The cuff leak test: does it "leak" any information?

Post-extubation stridor and upper-airway obstruction are multifactorial in etiology and can occur as a result of laryngotracheal edema, intubation trauma, excessive cuff pressure with mucosal ulceration, and prolonged intubation with secondary inflammation and granuloma formation.1 Cuff leak tests (CLTs) were introduced in an attempt to predict post-extubation upper-airway obstruction and reduce the incidence of extubation failure. Qualitative CLTs were performed by deflating the endotracheal tube (ETT) cuff, blocking the ETT opening, and listening for an audible leak around the ETT while patients were spontaneously breathing.2 In an effort to increase the accuracy of CLTs in detecting post-extubation stridor, methods of quantifying a cuff leak were introduced. Miller and Cole3 described the cuff-leak test with the ventilator set in assist-control mode at a tidal volume (VT) of 10–12 mL/kg. An inspiratory VT and 6 subsequent expiratory VT values were recorded after oropharyngeal suctioning and ETT cuff deflation. The cuff leak was measured as the difference between the preset inspiratory VT and the average of the 3 lowest of the subsequent 6 expiratory VT values. The threshold cuff-leak volume was determined by visual inspection of the receiver-operating characteristic plot. A leak of 110 mL was considered a positive result of the CLT and indicated that patients were at risk for post-extubation stridor secondary to laryngeal edema.3 This quantitative cuff leak has been expressed as an absolute volume or as a percentage of the inspired VT. When the cuff leak volume is 110–130 mL3,4 or 10– 15.5%5,6 of the delivered VT, the risk for post-extubation stridor is significantly elevated. Other attempts have focused on quantifying a cuff leak volume in spontaneously breathing patients receiving CPAP.7 The leak volume was calculated as the difference between the expiratory VT with inflated cuff and the expiratory VT with deflated cuff. Even with quantifiable cuff leak volumes, studies reported a low sensitivity and a low positive predictive value of cuff leak volumes in detecting post-extubation stridor.3– 5,8 This was attributed to several factors, including the lack of standardization of the ratio of ETT size to the laryngeal diameter (a large ETT will result in a smaller cuff leak volume for the same laryngeal diameter), and the possible contribution of the exhaled limb of the breathing circuit and the ventilator to an increased airway resistance and therefore an increase in cuff leak volume. In an effort to eliminate the ETT size as a confounding variable, Gros et al, in this issue of RESPIRATORY CARE, evaluated the use of intra-individual variation of the cuffleak test ( CLT), as a predictor of post-extubation stridor.9 They performed the CLT (as proposed by Miller and Cole) immediately after intubation (T0) and before extubation (T1) to evaluate the differences in cuff leak: CLT CLT1 – CLT0. A positive CLT was defined as CLT 0 mL, according to the receiver-operating characteristic curve.