LAUSR

We read with great interest the article by Ibarra-Estrada et al (1). We congratulate the authors for their fascinating randomized controlled trial. However, we would like to highlight specific points regarding the study. The authors have taken the high pressure (P-high) based on the plateau pressure (Pplat) in the previous volume-controlled ventilation mode. According to the authors, this derivation of P-high on airway pressure release ventilation (APRV) mode is based on a previously unpublished protocol. The APRV group had tidal volume (TV) of 7.4 ± 1.1, 8.1 ± 1.3, and 8.6 ± 1.0 on days 3, 5, and 7, respectively. Although the TV generated on APRV cannot be equated with the TV generated on low tidal volume (LTV) ventilation, it still places patients at risk of ventilator-induced lung injury due to the high TV generated (2). APRV encourages spontaneous breathing efforts. This may increase the final endinspiratory transpulmonary pressure much higher than the set P-high of 30. We suggest using 2–5 cm H2O above mean airway pressure (Pmean) to limit adverse events such as barotraumas. Our suggestion is based on the physiologic concept that under normal conditions, the Pmean correlates with the mean alveolar pressure, which is in turn a surrogate marker of the stresses on the lung parenchyma with ventilation (3). A high frequency of severe hypercapnia in the APRV group (42%) was seen, which was also statistically significant (p = 0.009). Patients with severe obstructive lung disease are not ideal candidates for APRV. The high inspiratory time in APRV leads to hypercapnia. A few case reports have used APRV in resistant cases of chronic obstructive pulmonary disorder to reduce hypercapnia. However, in such cases, multiple adjustments in the ventilatory settings of APRV have been made to achieve control of the hypercapnia (4). No such adjustments were accommodated in the trial protocol for COPD patients. Another reason for the lower incidence of hypercapnia in LTV group could be allowing for the Pplat Rohit Kumar Patnaik, DM