Improved survival of hemorrhagic shock with oxygen and hypothermia in rats

Effects of ketamine analgesia on cardiorespiratory responses and survival to trauma and hemorrhage in rats

Ketamine is the recommended analgesic on the battlefield for soldiers with hemorrhage, despite a lack of supportive evidence from laboratory or clinical studies. Hence, this study determined the effects of ketamine analgesia on cardiorespiratory responses and survival to moderate (37% blood volume; n = 8/group) or severe hemorrhage (50% blood volume; n = 10/group) after trauma in rats. We used a conscious hemorrhage model with extremity trauma (fibular fracture + soft tissue injury) while measuring mean arterial pressure (MAP), heart rate (HR), and body temperature (T_b) by telemetry, and respiration rate (RR), minute volume (MV), and tidal volume (TV) via whole body plethysmography. Male rats received saline (S) or 5.0 mg/kg ketamine (K) (100 µL/100 g body wt) intra-arterially after trauma and hemorrhage. All rats survived 37% hemorrhage. For 50% hemorrhage, neither survival times [180 min (SD 78) vs. 209 min (SD 66)] nor percent survival (60% vs. 80%) differed between S- and K-treated rats. After 37% hemorrhage, K (compared with S) increased MAP and decreased T_b and MV. After 50% hemorrhage, K (compared with S) increased MAP but decreased HR and MV. K effects on cardiorespiratory function were time dependent, significant but modest, and transient at the analgesic dose given. K effects on T_b were also significant but modest and more prolonged. With the use of this rat model, our data support the use of K as an analgesic in injured, hypovolemic patients.NEW & NOTEWORTHY Ketamine administration at a dose shown to alleviate pain in nonhemorrhaged rats with extremity trauma had only modest and transient effects on multiple aspects of cardiorespiratory function after both moderate (37%) and severe (50%) traumatic hemorrhages. Such effects did not alter survival.

Hyperoxia or Therapeutic Hypothermia During Resuscitation from Non-Lethal Hemorrhagic Shock in Swine

We previously demonstrated beneficial effects of 22 h of hyperoxia following near-lethal porcine hemorrhagic shock, whereas therapeutic hypothermia was detrimental. Therefore, we investigated whether shorter exposure to hyperoxia (12 h) would still improve organ function, and whether 12 h of hypothermia with subsequent rewarming could avoid deleterious effects after less severe hemorrhagic shock.Twenty-seven anesthetized and surgically instrumented pigs underwent 3 h of hemorrhagic shock by removal of 30% of the blood volume and titration of the mean arterial blood pressure (MAP) to 40 mm Hg. Post-shock, pigs were randomly assigned to control, hyperoxia (FIO2 100% for 12 h) or hypothermia group (34°C core temperature for 12 h with subsequent rewarming). Before, at the end of shock, after 12 and 23 h of resuscitation, data sets comprising hemodynamics, blood gases, and parameters of inflammation and organ function were acquired. Postmortem, kidney samples were collected for immunohistochemistry and western blotting.Hyperoxia exerted neither beneficial nor detrimental effects. In contrast, mortality in the hypothermia group was significantly higher compared with controls (67% vs. 11%). Hypothermia impaired circulation (MAP 64 (57;89) mm Hg vs. 104 (98; 114) mm Hg) resulting in metabolic acidosis (lactate 11.0 (6.6;13.6) mmol L vs. 1.0 (0.8;1.5) mmol L) and reduced creatinine clearance (26 (9;61) mL min vs. 77 (52;80) mL min) compared to the control group after 12 h of resuscitation. Impaired kidney function coincided with increased renal 3-nitrotyrosine formation and extravascular albumin accumulation.In conclusion, hyperoxia proved to be safe during resuscitation from hemorrhagic shock. The lacking organ-protective effects of hyperoxia compared to resuscitation from near-lethal hemorrhage suggest a dependence of the effectiveness of hyperoxia from shock severity. In line with our previous report, therapeutic hypothermia (and rewarming) was confirmed to be detrimental most likely due to vascular barrier dysfunction.

Induced Hypothermia Does Not Harm Hemodynamics after Polytrauma: A Porcine Model

BACKGROUND

The deterioration of hemodynamics instantly endangers the patients' life after polytrauma. As accidental hypothermia frequently occurs in polytrauma, therapeutic hypothermia still displays an ambivalent role as the impact on the cardiopulmonary function is not yet fully understood.

METHODS

We have previously established a porcine polytrauma model including blunt chest trauma, penetrating abdominal trauma, and hemorrhagic shock. Therapeutic hypothermia (34°C) was induced for 3 hours. We documented cardiovascular parameters and basic respiratory parameters. Pigs were euthanized after 15.5 hours.

RESULTS

Our polytrauma porcine model displayed sufficient trauma impact. Resuscitation showed adequate restoration of hemodynamics. Induced hypothermia had neither harmful nor major positive effects on the animals' hemodynamics. Though heart rate significantly decreased and mixed venous oxygen saturation significantly increased during therapeutic hypothermia. Mean arterial blood pressure, central venous pressure, pulmonary arterial pressure, and wedge pressure showed no significant differences comparing normothermic trauma and hypothermic trauma pigs during hypothermia.

CONCLUSIONS

Induced hypothermia after polytrauma is feasible. No major harmful effects on hemodynamics were observed. Therapeutic hypothermia revealed hints for tissue protective impact. But the chosen length for therapeutic hypothermia was too short. Nevertheless, therapeutic hypothermia might be a useful tool for intensive care after polytrauma. Future studies should extend therapeutic hypothermia.

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.

Life or death? A physiogenomic approach to understand individual variation in responses to hemorrhagic shock

Severe hemorrhage due to trauma is a major cause of death throughout the world. It has often been observed that some victims are able to withstand hemorrhage better than others. For decades investigators have attempted to identify physiological mechanisms that distinguish survivors from nonsurvivors for the purpose of providing more informed therapies. As an alternative approach to address this issue, we have initiated a research program to identify genes and genetic mechanisms that contribute to this phenotype of survival time after controlled hemorrhage. From physiogenomic studies using inbred rat strains, we have demonstrated that this phenotype is a heritable quantitative trait, and is therefore a complex trait regulated by multiple genes. Our work continues to identify quantitative trait loci as well as potential epigenetic mechanisms that might influence survival time after severe hemorrhage. Our ultimate goal is to improve survival to traumatic hemorrhage and attendant shock via regulation of genetic mechanisms and to provide knowledge that will lead to genetically-informed personalized treatments.

Plasma and myocardial visfatin expression changes are associated with therapeutic hypothermia protection during murine hemorrhagic shock/resuscitation

AIM

Cytokine production during hemorrhagic shock (HS) could affect cardiac function during the hours after resuscitation. Visfatin is a recently described protein that functions both as a proinflammatory plasma cytokine and an intracellular enzyme within the nicotinamide adenine dinucleotide (NAD(+)) salvage pathway. We developed a mouse model of HS to study the effect of therapeutic hypothermia (TH) on hemodynamic outcomes and associated plasma and tissue visfatin content.

