Comparative anesthetic and cardiopulmonary effects of pre- versus postoperative butorphanol administration in hispaniolan Amazon parrots (Amazona ventralis) anesthetized with sevoflurane.
Key words: sevoflurane, butorphanol, cardiopulmonary, analgesic, anesthetic, avian, birds, Hispaniolan Amazon parrots, Amazona ventralis
Pain management in veterinary patients is complex and is especially challenging in avian species. As in mammals, pharmaceutical effects in one avian species cannot necessarily be extrapolated to another species. Therefore, family-specific and, preferably, even species-specific studies are necessary to evaluate and standardize the response of avian patients to analgesic agents.
Early scientific evaluation of pain in avian species was studied in the rock dove (Columba livia). (1-5) Recently, several studies have evaluated pain and analgesic effects of opioids in several psittacine bird species. (6-9) Butorphanol tartrate was found to provide analgesia in African grey parrots (Psittacus erithacus) and Hispaniolan Amazon parrots (Amazona ventralis); for preoperative or postoperative analgesia, the recommended dose was 1-3 mg/kg IM. (10) However, these studies evaluated pain and its management in a controlled, nonclinical setting.
Butorphanol tartrate is a synthetically derived partial agonist opioid. It is structurally related to morphine but exhibits pharmacologic actions similar to other partial agonists. In mammals, butorphanol is considered to be 4-7 times more potent an analgesic than morphine. Its agonist activity is primarily exerted at kappa and sigma receptors, and its site of action for analgesia is the limbic system. (11) Pigeons have been shown to have more kappa than mu opioid receptors, suggesting why birds may have a relatively decreased response to mu agonists like morphine, buprenorphine, and fentanyl. (10)
Advantages of providing preemptive analgesia include a balanced anesthetic regimen and pain relief during relatively smoother recoveries from painful procedures. (12) However, a common concern when administering opioid agents before a painful procedure requiring anesthesia is whether the effects of the opioid could negatively affect the cardiopulmonary status of the patient during the procedure or prolong anesthetic recovery. Another reported benefit of opioid use is the anesthesia-sparing effect, although no studies have been reported in psittacine bird species. (13,14)
The use of sevoflurane as an anesthetic inhalation agent has been reported in psittacine birds, chickens, and pigeons. (15-18) The minimum anesthetic concentration of sevoflurane in chickens (2.21% [+ or -] 0.32%) was within the range of the minimum alveolar concentration reported in mammals. (17) In one study involving 10 psittacine birds, no significant difference in time to extubation was found between sevoflurane and isoflurane, each administered at 2%; however, a significantly longer time to intubation was seen with sevoflurane. The difference was attributed to administration of sevoflurane below the suspected minimum alveolar concentration for birds. (16)
The purpose of this study was to evaluate in Hispaniolan Amazon parrots the cardiovascular and anesthetic effects of butorphanol tartrate used in conjunction with sevoflurane for a common clinical procedure.
Materials and Methods
Twenty-two adult Hispaniolan Amazon parrots were used in the study. The mean weight of the birds was 0.291 kg, with a range of 0.260-0.340 kg. Procedures performed were in accordance with and approved by the University of Tennessee's Institutional Animal Care and Use Committee. All birds were categorized as healthy based on recent normal physical examination findings and unremarkable Gram's-stained fecal samples, direct fecal smears, complete blood cell counts, plasma biochemical profiles, and results of plasma protein electrophoresis. Birds were randomly assigned to receive butorphanol tartrate (2 mg/kg in the pectoral muscle; Torbugesic, Fort Dodge, Fort Dodge, IA, USA) either 20 minutes before induction of anesthesia with sevoflurane (B-S group, n = 11) or immediately after the anesthetic period (S group, n = 11). The same birds were then assigned to the other group 21 days later in a crossover study. Prior to treatment, the heart rate and respiratory rate were recorded for each bird.
