Temporal trends and current practice patterns for intraoperative ventilation at U.S. academic medical centers: a retrospective study

Abstract

Background: Lung protective ventilation strategies utilizing lower tidal volumes per predicted body weight (PBW) and positive end-expiratory pressure (PEEP) have been suggested to be beneficial in a variety of surgical populations. Recent clinical studies have used control groups ventilated with high tidal volumes without PEEP based on the assumption that this reflects current clinical practice. We hypothesized that ventilation strategies have changed over time, that most anesthetics in U.S. academic medical centers are currently performed with lower tidal volumes, and that most receive PEEP.

Methods: Intraoperative data were pooled for adults undergoing general anesthesia with tracheal intubation. Median tidal volumes per kilogram of PBW were categorized as > 10, 8-10 and < 8 mL per kg of PBW. The percentages of cases in 2013 that were performed with median tidal volumes < 8 mL per kg of PBW and PEEP were determined. As a secondary analysis, a proportional odds model using institution, year, height, weight and gender determined the relative associations of these factors using categorical and interquartile odds ratios.

Results: 295,540 cases were analyzed from 5 institutions over a period of 10 years. In 2013, 59.3% of cases used median tidal volumes < 8 mL per kg of PBW, 83.3% used PEEP, and 51.0% used both. Of those cases with PEEP, 60.9% used a median pressure of ≥ 5 cmH2O. Predictors of lower categories of tidal volumes included height (odds ratio (OR) 10.83, 95% confidence interval [10.50, 11.16]), institution (lowest OR 0.98 [0.96, 1.00], highest OR 9.63 [9.41, 9.86]), year (lowest OR 1.32 [1.21, 1.44], highest OR 6.31 [5.84, 6.82]), male gender (OR 1.10 [1.07, 1.12]), and weight (OR 0.30 [0.29, 0.31]).

Conclusion: Most general anesthetics with tracheal intubation at the institutions surveyed are currently performed with a median tidal volume < 8 mL per kg of PBW, most are managed with PEEP of ≥ 5 cmH2O and approximately half utilize both. Given the diversity of the institutions included, this is likely reflective of practice in U.S. academic medical centers. The utilization of higher tidal volumes without PEEP in control groups for clinical research studies should be reconsidered.

Keywords: Intraoperative ventilation; Lung protective ventilation; Practice patterns.

Figures

Figure 1

Flow chart for cases included; A flow chart demonstrating the sequential exclusions applied to the initial set of cases, resulting in the cases included for analysis. ASA = American Society of Anesthesiologists Physical Status Classification.

Figure 2

Ventilation parameters set by the anesthesia provider; Ventilation parameters set by the anesthesia provider over time (2005–2013) at five U.S. academic medical centers. At top left, average of median exhaled tidal volume per kilogram of predicted body weight (PBW). At top right, percentage of cases utilizing positive end expiratory pressure (PEEP). At bottom left, average of median respiratory rate (RR). At bottom right, average of median fraction of inspired oxygen (FiO2). Error bars indicate 25th and 75th percentile ranges.

Figure 3

Tidal volumes and PEEP; Median exhaled tidal volumes were grouped into categories of < 8 mL per kg of predicted body weight (PBW), 8–10 mL per kg of PBW and > 10 mL per kg of PBW. Median positive end-expiratory pressure (PEEP) values were grouped into categories of no PEEP, 1–4 cm H2O, 5–10 cm H2O and > 10 cm H2O. Counts of cases with tidal volumes and PEEP usage are displayed above for each year analyzed.

Figure 4

Physiologic parameters; Physiologic parameters resulting from ventilation strategies (2005–2013) at five U.S. academic medical centers. Average of median peak inspiratory pressure (PIP) at top, average of median blood oxygen saturation (SpO2) in middle, and average of median end-tidal carbon dioxide (EtCO2) at bottom. Error bars indicate 25th and 75th percentile ranges.

Figure 5

Proportional odds model estimates; The proportional odds model estimates of the odds of receiving lower tidal volume ventilation for each variable compared to a reference value, with median exhaled tidal volume categorized as > 10 mL per kg of predicted body weight (PBW), 8–10 mL per kg of PBW, and < 8 mL per kg of PBW. The triangles mark the estimate centers, with 95% confidence intervals indicated with the bars extending from the centers. For the categorical variables of year, gender and center, the estimates provided are odds of receiving lower tidal volume ventilation relative to 2005, females and center A, respectively. For height and weight, the estimates provided are the interquartile odd ratio, indicating the odds of receiving lower tidal volume ventilation at the 75th percentile of those variables compared to the 25th percentile. The p-value for each estimate is p < 0.0001 based on a likelihood ratio test with 11 degrees of freedom.