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FIELD USE OF ISOFLURANE AS AN INHALANTANESTHETIC IN THE AMERICAN MARTEN (MARTESAMERICANA)

Authors: Desmarchelier, Marion, Cheveau, Marianne, Imbeau, Louis,and Lair, Stéphane

Source: Journal of Wildlife Diseases, 43(4) : 719-725

Published By: Wildlife Disease Association

URL: https://doi.org/10.7589/0090-3558-43.4.719

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FIELD USE OF ISOFLURANE AS AN INHALANT ANESTHETIC IN THE

AMERICAN MARTEN (MARTES AMERICANA)

Marion Desmarchelier,1 Marianne Cheveau,2 Louis Imbeau,2 and Stephane Lair1,3

1 Service de Medecine Zoologique, Departement de Sciences Cliniques, Faculte de Medecine Veterinaire, Universite deMontreal, C.P. 5000, St. Hyacinthe, Quebec J2S 7C6, Canada2 Chaire Industrielle CRSNG-UQAT-UQAM en Amenagement Forestier Durable, Universite du Quebec en Abitibi-Temiscamingue, Departement des Sciences Appliquees, 445 boul. de l’Universite, Rouyn-Noranda, Quebec J9X 5E4,Canada3 Corresponding author (email: [email protected])

ABSTRACT: We evaluated the effectiveness and practicality of using isoflurane as an inhalationanesthetic with oxygen as a gas carrier for American martens (Martes americana) in a field setting.Sixty-eight martens were trapped in the Waswanipi Cree Model Forest (Quebec, Canada) fromOctober to November 2005 and anesthetized with isoflurane in 100% oxygen (1 l/min) using a facemask. Induction setting of isoflurane was 3% for all animals. Mean (6SD) length of induction was1.861.2 min. Maintenance isoflurane settings ranged from 1% to 4%. Procedures lasted anaverage of 16.467.1 min and were uneventful. Length of recovery, defined as the interval betweenthe end of the procedure and animal release, was short (6.362.8 min), and well below reportedlengths of recovery using injectable anesthetics ($70 min). As compared to open dropadministration of isoflurane described in previous studies, the use of an anesthesia machineprevents the risk of potential fatal anesthetic overdose. We conclude that among anesthesiatechniques currently available, isoflurane with oxygen as a gas carrier is a safe and useful fieldanesthetic in martens, when issues with equipment portability can be overcome.

Key words: American marten, anesthesia, field study, inhalant, isoflurane, Martesamericana, restraint cone.

INTRODUCTION

The choice of an anesthetic agent inwild mammals depends on numerousfactors, such as field logistic constraints,equipment cost, and safety for bothanimals and staff. Chemical immobiliza-tion with injectable agents requires littleequipment and is relatively simple toadminister. In addition, newer drugs areassociated with fewer adverse effects thanolder agents. As a result, injectable drugsare frequently used for the anesthesia ofwild mammals in the field. However,recoveries can be prolonged, control ofanesthesia levels is limited, and mostinjectable drugs are associated with car-diovascular and respiratory side effects.Inhalant anesthesia reduces the hazards ofgeneral anesthesia and ensures a rapidpostoperative recovery of vital functions(Calvey and Williams, 2001).

American marten (Martes americana)has been recognized throughout its rangeas being sensitive to anthropogenic forest

disturbances such as commercial forestry(e.g., Potvin et al., 2000). In this context,marten population maintenance is oftenrecommended as an indicator for foresthabitat integrity (Thompson, 1991). Inaddition to this, the marten is an impor-tant species for fur trapping by local andnative peoples.

Different anesthetic protocols havebeen reported for the field anesthesia ofthis mustelid, either using injectable drugs(Belant, 1992; Kreeger, 1999; Belant,2005) or inhaled agents (Herman et al.,1982; Potvin et al., 2004). However, to thebest of our knowledge, field use ofisoflurane using a portable anesthesiamachine with a precision vaporizer pre-viously has not been described for mar-tens. The objective of our study was toassess the efficiency, practicality, andusefulness of isoflurane inhaled anestheticwith oxygen as a gas carrier for Americanmartens in a field setting and compare thatprotocol with other published methods forthis species.

