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Description / Table of Contents: Abstract Exact and quick measurements of basic laboratory parameters are important in selected patients in the perioperative period. Depending on the capabilities of a hospital’s central laboratory, the anaesthesiologist may only obtain such laboratory tests after unacceptable delays. This problem may be overcome by a new bedside measurement device that has become available from i-STAT Corporation, Princeton, USA. The hand-held, battery-driven analyser accepts blood specimens that are injected into a disposable cartridge (EG7+) and measures acidity, blood gas tensions, haematocrit, and electrolytes. The aim of this study was to determine the accuracy of such measurements by comparing them with measurements obtained by conventional laboratory test methods. Methods: Heparinised arterial blood specimens were collected in duplicate from 49 surgical patients. Measurements of ionised calcium (Ca), sodium (Na), potassium (K), pH, pCO2, pO2, base excess (BE), haematocrit (Hct), and haemoglobin (Hb) obtained by the i-STAT analyser were compared with measurements from the calibrated analysers ABL 615 and EML 100 (Radiometer, Copenhagen). Because the i-STAT analyser calculates the Hb concentration from a conductometrically measured Hct, 19 blood specimens were centrifuged in order to compare test results with conventionally obtained Hct and Hb values. As the Hct test sensitivity with the i-STAT changes with diluted blood due to its low albumin concentration, Hct and Hb measurements during cardio-pulmonary bypass (CPB) must be corrected by activating an analyser-implemented correction algorithm (Hct/CPB and Hb/CPB). Correlation analysis was performed between conventional measurements and i-STAT values (Ca, Na, K, Hct, pCO2, pO2), between values that the i-STAT analyser derives (Hb, HCO3, BE) and conventionally obtained results, and between normal and CPB-corrected Hct and Hb values. Accuracy was judged according to the national quality standard, whic h requires test results to lie within the 95% confidence interval of conventional tests. Results: Each blood specimen was analysed: erroneous results or technical failures did not occur. Measurement of one set of i-STAT values required 2.5 min. Correlation coefficients (r) between conventional and i-STAT results were: 0.85 for CA, 1.0 for K; 0.86 for Na; 0.99 for pH; 0.98 for pCO2; 0.99 for pO2; 0.93 for HCO3; 0.93 for BE; 0.46 for Hb values not corrected for CPB and 0.95 for CPB-corrected Hb; and 0.74 for Hct values not corrected for CPB and 0.98 for CPB-corrected Hct. The correlation coefficient for Hct between centrifuged and CPB-uncorrected i-STAT values was 0.81 and that for CPB-corrected values was 0.98. National accuracy requirements were not met for tests of: Ca (by 0.02 mmol/l); pH (by 0.01); pO2 including hyperoxic values (by 26.7 mmHg, but were met for pO2 values 〈200 mmHg); Hb (by 1.6 g/dl); Hb/CPB (by 0.8 g/dl); and Hct (by 6.5%, but were met for Hct/CPB values). All other tests fulfilled the required standards. Conclusion: This analyser is easy to use, reliable, and portable, and therefore suitable for the operating room, for analyses during emergencies, on peripheral wards, for preclinical screening, or at times when availability of lab tests is time-consuming or limited. The test accuracy for electrolytes, blood gases, and Hb is high enough to justify routine use of the i-STAT analyser in clinical practice. That the nationally required quality standards for Ca, pH, and Hb were not met is not of importance because the measured deviation was too small to have clinical relevance. When analysing diluted blood with a low Hct and low oncotic pressure, it is important to activate the analyser’s correction algorithm „CPB”, because the obtained results will then comply with the required accuracy.

