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

Effects of Hyperoxia and Mild Therapeutic Hypothermia During Resuscitation From Porcine Hemorrhagic Shock

OBJECTIVE

Hemorrhagic shock-induced tissue hypoxia induces hyperinflammation, ultimately causing multiple organ failure. Hyperoxia and hypothermia can attenuate tissue hypoxia due to increased oxygen supply and decreased demand, respectively. Therefore, we tested the hypothesis whether mild therapeutic hypothermia and hyperoxia would attenuate postshock hyperinflammation and thereby organ dysfunction.

DESIGN

Prospective, controlled, randomized study.

SETTING

University animal research laboratory.

SUBJECTS

Thirty-six Bretoncelles-Meishan-Willebrand pigs of either gender.

INTERVENTIONS

After 4 hours of hemorrhagic shock (removal of 30% of the blood volume, subsequent titration of mean arterial pressure at 35 mm Hg), anesthetized and instrumented pigs were randomly assigned to "control" (standard resuscitation: retransfusion of shed blood, fluid resuscitation, norepinephrine titrated to maintain mean arterial pressure at preshock values, mechanical ventilation titrated to maintain arterial oxygen saturation > 90%), "hyperoxia" (standard resuscitation, but FIO2, 1.0), "hypothermia" (standard resuscitation, but core temperature 34°C), or "combi" (hyperoxia plus hypothermia) (n = 9 each).

MEASUREMENTS AND MAIN RESULTS

Before, immediately at the end of and 12 and 22 hours after hemorrhagic shock, we measured hemodynamics, blood gases, acid-base status, metabolism, organ function, cytokine production, and coagulation. Postmortem kidney specimen were taken for histological evaluation, immunohistochemistry (nitrotyrosine, cystathionine γ-lyase, activated caspase-3, and extravascular albumin), and immunoblotting (nuclear factor-κB, hypoxia-inducible factor-1α, heme oxygenase-1, inducible nitric oxide synthase, B-cell lymphoma-extra large, and protein expression of the endogenous nuclear factor-κB inhibitor). Although hyperoxia alone attenuated the postshock hyperinflammation and thereby tended to improve visceral organ function, hypothermia and combi treatment had no beneficial effect.

CONCLUSIONS

During resuscitation from near-lethal hemorrhagic shock, hyperoxia attenuated hyperinflammation, and thereby showed a favorable trend toward improved organ function. The lacking efficacy of hypothermia was most likely due to more pronounced barrier dysfunction with vascular leakage-induced circulatory failure.

Gradually increased oxygen administration promoted survival after hemorrhagic shock

Gradually increased oxygen administration (GIOA) seems promising in hemorrhagic shock. However, the effects of GIOA on survival remain unclear, and details of GIOA are to be identified. After the induction of hemorrhagic shock, the rats were randomized into five groups (n = 9): normoxic group (Normo), hyperoxic group (Hypero), normoxic to hyperoxic group (GIOA1), long-time hypoxemic to hyperoxic group (GIOA2), and short-time hypoxemic to hyperoxic group (GIOA3). Survival was recorded for 96 h, plasma alanine transaminase, oxidative stress, hemodynamics, and blood gas were measured. The mean survival time of the GIOA3 was significantly longer than that of the Normo, Hypero, and GIOA2. Plasma alanine transaminase levels were significantly lower in the Normo, GIOA1, and GIOA3 compared to the Hypero and GIOA2 at 2 h post-resuscitation (PR). Plasma 3-nitrotyrosine levels at 2 h PR were significantly lower in the GIOA2 and GIOA3 compared to the Normo and Hypero. Central venous oxygen saturation at 2 h PR in the GIOA3 was significantly higher than the Normo; however, no significant difference was observed between GIOA1 and Normo. Besides, at 2 h PR, mean arterial pressure in the GIOA3 was significantly higher than the GIOA2; however, no significant difference was observed between GIOA1 and GIOA2. (1) GIOA could significantly prolong survival time compared to normoxemic resuscitation and hyperoxic resuscitation; (2) early moments of GIOA are critical to the benefits; and (3) hypoxemia at onset of resuscitation may be imperative, more works are needed to determine the optimal initial oxygen concentration of GIOA.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.

The effects of hyperoxaemia on tissue oxygenation in patients with a nadir haematocrit lower than 20% during cardiopulmonary bypass

Excessive haemodilution and the resulting anaemia during CPB is accompanied by a decrease in the total arterial oxygen content, which may impair tissue oxygen delivery. Hyperoxic ventilation has been proven to improve tissue oxygenation in different pathophysiological states of anaemic tissue hypoxia. The aim of this study was to examine the influence of arterial hyperoxaemia on tissue oxygenation during CPB. Records of patients undergoing isolated CABG with CPB were retrospectively reviewed. Patients with nadir haematocrit levels below 20% during CPB were included in the study. Tissue hypoxia was defined as hyperlactataemia (lactate >2.2 mmol/L) coupled with low ScVO2 (ScVO2 <70%) during CPB. One hundred patients with normoxaemia and 100 patients with hyperoxaemia were included in the study. Patients with hyperoxaemia had lower tissue hypoxia incidence than patients with normoxaemia (p<0.001). Compared with patients without tissue hypoxia, patients with tissue hypoxia had significantly lower PaO2 values (p<0.001) and nadir haematocrit levels (p<0.001). Nadir haematocrit levels <18% (OR: 5.3; 95% CI: 2.67-10.6; p<0.001) and hyperoxaemia (OR: 0.28; 95% CI: 0.14-0.56; p<0.001) were independently associated with tissue hypoxia.

