Instrumental variability of respiratory blood gases among different blood gas analysers in different laboratories.

The aim of this study was to test the hypothesis that differences in oxygen tension (PO2) and carbon dioxide tension (PCO2) values from measurements performed on different blood gas analysers in different laboratories are clinically insignificant. Samples of fresh whole human tonometered blood (PO2 8.1 kPa (60.8 mmHg); PCO2 5.3 kPa (39.9 mmHg)) were placed in airtight glass syringes and transported in ice-water slush. Blood gas analysis was performed within 3.5 h by 17 analysers (10 different models) in 10 hospitals on one day. The mean of the differences between the measured and target values was -0.01+/-0.19 and 0.21+/-0.13 kPa (-0.06+/-1.45 and 1.55+/-1.01 mmHg) for PO2 and PCO2, respectively. The mean of the differences between two samples on one analyser was 0.06+/-0.06 and 0.04+/-0.03 kPa (0.47+/-0.48 and 0.29+/-0.24 mmHg), respectively. For PO2 and PCO2 the interinstrument standard deviations (s(b)) were 0.18 and 0.13 kPa (1.38 and 0.99 mmHg), respectively, whereas the intra-instrument standard deviations (s) were 0.06 and 0.03 kPa (0.47 and 0.26 mmHg), respectively. Both for PO2 and PCO2 the ratios of s(b)2 and s2 were statistically significant (analysis of variance (ANOVA) p<0.001). The standard deviations of a random measurement on a random analyser were 0.19 and 0.14 kPa (1.46 and 1.02 mmHg) for PO2 and PCO2, respectively. We conclude that the variability in measurement of blood gas values among different blood gas analysers, although negligible, depends much more on inter- than intra-instrument variation, both for oxygen tension and carbon dioxide tension. Technical improvements and adequate quality control programmes, including tonometry, may explain why the variability in blood gas values depends mainly on errors in the pre-analytical phase.

Epidural morphine anesthesia for abdominal aortic surgery--pharmacokinetics.

Plasma and CSF pharmacokinetics of morphine given epidurally in combination with general anesthesia for abdominal aortic surgery were recorded. The initial plasma and CSF concentrations of morphine appeared at two minutes. The peak plasma concentrations of morphine were recorded at 8.0 +/- 2.6 minutes after epidural injection. Plasma mean residence time was 84 +/- 25.7 minutes, Vdss 121 +/- 30 L, and C1 1.5 +/- 0.32 L/min. Free morphine was not detected in plasma 360 minutes after epidural administration. The fraction of the epidural morphine that crossed the dura was 3.15% +/- 2.4 The peak CSF morphine concentrations were recorded at 56 +/- 31 minute. MRT (200 +/- 28 minute), Vdss (65 +/- 33.8 ml), and CL (0.32 +/- 0.15 ml/min) showed that variable fractions of morphine remained many hours in the CSF. Factors that could produce the interindividual variability of plasma and CSF concentrations and pharmacokinetics of epidural morphine were discussed. Abdominal aortic surgery appears to influence both plasma and CSF pharmacokinetics.

The pharmacokinetics of intradural morphine in major abdominal surgery.

The pharmacokinetics of intradural morphine used for major abdominal surgery were evaluated. Lumbar spinal fluid and plasma concentrations were measured at intervals after morphine 0.05 mg/kg had been injected intradurally in 21 patients scheduled for elective abdominal aortic surgery. The CSF morphine concentrations were fitted by a biexponential function. A non-compartmental model based on statistical moment theory was used for calculating the intradural morphine disposition. Mean residence time was 137 +/- 54.9 minutes, mean initial volume of distribution 15 +/- 5.49 ml, mean volume of distribution at steady-state 42 +/- 18.25 ml and mean clearance 0.34 +/- 0.18 ml/min (0.02 +/- 0.01 L/h). The moments of the morphine concentration-time curves and the pharmacokinetic parameters varied between the patients. They were not significantly different with regard to morphine dosage, or patient sex or age. Free morphine could not be detected in plasma. Morphine-3-glucuronide appeared in plasma at 5 minutes, increased to a maximum at 240 minutes and fell below the detection limit at about 16 hours after morphine administration. Possible clinical causes of interindividual variations in the CSF morphine concentrations and the pharmacokinetics of intradural morphine are discussed.

A comparative study of the electrode systems of three pH and blood gas apparatus.

We present a comparative evaluation of the electrode systems of three modern blood gas analysers: IL-413, ABL-1 and AVL-937C. The response curves, accuracy and precision of the pH-, pCO2- and pO2-electrodes were established with tonometered blood and buffer solutions. pH values (range 6.8-7.8) measured on the AVL deviate (-0.03 pH for blood and +0.03 pH for buffer) from those of BMS2 Mk2; whereas on the IL and ABL analysers the pH values deviate by not more than 0.01 pH. The standard deviation was better than 0.005 pH. pCO2 values of blood and buffer (range 14-106 mm Hg) deviate from the calculated tonometer values by quantities ranging from 3 to 10 mm Hg. The average precision (CV)1) of the pCO2 measurement on each analyser was better than 1.8%. pO2 values of blood (range 0-130 mm Hg) did not differ by more than 3 mm Hg from the calculated values. Above 130 mm Hg a linear negative increasing difference was seen. For buffer solutions a linear relationship between pO2 difference and pO2 value was found over the whole range from zero up to 642 mm Hg: a positive difference below and a negative difference above the pO2 of the previous calibration; if the calibration pO2 is higher, the sample pO2 is shifted to a higher value. The average precision of the pO2 measurements was better than 3%. In the (patho)-physiological range the three instruments may provide suitable results for the clinician. Suggestions are made for standardization and improvement of the electrode systems.

The effects of highly selective vagotomy on secretion and emptying of the stomach.

The results of a prospective study of 60 patients with nonobstructive duodenal ulcer treated by highly selective vagotomy show that the gastric acid secretion postoperatively is effectively reduced. Judgment of completeness of highly selective vagotomy is only possible by means of an intragastric pH-metry during operation. The Hollander test answers it insufficiently. In a number of patients, highly selective vagotomy caused a fast initial phase of gastric emptying of porradge. The impression is that the contractional activity of the antrum has the same pattern before and after highly selective vagotomy.

Evaluation of ampouled tonometered buffer solutions as a quality-control system for pH, pCO2, and pO2 measurement.

In response to the need for an adequate quality-control system for blood-pH and blood-gas analyzers, we investigated the practical application of ampouled phosphate-bicarbonate-chloride solutions tonometered with mixtures of carbon dioxide, oxygen, and nitrogen. This system offers three discrete sets of pH, pCO2, AND PO2 values, which are consistent with normal and pathophysiologically high and low values. The stated values were based on the U.S. National Bureau of Standards scale for pH and on gas analysis for pCO2 and pO2. Influence of temperature, air contact, calibration gas, and storage was established. Internal and external quality control by means of these ampoules is presented. The system is stable, accurate, precise, and suitable for simultaneous quality control of pH, pCO2, and pO2 measurements.