1751-0147-49-34 jurnal anestesi

ral

ssBioMed CentActa Veterinaria Scandinavica

Open AcceResearchMetabolism before, during and after anaesthesia in colic and healthy horsesAnna H Edner*1, Grel C Nyman2 and Birgitta Essn-Gustavsson1

Address: 1Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden and 2Department of Medical Sciences, Clinical Physiology, University hospital, Uppsala, Sweden

Email: Anna H Edner* - [email protected]; Grel C Nyman - [email protected]; Birgitta Essn-Gustavsson - [email protected]

* Corresponding author

AbstractBackground: Many colic horses are compromised due to the disease state and from hours ofstarvation and sometimes long trailer rides. This could influence their muscle energy reserves andaffect the horses' ability to recover. The principal aim was to follow metabolic parameter before,during, and up to 7 days after anaesthesia in healthy horses and in horses undergoing abdominalsurgery due to colic.

Methods: 20 healthy horses given anaesthesia alone and 20 colic horses subjected to emergencyabdominal surgery were anaesthetised for a mean of 228 minutes and 183 minutes respectively.Blood for analysis of haematology, electrolytes, cortisol, creatine kinase (CK), free fatty acids (FFA),glycerol, glucose and lactate was sampled before, during, and up to 7 days after anaesthesia. Arterialand venous blood gases were obtained before, during and up to 8 hours after recovery. Glutealmuscle biopsy specimens for biochemical analysis of muscle metabolites were obtained at start andend of anaesthesia and 1 h and 1 day after recovery.

Results: Plasma cortisol, FFA, glycerol, glucose, lactate and CK were elevated and serumphosphate and potassium were lower in colic horses before anaesthesia. Muscle adenosinetriphosphate (ATP) content was low in several colic horses. Anaesthesia and surgery resulted in adecrease in plasma FFA and glycerol in colic horses whereas levels increased in healthy horses.During anaesthesia muscle and plasma lactate and plasma phosphate increased in both groups. Inthe colic horses plasma lactate increased further after recovery. Plasma FFA and glycerol increased8 h after standing in the colic horses. In both groups, plasma concentrations of CK increased andserum phosphate decreased post-anaesthesia. On Day 7 most parameters were not differentbetween groups. Colic horses lost on average 8% of their initial weight. Eleven colic horsescompleted the study.

Conclusion: Colic horses entered anaesthesia with altered metabolism and in a negative oxygenbalance. Muscle oxygenation was insufficient during anaesthesia in both groups, although to a lesserextent in the healthy horses. The post-anaesthetic period was associated with increased lipolysisand weight loss in the colic horses, indicating a negative energy balance during the first week post-operatively.

Published: 15 November 2007

Acta Veterinaria Scandinavica 2007, 49:34 doi:10.1186/1751-0147-49-34

Received: 3 July 2007Accepted: 15 November 2007

This article is available from: http://www.actavetscand.com/content/49/1/34

2007 Edner et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Page 1 of 16(page number not for citation purposes)

Acta Veterinaria Scandinavica 2007, 49:34 http://www.actavetscand.com/content/49/1/34

BackgroundAn approximately ten-fold higher incidence of anaes-thetic-related deaths has been reported in colic horsesundergoing emergency abdominal surgery in comparisonwith healthy horses undergoing elective anaesthetic pro-cedures [1-3]. Attempts have been made in several studiesto identify parameters that may be used to predict theprobability of survival in colic horses [4-12]. The best pre-dictors seem to be parameters that assess the cardiovascu-lar function of the horse. The progress of different clinical-chemical parameters has been studied in venous or arte-rial blood during and after anaesthesia in horses subjectedto emergency abdominal surgery [9,13-15]. Metabolicchanges that occur locally in a muscle can be studied byanalysis of muscle biopsy specimens and microdialysistechniques. Studies have shown that anaesthesia inhealthy horses is associated with anaerobic metabolismobserved as a degradation of adenosine triphosphate(ATP) and creatine phosphate (CP) and production of lac-tate within the muscle [16,17]. This may be related to gen-eral hypoperfusion caused by the anaesthetic agents per se[18] or to compressive forces, or both restricting localblood perfusion [19,20].

In the colic horse, the normal metabolic rate and path-ways are altered by several factors such as circulatoryinsufficiency, endotoxaemia and acid-base disorders. Inaddition, the horses are in pain, have starved for hours orup to several days, and often have been transported forsome distance. All these factors are potential sources ofstress that result in an increased demand for energy.

