Chest Compressions and Defibrillation as Aerosolgenerating Procedures

Methodology

Scoping reviews offer flexibility when reviewing literature that spans multiple, diverse methodologies and allow a broad overview of a topic to be created. As such, they have been described as an appropriate alternative to traditional systematic reviews when tackling limited evidence obtained using differing methodologies (Peterson et al, 2017; Munn et al, 2018).

A literature search was performed using systematic principles aligned to Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) (Tricco et al, 2018). Five key databases were searched: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), SCOPUS, the Cochrane Library and MEDLINE. Key search terms included combinations of ‘AGP’, ‘aerosol’, ‘droplet’, ‘bioaerosol’, ‘defib*’, ‘CPR’, ‘resus*’, ‘compression’, ‘transm*’, ‘COVID*’, ‘SARS’, ‘coronavirus’, ‘ebola’ and ‘airborne’. Boolean operators and MeSH terminology were also used.

Identified articles were subject to title and abstract analysis to obtain relevant papers and were screened using inclusion and exclusion criteria. Duplicates and foreign language papers without a translation into English were excluded. The remaining papers then underwent full text review. Relevant papers were included as part of the review with relevance defined as articles that specifically discussed either chest compressions or defibrillation as a source of transmission of disease or potential AGP. Grey literature and searches of reference lists also highlighted papers of interest and were again included for full-text review. Following full analysis, findings were chartered in a table with common findings and themes were colour-coded. All of this was undertaken by a solo researcher.

Results

The search strategy identified 13 papers specifically discussing chest compressions or defibrillation as possible AGPs/sources of nosocomial infection (Figure 1). Literature dates ranged from 2004 to 2021 and were predominately retrospective in nature. Only two prospective papers were identified.

Evidence identified through the search criteria consisted of case reviews, retrospective cohort studies and systematic reviews (Table 1).

Case study and retrospective cohort study data showed that SARS-CoV-2 was not the first coronavirus to present a threat to health workers treating critically ill patients. Similar concerns regarding nosocomial transmission during resuscitation were raised during SARS and Middle East respiratory syndrome (MERS) outbreaks in Canada and Saudi Arabia respectively (Christian et al, 2004; Loeb et al, 2004; Raboud et al, 2010; Nam et al, 2017). Similarly, in an outbreak of severe fever with thrombocytopenia syndrome (not caused by a coronavirus) in South Korea, four out of seven health professionals involved in cardiopulmonary resuscitation (CPR), wearing varying levels of PPE, subsequently contracted the disease (Kim et al, 2015).

The search identified three notable systematic reviews, which were included in this review. A consistent finding across all three was that chest compressions and defibrillation were thought to pose a low risk of transmission of respiratory disease compared to the perceived higher risk procedure of endotracheal intubation (Tran et al, 2012; Brown and Chan, 2020; Couper et al, 2020).

Prospective studies used animal or cadaver models to investigate chest compressions and defibrillation as potential AGPs. A pilot study by Hsu et al (2021a) involved induced cardiac arrest in three Yorkshire swine which then underwent chest compressions and defibrillation while attached to an aerosol analyser. No difference was seen in the level of aerosols generated by chest compressions alone, but significantly larger aerosols were observed immediately after chest compressions were initiated following defibrillation. The limitations of the study design are apparent, particularly with regards to sample size and anatomical differences between pigs and humans. The authors also conceded they had neglected to measure humidity, temperature and air flow, all of which are known to influence aerosol dispersion. Furthermore, the equipment used by Hsu et al (2021a) measured aerosols with particles that measured <10μm, therefore not gaining an understanding of aerosols with larger particles that might be created.

Ott et al (2020) concluded that chest compressions were a potential AGP from using ultraviolet-sensitive detergent in their mannequin and cadaver simulation models. Their study design involved filling the lungs and airways of mannequins and cadavers with nebulised detergent, then using periodic, ultraviolet-sensitive photography to track aerosol dispersion during chest compressions. This methodology meant aerosol distribution could be estimated; however, size and quantity were not measurable. Limitations were cited as an inability to translate aerosol dispersion into risk of infection, likely because of the inability to quantify aerosol volume or mass, as well as man-made aerosols not being truly representative of what might be seen in real life.

