In vitro evaluation of the effect of hypothermia on coagulation in dogs via thromboelastography

Impact of general anesthesia on rotational thromboelastometry (ROTEM) parameters and standard plasmatic coagulation tests in healthy Beagle dogs

OBJECTIVE

To assess the influence of general anesthesia on rotational thromboelastometry (ROTEM) and standard coagulation testing in healthy dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

10 healthy Beagle dogs.

METHODS

Dogs were administered methadone (0.2 mg/kg) intramuscularly. Anesthesia was co-induced intravenously 30 min later with midazolam (0.1 mg/kg) and propofol to effect, and maintained with sevoflurane. Crystalloids were administered at 5 ml/kg/h. Blood was sampled by direct venipuncture before induction (T0) and 3.5 h later (T3.5) and ROTEM parameters (ExTEM, InTEM, FibTEM, ApTEM), standard plasmatic coagulation tests (prothrombin time [PT], activated partial thromboplastin time [aPTT], fibrinogen concentration), hematology, ionized calcium, triglycerides, pH, lactate and body temperature were compared over time with Students t - test or Wilcoxon matched pairs signed-rank tests.

RESULTS

The following variables dropped significantly between T0 and T3.5: body temperature (p < 0.0001), hematocrit (p < 0.0001), platelet count (p < 0.01), pH (p < 0.01), triglycerides (p < 0.01), fibrinogen concentration (p < 0.01), ExTEM, FibTEM (p < 0.01) and ApTEM (p < 0.05) clotting times. Lactate concentration (p < 0.01), aPTT (p < 0.05) and FibTEM maximum clot firmness increased (p < 0.05). No changes were noted in ionized calcium, PT and InTEM values.

CONCLUSION AND CLINICAL RELEVANCE

General anesthesia with concurrent hemodilution and hypothermia induced significant but clinically irrelevant changes in coagulation variables measured at 37 °Celsius. Blood samples from anaesthetized animals can be used for determination of coagulation status in dogs.

The effect of analytical temperature on thromboelastography tracings in dogs

Viscoelastic testing methods such as thromboelastography (TEG) are becoming increasingly available to veterinarians in a clinical setting. TEG is useful in determining therapeutic transfusion needs and assessing global abnormalities of hemostasis of patients, given that it provides a more comprehensive assessment of coagulation than traditional tests. TEG is standardly performed at 37°C, which is considered a normal body temperature for human patients; however, 37°C is lower than normal body temperature for most canine patients. In an in vitro study, we investigated the potential effect that this difference in body temperature and test temperature might have on TEG results. Citrated blood samples were collected from clinically normal, as well as sick, dogs with various body temperatures. Samples were analyzed concurrently at the patient's body temperature and at 37°C. There was very high correlation between TEG performed at body temperature and at 37°C for R (min) and MA (mm), high correlation for K (min) and alpha angle (deg), and moderate correlation for LY30 (%) and LY60 (%). For canine patients with normal to mildly abnormal body temperatures, performance of TEG at the standard 37°C is acceptable.

Use of Thromboelastography in Clinical Practice

Viscoelastic testing, such as thromboelastography or thromboelastometry, is performed on whole-blood samples, which include both soluble plasma factors as well as blood cells and platelets bearing tissue factor and phospholipid. This methodology allows identification of fibrinolysis and can provide analysis of platelet function. Viscoelastic testing has become increasingly accessible and popular in emergency and critical care settings in recent years and can provide important information for the diagnosis and management of patients with hemostatic disorders. This article discusses the principles and interpretation of viscoelastic testing, application to small animal emergency and critical care medicine, and potential advantages and disadvantages.