CONCLUSIONS

Hyperoxaemia during CPB may be protective against tissue hypoxia in patients with nadir haematocrit levels <20%.

Trauma and aggressive homeostasis management

Homeostasis refers to the capacity of the human body to maintain a stable constant state by means of continuous dynamic equilibrium adjustments controlled by a medley of interconnected regulatory mechanisms. Patients who sustain tissue injury, such as trauma or surgery, undergo a well-understood reproducible metabolic and neuroendocrine stress response. This review discusses 3 issues that concern homeostasis in the acute care of trauma patients directly related to the stress response: hyperglycemia, lactic acidosis, and hypothermia. There is significant reason to question the "conventional wisdom" relating to current approaches to restoring homeostasis in critically ill and trauma patients.

Hypothermia increases rebleeding during uncontrolled hemorrhage in the rat

Trauma registers show that hypothermia (HT) is an independent risk factor for death during hemorrhagic shock, although experimental animal studies indicate that HT may be beneficial during these conditions. However, the animal models were not designed to detect the expected increase in bleeding caused by HT. In a new model for uncontrolled bleeding, 40 Sprague-Dawley rats were exposed to a standardized femoral artery injury and randomized to either normothermia or HT. Ketamine/midazolam was used to minimize hemodynamic changes due to the anesthesia. The hypothermic rats were cooled to 30°C and rewarmed again at 90 min. The study period was 3 h. The incidence, onset time, duration, and volume of bleedings as well as hemodynamic and metabolic changes were recorded. There was no difference between groups with respect to the initial bleeding. Rebleedings occurred among 60% of the animals in both groups. Hypothermic rebleeders had more, larger, and longer rebleedings, resulting in a total rebleeding volume amounting to 41% of their estimated blood volume. The corresponding figure for the normothermic rebleeders was 3% (P < 0.001). Total rebleeding volume was significantly larger in the hypothermic group, even at body temperatures greater than 35°C. We conclude that the risk of rebleeding from a femoral injury is greater in the presence of cooling and HT. The larger rebleeding volumes seen even at body temperatures greater than 35°C indicate that factors other than temperature-induced coagulopathy also contributed to the increased hemorrhage.

Putting life on hold-for how long? Profound hypothermic cardiopulmonary bypass in a Swine model of complex vascular injuries

BACKGROUND

Rapid induction of profound hypothermia for emergency preservation and resuscitation can improve survival from uncontrolled lethal hemorrhage in large animal models. We have previously demonstrated that profound hypothermia (10 degrees C) must be induced rapidly (2 degrees C/min) and reversed gradually (0.5 degrees C/min) for best results. However, the maximum duration of hypothermic arrest in a clinically relevant trauma model remains unknown.

METHODS

Uncontrolled lethal hemorrhage was induced in 22 swine by creating an iliac artery and vein injury, followed 30 minutes later (simulating transport time) by laceration of the descending thoracic aorta. Through a thoracotomy approach, a catheter was placed in the aorta, and cold organ preservation solution was infused using a roller pump to rapidly induce profound hypothermia (10 degrees C) which was maintained with low-flow cardiopulmonary bypass. Vascular injuries were repaired during the asanguinous hypothermic low flow period. Profound hypothermia was maintained (n = 10-12 per group) for either 60 minutes or 120 minutes. After repair of injuries, animals were rewarmed (0.5 degrees C/min) and resuscitated on cardiopulmonary bypass, and whole blood was infused during this period. Animals were monitored for 4 weeks for neurologic deficits, organ dysfunction, and postoperative complications.

RESULTS

The 4-week survival rates in 60- and 120-minute groups were 92% and 50%, respectively (p < 0.05). The surviving animals were neurologically intact and had no long-term organ dysfunction, except for one animal in the 120-minute group. The animals subjected to 120 minutes of hypothermia had significantly worse lactic acidosis, displayed markedly slower recovery, and had significantly higher rates of postoperative complications, including late deaths because of infections.

CONCLUSION

In a model of lethal injuries, rapid induction of profound hypothermia can prevent death. Profound hypothermia decreases but does not abolish metabolism. With current methods, the upper limit of hypothermic arrest in the setting of uncontrolled hemorrhage is 60 minutes.

Trauma and aggressive homeostasis management

Three important issues concerning homeostasis in the acute care of trauma patients that are related directly to the stress response are hyperglycemia, lactic acidosis, and hypothermia. Recently, there has been a resurgence of interest in investigating the effects of aggressive thermal and glucose concentration and volume resuscitation on outcomes in critically ill and trauma patients. Significant reason exists to question the "conventional wisdom" relating to current approaches to restoring homeostasis in this patient population.

