In vivo study of bleeding time and arterial hemorrhage in hypothermic versus normothermic animals

Comparison of two passive warming devices for prevention of perioperative hypothermia in dogs

OBJECTIVE

To compare effects of two passive warming methods combined with a resistive heating mat on perioperative hypothermia in dogs.

MATERIALS AND METHODS

Fifty-two dogs were enrolled and randomly allocated to receive a reflective blanket (Blizzard Blanket) or a fabric blanket (VetBed). In addition, in the operating room all dogs were placed onto a table with a resistive heating mat covered with a fabric blanket. Rectal temperature measurements were taken at defined points. Statistical analysis was performed comparing all Blizzard Blanket-treated to all VetBed-treated dogs, and VetBed versus Blizzard Blanket dogs within spay and castrate groups, spay versus castrate groups and within groups less than 10 kg or more than 10 kg bodyweight.

RESULTS

Data from 39 dogs were used for analysis. All dogs showed a reduction in perioperative rectal temperature. There were no detected statistical differences between treatments or between the different groups.

CLINICAL SIGNIFICANCE

This study supports previous data on prevalence of hypothermia during surgery. The combination of active and passive warming methods used in this study prevented the development of severe hypothermia, but there were no differences between treatment groups.

Localized control of exsanguinating arterial hemorrhage: an experimental model

To develop an arterial injury model for testing hemostatic devices at well-defined high and low bleeding rates.

MATERIAL AND METHOD

A side-hole arterial injury was created in the carotid artery of sheep. Shed blood was collected in a jugular venous reservoir and bleeding rate at the site of arterial injury was controlled by regulating outflow resistance from the venous reservoir. Two models were studied: uncontrolled exsanguinating hemorrhage and bleeding at controlled rates with blood return to maintain hemodynamic stability. Transcutaneous Duplex ultrasound was used to characterize ultrasound signatures at various bleeding rates.

RESULTS

A 2.5 mm arterial side-hole resulted in exsanguinating hemorrhage with an initial bleeding rate of 400 ml/min which, without resuscitation, decreased to below 100 ml/min in 5 minutes. After 17 minutes, bleeding from the injury site stopped and the animal had lost 60% of total blood volume. Reinfusion of shed blood maintained normal hemodynamics and both high and low bleeding rates could be maintained without hemorrhagic shock. Bleeding rate at the arterial injury site was held at 395±78 ml/min for 8 minutes, 110±11 ml/min for 15 minutes, and 12±1 ml/min for 12 minutes. Doppler flow signatures at the site of injury were characterized by high peak and end-diastolic flow velocities at the bleeding site which varied with the rate of hemorrhage.

CONCLUSION

We have developed a hemodynamically stable model of acute arterial injury which can be used to evaluate diagnostic and treatment methods focused on control of the arterial injury site.

Coagulopathy in trauma: optimising haematological status

It is estimated that 10 000 people per year die following trauma in England and Wales and 30—40% do so due to uncontrolled haemorrhage. By the time the patient reaches hospital, coagulopathy is often already installed and needs to be corrected promptly to prevent further haemorrhage and allow effective treatment of injuries. The coagulopathy is multifactorial with the leading causes being acidosis, hypothermia and massive transfusion. Early recognition of the condition is imperative using standard coagulation testing; however, there are limitations in this setting. Newer methods of testing `global haemostasis' using thromboelastography are becoming more popular but need further validation. Treatment of coagulopathy requires a multidisciplinary approach. Blood product transfusion remains the cornerstone of management but newer pharmacological agents such as recombinant factor VIIa are increasingly being used. Here we review the pathogenesis, investigation and management of the coagulopathy of trauma.

Massive transfusion and coagulopathy: pathophysiology and implications for clinical management

PURPOSE

To review the pathophysiology of coagulopathy in massively transfused, adult and previously hemostatically competent patients in both elective surgical and trauma settings, and to recommend the most appropriate treatment strategies.

METHODS

Medline was searched for articles on "massive transfusion," "transfusion," "trauma," "surgery," "coagulopathy" and "hemostatic defects." A group of experts reviewed the findings.

