History
An 11-month-old 8.5-kg (18.7-lb) male red kangaroo (Macropus rufus) was referred to the Michigan State University Veterinary Medical Center for evaluation and treatment of bilateral antebrachial fractures obtained 2 days prior when moved to a new enclosure. The left antebrachium had short oblique open grade 1 fractures1,2 of the proximal diaphyseal region of the radius and mid-diaphyseal region of the ulna. The right antebrachium had short oblique closed fractures of the proximal diaphyseal regions of the radius and ulna. On the day of the injury, the referring veterinarian initiated medical treatment with meloxicam (0.1 mg/kg [0.05 mg/lb], PO, q 24 h) and enrofloxacin (12 mg/kg [5.5 mg/lb], PO, q 24 h).
On initial evaluation by anesthesia staff of the Veterinary Medical Center, the kangaroo had a heart rate and respiratory rate within reference ranges,3 although rectal temperature (34.5°C [94.1°F]; reference range,4 35° to 36.9°C [95° to 98.4°F]), PCV (35%; reference range, 46% to 51%), and plasma total protein concentration (5 g/dL; reference range,5 6 to 6.8 g/dL) were below lower reference limits. The kangaroo did not show signs of severe pain, but behaved normally and reportedly had a normal appetite at the time.
Question
How might one anesthetize and monitor a juvenile red kangaroo for surgical correction of bilateral antebrachial fractures, and what are early signs indicative of too light of an anesthetic plane in a red kangaroo?
Answer
The anesthetic regimen included preanesthetic medication with midazolam (0.4 mg/kg [0.18 mg/ lb], IM) and methadone (0.5 mg/kg [0.23 mg/lb], IM) administered into the epaxial muscles of the kangaroo with a 22-gauge needle attached to a 3-mL Luer lock syringe. Physical restraint and IM injection were easily managed because of the kangaroo's acclimation to human handling. A 20-gauge IV catheter was placed in the right lateral coccygeal vein (Figure 1).5
Photograph of an anesthetized 11-month-old 8.5-kg (18.7-lb) male red kangaroo (Macropus rufus) during radiography prior to surgical correction of bilateral antebrachial fractures that had occurred 2 days earlier when the kangaroo had been moved to a new enclosure. A 20-gauge catheter has been placed in the right lateral coccygeal vein (white arrow) through which fluid therapy and medications were administered, and a 20-gauge catheter has been placed in the left medial metatarsal artery (yellow arrow) by which direct blood pressure was measured.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
Photograph of an anesthetized 11-month-old 8.5-kg (18.7-lb) male red kangaroo (Macropus rufus) during radiography prior to surgical correction of bilateral antebrachial fractures that had occurred 2 days earlier when the kangaroo had been moved to a new enclosure. A 20-gauge catheter has been placed in the right lateral coccygeal vein (white arrow) through which fluid therapy and medications were administered, and a 20-gauge catheter has been placed in the left medial metatarsal artery (yellow arrow) by which direct blood pressure was measured.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
Photograph of an anesthetized 11-month-old 8.5-kg (18.7-lb) male red kangaroo (Macropus rufus) during radiography prior to surgical correction of bilateral antebrachial fractures that had occurred 2 days earlier when the kangaroo had been moved to a new enclosure. A 20-gauge catheter has been placed in the right lateral coccygeal vein (white arrow) through which fluid therapy and medications were administered, and a 20-gauge catheter has been placed in the left medial metatarsal artery (yellow arrow) by which direct blood pressure was measured.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
General anesthesia was induced with 3% isoflurane in oxygen delivered at a rate of 5 L/min through a rebreathing circuit system attached to a tightly sealed face mask, prior to preoperative radiography. Once the kangaroo's eyes had rotated ventromedially, the blink reflex was lost, and the kangaroo did not respond to a pinch applied to its toes, endotracheal intubation was then attempted. Until intubation was achieved, isoflurane was provided through the tightly sealed face mask as needed to maintain the proper depth of anesthesia.
