Effect of Variation in Arterial Carbon Dioxide Levels on Cerebral-Somatic Oxygenation in Children with Cyanotic Congenital Heart Disease

Abstract

Background: Hypocapnia is suggested in decreasing pulmonary vascular resistance in cyanotic congenital heart disease patients undergoing definitive repair. But its effects on cerebral and renal circulation are unclear. Hence the effect of changes in arterial blood carbon dioxide tensions (PaCo2 ) on cerebral (ScO2 %) and renal (SsO2 %) oxygenation indices using Near Infrared spectroscopy (NIRS) is examined. Methods: We did a prospective observational study in sixty-eight children who underwent elective cardiac surgery for various cyanotic congenital heart diseases. PaCo2 , ScO2 % and SsO2 % were obtained before induction of anesthesia, after anesthesia induction at normocapnic or mild hypercapnic ventilation (EtCo2 =40 mmHg) and again at hypocapnic ventilation (EtCo2 =30 mmHg). Regression analysis was done between PaCo2 and NIRS-C/ScO2 % and PaCo2 and NIRS-R/SsO2 % at both EtCo2 40 and 30 mmHg. Repeated measure analysis performed to evaluate the significance of change in NIRS-C and NIRS-R from pre-anesthesia induction to when EtCo2 was 40 and then 30 mmHg post anesthesia induction. Results: With decrease in EtCo2 , PaCo2 (p=0.0001), NIRS-C (p=0.0001) and NIRS-R (p=0.0001) decreased significantly. At EtCo2 of 40 and 30 mmHg, PaCo2 had significant positive correlation with NIRS-C (R2 =0.77, p=0.0001 and R2 =0.92, p=0.0001 respectively) and had insignificant correlation with NIRS-R (R2 =0.03, p=0.12 and R2 =0.008, p=0.46 respectively). Significant changes in NIRS-C {p=0.0001} and NIRS-R {p=0.0001} occurred from pre-induction to when EtCo2 was 40 and then to 30 mmHg. Conclusion: A decrease in NIRS-C and NIRS-R is probably from decreased cerebral and splanchnic blood flow during hypocapnic ventilation, leading to demand supply mismatch. Hypocapnic ventilation in cyanotic children has potential to cause cerebral hypoxia. Abbreviations: CCHD: Cyanotic Congenital Heart Disease; QP: Pulmonary blood flow; Do2 : Oxygen delivery; SpO2 : peripheral pulse oximetry; NIRS: Near Infrared Spectroscopy; NIRS-C/ScO2 %: Regional Cerebral Oxygen saturation; NIRS-R/SsO2 %: Regional Somatic/renal Oxygen saturation; HCT: Hematocrit; ECG: Electrocardiography; CPB: cardiopulmonary bypass; TOF: Tetralogy of fallot; BDG: Bidirectional Glenn Shunt; BT shunt: Blalock Taussig shunt; DORV: Double outlet right ventricle; FiO2 : Inspired oxygen concentration; ABG: Arterial blood gas; PaO2 : Arterial oxygen partial pressure; PaCo2 : Arterial carbon dioxide partial pressure; HR: Heart rate; MAP: Mean Arterial Pressure; CVP: Central Venous Pressure