Clinical Aerosol Generating Procedures and Coughing: Quantification of Risk and Mitigation Strategies to Reduce Airborne Transmission of Infections

Background: The risks to healthcare workers of contracting COVID-19 have been well reported, but exposure of healthcare workers to aerosols generated during cardiopulmonary resuscitation (CPR) from patients infected with COVID-19 are uncertain. Moreover, the risks to healthcare workers during patient interactions and any benefits of a source control device within an ambulance setting (e.g., surgical mask) to mitigate risk are poorly understood. These gaps are addressed in this Thesis through two research projects, viz., CAS-19 (“Cough in an ambulance setting during the COVID-19 era”) and STOPGAP (“Study of cardiopulmonary resuscitation activities thought to generate aerosol particles”). Methodology: The CAS-19 research project consisted of three phases: (i) Characterisation of a human cough, (ii) design and validation of a novel anthropomorphic cough simulator (NACS) and (iii) the investigation of bioaerosol distribution from cough in an ambulance setting. Phases (i) and (ii) were laboratory-based experimental studies. Phase (iii) was a laboratory-based repeated measures experimental study. Studies performed under the STOPGAP project were designed to ascertain which components of CPR are aerosol generating and, if so, to identify the level of aerosol generation during CPR. The study used a multi-method design, consisting of two clinical streams that sought to measure aerosol generation from patients undergoing CPR in an out-of-hospital setting and within an Emergency Department. The research was classified as an observational study, using real-world CPR attempts. Results: In an ambulance setting, a marked difference in efficacy of a surgical face mask was reported when comparing the particle mass concentration (PMC) and particle number concentration (PNC). A statistically significant interaction between mask use and clinician position was found when analysing total net PMC (p = 0.0012) but this finding was not present when comparing total net PNC (p = 0.5430). A significant difference was also found when independently comparing the total net PMC of mask use as a source control device vs no mask use (p = 0.0002) and clinician position (p = 0.0154). There was no significant difference in the total net PNC when comparing mask use (p = 0.6659) but a significant difference in aerosol exposure was found when analysing the clinician’s position (p = 0.0033). During STOPGAP, 19 episodes of mask ventilation were analysed over four CPR attempts and did not consistently show an increase in particle generation related to the event. Seven episodes of suctioning were analysed over four CPR attempts, with two showing an increase in particle generation and two showing a decrease in particle generation. All data was obtained from participants recruited in the out-of-hospital setting (18). No participants were recruited from the Emergency Department setting. Discussion: For CAS-19, the position of the clinician within the ambulance during the coughing event impacted the level of exposure. An anterior position (clinician directly in front of the cough) presented the highest risk. Statistical tests showed that utilising a surgical face mask as a source control device on the coughing patient was effective in reducing the total net PMC but was much less effective in reducing the total net PNC. During STOPGAP, mask ventilation appeared to result in particle generation during one resuscitation attempt but with episodes of mask ventilation not being isolated during data collection it was difficult to draw conclusions with any degree of certainty. Suctioning was associated with a rise in particle concentration post-procedure. However, a single suctioning event heavily influenced this finding. Stipulations by the Research Ethics Committee (REC) relating to the consenting process had a detrimental impact on the ability to recruit participants. Conclusions: It is recommended that all patients with the symptom of ‘cough’, should be asked to wear a surgical face mask when being conveyed by an ambulance and healthcare workers should avoid undertaking care activities directly in front of the patient. The STOPGAP research piece highlighted the need for further research relating to mask ventilation but it is recommended that once a decision has been made to commence CPR, emphasis should be placed on early securement of a closed-circuit airway device. Overall, these data did not provide definitive evidence to determine if suctioning or during CPR resulted in particle generation or elimination. Pro-active engagement with REC’s is required in order to improve the understanding of the challenges faced by researchers in the pre-hospital setting and thereby improving the experiences of those conducting acute medicine research. The findings within this thesis not only provide recommendations relating to modern-day viruses but will also be critical for future novel viruses, whose characteristics are not yet known.