Effects of halogenated and non-halogenated anesthetics on diaspirin cross-linked hemoglobin induced contractions of porcine pulmonary veins

The differential effects of intravenous anesthetics on myofilament Ca2+ sensitivity in pulmonary venous smooth muscle

BACKGROUND

Pulmonary venous contraction can increase pulmonary capillary pressure and pulmonary edema. In the present study, we investigated the direct effects of ketamine, etomidate, thiopental, and midazolam on pulmonary venous contraction and myofilament Ca2+ sensitivity in permeabilized pulmonary venous smooth muscle (PVSM).

METHODS

The effects of these IV anesthetics on acetylcholine contraction were assessed in isolated canine pulmonary vein rings. Tension and [Ca2+]i were measured simultaneously in fura-2 loaded endothelium-denuded PVSM strips after being permeabilized with alpha-toxin. The effects of the IV anesthetics on tension ([Ca2+]i remains constant) in the absence or the presence of muscarinic receptor activation (acetylcholine) were assessed. The immunofluorescence technique and confocal microscopy were used to localize the cellular distribution of protein kinase C (PKC) isoforms in PVSM cells before and after the addition of ketamine.

RESULTS

Ketamine, etomidate, and midazolam each attenuated acetylcholine contraction dose-dependently, whereas thiopental had no effect. None of the IV anesthetics alone had an effect on tension in strips at constant [Ca2+]i (i.e., they had no direct effect on myofilament Ca2+ sensitivity). Acetylcholine increased tension by 56% +/- 7% at constant [Ca2+]i. In acetylcholine-stimulated strips, etomidate, midazolam, and thiopental had no additional effect on tension at constant [Ca2+]i, whereas ketamine decreased tension by 33% +/- 3%. Activation with acetylcholine induced translocation of PKC from cytoplasm to membrane, and this effect was blocked by ketamine.

CONCLUSIONS

Ketamine, etomidate, and midazolam each attenuated acetylcholine-induced pulmonary venous contraction. Ketamine attenuates acetylcholine contraction by inhibiting the acetylcholine-induced increase in myofilament Ca2+ sensitivity and the acetylcholine-induced translocation of PKCalpha.

Effect of diaspirin crosslinked hemoglobin (DCLHb HemAssist) during high blood loss surgery on selected indices of organ function

BACKGROUND

The safety of the hemoglobin based oxygen carrier diaspirin crosslinked hemoglobin (DCLHb) has been reported only in the low (50-200 mg/kg) dose range [Przybelski. R.J.; Daily, E.K.; Kisicki, J.C.; Mattia-Goldberg, C.; Bounds, M.J.; Colburn, W.A. Phase I study of the safety and pharmacologic effects of diaspirin crosslinked hemoglobin solution. Crit. Care Med. 1996, 24 (12), 1993-2000, Bloomfield, E.; Rady, M.; Popovich, M.; Esfandiari, S.; Bedocs, N. The use of diaspirin crosslinked hemoglobin (DCLHb 1996, 95, (3A), A220.]. We conducted a randomized prospective open-label trial of DCLHb and packed red blood cells (PRBCs) in high-blood loss surgical patients to show the effect of 750 ml DCLHb (approximately 1000 mg/kg) on selected indices of organ function.

METHOD

After institutional approval, 24 patients scheduled to undergo elective orthopedic or abdominal surgery, were randomized to receive either PRBCs or 10% DCLHb within 12 hours after the start of surgery. Patients with renal insufficiency, abnormal liver function, severe coronary artery disease (CAD) and ASA physical status > or = IV were excluded. The anesthetic technique was left to the judgment of the anesthesiologist. Autologous predonation and intraoperative blood conservation techniques were utilized as appropriate. The indications for blood transfusion were individualized on disease state, stage of surgery, and plasma Hb concentration. Laboratory studies were obtained preoperatively and up to 28 days postoperatively. Patients were observed daily for development of jaundice, hematuria, nausea, vomiting, gastrointestinal discomfort, cardiac, respiratory, and infectious complications. Organ effects were assessed with urinalysis, creatinine clearance, electrocardiogram (ECG), and a panel of blood and serum laboratory tests.

RESULTS

The dose of DCLHb administered ranged from 680-1500 mg/kg (mean = 999 mg/kg). Estimated blood loss was 27 +/- 13 ml/kg and 31 +/- 15 ml/kg in the control and DCLHb groups, respectively. Fewer PRBCs (1.9 +/- 1.2 vs. 3.4 +/- 2.4 units. P = 0.06) were transfused to DCLHb patients on the operative day although this difference was no longer apparent later on. In the DCLHb group, 4/12 patients avoided any allogeneic PRBC transfusion vs. none in the control group (P = 0.09). Systolic, diastolic and mean blood pressure increased moderately after DCLHb for a period of 24-30 hours. There were no occurrences of cardiac ischemia. myocardial infarction, stroke, or pulmonary edema, by clinical or laboratory parameters up to the 28th postoperative day (POD). Seven of 12 (58%) DCLHb patients had yellow skin discoloration vs. none in the PRBC group (P < 0.01). Two of four non-urologic surgery patients developed asymptomatic postoperative hemoglobinuria after DCLHb. Creatinine clearance was unchanged postoperatively. Because of hemoglobin interference, bilirubin, gamma-glutamyl transferase (GGT), and amylase could not be measured reliably on POD1; on POD2. amylase was transiently elevated to 3 times ULN along with mild elevations of bilirubin, transaminases and BUN. Mean total creatine phoshokinase (CPK) peaked at 8 times the upper limit of normal (ULN) in the DCLHb group, compared with less than twice ULN for controls. Three DCLHb patients had prolonged ileus. Two of these patients had postoperative hyperamylasemia, one of whom developed mild pancreatitis. DCLHb did not affect white blood cell count or coagulation tests.

