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The ranges of measurements for digital SpO2 (85 to 100%, n ¼ 225), forehead SpO2 (41 to 100%, n ¼ 225) and ear SpO2 (60 to 100%, n ¼ 206) were compared with values of SaO2 (65 to 100%, n ¼ 230). Bias, precision, limits of agreement and ATI for all measurements (n ¼ 230), hypothermia (n ¼ 82), low perfusion index state (n ¼ 57) and norepinephrine infusion (n ¼ 54) are reported in Table 1. Intraclass correlation coefficients between arterial SaO2 and digital, forehead and ear SpO2 values were 0.64, 0.46 and 0.52, respectively. The dose regimen for norepinephrine ranged from 0.01 to 0.30 mg kg1 min1. We report in the current study, conducted in patients undergoing elective cardiac surgery with CPB, only marginal agreement in general between arterial SaO2 and digital SpO2, and unacceptable agreement with cephalic sites of SpO2 as determined using the ATI. Moreover, cephalic sites were not more accurate during hypothermia, low perfusion index state or norepinephrine infusion, all clinical scenarios potentially associated with an increase in vasomotor tone. To date, few studies have compared cephalic and digital SpO2 and have reported contrasting results. Forehead SpO2 must be assessed using a specific reflectance sensor because disposable finger sensors placed on the forehead are inaccurate in more than 50% of individuals.4 Blaylock et al.5 found no differences between all sensors during the perioperative period, while Schallom et al.6 concluded that forehead sensors improved the accuracy of measurement of SaO2 in critically ill and trauma patients. Nesseler et al.7 found that forehead SpO2 measurements seemed more accurate than digital SpO2 in critically ill patients requiring high-dose vasopressor therapy. Thus, the lower doses of norepinephrine we used in the current study may partially explain the absence of benefit of cephalic sites in assessing SpO2. In conclusion, we did not find that cephalic were superior to SpO2 digital sensors in routine cardiac surgery and that the agreement with SaO2 was, in general, only marginal for digital SpO2 and unacceptable for both cephalic SpO2 sites of measurement. Other studies are warranted to assess the potential clinical interest of cephalic sites of SpO2 measurement before recommending their wider use.

Acknowledgements relating to this article Assistance with the study: none. Financial support and sponsorship: the authors thank Covidien (Mansfield, Massachusetts, USA) for providing all the facilities necessary for pulse oximetry monitoring. Covidien was neither involved in the study design nor in the data collection or writing the manuscript. Conflicts of interest: none.

References 1

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Haynes AB, Weiser TG, Berry WR, et al. A surgical surgery checklist to reduce morbidity and mortality in a global population. N Engl J Med 2009; 360:491–499. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat 2007; 17:571– 582. Columb MO. Clinical measurement and assessing agreement. Curr Anaesth Crit Care 2008; 19:328–329. Smithline HA, Rudnitzky N, Macomber S, Blank FS. Pulse oximetry using a disposable finger sensor placed on the forehead in hypoxic patients. J Emerg Med 2010; 39:121–125. Blaylock V, Brinkman M, Carver S, et al. Comparison of finger and forehead oximetry sensors in postanesthesia care patients. J Perianesth Nurs 2008; 23:379–386. Schallom L, Sona C, McSweeney M, Mazuski J. Comparison of forehead and digit oximetry in surgical/trauma patients at risk for decreased peripheral perfusion. Heart Lung 2007; 36:188–194. Nesseler N, Fre´nel JV, Launey Y, et al. Pulse oximetry and highdose vasopressors: a comparison between forehead reflectance and finger transmission sensors. Intensive Care Med 2012; 38:1718– 1722. DOI:10.1097/EJA.0000000000000129

