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Blood lactate and mixed venous-arterial PCO2 gradient as indices of poor peripheral perfusion following cardiopulmonary bypass surgry


Conventional indices of tissue perfusion after surgery involving cardiopulmonary bypass (CPB) may not accurately reflect disordered cell metabolism. Venous hypercarbia leading to an increased veno-arterial difference in CO2 tensions (V-aCO2 gradient) has been shown to reflect critical reductions in systemic and pulmonary blood flow that occur during cardiorespiratory arrest and septic shock. We therefore measured plasma lactate levels and V-aCO2 gradients in 10 patients (mean age 57.2 years) following CPB and compared them with conventional indices of tissue perfusion. Plasma lactate levels, cardiac index (CI) and oxygen uptake\((\dot VO_2 )\) all increased significantly (p<0.05 vs baseline levels) up to 3h following surgery. Oxygen delivery\((\dot DO_2 )\) did not change. Plasma lactate levels correlated significantly with CI (r=0.47,p<0.01). V-aCO2 fell significantly with time (p<0.01 vs baseline). There was an inverse relationship between V-aCO2 and cardiac index and V-aCO2 and lactate (r=−0.37,p<0.05;r=−0.3,p<0.05 respectively). We conclude that blood lactate, CI and\(\dot VO_2 \) increase progressively following CPB. An increase in lactate was associated with a decrease in V-aCO2. An increase in V-aCO2 was not therefore associated with evidence of inadequate tissue perfusion as indicated by an increased blood lactate concentration.

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Ariza, M., Gothard, J.W.W., Macnaughton, P. et al. Blood lactate and mixed venous-arterial PCO2 gradient as indices of poor peripheral perfusion following cardiopulmonary bypass surgry. Intensive Care Med 17, 320–324 (1991). https://doi.org/10.1007/BF01716189

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Key words

  • Blood lactate
  • Acid base balance
  • Cardiopulmonary bypass