Profound hypothermic cardiopulmonary bypass facilitates survival without a high complication rate in a swine model of complex vascular, splenic, and colon injuries

BACKGROUND

Induction of a profound hypothermia for emergency preservation and resuscitation in severe hemorrhagic shock can improve survival from lethal injuries, but the impact of hypothermia on bleeding and infectious complications has not been completely determined.

STUDY DESIGN

Uncontrolled hemorrhage was induced in 26 swine (95 to 135 lbs) by creating an iliac artery and vein injury, and 30 minutes later, by lacerating the descending thoracic aorta. Through a left thoracotomy approach, profound total body hypothermia (10 degrees C) was induced (2 degrees C/min) by infusing cold organ preservation solution into the aorta. The experimental groups were: vascular injuries alone (group 1, n=10), vascular and colon injuries (group 2, n=8), and vascular, colon, and splenic injuries (group 3, n=8). All injuries were repaired during 60 minutes of low-flow cardiopulmonary bypass (CPB) with hemodilution and profound hypothermia; then the animals were slowly rewarmed (0.5 degrees C/min) back to normothermia. Survivors were monitored for 6 weeks for postoperative bleeding, neurologic deficits, cognitive function (learning new skills), organ dysfunction, and septic complications.

RESULTS

Six-week survival rates were 90% in group 1, 87.5% in group 2, and 75% in group 3 (p > 0.05). One animal in each group died from acute cardiac failure during the early postoperative phase. Splenic salvage was possible in all animals, and none required complete splenectomy for hemorrhage control. All surviving animals were neurologically intact, displayed normal learning capacity, and had no longterm organ dysfunction. None of the animals had postoperative hemorrhage or experienced septic complications. One animal in group 3 died on the ninth postoperative day because of bowel obstruction (volvulus).

CONCLUSIONS

Induction of profound hypothermia can preserve the viability of key organs during repair of lethal injuries. This strategy can be used even in the presence of solid organ and bowel injuries to improve survival, without any considerable increase in postoperative complication rates.

Cardiovascular responses to oxygen inhalation after hemorrhage in anesthetized rats: hyperoxic vasoconstriction

Oxygen inhalation is recommended for the initial care of trauma victims. The improved survival seen in early hemorrhage is normally associated with an increase in blood pressure. Although clinical use of oxygen can occur late after hemorrhage, the effects of late administration have not been specifically examined. Anesthetized rats were studied using an isobaric hemorrhage model with target pressures of either 70 or 40 mmHg. At various times after hemorrhage, the feedback control of the blood pressure was stopped and the inspired gas was changed from room air to 100% oxygen. The results show that shortly after hemorrhage to 70 mmHg, oxygen inhalation results in an increase in mean arterial blood pressure of 60 +/- 3 mmHg, which is associated with a large increase in total peripheral resistance from 0.89 +/- 0.05 to 1.25 +/- 0.1 peripheral resistance units. The blood pressure response is essentially unchanged with time, and it is not altered by a 10-min exposure to N(G)-nitro-l-arginine methyl ester. At a target pressure of 40 mmHg, the initial blood pressure response to oxygen is the same, but it gradually decreases as the animal develops a lactic acidosis. We conclude that the therapeutic value of oxygen needs to be separately evaluated for late hemorrhage.

Does the Rate of Rewarming from Profound Hypothermic Arrest Influence the Outcome in a Swine Model of Lethal Hemorrhage?

BACKGROUND

Rapid induction of profound hypothermic arrest (suspended animation) can provide valuable time for the repair of complex injuries and improve survival. The optimal rate for re-warming from a state of profound hypothermia is unknown. This experiment was designed to test the impact of different warming rates on outcome in a swine model of lethal hemorrhage from complex vascular injuries.

METHODS

Uncontrolled lethal hemorrhage was induced in 40 swine (80-120 lbs) by creating an iliac artery and vein injury, followed 30 minutes later (simulating transport time) by laceration of the descending thoracic aorta. Through a thoracotomy approach, a catheter was placed in the aorta and hyperkalemic organ preservation solution was infused on cardiopulmonary bypass to rapidly (2 degrees C/min) induce profound (10 degrees C) hypothermia. Vascular injuries were repaired during 60 minutes of hypothermic arrest. The 4 groups (n = 10/group) included normothermic controls (NC) where core temperature was maintained between 36 to 37 degrees C, and re-warming from profound hypothermia at rates of: 0.25 degrees C/min (slow), 0.5 degrees C/min (medium), or 1 degrees C/min (fast). Hyperkalemia was reversed during the hypothermic arrest period, and blood was infused for resuscitation during re-warming. After discontinuation of cardiopulmonary bypass, the animals were recovered and monitored for 6 weeks for neurologic deficits, cognitive function (learning new skills), and organ dysfunction. Detailed examination of brains was performed at 6 weeks.

