Cerebral oxygenation during intermittent hypoxemia and bradycardia in preterm infants.

BACKGROUND: Episodes of hypoxemia and bradycardia frequently occur with apnea of prematurity in preterm infants. Little is known about the impact of different event types on the brain. OBJECTIVES: To describe the influence of hypoxemia and bradycardia, either isolated or in combination, on cerebral oxygenation. METHODS: In 16 preterm infants with intermittent hypoxemia and/or bradycardia, cerebral tissue oxygen saturation (StO2, as measured by near-infrared spectroscopy), heart rate and pulse oximetric saturation (SpO2) were recorded simultaneously for 16 h. Events were classified as isolated bradycardia (type 1), isolated hypoxemia (type 2) or combined (simultaneous, type 3; bradycardia first, type 4; hypoxemia first, type 5). Primary outcome was a score representing the area below baseline for cerebral StO2 desaturation during an event. Secondary outcomes were duration and depth of cerebral desaturation. RESULTS: Patients had a median (range) gestational age of 25.9 (22.6-30.4) weeks and a postnatal age of 32.5 (7-58) days. The median (quartiles) number of events was 49 (34-58). Isolated hypoxemias were the most frequent events (24; 9-36) and isolated bradycardias the least common (0; 0-1). Cerebral StO2 baseline was not different between event types. Cerebral desaturation score, duration of event and depth of cerebral desaturation were smallest for isolated bradycardias and largest for combined events, especially for those starting with hypoxemia followed by bradycardia. Regardless of event type, 12/16 infants maintained cerebral StO2 >60% despite severe SpO2 desaturations. CONCLUSIONS: Isolated bradycardias had the lowest impact on cerebral desaturation, and combined events had the highest. Most infants preserved cerebral oxygenation >60% during events.

Cerebral desaturations in preterm infants: a crossover trial on influence of oxygen saturation target range.

OBJECTIVE: To test the hypothesis that a higher pulsoximetric arterial oxygen saturation (SpO2) target range is associated with reduced cerebral tissue oxygen desaturations from baseline during events of hypoxaemia or bradycardia. DESIGN: Randomised crossover trial. SETTING: Single tertiary care neonatal intensive care unit. PATIENTS: Sixteen preterm infants with severe intermittent hypoxaemia or bradycardia. INTERVENTIONS: SpO2 target was set to 80-92% and 85-96% for 4 h each in random sequence. On a subsequent day, the target sequence was reversed and the study was repeated. MAIN OUTCOME MEASURES: We simultaneously recorded cerebral tissue oxygen saturation (cerebral StO2), SpO2 and heart rate. Cerebral StO2 was measured by near infrared spectroscopy. The primary outcome was the cumulative cerebral StO2 desaturation score representing the area below a cerebral StO2 baseline value before onset of each hypoxaemic or bradycardic event. RESULTS: During low SpO2 target range the median (IQR) cumulative cerebral StO2 desaturation score was higher (27384 (15825-37396) vs 18103 (6964-32946), p=0.011) and the mean (±SD) number of events was higher (29.1 (±15.3) vs 21.1 (±11.4), p=0.001). More time was spent with SpO2 below 80% (57.2 (±24.8) min vs 34.0 (±29.6) min, p=0.006). Total time of hyperoxaemia (defined as SpO2 ≥97% and ≥99%, respectively) and total time with cerebral StO2 <60% and <55% were similar. CONCLUSIONS: A lower SpO2 target range was associated with a greater cumulative cerebral StO2 desaturation score, caused by more frequent SpO2 desaturations. However, time at very low cerebral StO2 was not affected. Episodes of hyperoxaemia were not reduced.