The development, application and interpretation of risk models is becoming an important activity in a number of surgical disciplines. In this paper, we discuss the many issues that arise when constructing a risk model, with particular reference to the development of a risk model for thoracic surgery. First, we briefly revisit the origins of risk modelling in cardiothoracic surgery.

Background and objective: Diabetes mellitus associated with hypertension often causes perioperative complications. The α1-adrenoceptor antagonist/5-hydroxytryptamine-1A receptor agonist urapidil is an approved drug used in hypertension and hypertensive emergencies. 5-Hydroxytryptamine-1A (5-HT1A) receptor agonists impair glucose metabolism. To evaluate a possible dose-dependent hyperglycaemic effect of urapidil due to its 5-HT1A receptor agonistic properties, the effect of three doses of urapidil on hyperglycaemia in the streptozotocin diabetic rat was investigated.

Methods: Male Wistar-Kyoto rats were made diabetic by streptozotocin and randomly allocated to the following daily treatments for 7 days (n = 6 each): urapidil 6 mg kg−1, urapidil 20 mg kg−1, urapidil 60 mg kg−1, insulin 4 IU kg−1 subcutaneously. One diabetic group and one non-diabetic healthy group served as controls.

Results: Treatment for 7 days with urapidil 20 mg kg−1 and urapidil 60 mg kg−01 reduced mean glucose concentrations significantly (urapidil-20: 15.6 ± 1.1 mmol L−1P = 0.023; urapidil-60: 15.8 ± 0.8 mmol L−1, P = 0.04) compared with diabetic controls (20.9 ± 0.8 mmol L−1), whereas those after urapidil 6 mg kg−1 were similar to diabetic controls. Insulin treatment normalized blood glucose concentrations.

Conclusions: The α1-adrenoceptor antagonist/5-HT1A receptor agonist urapidil has no hyperglycaemic effect on experimental diabetes mellitus, even in high doses, despite its 5-HT1A receptor agonistic properties.

Summary

Background and objective: Intrathecal ketamine as the sole anaesthetic agent has demonstrated a lack of cardiovascular depression that should be of advantage in an elderly population. S(+) ketamine has three-times the analgesic potency of R(−) ketamine and its antinociceptive effects after intrathecal administration in rats are known. We decided to evaluate the effects of intrathecal S(+) ketamine added to a small dose of spinal bupivacaine in elderly patients undergoing transurethral prostate surgery.

Methods: Forty males over 60 yr old, scheduled for transurethral prostate resection under spinal anaesthesia, were studied in a prospective, double-blinded, randomized way. Patients were allocated to receive either bupivacaine 10 mg or bupivacaine 7.5 mg combined with S(+) ketamine 0.1 mg kg−1. Spinal block onset time, maximum sensory level, duration of blockade, haemodynamic variables, postoperative analgesic requirements and adverse events were recorded.

Results: Onset times of motor and sensory block were shorter in the bupivacaine plus S(+) ketamine group. Incomplete motor block of the lower extremities was seen in 80% of the patients in bupivacaine plus S(+) ketamine group. Duration of complete motor block and spinal analgesia was shorter in the bupivacaine plus S(+) ketamine group. There was no significant difference in arterial pressure. Heart rate decreased after spinal anaesthesia in the bupivacaine plus S(+) ketamine group and was significantly lower until the end of anaesthesia. The incidence of adverse effects was not different between groups.

Conclusions: Intrathecal S(+) ketamine administered with a low dose of bupivacaine provides shorter motor and sensory block onset time, shorter duration of action and less motor blockade in elderly males.

Background and objective: The aim was to examine the course of intraocular pressure after relaxation with different doses of cisatracurium.

Methods: The investigation was carried out as a prospective, randomized double-blind study in a crossover design in 30 postoperative patients with stable haemodynamic and respiratory function (ASA I and II). To exclude any disrupting factors, patients remained intubated and continuously sedated. Twenty patients received an intubation dose (2 × ED95) of cisatracurium (0.1 mg kg−1) compared with atracurium (0.5 mg kg−1). In a second series, 10 patients were given an effective dose, ED95 (0.05 mg kg−1), and a repeat dose (0.02 mg kg−1) of cisatracurium. The intraocular pressure was determined before (T0) as well as 1 (T1), 5 (T5), 10 (T10), 15 (T15), 20 (T20) and 45 (T45) min after bolus administration.

Results: Intraocular pressure decreased after an intubation dose of either cisatracurium or atracurium, and reached a minimum after 10 min (6.7 ± 2.2 and 7.9 ± 2.1 mmHg, respectively). There was no significant difference between either muscle relaxant (P = 0.27). When lower doses of cisatracurium (0.05 and 0.02 mg kg−1) were applied, the intraocular pressure also decreased, albeit to a lesser extent and with a delayed onset (8.4 ± 1.9 mmHg after 10 min, 9.9 ± 3.4 mmHg after 15 min). There was no significant difference between dosages (P = 0.44).