Intubation was first attempted with the kangaroo positioned in dorsal recumbency with its neck extended. A laryngoscopea was used in an attempt to visualize the rima glottidis; however, the airway was difficult to see because of the kangaroo's small size and long oral cavity.6 Therefore, the kangaroo was repositioned to sternal recumbency with its neck extended for placement of a 5-mm-internal-diameter endotracheal tube (ETT).b A laryngoscope was used to improve visualization of the oral cavity, and a bronchoscopec placed within the lumen of the ETT was used to provide visualization of the rima glottidis and serve as a stylet for the ETT. The ETT met no resistance when inserted into the trachea and was considered an appropriate size for the kangaroo. Placement of the ETT in the trachea was confirmed with the bronchoscope and capnography. A normal capnographic waveform and end-tidal partial pressure of CO2 (Petco2) between 30 and 55 mm Hg were noted on the capnogram during spontaneous and manually assisted ventilation. The seal around the cuff of the ETT was checked by squeezing the rebreathing bag and ensuring that the pressure within the system stayed at 20 cm H2O. There was no leak detected, thus no need to inflate the cuff of the ETT. The kangaroo was connected to a small animal anesthesia machine,d and general anesthesia was maintained with 1% to 2% isoflurane (vaporizer setting) in oxygen (0.8 to 1 L/min) delivered through a pediatric rebreathing anesthesia circuit and precision out-of-circuit vaporizer. Lactated Ringer solution (10 mL/kg/h [4.5 mL/lb/h], IV) was administered through the coccygeal venous catheter with an IV fluid pumpe for the duration of the anesthetic procedure.
A multiparameter monitorf was used throughout the anesthetic period to monitor oxygen saturation of hemoglobin (with a pulse oximeter placed on the tongue), direct blood pressure (via a 20-gauge catheter placed in the left metatarsal artery and attached to an arterial line transducerg; Figures 1 and 2), body temperature (monitored via the use of an esophageal stethoscope temperature sensorh placed in the esophagus), cardiac activity (with lead II ECG), and Petco2 (with mainstream capnography). Oxygen saturation of hemoglobin remained between 97% and 100% throughout the procedure. When breathing spontaneously, the kangaroo hypoventilated (Petco2 > 55 mm Hg). Therefore, a mechanical ventilatori set to deliver a tidal volume of 10 mL/kg and peak inspiratory pressure of 18 cm H2O, was used to maintain normocapnia (Petco2 between 35 and 50 mm Hg). Two different patient-warming systemsj,k were used during the procedure.
A closer view of the hind limbs of the same red kangaroo from Figure 1. Notice the clipped and prepared area of the left hind limb with the medial metatarsal artery (yellow arrow) evident before catheter placement (A) and the same artery with a 20-gauge catheter in place (B).
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
A closer view of the hind limbs of the same red kangaroo from Figure 1. Notice the clipped and prepared area of the left hind limb with the medial metatarsal artery (yellow arrow) evident before catheter placement (A) and the same artery with a 20-gauge catheter in place (B).
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
A closer view of the hind limbs of the same red kangaroo from Figure 1. Notice the clipped and prepared area of the left hind limb with the medial metatarsal artery (yellow arrow) evident before catheter placement (A) and the same artery with a 20-gauge catheter in place (B).
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1473
During the early stages of the procedure, the kangaroo developed signs (increased heart and respiratory rates, high blood pressure, and forelimb movement) indicative of a light plane of anesthesia. To reestablish a surgical plane of anesthesia, methadone (0.2 mg/ kg [0.09 mg/lb], IV) and alfaxalone (0.6 mg/kg [0.27 mg/lb], IV) were administered through the coccygeal venous catheter. When a subsequent bolus of alfaxalone (0.3 mg/kg [0.14 mg/lb], IV) was administered to maintain a surgical plane of anesthesia, personnel discovered that an increase in the kangaroo's tail tone was the initial sign of inadequate anesthesia in this kangaroo. Throughout the rest of the anesthetic procedure, tail tone and especially arching of the tail as a result of increased tail tone were used as reliable initial indicators of the kangaroo developing a light plane of anesthesia.
