A simple survival model of volume-controlled hemorrhagic shock in awake rats

Unexpected 100% survival following 60% blood loss using small-volume 7.5% NaCl with adenocaine and Mg(2+) in the rat model of extreme hemorrhagic shock

Hemorrhage is responsible for up to 40% of trauma mortality, and of these deaths, 33% to 56% occur during the prehospital period. In an effort to translate the cardioprotective effects of Adenocaine (adenosine, lidocaine) and Mg (ALM) from cardiac surgery to resuscitation science, we examined the early resuscitative effects of 7.5% NaCl with ALM in the rat model of 60% blood loss. Male Sprague-Dawley rats (250-350 g, n = 40) were anesthetized and randomly assigned to one of five groups: (a) untreated, (b) 7.5% NaCl, (c) 7.5% NaCl/6% dextran 70, (d) 7.5% NaCl/Mg, and (e) 7.5% NaCl/ALM. Blood withdrawal occurred over ∼50 min (MAP 30-35 mmHg), and rats were left in shock for 30 min. Total shock time was ∼80 min; 0.3-mL bolus was injected intravenously over 10 s, and hemodynamics monitored for 60 min (phase 1). Shed blood was reinfused and function monitored for a further 60 min (phase 2). Lead II electrocardiogram, arterial pressures, mean arterial pressure (MAP), pulse pressure (PP), heart rate (HR), and rate-pressure product were monitored. Mortality was as follows: untreated (100%), 7.5% NaCl (75%), 7.5% NaCl/6% dextran 70 (87.5%), 7.5% NaCl/Mg (62.5%), and 7.5% NaCl/ALM (0%). Deaths occurred at different times depending on treatment group and paralleled differences in the total number of ventricular arrhythmias with the highest number in untreated animals (49 ± 17) and lowest in 7.5% NaCl/ALM rats (2 ± 1.8) (P < 0.05). At the end of phase 1, MAP of 7.5% NaCl/ALM-treated animals increased from 29 to 40 mmHg (P < 0.05). At the end of phase 2, MAP, PP, HR, and rate-pressure product in the ALM group were 75%, 193%, 96%, and 83% of their preshock values. Small-volume (∼1 mL/kg) i.v. bolus of 7.5% NaCl/ALM led to 100% survival following 60% blood loss with higher MAP than any group, an 89% to 96% reduction in the total number of arrhythmias, and a stable HR.

LOW-VOLUME RESUSCITATION COCKTAIL EXTENDS SURVIVAL AFTER SEVERE HEMORRHAGIC SHOCK

After severe hemorrhage, low-volume resuscitation with hypertonic fluids is increasingly preferred to more aggressive resuscitation strategies. Oxygen delivery to the tissues may be improved by augmentation with hemoglobin [Hb]-based oxygen-carrying compounds (HBOCs); however, previous studies have reported negative outcomes presumably related to extravasation of tetrameric Hb. The purpose of this study was to evaluate a novel large molecular weight polymer of cross-linked bovine Hb (OxyVita; OXYVITA Inc, New Windsor, NY) in a cocktail of hypertonic saline and Hextend (HX; HBOC-C) as an alternative to standard small-volume resuscitation using Hextend (HX) only. Outcomes were survival to 3 h and duration of MAP support more than 60 mmHg without additional fluid support. Conscious male Long-Evans rats were hemorrhaged to 60% total blood volume over 40 min. There were 4 groups: HBOC-C administered in a pressure-titrated infusion, HX titration, HBOC-C administered as a bolus, and HX bolus. Cardiovascular parameters, arterial gases, acid-base status, metabolites, electrolytes, Hb level, and oxygen saturation were measured at baseline, during each 20% hemorrhage increment, and 1, 2, and 3 h after the initiation of hemorrhage. Small-volume resuscitation with HBOC-C significantly improved survival to 3 h and improved MAP support times regardless of method of administration. However, physiological status at the end of hemorrhage significantly influenced survival regardless of resuscitation treatment. These results suggest that HBOC-augmented hypertonic cocktails are of promise in improving survival and providing target MAP support during small-volume resuscitation. Experimental evaluation of any resuscitation therapy should account for the degree of preexisting physiological compromise before therapy is initiated.

Physiologic response to hemorrhagic shock depends on rate and means of hemorrhage

BACKGROUND

Traditional models of shock classify severity based on the volume of hemorrhage. Clinically, hemorrhage occurs at a variable rate, usually slowing as blood pressure drops; however most animal experimental models use a constant rate of hemorrhage. Our hypothesis was that rapid bleeding followed by slower bleeding using a fixed total volume would result in a greater physiologic insult.

