Hemodynamic and metabolic responses to repeated hemorrhage and resuscitation with hypertonic saline dextran in conscious swine.

Previous work in our laboratory has demonstrated that HSD is an effective small-volume resuscitation fluid for the treatment of hemorrhagic hypotension, but limitations to its usefulness in severe hemorrhage have not been explored. In the present study, animals (N = 12) were bled from an arterial line at a rate of 1 mL/kg/min until continuously monitored aortic blood flow was reduced to one-half its baseline value, and then they were immediately resuscitated with 7.5% NaCl/6% dextran 70 (hypertonic saline dextran, 4 mL/kg) administered intravenously over 3 min. After recording the maximum improvement in blood pressure, blood samples were obtained and the hemorrhage-resuscitation sequence was repeated until no further measurable increase in cardiac index or blood pressure could be elicited by resuscitation. In the majority of the animals, cardiac index and right and left ventricular stroke work could be improved at least through two bleedings and resuscitation. These improvements sufficed to increase oxygen delivery and consumption, despite the decreases in hematocrit induced by bleeding, transcapillary refill, and asanguinous fluid administration. Under these severe hemorrhage conditions, the acid-base imbalance was not improved by hypertonic saline dextran, and the rate of increase in acidosis was not affected by its administration. We observed a progressive decrease in base excess from +1.35+/-3.19 (mean +/- standard error) to -12.9+/-2.1 mEq/L even when resuscitation improved oxygen consumption significantly by 95+/-20%. In animals that survived as many as three bleedings and resuscitation, the depletion of buffering capacity of the blood was most predominant, and bicarbonate reached a nadir of 7.62 mEq/L with a base excess of -22.4 mEq/L. It is evident that restoration of perfusion in shock treats only a portion of the physiologic dysfunction, leaving major metabolic derangements uncorrected.

Resuscitation from severe hemorrhage.

The potential to be successfully resuscitation from severe traumatic hemorrhagic shock is not only limited by the "golden 1 hr", but also by the "brass (or platinum) 10 mins" for combat casualties and civilian trauma victims with traumatic exsanguination. One research challenge is to determine how best to prevent cardiac arrest during severe hemorrhage, before control of bleeding is possible. Another research challenge is to determine the critical limits of, and optimal treatments for, protracted hemorrhagic hypotension, in order to prevent "delayed" multiple organ failure after hemostasis and all-out resuscitation. Animal research is shifting from the use of unrealistic, pressure-controlled, hemorrhagic shock models and partially realistic, volume-controlled hemorrhagic shock models to more realistic, uncontrolled hemorrhagic shock outcome models. Animal outcome models of combined trauma and shock are needed; a challenge is to find a humane and clinically realistic long-term method for analgesia that does not interfere with cardiovascular responses. Clinical potentials in need of research are shifting from normotensive to hypotensive (limited) fluid resuscitation with plasma substitutes. Topics include optimal temperature, fluid composition, analgesia, and pharmacotherapy. Hypotensive fluid resuscitation in uncontrolled hemorrhagic shock with the addition of moderate resuscitative (28 degrees to 32 degrees C) hypothermia looks promising in the laboratory. Regarding the composition of the resuscitation fluid, despite encouraging results with new preparations of stroma-free hemoglobin and hypertonic salt solutions with colloid, searches for the optimal combination of oxygen-carrying blood substitute, colloid, and electrolyte solution for limited fluid resuscitation with the smallest volume should continue. For titrating treatment of shock, blood lactate concentrations are of questionable value although metabolic acidemia seems helpful for prognostication. Development of devices for early noninvasive monitoring of multiple parameters in the field is indicated. Molecular research applies more to protracted hypovolemic shock followed by the systemic inflammatory response syndrome or septic shock, which were not the major topics of this discussion.

Suspended animation for delayed resuscitation.

