Maximum inspiratory pressure, a surrogate parameter for the assessment of ICU-acquired weakness

Seventy-four patients were recruited in the study and prospectively evaluated in a multidisciplinary university ICU towards the appearance of ICU-AW. APACHE II admission score was 16 ± 6 and ICU stay 26 ± 18 days. ICU-AW was diagnosed with the Medical Research Council (MRC) scale for the clinical evaluation of muscle strength. MIP was measured using the unidirectional valve method, independently of the patients' ability to cooperate.A significant correlation was found between MIP and MRC (r = 0.68, p < 0.001). Patients that developed ICU-AW (MRC<48) had a longer weaning period compared to non ICU-AW patients (12 ± 14 versus 2 ± 3 days, p < 0.01). A cut-off point of 36 cmH2O for MIP was defined by ROC curve analysis for ICU-AW diagnosis (88% sensitivity,76% specificity). Patients with MIP below the cut-off point of 36 cmH2O had a significant greater weaning period (10 ± 14 versus 3 ± 3 days, p = 0.004) also shown by Kaplan-Meier analysis (log-rank:8.2;p = 0.004).MIP estimated using the unidirectional valve method may be a potential surrogate parameter for the assessment of muscle strength compromise, useful for the early detection of ICU-AW.ICU-acquired weakness (ICU-AW) is a well recognised complication, with an incidence of 10-25%, among long-term mechanically-ventilated patients [1-5]. ICU-AW presents with profound muscle weakness and difficulty to wean from mechanical ventilation (MV); it results in prolonged Intensive Care Unit (ICU) and hospital stay and even in increased mortality [6,7]. Clinical, electrophysiological and histological approaches have been used for the diagnosis [2,8,9]. Clinical detection is based on the assessment of skeletal muscle weakness. A standardized and reliable method to evaluate limb muscle groups is the Medical Research Council (MRC) muscle strength score [10-12] which has been used for the diagnosis of ICU-AW [2,9,13-15].Although ICU-AW was firstly described in patients with prolonged time to successful weaning from the ventilator