Effects of Intramuscular Alfaxalone/Acepromazine on Echocardiographic, Biochemical, and Blood Gas Measurements in Healthy Cats
ABSTRACT
The effects of intramuscular injection of alfaxalone ([ALF] 5 mg/kg), acepromazine ([ACE] 0.05 mg/kg), and an ALF-ACE combination ([AA] 0.025 mg/kg ACE followed by 2.5 mg/kg ALF) on the sedation, echocardiographic, biochemical, and blood gas indexes and recovery were evaluated in seven cats. No sedation was obtained with ACE, and sedation scores were higher with ALF than with AA treatment. Compared with baseline, an increase in heart rate occurred after ACE, and all treatments caused a decrease in systemic arterial pressure. Decreased left ventricular internal dimension in diastole, end-diastolic volume of the left ventricle, stroke volume, and left atrial dimension were identified after AA. There were minimal changes in echocardiographic variables after ALF. Biochemical and blood gas analysis showed no significant changes after all treatments. Although the difference in quality of recovery between the AA and ALF treatment groups was insignificant, all cats treated with AA or ALF showed ataxia. The AA combination did not change the recovery score, and tremor and twitching were identified more frequently with AA than ALF. ALF had no significant effects on echocardiographic, biochemical, or blood gas variables. ALF could be considered a useful sedative option for diagnostic procedures and echocardiography in cats.
Introduction
In veterinary clinics, sedation is often required when there are handling difficulties, particularly with aggressive and fractious cats.1 Sedatives and anesthetic drugs can reduce patient stress, ensure patient and clinician safety in a variety of situations, and increase the quality of diagnostic procedures, such as echocardiography and blood sample collection.1 As it is important to obtain proper data for diagnosis, the administered sedatives and anesthetic drugs should have minimal cardiovascular and biochemical effects.2
Alfaxalone (ALF), a neuroactive steroid drug that produces central nervous system depression by activity at γ–aminobutyric acid A receptors, is relatively short acting, nonirritant, and noncumulative, making it suitable for both the induction and maintenance of anesthesia.3 ALF caused a dose-dependent unconsciousness, decrease in heart rate, arterial blood pressure, and systemic vascular resistance, but the changes were minimal, up to 15 mg/kg in cats.3,4 Previous authors have reported stable cardiorespiratory data, such as pulse rate, blood pressure, respiratory rate, saturation of oxygen with hemoglobin, and end tidal carbon dioxide partial pressure in cats after intramuscular (IM) injection of ALF (5 mg/kg) with dexmedetomidine (0.01 mg/kg) and hydromorphone (0.1 mg/kg).5 Another study showed that IM injections of ALF (2 mg/kg) and butorphanol (0.2 mg/kg) did not cause any significant changes in echocardiographic measurements.4 Although IM injection of ALF induces rapid and short-lasting sedation, 5–10 mg/kg (0.5–1 mL/kg body weight) of ALF via IM injection caused moderate-to-profound discomfort and poor recovery.4,5
Acepromazine (ACE), a phenothiazine sedative that inhibits central dopamine receptors, may be given to cats at dose rates of 0.02–0.1 mg/kg to increase sedation and provide a better quality of recovery from anesthesia.3,6 ACE causes a nonspecific α-adrenergic receptor blockade, which leads to peripheral vasodilation and decrease in arterial blood pressure.5 However, there is little information regarding the effect of IM administration of ACE and ALF on echocardiographic measurements.
The authors hypothesized that ALF would not affect echocardiographic, biochemical, and blood gas variables, and ALF with ACE could provide advantages over ALF alone. The purposes of this study were to evaluate the effects of ALF and ACE on echocardiographic and biochemical variables and clinical safety as well as to determine whether injection volume and adverse effects in recovery can be reduced when ALF is combined with ACE.
