Acidosis following thoracic surgery.

Sir,—Dr Pandit and his colleagues suggest that patients develop a mixed respiratory and metabolic acidosis following a thoracotomy {Brit. J. Anaesth. (1973), 45, 79). However, the results they present do not necessarily support this conclusion. The investigation would have been more convincing if measurements had been made at each stage in all the patients. Incidentally, there are some discrepancies between the figures; for example, for the preinduction phase there are 20 values for pH and base excess but only 18 for the carbon dioxide tension. We are not certain which patients were given sodium bicarbonate, for whilst figure 3 divides the base excess values for the 60-min stage into those who did and those who did not receive bicarbonate, figures 1 and 2 show no such classsification for the pH and Pco2 values. It is well known that indices of a metabolic acidosis such as base excess will show an apparent metabolic acidosis as the carbon dioxide tension of a patient is increased (e.g. Holaday, Ma and Papper, 1957; Stoker et al., 1972). The mean values for the pH and Pco2 for the "prereversal" and the "15-min postoperative" stages presented by Dr Pandit would fit such an in-vivo carbon dioxide titration curve. Thus there appears to be no need to invoke an additional metabolic acidosis. Whilst in individual patients sodium bicarbonate may be of therapeutic benefit following a thoracotomy we do not feel that its routine administration is supported by the results given in this paper. JOAN C. BEVAN D. R. BEVAN J. NORMAN London