PRINCIPAL FINDINGS

Coagulopathy will result from hemodilution, hypothermia, the use of fractionated blood products and disseminated intravascular coagulation. The clinical significance of the effects of hydroxyethyl starch solutions on hemostasis remains unclear. Maintaining a normal body temperature is a first-line, effective strategy to improve hemostasis during massive transfusion. Red cells play an important role in coagulation and hematocrits higher than 30% may be required to sustain hemostasis. In elective surgery patients, a decrease in fibrinogen concentration is observed initially while thrombocytopenia is a late occurrence. In trauma patients, tissue trauma, shock, tissue anoxia and hypothermia contribute to the development of disseminated intravascular coagulation and microvascular bleeding. The use of platelets and/or fresh frozen plasma should depend on clinical judgment as well as the results of coagulation testing and should be used mainly to treat a clinical coagulopathy.

CONCLUSIONS

Coagulopathy associated with massive transfusion remains an important clinical problem. It is an intricate, multifactorial and multicellular event. Treatment strategies include the maintenance of adequate tissue perfusion, the correction of hypothermia and anemia, and the use of hemostatic blood products to correct microvascular bleeding.

Massive transfusion and coagulopathy: pathophysiology and implications for clinical management

PURPOSE

To review the pathophysiology of coagulopathy in massively transfused, adult and previously hemostatically competent patients in both elective surgical and trauma settings, and to recommend the most appropriate treatment strategies.

METHODS

Medline was searched for articles on "massive transfusion," "transfusion," "trauma," "surgery," "coagulopathy" and "hemostatic defects." A group of experts reviewed the findings.

PRINCIPAL FINDINGS

Coagulopathy will result from hemodilution, hypothermia, the use of fractionated blood products and disseminated intravascular coagulation. The clinical significance of the effects of hydroxyethyl starch solutions on hemostasis remains unclear. Maintaining a normal body temperature is a first-line, effective strategy to improve hemostasis during massive transfusion. Red cells play an important role in coagulation and hematocrits higher than 30% may be required to sustain hemostasis. In elective surgery patients, a decrease in fibrinogen concentration is observed initially while thrombocytopenia is a late occurrence. In trauma patients, tissue trauma, shock, tissue anoxia and hypothermia contribute to the development of disseminated intravascular coagulation and microvascular bleeding. The use of platelets and/or fresh frozen plasma should depend on clinical judgment as well as the results of coagulation testing and should be used mainly to treat a clinical coagulopathy.

CONCLUSIONS

Coagulopathy associated with massive transfusion remains an important clinical problem. It is an intricate, multifactorial and multicellular event. Treatment strategies include the maintenance of adequate tissue perfusion, the correction of hypothermia and anemia, and the use of hemostatic blood products to correct microvascular bleeding.

A pilot investigation of mild hypothermia in neonates receiving extracorporeal membrane oxygenation (ECMO)

OBJECTIVE

To investigate the safety and feasibility of using mild hypothermia in neonates receiving extracorporeal membrane oxygenation (ECMO). Study design A prospective, nonrandomized pilot study of 25 neonates referred for ECMO. Whole body cooling was achieved by adjustment of the temperature of the extracorporeal circuit water bath. Five groups (N=5 per group) were each studied for the first 5 days of ECMO. The first group was maintained at 37 degrees C throughout the study period. Subsequent groups were cooled to 36 degrees C, to 35 degrees C, and, finally, to 34 degrees C, respectively, for 24 hours and the final group to 34 degrees C for 48 hours before being rewarmed to 37 degrees C. Patients were carefully assessed clinically and biologically. In addition to routine laboratory tests, cytokines (IL-6 and IL-8), complement (C3a), and molecular markers of coagulation (thrombin/antithrombin III [TAT], antithrombin III, and plasmin-alpha2plasminogen) were measured.

RESULTS

No major clinical or circuit problems were noted during cooling or rewarming. In particular, there were no problems of bleeding or cardiac arrhythmia. No significant difference was found between groups in terms of molecular markers of coagulation, complement, cytokines, and platelet transfusions.

