Ineffective effort in patients with acute brain injury undergoing invasive mechanical ventilation

Background: Ineffective inspiratory effort (IE) is a frequent patient-ventilator asynchrony in invasive mechanical ventilation. However, its characteristics in patients with acute brain injury have been rarely reported. This study aimed to investigate the incidence of IE and to explore its relationship with respiratory drive in patients with acute brain injury undergoing invasive mechanical ventilation.

Methods: We retrospectively analyzed a clinical database which assessed patient-ventilator asynchrony in patients with acute brain injury. IE was identified based on airway pressure, flow, and esophageal pressure waveforms collected at 15-min intervals, four times daily. At the end of each dataset recording, airway occlusion pressure (P_0.1) was determined by the airway occlusion test. IE index was calculated to indicate the severity of IE. The incidence of IE in different types of brain injuries, as well as its relationship with P_0.1 were determined.

Results: We analyzed 852 datasets of 71 patients with P_0.1 measured and undergoing mechanical ventilation for at least three days after enrollment. IE was detected in 688 (80.8%) datasets, with a median index of 2.2% [interquartile range (IQR) 0.4-13.1]. Severe IE (IE index ≥10%) was detected in 246 (28.9%) datasets. The post‐craniotomy for brain tumor and the stroke groups had higher IE index and lower P_0.1, compared with the TBI group (2.6% [IQR 0.7-9.7] vs. 2.7% [IQR 0.3-21.0] vs. 1.2% [IQR 0.1-8.5], P=0.002; 1.4cmH₂O [IQR 1.0-2.0] vs. 1.5cmH₂O [IQR 1.0-2.2] vs. 1.8cmH₂O [IQR 1.1-2.8], P=0.001). Low respiratory drive (P_0.1<1.14 cmH₂O) was independently associated with severe IE in the expiratory phase, even after adjusting for confounding factors by logistic regression analysis (odds ratio: 5.18 [95% confidence interval: 2.69-10.00], P<0.001).

Conclusion: IE was very common in patients with acute brain injury. Low respiratory drive was independently associated with severe IE in the expiratory phase.