Extubation, defined as the removal of the endotracheal tube used in mechanically ventilated patients, is one of the most critical steps in the care of Intensive Care Unit (ICU). Expeditious yet safe extubation is critical, as prolonged mechanical ventilation harms patients and failed extubation (requiring re-intubation within 48 hours) is associated with increased morbidity, mortality and elevated costs.
Spontaneous breathing trials (SBTs) are the current standard of care to assist in the determination of timing of extubation. During SBTs, patients are subjected to trials of reduced ventilatory support, taking on a greater workload of breathing and simulating breathing after extubation. Absence of rapid shallow breathing or other evidence of increased stress during an SBT are the current standard indicators that it is safe to extubate. Despite this practice, numerous literature reports document an average failed extubation rate of 15%.
In 2009, researchers from the CCCTG, led by Andrew Seely
, and others from 12 hospitals across Canada and the United States, initiated the Weaning and Variability Evaluation (WAVE) study
, a large prospective, blinded observational multicenter cohort study to improve safety when liberating patients from mechanical ventilation by evaluating novel means to predict extubation failure, utilizing continuous variability monitoring. In particular, WAVE researchers investigated the added value of using heart and respiratory rate variability (HRV and RRV) during SBTs to predict extubation failure. Variability analysis documents the degree and patterns of change of physiologic parameters over intervals-in-time. Loss of variability is generally indicative of reduced adaptability, increased stress and illness severity.
721 ICU patients were enrolled and high quality continuous heart rate and respiratory rate data from 434 patients were used to train and validate a predictive model, and estimate the probability of extubation failure (WAVE score), based on a small subset of variability measures. The WAVE score was able to predict extubation failures better than simple vitals, clinical impression and commonly used indices, such as the rapid shallow breathing index (RSBI), in particular in patients perceived as high-risk. Altered HRV and RRV (during the SBT prior to extubation) were shown to be significantly associated with extubation failure.
The results of the WAVE study were published in Critical Care
. The WAVE score represents a promising new prognostic tool for the assessment of extubation readiness in critically ill patients.