reprint requests to Dr. Yeager at the Department of Anesthesiology, Dartmouth-Hitchcock Medical Center, 2 Maynard Street, Hanover, NH 03766, USA. Received for publication November 6, 1989; accepted for publication November 7, 1989. © 1990 Butterworth Publishers
Early practitioners of anesthesia had only a few clinical decisions to make. After they decided whether it was prudent to proceed with anesthesia induction at all, they chose one of the few agents available. Beyond these few preoperative decisions, the consequences of anesthesia were determined primarily by the physical skill with which it was administered. Although this skill is still important, its preeminence in determining the consequences of anesthesia has been tempered in recent years. Today, practicing anesthesiologists are confronted daily with a wide variety of important clinical decisions. They are involved in preoperative patient assessment, preoperative treatments designed to reduce operative morbidity, initiating and using various intraoperative physiologic monitors, and extending anesthetic management well into the postoperative period. Decisions reached in any of these important categories may have a profound effect on the course of the operation and on the course of postoperative events. Perhaps the most basic decision is made when choosing a particular anesthetic agent or technique for an operation. Here our choices are no longer so limited (they sometimes seem unlimited). And if choosing an anesthetic agent or technique is a basic decision, one might suppose that there would be a plethora of good clinical information that evaluates the important clinical effects of different agents and techniques. In fact, there is very little. There is a good deal of literature regarding the physiologic effects of a single agent or technique but very few comparisons. In this issue of The Journal of Clinical Anesthesia, Damask et al. present the results of a clinical study that compares the hemodynamic consequences of two different anesthetic techniques: lumbar epidural anesthesia and general endotracheal anesthesia. The study included patients undergoing lower extremity vascular reconstruction. Since one recent survey found that approximately 50% of practitioners use general anesthesia for vascular surgery and approximately 50% use regional anesthesia,' the techniques chosen for this study have clinical relevance. Also, since this patient population is known to have a high incidence of myocardial disease, especially coronary artery disease," the measured param-
J. Clin.
Anesth., vol. 2, March/April 1990
67
Editorial
eters are relevant. Finally, the protocols that were used for managing patients randomized to either group are probably representative of current anesthesia practice in many operating rooms. The results of the study suggest that lumbar epidural anesthesia maintains better control of some determinants of myocardial performance and oxygen demand than does general anesthesia. Overall, these results are consistent with other studies that have examined some of the measured parameters in different clinical settings. 3-8 Shortly after induction, the rate pressure product (RPP) was decreased in both groups compared to their own preinduction values. During the operation, the two groups appeared to be remarkably similar with the exception of a persistently higher heart rate (HR), central venous pressure (CVP), and pulmonary capillary occlusion pressure (PCOP) in the general anesthesia group. These differences were significant at some, but not all, of the measurement times. At the conclusion of the case and in the recovery room, the intergroup differences again became apparent, with the general anesthesia group manifesting a significantly higher RPP than the epidural anesthesia group. The design of the study allows us to draw no conclusions regarding the etiology of the observed differences. The higher RPP in the general anesthesia group may well be a consequence of less control of the stress response to surgery. Certainly regional anesthesia has been repeatedly shown to provide more control of this response when compared with general anesthesia." Regional anesthesia and analgesia also result in an apparent lowering of adrenergic tone as assessed by blood catecholamine levels.v!? A direct effect of regional anesthesia on the arterial resistance and/or venous capacitance vessels also may be involved in lowering of the arterial pressure.v-" The lower HR in the lumbar epidural anesthesia group could be due to an increase in vagal tone (rather than a decrease in sympathetic tone);'! The relatively higher CVP and PCOP in the general anesthesia group may be due to the need for positive pressure ventilation in that group, as the authors point out. It also may be due to pooling of blood in the lower extremities- or in the mesenteric circulation of the patients who received epidural anesthesia. 