• R Proietti, M Antonelli, F Cavaliere, G Conti, A Arcangeli, and M Pennisi.
• Institute of Anaesthesia and Intensive Care, Catholic University of the Sacred Heart, Largo Francesco Vito, 1, 00168 Rome, Italy, Italy, f.cavaliere@rm.unicatt.it.
• Intensive Care Med. 2002 May 1;28(5):609-615.

AbstractObjective.To investigate the effects of some acid-base abnormalities on blood capacity of transporting CO2. Design. Prospective study. Setting. General and Cardiosurgical ICUs of a University hospital. Patients. Six groups of ten patients characterized by: metabolic alkalosis; respiratory alkalosis; absence of acid-base abnormalities; metabolic acidosis; uncompensated respiratory acidosis; and compensated respiratory acidosis. Measurements and results. The CO2 dissociation curve, Haldane effect, and the ratio Ra-v between Ca-vCO2 and Pa-vCO2 were calculated from arterial and mixed-venous blood gas analyses. The CO2 dissociation curve was shifted upwards by metabolic alkalosis and compensated respiratory acidosis and downwards by metabolic acidosis. The slope of the curve was unaffected, but CO2 transport not due to Haldane effect was significantly lower in respiratory acidosis since the slope was less steep at higher PCO2 values. In comparison with controls, patients affected by metabolic acidosis showed lower Haldane effect values (0.18±0.15 vs 0.59±0.26 ml of CO2 per ml of arterial-mixed venous O2 content difference; P <.05) and Ra-v values (0.43±0.10 vs 0.84±0.17 ml of CO2 transported by 100 ml of blood per Torr of arterial-mixed venous PCO2 gradient; P <.05). Conclusions. Our findings suggest that acid-base abnormalities, particularly metabolic acidosis, markedly affect blood capacity of transporting CO2 and may worsen tissue hypercarbia associated with hypoperfusion. However, because of possible errors due to small measurements and the assumptions of the method, in the future definitive clarification will require the construction of original CO2 dissociation curves for each acid-base abnormality.

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