RESULTS

All the normothermic animals died, whereas survival rates for slow, medium and fast re-warming from hypothermic arrest were 50, 90, and 30%, respectively (p < 0.05 slow and medium warming versus normothermic control, p < 0.05 medium versus fast re-warming). All the surviving animals were neurologically intact, displayed normal learning capacity, and had no long-term organ dysfunction.

CONCLUSIONS

Rapid induction of hypothermic arrest maintains viability of brain during repair of lethal vascular injuries. Long-term survival is influenced by the rate of reversal of hypothermia.

Mild hypothermia improves survival after prolonged, traumatic hemorrhagic shock in pigs

INTRODUCTION

Clinical studies have demonstrated improved survival after cardiac arrest with induction of mild hypothermia (34 degrees C). Infusion of ice-cold saline seems beneficial. The American Heart Association recommends therapeutic hypothermia for comatose survivors of cardiac arrest. For hemorrhagic shock (HS), laboratory studies suggest that mild hypothermia prolongs the golden hour for resuscitation. Yet, the effects of hypothermia during HS are unclear since retrospective clinical studies suggest that hypothermia is associated with increased mortality. Using a clinically relevant, large animal model with trauma and intensive care, we tested the hypothesis that mild hypothermia, induced with intravenous cold saline (ice cold or room temperature) and surface cooling, would improve survival after HS in pigs.

METHODS

Pigs were prepared under isoflurane anesthesia. After laparotomy, venous blood (75 mL/kg) was continuously withdrawn over 3 hours (no systemic heparin). At HS 35 minutes, the spleen was transected. At HS 40 minutes, pigs were divided into three groups (n = 8, each): 1) Normothermia (Norm)(38 degrees C), induced with warmed saline; 2) Mild hypothermia (34 degrees C) induced with i.v. infusion of 2 degrees C saline (Hypo-Ice) and surface cooling; and 3) Mild hypothermia (34 degrees C), induced with room temperature (24 degrees C) i.v. saline (Hypo-Rm) and surface cooling. Fluids were given when mean arterial pressure (MAP) was <30 mmHg. At HS 3 hours, shed blood was returned and splenectomy was performed. Intensive care was continued to 24 hours.

RESULTS

At 24 hours, there were two survivors in the Norm group, four in the Hypo-Ice group and seven in the Hypo-Rm group (p < 0.05 versus the Norm group, Log Rank). Time required to achieve 34 degrees C was 17 +/- 9 minutes in the Hypo-Ice group and 15 +/- 4 minutes in the Hypo-Rm group (NS). Compared with the Hypo-Rm group, the Hypo-Ice group required less saline during early HS (321 +/- 122 versus 571 +/- 184 mL, p < 0.05). The Hypo-Ice group also had higher lactate levels than the Hypo-Rm group (p < 0.05). Hypothermia did not cause any increase in bleeding compared with normothermia.

CONCLUSION

Mild hypothermia during HS, induced by infusion of room temperature saline and surface cooling, improves survival in a clinically relevant model of HS and trauma. However, the use of iced saline in this model had detrimental effects and did not cool the animal more quickly than room temperature fluids. These findings suggest that optimal methods for induction of hypothermia need to be addressed for each potential indication, e.g. cardiac arrest versus HS.

A portable cardiopulmonary bypass/extracorporeal membrane oxygenation system for the induction and reversal of profound hypothermia: feasibility study in a Swine model of lethal injuries

The Cleveland Clinic Foundation's (CCF) cardiopulmonary bypass/extracorporeal membrane oxygenation (CPB/ECMO) system capabilities were tested in a hypothermia trauma management feasibility study in a porcine animal model at the Uniformed Services University of the Health Sciences (USUHS, Bethesda, MD, U.S.A.). In this survival series, the CCF system was used in a simulated forward lines combat casualty application where lethal uncontrolled hemorrhage from major vascular injuries was repaired under a state of profound hypothermic arrest (suspended animation), followed by recovery and monitoring in an intensive care unit (ICU) setting. The animals were monitored for survival, neurological impact, cognitive functions, organ damage, and delayed complications over 3 weeks. A survival rate of 83% matched rates previously found using conventional equipment. Neurological findings, organ dysfunction, and complication rates also were no different from previous studies using standard equipment. Successful survival results demonstrated that the CCF CPB/ECMO system could be used to induce a period of profound hypothermic arrest for the repair of lethal traumatic injuries. The logistical advantages of this system make it an attractive choice for use in austere settings and during transport.

