Pathogenic Link Between Postextubation Pneumonia and Ventilator-Associated Pneumonia: An Experimental Study

Abstract

Introduction The presence of an endotracheal tube is the main cause for developing ventilator associated pneumonia (VAP), but pneumonia can still develop in hospitalized patients after endotracheal tube removal (Post-Extubation Pneumonia, PEP). We hypothesized that short-term intubation (24h) can play a role in the pathogenesis of PEP. To test such hypothesis, we initially evaluated the occurrence of lung colonization and VAP in sheep that were intubated, and mechanically ventilated for 24h. Subsequently, we assessed the incidence of lung colonization and PEP at 48 h after extubation, in sheep previously ventilated for 24h. Methods To simulate intubated ICU patients placed in semi-recumbent position, fourteen sheep were intubated and mechanically ventilated with the head elevated 30° above horizontal. Seven of them were euthanized after 24h (Control Group) while the remaining were euthanized after been awaken, extubated and left spontaneously breathing for 48h after extubation (Awake Group). Criteria of clinical diagnosis of pneumonia were tested. Microbiological evaluation was performed on autopsy in all sheep. Results Only one sheep in the Control Group met the criteria of VAP after 24h of mechanical ventilation. However, heavy pathogenic bacteria colonization of trachea, bronchi and lungs (range, 104-109 CFU/g) was reported in four out of seven sheep (57%). In the Awake Group, one sheep was diagnosed with VAP and three developed PEP within 48h post extubation (42%), with one euthanized at 30h because of respiratory failure. On autopsy, five sheep (71%) confirmed pathogenic bacterial growth in the lower respiratory tract (range, 103-109 CFU/g). Discussion Twenty-four hours of intubation and mechanical ventilation in semi-recumbent position leads to significant pathogenic colonization of the lower airways, which can promote the development of PEP. Strategies directed to prevent pathogenic microbiological colonization before and after mechanical ventilation should be considered in order to avert the onset of PEP.

Prevention of Lung Bacterial Colonization With a Leak-Proof Endotracheal Tube Cuff: An Experimental Animal Study

“…Colonized subglottic secretions that leak across the folds of the ETT cuff, 7 ineffective mucociliary clearance caused by the cuff, 5 impairment of the protective cough reflex after endotracheal intubation, 19 aerosolization of the biofilm along the inner surface of the ETT that acts as a bacterial reservoir, 20 and the development of atelectasis 21 all contribute to increase the risk of lung colonization and, eventually, pneumonia. Furthermore, in the semirecumbent position, gravity directly acts on lung colonization and pneumonia, as described in both animal models 4,7,8,22 and human subjects, 23,24 and as recently confirmed by the Gravity-trial Network. 24 As shown in clinical studies, although the shape does not affect the frequency of pneumonia, 25,26 the material of the ETT cuff can exhibit a different performance in terms of pneumonia prevention.…”

“…This caused inflammation of the lung parenchyma and led to hypoxemia, a pathophysiologic sign of respiratory failure. 4,5,7,8 Results of our study indicated that the change of a single variable during intubation and mechanical ventilation (ETT cuff) might play a major contributing role in the multifaceted pathogenesis of VAP because it can radically influence the risk of lung bacterial colonization.…”

“…Thirteen adult female Yucatan minature pigs (median (IQR) age, 8 [7][8][9] months; weight, 34 [27][28][29][30][31][32][33][34][35][36][37] kg) were studied and considered healthy based on clinical criteria, laboratory data, and chest radiographs performed the day before the experiment.…”

“…[4][5][6][7] The lack of a complete seal with an ETT cuff may allow lung colonization and serve as a source for VAP or postextubation pneumonia. 8…”

An Artificial Cough Maneuver to Remove Secretions From Below the Endotracheal Tube Cuff

“…Endotracheal intubation and mechanical ventilation considerably impair airway defenses, increasing the risk of bacterial colonization and ventilator-associated pneumonia. 2,3 The endotracheal tube (ETT) cuff, which allows positivepressure ventilation and prevents aspiration, compromises mucociliary clearance by mechanically preventing the flow of mucus toward the oropharynx. 4,5 Therefore, secretions accumulated in the trachea must be removed by endotracheal suctioning.…”