The Efficacy of Norepinephrine on Hemorrhagic Shock in Relation to Myocardial Catecholamines

The catecholamine content was examined in the myocardium of dogs subjected to hemorrhagic hypotension of 40mmHg for a duration of one to hive hours respectively. No marked changes were noticed within two hours after production of homorrhagic hypotension but a significant reduction was found at the end of three hours of hypotension. The reduction of myocardial catecholamines was progressively pronounced with the prolonging the hypotensive period over three hours.

Dogs were bled rapidly to an arterial blood pressure of 40mmHg and maintained at this hypotensive level for four hours, followed by reinfusion of the withdrawn blood. Eight out of 11 dogs succumbed within l2 hours, showing a 73 per cent mortality. The myocardial catecholamines in the surviving dogs returned almost to the normal level within 12-15 hours after the blood reinfusion, while those in the dogs which succumbed showed the same low level which was produced during hemorrhagic hypotension. It was also shown that the reduced myocardial catecholamines resulting from the hypotension will not be restored immediately after the reinfusion of the withdrawn blood.

When norepinephrine was infused at a rate of five to seven µg/kg/min for an hour before the reinfusion of the withdrawn blood, five out of six dogs died within 12 hours, showing a 82 per cent mortality. This result appears to indicate that norepinephrine infusion during oligemic hypotension may hasten death or not decrease the mortality of the animals. On the other hand, when norepinephrine was infused at a rate of three µgkg/min for an hour following reinfusion of the withdrawn blood five out of 15 dogs died, indicating a significant increase of survival rate from hemorrhagic shock. The myocardial catecholamines of surviving dogs and dogs which succumbed following the administration of norepinephrine after blood reinfusion were similar respectively to those of dogs which survived and of dogs which died after blood reinfusion without norepinephrine.

When norepinephrine (3 µgkg/min) was infused for hour following blood reinfusion in the dogs pretreated with either dibenzyline (3mg/kg) or dichloroisoproterenol (1mg/kg), the beneficial effect of norepinephrine on the survival rate from hemorrhagic shock appeared to be absent.

The efficacy of norepinephrine on the survival from hemorrhagic shock was discussed on the basis of myocardial catecholamine depletion.