Profiling biochemical and hemodynamic markers using chronically instrumented, conscious and unrestrained rats undergoing severe, acute controlled hemorrhagic hypovolemic shock as an integrated in-vivo model system to assess new blood substitutes

The aim of the present study was to assess several biochemical and physiological endpoint parameters alongside controlled hemorrhagic and recovery phases of chronically instrumented, conscious and unrestrained healthy rats. Male Sprague-Dawley rats (12-14 weeks; 430+/-20 g; n=22-18) were instrumented with a saline-perfused femoral arterial catheter and placed individually in a metabolic cage for up to 20 days, allowing instant assessments of the hemodynamic profile and blood and urine sampling for hematological profile and biochemical measurements to assess hepatic, renal and metabolic functions. In addition, body weight, food and water intake, and diuresis were monitored daily. After a 7-day stabilization period, the rats underwent severe and acute hemorrhagic shock (HS) (removal of 50% of total circulating blood volume), kept in hypovolemic shock for an ischemic period of 50 min and then resuscitated over 10 min. Gr. 1 was re-infused with autologous shed blood (AB; n=10) whereas Gr. 2 was infused 1:1 with a solution of sterile saline-albumin (SA; 7% w/v) (n=8-12). Ischemic rats recovered much more rapidly following AB re-infusion than those receiving SA. Normal hemodynamic and biochemical profiles were re-established after 24 h. Depressed blood pressure lasted 4-5 days in SA rats. The hematological profile in the SA resuscitated rats was even more drastically affected. Circulating plasma concentrations of hemoglobin (-40%), hematocrit (-50%), RBC (-40%) and platelets (-41%) counts were still severely decreased 24 h after the acute ischemic event whereas WBC counts increased 2.2-fold by day 4. It took 5-9 days for these profiles to normalize after ischemia-reperfusion with SA. Diuresis increased in both groups (by 45+/-7% on day 1) but presented distinct electrolytic profiles. Hepatic and renal functions were normal in AB rats whereas altered in SA rats. The present set of experiments enabled us to validate a model of HS in conscious rats and the use of an integrated in vivo platform as a valuable tool to characterize HS-induced stress and to test new classes of blood substitutes in real time, post-event, over days.

Induction of profound hypothermia modulates the immune/inflammatory response in a swine model of lethal hemorrhage

Profound hypothermic arrest ("suspended animation") is a new strategy to improve outcome following uncontrolled lethal hemorrhage (ULH). However, the impact of this approach on the immune/inflammatory response is unknown. This experiment was conducted to test the influence of profound hypothermia on markers of immune/inflammatory system.

METHODS

ULH was induced in 32 female swine (80-120 lb) by creating an iliac artery and vein injury, followed 30 min later by laceration of the descending thoracic aorta. Through a left thoracotomy approach, total body hypothermic hyperkalemic metabolic arrest was induced by infusing organ preservation fluids into the aorta using a cardiopulmonary bypass machine (CPB). Experimental groups were (1) normothermic controls (no cooling, NC), or hypothermia induced at the following rates: (2) 0.5 degrees C/min (slow, SC), (3) 1 degrees C/min (medium, MC) and (4) 2 degrees C/min (fast, FC). Vascular injuries were repaired during 60 min of profound (10 degrees C) hypothermic arrest. Hyperkalemia was reversed by hypokalemic fluid exchange, and blood was infused for resuscitation during re-warming (0.5 degrees C/min). The surviving animals were monitored for 6 weeks. Levels of IL-1, TNFalpha, IL-6, IL-10, TGF-1 beta and heat shock protein (HSP-70) were measured by ELISA in serum samples collected serially during the experiment and post-operatively.

RESULTS

Some of the immune markers were influenced by the use of CPB, independent of hypothermia (decrease in TGF-1 beta and increase in IL-1 beta). Hypothermia caused a significant decrease in IL-6, and an increase in HSP-70 expression compared to normothermic controls, independent of the cooling rate. An increase in IL-10 levels was noted which was influenced by the rate of cooling (p<0.05, MC versus NC).

CONCLUSIONS

Profound hypothermia modulates the post-shock immune/inflammatory system by attenuating the pro-inflammatory IL-6, increasing anti-inflammatory IL-10 and augmenting the protective heat shock responses.

Titrated hypertonic/hyperoncotic solution for hypotensive fluid resuscitation during uncontrolled hemorrhagic shock in rats

BACKGROUND

In volume- or pressure-controlled hemorrhagic shock (HS) a bolus intravenous infusion of hypertonic/hyperoncotic solution (HHS) proved beneficial compared to isotonic crystalloid solutions. During uncontrolled HS in animals, however, HHS by bolus increased blood pressure unpredictably, and increased blood loss and mortality. We hypothesized that a titrated i.v. infusion of HHS, compared to titrated lactated Ringer's solution (LR), for hypotensive fluid resuscitation during uncontrolled HS reduces fluid requirement, does not increase blood loss, and improves survival.

METHODS

We used our three-phased uncontrolled HS outcome model in rats. HS phase I began with blood withdrawal of 3 ml/100g over 15 min, followed by tail amputation. Then, hydroxyethyl starch 10% in NaCl 7.2% was given i.v. to the HHS group (n=10) and LR to the control group (n=10), both titrated to prevent mean arterial pressure (MAP) from falling below 40 mmHg during HS time 20-90 min. At HS 90 min, resuscitation phase II of 180 min began with hemostasis, return of all the blood initially shed, plus fluids i.v. as needed to maintain normotension (MAP>or=70 mmHg). Liver dysoxia was monitored as increase in liver surface pCO2 during phases I and II. Observation phase III was to 72 h.