Effect of rest temperature on rotational thromboelastometry in New Zealand White rabbits

With the increasing popularity of viscoelastic coagulation analyzers, such as rotational thromboelastometry [ROTEM] and thromboelastography, the need for standardized methodology for appropriate interpretation has become increasingly important. Viscoelastic analysis is heavily influenced by a multitude of pre-analytic factors, both in vivo and in vitro, leading to a large amount of variation between institutions. We investigated the effect of room temperature during a 30-min sample rest time on ROTEM, which analyzed both intrinsic and extrinsic pathways. We also evaluated the feasibility of using ROTEM to assess coagulation in non-anesthetized domestic rabbits. Rabbits were selected because they are a common companion animal that could benefit from the use of viscoelastic analysis for various disease processes that could lead to coagulopathies. Citrated whole blood was collected from 10 rabbits and allowed to rest upright for 30 min either at room temperature (~ 21°C) or in a tube warmer (37°C) before analysis. There was no significant difference in results between room temperature and warmed samples, which suggests that allowing samples to rest at room temperature is acceptable clinically. Additionally, blood collection and analysis were feasible in all rabbits.

Prewarming Followed by Active Warming is Superior to Passive Warming in Preventing Hypothermia for Short Procedures in Adult Rats (Rattus norvegicus) Under Isoflurane Anesthesia

General anesthesia is a common procedure in laboratory rats; however, it impairs thermoregulation, rapidly leading to hypothermia as warm core blood is distributed to the cooler periphery. The protective strategy of prewarming before the onset of anesthesia delays hypothermia, but only for a short period. This prospective, randomized, cross-over, experimental study in adult male and female SD rats (n = 8) was designed to compare passive (fleece blanket) and active (temperature controlled heating pad) warming. Initial treatment order was randomized, with a cross-over after a minimum 5 d washout period. Both groups underwent a period of prewarming in a warming box to increase core temperature by 1% (median 0.4 °C). At completion of prewarming, general anesthesia was induced and maintained for 30 min with isoflurane carried in oxygen. Core temperature was monitored for a further 30 min after anesthesia. Active warming resulted in higher core temperatures during anesthesia. During passive warming, hypothermia occurred after approximately 30 min of anesthesia and continued into recovery. In contrast, active warming prevented hypothermia. Prewarming followed by passive warming delayed hypothermia for approximately 30min, but active warming was more effective at maintaining normothermia both during and after general anesthesia.

Intraoperative anaesthetic complications in dogs undergoing general anaesthesia for thoracolumbar hemilaminectomy: a retrospective analysis

OBJECTIVE

To establish the incidence of intraoperative anaesthetic complications in dogs undergoing general anaesthesia (GA) for thoracolumbar hemilaminectomy (TH), to determine whether GA duration affects incidence of intraoperative complications and to identify associations between intraoperative complications.

STUDY DESIGN

Retrospective observational study.

ANIMALS

A total of 224 client-owned dogs of various breeds undergoing TH for intervertebral disc extrusion.

METHODS

Anaesthetic records of dogs undergoing TH at a university teaching hospital between 2010 and 2016 were analysed. Data recorded included breed, sex, body weight, GA duration, magnetic resonance imaging (MRI) under the same GA, pharmacological intervention to increase heart rate (PIHR), hypotension (mean arterial blood pressure < 60 mmHg for ≥ 10 minutes), mechanical ventilation (MV) for inadequate ventilation, hypothermia (oesophageal temperature < 37 °C), oesophageal temperature ≥ 39 °C (T ≥ 39 °C), temperature trend, regurgitation and use of alpha-2 adrenoreceptor agonists, acepromazine, ketamine or lidocaine. Multivariate logistic regression models were fitted for hypothermia, T ≥ 39 °C, hypotension and PIHR with forced inclusion of GA duration.

RESULTS

Hypothermia was the most common complication (63.8% incidence), followed by MV implementation (63.4%), hypotension (33.9%), PIHR (24.6%), T ≥ 39 °C (20.5%) and regurgitation (4.9%). Multivariate models revealed that MRI and hypotension were associated with an increased risk of hypothermia, whilst increasing body weight, alpha-2 adrenoreceptor agonists and MV were associated with a reduced risk. Alpha-2 adrenoreceptor agonists and GA duration were associated with an increased risk of T ≥ 39 °C, whilst hypotension was associated with a reduced risk. Hypothermia and PIHR were associated with an increased risk of hypotension, whereas increased body weight was associated with a reduced risk. MV and hypothermia were associated with an increased risk of PIHR, whereas increased body weight was associated with a reduced risk.