METHODS

Mice were bled and maintained at a mean arterial pressure (MAP) of 35 mmHg. After 30 min, animals (n=52) were randomized to normothermia (NT, 37+/-0.5 degrees C) or TH (33+/-0.5 degrees C) followed by rewarming at 60 min following resuscitation. After 90 min of HS (S90), mice were resuscitated and monitored for 180 min (R180). Visfatin, interleukin 6 (IL-6), keratinocyte-derived chemokine (KC), tumor necrosis factor-alpha (TNF-alpha), and myoglobin were measured by ELISA.

RESULTS

Compared to NT, TH animals exhibited improved R180 survival (23/26 [88.5%] vs. 13/26 [50%]; p=0.001). Plasma visfatin, IL-6, KC, and TNF-alpha increased by S90 in both groups (p<0.05). TH attenuated S90 plasma visfatin and, after rewarming, decreased R180 plasma IL-6, KC, and myoglobin (p<0.05) relative to NT. Heart and gut KC increased at S90 while IL-6 increases were delayed until R180 (p<0.05). NT produced sustained elevations of myocardial KC but decreased visfatin by R180, effects abrogated by TH (p<0.05).

CONCLUSIONS

In a mouse model of HS, TH improves hemodynamics and alters plasma and tissue proinflammatory cytokines including the novel cytokine visfatin. TH modulation of cytokines may attenuate cardiac dysfunction following HS.

Impact of hypothermia in the rural, pediatric trauma patient

OBJECTIVE

Hypothermia is an independent predictor of mortality in adult trauma studies. However, the impact of hypothermia on the pediatric trauma population has not been described. The purpose of this study is to evaluate hypothermia as a cofactor to mortality, complications, and among survivors, hospital length of stay parameters in the pediatric trauma population.

DESIGN

Retrospective review of a prospectively collected database (National Trauma Registry of the American College of Surgeons) over a 5-yr period (July 2002 to June 2007).

SETTING

A rural, level I trauma center.

PATIENTS

One thousand six hundred twenty-nine pediatric patients admitted with a traumatic injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Multivariate regression models were used to evaluate the association of hypothermia with mortality, infectious complications, organ dysfunction, and among survivors, hospital length of stay parameters. Of 1,629 pediatric trauma patients admitted, 182 (11.1%) patients were hypothermic (temperature below 36 degrees C) on admission. Hypothermia had an adjusted odds ratio (AOR) of 2.41 (95% confidence interval [CI], 1.12-5.22, p = .025) for mortality. After controlling for covariates, hypothermia had associations with developing pneumonia (AOR, 0.185, 95% CI, 0.040-0.853; p = .031) and a bleeding diathesis (AOR, 3.14, 95% CI, 1.04-9.44; p = .042). The median days in the hospital, intensive care unit (ICU), and ventilator were longer in the hypothermic cohort; however, after controlling for covariates, hypothermia was not associated with differences in hospital days, ICU days, or ventilator days.

CONCLUSIONS

Hypothermia is a common problem at admission among pediatric trauma patients. Hypothermia is associated with an increase in the odds of death and the development of a bleeding diathesis, while having decreased odds for developing pneumonia. While the length of stay indicators were longer in the hypothermic cohort among survivors, no significant association was noted with hypothermia for hospital, ICU, or ventilator days after controlling for confounders.

Impact of hypothermia (below 36 degrees C) in the rural trauma patient

BACKGROUND

Hypothermia is an independent predictor of mortality based on urban studies. But this association has not been described in the rural setting. This study's purpose was to evaluate hypothermia as a cofactor to mortality, complications, and hospital length of stay (LOS) parameters in the rural trauma setting.

STUDY DESIGN

The National Trauma Registry of the American College of Surgeons database for our rural, Level I trauma center was queried for a 5-year period (July 2002 to June 2007) to identify adult trauma patients. Multivariate regression models were used to evaluate the association of hypothermia with mortality; infectious complications; organ dysfunction; and, among survivors, hospital LOS parameters.

RESULTS

Of 9,482 adult patients admitted, 1,490 (15.7%) patients were hypothermic. Hypothermia had an adjusted odds ratio of 1.70 for mortality (95% CI, 1.35 to 2.12; p < 0.001). After controlling for covariates, hypothermia was not significantly associated with infectious complications or organ dysfunction, except for arrhythmia (adjusted odds ratio, 1.40; CI, 1.03 to 1.90; p = 0.031). Hypothermia was not associated with a difference in ICU (p = 0.310) or ventilator (p = 0.144) LOS. But a slight increase in hospital days was noted in the hypothermic patient (hazards ratio, 0.890 for discharge; 95% CI, 0.838 to 0.946; p < 0.001).

CONCLUSIONS

Hypothermia is a common problem at admission in a rural trauma center. It is associated with an increase in hospitalized days but not with increased ICU or ventilator days among survivors. Other than arrhythmias, it was not significantly associated with other National Trauma Registry of the American College of Surgeons infectious or organ dysfunction complications. Hypothermia is an independent risk factor for mortality in the rural trauma patient.

Therapeutic hypothermia: the Safar vision

At the 2(nd) International Brain Hypothermia conference, in Miami, the late Dr. Peter Safar was honored for his many contributions to the field of therapeutic hypothermia. Therapeutic hypothermia played a central role in his overall vision for optimized resuscitation and neurointensive care, across a large number of potential insults. The successful use of therapeutic hypothermia in comatose patients after cardiac arrest, for example, was already included in the historic first "ABCs" of resuscitation, published by Safar in 1964. This review addresses key historical events in the development and implementation of therapeutic hypothermia across a number of central nervous system insults. A discussion of future potential uses of this therapy in a variety of applications as part of the Safar vision is also presented.

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.

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.

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.

Effect of systemic hypothermia on local soft tissue trauma-induced microcirculatory and cellular dysfunction in mice*

OBJECTIVE

Changes in body temperature occur as a systemic reaction to severe trauma; however, its role in the manifestation of injury remains unclear. Thermoregulatory responses vary considerably from fever to hypothermia. Although hypothermic trauma patients seem to have a worse prognosis, there is the question whether hypothermia per se or the severity of trauma producing the hypothermia is responsible for aggravated injury and increased mortality rate. The present study unravels how moderate to severe systemic hypothermia modulates local microcirculatory dysfunction and cellular injury in local soft tissue trauma.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university.

SUBJECTS

C57BL/6J mice.

INTERVENTIONS

A model involving standardized drop weight device-induced tissue trauma and high-resolution multifluorescence microscopy in the dorsal skinfold chamber was used to show arteriolar vasoconstriction, reduction of blood flow, nutritive perfusion failure, and apoptotic cell death at 1 hr after trauma.

MEASUREMENTS AND MAIN RESULTS

During the 8-hr posttrauma observation period, microcirculation, but not apoptosis, restituted to almost baseline level. Concomitant systemic hypothermia of either 34 degrees C or 30 degrees C did not affect late manifestation of apoptotic cell death but aggravated initial microcirculatory dysfunction and inhibited recovery during the 8-hr follow-up period.

CONCLUSIONS

Our study provides evidence that systemic hypothermia may aggravate soft tissue trauma-associated microcirculatory dysfunction. These experimental results clearly support clinical efforts to prevent hypothermia in the acutely traumatized patient.

