Abstract

Most previous reports of anesthesia in the rhinoceros describe the use of injectable agents for capture and translocation or for short clinical procedures. One recent case report documents the use of etorphine followed by guaifenesin, thiopental, and isoflurane to provide surgical anesthesia for abdominal exploration through a flank incision in a white rhinoceros.¹ That animal was euthanatized while under anesthesia, therefore, the nature of recovery could not be determined.

This report describes anesthesia for ventral midline celiotomy, ovariectomy, and partial hysterectomy in a 22-year-old 1955 kg female Indian rhinoceros (Rhinoceros unicornis) with a diagnosis of multiple leiomyomas involving the vagina and uterus.

Etorphine, 2.4 mg, was injected into the muscles on the medial aspect of the hind limb, using a rifle and plastic projectile syringe (Vario System, Telinject, Inc., Saugus, CA, USA). After a brief period of mild hypermetria and ataxia the rhinoceros stood quietly. It was approached 8 minutes after darting, whereupon it walked into a corner of the paddock and head-pressed. Respiration rate at that time was 12 BPM and pulse rate, taken from the tail, was 76 BPM. Web slings, 9 ft long × 4 in wide (Mill Valley Splicing Co., Inc., Belchertown, MA, USA) were then placed, one around its abdomen and one around its thorax and in front of one shoulder, after which it laid down. Respiration rate had decreased to 4 BPM, but it increased again when it was pulled out of the corner using the slings and a 16,400 lb capacity fork lift (Caterpillar, Inc., Peoria, IL, USA). Leg movement occurred during positioning and the rhinoceros was given 0.2 mg etorphine IV. An infusion of 12 g guaifenesin with 0.45 g thiopental was given IV through an 18-ga 2 in catheter placed in an auricular vein to eliminate chewing motions, and to relax its jaw for intubation. A 35-mm ID cuffed silicone tube (Bivona, Inc., Gary, IN, USA) was introduced over an adult equine nasogastric tube which had been placed manually through the glottis into the trachea. Swallowing was present during intubation, but the rhinoceros did not cough. Additional guaifenesin, 22 g, and thiopental, 0.75 g, were given over the next 10 minutes while the rhinoceros was further positioned and anesthesia equipment was brought into the paddock. Two 9 French 15-cm wire guided catheters (Cook Veterinary Products, Bloomington, IN, USA) were placed in the left (dependent) cephalic vein. The location of the vein was clearly visible, but a surgical cut-down was necessary to penetrate the thick skin overlying the vessel. A 16-ga 24 in catheter (Intracath, Becton Dickinson Vascular Access, Sandy, UT, USA) was later placed in the opposite cephalic vein. Intravenous fluids (Ringer’s lactate solution) were given through large animal IV administration sets (Stat IV-1000 large animal, International Win, LTD., Kennett Square, PA, USA). A total volume of 80 L was administered.

A 22-ga 1 in catheter was placed in a right external auricular artery for measurement of arterial pressure (MAP) and blood gases.

At the time of initiation of isoflurane-O₂ anesthesia, (55 minutes after induction with etorphine) heart rate was 60 BPM, respiratory rate was 8 BPM, and mean arterial pressure (MAP) was 76 mm Hg. Isoflurane-O² was given using a large animal circuit (Narkovet E, North American Drager, Telford, PA, USA) with a 30 L rebreathing bag. Initial delivered isoflurane concentration was 5% in an O² flow of 15 LPM. After approximately 10 minutes, those settings were reduced to 2–3% and 10 LPM where they remained for approximately 1.5 hours. End tidal (ET) CO₂ was monitored using a sidestream capnometer (Normocap 200, Datex Medical Instrumentation, Inc., Tewksbury, MA, USA).

Electrocardiogram (base-apex lead configuration), direct arterial pressure, nasal temperature and relative O₂ saturation (SpO₂) were monitored continuously using a portable monitor (Propaq 106, Protocol Systems, Beaverton, OR, USA). For SpO₂ monitoring, a reflectance transducer, (RS-10, Nellcor, Inc., Hayward, CA, USA) was placed on the gingiva or between the endotracheal tube and hard palate. During placement of the IV lines, instrumentation, initial surgical scrub, and stabilization of the anesthetic level a structure was erected to hold a tarpaulin over the anesthetized rhinoceros, and a 14 in wide × 8 ft long × 6 in deep trench was dug in the paddock parallel to its back. Using the fork lift to pull leg ropes, the rhinoceros was rolled into dorsal recumbency, with its midline in the trench, approximately 1.33 hours after etorphine induction. Mattresses and hay were placed alongside the trench to further secure its position. The arterial catheter had been dislodged during positioning, and a second 22-ga 1 in catheter was placed in an artery on the inside surface of the pinna. Mean arterial pressure was found to have decreased to 56 mm Hg, and a dobutamine (Dobutrex, Abbott Laboratories, North Chicago, IL, USA) infusion was begun at a rate of 1.0 µg/kg/m. Within 5 minutes, heart rate increased to 80 BPM with only a modest increase in MAP to 62 mm Hg, and a phenylephrine infusion (phenylephrine HCl, USP, Elkins-Sinn, Inc., Cherry Hill, NJ, USA) was added at a rate of 0.03 to 0.06 µg/kg/m. The phenylephrine, combined with dobutamine, 0.125–0.25 µg/kg/m, increased mean arterial pressure to 90 mm Hg with a heart rate of 65–70 BPM.

