Metabolism before, during and after anaesthesia in colic and healthy horses

Rutland C. Equine Stress: Neuroendocrine Physiology and Pathophysiology

This review presents new aspects to understanding the neuroendocrine regulation of equine stress responses, and their influences on the physiological, pathophysiological, and behavioral processes. Horse management, in essence, is more frequently confirmed by external and internal stress factors, than in other domestic animals. Regardless of the nature of the stimulus, the equine stress response is an effective and highly conservative set of interconnected relationships designed to maintain physiological integrity even in the most challenging circumstances (e.g., orthopedic injuries, abdominal pain, transport, competitions, weaning, surgery, and inflammation). The equine stress response is commonly a complementary homeostatic mechanism that provides protection (not an adaptation) when the body is disturbed or threatened. It activates numerous neural and hormonal networks to optimize metabolic, cardiovascular, musculoskeletal, and immunological functions. This review looks into the various mechanisms involved in stress responses, stress-related diseases, and assessment, prevention or control, and management of these diseases and stress. Stress-related diseases can not only be identified and assessed better, given the latest research and techniques but also prevented or controlled.

Effects of xylazine and adrenaline combinations: Preliminary clinical application for non-surgical protocols of nephrosplenic entrapment in horses

Background and Aim:

The medical treatment of horses with nephrosplenic entrapment (NSE) of the large colon through administrating phenylephrine and rolling during general anesthesia was effective and less expensive than surgical treatment. However, the selection of drugs for non-surgical treatment of NSE is not a usual method for clinical practice. This study aimed to identify the effects of combined drugs on the cardiac and splenic response in horses and provide information on the NSE of the large colon for clinical application.

Materials and Methods:

Six healthy Thai native crossbred horses were enrolled in this study. Horses received two protocols with a withdrawal period of 14 days: Group 1 received xylazine (0.5 mg/kg IV) and adrenaline (1 mcg/kg IV), and Group 2 received xylazine (0.5 mg/kg IV) and adrenaline (3 mcg/kg IV). Heart rate (HR), HR variability (HRV), heart dimensions, and the splenic response of six horses were measured before the sedation, 30 and 60 min later, and 65, 70, 75, 80, 90, and 100 min after adrenaline administration. Doppler was used to obtain systolic blood pressure.

Results:

The HRV low-frequency and high-frequency power ratios decreased after using xylazine. Hypertension was observed after adrenaline administration. In this study, there were only minimal differences in the HR and respiratory rate between groups. However, overall cardiac and splenic parameters were statistically higher in Group 2.

Conclusion:

This study suggested that xylazine and three micrograms of adrenaline preserved the cardiac autonomic activity balance and were safe to use non-surgical applicability in horses.

Comparison of liberal and goal-directed fluid therapy after small intestinal surgery for strangulating lesions in horses

BACKGROUND

There are few guidelines for the appropriate mode of fluid administration during and after colic surgery, and is challenging to reach the right balance while avoiding overhydration. This study aimed to compare goal-directed fluid therapy (GDFT) and 'liberal' fluid regimens (LFRs) in horses undergoing small intestinal surgery.

METHODS

Eighteen horses subjected to small intestinal surgery were matched according to the surgical lesion, type of anastomosis, length of resection, and duration of clinical signs. Horses in the LFR group were administered intravenous (IV) fluids for at least 24 h. In the GDFT group, IV fluids were administered only when considered necessary based on clinical parameters. Postoperative reflux (POR), packed cell volume, total protein, heart rate, venous lactate level, complications, and long-term survival rates were compared.

RESULTS

Three horses in the LFR and one in the GDFT group developed POR. Horses in the GDFT group had a shorter time interval to first oral water intake and shorter hospitalisation time. Postoperative complication rates and survival were not different between groups.

CONCLUSION

Further studies are necessary to set guidelines for the evaluation of hydration status and to plan postoperative fluid administration; however, GDFT may be a valid alternative to liberal fluid therapy after colic surgery.

