Determining respiratory rate using measured expiratory time constant: A prospective observational study

Area of Science:

• Critical Care Medicine
• Respiratory Physiology
• Mechanical Ventilation

Background:

• High respiratory rate (RR) in mechanical ventilation can cause intrinsic positive end-expiratory pressure (PEEPi), cardiovascular depression, and ventilator-induced lung injury.
• Optimal RR settings remain unclear, potentially leading to suboptimal lung emptying dynamics.

Purpose of the Study:

• To investigate if clinician-set RR exceeds the frequency needed for optimal lung emptying, considering the expiratory time constant (RCEXP).
• To evaluate the utility of measuring RCEXP for adjusting RR in pressure-controlled ventilation.

Main Methods:

• A prospective, multicenter observational study involving 56 intensive care patients on pressure-controlled ventilation.
• Measured expiratory time constant (RCEXP) and compared the set RR to a predicted RR (RRp) based on RCEXP.
• Analyzed a subgroup of patients with prolonged RCEXP.

Main Results:

• The mean difference between set RR and RRp was 2.8 bpm.
• 52% of patients had prolonged RCEXP (>0.8 s), with a mean RR difference of 3.1 bpm.
• Patients with prolonged RCEXP exhibited significantly higher PEEPi (4.4 cmH2O) compared to those with RCEXP ≤ 0.8 s (1.5 cmH2O).

Conclusions:

• Clinician-set RR frequently exceeded the RR predicted by measured RCEXP.
• Measuring RCEXP is a valuable tool for optimizing RR during mandatory mechanical ventilation.
• Adjusting RR based on RCEXP may help mitigate risks associated with high respiratory rates, such as PEEPi.