Summary

Background and objective: To evaluate and compare the effect of two clinically available central nervous system stimulants, namely doxapram and aminophylline on arousal from sevoflurane anaesthesia and bispectral index. Methods: This randomized, double-blind, placebo-controlled, prospective study was conducted in 90 adult females, ASA I–II, scheduled for elective lower abdominal surgeries at Taipei Medical University Hospital. At 5 min before the completion of surgery, under sevoflurane anaesthesia, patients were divided into three groups to receive doxapram 1 mg kg−1, aminophylline 2 mg kg−1 or saline placebo intravenous. Standard vital signs, end-tidal CO2, end-expiratory sevoflurane concentration, bispectral index and neuromuscular blockade were measured plus clinical parameters of recovery from general anaesthesia. Results: Compared with the control group, patients receiving doxapram or aminophylline showed a similarly faster recovery from sevoflurane anaesthesia correlated with increase in bispectral index. Conclusion: Intravenous administration of doxapram 1 mg kg−1 or aminophylline 2 mg kg−1 hastened the early recovery from sevoflurane anaesthesia. The arousal effect of aminophylline and doxapram appears to be similar.

Summary

Background and objective: Malignant hyperthermia is an inherited disorder of skeletal muscle characterized by muscle contracture and hypermetabolic crisis following exposure to halogenated anaesthetics and depolarizing muscle relaxants. We planned this follow-up to get more information about the safety of non-triggering anaesthesia in susceptible patients; the safety of the use of trigger agents in non-susceptible patients and any minor sequelae following the biopsy. Methods: A questionnaire was sent to 244 patients tested for susceptibility between 1998 and 2004 enquiring about sequelae from the biopsy, subsequent experience with anaesthesia and difficulties encountered because of the investigation. Results: Replies were received from 129 patients. Thirty-four complained about sequelae from the biopsy: 10 reported headache and nausea; 16 experienced pain and a lack of strength in the biopsed leg and 8 found the scar less than satisfactory. Ten patients found it difficult to find a diagnostic centre. Eighteen reported problems and/or delay when they had needed a subsequent anaesthetic. Fourteen patients found the anaesthesiologist reluctant to anaesthetize them and four experienced a delay. Forty-three patients received anaesthesia since their biopsy. Complete medical records were available for 24 anaesthetic exposures in 23 patients. No documented perioperative complications occurred. Only three non-susceptible patients received one trigger agent. Conclusions: It is safe to use trigger-free anaesthesia in susceptible patients. The difficulties encountered by patients to be anaesthetized and the management of the majority of non-susceptible patients during general anaesthesia show the need of more accurate educational programmes and methods for promoting patient-centred care.

Background and objective Few and conflicting data are available regarding the changes of plasma potassium concentration during acute respiratory acidosis in human beings. This study compares the acute changes in plasma potassium concentration in acutely hypercapnic patients and in non–hypercapnic patients during general anaesthesia.

Methods Thirty-three patients undergoing interventional rigid bronchoscopy were studied. Ventilation of the lungs was randomly conducted using either spontaneous–assisted ventilation or intermittent negative–pressure ventilation. All patients received the same anaesthetic protocol. Arterial blood gases and osmolality, and plasma concentrations of glucose, sodium, potassium and chloride were measured.

Results Intraoperatively, PaCO2 was higher during spontaneous-assisted ventilation than during intermittent negative-pressure ventilation (9±1.8 vs. 5.4±1.2 kPa, P < 0.001) and the pH was also lower during spontaneous-assisted ventilation than during intermittent negative-pressure ventilation (7.24±0.07 vs. 7.4 ±0.08, P < 0.001). Plasma potassium concentration remained similar in both groups (3.8± 0.2mmolL−1 with spontaneous–assisted ventilation vs. 3.7± 0.4mmol L−1 with intermittent negativepressure ventilation).

Conclusion Acute respiratory acidosis does not affect plasma potassium concentration.

Summary

Background and objective: Isoflurane is commonly used for neurosurgery but the effects of sevoflurane on human cerebral blood flow and cerebral metabolic rate of oxygen have not been fully evaluated. We therefore assessed the effects of sevoflurane and isoflurane on global cerebral blood flow and cerebral metabolic rate of oxygen in patients without noxious stimuli or neurological disorders.

Methods: General anaesthesia was induced with midazolam (0.2 mg kg−1) and fentanyl (5 μg kg−1) in 20 ASA I patients undergoing knee joint endoscopic surgery. Epidural anaesthesia was also performed to avoid noxious stimuli during surgery. Cerebral blood flow and cerebral arteriovenous oxygen content difference was measured using the Kety–Schmidt method with 15% nitrous oxide as a tracer before and after administration of either sevoflurane or isoflurane (1.5 minimum alveolar concentration, 60 min) and cerebral metabolic rate of oxygen was then calculated.

Results: Sevoflurane and isoflurane both increased cerebral blood flow (17%, P < 0.05; 25%, P < 0.05, respectively) and decreased cerebral metabolic rate of oxygen (26%, P < 0.01; 38%, P < 0.01, respectively). There were no significant differences in cerebral blood flow and cerebral metabolic rate of oxygen between sevoflurane and isoflurane.

