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Korean Journal of Anesthesiology 1999;36(1):69-74.
DOI: https://doi.org/10.4097/kjae.1999.36.1.69   
The Relationship between PaCO2 - PETCO2 Difference and SpO2 in Patients with Congenital Cyanotic Heart Disease.
Young Jhoon Chin, Chan Jong Chung, Sang Bum Kim
Department of Anesthesiology, College of Medicine, Dong-A University, Pusan, Korea.
In neonates and infants with congenital cyanotic heart disease, venous blood, rich in CO2 and poor in O2, is mixed with pulmonary venous blood at left heart. As a consequence, any given degree of decreases in SpO2 is accompanied by obligatory increase in PaCO2 - PETCO2 difference. This study was designed to evaluate these relationship in 20 pediatric patients.
After endotracheal intubation with high dose fentanyl and pancuroniun, PETCO2 was measured by capnometer (side stream, sample gas flow rate of 200 ml/min; sampling site at elbow connector area) and SpO2 probe was attached at toe or finger. Observations were made 4 or 5 times before initiation of CPB. Ventilation was controlled by pressure type ventilator, partial rebreathing circuit at frequency of 25-35 breaths/min, an inspiratory time of 25% with an end-inspiratory pause of 10%, and peak airway pressure of 20 +/- 2 cmH2O.
: Mean values of PaCO2 - PETCO2 difference were increased linely with decreases in SpO2. The regression equation is mean (PaCO2 - PETCO2) (mmHg) = 23.9 0.22 mean SpO2 (r= 0.51, p=0.028) CONCLUSIONS: The relationship between PaCO2 - PETCO2 was found to agree with that predicted by theory confirming that in congenital cyanotic heart patients, PaCO2 increases by 2-5 mmHg for every 10% reduction in SpO2. This relationship may be useful when attemping to estimate PaCO2 from PETCO2 in the management of congenital cyanotic heart patients.
Key Words: Heart, cyanotic congenital disease; Hemoglobin, Oxygen Saturation; Monitoring, carbon dioxide, end-tidal, pulse oximetry


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