the metablog

Old, new and current trends in obstetric anaesthesia

Tue, 02 Jun 2020 08:00:00 +0000

Some interesting research on common and not-so-common obstetric anaesthesia topics: both new trends and continuing trends, as well as a cautionary medicolegal reminder.

Supraglottic airways for GA Caesarean?

Metodiev & Mushambi's editorial looks at the attitude shift among obstetric anaesthesiologists to more favourably consider the LMA or SGA for Caesarean section under GA.

They review the evidence for aspiration risk, particularly noting what we learned from NAP4 (2011) but contrast this with many studies showing safety of SGAs for GA CS (over 8,000 patients in total, with Halaseah 2010 investigating 3,000 alone!). Interesting, but before we get too excited keep in mind that the populations studied are likely very different from parturients you may typically look after.

They conclude:

"...there is insufficient evidence to recommend universal or selective replacement of tracheal tubes with SGA devices during general anaesthesia for Caesarean delivery. Aspiration remains the main concern." – Metodiev & Mushambi (2020)

Cautionary reminders of neuraxial injury

McCombe & Bogod reviewed 21 years of obstetric anaesthetic medicolegal claims, noting common themes around consent, types of nerve injury, and recognition and management failures.

Not only is neurological injury the second most common reason for obstetric anaesthetic claims (behind inadequately managed pain during Caesarean section), it carries the highest average claim cost.

The review is full of many useful observations, but Reynold's 2000 advice regarding interspace level choice for spinal access is by far the most important: always access the intrathecal space at the lowest possible level, and "...the L2/3 interspace should not be an option."

McCombe & Bogod spend some time exploring the variability of cord termination level, individual variability of the intercristal line, and the inaccuracy of anaesthetist interspace level estimation. Well worth reading the whole review.

Which vasopressor for spinal hypotension?

Although most recent consensus guidelines have recommended phenylephrine infusion for managing hypotension during neuraxial anaesthesia for Caesarean section, Singh's 2020 meta-analysis suggests otherwise.

Performing a Bayesian network meta-analysis of 52 high-to-moderate quality RCTs with over 4,000 patients, they compared multiple vasopressors directly and indirectly to produce a probabilistic hierarchy of benefit for improving neonatal and maternal outcomes.

They found that norepinephrine (noradrenaline), metaraminol, and mephentermine showed the lowest likelihood of adverse neonatal acid-base effects, and ephedrine the greatest.

These top three vasopressors (notably not phenylephrine) vied similarly for secondary outcomes, with an 85% combined-probability that metaraminol & norepinephrine are the two best agents for avoiding maternal nausea and vomiting.

Fitzgerald et al. conducted a similar network meta-analysis earlier in the year, although using different methodology and a different mix of trials, also ranked metaraminol and norepinephrine ahead of phenylephrine.

Alternatives to intrathecal heavy bupivacaine

Finally, in this time of common drug shortages it's reassuring to have confidence in acceptable alternatives. Two recent meta-analyses have compared intrathecal heavy bupivacaine to both plain and ropivacaine.

Sng et al. conducted a Cochrane review of hyperbaric vs isobaric/plain bupivacaine for Caesarean section, including 10 studies and over 600 subjects. They found that intrathecal hyperbaric and isobaric bupivacaine were equally clinically effective, although hyperbaric showed slightly faster block onset (but only by 1 minute!).

Malhotra et al. compared intrathecal bupivacaine to intrathecal ropivacaine using a meta-analysis of 13 trials including over 700 patients. They found intrathecal ropivacaine results in faster recovery of motor block, but no difference in onset of motor or sensory effects. (It's generally accepted to use a dose-equivalence of at least 1.5:1 ropivacaine:bupivacaine, based on previous studies showing rough equivalence at this ratio.)

Neither study demonstrated any difference in the risk of conversion to general anaesthesia, need for intraoperative supplemental analgesia or vasopressor requirement – although patients receiving ropivacaine requested postoperative analgesia earlier.

Nonetheless, either is an acceptable alternative to intrathecal heavy bupivacaine.

The elephant in the room

The funny thing with obstetric anaesthesia is the more things appear to change, the more... well, actually things don't even seem to change all that much.

