The implications of vaping for the anaesthetist

Learning objectives.

By reading this article, you should be able to:

• •Discuss the known and potential adverse health consequences of vaping.
• •Describe the current regulatory environment pertaining to vaping.
• •Discuss the role of e-cigarettes in assisting smoking cessation.
• •Outline the perioperative considerations for patients who use e-cigarettes.

Key points.

• •E-cigarettes deliver a flavoured aerosol for inhalation that may contain nicotine.
• •The use of e-cigarettes has increased sharply, ahead of clear medical evidence of outcomes, and requiring rapid changes to legislation.
• •E-liquids may contain substances (e.g. vitamin E acetate) linked with significant respiratory harm.
• •The UK supports the use of e-cigarettes to help people who smoke to quit.
• •The anaesthetic implications of vaping are likely to be less severe than those of cigarette smoking.

Aerosolised drugs have been used to treat asthma since the 1950s. However, the recreational practice of inhaling aerosols (vaping) has become prevalent in recent years. Both medicine and the law have lagged behind this rapid increase in use. Understanding of the health effects of recreational aerosols is incomplete, and although work is underway, robust legislation and regulation is yet to be developed and applied to the wide variety of products.

Electronic cigarettes (e-cigarettes) are devices that emulate the experience of smoking. When activated, e-cigarettes produce an aerosol, known as ‘vapour’ that is inhaled by the user. An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. The terms ‘electronic cigarettes’ and ‘vaping products’ encompass both electronic nicotine delivery systems (ENDS) and electronic non-nicotine delivery systems (ENNDS). People who use e-cigarettes can be referred to as ‘vapers’, with the act of using an e-cigarette termed ‘vaping’.

Little research has been carried on the specific effects of vaping on perioperative outcomes and anaesthetic care. This article provides an overview of vaping for the anaesthetist, drawing on data from the UK, USA and Australasia, and identifies areas where further research would be beneficial.

E-cigarette design and vaping liquid

In their most basic form, e-cigarettes comprise a battery, a heating coil within a vaporisation chamber and a reservoir containing the vaping liquid (e-liquid, vape juice or e-juice) (Fig. 1). Since the introduction of the first generation of e-cigarettes to the USA and European markets in 2006, three further generations have been developed to establish the range of devices available for use today (Fig. 2).

Fig 1.

Anatomy of an e-cigarette. Source CDC: Centers for Disease Control and Prevention. E-cigarettes, or vaping, products visual dictionary. Available at no charge fromhttps://www.cdc.gov/tobacco/basic_information/e-cigarettes/pdfs/ecigarette-or-vaping-products-visual-dictionary-508.pdf (accessed 14 November 2020). Reproduction of material produced by the CDC within this article does not constitute endorsement or recommendation of the authors, BJA Education, or this article by the US Government, Department of Health and Human Services, or Centers for Disease Control and Prevention.

Fig 2.

The evolution of e-cigarette, or vaping, products. Products have evolved rapidly to be more attractive to users, especially youths, and offer a wider range of vaping experiences. Source CDC: Centers for Disease Control and Prevention. E-cigarettes, or vaping, products visual dictionary. Available at no charge fromhttps://www.cdc.gov/tobacco/basic_information/e-cigarettes/pdfs/ecigarette-or-vaping-products-visual-dictionary-508.pdf (accessed 14 November 2020). Reproduction of material produced by the CDC within this article does not constitute endorsement or recommendation of the authors, BJA Education, or this article by the US Government, Department of Health and Human Services, or Centers for Disease Control and Prevention.

E-liquid typically consists of a base of propylene glycol, glycerol, or both, flavours and potentially nicotine or other active ingredients. Electronic nicotine delivery systems contain nicotine in concentrations up to 36 mg ml⁻¹. Accuracy of the nicotine concentration listed on e-cigarettes has been found to be unreliable, with a 2018 US study finding that samples labelled 0 mg ml⁻¹ nicotine contained up to 23.9 mg ml⁻¹.¹ The systemic absorption of nicotine from e-cigarettes is affected by the e-liquid nicotine concentration, and the nature of the vaping device and inhalation technique. Nicotine concentrations achieved after e-cigarette use vary although cotinine concentrations, indicating nicotine exposure over the previous 3–4 days, are comparable between experienced e-cigarette users and people who smoke.² Most manufactured cigarettes contain approximately 10 mg nicotine with only about 1 mg nicotine being absorbed per cigarette. A number of studies have reported arterial nicotine concentrations after combustible cigarette use between 20 and 100 ng ml⁻¹.² Nicotine binds to nicotinic cholinergic receptors, resulting in the secretion of neurotransmitters including dopamine, glutamate and gamma-aminobutyric acid, which are important in the establishment of nicotine dependency.

