An index of permeability of the alveolar-capillary membrane was derived from the relative extraction from the lung into arterial blood of 2 tracers, 125I-antipyrine and 51Cr-ethylenediaminetetraace...

Obese patients are known to metabolise anaesthetic agents more than patients of normal weight. The extent of this was investigated by the measurement of serum fluoride concentrations in 10 morbidly obese patients undergoing gastroplasty. Five were allocated to receive enflurane and five to receive isoflurane supplemented anaesthesia. The mean peak serum fluoride concentrations after enflurane anaesthesia were greater (22.7 μmol/litre, SE 2.9) than after isoflurane anaesthesia (6.5 μmol/ litre. SE 0.6). The mechanisms and implications of this finding are discussed.

We examined the effect of nicotine on pulmonary epithelial permeability in man. Nicotine was administered from a chewing gum base given over a seven-day period. An index of pulmonary permeability was derived from the rate of clearance from the lung into the blood of 99mTcDTPA (diethylenetriamine pentacetate). In five nonsmoking volunteers there was no change in permeability for the seven-day study period. This lack of effect of nicotine alone was in striking contrast to the increase in epithelial permeability observed in five nonsmoking subjects who took up cigarette smoking.

The effect of the application of a tourniquet to a limb and the release of the accumulated metabolites have been investigated with reference to the acid-base level in the blood from the limb and in the right atrium. Investigations have been carried out experimentally in rhesus monkeys and observations have been made on patients undergoing reconstructive operations on the knee. The acidotic blood from the ischaemic limb produces little systemic effect. The limb recovers in approximately 40 minutes after a tourniquet has been in place for four hours. Three hours is recommended as a reasonable upper limit for the safe application of a pneumatic tourniquet.

An index of permeability of the alveolar-capillary membrane was derived from the relative extraction from the lung into arterial blood of 2 tracers, 125I-antipyrine and 51Cr-ethylenediaminetetraacetate. The effect on this index of aspirating 2 ml of isotonic saline, distilled water, or 10(-1) M hydrochloric acid per kg of body weight was studied in 3 groups of rabbits. The severity and time course of changes in the permeability index were correlated with changes in lung mechanics, gas exchange, serial chest roentgenograms, ratio of extravascular lung water to dry weight, and histologic findings. Aspiration of saline produced no change in the permeability index; aspiration of water produced a large mean +/- SEM increase in the index, from a baseline of 0.025 +/- 0.002 to 1,050 +/- 0.054 (P less than 0.001), but this value returned to baseline 15 min later. After hydrochloric acid, the permeability index increased from a baseline of 0.027 +/- 0.003 to 1.068 +/- 0.098 (P less than 0.005), with no evidence of resolution after 60 min. Changes in lung mechanics, gas exchange, and roentgenograms were smallest after aspiration of distilled water and greatest after aspiration of hydrochloric acid. The functional changes after aspiration of water and saline recovered at a rate proportional to the known clearance rates of these liquids from the lung. The changes after hydrochloric acid either showed no tendency toward recovery or, in the case of the roentgenograms, worsened with time. There were no detectable histologic abnormalities or an increase in the ratio of extravascular lung water to dry weight after aspiration of water or saline, but there were extensive histologic abnormalities and a 70 per cent increase in lung water after acid. The increase in the permeability index after aspiration of water was too transient to exert a deleterious effect. In contrast, the persistence of the increase in the permeability index after hydrochloric acid was associated with persistent functional changes attributable to the considerable increase in lung water.

A change in alveolar capillary membrane permeability was induced in anesthetized rabbits by intratracheal injection of either hydrochloric acid or hypotonic saline (2 ml per kg of body weight). The...

Six healthy seated male subjects (aged 36–54 yr) inhaled 100% oxygen for 10 min at normal lung volume and then for a further 5 min with forced maximal expirations. Following this manoeuvre, changes in arterial Po2 ranged from a decrease of 16.7 kPa to an increase of 2 kPa (—125 to +15 mm Hg) while breathing 100% oxygen, and a decrease of 1.8 kPa to an increase of 1.1 kPa (—13.5 to + 8.6 mm Hg) while breathing air. Functional residual capacity (FRC) was unchanged in one subject, but decreased by 0.04–1.15 litre in the others. The chest radiograph was unaltered in the subjects with zero and 0.04 litre decreases in FRC. Three of the other subjects showed line shadows at the bases, while the subject with the largest decrease in FRC showed extensive areas of collapse. There was a good correlation between changes in arterial Po2, FRC and the chest radiograph. Substernal discomfort was felt when those subjects with positive radiographic changes attempted to make a maximal inspiration. All changes were reversed by taking five maximal forced inspirations. Arterial Po2 changes while breathing 100% oxygen provided the most sensitive indication of collapse. Changes in FRC and arterial Po2 while breathing air were generally within the normal reference range of these variables, and therefore of little diagnostic value in the absence of control measurements. Under such circumstances, chest radiography seems to be the most sensitive indication of pulmonary collapse occurring in the upright position.

Several enzymes of the Embden-Myerhof pathway were found, in vitro, to be insensitive to high concentrations of halothane. However, glutamate dehydrogenase was inhibited in vitro in a dose-dependent manner by methoxyflurane, trichloroethylene, diethyl ether and halothane in concentrations greater than those used in clinical practice. This allosteric enzyme is believed to be involved with central nervous transmission. The inhibition of activity was immediate and reversible with all the agents investigated. In the presence of halothane, enzyme kinetic experiments demonstrated that the inhibition was of the non-competitive type thus suggesting that anaesthetic agents induced conformational changes in the glutamate dehydrogenase molecule.

The helium dilution technique for the measurement of functional residual capacity (FRC) is reviewed with special reference to anaesthesia. A modification is described which permits measurements to be made during intermittent positive pressure ventilation. This modification causes minimal interference with the circuit as it is used for spontaneous respiration. The measuring circuit may be alternated with an open circuit without disturbance of the pattern of breathing (spontaneous or artificial). Potential errors in the measurement of FRC during anaesthesia are considered and assessment of linearity, reproducibility and accuracy is described.

Functional residual capacity has been measured by helium dilution in 26 spontaneously breathing patients before and immediately after anaesthesia, which was induced with thiopentone and maintained with halothane. The mean reduction was 390 ml (16.1% or pre-induction value) and the change was highly significant (P less than 0.001). The decrease in FRC correlated with age (r equals 0.41: P less than 0.005) and less (P less than 0.001). The decrease in FRC correlated with age (r equals 0.41; P less than 0.005) and less satisfactorily with the weight/height ratio (r equals 0.31; P less than 0.05) which itself correlated with age. Inspired oxygen concentration, expiratory reserve volume and the presence of phasic expiratory muscle activity bore no significant relationship to the decrease in FRC. There was no evidence of any progressive change in FRC between 6 and 20 min after the induction of anaesthesia.