INDIRECT BLOOD PRESSURE MEASUREMENT IN ANAESTHETISED ANIMALS

The technique of indirect blood pressure measurement described by Wilson and Clark (1964) has been found to be applicable to anaesthetised animals and the technique has been easily modified for use in sheep, cattle and horses. Experimental work in dogs has shown that the width of the cuff has an important bearing on the accuracy of the indirect readings obtained. It would appear at present that for dogs at least two cuff widths should be used. A cuff 2.5 cm wide should be used for dogs under 12 kg and one 3.75 cm wide for heavier dogs. The length of the cuff appears to be unimportant providing the inflatable portion encircles the limb and the cuff is not applied too loosely or too tightly. A cuff length of 25 cm should be suitable for most animals. The occluding cuff used by Wilson and Clark (1964) measured 25 times 3.2 cm and these authors found good correlation with directly measured systolic pressure in a 12 kg dog. The technique can be readily applied to horses and sheep but careful placement of the occluding cuff in cattle is required to provide adequate transmission of the cuff pressure to the coccygeal vessels. Cuff widths of 3.75 cm are recommended for use on the tail in horses and cattle and a cuff 2.5cm wide on the hind limb for sheep. In dogs good correlation has been found between indirect and direct systolic pressure even with cuffs of different widths. This is adequate for routine anaesthetic work where changes in pressure are of more importance than absolute values. For comparative work between different animals it would be important to use cuffs of the correct width for the different sizes of animal.