Introduction Identifying the earliest time for initiation of weaning from mechanical ventilation (MV) is important. Weaning trials and guidelines apply screening criteria which have not been validated and which may actually delay weaning from MV if too prescriptive. This study aimed to observe physician-led utilisation of pressure support ventilation (PSV), referenced to four screening criteria commonly reported in weaning trials (PaO2:FiO2 ≥26.3kPa, positive end expiratory pressure (PEEP) ≤5cmH2O, Richmond Agitation and Sedation Scale (RASS) >-3 and cardiovascular stability (HR <120, MAP >65mmHg and no inopressor support)), hypothesising that these criteria would not predict ability to sustain a PSV trial for 24hours.
Method Prospective observational cohort study of adult patients receiving MV in a thirty-bed ICU in a university hospital. Routine post-operative patients were excluded. Logistic regression analysis identified factors associated with PSV failure. Outcome is reported according to adherence to the screening criteria.
Results 209 patients were included (mean ± SD age 62.6 ± 15.9years, M:F 115:94, APACHE II 16.7 ± 6.1, 48% medical, 20% elective surgical, 32% emergency surgical admissions). Median (IQR) time to initiate PSV was 11.0 (5.0–22.0)hours, and duration of weaning to extubation was 43.0 (13.0–121.5)hours. PSV weaning was initiated despite significant hypoxia (PaO2:FiO2 35.8 ± 15.9kPa), moderate PEEP levels (7.5 ± 2.5cmH2O), deep sedation (44% RASS≤-3) and cardiovascular instability (48.8%) (Table 1). At PSV initiation, 85% of patients violated at least one screening criterion, yet 74.6% of patients remained stable for 24 hours. Logistic regression identified no association between individual screening criteria and PSV failure. Failure to sustain a PSV trial was associated with ventilation >7 days (RR = 2.12 [1.33, 3.38] p = 0.002) and ICU mortality (RR = 2.94 [1.46, 5.94] p = 0.002).
Conclusion Physician-led PSV weaning was often initiated early before patients fulfilled conventional screening criteria. Despite this, PSV trials were well tolerated in the majority with active weaning in pressure support subsequently achieved. Individual screening criteria were not associated with PSV failure. Of clinical significance, failure to sustain a PSV trial could be an early indicator of prolonged mechanical ventilation and ICU mortality, and predictive characteristics of this warrant further investigation. Application of screening criteria, as reported in weaning literature, may delay initiation of weaning in some patients.
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