We just need regular reminding of the importance of the basics: vasopressors for spinal hypotension, intrathecal access at the lowest accessible interspace, one long-acting LA is similar to the next, and treat the obstetric airway with respect.

Relevant studies:

Metodiev Y Mushambi M. Supraglottic airway devices for Caesarean delivery under general anaesthesia: for all, for none, or for some? Br J Anaesth. 2020 Mar 18.
McCombe K Bogod DG. Learning from the law. A review of 21 years of litigation for nerve injury following central neuraxial blockade in obstetrics. Anaesthesia. 2020 Apr 1; 75 (4): 541-548.
Singh PM, Singh NP, Reschke M et al. Vasopressor drugs for the prevention and treatment of hypotension during neuraxial anaesthesia for Caesarean delivery: a Bayesian network meta-analysis of fetal and maternal outcomes. Br J Anaesth. 2020 Mar 1; 124 (3): e95-e107.
Fitzgerald JP, Fedoruk KA, Jadin SM et al. Prevention of hypotension after spinal anaesthesia for caesarean section: a systematic review and network meta-analysis of randomised controlled trials. Anaesthesia. 2020 Jan 1; 75 (1): 109-121.
Sng BL, NLR Han, Leong WL et al. Hyperbaric vs. isobaric bupivacaine for spinal anaesthesia for elective caesarean section: a Cochrane systematic review. Anaesthesia. 2018 Apr 1; 73 (4): 499-511.
Malhotra R, Johnstone C, Halpern S et al. Duration of motor block with intrathecal ropivacaine versus bupivacaine for caesarean section: a meta-analysis. Int J Obstet Anesth. 2016 Aug 1; 27: 9-16.

All Things Endotracheal

Sun, 24 May 2020 08:20:00 +0000

There have been some interesting papers recently exploring all-things endotracheal, relevant to anaesthesiologists, intensivists and emergency physicians alike.

Some challenge long-accepted dogma (ETT size), others confirm natural trends (cuffed paediatric tubes), or delve into ventilation physiology long forgotten by some of us (the ventral shift...).

Here's a brief stroll through five articles that may challenge your practice.

Choose smaller...

First, Karmali & Rose challenge the dogma surrounding endotracheal tube sizing in adult anaesthesia. They explore both the functional consequences of ETT size, good and bad, as well as the implications for airway trauma.

They describe how a modern ETT ≥ 6.0mm ID will accomodate most intraluminal devices, and in fact smaller sizes might even facilitate some airway procedures. Similarly, inspiratory and expiratory flow dynamics of smaller ETTs are inconsequential for most fit and healthy patients.

Noting that there is wide individual variation in tracheal dimensions, such that some patients are poorly served by a traditional ETT-size choice, they highlight the correlation between ETT size and airway trauma, hoarseness and sore throat, noting that for many patients a 'large' ETT offers little practical benefit.

"Instead of opting for ‘the largest tube that the larynx will comfortably accommodate’, we perhaps should consider using the smallest tube which permits the safe conduct of anaesthesia."

For routine anaesthesia of ASA 1 & 2 patients, an ETT sized 6.0-7.0 mm is probably the best balance between ventilation needs and airway trauma.

Don't cough

Yang et al.'s high quality meta-analysis explores the use of intravenous lidocaine/lignocaine to reduce a common, but potentially significant post-operative problem: coughing on extubation. Both coughing (reported incidence 15-94%) and post-operative sore throat (21-72%) are common among surgical patients.

This meta-analysis of 16 trials (though only 1,516 total subjects) showed a significant reduction in cough RR 0.64 (0.48-0.86 & NNT=5), and post-operative sore throat RR 0.46 (0.32-0.67), though no difference in laryngospasm, adverse events or time to extubation when using modern volatile agents.

However, they could make no clear recommendation of optimal timing or dose of lidocaine – although past reviews had found suggestion of a dose-effect, settling on 1.5 mg/kg as the best choice (Clivio et al. 2019).

Regardless, a simple intervention with peri-operative IV lidocaine reduces coughing on extubation and reduces post-operative sore throat, without any apparent increase in adverse events.

To cuff or not?

