Evaluation of cardiorespiratory effects of combinations of dexmedetomidine and atropine in cats

Comparison of intra and postoperative analgesia efficacy of intraperitoneal levobupivacaine alone or in combination with dexmedetomidine in cats undergoing ovariohysterectomy; a randomized, prospective, blinded, clinical trial

This study aimed to compare the analgesic and cardiopulmonary effects of levobupivacaine with or without dexmedetomidine, in cats undergoing ovariohysterectomy. In this prospective, randomized, and blinded clinical trial, 24 healthy cats were recruited. Animals received either saline (S group; 2 mL NaCl), levobupivacaine alone (Lev; 0.35 mg/kg), or levobupivacaine with dexmedetomidine (LevDex group; 0.004 mg/kg), which was infiltrated intraoperatively into the subcutaneous tissue at various incision sites, including the right and left ovarian pedicles and the caudal aspect of the uterine body. Intraoperative analgesia was evaluated using a cumulative pain scale, while postoperative analgesia was assessed at various time points: before surgery (Tb), and at 0 (T0), 1 (T1h), 2 (T2h), 4 (T4h), 8 (T8h), 12 (T12h), and 24 (T24h) hours after the procedure, using the UNESP-Botucatu multidimensional composite pain scale (MCPS). Significant decreases in heart rate, respiratory rate, and mean arterial pressure were observed in LevDex group as compared to S and Lev groups (p < 0.05). The S group required significantly more rescue morphine doses than the LevDex group (p = 0.029), but the difference was not significant when compared to the Lev group (p = 0.123). At T1h and T2h, the S group had significantly higher MCPS scores than both the Lev and LevDex groups (p = 0.029). However, at T8h, no significant difference was found between the S and LevDex groups (p = 0.741). While adding dexmedetomidine to levobupivacaine may slightly prolong postoperative analgesia, this combination does not provide significant additional benefit over levobupivacaine alone in terms of response to surgical stimulation.

Influence of gabapentin on the degree of sedation, physiological variables and propofol dosage in cats premedicated with acepromazine and methadone: a randomized, prospective, blinded, clinical study

This study evaluated the influence of gabapentin on sedation, propofol dosage, and physiological variables in cats premedicated with acepromazine and methadone. Thirty-four cats were randomly assigned to receive 100 mg of oral gabapentin (Gabapentin group) or placebo (Control group) 100 min before intramuscular premedication with acepromazine (0.05 mg/kg) plus methadone (0.3 mg/kg). Variables recorded included sedation, using the Dynamic Interactive Visual Analog Scale (DIVAS, range 0-100 mm) and a Numeric Descriptive Scale (NDS, range 0-14), heart rate, respiratory rate and Doppler systolic arterial pressure (SAP). All variables were measured before (T0), 100 min after administration of gabapentin or placebo (T1), and 30 min after premedication (T2). Physiological variables were also recorded after anesthetic induction with propofol (T3). At T2, NDS scores were higher in Gabapentin than the Control group [median (interquartile range): 4 (2-5) versus 2 (1-4), p = 0.028], whereas DIVAS scores were not significantly different [Control: 9 (4-13); Gabapentin: 12 (5-32)]. Despite the significant difference between groups in NDS scores, overall sedation scores were mild at T1 and T2 regardless of gabapentin administration. The propofol dosage did not differ between groups. The most concerning adverse effect was arterial hypotension (SAP < 90 mmHg), recorded only at T3 in 71% of cats in the Control group and 100% in the Gabapentin group, without significant difference between groups. Administration of gabapentin before premedication with acepromazine and methadone in healthy cats did not result in a clinically significant influence on sedation levels, physiological variables, or propofol dosage required for anesthesia induction.

Retrospective Comparison of the Anesthetic Effects of Tiletamine-Zolazepam with Dexmedetomidine and Ketamine with Dexmedetomidine in Captive Formosan Serow (Capricornis swinhoei)

Formosan serows are endemic to the mountainous regions of Taiwan. This crossover study aimed to assess and compare the anesthetic induction and recovery using either dexmedetomidine-tiletamine-zolazepam (DZ) or dexmedetomidine-ketamine (DK) by intramuscular injection from a blow-dart in a zoo environment. Ten anesthetic procedures were performed with five adult Formosan serows. Each participant was anesthetized with both combinations at least once with a minimal 12-month washout. The average dosages were 22.6 ± 8.3 µg/kg and 35.8 ± 2.5 µg/kg for dexmedetomidine and 185.6 ± 123.6 and 357.8 ± 25.2 µg/kg for atipamezole for the DZ and DK groups, respectively. The doses of tiletamine-zolazepam and ketamine were 2.1 ± 0.25 mg/kg and 3.6 ± 0.3 mg/kg, respectively, in the DZ and DK groups. All participants were induced within 10 min (median: 8 min for both groups), except one serow in the DK group with an induction time of 22 min. Serows in the DZ group had a lower respiratory rate (p = 0.016) and lower rectal temperature (p = 0.008) than those in the DK group. The quality of recovery was poor for DZ because of paddling, prolonged recovery, and ataxia after antagonism of dexmedetomidine with atipamezole. The induction of anesthesia with dexmedetomidine-tiletamine-zolazepam was uneventful and rapid. However, recovery from this combination was not smooth.