MATERIALS AND METHODS

Yorkshire pigs (S and S Farms, Ranchita, CA) underwent placement of jugular and femoral catheters after anesthesia. All animals were hemorrhaged a total of 30 mL/kg. The animals were divided into constant rate hemorrhage over 10 min (Constant-10) (3 mL/kg/min), constant rate hemorrhage over 20 min (Constant-20) (1.5 mL/kg/min), or a varying rate of hemorrhage of 2.15 mL/kg/min over 7 min, and then 1.15 mL/kg/min over the remaining 13 min (Physiologic-20). Shock, mean arterial pressure (MAP) < or = 20 mmHg, was maintained for 60 min. Resuscitation was performed with Ringer's lactate (RL) and shed blood (2:1 ratio), until shed blood was exhausted and then only RL to maintain a MAP > or =60 mmHg for 3 h.

RESULTS

Physiologic-20 shock resulted in significantly increased maximal heart rate, peak serum lactate, and volume of required RL resuscitation. Adequacy of resuscitation was ensured by MAP, urine output, and clearance of serum lactate.

CONCLUSIONS

A more physiologic method of fixed volume hemorrhagic shock results in a significantly increased physiologic response as demonstrated by increased volume of fluid resuscitation. This differential physiologic response may represent an improved hemorrhagic shock model, and could have implications for future hemorrhagic shock studies.

A temporal study of gene expression in rat lung following fixed-volume hemorrhage

Previous studies have indicated that hemorrhage may predispose the lung to respiratory distress syndrome. Gene expression profiling with oligonucleotide microarrays was used to evaluate the genetic responses of the lung to hemorrhage. Conscious rats, chronically instrumented with a catheter and telemetry device to record blood pressure, heart rate, and temperature, had 40% of their estimated blood volume removed at a rate of 1 ml/min over 7-10 min. Groups of three or more rats were euthanized at 1, 3, 6, 16, 24, 48, or 72 h following hemorrhage. Two additional groups were unmanipulated controls and instrumented animals with sham hemorrhage. Total RNA was isolated from lung, reverse-transcribed to cDNA, fluorescently labeled, and hybridized to oligonucleotide microarrays probing 5,671 rat genes. After hemorrhage, statistically detectable alteration of expression was seen in approximately 0.8% of the genes at some time during the 72-h test period (vs. sham hemorrhage) as determined by false discovery rate statistics in the statistical analysis of microarrays program. A subset was confirmed by RT-PCR analysis. Hemorrhage influenced genes that regulate intracellular signaling and structure, growth factors, and hormonal receptors. There also appeared to be increased expression of genes that may mediate sequestration of neutrophils and mononuclear cells from the circulation. This hemorrhage model, although producing severe hemodynamic alterations, avoided mortality and histological evidence of lung damage, a feature intended to help ensure reliable evaluation of gene expression. These results indicate that gene expression profiling with microarrays provides a new tool for exploring the response of a tissue to systemic blood loss.

Bowhunting deer

There are conflicting views about the humaneness of the handbow as a recreational hunting method for deer. Some claim that it is the most humane hunting method, whilst others report higher wounding rates and crippling losses than with the rifle. This commentary summarises the factors affecting the likelihood of a quick death, the types of equipment commonly used, the vital target areas, the influence of blood loss on blood pressure and brain function and the prevalence of wounding during routine bowhunting. Some requirements in Bowhunters Association Codes of Conduct are also described. It is concluded that where bowhunting is allowed, Codes of Conduct should emphasise the hunters' responsibility to track and despatch injured animals, and adherence to the Codes should be encouraged, if not enforced.

Rapid rewarming after mild hypothermia accentuates the inflammatory response after acute volume controlled haemorrhage in spontaneously breathing rats

