Anesthetic Complications and Clinical Intervention in Opioid-Anesthetized Captive Elephants
Providing safe and effective anesthesia for captive African (Loxodonta africana) and Asian (Elephas maximus) elephants pose a significant clinical challenge to the zoo veterinarian.2,3,5,8,9 Challenges include unique anatomy, physiology and behavior, which require specialized equipment, facilities and trained personnel. Since captive elephants are prone to certain medical disorders (dental, tusk, foot, nail problems), anesthesia, sometimes prolonged, will be necessary to provide the required veterinary care. In captive elephants, this may be an infrequent event; therefore, it is difficult for zoo veterinarians to gain experience and confidence in elephant anesthesia. Furthermore, elephants are of great institutional and ecologic importance, which adds to the growing list of formidable challenges. This latter consideration should not change the principles or risks associated with anesthesia, but may add to the apprehension when deciding to anesthetize these charismatic animals. Hopefully, these challenges do not lead to delayed medical intervention and care.
Over the past 15 years, the authors have been involved in over 100 prolonged anesthetic events in captive and free-ranging elephants. This represents no claim to be experts but only reflects a privileged and valued experience worth sharing. Complications observed during these events include non-compliant patients, respiratory acidosis, lactic acidemia, hypoxia, hypoventilation, hypercapnia, hypertension, hypotension, ventilation-perfusion mismatch, endobronchial intubation, kinked endotracheal tubes, neuropraxia, prolonged recumbency, improper substrate, inability to stand, prolonged induction and recovery, inappropriate depth of anesthesia, bloat and inadequate equipment and facilities. Although certain complications are difficult to avoid, we will discuss preventative measures and clinical interventions proven to be effective in minimizing physiologic impact on the anesthetized patient.
Complications and Clinical Interventions During Elephant Anesthesia
Patient Positioning and Controlled Recumbency
A successful elephant anesthesia begins with proper positioning of the recumbent patient with adequate space to perform the procedure. Due to space limitations in some facilities, maintaining control of recumbency is critical to ensure the proper position for the intended procedure. This can be accomplished in both ‘free’ and ‘protected’ contact management systems. In protected contact, prior training of the patient is imperative to accept placement of ‘tack and rigging’, such as anklets and ropes. Sedation and cautious free contact with experienced personnel may be necessary in some cases and should be discussed ahead of time.
The procedure area must be of adequate size to allow access with heavy machinery and be equipped with appropriate mechanical advantage devices, such as an overhead hoist or crane, sturdy posts, and appropriately placed ‘dead man’ anchors. A method to lift the animal back to its feet is extremely important and must be discussed prior to the procedure. During recovery, it is important that elephants have adequate space to rock back and forth and extend its legs to gain sternal position prior to standing.
A key component in the ‘rigging’ process is to have the patient pre-trained to accept anklets and tethers on all four legs to assist in the controlled ‘pull-down’ to recumbency as the anesthetic takes effect. Methods for rigging an elephant have been previously described.1 A non-tightening, one-inch diameter rope is preplaced around the patient’s neck. This loop prevents the ‘pull-down’ rope from slipping over the back of the elephant during controlled recumbency. The next step is to place two belly straps (8-inch wide) around the animal’s body, which will be used to lift the animal into a standing position if it cannot get up on at the end of the procedure. The pull-down rope is attached to the anklet of the intended down side rear leg, directed under the abdomen and toward the opposite side shoulder, thru the dorsal aspect of the neck loop and pulled in the direction of the intended recumbent side of the elephant.
As the animal becomes unsteady on its feet, tension is placed on the pull-down rope with manpower or heavy machinery to guide the elephant into recumbency. Specialized devices such as ‘block and tackle’ and ‘snatch block’ pulley systems are necessary to redirect and offer mechanical advantage over the great weight of the animal, which at this time would prefer to remain standing. Strong tension, applied perpendicular to the long axis of the body, must be maintained on the pull-down rope or the animal may lean against the exerted force and go down on the wrong side or in an improper position.
To prevent nerve damage during recumbency and neuropraxia during recovery, adequate padding must be provided under the patient. This may include deep sand or hay, specialized air bags, twin bed mattresses or combinations. Two mattresses are tied together and placed under the shoulder and hip for an average size adult cow. Ropes are attached and used to guide the mattresses under the animal just before recumbency. Once down, it is unlikely to re-position this padding. The head and legs can be lifted to add padding such as large tire inner tubes, however. To reposition the patient, the previously placed belly straps can be used with strategically placed pulleys and mechanical devices to perform minor adjustments.