Journal of Wildlife Diseases, 43(4), 2007, pp. 719–725# Wildlife Disease Association 2007

719


MATERIALS AND METHODS

The study was conducted in October andNovember 2005 at the Waswanipi Cree ModelForest, municipality of James Bay, Quebec,Canada (49u709N, 76u509W). This project wascarried out according to animal utilizationprotocols approved by the animal care com-mittees of the institutions involved in thisproject, both of which operate under theauspices of the Canadian Council on AnimalCare.

Martens were captured in live traps (model202, Tomahawk Live Trap Company, Toma-hawk, Wisconsin, USA) covered with branchesof spruce or fir, and baited mostly with beaveror hare flesh and trapping lures. Each trap waschecked daily. Trapped martens were trans-ferred into an open-ended restraining conemade of fabric with a 25-mm-diameter open-ing that allowed safe restraint of the animal

with direct open access to its snout (Fig. 1).Anesthesia was induced with a facial mask(Guinea pig mask, 11/16’’ diameter, J. A.Webster, Inc., Sterling, Massachusetts, USA)placed over the snout with isoflurane (AErra-neH, Baxter, Toronto, Ontario, Canada) set at3% and delivered in 1 l/min oxygen usinga custom-made portable anesthesia machine.This machine was built using a semiopen,nonrebreathing Mapleson D modified Baincircuit connected to an isoflurane vaporizer(Tec-3 Model, Dispomed, Joliette, Quebec,Canada) and an oxygen flow meter (Dis-pomed). The system was firmly fixed insidea solid plastic case (57 3 46 3 33 cm,Stormcase model IM2750, Hardigg, Saint-Jean-sur-le-Richelieu, Quebec, Canada) toprovide adequate resistance to rough condi-tions during transport. The total weight of thisassembly was 10.2 kg. A portable type Emedical oxygen cylinder (67 cm long 3

FIGURE 1. Restraint cone used to immobilize martens for mask induction with isoflurane. A. The fabriccone is connected to the trap to allow transfer of the animal. B. Mask induction of the animal in the restraintcone is greatly facilitated by the safe access to its snout via the opening in the extremity of the cone.

720 JOURNAL OF WILDLIFE DISEASES, VOL. 43, NO. 4, OCTOBER 2007


10 cm in diameter and weighing 7.7 kg) wasused as a source of oxygen.

The procedures were performed on theback seat of a crewcab at ambient tempera-tures varying from 1.5 to 25.8 C (10.463.9 C,mean6SD) in the truck. When sufficientlevels of anesthesia were obtained, the iso-flurane setting was decreased to an appropri-ate level, defined as maintaining inhibition ofanimal movement. Martens were weighed andmorphometric measurements were made.Heart rate and hemoglobin oxygen saturation(SpO2) were monitored with a pulse oximeter(OxiMax NPB-75H Handheld Capnograph/Pulse Oximeter, Nellcor Puritan Bennett,Plesanton, California, USA) with the probeplaced on a forelimb digit. Respiratory rateswere determined by counting complete tho-racic cycles for 30 sec every 5 min. End-tidalcarbon dioxide partial pressures (ETCO2)were measured in some individuals witha microstream capnograph (OxiMax NPB-75H) via a pediatric nasal cannula (diameter2.5 mm, Smart CapnolineH Oral/Nasal circuit,Nellcor Puritan Bennett, Plesanton, Califor-nia, USA) which was inserted about 5–7 mminside the nares. Rectal temperatures weremonitored throughout the procedure andrecorded once on average 12 min after thebeginning of anesthesia. Ambient tempera-tures were measured at the beginning and theend of the procedure in the truck, near thevaporizer. When ambient temperatures werelow, hypothermia was prevented by turningthe engine on with the door closed but windowpartially opened.