We hypothesised that colic horses enter anaesthesia in astate of metabolic stress causing muscle metabolicchanges that postoperatively differ from that in healthyhorses recovering from anaesthesia. The aim of this studywas therefore to follow metabolic parameters in colichorses and in healthy horses by analysing blood and mus-cle biopsy samples before, during, and up to 7 days afteranaesthesia.

MethodsStudy designThis was a prospective clinical study performed on colichorses with a reference group consisting of clinicallyhealthy research horses submitted to an experimental pro-cedure. The study was approved by the Ethical Committeeon Animal Experiments in Uppsala, Sweden.

Colic horsesThe study comprised 20 horses subjected to acute abdom-inal surgery (referred to as C1C20) at the horse clinic ofthe Swedish University of Agricultural Sciences (SLU),

total duration of colic is given in Tables 1 and 2. Thehorses were referred by field practitioners or smallerequine clinics because of unresolved acute colic of varyingaetiology. The mean ( SD) distance travelled was 103(83) km. All colic horses but two had been treated imme-diately before referral, in most cases with an analgesic orspasmolytic drug (dipyrone, detomidine, butorphanol,flunixin meglumin). Other administered drugs were intra-venous vitamin B, antibiotics, orally administered min-eral oil and water, and intravenous (IV) electrolytes.

On arrival at SLU, all horses were examined clinically bythe veterinarian on duty. Therapy was initiated immedi-ately according to the severity of the clinical signs and theclinic routines and consisted of administration of an anal-gesic or spasmolytic agent as stated above or of xylazine,romifidine and hyoscine butylbromide, administration ofintravenous electrolytes (Ringer acetat, Pharmacia &Upjohn, Sweden) and/or a dextran colloid (Macrodex,Meda AB, Solna, Sweden). Other treatment before surgeryconsisted of antibiotics and a booster dose of tetanus vac-cine. The decision concerning surgery was taken by the cli-nician. The approximate length of time (and duration offood withdrawal) from the observation of colic signs tothe time of surgery varied from 3 hours up to 2.5 days,with a median of 14 hours. All colic horses destined foracute abdominal surgery whose owner gave theirinformed consent to participation entered the study. Thestudy was closed when 20 horses (5 Standardbred trotters,10 Warmblooded riding horses, 1 Shetland pony, 1 Welshcob, 1 pony cross, 1 Arabian and 1 Icelandic horse) hadentered.

When the preoperative clinical status was judged retro-spectively, four colic horses were considered to have beenin a markedly worse condition than the other colic horses,and these four are referred to as ASA 5 (American Societyof Anaesthesiologists physical status grade 5). The othercolic horses were regarded as ASA 4.

Reference horsesAs a reference group, 20 healthy, Standardbred trotters(referred to as H1H20) owned by the former Depart-ment of Large Animal Clinical Sciences, SLU, Uppsala,Sweden, were studied. They are hereafter referred to as the

Table 1: Description of the 20 colic and 20 healthy horses included in the study

Colic horses Healthy horses

Weight 527 106 kg (230698) 495 47 kg (411584)Age 11 6 years (222) 8 5 years (319)Sex 10 mares, 8 geldings, 2 stallions 12 mares, 8 geldingsPage 2 of 16(page number not for citation purposes)

from January to April 2001 and from January to June2002. Information regarding breed, age, sex, weight and For weight and age the mean values ( SD) are given with the range

within parentheses.


"healthy horses". These horses were anaesthetised in dor-sal recumbency for participation in two other anaesthesiaresearch projects and data was collected in January 2000and October 2001 (Table 2). In these horses the effect onperipheral perfusion was studied during spontaneousbreathing and/or mechanical ventilation with intermit-tent positive pressure ventilation. Prior to the study nohorse had shown clinical signs of disease or was receivingany treatment, and none had a recent history of colic.They were housed at the department, where they werekept outdoor during the day and stabled at night. Theywere fasted for 12 hours before anaesthesia.