TSC for hemorrhagic shock: effects on cytokines and blood pressure

Previous studies have shown that administering trans-sodium crocetinate (TSC) as a treatment of hemorrhagic shock leads to increased whole-body oxygen consumption and survival as well as protection of the liver and kidney. It has been suggested that TSC increases oxygen delivery by increasing the diffusivity of oxygen through plasma. However, as with any novel mechanism of action, there are always questions about whether the results could also be ascribed to other, previously described mechanisms of action. This study was designed to look at some aspects of that by examining the effect of different TSC dosing regimens on the blood pressure and the production of cytokines after hemorrhage because both responses have been reported with compounds that act via other mechanisms. In a constant-pressure rat model of hemorrhagic shock, it was seen that a singe bolus injection of TSC results in an immediate but transient increase in the arterial blood pressure. This is similar to the effect reported previously for using 100% oxygen. It was also found that if the TSC injections were repeated periodically over an hour, a sustained increase in the blood pressure would occur. Because inflammatory cytokines have been implicated in mortality and tissue damage, it has been suggested that TSC may affect the production of cytokines. Thus, the effect of TSC on the production of TNF-alpha and IL-10 was also examined. The data show that treatment with TSC results in lower concentrations of TNF-alpha in the liver and spleen as well as lower concentrations of IL-10 in the spleen. Again, similar effects on other cytokines have been seen with 100% oxygen. These results support the hypothesis that the effects of TSC on hemorrhagic shock are mediated via an effect on oxygen.

Admission hypothermia and outcome after major trauma

OBJECTIVE

Uncontrolled exposure hypothermia is believed to be deleterious in the setting of major trauma. Prevention of hypothermia in the injured patient is currently practiced in both prehospital and in-hospital settings. However, this standard is based on studies of limited patient series that were not designed to identify the independent relationship between hypothermia and mortality. Recent studies suggest that therapeutically applied hypothermia may benefit selected patient subsets. The goal of this study was to evaluate the independent association between admission hypothermia and mortality after major trauma, with adjustment for clinical confounders.

DESIGN

Retrospective analysis of a statewide trauma registry. The primary outcome was death at hospital discharge. The key exposure was hypothermia, defined as body temperature </=35 degrees C at admission. Multivariate regression was used to risk-adjust for age, severity and mechanism of injury, and route of temperature measurement. Additional adjustment for prehospital exposure time and intravenous fluid therapy was also evaluated.

SETTING

Trauma centers of the Commonwealth of Pennsylvania.

PATIENTS

All trauma patients >/=16 yrs of age for the years 2000-2002. Transferred patients were excluded. Patients were excluded if temperature or route of temperature measurement was not known. Both the full cohort and a subset with isolated severe head injury were evaluated.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 38,520 patients, 1,921 (5.0%) were hypothermic at admission. Admission hypothermia was independently associated with increased odds of death in both the full cohort (odds ratio, 3.03; 95% confidence interval, 2.62-3.51) and the subset with isolated severe head injury (2.21; 1.62-3.03), with adjustment for age, severity and mechanism of injury, and route of temperature measurement.

CONCLUSIONS

Admission hypothermia is independently associated with increased adjusted odds of death after major trauma. The increase in mortality is not completely attributable to physiologic presentation or injury pattern or severity.

The Pre-Optic Anterior Hypothalamus (POAH) partially mediates the hypothermic response to hemorrhage in rats

Two sets of experiments were performed to characterize the role of the Pre-Optic Area of the Anterior Hypothalamus (POAH) in the decrease in set point and hypothermia that follows severe hemorrhage. In the first set, lidocaine or artificial cerebrospinal fluid (ACSF) was microinjected into the POAH of rats at the time of hemorrhage. Lidocaine microinjection attenuated the hemorrhagic hypothermia by approximately 50%. The mean drop in core temperature (Tc) following hemorrhage was 1.5 degrees C with ACSF microinjection (N = 6), 0.70 degrees C (N = 6) with lidocaine, and 1.77 degrees C (N = 6) after sham microinjection. This partial attenuation of the hemorrhagic hypothermic response indicates that an intact POAH is necessary for at least some of the hypothermia following hemorrhage. In the second experimental set, hypothalamic tissue temperature (Thyp) was modulated in an attempt to alter the hemorrhagic hypothermic response. Bilateral closed-ended cannulas were inserted into the POAH. One cannula consisted of a water-perfused thermode to change local tissue temperature. The other housed a thermocouple to measure local temperature. The effectiveness of the thermode was first confirmed in conscious rats, evidenced by an inverse deflection in Tc upon Thyp modulation. Then, the POAH region was either heated, cooled, or sham perfused following hemorrhage. The mean drop in Tc following hemorrhage was 2.16 degrees C (N = 5) with hypothalamic heating, 1.35 degrees C (N = 5) with cooling, and 1.44 degrees C (N = 5) following the sham perfusion control. Heating of the POAH significantly exacerbated the hemorrhagic hypothermic response. These data further suggest that the POAH is at least partially responsible for mediating hemorrhagic hypothermia.

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.

Systemic responses to prolonged hemorrhagic hypotension

Studies are needed to provide a rigorous examination of the relevance of monitored variables during prolonged hemorrhagic hypotension (HH). This study was designed to investigate the parameters that describe biochemical and O2 transport patterns in animals subjected to HH. Systemic parameters that could differentiate survivors from nonsurvivors were identified. An aortic flow probe was implanted in rats ( n = 21) for continuous measurement of cardiac output. Experiments were performed 6–9 days after surgery. Rats were bled to a mean arterial pressure of 40 mmHg and kept at that level using Ringer-lactate solution. Arterial and venous blood pressures, gases, acid-base status, glucose, lactate, electrolytes, hemoglobin, O2 saturation, heart and respiratory rates, total peripheral resistance, and O2 delivery and consumption were measured before hemorrhage, soon after 40 mmHg was reached, and 0.5, 1, 2, 3, and 4 h later. Fifty-three percent of rats survived ≥3 h (survivors); others were considered nonsurvivors. Nonsurvivors showed a significantly greater degree of metabolic acidosis than survivors. Arterial Po2, respiratory rate, O2 saturation, O2 content, glucose, and pH were significantly higher in survivors. The rate of Ringer-lactate infusion, arterial K+, and Pco2 were lower in survivors. Arterial K+ and respiratory rate were the only parameters significantly different between survivors and nonsurvivors at all time points during HH. Arterial levels of K+ showed the clearest distinction between survivors and nonsurvivors and may explain the sudden death experienced by animals during HH. The data suggest that early respiratory and metabolic compensations are essential for survival of prolonged HH.

Hypothermia in the trauma patient

Hypothermia is a common finding in severely injured patients. Historically described as a consequence of wartime casualties where cold exposure was common, this topic has resurfaced in the trauma literature because of the increasing recognition of the morbidity and mortality associated with hypothermia. Hypothermia, along with acidosis and coagulopathy, has been identified as a component of the "lethal triad" in injured patients, and has been shown to contribute to increased mortality in these patients. Decreases in core temperature during the course of initial evaluation and resuscitation are common, and can contribute to poor outcomes in the injured patient. As induced hypothermia has been shown to be beneficial in some clinical situations, recent animal studies have attempted to investigate whether hypothermia in the trauma patient has any beneficial effects. This review examines the incidence and pathophysiology of hypothermia, and discusses mechanisms of heat loss and rewarming techniques that can be utilized in the trauma patient.