Some e-liquids contain cannabinoids such as tetrahydrocannabinol (THC). E-cigarette vapour contains chemicals with carcinogenic potential including glycols, acetone, aldehydes, volatile organic compounds, polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines, metals (including tin, chromium, silver, copper, lead, arsenic and nickel) and silicate particles. There is evidence the heating coil may be a source of the metallic contamination. Bacterial endotoxins and fungal glucans have also been identified in e-liquids. According to a 2016 WHO report there were close to 8000 unique flavours of e-liquid, with the flavourings having an unclear risk of adverse health consequences with long-term use.³ Butanedione, a flavouring used in popcorn and in e-liquids, has been shown to cause bronchiolitis obliterans or ‘popcorn lung’ when heated and inhaled in significant doses over time.² The toxicants produced in the combustion of traditional cigarettes are found in higher concentrations and in higher numbers than e-cigarettes.²

Reports by Public Health England (PHE) and the Royal College of Physicians (RCP) acknowledge that e-cigarettes are not risk-free but estimate that they are unlikely to present more than 5% of the health risks of cigarette smoking.^2,4

Epidemiology of e-cigarette use

E-cigarettes were developed and first made available in China in 2003, and were introduced to Western markets in 2006. The global market for e-cigarettes was estimated to be almost $10 billion in 2015.³ The long-term future of e-cigarettes is unclear, given increasing but varied regulation, improved understanding of the health implications of use and evolution of alternative nicotine delivery systems, such as those launched by the tobacco industry that heat but do not burn tobacco.

Public Health England reported on the use of e-cigarettes in 2020.⁵ The rate of cigarette smoking among adults in England was around 15% in 2019. The prevalence of vaping among adults in England has remained steady since 2014 and in 2019 was found to be 5–7%, although this was higher among people who currently (14–20%) and formerly smoke (12–13%). Comparative data from the two main world markets for e-cigarettes show that 3.2% of US adults were current users of e-cigarettes in 2018, as were 2% of European Union adults in 2017.^6,7

An estimated 27.5% of high school students (mean age 16.1 yrs) and 10.5% of middle school students (mean age 12.7 yrs) in the USA are current users of e-cigarettes.⁸ The concerning increase in youth vaping has seen the problem defined by many groups as the ‘youth vaping epidemic’. There is growing use of vaping devices containing cannabinoids as the legality of cannabis products evolves.

Regulation of vaping products internationally

Health authorities consider two main categories of e-cigarette user: current or recent users of combustible cigarettes looking to stop, and people who have never used combustible cigarettes. Health authorities express concern that the latter group will switch to smoking, while acknowledging that the former group could use vaping as a means of harm reduction or an aid to quitting.

A 2016 report by WHO outlined a series of potential regulatory measures that could be implemented to achieve the goals of preventing first use of e-cigarettes among people who do not smoke and youth; minimising possible health risks to e-cigarette users and protection of non-users from exposure to their emissions; preventing unproved health claims being made about vaping products and protecting tobacco control activities from all commercial and other vested interests.³ WHO has suggested several measures including outlawing the use of ENDS and ENNDS in all indoor spaces or where smoking is prohibited; banning or restricting advertising, promotion and sponsorship of ENDS and ENNDS; strongly enforcing laws on minimum age of purchase; limiting levels and number of specific flavours allowed in ENDS and ENNDS to reduce uptake by young people; and standardising the manufacture of vaping devices and components under effective electrical equipment safety regulations.⁷ WHO's conservative position on vaping has attracted criticism from some groups.

The UK

Under the UK's system of regulation ENDS and ENNDS can be sold legally. The nicotine content of vaping liquid cannot exceed 20 mg ml⁻¹. E-cigarettes cannot be sold to people under 18 yrs old. Mandatory health warnings must be displayed on packaging. Cannabinoids, colourings and some other additives (such as vitamin E acetate) are prohibited. Recent reports by both PHE and by the Tobacco Advisory Group of the RCP acknowledge that there is insufficient evidence, but suggest the use of e-cigarettes is a viable, harm reduction alternative to combustible cigarettes.^2,5 The NHS has actively promoted vaping as a smoking cessation tool. E-cigarette products are not licensed as medical devices.