Shah and Carlisle address the steady shift in paediatric anaesthesia to use cuffed endotracheal tubes, beginning with the arrival of the Microcuff™ tube.

They challenge historical airway anatomy & physiology myths that once encouraged the use of uncuffed ETTs in children, and the questionable reliability of the widely-used Cole formula for tube size prediction (size = age/4 + 4; correct in only 50-75%).

More recently, Chamber's RCT compared cuffed and uncuffed ETTs in children undergoing elective general anaesthesia, and found that cuffed tubes improved ventilation and reduced short-term post-operative respiratory complications, in addition to decreasing tube changes.

Shah & Carlisle report on their updated meta-analysis, also showing that cuffed tracheal tubes in children result in fewer tube changes and less sore throat, but no difference in risk of laryngospasm.

Using a modern Microcuff™ or equivalent cuffed ETT that is 0.5 mm smaller in size than an equivalent uncuffed tube, offers functional, ventilation and safety benefits.

The ventral shift

Lumb and colleagues take us back to our physiological roots, confirming the well-known observation of a ventral ventilation shift under supine positive pressure ventilation, quantifying the contribution from the endotrachial tube itself (~16% of the change), versus from muscle relaxation and IPPV (noting some shift is also seen with an LMA under PSV).

While anaesthetists understand the detrimental effect of inadvertent endobronchial intubation, simply having the ETT tip close to the carina also worsens V/Q mismatch and is not as well appreciated. In these situations, tube withdrawal and/or 90^o rotation may improve V/Q match.

Plumbing nasal tube depths

Finally, as a bonus, Massoth et al. demonstrate that nasolaryngeal distance can be reliably predicted using their derived formula:

NLD (mm) = 1.1 × body height (cm) – 13.2

Although the accuracy of this simple formula is interesting, the authors noted the wide variability in nasal tubes from different manufacturers, particularly in length and guide markings for the same-sized tube. Thus correct ETT depth is probably better determined clinically: visually observing the cuff pass the cords, and auscultation to exclude endobronchial intubation – although this predictive-depth formula may be a useful sanity-check.

For abstracts, article summaries and full-text links:

Karmali S Rose P. Tracheal tube size in adults undergoing elective surgery - a narrative review. Anaesthesia. 2020 May 16.
Yang SS, Wang NN, Postonogova T et al. Intravenous lidocaine to prevent postoperative airway complications in adults: a systematic review and meta-analysis. Br J Anaesth. 2020 Mar 1; 124 (3): 314-323.
Shah A Carlisle JB. Cuffed tracheal tubes: guilty now proven innocent. Anaesthesia. 2019 Sep 1; 74 (9): 1186-1190.
Lumb AB, Savic L, Horsford MR et al. Effects of tracheal intubation and tracheal tube position on regional lung ventilation: an observational study. Anaesthesia. 2020 Mar 1; 75 (3): 359-365.
Massoth C, Schülke C, Köppe J et al. Nasolaryngeal Distances in the Adult Population and an Evaluation of Commercially Available Nasotracheal Tubes. Anesth. Analg. 2020 Apr 1; 130 (4): 1018-1025.

More related articles can also be found on metajournal's intubation, tracheal tube, and mechanical ventilation topic pages.

Thoughts on PPE

Sun, 17 May 2020 02:38:00 +0000

Amidst the medical anxiety surrounding COVID-19, no issue appears more emotive than the use and access to personal protective equipment (PPE).

Whether anaesthesia, intensive care or those poor bastards on the front-line in emergency departments and ambulances, adequate PPE has never been simultaneously so important across the entire planet. To outsiders the emotion and fear may seem excessive, but for healthcare workers fear is protective.

It was recently said that for anaesthesia this is our first modern "pilot goes down with the plane" safety issue. While we might be stretching that metaphor too far, it does help to frame our collective anxiety. It reveals both the shared hazard of a contagion, and also the foundation for the anxiety many feel.

A word on framing the message

As doctors we get easily caught up in own world. Sometimes this carries over into how we communicate important ideas to the community, particularly when it's also a personally emotive issue like PPE. Personal emotion is a great motivator, perhaps even a good dressing for a message, but it is a terrible way to guide communication strategy.