CONCLUSION

Administration of approximately 1000 mg/kg DCLHb was associated with transient arterial hypertension, gastrointestinal side effects, laboratory abnormalities, yellow skin discoloration, and hemoglobinuria. These observations point to opportunities for improvement in future synthetic hemoglobin design.

Regional vascular effects of rHb1.1, a hemoglobin-based oxygen carrier

The goals of this study were to determine the effects of recombinant human hemoglobin (rHb1.1, 1 g/kg i.v.) on systemic hemodynamics, regional blood flows, and regional vascular resistances in rats. Cardiac output (CO) and regional blood flow in 13 tissues were determined by using the radiolabeled-microsphere method during halothane anesthesia. Microspheres were injected at three time points: before (control, t = 0), t = 30 [10 min after a 20-min infusion of vehicle (diluent) or rHb1.1], and at t = 120 min. Infusion of diluent did not alter CO, heart rate (HR), mean arterial pressure (MAP), or systemic vascular resistance (SVR) and had minimal effects on regional blood flows. Infusion of rHb1.1 did not alter CO or HR but did increase MAP and SVR compared with diluent. Infusion of rHb1.1 increased blood flow to the heart and decreased blood flow to the gastrointestinal tract (GIT) and liver. Compared with the corresponding values in the diluent-treated rats, resistance was increased after rHb1.1 in spleen, kidney, and hepatic artery. In conclusion, rHb1.1 administration increased MAP and SVR. The vasoconstriction was heterogeneous and was associated with increased coronary blood flow and with increased regional resistance in kidney, spleen, and hepatic artery, compared with diluent-infused controls.

Actions of diaspirin cross-linked hemoglobin on isolated rat and dog vessels

The objectives of these studies were to investigate the responses of isolated blood vessels from rats and dogs to the administration of diaspirin cross-linked hemoglobin (DCLHb) and to determine the mechanisms of these responses. Isolated vascular rings (3 to 5 mm) were suspended at optimal passive tension in Krebs-filled (37 degrees C) tissue baths and bubbled with 95% O2-5% CO2, and isometric tension was recorded. With the vessels under basal conditions increasing concentrations of DCLHb (10(-8)-3 x 10(-6) mol/L) were added. DCLHb addition was repeated during a submaximal contraction with norepinephrine and again during acetylcholine relaxation. The effects of the nitric oxide synthase inhibitor L-nitro arginine (10(-5) mol/L) on the responses to DCLHb were also determined. Dog vessels developed very little tension (1% to 5% of norepinephrine maximum), whereas rat arteries contracted between 9% and 15% when exposed to DCLHb under basal conditions. However, both the dog and rat vessels developed significant tension to DCLHb when they were precontracted (5% to 54%) and also when they were relaxed with acetylcholine (21% to 93%). L-nitro arginine eliminated the contractile responses to DCLHb but did not cause contraction of any of the vessels under basal conditions. We conclude that in this model the mechanism of DCLHb-induced contractions of in vitro dog and rat vessels is dependent on interference with nitric oxide. This is similar to the mechanism of DCLHb action in isolated pig vessels reported previously. Differences in responses of dog, rat, and pig vessels under basal conditions in vitro are the result of active generation of nitric oxide by pig but not by dog or rat vessels.

Diaspirin cross-linked hemoglobin does not alter isolated human umbilical artery or vein tone

Diaspirin cross-linked hemoglobin (DCLHbTM; Baxter Healthcare Corp., Round Lake, IL, USA) is undergoing clinical trials as a blood substitute. Administration of DCLHb is associated with an increase of mean arterial pressure in vivo and contraction of selected adult isolated blood vessels of from certain species in vitro. The mechanisms of these pressor effects may be due to scavenging of the endothelium derived relaxing factor, nitric oxide (NO), by hemoglobin. Unlike adult blood vessels, prostacyclin (PGI2) rather than EDNO is the important relaxing agent in human umbilical vessels. In this study, we examined if DCLHb had vasoconstrictor effects on isolated human umbilical vessels. Human umbilical veins and arteries were excised, cut into rings and placed in organ chambers filled with 25 ml Krebs-Ringer solution (37 degrees C). 5-hydroxytryptamine (5-HT, 0.01-10 microM) increased the tension of human umbilical arteries (HUA, from 0.4 +/- 0.2 g to 2.6 +/- 0.4g) and veins (HUV, from 0.8 +/- 0.4g to 2.5 +/- 0.4g) in a dose-dependent manner. DCLHb (0.01-10 microM) did not have a significant effect on HUA and HUV. Substance P (1 microM, via prostanoid synthesis) and nitroglycerin (NG, 1 microM) but not acetylcholine (ACh, 1 microM) caused relaxation of both HUA and HUV. The NO synthase inhibitor L-NA did not have significant effects on HUA and HUV. DCLHb did not alter 5-HT preconstricted tension of HUA and HUV. The basal cGMP contents of HUA and HUV were low. These results support our previous finding that DCLHb-induced vasoconstriction in isolated vessels is dependent primarily on the binding of NO by hemoglobin.