Ambiguity of language

Inconsistencies regarding terminology, specifically regarding CPR, were noted.

CPR traditionally comprises chest compressions and assisted ventilations, either via mouth-to-mouth or bag-valve mask ventilations. Guidelines have been adapted to encourage compression-only CPR due to the reluctance of lay people to perform assisted ventilations. Partly due to a lack of understanding of the techniques involved or, more notably, fear of disease transmission through mouth-to-mouth ventilation (Taniguchi et al, 2007)—a fear exacerbated through the pandemic (Bray, 2020).

This ambiguity of language regarding CPR seen throughout the literature meant it was difficult to draw specific conclusions regarding chest compressions as a possible AGP.

Discussion

This review of the limited literature has demonstrated a pressing need for clarity to better understand aerosol production during resuscitation procedures. There was a paucity of evidence regarding chest compressions and defibrillation as potential AGPs, with no study offering definitive, conclusive findings. This dearth of evidence has led to contradictory guidelines being produced, with documented confusion among health professionals and reported feelings of mistrust in policies. The effect is that health professionals could potentially not be complying with PPE guidelines, putting themselves and others at risk (Cheruku et al, 2020; Houghton et al, 2020; Payne and Peache, 2021; Perkins et al, 2021).

Retrospective evidence analysed within this review suggests the risk of contracting respiratory disease through chest compressions and defibrillation is low. However, data contributing to this viewpoint have been demonstrated to be of poor quality in various systematic reviews, with caution repeatedly urged within the literature should one wish to draw definitive conclusions.

Uncertainty has arisen because of the multiple confounding variables and significant biases associated with retrospective data. Resuscitation of patients in cardiac events inevitably involves multiple procedures performed simultaneously, which means that case review data cannot be used to pinpoint the specific point of nosocomial transmission.

A general assumption exists within literature that nosocomial transmission in a resuscitative attempt originates from being in close proximity to the airway, with transmission often presumed to be a result of endotracheal intubation, which is perceived as a high-risk procedure (Tran et al, 2012; Brown and Chan, 2020; Couper et al, 2020).

Emerging literature casts doubt on the validity of this assumption. Recently published quantitative studies have shown elective intubation to produce very few aerosols—significantly fewer than coughing (Brown et al, 2021). Similar findings have been demonstrated during insertion and removal of supraglottic airways (Shrimpton et al, 2021). These findings have led to calls for reviews of which procedures should be defined as an AGP. When considering these findings in relation to prehospital working, a point of consideration in both studies is the environment in which the investigated intervention occurred.

Both Brown et al (2021) and Shrimpton et al (2021) investigated aerosol production in the controlled environment of hospital theatres. Routine practice would involve prior assessment and grading of airways. Similarly, patients would be fully anaesthetised, making no respiratory effort and kept nil by mouth before the procedure. In the case of Shrimpton et al (2021), patients with difficult airways were excluded from the study. These safety and screening measures would not be afforded to the prehospital rescuer. Prehospital patients do not present fully anaesthetised so could potentially make a respiratory effort at any moment, further complicating matters. As such, this is an area that would benefit from further investigation.

No studies were identified that had attempted to record real-time aerosol data during active emergency resuscitation in human subjects and very little data exist investigating size, volume or distribution of aerosols generated by these procedures. The two prospective studies identified via the search strategy suggest chest compressions and defibrillation are potential AGPs. However, both were subject to significant limitations. Although innovative in their study design, the use of small sample sizes impacted their findings. Methodological techniques that were not reflective of true resuscitative events meant that generalised conclusions were impossible. Both studies conceded this point, highlighting the need for further research (Ott et al, 2020; Hsu et al, 2021a).

With no definitive, evidence-based answer regarding defibrillation or chest compressions being aerosol generating or, more importantly, whether these procedures pose a risk of transmission of respiratory disease to health professionals, one must consider their respective risk in relation to the nature of respiratory viral transmission and aerosol production.

