Systemic and pulmonary hypertension, possibly related to nitric oxide scavenging by free hemoglobin (Hb), is often seen during resuscitation with hemoglobin-based oxygen carriers (HBOCs). Recently, a second-generation HBOC, rHb2.0 for Injection (rHb), has been developed using recombinant human Hb that has reduced reactivity with nitric oxide. The current study evaluates the efficacy of this novel compound for resuscitation in a swine model of uncontrolled perioperative hemorrhage.
After instrumentation, animals underwent splenectomy and rapid hemorrhage to a systolic blood pressure of 35 mm Hg and isoelectric electroencephalography. 15 minutes of shock was followed by resuscitation over 30 minutes. In phase I, 18 animals were randomized into three resuscitation groups: (1) lactated Ringer’s (LR) equal to three times the shed blood, the negative control group; (2) heterologous blood (BL) equal to Hb 2 g/kg, the positive control group; and (3) rHb equal to 2 g/kg, the treatment group. In phase II, six animals underwent the same experiment with a first-generation HBOC, diaspirin cross-linked Hb (DCLHb) equal to 2 g/kg, an additional control group. On day 0 after 2 hours of observation, spontaneously breathing animals were returned to their cages. Surviving animals were redosed on days 1, 2, and 3 (rHb/DCLHb 1 g/kg; LR/BL-LR 500 mL). Survivors were killed on day 5 and organs harvested for histologic examination. Group comparisons were performed using Student’s t test, repeated-measures analysis of variance, and χ2 test. Significance was set at 95% confidence intervals.
After resuscitation, systemic mean arterial pressure (MAP) (baseline = 107 ± 15 mm Hg) was 128 ± 34 and 108 ± 15 mm Hg in rHb and BL animals, respectively, and remained stable. In LR and DCLHb animals, after normalization, MAP declined to 67 ± 13 and 84 ± 34 mm Hg, respectively. The rHb group maintained higher MAP than the LR and BL groups (p < 0.05 vs. both). With resuscitation, mean pulmonary arterial pressure (PAP) (baseline = 25 ± 5 mm Hg) increased in rHb (40 ± 4 mm Hg), BL (34 ± 3 mm Hg), and DCLHb (40 ± 3 mm Hg) groups, but stayed elevated only in the DCLHb group (36 ± 3 mm Hg). PAP in the rHb group was similar to the BL group (p > 0.05), and both rHb and BL groups showed a higher PAP than the LR group (p < 0.05 vs. both). PAP was highest in the DCLHb group (p < 0.05 vs. rHb). Cardiac output of rHb and BL groups was similar (p > 0.05) throughout the observation period. Arterial lactate increased to 5.6 ± 2.5 mmol/L with shock and then normalized to < 2.0 mmol/L in the rHb, BL, and LR groups within 30 minutes of resuscitation. It remained elevated to > 3.5 mmol/L and showed a delayed increase in the DCLHb group (p < 0.05). Causes and number of deaths were as follows: rHb, zero of six; BL-transfusion reaction, one of six; LR-irreversible shock, four of six; and DCLHb-ventricular failure, six of six. There was no significant increase in plasma methemoglobin (rHb) and no difference in liver or cardiac enzymes (rHb vs. BL). No histologic abnormalities were seen in the rHb group except for cytoplasmic vacuolation, a process thought to be related to metabolism of the test article.
rHb2.0 for Injection, a second-generation recombinant human HBOC, performs as well as heterologous blood for resuscitation after perioperative blood loss, does not cause sustained pulmonary hypertension, maintains adequate cardiac output and oxygen delivery, and is superior to either LR or DCLHb.
From the Departments of Surgery (A.K.M., M.E.K., P.R.M., T.C.F., K.G.P.) and Physiology (J.C.H., K.G.P.), University of Tennessee Health Science Center, Memphis, Tennessee.
Submitted for publication May 7, 2002.
Accepted for publication January 27, 2003.
Supported by Office of Naval Research grant N00014-96-1-0664 and a research grant from Baxter Hemoglobin Therapeutics, Boulder, Colorado.
Presented at the 32nd Annual Meeting of the Western Trauma Association, February 24–March 1, 2002, Whistler-Blackcombe, British Columbia, Canada.
Address for reprints: Ajai K. Malhotra, MD, Department of Surgery, Medical College of Virginia, Virginia Commonwealth University, P.O. Box 980454, Richmond, VA 23298; email: email@example.com.