RESULTS

During HS, preventing a decrease in MAP below 40 mmHg required HHS 4.9+/-0.6 ml/kg (all data mean+/-S.E.M.), compared to LR 62.2+/-16.6 ml/kg (P<0.001), with no group difference in MAP. Uncontrolled blood loss during HS from the tail stump was 13.3+/-1.9 ml/kg with HHS infusion, versus 12.6+/-2.5 ml/kg with LR infusion (P=0.73). Serum sodium concentrations were moderately elevated at the end of HS in the HHS group (149+/-3 mmol/l) versus the LR group (139+/-1 mmol/l) (P=0.001), and remained elevated throughout. Liver pCO2 increased during HS in both groups equally (P<0.001 versus baseline), and tended to return to baseline levels at the end of HS. Blood gas and lactate values throughout did not differ between groups. During HS, 2 of 10 rats in the HHS group versus 0 of 10 in the LR group died (P=0.47). There was no difference between HHS and LR groups in survival rates to 72 h (3 of 10 in the HHS group versus 2 of 10 in the LR group) (P=1.0). Survival times, by life table analysis, were not different (P=0.75).

CONCLUSION

In prolonged uncontrolled HS, a titrated i.v. infusion of HHS can maintain controlled hypotension with only one-tenth of the volume of LR required, without increasing blood loss. This titrated HHS strategy may not increase the chance of long-term survival.

The rate of induction of hypothermic arrest determines the outcome in a Swine model of lethal hemorrhage

BACKGROUND

Lethal injuries can be surgically repaired under asanguineous hypothermic condition (suspended animation) with excellent outcome. However, the optimal rate for the induction of hypothermic metabolic arrest following uncontrolled lethal hemorrhage (ULH) is unknown.

METHODS

ULH was induced in 32 female swine (80-120 lbs) by creating an iliac artery and vein injury, followed 30 minutes later by laceration of the descending thoracic aorta. Through a left thoracotomy approach, total body hypothermic hyperkalemic metabolic arrest was induced by infusing organ preservation fluids into the aorta. Experimental groups were: normothermic controls (no cooling, NC), or hypothermia induced at a rate of 0.5 degrees C/min (slow, SC), 1 degrees C/min (medium, MC), or 2 degrees C/min (fast, FC). Vascular injuries were repaired during the 60 minutes of profound (10 degrees C) hypothermic arrest. Hyperkalemia was reversed by hypokalemic fluid exchange, and blood was infused for resuscitation during the re-warming (0.5 degrees C/ minute) period. The survivors were monitored for 6 weeks.

RESULTS

The 6 week survival rates were 0% (NC), 37.5% (SC), 62.5% (MC), and 87.5% (FC) respectively (p < 0.05 MC&FC versus NC). All of the surviving hypothermic arrest animals were neurologically intact and displayed no long term organ dysfunction.

CONCLUSION

Hypothermic metabolic arrest can be used to maintain viability of key organs during repair of lethal injuries. Survival is influenced by the rate of cooling with the best outcome following rapid induction of hypothermia.

Die Behandlung des hämorrhagischen Schocks

The future of shock treatment depends on the importance of scientific results, and the willingness of physicians to optimize, and to reconsider established treatment protocols. There are four major potentially promising approaches to advanced trauma life support. First, control of hemorrhage by administration of local hemostatic agents, and a better, target-controlled management of the coagulation system. Second, improving intravascular volume by recruiting blood from the venous vasculature by preventing mistakes during mechanical ventilation, and by employing alternative spontaneous (i.e. use of the inspiratory threshold valve) or artificial ventilation strategies. In addition, artificial oxygen carriers may improve intravascular volume and oxygen delivery. Third, pharmacologic support of physiologic, endogenous mechanisms involved in the compensation phase of shock, and blockade of pathomechanisms that are known to cause irreversible vasoplegia (arginine vasopressin and K(ATP) channel blockers for hemodynamic stabilization). Fourth, employing potentially protective strategies such as mild or moderate hypothermia. Finally, the ultimate vision of trauma resuscitation is the concept of "suspended animation" as a form of delayed resuscitation after protection of vital organ systems.