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.

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.

Moderate hypothermia prevents brain stem oxidative stress injury after hemorrhagic shock

BACKGROUND

The purpose of this study was to investigate the effects of temperature on oxidative stress in brain stem tissue induced by hemorrhagic shock. We researched the hemorrhagic oxidative stress at various core temperatures using reduced glutathione (GSH) levels and thiobarbituric acid-reactive substances (TBARS) as markers of lipid peroxidation in brain stem homogenate.

METHODS

Forty rats were divided into four groups, of which one constituted the nonbleeding normothermia control group. In all of the three study groups, 40% of estimated blood volume was removed while they were being held at normothermia, mild hypothermia (32 degrees C), or moderate hypothermia (28 degrees C). Parameters including mean arterial pressure, rectal temperature, and heart and breathing rates were monitored and recorded during the procedures. After an hour at shock state, tissue samples were removed by craniectomy.

RESULTS

The tissue levels of TBARS increased significantly in normothermic and mild hypothermic hemorrhagic shock groups (10.74 nmol/g and 8.26 nmol/g) as compared with the control group (3.50 nmol/g) (p < 0.001). However, the tissue TBARS level in the moderate hypothermia group was only minimally increased (4.53 nmol/g). GSH showed a slight decrease in normothermic and mild hypothermic bleeding rats, and were unchanged in the moderate hypothermic rats.

CONCLUSION

Moderate systemic hypothermia (28 degrees C) appears to protect brain stem tissue from oxidative stress during severe hemorrhagic shock in rats, as indicated by insignificant change in tissue TBARS and GSH concentrations. These results suggest antioxidant protective effects of moderate systemic hypothermia in metabolically active brain stem tissue during hemorrhagic shock. Similar effects in humans remain to be studied.

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.

Low-volume fluid resuscitation for presumed hemorrhagic shock: helpful or harmful?

For the past 4 decades, the standard approach to the trauma victim who is hypotensive from presumed hemorrhage has been to infuse large volumes of fluids as early and as rapidly as possible. The goals of this treatment strategy are rapid restoration of intravascular volume and vital signs towards normal, and maintenance of vital organ perfusion. The most recent laboratory studies and the only clinical trial evaluating the efficacy of these guidelines however, suggest that in the setting of uncontrolled hemorrhage, today's practice of aggressive fluid resuscitation may be harmful, resulting in increased hemorrhage volume and subsequently greater mortality. This has been demonstrated in animal models representative of penetrating trauma as well as those representative of blunt trauma. The data strongly suggest that limited or hypotensive resuscitation may be preferable for the trauma victim with the potential for ongoing uncontrolled hemorrhage. Limited resuscitation provides a mechanism of avoiding the detrimental effects associated with early aggressive resuscitation, while maintaining a level of tissue perfusion that although decreased from the normal physiologic range is adequate for short periods. Large randomized clinical trials are necessary to confirm this new laboratory data. Future research should focus on developing resuscitation methods that may actually enhance tissue perfusion during limited resuscitation and therefore offset its potential detrimental effects.

Mild hypothermia increases survival from severe pressure-controlled hemorrhagic shock in rats

BACKGROUND

In previous studies, mild hypothermia (34 degrees C) during uncontrolled hemorrhagic shock (HS) increased survival. Hypothermia also increased mean arterial pressure (MAP), which may have contributed to its beneficial effect. We hypothesized that hypothermia would improve survival in a pressure-controlled HS model and that prolonged hypothermia would further improve survival.

METHODS

Thirty rats were prepared under light nitrous oxide/halothane anesthesia with spontaneous breathing. The rats underwent HS with an initial blood withdrawal of 2 mL/100 g over 10 minutes and pressure-controlled HS at a MAP of 40 mm Hg over 90 minutes (without anticoagulation), followed by return of shed blood and additional lactated Ringer's solution to achieve normotension. Hemodynamic monitoring and anesthesia were continued to 1 hour, temperature control to 12 hours, and observation without anesthesia to 72 hours. After HS of 15 minutes, 10 rats each were randomized to group 1, with normothermia (38 degrees C) throughout; group 2, with brief mild hypothermia (34 degrees C during HS 15-90 minutes plus 30 minutes after reperfusion); and group 3, with prolonged mild hypothermia (same as group 2, then 35 degrees C [possible without shivering] from 30 minutes after reperfusion to 12 hours).

RESULTS

MAP during HS and initial resuscitation was the same in all three groups, but was higher in the hypothermia groups 2 and 3, compared with the normothermia group 1, at 45 and 60 minutes after reperfusion. Group 1 required less blood withdrawal to maintain MAP 40 mm Hg during HS and more lactated Ringer's solution for resuscitation. At end of HS, lactate levels were higher in group 1 than in groups 2 and 3 (p < 0.02). Temperatures were according to protocol. Survival to 72 hours was achieved in group 1 by 3 of 10 rats, in group 2 by 7 of 10 rats (p = 0.18 vs. group 1), and in group 3 by 9 of 10 rats (p = 0.02 vs. group 1, p = 0.58 vs. group 2). Survival time was longer in group 2 (p = 0.09) and group 3 (p = 0.007) compared with group 1.

CONCLUSION

Brief hypothermia had physiologic benefit and a trend toward improved survival. Prolonged mild hypothermia significantly increased survival after severe HS even with controlled MAP. Extending the duration of hypothermia beyond the acute phases of shock and resuscitation may be needed to ensure improved outcome after prolonged HS.

Peritoneal ventilation with oxygen improves outcome after hemorrhagic shock in rats

OBJECTIVE

In experimental pulmonary consolidation with hypoxemia in rabbits, peritoneal ventilation (PV) with 100% oxygen (PV-O2) improved PaO2. We hypothesized that PV-O2 could improve outcome after hemorrhagic shock (HS) with normal lungs, by mitigating dysoxia of the abdominal viscera.

DESIGN

Randomized, controlled, laboratory animal study.

SETTING

University animal research facility.

SUBJECTIVE

Male Sprague-Dawley rats.

INTERVENTIONS

Thirty rats under light anesthesia (N2O/oxygen plus halothane) and spontaneous breathing underwent blood withdrawal of 3 mL/100 g over 15 mins. After volume-controlled HS phase 1 of 60 mins, resuscitation phase 2 of 60 mins included infusion of shed blood and, if necessary, additional lactated Ringer's solution intravenously to control normotension from 60 to 120 mins. This was followed by observation phase 3 for 7 days. We randomized three groups of ten rats each: group I received PV-O2, starting at 15 mins of HS at a rate of 40 inflations/min, and a peritoneal "tidal volume" of 6 mL, until the end of phase 2. Group II received the same PV with room air (PV-Air). Control group III was treated without PV.