The USA

US health authorities have adopted a more cautious approach with regard to assisted smoking cessation and have established a set of policies targeting the ‘youth vaping epidemic’. Concerned by the sharp increase in the use of tobacco products, particularly e-cigarettes, in young people, the Food and Drug Administration (FDA) expanded the Centre for Tobacco Products' regulatory authority in 2016 to cover all tobacco products including ENDS that meet the required definition and which were previously not subject to oversight.⁹

The FDA now prevents the sale of tobacco products, including e-cigarettes, to those aged less than 21 yrs, prohibits the sale of these products in vending machines and mandates health warning labelling on products. However, there is no maximum nicotine content in vaping liquid, and advertising is still permitted. In January 2020, the FDA issued an enforcement policy against e-cigarettes containing flavours including fruit and mint.⁹ In April 2020, the FDA sent warning letters to retailers and manufacturers selling products intended to promote vaping among young people, such as backpacks and sweatshirts designed to hold and conceal e-cigarettes.¹⁰ Manufacturers of e-cigarettes were required to submit an application for FDA approval by September 2020, disclosing the ingredients in their products and demonstrating that their products provide a net public health benefit.⁹

Australasia

In New Zealand, the Smoke-free Environments and Regulated Products (Vaping) Amendment Act 2020 commenced on 11 November 2020. This restricts sale to those more than 18 yrs of age, limits claims of therapeutic benefit and provides safety standards for products to be sold. In Australia (with the exception of South Australia), it is illegal to buy, possess or use liquid containing nicotine for the purposes of vaping unless prescribed by an Australian doctor. With the exception of some specific states, the use of ENNDS is legal. From 21 October 2021, consumers will require a doctor's prescription to import nicotine e-cigarettes and child-resistant closures will be required for liquid nicotine.

Assisted smoking cessation

The perioperative period presents a teachable moment for smoking cessation. Patients who stop smoking before surgery have improved perioperative outcomes, with a longer period of cessation leading to greater benefit. Patients may question their anaesthetist about using e-cigarettes to help quit smoking.

There is no international consensus regarding best practice use of e-cigarettes as part of an assisted smoking cessation strategy. The absence of consensus arises partly from an insufficient body of literature exploring the long-term health effect of vaping, the uncertainty regarding the efficacy of e-cigarettes in assisting smoking cessation and the concern of losing ‘social gains’ made in the campaign against combustible cigarette use.

Issues for policy makers to consider include the potential harms to youth with increased availability of ENDS; the risk of e-cigarette, or vaping use-associated lung injury (EVALI) especially with unregulated product use (see below); the risk to health more generally, including the risk of dependence and the potential ‘renormalisation’ of smoking associated with the introduction and widespread use of a variant tobacco product.

Perhaps the most obvious perceived benefit of e-cigarette use over more established nicotine replacement therapies (NRT) is the substitution of combustible cigarettes with an alternative practice that reflects the sensorimotor experience of smoking. The retention of the physical aspects of the smoking ritual may assist in craving reduction and thus improve therapy efficacy.¹¹

A 2020 Cochrane Collaboration review examined the safety and efficacy of e-cigarettes in helping people who smoke achieve long-term cessation. It identified moderate certainty evidence to suggest ENDS increased quit rates compared with ENNDS and compared with NRT. There was no clear evidence of harm from ENDS, although follow-up was limited to a maximum of 2 yrs across the included studies.¹²

A small 2018 pilot trial comparing nicotine patches with e-cigarettes for perioperative smoking cessation showed comparable quit rates and acceptability between the two strategies.¹³ A seminal 2019 RCT compared e-cigarettes with traditional NRT among 886 subjects and showed e-cigarettes were more effective for smoking cessation than NRT when both of the products were used alongside behavioural support. The 1-yr abstinence rate was 18% and 9.9% in the e-cigarette and NRT groups, respectively (relative risk 1.83; 95% confidence interval 1.30–2.58: p<0.001).¹⁴

In the USA, the FDA has not endorsed the use of e-cigarettes for smoking cessation, although the Centers for Disease Control and Prevention (CDC) acknowledge that e-cigarettes may benefit adults who smoke if used as a complete substitute for combustible cigarettes. Importantly, the harms of vaping in the perioperative period, and therefore the benefits of transitioning from combustible cigarettes to e-cigarettes, remain unclear.