Materials and Methods
Animals
This study was approved by the Institutional Animal Care and Use Committee of Seoul National University (SNU-140324-2). Seven adult cats (five domestic shorthairs, along with one Siamese and one Persian) were enrolled for this study. The cats were enrolled in this study after the owner's written informed consent was obtained. The cats weighed 4.6 ± 1.3 kg (mean ± SD) and were aged 2.7 ± 1.3 yr. The cats underwent a complete physical examination, complete blood count, blood chemistry analysis, venous blood gas analysis, thoracic and abdominal radiographs, abdominal ultrasonography, and echocardiography. Cats with any functional or anatomical abnormalities were excluded from the study. The cats were assessed as clinically healthy based on a complete physical examination and laboratory testing.
Study Design
The study was conducted as a randomized crossover design, and the variables were measured in the following order (Figure 1). More than 7 days was allowed between treatments to avoid residual drug effects. Systolic arterial blood pressure (SAP) and body temperature measurements, echocardiography, and blood sampling were conducted as a baseline assessment before injection. The three treatments were injected into each cat’s quadriceps muscle, using a 25 gauge needle, using two separate injections for AA and ALF treatments. The treatments were ACE (acepromazinea) 0.05 mg/kg IM; ALF (alfaxaloneb) 5 mg/kg IM, splitting the volume of drug into two injection sites; and AA, which consisted of ACE 0.025 mg/kg IM, immediately followed by ALF 2.5 mg/kg IM. After the treatment injections were administered, sedation scores were evaluated by a single experienced person in a quiet room for 10 min (at 0, 2, 4, 6, 8, and 10 min) according to the criteria described in Table 1.2 High scores represented a good quality of sedation for carrying out diagnostic procedures. To assess response to tactile and auditory stimulation, the examiner pinched the cat’s interdigital skin lightly with the fingers and clapped the hands. The total sedation score was calculated from the area under the curve for the five points in time. At 10 min after administration, echocardiography was repeated for 30 min, followed by SAP, body temperature measurements, and blood sampling. At 45 min after drug administration, the authors observed the cats as to when they became sternal and then standing position. The quality of recovery was evaluated by a single experienced person using a recovery scoring system with scores ranging from 0 to 14 in Table 2; the occurrence of adverse event was recorded during the study.2
Citation: Journal of the American Animal Hospital Association 55, 2; 10.5326/JAAHA-MS-6630
Blood Pressure and Body Temperature Measurements
Indirect SAP measurements were conducted with a Doppler ultrasonic flow detectorc. The Doppler probe was placed over the palmar digital artery and occluding cuff (40% of the leg circumference) and a sphygmomanometer was placed above the carpus. Measurements were taken three times by a single person and averaged. A thermometer was placed in the rectum to measure body temperature. At 40 min after drug administration, post SAP and body temperature were measured.
Echocardiography
All examinations were performed by a single experienced echocardiographer using an ultrasound systemd equipped with a 3–8 MHz phased-array sector transducer. A lead Ⅱ electrocardiogram was simultaneously displayed on the ultrasound monitor for timing purposes and the heart rate (HR) was counted automatically.
All echocardiographic values were measured in accordance with recommendations of the Echocardiography Committee of the Specialty of Cardiology, American College of Veterinary Internal Medicine, and the standard methods described previously.7–10
Measurements of the M-mode left ventricular parameters were obtained from a two-dimensional guided M-mode on the right parasternal short-axis view at the level of the papillary muscles. The variables measured were interventricular septal thickness (IVS) in diastole and systole, left ventricular free-wall thickness in diastole and systole, and left ventricular internal dimension in diastole (LVDd) and systole. The end-diastolic and end-systolic volumes of the left ventricle (EDV and ESV) were calculated using the Teichholz method.11 The left ventricular ejection fraction ([EDV – ESV] / EDV × 100) and fractional shortening ([LVDd – LVD systolic] / LVDd × 100) were calculated. HR was simultaneously recorded with an M-mode measurement. Left ventricular stroke volume (SV = EDV – ESV) and cardiac output (SV × HR) were calculated. Assessments of left atrial (LA) and aortic root dimensions (Ao) were performed from the right parasternal short-axis view from a two-dimensional image at the heart base, and the ratio between LA and Ao (LA/Ao) was calculated.12
Peak velocities of the aortic (Ao velocity) and pulmonic flow were measured from the left apical five-chamber view and the right parasternal short-axis view using pulsed-wave Doppler. Transmitral (MV) inflow was taken from the left apical four-chamber view by pulsed-wave Doppler to measure the peak velocity of early diastolic (Peak E) and late diastolic (Peak A) MV flow and deceleration time in early diastole (MV E dec time). The ratio between peak E and peak A was calculated (MV inflow E/A). When peak E and peak A were summated because of tachycardia, the measurements were excluded from the data.
