Near-infrared spectroscopy in the detection of regional tissue oxygenation during hypoxic events in preterm infants undergoing critical care

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Objectives:To determine whether pulse oximetry-detected episodes of desaturation are associated with impairment of cerebral and somatic (renal) tissue oxygenation in mechanically ventilated preterm neonates.Design:Observational cross-sectional study.Setting:Neonatal intensive care unit of a university-affiliated children's hospital.Patients:Ten mechanically ventilated preterm (gestational age 24–32 wks) infants.Interventions:In addition to the traditional monitoring of hemodynamic variables that included pulse oximetry (Sao2), near-infrared spectroscopy (NIRS) was used to evaluate the cerebral and somatic (renal) tissue oxygen saturation (rSO2C and rSO2R, respectively).Measurements and Main Results:A total of 40 rSO2C and rSO2R measurements were simultaneously recorded: 20 during hypoxic events when the Sao2 was ≤80% for ≥4 secs (cases) and generally ranged between 70% and 80%, and 20 measurements when the Sao2 was ≥85% (paired controls). Additionally, the fractional oxygen extraction (FOE) from the cerebral (FOEC) and renal (FOER) tissue was calculated. All the measurements were made under steady conditions during a 2-hr period. The rSO2C, rSO2R, FOEC, and FOER among the cases (Sao2 ≤ 80%) and controls (Sao2 ≥ 85%) were compared using the paired Student's t-test. Both rSO2C and rSO2R during the desaturation episodes were lower than in the controls (51.6 ± 6.3% vs. 66.2 ± 10.2%, p < .0001 and 61.1 ± 6.8% vs. 80.1 ± 10.0%, p < .0001, respectively). The FOEC during the hypoxic episodes was comparable with control levels but increased in renal tissue. However, during two of the desaturation episodes (10%), the rSO2C and FOEC levels (which were <44% and >0.47, respectively) may reflect compromised tissue oxygen supply.Conclusions:In the majority of mechanically ventilated preterm neonates, the reduction in cerebral and renal tissue oxygenation associated with short periods of decreased arterial saturation to 70–80% does not significantly compromise oxygen utilization in the cerebral tissue but increases oxygen extraction in the renal tissue, which might cause ischemic tissue injury following a further reduction in oxygen delivery.

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