Description / Table of Contents: Abstract A combination of epidural opioids with local anaesthetics has been used to improve pain relief during labor and to reduce side effects, such as muscle weakness, usually seen when local anaesthetics are used alone. The addition of epidural fentanyl (F) produces highly effective analgesia, the only side effect being mild itching. Initial trials investigated the improvement in analgesia after a single administration of F during first- but not during second-stage labor. Even though pain perception during second-stage labor under epidural analgesia with local anaesthetics can be severe, the addition of opioids was avoided for fear of neonatal or maternal depression. A recent report found maternal and umbilical plasma concentrations following injection of 100 μg F to be safe and the investigators speculated that repeated addition of epidural/F to injections of local anaesthetic may prove beneficial for the parturient without exposing the mother or fetus to risk. We therefore studied maternal analgesia, maternal and umbilical plasma levels and associated side effects following repeated addition of 100 μg F to bupivacaine epidural analgesia during labor. Methods. Following institutional and governmental approval 53 parturients were randomly assigned to receive either 8 ml bupivacaine 0.25%+0.1 mg fentanyl (B+F group; n=28) or 8 ml bupivacaine 0.25%+2 ml saline (BUP group; n=25) in an epidural catheter at L2/3. The same dose was reinjected upon the patients' request regardless of the degree of cervical dilatation. Blood pressure, heart rate, respiratory rate and the incidence of side effects were recorded before and following each epidural injection. Pain relief was determined at each injection and following cord clamping using the visual analogue pain scale (VAS; 0–100 mm). Maternal venous blood samples were collected to measure plasma F concentrations before and 20 and 40 min after each injection and at birth when umbilical venous and arterial blood was obtained. After centrifugation the samples were maintained at −20° C and then analyzed by radioimmunoassay. At delivery, Apgar scores and umbilical venous and arterial blood gas values were determined. Results. Both groups were comparable for age, weight, height, gestational age and parity. A total of 48 epidural injections were evaluated in the B+F group, 43 in the BUP group. No statistically significant group difference was found between the frequency of injections per delivery (B+F: 2.2; BUP: 1.8); regarding the time between the initial and the first top-up dose (B+F: 144 min; BUP: 140 min) or regarding the interval between the last injection and birth (B+F: 94 min; BUP; 90 min). However, the quality of pain relief during labor and particularly at birth was significantly improved by F (mean VAS in B+F group: 6 mm; mean VAS in BUP group: 42 mm). Mild itching was observed in 43% of patients receiving F, moderate shivering in 13% versus 40% in patients not receiving F. At control mean maternal F plasma levels were not zero but 0.25 ng/ml. After the initial injection and following the first and second top-up dose mean maximum maternal F plasma concentrations were 0.54 ng/ml (±0.32; ±SD), 0.88 ng/ml (±0.62) and 1.06 ng/ml (±0.4) (range 0.18–2.76 ng/ml), respectively. The increase in maternal F concentrations with increasing injection frequency was statistically significant (P〈0.02). Mean umbilical venous and arterial F concentrations at birth were 0.72 ng/ml (±1.16) and 0.62 ng/ml (±0.52). No significant group differences were found regarding Apgar scores or umbilical blood gas analyses. In one newborn, radioimmunoassay resulted in unexplainably high umbilical F concentrations without any clinical signs of sedation, depressed vigilance and without any sequellae. Discussion. Repeated addition of 100 μg F to epidural anaesthesia with bupivacaine significantly improves analgesia and provides pain relief not only during the first but also through the very painful second stage of labor. In this study, F did not affect the onset or the duration of analgesia, probably due to the fact that bupivacaine was used at a fixed and (compared to other studies) relatively high concentration. We did not observe clinically relevant side effects in the mother or the newborn. Although epidural injections of 100 μg F were repeatedly administered, the mild dose-dependent increases of maternal and of umbilical plasma F concentrations had no effect and caused no clinical signs of depression. The specificity of radioimmunoassay for fentanyl in parturients is questioned.

Description / Table of Contents: Abstract Epidural anaesthesia for elective caesarean section can have advantages over general anaesthesia. The anaesthesiologist can avoid endotracheal intubation as well as fetal depression following placental transfer of systemic anaesthetics. However, despite reaching an effective blockade preoperatively, intraoperative discomfort and pain may occur during epidural anaesthesia with local anaesthetics alone, necessitating supplemental systemic analgesics or even conversion to general anaesthesia [21]. Addition of epidural fentanyl has been shown to improve onset and quality of perioperative analgesia without evident side effects for mother or newborn [24]. Nevertheless, administration of epidural opioids before cord clamping is still hotly debated, some fearing maternal and or neonatal depression [6, 26]. The aim of the present study was to investigate the quality of analgesia, associated side effects and the resulting maternal and neonatal plasma opiate concentrations after a single preoperative addition of 0.1 mg fentanyl to epidural bupivacaine analgesia in