For induction, sevoflurane (Ultane, Abbott Laboratories, North Chicago, IL, USA) was delivered at a rate of 2 L/min via facemask using a nonrebreathing system to provide an end-tidal concentration of 7% in oxygen. Once a bird lost the righting reflex, it was intubated with a 3.0-mm uncuffed endotracheal tube. Each bird was then placed in right lateral recumbency on a forced-air warming unit (Bair Hugger, Augustine Medical Inc, Eden Prairie, MN, USA). The bird was prepared for left coelomic endoscopy for gonadal evaluation as previously described. (19) Sevoflurane levels were adjusted based on the individual bird's anesthetic parameters and response to the procedure. Intermittent positive-pressure ventilation at a rate of 4 breaths/min was administered throughout the procedure. Once the endoscopy procedure was completed at 40 minutes postinduction, sevoflurane administration was discontinued; the anesthesia delivery system was disconnected from the endotracheal tube, flushed, and reconnected to deliver 100% oxygen. The bird was extubated once it began struggling or coughing.
Anesthesia and cardiopulmonary parameters
Intubation and extubation times were determined for each bird. Intubation time was defined as the time from the onset of sevoflurane administration to loss of the righting reflex. Extubation time was defined as the time from discontinuation of anesthesia delivery to extubation. Each bird was recovered from anesthesia while being held in a towel, then released into a transport carrier. Recovery time was defined as the time from discontinuation of anesthesia to the bird standing.
Heart rate (HR), respiratory rate (RR), relative arterial oxygen saturation (Sp[O.sub.2]), and end-tidal carbon dioxide concentrations (Et[CO.sub.2]) were determined at 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, and 40 minutes following sevoflurane induction for both groups. Heart rate was measured via auscultation with a pediatric stethoscope, and respiratory rate was monitored visually. During both protocols, Et[CO.sub.2] was sampled at a gas flow rate of 75 ml/min through a 20-gauge catheter preinserted into the tip of the endotracheal tube and connected to a calibrated in-line infrared gas analyzer (V9004 Capnograph, SurgiVet, Inc, Waukesha, WI, USA), and Sp[O.sub.2] values were estimated with a pulse oximeter probe (Vet/Ox 4404 Graphic Oximeter, Heska Corp, Fort Collins, CO, USA) placed over the metatarsal artery.
Statistical analysis was performed using a statistical software package (Statistical Package for the Social Sciences, SPSS Inc, Chicago, IL, USA). Values were reported as mean [+ or -] standard error. All analyses used a P < .05 criteria for significance unless otherwise indicated. Dependent sample t tests for pairwise comparisons were used to evaluate the effect of preoperative butorphanol administration on induction time, recovery time, HR, RR, Sp[Osub.2], Et[CO.sub.2], and anesthetist-selected sevoflurane level. Pearson correlation (2-tailed) was used to evaluate the relationship between time-specific values and group-specific baseline values as well as relationships within groups among induction, extubation, and recovery times.
Intubation and extubation times were not significantly different between B-S group birds (40 [+ or -] 2 seconds and 2.3 [+ or -] 0.4 minutes, respectively) and S group birds (38 [+ or -] 2 seconds and 2.6 [+ or -] 0.5 minutes, respectively). No significant difference in recovery time was noted between B-S group birds (3.8 [+ or -] 0.4 minutes) and S group birds (4.6 [+ or -] 0.5 minutes).
In B-S group birds, the HR at 30 minutes increased significantly compared with baseline (399 [+ or -] 13 beats/min and 357 [+ or -] 13 beats/min, respectively; P = .04), while compared with baseline HR in S group birds (377 [+ or -] 15 beats/min), the HR was significantly decreased at both 15 minutes (334 [+ or -] 8 beats/min; P = .006) and 25 minutes (326 [+ or -] 15 beats/min; P = .03). Between groups, the HR was significantly increased in B-S group birds compared with S group birds at both 25 minutes (388 [+ or -] 12 beats/rain and 326 [+ or -] 15 beats/min; P = .003) and 30 minutes (399 [+ or -] 13 beats/min and 334 [+ or -] 20 beats/min, respectively; P = .02) (Fig 1).
[FIGURE 1 OMITTED]
Respiratory rates were significantly lower in both groups throughout the anesthetic event compared with baseline, with the exception of the RR at 30 minutes in birds from the B-S group. Birds in the B-S group had significantly lower respiratory rates at baseline and after 1 minute of anesthesia (42 [+ or -] 6 breaths/rain and 29 [+ or -] 2 breaths/rain, respectively) compared with birds in the S group (75 [+ or -] 9 breaths/ min [P = .006] and 37 [+ or -] 3 breaths/min [P = .02], respectively) (Fig 2).
