, Volume 22, Issue 4, pp 277-285

Relationship between pulmonary oxygen consumption, lung inflammation, and calculated venous admixture in patients with acute lung injury

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Abstract

Objective

To determine in patients with acute lung injury whether increased pulmonary oxygen consumption (VO2pulm), computed as the difference between oxygen consumption measured by indirect calorimetry (VO2meas) and calculated by the reverse Fick method (VO2Fick), would: (1) correlate with the degree of lung inflammation assessed by bronchoalveolar lavage (BAL); (2) lead to an overestimation of calculated venous admixture (Qva/Qt).

Design

Prospective study.

Setting

University hospital, medical intensive care unit.

Intervention

None.

Measurements and results

In nine mechanically ventilated patients with acute lung injury (Apache II 12±5, lung injury score 2±0.6, mean±SD), whole-body VO2 (VO2wb) was determined simultaneously by indirect calorimetry and the reverse Fick technique, after which BAL was immediately performed. VO2meas was significantly higher than VO2Fick (128±24 and 102±18 ml/min per m2, respectively,p<0.001). Median VO2pulm was 25.3 ml/min per m2 (range 1.98–51.5), thus representing 19±11% of VO2wb. Total BAL cellularity was increased in all patients (median 47, range 24–200×104/ml), as was the total polymorphonuclear (PMN) count (median 78 range 5–93×104/ml). Macrophage counts were in the normal range. There were raised BAL levels of interleukin-6 (IL-6) (median 945, range 23–1800 ng/ml) and elastase (median 391, range 5–949 ng/ml). Median protein levels were 270 μg/ml (range 50–505). There was no correlation between VO2pulm and BAL cellularity, PMNs, elastase, IL-6, or protein. Qva/Qt was 31.7±8%. Qva/Qt, corrected for the presence of VO2pulm, (Qva/Qtcorr), was 30.3±8% (p<0.01 vs Qva/Qt), a 4.2% overestimation due to VO2pulm. There was no correlation between Qva/Qt or Qva/Qtcorr and VO2pulm.

Conclusions

In mechanically ventilated patients with acute lung injury, VO2pulm was increased and led to a 19% underestimation of VO2wb determined by the reverse Fick method, as well as to a 4.2% overestimation of calculated Qva/Qt. Lung inflammatory activity was increased, as assessed by BAL cellularity, IL-6 and elastase levels. However, there was no correlation between VO2pulm and the intensity of pulmonary inflammation.