After a complete physical examination,blood was sampled via a jugular vein, feceswere collected from the rectum or in the trap,and a first premolar tooth was extracted usinga small root elevator (Super Slim FelineElevator, J. A. Webster Inc., Sterling, Massa-chusetts, USA) and extraction forceps. An earswab was taken for parasitologic examinationand an ear tag was installed. Radio transmit-ters were also attached in selected females (18of 27 females) using a collar. Isofluraneadministration was discontinued when theprocedure was completed. Oxygen was de-livered via face mask until the marten startedto move.

The animals were left in the trap to recoverand released as soon as the level of wakeful-ness was believed to be sufficient. Length ofinduction was defined as the interval betweenthe beginning of mask induction and a lack ofresponse to tactile stimuli. Length of recoverywas defined as the interval between the end ofanesthesia (isoflurane50%) and the momentwhen the marten was ready for release

(normal gait and normal behavior such asvocalization and signs of aggression).

Statistical analyses were performed usingSAS 9.1 (Cary, North Carolina, USA). t-testsfor unequal variances were used to examinethe effects of period of the day (AM versus PM,which could represent the time spent by themarten inside the trap) on the induction,recovery, and procedure times. Linear re-gression models were used to test the relation-ship between weight, body index (weightdivided by the total length), ambient temper-ature, minimum and maximum settings ofisoflurane, and on the lengths of induction,recovery, and procedure. Alpha was set to0.05.

RESULTS

Forty-one male (weighing 9536131 g)and 27 female (weighing 6806107 g)martens were anesthetized during theproject. Each captured marten was an-esthetized once. Although some animalsappeared subjectively thin, no significantanomalies were observed during thephysical examination. All procedures wereuneventful and no anesthesia-related mor-tality occurred. Minimum and maximummaintenance isoflurane settings rangedfrom 1.0% to 2.5% (1.460.3%) and from2.0% to 4.0% (3.060.2%), respectively.Inductions and recoveries were usuallyrapid and smooth, with animals exhibitingminimal agitation. Mean length of in-duction was 1.8561.20 min (range: 0.5–6 min) and the whole procedure lasted16.467.1 min (range: 9–35 min). Recov-ery took place in 6.362.8 min (range: 2–17 min). Respiratory parameters and heartrates were recorded in 18 and 8 martens,respectively, on average 10 min after thebeginning of anesthesia. Mean respiratoryrate was 31611.5 movements per minute(mpm) (range: 12–64). Mean heart ratewas 216617 beats per minute (bpm)(range: 200–240). Mean ETCO2 was40.465.8 mm Hg (range: 32–53 mm Hg)and all values of SpO2 remained above95% during the procedure. Mean rectaltemperature, recorded on average 12 minafter induction, was 37.461.5 C (range:34.0–40.1 C). No relationship was ob-

DESMARCHELIER ET AL.—FIELD USE OF ISOFLURANE IN AMERICAN MARTINS 721


served between the other variables testedand the lengths of induction, recovery, andprocedure.

We compared the lengths of inductionand lengths of recovery obtained in ourstudy with results from previously pub-lished anesthetic protocols in martens(Table 1). Twenty-seven of the 68 martens(40%) were recaptured at least oncebetween one and 33 days after anesthesia.All recaptured animals were very activeand appeared to behave normally. Lessthan 75 ml of isoflurane and three type Emedical oxygen cylinders were necessaryto anesthetize the 68 martens used in thisstudy.

DISCUSSION

Anesthesia of free-ranging animals ina field setting is often challenging. Age andhealth status are often uncertain, and thebody condition of wild animals is regularlysuboptimal. In addition, capture-relatedstress can lead to increased plasma levelsof glucocorticoids and catecholamines(Spraker, 1982). As a consequence, anyadverse effects of anesthetic agents arelikely to be greater than those observed indomestic animals. Capture and prolongedcontainment in live traps, followed byhandling and anesthesia, certainly carriessome physiological implications, as well asnegative effects on the animal’s well-being(Mathews et al., 2002). As animal users,scientists are ethically responsible for

refining handling techniques used in orderto minimize any negative effects of theirinterventions on individuals and the pop-ulation as a whole. Field biologists benefitconsiderably from refining interventionsto reduce sampling variances.