Conclusions: Sevoflurane and isoflurane similarly increased cerebral blood flow and decreased cerebral metabolic rate of oxygen in human beings anaesthetized with midazolam and fentanyl.

Background and objective: The aim was to compare the effects of two different priming doses and priming intervals with the standard intubating dose of rocuronium on the onset time and intubation conditions.

Methods: After induction of anaesthesia, 75 patients were randomly assigned to one of five groups. Patients in Group 1 received a priming dose of rocuronium 0.06 mg kg−1 followed 2 min later by rocuronium 0.54 mg kg−1, Group 2 received a priming dose of 0.10 mg kg−1 followed 2 min later by a rocuronium injection of 0.50 mg kg−1. Group 3 was given a priming dose of 0.06 mg kg−1 followed 3 min later by administration 0.54 mg kg−1, where Group 4 received a priming dose of 0.10 mg kg−1 followed 3 min later by injection of 0.50 mg kg−1. Group 5 received a placebo injection followed 3 min later by rocuronium 0.60 mg kg−1.

Results: Priming with a 3 min priming interval shortened the onset time of rocuronium irrespective of the dosage of (P < 0.001). Clinical duration of action was significantly longer after priming in Group 4 than in Group 5. Clinically acceptable intubation conditions were obtained in all patients.

Conclusions: Priming with a 3 min priming interval was effective when rapid tracheal intubation with rocuronium was necessary. However, priming with rocuronium should be used carefully with special attention given to the possibility of hypoxia and aspiration of gastric contents in awake patients.

We determined the effects of pretreatment with midazolam or fentanyl on the ease of laryngeal mask airway insertion using propofol without a muscle relaxant. One hundred and eighty ASA class I or II patients were randomly allocated to one of three groups, 60 patients per group, to receive either placebo (Group C), midazolam 0.05 mg kg−1 (Group M) or fentanyl 2 μg kg−1 (Group F), respectively. Following intravenous administration of these drugs, Group C received propofol 2.5 (Group C-2.5) or 3.0 mg kg−1 (Group C-3.0). Group M and Group F received propofol 2.0 or 2.5 mg kg−1 (Group M-2.0, M-2.5, F-2.0 and F-2.5, respectively). There was a smaller incidence of severe head and limb movements on LMA insertion in Group M-2.5, Group F-2.0 and Group F-2.5 than in Group C-2.5. Airway obstruction and inadequate jaw relaxation, which were occasionally recognized in Group C and Group F patients, were not observed in Group M-2.5. Overall the ease of LMA insertion was significantly better in Group M-2.0, Group M-2.5 and Group F-2.5 than in Group C 2.5, however, the blood pressure in Group F after LMA insertion was significantly lower than in Group M. We conclude that pretreatment with midazolam 0.05 mg combined with propofol 2.5 mg kg−1 provides safe and satisfactory conditions for LMA insertion.

The microbiological contamination of 250 breathing system tubes after use in anaesthesia circle systems with reduced fresh gas flow was investigated. The lungs of 50 patients were ventilated without any filtering device between the endotracheal tube and the Y-piece. A total of 51, 49 and 100 patients, respectively, were given different types of heat and moisture exchanger with electret filters (HMEF). With no filtering device the tubing system was contaminated by micro- organisms originating from the patient's tracheal secretion in 13% of the patients. In contrast, no bacterial migration into the tubing system was detected when any of the investigated HMEF-devices were used. We therefore conclude that heat and moisture exchangers with electret filters prevent contamination of the anaesthesia breathing system with microorganisms from the patients airways.

Postoperative renal impairment is a recognized complication of infrarenal aortic cross-clamping. Fenoldopam, a selective dopamine agonist, may increase renal blood flow and decrease tubular oxygen consumption. The objective of this study was to quantify the effects of fenoldopam (0.1 μg kg−1 min−1) on renal blood flow and renal tubular function in anaesthetized dogs that have undergone aortic cross clamping. Eight labrador dogs were selected to receive either saline or fenoldopam (0.1 μg kg−1 min−1) intravenously. Arterial pressure, heart rate, renal blood flow, urinary output, fractional excretion of sodium, creatinine clearance and lithium clearance were measured (a) prior to infusions of saline or fenoldopam (b) 1 h after commencing the infusion (c) during a 90 min period of infrarenal aortic cross-clamping with concurrent infusion of fenoldopam or saline and (d) for 1 h after simultaneous aortic declamping and discontinuation of the infusions. There was no haemodynamic instability upon commencing the infusion of fenoldopam (0.1 μg kg−1 min−1). Creatinine clearance (2.03±0.5–2.45±0.3 mL min−1 kg−1 (mean±SD)), urine output (0.23±0.16–0.35±0.23 mL min−1 (mean±SD)), and fractional excretion of sodium (0.7±0.52–1.3±0.73% (mean±SD)) increased (P < 0.05), following commencement of the fenoldopam infusion. Fractional excretion of sodium (1.2±0.7% (mean±SD)) and urine output (0.36±0.21 mL min−1 (mean±SD)) were maintained during the aortic cross-clamp period (P < 0.05). Renal blood flow increased when the fenoldopam infusion was commenced (145±43.3–161±39.2 mL min−1 (mean±SD)) and remained greater than baseline during the aortic cross-clamping period (152±44 mL min−1 (mean±SD)), although these increases did not reach statistical significance. The most striking abnormalities observed by electron microscopy were marked disruption of the microvillus brush border in proximal tubules, vacuolation and separation of epithelial cells on basolateral infolds. The changes were similar in the two groups. In conclusion fenoldopam (0.1 μg kg−1 min−1) may have renoprotective effects which persist during infrarenal aortic cross clamping.