Suspended animation is defined as the therapeutic induction of a state of tolerance to temporary complete systemic ischemia, i.w., protection-preservation of the whole organism during prolonged circulatory arrest ( > or = 1 hr), followed by resuscitation to survival without brain damage. The objectives of suspended animation include: a) helping to save victims of temporarily uncontrollable (internal) traumatic (e.g., combat casualties) or nontraumatic (e.g., ruptured aortic aneurysm) exsanguination, without severe brain trauma, by enabling evacuation and resuscitative surgery during circulatory arrest, followed by delayed resuscitation; b) helping to save some nontraumatic cases of sudden death, seemingly unresuscitable before definite repair; and c) enabling selected (elective) surgical procedures to be performed which are only feasible during a state of no blood flow. In the discussion session, investigators with suspended animation-relevant research interests brainstorm on present knowledge, future research potentials, and the advisability of a major research effort concerning this subject. The following topics are addressed: the epidemiologic facts of sudden death in combat casualties, which require a totally new resuscitative approach; the limits and potentials of reanimation research; complete reversibility of circulatory arrest of 1 hr in dogs under profound hypothermia ( < 10 degrees C), induced and reversed by portable cardiopulmonary bypass; the need for a still elusive pharmacologic or chemical induction of suspended animation in the field; asanguinous profound hypothermic low-flow with cardiopulmonary bypass; electric anesthesia; opiate therapy; lessons learned by hypoxia tolerant vertebrate animals, hibernators, and freeze-tolerant animals (cryobiology); myocardial preservation during open-heart surgery; organ preservation for transplantation; and reperfusion-reoxygenation injury in vital organs, including the roles of nitric oxide and free radicals; and how cells (particularly cerebral neurons) die after transient prolonged ischemia and reperfusion. The majority of authors believe that seeking a breakthrough in suspended animation is not utopian, that ongoing communication between relevant research groups is indicated, and that a coordinated multicenter research effort, basic and applied, on suspended animation is justified.

Resuscitation from hypovolemia in swine with intraosseous infusion of a saturated salt-dextran solution.

Prehospital fluid resuscitation of traumatic injury is limited by difficulty in delivering large volumes of fluid in the field and time delays associated with gaining vascular access. We addressed these limitations in 14 anesthetized swine by evaluating a highly efficient volume expander, a near-saturated salt-dextran solution (SSD) administered through a new device, which gains vascular access via intraosseous (IO) infusion into the sternal bone marrow. After a steady-state baseline was achieved, all animals were hemorrhaged to 45 mm Hg for one hour. Half of the hemorrhaged animals were infused intraosseously with either normal saline (NS) or SSD until cardiac output was restored to the baseline value. No further infusion was given and animals were monitored for 2 hours. Both regimens were able to restore cardiac output to the baseline value, but only 1.3 +/- 0.1 mL/kg of SSD was required vs. 31.6 +/- 6.3 mL/kg for NS. In addition, cardiac output was better sustained after 2 hours with SSD than with NS. No deleterious effects of IO infusion of SSD were observed. From the improvement in cardiovascular variables and the lack of significant sternal or pulmonary pathologic perturbations, these data suggest that IO infusion of SSD can effectively treat hypovolemia and may allow field treatment when logistic considerations make conventional resuscitation impractical.

Use of hypertonic saline/dextran versus lactated Ringer's solution as a resuscitation fluid after uncontrolled aortic hemorrhage in anesthetized swine.

STUDY OBJECTIVE: We tested the hypothesis that following aortotomy, administration of hypertonic saline/dextran increases hemorrhage and mortality. We also compared hypertonic saline/dextran with the standard therapy of attempting to replace three times the amount of lost blood with lactated Ringer's solution. DESIGN: In this model of uncontrolled arterial hemorrhage resulting from aortotomy, 24 anesthetized Yorkshire swine underwent splenectomy, stainless steel wire placement in the infrarenal aorta, and instrumentation with Swan-Ganz and carotid artery catheters. The wire was pulled, producing a 5-mm aortotomy and spontaneous intraperitoneal hemorrhage. INTERVENTIONS: The animals were randomly assigned to one of three study groups: control; hypertonic saline/dextran group in which six minutes after aortotomy a 4-mL/kg mixture of IV 7.5% NaCl and 6% Dextran-70 was given over one minute; or lactated Ringer's group in which six minutes after aortotomy 80 mL/kg IV lactated Ringer's was given over nine minutes. MEASUREMENTS AND MAIN RESULTS: The volume of hemorrhage and the mortality rate in hypertonic saline/dextran-treated animals were significantly greater than in the nonresuscitated controls (1,340 +/- 230 mL versus 783 +/- 85 mL and five of eight versus zero of eight, respectively; P less than .05). Although the mortality rate in the lactated Ringer's group was not significantly different from the hypertonic saline/dextran group, survival time was significantly shorter than in the hypertonic saline/dextran group. CONCLUSION: In this model of uncontrolled hemorrhage, immediate IV administration of hypertonic saline/dextran significantly increased hemorrhage volume and mortality. However, the accentuation of hemorrhage and reduction in survival were not as great as that produced by the standard practice of attempting to replace the lost blood with three times that volume of lactated Ringer's.