Clinical evaluation of acoustic respiration rate monitoring compared with conventional systems in the postanaesthesia care unit Tomoko Fukada, Hiroko Iwakiri, Minoru Nomura and Makoto Ozaki From the Department of Anaesthesiology, Tokyo Women’s Medical University, School of Medicine, Tokyo, Japan (TF, HI, MN, MO) Correspondence to Tomoko Fukada, Department of Anaesthesiology, Tokyo Women’s Medical University, School of Medicine, 8-1 Kawadacho Shinjukuku, Tokyo 162-8666, Japan Tel: +81 3 3353 8111; fax: +81 3 5269 7336; e-mail: [email protected] Published online 17 November 2014

Editor, Monitoring the respiratory rate of postoperative patients is necessary to detect respiratory depression related to opioid administration or residual effects of anaesthetics or muscle relaxants.1–4 Oxygen saturation (SpO2) is often used as an index of respiratory condition instead of respiratory rate. However, the administration of supplemental oxygen makes SpO2 a very late detector of respiratory depression. To prevent respiratory depression, it is important to monitor respiratory rate accurately in postoperative patients without causing discomfort. The respiratory rate can be considered as an indirect measure of CO2 retention. Acoustic respiration rate (RRa, Rad-87; Masimo Japan Corp., Tokyo, Japan) was recently developed as a noninvasive method to monitor respiratory rate. An adhesive neck sensor detects respiratory sounds from the neck during the inspiratory and expiratory phases. We hypothesised that RRa is a highly accurate and noninvasive

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62 Correspondence

Comparison of acoustic respiration rate, thoracic impedance pneumography and capnography with visual inspection of chest movement over 1 min in postoperative patients

Table 1

All patients (n ¼ 1270) Bias [95% CI] (min1) SD (min1) Limits of agreement (min1) Patients with RR 10 min1 (n ¼ 196) Bias [95% CI] (min1) SD (min1) Limits of agreement (min1)

RRa-EYE

CAP-EYE

TIP-EYE

0.2M [0.4 to 0.1] 2.2 4.5 to 4.0

1.8M [2.0 to 1.6] 3.1 7.9 to 4.3

0.9M [0.7 to 1.1] 3.3 5.5 to 7.4

0.2 [0 to 0.4] 1.7 3.1 to 3.4

1.2 M[1.6 to 0.8] 2.9 6.8 to 4.4

1.8M [1.3 to 2.2] 3.4 4.9 to 8.4

CAP, capnography; CI, confidence interval; EYE, visual inspection of chest movement over 1 min; RRa, acoustic respiration rate; SD, standard deviation; TIP, thoracic impedance pneumography. M P  0.05.

method to monitor respiratory rate. Therefore, we compared this technique with mainstream capnography [CAP, Cap  ONE (Oral Nasal Expiration) TG-920P; Nihon Kohden Corp., Tokyo, Japan], thoracic impedance pneumography (TIP, BSM-6000 Life Scope Bedside Monitor; Nihon Kohden Corp., Tokyo, Japan) and visual inspection of chest movement over one minute (EYE). Ethical approval for this study (No. 2519) was provided by the Ethics Committee of Tokyo Women’s Medical University, Tokyo, Japan (Chairperson Prof S. Miyazaki) on 27 June 2012, and written informed consent was obtained from all patients. This study was conducted in the PACU of Tokyo Women’s Medical University Hospital from July 2012 to February 2013. The individuals were postoperative patients aged at least 20 years. The surgery did not involve the neck, face or chest. The adhesive sensor of the RRa was applied firmly to the front of the patient’s neck, slightly to the side, where respiration-related vibration is the strongest. The amplitude of the acoustic signal is proportional to the sensor position, strength of the breath and sound conduction from the trachea through the muscles and skin of the patient’s neck. It is also important to measure SpO2 simultaneously because RRa is correlated with SpO2 during conversion into electrical signals. An SpO2 sensor was attached to a finger or toe outside the sphygmomanometer manchette. For CAP, the airway adaptor (YG-121T; Nihon Kohden Corp.) was inserted into both nostrils. This adaptor is attached to a mouth guide and can measure orally and nasally expired CO2, and respiratory rate is calculated from change of expired CO2. For TIP, two electrodes (Kendall ECG Electrodes; Covidien Japan Corp., Tokyo, Japan) were attached to the chest wall, with the positive electrode on the right subclavian fossa and the negative electrode on the fifth left midclavicular intercostal space or lowest anterior axillary rib. EYE were counted by an experienced PACU staff member.

