Aerosol Generating Procedures

Aerosol Generating Procedures (AGP)

High level of certainty:

  1. An Aerosol Generating Procedure (AGP) describes an activity that can result to the release of small airborne particles (aerosols) or droplets. Under certain conditions, the release might contain potentially transmissible quantities of virial material; the current focus of this document.
  2. The mechanisms of aerosol release are associated with:
    1. Low temperature (usually under 60°C) evaporation processes where virial material could survive and be suspended in air
    2. Operations generally involving high shear stresses or/and rates on materials that could potentially be suspended in air
    3. Aerodynamic interactions between materials/streams of materials that could generate or/and intensify or/and spread new or pre-existing aerosols/pre aerosolised material
  3. AGPs with virus transmission potential are diverse and could include, apart from medically associated operations, common activities such as playing wind instruments1, singing2, sneezing, coughing, physically intensive activities that involve vigorous exhalation etc.
  4. Public Health England (PHE) lists the following medical procedures for COVID-19 associated with increased risk of respiratory transmission3,4:
    1. tracheal intubation and extubation
    2. manual ventilation
    3. tracheotomy or tracheostomy procedures (insertion or removal)
    4. bronchoscopy
    5. dental procedures (using high speed devices, for example ultrasonic scalers/high speed drills)
    6. non-invasive ventilation (NIV); Bi-level Positive Airway Pressure Ventilation (BiPAP) and Continuous Positive Airway Pressure Ventilation (CPAP)
    7. high flow nasal oxygen (HFNO)
    8. high frequency oscillatory ventilation (HFOV)
    9. induction of sputum using nebulised saline
    10. respiratory tract suctioning
    11. upper ENT airway procedures that involve respiratory suctioning
    12. upper gastro-intestinal endoscopy where open suction of the upper respiratory tract occurs
    13. high speed cutting in surgery/post-mortem procedures if respiratory tract/paranasal sinuses involved
  5. A broader and more detailed list of procedures is created via an extensive literature review which adds the following procedures to the PHE list or generalises some specific processes already listed5:
    1. Breaking closed ventilation systems (intentionally or unintentionally)
    2. Cardiopulmonary resuscitation
    3. Chest physiotherapy
    4. Colonoscopy
    5. Coughing
    6. ENT and neurosurgery
    7. Nitrous oxide (Entonox) administration
    8. GI endoscopy (not further specified)
    9. Handling soiled laundry
    10. High-flow oxygen therapy
    11. Intra/extra pulmonary high-frequency oscillation devices
    12. Labour and delivery
    13. Lung function testing
    14. Manipulation of masks
    15. Mechanical insufflation and exsufflation
    16. Nasogastric tube insertion
    17. Nasopharyngeal aspirate
    18. Nasopharyngeal and oropharyngeal swabbing
    19. Nasopharyngoscopy or laryngoscopy
    20. Nebulised or aerosol therapy
    21. Prone positioning
    22. Suction of body fluids (not further specified)
    23. Supraglottic airways
    24. Thoracic surgery and procedures
    25. Toilet use and flushing
    26. Tracheostomy and tracheostomy procedures
    27. Upper GI endoscopy
    28. Vacuum cleaning

Low level of certainty:

  1. Amount and variability of overall viable SARS-CoV-2 virons released from each AGP and associated transmissivity thread.
  2. Types/measurement methods to adequately quantify/measure released material.
  3. For dental operations and their subsequent use of high rotating speed pneumatic powered equipment (e.g. microturbine handset drills), a suggestion of using lower speed, high torque, electrically powered micromotor handsets seems to be reducing the amount of expelled material6,7.
  4. Mitigation routes (including dynamic prediction of fallow times) per process.
  5. There is a lack of high quality studies which have examined the risk of transmission of microbes responsible for acute respiratory infections to healthcare workers caring for patients undergoing AGP8.
  6. Lack of precision in the definition for aerosol generating procedures8.

Unknown:

  1. Amount of actual virial material in released emissions per droplet/particle especially when AGP involves secondary fluids (e.g. water for instrument cooling etc.)
  2. Threshold of virial content volume in droplet to transmit the virus
  3. Aerosol and droplet emission generation mechanisms at the microscale to allow specific mitigation processes as a result of altered/modified operation of action or/and design of instrumentation used.
  4. Characteristics of expelled particles/droplets for each procedure including velocity and trajectory from source.

References

  1. He, R., Gao, L., Trifonov, M. & Hong, J. Aerosol generation from different wind instruments. J. Aerosol Sci. 151, 105669 (2021).
  2. Bahl, P. et al. Droplets and Aerosols Generated by Singing and the Risk of Coronavirus Disease 2019 for Choirs. Clin. Infect. Dis. 2019–2021 (2020). doi:10.1093/cid/ciaa1241
  3. Public Health England. COVID-19: Guidance for the remobilisation of services within health and care settings. Infection prevention and control recommendations. Infection prevention and control recommendations (2020).
  4. Assessing the evidence base for medical procedures which may create a higher risk of respiratory infection transmission from patient to healthcare worker. (2020).
  5. Jackson, T. et al. Classification of aerosol-generating procedures: a rapid systematic review. BMJ Open Respir. Res. 7, e000730 (2020).
  6. Implications of COVID-19 for the safe management of general dental practice A practical guide. 06-16 (2020).
  7. Mitigation of Aerosol Generating Procedures in Dentistry. (2020).
  8. Tran, K., Cimon, K., Severn, M., Pessoa-Silva, C. L. & Conly, J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One 7, (2012).