Effects of supplementation with combination of polyunsaturated oils in diet of horses in maintenance and during marcha training

Abstract This study aimed to evaluate the effects of supplementation with polyunsaturated oil on lipid and mineral blood biomarkers in two different groups of horses. Was used 6 healthy horses in maintenance (MT-g) and 10 healthy horses in marcha gait training (GT-g). The MT-g and the GT-g received 100mL and 300mL/day/animal of combination of polyunsaturated oils, respectively, during 8 weeks. Blood was collected in pre-test and after 4 and 8 weeks, after overnight fasting and it was measured: total cholesterol, HDL cholesterol, LDL cholesterol, triglyceride, NEFA, LPS, glycerol, Ca, P, Mg, and Cl. The supplementation produced significant increase in NEFA and reduction in lipase in both groups. In addition, the LPS content in both groups had a large decrease (~35%) from the pre-test to the 8th week of supplementation. In the MT-g, the LDL cholesterol and glycerol increased significantly after 4 weeks but returned to the pre-test levels after 8 weeks, and the triglyceride content decreased (~62%) after 4 weeks. The total cholesterol concentration in the GT-g increased after 4 weeks (~70%), but after 8 weeks it decreased to levels similar to those observed in the pre-test. The mineral biomarkers increased in the MT-g and GT-g, after 8 weeks. In the MT-g and in the GT-g, Ca decreased. In conclusion, supplementation with a combination of polyunsaturated oils increased NEFA concentration and reduced LPS activity in both groups, unlike the concentrations of the other biomarkers that showed different variations between groups, indicating that both NEFA and LPS the changes in their concentrations during supplementation may be more sensitive and more indicated for these types of evaluation. In addition, some blood mineral concentrations reduced significantly in both groups of horses, and thus, they need to be evaluated in horses under chronic oil supplementation

Effects of pulsed inhaled nitric oxide on arterial oxygenation during mechanical ventilation in anaesthetised horses undergoing elective arthroscopy or emergency colic surgery

BACKGROUND

Administration of pulsed inhaled nitric oxide (PiNO) improves arterial oxygenation in spontaneously breathing anaesthetised healthy horses and in horses undergoing colic surgery. However, because hypoventilation commonly occurs, horses are often mechanically ventilated to prevent hypercarbia.

OBJECTIVES

To evaluate the effects of PiNO on arterial oxygenation during anaesthesia in mechanically ventilated healthy horses and horses undergoing colic surgery.

STUDY DESIGN

Prospective nonblinded clinical trial.

METHODS

Fifty horses undergoing elective arthroscopy (Group A) and 30 horses undergoing colic surgery (Group C) in dorsal recumbency were included in the study. Every second horse in each group received PiNO (A-INO, C-INO), the others served as controls (A-CN, C-CN). All horses were mechanically ventilated and anaesthesia was maintained with isoflurane. PiNO was mechanically delivered at the proximal end of the endotracheal tube as a pulse during the first part of each inspiration. Data were collected at the start (baseline, before PiNO) and at the end of inhalation anaesthesia. The Tukey method was used to compare baseline and end values for each parameter.

RESULTS

Arterial oxygen tension (PaO₂ ) increased from (median [IQR]) 13.6 (9.3, 30.1) at baseline to 24.2 (18.6, 37.0) kPa at the end of anaesthesia in A-INO (P = 0.005) and from 7.7 (6.4, 8.5) to 15.5 (9.9, 26.9) kPa in C-INO (P = 0.007). Mean (95% CI) difference in F-shunt between baseline and end were -6 (-10; -1) and -11 (-22; -1) % in A-INO (P = 0.005) and C-INO (P = 0.04) respectively. There was no change in PaO₂ or F-shunt from baseline to end of anaesthesia in A-CN or C-CN.

MAIN LIMITATIONS

Cardiac output was not measured, thus O₂ delivery could not be calculated.

CONCLUSIONS

The combination of mechanical ventilation and PiNO improved pulmonary gas exchange during anaesthesia by a simultaneous decrease in F-shunt and improved alveolar ventilation.

Effect of detomidine or romifidine constant rate infusion on plasma lactate concentration and inhalant requirements during isoflurane anaesthesia in horses

OBJECTIVE

Influence of detomidine or romifidine constant rate infusion (CRI) on plasma lactate concentration and isoflurane requirements in horses undergoing elective surgery.

STUDY DESIGN

Prospective, randomised, blinded, clinical trial.

ANIMALS

A total of 24 adult healthy horses.