Accidental hypothermia is a common companion of trauma/haemorrhage, and several clinical studies have identified reduced body temperature as an independent risk predisposing to increased morbidity and mortality. Accordingly, the majority of trauma care guidelines prescribe early and aggressive rewarming of hypothermic patients. Enzyme reactions are generally downregulated at temperatures below 37 degrees C, including most of those responsible for the inflammatory response. The rationale for adhering to these recommendations uncritically may therefore be questioned. In a rat model of mild hypothermia and haemorrhagic shock we wanted to compare the influence of rapid rewarming with persistently reduced temperature on the synthesis of early inflammatory mediators and organ function. Thirty-four male albino Sprague-Dawley rats were studied. Withdrawal of 2.5 ml blood/100 g body weight was performed over 10 min, with simultaneous reduction of body temperature to 32.5-33.5 degrees C. Seventy-five minutes after initiation of bleeding, two-thirds of the shed blood was retransfused. One group (n=17) was rewarmed to normothermia, the other (n=17) was kept hypothermic. The study was terminated after an observation period of 2 h. At the end of the study the rewarmed animals had a significantly lower mean arterial pressure, higher heart rate, higher synthesis of reactive oxygen species from peritoneal phagocytes, increased circulating levels of nitric oxide, and higher values of the organ markers aspartate aminotransferase and urea. The pro-inflammatory cytokines TNF-alpha and IL-6, the anti-inflammatory cytokine IL-10, the organ markers alanine aminotransferase, alpha-glutathione S-transferase and creatinine, as well as organ injury scores were equal in both groups. Three rewarmed rats died prematurely, versus one hypothermic animal. In conclusion, the results suggest that during the early stages after haemorrhagic shock, rapid rewarming from mild hypothermia may have unfavourable effects both on basic haemodynamic variables, and on the internal inflammatory environment of cells and tissues.

Effect of a delta receptor agonist on duration of survival during hemorrhagic shock

OBJECTIVES

Selective delta receptor agonists have been shown to stabilize membrane physiologic processes, reduce metabolic rates, and provide protection against ischemic insults through K(ATP) channel opening in a variety of organ beds. However, their potential for affecting outcomes in states of generalized ischemia has not been explored. The authors examined the effect of the nonselective delta receptor agonist, DADLE (D-Ala2-Leu5-enkephalin), on hemodynamic stability and duration of survival in an animal model of severe hemorrhagic shock.

METHODS

Conscious Sprague Dawley rats with indwelling catheters were hemorrhaged at a rate of 3.25 mL/100 grams over 20 minutes after half of the group received 1% DADLE (1 mg/kg IV). Following the hemorrhage, all rats were continuously monitored for heart rate (HR), mean arterial pressure (MAP), and life signs for up to three hours (death defined as apnea, systolic blood pressure < 30 mm Hg without pulsations, and electroencephalographic silence). Survival rates and hemodynamic trends were compared between the control and DADLE-treated groups.

RESULTS

In the 14 rats studied (8 DADLE; 6 controls), initial hemorrhage resulted in similar hemodynamic shock (average MAP fall: 118 to 59 vs 119 to 55 mm Hg). Analysis of survival at 3.5 hours revealed statistically significant differences between the control and DADLE groups. While 50% of the DADLE group survived past the three hours, no control animals were still alive at the end of the experimental period. The MAP trended downward and the HR increased for the control group, but all hemodynamic parameters stabilized in the rats treated with DADLE.

CONCLUSIONS

Most current strategies for treating shock focus on the supply side of resuscitation. The coordinated various actions of DADLE have the potential to work in concert in the intact organism to improve overall survival during severe hemorrhagic shock. In an animal model of severe hemorrhagic shock, there was improvement in hemodynamic stability and a prolonged survival with DADLE treatment. Physiologic manipulation with DADLE appears to be a way to improve survival during shock with possible clinical implications.

Extending the golden hour of hemorrhagic shock tolerance with oxygen plus hypothermia in awake rats. An exploratory study

In a previous study of volume-controlled hemorrhagic shock (HS) in awake rats, without fluid resuscitation, either breathing of 100% oxygen or moderate hypothermia while breathing air, increased survival time. We hypothesized that combining oxygen and hypothermia can maximally extend the "golden hour" of HS from which resuscitation can be successful in terms of survival rate. Rats were prepared under light general anesthesia, breathing spontaneously via face mask, and then awakened for 2 h. Then, 3.25 ml arterial blood/100 g were withdrawn over 20 min. At the end of HS of 30, 60, 90 or 180 min duration, the shed blood was reinfused. Breathing was spontaneous. Survival endpoint was 24 h or earlier death. HS of 30 or 60 min was used for preliminary experiments; HS of 90 or 180 min for 35 definitive experiments. Control groups A-1 and B-1 had normothermia (rectal temperature 37.5 degrees C) and were breathing air. Treatment groups A-2 and B-2 had total body surface cooling during HS to rectal temperature 32 degrees C and were breathing 100% O(2). Arterial pressure during HS was higher in the hypothermia-O(2) groups. With HS of 90 min, in the normothermia-air group A-1 (n=10), none of the 10 rats survived to 3 h; while in the hypothermia-O(2) group A-2 (n=5), all rats survived to 24 h (P<0.001). With HS of 180 min, in the normothermia-air group B-1 (n=10), three of 10 rats survived to 3 h and 24 h (hypotension during HS in these three survivors was less severe than in the non-survivors); and in the hypothermia-O(2) group B-2 (n=10) all 10 rats survived to 24 h (P<0.003). We conclude that moderate hypothermia (32 degrees C) plus 100% oxygen inhalation during volume-controlled HS in awake rats mitigates hypotension and increases the chance of survival. It enables survival even after 3 h of moderate HS.