After surgery (open reduction and internal fixation with placement of 2.0-mm locking compression plates on the radii and 2.0-mm dynamic compression plates on the ulnae), the metatarsal arterial catheter (used in monitoring direct blood pressure) was removed. The kangaroo's heart rate was 80 beats/min, respiratory rate was 8 breaths/min, and rectal temperature was 33.4°C (92.1°F). The kangaroo was administered meloxicam (0.1 mg/kg, SC) and methadone (0.2 mg/kg, IV) for pain management, and an additional dose of methadone (0.2 mg/kg) was available for rescue analgesia, but this was not needed. Recovery was smooth and uneventful, and the cocygeal venous catheter was removed once the kangaroo ambulated well on its own (approx 30 minutes after recovery) and showed interest in food (approx 60 minutes after recovery). The kangaroo interacted normally with caregivers and did not exhibit obvious signs of pain or discomfort.
The day after surgery, the kangaroo was discharged with activity restrictions. The kangaroo was returned 8 weeks later for recheck physical and radiographic examinations. Midazolam (0.4 mg/kg, IM) and methadone (0.5 mg/kg, IM) were administered for sedation. Examination findings indicated that osseous union was progressing appropriately and that there were no signs of implant-associated complications. The kangaroo's activity restriction was diminished.
Discussion
Little information on anesthesia in red kangaroos was available at the time of this case. Therefore, an anesthetic protocol was selected on the basis of recommendations from an expert,1 the experience of the anesthesia team, and a desire to use reversible anesthetic agents. Methadone (a pure μ-opioid receptor agonist and N-methyl-d-aspartate receptor antagonist) provided sedation and analgesia, and midazolam (a benzodiazepine) provided sedation and muscle relaxation for the kangaroo. Use of α2-adrenergic receptor agonists was avoided because of the animal's young age and the potential for such drugs to compromise cardiac function by decreasing heart rate and stroke volume.
The premedication protocol chosen provided excellent sedation of the kangaroo for transfer from the hospital's wildlife ward to the anesthesia preparation room on the day of surgery as well as for the follow-up physical and radiographic examinations 8 weeks later. On the day of surgery, premedication resulted in a level of sedation such that the kangaroo did not respond negatively to placement of a face mask for preoxygenation. Therefore, mask induction with isoflurane in oxygen was chosen instead of administration of injectable induction agents that might have resulted in apnea, such as has been associated (40% to 54% incidence of apnea) with use of propofol and alfaxalone in dogs.7,8 If injectable induction agents had been used and apnea developed, securing the airway for delivery of oxygen to the kangaroo would have been complicated. Nasotracheal intubation, although possible in red kangaroos,9 was not performed because of the potential trauma that could have resulted from attempting to pass an ETT through the kangaroo's narrow nasal passageway. Maintenance of anesthesia by delivery of inhalant anesthetic agents through use of a face mask has been reported in kangaroos10; however, it was deemed safer to acquire a patent and secured airway through use of an ETT because of the estimated duration of surgery and reported risk of regurgitation in red kangaroos.9
Analgesia was provided by the administration of methadone before and during surgery. Brachial plexus regional nerve blocks were also considered but not performed because of the bilateral nature of the fractures and risk of diaphragmatic function loss if the phrenic nerves, because of their close proximity, were also affected by the blocks. If the regional blocks had been performed and the phrenic nerves were affected, the kangaroo could have lost the ability to breathe spontaneously until the regional blocks wore off.11,12
Because there were no published data defining blood pressure in healthy red kangaroos, hypotension was defined for this kangaroo as mean arterial pressure (MAP) < 60 mm Hg on the basis of data from other domestic species13 and a study14 that indicated blood pressure of kangaroos was similar to that reported in other mammals. Monitoring the kangaroo's MAP and ECG during anesthesia was important because the kangaroo became bradycardic (50 beats/min; reference range, 60 to 118 beats/min) and hypotensive (MAP, 48 mm Hg) at the start of surgery.14 To manage the kangaroo's bradycardia and hypotension, glycopyrrolate (0.01 mg/kg [0.005 mg/lb], IV) was administered, increasing the heart rate to 74 beats/min and MAP to 70 mm Hg. Within 15 minutes after administration of glycopyrrolate, hypotension (MAP, 50 mm Hg) returned. Therefore, a constant rate infusion of dopamine in sterile saline (0.9% NaCl) solution (5 to 8 μg/kg/min [2.3 to 3.6 μg/lb/min] was started in an attempt to improve cardiac output and blood pressure. After 5 minutes of dopamine infusion, MAP improved and remained between 60 and 75 mm Hg. Additional support for blood pressure was provided by administration of ketamine (loading dose of 0.5 mg/kg, IV, followed by a constant rate infusion of 10 μg/kg/min, IV, diluted in sterile saline solution) as an additional infusion, which also has an inhalant-anesthetic sparing effect.15 Additionally, ketamine has been reported16 to augment analgesia and aid in preventing hyperalgesia in dogs. Infusions of ketamine and dopamine were discontinued during recovery once the kangaroo became normotensive.
