Humidity and Temperature Changes during Low Flow and Closed System Anaesthesia

Water humidity and temperature were measured in the proximal end of the inspiratory limb in anaesthetic circuits used to anaesthetize three groups of adult patients using various fresh gas flows (FGF). Humidity increased as FGF's were lowered, with 98% water humidification achieved when FGF's of less than 0.5 1/min were administered. Temperature at the same site changed about 1–2.5C in inverse proportion to the volume of FGF. This advantage of closed system and low flow anaesthesia is a further reason for their wide-spread utilization.     

Flow Pattern and Respiratory Characteristics during Halothane Anaesthesia

Using pneumotachography, the flow pattern was analysed in detail and tidal volume, respiratory rate, dead-space to tidal volume ratio (VD/VT) and carbon dioxide output were measured in adults (Group A, n = 12) and 3-8-year-old children (Group B, n = 10) during spontaneous breathing anaesthesia with halothane and surgery. The respiratory cycle was divided by equidistant points into 40 parts and the flow at each point related to peak inspiratory and expiratory flow. Thus a relative flow pattern was derived. This relative flow pattern was almost identical in both groups. Characteristically, the flow curve showed rapid turns from high expiratory to high inspiratory flow rates without any end-expiratory flow pause (except in one adult). The minute ventilation was 6.6 +/- 2.0 1 X min-1 in Group A and 3.4 +/- 0.6 1 X min-1 in Group B, being correlated both to body weight and body surface area in Group A but not in Group B. The tidal volume was 210 +/- 60 ml in Group A and 78 +/- 13 ml in Group B, respiratory rate 31 +/- 4 X min-1 and 44 +/- 10 X min-1, respectively, and the VD/VT ratio 0.40 +/- 0.10 and 0.55 +/- 0.12, respectively. Carbon dioxide output was 173 ml X min-1 (STPD) in the adults and 82 +/- 13 ml X min-1 (STPD) in the children. It was correlated to both body weight and body surface area in the adults but not in the children.     

Influence of Anaesthesia on Blood Flow to the Calves During Surgery

The blood flow to the calves during abdominal surgery under different kinds of general anaesthesia was measured by strain gauge plethysmography in 12 patients. The volume flow increased 100% during surgery in both light and deep anaesthesia, caused by a decrease in peripheral resistance. The increase in volume flow could partly be explained by the anaesthesia itself, possibly induced by the use of a nitrous oxide-oxygen gas mixture. The surgical procedure caused a further increase in volume flow. Possible underlying mechanisms are discussed.     

Anaesthesia for the elderly

The elderly constitute a group of patients who, in addition to their recognized pathology, may also suffer from age related changes in organ systems, deficiencies of which may be manifest as failure in the perioperative period. The significance of systolic hypertension and rigid arteries has attracted relatively little attention in anaesthetic literature. The problem of cognitive failure after major surgery remains a substantial problem of which anaesthetists need to be aware.     

Anaesthesia for the neonate

Canadian Journal of Anesthesia/Journal canadien d'anesthésie -