Letters to the Editor

when the DLT connector is clamped off as a precursor to initiating OLV. This action will ensure that a potentially large volume of ambient air, with slowly diffusing nitrogen,4 will be prevented from “washing” into the nonventilated lung with each ongoing respiratory excursion of the ventilated lung before the pleura is opened.5 The airway should NOT be left “open to air”! John Pfitzner, FRCA Department of Anaesthesia The Queen Elizabeth Hospital Woodville, South Australia, Australia [email protected] REFERENCES 1. Yoshimura T, Ueda K, Kakinuma A, Sawai J, Nakata Y. Bronchial blocker lung collapse technique: nitrous oxide for facilitating lung collapse during one-lung ventilation with a bronchial blocker. Anesth Analg 2014;118:666–70 2. Pfitzner J, Peacock MJ, Harris RJ. Speed of collapse of the nonventilated lung during single-lung ventilation for thoracoscopic surgery: the effect of transient increases in pleural pressure on the venting of gas from the non-ventilated lung. Anaesthesia 2001;56:940–6 3. Young Yoo J, Hee Kim D, Choi H, Kim K, Jeong Chae Y, Yong Park S. Disconnection technique with a bronchial blocker for improving lung deflation: a comparison with a doublelumen tube and bronchial blocker without disconnection. J Cardiothorac Vasc Anesth [Epub ahead of print] 4. Ko R, McRae K, Darling G, Waddell TK, McGlade D, Cheung K, Katz J, Slinger P. The use of air in the inspired gas mixture during two-lung ventilation delays lung collapse during one-lung ventilation. Anesth Analg 2009;108:1092–6 5. Pfitzner J, Peacock MJ, McAleer PT. Gas movement in the nonventilated lung at the onset of single-lung ventilation for videoassisted thoracoscopy. Anaesthesia 1999;54:437–43 DOI: 10.1213/ANE.0000000000000336

In Response We agree with Dr. Pfitzner1 that the “scatter” of lung deflation scores likely reflects the variation in the physiology and pathophysiology of patients in our study2 even though lung function tests showed that there was no difference between the 2 study groups. We understand the concern that markedly varying volumes of alveolar gas were suctioned before the onset of small airway closure, which might have confounded lung deflation scores. However, the level of suction used in our study was low and the Arndt® bronchial blocker (Cook® Critical Care, Bloomington, IN) suction channel had high flow resistance due to a small caliber size and diameter; therefore, it is unlikely that a significant amount of air was suctioned. The study by Narayanaswamy et al.3 showed that application of suction failed to improve lung collapse with the Arndt bronchial blocker. Thus, difference in volumes of alveolar gas suctioned should not be a major cause of the observed differences in lung deflation scores. We also agree that a delay in balloon inflation can facilitate elastic recoil lung collapse and improve lung deflation.4 However, we focused on the effect of nitrous oxide for facilitating absorption atelectasis in our study. Therefore, the ­balloon was kept inflated at the initiation of one-lung ­ventilation in our study. Finally, Dr. Pfitzner et al.5 commented on the potential ambient air “washing” into the nonventilated lung before

October 2014 • Volume 119 • Number 4

the pleura was open. According to his study, influx of air could be up to 320 mL when a double-lumen tube (DLT) was used. However, considering the radius and length of each device (6 mm and 42 cm in 35 F DLT and 1.4 mm and 78 cm in Arndt bronchial blocker, respectively), volumetric flow rate in the bronchial blocker’s suction channel is 0.15% of the DLT flow rate when the Hagen-Poiseuille equation6 is applied. Therefore, the effect of gas influx through the suction channel should be negligible on lung collapse when the bronchial blocker is used for lung isolation. Tatsuya Yoshimura, MD Department of Anesthesiology Shin-yurigaoka General Hospital Tokyo, Japan Kenichi Ueda, MD Department of Anesthesia University of Iowa Hospitals and Clinics Iowa City, Iowa [email protected] REFERENCES 1. Pfitzner J. Facilitating lung collapse during one lung ventilation can be rational. Anesth Analg 2014;119:1002 2. Yoshimura T, Ueda K, Kakinuma A, Sawai J, Nakata Y. Bronchial blocker lung collapse technique: nitrous oxide for facilitating lung collapse during one-lung ventilation with a bronchial blocker. Anesth Analg 2014;118:666–70 3. Narayanaswamy M, McRae K, Slinger P, Dugas G, Kanellakos GW, Roscoe A, Lacroix M. Choosing a lung isolation device for thoracic surgery: a randomized trial of three bronchial blockers versus double-lumen tubes. Anesth Analg 2009;108:1097–101 4. Young Yoo J, Hee Kim D, Choi H, Kim K, Jeong Chae Y, Yong Park S. Disconnection technique with a bronchial blocker for improving lung deflation: a comparison with a doublelumen tube and bronchial blocker without disconnection. J Cardiothorac Vasc Anesth 2013; [Epub ahead of print] 5. Pfitzner J, Peacock MJ, Harris RJ. Speed of collapse of the nonventilated lung during single-lung ventilation for thoracoscopic surgery: the effect of transient increases in pleural pressure on the venting of gas from the non-ventilated lung. Anaesthesia 2001;56:940–6 6. Mujica-Lopez KI, Pearce MA, Narron KA, Perez J, Rubin BK. In vitro evaluation of endotracheal tubes with intrinsic suction. Chest 2010;138:863–9 DOI: 10.1213/ANE.0000000000000349

Prevention of Postoperative Nausea and Vomiting: A Thought on Ondansetron To the Editor