METHODS

All horses were administered intramuscular acepromazine (0.02 mg kg^-1) and either intravenous detomidine (0.02 mg kg^-1) (group D), romifidine (0.08 mg kg^-1) (group R) or xylazine (1.0 mg kg^-1) (group C) prior to anaesthesia. Group D was administered detomidine CRI (10 μg kg^-1 hour^-1) in lactated Ringer's solution (LRS), group R romifidine CRI (40 μg kg^-1 hour^-1) in LRS and group C an equivalent amount of LRS intraoperatively. Anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. Plasma lactate samples were taken prior to anaesthesia (baseline), intraoperatively (three samples at 30 minute intervals) and in recovery (at 10 minutes, once standing and 3 hours after end of anaesthesia). End-tidal isoflurane percentage (Fe'Iso) was analysed by allocating values into three periods: Prep (15 minutes after the start anaesthesia-start surgery); Surgery 1 (start surgery-30 minutes later); and Surgery 2 (end Surgery 1-end anaesthesia). A linear mixed model was used to analyse the data. A value of p<0.05 was considered significant.

RESULTS

There was a difference in plasma lactate between 'baseline' and 'once standing' in all three groups (p<0.01); values did not differ significantly between groups. In groups D and R, Fe'Iso decreased significantly by 18% (to 1.03%) and by 15% (to 1.07%), respectively, during Surgery 2 compared with group C (1.26%); p<0.006, p<0.02, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Intraoperative detomidine or romifidine CRI in horses did not result in a clinically significant increase in plasma lactate compared with control group. Detomidine and romifidine infusions decreased isoflurane requirements during surgery.

Lack of association between arterial oxygen tensions in horses during exploratory coeliotomy and post-operative incisional complications: A retrospective study

The aim of this retrospective study was to determine if there was an association between the lowest arterial blood oxygen tensions (PaO2) measured during anaesthesia and post-operative incisional complications in horses. Clinical records of 278 horses undergoing ventral midline coeliotomy from 1 January 2010 to 31 December 2013 were examined. The frequency of incisional complications was 32.0% (n = 89). In a multivariable model, intra-operative arterial blood oxygen tensions (PaO2) were not significantly associated with development of an incisional complication (P = 0.351). Using hypertonic (7.2%) saline (P = 0.028, OR 3.167, 95% CI 1.132-8.861), increasing total plasma protein concentration (TP) (P = 0.002, OR 1.061 per g/L, 95% CI 1.021-1.102), an intestinal resection (P <0.001, OR 4.056, 95% CI 2.231-9.323), increasing body mass (P = 0.004, OR 1.004 per kg, 95% CI 1.001-1.006) and the use of penicillin alone compared with penicillin and gentamicin pre-operatively (P = 0.009, OR 4.145, 95% CI 1.568-10.958) increased the risk of incisional complications. The study was unable to demonstrate a link between low intra-operative PaO2 and increased risk of post-operative incisional complications.

Evaluation of plasma muscle enzyme activity as an indicator of lesion characteristics and prognosis in horses undergoing celiotomy for acute gastrointestinal pain

Background

In horses undergoing celiotomy for acute gastrointestinal pain, identification of variables correlating with lesion severity and location, and survival provide veterinarians and owners with information that aids in making informed decisions regarding appropriate treatment. Muscle enzyme activity is often increased in horses undergoing celiotomy for acute gastrointestinal pain and it is not known if muscle enzyme activity increase is specific to lesion type or impacts prognosis for survival. The objective of this study was to evaluate the relationship of pre-operative increase in muscle enzyme activities with intestinal lesion characteristics, specifically lesion location (large versus small intestine) and whether it was strangulating versus nonstrangulating, and case survival in horses undergoing celiotomy for acute gastrointestinal pain.

Methods

Records of 241 horses undergoing exploratory laparotomy for colic were reviewed retrospectively. Evaluation of preoperative plasma aspartate aminotransferase (AST), creatine kinase (CK), sorbitol dehydrogenase (SDH), and gamma-glutamyltransferase (GGT) activities, fibrinogen and glucose concentrations, and hematocrit (HCT) and their association with gastrointestinal lesion characteristics and survival was performed.

Results

Pre-operative increase in plasma CK and AST activity, and HCT and decrease in plasma bilirubin concentration were significantly associated with presence of lesions resulting in intestinal ischemia. Increase in plasma CK activity and HCT were significantly associated with a decreased probability of survival to hospital discharge. Plasma GGT and SDH activity, and glucose and fibrinogen concentration were not significantly associated with survival or severity of disease in multivariate analysis.