Pulsed-wave tissue Doppler imaging (PW-TDI) of mitral annulus motion was recorded from the left apical four chamber view. Peak early diastolic (E’) and peak late diastolic (A’) velocities and isovolumic relaxation time were measured for both the septal and lateral mitral valve annulus. The ratios between E’ and A’ (E’/A’) and peak E and E’ (E/E’) were calculated. When E’ and A’ were summated because of tachycardia, the measurements were excluded from the data. All measurements were taken from three cardiac cycles and averaged.
Blood Sampling and Analysis
A sample of 4 mL of blood was collected from a jugular or medial saphenous vein with a 22 gauge disposable needle. To reduce the cardiovascular effects of stress on the cats, baseline blood sampling was conducted after echocardiography. Blood samples in plain tubes were used for biochemical analysis. Alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total protein, albumin, blood urea nitrogen, creatinine, and glucose were measured using an automatic analyzere. The blood in the serum separating tube for cortisol measurement was centrifuged to separate the plasma, which was frozen at –20°C until analysis. Cortisol concentration was measured using an immunoassay analyzerf. Samples for blood gas analysis were collected anaerobically into a heparinized 1 mL syringe. The blood samples were immediately analyzed via a blood gas analyzerg. The blood gas analyzer measured the pH, carbon dioxide partial pressure, oxygen partial pressure, sodium, potassium, and calcium, and the base excess, bicarbonate, total carbon dioxide, and hematocrit were calculated.
Statistical Analysis
Statistical analyses were carried out using commercially available softwareh. All variables were considered nonparametric data because of the small number of subjects. HR, SAP, temperature, echocardiographic results, serum chemistry, and blood gas variables were analyzed with a Wilcoxon signed-rank test to compare results between baseline and treatment. A Kruskal-Wallis test was used to analyze the differences between treatments, followed by a Bonferroni post hoc analysis. Sedation score was evaluated for five time points (every 2 min for 10 min). To make the area under the curve, total sedation score was calculated with the trapezoidal method before comparison. Recovery time to the sternal and standing positions and sedation and recovery scores were analyzed by Wilcoxon rank-sum tests. The data is presented as median (min, max). P values of <.05 were considered statistically significant.
Results
Blood Pressure and Body Temperature
Blood pressure and body temperature were measured at baseline and 40 min after drug administration. The baseline SAP for ACE, ALF, and AA were 140 (110, 200), 120 (100, 180), and 135 (110, 155) mm Hg, respectively, and each SAP changed to 100 (70, 110), 130 (85, 150), and 95 (0, 115) mm Hg after administration of each treatment, respectively. Compared with the baseline, the decrease in SAP occurred after ACE and AA administration (P < .05). The baseline body temperature values for ACE, ALF, and AA were 38.7 (38.5, 39.1), 38.4 (38.2, 39), and 38.6 (38.3, 38.8)°C, respectively, and each body temperature decreased to 38.1 (37.6, 38.5), 37.4 (37, 38.3), and 37.7 (37, 38.3), respectively. Body temperature was lower than the baseline value after all treatments, but the differences between the treatments were not significant.
