762-6 Cerebral Oxygenation During Paediatric Cardiac Surgery: Identification of Vulnerable Periods by Near Infrared Spectroscopy

Maintenance of cerebral oxygenation is vital in paediatric cardiac surgery. Near infrared spectroscopy (NIRS) can measure regional cerebral oxygenation (rSO2). As the cerebral microvasculature is predominantly venous by volume, changes in (rSO2) should reflect changes in jugular bulb oxygen saturations (SjO2). We investigated the role of NIRS (Invos 3100, Somanetics Inc) in 19 children (median age 1.2 years, range 2 weeks–9.7 years) undergoing cardiac surgery (17 with cardiopulmonary bypass, 8 with circulatory arrest). For all patients combined, simple linear regression confirmed a strong relationship between rSO2 a SjO2: rSO2 = 0.69SjO2 + 23, r = 0.71, p l 0.0001. For individual patients the correlations were closer with a median r = 0.91 (range 0.68–0.96). Prebypass 10/18 patients had a fall in rSO2≥ 15% points for a minimum of 3 minutes. In 5 patients rSO2 reached l35%. The causes for cerebral desaturatio were 1) anaesthetic induced cyanotic spells or cardiac depression in the setting of pre-existing cardiac failure and 2) handling and dissection around the heart prior to and going onto bypass. Bypass universally raised the rSO2 by a mean 18% points to a mean maximum of 75%. Circulatory arrest at l20° (11 episodes, mean arrest time 45 minutes, range 23–61) caused the rSO2 to fall by a mean 0.25%/min. Rate of fall in rSO2 in 3 patients arrested at g20° was 6–11 × higher (1.5–2.7%/min). Rate of decay was correlated with the temperature at onset of arrest (r = 0.84, p = 0.0002). The mean rSO2 at the end of arrest was 66 range 30–88). Reperfusion following arrest caused an initial mean rise in rSO2 of 11% (range 2–23) and with rewarming a mean fall of 15% (range 1–30). Rewarming in patients not arrested resulted in a mean fall in rSO2 of 12% (range 2–44). Discontinuation of bypass was associated with a further precipitous fall in rSO2 in 5 patients. Postbypass 3 patients had rSO2 l50%. The study shows rSO2 correlates well with SjO2 particularly in individual patients. Prebypass and early postbypass appear to be vulnerable periods for maintenance of cerebral oxygenation. NIRS is a promising tool for monitoring cerebral O2 supply/demand relationships in paediatric cardiac surgery, especially during circulatory arrest when no other monitoring modalities are available.