EVALI and other harms

While continuing uncertainty surrounding the harms of e-cigarette use is reflected in international healthcare policy and regulation measures, a number of harms can be clearly identified: EVALI, the youth vaping epidemic, nicotine overdose and burn injuries.

EVALI

E-cigarette, or vaping use-associated lung injury is an acute or subacute lung injury of unclear aetiology and is a diagnosis of exclusion. It first came to the attention of authorities in 2019 when a group of e-cigarette users in the USA presented with severe acute respiratory distress. The cases, largely among young males, sharply increased in August 2019 and peaked in September 2019. As of 18 February 2020, there were a total of 2807 hospitalised patients or deaths reported to the CDC, and 68 deaths have been confirmed in the USA.

The CDC-confirmed case definition of EVALI includes use of an e-cigarette in the preceding 90 days, the presence of pulmonary infiltrates and absence of pulmonary infection or other plausible diagnosis. Patients may present with non-specific respiratory symptoms (dyspnoea, chest pain, cough) and fever, nausea, vomiting, diarrhoea and abdominal pain. Tachycardia, tachypnoea and reduced oxygenation are common presenting features and many patients have mildly increased transaminase concentrations.¹⁵ In a recent article outlining proposed mechanisms of EVALI, parallels are drawn between EVALI and coronavirus disease 2019 (COVID-19), with injury to both alveolar epithelial and vascular endothelial cells highlighted as being at the core of both disease processes.¹⁶

Vitamin E acetate, an additive found in predominantly THC-containing e-cigarettes, is strongly linked with the 2019 outbreak referred to above. The CDC identified that more than 80% of hospitalised patients presenting with EVALI, and for whom substance use data were available, reported the use of a THC-containing vaping product.¹⁷ In a recent study, bronchoalveolar-lavage (BAL) fluid containing vitamin E acetate was found in 94% of patients with EVALI but not in control patients. Tetrahydrocannabinol or its metabolites were detected in BAL fluid, or patients had reported vaping THC-containing products, in 94% of cases of EVALI.¹⁸ E-liquids obtained via illicit means are implicated in the majority of cases.

Although the literature to date suggests that the use of vitamin E acetate and THC-containing vaping products is associated, or perhaps causative of EVALI, other potential toxicants in vaping liquids may be implicated. There has been no similar outbreak of EVALI in the UK, although a number of deaths have been linked to vaping product use.⁵

In the UK, any safety concerns or presumed adverse effects related to e-cigarette use and all suspected cases of EVALI should be reported via the Yellow Card scheme website (link found at the conclusion of this article).

Youth vaping epidemic

There is strong evidence that e-cigarettes are a gateway to smoking for young people, with one recent systematic review suggesting that adolescent e-cigarette users are between three and five times more at risk of future cigarette use compared with those who have never used e-cigarettes.¹⁹ A 2019 US survey published in JAMA identified that 27.5% of high school students and 10.5% of middle school students reported current use of e-cigarettes. This same study suggested that the fourth generation of e-cigarettes or ‘mod pods’, especially the brand Juul, were the most common devices used.⁸ Contributing factors to this trend include the introduction of sleek, USB-like devices with attractive and novel flavours that can be used discreetly. These new devices can provide significantly higher nicotine delivery to users, with the nicotine present in the less irritant nicotine-salt form. Nicotine is harmful to the developing brain and may lead to learning and anxiety disorders and impairment in memory and attention.^3,8 Cannabis, also known to be harmful to the developing brain, is increasingly being legalised and when combined with increasing youth e-cigarette use, there is potential for significant public harm.

Nicotine overdose

When used as directed, nicotine-containing products have very low potential to cause nicotine toxicity. Exposures to liquid nicotine among children under the age of 6 yrs in the USA (reported to US poison control centres) increased by 1398.2% (0.7–10.4 per 100,000 children) from 2012 to 2015. However, rates of exposure subsequently decreased in 2016, perhaps because of the introduction of a number of regulatory measures, including child-resistant packaging.²⁰ There was a trend towards increasing numbers of children exposed to e-liquid recorded by the UK National Poisons Information Service during the period April 2008 to March 2016 with almost no exposures before 2012, increasing to a rate of more than 100 enquiries per year.