oxygen through a facemask in the PACU. The anaesthetic and operating times were 233 (72) and 156 (65) min, respectively. None of these patients experienced arterial desaturation, and the respiratory rate of 102 patients remained at least 6 min1. BlandAltman plots were used to compare the accuracy of the three monitoring systems to EYE (Table 1). The bias, SD and limit of agreement for all patients were lower for the RRa-EYE comparison than for the CAP-EYE and TIPEYE comparisons. When respiratory rate was 10 min1 or less, careful monitoring was required, but no difference was observed between RRa and EYE.

A total of 103 out of 106 patients completed the entire respiratory rate protocol (ASA I/II/III, 78/14/11; male/female 48/55). They had a mean (SD) age of 62 (15) years, weight of 59 (12) kg and BMI of 23 (4) kg m2 respectively. Anaesthesia was total intravenous (N ¼ 93) or by inhalation (N ¼ 10), and they received 5 l min1

Acknowledgements relating to this article

The main disadvantage of the RRa system is that respiratory rate cannot be detected without SpO2 monitoring, and poor peripheral circulation or artefacts interfere with SpO2. In order to monitor respiratory rate by CAP accurately, the mouth guide of the airway adaptor must be placed 1 cm or less from the lips and when using an oxygen mask, the oxygen flow rate must be at least 5 l min1. However, some patients removed the airway adaptor from their nostrils, particularly those with a stomach tube, due to sensor discomfort. The accuracy of TIP is influenced by electrode positioning, patient movement and shivering because TIP does not measure the actual respiratory airflow. Moreover, an instance of normal impedance trace during apnoea due to airway obstruction has been reported.5 On the contrary, monitoring respiratory rate by EYE provides additional valuable information, such as breathing pattern and facial colour. The observer can also address complaints immediately. However, it is the least convenient method because it can only be performed intermittently and depends on staff availability. We concluded that the RRa is a highly accurate and noninvasive device for the rapid detection of respiratory depression. Assistance with the letter: we would like to thank Yuri Tsuchiya, MD, and Yuko Uenaka, RN, for their help in collecting data and all PACU staff for their cooperation. Financial support and sponsorship: all the equipment and sensors were purchased by our hospital as standard patient monitoring care

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Correspondence 63

and the costs of research personnel were funded by our department. Conflicts of interest: none.

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Cashman JN, Dolin SJ. Respiratory and haemodynamic effects of acute postoperative pain management: evidence from published data. Br J Anaesth 2004; 93:212–223. Overdyk FJ, Carter R, Maddox RR, et al. Continuous oximetry/ capnometry monitoring reveals frequent desaturation and bradypnea during patient-controlled analgesia. Anesth Analg 2007; 105:412–418. Debaene B, Plaud B, Dilly M-P, Donati F. Residual paralysis in the PACU after a single intubationg dose of nondepolarizing muscle relaxant with an intermediate duration of action. Anesthesiology 2003; 98:1042– 1048. Murphy GS, Szokol JW, Marymont JH, et al. Residual neuromuscular blockade and critical respiratory events in the postanesthesia care unit. Anesth Analg 2008; 107:130–137. Wilkinson JN, Thanawala VU. Thoracic impedance monitoring of respiratory rate during sedation – is it safe? Anaesthesia 2009; 64:447–458. DOI:10.1097/EJA.0000000000000193

