Articles: closed-circuit-anesthesia.
-
A marked decrease in both personal and environmental pollution with anaesthetic gases as well as in costs is possible with anaesthesia machines which can be run with a low fresh gas flow (FGF) [9]. Low-flow anaesthesia can be performed with appropriately equipped circle systems, although strongly reduced FGF minimises the control of depth of anaesthesia and gas concentrations. Microprocessor-controlled feedback systems allow the utilisation of closed-circuit systems throughout the whole duration of anaesthesia, maintaining full anaesthetic control [3,5]. ⋯ With the method of quantitative anaesthesia as performed by the PhysioFlex, it is now possible to reduce gas expenditure according to the requirements of the patient as well as maintaining full control of anaesthesia depth. Simultaneously, multiple secured feedback control systems guarantee adequate monitoring and storage of respiratory and metabolic parameters. The duration of nitrous oxide wash-out can be a problem, in particular, when a changeover to O2/air is required.
-
A fault in the assembly of a Matrix Large Animal Circle anaesthetic machine resulted in reversal of fresh gas flow through the vaporizer. The fault was discovered only after the sudden development of excessive depth of anaesthesia in two equine patients. Laboratory investigations were conducted to determine the effect of flow reversal on vaporizer output. Results indicated that output concentration was approximately doubled under these conditions.
-
We have studied the automatic administration of alfentanil during alfentanil-nitrous oxide anaesthesia in 11 patients using a closed-loop feedback control system based on EEG analysis. We chose a median EEG frequency of 2-4 Hz as the EEG set point. ⋯ The average effective therapeutic infusion of alfentanil was 0.140 (0.032) mg min-1. We conclude that EEG feedback control may be useful in assessing and defining the dose requirements of alfentanil.
-
The aim of this study was to devise and validate a technique to deliver constant air-oxygen mixtures from a standard anaesthetic machine using only oxygen as the compressed gas source. The common gas outlet was modified to allow measured quantities of ambient air to be insufflated via a three-way attachment into a closed circle absorber system with a double-circuit collapsible bellows ventilator. During positive pressure ventilation, leakages of between 50-150 ml.min-1 occur from the circuit and nomograms of the minimal air and oxygen flow rates needed to maintain constant oxygen concentrations in the presence of the leaks were then mathematically derived. ⋯ Next, the technique was studied on 18 patients who underwent isoflurane or propofol anaesthesia (duration 40-210 min) for various surgical procedures. Pooled mean values (SD) obtained were 29.3% (1.86), 40.95% (1.65) and 50.06% (1.41) respectively for predicted oxygen concentrations of 30, 40 and 50% respectively. We conclude that this technique can be used to deliver constant air-oxygen mixtures accurately during inhalational or total intravenous anaesthesia when N2O is contraindicated but a source of compressed air is not readily available.
-
We studied low flow closed anesthesia technique for oxygen, nitrous oxide and isoflurane using Engström Elsa Anesthesia System in 47 patients undergoing elective surgery. In the low flow group, anesthesia was maintained with oxygen 300 ml.min-1, nitrous oxide 300 ml.min-1 and optimal concentration of isoflurane after endotracheal intubation. The inspired oxygen concentration was kept higher than 35% through the operation. ⋯ In order to maintain the inspired oxygen concentration at 35%, the flow of nitrous oxide should have been reduced as low as to 150 ml.min-1 after 240 min. The volumes of consumption of nitrous oxide and isoflurane in the low flow and minimal flow groups were reduced to one fifth and one third respectively, compared with those of the high flow group. In conclusion, we can perform low flow closed anesthesia safely and easily with this equipment.