12 Any or all of these physiologic events may have been operative in this study. We continue to learn about the effects of different anesthetic techniques on hemodynamic performance. In the future, as a consequence of studies such as this one, we hope to be able to predict with greater accuracy the favorable and unfavorable consequences of our decisions regarding choice of anesthetic agents and techniques. In the meantime, how should we incorporate information such as that reported here into our everyday practice? There are at least two answers to this question. The first answer depends on the goals of the anesthetic management plan for an individual patient. In the study reported by Damask et al., the notable difference between the two anesthetic techniques was a reduction in RPP in the epidural anesthesia group. Or was it an increase in RPP in the general anesthesia group? What's the difference? The difference depends on the patient. With a lower RPP, the determinants of myocardial oxygen demand will be lower. For the patient with clinically significant coronary artery disease, that finding may have an important advantage. Fortunately, or unfortunately, the determinants of myocardial oxygen demand are also the determinants of myocardial performance (stroke volume and cardiac output). The vascular surgical patient who receives an epidural anesthetic will often manifest a reduction in myocardial performance, compared with a patient who receives a gen68
J. Clin. Anesth., vol. 2, March/April 1990
Regional anesthesia: Yeager
eral anesthetic. 1.3 This fact may be important with regard to peripheral oxygen delivery." Which effect is clinically more important: a reduction in myocardial oxygen demand or a reduction in myocardial performance? Clearly, the answer requires a good deal ofjudgment and an appreciation of the unique physiology of each individual patient. The issue is further complicated by the fact that there are so many ways to manage hemodynamic variables in the surgical patient. The choice of anesthetic technique is just one of them. One could argue the benefit of choosing an anesthetic technique first as a means of managing hemodynamics. Alternately, one could argue that the choice of anesthetic technique is not as important as knowing how to manipulate hemodynamic variables by any of a variety of mechanisms using other vasoactive drugs. Possibly either approach will do, as long as the dictates of good anesthetic care and hemodynamic management are satisfied. The second answer is related, in a sense, to the constant evolution of our specialty. As the practice of anesthesiology matures, several themes become more apparent in our everyday practice. These themes include the postoperative nature of morbidity, the principle of kinetic matching, proactive management, and drug specificity. Serious morbidity (and vascular surgical patients are certainly at risk) is by and large a postoperative event. 13.14 Our intraoperative management has improved to the point where a patient who dies in the operating room because he or she "didn't take to anesthesia" is a modern-day rarity. We have learned repeatedly that serious morbidity, especially cardiovascular morbidity, occurs outside the operating room. If anesthesiologists are to have an impact on postoperative morbidity, they must be involved in postoperative care. Their involvement with critical care services and with postoperative pain services are examples of how this impact can be achieved. General anesthesia is usually terminated at the end of an operative procedure. Regional anesthesia may continue for a short time afterward. In marked contrast, the human physiologic response to major surgery begins with incision and continues for days into the postoperative period. IS Thus, although there are frequently reasons to use a short-acting drug in the operating room, the kinetics of such agents do not match those of the human response to surgical trauma. The results of Damask et al. tend to support this thesis. As soon as the general anesthetic was discontinued in the general anesthesia group, RPP increased significantly. In this group, the kinetics of the anesthetic intervention did not match the kinetics of the patients' response to the surgery. Prophylaxis is better than cure. Contemporary management of highrisk surgical patients supports this view. Prospective interventions designed to prevent an unfavorable perioperative event have a far more positive impact than interventions after the fact." Proactive management of the pain of surgery can be included in this category. We are beginning to learn why it is easier to control pain by anticipating a noxious stimulus than it is to control pain once it has been perceived."? . Finally, drug specificity seems to be a common goal. This goal is particularly obvious when one considers the new synthetic narcotics and nondepolarizing muscle relaxants currently on the market. One of their great advantages appears to be their lack of cardiovascular side effects, especially when compared with drugs such as morphine, curare, and pancuronium. Etomidate and adrenal suppression can be cited as an example of a potentially undesirable lack of drug specificity. Seen in this way, one of the advantages of regional anesthesia is the word regional. By virtue of
