Abstract
The virus responsible for the coronavirus-19 pandemic is predominantly spread by droplet and contact routes of transmission. Many airway management interventions, particularly when applying positive pressure to the airway, generate aerosol particles which pose a further risk of airborne viral transmission. The fundamental principles of airway management in the setting of a respiratory epidemic are not changed but it is essential to maximise safety for both the patient and all staff involved in caring for them. The airway manager should fully understand and apply principles of infection prevention and control, including understanding and matching personal protective equipment (PPE) to the prevailing mode of viral transmission. Airway management should be meticulously planned, safe for the patient and staff, be undertaken by skilled operators using reliable, well-practised techniques and should aim to achieve high first-attempt success rates so that securing the airway is timely and swift.
Epidemic and Pandemic Infection
This chapter is written during the 2019–20 coronavirus pandemic. It is a period of dramatic change and learning. We have attempted to write a chapter that is accurate but the fast-moving evidence means that there may be changes between our writing and publication. While the chapter focuses on coronavirus disease 2019 (COVID-19) the principles can be broadly applied to any contagious respiratory pathogen.
On the last day of 2019, the World Health Organization (WHO) was informed by the Chinese authorities of an unexplained cluster of pneumonias in Wuhan in the Hubei province. Over the coming months this cluster grew to an epidemic in China – affecting more than 80,000 patients, and then to a pandemic (declared by WHO on 11 March 2020) affecting all countries and at the time of writing (early April 2020) affecting more than 1.9 million patients and more than 100,000 deaths. It is likely that the worst is yet to come and that numbers may increase many-fold before we see beyond the pandemic.
The illness, due to a coronavirus (of the common cold variety) called SARS-CoV-2, causes a predominantly respiratory illness: COVID-19. In the vast majority of patients, it is a mild, or even unnoticed illness. Indeed, it is so mild that its epidemiology is hard to study because it is impossible to determine how many people have had the illness simply by symptoms. Population studies exploring antibody presence will in due course determine that but at present there is uncertainty.
The virus is very infectious and for each patient with the disease the infectivity rate (i.e. the number of patients each individual will infect without counter measures, termed R0) is 2.5–3. For comparison, the R0 of influenza is around 1.3 and of Ebola 2.0. Because of its geometric progression, after 10 cycles of infection, perhaps in one month, a single patient with influenza would have infected 14 others, while COVID-19 would have spread to 59,000 patients. It is this potential for spread and the high fatality rate that accounts for its devastation.
Controlling the illness is about containment – to reduce R0. If this can be reduced to below 1 the epidemic will eventually peter out. Outside hospitals this relies on restricting physical contact and many countries have been placed in lockdown for several months. Within hospitals, containment is intended to prevent cross-infection from infected patients to staff (or vice versa) or other patients.
Current best estimates are that 30–80% of the population will contract the virus – there is no pre-existing immunity. The fatality rate depends on which denominator is used – the number of infections, or the number of detected cases. Overall, it is likely that the overall infection fatality rate is approximately 1%. By comparison for influenza it is between 0.1% and 0.01%. The disease severity is summarised in Figure 38.1.
Figure 38.1 The epidemiology of coronavirus disease 2019. The upper figure explains the terms used in describing infections, cases, deaths etc. and the ascertainment, case fatality and infection fatality rates. The lower figure gives an estimate of the likely numbers when 100 cases are identified in a community.
COVID-19 causes a severe viral pneumonia in a significant number of patients. In the early stages this may be associated with pulmonary microthrombotic disease. Typically, 7–10 days into the illness this can progress to severe acute respiratory syndrome typically with hypoxaemia without hypercapnia. While some patients can be managed with continuous positive airway pressure (or high flow nasal oxygen (HFNO)) the failure rates are high and tracheal intubation for controlled ventilation in intensive care is often required. Myocardial and renal failure and thrombotic complications may also occur but the predominant illness is respiratory. Treatment is currently supportive, although multiple therapeutic interventions are being explored. Mortality in those requiring ventilation is approximately 50%.
Mortality will vary by country, affected by overall healthcare structure and by the dynamic preparation that was possible before the epidemic surge hit, to both slow down spread within that country and to expand hospital and critical care services. Risk factors for mortality include increasing age (rising from the mid-50s), non-white ethnicity and those with cardiovascular or respiratory disease, hypertension, diabetes, immunosuppression or cancer. Obesity is also prominent in some series.