[FIGURE 2 OMITTED]
Relative arterial oxygen saturation values in all birds were greater than 90%; when compared with baseline Sp[O.sub.2] values, no statistically significant differences were found within or between groups (Fig 3). All birds in both groups were normocapnic for the first 35 minutes of sevoflurane anesthesia but exhibited mild hypercapnia (Et[CO.sub.2] > 45 mm Hg) at the final 40-minute measurement (Fig 3). No statistically significant differences in Et[CO.sub.2] compared with baseline were noted within or between groups.
[FIGURE 3 OMITTED]
The lower level of sevoflurane administered at 20 minutes to B-S group birds (3.0% [+ or -] 0.1%) compared with S group birds (3.5% [+ or -] 0.2%) was statistically significant (P = .04) (Fig 4).
[FIGURE 4 OMITTED]
No anesthetic parameters, including intubation, extubation, and recovery times, were significantly different between the group of birds administered butorphanol 20 minutes before induction of anesthesia with sevoflurane or immediately after the anesthetic period. In a study evaluating psittacine birds, the mean induction time for sevoflurane was [greater than or equal to] 4.4 minutes compared with 40 and 38 seconds for the Hispaniolan Amazon parrots in the B-S group and S group of this study, respectively. (16) However, sevoflurane was delivered at a concentration of 7% in the present study compared with an initial concentration in the previously mentioned study of 2%, with gradual increments of 0.5%. Another study measured extubation and recovery times in chickens anesthetized with sevoflurane alone. For chickens undergoing controlled ventilation, extubation time was 4.7 [+ or -] 1.2 minutes, while recovery time was 21.4 [+ or -] 8.5 minutes. (18) In comparison, extubation times for the Hispaniolan Amazon parrots in the present study were 2.3 [+ or -] 0.4 minutes and 2.6 [+ or -] 0.5 minutes for the B-S group and S group, respectively, and recovery times for the 2 respective groups were 3.8 [+ or -] 0.4 minutes and 4.6 [+ or -] 0.5 minutes. However, in the previous study, the chickens were anesthetized for a longer time (126 [+ or -] 7 minutes compared with 36 [+ or -] 14 minutes for the Amazon parrots of the current study), noxious stimuli (eg, endoscopic manipulations) were not applied, and no supplementary analgesic agents were provided. (18) Species differences may also play a role in response to anesthetic agents.
In chickens, HR did not change significantly as sevoflurane levels were increased during controlled ventilation; however, a significant increase in HR was noted when sevoflurane concentrations were increased from 2.2% to 4.4% during spontaneous ventilation. (18) In the present study, the HR of Amazon parrots in the B-S group increased significantly at 30 minutes postinduction, while it decreased significantly at 25 minutes in the S group birds. Interestingly, sevoflurane levels administered showed a trend (P < .10) or were significantly less in B-S group birds at 10, 15, and 20 minutes postinduction (3.3% [+ or -] 0.1%, 3.0% [+ or -] 0.1%, and 2.7% [+ or -] 0.2%, respectively) compared with the levels administered to S group birds (3.7% [+ or -] 0.2%, 3.5% [+ or -] 0.2%, and 3.2% [+ or -] 0.2%, respectively). Between groups, statistical differences were not noted until 25 and 30 minutes postinduction, when the HR of B-S group birds were higher than that of S group birds. These findings may indicate that butorphanol initially provided analgesia and, therefore, an anesthesia-sparing effect. However, at 50 minutes after butorphanol administration (30 minutes into recorded measurements), anesthesia-sparing effects may have decreased, leading to inadequate analgesia from the sevoflurane alone and resulting in an increased HR. Perhaps to compensate, the anesthetist may have increased the sevoflurane concentration delivered to B-S group birds to a level similar to that administered to S group birds. Because sevoflurane concentration is subjectively based on each anesthetist's assessment of the anesthetic level of the patient, statistical analyses of correlations between cardiopulmonary parameters and sevoflurane concentration were not performed. Anecdotally, some avian veterinarians administer analgesia after anesthetic induction but before preparation of the bird for a painful procedure. The current study did not evaluate such a protocol, but future studies should. Further studies are needed to evaluate the anesthesia-sparing effects of butorphanol in sevoflurane-anesthetized birds. In mammals, butorphanol is reported to decrease heart rate secondary to increased parasympathetic tone and mild decreases in arterial blood pressures. (11)
