Low Tidal Volume Compliance Still Lacking in Mechanical Ventilation

Implementation of a well-established protective ventilation setting was limited in practice in the U.S. and U.K., electronic health records showed.

From the records of mechanically ventilated people, median tidal volume was 7.48 mL/kg of predicted body weight in a U.K. database and 7.91 mL/kg in the U.S., both approaching the accepted upper limit of <8 mL/kg, reported Charlotte Summers, PhD, of the University of Cambridge in England, and colleagues.

Among those at higher risk of not receiving low tidal volume mechanical ventilation (LTVV) were people of shorter stature, namely U.K. patients under 160 cm tall (5’3″) and U.S. patients under 165 cm (5’5″). What’s more, in both countries, women and patients with a body mass index (BMI) above 30 were at a higher risk of receiving ventilation at a median tidal volume exceeding 8 mL/kg, according to the retrospective study published in CHEST.

“Despite the different environments, patient populations, ICU admission criteria, and health systems in the U.K. and USA, we observed the same factors were associated with implementation of LTVV,” Summers and colleagues wrote.

Protective ventilation with lower tidal volumes — usually in the range of 4-8 mL/kg of predicted body weight — is widely recommended because it has been shown to improve survival in people with acute lung injury and acute respiratory distress syndrome (ARDS).

The present findings of nonadherence to LTVV are somewhat surprising given the long-time understanding on LTVV’s effects and previous studies indicating non-compliance — but implementing LTVV can be challenging, Samuel Acquah, MD, of the Mount Sinai Hospital in New York City, pointed out.

“At initiation of mechanical ventilation, the ideal body weight is usually not known, making it difficult to calculate the ideal tidal volume,” he told MedPage Today via email. “Other barriers are mostly due to the very busy nature of the ICU and the fact that the initial settings are usually done in the emergency department or outside the ICU and not subsequently changed.”

His hope is that for providers, these findings “will be a wake up call to come up with innovative ways to ensure adherence,” noting that he has seen treatment processes change in his own practice.

“We initially had the same issues with compliance to low tidal volume ventilation, however, we have used a combination of alerts on electronic medical records — when physicians order tidal volume — to tie it to ideal body weight combined with a daily report to respiratory therapists and the treating team, which highlights noncompliance and helps to improve adherence,” Acquah said.

He suggested that other centers also calculate each person’s ideal body weight and have alerts in the electronic medical record to allow ordering of tidal volume only based on ideal body weight.

For their multicenter study, Summers and colleagues relied on the electronic ICU clinical relational database (eICU-CRD) for U.S. data, whereas U.K. data were collected from the Critical Care Health Informatics Collaborative (CCHIC).

A total of 5,466 patients from CCHIC and 7,384 patients from eICU-CRD were included in the study. Patients from the U.K. database received ventilation for a median of 6.9 days, while U.S. database patients received it for 5.8 days.

U.K. patients who had a median tidal volume of less than 8mL/kg had significantly lower 30-day mortality (HR 0.86, 95% CI 0.76-0.97), whereas this relationship did not reach significance in the U.S. patients (HR 0.90, 95% CI 0.86-1.00).

Longitudinal trends suggest a fall in tidal volume over time in U.K. centers after December 2016.

Researchers noted that theirs was a post hoc study that could not determine whether patients received controlled or spontaneous ventilatory modes. They acknowledged that they were also unable to analyze the impacts of mechanical power or driving pressure on patient outcomes, and they lacked the ability to account for other factors that may result in the choice of a higher tidal volume.

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