Slow-wave flowmotion in rabbit skeletal muscle after acute fixed-volume hemorrhage.

Laser Doppler flux (LDF) was used to detect flowmotion (regular cyclic alterations in red blood cell flux) in the left gastrocnemius muscle of 14 rabbits that were bled 30% of their blood volume and let to recover spontaneously for 30 min. Only rabbits that met stated inclusion criteria during control conditions were used in the study. During control conditions when femoral artery pressure averaged 68 mm Hg (range 60-80), no animal displayed regular flowmotion. After the end of the acute hemorrhage, arterial pressure was 35 mm Hg (20-51) and slow wave flowmotion appeared instantaneously in 13 of the 14 animals. The maximum relative amplitude of the induced flowmotion was 31% (7-100) and the frequency was 1.8 cycles per minute (cpm) (1.4-4.0). Flowmotion persisted throughout the 30 min observation period in 11 animals, during which time arterial pressure recovered to 46 mm Hg (42-50). Fast-wave flowmotion was not detected in the present study. These results suggest that slow-wave flowmotion as measured with LDF is not a phenomenon characteristic of normal regulation of blood flow in skeletal muscle. After a 30% fixed-volume hemorrhage, slow-wave flowmotion is induced as arterial pressure drops below a certain threshold.

The detrimental effects of intravenous crystalloid after aortotomy in swine.

We tested the hypothesis that, after aortotomy, rapidly replacing three times the blood volume deficit with intravenous crystalloid will increase hemorrhage and decrease survival. Sixteen anesthetized Yorkshire swine underwent splenectomy and stainless steel wire placement in the infrarenal aorta and were instrumented with pulmonary artery and carotid artery catheters. The wire was pulled, producing a 5 mm aortotomy and spontaneous intraperitoneal hemorrhage. The animals had been alternately assigned to either an untreated control group (n = 8) or a treatment group (n = 8), which received 80 ml/kg lactated Ringer's solution intravenously. The volume of hemorrhage and the mortality rate were significantly increased (p less than 0.05) in the treatment group receiving lactated Ringer's solution relative to the control animals (2142 +/- 178 ml versus 783 +/- 85 ml, and eight of eight animals versus zero of eight animals, respectively). From these data we conclude that, in this model of uncontrolled arterial hemorrhage resulting from abdominal aortotomy, rapidly administering lactated Ringer's solution intravenously significantly increases hemorrhage and death.

Microvascular responses in rabbit skeletal muscle after fixed volume hemorrhage.

The effect of hemorrhage on the microvascular responses in the tenuissimus muscle was studied by means of intravital microscopy in rabbits anesthetized with urethan. The rabbits were bled 30% of their calculated blood volume within 3 min. Hemorrhage initially caused mean arterial pressure to drop from 70 +/- 7 to 26 +/- 5 mmHg. During the subsequent 30-min observation period it increased to 43 +/- 8 mmHg. The transverse arterioles (TRs), supplying both muscle tissue proper and adjacent connective tissue, gradually constricted to 75% of control over the 30-min period. Terminal arterioles (TEs) branching from the TR in the muscle tissue constricted to 65% in 10 min and then gradually relaxed, eventually reaching 80% of control diameter. The constriction of the TEs was confined to a short sphincterlike structure (10-20 microns) at the origin of the bifurcation. Upon constriction, the diameter of the sphincterlike structure was less than the critical diameter for erythrocyte passage. Given that the effective blood viscosity in the narrow TE is strongly dependent on luminal diameter, the overall effect on blood flow and its distribution in the tenuissimus muscle was a dramatic reduction of volume flow to 20-30% of the control value. During the early phase, the reduced flow was diverted to the connective tissue at the expense of nutrient flow to the muscle tissue. This early blood flow pattern gradually reversed, partially restoring nutrient flow to the muscle fibers.

Hemodynamic response to abdominal aortotomy in the anesthetized swine.

