Theophylline disposition in acutely ill hospitalized patients. The effect of smoking, heart failure, severe airway obstruction, and pneumonia

Theophylline disposition (clearance, volume of distribution, and half-life) was measured in 31 normal volunteers and 26 acutely ill patients with airway obstruction within 24 hours of hospital admission and again when intravenous aminophylline was discontinued 2 to 10 days later. Sex, age, race, the diagnosis of asthma, and the diagnosis of chronic bronchitis were not significantly correlated with clearance. Clearance was significantly increased in smokers and significantly decreased in patients with congestive heart failure, pneumonia, and severe bronchial obstruction. The volume of distribution was not correlated with these variables. Within 24 hours of admission, the mean clearance in our patients without congestive heart failure or pneumonia was 44.5 ml per hour per kg of body weight, 40 per cent less than the value on which the widely used 0.9 mg per kg per hour dosage is based. The unexplained interindividual variability of clearance was significantly higher amont patients than control subjects, but intraindividual variability in clearance was not different in these 2 groups after correction for the effects of smoking, congestive heart failure, and so on. Large variability in clearance among patients makes the plasma theophylline concentration resulting from any dosage relatively uncertain. Based on the the results of this study, recommendations are made concerning theophylline dosage computation, and the clinical circumstances calling for determination of plasma theophylline concentrations.

Total body and exchangeable potassium in chronic airways obstruction: a controversial area?

Potassium deficiency is an important complication in the treatment of heart disease. However, there is a serious dichotomy in the literature. Severe potassium depletion has been reported in this condition when exchangeable potassium was measured whereas normal levels or marginal depletion were found in measurements of total body potassium. To clarify this situation, simultaneous measurements of total body potassium by whole-body counting, and of exchangeable potassium by isotope dilution using 43K, were made in 10 male subjects with established airways obstruction. Sequential determinations showed that exchangeable potassium increased up to 68 hours after administration, and values obtained at only 24 hours would have been a substantial underestimate. In this group of subjects neither total body nor exchangeable potassium at 48 hours was significantly different from the expected normal value.

The roles of ventilation and perfusion in lung metabolism

The lung, like other viable organs, requires the adequate supply of oxygen and metabolic substrates for its functional and structural integrity. Therefore, we studied the metabolic and ultrastructural consequences in the canine lung following bronchial and/or pulmonary arterial occlusions. The results indicate that the lung can maintain its bioenergetic levels for 5 hours with either the ventilation or perfusion alone. Ultrastructural changes appear to precede metabolic alterations measured. When both the ventilation and perfusion were interrupted, rapid biochemical and structural deteriorations occurred, whereas the combinations of alveolar obliteration and hypoxemia, induced with low F102, produced intermediate damage. The implications of these findings on the pathogenesis and evolution of acute respiratory distress syndrome, on the lung preservation for transplantation, and on the rationale for membrane oxygenator support are discussed.

Metabolic acidosis in status asthmaticus

Blood gases and acid-base balance were measured in a group of patients in status asthmaticus. Simple or combined metabolic acidosis was found in 37.9% of the patients. In 25 of these, lactic acid (LA), pyruvic acid (PA) and LA/PA were increased. Increased glycolysis and anaerobic respiratory muscle glycolysis during extreme airways obstruction may be instrumental in these changes. Base deficit, not accounted for by organic acid increase, may be dependent on previously present hypocapnic hyperventilation. Possibly hyperlactemia provoked by hyperventilation may be exaggerated in severe asthma.

Impaired water handling in chronic obstructive airways disease

The response to a standard water load (20 ml/kg body weight) was studied in 20 patients with chronic obstructive airways disease and in 13 healthy subjects. The percentage of the water load excreted in four hours was significantly lower in the patients (mean 51%) than in the controls (mean 106%). The maximum urine flow, osmolar clearance, free water clearance, and creatinine clearance were also significantly reduced in the patients. There was a significant inverse correlation between the percentage of load passed and the arterial PCO(2) (r = -0.798). Among the several possible causes of the reduced excretion of water which are discussed is a direct effect of hypercapnia.