British journal of anaesthesia
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Randomized Controlled Trial Clinical Trial
Influence of pulse oximeter lower alarm limit on the incidence of hypoxaemia in the recovery room.
In a prospective, randomized study, we have investigated the effects of two arbitrary pulse oximeter lower alarm limit (LAL) settings (90% = group 90, n = 320 and 85% = group 85, n = 327) on the incidence of hypoxaemia in the recovery room. In group 90, we calculated the theoretical effect of elimination of transient episodes of low pulse oximeter oxyhaemoglobin saturation (SpO2) by introducing a time delay between the onset of the alarm condition and triggering of the alarm. When only hypoxaemic episodes lasting more than 1 min were included, SpO2 < or = 90% occurred in 11% of patients in group 90 and in 20% in group 85 (relative risk (RR) 1.84, confidence interval (CI) 1.26-2.69; P < 0.01). ⋯ Introducing a theoretical delay of 15 s in group 90 between crossing the alarm threshold and triggering the alarm would have reduced the number of alarms by 60%. The results of the study suggest that decreasing the alarm limit in an attempt to reduce frequent false alarms may lead to an increase in more relevant episodes of hypoxaemia and setting the LAL at 85% cannot be recommended routinely. Introducing a 15 s delay in group 90 would reduce the number of alarms by the same amount as changing the LAL from 90% to 85%.
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Randomized Controlled Trial Clinical Trial
Does nitrous oxide antagonize sevoflurane-induced hypnosis?
We have studied 64 ASA I and II patients (aged 20-60 yr) to determine if nitrous oxide affects sevoflurane requirement for achieving 50% probability of no movement in response to verbal commands (MACawake). Patients were allocated randomly to one of four nitrous oxide concentration groups (0, 20, 40 and 60 vol.%). Patients in each group received sevoflurane at two different end-tidal concentrations according to a predetermined randomization table. ⋯ The MACawake for sevoflurane was 0.63% and this was reduced significantly in a non-linear manner by increasing nitrous oxide concentration. A 50% reduction in MACawake was produced by a nitrous oxide concentration of 45%. The reduction in MACawake by nitrous oxide was non-linear; the interaction coefficient between nitrous oxide and sevoflurane being significantly less than zero (P = 0.0238), indicating that the reduction in MACawake by nitrous oxide was smaller than would be expected from simple additivity and that nitrous oxide antagonized the effects of sevoflurane in preventing response to verbal commands.
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Case Reports
Thermal softening of tracheal tubes: an unrecognized hazard of the Bair Hugger active patient warming system.
The Bair Hugger system is a new and highly effective active patient warming system which produces a layer of warm air between the patient and the warming system. We report an instance of marked softening and distortion of a polyvinyl chloride tracheal tube caused by this layer. We also present laboratory data indicating that this is a likely problem under routine theatre conditions, with suggestions for prevention.
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We have investigated the effect of temperature on the blood-gas solubility of desflurane, sevoflurane, enflurane and halothane. Blood was equilibrated with gas mixtures of known composition in open cuvette or closed flask tonometers over a temperature range of 29-39 degrees C, and the concentration of each anaesthetic in blood was measured at 37 degrees C by repeated headspace analysis using a gas chromatograph. Solubility increased by 5.4% of the solubility at 37 degrees C for each degree that equilibration temperature was reduced. This result was true for all anaesthetics in all blood samples, and is in keeping with results for other volatile anaesthetics.
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A retrospective review over 6 yr of patients presenting to the hand clinic was performed to identify cases of postoperative brachial plexopathy (PBP) and to assess both prognosis and early indices of prognosis. Over this period (1989-1995), 22 patients were referred by the hospital's surgical departments to the hand clinic because of PBP. Eight cases followed open heart surgery (OHS) and 14 followed non-cardiac surgery (NCS). ⋯ At a 1 week "prognostic milestone", 79% of NCS patients with significant symptomatology enjoyed complete recovery although this took as long as 5 months to 1 yr in 50% of patients. At a 6-8 week "prognostic milestone", 50% of those who had not yet had improvement in the motor deficit suffered residual neurological deficit. All patients recovered to a significant extent even when recovery was not complete and none suffered from late deterioration or chronic pain.