Impact of Different Sweep Gas Flow Rates on Respiratory Alkalosis and Cerebral Oxygenation during Cardiopulmonary Bypass
Melis Tosun, Behiç Danışan, Bülent Güçyetmez, Fevzi Toraman
Acıbadem Bakırköy Hastanesi
Giriş: There is no consensus on the ideal volume of sweep gas flow during cardiopulmonary bypass (1). The gas exchange efficiency in blood passing through an oxygenator depends on four variables: blood flow, gas solubility, temperature, and partial gas pressure difference, which is the most critical and mainly influenced by the sweep gas flow rate(2). High sweep gas flow rates can lead to respiratory alkalosis and hypocapnic cerebral alkalosis, which can cause neurological complications (3,4).
Gereç ve Yöntem: This study involved 84 patients who were over 18 and scheduled to undergo elective open-heart surgery with cardiopulmonary bypass. Before rewarming, the participants were randomly assigned to one of the three groups based on their sweep gas flow rates (Group 1: 1.35 L/m2/min, Group 2: 1.2 L/m2/min, and Group 3: 1 L/m2/min). Throughout the surgery, arterial blood gases were sampled at six different time points, and rSO2 levels were monitored bilaterally on the forehead.
Bulgular: All groups experienced a decrease in PaCO2 levels after the onset of hypothermia, which went below the normal range at a moderate hypothermia level of 32°C. During both the baseline and hypothermic periods, the PaCO2 levels between groups were similar. However, after rewarming, Group 3 had significantly higher PaCO2 levels than Groups 1 and 2 (P<0.001). Additionally, during the same period, Group 3 had significantly higher regional cerebral oxygen saturation (rSO2) levels than Group 1 and Group 2 (p=0.005). For all patients, there was a significant correlation between delta-PaCO2 and delta-rSO2 levels after rewarming (r=0.45, P<0.001).
Tartışma ve Sonuç: This study has shown that using alternative sweep gas rates in different phases of the CPB is more effective than keeping the sweep gas flow at a constant rate throughout the process. This helps maintain PaCO2 within physiological limits. The study also found that rSO2 was better preserved when PaCO2 was maintained within physiological limits.
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