Access to PPE is not just about protecting the safety of healthcare workers – it's not even just about sustaining this essential workforce for the need of the community. The most important reason that hospital PPE should be a priority for those outside hospitals is that healthcare workers (HCW) and hospitals may be an important vector for spreading the virus.

Whether during the early stages of COVID-19 in China, Italy, UK or the US, hospitals inadvertently led to CoV-SARS-2 transmission among patients, staff, families and the wider community. In some outbreaks healthcare workers have made up 20% of all confirmed COVID cases.

In the recent 'small' North West Tasmanian outbreak, requiring a lockdown of almost 5,000 exposed people to control, more than 60% of confirmed cases were healthcare workers. Setting aside the worrying over-representation of severe disease among infected HCWs, we should prioritise adequate PPE for health staff for no other reason than the need to keep our communities safe.

So take a walk with me through the little evidence we do have on COVID-19 and PPE for front-line healthcare workers, particularly as it relates to critical care.

The PPE evidence

Digging through the COVID PPE evidence it's quickly apparent that publications fall mainly into three groups:

Non-clinical laboratory and simulation studies.
SARS-1 experience studies.
Systematic reviews, usually incorporating #1 and #2.

All articles referred here are collected together in "Anaesthesiology, Personal Protective Equipment (PPE) and COVID" many with quickly digestible metajournal summaries.

There are also two interesting influenza-N95 meta-analyses (Radonovich 2019 & Long 2020) that I'll touch on later.

There are some good recent reviews out there: Cook (Anaesth 2020), Lockhart (CJA) and Odor (BJA) all cover similar ground, though with slightly different emphasis. Importantly they each need to be considered in the context of the health systems that the authors inhabit.

While the principles they express are consistent with various national PPE guidelines (which are generally good guidelines!), setting out a protection hierarchy for contact, droplet and airborne exposure,¹ the reader senses an unspoken tension that's implied yet never quite articulated:

PPE guidelines are a necessary and pragmatic safety compromise.

This compromise is necessary because of the globally-limited supply of N95 masks and other PPE. Rather than continuing the unproductive and chiding tone around the notion of "inappropriate PPE use" (a real issue to be sure!), it would be better to acknowledge the grey of risk-benefit calculus and how this informs the guidelines.

Typical hospital safety protocols (think 'Universal Precautions' or the WHO's impractical '5 Moments of Hand Hygiene') are an evenly applied 'bundle' of intervention, disconnected from the risk-context of an individual patient.² This is the safety climate that we have been encultured into: universal rules, deemphasising both individual perceived risk and the evidence basis for discrete bundle ingredients.³

This is not the world that COVID PPE must inhabit. There can be no universal single rule, and there can be no bundles of PPE. We just don't have the supply.

So let me spell it out: global supply of respirator masks is incredibly limited. We need to accept that while in a perfect world an N95 mask would be used as a minimum for all contact with COVID risk patients, this is not possible. The unspoken tension of PPE is the perfect vs pragmatic. The wishful vs reality. An asymptotic curve of risk, rising out of the murky waters of unknown prevalence.

Supply limits, stacked on estimates, unknowns and uncertainties. It's turtles all the way down.⁴

In the time before COVID, Australia, the UK and Canada had no local manufacturing of single-use N95 masks (Australia and the UK still have none!). The United States, a country of 330 million people, had a single, sole local manufacturer.

Yet while our N95 supply is limited, our capacity to consume is not. My friend Dr Dan Holmes tells me that during SARS one Canadian hospital went through 18,000 N95s each day! Even then Canada's 375 SARS cases were enough to bring Toronto's health system to its knees.

So this is the context within which our PPE guidelines must exist: a contagious and potentially deadly disease, a global scarcity of protective equipment, and a thin evidence base. This will change in the future, but today this is what we must work with.

Airborne or not: a distraction

Much of the PPE debate revolves around the risk of SARS-CoV-2 airborne transmission, an unfortunate distraction. In general there is too much emphasis on rationalising guidelines (contact, droplet, airborne) with limited and over-simplified science – and not enough acknowledgement of risk-benefit pragmatism.

