Der Anaesthesist
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Oxygen uptake (VO2) and carbon dioxide elimination (VCO2) can be measured with an indirect calorimeter, this method is well established in routine monitoring of ICU patients to evaluate metabolic state as a reflection of stress. In various experimental studies it was demonstrated that anaesthetics can influence whole-body metabolism. The purpose of this study was to examine whether indirect calorimetry can be used intraoperatively during routine anaesthesia and whether presumable changes in metabolism can be detected immediately. ⋯ VCO2 seems to increase less after declamping, perhaps due to the CO2 pool of the organism or to a change in metabolism from carbohydrate to mainly fat oxidation. The results of this study demonstrate that indirect calorimetry can easily be performed during anaesthesia and surgery. Preconditions are a non-rebreathing system without airleak, constant FiO2 < 0.6 and no use of nitrous oxide.
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Epidemiologic studies have shown that trace concentrations of inhalation anaesthetics polluting the air of operating theatres could have deleterious effects on the personnel's health. Nitrous oxide (N2O) oxidises vitamin B12 and thus decreases DNA production by inactivation of methionine synthase. Therefore, the United States and most European health authorities recommend threshold values to protect against potential health risks. ⋯ Exposure to N2O in a climatised RR is determined by several factors: (1) efficacy of air conditioning, with 10.7 changes per hour without recirculation; (2) recovery room size; (3) transport of the patients takes about 15 min, during which some quantities of N2O leave the patient; and (4) high numbers of patients staying 2 and more hours in the recovery room and exhaling smaller concentrations of N2O into the room air. Because of these factors, all measured values are significantly below the standard international threshold values. Under other conditions of room design, such as ventilation and size, measured values may be higher.
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Breathing filters or heat and moisture exchangers (HME), which are placed between a tracheal tube and the Y-piece, allow reuse of breathing tubes without changing between operations. During low-flow and minimal-flow anaesthesia, condensed water accumulates in the breathing circuit. An evaluation of the volume of condensed water is given (Fig. 1). ⋯ For the experiments, a commercial breathing circuit and ventilator (Dräger Sulla 808 + Ventilog) and patient model (Fig. 2) were used; 12 breathing filters/HMEs of different manufacturers were tested. Only 3 filters were not permeable to the test volume of 20 ml water. The authors suggest the water volume be checked routinely and the breathing tubes be emptied if necessary.
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Randomized Controlled Trial Clinical Trial
[Analgesia-sedation for maxillo-facial surgery with midazolam-pentazocine and miazolam-ketamine. Clinical double-blind study of anxiety, analgesia, sedation and amnesia].
Ketamine and midazolam, applied as intravenous medication for conscious sedation in day-case maxillo-facial surgery, has been proven to be superior to pentazocine and midazolam concerning cardiovascular parameters and respiratory depression. The aim of this study was to evaluate the effects of low-dose ketamine/midazolam on anxiety, analgesia, amnesia and subjective feelings. METHODS. 140 out-patients (ASA I) were randomly divided into four groups. The double-blind study was prospective. ⋯ Local anaesthesia (LA), articaine 4% plus epinephrine 1:200,000 (n = 35); test group P/M: LA, additional pentazocine 0.40 mg/kg bw and midazolam 0.075 mg/kg bw i.v. (n = 35); test group K25/M: LA, additionally ketamine 0.25 mg/kg bw and midazolam 0.075 mg/kg bw i.v. (n = 35), test group K50/M: LA, additionally ketamine 0.5 mg/kg bw and midazolam 0.075 mg/kg bw i.v. (n = 35). LA was injected 3 min after application of the systemic medication in the test groups or application of a placebo (saline 0.9%) in the control group. Three further minutes later, operation was started. For evaluation questionnaires, visual analogue scales (VAS) and the state-trait anxiety inventory (STAI) were used. For testing retrograde and anterograde amnesia, acoustic sensations were delivered before application of the systemic medication (a Christmas carol) and during operation (the German national anthem). RESULTS. The control group and the test groups were comparable with regard to biological data, duration of operation, applied dosage of local anaesthetics and actual anxiety before operation. The patients in all test groups rated intraoperative anxiety as mild, in contrast to the control group. Nearly no pain sensation during the operation was remembered in all test groups. Retrograde amnesia was not found in any group. Complete anterograde amnesia was observed in all test groups with respect to the intraoperative sensation, but even in the control group 50% of the patients did not remember having heard the national anthem. As subjective feelings negative criteria were mainly reported in the control group, where as in all test groups positive sensations dominated. Dreams were reported mostly after the higher dosage of ketamine, but no patient experienced any unpleasant dreams. The clinical assessment of the different regimes were excellent for test groups P/M and K50/M, modest for the control group and test group K25/M. Postoperatively, patients of test group P/M were remarkably sedated, but no clinically relevant sedation or motor weakness were observed in the other groups. Postoperative pain sensations were rated more intense in all test groups than in the control group. In test groups P/M and K25/M an increasing pain level was recorded during the postoperative period, with the consequence of a higher demand rate for analgesics. CONCLUSIONS. Dental surgery can be performed safely with low-dose ketamine/midazolam. Compared to pentazocine/midazolam, the higher dosage of ketamine (0.5 mg/kg bw) showed identical results intraoperatively, but was superior during the postoperative period (vigilance), and thus may represent a suitable dosage. The lower dosage of ketamine resulted in worse operating conditions, but a dosage higher than 0.5 mg/kg bw might lead to unconscious sedation and might increase the frequency of unpleasant dreams.