Echocardiography
The baseline HR for ACE, ALF, and AA were 197 (115, 221), 197 (141, 246), and 200 (153, 217) beats/min, respectively, and each HR changed to 207 (139, 257), 190 (164, 257), and 233 (140, 261) beats/min after administration of each treatment, respectively. There were no significant differences in baseline HRs between treatments. Compared with the baseline, an increase in HR occurred after ACE administration (P = .046). There was an increase in IVS systole (from 0.73 [0.58, 0.83] to 0.75 [0.66, 0.87] cm, P = .043) and a decrease in peak E (from 0.80 [0.64, 1.17] to 0.64 [0.55, 0.97] m/s, P = .043) after ACE was compared with the baseline value. Decreases were observed after AA treatment compared with baseline values in IVS diastole (from 0.50 [0.43, 0.57] to 0.46 [0.37, 0.52] cm, P = .046), LVDd (from 1.38 [1.32, 1.59] to 1.28 [1.16, 1.47] cm, P = .018), EDV (from 4.85 [4.45, 7.2] to 3.99 [3.16, 5.83] mL, P = .018), SV (from 3.93 [3.82, 6.51] to 3.48 [2.09, 4.86] mL, P = .018), and LA (from 1.14 [0.95, 1.27] to 1.07 [0.86, 1.23] cm, P = .028). A decrease in Ao diameter occurred after ALF (from 0.84 [0.69, 1.20] to 0.82 [0.62, 1.16] cm, P = .018). All treatments had no or minimal influence on PW-Doppler of Ao and pulmonic velocity, MV inflow, and PW-TDI values at the mitral annulus. Echocardiographic values did not differ significantly among the three treatments.
Biochemistry and Venous Blood Gas Analysis
Blood sampling was performed at baseline and following echocardiography (40 min). In the blood samples, the baseline and treatment values for serum chemistry were within normal ranges, and there were no statistical differences among treatments, although minor changes were identified after ACE treatment (in alanine aminotransferase, alkaline phosphatase, total protein, and albumin) and after ALF (in creatinine). There was an increase in cortisol levels after ACE (P = .028); however, AA and ALF induced nonsignificant reductions in cortisol. Comparisons among the treatments showed that cortisol levels were higher after ACE compared with AA and ALF, but the difference between AA and ALF was not significant (Table 3). There were no statistical differences in the clinically relevant venous blood gases with any of the treatments (Table 3).
Sedation
Six out of the seven cats were not sedated when treated with ACE. One cat showed mild ataxia at 8 min and was sedated for 40 min. All cats were sedated with AA and ALF. The sedation scores were 10 (4, 21) after AA treatment and 24 (13, 28) after ALF treatment. The sedation scores were significantly higher following ALF than following AA (P = .012) (Figure 2A).
Citation: Journal of the American Animal Hospital Association 55, 2; 10.5326/JAAHA-MS-6630
Recovery
The ACE treatment was excluded from the recovery evaluation because all cats were not recumbent, and one sedated cat awoke from sedation approximately 40 min after injection. In AA treatment, four of the seven cats awoke from sedation 40 min after AA administration; at that time, sternal recumbency and standing were not measurable in four and two cats, respectively. The times to sternal recumbency were 0 (0, 47) min (n = 3/7) and the times to standing were 5 (0, 57) min (n = 5/7) with the AA treatments. All the cats were sedated with ALF. The times to sternal recumbency were 35 (10, 70) min and the times to standing were 40 (15, 90) min (n = 7) with the ALF treatments. The recovery time was therefore significantly faster after AA than after ALF (time to sternal recumbency P = .045, time to standing position P = .045; Figures 2B, C). Recovery scores were 6.0 (2, 9) and 8.5 (6, 9) after AA and ALF treatments, respectively. The difference in the quality of recovery between the AA and ALF treatments was not statistically significant. In recovery, all the cats displayed mild to moderate ataxia after treatment with AA and ALF. There was paddling, muscle twitching, or movement in two of the seven cats after AA and in one of the seven cats after ALF.
