Alveolar-arterial oxygen gradients before extracorporeal life support for severe pediatric respiratory failure: improved outcome for extracorporeal life support-managed patients?

F W Moler, J M Palmisano, J R Custer, J N Meliones, R H Bartlett
Critical Care Medicine 1994, 22 (4): 620-5

OBJECTIVE: Recent reports have described the usefulness of the alveolar-arterial oxygen tension difference (P[A-a]O2) in predicting mortality in children with acute respiratory failure managed with mechanical ventilation. We reviewed our experience with extracorporeal life support for acute pediatric respiratory failure and specifically examined P(A-a)O2 measurements during the 24 hrs before extracorporeal life support to determine if defined cutoffs established with conventional mechanical ventilation were applicable to extracorporeal life-support survival.

DESIGN: Retrospective, case-series chart review.

SETTING: A university tertiary medical center.

PATIENTS: Infants and children (n = 36), one month to 18 yrs of age, with severe life-threatening respiratory failure who were believed to have failed conventional mechanical ventilatory support.

INTERVENTIONS: Veno-venous or veno-arterial extracorporeal life support.

MEASUREMENTS AND MAIN RESULTS: From 1982 to 1992, we managed 36 pediatric patients with severe respiratory failure using extracorporeal life support. We identified 28 patients who had P(A-a)O2 values of > 400 torr (> 53.3 kPa) for the 24-hr time period before placement on bypass. At the time of bypass initiation, all blood gas and mechanical ventilator parameters except PaCO2 showed trends of worsening pulmonary function, compared with measurements done 24 hrs before bypass initiation. Oxygenation-related variables showed statistically significant worsening trends when measured 24 hrs before bypass, compared with the time of bypass: P(A-a)O2 539 vs. 582 torr (71.9 vs. 77.6 kPa), p < .01; PaO2/FIO2 ratio 70 vs. 57 torr (9.3 vs. 7.6 kPa), p < .05; oxygenation index 32 vs. 47 cm H2O/torr, p < .01; and FIO2 0.94 vs. 0.98, p < .05. Sixty-one percent of extracorporeal life support-managed patients (17 of 28) survived their life-threatening respiratory illness to be discharged home.

CONCLUSIONS: Based on previous reports of the utility of P(A-a)O2 measurements to predict mortality, our preliminary evidence suggests that extracorporeal life support results in 62% survival for pediatric respiratory failure patients predicted to have no chance of survival using conventional mechanical ventilation. Prospective, randomized trials of children with severe acute respiratory failure managed with mechanical ventilation vs. extracorporeal life support may be indicated.

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