MEASUREMENTS AND MAIN RESULTS

During the second half of HS phase 1, mean arterial pressures were higher in the PV-O2 group I compared with the PV-Air group II and control group III (p < .05). All 30 rats survived the 120 mins of phases 1 and 2. Survival to 7 days was achieved by ten of ten rats in PV-O2 group I; by nine of ten in PV-Air group II; and by five of ten in control group III (p < .05 vs. group I; NS vs. group II). Survival times of <7 days were 5 days in the one death of group II and ranged between 6 hrs and 4 days in the five deaths of group III. In 7-day survivors, neurologic deficit scores (0% to 10% = normal, 100% = death) were normal, ranging between zero and 8%. Necropsies of rats that died during phase 3 showed multiple areas of necrosis of the gut, some with perforations. Necropsies in the five survivors to 7 days of group III showed marked macroscopic and microscopic changes (scattered areas of necrosis of stomach and intestine, adhesions, and pale areas in the liver). These changes were absent or less severe in the nine survivors of group II. Viscera appeared normal in all ten rats of PV-O2 group I.

CONCLUSIONS

Peritoneal ventilation with oxygen during and after severe hemorrhagic shock in rats seems to decrease morbidity and mortality by helping preserve viability of abdominal viscera.

Effects of increased oxygen breathing in a volume controlled hemorrhagic shock outcome model in rats

It is believed that victims of traumatic hemorrhagic shock (HS) benefit from breathing 100% O(2). Supplying bottled O(2) for military and civilian first aid is difficult and expensive. We tested the hypothesis that increased FiO(2) both during severe volume-controlled HS and after resuscitation in rats would: (1) increase blood pressure; (2) mitigate visceral dysoxia and thereby prevent post-shock multiple organ failure; and (3) increase survival time and rate. Thirty rats, under light anesthesia with halothane (0. 5% throughout), with spontaneous breathing of air, underwent blood withdrawal of 3 ml/100 g over 15 min. After HS phase I of 60 min, resuscitation phase II of 180 min with normotensive intravenous fluid resuscitation (shed blood plus lactated Ringer's solution), was followed by an observation phase III to 72 h and necropsy. Rats were randomly divided into three groups of ten rats each: group 1 with FiO(2) 0.21 (air) throughout; group 2 with FiO(2) 0.5; and group 3 with FiO(2) 1.0, from HS 15 min to the end of phase II. Visceral dysoxia was monitored during phases I and II in terms of liver and gut surface PCO(2) increase. The main outcome variables were survival time and rate. PaO(2) values at the end of HS averaged 88 mmHg with FiO(2) 0.21; 217 with FiO(2) 0.5; and 348 with FiO(2) 1. 0 (P<0.001). During HS phase I, FiO(2) 0.5 increased mean arterial pressure (MAP) (NS) and kept arterial lactate lower (P<0.05), compared with FiO(2) 0.21 or 1.0. During phase II, FiO(2) 0.5 and 1. 0 increased MAP compared with FiO(2) 0.21 (P<0.01). Heart rate was transiently slower during phases I and II in oxygen groups 2 and 3, compared with air group 1 (P<0.05). During HS, FiO(2) 0.5 and 1.0 mitigated visceral dysoxia (tissue PCO(2) rise) transiently, compared with FiO(2) 0.21 (P<0.05). Survival time (by life table analysis) was longer after FiO(2) 0.5 than after FiO(2) 0.21 (P<0. 05) or 1.0 (NS), without a significant difference between FiO(2) 0. 21 and 1.0. Survival rate to 72 h was achieved by two of ten rats in FiO(2) 0.21 group 1, by four of ten rats in FiO(2) 0.5 group 2 (NS); and by four of ten rats of FiO(2) 1.0 group 3 (NS). In late deaths macroscopic necroses of the small intestine were less frequent in FiO(2) 0.5 group 2. We conclude that in rats, in the absence of hypoxemia, increasing FiO(2) from 0.21 to 0.5 or 1.0 does not increase the chance to achieve long-term survival. Breathing FiO(2) 0.5, however, might increase survival time in untreated HS, as it can mitigate hypotension, lactacidemia and visceral dysoxia.

Reduced metabolic rate accompanies the hemorrhage-induced hypothermia in conscious rats

The mechanism for the hemorrhage-induced drop in body temperature is unknown. This study determined the alterations in cutaneous heat exchange and metabolic heat production caused by a moderate hemorrhage in conscious rats. Chronically instrumented rats were subjected to a 16 ml/kg hemorrhage, followed by a 4-h recovery period, while monitoring body core temperature and cutaneous temperature. Cutaneous heat transfer was disrupted by housing the animals at an elevated (28 degrees C) ambient temperature. A separate group of experiments measured the change in oxygen consumption in the post-hemorrhage period. Moderate hemorrhage caused a drop in body core temperature which stabilized at 0.7+/-0.3 degrees C below control in the second hour following hemorrhage. Disruption of cutaneous heat exchange by reducing the thermal gradient did not diminish the hemorrhage-induced hypothermia. Hemorrhage caused a significant decline of oxygen consumption (-0. 21+/-0.05 ml O(2)/g per h). This 16% drop in resting oxygen consumption was prevented by immediately retransfusing the aspirated blood back into the rat. These data indicate that a decrease in metabolic heat production mediates the drop in body core temperature caused by moderate hemorrhage in conscious rats.

Should normothermia be restored and maintained during resuscitation after trauma and hemorrhage?

BACKGROUND

Although hypothermia often occurs after trauma and has protective effects during ischemia and organ preservation, it remains unknown whether maintenance of hypothermia or restoring the body temperature to normothermia during resuscitation has any deleterious or beneficial effects on heart performance and organ blood flow after trauma-hemorrhage.

METHODS

Male rats underwent laparotomy (i.e., induced trauma) and were exsanguinated to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximum shed volume was returned in the form of Ringer's lactate. Body temperature decreased from approximately 36.5 degrees C to below 32 degrees C. The animals were then resuscitated with four times the volume of maximal bleedout with Ringer's lactate. In one group, body temperature was rewarmed to 37 degrees C during resuscitation. In another group, body temperature was maintained at hypothermia (32 degrees C) for 4 hours after resuscitation. In an additional group, the body temperature was kept at 37 degrees C during hemorrhage as well as during resuscitation. Left ventricle performance parameters such as maximal rate of left ventricular pressure increase and decrease (+/-dP/dt(max)) were measured up to 4 hours. Cardiac output and regional blood flow were determined by radioactive microspheres at 4 hours after the completion of resuscitation.

RESULTS

The maintenance of normothermia during hemor. rhage or prolonged hypothermia after resuscitation depressed the left ventricular performance parameters, cardiac output, and regional blood flow in various organs. Rewarming the body to normothermia during resuscitation, however, significantly increased heart performance, cardiac output (from hypothermia 16.2 +/- 1.4 to 22.3 +/- 1.4 mL/min per 100 g body weight,p < 0.05) and total hepatic blood flow (from hypothermia 117.5 +/- 5.3 to 166.0 +/- 9.3 mL/min per 100 g tissue, p < .05).

CONCLUSION

Our data indicate that restoration of normothermia during resuscitation improves cardiac function and hepatic blood flow compared with hypothermia.