AnaesthesiaColic horsesSince the colic horses had been medicated by the referralveterinarian and by the clinician at the University clinic,additional premedication with low a dose of an alpha-2adrenoceptor agonist and butorphanol was only given toa few horses before induction. In 15 horses, anaesthesiawas induced with an intravenous infusion of guaifenesin(Myolaxinvet, diluted to 7.5%, Vtoquinol AG, Belp,Switzerland) to effect and a bolus dose of 3.14.4 mg/kgthiopentone sodium (PentothalNatrium, Electra-BoxPharma AB, Tyres, Sweden). Ketamine (1.92.4 mg/kgIV, Ketaminolvet, Intervet AB, Danderyd, Sweden) withdiazepam (0.020.03 mg/kg IV, Diazepam-ratiopharm10, PharmaMedics, Bassersdorf, Switzerland) was used forinduction in three horses. In two horses anaesthesia wasinduced with guaifenesin and ketamine (1.6 mg/kg and2.1 mg/kg IV respectively). After intubation, the horseswere transported into the theatre and placed in dorsalrecumbency on a medical foam mattress (Tempur AB,DanFoam, Denmark) with the hind limbs supported in asemi-flexed position. In all horses, anaesthesia was main-tained with isoflurane in oxygen delivered by a semi-closed large animal anaesthetic circuit. Breathing wasspontaneous during the whole anaesthetic procedure in

dure in 7 horses. During anaesthesia, all horses were givenan IV infusion of Ringer acetate. To keep the mean sys-temic arterial blood pressure (MSAP) above 70 mmHg, adextran colloid, up to 10 mL/kg, was administered IV. Ifno effect was seen within 30 minutes or if mean systemicarterial pressure (MSAP) was below 50 mmHg, dob-utamine was given symptomatically IV (0.55 g/kg/min)to maintain or reach an MSAP of 70 mmHg. After anaes-thesia the horses were allowed to recover in a padded stallbefore being taken to their stables. The horses were extu-bated after the swallowing reflex had returned or when insternal recumbency if gastric regurgitation was suspected.Oxygen was insufflated at 15 L/min through a nostril untilthe horse gained the sternal position.

Healthy horsesThe healthy horses were premedicated with detomidine(10 g/kg IV, Domosedan vet, Orion, Animal Health, Sol-lentuna, Sweden) and 10 minutes later anaesthesia wasinduced IV with guaifenesin to effect and a bolus dose ofthiopentone sodium (4.5 mg/kg IV). Intubation andmaintenance of anaesthesia were as described above. Inten horses IPPV was used during the whole procedure and9 horses were ventilated both by spontaneous breathingand IPPV. One horse was breathing spontaneously for thewhole procedure. During anaesthesia, all horses weregiven an infusion of Ringer acetate. After anaesthesia thehorses were allowed to recover in a padded stall asdescribed above. Fourteen of the 20 healthy horses weregiven xylazine and flunixin after discontinuation of inha-lation anaesthesia. No recovery assistance was given.

Post anaesthesiaMedical treatment in the 7-day observation period afteranaesthesia was provided by the treating veterinarian asjudged by the horse's condition.

Feed was provided to the colic horses at the decision of the

Table 2: Anaesthesia, recovery and survival rates in 20 colic and 20 healthy horses

Colic horses Healthy horses

Duration of anaesthesia 183 62 mins (45300) 228 26 mins (189273)Recovery time to standing 64 45 mins (15180) 52 19 mins (1886)Number of attempts to stand 1.4 0.6 (13) 2.4 1.2 (14)Survival rate 11/20 20/20Time of death/euthanasia 3 during anaesthesia, 2 in recovery, 2 within 24 h after standing, 2 between DAY

2DAY 7Reasons for euthanasia or death 2 circulatory failure, 1 acute myocardial degeneration (autopsy diagnosis), 2

surgical findings, 1 ruptured stomach, 1 laminitis, 1 endotoxaemia, 1 endocarditis (chronic but not diagnosed before anaesthesia)

The mean values ( SD) are given with the range within parentheses.EHV = equine herpes virus; DAY 2 and 7 = 2 and 7 days after anaesthesia.Page 3 of 16(page number not for citation purposes)

13 horses and was controlled using intermittent positivepressure ventilation (IPPV) for most or part of the proce-

clinician in charge and consisted of increasing rations ofhay and a wet mixture of beet pulp, wheat and barley


bran. The horses were hand-walked several times daily.The healthy horses were provided with water and hay(approximately 8 kg/day) when they had fully recoveredfrom anaesthesia, and were turned out into a paddock theday after anaesthesia. They were fed the wet mixturedescribed for the colic horses at 0.51 kg/day.