The effects of adding midazolam and bupivacaine to human cerebrospinal fluid in glass test tubes were examined by looking for changes in pH and a reduction in the transparency of the solution. Midazolam (n=6), 0.25% bupivacaine (n=6), 5 mg of midazolam in 6 mL of 0.25% bupivacaine (n=6) and 5 mg of midazolam in 10 mL of saline (n=6) were added to 1.5-mL samples (n=24) of cerebrospinal fluid taken at the time spinal anaesthesia was begun. Transparency and pH were checked after each increment. Cerebrospinal pH was decreased to below 7.0 by adding more than 3 mg of midazolam, more than 1.9 mL of 0.25% bupivacaine or 1.3 mL of the mixture. Cerebrospinal transparency was decreased by adding more than 0.7 mg of midazolam, 1.1 mL of 0.25% bupivacaine or 0.6 mL of the mixture. Midazolam in saline neither decreased the pH below 7.0 nor reduced transparency. These results do not suggest that clinically useful doses of intrathecal or epidural midazolam are neurotoxic.

Summary

Background and objective: Thiopental has been reported to reduce sympathetic tone, however, it is not clear whether change in heart rate variability is associated with depth of anaesthesia. The purpose of the present study was to evaluate changes in heart rate variability at different depths of hypnosis during induction of anaesthesia with thiopental. Methods: We studied 17 ASA I patients scheduled for minor surgery. The depth of hypnosis was monitored by the BIS. Spectral analysis of heart rate variability using a maximum entropy method resulted in a characteristic power spectrum with two main regions, a high frequency and a low frequency. Haemodynamics, entropy, low frequency, high frequency and low frequency/high frequency were monitored in an awake state and after the induction of anaesthesia. Results: Heart rate increased in a BIS-dependent manner, whereas blood pressure showed no significant changes during the study period. High frequency, entropy and low frequency decreased with a reduction in the BIS value. Low frequency/high frequency showed no significant change during the study period. Conclusions: Induction of anaesthesia with thiopental increased heart rate and decreased high frequency, entropy and low frequency in a BIS-dependent manner, indicating that thiopental reduces cardiac parasympathetic tone depending on the depth of hypnosis.

Summary

Perioperative brain protection refers to prophylactic measures instituted during the perioperative period to prevent or reduce ischaemic damage and to improve neurological outcome. In that context, strategies for protecting the brain rely on the control of physiological variables, anaesthesia, administration of non-anaesthetic pharmacological agents and preconditioning. Avoiding hyperthermia, hyperglycaemia and arterial hypotension are passive neuroprotective measures acknowledged in human beings. The protective effect of anaesthesia, compared to the awake state, is demonstrated in animals but remains to be validated in clinical practice. Laboratory studies investigating pharmacological neuroprotection have shown interesting results but most clinical trials have been disappointing except for a few drugs in specific settings. Preconditioning which results in the induction of some resistance to ischaemia appears as a promising strategy. Up to now, the translation of beneficial experimental results into clinical success is considered an entirely permissible hope but remains an unachieved objective.

Background and objective: The effect of anaesthesia and surgery on gastric emptying is not constant, and this has not been previously studied in patients undergoing thoracotomy for lung resection with a bupivacaine-fentanyl epidural infusion for analgesia. There are important implications in this group of patients with regards to the recommencement of important oral medication as well as the risks of aspiration of gastric contents. The study examined gastric emptying in these patients until the second postoperative day.

Methods: In a prospective repeated measures study, the effect of fentanyl-bupivacaine epidural analgesia at the mid-thoracic level on gastric emptying was assessed in 11 patients undergoing thoracotomy for lung resection. Gastric emptying was measured using a paracetamol absorption technique. Patients acted as their preoperative controls and were assessed 4 h postoperatively and on the second postoperative day.

Results: The mean (SEM) maximum plasma paracetamol concentration was 204.6 (20.4) μmol L−1 before operation, 61 (9.5) μmol L−1 4 h postoperatively and 114.3 (22.6) μmol L−l on the second postoperative day. Mean (SEM) paracetamol absorption at 120 min was 15 638 (1441) μmol min L−l preoperatively, 5731 (821) μmol min L−l4 h postoperatively and 9325 (1759) μmol min L−l on the second postoperative day. Postoperative values were significantly (P < 0.005) less than the preoperative values.

Conclusions: After thoracotomy, gastric emptying was delayed until at least the second postoperative day in patients receiving mid-thoracic fentanyl-bupivacaine epidural analgesia.