CARDIOVASCULAR, HORMONAL, AND METABOLIC RESPONSES TO SEVERE PROLONGEDHEMORRHAGE IN ADULT SHEEP

Over a 54-hour period, blood was removed from 8 adult sheep (body weig ht, 38.1 +/- 0.5 kg, mean +/- SEM) in 9 episodes, 5 on day 1, 3 on day 2, and 1 on day 3. Cumulative blood loss was 1,630 +/- 63, 2,380 +/- 71, and 2,693 +/- 69 ml on days 1, 2, and 3, respectively. Blood sampl es (20 ml) were collected from 5 control ewes (33.8 +/- 2.8 kg) at equ ivalent times. Over the first day, mean arterial blood pressure decrea sed in the hemorrhaged sheep from 101 +/- 2 mm of Hg to 76 +/- 5 mm of Hg; but returned to control values by the beginning of the second day and, thereafter, was not different from control values. Heart rate wa s increased after the first hemorrhage episode and remained high throu ghout the entire protocol. Over the entire period, there were statisti cally significant decreases in hematocrit, plasma osmolality, sodium, total calcium (P < 0.001), potassium, and chloride values (P < 0.05). There was no change in plasma phosphate, bicarbonate, creatinine, or m agnesium concentrations and an increase in plasma urea nitrogen (P < 0 .001) concentrations. Plasma arginine vasopressin concentration was in creased significantly (P < 0.001) over the entire period. Plasma ACTH concentration was significantly (P < 0.05) increased over time, but on ly some values on day 1 were significantly outside the normal range of the control group data. Because of wide variation between sheep, the group data for aldosterone were not significantly different from contr ol values. Blood volume was restored on day 1 with fluid of osmolality , Na, and Cl composition equivalent to that of plasma. The effects of arginine vasopressin were apparent by day 2, when the major decrease i n osmolality and Na and Cl concentrations were observed. The sheep has good capacity to withstand severe, prolonged hemorrhage, most likely because of a large reserve of RBC in the spleen; hematocrit remained a t 31% of control values when an estimated 100% of initial circulating blood volume had been removed.