Tethers, anklets and neck ropes are removed prior to administration of the anesthetic reversal drugs. In uncomplicated recoveries, belly straps should fall off as the animal stands. If some control of the animal is necessary on recovery, a long tether can remain on one of the front legs. Also, prior to recovery, evaluate the area to ensure it is suitable for the animal to rock up to a sternal position before standing. If the patient cannot gain sternal recumbency, the anterior belly strap and mechanical devices may be needed to pull on the patient’s shoulders for assistance to the sternal position. All four legs must then be positioned under the animal to obtain the normal kneeling position prior to standing.
If the patient is unable to stand, lifting with a hoist or crane will be necessary before the animal exhausts itself to the point where standing is no longer possible. Working on the dorsal aspect of the animal, the preplaced belly straps are attached to a ‘spreader bar’ to better distribute the weight of the patient during lifting with the hoist or crane. The animal should be kept calm and comforted while in the sling mechanism and the hoist is relaxed as the patient gains stability on its feet. This may take minutes to hours. During assisted recoveries, experienced personnel may need to work in close proximity of the animal and this should be discussed ahead of time so it is not a surprise to management.
Choice of Drugs and Drug Combinations
Drugs and dosages used in elephant anesthesia are well described in the literature.2,3,5 Special consideration must be made in certain elephant cases for the type and timing of drugs to match the patient’s behavior, training, quality of facility and intended procedure. An untrained, non-compliant elephant in a deficient barn will likely need a different anesthetic protocol than a well-trained patient in a quality facility. Sedation may be necessary to station the animal in a stall or elephant restraint device so ropes, straps and anklets can be pre-placed to assist in patient positioning during induction.
The anesthetic induction dose for elephants often contains a potent opioid and a sedative delivered by dart. Commonly, etorphine is provided at 2–4 μg/kg and is sufficient to keep the patient at a safe depth of anesthesia for approximately 60 min, in the author’s experience. Administration of high induction doses may pose a problem early in anesthesia since this is when the patient is often being moved into position and monitoring becomes difficult. Therefore, maintenance anesthetic agents may be needed to complete lengthy medical procedures. Constant rate infusion (CRI) of etorphine has been used in numerous physical status I and II, captive and free ranging elephants (J.R. Zuba, pers. comm.) while offering titratable, predictable and reversible effects. This author recommends a starting CRI rate of approximately 20% of a proper induction dose of etorphine administered i.v. per hour. This is approximately 0.4–0.6 μg/kg/hr of etorphine and should be started at approximately 60 min following induction for prolonged anesthesia. Anesthetic depth should be evaluated prior to initiation of CRI, of course. The authors do not use gas anesthesia due to the inability to quickly and completely reverse effects, if needed.
Standard monitors include temperature, manual pulse and respirations, pulse oximetry, capnography, electrocardiogram, direct and indirect blood pressure and blood gas analysis. In the authors experience direct blood pressure, ECG, capnography and blood gas offers the most reliable physiologic information on elephant patient status. The ear is routinely used for oximetry measurements in elephants but can be unreliable in authors experience due to movement, skin thickness and low perfusion. A newly released pulse oximeter with improved technology (Radical-7, Masimo Corporation, 40 Parker Irvine, CA, USA) showed superior comparability with blood gas values than standard oximetry in a recent clinical case by the authors. This technology is new to the veterinary market and shows promise during motion and low perfusion conditions as well as the thick and colored skin of the elephant ear.
Control of Respiration
Since potent opioids (i.e., etorphine, carfentanil and thiafentanil) are key induction agents used to anesthetize elephants, some degree of respiratory depression is expected in prolonged procedures. Anesthetized elephants are routinely placed in lateral recumbency, which may further complicate the breathing ability of the patient over time. In the author’s experience, some degree of hypoventilation will occur in opioid-anesthetized elephants in lateral recumbency in procedures as early as 30 min—and certainly in cases lasting 45 min or more. Therefore, it is extremely important to have the ability to access the airway and assist ventilation as it is in other animals to maintain pH, PaCO2, and PaO2 in normal range.
This, of course, will require the need to intubate and ventilate. The authors have developed endotracheal tubes (ETT) of various sizes (35, 45 and 52 mm I.D. and lengths of 1.6–1.8 m) for elephants ranging from 1000–6000 kg. These tubes will be available to others, soon (J. R. Zuba, pers. comm.). Intubation using the stylet technique is usually simple and quick since induction doses typically produce a patient with a lack of jaw tone. The mouth is opened with a strap around the lower jaw tethered to a 4-m rope routed between the front legs of the patient and pulled caudally to open the mouth. The intubator’s gloved arm and hand is introduced between the narrow dental arcade; the soft palate is elevated to gain access to the tracheal opening; fingers are placed within rim of the glottis and a 1 cm dia., 2-meter-long polypropylene stylet is advanced 15–20 cm into the tracheal lumen. The free end of the stylet is placed through the ETT’s ‘Murphy eye’ and the tube is advanced into the trachea using the stylet as a guide. The tube is secured to the tusk or trunk.