The anesthesia protocol used in ourstudy enabled us to perform all proce-dures rapidly and safely for both staff andanimals; no mortality or anesthesia prob-lems occurred in the 68 martens. In-duction and recovery were rapid andsmooth, and cardiorespiratory parametersremained within the acceptable range foranesthetized animals at all times.

Kreeger et al. (1998) noted that a greatdeal of maintenance for the vaporizer wasrequired when using isoflurane with ananesthesia machine. The vaporizer weused was calibrated only once, at thebeginning of the project. The possibility ofinaccuracy due to decalibration or varia-tion in ambient temperature was over-come by adjusting the vaporizer settingaccording to animal response. Neverthe-less, because we used this vaporizer out-side its recommended range of tempera-tures (15 C to 35 C), the reported settingsof isoflurane are not necessary equal to theactual concentration delivered. Eventhough isoflurane has a slightly pungentand ethereal odor and can irritate theupper airways (Calvey and Williams,2001), martens tolerated induction viaface mask well; this is consistent withobservations of Siberian polecats (Gaynor

TABLE 1. Comparison of induction and lengths of recovery with different anesthesia techniques described inAmerican martens.

Anestheticagenta Route of administration n

Induction (min) Recovery (min)

ReferenceMean6SD (Range) Mean6SD (Range)

Isoflurane Semi-open,non-rebreathing

68 1.861.2 (0.5–6.0) 6.362.8 (2.0–17.0) Current report

Isoflurane Open drop 62 1.660.8 (0.5–4.8) 3.662.4 (0.5–9.7) Potvin et al., 2004Halothane Open drop 264 2.660.7 (1.5–8.3) 3.161.5 (1.0–10.0) Herman et al., 1982TZX Injectable 19 2.561.8 (0.8–6.1) 70.8631.9 (30–122) Belant, 2005KX Injectable 5 1.860.5 (1.2–2.5) 100.4643.2 (62–175) Belant, 1992

a TZX: tiletamine-zolazepam + xylazine; KX: ketamine + xylazine.



et al., 1997), sea lion pups (Heath et al.,1997), beavers (Breck and Gaynor, 2003),and ferrets (Lawson et al., 2006). Isoflur-ane is a volatile agent with a low blood:gassolubility coefficient (1.4 versus 2.4 forhalothane) and low tissue solubility, re-sulting in extremely rapid induction andrecovery (Calvey and Williams, 2001).

The two reported protocols using in-jectable agents in martens were associatedwith prolonged and variable length ofrecovery when compared to inhaledagents (Table 1). These lengthy recoveriescould be detrimental for the animals byincreasing the level of stress and thepotential for detrimental hypothermia,especially at relatively cold ambient tem-peratures. Enduring residual anestheticeffects could also prevent the animal fromresuming normal activities such as huntingand caring for young. In addition, longrecoveries increase post-procedural mon-itoring time by handlers, which diminishesthe productivity of the field team andtherefore adds to the cost of the project.Because dosages of injectable agents areapproximate, premature recoveries canoccur, potentially exposing the handler tobites and zoonotic disease transfer. In-halant anesthesia allows for rapid modifi-cations of anesthesia depth and thereforeprevents such undesirable outcomes. Thedefinition of the length of recovery variesbetween studies limiting useful compar-isons of the different protocols. Belant(1992, 2005) defines recovery length asthe time between immobilization and theanimal’s ability to maintain an uprightposture and respond to external stimuli.Potvin et al. (2004) described recoverytime as the time between recumbency andthe moment when the animal stood uponce released. In the Herman et al. (1982)study, the length of recovery was notclearly defined.

