Can early diaphragm dysfunction in critically ill ventilated patients predict clinical outcomes? A pilot study

Diaphragm dysfunction (DD) is a keystone factor in difficult weaning from invasive mechanical ventilation (IMV). Diaphragm ultrasound (DUS) is the preferred method for the evaluation of diaphragm function in the Intensive Care Unit (ICU) setting, namely through the diaphragm thickening fraction (DTF). However, its potential role in the decision-making process of mechanical ventilation weaning is yet to be established. We aimed to assess the incidence of early DD and its role as a predictor of prolonged IMV.

We conducted a prospective, non-interventional study in a university hospital ICU. Non-consecutive adult patients subject to at least 48h of IMV were enrolled. Exclusion criteria was a prior period of IMV in the past three months. DUS was performed at 48h of IMV. End-inspiratory and end-expiratory diaphragm thickness were measured using M-mode, with a high-frequency linear probe placed at the zone of apposition of the diaphragm. The mean values of three measurements were used to calculate DTF. Interobserver measurement variability was not evaluated.

Forty-five patients were included. Thirty-eight percent were female, average age was 62.3 years. Mean Simplified Acute Physiology Score (SAPS) II and Sequential Organ Failure Assessment (SOFA) at admission were 50.9 and 9.02, respectively. Mean DTF was 23.46%±17.15. Average IMV duration was 9.36±7.66 days. Half of patients had DD at 48h of IMV. A weak negative correlation was observed between DTF, days of endotracheal intubation (Sp -0.27; p=0.07) and days of IMV (Sp -0.25; p=0.09). Using DTF cut-off values of 20% and 30%, DTF at 48h of IMV was not associated with prolonged IMV (p-values 0.17 and 0.58, respectively).

In our study, there was a high prevalence of DD at 48h of IMV, as suggested in previous literature. Diaphragm dysfunction at 48h when measured through DTF did not seem to predict prolonged IMV. Late VAP incidence was associated with DD. Diaphragm ultrasound is well-established for diaphragm functional assessment, but further research regarding its trajectory during critical illness is needed to clarify its application in clinical practice.