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n a recent article, Gan et al.1 stated ondansetron to be the standard for antiemesis with regard to postoperative nausea and vomiting and recommended 4 mg IV as suggested by the quantitative systematic review performed by Tramèr et al.2 While I agree that 4 mg may be the optimal IV dose for early outcomes within the first 6 hours according to the original article by Tramèr, it is also perhaps worth considering that 8 mg IV was concluded to be the optimal IV dose

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E Letters to the Editor for late outcomes (within the first 48 hours) and may perhaps confer more benefits and a better patient experience. Rebecca Helen Rehill, MBBS, BSc Department of Anaesthetics Royal Sussex County Hospital Brighton, United Kingdom [email protected] REFERENCES 1. Gan TJ, Diemunsch P, Habib AS, Kovac A, Kranke P, Meyer TA, Watcha M, Chung F, Angus S, Apfel CC, Bergese SD, Candiotti KA, Chan MT, Davis PJ, Hooper VD, Lagoo-Deenadayalan S, Myles P, Nezat G, Philip BK, Tramèr MR; Society for Ambulatory Anesthesia. Consensus guidelines for the management of postoperative nausea and vomiting. Anesth Analg 2014;118:85–113 2. Tramèr MR, Reynolds DJ, Moore RA, McQuay HJ. Efficacy, dose-response, and safety of ondansetron in prevention of postoperative nausea and vomiting: a quantitative systematic review of randomized placebo-controlled trials. Anesthesiology 1997;87:1277–89 DOI: 10.1213/ANE.0000000000000363

A Secondary Analysis of a Randomized Placebo-Controlled Trial Comparing the Analgesic Effects of Oxytocin with Carbetocin: Postcesarean Delivery Morphine Equivalents To the Editor

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esarean delivery patients release endogenous oxytocin, and the pain-relieving effect of the endogenous oxytocin might be substantial.1 The 2 oxytocin receptor agonists, oxytocin and carbetocin, may interact with endogenous oxytocin. One study evaluating the effect of carbetocin on pain after cesarean delivery demonstrated a significant reduction of pain intensity after a single injection of carbetocin 100 μg compared with oxytocin 10 U followed by an infusion of oxytocin.2 The unexpected finding of a clinically and statistically significant pain-relieving effect of carbetocin is interesting. 25

MME (SD)

20

Placebo Oxytocin Carbetocin

15 10 5 0 0–8h

0 – 24 h

0 – 48 h

0 – 72 h

Figure 1. Cumulative consumption of opioids presented as mean morphine mg equivalents (MME) and standard deviation (SD).

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As a secondary analysis of data from a previously published randomized controlled trial to study differences in hemodynamic side effects, uterine tone, and blood loss among IV carbetocin 100 μg, oxytocin 5 U, and placebo,3 we analyzed opioid consumption data. After completion of the study, the IRB approved review of the medical records of patients included in the original study for the purpose of this secondary analysis. The identity and dose of all analgesic agents (morphine, ketobemidone, and oxycodone) administered in the first 72 hours were abstracted from the record and converted to morphine milligram equivalents (MME).4 All patients in the protocol analyses were given oral paracetamol 4 g/d and i­ buprofen 1600 mg/d. Of the 185 patients screened, 76 patients having cesarean delivery under spinal anesthesia (bupivacaine 10 mg + fentanyl 20 μg) were randomized. The cumulative mean consumption of opioids 0 to 48 hours after surgery was 23.1 MME (SD 4.6) in the placebo group (N = 20), 22.7 MME (SD 6.0) after oxytocin 5 U (N = 17), and 21.8 MME (SD 4.4) after carbetocin 100 μg (N = 19) (Fig. 1). The differences were not statistically significant (Kruskal-Wallis test). In contrast to De Bonis et al.,2 we failed to show a difference between the 2 drugs. Future trials assessing the analgesic effect of oxytocin and carbetocin should be sufficiently powered to detect significant differences in pain intensity and rescue analgesic consumption, as well as the rate of adverse events. Patient Consent Statement: Written consent was obtained from the patients.

Ewa Gawecka, MBChB Department of Anesthesiology Division of Emergencies and Critical Care Oslo University Hospital Oslo, Norway [email protected] Leiv Arne Rosseland, MD, PhD Department of Anesthesiology Division of Emergencies and Critical Care Oslo University Hospital Oslo, Norway Institute of Clinical Medicine Faculty of Medicine University of Oslo Oslo, Norway REFERENCES 1. Takeda S, Kuwabara Y, Mizuno M. Effects of pregnancy and labor on oxytocin levels in human plasma and cerebrospinal fluid. Endocrinol Jpn 1985;32:875–80 2. De Bonis M, Torricelli M, Leoni L, Berti P, Ciani V, Puzzutiello R, Severi FM, Petraglia F. Carbetocin versus oxytocin after caesarean section: similar efficacy but reduced pain perception in women with high risk of postpartum haemorrhage. J Matern Fetal Neonatal Med 2012;25:732–5 3. Rosseland LA, Hauge TH, Grindheim G, Stubhaug A, Langesæter E. Changes in blood pressure and cardiac output during cesarean delivery: the effects of oxytocin and carbetocin compared with placebo. Anesthesiology 2013;119:541–51 4. Von Korff M, Saunders K, Thomas Ray G, Boudreau D, Campbell C, Merrill J, Sullivan MD, Rutter CM, Silverberg MJ, Banta-Green C, Weisner C. De facto long-term opioid therapy for noncancer pain. Clin J Pain 2008;24:521–7 DOI: 10.1213/ANE.0000000000000372

anesthesia & analgesia

Prevention of postoperative nausea and vomiting: a thought on ondansetron.

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