Cardiovascular effects of thoracic compression in horses subjected to euthanasia

Six horses scheduled for euthanasia were instrumented for the measurement of blood flow by thermodilution, pulmonary arterial, right atrial and arterial blood pressures and collection of arterial blood for pH and blood gas analysis. The horses were anaesthetised with intravenous (iv) thiamylal sodium (10 mg/kg) and placed in right lateral recumbency. After euthanasia with an overdose of pentobarbitone sodium (100 mg/kg, iv) and loss of the electrocardiogram and arterial pulse pressure, thoracic compression at rates of 40, 60 and 80 compressions/min was instituted. Thoracic compression was accomplished by an investigator who delivered a blow to the chest wall with his knee while dropping from a standing or crouching position. Compression rates of 40, 60 and 80/min produced blood flows of 5.65 +/- 0.5, 6.33 +/- 1.11 and 8.28 +/- 2.16 litres/min, respectively. Compression rates of 80/min produced significantly (P < 0.05) greater blood flows and mean arterial blood pressures than did slower rates. The blood flows produced by 80 thoracic compressions/min were approximately 50% of those reported for deeply anaesthetised horses and while not sufficient to sustain life might be used to prolong life in order to facilitate distribution of resuscitative drugs to vital tissues.