Although not initially appreciated because obscured by surgical drapes, an increase in the kangaroo's tail tone, especially arching of the tail, was noted during surgery to precede forelimb movement as an indication of a light plane of anesthesia. Arching of the tail was found to be a reliable indicator of an early change in the plane of anesthetic depth in the kangaroo of this report. Increase in muscle tone has been reported as an indicator of an inadequate surgical plane of anesthesia in other species, such as horses,17 iguanas,18 and red-eared sliders,19 and in these species, the extent of relaxation of the neck, tail, and jaw muscles as well as anal sphincter tone have been used to assess depth of anesthesia. Tail tone, as observed in this kangaroo, could prove to be an early indicator of inadequate anesthetic depth in red kangaroos, and future studies should investigate use of tail tone as a reliable indicator of anesthetic depth in red kangaroos.
When a light plane of anesthesia was noticed during the procedure, alfaxalone was administered to return the kangaroo to an adequate anesthetic depth. This drug was chosen on the basis of its use in other species (eg, wallabies20) even though the drug had not been studied in red kangaroos.
Despite the use of multiple warming devices during surgery, the kangaroo's body temperature was below the lower reference limit during surgery. Additional steps taken to raise the kangaroo's body temperature included the use of 2 warming devices (1 placed below and 1 placed around the patient). Despite the use of these devices, the kangaroo was still mildly hypothermic. The mild hypothermia may be explained by the vasodilator effect that the inhalant anesthetic agent had on the blood vessels and the resultant loss of heat from the body.
In summary, a combination of methadone and midazolam provided excellent analgesia and sedation in the red kangaroo of this report. Intubation was difficult, suggesting that bronchoscopy should be available when juvenile red kangaroos are anesthetized. Increased tail tone, a previously unreported finding in kangaroos, preceded limb movement and provided an early indication of inadequate anesthetic depth in this red kangaroo. Future studies should investigate use of tail tone as a reliable indicator of anesthetic depth in red kangaroos.
Acknowledgments
The authors declare that there were no conflicts of interest. The authors thank Dr. Darryl Heard for advice on selection of a premedication protocol.
Footnotes
Miller laryngoscope, blade size 4, Welch Allyn Inc, Skaneateles Falls, NY.
Sheridan/CF Murphy eye cuffed ETT, Teleflex Inc, Morrisville, NC.
BF3-C20 fiber-optic bronchoscope, 3.6 mm, Olympus America Inc, Center Valley, Pa.
Matrix Medical LLC, Minneapolis, Minn.
Flo-Gard 6201, Baxter International Inc, Deerfield, Ill.
Bedside Monitor, Nihon Kohden Corp, Tokyo, Japan.
DTXPlus single blood pressure transducer set, Argon Medical Devices Inc, Frisco, Tex.
Esophageal temperature sensor, 18F, Smiths Medical ASD Inc, Saint Paul, Minn.
Veterinary anesthesia ventilator, Hallowell EMC, Pittsfield, Mass.
Bair Hugger warming unit, Augustine Medical Inc, Eden Prairie, Minn.