Burn injuries

E-cigarettes have been reported to cause injuries ranging from full-thickness burns to explosion trauma, with the problem described in the burns literature as an ‘unrecognised epidemic’ in its own right. E-cigarettes contain a heating element in the vaporising chamber that heats the e-liquid to temperatures typically between 100 and 250°C. Burn injuries can occur from a combination of thermal and chemical mechanisms. A 2020 publication identified an estimated 3369 e-cigarette-related explosion and burn injuries presenting to US emergency departments between 2015 and 2019.²¹ It has been suggested the likely mechanism is ‘thermal runaway’ malfunction of the lithium-ion batteries. Areas affected include the face, hands and notably the thigh and groin, sustained while the device is stored within clothing.

Vaping and COVID-19

The effect of vaping on susceptibility to COVID-19 and the risks associated with the social practices of vaping during a pandemic, have attracted interest. Sharing e-cigarettes, and exposure to exhaled vapour clouds, have been identified as a potential transmission vector, especially among youths. A widely-reported 2020 study of 4351 young adults and adolescents aged 13–24 yrs identified that a diagnosis of COVID-19 was five times more likely among young people who had ever previously used e-cigarettes and seven times more likely among young people who had ever used e-cigarettes and combustible cigarettes, and 6.8 times more likely among past 30-day users of e-cigarettes and combustible cigarettes.²²

The CDC discontinued publishing updates of EVALI cases in February 2020. The large increase in patients presenting to hospital with respiratory symptoms during the COVID-19 pandemic has made accurate ongoing characterisation of the EVALI epidemic difficult.

There is evidence to suggest an increased susceptibility of e-cigarette users to severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2). Angiotensin-converting enzyme-2 (ACE2), which is expressed in human airway epithelium, is the binding site for SARS-CoV-2 and mediates its entry into cells.²³ Nicotine induces an increase in ACE2 expression in human bronchial epithelial cells. Angiotensin-converting enzyme-2 expression is induced by those who actively smoke and indirect studies have shown people who smoke have an increased risk of severe disease associated with SARS-CoV-2 infection.^24,25 Impaired mucociliary clearance and the presence of increased oxidative stress and inflammatory responses in the lung could potentially contribute to the increased susceptibility of people who smoke or vape to SARS-CoV-2.²⁵ The impact of vaping as opposed to combustible cigarette use on COVID-19 vulnerability is currently less clear.

Implications of vaping for anaesthesia practice

It is evident that smoking causes harm in the perioperative period with increased respiratory, cardiac and wound complications. A 2011 study of patients undergoing non-cardiac surgery showed that current smoking (had smoked within the last year compared with never smoked) was associated with a 40% increased odds of 30-day mortality and 30–100% increased odds of major morbidity including surgical-site infection, pneumonia, myocardial infarction and septic shock.²⁶ In contrast, there remains a lack of evidence regarding the effect of vaping on perioperative outcomes, and therefore no consensus on the approach to perioperative e-cigarette use. The use of e-cigarettes may suggest a prior smoking history and this should be considered in the assessment of the patient's perioperative risk. It is unlikely that vaping product use will cause as much concern as smoking combustible cigarettes, given that the suggested harm of vaping is less than 5% of combustible cigarettes.^2,4

We recommend that anaesthetists directly question patients about their use of vaping products in addition to querying smoking, alcohol and illicit drug use history during routine preoperative assessment. We suggest asking about vaping frequency, the type of vaping device and liquid used, including nicotine concentration.

Perioperative complications

The limited evidence to date raises concern for cardiovascular, respiratory and wound complications associated with e-cigarette use. A growing body of literature describes alteration at a cellular and biochemical level, although convincing data on outcomes, particularly in an anaesthetic context, remain lacking. Some parallels may be drawn between the physiological and pharmacological effects of smoking and vaping.