On the future of reanimatology

This article is adapted from a presentation given at the 1999 SAEM annual meeting by Dr. Peter Safar. Dr. Safar has been involved in resuscitation research for 44 years, and is a distinguished professor and past initiating chairman of the Department of Anesthesiology and Critical Care Medicine at the University of Pittsburgh. He is the founder and director of the Safar Center for Resuscitation Research at the University of Pittsburgh, and has been the research mentor of many critical care and emergency medicine research fellows. Here he presents a brief history of past accomplishments, recent findings, and future potentials for resuscitation research. Additional advances in resuscitation, from acute terminal states and clinical death, will build upon the lessons learned from the history of reanimatology, including optimal delivery by emergency medical services of already documented cardiopulmonary cerebral resuscitation, basic-advanced-prolonged life support, and future scientific breakthroughs. Current controversies, such as how to best educate the public in life-supporting first aid, how to restore normotensive spontaneous circulation after cardiac arrest, how to rapidly induce mild hypothermia for cerebral protection, and how to minimize secondary insult after cerebral ischemia, are discussed, and must be resolved if advances are to be made. Dr. Safar also summarizes future technologies already under preliminary investigation, such as ultra-advanced life support for reversing prolonged cardiac arrest, extending the "golden hour" of shock tolerance, and suspended animation for delayed resuscitation.

Therapeutic hypothermia in traumatology

Despite its proven clinical application for protection-preservation of the brain and heart during cardiac surgery, hypothermia research has fallen in and out of favor many times since its inception. Since the 1980s, there has been renewed research and clinical interest in therapeutic hypothermia for resuscitation of the brain after cardiac arrest or TBI and for preservation-resuscitation of extracerebral organs, particularly the abdominal viscera in low-flow states such as HS. Although some of the fears regarding the side effects of hypothermia are warranted, others are not. Without further laboratory and clinical studies, the significance of these effects cannot be determined and ways to overcome these problems cannot be developed. Currently, at the turn of the century, there are significant data demonstrating the benefit of mild-to-moderate hypothermia in animals and humans after cardiac arrest or TBI and in animals during and after HS. The clinical implications of uncontrolled versus controlled hypothermia in trauma patients and the best way to assure poikilothermia for cooling without shivering are still unclear. It is time to consider a prospective trial of therapeutic, controlled hypothermia for patients during traumatic HS and resuscitation. The authors believe that the new millennium will witness remarkable advantages of the use of controlled hypothermia in trauma. Starting in the prehospital phase, mild hypothermia will be induced in hypovolemic patients, which will not only decrease the immediate mortality rate but perhaps also will protect cells and reduce the likelihood of secondary inflammatory response syndrome, multiple organ failure, and late deaths. The most futuristic applications will be hypothermic strategies to achieve prolonged suspended animation for delayed resuscitation in traumatic exsanguination cardiac arrest.

Mild or moderate hypothermia but not increased oxygen breathing prolongs survival during lethal uncontrolled hemorrhagic shock in rats, with monitoring of visceral dysoxia

OBJECTIVE

To test the hypotheses that during lethal uncontrolled hemorrhagic shock (UHS) in rats compared with normothermia and room air breathing: a) mild hypothermia would prolong survival time as well as moderate hypothermia; b) oxygen breathing would prolong survival further; and c) hypothermia and oxygen would mitigate visceral ischemia (dysoxia) during UHS.

DESIGN

Prospective, randomized, controlled laboratory animal study.

SETTING

Animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTION

Fifty-four rats were lightly anesthetized with halothane during spontaneous breathing. UHS was induced by blood withdrawal of 3 mL/100 g over 15 mins, followed by 75% tail amputation with topical application of heparin. Five minutes after tail cut, rats were randomly divided into nine groups (6 rats each) with three rectal temperature levels (38 degrees C [100.4 degrees F; normothermia] vs. 34 degrees C [93.2 degrees F; mild hypothermia] vs. 30 degrees C [86 degrees F; moderate hypothermia]) by surface cooling; each with 3 FIO2 levels (0.25 vs. 0.5 vs. 1.0). Rats were observed without fluid resuscitation until death (apnea and pulselessness). Visceral ischemia was monitored by observing liver and gut surface PCO2.

MEASUREMENTS AND MAIN RESULTS

Mean survival time, which was 51 mins in the control group with normothermia and FIO2 of 0.25, was more than doubled with hypothermia, to 119 mins in the combined mild hypothermia groups (p < .05) and to 132 mins in the combined moderate hypothermia groups (p < .05; NS for moderate vs. mild hypothermia). FIO2 had no statistically significant effect on survival time. Increases in visceral surface PCO2 correlated with hypotension (r2 = .22 for intestine and .40 for liver). Transiently, increased FIO2, not hypothermia, mitigated visceral ischemia.

CONCLUSIONS

Both mild and moderate hypothermia prolonged survival time during untreated, lethal UHS in rats. Increased FIO2 had no effect on survival. The effects of hypothermia and increased FIO2 during UHS on viscera, the ability to be resuscitated, and outcome should be explored further.

Acute metabolic and endocrine effects of induced hypothermia in hemorrhagic shock: an experimental study in the pig

BACKGROUND

Hypothermia is considered harmful in trauma patients. In surgery, hypothermia is occasionally used to reduce metabolism and protect the brain. Recent studies in animals have also shown protective effects of hypothermia in hemorrhagic shock. The aim of this study was to evaluate the metabolic and endocrine effects of induced hypothermia in hemorrhagic shock.

METHODS

Half of the individually calculated blood volume was removed from 17 anesthetized piglets. They were then randomized to normothermia or hypothermia and followed for 4 hours after hemorrhage.

RESULTS

In the hypothermic pigs, arterial PO2 increased from 10.3 +/- 0.7 to 16.4 +/- 0.9 kPa, but it remained unchanged in the normothermic group. The serum levels of potassium increased from 3.9 +/- 0.2 to 5.0 +/- 0.2 mmol/L in the normothermic group. In the hypothermic pigs, the potassium levels temporarily decreased from 3.8 +/- 0.1 to 3.0 +/- 0.1 mmol/L but then returned to baseline levels. The levels of serum catecholamines surged in both groups during hemorrhage. They remained elevated in normothermic pigs but declined in the hypothermic group.

CONCLUSION

In porcine hemorrhagic shock, induced hypothermia increases arterial oxygen tension and stabilizes serum levels of potassium and catecholamines.

Hypothermia, but not 100% oxygen breathing, prolongs survival time during lethal uncontrolled hemorrhagic shock in rats

OBJECTIVE

To test the hypothesis that moderate hypothermia (Hth) (30 degrees C) or breathing 100% oxygen (best with both combined) would prolong survival during lethal uncontrolled hemorrhagic shock (UHS) compared with normothermia (38 degrees C) and breathing air.

METHODS

Forty Sprague-Dawley rats were anesthetized with halothane during spontaneous breathing of N2O/O2 (50:50). UHS was induced by volume-controlled blood withdrawal of 3 mL/100 g over 15 minutes, followed by 75% tail amputation and randomization to one of four UHS treatment groups (10 rats each): group 1 (control) was maintained on room air and rectal temperature of 38 degrees C; group 2 (Hth) was maintained on air and 30 degrees C; group 3 (O2) was maintained on FiO2 100% (starting immediately after tail cut) and 38 degrees C; and group 4 (O2-Hth) was maintained on FiO2 100% and 30 degrees C. Rats were observed otherwise untreated until death (apnea and pulselessness) or for a maximum of 5 hours.

