British journal of anaesthesia
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Clinical Trial
Effect of surface electrode position on the compound action potential evoked by ulnar nerve stimulation during isoflurane anaesthesia.
The effect of surface electrode positioning on the evoked compound action potential was studied during isoflurane anaesthesia without neuromuscular block. In 20 ASA I-II patients (age 36-50 yr), the response after supramaximal ulnar nerve stimulation was analysed with a neuromuscular relaxation monitor (Relaxograph, Datex) and with a memory recorder. Seven pairs of surface recording electrodes were compared: (1) adductor pollicis muscle vs second finger; (2) adductor pollicis m. vs first finger; (3) first dorsal interosseus m. vs second finger; (4) abductor digiti minimi m. vs fifth finger; (5) adductor pollicis m. vs second dorsal metacarpal; (6) abductor digiti minimi m. vs fourth dorsal metacarpal; (7) thenar vs hypothenar. ⋯ Peak-to-peak amplitude at pair 3 was the greatest (12.5 (SD 3.7) mV) compared with pair 4 (9.4 (SD 2.0) mV) and pair 1 (8.5 (SD 2.0) mV). A close correlation between the amplitudes and integrated areas was found. The first dorsal interosseus muscle response was optimal and the electrodes were simple to fix; this site may be recommended for clinical monitoring.
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Comparative Study
Cerebral effects of sevoflurane in the dog: comparison with isoflurane and enflurane.
The cerebral effects of sevoflurane were compared in dogs with those of enflurane and isoflurane. Initially, the minimum alveolar concentrations (MAC) of sevoflurane and enflurane were determined and the electroencephalographic (EEG) responses to increasing doses of sevoflurane (1.5, 2.0 and 2.5 MAC) or enflurane (1.5 and 2.0 MAC) in unparalysed animals were examined. Administration of sevoflurane was not associated with seizure activity at any concentration either during normocapnia (PaCO2 5.3 kPa) or hypocapnia (PaCO2 2.7 kPa), even in the presence of intense auditory stimuli. ⋯ In a separate group of dogs, the effects of increasing concentrations of sevoflurane and isoflurane (0.5, 1.5 and 2.15 MAC) were compared directly on arterial pressure, cardiac output and heart rate, cerebral blood flow and the cerebral metabolic rate for oxygen (CMRO2) using the venous outflow technique. Sevoflurane, in common with isoflurane, had minimal effects on cerebral blood flow at the concentrations studied, but significantly reduced the CMRO2 at end-tidal concentrations sufficient to produce a burst suppression pattern on the EEG (approximately 2.15 MAC). Both sevoflurane and isoflurane significantly decreased arterial pressure in a dose-dependent manner, but neither drug significantly altered cardiac output.
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We have examined the effects on the cardiovascular system and on regional blood flow of propofol and thiopentone when administered with IPPV (FIO2 0.4). A longitudinal study design was used in which 16 studies were performed in eight sheep for 30 min before, during the last 30 min of 70 min anaesthesia, and for 6 h after anaesthesia. During anaesthesia with propofol and thiopentone, mean total body oxygen consumption decreased, respectively, by 47% (P less than 0.001) and 24% (P less than 0.01) of pre-anaesthesia baseline values, mean heart rate increased by approximately 50% (P less than 0.05) with both agents, mean arterial pressures increased by approximately 50% (P less than 0.05) with both agents and the mean cardiac output was unaltered with propofol anaesthesia but was decreased by 20% (P less than 0.05) with thiopentone anaesthesia. ⋯ Mean hepatic blood flow decreased consistently by a mean of 17% (P less than 0.01) during propofol anaesthesia, and inconsistently during thiopentone anaesthesia so that it was not significantly different from baseline values. Mean renal blood flow decreased during propofol anaesthesia by 7% (P less than 0.05) and by 27% (P less than 0.001) during thiopentone anaesthesia. Whereas most variables returned to baseline values within 2 h after propofol anaesthesia, this took 5 h after thiopentone anaesthesia.
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Randomized Controlled Trial Clinical Trial
Isoflurane with either 100% oxygen or 50% nitrous oxide in oxygen for caesarean section.
Two hundred mothers undergoing general anaesthesia for Caesarean section were allocated randomly to receive either 100% oxygen (group 100) or 50% nitrous oxide in oxygen (group 50), both supplemented with isoflurane. In each group the concentrations of isoflurane were chosen to deliver 1.5 MAC for the first 5 min after induction and 1.0 MAC thereafter. The mean umbilical venous PO2 was greater in group 100 for emergency sections (P = 0.001). ⋯ There were no instances of awareness, although two patients in group 100 and three in group 50 reported dreaming. This study confirms earlier findings that the use of 100% oxygen can significantly improve fetal oxygenation during Caesarean section, with particular benefit in emergency cases. This is associated with a lower incidence of neonatal resuscitation.
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A case of prolonged neuromuscular block following the administration of suxamethonium is reported. Three hours after administration of suxamethonium, a well defined, recovering phase II block was demonstrated with a T4:T1 ratio of 0.25, and neostigmine was administered. Although the T4:T1 ratio was improved to 0.9, T1 remained at 25% of control, and significant paralysis persisted which responded to administration of cholinesterase. It is concluded that neuromuscular monitoring cannot reliably predict reversibility in such cases and that, even after 3 h, antagonism of prolonged suxamethonium block should commence with cholinesterase, followed by neostigmine if necessary.