When analyzing the RR of the 2 groups of birds, the decrease in RR by time of sevoflurane induction in the B-S group was statistically and clinically significant compared with that of the S group, even though the B-S group birds were handled to receive their butorphanol injections, while S group birds were not handled before the administration of sevoflurane. Subjectively, no noticeable difference was reported in the activity or mentation of the butorphanol-treated birds compared with the untreated group. The decrease in RR in the preoperatively treated birds compared with untreated birds was still noted 1 minute postinduction but was not present 2 minutes postinduction or thereafter. A lower dose of butorphanol (1 mg/kg) administered to cockatoos (Cacatua species) anesthetized with isoflurane did not significantly change the respiratory rate. (6) Butorphanol administered to dogs elevates the central nervous system threshold to levels of [CO.sub.2] but does not depress respiratory sensitivity. (11) As expected, throughout sevoflurane anesthesia in birds of both groups, RR was significantly decreased compared with baseline levels. In chickens, a similar RR depression was noted during administration of sevoflurane in those undergoing both spontaneous and controlled ventilation. (18)
Pulse oximetry is used in humans and mammals as a noninvasive method of estimating Sp[O.sub.2]. Pulse oximetry used with psittacine birds and pigeons was found to have poor accuracy when recording oxygen saturation and had a high incidence of motion artifact in procedures such as coelomic endoscopy. (20) Spectralphotometric analyses revealed different photometric behavior between avian and human hemoglobin, which likely results in an underestimation of the actual oxygen saturation value in birds. (20) However, pulse oximetry may be used to indicate trends of Sp[O.sub.2] in avian patients. (20) In the present study, Sp[O.sub.2] was >90% throughout the procedure, suggesting that spontaneous and assisted ventilation maintained adequate oxygenation in Amazon parrots of both groups.
In a previous study, a strong correlation was reported between Et[CO.sub.2] and Pa[CO.sub.2] in African grey parrots, although Et[CO.sub.2] consistently overestimated Pa[CO.sub.2] by 5 mm Hg. (21) In addition, Et[CO.sub.2] correlated well with arterial blood pH. The Et[CO.sub.2] values in the present study indicated that all the birds were normocapnic, and no significant differences were observed between groups. Mild hypercapnea (Et[CO.sub.2] > 45 mm Hg) was noted at the final measurement time (40 minutes) in both groups.
Further studies are needed to replicate these findings. With a greater number of birds, several of the trends discussed might actually become statistically significant. Evaluation of other psittacine bird species, higher butorphanol dosages, variations in dosage frequency, and surgical procedure variability are possible directions for future studies.
Acknowledgments: We thank the Office of Research and Graduate Programs at The University of Tennessee, College of Veterinary Medicine; the Mid-Atlantic States Association of Avian Veterinarians; and the Tennessee Valley Exotic Bird Club for their financial support. We also thank Dr Jessi Smith-Klaphake for statistical evaluation and interpretation and Dr Edward Ramsay for his assistance during the endoscopy procedures.
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From the Department of Small Animal Clinical Sciences, C247 Veterinary Teaching Hospital, College of Veterinary Medicine, The University of Tennessee, 2407 River Dr, Knoxville, TN 37996-4550, USA.
Eric Klaphake, DVM, Juergen Schumacher, Dr Med Vet, Dipl ACZM, Cheryl Greenacre, DVM, Dipl ABVP (Avian), Michael R Jones, DVM, Dipl ABVP (Avian), and Nancy Zagaya, LVMT
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|Title Annotation:||Original Studies|
|Author:||Klaphake, Eric; Schumacher, Juergen; Greenacre, Cheryl; Jones, Michael P.; Zagaya, Nancy|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Mar 1, 2006|
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