CONCLUSIONS

Applying mild hypothermia (34 degrees C) for 24 or 48 hours to neonates receiving ECMO is both feasible and safe.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

A Randomized, Controlled Trial Comparing Arteriovenous to Venovenous Rewarming of Severe Hypothermia in a Porcine Model

BACKGROUND

The purpose of this study was to evaluate active rewarming using continuous arteriovenous rewarming (CAVR) and continuous venovenous rewarming (CVVR) methods during severe hypothermia using an electromagnetic fluid warmer. Rapid rewarming using these techniques is superior to passive rewarming and is possible with commercially available equipment.

METHODS

Eighteen swine (55-65 kg) were assigned to CAVR, CVVR, or control. Vascular access was obtained via central lines (8.5-French) in all subjects. Subjects were cooled to 27 degrees C (80.6 degrees F) in an ice bath, and then dried, covered, and connected to the rewarming device. The carotid artery (CAVR) or internal jugular vein (CVVR) was used for circuit inflow. Warmed 39 degrees C (102.2 degrees F) blood was returned via the femoral vein. Hemodynamic parameters and temperatures (pulmonary artery and rectal) were recorded until reaching an endpoint of a pulmonary artery temperature of 37 degrees C (98.6 degrees F).

RESULTS

Mean rewarming time in the CAVR group was 2 hours 14 minutes, with a mean rewarming rate of 4.5 degrees C/h (8.1 degrees F/h, 0.034 degrees C/kg/h). Total circulating volume averaged 65 L. CVVR averaged 3 hours 8 minutes, with a mean rewarming rate of 3.2 degrees C/h (5.8 degrees F/h, 0.024 degrees C/kg/h). Total circulating volume averaged 67 L. Controls averaged 10 hours 42 minutes, with a mean rate of 0.9 degrees C/h (1.7 degrees F/h, 0.007 degrees C/kg/h). The CAVR group was faster than the CVVR group in both the rewarming rate and total time to rewarming (p = 0.034 and p = 0.040, respectively). Both experimental groups were significantly different from controls in rewarming rate and total time to rewarming (p < 0.001).

CONCLUSION

CAVR offers the most rapid rate of rewarming. CVVR offers a rapid rate using less invasive procedures. Both techniques are markedly superior to passive rewarming methods typically used during early resuscitation.

The effect of graded hypothermia (36 degrees C-32 degrees C) on hemostasis in anesthetized patients without surgical trauma

The isolated effects of hypothermia on hemostasis have not been investigated in healthy humans. We cooled 16 anesthetized patients scheduled for elective intracranial surgery to 32 degrees C body core temperature and assessed prothrombin time (PT), activated partial thromboplastin time, thrombelastogram (TEG), closure time, and platelet count at 36 degrees C, 34 degrees C, and 32 degrees C body core temperature after the induction of anesthesia but before surgical intervention. Activated partial thromboplastin time, hematocrit, and closure time did not change, whereas PT and platelet count decreased during cooling. Platelet count decreased without a decrease in hematocrit; hence, a dilution by administered fluids seemed unlikely. The small decrease of platelet count is probably clinically irrelevant in patients with normal platelet count and function. The small decrease in PT indicates an alteration of the extrinsic pathway of coagulation. TEG measurements showed a delay of clot formation in temperature-adjusted measurements but showed no change if the test temperature was 37 degrees C. This indicates that hypothermia reduces plasmatic coagulation and platelet reactivity. However, the clot strength is not altered by hypothermia. All coagulation variables remained within the normal ranges. Our results may indicate that moderate short-term (4-h) hypothermia has only minor adverse effects in healthy humans. We can make no statement about the effects of hypothermia of longer duration.

IMPLICATIONS

This study investigated the isolated effects of hypothermia in healthy anesthetized humans. We found only minor effects of body temperature reduction to 32 degrees C on assessed coagulation variables, indicating only minor effects in otherwise healthy humans.

Abdominal packing for surgically uncontrollable hemorrhage in ruptured abdominal aortic aneurysm repair

Emergency surgery for ruptured abdominal aortic aneurysms is accompanied with massive blood loss and is correlated with high incidences of coagulopathy. Following established results with abdominal packing to control hepatic hemorrhage, we present this technique for uncontrollable hemorrhage in patients with ruptured abdominal aortic aneurysm. The experience with this technique in 46 patients is described.

