Consensus, consent and consciousness

Hypotension following spinal anaesthesia for caesarean section is common with significant maternal and foetal consequences. Despite this, practices vary markedly and there has, thus far, been a lack of formal guidance. This month in Anaesthesia sees the publication of an international consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. (Developing a consensus statement is a complex process, as there are few simple black and white recommendations that can be supported with robust scientific evidence.) Ten key recommendations for best practice are provided including, for example, a phenylephrine infusion starting at 25-50 mcg.min^-1 and titrated to systolic blood pressure (≥ 90% baseline), left lateral uterine displacement and the consideration of colloid or crystalloid pre-loading. Jeremy Campbell and Gary Stocks argue this puts right a surprising lack of guidance for an important group of patients, and its introduction will no-doubt improve foetal outcomes and the birthing experience of all mothers undergoing caesarean section under spinal anaesthesia. Although we may have not, just yet, discovered the Holy Grail of obstetric anaesthesia (and some have highlighted the limitations of a consensus approach), this guidance certainly provides clear, sensible and practical advice to all.

The consensus statement and editorial are accompanied by two similarly themed original research articles. The first, by Zieleskiwicz et al., investigates the association between maternal hypotension following spinal anaesthesia and point-of-care ultrasound derived subaortic ΔVTI before and after performance of a passive leg raise manoeuvre prior to spinal anaesthesia for caesarean section. They found a subaortic ΔVTI of ≤ 8% and ≥ 21% to be predictive of absence or occurrence of hypotension respectively. Secondly, Dyer et al. report their RCT of maternal cardiac output response to colloid preload and vasopressor therapy during spinal anaesthesia for caesarean section in patients with severe pre-eclampsia. They found cardiac output increased following spinal anaesthesia in women with severe early onset pre-eclampsia, and a small dose of phenylephrine reversed this haemodynamic change more effectively than ephedrine. Lower doses of phenylephrine are therefore recommended for such patients, where required.

How well do you understand and practice consent for anaesthesia? Nicholas Chrimes and Stu Marshall discuss the barriers to informed consent in anaesthesia and argue certain practical challenges may deny patients their legal right to make decisions about their care. They call for better alignment between the principles of consent and the realities of clinical practice in light of recently published guidelines. (The 2017 AAGBI consent for anaesthesia guideline is a ‘must read’ for every anaesthetist!) For example, if patients are to be informed of and give permission for every individual element contributing to their anaesthetic, together with every possible complication, they argue obtaining informed consent for anaesthesia may be at best extremely challenging and at worst, impossible.

Does loss or responsiveness (LOR) and recovery of responsiveness (ROR) occur at the same concentration of anaesthetic agent? Not according to the study by Sepúlveda et al. where propofol was administered to 19 healthy volunteers using a Schnider effect site target controlled infusion (Figure 1). They found LOR ensued at a higher propofol concentration than ROR and conclude this may suggest evidence of neuronal inertia in transitioning between LOR and ROR. In the accompanying editorial, Frank Engbers asks, is unconsciousness simply the reverse of consciousness? He argues ROR is likely dependent upon external and internal stimuli as well as the anaesthetic drug concentration. An observed hysteresis between LOC and ROC, although not illogical, may therefore be explained by many factors other than brain inertia.

Figure 1 Observed numbers of unresponsive subjects during induction (red line) and recovery (blue line) periods as a function of Schnider model predicted effect-site concentration (a) and measured plasma concentration (b).

We are delighted to have published two narrative reviews this month and each provides a summary of recent evidence for core anaesthetic topics. They are, therefore, essential reading for all. Firstly, Tim Cook emphasises the critical importance of communication, decision-making and non-technical practice with regards the avoidance of major airway complications. (He describes this as everything he has ever said on twitter in one long article!) Highlights include a description of themes emergent from fatal case reviews (Figure 2) and a novel cognitive aid for dealing with an evolving airway crisis, the Vortex approach© (Figure 3). The second review from Tasbihgou et al. presents a synthesis of recent evidence with regards accidental awareness under general anaesthesia (AAGA). They argue AAGA is both common and preventable yet associated with severe psychological consequences in some. They therefore call for anaesthetic departments to implement and maintain strategies to limit its occurrence.

Figure 2 Recognisable events and pitfalls of fatal airway complications.

Figure 3 The Vortex approach© to airway management (vortexapproach.org; reproduced with the permission of Nicholas Chrimes.

If a patient develops intra-operative anaphylaxis and is successfully resuscitated, should planned surgical procedures continue? Sadleir et al. argue it seems reasonable to do so following grade 1, 2 and 3 immediate hypersensitivity reactions (Figure 4) based on their retrospective analysis of 223 patients over nine years in Western Australia. This, however, is as long as the continuing management of acute hypersensitivity does not prevent successful completion of surgery, or proceeding with surgery does not prevent resuscitative efforts, should they be required. Elsewhere this month Henningsen et al. report a qualitative study of patient experiences with regards peripheral nerve blockade for ankle fracture surgery, Tallent et al. evaluate the ‘ISO-Gard’ oxygen/scavenging mask as a means to reduce the level of exhaled sevoflurane/desflurane below recommended exposure limits and László et al. describe a method of teaching flexible fibreoptic tracheal intubation in cadavers preserved using Thiel’s method as compared with manikins.

Figure 4 Classification of severity of acute hypersensitivity reactions.

Finally, preparations are well underway for the AAGBI Winter Scientific Meeting in London (10^th-12th January). Congratulations to all those with an accepted abstract! Our ‘How to publish a paper’ workshop (11^th January, 2-4pm) is once again free to all attendees. Matt Wiles chairs the Friday morning Anaesthesia session with topics for discussion including respiratory, cardiovascular and blood transfusion associated complications. Our stand will be open throughout and we very much hope to see you there!

Mike Charlesworth, Editor Fellow