The world is not binary, and neither is risk. When it comes to valuable, single-use safety equipment we must deploy it with consideration of a dynamic risk-cost-benefit balance. This is in essence what the guidelines try to do.

First, on droplet-vs-airborne spread, this is at best a conceptual simplification that we over-fixate on. Wilson (Anaesth 2020) makes the useful argument that 'time exposed' is probably more important.

Wilson et al's article is a must read, being the best current exploration of the science of respiratory transmission. It challenges the simplistic droplet vs aerosol concept. Wilson conceptualises infection risk as being proportional to aerosol concentration in the breathing zone, minute ventilation of the exposed person, time-exposed, and then inversely proportional to protective mask efficiency:

infection risk ∝ 𝑏 × 𝑣 × 𝑡 / 𝑒

Where: 𝑏 = breathing-zone particle viable virion aerosol concentration, 𝑣 = minute volume of healthcare worker, 𝑡 = time exposed, 𝑒 = mask efficiency.

Amidst the airborne uncertainty, there are anecdotal examples of COVID aerosol transmission, plus lab studies (of unclear clinical significance) showing substantial spread of viral particles (Bahl 2020 J Inv Dis). We should also pause to consider the large Amoy Gardens apartment outbreak of SARS in 2003, showing evidence of extensive airborne spread.

Nonetheless we shouldn't fixate on what IS or IS NOT an aerosol generating procedure (AGP) as this is only a surrogate for what really matters: risk of infection. And we have some data on that already.

Top of the list is intubation (OR 6.6), followed by non-invasive ventilation (OR 3.1), tracheostomy (4.2) and manual ventilation before intubation (2.8) – from a 2012 SARS meta-analysis (Tran 2012 PLOS ONE)⁵.

If we then include Wilson's argument of 'time exposed' (to aerosol risk) with consideration of small enclosed spaces with poor ventilation, we have a pretty good conceptualisation to use for assessing individual risk.

Let's talk about PPE specifics

Which then brings us to PPE itself. First let's touch on the evidence for N95+ respirator masks. Although the physical science says these are more protective than surgical masks, the limited clinical evidence has NOT yet shown this.

Two meta-analyses of RCTs (Radonovich 2019 & Long 2020) looking at influenza in healthcare workers failed to show any benefit of N95 over standard masks. Additionally there are many anecdotal stories of healthcare workers unknowingly exposed to COVID aerosols but successfully protected by surgical masks.

Though these studies were not specifically looking at either, 1. coronaviruses; or 2. high-risk events like intubation, they should give us some reassurance about the safety of current COVID contact and droplet precautions in the absence of known high-risk procedures.

Specifically on intubation PPE, although similar the guidelines do differ at points. Lockhart (CJA 2020) in particular proposes adding both double gloves and neck protection to the N95-mask/eye/gown mix, noting that simulation and lab studies show neck and glove-gown interfaces are common sites of contamination. Verbeek's Cochrane 2020 update covers the research behind these and other recommendations.

There is some important PPE evidence...

Other PPE learnings from both real-world and simulation studies appear repeatedly, and deserve emphasis:

PPE is not enough on its own, it must be part of a larger institutional safety system.
Training in donning & doffing is essential. Practice, simulation, fit-test respirators.
Time management is critical: do not rush donning and doffing. Rushing in to resuscitate deteriorating patients compromises personal protection and results in tragedy.
Muñoz-Leyva & Niazi (2020) have more on common PPE failures.

Personal protective equipment use is an expression of safety culture.

The more complex the PPE (eg. hoods, PAPR) the greater the risk of self-contamination when doffing. Doffing safely takes training and repetition.
More complex PPE impedes other interventions, like intubation and CPR. Small marginal safety gains from complex PPE begin to have disproportionately greater impact on the very procedures we are seeking protection from. Consider this!
Intubation boxes likely increase intubation time, decrease first-pass intubation success, and increase PPE breaches (Begley 2020). You probably shouldn't use them.
Conversely, even fit-tested N95 masks may not protect adequately during CPR (Hwang 2020).

