It is well-known from in-vitro experiments and analysis of catheters and endotracheal tubes (ET tubes) removed from patients, such as, that microorganisms settle on surfaces and form a biofilm within 24 hours. The pathogen microorganisms harboring the inner surfaces of the ET tube and the turbulent air flow through the ET tube (flow velocity approximately 1.5 m/s) create an optimal condition for an effective transmission of harmful microorganisms directly into the lungs of the ventilated patient. An extensive but not exhaustive list of scientific literature covering biofilm formation in ET tubing can be found at the end of this post.
It was shown by Inglis and co-workers (1989) how far from the ET tube exit microorganisms were projected with a normal ventilator air flow rate. ET tubes with ID = 8 – 9.5 mm immediately removed from patients were connected to a ventilator with an air flow rate of 1 liter/s. The projected distance of the microorganisms from the ET tube exit was determined by the use of large nutrient agar plates placed in extension from the exit of the patient tubes. Microorganisms from the biofilm (up to 106 CFU/cm) were projected up to 45 cm from the exit of the patient’s ET tube. The results of the experiment demonstrated that pathogenic organisms harboring the ET tube can be carried by the air flow directly into the patient’s lungs.
A risk for both patients and staff
Ventilator associated diseases are considered to be multi-factorial of nature. At the same time, however, the reduction of the contamination level in the clinical environment is a necessary condition to reduce the number of hospital infections. There is a reason why cleaning, use of face masks, use of alcohols and disinfectants and UVC disinfection robots are widely used in hospital environments. In the ultimate limit: No pathogens = no infections. During the coronavirus crisis the implications of limited supplies of protective equipment have been discussed. The clinical staff draws the attention to the conditions during suction and maintenance of the ET tubes during ventilation of the patient. The microbial burden in the air space close to patient is high during ET maintenance and poses a threat to the staff. It is also argued that the level of microbial burden i.e. absolute number of cells and virus not only influences the outbreak of an infection but also affects the degree of the infection.
Prolonged ventilation of Covid-19 patients
In addition, patients with Covid-19 are expected to be hospitalized and ventilated for a longer period. According to various sources 2- 3 weeks in a ventilator are not uncommon compared to normally 1 week. Methods for disinfection of the ET tube lumen should attract attention both to protect critical ill patients and clinical staff during their maintenance procedures.
- F. d. Sotile et al: Nosocomial pulmonary infection: possible etiologic significance of bacterial adhesion to endotracheal tubes. Critical Care Medicine (1986)
- T. J. J, Inglis et al: Tracheal tube biofilm as a source of bacterial colonization of the lung. J. of Clin. Microbiol., Sep. 1989.
- T. J. J, Inglis: Evidence for dynamic phenomena in residual tracheal tue biofilm. Brit. Journ. Anaesthesia (1993)
- T. J. J, Inglis wt al: Structural feature of tracheal tube biofilm formed during prolonged mechanical ventilation. CHEST (1995)
- C. Feldman et al: The presence and sequence of endotracheal tube colonization in patients undergoing mechanical ventilation. Eur Respir J (1999)
- C. G. Adair et al: Implications of endotracheal tube biofilm for ventilator associated pneumonia. Intensive Care Med (1999)
- S. D. Perkins et al: Endotracheal tube biofilm inoculation of oral flora and subsequent colonization of opportunistic pathogens. Int. J. of Med. Microbiol (2010)
- Gil-Perotin et al: Implications of endotracheal tube biofilm in ventilator-associated pneumonia response: a state of concept. Critical Care (2012)
- Alison Wilson et al: Advanced endotracheal tube biofilm stage, not duration of intubation, is related to pneumonia. J. Trauma (2012)
- P-E. Danin et al: Description and Microbiology of endotracheal tube biofilm in mechanically ventilated subjects. Respiratory Care (2015)
- O. Diaconu et al: Endotracheal tube biofilm and its impact on the pathogenesis of ventilator-associated pneumonia. J. of Critical Care Medicine (2018)