CONCLUSIONS AND CLINICAL RELEVANCE

Increasing GA duration was associated with increased risk of T ≥ 39 °C, but not any other intraoperative complications.

Thromboelastography in wild Florida manatees (Trichechus manatus latirostris)

BACKGROUND

Thromboelastography (TEG) provides a comprehensive evaluation of blood clot formation. This test can be used to identify abnormalities in coagulation by assessing multiple aspects of the clotting cascade, including the speed of clot initiation and formation, clot strength, and ultimately fibrinolysis. Thromboembolic disease has been hypothesized to play a role in the pathophysiology of cold stress syndrome (CSS), an important cause of mortality in the threatened Florida manatee (Trichechus manatus latirostris).

OBJECTIVES

The objective of this study was to establish thromboelastography RIs using the TEG 5000 with citrated whole blood samples and kaolin activation in wild, healthy manatees.

METHODS

In December 2014 and January 2015, 29 wild manatees (17 male and 12 female) were blood sampled as part of the annual wild manatee health assessments organized by United States Geological Survey (USGS). TEG was performed using citrated kaolin-activated samples.

RESULTS

The samples were obtained from manatees caught in Crystal River, Citrus County, and used to identify the mean ± SD of normal TEG parameters: R = reaction time 2.1 minutes (0.8), K = clot formation time 0.8 min (0), α angle = 83.1° (2), MA = maximum amplitude 75 mm (7.6), and LY30 = clot lysis 0.41% (0.68). No significant differences were found between manatee size, sex, or time between sampling and running the test.

CONCLUSIONS

Manatee TEG parameters demonstrate a relatively hypercoagulable condition when compared to other mammals. This information will facilitate detection of changes in hemostasis during injury and disease and provide a valuable reference range.

Hypothermia and targeted temperature management in cats and dogs

OBJECTIVE

To review current knowledge surrounding the effects, treatment, and prognosis of hypothermia in people, dogs, and cats, as well as the application of therapeutic hypothermia in clinical medicine.

ETIOLOGY

Hypothermia may be a primary or secondary condition, and may be due to environmental exposure, illness, medications, anesthesia, or trauma. Hypothermia has been applied therapeutically in human medicine for a variety of conditions, including postcardiac arrest. In veterinary medicine, the technique has been applied in cardiac surgeries requiring bypass and in a patient with intractable seizures.

DIAGNOSIS

Hypothermia can be diagnosed based on presenting temperature or clinical signs, and appropriate diagnosis may require nontraditional thermometers.

THERAPY

Rewarming is the primary treatment for accidental hypothermia, with intensity ranging from passive surface rewarming to extracorporeal rewarming. The goal is to return the core temperature to a level that restores normal physiologic function of all body processes. Other supportive therapies such as intravenous fluids are typically indicated, and if cardiopulmonary arrest is present, prolonged resuscitation may be required. In cases of secondary hypothermia, reversal of the underlying cause is important.

PROGNOSIS

There are few prognostic indicators in human and veterinary patients with hypothermia. Even the most severely affected individuals, including those presenting in cardiopulmonary arrest, have potential for complete recovery with appropriate therapy. Therapeutic hypothermia has been shown to improve outcome in people following cardiac arrest. Further studies are needed to examine this application in veterinary medicine, as well as appropriate therapy and prognosis for cases of spontaneous hypothermia.

Effects of anesthetic induction with a benzodiazepine plus ketamine hydrochloride or propofol on hypothermia in dogs undergoing ovariohysterectomy

OBJECTIVE

To assess the effect of anesthetic induction with a benzodiazepine plus ketamine or propofol on hypothermia in dogs undergoing ovariohysterectomy without heat support.

ANIMALS

23 adult sexually intact female dogs undergoing ovariohysterectomy.

