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Adjustment of sweep gas flow during cardiopulmonary bypass
Hasan Karabulut1, Fevzi Toraman, Sümer Tarcan
1Department of Cardiovascular Surgery, Acibadem Hospital, Kadikoy, Istanbul, Turkey.
Insights
Optimizing sweep gas flow during cardiopulmonary bypass (CPB) is crucial. Maintaining flow between 1.35 and 1.60 l/min/m2 prevents hypocapnia and associated risks during cardiac surgery.
Area of Science:
- Cardiology
- Anesthesiology
- Biomedical Engineering
Background:
- Cardiopulmonary bypass (CPB) is essential in cardiac surgery.
- Optimal sweep gas flow to the oxygenator during CPB remains undetermined.
- This study investigates the ideal sweep gas flow for patient safety and physiological stability.
Purpose of the Study:
- To determine the optimal sweep gas flow rate for oxygenators during cardiopulmonary bypass.
- To evaluate the impact of different sweep gas flow rates on blood gas parameters (pCO2, pH) during CPB.
- To identify sweep gas flow settings that minimize adverse physiological effects.
Main Methods:
- Thirty patients undergoing isolated CABG were randomized into three groups with varying sweep gas flow rates (1.35, 1.60, and 2.0 l/min/m2).
- Blood gas analysis was performed at four time points: before CPB, 5 minutes after CPB initiation, before rewarming, and at the end of rewarming.
- Standardized anesthetic and surgical techniques were applied across all groups.
Main Results:
- Lower sweep gas flow (1.35 l/min/m2) resulted in higher pCO2 levels initially.
- Higher sweep gas flow rates (1.60 and 2.0 l/min/m2) led to significant pCO2 decrease and alkalosis, particularly at lower temperatures.
- The highest flow rate (2.0 l/min/m2) caused hypocapnia and alkalosis exceeding physiological limits during hypothermia.
Conclusions:
- Sweep gas flow to the oxygenator during CPB should be maintained between 1.35 and 1.60 l/min/m2.
- Higher flow rates risk hypocapnia, leading to alkalosis with detrimental effects on lung mechanics, cerebral blood flow, and cardiovascular function.
- This range ensures adequate CO2 removal without inducing harmful physiological disturbances.
Abstract:
Cardiopulmonary bypass (CPB) is one of the major tools of cardiac surgery. However, no clear data are available for the ideal value of sweep gas flow to oxygenator during CPB. The aim of this study was to determine the best value for sweep gas flow during CPB. Thirty patients undergoing isolated CABG were randomly and equally allocated into three groups. Sweep gas flow to oxygenator was kept at 1.35 l/min/m2 in group 1, 1.60 l/min/m2 in group 2, and 2.0 l/min/m2 in group 3. All patients were operated on under the same anaesthetic regime and surgical techniques. Samples for blood gas analysis were collected at T1: before CPB; T2: 5 min after the initiation of CPB; T3: just before rewarning; and T4: at the end of rewarming. Five minutes after the initiation of CPB (T2), pCO2 decreased significantly in groups 2 and 3 compared to group 1 (p < 0.02). With the addition of hypothermia (T3), the changes in the pH and pCO2 became more profound and, in this period, the levels in group 3 patients outranged the physiologic limits, with pCO2 and pH values being 28 +/- 3 mmHg and 7.50 +/- 0.04, respectively. At the end of the rewarming period (T4), in spite of increased carbon dioxide production, pCO2 values were below the physiologic limits in groups 2 and 3. We conclude that sweep gas flow to the oxygenator should be kept between 1.35 and 1.60 l/min/m2 during CPB to avoid hypocapnia, which results in alkalosis and has hazardous effects on lung mechanics, cerebral blood flow, and the cardiovascular system.