Anaesthesia
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In this review, Wilson, Norton, Young & Collins challenge the overly-simplistic view that SARS-CoV-2 transmission risk can be easily divided between droplet-contact and aerosol precautions.
Why is this important?
Many national societies have policies on Personal Protective Equipment (PPE) guided by classification of COVID exposure into aerosol-generation procedures (AGP) or other exposures. Although founded in some evidence, there are questions as to whether PPE shortage and availability also drives these recommendations. Widespread concern over healthcare worker (HCW) infection is understandable, given that during SARS 20% of infections were among HCWs.
Understanding the science behind respiratory particle generation and transmission helps to inform our understanding of how best to use limited PPE.
On the science of respiratory shedding
Aerosol generation is important because virus inhalation and deposition in small distal airways may be associated with greater infection risk and disease severity. Wilson et al. describe three mechanisms of aerosol generation:
- Laryngeal activity - talking, coughing, sneezing.
- High velocity gas flow - eg. high-flow oxygen
- Cyclical opening & closing of terminal airways.
Notably, the clinically features of COVID itself make all three high-risk mechanisms more likely. Additionally various studies show that even talking and tidal volume breathing produce large numbers and size ranges of respiratory droplets.
Exposure relative risk is primarily about proximity and exposure duration
Further, considering retrospective data form SARS HCW infections involving various procedures (eg. intubation, HCW infection RR 4.2; oxygen mask manipulation RR 9; urinary catheterisation RR 5), Wilson et al. propose that healthcare work risk can be considered:
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
And on intubation:
"...[other] healthcare workers should stand over 2 m away and out of the direct exhalation plume. During a rapid sequence intubation muscle relaxation should be protective as coughing will be prevented and high airway gas flow and expiratory output will terminate. When expiratory flow is ended ... aerosol particles should start settling in the airways. The forces generated in gentle laryngoscopy are unlikely to cause aerosol formation."
"...[there is] limited evidence to suggest AGPs cause an increase in airborne healthcare worker transmission as this has not been studied. The few studies to sample pathogenic airborne particles in relation to procedures show no increase with the majority of AGPs."
Bear in mind...
Much of the evidence guiding our understanding of SARS-CoV-2 transmission is founded on understanding and research focusing on the 2003 SARS pandemic (SARS-CoV-1) and influenza research. Although sharing similarities, "...each has its own infective inoculum and aerosol characteristics."
What's the bottom-line?
Transmission of SARS-CoV-2 should be conceptualised as a spectrum of risk where time exposed may be the dominant factor and droplet-airborne spread is a complex continuum of varying probability of infection. Many 'non-AGP' events could in fact be higher risk than those traditionally considered AGP, such as intubation.
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Why the interest?
The combination of a deadly contagion (COVID-19) and recognition that endotracheal intubation is a high risk procedure for the airway technician has lead to the development of novel medical equipment. One such innovation is the clear-perspex 'intubating box' designed to contain viral-aerosols released during intubation. There has been limited prior evaluation of the safety or efficacy of such devices, despite their promotion.
What did they do?
Begley et al. conducted 36 simulated intubations with twelve PPE-adorned1 anaesthetists, with and without intubating boxes. They primarily aimed to quantify the effect on time to intubation.
Investigators tested both a first-generation and newer generation device. Each of twelve senior anaesthesiologists performed three block-randomised intubations: no box, original, and latest-design box. The airway manikin tongue was inflated to simulate a grade 2A airway.
And they found...
Intubation time was significantly increased by both the older and newer box designs (x̄=48s and x̄=28s longer respectively, though with wide confidence intervals). More relevantly there were frequent prolonged-duration intubations with the box (58% >1 minute, 17% >2 min), but none without the box.
Most worrying, there were eight breaches of PPE caused by box use, seven occurring with the newer, more advanced design.
"PPE breaches often seemed to go unrecognised by participants, potentially increasing their risk further."
Reality check
Despite the superficial appeal of an intubation box, this simulation study warns that such devices fail both to support safe and timely intubation and to protect the clinician – the very arguments used to advocate for its use.
These failings occur before even considering the actual effectiveness in reducing viral exposure, the box's impact on emergent airway rescue, or the practicality of cleaning a reusable device now coated with viral particles.
The intubating aerosol box appears dead on arrival.
Bonus biases
Begley notes the appeal of such novel devices may be partly driven by 'gizmo idolatry' (Leff 2008) and 'MacGyver bias' (Duggan 2019), blinding clinicians to consider unknown consequences of box use and discounting resultant hazards.
summary
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Local COVID PPE guidelines were used: face-shield, goggles/glasses, mask, gown & gloves. ↩
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An editorial on pandemic information overload?
Yep. 😉
But setting aside the irony of adding 2,000 more words on COVID-19 information overload, Kearsley & Duffy neatly explore the challenge:
"Since the outbreak of this pandemic, our e-mail inboxes, social media feeds and even general news outlets have become saturated with new guidelines, revisions of guidelines, new protocols and updated protocols, all subject to constant amendments."
What's the thesis?
The authors' argument is that too much information in the era of COVID may be a bad thing: the marginal benefit of 'more' may be overwhelmed by the negative cost.
They acknowledge the tension between the pragmatic and perfect when it comes to information sources in the face of a rapidly advancing disease – and in particular the recurrent waves of shifting clinical guidelines.
Kearsley & Duffy mention the important role of rapid research, worryingly tempered by a surge in volume, but fall in quality, along with mainstream promotion of non-peer reviewed and pre-print investigations. They note how information technology in the pandemic climate exploits our biases: confirmation, anchoring, and novelty.
At an individual level they discuss the risk of pandemic 'alert fatigue', the growth of social media and excessive information sharing making quality assessment difficult, and the negative effect of both on well-being.
The take-home
We each have significant personal responsibility to consider the consequences when sharing information, especially if incomplete or risk of misunderstanding when stripped of context.
summary"As we learn to live with this virus it is important for us to be cognisant that we are all at risk of error; we need to work to reduce information overload and focus on unifying our approach to both information dissemination and presentation. We must go back to basics and apply the well-practiced human factors principles of good teamwork, communication and leadership.
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We need to avoid a situation where a crisis is overmanaged and underlead; “Ipsa scientia potestas est" or 'knowledge itself is power' – from what COVID-19 is teaching us however, can too much knowledge be a bad thing?"
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Multicenter Study Observational Study
Peri-operative administration of tranexamic acid in lower limb arthroplasty: a multicentre, prospective cohort study.
In the UK, tranexamic acid is recommended for all surgical procedures where expected blood loss exceeds 500 ml. However, the optimal dose, route and timing of administration are not known. This study aimed to evaluate current practice of peri-operative tranexamic acid administration. ⋯ Current standard of care in the UK is to administer 1000 mg of tranexamic intravenously either pre- or intra-operatively. Approximately one-third of patients present for surgery with anaemia, although the overall red blood cell transfusion rate is low. These data provide useful comparators when assessing the efficacy of tranexamic acid and other patient blood management interventions in future studies.