Haemodynamic, respiratory, and blood gas measurementsDuring anaesthesia MSAP, heart rate (HR), oxygen satura-tion and an electrocardiogram (ECG) were monitored(Datex light, Datex Engstrm Instrumentation Corpora-tion, Helsinki, Finland). Blood pressure was measuredinvasively through a catheter in a facial artery. In two caseswhere a permanent catheter failed to function, arterialblood pressure was measured non-invasively (oscillomet-rically) with a pneumatic cuff placed around the tail base.Respiratory parameters (expired volume, inhaled andexhaled isoflurane, carbon dioxide and oxygen and in thecase of IPPV, peak inspiratory pressure and expiratory vol-umes) were monitored by side-stream spirometry (Cap-nomac Ultima, Datex Engstrm InstrumentationCorporation, Helsinki, Finland). Respiratory rate wascounted by observing the costo-abdominal movements.Physiological parameters were assessed before anaesthesia(HR, RR, mucous membranes; MM, capillary refill time;CRT, peripheral pulse) and in 5-minute intervals duringanaesthesia (HR, RR, MM, CRT, peripheral pulse). Untilthe standing position was reached, the horses were exam-ined every 1030 minutes and after recovery at least everyhour during the first 24 hours (HR, RR, mucous mem-branes, peripheral pulse).

Arterial (a) and jugular venous (v) blood samples weredrawn into heparinised syringes, placed on ice and ana-lysed within 10 minutes for oxygen and carbon dioxidetensions (PO2, PCO2), pH and haemoglobin saturation ofoxygen (SatO2) while bicarbonate (HCO3-) and baseexcess (BE) were calculated (ABL5, Radiometer MedicalA/S, Copenhagen, Denmark). A correction for current rec-tal temperature was made. Blood gases (a, v) wereobtained immediately after induction and every hour dur-ing anaesthesia in all horses. Before anaesthesia venousblood gas samples were obtained from six colic horsesand two healthy horses. After anaesthesia and up to eighthours after recovery to standing venous blood gas sampleswere obtained from eight colic and seven healthy horses.

SamplesSampling and analyses of bloodVenous blood was sampled in the awake state beforeinduction (PRE), at every hour of anaesthesia (AN 1, AN2, etc), 15 minutes and every hour after discontinuation ofinhalation anaesthesia while the horse was still recum-

POST 1, POST 2, etc and DAY 1), and thereafter at 24-hour intervals for 7 days after anaesthesia (DAY 2, DAY 3,etc).

The blood samples were collected from a catheter in thejugular vein. Samples for assays of plasma lactate, glyc-erol, glucose, free fatty acids (FFA), cortisol and creatinekinase (CK) were taken in heparinised vials, while vialscontaining no additive were used for measurements ofserum sodium, potassium, chloride, total calcium andinorganic phosphate total protein and albumin. Sampleswere kept on ice until they were centrifuged (within 30minutes) and stored at -80C until analysed. Blood fordetermination of haemoglobin (Hb), haematocrit (Hct)and white blood cell count (WBC) was collected in EDTAvials, and stored at 5C until analysed within 36 hours.

The plasma lactate concentration was assayed with a lac-tate analyser (Analox GM7, Analox Ltd, London, GreatBritain). Glycerol was determined using a commercial kit(EnzyPlus, Diffchamb AB, Vstra Frlunda, Sweden). Glu-cose and CK were assayed by modified fluorometric meth-ods [21]. FFA was determined with a kit from Wako(NEFA C test, Wako Chemicals GmbH, Neuss, Germany).Plasma cortisol was measured by a competitive immu-noassay method (Immulite Cortisol, DPC, Los Angeles,CA, USA). Serum sodium, potassium chloride, total cal-cium, inorganic phosphate and albumin concentrationswere determined by a spectrophotometric method usingstandardized reagent kits (Konelab 30, Kone Instruments,Espoo, Finland). Total protein was determined by refrac-tometry. Hb was measured with a quantitative reflectancetest (Reflotron, Boeringer Mannheim Scandinavia AB,Bromma, Sweden), and for Hct measurement a capillarymicrocentrifuge was used. The total and differential WBCwere determined by a spectrophotometric test (CELL-DYN 3500, ABBOTT, Abbott Laboratories, Abbott Park,IL, USA).

Muscle biopsy sampling and analysesA biopsy specimen was obtained from the right gluteusmedius immediately after induction of anaesthesia (ANSTART) and at the end of anaesthesia (AN END) in allhorses. In six colic horses and in seven healthy horses asample was obtained 1 hour after recovery to standing(POST 1). In 13 colic horses and in the seven healthyhorses, a biopsy sample was also obtained the day aftersurgery (DAY 1).

