An analysis of pre-operative PaO2 in a general surgical population.

Two hundred and thirty one patients awaiting elective surgery were divided on the basis of spirometric examination into normal (group A) and those with increased airway resistance (group B). The mean arterial oxygen tension.for the 151 normal subjects was 96-3 (±11-6) mm. Hg. There was a significant inverse correlation of Pao2 with age and dynamic lung volumes. The 80 patients in group B were significantly older and their mean Pao2 was 88-7 (±12-9) mm. Hg. There was, however, no correlation between Pao2 and age in this group, probably because the increased airway resistance had a greater influence in lowering the arterial oxygen tension than did the age factor alone. The increasing use of the oxygen electrode in clinical practice has awakened interest in the normal arterial oxygen tension (Pao2). This is authoritatively stated to be 100 mm. Hg (Roughton, 1964) but, until the normal range is known, the interpretation of the significance of single values under clinical conditions is uncertain. This is especially important in the post-operative patient, as the development of hypoxaemia can be expected in all patients after abdominal operations (Diament and Palmer, 1966). There are, however, few published reports of the Pao2 in patients awaiting surgery. Conway, Payne, and Tomlin (1965) found a mean Pao2 of 91-8 (±8-7) mm. Hg for a group of 70 pre-operative patients who were clinically free of cardio-respiratory disease. We have measured the blood-gas tensions and carried out spirometric measurements on a group of patients who were undergoing elective abdominal surgery. None of these patients had any clinical evidence of cardio-respiratory disease and all were considered fit for major surgical procedures. However, subclinical respiratory impairment is often present in these patients (Diament and Palmer, 1967). Therefore, on the basis of spirometry, they were divided into two groups-group A in whom the forced expiratory volume in one second expressed as a percentage of the forced vital capacity (F.E.V. I%) was greater than 70 and who were considered, therefore, not to have increased airways resistance, and group B in whom the F.E.V.1 % was less than 70 and who were considered to have some obstruction to air flow. In both groups, an analysis was made to determine how the Pao2 varied with age, sex, height, weight, smoking habits, the dynamic lung-volumes and the arterial carbon dioxide tension (PacoO) PATIENTS AND METHODS The number of men and women in the groups, their mean ages in …