J. Clin.
Anesth., vol. 2, March/April 1990
69
Editorial
its mechanism of delivery, regional anesthesia has specificity of drug action (relative absence of systemic effects) as a largely built-in feature. Anesthetic management decisions do make a difference. But in order to detect the difference, one must first search for it. Before Mendelsohn's classic description of the acid aspiration syndrome, a decision to administer mask anesthesia rather than endotracheal anesthesia had little to do with the incidence of postoperative fever and pneumonia. In how many other ways do the anesthetic choices that we make every day affect the course of our patients' operation and recovery?
References 1. Bunt T], Manczuk M, Varley K: Continuous epidural anesthesia for aortic surgery: thoughts on peer review and safety. Surgery 1987;101:706-14. 2. Hertzer NR, Beven EG, Young Rj, et al: Coronary artery disease in peripheral vascular patient. A classification of 1000 coronary angiograms and results of surgical management. Ann Surg 1984; 199:223-33. 3. Lundbergj, Norgren L, Thomson D, et al: Hemodynamic effects of dopamine during thoracic epidural analgesia in man. Anesthesiology 1987;66:641-6. 4. Baron jF, Coriat P, Mundler 0, et al: Left ventricular global and regional function during lumbar epidural anesthesia in patients with and without angina pectoris. Influence of volume loading. Anesthesiology 1987;66:621-7. 5. Reiz S, Nath S, Ponten, et al: Effects of thoracic epidural block and the betal-adrenoreceptor agonist prenalterol in the cardiovascular response to infrarenal aortic cross clamping in man. Acta Anaesthiol Scand 1979;23:395-403. 6. LunnjK, Dannemiller F], Stanley TH: Cardiovascular responses to clamping the aorta during epidural and general anesthesia. Anesth Analg 1979;58: 372-6. 7. Wattwil M, Sundberg A, Arvill A, et al: Circulatory changes during high thoracic epidural anaesthesia-influence of sympathetic block and of systemic effect of the local anaesthetic. Acta Anaesthesiol Scand 1985;29:849-55. 8. Reinhart K, Foehring U, Kersting T, et al: Effects of thoracic epidural anaesthesia on systemic hemodynamic function and systemic oxygen supplydemand relationship. Anaesth Analg 1989;69:360-9. 9. Kehlet H: The endocrine responses to regional anesthesia. Int Anesthesiol Clin 1988;26: 182-6. 10. Breslow Mj, jordan DA, Christopherson R, et al: Epidural morphine decreases postoperative hypertension by attenuating sympathetic nervous system hyperactivity.JAMA 1989;261:3577-81. II. Baron jF, Decaux-jacolot A, Edouard A, et al: Influence of venous return on baroreflex control of heart rate during lumbar epidural anesthesia in humans. Anesthesiology 1986;64: 188-93. 12. Johansson K, Ahn H, Lindhagen j, et al: Effect of epidural anaesthesia on intestinal blood flow. Br J Surg 1988;75:73-6. 13. Diehl jT, Cali FR, Hertzer NR, et al: Complications of abdominal aortic reconstruction. Ann Surg 1983;197:49-56. 14. Rao TLK, jacobs KH, EI-Etr AA: Reinfarction following anesthesia in patients with myocardial infarction. Anesthesiology 1983;59:499-505. 15. Chernow B, Alexander HR, Smallridge RC, et al: Hormonal responses to graded surgical stress. Arch Intern Med 1987; 147: 1273-8. 16. Del Guercio LRM, CohnjD: Monitoring operative risk in the e1derly.JAMA 1980;243: 1350-5. 17. Armitage EN: Postoperative pain-prevention or relief? [Editorial]. Br J Anaesth 1989;63:136-7.
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