The muscle samples were taken from a site half-way on amidline between the distal border of the tuber coxae andthe tail base. Samples were obtained with a Bergstrmmuscle biopsy needle (external diameter 5 mm) after sur-Page 4 of 16(page number not for citation purposes)

bent (REC 15', REC 1, etc), 15 and 30 minutes, and 1, 2,4, 8, 12, and 24 hours after standing (POST 15', POST 30',

gical preparation and, in the awake horse, after local anal-gesia, 2 mL of 2% lidocaine (Xylocain, AstraZeneca AB,


Sdertlje, Sweden) instilled subcutaneously and underthe fascia. A 10-mm incision was made through the skinand fascia with a scalpel and muscle samples wereobtained from a site 56 cm deep into the muscle belly.Subsequent biopsy samples were obtained through thesame incision. The samples were immediately frozen inliquid nitrogen and stored at -80 until analysed. Theywere freeze-dried, dissected free from connective tissue,blood and fat, and then weighed (12 mg dry weight;d.w.) and extracted in perchloric acid before being neu-tralized with potassium hydroxide.

The concentrations of adenine nucleotides (ATP, adenos-ine diphosphate; ADP, adenosine monophosphate AMP)and inosine monophosphate (IMP) were determined by amodified high performance liquid chromatography(HPLC) technique using a C:18 (250 4.6, 5 mm) col-umn [22]. CP and creatine were determined with anHPLC technique [23]. Muscle lactate was assayed by amodified fluorometric method [21].

Other measurements and observationsAll horses were weighed before anaesthesia. The colichorses and seven healthy horses were weighed after recov-ery, before being taken to their stables and, when possible,daily until DAY 7. The same scales were used at all timepoints. Unfortunately, these were not calibrated betweeneach horse. Rectal temperature was measured in all horsesbefore, at every hour and at the end of anaesthesia. There-after rectal temperature was measured immediately beforeeach sampling for measurement of blood gases. The gaitand movements at walk were examined after recovery anddaily if any signs of lameness or limb dysfunction wereseen at recovery. Any other occurring complications suchas diarrhoea and laminitis were noted.

Statistical analysisComparisons of plasma samples concentrations betweengroups at PRE were performed using Mann-Whitney U-test for variables not being normally distributed and Stu-dent's t-test for independent samples for those variableswith normal distribution (Statistica 6.0 and 7.0, StatSoft,Inc. Tulsa OK, USA).

Changes from PRE to END for blood analytes, HR, MSAPand temperature, and from PRE to POST 4 for pHv wereanalysed with an ANOVA for repeated measures followedby Tukey Post Hoc test for unequal N or planned compar-isons when the sphericity assumptions were violated. Ifthe interaction Group*Time was significant, simple effectswere examined, i.e. effects of one factor holding the otherfactor fixed. The p-values were then corrected according tothe Bonferroni procedure. When Levene's test for homo-

SAS (SAS System 9.1, SAS Institute Inc., Cary, NC, USA).In these analyses, a p-value of < 0.05 was considered sig-nificant. Mixed model repeated measures analyses (ProcMixed in SAS) were used to examine the pattern of changein the blood variables from PRE to postoperative periodup to one week after anaesthesia. Different covariance pat-tern models were tested, compound symmetry, heteroge-neous compound symmetry, first order autoregressiveand heterogeneous first order autoregressive models.When the variances in the two groups were inhomogene-ous, separate covariance pattern was estimated for eachgroup. The covariance structure with the smallest value ofAkaike's Information Criterion was considered mostappropriate. Group and Time were modelled as fix factors.The Group*Time interaction refers to the statistical test ofwhether the mean change over time is the same for thetwo groups. In case of a significant interaction, simpleeffects were examined, i.e. effects of one factor holding theother factor fixed. The distribution of CK, glycerol and lac-tate were positively skewed and were log transformedbefore formal analyses. Due to multiple comparisons, sig-nificance was considered when p < 0.01 [24-26].

Changes in weight and the results from muscle biopsysample assays were analysed with a Mann-Whitney U testfor comparisons between groups and a Friedman ANOVAfor analysis of changes within groups (Statistica 6.0). P

1751-0147-49-34 jurnal anestesi

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