Large animal ventilators are easily adapted for use in smaller elephants, whereas two coupled LA ventilators may be necessary in larger patients. However, this may be cumbersome in small elephant barns or under field conditions. A full-sized elephant ventilator is available (Mallard Medical, Inc., Redding, CA) but it may be too large for small areas or field conditions. Horne et al.,5 published a report on a handmade portable ventilator to provide IPPV in elephants under field conditions using 100% compressed oxygen. A novel portable, manually triggered, compressed oxygen-powered, venturi-ventilator9 has been developed and tested in captive and free ranging elephants (J.R. Zuba, pers. comm.) and is near production. This device is more powerful than other portable demand ventilators and is capable of assisting ventilation in elephants, or other megavertebrates, up to 6500 kg.
Control of Blood Pressure
Normal blood pressure values for captive and free ranging elephants have been reported.4,7 Free-ranging African elephants are routinely given azaperone with the etorphine induction dart as a hypotensive/sedation agent to protect against hypertension and pulmonary bleeding (pink foam syndrome).5 Recently, other investigators (G.J. Fleming and J.R. Zuba, pers. comm.) have given 10 mg i.v. boluses of azaperone, as needed, to control elevated blood pressures under similar field conditions.
Interestingly, hypotension seems to predominate captive, opioid-anesthetized elephants – especially during procedures lasting over 60 min. Unfortunately, there is a lack of information on how to properly manage critically low blood pressures in elephants. Equine doses of vasoactive drugs found in veterinary literature6 have been used successfully by this author (JRZ) as a guide for the treatment of hypotension in opioid-anesthetized elephants. Ephedrine, 30–50 ug/kg i.v., as needed, has resulted in 15–50% increase in mean arterial pressures within 3–4 min in hypotensive elephants. Duration of action is approximately 15–20 min. Dobutamine boluses or by constant rate infusion have also been used at equine doses with similar success by this author. Further research is necessary to better understand the pharmacokinetics and pharmacodynamics of these drugs in elephants.
Although the number of cases is limited, the authors recommend high-flow fluid pumps (Masterflex L/S, digital peristaltic pump, Cole-Parmer Co., Vernon Hills, Illinois) for the rapid infusion of maintenance volumes that cannot be matched by gravity alone. In a non-scientific, bench top test by this author, this pump delivered 70 L/hr of saline through a 10-ga catheter into a collection vessel. This volume and rate has not been tested on an elephant patient and infusion trauma to a single catheterized peripheral vein needs to be considered. These pumps can also be set to provide fluids by multiple lines to several catheter sites.
Signalment: Male, 22 yo, 4774 kg, African elephant, protected contact, tusk fracture with exposed pulp, very suspicious/anxious but fairly well-trained patient
Procedure: Partial pulpotomy, with expected anesthesia time of 3 hr
Anesthesia: Single dart of 15 mg etorphine and 25 mg medetomidine for induction; intubate with 45 mm ETT and ventilate; CRI of 4.3 mg etorphine over 94 min for maintenance; 1000 mg naltrexone and 120 mg atipamezole for reversal
Complications: Anxious and suspicious during induction, recumbent in improper position for procedure, bloat, hypotension, hypoventilation, respiratory acidosis, lactic acidemia, neuropraxia
Interventions: Use of heavy machinery, mechanical advantage equipment, straps and ropes to move animal into proper position; i.v. boluses of 150 mg ephedrine provided four times for hypotension (MAP<80 mm Hg) with positive results; IV fluids at 20 L/hr for vascular support; the rate of IPPV with the portable ventilator is increased in response to bloat-induced decreased tidal volumes and hypercapnia; keepers are able to verbally assist in control of anxious patient during recovery and while the neuropraxia of the dependent left rear limb resolves.
Signalment: Female, 42 yo, 2516 kg, Asian elephant, protected contact, reflux of fluid of unknown origin, calm but debilitated patient
Procedure: Esophagoscopy, gastroscopy, with expected anesthesia time of 2–3 hr
Anesthesia: Sedation with 35 mg detomidine and 70 mg azaperone; 7 mg etorphine induction; intubate with 35 mm ETT and ventilate; maintenance with 0.5–1.0 mg i.v. boluses of etorphine, as needed; reverse with 800 mg naltrexone and 260 mg yohimbine
Complications: Geriatric, debilitated, physical status IV, prolonged anesthesia, mild hypo- and hypertension, respiratory acidosis, hypoventilation, lactic acidemia, prolonged recumbency, unable to stand
Interventions: Pre-procedural discussion with management of poor physical status and anesthetic risk; use of overhead hoist is anticipated; pre-placement of body straps to assist in standing if needed; bed mattresses under all pressure points; blood pressure fluctuates during anesthesia but no vasoactive drugs provided; assisted ventilation with portable ventilator; use of overhead hoist and straps for 1.5 hr to assist a debilitated patient to stand on its own
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