Andrew B. Carlson

Warm Water Cooling

The production of hypothermia by surface cooling is a well-established and documented subject. This type of hypothermia is used in a wide variety of operations in neurological and cardiovascular surgery. The technique for inducing surface cooling as described in most publications on the subject is fairly well standardised. Premedication of these patients varies with authors and their anaesthetic techniques. Phenothiazines, in particular chlorpromazine, are commonly used. Anti-sialogogues, atropine or hyoscine are given and the patients anaesthetised by techniques usually practised in the particular centre. Maintenance may be by controlled or spontaneous respiration, though the former is often preferred. Volatile anaesthetics, mainly halothane or ether, are added to the gases. Cooling may be between blankets, in a bath or in a cabinet. The last-named method has many advantages, but owing to the apparatus required is not widely used. Water is the commonest surface coolant, and it is with its use that this study is concerned. The common factor in all the techniques detailed above is the use of cold water. Some authors take 6°C. as their temperature, others prefer iced water. The pattern of cooling with cold water is constant. Initially oesophageal, rectal and pharyngeal temperatures show little change. The skin temperature falls at once, as might be expected, and rapidly goes on falling to near that of the water. After 10 to 15 minutes the deep temperatures begin to fall, the oesophageal and pharyngeal leading the rectal. When cooling is stopped, by removing the patient from the bath, or warming the blankets, the “after-drop” sets in. The deep temperatures fall a further 2” to 4” as the cold peripheral tissues of the body “shell” are warmed from within. The rectal temperature is the last to fall to the desired level. Although widely used, this technique seems to suffer from several disadvantages. The peripheral tissues become extremely vasoconstricted, no matter what vasodilators are used. Metabolic acidosis is a well-known complication of hypothermia, even by extracorporeal methods. The greater the cooling of the peripheral tissues, the greater the acidosis, both from vasoconstriction and