This study was conducted to determine the hemodynamic response to uncontrolled hemorrhage following aortotomy in anesthetized swine. Eight Yorkshire swine underwent splenectomy and stainless steel wire placement in the anterior infrarenal aorta and were instrumented with Swan-Ganz and carotid artery catheters. Following an equilibration period, the wire was pulled. This produced a 5 mm aortotomy and spontaneous intraperitoneal hemorrhage. Serial measurements of mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), and cardiac output (CO) were obtained. From baseline to 5 min after aortotomy, there was a profound decrease in MAP in conjunction with a significant decrease in CO and MPAP. After the initial 5 min period, there was a progressive elevation in MAP, CO, and MPAP. Peripheral vascular resistance (PVR) was significantly decreased after aortotomy and returned to baseline after 60 min. From these data, we conclude that aortotomy produces a rapid depression and spontaneous recovery in MAP, CO, and MPAP. Aortotomy also produces a significant decrease in PVR, which is not generally associated with hemorrhagic hypotension.

Human thermoregulation after atropine and/or pralidoxime administration.

The effects of intramuscular saline (control), atropine (2 mg), and/or pralidoxime (600 mg) on heat exchange was evaluated in four healthy males during seated, cycle exercise (55% Vo2 peak) in a temperate environment (Ta = 30.3 degrees C, Pw = 1.0 kPa). Esophageal (Tes), rectal (Tre), and mean skin temperatures (Tsk), and chest and forearm sweating (ms) were continuously measured. Skin blood flow (FBF) from the forearm was measured twice each minute by venous occlusion plethysmography. Whole body sweating was calculated from weight changes. The expected result of atropine injection, decreased eccrine sweating (-60%, p less than 0.05) and elevated esophageal (+0.4 degree C, p less than 0.05) and skin temperatures (+2.1 degrees C, p less than 0.05) was observed relative to control. Heart rate (+28 b X min-1) and FBF (+9 ml X 100 ml-1 X min-1) were higher after atropine. Pralidoxime, in general, did not affect the core and skin temperature responses to the exercise differently from control; however, a slightly elevated FBF (+3 ml X 100 cc-1 X min-1, 33%) compensated for the reduction in whole body sweating (-45%, p less than 0.05] that we observed. The combination of the drugs resulted in significantly higher esophageal (0.4 degree C) and skin (0.9 degree C) temperatures than atropine alone, as has been previously shown. The thermoregulatory disadvantage of inhibited sweating by atropine was partially compensated for by enhanced skin blood flow in this environment where Ta less than Tsk. Pralidoxime was shown to decrease whole body sweating, by a mechanism as yet unexplained.

Uptake and release of adenosine by cultured rat aortic smooth muscle.

We wanted to determine whether CO2, H+ and K+ affect the adenosine metabolism of vascular smooth muscle in a way that could account for the effects of these substances on vascular reactivity and their ability to modulate adenosine-induced vascular relaxation. Accordingly, 1-week-old cultures of rat aortic smooth muscle were incubated in phosphate-buffered saline with various [K+]'s and pH's and aerated in an incubation chamber with gases containing various proportions of CO2. Uptake was measured as 14C incorporation into cellular constituents during exposure to 2 microM [14C]adenosine. Release was measured as net extracellular adenosine accumulation. Uptake of adenosine was not significantly affected by any of the experimental maneuvers, except that it was greatly attenuated by dipyridamole (10(-5) and 10(-4) M) and transiently enhanced by the low CO2 levels. Adenosine release, however, was depressed by lowering atmospheric CO2 (0% vs 5%) and also by normocapnic acidosis (pH 6.8 vs pH 7.4). We conclude that vascular smooth muscle in culture releases adenosine at a rate that might have vasoactive significance in vivo. Furthermore, some of the vascular actions of CO2 and H+, but not those of K+, may be partially explained by their effects on vascular smooth muscle's adenosine metabolism.

Metabolic characteristics of cells cultured from human umbilical blood vessels: comparison with 3T3 fibroblasts.

Little metabolic information is available for cells cultured from umbilical vascular tissue. These studies were undertaken to compare the metabolism of cells isolated from human umbilical arteries and veins with that of umbilical vascular segments. These studies also compared umbilical vascular cells to standard fibroblast preparations. Oxygen consumption by umbilical venous cells or tissues was greater than that for either arterial cells or tissues. Cellular adenosine triphosphate (ATP) content was greater in umbilical venous than arterial cells. However, an oxidation-phosphorylation ratio (R) was constant for either arterial or venous cells. Oxygen consumption by vascular cells was greater than that by nonvascular cells, as was cellular ATP content. R for nonvascular cells was much greater than that for vascular cells, indicating loose coupling between oxygen consumption and cellular ATP content. Finally, cellular oxygen consumption was dependent upon cell density, and upon media serum content in vascular endothelial cells. We conclude therefore that the metabolism of umbilical vascular cells in culture reflects that of the parent tissue but is different from that of either vascular or nonvascular fibroblasts.

