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Since its inception, administering and ensuring anaesthesia during cardiopulmonary bypass has been challenging. Partly because of the difficulty of administering volatile agents during cardiopulmonary bypass, total intravenous anaesthesia has been a popular technique used by cardiac anaesthetists in the last two decades. However, the possibility that volatile agents reduce mortality and the incidence of myocardial infarction by preconditioning the myocardium has stimulated a resurgence of interest in their use for cardiac anaesthesia. The aim of this review is to provide an overview of the administration of volatile anaesthetic agents during cardiopulmonary bypass for the maintenance of anaesthesia and to address some of the practical issues that are involved in doing so.

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Summary Intrathecal morphine is an analgesic option for major hepatopancreaticobiliary procedures but is associated with a risk of respiratory depression. We hypothesised that a postoperative low‐dose naloxone infusion would reduce the incidence of respiratory depression without an increase in pain scores. Patients scheduled for major open hepatopancreaticobiliary surgery and who were receiving 10 μg.kg−1 intrathecal morphine were eligible for inclusion. Patients were allocated randomly to receive a postoperative infusion of naloxone 5 μg.kg−1.h−1 (naloxone group) or saline at an identical infusion rate (control group) until the morning after surgery. Clinicians, nursing staff and patients were blinded to group allocation. The primary outcome measure was the incidence of respiratory depression (respiratory rate < 10 breaths.min−1 and/or oxygen saturation < 90%). Secondary outcome measures included: arterial partial pressure of carbon dioxide; pain score; requirement for supplemental analgesic; and incidence of nausea and vomiting, pruritus and sedation. In total, data from 95 patients (48 in the naloxone group and 47 in the control group) were analysed. The incidence of respiratory depression was lower in the naloxone group compared with the control group (10/48 vs. 21/47 patients, respectively; p = 0.037, relative risk 0.47 (95%CI 0.25–0.87). Maximum pain scores were greater for patients allocated to the naloxone group compared with control (median 5 (95%CI 4–6) vs. 4 (95%CI 2–4), respectively; p < 0.001). A low‐dose naloxone infusion decreases the incidence of respiratory depression following intrathecal morphine administration in patients having major hepatopancreaticobiliary surgery at the expense of a small increase in postoperative pain.

BackgroundIntrathecally administered morphine is effective as part of a postoperative analgesia regimen following major hepatopancreaticobiliary surgery. However, the potential for postoperative respiratory depression at the doses required for effective analgesia currently limits its clinical use. The use of a low-dose, prophylactic naloxone infusion following intrathecally administered morphine may significantly reduce postoperative respiratory depression. The NAPRESSIM trial aims to answer this question.Methods/design‘The use of low-dose, prophylactic naloxone infusion to prevent respiratory depression with intrathecally administered morphine’ trial is an investigator-led, single-centre, randomised, double-blind, placebo-controlled, double-arm comparator study. The trial will recruit 96 patients aged > 18 years, undergoing major open hepatopancreaticobiliary resections, who are receiving intrathecally administered morphine as part of a standard anaesthetic regimen. It aims to investigate whether the prophylactic administration of naloxone via intravenous infusion compared to placebo will reduce the proportion of episodes of respiratory depression in this cohort of patients.Trial patients will receive an infusion of naloxone or placebo, commenced within 1 h of postoperative extubation continued until the first postoperative morning. The primary outcome is the rate of respiratory depression in the intervention group as compared to the placebo group. Secondary outcomes include pain scores, rates of nausea and vomiting, pruritus, sedation scores and adverse outcomes. We will also employ a novel, non-invasive, respiratory minute volume monitor (ExSpiron 1Xi, Respiratory Motion, Inc., 411 Waverley Oaks Road, Building 1, Suite 150, Waltham, MA, USA) to assess the monitor’s accuracy for detecting respiratory depression.DiscussionThe trial aims to provide a clear management plan to prevent respiratory depression after the intrathecal administration of morphine, and thereby improve patient safety.Trial registrationClinicalTrials.gov, ID: NCT02885948. Registered retrospectively on 4 July 2016.Protocol Version 2.0, 3 April 2017.Protocol identification (code or reference number): UCDCRC/15/006EudraCT registration number: 2015-003504-22. Registered on 5 August 2015.Electronic supplementary materialThe online version of this article (doi:10.1186/s13063-017-2370-0) contains supplementary material, which is available to authorized users.