HotDog patient-warming unit, Augustine Medical Inc, Eden Prairie, Minn.
Heard D, University of Florida, Gainesville, Fla: Personal communication, 2017.
References
1. Gustilo RB, Anderson JT. Prevention of infection in the treatment of one thousand and twenty-five open fractures of long bones: retrospective and prospective analyses. J Bone Joint Surg Am 1976;58:453–458.
2. Gustilo RB, Mendoza RM, Williams DN. Problems in the management of type III (severe) open fractures: a new classification of type III open fractures. J Trauma 1984;24:742–746.
3. Holz P. Marsupials. In: West G, Heard D, Caulkett N, eds. Zoo animal and wildlife immobilization and anesthesia. Ames, Iowa: Blackwell Publishing Ltd, 2007;341–346.
4. Brown GD, Dawson TJ. Seasonal variations in the body temperatures of unrestrained kangaroos (Macropodidae: Marsupialia). Comp Biochem Physiol A 1977;56:59–67.
5. Holz P. Marsupials. In: Miller RE, Fowler ME, eds. Zoo and wildlife medicine. 5th ed. St Louis: WB Saunders Co, 2003;288–303.
6. Richardson KC, Cullen LK. Anesthesia of small kangaroos. J Am Vet Med Assoc 1981;179:1162–1165.
7. Bauquier SH, Golder FJ. Extended anaesthesia and nasotracheal intubation of a red kangaroo (Macropus rufus). Aust Vet J 2010;88:449–450.
8. Muñoz KA, Robertson SA, Wilson DV. Alfaxalone alone or combined with midazolam or ketamine in dogs: intubation dose and select physiologic effects. Vet Anaesth Analg 2017;44:766–774.
9. Lerche P, Nolan AM, Reid J. Comparative study of propofol or propofol and ketamine for the induction of anaesthesia in dogs. Vet Rec 2000;146:571–574.
10. Knafo SE, Rosenblatt AJ, Morrisey JK, et al. Diagnosis and treatment of mesenteric volvulus in a red kangaroo (Macropus rufus). J Am Vet Med Assoc 2014;244:844–850.
11. Riazi S, Carmichael N, Awad I, et al. Effect of local anaesthetic volume (20 vs 5 mL) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br J Anaesth 2008;101:549–556.
12. Stradling JR, Kozar LF, Dark J, et al. Effect of acute diaphragm paralysis on ventilation in awake and sleeping dogs. Am Rev Respir Dis 1987;136:633–637.
13. Weiser MG, Spangler WL, Gribble DH. Blood pressure measurement in the dog. J Am Vet Med Assoc 1977;171:364–368.
14. Maxwell GM, Elliott RB, Kneebone GM. Hemodynamics of kangaroos and wallabies. Am J Physiol 1964;206:967–970.
15. Grimm KA, Lamont LA. Clinical pharmacology. In: West G, Heard D, Caulkett N, eds. Zoo animal and wildlife immobilization and anesthesia. Ames, Iowa: Blackwell Publishing Ltd, 2007;1–36.
16. Wagner AE, Walton JA, Hellyer PW, et al. Use of low doses of ketamine administered by constant rate infusion as an adjunct for postoperative analgesia in dogs. J Am Vet Med Assoc 2002;221:72–75.
17. Thakur BP, Sharma SK, Sharma A, et al. Clinical evaluation of xylazine-butorphanol-guaifenesin-ketamine as short-term TIVA in equines. Vet Med Int 2011;2011:506831.
18. Bertelesen MF, Sauer CD. Alfaxalone anaesthesia in the green iguana (Iguana iguana). Vet Anaesth Analg 2011;38:461–466.
19. Ziolo MS, Bertelsen MF. Effects of propofol administered via the supravertebral sinus in red-eared sliders. J Am Vet Med Assoc 2009;234:390–393.
20. Bouts T, Karunaratna D, Berry K, et al. Evaluation of medetomidine-alfaxalone and medetomidine-ketamine in semi-free ranging Bennett's wallabies (Macropus rufogriseus). J Zoo Wildl Med 2011;42:617–622.