Effect of adenosine on calcium uptake by intact and cultured vascular smooth muscle.

The effect of adenosine (ADO), a potent vasodilator, on the cellular calcium uptake by vascular smooth muscle (VSM) was studied. In addition, similar experiments were conducted with other vasoactive agents to ensure the validity of results obtained with the cultured VSM cell model. Primary VSM monolayers from rat aorta were incubated for 30 min in 45Ca-enriched physiological salt solution (PSS) (37 degrees C) and washed with 20 mM Ca-EGTA (4 degrees C) to remove extracellular 45Ca. Calcium uptake with 4.6 mM K+ was 65.3 +/- 2.4 pmol Ca/10(5) cells. Verapamil (10(-6) M) or 4 degrees C incubation decreased this value 27 and 65%, respectively, whereas ADO (10(-7) M) and isoproterenol (10(-6) M) elevated calcium uptake 21 and 9%, respectively. Elevation of extracellular K+ (25 mM) increased calcium uptake to 87.8 +/- 5.0 pmol Ca/10(5) cells. ADO (10(-7) M), isoproterenol (10(-6) M), and 4 degrees C incubation significantly attenuated this K+-induced increase 25, 19, and 64%, respectively. The calcium uptake of nondepolarized cells was not changed by norepinephrine (10(-6) M) in the presence of either alpha- or beta-adrenergic blockade. Experiments were performed in a similar manner with porcine carotid artery strips in the presence of alpha- and beta-adrenergic blockade. Calcium uptake increased from 2.3 +/- 0.2 X 10(-7) to 3.0 +/- 0.1 X 10(-7) mol Ca/g wet wt after elevation of the medium K+ to 25 mM. This increase was inhibited by 10(-6) M ADO. ADO (10(-6) M) was found to have no effect on the 45Ca efflux from cultured VSM. It is concluded that ADO relaxes VSM by reducing the inward movement of calcium during stimulation. The significant ADO-induced elevation of cellular calcium under conditions when cultured cells were not partially depolarized suggests the existence of an enhanced calcium sequestration within these cells.

Growth of aortic vascular smooth muscle cells in lowered oxygen tension.

Primary cultured of vascular smooth muscle cells, isolated from rat aorta, were grown under normoxic (20% O(2)) and mildly hypoxic (5% O(2)) conditions. Cells from both conditions were compared for growth characteristics, morphology, protein synthesis, lysosomal enzyme activity, and oxygen consumption. In no case was a consistently significant difference observed. These observations indicate that these cells can adapt or are adapted to mildly hypoxic conditions. Moreover, these results may indicate that the culture of vascular smooth muscle cells in mild hypoxia represents a closer approximation of in vivo growth conditions for these cells.

Reduced high-energy phosphate levels in rat hearts. I. Effects of alloxan diabetes.

Significant alterations in heart carbohydrate and lipid metabolism are present 48 h after intravenous injection of alloxan (60 mg/kg) in rats. It has been suggested that uncoupling of oxidative phosphorylation occurs in the alloxanized rat heart in vivo, whereas normal oxidative metabolism has been demonstrated in alloxan-diabetic rat hearts perfused in vitro under conditions of adequate oxygen delivery. We examined the hypothesis that high-energy phosphate metabolism might be adversely affected in the alloxan-diabetic rat heart in vivo. Phosphocreatine and ATP were reduced by 58 and 45%, respectively (P is less than 0.001). Also, oxygen-dissociation curves were shifted to the left by 4 mmHg, and the rate of oxygen release from blood was reduced by 21% (P is less than 0.01). Insulin administration normalized heart high-energy phosphate compounds. ATP production was accelerated in diabetic hearts perfused in vitro with a well-oxygenated buffer. These studies support the hypothesis that oxidative ATP production in the alloxan-diabetic rat heart is reduced and suggest that decreased oxygen delivery may have a regulatory role in the oxidative metabolism of the diabetic rat heart.

Reduced myocardial ATP and creatine phosphate in diabetes: role of 2,3-diphosphoglycerate.

Observations are presented which suggest that myocardial cellular hypoxia may account for the reduction in myocardial ATP and CP in the ketoacidotic diabetic state. It is suggested that reduced 2,3-diphosphoglycerate adversely affects oxygen release from the red blood cell, thereby leading to myocardial cellular hypoxia.