Clinicians often follow a checklist to assess readiness for weaning and the likelihood of succeeding, although generally not systematically as suggested by the weaning assessment program of Burns et al.4
Clinicians assess respiratory mechanics prior to and during an SBT when predicting successful DOMV. Parameters commonly examined prior to an SBT include the RSBI, negative inspiratory pressure (NIP), respiratory drive (P0.1), inspiratory muscle pressure generated, P0.1/NIP ratio, inspiratory muscle pressure/NIP ratio, V̇e, RR, spontaneous tidal volume, work of breathing, pressure-time product, wean index, CROP (ie, compliance, respiratory rate, oxygenation, and pressure), and dead space ratio.,1,3,5
Variables trended over an SBT include RR, tidal volume, oxygen cost of breathing, oxygenation, RBSI, and NIP.1,3,5
Predictions from these parameters were encouraging at first, but a rigorous analysis by Meade et al1
demonstrated that the present cadre of parameters was indiscriminant. Both the RSBI (threshold, 105 breaths/min/L) and RR (threshold, 38 breaths/min) performed well but were of limited value. The likelihood ratios for RBSI and RR in predicting successful extubation were 1.58 and 1.50, respectively. The likelihood ratios for failure were 0.22 and 0.23, respectively. The sensitivities and specificities for the two were 0.92 and 0.93, respectively, and 0.45 and 0.47, respectively. The best predictor was the P0.1/maximal inspiratory pressure ratio, with likelihood ratios for success and failure of 16.3 and 0.15, respectively, and those for sensitivity and specificity of 0.69 and 0.96, respectively.