Exchange of respiratory gases in chronic uraemia and anaemia, in relation to anaesthesia.

AMONG THE PROBLEMS presented by the chronic uraemie patient, the anaesthetist is particularly concerned with anaemia, a-3 acid-base and electrolyte upsets, and impaired renal excretion of drugs. When such patients are on chronic haemodialysis programs, they frequently present for surgical creation or revision of arteriovenous shunts and fistulae. Usually, these procedures are done under local or regional anaesthesia, but for some general anaesthesia may be indicated because of temperamental unsuitability to, or outright refusal of, local anaesthesia. The standard method of laboratory assessment of respiratory gas exchange is the determination of partial pressures of carbon dioxide and oxygen in arterial blood. However, in anaemia, with the associated decrease in oxygen content of blood, arterial blood gas tensions, indicating the effectiveness of gas exchange between pulmonary blood and alveolar air, do not offer all the desired information, especially concerning tissue gas exchanges. Events occurring at the t issue/blood gas exchange area must be at least as important to the organism as those in the a i r /b lood exchange area. Since direct measurement of tissue gas tensions is not generally feasible, other indicators must be sought. End-capillary blood gas tensions reflect the tensions in the tissue with which that blood has equilibrated. 4 Therefore, postulating that central venous blood gas tensions might be a valuable indicator of tissue gas tensions (since. central venous blood is in effect pooled end-capillary blood, albeit not perfectly mixed) we studied arterial and central venous blood gas and hydrogen ion status in five chronic uraemic patients receiving general anaesthesia for arterio-venous shunt or fistula. Their ages ranged from 20 to 52 years. All were anaemic (haemoglobin 4.5 to 6.8 gm~) and azotaemic (BUN 42 to 65 mgm%). In some, electrolyte abnormalities of mild to moderate degree were present. These data are itemized in Table I.