Objective: Mechanical ventilation is thought to increase the risk of nosocomial pneumonia by permitting leakage of bacteria-laden gastro-oropharyngeal secretions into the upper airways. The goal of this study was (a) to validate radiographic signs of pooled secretions above endotracheal-tube cuffs (supracuff liquid) in an animal model and (b) to determine whether suctionable pooled supracuff liquid can be identified on bedside radiographs of intubated patients.
Materials and methods: Diagnostic criteria for supracuff liquid were initially validated by three radiologists interpreting 162 randomized radiographs made in an intubated sheep cadaver. The primary criteria included (a) replacement of the normal supracuff lucency with liquid opacity and (b) the formation of a sharp interface between the lucency of the upper edge of the cuff below and the liquid above. Graded infusions of 0, 3, 8, 13, and 23 ml of saline were made in triplicate into the space above the cuff, and radiographs were evaluated for the presence or absence of saline. The validated diagnostic criteria were used by two radiologists to estimate the frequency with which pooled liquid was seen on portable chest radiographs of 47 patients undergoing elective short-term postanesthetic mechanical ventilation.
Results: In the sheep-cadaver model, the diagnostic criteria for supracuff liquid allowed successful differentiation between no liquid, a small amount of liquid (3-8 ml), and a large amount of liquid (13-23 ml; c2, p < .0001). In a clinical study, radiographic signs of supracuff liquid were identified in 57% of 47 patients. In a small subset of patients (n = 18), the estimated liquid volume (mean +/- SEM) was calculated to be 7.8 +/- 1.1 ml (range = 2.1-18.4 ml).
Conclusions: Radiography is a sensitive means of identifying small volumes of supracuff liquid above the inflated cuffs of endotracheal tubes. Potentially contaminating liquid pooled above the cuff of an endotracheal tube can be identified in about half of patients undergoing short-term mechanical ventilation. Our results suggest the suction of the supracuff space may be a reasonable prophylactic maneuver against nosocomial pneumonia. A much larger study is suggested to investigate the actual relation between pooled supracuff liquid and the development of nosocomial pneumonia.