Finally, Lockhart (CJA 2020) strongly discourages MacGyvering homemade PPE combinations. This also extends to the intubating boxes and other inventions that seem to be more of a target for latent anaesthesia anxiety than practical solutions. Don't do this stuff. Adding extra complexity to otherwise routine procedures without evidence of benefit is likely more harmful than helpful ⁶

So, the various guidelines are not trying to hide anything, even though they appear reluctant to acknowledge the necessary and pragmatic compromise on using items like N95 masks. They are balancing the limited supply of PPE and trying to match this to the (somewhat) evidence-based demand. If you have access to reusable PPE, training and processing, then this might obviate some limits.

The old anaesthetic adage of "it's not what's in the syringe but who's behind it that matters" applies equally to PPE. Once we reach a suitable level of protection for a specific risk context, then fastidious conduct and disciplined use is probably the most important safety factor.

Be pragmatic. Practice what you use. Don't do stupid things.

Abstracts from all the referenced articles, many with summaries, can be found collected on metajournal: "Anaesthesiology, Personal Protective Equipment (PPE) and COVID", along with many more in the growing index of PPE-specific articles and general COVID articles relevant to anaesthesiologists, intensivists and emergency physicians.⁷

Lockhart interestingly also adds double gloves and neck protection for protection during aerosol-generating procedures, an important consideration. Click through for a Metajournal summary. ↩
That is, these protocols and recommendations are intended to be universally applied by health workers to their care of every patient, regardless of risk and hazard, even though infective risk of either patient or healthcare worker is typically low. They are important foundational principles for occupational safety, but arise in an era where there was not limited supply of gloves, goggles or hand sanitiser. Today we do not live in that world. ↩
The whole 'bundle of care' concept is both interesting, outcome improving and sometimes contentious: "... a structured way of improving the processes of care and patient outcomes: a small, straightforward set of evidence-based practices — generally three to five — that, when performed collectively and reliably, have been proven to improve patient outcomes." (Institute for Healthcare Improvement) It can be contentious when components of the bundle have only relatively lower-quality evidence supporting their benefit, but when 'bundled' with other interventions, we see a significant net improvement. Is this because of treatment effect, sum-greater-than-the-whole synergism, insufficient sample size, or are we just hiding non-beneficial interventions alongside the useful? ↩
'Turtles all the way down' is more accurately an expression of infinite regression, whereas PPE risk-benefit assessment is more about the consequential widening of error when we multiply multiple estimates with their own uncertainties: What is the local population prevalence? What is the pretest probability for this patient? Is a particular component of PPE effective? What is the exposure risk of an interaction? A procedure? What is the infection risk if exposed? What is the hazard for the individual if infected? At some point the error margins are so large that attempting to quantify (vs qualify) the risk is an unhelpful distraction. It's more like turtles multiplied together... ↩
Interestingly, other intubation-associated procedures, endotracheal aspiration, suctioning, bronchoscopy, nebulising, O₂ administration, high-flow O₂, O₂ or BiPAP mask manipulation, defibrillation, chest compressions, NT tube insertion, and sputum collection were not significant. This however is more likely indicative of the small case numbers available – even the procedures of significant risk demonstrated wide confidence intervals and so are more useful as a guide to ranked risk than absolute risk itself. ↩
Aside, @DrLauraDuggan and @Hypoxicchicken et al.'s 2019 editorial 'The MacGyver bias and attraction of homemade devices in healthcare' is a good and relevant read. Leff & Finucane's (JAMA 2008) 'gizmo idolatry' commentary is also related. ↩
The original Twitter thread that birthed this essay is here: https://threadreaderapp.com/thread/1255698218588856320.html ↩

Peer-reviewed COVID-19 articles on metajournal

Tue, 05 May 2020 09:53:00 +0000

Metajournal now has a dedicated index of peer-reviewed COVID-19 articles published in critical care, anesthesia, emergency medicine and resuscitation journals, along with relevant coronavirus articles from major general medical publications, including Lancet, BMJ, NEJM, JAMA, MJA & CMAJ – plus specialist articles from infectious disease, epidemiology and immunology journals.

→ metajournal.com/covid

This shows the latest covid and pandemic articles as they are indexed, or click on the 'Best' tab to see the highest quality and most important articles – many of which have metajournal summaries.