comparison to epidural bupivacaine analgesia alone. Methods. Following governmental and ethics committee approval, 43 elective consenting patients for caesarean section were randomized to receive double-blind injections of either 8 ml 0.5% bupivacaine+0.1 mg fentanyl (B+F group, n=22) or 8 ml 0.5% bupivacaine +2 ml saline (Bup group, n=21) into an epidural catheter. In both groups additional injections of bupivacaine were given to achieve sensory blockade up to T4. Systolic blood pressure, heart and respiratory rates were measured regularly. Quality of intraoperative pain relief was assessed at delivery, uterine eventration, and during uterine and abdominal closure using a visual analogue scale (VAS). The duration of postoperative analgesia was compared between groups, as well as the incidence of nausea, itching or sedation. Similarly, Apgar scores and umbilical arterial and venous blood gas analyses were compared. Fentanyl concentrations were determined in maternal venous blood sampled before and 20 and 40 min after epidural injection and at birth, and in umbilical venous and arterial blood sampled after delivery. Radioimmunoassay analysis was performed from plasma specimens centrifuged and frozen at −20° C [19]. The statistical level of significance was defined as P〈0.05. Results. Groups were comparable regarding age, weight and time of gestation. Total bupivacaine doses and injection to delivery times were similar in both groups. Figure 1 shows that there were 40% more pain-free (VAS=0) patients in the B+F group during uterine eventration and wound closure (P〈0.05). Mean postoperative duration of analgesia was significantly longer in the B+F group (382 vs 236 min). The rate of nausea and mild itching was significantly higher in the B+F group. Respiratory depression was never detected in patients or newborns. Small group differences in blood pressure or respiratory rate were inconstant and clinically irrelevant, as were differences in umbilical venous pCO2. One hundred and twenty-five blood samples were analysed for fentanyl concentrations. The mean fentanyl concentration before epidural injection was not zero, but 0.25 ng/mg (range 0.02–0.32). Maternal concentrations at 20 and 40 min after injection were 0.55 ng/ml (0.12–1.14) and 0.52 ng/ml (0.26–1.04) (Fig. 3). At delivery, mean maternal fentanyl concentration was 0.58 ng/ml (0.14–1.18); mean umbilical arterial and venous concentrations were 0.51 ng/ml (0.04–1.8) and 0.41 ng/ml (0.18–1.2), respectively. Rare results of fentanyl concentrations 〉1.0 ng/ml correlated neither with sedation, maternal respiratory rate and side effects, nor with Apgar scores and umbilical blood gas values. No Apgar score at 5 min was below 9, and no umbilical pH was below 7.20. Conclusion. We conclude that preoperative epidural addition of 0.1 mg fentanyl to 0.5% bupivacaine significantly improves intraoperative pain relief during elective caesarean section and prolongs postoperative analgesia. This important advantage of fentanyl is associated with an increased incidence of nausea and mild itching. No clinically significant fentanyl-associated depression of vigilance could be detected in the mother or newborn. The resulting plasma fentanyl concentrations are within safe limits. When administered epidurally and preoperatively for caesarean section, maternal plasma levels of fentanyl do not decrease significantly until birth. In the radioimmunoassay an unknown substance cross-reacts like fentanyl.

Description / Table of Contents: Abstract The purpose of the present study was to compare two sedation regimens with either propofol (P) or methohexital (M) for elective magnetic resonance imaging (MRI) in children with respect to safety, side effects, recovery, and discharge time. Methods. After Institutional Review Board approval, 120 unpremedicated children with a mean age of 26.5 ±21.4 months (M) and 28.1±19.9 months (P) were randomly assigned to receive a hypnotic induction dose of either M or P. Supplemental bolus injections of M or P were administered to maintain adequate sedation. The following parameters were measured: heart rate, oxygen saturation by pulse oximetry (SpO2), respiratory rate, end-tidal CO2 (PetCO2), side effects, and recovery and discharge times. Results. Spontaneous respiration was maintained in all patients, and ventilatory support was only necessary for 2 min in 1 M patient immediately after the induction dose. The mean loading and total doses for M were 2.3±0.7 and 6.1±3.3 mg/kg respectively, and for P 2.3±0.9 and 5.8±2.7 mg/kg. Following induction SpO2 〈90% occurred in 0.49% with M and in 0.64% with P (n.s.). Apnoe 〉20 s was observed in 2 children each after M and P (n.s.). The frequency of hypoventilation (PetCO2〉48 mmHg) was 0.36% in the M group and 0.71% in the P group (n.s.). MRI sequences had to be repeated in 5% of the children in each group because of spontaneous movements. The heart rate fell significantly during MRI in both groups, while P children had lower frequencies than M children (P〈0.01). Recovery and discharge times were significantly shorter in the P group, at 0.8 min (0.08–4.8) and 2.2 min (0.2–15.0), compared to 1.5 min (0.3–28.5) and 3.5 min (0.6–40.0) in patients receiving P (P〈0.01). No patient required admission to the postanaesthesia care unit and all were free from nausea and vomiting. Discussion. Intravenous sedation with M or P using the reported technique is a safe regimen for children undergoing elective MRI. The fast recovery and discharge times seem to offer advantages over general anaesthesia with endotracheal intubation. The faster recovery and discharge of only a few minutes after P compared with M is without clinical relevance.