[Variations of esophageal temperature during general anesthesia with a low-flow circuit].

BACKGROUND: Anaesthesia drugs cause the cutaneous vasodilatation that produces core temperature lowering at the beginning of general anaesthesia; when the thermal threshold for vasoconstriction is reached the cutaneous heat losses are decreased. Furthermore, the soda lime begins to produce water and heat after 40 minutes of closed circuit ventilation. WORK HYPOTHESIS: The technique of inhalatory anaesthesia affects the thermal loss of patients after some hours of ventilation. DESIGN: Prospective randomized clinical trial. SETTING: Surgical Clinical operating theatre of the University of Florence. PATIENTS: 50 patients submited to abdominal non vascular surgery, for longer than 2 hours, with xifo-pubic cut, subdivided into two groups with the same anthropometric characters and age; the first ventilated with open system, the second with low flow circuit (fresh gas flow 700 ml/min). STATISTIC: "t" Student test; MEASURES: Lower one third oesophageal and inspiratory jaw of the circuit temperatures recorded for three hours. MAIN RESULTS: The savings of low flow anaesthesia begin to be significant in the third hour of anaesthesia. CONCLUSIONS: The thermal saving of closed circuit anaesthesia is, very probably, related to the humidifying and the warming of inspired air by soda lime reaction; the effect is more evident if cutaneous losses are reduced.