PROCEDURES

Baseline rectal temperature, heart rate, and respiratory rate were recorded prior to premedication with buprenorphine (0.02 mg/kg, IM) and acepromazine (0.05 mg/kg, IM). Anesthesia was induced with midazolam or diazepam (0.25 mg/kg, IV) plus ketamine (5 mg/kg, IV; n = 11) or propofol (4 mg/kg, IV; 12) and maintained with isoflurane in oxygen. Rectal temperature was measured at hospital intake, prior to premedication, immediately after anesthetic induction, and every 5 minutes after anesthetic induction. Esophageal temperature was measured every 5 minutes during anesthesia, beginning 30 minutes after anesthetic induction. After anesthesia, dogs were covered with a warm-air blanket and rectal temperature was measured every 10 minutes until normothermia (37°C) was achieved.

RESULTS

Dogs in both treatment groups had lower rectal temperatures within 5 minutes after anesthetic induction and throughout anesthesia. Compared with dogs that received a benzodiazepine plus ketamine, dogs that received a benzodiazepine plus propofol had significantly lower rectal temperatures and the interval from discontinuation of anesthesia to achievement of normothermia was significantly longer.

CONCLUSIONS AND CLINICAL RELEVANCE

Dogs in which anesthesia was induced with a benzodiazepine plus propofol or ketamine became hypothermic; the extent of hypothermia was more profound for the propofol combination. Dogs should be provided with adequate heat support after induction of anesthesia, particularly when a propofol-benzodiazepine combination is administered.

Effects of in vitro hemodilution with crystalloids, colloids, and plasma on canine whole blood coagulation as determined by kaolin-activated thromboelastography

OBJECTIVE

To investigate the effects of in vitro hemodilution with lactated Ringers solution (LRS), hetastarch (HES), and fresh frozen plasma (FFP) on whole blood coagulation in dogs as assessed by kaolin-activated thromboelastography.

DESIGN

In vitro experimental study.

SETTING

University teaching hospital.

ANIMALS

Six healthy client-owned dogs.

INTERVENTIONS

Whole blood was collected and diluted in vitro at a 33% and 67% dilution with either LRS, HES, or FFP.

MEASUREMENTS AND MAIN RESULTS

Kaolin-activated thromboelastography was performed on each sample as well as a control. Thromboelastographic parameters R (min), alpha (deg), K (min), and MA (mm) were measured and compared to the sample control for each dilution using mixed model methodology. Prolongation in coagulation times were seen at both dilutions with LRS and HES. There was no significant difference in R times at the 33% dilution, but R time was significantly prolonged at the 67% dilution with HES (P = 0.004). MA was significantly decreased for LRS at both dilutions (P = 0.013, P < 0.001) and more profoundly decreased for HES (P < 0.001, P = 0.006). No significant difference in any parameter was found for FFP.

CONCLUSIONS

In vitro hemodilution of whole blood with both LRS and HES but not FFP resulted in significant effects on coagulation with HES having a more profound effect. In vivo evaluation of changes in coagulation with various resuscitation fluids is warranted and may be clinically relevant.

Therapeutic hypothermia for stroke: Where to go?

Ischemic stroke is a major cause of death and long-term disability worldwide. Thrombolysis with recombinant tissue plasminogen activator is the only proven and effective treatment for acute ischemic stroke; however, therapeutic hypothermia is increasingly recognized as having a tissue-protective function and positively influencing neurological outcome, especially in cases of ischemia caused by cardiac arrest or hypoxic-ischemic encephalopathy in newborns. Yet, many aspects of hypothermia as a treatment for ischemic stroke remain unknown. Large-scale studies examining the effects of hypothermia on stroke are currently underway. This review discusses the mechanisms underlying the effect of hypothermia, as well as trends in hypothermia induction methods, methods for achieving optimal protection, side effects, and therapeutic strategies combining hypothermia with other neuroprotective treatments. Finally, outstanding issues that must be addressed before hypothermia treatment is implemented at a clinical level are also presented.