Anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
The effect of cerebrospinal fluid dilution of isobaric 0.5% bupivacaine used for spinal anaesthesia.
A prospective study was conducted to see the effect on spinal anaesthesia of the dilution of isobaric 0.5% bupivacaine with cerebrospinal fluid. Sixty patients were randomly allocated to three groups. In group 1, patients received 3 ml isobaric 0.5% bupivacaine intrathecally without aspirating cerebrospinal fluid. ⋯ The only statistical difference was the time to reach complete motor block, which was shorter in group 1 as compared to groups 2 and 3 (6.9 SD 1.4 min versus 11.3 SD 3.0 and 13.5 SD 3.9 min respectively). The mean value of maximum decrease in systolic blood pressure was small, being less than 15% of the pre-operative value for each group. In conclusion, the effect of diluting isobaric 0.5% bupivacaine with cerebrospinal fluid, 1 ml and 2 ml, is minimal and it is an unnecessary procedure with limited clinical effect.
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Increased duration of anaesthetic administration has implications for recovery from anaesthesia, has cardiovascular effects, and potential for toxicity through metabolism and breakdown of the anaesthetics. Recovery of function after desflurane or sevoflurane anaesthesia, because of the low blood gas and tissue solubilities of these agents, is more rapid than after halothane, isoflurane or enflurane, with recovery being most rapid after desflurane. Increased duration of anaesthesia amplifies the differences in rate of recovery because of the additional anaesthetic (greater with more soluble agents) dissolved in tissues. ⋯ Sevoflurane undergoes considerable metabolism, producing free fluoride ion, with plasma concentrations proportional to dose and duration of anaesthesia exceeding 50 microM in approximately 7% of patients. In rats, the effects of a toxic breakdown product of sevoflurane, CF2 = C(CF3)OCH2F (compound A), are also dose- and duration-dependent, with lower concentrations producing toxic effects as duration of exposure increases. The clinical importance of the metabolism and in vitro breakdown of sevoflurane has still to be adequately tested.
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Desflurane is a new volatile, inhaled anaesthetic that differs significantly from presently available inhaled agents in being halogenated solely with fluorine. This fluorination produces a lower solubility and increased resistance to biodegradation. ⋯ Limitations include a lesser potency and greater pungency at concentrations exceeding 1 minimum alveolar concentration (MAC). Other pharmacological properties are similar to those of isoflurane.
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In 1994, 66% of all surgery in the USA was performed as ambulatory surgery. Day surgery is also expanding to other countries worldwide. To provide safe anaesthesia and good outcomes for longer and more extensive operations performed in ambulatory facilities, patients must be carefully evaluated before surgery, their home readiness must be assessed, and they must fully understand all relevant information. ⋯ If a patient does not have an escort home, the surgical procedure should be cancelled or the patient admitted to the hospital. As the number of patients and complexity of scheduled surgical procedures increases, the outcome of day surgery will increasingly depend on the anaesthetist's skills. The recently introduced short-acting drugs may further improve the outcome after day surgery by facilitating rapid recovery and an early return to normal daily activities.
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Although many anaesthesia machines are equipped with circle rebreathing systems, inhalational anaesthesia remains frequently performed using relatively high fresh-gas flows. The major advantages of rebreathing techniques can be achieved only if the fresh-gas flow is reduced to 1 l.min-1 or less. Although there are potential risks associated with low-flow anaesthesia, modern anaesthesia machines meet all the technical requirements for the safe use of low-flow techniques if they are used in conjunction with equipment for monitoring inhaled and exhaled gas concentrations; these monitors are already increasingly available and, in the near future, are likely to become an obligatory safety standard in many countries. For both economic and ecological reasons, the use of new inhalational anaesthetics, with low tissue solubility and low anaesthetic potency, can be justified only if the efficiency of administration is optimised by using low-flow anaesthetic techniques.