432 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



REFERENCE 



1. Adams-Ray, J., and Persson, P. O. : En ny metod for nedkylning av forsoksdjur vid hypo- 

 termistudier, Kylt. Tidskr. 4: 37, 38, 1953. 



Dr. A. Rihcri: We have had a good deal of experience with experimental hypo- 

 thermia, and have used a bath of water and crushed ice. We have never had any 

 trouljle with our dogs during cooling. We have never had any case of ventricular 

 fibrillation due to hypothermia alone in about 400 dogs operated up to the present 

 time. We also use a cooling blanket when we operate on adults. With children we 

 have used ice bags ; this is a very simple technique and, so far, we have not had any 

 trouble with fat necrosis. In this way hypothermia is induced in children very fast. 

 It takes about 1 5 or 20 minutes to cool a small child from 37 down to 30-28 degrees 

 centigrade, at which time the patient is put on the blanket, which is rewarmed as 

 soon as the cardiac part of the operation is over. When the blanket is used for 

 cooling, the time required is long and the surgeon is obliged to wait, sometimes 

 hours, before the patient has reached the temperature desired. This can be obviated 

 by careful planning. 



I wish to emphasize Dr. Muller's point that the blanket is very helpful, but also 

 that the danger of burns is a real one and must not be overlooked. 



Dr. R. O. Hcimbccker: Many factors help to determine the pH changes and 

 value of assisted ventilation under hypothermia. The method of cooling and degree 

 of anesthesia are important. 



We find that surface cooling with blankets is quite a different situation from 

 cooling with ice water, in that the latter is a strong stimulus to spontaneous hyper- 

 ventilation by the anesthetized patient. 



In cardiac cases in which the chest is, of course, open, hyperventilation is im- 

 portant, while in the neurosurgical cases in which the chest is closed, spontaneous 

 respiration seems adequate. 



Dr. F. Gollan: The induction of hypothermia by means of a small pump-oxygena- 

 tor has drawbacks as well as advantages. The drawbacks are due to difficulties in 

 the technique of extracorporeal circulation and oxygenation. They can be overcome 

 by systematic experimentation under controlled conditions. The advantages are of 

 a physiological nature, and I am confident that those investigators who are patient 

 enough to master the technique will be gratified by the results. 



This is not the place to go into a detailed description of the instrument and I 

 just would like to show a diagram of the principle used (fig. 1). Oxygen is forced 

 through a microporous porcelain disc into venous blood which is promptly oxy- 

 genated by the dispersion of these fine bubbles (Clark, Gollan and Gupta in 1950). 

 The fine oxygen bubbles are then made to coalesce into large ones by leading the 

 blood over a large surface coated with an antifoam compound. The large bubbles 

 are separated from the blood by a screen and rise to the lower surface of another 

 porcelain filter of much larger pore size. This filter is made non-wettable so that the 

 blood will be repelled whereas the excess of free oxygen and carbon dioxide can 

 filter through. Thus, by a change of surface tension a small closed and disposable 

 plastic chamber can oxygenate 2 liters of blood per minute. Circulation is provided 

 by a finger-pump and temperature changes are produced by a coil in the system. 