If you want to stay up to date with the latest COVID-19 articles, make sure to follow the relevant coronavirus topics by clicking on the red topic tags at the top of the page. Relevant articles will then be included in your weekly metajournal email if you are a metajournal subscriber.

There are already over 1,000 peer-reviewed covid articles indexed.

If you are looking specifically for articles covering Personal Protective Equipment (PPE) in the time of covid, the PPE article index along with the "Anaesthesiology, Personal Protective Equipment (PPE) and COVID" collection, has you covered. 😷

Biased thinking in a time of COVID

Fri, 17 Apr 2020 01:16:00 +0000

The 2020 coronavirus pandemic for all it's horror and challenge, has highlighted certain uncomfortable truths about the human condition. One of these has been the impact of our cognitive short-comings: our difficulty understanding the non-linear and non-binary, and our susceptibility to cognitive biases.

Many of these problems led to missteps at the beginning of the pandemic response, and now early in the fight continue to impede our decisions. By better understanding these cognitive traps we can at least be more alert to our blind spots and alter our actions in response.

As early data seeped out of China in January, quickly followed by cases appearing in global travel hubs, many national governments along with their populations refused to acknowledge the pandemic threat. Even as Northern Italy's health system first bent then broke, surpassing China's own COVID death count a mere 47 days after Italy's first confirmed case, world governments continued to water-down the threat.

Humans struggle with exponential growth

We perceive our world in linear terms. Although we live each day with many examples of exponential growth and decay – population growth, the spread of a forest fire, compound interest, student debt, the growth of a single fertilised egg into a human baby – we seem to ignore their exponential nature.¹ We are instead surprised at the magnitude and complexity of the phenomenon, wilfully ignorant of the exponential journey that brought us to that point.

Governments and populations across the world struggled with the same blind spot in their responses to the 2019 coronavirus. As the number of infected doubled every few days it should have been obvious that this would quickly lead to an unprecedented health crisis. Exponential processes are force multipliers on both the downside, accentuating bad outcomes, but also critically on the upside, allowing early intervention to create disproportionately greater future benefit.

When one person may infect two, three or even more people, with each then leading to a cascading flow of infected contacts, simply by preventing a single early infection we may avoid thousands more only a few weeks later.

As deaths in New York alone cross 10,000, it was estimated that beginning social distancing measures a mere week earlier would have avoided half the total deaths. The UK suffered a similar catastrophic fate due to testing delays and inaction, and today continues to struggle to control the result.

Because populations do not easily understand exponential consequences – and most governments have struggled to communicate it – there is little impetus to act while the sick are few and death is rare. Instead they wait.

In contrast to the European and North American experience, Australia's earlier intervention appears to have so far avoided the expected disaster beyond even the most optimistic projections. This appears to be the result of both the non-linear nature of disease transmission, and some degree of hysteresis² from rapid behavioural changes in the Australian population.

One of the problems with exponential processes³ is that outcomes are a lagging indicator of what has already happened, particularly when a disease has a long incubation time and a slow severity progression. If you wait for scores of dying patients to arrive in your hospital before acting, a much larger number have already been infected and begun their own downward spiral in the community. This lag between infection and the signal to act is what brings health systems to their knees.

Ignorance of exponential growth and misunderstanding the nature of a lagging signal led many governments to squander the disproportionately lower cost of early intervention. Most notably the United States failed to act when the problem appeared superficially small – but conversely when small interventions would have avoided asymmetrically greater suffering and death. This became Trump's infamous missed month of February, contributing to otherwise avoidable deaths. At the time these interventions may have appeared excessive, but we now look back at those missed opportunities with quaint innocence.

"Everything we do before a pandemic will seem alarmist. Everything we do after a pandemic will seem inadequate." – Michael O. Leavitt (2007) then Secretary of the U.S. Department of Health and Human Services.

Humans are terrible with uncertainty

Perhaps the most jarring effect of the pandemic has been the uncertainty. The reassertion of reality, cutting through the veneer of our optimistic perception that we live predictable, constant, stable lives.

Discomfort with uncertainty encourages us to embrace biased patterns of thinking, to be comforted by the false-certainty they offer. We tend to believe that things will continue the way they always have. This normalcy bias⁴ is particularly unhelpful during disaster preparation and response, impeding and slowing our acceptance of new information and leading us to preference inaction over action. Yet a posture toward action is the very thing we need when responding to a planet-sized catastrophe.