HYPEROXIC VENTILATION REDUCES SIX-HOUR MORTALITY AFTER PARTIAL FLUID RESUSCITATION FROM HEMORRHAGIC SHOCK

Ventilation with 100% oxygen (Fio(2) 1.0; hyperoxic ventilation; HV) as an alternative to red blood cell transfusion enables survival in otherwise lethal normovolemic anemia. The aim of the present study was to investigate whether HV as a supplement to fluid infusion therapy could also restore adequate tissue oxygenation and prevent death in otherwise lethal hemorrhagic shock. In 14 anesthetized pigs ventilated on room air (Fio(2) 0.21), hemorrhagic shock was induced by controlled withdrawal of blood (target mean arterial pressure 35-40 mmHg) and maintained for 1 h. Subsequently, the animals were partially fluid-resuscitated (i.e., replacement of lost plasma volume) either with hydroxyethyl starch (6% HES, 200/0.5) alone (G 0.21) or with HES supplemented by HV (G 1.0). After completion of partial fluid resuscitation, all animals were followed up for the next 6 h. Five of seven animals of G 0.21 died within the 6-h observation period (i.e., 6-h mortality 71%). Death was preceded by a continuous increase of the serum concentrations of arterial lactate and persistent tissue hypoxia. In contrast to that, all animals of G 1.0 survived the 6-h observation period without lactic acidosis and with improved tissue oxygenation (i.e., 6-h mortality 0%; G 0.21 versus G 1.0 P < 0.05). In anesthetized pigs submitted to lethal hemorrhagic shock, the supplementation of partial fluid resuscitation with HV improved tissue oxygenation and enabled survival for 6 h.

Effect of resuscitative mild hypothermia and oxygen concentration on the survival time during lethal uncontrolled haemorrhagic shock in mechanically ventilated rats

OBJECTIVE

To test the hypothesis that resuscitative mild hypothermia (MH) (34 degrees C) or breathing fractional inspired oxygen (FIo2) of 1.0 would prolong survival time during lethal uncontrolled haemorrhagic shock (UHS) in mechanically ventilated rats.

METHODS

Forty Wistar rats were anaesthetized with halothane, nitrous oxide and oxygen (70/30%), intubated and mechanically ventilated. UHS was induced by volume-controlled blood withdrawal of 3 ml/100 g over 15 min, followed by 75% tail amputation of its length. The animals were randomly divided into four UHS treatment groups (10 rats in each group): group 1 was maintained on an FIo2 of 0.21 and rectal temperature of 37.5 degrees C. Group 2 was maintained on an FIo2 of 0.21 and induced MH. Group 3 was maintained on an FIo2 of 1.0 and 37.5 degrees C. Group 4 was maintained on an FIo2 of 1.0 and MH. Rats were observed otherwise untreated until death.

RESULTS

During the initial blood withdrawal, mean arterial pressure (MAP) decreased to 40 mmHg, and the heart rate (HR) increased up to 400 beats/min. The induction of MH increased MAP to 60 mmHg and increased survival time. Moreover, it reduced the HR to 300 beats/min but did not increase bleeding. Ventilation with an FIo2 of 1.0 did not influence MAP, blood loss or survival time, but increased arterial oxygen tension. The mean survival time was 62, 202, 68 and 209 min in groups 1, 2, 3 and 4, respectively. Blood loss from the tail was 1.0, 1.2, 0.9 and 0.7 ml, respectively, in groups 1, 2, 3 and 4.

CONCLUSION

MH prolonged the survival time during UHS in mechanically ventilated rats. However, an FIo2 of 1.0 did not influence the survival time or blood loss from the tail.

After spontaneous hypothermia during hemorrhagic shock, continuing mild hypothermia (34 degrees C) improves early but not late survival in rats

BACKGROUND

Spontaneous hypothermia is common in victims of severe trauma. Laboratory studies have shown benefit of induced (therapeutic) mild hypothermia (34 degrees C) during hemorrhagic shock (HS). Clinical data, however, suggest that hypothermia, which often occurs spontaneously in trauma patients, is detrimental. Because critically ill trauma patients are usually cool, the clinical question, which has not been explored in the laboratory with long-term outcome, is whether maintaining hypothermia or actively rewarming the patient improves outcome. We hypothesized that after spontaneous cooling during HS, continuing mild therapeutic hypothermia during resuscitation is beneficial compared with active rewarming.

METHODS

In study A, under light isoflurane anesthesia, 24 Sprague-Dawley rats were bled over 10 minutes to, and maintained at, mean arterial pressure (MAP) of 40 mm Hg until reuptake of 30% of maximal shed blood volume was needed. Rectal temperature (Tr) decreased spontaneously to, and was then maintained at, 35 degrees C during HS. Fluid resuscitation included the remaining shed blood and up to 400 mL/kg of lactated Ringer's solution with 5% dextrose over 4 hours. During resuscitation, three groups (n = 8 each) were studied: normothermia (rapid rewarming to Tr 37.5 degrees C at the beginning of resuscitation); hypothermia-2 h (cooling to Tr 34 degrees C to resuscitation time 2 hours); and hypothermia-12 h (cooling to Tr 34 degrees C to 12 hours). Rats were observed to 72 hours. In study B, more severe HS than in study A was studied. HS was induced with 3 mL/100 g blood withdrawal over 15 minutes followed by maintenance of MAP of 40 mm Hg until 50% of maximal shed blood volume was needed. Two groups (n = 8 each) were studied: normothermia and hypothermia-12 h. Data are presented as mean +/- SD or median (range).