Respiratory aerosol particles and droplets have historically been defined as being under 5μm and droplets exceeding this are arbitrarily cut off. Droplets follow a ballistic trajectory whereas aerosols remain suspended in the air, akin to smoke. It has since emerged, through advances in aerosol-measuring technology, that this might be over simplistic. Particles of up to 100μm have been found to remain suspended in air for up to 5 seconds. SARS-CoV-2 measures approximately 0.1μm, with aerosol particles of under 5μm or more able to carry virions (Bar-On et al, 2020; Lee, 2020; Wang et al, 2021). These measurements have implications when considering what appropriate levels of PPE would be.

People create respiratory particles, both droplets and aerosols, through the turbulence of exhaled air passing over moist, mucous-lined airways. This air force liberates aerosols that are then exhaled, coughed or sneezed from the airway (Edwards et al, 2021). Once aerosolised, particles are then subject to the effects of temperature and humidity, which can further alter their size and aerodynamic properties, as does the speed at which they leave the airway (Drossinos et al, 2021; Klompas et al, 2021).

Physiological conditions that alter the surface tension and viscoelasticity of the mucous-lined airways can increase the propensity for respiratory particle generation, in which surfactant properties play a crucial role. Factors such as age, weight, diet and COVID-19 infection can change lung surfactant properties and lead to a greater production of droplets and aerosols (Edwards et al, 2021). The force of compressing a patient’s chest to manually affect intrathoracic pressure, as seen during chest compressions, has been demonstrated to create an expiratory passive tidal volume as high as 45.8ml (McDannold et al, 2018). Similarly, defibrillation causes a violent muscular contraction. One can thus see how chest compressions or defibrillation might lead to production of respiratory aerosols and be a risk factor in the transmission of respiratory disease.

On 28 September 2021, Public Health England (PHE) released its updated interpretation of the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) review, examining the evidence regarding chest compressions and defibrillation as AGPs. This was reviewed on 14 April 2022 but later withdrawn in May 2022. Within this document PHE published the following quote from NERVTAG:

This is caveated with a suggestion that health organisations may wish to use higher levels of PPE for staff tasked with the delivery of chest compressions. PHE has since been replaced by the UK Health Security Agency and Office for Health Improvement and Disparities. More recently, NHS England (NHSE) published a rapid review of AGPs in June 2022, in which chest compressions or defibrillation are not mentioned (NHSE, 2022). Interestingly the Resuscitation Council UK (RCUK) advised members of the public to not delay chest compressions on out-of-hospital cardiac arrest patients. Both RCUK and the Royal College of Nursing (RCN) advocate higher levels of PPE (FFP3 masks or respirators) for health care workers performing chest compressions for suspected or confirmed COVID-19 (RCUK, 2022; RCN, 2023). The RCN takes a different stance with regards to how it advises its members when faced with cardiac arrest patients outside of hospital.

Similarly, the American Heart Association (Hsu et al, 2021b), in an attempt to address rising mortality rates seen in patients experiencing an out-of-hospital cardiac arrest, recommend there be no delay in compression or defibrillation in regions where vaccinations have been widely distributed. This is in contrast to the WHO’s (2021) stance; CPR remains on its list of AGPs, alongside tracheal intubation, manual ventilation and non-invasive ventilation. Table 2 shows the WHO’s (2021) full list of AGPs.

Without formal quantification of aerosols during real-time resuscitation with a focus on chest compressions and defibrillation specifically, disagreement and debate regarding the most appropriate course of action will remain.

Conclusions

The evidence base regarding chest compressions and defibrillation as possible AGPs is highly limited and subject to multiple confounding factors and biases. Literature suggests chest compressions and defibrillation to be of low risk of transmission of respiratory diseases. This is partly because, during a cardiac arrest, these procedures occur simultaneously to the perceived high-risk procedures associated with airway management.

Literature repeatedly theorises the origin of nosocomial transmission during a resuscitation attempt to be airway management procedures, specifically endotracheal intubation. Emerging evidence in controlled hospital settings suggests elective intubation and supraglottic airway insertion might not be as high risk as initially thought, generating fewer aerosols than coughing (Brown et al, 2021; Klompas et al, 2021; Shrimpton et al, 2021).

It is a recommendation from this review that urgent research is carried out to establish which procedures of resuscitation generate aerosols, with clarity required regarding chest compressions and defibrillation, specifically to reassure rescuers and benefit patients in cardiac arrest.

Key points

CPD Reflection Questions