Direct injection method for gas chromatographic measurement of inhalation anesthetics in whole blood and tissues

The effect of a right-to-left intracardiac shunt on the rate of rise of arterial and end-tidal halothane in children

In this prospective study, we evaluated the effect of a right-to-left intracardiac shunt on the rate of rise of end-tidal and arterial halothane concentration in children. Six children aged 23-43 mo undergoing surgical closure of atrial fenestration after Fontan procedure were given 0.8% inspired halothane. End-tidal halothane was recorded at 1-min intervals after the introduction of halothane. Arterial halothane concentrations were determined 0, 1, 3, 5, 10, and 15 min after the introduction of halothane. The sampling was performed before and after closure of the atrial fenestration. The ratio of pulmonary to systemic blood flow (Qp/Qs) increased in this patient population, from 0.58 +/- 0.04 to 0.88 +/- 0.12 (P = 0.01). The rate of rise of end-tidal halothane did not change significantly with a decrease in the magnitude of the right-to-left intracardiac shunt after closure of the atrial fenestration. The ratio of arterial to inspired halothane concentrations at 1, 3, 5, 10, and 15 min were lower before closure of the atrial fenestration compared with after closure (P < 0.05). We conclude that the presence of a right-to-left intracardiac shunt significantly slows the rate of rise of arterial halothane in the face of a constant inspired concentration. The rate of rise of end-tidal halothane is not significantly affected in the presence of a right-to-left intracardiac shunt.

IMPLICATIONS

In this prospective study, we found a slower rate of rise of halothane in arterial blood in children with right-to-left intracardiac shunting. Induction of anesthesia by inhalation of volatile anesthetics may therefore be slower in these children.

Effects of four volatile anesthesics on postanesthetic ventilation: a comparison of halothane, enflurane, isoflurane, and sevoflurane

To investigate the effects of four volatile anesthetics (halothane, enflurane, isoflurane, and sevoflurane) on postanesthetic ventilation and levels of consciousness, we enrolled 24 patients undergoing tympanoplasty in this study. Anesthesia was maintained with 67% nitrous oxide and one of four volatile anesthetics. We measured end-tidal carbon dioxide concentration (C_ETco₂), minute volume ([Formula: see text]) and respiratory rate (RR), and determined the volatile anesthetic concentration in whole arterial blood (C_BAnesth) and arterial carbon dioxide tension (Paco₂) at 20 min and 2h after tracheal extubation. We also observed the level of consciousness (awake, drowsy, and asleep) before the measurement. Ventilatory variables were similar among the four groups at 20 min, although the ratio of volatile anesthetic concentration in the alveoli to the minimum alveolar concentration (MAC) (C_AAnesth/MAC ratio) calculated from C_BAnesth in the halothane group was twice those in the other groups. In the halothane group, Paco₂ was significantly higher, and[Formula: see text] and RR were significantly lower compared with the isoflurane and sevoflurane groups at 2h. Halothane tended to prolong the recovery of levels of consciousness. We conclude that isoflurane and sevoflurane provide clinical advantages over halothane on postanesthetic ventilation and recovery of levels of consciousness.

Effects of halothane, enflurane and pentobarbital on brain histamine dynamics in mice

The effects of halothane, enflurane, ketamine and pentobarbital on brain histamine dynamics were examined in mice. Brain histamine and tele-methylhistamine, a predominant metabolite of brain histamine, were simultaneously measured by high-performance liquid chromatography with fluorescence detection. Anaesthesia with the four agents had no effect on brain histamine content. The tele-methylhistamine content significantly increased during 1 h and 2 h anaesthesia with halothane (0.051 mmol/l or 0.76 mol/l) and 2 h anaesthesia with enflurane (0.11 mol/l or 0.16 mol/l). Enflurane and pentobarbital significantly inhibited the histamine depletion induced by alpha-fluoromethylhistidine (50 mg/kg, intraperitoneally), a specific inhibitor of histidine decarboxylase, suggesting that these agents decrease the histamine turnover. However, halothane and ketamine were ineffective in this respect. These results emphasize that various anaesthetics have different influences on brain histamine dynamics. Since there have been findings suggesting that brain histaminergic systems are involved in physiological functions such as regulation of blood pressure, body temperature and hormone secretion, changes in the brain histamine turnover should be given due attention with regard to physiological changes during anaesthesia.

Estimation of nitrous oxide in blood. Gas chromatographic analysis of trace or analgesic levels

The estimation of nitrous oxide (N20) at trace and analgesic levels in whole blood is described. A micro-ionisation cross section (MICS) detector was used to measure trace levels of N2O (0.69 to 17.88 mumol N20/litre of blood); whilst a thermal conductivity (TC) detector was used to determine levels from 0.17 to 13.34 mmol N20/litre of blood. The coefficient of variation was 1.3% and 3.2% for the TC and MICS detectors respectively. The technique equals the precision of previously described methods but is considerably quicker. It appears to be suitable for use in the measurement of blood levels of N20 in both theatre personnel and patients undergoing anaesthesia.

Routine direct injection gas--liquid chromatographic procedure for the analysis of volatile halogenated anaesthetics in whole blood using a new external injection port

This communication describes the design and construction of a new external injection port for the direct gas--liquid chromatographic analysis of volatile compounds in whole blood. Aliquots (4--40 microliter) of EDTA anti-coagulated blood containing the volatile compound and a weighed quantity of the internal standard, isobutanol, were injected into the disposable glass wool filter of the carrier gas stream directly onto the chromatographic column. Typical data are presented from chromatography performed with dual 6 ft. x 2 mm I.D. glass columns containing Chromosorb 101 programmed from 110--180 degrees at 6 degrees/min and the external injection port maintained at 180 degrees. The method eliminated the problems usually associated with direct injection methods and permitted the accurate analysis of halothane, methoxyflurane, diethyl ether and ethanol over the approximate range 1--100 mg%. Using this analytical procedure the distribution of halothane between the cells and plasma of human blood at 4 degrees was found to be 2.0 +/- 0.2.

Determination of benzene and toluene in blood by means of a syringe-equilibration method using a small amount of blood

A gas chromatographic determination of benzene and toluene in blood with a small amount of blood sample, 0.02 or 0.1 ml, is described. In the method an aliquot of the blood sample in a sealed hypodermic syringe of 2 ml capacity is equilibrated at 37 degrees C in a thermo-regulated water-bath. After establishing equilibrium 1 ml of overlying air is submitted to gas chromatographic analysis. The value of this method was verified by experiments in which men, rabbits, and rats were exposed to benzene and toluene mixtures of various concentrations.