Among the volatile anesthetics com-monly used in veterinary anesthesia, iso-flurane is considered to have the fewesteffects on the heart but its effects onrespiration are more pronounced than

with halothane (McKelvey and Hollings-head, 2003). Only 0.2% of the isofluranedose is metabolized (Calvey and Williams,2001), which allows for its utilization inneonatal and geriatric animals, as well asin animals with hepatic or renal damage(McKelvey and Hollingshead, 2003). Car-diovascular depression is a common sideeffect of most injectable agents. Meanheart rates measured during tiletamine-zolazepam-xylazine and ketamine-xylazineanesthesia were, respectively, 163634bpm (Belant, 2005) and 12567.5 (SE)bpm (Belant, 1992), compared to216617.2 bpm in the present study. Meanrespiratory rates were superior with in-jectable agents (67630 mpm and 65615.1[SE] mpm, respectively) compared toinhalation agents (31611.5 mpm, similarto normal respiratory rates of a similarly-sized mustelid, the domestic ferret (33–36 mpm; Fox, 1998)). Moreover, isoflur-ane is delivered in 100% oxygen, andoxygen arterial partial pressure is likely tobe greater using this technique. In ourstudy, ventilation was assessed in 18martens by measuring ETCO2. All valuesobtained were in the expected range fora small mammal and indicated thatventilation and pulmonary gas exchangeswere adequate throughout the procedure.An added safety feature of precisionvaporizer delivered inhalant anesthesia isthat endotracheal intubation and assistedmanual ventilation are possible if apneaoccurs. General anesthesia can inducehypothermia, because muscular activityand metabolism are depressed. In thepresent study, mean rectal temperature12 minutes after induction with isoflurane(37.4 6 1.5 C) were similar to thosereported with the combination of tileta-mine-zolazepam-xylazine (37.0 6 2.2 C)(Belant, 2005).

Inhaled agents have been used in free-ranging martens with open drop exposureby injecting the liquid agent into a closedchamber (Herman et al., 1982; Potvin etal., 2004). Halothane and isoflurane arecompounds with a high vapor pressure



and evaporate so easily that they can reacha concentration of more than 30% ata barometric pressure of 760 mm Hg,depending on ambient temperatures(Mathew et al., 2002). That level couldcause a fatal anesthetic overdose (McKel-vey and Holligshead, 2003). A precisionvaporizer limits the evaporation of theseagents and allows for their safe use inanesthesia. Use of an anesthesia machinealso permits maintenance of the animalunder an appropriate level of anesthesiafor as long as needed.

Even if toxicity to isoflurane has notbeen clearly demonstrated, exposure ofstaff to the anesthetic gas is always anissue. Induction via a face mask reducesthis exposure when compared to inductionin a closed chamber.

The major disadvantages of the use ofisoflurane anesthesia in the field are theweight and bulk of the equipment forremote use, and that mask inductionwithout injectables requires adequatecontrol and restraint of the animal. Ourmethod for induction worked very well forthis purpose. Oxygen cylinders can bea safety issue for air transport. Kreeger(1999) reported that a great deal oftraining was necessary to work with ananesthesia machine. For our study, wild-life biologists and technicians were trainedby a veterinarian at the beginning of thestudy until an adequate number of animalswere handled (n510–15) and they did notencounter any difficulties using the ma-chine on their own. Because no mortalitiesoccurred, training appeared sufficient.Anesthesia is never risk-free and whateverthe technique used, adequate training ofthe staff is recommended to improveanesthesia safety as much as possible.

In our study, isoflurane anesthesiaproved safe, easy to use, and providedsmooth and rapid inductions and recov-eries. Additional costs of this techniquewere considered to be balanced by theimprovement of animal welfare and over-all anesthesia security, and by the gain inproductivity of the field team. When

equipment transport is possible, isofluraneinhalant anesthesia with a precision va-porizer provided excellent results in theAmerican marten under field conditions.

ACKNOWLEDGMENTS

This work was supported by grants from theNSERC-UQAT-UQAM industrial chair inSustainable Forest Management, Fonds que-becois pour la recherche sur la nature et lestechnologies (FQRNT), and Fondation de lafaune du Quebec (FFQ). We sincerely thankthe Waswanipi Cree Model Forest for itssupport while conducting this study, as well asEdward and Norman Ottereyes for theirauthorizations to work on their familial trap-lines. We are grateful to Pierre Fournier andGinette Baril for their help in the field, and toGuy Beauchamp for statistical assistance.

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Received for publication 12 December 2006.



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