Discussion
This study found that only minimal changes in biochemical and blood gas indexes in healthy cats occur following administration of ACE, ALF, and AA. In the evaluation of the effects of ALF, ACE, and AA on echocardiography, it was found that administration of ALF did not induce changes in echocardiographic variables except Ao diameter, and both ACE and AA altered certain echocardiographic variables. One unanticipated finding was that combining ALF and ACE did not change the recovery score, although injection volume was reduced. In contrast to the wide individual variations in recovery, ALF induced adequate sedation for diagnostic procedures.
In the current study, a significant increase in HR occurred after ACE. SAP was decreased following all treatments, with the largest decline occurring after ACE. These results might be attributable to nonspecific α-adrenergic blockade, which causes vasodilation and subsequent decreases in systemic vascular resistance and systolic blood pressure.3,6 It is reasonable to conclude that the significant increase in HR after ACE was because of reflex tachycardia produced by vasodilation and decreased SAP associated with ACE.
Baseline echocardiographic values were within the reference ranges in all the cats and did not differ among the treatments.9,10,16,17 ACE caused significant change in HR because of decreased blood pressure and/or excitement associated to inadequate sedation. HR can influence echocardiographic variables independent of the effects of sedatives and anesthetics. A decrease in SV can be associated with impaired ventricular filling because of very high HR.2,18 However, the variables were not statistically significant in the ACE group of this study. ACE could cause significant changes in echocardiographic measurements because of hypotension subsequent to the decrease in preload. In this study, a decrease in preload was expressed in low LVDd and EDV values, leading to a decrease in SV (∼25%) after AA treatment, including ACE. Although both ACE and AA groups include ACE, only the AA group showed significant change in echocardiographic values. It was hypothesized that the cause of this result was the effect of combination with ACE and ALF. Administration of ALF did not induce changes in echocardiographic variables, except in Ao diameter. Rapid HR (>200 beats per min) resulted in a complete loss of separation between the two diastolic filling phases in MV inflow and PW-TDI at the mitral annulus.19 In this study, summations between E and A and between E’ and A’ were observed following treatment with ACE and AA compared with ALF alone.
Baseline and treatment serum chemistry values were clinically normal and had minimal statistical differences. In stressful situations, physiological responses activate the hypothalamic-pituitary-adrenal system, as measured by elevated levels of plasma cortisol concentration. This response, reported among animals in public shelters, is used as an indicator of stress or pain in cats.20–24 Anesthetic medications may decrease stress hormonal responses in the perioperative period.24 In the research by Väisänen et al., 20 µg/kg of medetomidine and 0.2 mg/kg of butorphanol caused a decrease in perioperative concentrations of cortisol.24 In the present study, the increase in cortisol levels after ACE was likely caused by sequential procedures during inadequate sedation, whereas the AA and ALF treatments induced sufficient sedation to produce a decrease in cortisol level.
In previous reports on IM injections in cats, 5 mg/kg ALF with dexmedetomidine resulted in a loss of the withdrawal reflex after a mean time of 7.2 ± 2.5 min and 2 mg/kg ALF with 0.2 mg/kg butorphanol resulted in lateral recumbency, loss of response to stimulus, and muscle relaxation within 10 min.4,5 In the current study, AA and ALF administration also caused sedation within 10 min. However, there was no link with the sedation score, and the adverse effects of tremor and twitching were identified more frequently after AA treatment than after ALF treatment. In some cases, these involuntary movements interfered with the echocardiographic procedure. In the present study, the 5 mg/kg dose (0.5 mL/kg body weight) of ALF via IM administration caused discomfort, even at the low end of the recommended dose range from the product information sheet, because of the relatively high injection volume.26 In the research by Grubb et al., 10 mg/kg (1 mL/kg body weight) of ALF via IM injection caused moderate-to-profound discomfort.5 These results suggest that the 5–10 mg/kg dose of ALF was not a practical volume for IM injection in aggressive cats.