Surgery began 2.2 hours after etorphine induction. The rhinoceros did not show any clinical signs of arousal in response to surgical stimulation, but arterial blood pressure increased dramatically during traction on the ovaries, and MAP varied between 70 and 150 mm Hg during the surgical procedure. Dobutamine and phenylephrine were discontinued and not used again until ovariectomy and partial hysterectomy were completed, and closure of the abdominal incision was begun, at which time MAP decreased to 65 mm Hg.

Although spontaneous respiratory rate was 8 BPM and SpO₂ readings had remained above 95%, ET CO₂ had risen to 74 mm Hg 15 minutes after the rhinoceros had been placed in dorsal recumbency. An arterial blood gas determination at that time indicated that PaCO₂ was 99 mm Hg. Arterial PO₂ was only 84 mm Hg (Table 1) despite the presumed inspired O₂ concentration of >90%. Controlled intermittent positive pressure ventilation (CV) was initiated using a Bird Mark 9 respirator (Bird Products, Palm Springs, CA, USA) driven by O₂ at a cylinder outlet pressure of 65 PSI, and a 30-L reservoir bag in a 38-L “barrel.” Respiratory rate was controlled at 9–10 BPM and plateau airway pressure, measured at the endotracheal tube was ∼25 cm H₂O. An arterial blood gas determination 45 minutes after initiation of CV indicated that PaO₂ had risen slightly to 97 mm Hg, and PaCO₂ had decreased to 55 mm Hg. Forty-five minutes later, PaO₂ had decreased again, and an attempt was made to provide positive end expiratory pressure (PEEP) at ∼10 cm H₂O. Arterial O₂ tension decreased further to 60 mm Hg during PEEP, and it was discontinued (Table 1). Tidal volume was increased by increasing plateau airway pressure to ∼34 cm H₂O, and PaO₂ increased to 72–74 mm Hg.

Table 1. Arterial blood gas determinations

^aControlled intermittent positive pressure ventilation
^bPositive end expiratory pressure

After the first 1.5 hours of inhalation anesthesia, O₂ flow to the breathing circuit was lowered to 3 LPM. This flow was maintained for the remaining 4.5 hours and appeared to be equal to metabolic O₂ requirements for the rhinoceros. The soda lime was changed once during the procedure, because inspired CO₂ rose above 0 mm Hg. Ventilation was continued during the soda lime change using a 160 LPM demand valve (LSP model 063–050, Allied Health, St. Louis, MO, USA) and it was possible to keep ETCO₂ at 45 mm Hg using this device.

Ambient temperature was measured at 24°C at the midpoint of the anesthetic period, and the rhino’s nasal temperature remained at 35.3°C during the last 4 hours of anesthesia.

Isoflurane delivery was discontinued at the beginning of abdominal closure, 5.25 hours after etorphine induction. Blood pressure increased gradually over the next 1.5 hours, but no signs of arousal from anesthesia were noted. Surgery was completed 6.5 hours after etorphine induction. The rhinoceros was put in lateral recumbency and naltrexone HCl (INADA 6277, Wildlife Pharmaceuticals, Fort Collins, CO, USA) 240 mg IV and 240 mg IM were given 7 hours after the initial etorphine injection. The endotracheal tube was pulled as it rolled to a sternal position, and the rhinoceros stood 1.5 minutes after naltrexone administration. The rhinoceros stood quietly, and seemed aware of auditory, but not visual stimuli for approximately 10 minutes. At 15 minutes, it could apparently see and was walking with some ataxia, and at 17 minutes it was trotting and charged a member of the staff, running him out of the paddock. Other than mild ataxia it appeared to have no gait abnormalities.

Although the rhinoceros recovered well initially, unfortunately, it died approximately 32 hours later as a result of hemorrhage from the left ovarian pedicle. The rapid recovery from 7 hours etorphine-isoflurane anesthesia demonstrates that this technique can be used to safely anesthetize adult rhinoceros in dorsal recumbency for long periods of time, provided that cardiovascular and respiratory monitoring and support are available.

Literature Cited

1.  Cornick-Seahorn JL, Mikota SK, Schaeffer DO, Ranglack GS, Boatright SB. Isoflurane anesthesia in a rhinoceros. J Am Vet Med Assoc. 1995;206:508–511.