Response

We appreciate the interest from Dr. Meng and colleagues in our recent randomized trial comparing the effect of ventilator modes on clinical outcomes in critically ill adults.¹ The authors raise two relevant points.

First, the authors highlight that patient characteristics may modify the effect of ventilator mode on clinical outcomes, highlighting chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). We agree. In prior surveys clinicians have expressed similar beliefs that patient physiology may modify the effect of ventilator mode on outcomes, disagreeing however on which mode is best and for whom.^2,3 In our randomized trial, we evaluated for effect modification analyses by 12 baseline characteristics (e-Figures 11–14 in the supplement). Among the 210 patients with ARDS, the number of ventilator-free days was numerically lower with volume control than with adaptive pressure control (odds ratio, 0.69; 95%, 0.28 to 1.67) and with pressure control than with adaptive pressure control (odds ratio, 0.70; 95% CI, 0.34 to 1.47) (P value for interaction = 0.80). Among the 99 patients with COPD, the number of ventilator-free days was numerically lower with volume control than with pressure control (odds ratio, 0.64; 95% CI, 0.26 to 1.59) and with volume control than with adaptive pressure control (odds ratio, 0.54; 95% CI, 0.19 to 1.49) (P value for interaction = 0.46). While our pilot trial did not find statistically significant differences across these subgroups, the findings deserve further examination. Future clinical trials should be adequately powered to understand the effects of ventilator mode on clinical outcomes within important subgroups of patients or even for individual patients.⁴

Second, the authors inquire about reasons that clinicians changed from the ventilator mode assigned by the trial. While 94.7% of breaths in the first 72 hours were delivered using the assigned ventilator mode, clinicians were permitted to change to a different mode if they felt it was best for patient care. We collected the clinical reason for such changes (e-Table 10 of the supplement). The most common reasons were elevated peak pressures in the volume control group (7.2% of patients), a requirement for increased minute ventilation to treat acidosis in the pressure control group (6.1%) and adaptive pressure control group (1.1%), and excessive work of breathing in the adaptive pressure control group (1.1%). Clinicians were able to manage the vast majority of patients in all three groups in the assigned mode for the duration of the trial.