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:

  1. Non-clinical laboratory and simulation studies.
  2. SARS-1 experience studies.
  3. 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

  1. Lockhart interestingly also adds double gloves and neck protection for protection during aerosol-generating procedures, an important consideration. Click through for a Metajournal summary. 

  2. 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. 

  3. 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? 

  4. '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... 

  5. 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. 

  6. 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. 

  7. The original Twitter thread that birthed this essay is here: