Continuous digital hypothermia for prevention and treatment of equine acute laminitis: A practical review.

Laminitis is a severely debilitating and life-threatening condition that occurs as a consequence of different primary triggering factors. Continuous digital hypothermia (CDH) is recommended in horses at risk of, or diagnosed with, acute laminitis due to its several physiological and biochemical alterations that may be positive for the prevention and early treatment of the condition, representing a low risk of adverse effects. Modulation of the inflammatory response, profound vasoconstriction, and prevention of tissue damage are the most notable protective effects of cryotherapy on the lamellae. This practical review aims to summarize the published literature evaluating CDH efficacy in the prevention and early treatment of acute laminitis in horses, highlighting the most important clinical findings and discussing the best methods to provide cryotherapy. Nineteen publications evaluated different CDH methods, including the use of commercially available ice boots or fluid bags filled with iced water or crushed ice, as well as alternatives to immersion in ice, e.g., frozen gel packs and a perfused cuff prototype. Although some techniques were effective for cooling and maintaining the hooves below the optimal temperature of 10 °C, relevant limitations such as labor intensiveness, reliance on an ice source and price make its use impractical in some clinical situations. Twelve experimental studies assessed the efficacy of CDH on the prevention or early treatment of laminitis, finding multiple positive effects in terms of clinical improvement, immunological and inflammatory modulation, and histological protection. After the analysis of the literature, the clinical importance of CDH in different stages of laminitis remains clear. However, it also highlights the need for a safer, more user-friendly, and more effective method of cryotherapy that can be used both in a hospital and an ambulatory setting.

The effect of regional hypothermia on mechanical nociceptive thresholds in the equine distal forelimb.

Regional hypothermia has shown promise as analgesic in horses when used to manage painful conditions of the distal limb such as laminitis. In this prospective study, the analgesic effects of regional hypothermia were assessed using mechanical nociceptive thresholds during distal limb cooling. The study population consisted of eight healthy adult Standardbred horses, selected from a teaching herd. A distal forelimb of each horse was cooled using water immersion at the following sequential target water temperatures: 34 °C, 20 °C, 10 °C, 5 °C, 1 °C, 5 °C, 10 °C, 20 °C. Limb surface temperature was measured after 30 min at each target water temperature and the mechanical force required to elicit a response (mechanical nociceptive threshold) was determined using a pneumatic actuator. Both forelimbs of each horse were tested one week apart. At skin surface temperatures above 7 °C, there was little association between skin surface temperature and the mechanical force required to elicit a response. As the skin surface temperature decreased below 7 °C, there was a rapid increase in the force required to elicit a response (P = 0.036). Skin surface temperatures of <7 °C required water temperatures below 2 °C. The results of this study suggest that hypothermia has potential to provide distal limb analgesia in horses at skin surface temperatures below 7 °C. Further evaluation of the technique is warranted.

Effect of digital hypothermia on lamellar inflammatory signaling in the euglycemic hyperinsulinemic clamp laminitis model.

BACKGROUND: Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycemic hyperinsulinemic clamp (EHC) model of laminitis, but the protective mechanisms are unclear. HYPOTHESIS/OBJECTIVES: To determine if CDH inhibits lamellar inflammatory signaling in the EHC model of laminitis. ANIMALS: Eight Standardbred horses. METHODS: Prospective experimental study. Horses underwent an EHC, with 1 forelimb treated with CDH and the other kept at ambient temperature (AMB). Horses were euthanized 48 hours after initiation of the EHC and lamellar tissue was analyzed via polymerase chain reaction (pro-inflammatory cytokine and chemokine genes-CXCL1, CXCL6, CXCL8, IL-6, MCP-1, MCP-2, IL-1ß, IL-11, cyclooxygenase 1 and 2, tumour necrosis factor-alpha [TNF-α], E-selectin, and intercellular adhesion molecule-1 [ICAM-1]) and immunoblotting (phosphorylated and total signal transducer and activator of transcription 1 [STAT1] and STAT3). RESULTS: Compared to AMB, lamellar messenger ribonucleic acid (mRNA) concentrations of CXCL6 (P =.02), CXCL8 (P = .008), IL-6 (P = .008), IL-1ß (P = .008), IL-11 (P = .008), and cyclooxygenase-2 (P = .008) were decreased in CDH. Cyclooxygenase-1 (P = .008) was increased in CDH, while CXCL1 (P = .15), MCP-1 (P = .05), MCP-2 (P = .46), TNF-α (P = .05), E-selectin (P = .15), and ICAM-1 (P = .15) mRNA were not significantly different. Compared to AMB, lamellar concentration of total STAT3 protein was decreased in CDH (P < .001), but there was no change in phosphorylated STAT3 (P-STAT3 [S727] P = .19; P-STAT3 [Y705] P = .05). There was no change in lamellar concentrations of total STAT1 (P = .75) or phosphorylated STAT1 (P-STAT1 [S727], P = .25; P-STAT1 [Y701], P = .64). CONCLUSIONS AND CLINICAL IMPORTANCE: These data add further support for the use of CDH as a first aid treatment for severe acute laminitis associated with hyperinsulinemia in horses.

Ketamine-dexmedetomidine combination and controlled mild hypothermia for the treatment of long-lasting and super-refractory status epilepticus in 3 dogs suffering from idiopathic epilepsy.

OBJECTIVE: To describe the use of a ketamine-dexmedetomidine combination and mild hypothermia for the treatment of status epilepticus in 3 dogs that did not respond to GABAergic medication. CASE SERIES SUMMARY: Three dogs, each with a diagnosis of idiopathic epilepsy, were presented to the emergency department in a state of status epilepticus. The dogs were treated unsuccessfully with benzodiazepine as a first-line therapy that was followed by IV propofol anesthesia maintained for at least 12 hours. When general anesthesia was discontinued, seizures reoccurred. All 3 dogs then received a bolus of ketamine (1 mg/kg, IV) over a period of 5 minutes that was followed by a bolus of dexmedetomidine (3 µg/kg, IV) over the same time period and then followed by a continuous infusion for 12 hours of ketamine at a constant rate of 1 mg/kg/h and dexmedetomidine at a variable rate of 3-7 µg/kg/h. Body temperature was maintained between 36.7 and 37.7°C at a state of mild hypothermia throughout treatment. The dogs recovered uneventfully over 48 hours after treatment was discontinued with no evidence of seizures. No notable alterations in physiological parameters were observed during the drug infusions. All dogs were discharged following examinations that showed normal neurological function. NEW OR UNIQUE INFORMATION PROVIDED: This case series highlights the potential benefits of a ketamine-dexmedetomidine infusion combined with mild hypothermia for the treatment of status epilepticus refractory to GABAergic therapy in dogs suffering from idiopathic epilepsy. After the dogs were weaned from the ketamine-dexmedetomidine infusion, all dogs experienced complete recovery. Thus, this case series introduces a novel approach to treat this intense condition.

Critical Evaluation of Whole-Body Cryostimulation Protocol in Race Horses.

Cold therapy is commonly used to relieve pain and inflammation and to aid in muscle recovery after exercise in human medicine. A number of applications have also been observed in veterinary practice. In this article, a critical evaluation of equine protocol applied with a new commercial concept of equine whole-body cryostimulation (WBC) was made. With this new concept of WBC, the protocol usually utilized for relieving pain and discomfort in humans has been extended to horses. The investigations described herein focus on the reduction of horse skin temperature when applying human WBC protocols. Based on infrared thermography measurements, results show that exposing a horse for 3 minutes to a temperature of -140°C, which are conventional parameters used for humans, does not induce sufficient skin thermal gradients in horses. Consequently, beneficial cold reflexes such as vasomotor, neuroconduction, and biochemical reactions cannot be triggered. Further investigations should therefore be carried out to design an adequate protocol specifically aimed at horses.

[Perioperative hypothermia in dogs receiving combined administration of acepromazin and metamizol]. / Untersuchung der perioperativen Hypothermie bei kombinierter Gabe von Acepromazin und Metamizol beim Hund.

OBJECTIVE: Evaluation the development of perioperative body temperature while administrating a combination of acepromazine and metamizol (AM) versus anesthesia with acepromazine (A) alone. MATERIAL AND METHODS: In this prospective, quasi-randomized controlled study 20 dogs undergoing standardized tibial plateau leveling osteotomy were alternatingly assigned to group A or group AM (n = 10 each). The patients' body temperature values were recorded from the time of premedication up to its post-surgical return to reference values. RESULTS: Body temperature decreases during anesthesia in both groups were comparable (p = 0.12). Postoperatively on the other hand, temperature development differed significantly between the two groups (p = 0.0455). In 6 dogs of the group AM, body temperature continued to decrease following extubation prior to returning to normothermic values. CONCLUSION: Intraoperatively, all patients developed hypothermia, regardless of the investigated anesthetic medication administered. Postoperatively, patients not receiving metamizol reached normothermia more rapidly.

Effect of Continuous Digital Hypothermia on Lamellar Inflammatory Signaling When Applied at a Clinically-Relevant Timepoint in the Oligofructose Laminitis Model.

BACKGROUND: Although continuous digital hypothermia (CDH) protects lamellae from injury in the oligofructose (OF) model of sepsis-related laminitis (SRL), conflicting results exist from these studies regarding effects of CDH on lamellar inflammatory events. HYPOTHESIS/OBJECTIVES: To determine the effect of CDH on lamellar inflammatory events in normal and OF-treated horses when instituted at a clinically relevant time point (onset of clinical signs of sepsis in this model). ANIMALS: Standardbred geldings (n = 15) aged 3-11 years were used. METHODS: In a randomized, controlled discovery study, animals were administered either OF (OF group, n = 8) or water (CON group, n = 8) by nasogastric tube and CDH was initiated in one forelimb (ICE) 12 hours later. Lamellar tissue samples were collected 24 hours after initiation of CDH (ICE and ambient [AMB] forelimbs). Lamellar mRNA concentrations of inflammatory mediators and lamellar leukocyte numbers were assessed using qPCR and immunohistochemistry, respectively; values from four sample groups (CON AMB, OF AMB, CON ICE, and OF ICE) were analyzed using mixed model linear regression. RESULTS: Although lamellar mRNA concentrations of multiple inflammatory mediators (IL-1ß, IL-6, CXCL1, MCP2, COX-2) were increased after OF administration (OF AMB group versus CON AMB; P < 0.05), only 2 inflammatory mediators (IL-6 and COX-2) and lamellar leukocyte numbers were decreased with CDH (OF ICE versus OF AMB; P < 0.05). CONCLUSIONS AND CLINICAL IMPORTANCE: Continuous digital hypothermia initiated at a time point similar to that commonly used clinically (clinical onset of sepsis) resulted in a more focused inhibition of inflammatory signaling.

Cold block of in vitro eyeblink reflexes: evidence supporting the use of hypothermia as an anesthetic in pond turtles.

Use of hypothermia as a means of anesthesia for amphibians and reptiles is prohibited by agencies that establish veterinary guidelines. This has recently been called into question by members of the scientific community based on reviews of published literature. Using pond turtles (Trachemys scripta elegans), hypothermia as a method for anesthesia to precede euthanasia by decapitation was assessed. Turtles were subjected to hypothermia using a cooling followed by freezing protocol. Body temperature measurements ranged between -1 and -2°C while core body temperature was -1°C. Ice crystal formation was never observed. A protective reflex to noxious stimuli, the eyeblink response, was recorded from in vitro brainstem preparations subjected to cold. At 5-6°C, reflex responses were suppressed, demonstrating minimal synaptic transmission in brain circuits above temperatures used for hypothermia induction. These and previous data indicate that a re-evaluation of the use of hypothermia as an anesthetic in amphibians and reptiles is warranted.

Quantification of Induced Hypothermia from Aseptic Scrub Applications during Rodent Surgery Preparation.

Laboratory mice (Mus musculus) are prone to develop hypothermia during anesthesia for surgery, thus potentially impeding anesthetic recovery, wound healing, and future health. The core body temperatures of isoflurane-anesthetized mice are influenced by the choice of supplemental heat sources; however, the contribution of various surgical scrubs on the body temperatures of mice under gas anesthesia has not been assessed. We sought to quantify the effect of using alcohol (70% isopropyl alcohol [IPA]) compared with saline to rinse away surgical scrub on the progression of hypothermia in anesthetized mice (n = 47). IPA, room-temperature saline, or warmed saline (37 °C) was combined with povidone-iodine and then assessed for effects on core (rectal) and surface (infrared) temperatures. Agents were applied to a 2×2-cm shaved abdominal area of mice maintained on a water-recirculating blanket (at 38 °C) under isoflurane anesthesia (1.5% to 2.0% at 0.6 L/min) for 30 min. Although all scrub regimens significantly decreased body temperature at the time of application, treatments that included povidone-iodine led to the coldest core temperatures, which persisted while mice were anesthetized. Compared with room-temperature saline and when combined with povidone-iodine, warming of saline did not ameliorate heat loss. IPA alone demonstrated the most dramatic cooling of both surface and core readings at application but generated an unanticipated warming (rebound) phase during which body temperatures equilibrated with those of controls within minutes of application. Although alcohol is inappropriate as a stand-alone agent for surgical skin preparation, IPA is a viable alternative to saline-based rinses in this context, and its use should be encouraged within institutional guidance for rodent surgical procedures without concern for prolonged hypothermia in mice.

Effect of Delayed Digital Hypothermia on Lamellar Inflammatory Signaling in the Oligofructose Laminitis Model.

BACKGROUND: In the oligofructose (OF) model of sepsis-related laminitis (SRL), digital hypothermia ("cryotherapy") initiated before the onset of clinical signs is reported not only to limit lamellar injury, but also to cause marked inhibition of lamellar inflammatory signaling. HYPOTHESIS/OBJECTIVES: Because hypothermia also has been reported to be protective when not initiated until the onset of lameness in the OF model of SRL, we hypothesized that the lamellar protection conferred by hypothermia is caused by local lamellar inhibition of inflammatory signaling as described when hypothermia was initiated earlier in the disease process. ANIMALS: Eight Standardbred geldings aged 3-11 years with no lameness and no abnormalities of the feet detectable by gross or radiographic examination. METHODS: Using the OF model of SRL, lamellar mRNA concentrations of proinflammatory cytokines, chemokines, and endothelial adhesion proteins were compared between samples from treated limbs (CRYO, submerged in ice water for 36 hour starting at the onset of lameness), untreated limbs (NON-CRYO, opposite limb from CRYO limbs maintained at ambient temperature), and untreated limbs from normal horses in which laminitis was not induced (CON). RESULTS: Although OF administration resulted in increases in lamellar mRNA concentrations of several inflammatory mediators in NON-CRYO limbs (vs CON), digital hypothermia had no significant effect on these increases. CONCLUSIONS AND CLINICAL IMPORTANCE: The lack of inflammatory inhibition in lamellar tissue samples in our study indicates that the protective effects of digital hypothermia instituted at the onset of clinical signs of laminitis do not arise from inhibition of inflammatory pathways.

The effect of hypothermia on influx of leukocytes in the digital lamellae of horses with oligofructose-induced laminitis.

Sepsis-related laminitis (SRL) is a common complication in the septic/endotoxemic critically-ill equine patient, in which lamellar injury and failure commonly lead to crippling distal displacement of the distal phalanx. Similar to organ injury in human sepsis, lamellar injury in SRL has been associated with inflammatory events, including the influx of leukocytes into the lamellar tissue and markedly increased expression of a wide array of inflammatory mediators at the onset of Obel grade 1 (OG1) laminitis. The only treatment reported both clinically and experimentally to protect the lamellae in SRL, local hypothermia ("cryotherapy"), has been demonstrated to effectively inhibit lamellar expression of multiple inflammatory mediators when initiated at the time of administration of a carbohydrate overload in experimental models of SRL. However, the effect of hypothermia on leukocyte influx into affected tissue has not been assessed. We hypothesized that cryotherapy inhibits leukocyte emigration into the digital lamellae in SRL. Immunohistochemical staining using leukocyte markers MAC387 (marker of neutrophils, activated monocytes) and CD163 (monocyte/macrophage-specific marker) was performed on archived lamellar tissue samples from an experimental model of SRL in which one forelimb was maintained at ambient temperature (AMB) and one forelimb was immersed in ice water (ICE) immediately following enteral oligofructose administration (10g/kg, n=14 horses). Lamellae were harvested at 24h post-oligofructose administration (DEV, n=7) or at the onset of OG1 laminitis (OG1, n=7). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n=10 (40× fields/digit for MAC387 and 20x fields/digit for CD163)] obtained using Aperio microscopy imaging analysis software. Data were assessed for normality and analyzed with a paired t-test and one-way ANOVA with significance set at p<0.05. MAC387-positive cells were present in low numbers in the lamellar tissue and were decreased in the hypothermic limbs (vs. AMB limbs, p<0.05) in the OG1 group; no change in CD163-positive cell numbers was noted across the conditions of the model. This study demonstrated that hypothermia of the distal limbs instituted early in the disease process in the horse at risk of SRL significantly attenuates the increase of MAC387-positive leukocytes in the digital lamellae, but has minimal effect on increases in lamellar concentrations of the major leukocyte cell type present in that tissue, CD163-positive mononuclear cells.

Therapeutic hypothermia applicable to cardiac surgery.

OBJECTIVE: To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH. DATABASES USED: Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded. CONCLUSIONS: Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Does insulin impact cold-induced fluid- and protein-extravasation?

BACKGROUND: Insulin has been shown to stabilize the endothelial barrier via inactivation of the endothelial contractile machinery and enhancement of cell-cell adhesions. Here we explored if insulin by its endothelial-stabilizing and anti-inflammatory properties could influence the increase of fluid- and protein-extravasation during hypothermia. METHODS: Two groups of animals (n=10, each) were cooled to 28°C, with insulin-infusion (I-group) or without (C-group), in a randomly controlled study. Fluid balance, hemodynamics, plasma volume (PV), colloid osmotic pressures in plasma (COPp) and interstitial fluid (COPi), hematocrit (Hct), cytokine profiles, serum-albumin- and protein-concentrations were measured and fluid extravasation rate (FER) and albumin-and protein-masses calculated. RESULTS: During 240 min of hypothermia the albumin- and protein-masses together with COPp decreased significantly in both groups. COPi remained essentially unchanged. Plasma volume decreased significantly in the C-group, whereas only a decreasing trend was present in the I-group. Hemoconcentration was significant in both study groups reflected by the Hct-values. A slight increasing trend of FER was seen in both groups from 0.10 (0.04) ml/kg/min and 0.09 (0.05) mg/kg/min, C-group and I-group, respectively, to 0.14 (0.05) mg/kg/min and 0.12 (0.03) mg/kg/min, during the hypothermic period. Between-group differences were absent for all listed parameters including FER. CONCLUSION: Insulin administration does not impact fluid and protein extravasation significantly in animals undergoing cooling and prolonged hypothermia.

Systematic review and meta-analysis of therapeutic hypothermia in animal models of spinal cord injury.

BACKGROUND: Therapeutic hypothermia is a clinically useful neuroprotective therapy for cardiac arrest and neonatal hypoxic ischemic encephalopathy and may potentially be useful for the treatment of other neurological conditions including traumatic spinal cord injury (SCI). The pre-clinical studies evaluating the effectiveness of hypothermia in acute SCI broadly utilise either systemic hypothermia or cooling regional to the site of injury. The literature has not been uniformly positive with conflicting studies of varying quality, some performed decades previously. METHODS: In this study, we systematically review and meta-analyse the literature to determine the efficacy of systemic and regional hypothermia in traumatic SCI, the experimental conditions influencing this efficacy, and the influence of study quality on outcome. Three databases were utilised; PubMed, ISI Web of Science and Embase. Our inclusion criteria consisted of the (i) reporting of efficacy of hypothermia on functional outcome (ii) number of animals and (iii) mean outcome and variance in each group. RESULTS: Systemic hypothermia improved behavioural outcomes by 24.5% (95% CI 10.2 to 38.8) and a similar magnitude of improvement was seen across a number of high quality studies. The overall behavioural improvement with regional hypothermia was 26.2%, but the variance was wide (95% CI -3.77 to 56.2). This result may reflect a preponderance of positive low quality data, although a preferential effect of hypothermia in ischaemic models of injury may explain some of the disparate data. Sufficient heterogeneity was present between studies of regional hypothermia to reveal a number of factors potentially influencing efficacy, including depth and duration of hypothermia, animal species, and neurobehavioural assessment. However, these factors could reflect the influence of earlier lower quality literature. CONCLUSION: Systemic hypothermia appears to be a promising potential method of treating acute SCI on the basis of meta-analysis of the pre-clinical literature and the results of high quality animal studies.

Challenges of cardiopulmonary bypass-a review of the veterinary literature.

Cardiopulmonary bypass (CPB) has been used in veterinary medicine in experimental surgery and to address congenital and acquired diseases. We review the veterinary literature and expose common challenges of CPB in dogs and cats. Specifically, we describe the most specific elements of this technique in veterinary patients. The variety in animal size has made it difficult to standardize cannulation techniques, oxygenators, and priming volumes and solutions. The fact that one of the most common cardiovascular disorders, mitral valve disease, occurs predominantly in small dogs has limited the use of bypass in these patients because of the need for small, low prime oxygenators and pumps that have been unavailable until recently. Coagulation, hemostasis, and blood product availability have also represented important factors in the way CPB has developed over the years. The cost and the challenges in operating the bypass machine have represented substantial limitations in its broader use.

Effects of selective head cooling on cerebral blood flow and metabolism in newborn piglets after hypoxia-ischemia.

AIM: the effect of selective head cooling on cerebral blood flow (CBF) and cerebral metabolism rate (CMR) was investigated in newborn piglets. METHODS: seven days old newborn piglets were randomly assigned to one of the following three groups: Selective head cooling in normal piglets (n=4), selective head cooling after HI (n=6) and normal temperature after HI (n=6). CBF was measured with color microspheres. Cerebral oxygenation metabolism rate (CMRO(2)), Cerebral glucose consumption (CMR(Glu)) and Cerebral lactate production (CMR(lac)) were calculated. RESULT: in normal piglets, CBF, CMRO(2) and CMR(glu) were significantly decreased at both 35°C (P<0.05) and 32°C (P<0.01), while CMR(lac) did not change. Compared to baseline, CBF and CMRO(2) were significantly reduced (P<0.05), while CMR(glu) and CMR(lac) were significantly increased (P<0.01), AVDO(2) was decreased (P<0.05), while AVD(glu) and AVD(lac) were significantly increased (P<0.01 respectively) in HI piglets with normal temperature respectively. Compared to normal temperature after HI, selective head cooling after HI significantly reduced CMR(glu) and CMR(lac), and AVDO(2), AVD(glu), AVD(lac) were improved at 35°C. CONCLUSION: selective head cooling not only reduced energy consumption, but also improve brain oxygen metabolism in newborn after HI.

Differential changes of regional cerebral blood flow in two bat species during induced hypothermia measured by perfusion-weighted magnetic resonance imaging.

Cerebral blood flow (CBF) of a vespertilionid bat, Miniopterus fuliginosus (M. f.), and a pteropodid bat, Rousettus leschenaultii (R. l.) was measured non-invasively during induced hypothermia (37-10°C for M. f. and 37-24°C for R. l.) with perfusion-weighted magnetic resonance imaging. In both species, the average CBF was found to decrease with rectal temperature. The patterns of hypothermia-induced regional CBF changes, however, were different between the two species. In the pteropodid bat, the extent of CBF decrease at lower rectal temperature was similar in the cortex and thalamus, resulting in an unchanged thalamus/cortex CBF ratio. In contrast, the thalamus/cortex CBF ratio in the vespertilionid species increased progressively with decreasing rectal temperature (1.52 ± 0.14 at 37 ± 1°C vs. 2.28 ± 0.29 at 10 ± 1°C). These results suggest that the manner in which the two bat species cope with low body temperature may be reflected by a differential CBF regulation between thalamus and cortex.

Open heart surgery with deep hypothermia and cardiopulmonary bypass in small and toy dogs.

OBJECTIVE: To evaluate open heart surgery with deep surface-induced hypothermia (sHT) and low-flow cardiopulmonary bypass (CPB) in small and toy-breed dogs. STUDY DESIGN: Case series. ANIMALS: Small breed dogs (n=8) weighing <5.5 kg with naturally occurring cardiac disease. METHODS: Deep sHT under isoflurane anesthesia and low-flow rate CPB with a small-volume prime circuit were used. Ventricular septal defect was closed directly in 2 dogs and severe mitral regurgitation was corrected with mitral valvuloplasty (MVP) in 5 dogs and mitral valve replacement in 1 dog. RESULTS: All dogs survived surgery; 1 dog died 6 days and 1 died 2 months after MVP. The other 6 dogs lived (mean follow-up, 32.8 months; range, 12-65 months). Mean body weight at surgery was 3.6 kg (range, 2-5.3 kg). Mean lowest esophageal temperature was 21.4 degrees C (range, 19.8-23.8 degrees C). Mean lowest pump flow volume was 29.2 mL/kg/min (range, 9.4-57.7 mL/kg/min) during aortic cross-clamping (mean, 53.5 minutes; range, 25-79 minutes). Mean hematocrit before CPB was 38.6% (range, 33-47%) and 20.3% (range, 13-24%) during CPB with a small circuit priming volume of 225-260 mL. CONCLUSION: Deep sHT with low-flow rate CPB may be used for open heart surgery in small dogs weighing <5.5 kg. CLINICAL RELEVANCE: Open heart surgery for selected congenital defects and acquired defects in small and toy-breed dogs may be successfully performed using deep sHT and CPB.