British journal of anaesthesia
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Administration of nitrous oxide is useful for providing sedation and analgesia. The therapeutic range for nitrous oxide is 20-30%. Several oxygen treatment devices have been used for administering nitrous oxide, but little is known about the concentrations of nitrous oxide and oxygen delivered to the trachea. ⋯ With a 1:1 nitrous oxide-oxygen mixture in the primary flow for all systems, end-expired nitrous oxide concentrations varied between 6.5% and 34.3%. Therapeutic concentrations were produced using the Hudson (nominal oxygen concentration 60%) fixed-performance mask, the variable performance Hudson mask at 4 litre min-1, the MC masks at 4 and 6 litre min-1 and the nasal prongs at 6 and 8 litre min-1. Simultaneous end-expired oxygen concentrations for all devices tested were within a safe range.
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We have assessed the characteristics of the Ohmeda Enclosed Afferent Reservoir Breathing System (EAR) using simulated spontaneous ventilation and controlled ventilation. The additional work of breathing through the system was measured and shown to be comparable to that of a modified Mapleson D breathing system (Bain) for fresh gas flows producing similar end-tidal carbon dioxide concentrations. ⋯ Measurement of the volume of carbon dioxide rebreathed using simulated spontaneous ventilation led to the prediction that rebreathing of carbon dioxide would begin to occur in the EAR when fresh gas flow to total ventilation ratio (VF: VE) was approximately 0.87. However, comparison of the results of model lung tests and clinical data suggests that great caution should be taken in extrapolating such results into clinical advice.
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We have studied the effect of halothane on diaphragmatic contractile function by measuring transdiaphragmatic pressure (Pdi) and electromyogram of the diaphragm (Edi) during various stimulation frequencies in 15 pentobarbitone-anaesthetized dogs undergoing mechanical ventilation. We have examined also the effect of halothane on the fatigued diaphragm by repeating the measurements 5, 10, 15, 30, 60 and 90 min after 30 min of tetanic stimulation applied to the phrenic nerves. Administration of 1-2 MAC of halothane did not affect Pdi at any given stimulation frequency. ⋯ Edi was unaffected by halothane, except for a small decline during 100-Hz stimulation with 2 MAC. In contrast with the changes in Pdi, Edi during recovery from fatigue was the same as that determined before fatigue. It is concluded that halothane, in clinical concentrations, did not depress the contractile function of fresh or fatigued diaphragm in vivo.
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Randomized Controlled Trial Multicenter Study Comparative Study Clinical Trial
Efficacy of orally administered ondansetron in the prevention of postoperative nausea and vomiting: a dose ranging study.
In a placebo-controlled, double-blind study, we have compared the efficacy of ondansetron 16 mg, 8 mg and 1 mg administered 8-hourly for prevention of postoperative nausea and vomiting. We studied 995 patients undergoing major gynaecological surgery; 982 were included in the analysis. ⋯ The frequency of nausea was 75%, 70%, 56% and 55% after placebo and ondansetron 1 mg, 8 mg and 16 mg, respectively; the corresponding frequencies of vomiting were 60%, 55%, 37% and 37%. Ondansetron 8 mg was as effective as 16 mg and both resulted in significant reductions in nausea and vomiting compared with placebo and ondansetron 1 mg (P less than 0.001).
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Randomized Controlled Trial Comparative Study Clinical Trial
IV diclofenac in post-thoracotomy pain.
We have studied the efficacy of a continuous i.v. infusion of diclofenac 2 mg kg-1/24 h given for 2 days after major thoracic surgery in 30 patients in a double-blind, placebo-controlled, parallel-group design. The patients were able to obtain additional pain relief as on demand morphine boluses. In the diclofenac group, the consumption of morphine was reduced by 60% during the first and by 76% during the second day after operation compared with the control group. ⋯ Urine output was significantly less during the first day after operation in the diclofenac group compared with the control group, but was normal on the second day after operation; plasma creatinine concentrations were unchanged. I.v. diclofenac infusion combined with opioids delivered via a patient-controlled analgesia device seems a valuable method of pain relief after thoracic surgery in patients in whom more invasive techniques, such as extradural local anaesthetics and opioids, cannot be used. However, non-steroidal anti-inflammatory drugs should be used cautiously, if at all, in patients who are at risk of acute renal failure.