The residual effects of hemorrhagic shock on pain reaction and c-fos expression in rats

To investigate the residual effects of hemorrhagic shock on pain reaction and c-fos expression, we performed formalin tests after hemorrhage and reinfusion in rats. Twenty adult male Sprague-Dawley rats were divided into Control (n = 10) and Postshock (n = 10) groups. The mean blood pressure of the Control group was 100-120 mm Hg, and that of the Postshock group was kept at 50-60 mm Hg for 30 min by draining blood. After 15 min of returning mean blood pressure to normal levels in the Postshock group, 10% formalin (3.7% formaldehyde solution, 100 microL) was injected into the left rear paw of both groups. Nociceptive behaviors were observed for 1 h after the formalin injection. The rats were killed at 2 h after the formalin injection, and the lumbar spinal cord was then stained for c-fos immunohistochemistry by using the avidin-biotin-peroxidase method. Animals in the Postshock group showed considerably less nociceptive behavior than those in the Control group. C-fos expression in the deep layer (IV-VI) of the spinal cord was significantly less in the Postshock group. In conclusion, decreases of nociceptive behaviors and c-fos expression were observed under normotensive conditions after hemorrhagic shock. The mechanisms governing these reactions remain unclear.

IMPLICATIONS

Formalin tests were performed after hemorrhage and reinfusion in rats. A stress-induced analgesia was observed under normotensive conditions after hemorrhagic shock. The mechanisms remain unclear.

The influence of hemorrhagic shock on the pharmacokinetics and the analgesic effect of morphine in the rat

The influence of hemorrhagic shock (removal of 30% of the blood volume) on the pharmacokinetics and the analgesic effect of morphine was investigated in conscious rats. Plasma concentrations of morphine after a bolus injection (5 mg/kg) are higher in the shock animals, which is attributed to a small decrease in clearance (-22%; P > 0.05) and a significant decrease in distribution volume (-33%; P < 0.05) of the drug. The areas under the plasma concentration-time curve of the metabolite morphine-3-glucuronide (M3G) are significantly higher (+237%; P < 0.01) in the shock rats, which is probably explained by a decreased distribution and renal excretion. The analgesic effect of morphine was evaluated using the tail-flick test during a continuous infusion (10 mg/kg/h) with measurement of the plasma concentrations of morphine and M3G. Data from these experiments show higher plasma concentrations of morphine (+33%; P < 0.05) and M3G (+66%; P > 0.05) during shock, and a significantly increased analgesic effect (+43%; P < 0.05). Our data suggest that the increased analgesic effect of morphine during hemorrhagic shock can most likely be explained by pharmacokinetic changes resulting in higher morphine concentrations.

Hypothermia and minimal fluid resuscitation increase survival after uncontrolled hemorrhagic shock in rats

OBJECTIVE

To test the hypothesis that protective-preservative moderate hypothermia during uncontrolled hemorrhagic shock (UHS) in rats increases survival.

DESIGN

Randomized outcome study in rats.

MATERIALS AND METHODS

UHS phase I of 90 minutes, with initial withdrawal of 3 mL/100 g of blood plus tail amputation, was followed by hemostasis and all-out resuscitation phase II from 90 to 150 minutes, and observation phase III to 72 hours. Forty male rats under light anesthesia and spontaneous breathing were randomized into four groups: Group 1 received no fluid resuscitation during UHS and normothermia (37.5 degrees C) throughout. Group 2 received no fluid resuscitation and hypothermia (30 degrees C) from 15 to 120 minutes. Group 3 received lactated Ringer's solution to maintain mean arterial pressure at 40 mm Hg during UHS and normothermia. Group 4 received lactated Ringer's solution to a mean arterial pressure of 40 mm Hg during UHS and hypothermia from 15 to 120 minutes.