In the research by Grubb et al., the authors stated that cardiopulmonary parameters were within normal limits and remained stable following IM injection of ALF into cats; however, recovery was poor.5 In the current study, the most common adverse effect was ataxia after ALF injection (AA and ALF treatments). Various recovery quality levels have been reported after ALF, from extremely poor to smooth.4,5,13,14,27 Exaggerated and prolonged excitement and hyper-reactivity were reported after IM injection.5 Premedication with different drugs might produce variable recovery scores and prevent adverse effects.14,28–30 Because the maximal effects of ACE occur 30–45 min after IM injection, the authors expected that AA treatment would improve the quality of recovery.3 In the current study, however, combining ALF and ACE did not change the recovery score, although the times to sternal recumbency and standing were shortened. There were vast individual variations in time to sternal recumbency and standing, as well as in recovery scores and adverse effects, such as tremors and twitching. This was an unexpected finding because the ACE provide a quieter recovery from anaesthesia.3 An explanation for these results is that the recovery evaluation method of this study is mainly based on motor activity in amenable cats. Reliable, quieter recovery is achieved usually with ACE; the recovery effect might be different in aggressive and fractious cats.3,6
This study has several limitations. First, this study was carried out on healthy cats. The effects might be different in cats suffering from cardiac disease or metabolic disorders. Second, maximal effects of ACE are seen 30–45 min after IM injection.3 This means that the sedation score and echocardiographic values were being done before ACE had a chance to reach maximal effect, which would influence the results of the study. The short time frame and interacting every 2 min with a patient immediately after administering sedation likely affected their response. This may have contributed to why ACE did not produce any sedation in cats. In addition, although ACE has a maximal effect that occurs significantly later than ALF, the decrease in SAP and SV occurred after ACE and AA administration in this study. These results suggest that the peak effects of ACE may not have occurred and that echocardiographic results might be further affected when the drug reached peak effect. Third, although ALF is not licensed for IM or subcutaneous use in North America, IM administration of ALF has been used to provide sedation for simple procedures (e.g., IV access, blood collection, and diagnostics).26 However, prolonged excitement and hyper-reactivity were reported after ALF IM injection; the addition of sedative drugs may improve the quality of recovery that can be seen when only ALF is used.3,5 Finally, plasma cortisol levels were measured to evaluate the stress response related to the procedure.20–24 In this study, the increase in cortisol levels after ACE was likely caused by inadequate sequential procedures, or the peak effects of ACE may not have reached or the addition of ALF would produce lower concentrations of cortisol. However, because there is no control group to demonstrate an increase in cortisol levels without drug administration, it was not possible to evaluate the effect of ACE on plasma cortisol levels.
Conclusion
In the evaluation of the effects of ALF, ACE, and AA on clinical safety, usefulness, and echocardiography, it was found that both ACE and AA were inadequate to produce deep sedation, and they altered certain echocardiographic variables. Although ALF resulted in wide individual variations in recovery, sedation induced by IM injection of ALF at 5 mg/kg induced adequate sedation for diagnostic procedures and had minimal effects on echocardiographic and biochemical variables. Therefore, IM injection of ALF could be considered a safe and useful sedative option for diagnostic procedures and echocardiography in cats.
Sequential order of procedures. BP, blood pressure measurement; BS, blood sampling; Echo, echocardiography; INJ, injection of sedatives; Temp, body temperature.
(A) Box plots of sedation scores measured over 10 min, (B) box plots of time to sternal recumbency, and (C) standing following the IM injection of AA and ALF. The box indicates interquartile range. The whiskers and horizontal line in the box represent minimum/maximum and median, respectively. AA, acepromazine and alfaxalone combination; ALF, alfaxalone; AUC, area under the curve; IM, intramuscular.
Contributor Notes
B. Kim and M. Jang equally contributed to this study.