RESULTS

During the initial blood withdrawal, mean arterial pressure (MAP) decreased to an average of 24 mm Hg. Seventeen of 40 rats then showed an increase in MAP (attempted self-resuscitation). Induction of hypothermia increased MAP to around 35 mm Hg at 30 minutes but did not increase bleeding. Additional blood loss from the tail stump averaged 1.0, 2.3, 2.9, and 1.7 mL in groups 1, 2, 3, and 4, respectively (not significant). Breathing 100% oxygen did not affect MAP or blood loss. Survival time was a mean of 47 and 52 minutes in normothermic groups 1 and 3 versus 121 and 135 minutes in hypothermic groups 2 and 4, respectively (p < 0.001, Kaplan-Meier). Breathing FiO2 100% increased PaO2 but did not change MAP, blood loss, or survival time.

CONCLUSION

Moderate hypothermia, but not increased FiO2, prolonged survival time during untreated UHS in rats. The effect of hypothermia on survival after resuscitation from UHS needs to be determined.

Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats

It has been shown in dogs that mild hypothermia (34 degrees C) during or immediately after ventricular fibrillation cardiac arrest can improve cerebral outcome. The effect of mild hypothermia on outcome after 8 minutes of asphyxiation (5 minutes' cardiac arrest) was studied for the first time in rats. Restoration of spontaneous circulation was with external cardiopulmonary resuscitation and observation to 72 hours. Three groups of 10 rats each were studied. At 72 hours postarrest, compared with the normothermic control group 1, final overall performance categories (OPC) and neurological deficit scores (NDS) were numerically better in the resuscitative (post-arrest) hypothermia group 2 and significantly better in the protective (pre-intra-arrest) hypothermia group 3 (P < .05). Total brain histopathological damage scores (HDS) were 17 +/- 5 in group 1, 14 +/- 6 in group 2 (NS), and 6 +/- 2 in group 3 (P < .001 versus group 1). HDS correlated with OPC (r = .6, P < .05) and NDS (r = .7, P < .05). Mild hypothermia improved cerebral outcome after asphyxial cardiac arrest in rats, more when induced before than after arrest. The model's insult is within the therapeutic window, which makes it also suitable for screening other cerebral resuscitation potentials.

Contradictory effects of dopamine at 32 degrees C in pigs anesthetized with ketamine

BACKGROUND

In critically ill patients who were surface cooled to 33 +/- 2 degrees C, we have observed that dopamine sometimes causes a substantial decrease in blood pressure. The present study was designed to compare the effects of dopamine in normothermia to those seen after surface cooling to 32 degrees C.

METHODS

Seven pigs with a mean body weight of 21 kg were anesthetized with ketamine and muscle relaxation was induced with pancuronium. They were mechanically ventilated and given dopamine infusions (5 and 12 micrograms.kg-1.min-1)in normothermia and after surface cooling by cold water immersion to a central blood temperature of 32.0 degrees C (range 31.6-32.6 degrees C).

RESULTS

In normothermia, dopamine at a dose of 5 micrograms.kg-1.min-1 increased mean arterial blood pressure (MAP) by 16% (P < 0.01) and cardiac output (CO) by 9% (P = 0.051); at 12 micrograms.kg-1.min-1 dopamine increased MAP by 26% (P < 0.01) and CO by 18% (P < 0.01). In hypothermia, MAP and CO did not change at an administration rate of 5 micrograms.kg-1.min-1; at 12 micrograms.kg-1.min-1 CO was unchanged but MAP was significantly reduced by 15% (P < 0.01).

CONCLUSION

Dopamine increased CO and MAP in normothermia but not at 32 degrees C, where there was even a significant reduction of MAP in this porcine model.

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.

Resuscitation medicine research: quo vadis

Laboratory research should have clinical relevance. Topics should be selected according to need, gaps in knowledge, and opportunities; the investigator's background, expertise, interests, and ambitions; scientific, clinical, and socioeconomic importance; and feasibility of successful performance and conclusion. The current explosion of knowledge and sophistication of methods will require research by multidisciplinary teams. Systematic goal-oriented studies should be conducted in environments that encourage serendipitous discoveries. Mechanism- and outcome-oriented research, in laboratories and on patients, is needed. In cardiac arrest research, hearts and brains "too good to die" offer many challenges. In trauma research, particular challenges include protection-preservation during uncontrolled hemorrhagic shock, suspended animation for delayed resuscitation in exsanguination, and prevention of brain swelling after traumatic brain injury. Emergency physicians have the unique opportunity to initiate clinical resuscitation research in unexplored territory: the prehospital arena.

Peritoneal cooling for mild cerebral hypothermia after cardiac arrest in dogs

After normothermic cardiac arrest in dogs, we found that mild hypothermia (34 degrees C) of 1-2 h reduced brain damage, providing that hypothermia was achieved within 15 min of reperfusion. A clinically feasible rapid brain-cooling method is needed. As head-neck surface cooling alone in dogs was found to be too slow (0.1 degrees C/min), we reviewed peritoneal cooling in the Introduction and Discussion sections. PRELIMINARY EXPERIMENTS WITHOUT CARDIAC ARREST: In 5 dogs with spontaneous circulation and IPPV, 2 L of Ringer's solution at 10 degrees C were instilled into the peritoneal cavity, left for 5 min, and drained. Brain (tympanic membrane) temperature (Tty) decreased by a mean of 0.3 degrees C/min (12 min to 34 degrees C). Core (pulmonary artery) temperature (Tpa) decreased by a mean of 0.8 degrees C/min (5 min to 34 degrees C). COOLING AFTER CARDIAC ARREST: In our reproducible dog model of normothermic ventricular fibrillation cardiac arrest of 11 min (no flow), brief low-flow normothermic cardiopulmonary bypass (CPB) was used for reperfusion and restoration of spontaneous circulation (ROSC) within 2 min. In 24 dogs, mild hypothermia was induced by head-neck surface cooling with ice bags, starting with reperfusion, plus peritoneal lavage as above, starting with ROSC. All 24 dogs were resuscitated. Initial head-neck surface cooling alone over 2 min decreased Tty by only 0.15 degrees C/min. Subsequent additional peritoneal lavage decreased Tty by a mean of 0.3 degrees C/min (11 min to 34 degrees C); and Tpa 0.6 degrees C/min (7 min to 34 degrees C). There were no significant physiologic effects. We conclude that peritoneal instillation of cold Ringer's solution is more rapidly effective than other non-intravascular cooling methods reported previously. Peritoneal cooling should be tried in patients during CPR.

