The benefits of lung protective ventilation have been replicated in multiple trials1,2. However, we suspected that adherence to this standard of care remained poor. Using the NIHR critical care Health Informatics Collaborative (ccHIC) database, we analysed data from 11 teaching hospital intensive care units (22,524 patient episodes) to investigate real-world clinical practice.
The Critical Care Health Informatics Collaborative (ccHIC) datatbase contains the electronic health records of patients admitted to critical care units at the five Biomedical Research Centres in the UK (Cambridge, Imperial, Oxford, Kings, and University College London). The data are collected prospectively by clinical and audit staff and then transferred centrally to a secure location before being cleaned and validated, ready for interrogation by researchers.
Using the ccHIC database we were able to identify 1,248 patient episodes, where ventilation was continued for >48 hours, with 232,600 hours of concurrent mechanical ventilation and blood gas data of suitable quality for analysis. Short gaps in ventilation (<6 hours) were imputed based on the median of nearest known values, and only the single longest period of ventilation from each patient episode was analysed.
The median tidal volume received by patients was 7.3 mLkg-1PBW (IQR:5.7-8.8). Patients with severe respiratory failure (PaO2:FiO2 <13 kPa) received a median tidal volume of 7.1 mlkg-1PBW, and had 71% ICU mortality.
Female patients, especially those with higher BMI (>30 kgm-2) consistently received higher predicted body weight tidal volumes than males. The median tidal volumes, averaged over the first six hours following initiation of ventilation, delivered to males and females were 475 and 395 mls respectively. There was a failure of tidal volumes to improve after 24 hours and at times of the most severe respiratory failure (Table 2)
Patients with respiratory failure sufficient to qualify for recruitment into ARDSnet ARMA and more recent clinical trials (PaO2:FiO2 <20kPa with PEEP >5cmH20), who were exposed to tidal volumes ≥12 mLkg-1PBW for longer than two hours had significantly increased risk of ICU mortality (odds ratio =2.89 [1.25-7.2]; p=0.007); This was not observed for patients with PaO2:FiO2 >40 kPa (odds ratio =0.95 [0.58–1.56], p=0.91).
More than 15 years after the ARMA study1 demonstrated a mortality benefit from lung protective ventilation, failure to implement 6 mLkg-1PBW ventilation into clinical practice in multiple centres persists. We are exposing even patients with a severe respiratory failure (PaO2:FiO2 <13 kPa) to higher than recommended tidal volumes, with females and higher BMI patients at particular risk. We have also demonstrated that failure to institute lung protective ventilation in patients with a PaO2:FiO2 <20 kPa leads to increased ICU mortality, which is not present in patients with PaO2:FiO2>40 kPa.