Conclusions: Cisatracurium is a useful drug in patients when a decrease of intraocular pressure is wanted and where muscle relaxation is necessary and acceptable.

Summary

Background and objective: The aim was to determine the effect of acute and chronic administration of 7-nitroindazole, a selective neuronal nitric oxide synthase inhibitor, on the righting reflex ED50 and the minimum alveolar concentration during sevoflurane anaesthesia in rats.

Methods: 7-Nitroindazole was acutely (0, 50 and 100 mg kg−1) and chronically (0 and 150 mg kg−1 day−1, 4 days) administered to rats. After the preparation, the minimum alveolar concentration and the righting reflex ED50 were measured. The concentration of cGMP in the brain, cerebellum and spinal cord was also measured.

Results: Acute administration reduced the minimum alveolar concentration (50 mg kg−1, 58.8% (95% CI: 50.3–67.3%) of the baseline value, P < 0.01; 100 mg kg−1, 55.8 (46.9–64.7), P < 0.01) and the righting reflex ED50 (50 mg kg−1, 27.2 (17.2–37.2), P < 0.01; 100 mg kg−1, 14.3 (6.6–22.0), P < 0.01). Chronic administration did not reduce the minimum alveolar concentration; however, it reduced the righting reflex ED50 (65.3 (52.9–77.7), P < 0.01). Overall, the reduction in minimum alveolar concentration in the acute and chronic protocol did not correlate with that of the righting reflex ED50. 7-Nitroindazole (100 mg kg−1, acute) reduced the cGMP concentration within the cerebellum by 55.4%; however, it did not decrease concentrations in the brain or spinal cord.

Conclusions: Different mechanisms are responsible for the observed alterations to the minimum alveolar concentration and the righting reflex ED50 following treatment with 7-nitroindazole. The nitric oxide–cGMP pathway might play a less important role in the determination of minimum alveolar concentration than the righting reflex ED50.

A case is presented of a neonate with Hirschsprung's disease, associated with congenital central hypoventilation syndrome. After an ileostomy (at 2 days) and a stoma revision (at 10 days), postoperative pain management was established by continuous intravenous infusion of morphine, which caused severe postoperative respiratory depression. At 6 weeks a reexploration and stoma revision was performed using postoperative epidural analgesia with bupivacaine. This caused no respiratory depression. A colectomy under epidural analgesia at 8 months was also uneventful. Respiratory difficulties in children with congenital central hypoventilation syndrome associated with Hirschsprung's disease are discussed in relation to the technique of choice for postoperative pain management.

Summary

The aim of this Review is to introduce anaesthesiologists to the basic physical principles that are important for their work. A better understanding of the underlying processes during anaesthesia is required for greater safety and efficiency. Relevant physical quantities are presented along with the area of anaesthesiology where they are used. This approach provides better targeting to the needs of practising anaesthesiologists. This text has been a part of a specialist course in anaesthesiology at the University of Ljubljana for some years. Current results show that both the students and the specialist anaesthesiologists now show a better understanding of the underlying physical principles required for their work and are more successful in fulfilling the needs of their practical work.

Summary

Background and objective: To compare the effects of sevoflurane and desflurane anaesthesia on lipid peroxidation.

Methods: We studied 40 healthy patients undergoing elective laparoscopic cholecystectomy. Patients were randomly allocated to be anaesthetized either with sevoflurane (n = 20) or desflurane (n = 20). Anaesthesia was maintained with inspiratory concentrations of sevoflurane 1–1.5 MAC (n = 20) or desflurane (n = 20). Samples were taken for plasma malondialdehyde and superoxide dismutase assays before induction of anaesthesia, before skin incision and at the end of surgery. Alveolar cell samples were obtained from the lungs using the technique of protective blind bronchoalveolar lavage, after induction of anaesthesia and at the end of surgery for malondialdehyde and superoxide dismutase concentrations.