Conclusions

Plasma muscle enyzme activity may be useful as a prognostic indicator in equine colic cases. Given that increases in plasma CK and AST activity were significantly associated with nonsurvival and the presence of intestinal ischemia, preoperative increase in these enzyme activities could assist in identification of disease severity and prognosis of horses undergoing celiotomy for acute gastrointestinal pain. Further study is indicated to elucidate the etiology of increased muscle enzyme activity in horses with surgical colic disease observed in this preliminary study.

Serum cortisol concentrations in horses with colic

Few studies have evaluated cortisol concentrations in horses with colic. In humans with septic shock, high cortisol levels are associated with an increased risk of death. The objectives of this study were to compare the serum total cortisol concentrations (STCCs) in horses with colic to those without colic, and to assess whether the STCC relates to the pathological nature or outcome of the disease. STCCs were determined at presentation in horses with colic and in systemically healthy 'control' horses. Horses with colic were grouped based on clinical and clinico-pathological parameters at admission, treatment, lesion type and location, and outcome. Univariable and multivariable logistic regression were performed using two different outcome measures: (a) whether the horse had colic or not (yes vs. no), and (b) horse STCC (≥200 nmol/L vs. <200 nmol/L). Horses were more likely to have colic if they presented with high STCCs (≥200 nmol/L compared with <200 nmol/L). Horses with colic and with STCCs ≥200nmol/L were more likely to have moderate or severe colic signs (compared with mild colic) and heart rates >45 beats per min (compared with ≤45 beats per min). It was concluded that colic in horses is associated with elevated STCCs, and increased STCC in horses with colic appears to relate to the severity of the disease. STCCs may provide additional decision-making and prognostic information in horses with colic but further studies are required to avoid misinterpretations associated with the wide variation in STCCs.

Oxygenation and plasma endothelin-1 concentrations in healthy horses recovering from isoflurane anaesthesia administered with or without pulse-delivered inhaled nitric oxide

OBJECTIVE

To assess oxygenation, ventilation-perfusion (V/Q) matching and plasma endothelin (ET-1) concentrations in healthy horses recovering from isoflurane anaesthesia administered with or without pulse-delivered inhaled nitric oxide (iNO).

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Healthy adult Standardbred horses.

METHODS

Horses were anaesthetized with isoflurane in oxygen and placed in lateral recumbency. Six control (C group) horses were anaesthetized without iNO delivery and six horses received pulse-delivered iNO (NO group). After 2.5 hours of anaesthesia isoflurane and iNO were abruptly discontinued, inhaled oxygen was reduced from 100% to approximately 30%, and the horses were moved to the recovery stall. At intervals during a 30-minute period following the discontinuation of anaesthesia, arterial and mixed venous blood gas values, shunt fraction (Qs/Qt), plasma ET-1 concentration, pulse rate and respiratory rate were measured or calculated. Repeated measures anova and a Bonferroni post hoc test was used to analyze data with significance set at p < 0.05.

RESULTS

At all time points in the recovery period, NO horses maintained better arterial oxygenation (oxygen partial pressure: NO 13.2 ± 2.7-11.1 ± 2.7 versus C 6.7 ± 1.1-7.1 ± 1.1 kPa) and better V/Q matching (Qs/Qt NO 0.23 ± 0.05-0.14 ± 0.06 versus C 0.48 ± 0.03-0.32 ± 0.08%) than C horses. Mixed venous oxygenation was higher in NO for 25 minutes following the discontinuation of anaesthesia (NO 6.3 ± 0.2-4.5 ± 0.07 versus C 4.7 ± 0.6-3.7 ± 0.3 kPa). In both groups of horses arterial oxygenation remained fairly stable; venous oxygenation declined over this time period in the NO group but still remained higher than venous oxygen in the C group. ET-1 concentrations were higher at most time points in C than NO. Changes in other parameters were either minor or absent.

CONCLUSIONS AND CLINICAL RELEVANCE

Delivery of iNO to healthy horses during anaesthesia results in better arterial and venous oxygenation and V/Q matching (as determined by lower Qs/Qt) and lower ET-1 concentrations throughout a 30-minute anaesthetic recovery period.

