Practice of Excessive FIO2 and Effect on Pulmonary Outcomes in Mechanically Ventilated Patients With Acute Lung InjuryThe authors respond to: Practice of Excessive FIO2 and Effect on Pulmonary Outcomes in Mechanically Ventilated Patients With Acute Lung Injury

Samer Alkhuja; Sonal Rachmale; Kristen Duffy

doi:10.4187/respcare.02329

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 F_IO₂, understanding oxygen delivery (D_O₂) and balancing that with oxygen consumption should be stressed in the education of nurses and respiratory therapists. If D_O₂ 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: DO2=(SaO2)(Hb)(1.34)+(PaO2)×(0.003)×CO×10 Where S_aO₂ is percentage of oxygen saturation, Hb is hemoglobin, P_aO₂ is the arterial partial pressure of oxygen, and CO is cardiac output. Increasing P_aO₂ from 60 mm Hg to 100 mm Hg would only increase oxyhemoglobin concentration by around 10% (S_pO₂ from 90% to 100%), and increase oxygen content from dissolved O₂ by 40 × 0.003 = 0.12 mL/L, which is negligible, considering that the normal D_O₂ is approximately 1,000 mL/min. Further improvement in D_O₂ occurs when treating anemia and optimizing the cardiac output. Therefore, treating the anemia or low cardiac output should be done first, and mild hypoxemia may be acceptable in some situations, as reported by Martin et al.³ They suggested that hypoxia triggers a complex network of cellular signaling pathways that may result in protective responses.³

Protocol-driven F_IO₂ titration should be combined with a clear understanding that high F_IO₂ only slightly increases D_O₂. Healthcare providers need to be educated on the fundamentals of D_O₂ to avoid hyperoxygenation lung injury in mechanically ventilated patients.

Footnotes

The author has disclosed no conflicts of interest.

References

1.↵
1. Rachmale S,
2. Li G,
3. Wilson G,
4. Malinchoc M,
5. Gajic O
. Practice of excessive F_IO₂ and effect on pulmonary outcomes in mechanically ventilated patients with acute lung injury. Respir Care 2012;57(11):1887-1893.
OpenUrl Abstract/FREE Full Text
2.↵
1. Lumb AB,
2. Pearl RG
. Oxygen. In: Nunn's applied respiratory physiology. Philadelphia: Elsevier; 2005;116-200.
3.↵
1. Martin DS,
2. Khosravi M,
3. Grocott MPW,
4. Mythen MM
. Concepts in hypoxia reborn. Crit Care 2010;14(4):315.
OpenUrl PubMed

The authors respond to: Practice of Excessive F_IO₂ 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 F_IO₂. 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 F_IO₂.

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 F_IO₂. Protocols and alert-based oxygen titration are other methods to reduce excessive F_IO₂ and maintain appropriate F_IO₂ 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,