Evaluating Delivery of Low Tidal Volume Ventilation in Six ICUs Using Electronic Health Record Data

Abstract

Objectives: Mechanical ventilation with low tidal volumes is recommended for all patients with acute respiratory distress syndrome and may be beneficial to other intubated patients, yet consistent implementation remains difficult to obtain. Using detailed electronic health record data, we examined patterns of tidal volume administration, the effect on clinical outcomes, and alternate metrics for evaluating low tidal volume compliance in clinical practice.

Design: Observational cohort study.

Setting: Six ICUs in a single hospital system.

Patients: Adult patients who received invasive mechanical ventilation more than 12 hours.

Interventions: None.

Measurements and main results: Tidal volumes were analyzed across 1,905 hospitalizations. Although mean tidal volume was 6.8 mL/kg predicted body weight, 40% of patients were exposed to tidal volumes greater than 8 mL/kg predicted body weight, with 11% for more than 24 hours. At a patient level, exposure to 24 total hours of tidal volumes greater than 8 mL/kg predicted body weight was associated with increased mortality (odds ratio, 1.82; 95% CI, 1.20-2.78), whereas mean tidal volume exposure was not (odds ratio, 0.87/1 mL/kg increase; 95% CI, 0.74-1.02). Initial tidal volume settings strongly predicted exposure to volumes greater than 8 mL/kg for 24 hours; the adjusted rate was 21.5% when initial volumes were greater than 8 mL/kg predicted body weight and 7.1% when initial volumes were less than 8 mL/kg predicted body weight. Across ICUs, correlation of mean tidal volume with alternative measures of low tidal volume delivery ranged from 0.38 to 0.66.

Conclusions: Despite low mean tidal volume in the cohort, a significant percentage of patients were exposed to a prolonged duration of high tidal volumes which was correlated with higher mortality. Detailed ventilator records in the electronic health record provide a unique window for evaluating low tidal volume delivery and targets for improvement.

Figure 1.

Tidal volume settings and transitions over the first 48 hours of mechanical ventilation. Patients are categorized at 12-hour intervals as receiving tidal volumes in one of four groups: < 6.5 mL/kg predicted body weight (PBW), 6.5 – 8 mL/kg PBW, > 8 mL/kg PBW, or not intubated. This figure demonstrates that the majority of patients remained in the same tidal volume category over their episode of mechanical ventilation, and transitions between tidal volumes, while infrequent, occurred most often between hour 0 and 12.

Figure 2.

Individual ICU performance on mean tidal volume (Vt) and alternate measures of low tidal volume delivery. All tidal volumes are in mL/kg predicted body weight. Alternate measures include: initial Vt: mean of first recorded tidal volumes after ICU admission for each patient; >24 hrs (Vt > 8 mL/kg 24 hours): percentage of patients exposed to Vt > 8 mL/kg for 24 hours; Not decreased (Vt not decreased when > 8 mL/kg): rate that Vt was not lowered to < 8 mL/kg on a ventilator day when above > 8 mL/kg; Increased (Vt increased when < 8 mL/kg): rate that Vt was increased to > 8 mL/kg on a ventilator day when Vt < 8 mL/kg. Rates of changing tidal volume are per 100 ventilator-days. Further details of rate calculations provided in the supplement.