Pulmonary gas exchange and plasma lactate in horses with gastrointestinal disease undergoing emergency exploratory laparotomy: a comparison with an elective surgery horse population

OBJECTIVE

To characterize pulmonary gas exchange and arterial lactate in horses with gastrointestinal disease undergoing anesthesia, compared with elective surgical horses, and to correlate these variables with postoperative complications and mortality.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Horses undergoing emergency laparotomy for acute intestinal disease (n = 50) and healthy horses undergoing elective surgery in dorsal recumbency (n = 20).

METHODS

Arterial blood gas analysis was performed at predetermined intervals on horses undergoing a standardized anesthetic protocol. Alveolar-arterial oxygen gradient was calculated. Predictive factors for postoperative complications and death in colic horses were determined.

RESULTS

Arterial oxygen tension (P(a) O(2)) varied widely among horses in both groups. P(a) O(2) significantly increased in the colic group after exteriorization of the ascending colon. P(a) O(2) and alveolar-arterial oxygen gradient were not significantly different between groups, and neither were correlated with horse outcome. Arterial lactate in recovery ≥ 5 mmol/L was associated with a 2.25 times greater relative risk of complications and lactate ≥ 7 mmol/L was associated with a 10.5 times higher relative risk of death.

CONCLUSION

Colic horses in this population were not more likely to be hypoxemic than elective horses, nor was gas exchange impaired to a greater degree in colic horses relative to controls. Arterial lactate sampled immediately after anesthetic recovery was predictive for postoperative complications and death.

Endocrine dysregulation in critically ill foals and horses

Critical illness challenges many endocrine homeostatic systems to overcome diseases, stress, and hostile conditions that threaten survival. Coordinated and consecutive responses by the autonomic nervous system, endocrine metabolic adaptations to mobilize and conserve energy and electrolytes, cardiovascular adjustments to maintain organ perfusion, and immunomodulation to overcome infections and inflammation are required. Because most admissions to equine intensive care units are related to horses with gastrointestinal disease and septic foals, most endocrine information during critical disease are generated from these populations. This article presents an overview on endocrine responses to critical illness in horses and foals and also some comparative information.

Metabolism during anaesthesia and recovery in colic and healthy horses: a microdialysis study

BACKGROUND

Muscle metabolism in horses has been studied mainly by analysis of substances in blood or plasma and muscle biopsy specimens. By using microdialysis, real-time monitoring of the metabolic events in local tissue with a minimum of trauma is possible. There is limited information about muscle metabolism in the early recovery period after anaesthesia in horses and especially in the colic horse. The aims were to evaluate the microdialysis technique as a complement to plasma analysis and to study the concentration changes in lactate, pyruvate, glucose, glycerol, and urea during anaesthesia and in the recovery period in colic horses undergoing abdominal surgery and in healthy horses not subjected to surgery.

METHODS

Ten healthy university-owned horses given anaesthesia alone and ten client-owned colic horses subjected to emergency abdominal surgery were anaesthetised for a mean (range) of 230 min (193-273) and 208 min (145-300) respectively. Venous blood samples were taken before anaesthesia. Venous blood sampling and microdialysis in the gluteal muscle were performed during anaesthesia and until 24 h after anaesthesia. Temporal changes and differences between groups were analysed with an ANOVA for repeated measures followed by Tukey Post Hoc test or Planned Comparisons.

RESULTS

Lactate, glucose and urea, in both dialysate and plasma, were higher in the colic horses than in the healthy horses for several hours after recovery to standing. In the colic horses, lactate, glucose, and urea in dialysate, and lactate in plasma increased during the attempts to stand. The lactate-to-pyruvate ratio was initially high in sampled colic horses but decreased over time. In the colic horses, dialysate glycerol concentrations varied considerably whereas in the healthy horses, dialysate glycerol was elevated during anaesthesia but decreased after standing. In both groups, lactate concentration was higher in dialysate than in plasma. The correspondence between dialysate and plasma concentrations of glucose, urea and glycerol varied.

CONCLUSION

Microdialysis proved to be suitable in the clinical setting for monitoring of the metabolic events during anaesthesia and recovery. It was possible with this technique to show greater muscle metabolic alterations in the colic horses compared to the healthy horses in response to regaining the standing position.