Labetalol-induced hypotension decreases blood loss during uncontrolled hemorrhage

In a model of uncontrolled hemorrhagic hypotension (UCHH) in rats, we examined whether blood loss or blood chemistry were affected by (1) deliberate, controlled hypotension induced with labetalol (L) or sodium nitroprusside (SNP) and (2) intravenous (iv) fluid therapy. Two hours of UCHH was induced by resecting the distal 25% of the tail. L or SNP was infused with the aim of decreasing MAP to 50 mmHg. In the groups receiving iv fluid, 3 ml of 0.9% saline was given for each 1 ml of blood loss. L decreased blood loss (2.8 ± 2.0 and 3.0 ± 1.9 ml, respectively, in the groups not receiving and receiving iv fluid) compared to the groups not given hypotensive drugs (6.3 ± 4.1 and 13.5 ± 6.6 ml). SNP did not decrease blood loss (5.7 ± 4.7 and 11.0 ± 6.2 ml), increased serum potassium (5.0 ± 0.6 and 5.8 ± 0.4 mEq l^-1), and with accompanying iv fluid administration decreased hematocrit, worsened acidosis, and increased mortality. In this model of 2 h of UCHH in rats, hypotension to MAP of 50 mmHg with L but not with SNP decreased blood loss.