Iatrogenic jugular-carotid fistula despite ultrasound-guided vascular access Manuel F. Struck and Udo X. Kaisers From the Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany Correspondence to Manuel F. Struck, Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Liebigstr. 20, 04103 Leipzig, Germany Tel: +49 341 97 17700; fax: +49 341 97 17709; e-mail: [email protected]

CT was avoided due to low thyrotropin levels and renal dysfunction). Consequently, an endovascular repair of the JCF was performed placing a covered Fluency-stent-graft into the common carotid artery under general anaesthesia. Neurological examination after the end of anaesthesia revealed no deficit. Written informed consent to publish this case was obtained from the patient’s husband after progression and a fatal outcome to the liver failure. Puncture-related injuries of the neck region after intended internal jugular venous access are serious incidents that may cause life-threatening conditions. They include Horner’s syndrome, venous perforation, pneumothorax, cardiac tamponade, and thyroid injury or carotid artery lesion. If the arterial puncture is not recognised immediately and dilatation of the vessel and placement of the catheter follow, severe complications may result, such as arterial perforation, haemothorax, pseudoaneurysm and JCF.1 Although inadvertent carotid artery puncture accounts for the most frequent complication of jugular venous access, JCFs are rarely reported.2 Large-bore catheter devices, such as haemodialysis catheters, as reported in this case, are more likely to cause JCF than smaller catheters because vessel dilation and catheter placement may generate considerable injuries to vascular walls. JCFs commonly develop after removal of the catheter and persistence of the puncture channel. The transjugular jet of arterial blood can be limited to the jugular vein, but it can also spread into surrounding muscular and subcutaneous tissue, as in the case presented. The early repair of a JCF, either by an endovascular or surgical approach, is considered beneficial in the literature.2–4

Published online 7 March 2014

Editor, A 58-year-old woman presented to the ICU with druginduced liver failure and progressive renal dysfunction. Vascular access for haemodialysis was prepared using a 12 French haemodialysis catheter via a left internal jugular venous approach guided by ultrasound monitoring. Sonography presented a 12-o’clock configuration of the jugular-carotid anatomy. Vascular puncture appeared successful, and nonpulsatile dark-coloured blood was aspirated. After guide-wire insertion, puncture channel dilation and catheter insertion, pulsation of blood was visible immediately. Blood gas analysis revealed an arterial oxygen saturation. After consultation with a vascular surgeon, the haemodialysis catheter was removed and manual compression at the puncture site was applied for 30 min. Repeated sonography revealed a jugularcarotid fistula (JCF) confirmed by a pulsatile transjugular jet from the common carotid artery through the puncture channel into the sternocleidomastoid muscle. Manual compression was continued for another 60 min and vascular surgery was avoided. Within 24 h sonography and MRI confirmed a persisting JCF (contrast medium

The use of ultrasound for jugular venous access has recently been recommended to increase success rates and performance safety.5 There are numerous studies supporting the benefits of ultrasound use for vascular access.6,7 This case, however, illustrates that even under direct sonographic visualisation of the puncture process, misplacements of large-bore haemodialysis catheters are possible. We suggest that the JCF was caused by secondary vascular wall damage by the puncture needle while inserting the guide-wire. After successful puncture of the jugular venous wall, the operator requires both hands to fix the puncture needle and insert the guide-wire. This step is likely to be taken without ultrasound monitoring if a second person is not available to assist in keeping the ultrasound detector in place. Hence, the risk of secondary misplacement of the guide-wire increases despite an apparently correct position of the puncture needle. Depending on the location of neighbouring vascular structures and the angle of puncture direction, unintentional secondary perforation of jugular venous wall may be caused by slight movement of the puncture needle.8 The process of internal jugular vein catheterisation requires first, training, such as a simulation course (see,

Eur J Anaesthesiol 2015; 32:58–68 Copyright © European Society of Anaesthesiology. Unauthorized reproduction of this article is prohibited.

Clinical evaluation of acoustic respiration rate monitoring compared with conventional systems in the postanaesthesia care unit.

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