British journal of anaesthesia
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Comparative Study
Use of the laryngeal mask airway after oesophageal intubation.
We have compared insertion of a tracheal tube and laryngeal mask airway (LMA) both with and without the presence of a tube in the oesophagus in 20 ASA I and II patients undergoing elective laparoscopy. After induction of anaesthesia and neuromuscular block, we measured the times for an experienced anaesthetist to correctly position both an LMA and a tracheal tube with and without a tube in the oesophagus. The time to intubation was significantly less with the LMA than with the tracheal tube, both with and without an oesophageal tube in place (P < 0.05). We conclude that if a tracheal tube is placed unintentionally in the oesophagus, an LMA may be used subsequently to provide rapid and effective oxygenation of the patient.
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We have studied the effects of nitrous oxide on cerebral blood flow (CBF), cerebral blood flow velocity (CBFV) and intracranial pressure (ICP) during isoflurane-induced hypotension in 10 pigs. CBF was measured using laser Doppler flowmetry, CBFV in the right middle cerebral artery was calculated using Doppler ultrasound and ICP was measured using an extradural ICP monitor. Each animal was studied under four conditions, examined sequentially: (i) mean intra-arterial pressure (MAP) 85 mm Hg, maintained with isoflurane, (ii) MAP 50-55 mm Hg, induced by isoflurane only, (iii) MAP 85 mm Hg, maintained with isoflurane and 50% nitrous oxide, and (iv) MAP 50-55 mm Hg, induced by isoflurane and 50% nitrous oxide. ⋯ Comparing isoflurane-induced hypotension ((ii) vs (iv)), there was no statistical difference in either CBF or CBFV on addition of 50% nitrous oxide. The correlation between changes in CBF and CBFV was not significant. We conclude that the use of nitrous oxide during isoflurane-induced hypotension has no significant effect on CBF, CBFV or ICP compared with the use of isoflurane alone.
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Mechanical hyperventilation may produce hypocapnic apnoea below the carbon dioxide off-switch threshold whereas an increase in arterial PCO2 after post-hyperventilation apnoea causes reappearance of respiratory effort above the carbon dioxide on-switch threshold. To study the effects of surgical stimulation on these two thresholds, we have measured end-tidal PCO2 (PE'CO2) at the two thresholds, before and during surgical stimulation, in 14 patients undergoing mastectomy, anaesthetized with sevoflurane (1.2 MAC). Based on the reproducibility of the results, data from 11 patients were analysed and data from the three other patients were discarded. ⋯ During surgical stimulation, resting PE'CO2' off-switch threshold and on-switch threshold were 4.8 (0.2), 4.1 (0.2) and 4.7 (0.2) kPa, respectively. Although the off-switch threshold was significantly less than resting PE'CO2 (P < 0.01), there were no significant differences between resting PE'CO2 and on-switch threshold. These results indicate that surgical stimulation does not affect equally the carbon dioxide on- and off-switch thresholds.
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A 22-yr-old male had a head injury after a road traffic accident. His trachea was intubated for 5 days with a high-volume, low-pressure cuffed tracheal tube. ⋯ The patient underwent resection anastomosis of the destroyed tracheal segment which, on histological examination, showed fibrous tissue and bone formation. It is believed that excessive cuff pressure was the cause of the damage, as monitoring cuff pressure has not yet become a routine practice in anaesthesia and intensive care.
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The effect of temperature on the potencies of neuromuscular blocking agents remains unclear. This study was undertaken to examine the effects of different neuromuscular blocking agents at 37 and 27 degrees C at a constant carbon dioxide content (alpha stat principle). The effect of neostigmine 1 mumol litre-1 induced antagonism of these agents was also investigated. ⋯ The ratios of IC50 (inhibitory concentration, 50%) with and without neostigmine at hypothermia were slightly higher for the steroidal agents, indicating slight enhancement of antagonism by neostigmine at 27 degrees C. In contrast, the ratios were significantly greater at 27 degrees C (P < 0.05) for isoquinolinium agents, implying significant enhancement of antagonism. Our results indicate that at 27 degrees C the potency of all steroidal agents increased and neostigmine-induced antagonism was slightly enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)