Once experiencing an emergency or disaster, we can be biased toward wishful thinking, holding an unrealistic optimism that further undermines our response.

Most critical care doctors – anaesthesiologists, intensivists, emergency physicians – have experienced this at least once, early in their careers, irrationally hoping optimism and sheer force-of-will may avert a bad outcome. We grow out of this thinking very quickly.

"One day it’s like a miracle, [the coronavirus] will disappear.” – Trump, 27 Feb 2020.

We may wish this were true, but the obvious conflict between our wants and objective reality will inevitably reveal themselves. The danger of wishful thinking is that, like normalcy bias, it encourages inaction over action. As the reality of the situation diverged from our perception, the degree that we continue to adhere to unrealistic optimism only delays the needed response.

Add a dash of confirmation bias⁵ and motivated reasoning⁶, as information and emotional arguments supporting our optimism are prioritised, plus less common traps, like the boomerang⁷ and backfire effects⁸ where persuasive arguments lead to the adoption of opposing views, or contradictory evidence is rejected to strengthening false belief – and it's easy to see how cognitive biases have impeded a cohesive response to this pandemic.

For COVID-19, it's cognitive failings and biases all the way down.

And in a pandemic, biases might just get us killed.

Which relates to a question you might have, why the lily pad image heading this article? There's a classic thought experiment used to demonstrate our struggle with the non-linear: Lily pads are growing across a pond. On the first day there is only one lily pad, and it covers only a tiny surface of the pond. Everyday the area of the pond covered by lily pads doubles. How much of the pond is covered the day before it is completely covered? The answer? Only half the pond... ↩
Hysteresis describes situations where the state of a system is dependent on the history of the system – from what has come before, literally meaning 'lagging behind' in Greek. It is described in many domains, including chemistry, physics, engineering, biology and even economics. In critical care specialties it's most commonly observed in respiratory physiology as lung hysteresis, where the lung demonstrates different compliance during inspiration versus expiration as a consequence of surface tension. Anaesthesiologists also observe it when monitoring depth of anaesthesia, where there is often a different drug concentration required to maintain depth while descending and once reached, versus re-establish depth when it is being raised. Hysteresis is not a concept unknown to epidemiologists, thought to result from population behavioural changes. ↩
Note that early in a pandemic, growth is exponential, and this is what we are most interested in when discussing the costs and benefits of delaying action or acting early. However the resulting graph of infected population vs time is not an exponential ('logarithmic') curve, because at some point there will be very few people who are available to be infected, the curve begins to flatten, becoming more linear than exponential, and ultimately asymptotically reaching a maximum value. This gives a sigmoid or logistic curve. ↩
Omer & Alon. The Continuity Principle: A Unified Approach to Disaster and Trauma. Am J Community Psychol. 1994 Apr;22(2):273-87. ↩
Confirmation bias describes our preferencing of information that confirms and strengthens our belief when we are searching, recalling or interpreting information – that is, we are biased to confirm our existing beliefs even when wrong. This also relates to belief perseverance (our tendency for beliefs to persist even after we have been shown contradictory evidence) and the backfire effect. ↩
Motivated reasoning is similar yet distinct from confirmation bias, where instead of preferencing evidence supporting a belief, we employ emotional non-critical reasoning to reach a desired outcome or decision – we find the conclusions we want rather than those which are most correct or rational. For example, arguing that a nation's exceptionalism means it will avoid a coronavirus disaster, and so decide to not begin economically-damaging social distancing or the costs of increased testing. ↩
The boomerang effect was first described more than 70 years ago, where a persuasion attempt instead leads a subject to adopt the opposite position. It may be due to psychological reactance or cognitive dissonance, and is a important psychological consideration in modern public health interventions. ↩
The backfire effect describes how an argument or evidence may 'backfire' and lead a subject to strengthen their beliefs, even though (in fact, because) the presented evidence actually corrects or contradicts this belief. Although popularised in the aftermath of the 2016 US election, at best the backfire effect is very uncommon and has struggled with replication. ↩