Uncontrolled hemorrhagic shock outcome model in rats

During uncontrolled hemorrhagic shock (UHS) in acute animals models, attempts to achieve normotension with i.v. fluid resuscitation (FR) caused further bleeding and higher acute mortality. In the absence of a published clinically realistic long-term animal outcome study of UHS, we developed such a model in rats. In the preliminary study, phase I of the model involved 60 min of simulated 'pre-hospital' UHS by tail amputation and different FR regimens. Phase II involved 120 min of simulated 'hospital' treatment with hemostasis and all-out FR, including blood infusion. Phase III involved observing recovery and survival to 72 h (3 days). Rats were maintained under very light N2O-O2-halothane anesthesia and spontaneous breathing via mask during phases I and II and were awake during phase III. Tail amputation-induced UHS alone, studied in 4 groups of 10 rats each, resulted in unpredictable spontaneous hemostasis and great variability in shed blood volume, severity of shock, and mortality. The final model, which achieved consistent blood loss and outcome, included an initial volume-controlled hemorrhage of 3 ml/100 g over 15 min and untreated HS for another 15 min, followed by tail amputation for UHS over another 60 min. This phase I of 90 min was followed by phase II of 60 min. In group 1, without FR in phases I and II, all 10 rats died by 12 h. In group 2, without FR in phase I and hemostasis plus all-out FR with lactated Ringer's solution and blood to hematocrit (Hct) 30% in phase II, 5 of 10 rats died at the end of phase I and 9 of 10 died at the end of phase III. This final volume-initiated UHS model may be suitable for comparing different pre-hospital treatment modalities in terms of outcome.

The effect of resuscitative moderate hypothermia following epidural brain compression on cerebral damage in a canine outcome model

A canine model of temporary epidural cerebral compression and standardized intensive care was developed to evaluate the effect of resuscitative (postinsult) moderate systemic hypothermia. A balloon was inflated over the temporal region to maintain contralateral intraventricular pressure (IVP) at 62 mm Hg for 90 minutes. For a 66-hour period after initiation of brain compression, the intubated dogs received controlled ventilation and standard intensive care. From 66 to 90 hours postinjury, the extubated dogs were evaluated as to functional outcome. Morphological brain damage was evaluated at 90 hours or earlier if brain death occurred. Eight dogs in a control group were maintained at a body of temperature of 38 degrees C. Eight treated dogs had core body temperature reduced by surface cooling starting 15 minutes after balloon inflation, first to 31 degrees C for 5 hours and then to 35 degrees C from 5 to 62 hours after insult. Intraventricular pressure increased to 20 mm Hg or greater in the control group at a mean of 2.9 hours (range 2 to 4 hours) following the insult, and in the hypothermic group at a mean of 14.8 hours (range 5 to 30 hours)--that is, during the time period when the body temperature was 35 degrees C, not 31 degrees C (p = 0.01). There was no difference in peak pressures between the two groups. Brain death occurred in four of the eight dogs in the normothermic group at 18, 24, 24, and 48 hours (mean +/- standard deviation 28 +/- 13 hours) and in three of the eight in the hypothermic group at 27, 42, and 45 hours (mean 38 +/- 10 hours) (not significant). The animals surviving 90 hours (four in the normothermic and five in the hypothermic group) were neurologically near normal. The total mean macroscopically damaged brain volume was 2584 +/- 1890 cu mm in the normothermic versus 765 +/- 611 cu mm in the hypothermic group (p = 0.03). The mean necrotic volume was 741 +/- 599 cu mm in the normothermic versus 263 +/- 346 cu mm in the hypothermic group (p = 0.07). Microscopically, the damaged regions consisted of ischemic neurons, reactive glia, edema, vascular endothelial hypertrophy, and erythrocyte extravasation. It is concluded that, in this model, immediate postinsult hypothermia of 31 degrees C (not 35 degrees C) for 5 hours prevents a rise in IVP and significantly decreases cerebral tissue damage, but does not prevent brain herniation during rewarming.

Cerebral resuscitation after cardiac arrest: research initiatives and future directions

At present, fewer than 10% of cardiopulmonary resuscitation (CPR) attempts prehospital or in hospitals outside special care units result in survival without brain damage. Minimizing response times and optimizing CPR performance would improve results. A breakthrough, however, can be expected to occur only when cerebral resuscitation research has achieved consistent conscious survival after normothermic cardiac arrest (no flow) times of not only five minutes but up to ten minutes. Most cerebral neurons and cardiac myocytes tolerate normothermic ischemic anoxia of up to 20 minutes. Particularly vulnerable neurons die, in part, because of the complex secondary post-reflow derangements in vital organs (the postresuscitation syndrome) which can be mitigated. Brain-orientation of CPR led to the cardiopulmonary-cerebral resuscitation (CPCR) system of basic, advanced, and prolonged life support. In large animal models with cardiac arrest of 10 to 15 minutes, external CPR, life support of at least three days, and outcome evaluation, the numbers of conscious survivors (although not with normal brain histology) have been increased with more effective reperfusion by open-chest CPR or emergency cardiopulmonary bypass, an early hypertensive bout, early post-arrest calcium entry blocker therapy, or mild cerebral hypothermia (34 C) immediately following cardiac arrest. More than ten drug treatments evaluated have not reproducibly mitigated brain damage in such animal models. Controlled clinical trials of novel CPCR treatments reveal feasibility and side effects but, in the absence of a breakthrough effect, may not discriminate between a treatment's ability to mitigate brain damage in selected cases and the absence of any treatment effect. More intensified, coordinated, multicenter cerebral resuscitation research is justified.

Beneficial effect of mild hypothermia and detrimental effect of deep hypothermia after cardiac arrest in dogs

BACKGROUND AND PURPOSE

Mild cerebral hypothermia (34 degrees C) induced immediately after cardiac arrest improves outcome. Deep postarrest hypothermia (15 degrees C) has not been studied.

METHODS

We used our dog model of normothermic ventricular fibrillation (no blood flow) of 12.5 minutes, reperfusion by brief cardiopulmonary bypass, controlled ventilation to 20 hours, and intensive care to 72 hours. Head surface cooling and bypass cooling were performed from start of reperfusion to 1 hour. Five groups of six dogs each were compared: group I, normothermic controls; group II, deep hypothermia (15 degrees C); group III, moderate hypothermia (30 degrees C); group IV, mild hypothermia (34 degrees C); and group V, mild hypothermia with head surface cooling begun during no flow.

RESULTS

In control group I, five dogs remained comatose (overall performance category [OPC] 4) and one severely disabled (OPC 3). In group II, four dogs achieved OPC 4 and two dogs OPC 3 (NS versus group I). Compared with group I, OPCs were better in group III (p less than 0.05), group IV (p less than 0.05), and group V (p less than 0.05). Neurological deficit scores were also better in groups III, IV, and V than in groups I or II (p less than 0.05). Total brain histological damage scores were better in group III (p = 0.02), group IV (p = 0.06), and group V (p less than 0.05) than in group I. In group II, OPC and neurological deficit scores were the same and histological damage scores numerically worse than in group I and all were worse than in groups III, IV, and V (p less than 0.05). Cardiovascular complications and myocardial morphological damage in groups II and III were worse than in groups I, IV, and V (p less than 0.05).

CONCLUSIONS

Mild or moderate cerebral hypothermia induced immediately after cardiac arrest improves cerebral outcome, more likely when initiated during arrest, whereas deep postarrest hypothermia can worsen cerebral and cardiac outcome.