Aerosol dispersion in a ventilator circuit: towards a model for enhancing our understanding of ventilator-associated pneumonia

Gregory T Carroll, David L Kirschman

Abstract

Background

Patients receiving mechanical ventilation for more than 48 hours are at risk for developing ventilator-associated pneumonia (VAP). 

Methods

We investigated aerosol flow in a ventilator circuit attached to test lungs to better understand how airflow dynamics in ventilator tubing can contribute to the pathogenesis of VAP.  The ventilator was operated so that the lungs cyclically inflated and deflated.  Aerosolized saline was used as a surrogate for bioaerosols and was generated in the circuit with an aerosol generator attached to the tubing below an endotracheal cuff that sealed an endotracheal tube at the opening of the lungs.  We used a particle collector and analyzer attached to the circuit approximately two feet from the opening of the lungs to determine whether aerosols flowed into the tubing.

Results

We detected significant levels of aerosolized particles (P <0.05) that traveled retrogradely into the ventilator circuit.   The highest nozzle pressure tested, 13 hPa, produced mean 0.5, 0.7 and 1.0 mm aerosol levels of 24 ±5, 10±4 and 8±3 particles/ft ³, respectively.  The lowest nozzle pressure tested, 10 hPa, produced mean 0.5, 0.7 and 1.0 mm aerosol levels of 14 ±5, 4 ±2, and 3 ±2 particles/ft3.     

Conclusions

Aerosolized material that enters the circuit near the endotracheal cuff travels into the ventilator tubing during mechanical ventilation.  Our results suggest that infectious material could travel a similar route and contaminate the air in the ventilator circuit which then enters the patient.

Keywords

Ventilator-associated pneumonia, bioaerosol, aerosol, contamination, ventilator circuit

References

1. Behrendt CE. Acute respiratory failure in the United States: incidence and 31-day survival. Chest 2000; 118(4):1100-1105. https://doi.org/10.1378/chest.118.4.1100 PMid:11035684

2. Kahn JM, Goss CH, Heagerty PJ, et al. Hospital volume and the outcomes of mechanical ventilation. N Engl J Med 2006; 355(1):41-50. https://doi.org/10.1056/NEJMsa053993 PMid:16822995

3. Wunsch H, Linde-Zwirble WT, Angus DC, et al. The epidemiology of mechanical ventilation use in the United States. Crit Care Med 2010; 38(10):1947-1953. https://doi.org/10.1097/CCM.0b013e3181ef4460 PMid:20639743

4. Seneff MG, Zimmerman JE, Knaus WA, et al. Predicting the duration of mechanical ventilation. The importance of disease and patient characteristics. Chest 1996; 110(2):469-479. https://doi.org/10.1378/chest.110.2.469 PMid:8697853

5. Strausbaugh L. Nosocomial respiratory infections. In: Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. Philadelphia, PA: Churchill Livingstone; 2000; 3020-3027.

6. American Thoracic Society; Infectious Diseases Society of America. Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia. Am J Respir Crit Care Med 2005; 171(4):388-416. https://doi.org/10.1164/rccm.200405-644ST PMid:15699079

7. Reignier J, Mercier E, Le Gouge A, et al; Clinical Research in Intensive C, Sepsis G (CRICS) Group. Effect of not monitoring residual gastric volume on risk of ventilator-associated pneumonia in adults receiving mechanical ventilation and early enteral feeding: a randomized controlled trial. JAMA 2013; 309(3):249-256. https://doi.org/10.1001/jama.2012.196377 PMid:23321763

8. Seguin P, Laviolle B, Dahyot-Fizelier C, et al; Study of povidone iodine to reduce pulmonary Infection in head trauma and cerebral hemorrhage patients (SPIRIT) ICU Study Group; AtlanRéa Group. Effect of oropharyngeal povidone-iodine preventive oral care on ventilator-associated pneumonia in severely brain-injured or cerebral hemorrhage patients: a multicenter, randomized controlled trial. Crit Care Med 2014; 42(1):1-8. https://doi.org/10.1097/CCM.0b013e3182a2770f

9.Papazian L, Klompas M, Luyt CE. Ventilator-associated pneumonia in adults: a narrative review. Intensive Care Med 2020; 46(5):888-906. https://doi.org/10.1007/s00134-020-05980-0 PMid:32157357 PMCid:PMC7095206