Moderate hypothermia for 48 hours after temporary epidural brain compression injury in a canine outcome model

In a previous study with this dog model, post-insult hypothermia of 31 degrees C for 5 h prevented secondary intraventricular pressure (IVP) rise, but during 35 degrees C or 38 degrees C, one-half of the dogs developed delayed IVP rise to brain death. We hypothesized that 31 degrees C extended to 48 h would prevent brain herniation. Using epidural balloon inflation, we increased contralateral IVP to 62 mm Hg for 90 min. Controlled ventilation was to 72 h and intensive care to 96 h. Group 1 dogs (n = 10) were normothermic controls (37.5 degrees C). Group 2 dogs (n = 10) were surface-cooled from 15 to 45 min of balloon inflation and maintained at moderate hypothermia (31 degrees C) to 48 h. Rewarming was from 48 to 72 h. Four additional dogs of hypothermia Group 2 had to be excluded from analysis for pneumonia and/or bleeding diathesis. After balloon deflation, IVP increased to 20 mm Hg or greater at 154 +/- 215 (range 15-720) min following the insult in Group 1 and at 1394 +/- 1191 (range 210-3420) min in Group 2 (p = 0.004), still during 31 degrees C but without further increase during hypothermia. Further IVP rise led to brain death in Group 1 in 6 of 10 dogs at 44 +/- 18 (range 21-72) h (all during controlled ventilation); and in Group 2, in 6 of 10 dogs at 87 +/- 11 (range 72-96) h (p = 0.001), all after rewarming, during spontaneous breathing. Survival to 96 h was achieved by 4 of 10 dogs in Group 1, and by 7 of 10 dogs in Group 2 (NS). Three of the six brain deaths in Group 2 occurred at 96 h. The macroscopically damaged brain volume was only numerically smaller in Group 2. The vermis downward shift was 6.8 +/- 3.5 mm in Group 1, versus 4.7 +/- 2.2 mm in Group 2 (p = 0.05). In an adjunctive study, in 4 additional normothermic dogs, hemispheric cerebral blood flow showed post-insult hypoperfusion bilaterally but no evidence of hyperemia preceding IVP rise to brain death. In conclusion, in this model, moderate hypothermia during and for 48 h after temporary epidural brain compression can maintain a low IVP during hypothermia but cannot prevent lethal brain swelling after rewarming and may cause coagulopathy and pulmonary complications.

Therapeutic Moderate Hypothermia for Severe Traumatic Brain Injury

Use of therapeutic hypothermia to treat patients with severe traumatic brain injury was described more than 50 years ago. Unexpected improvement in some of these patients was attributed to hypothermia, but none of the early studies systematically evaluated the efficacy of hypothermia, and many patients were thought to have been harmed by the treatment, particularly when cooled below 30°C or when cooled for longer than 48 hours. Recent investigations have found that therapeutic moderate hypothermia (32–34°C) for relatively brief durations can improve histological and behavioral outcome following experimental brain injury. Cooling to this degree and duration has not been implicated as a cause for the cardiac arrhythmias, coagulation abnormalities, or infections attributed to hypothermia in the earlier studies. These laboratory investigations also defined several neurochemical mechanisms through which hypothermia may limit secondary brain injury and brain swelling. Four clinical trials of therapeutic moderate hypothermia were completed during the past three years; each detected a beneficial effect from cooling patients with severe traumatic brain injury to 32 to 34°C for up to 48 hours. In the largest of these studies, therapeutic moderate hypothermia was shown to cause a significant improvement in neurological outcomes 3, 6, and 12 months after injury for those patients with an initial Glasgow Coma Scale score of 5 to 7. The improvement in outcome for these patients was associated with a hypothermia-induced reduction of intracranial pressure and cerebrospinal fluid levels of interleukln-1β and glutamate.

Hypothermia in acute blunt head injury

Mild to moderate hypothermia has been employed since the 1940s in the treatment of acute blunt head trauma. The utility of hypothermia in ischemic injury has been confirmed, by both animal studies and clinical experience, in cardiovascular and neurological surgery. In blunt injury, though, only one prospective, randomized study has shown a statistically significant improvement in long term outcome. Clinical experience, animal data, proposed mechanisms, technical considerations, and potential risks are reviewed. Hypothermia remains controversial in the setting of blunt head injury but may prove to be a useful treatment modality.