RESULTS

UHS phase I was survived by 0 of 10 rats in group 1, 7 of 10 in group 2, 5 of 10 in group 3, and 10 of 10 in group 4 (p < 0.01 for group 1 vs. 2, 3, or 4; p < 0.05 for group 4 vs. 3). Survival to 72 hours was achieved by 0 of 10 rats in group 1, 3 of 10 in group 2 (p < 0.001 vs. group 1), 1 of 10 in group 3, and 7 of 10 in group 4 (p < 0.001 vs. group 1, and p < 0.01 vs. group 3). All 72-hour survivors were neurologically normal. Necropsies in rats that died early during phase III showed edema and gastrointestinal hemorrhages.

CONCLUSIONS

Moderate hypothermia or limited (hypotensive) fluid resuscitation --best both combined--increases survival during and after UHS in rats.

Regional heterogeneity of cerebral blood flow response to graded volume-controlled hemorrhage

OBJECTIVE

Of the animal models of human hemorrhagic shock, the volume-controlled hemorrhage model appears to come closer to the clinical situation than the commonly used pressure-controlled model, since the volume-controlled model allows regulatory adjustment of blood pressure. The effects of volume-controlled hemorrhage on local cerebral blood flow (LCBF) of conscious animals are not known. The present study investigates specific reaction patterns of LCBF in comparison to mean cerebral blood flow (CBF) during graded volume-controlled hemorrhagic shock in conscious rats.

METHODS

Conscious, spontaneously breathing, and minimally restrained rats were subjected to different degrees of volume-controlled hemorrhage (taking either 25, 30, 35, or 40 ml arterial blood/kg body weight (b.w.). Thirty minutes after the completion of blood taking, LCBF was determined during hemorrhagic hypovolemia using the autoradiographic iodo (14C) antipyrine method. A group of untreated rats (no hemorrhage) served as controls. LCBF was determined in 34 defined brain structures and mean CBF was calculated.

RESULTS

During less severe hemorrhage (25 and 30 ml/kg b.w.) mean CBF was significantly higher than in the control group (+19% and +25%). During severe hemorrhage (35 and 40 ml/kg b.w.) mean CBF remained unchanged compared to the control values, although significant increases in LCBF could be detected in many of the brain structures analyzed (maximum +44%). The mean coefficient of variation of CBF was increased, indicating a larger heterogeneity of LCBF values at shed blood volumes of 35 and 40 ml/kg b.w.

CONCLUSIONS

A comprehensive and novel description of the local distribution of CBF during graded volume-controlled hemorrhage in conscious rats shows unexpected increases in LCBF and mean CBF. This "hypovolemic cerebral hyperemia" might be caused by endogenous hemodilution, thus maintaining the blood supply to the brain during hypovolemic shock.

Coupling between local cerebral blood flow and metabolism after hypertonic/hyperoncotic fluid resuscitation from hemorrhage in conscious rats

The effects of small volume hypertonic/hyperoncotic fluid resuscitation from hemorrhage on brain metabolism and blood flow were evaluated by autoradiographic techniques with high spatial resolution. The data were compared to fluid resuscitation with a volume equal to shed blood of isotonic 6% hydroxyethyl starch solution (HES) and a control group without hemorrhage and fluid resuscitation (n = 6 in each group). In conscious rats, volume-controlled hemorrhage for 30 min (30 mL/kg body weight, resulting in a blood loss of approximately 50% of the circulating blood volume) was followed by intravenous infusion of a hypertonic/hyperoncotic saline hydroxyethyl starch solution (HTHO; 7.5% saline/10% hydroxyethyl starch, 4.0 mL/kg body weight). Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured in 34 brain structures 2 h after fluid resuscitation by means of the quantitative autoradiographic iodo [14C]antipyrine and 2-[14C]-deoxy-D-glucose methods. Compared to the untreated control group, LCBF increased significantly in all brain regions analyzed after fluid resuscitation with HTHO (mean, +63%) or HES (mean, +56%). The increases in LCBF after fluid resuscitation were sufficient to restore cerebral oxygen delivery to the level calculated for the untreated control group. LCGU was unchanged after fluid resuscitation. The close relationship between LCGU and LCBF observed in the control group (r = 0.95) was preserved after hemorrhage and fluid resuscitation with HTHO (r = 0.97) and HES (r = 0.96), although the LCBF-to-LCGU ratio was reset to a higher level (1.5 mL/mumol in the control group and 2.7 mL/mumol after fluid resuscitation with HTHO and HES, P < 0.05). We conclude that the increase in LCBF compensates for the reduction of arterial oxygen content to maintain cerebral oxygen delivery. Therefore, "small volume resuscitation" appears to be as effective as resuscitation with large volumes of isotonic HES in meeting the circulatory and metabolic demands of the brain tissue within the first 2 h after fluid resuscitation from hemorrhage.