RESULTS

In study A, both hypothermia groups had higher MAP and lower heart rates during resuscitation than the normothermia group (p < 0.01). Survival to 72 hours was achieved in three of eight rats in the normothermia group and two of eight in each hypothermia group. Thirteen of 17 deaths occurred after 24 hours. In study B, for resuscitation, the hypothermia group needed less fluid (53 +/- 6 mL vs. 79 +/- 32 mL, p < 0.05), but had higher MAP (p < 0.01), lower heart rate (p < 0.01), and lower lactate level (p = 0.06). All rats died before 72 hours. The hypothermia group had longer survival time (24.5 [13-48.5] hours) than the normothermia group (7.5 [1.5-19] hours) (p = 0.003 by life table analysis).

CONCLUSION

After spontaneous cooling during moderately severe HS, mild, controlled hypothermia during resuscitation does not seem to affect long-term survival. After more severe HS, hypothermia increases survival time. Hypothermia supports arterial pressure during resuscitation from severe HS.

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.

Mild hypothermia during hemorrhagic shock in rats improves survival without significant effects on inflammatory responses

OBJECTIVE

To explore the hypothesis that the survival benefit of mild, therapeutic hypothermia during hemorrhagic shock is associated with inhibition of lipid peroxidation and the acute inflammatory response.

DESIGN

Prospective and randomized.

SETTING

Animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats underwent pressure-controlled (mean arterial pressure 40 mm Hg) hemorrhagic shock for 90 mins. They were randomized to normothermia (38.0 +/- 0.5 degrees C) or mild hypothermia (33-34 degrees C from hemorrhagic shock 20 mins to resuscitation time 12 hrs). Rats were killed at resuscitation time 3 or 24 hrs.

MEASUREMENTS AND MAIN RESULTS

All seven rats in the hypothermia group and seven of 15 rats in the normothermia group survived to 24 hrs (p <.05). Hypothermic rats had lower serum potassium and higher blood glucose concentrations at 90 mins of hemorrhagic shock (p <.05). At resuscitation time 24 hrs, the hypothermia group had less liver injury (based on serum concentrations of ornithine carbamolytransferase and liver histology) and higher blood glucose than the normothermia group (p <.05). There were no differences in serum free 8-isoprostane (a marker of lipid peroxidation by free radicals) between the two groups at either baseline or resuscitation time 1 hr. Serum concentrations of interleukin- 1 beta, interleukin-6, and tumor necrosis factor-alpha peaked at resuscitation time 1 hr. Tumor necrosis factor-alpha concentrations were higher (p <.05) at resuscitation time 1 hr in the hypothermia group compared with the normothermic group. Serum cytokine concentrations were not different between survivors and nonsurvivors in the normothermia group. Serum cytokine concentrations returned to baseline values in both groups by 24 hrs. There were no differences in the number of neutrophils in the lungs or the small intestine between the groups. More neutrophils were found in the lungs at resuscitation time 3 hrs than at resuscitation time 24 hrs in both groups (p <.01).

CONCLUSIONS

These data suggest that lipid peroxidation and systemic inflammatory responses to hemorrhagic shock are minimally influenced by mild hypothermia, although liver injury is mitigated and survival improved. Other mechanisms of benefit from mild hypothermia need to be explored.

Veno-venous extracorporeal blood shunt cooling to induce mild hypothermia in dog experiments and review of cooling methods

Mild hypothermia (33-36 degrees C) might be beneficial when induced during or after insults to the brain (cardiac arrest, brain trauma, stroke), spinal cord (trauma), heart (acute myocardial infarction), or viscera (hemorrhagic shock). Reaching the target temperature rapidly in patients inside and outside hospitals remains a challenge. This study was to test the feasibility of veno-venous extracorporeal blood cooling for the rapid induction of mild hypothermia in dogs, using a simple pumping-cooling device. Ten custom-bred hunting dogs (21-28 kg) were lightly anesthetized and mechanically ventilated. In five dogs, two catheters were inserted through femoral veins, one peripheral and the other into the inferior vena cava. The catheters were connected via a coiled plastic tube as heat exchanger (15 m long, 3 mm inside diameter, 120 ml priming volume), which was immersed in an ice-water bath. A small roller-pump produced a veno-venous flow of 200 ml/min (about 10% of cardiac output). In five additional dogs (control group), a clinically practiced external cooling method was employed, using alcohol over the skin of the trunk and fanning plus ice-bags. During spontaneous normotension, veno-venous cooling delivered blood into the vena cava at 6.2 degrees C standard deviation (SD 1.4) and decreased tympanic membrane (Tty) temperature from 37.5 to 34.0 degrees C at 5.2 min (SD 0.7), and to 32.0 degrees C at 7.9 min (SD 1.3). Skin surface cooling decreased tympanic temperature from 37.5 to 34.0 degrees C at 19.9 min (SD 3.7), and to 32.0 degrees C at 29.9 (SD 5.1) (P=0.001). Heart rates at Tty 34 and 32 degrees C were significantly lower than at baseline in both groups, but within physiological range, without difference between groups. There were no arrhythmias. We conclude that in large dogs the induction of mild systemic hypothermia with extracorporeal veno-venous blood shunt cooling is simple and four times more rapid than skin surface cooling.