Symptoms such as throat irritation, chronic cough and sputum production have been shown to be prevalent among e-cigarette users. Erythematous and irritable airway mucosa, in addition to more severe bronchial injuries, have been seen among healthy e-cigarette users.²⁷ As with the use of combustible cigarettes, these findings suggest a tendency towards increased airway reactivity and bronchospasm, with some animal studies supporting these observations. E-cigarettes may reduce host defences, with reduced ciliary function and impaired cough reflex seen among users.²⁷ Studies have shown variable response of respiratory airway resistance to e-cigarette use, although nicotine may be directly implicated in bronchoconstriction via stimulation of afferent pathways in the bronchial mucosa and subsequent activation of a parasympathetic nervous system arc. There are some early indications from animal models that e-cigarette use may be associated with pulmonary changes consistent with chronic obstructive pulmonary disease.²⁷ How these physiological changes translate to rates of perioperative respiratory adverse events and postoperative pulmonary complications remains to be elicited. In the context of paediatric practice, the implications of passive vapour inhalation remain unclear.

The haemodynamic changes associated with e-cigarette use can include acute increases in HR and BP.²⁸ Most of the known cardiovascular effects of e-cigarettes are consistent with the known effects of nicotine. Nicotine stimulates catecholamine release and this may lead to exaggerated and unpredictable haemodynamic effects under anaesthesia. Platelet function may be affected by e-cigarettes, and there are early signals that e-cigarette use is associated with endothelial dysfunction and oxidative stress, which are linked with the development of cardiovascular disease. Nicotine has been shown to increase lipogenesis, angiogenesis and inflammation, which could increase the risk of thrombosis.²⁸ The anaesthetist should consider underlying cardiovascular disease during preoperative assessment, particularly among long-term users of e-cigarettes or people who previously smoked combustible cigarettes. Increased potential for myocardial arrhythmias and an unfavourable shift in the myocardial demand-supply ratio may be an added consequence of nicotine use.

E-cigarettes result in no significant carbon monoxide production, although the surgical literature suggests problems in wound healing and submucosal blood flow among surgical patients who vape. Nicotine itself has been associated with increased rates of wound infection.²⁹

Pharmacological implications

The interaction between anaesthetic agents and the constituent products of e-liquids depends on the type of e-cigarette used. Nicotine- and THC-containing e-liquids should be considered separately from those not containing these substances. E-liquids containing cannabinoids are likely to have similar anaesthetic implications to cannabinoids ingested by other routes. Volatile organic compounds such as toluene produced by e-cigarettes can cause CNS depression and may reduce anaesthetic dose requirement.

The anaesthetic implications of nicotine are similar to those of traditional cigarettes. However, the cytochrome enzyme induction seen among people who smoke is thought to be provoked in part by PAHs found in smoke, but largely absent from e-cigarette vapour. Use of e-cigarettes may theoretically increase metabolism of neuromuscular blocking drugs, opioids and sedatives, but evidence is lacking and clinical reports of problems seem to be absent.

It is not known whether nicotine vaping is protective for postoperative nausea and vomiting as is the case with smoking. The effects of vaping on postoperative pain are unknown.

Conclusions

Anaesthetists, with their roles in perioperative medicine or critical care, have an obligation to be familiar with the known health implications of vaping products. It may be some time before we are able to fully characterise the adverse health consequences of vaping. The use of vaping products, with or without nicotine, is increasing and has the potential to contribute to significant morbidity worldwide. However, it is clear that the use of regulated ENDS and ENNDS products is significantly less harmful than the use of combustible cigarettes. Of most concern from a public health perspective is the surge of vaping product use among people who have never smoked and youths; the possibility of significant pulmonary harm with respect to short-term and chronic use; burn and explosion injuries from defective devices and the increasing incidence of acute nicotine intoxication. The role of vaping products in assisted smoking cessation, including in the perioperative period, is beginning to be established in the literature. At the current time international approaches vary with respect to the incorporation of vaping products in smoking cessation guidelines.

Yellow card scheme link

Report suspected adverse reactions to e-cigarette use, including lung injury, via the yellow card scheme (https://yellowcard.mhra.gov.uk/yellowcards/tobaccoreportmediator/).

Declarations of interest

The authors declare that they have no conflicts of interest.

Biographies

Trent Cutts BBiomedSc MD is an anaesthesia provisional fellow and chief resident at Waikato Hospital in Hamilton, New Zealand.

Aidan O'Donnell BSc FRCA FANZCA is a consultant anaesthetist at Waikato Hospital specialising in obstetric anaesthesia. He is the author of Anaesthesia: A Very Short Introduction and is one of the editors of the Oxford Handbook of Anaesthesia.

Matrix codes: 1A02, 2A03, 2A12, 3I00

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.