Airway management is primarily required for the initiation of ventilation. However, during and after the peak of the epidemic patients with mild disease, but with unrelated conditions, may present for surgical care and it may be impossible to determine who does or does not have the infection.
Viral Transmission, Infection Control and Personal Protective Equipment
Viral Transmission
Airway management during a respiratory epidemic requires clear understanding of infection control measures. This understanding is fundamental to preventing cross-infection but also impacts on the planning, ease and speed of airway management and so affects patient and staff safety.
Spread of a respiratory illness may occur by three routes: contact, droplet or airborne (Figure 38.2). During a respiratory illness coughing and sneezing cause forceful expulsion of particles from the respiratory tract. In general terms particles of > 5 µm (but as large as 2000 µm) are subject to gravitational forces and fall near to the patient – mostly within 1 m, but perhaps up to 2 m away. If another person is close by these droplets may enter their respiratory tract via their mucosa. The particles settle on whatever surface they first meet and can remain there and be viable for many hours or even several days, becoming fomites. Anyone touching those surfaces may become contaminated with the virus. Droplets may account for well above 99% of the particulate volume of a cough or sneeze. Coughing and sneezing also produce an aerosol of smaller particles (< 5 µm) which may spread much further – up to 6 or 7 m – and may also remain in the air for a longer period of time. These small particles, if inhaled, may reach the alveoli. Certain medical procedures – including almost all aspects of airway management may also create respiratory aerosols – especially when the airway is at positive pressure and gas leaks from it. Aerosol generation and infectivity is complicated – aerosols may or may not contain viable virus and whether they do will depend on the stage of the illness, the location in the respiratory tract they were generated from and other factors including the type of mucus secreted and the extent to which that particular patient secretes the virus, which is not readily predictable from the severity of symptoms.
For SARS-CoV-2 spread is thought to be predominantly via droplet and contact transmission.
If another individual or healthcare worker is > 2 m away from a patient the risk of droplet transmission of infection is very low. Aerosol generating procedures (AGPs) are listed in Table 38.1 ‘The list is pragmatic and better evidence is needed to understand AGPs and risk better.’
Table 38.1 Aerosol generating (medical) procedures. The numbers in brackets indicate the rank order of decreasing risk for the top four procedures as reported by Tran et al. (2012)
| Respiratory aerosols |
|---|
|
| Blood or tissue fluid aerosols |
| Surgical procedures using high-speed devices (e.g. drilling, pulse lavage, sternotomy) |
* Chest compression is not considered by all organisations to be an aerosol generating procedure but the international consensus is that it is.
** Supraglottic airway insertion and removal is assumed but not proven to be an aerosol generating procedure.
Infection Prevention, Control and Personal Protective Equipment
There is a natural focus amongst staff on the equipment component of PPE but other aspects of infection control are equally important. PPE is only one part of a system to prevent contamination of those working near patients with COVID-19. The illness represents a risk to those staff, other staff and patients.
Other elements of a system to reduce cross-infection include:
Preventing patients, visitors or staff who have or have been exposed to COVID-19 entering hospitals without reason
Meticulous hand-washing and personal hygiene
Managing patients with known or suspected COVID-19 separately from those without it, through a cohort or isolation
Definition of clear personnel/patient pathways
Restricting staff and visitors in the location of patients with COVID-19 to only those needed
Wearing of a surgical face mask by suspected or infected patients
At least twice daily cleaning and decontamination of surfaces and equipment
Minimising unnecessary patient and surface contact during patient care
Best practice in donning, doffing and disposal of PPE
Prompt disposal of single-use equipment after use
Decontamination of reusable equipment according to manufacturer’s instructions
Appropriate waste management
Numerous non-governmental organisations have made recommendations about PPE and all are generally in agreement with each other. It is logical to match the PPE used to the mode and risk of viral transmission. This approach is summarised in Table 38.2.
Table 38.2 Personal protective equipment: matching use to the mode of viral transmission and relevant locations. Levels of protection are incremental: droplet precautions are also designed to prevent contact transmission; airborne precautions also to prevent droplet and contact transmission. A fluid resistant surgical face mask may be added in non-clinical and contact zones if prevalence of disease is high
| Precaution | When to use in a patient being treated as COVID-19 positive | What is it? |
|---|---|---|
| Non-clinical areas | No additional risk | Standard infection control precautions |
| Contact precautions | > 2 m away from patient |
|
| Droplet precautions | Within 2 m of patient |
|
| Airborne precaution** | Aerosol generating procedure |
|
* Eye protection may be goggles or a visor. Personal spectacles are insufficient.
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