Results: Plasma malondialdehyde increased more after the administration of desflurane than after sevoflurane: after induction 5.9 ± 0.6 nmol mL−1 for desflurane vs. 3.8 ± 0.5 nmol L−1 for sevoflurane (P < 0.001); at the end of the surgery: 6.7 ± 0.4 nmol mL−1 for desflurane vs. 4.2 ± 0.3 nmol mL−1 for sevoflurane (P < 0.001). There was a small but significant increase in plasma superoxide dismutase concentration after desflurane – from 24.2 ± 1.2 to 24.9 ± 0.9U mL−1 after induction and 25 ± 1U mL−1 at the end of the surgery (P < 0.01) but no increase with sevoflurane. Malondialdehyde concentrations increased significantly in the cells obtained by protective blind bronchoalveolar lavage at the end of surgery in the desflurane group (from 0.3 ± 0.1 to 1.7 ± 0.2 nmol mL−1 (P < 0.001)), but not in the sevoflurane group. There were no significant differences between the two anaesthetics in the amounts of superoxide dismutase in the samples obtained by protective blind bronchoalveolar lavage.

Conclusions: Desflurane may cause more systemic and regional lipid peroxidation than sevoflurane during laparoscopic cholecystectomy in healthy human beings.

Summary

Background and objectives: During partial liquid ventilation perfluorocarbons are instilled into the airways from where they subsequently evaporate via the bronchial system. This process is influenced by multiple factors, such as the vapour pressure of the perfluorocarbons, the instilled volume, intrapulmonary perfluorocarbon distribution, postural positioning and ventilatory settings. In our study we compared the effects of open and closed breathing systems, a heat-and-moisture-exchanger and a sodalime absorber on perfluorocarbon evaporation during partial liquid ventilation. Methods: Isolated rat lungs were suspended from a force transducer. After intratracheal perfluorocarbon instillation (10 mL kg−1) the lungs were either ventilated with an open breathing system (n = 6), a closed breathing system (n = 6), an open breathing system with an integrated heat-and-moisture-exchanger (n = 6), an open breathing system with an integrated sodalime absorber (n = 6), or a closed breathing system with an integrated heat-and-moisture-exchanger and a sodalime absorber (n = 6). Evaporative perfluorocarbon elimination was determined gravimetrically. Results: When compared to the elimination half-life in an open breathing system (1.2 ± 0.07 h), elimination half-life was longer with a closed system (6.4 ± 0.9 h, P < 0.01), a sodalime absorber (5.0 ± 0.6 h, P < 0.01) or a heat-and-moisture-exchanger (4.5 ± 0.8 h, P < 0.01). The combination of all three methods (7.1 ± 0.8 h) showed no significant additional effects (P > 0.05) when compared to a closed system. Conclusions: Evaporative perfluorocarbon loss can be reduced effectively with closed breathing systems, followed by the use of sodalime absorbers and heat-and-moisture-exchangers.

Summary

Background and objective: We set out to compare the efficacy of clevidipine and sodium nitroprusside infusions in the control of blood pressure and the haemodynamic changes they produce in hypertensive patients after operation for elective coronary bypass grafting.

Methods: Thirty patients were randomly allocated to receive either clevidipine or sodium nitroprusside after their mean arterial pressure (MAP) had reached >90 mmHg for at least 10 min in the postoperative period. The MAP was continuously measured and related to time. Thus, the efficacy of the drugs in controlling arterial pressure could be inversely related to the total area under the MAP–time curve outside a target MAP range of 70–80 mmHg normalized per hour (AUCMAP mmHg min h−1). Haemodynamic variables and the number of dose-rate adjustments required to maintain MAP were also studied.

Results: There was no statistically significant difference in the efficacy (AUCMAP mmHg min h−1) of clevidipine (106 ± 25 mmHg min h−1) compared with sodium nitroprusside (101 ± 28 mmHg min h−1). Nor was any significant difference found in the total number of dose adjustments required to control MAP within the target range. The heart rate in patients receiving clevidipine increased less than in those given sodium nitroprusside. Stroke volume, central venous pressure and pulmonary artery pressure were significantly reduced upon administration of sodium nitroprusside but not of clevidipine.

Conclusions: There was no significant difference between clevidipine and sodium nitroprusside in their efficacy in controlling MAP. The haemodynamic changes, including tachycardia, were less pronounced with clevidipine than with sodium nitroprusside.

A 21-year-old female weighing 55 kg was anaesthetized for facial reconstruction. After an initial bolus of pancuronium 5 mg and top-up doses of 2 mg at 135 min and 1 mg at 290 min and 335 min, no further relaxant was given for 130 min at which time neuromuscular transmission appeared fully recovered with a full train-of-four twitches and a sustained response to 50 Hz stimulation of the posterior tibial nerve. Subsequently, a single dose of mivacurium 8 mg(2 X ED95) produced extended paralysis with no response to train-of-four stimulation for 85 min. The prolonged effect of mivacurium may have been because of inhibition of plasma cholinesterase by pancuronium. The serum cholinesterase activity 12 h after surgery was 0.38 units mL−1 (normal range 0.65–1.0 units mL−1). There was no evidence of atypical choylinesterase.