Predictive value of the negative inspiratory force index as a predictor of weaning success: a cross-sectional study

Background: Identifying when intubated patients are ready to be extubated remains challenging. The negative inspiratory force (NIF) is a recommended predictor of weaning success. However, little is known about the role of NIF in the weaning process for the Asian surgical intensive population, especially for the Vietnamese population. Here, we aimed to investigate the cutoff threshold and predictive value of the NIF index for predicting the success of ventilator weaning in Vietnamese surgical intensive care patients. Methods: A cross-sectional study was conducted at the Surgical Intensive Care Unit of Viet Duc Hospital from October 2016 to August 2017. A total of 64 patients aged 16-70 years undergoing ventilatory support through an orotracheal tube satisfied the criteria for readiness to begin weaning. The correlation between the NIF index with outcomes of the weaning process was analyzed. Specificity (Sp), sensitivity (Se), positive predictive value (PPV), negative predictive value (NPV), receiver operating characteristic (ROC) curve, and area under the curve (AUC) were calculated. Results: The success rate of the entire weaning process was 67.2% (43/64). The median NIF values were -26.0 cm H2O (interquartile range [IQR], -28.0 to -25.0) in the successful weaning group and -24.0 cm H2O (IQR, -25.0 to -23.0) in the weaning failure group (P < 0.001). According to ROC analysis, an NIF value <=-25 cm H2O predicted weaning success (AUC, 0.836) with 91% Se, 62% Sp, 83% PPV, and 77% NPV. Conclusions: An NIF cutoff threshold <=-25 cm H2O can be used as predictor of weaning success in Vietnamese surgical intensive care patients.