10. Chastre J, Fagon JY. Ventilator-associated pneumonia. Am J Respir Crit Care Med 2002; 165(7):867-903. https://doi.org/10.1164/ajrccm.165.7.2105078 PMid:11934711

11. Zimlichman E, Henderson D, Tamir O, et al. Health care-associated infections: a meta-analysis of costs and financial impact on the US health care system. JAMA Intern Med 2013; 173(22):2039-2046. https://doi.org/10.1001/jamainternmed.2013.9763 PMid:23999949

12. Murphy SL, Xu J, Kochanek KD, Arias E. Mortality in the United States, 2017. NCHS Data Brief. 2018 Nov;(328):1-8.

13. Craven DE, Steger KA. Nosocomial pneumonia in mechanically ventilated adult patients: epidemiology and prevention in 1996. Semin Respir Infect 1996; 11(1):32-53.

14. Hospital-acquired pneumonia in adults: diagnosis, assessment of severity, initial antimicrobial therapy, and preventive strategies. A consensus statement, American Thoracic Society, 1995. Am J Respir Crit Care Med 1996; 153(5):1711-1725. https://doi.org/10.1164/ajrccm.153.5.8630626 PMid:8630626

15. Craven D, Goularte TA, Make B. Contaminated condensate in mechanical ventilator circuits. A risk factor for nosocomial pneumonia? Am Rev Respir Dis 1984; 129(4):625-628.

16. Malecka-Griggs B, Kennedy C, Ross B. Microbial burdens in disposable and nondisposable ventilator circuits used for 24 and 48 h in intensive care units. J Clin Microbiol 1989; 27(3):495-503. https://doi.org/10.1128/jcm.27.3.495-503.1989 PMid:2715321 PMCid:PMC267346

17. Cadwallader HL, Bradley CR, Ayliffe GA. Bacterial contamination and frequency of changing ventilator circuitry. J Hosp Infect 1990; 15(1):65-72. https://doi.org/10.1016/0195-6701(90)90022-G PMid:1968480

18. Li YC, Lin HL, Liao FC, et al. Potential risk for bacterial contamination in conventional reused ventilator systems and disposable closed ventilator-suction systems. PLoS One 2018; 13(3):e0194246. https://doi.org/10.1371/journal.pone.0194246 PMid:29547638 PMCid:PMC5856346

19. Popovic M, Beathe J, Gbaje E, et al. Effect of portable negative pressure units on expelled aerosols in the operating room environment. Reg Anesth Pain Med 2022; 47(7):426-429. https://doi.org/10.1136/rapm-2022-103489 PMid:35365549

20. Carroll GT, Kirschman DL. Removal of indoor aerosol particles generated in a medically relevant space using a portable airborne particle filtration device. Indoor Built Environ 2023;0(0). https://doi.org/10.1177/1420326X231197187

21. King M-F, Camargo-Valero MA, Matamoros-Veloza A, et al. An effective surrogate tracer technique for S. aureus bioaerosols in a mechanically ventilated hospital room replica using dilute aqueous lithium chloride. Atmosphere 2017; 8(12):238. https://doi.org/10.3390/atmos8120238

22. Upton SL, Mark D, Douglass EJ, et al. A wind tunnel test of newly developed personal bioaerosol samplers. J Aerosol Sci 1994; 25(8):1493-1501. https://doi.org/10.1016/0021-8502(94)90220-8

23. Kesavan J, Bottiger JR, McFarland AR.Bioaerosol concentrator performance: comparative tests with viable and with solid and liquid nonviable particles. J Appl Microbiol 2008; 104(1):285-295.

24. Foarde KK. Development of a method for measuring single-pass bioaerosol removal efficiencies of a room air cleaner. Aerosol Sci Technol 1999; 30(2):223-234. https://doi.org/10.1080/027868299304804

25. Craven DE, Connolly Jr MG, Lichtenberg DA, et al. Contamination of mechanical ventilators with tubing changes every 24 or 48 hours. N Engl J Med 1982; 306(25):1505-1509. https://doi.org/10.1056/NEJM198206243062501 PMid:7043269