To the Editor:
Rachmale et al1 evaluated prospectively the electronic medical records of 289 patients with acute lung injury, of whom 210 patients met their inclusion criteria, which were summarized in Table 1 in their article. One-hundred fifty-five patients (74%) were exposed to excessive oxygen.1 Prolonged exposure to excessive oxygen correlated with worsening of the oxygenation index at 48 hours, in a dose-response manner, and more days on mechanical ventilation, longer ICU and hospital stay, and worsening lung function.1 Given the importance of avoiding excessive FIO2, understanding oxygen delivery (DO2) and balancing that with oxygen consumption should be stressed in the education of nurses and respiratory therapists. If DO2 is reduced but remains above a critical value, oxygen consumption tends to be maintained at its normal value by increasing oxygen extraction.2
Oxygen delivery is commonly calculated using the equation:
Protocol-driven FIO2 titration should be combined with a clear understanding that high FIO2 only slightly increases DO2. Healthcare providers need to be educated on the fundamentals of DO2 to avoid hyperoxygenation lung injury in mechanically ventilated patients.
Footnotes
The author has disclosed no conflicts of interest.
- Copyright © 2013 by Daedalus Enterprises
The authors respond to: Practice of Excessive FIO2 and Effect on Pulmonary Outcomes in Mechanically Ventilated Patients With Acute Lung Injury
We thank Dr Alkhuja and Ms Duffy for reviewing our paper, their thoughtful insight about the physiology of oxygen delivery, and their call for education of health care staff about the same. We agree with their ideas about optimization of cardiac output and anemia for increasing oxygen delivery when required to do so. In our study we evaluated 289 patients, among whom 210 met our inclusion criteria, and 74% of those were exposed to excessive FIO2. On retrospective evaluation, we assessed for the nadir hemoglobin and cardiovascular status via the cardiovascular component of the Sequential Organ Failure Assessment (SOFA) score. The two groups were similar in these aspects during the period when excess oxygenation was assessed. We were limited by the retrospective nature of the study in assessing the course of actions taken to maintain optimal oxygenation prior to increasing the FIO2.
We also firmly believe in the education of respiratory therapists, nurses, medical trainees, and other healthcare providers about the role of the other determinants of oxygen delivery and their optimization prior to increasing the FIO2. Protocols and alert-based oxygen titration are other methods to reduce excessive FIO2 and maintain appropriate FIO2 titration in the ICU. At the same time, delineation of targets for “mild” or “acceptable” or permissive hypoxemia in various clinical situations needs to be studied further.
On behalf of all authors,
Footnotes
The authors have disclosed no conflicts of interest.