Influence of age on the cardiovascular response during graded haemorrhage in anaesthetized rats

The present study was designed to follow the cardiovascular response to graded haemorrhage in two groups of adult rats of different ages. Group A (n = 10) had a mean body weight (bwt) of 655 g (50 weeks old) and group B (n = 10) had a mean bwt of 250 g (12 weeks old). After induction of anaesthesia, the carotid artery was cannulated for continuous intra-arterial blood pressure monitoring and for controlled haemorrhage. Five per cent of the total blood volume (TBV) was removed every 15 min until a maximum of 50% was reached. Mean arterial pressure (MAP) fell by 4-9 mm Hg each time 5% TBV was removed in both groups, and at the end of the study the MAP was comparable in the two groups (34 +/- 10 mm Hg in group A and 28 +/- 8 mm Hg in group B). There were no significant changes in heart rate (HR) in the young animals during haemorrhage, while there was a significant drop in heart rate in the older animals when blood loss exceeded 15% of TBV (P < 0.05). A significant difference was also observed in HR between the two groups of animals with blood loss in excess of 20% TBV (P < 0.05). It was concluded that although the hypotension induced by graded haemorrhage was similar in young and old rats, the older animals were less able to maintain their HR, probably as a consequence of age- and anaesthetic-related changes in sympathetic activity.

Comparison of the effects of ACTH-(1-24), methylprednisolone, aprotinin, and norepinephrine in a model of hemorrhagic shock in rats

Rats bled to a severe condition of volume-controlled hemorrhagic shock were randomly assigned to one of the following treatments: (1) saline, 1 ml/kg i.v.; (2) saline, 0.2 ml/kg per min i.v. for 10 min; (3) ACTH-(1-24), 160 micrograms/kg i.v.; 4) methylprednisolone, 40 mg/kg i.v.; (5) methylprednisolone, 80 mg/kg i.v.; (6) aprotinin, 10,000 KIU/kg i.v.; (7) norepinephrine, 5 micrograms/kg per min i.v. for 10 min; (8) norepinephrine, 10 micrograms/kg per min i.v. for 10 min. All rats treated with saline or with either of the two doses of methylprednisolone, and half of the rats treated with aprotinin, died within the subsequent 2 h. On the other hand, rats treated with norepinephrine, at either dose, or with ACTH-(1-24) were all still alive 2 h later, a similar improvement in cardiovascular and respiratory parameters being obtained with the two treatments. The effect of ACTH on mean arterial pressure was however more sustained throughout the observation period. These results further support the potential usefulness of ACTH-(1-24) as first-aid treatment in cases of severe blood losses.

Improved survival of hemorrhagic shock with oxygen and hypothermia in rats

A previously established model in awake rats of hemorrhagic shock (HS) with 25% spontaneous survival rate (without resuscitation) was used to evaluate the effects of 4 novel life-supporting first aid (LSFA) measures on survival time and rate. After shed blood volume (SBV) of 3.25 ml/100 g, withdrawn over 20 min, hemodynamic and respiratory responses were recorded to 3 h and survival to 24 h. The 5 groups of 20 rats each (total n = 100) were as follows: group I, controls without treatment; II, oxygen 100% inhalation; III, external cooling to rectal temperature 30 degrees C; IV, Ringer's solution 5 ml/100 g rectally; and V, acoustic and surface stimuli for arousal. Survival rates were: control group I, 35% at 3 h and 15% at 24 h; oxygen group II, 75% (P less than 0.05 compared with group I) at 3 h and 60% (P less than 0.05 compared with group I) at 24 h; hypothermia group III, 65% at 3 h and 45% (P less than 0.05 compared with group I) at 24 h; rectal fluid group IV, 50% at 3 h and 40% at 24 h; stimulated group V, 15% at 3 h and 15% at 24 h. Compared with group I, median survival times during HS 0-3 h were longer in groups II and III; and self-resuscitation attempts were longer in groups II, III and IV. We conclude that in untreated severe hemorrhagic shock, chances of survival to delayed arrival of advanced life support with i.v. fluid resuscitation might be increased with O2 inhalation and/or moderate external cooling.