The Effect of a Subsequent Dose of Dexmedetomidine or Other Sedatives following an Initial Dose of Dexmedetomidine on Sedation and Quality of Recovery in Cats: Part I

Dexmedetomidine is an a2-agonist commonly used in veterinary practice. Occasionally, the administered dose of dexmedetomidine may result in insufficient sedation, and an additional dose or drug may be required. The sedative effects of seven different drugs administered at subsequent time points after an initial, insufficient dose of dexmedetomidine were evaluated. Seven adult cats participated in this crossover, blind, randomised study. The groups consisted of two consecutive doses of dexmedetomidine (15 + 10 μg/kg) (DD) or a dose of dexmedetomidine (15 μg/kg) followed by either NS 0.9% (DC-control group), tramadol 2 mg/kg (DT), butorphanol 0.2 mg/kg (DBT), buprenorphine 20 μg/kg (DBP), ketamine 2 mg/kg (DK), or midazolam 0.1 mg/kg (DM). Sedation was evaluated using the Grint sedation scale. In all groups, atipamezole was administered at the end of the evaluation, and recovery was assessed using the Lozano and Sams recovery scales. The DC and DM groups exhibited minimal sedative effects. The maximum sedative effect was observed in the DD and DK groups, while sedation in the DD and DK groups was significantly higher compared to the DC group. Recovery in all groups was uneventful, except in the DM group, where it was prolonged and difficult, although no statistically significant difference was detected. Therefore, insufficient sedation with dexmedetomidine can be enhanced by a subsequent dose of dexmedetomidine, ketamine, or butorphanol, whereas the addition of midazolam reduces sedation and prolongs recovery.

Sedative and cardiorespiratory effects of dexmedetomidine alone or combined with acepromazine in healthy cats

The purpose of this study was to assess sedation, emesis and cardiovascular effects of dexmedetomidine alone or combined with acepromazine in healthy cats. Fourteen male cats aged 0.9 ± 0.5 years and weighing 3.7 ± 0.7 kg were randomly assigned to one of two experimental groups: GD, dexmedetomidine 5 µg/kg; and GDA, dexmedetomidine 5 µg/kg with acepromazine 0.03 mg/kg, all intramuscularly. Measurements were recorded at baseline, at 20 minutes and then at 10-minute intervals following sedation and included heart rate (HR), respiratory rate (FR), systolic arterial pressure (SAP), rectal temperature (RT), number of episodes of emesis and sedation score (0-4). Data were compared using ANOVA for repeated measures followed by Šídák and Dunnet test. Sedation scores were compared between groups at T20 using Mann-Whitney test. Significance was considered when P <0.05. At T20, HR was significantly lower in GDA (99 ± 14 beats/min) compared with GD (133 ± 19 beats/min) and SAP was significantly lower in both groups compared with baseline (126 ± 14 vs. 148 ± 26 and 111 ± 13 vs. 144 ± 17 mmHg in GD and GDA, respectively). Duration of sedation was similar between groups, although sedation scores differed significantly at T20, with 1 (0-4) in GD and 4 (4-4) in GDA. More episodes of emesis were recorded in GD compared with GDA. The combination of dexmedetomidine and acepromazine produced more profound sedation with faster onset and lower incidence of emesis compared with dexmedetomidine alone in healthy cats.

DEXMEDETOMIDINE ALONE OR COMBINED WITH MORPHINE FOR EPIDURAL ANESTHESIA IN BITCHES UNDERGOING ELECTIVE OVARIOHYSTERECTOMY

The purpose of this study was to assess perioperative analgesia provided by the combination of epidural dexmedetomidine and morphine in bitches undergoing elective ovariohysterectomy. Twenty-four bitches were included in the study and allocated into three groups: GM, morphine 0.1 mg/kg; GD, dexmedetomidine 2 µg/kg; and GDM, dexmedetomidine and morphine at the same doses. All solutions were diluted in saline to a total of 0.36 mL/kg. Heart rate (HR), respiratory rate (FR) and systolic blood pressure (SAP) were recorded prior to epidural analgesia (TB), immediately following epidural analgesia (TEA), at surgical incision (TSI), at the first ovarian pedicle clamping (TOP1), at the second pedicle clamping (TOP2), at uterine stump clamping (TUC), at the start of abdominal cavity closure (TSC) and at the end of skin closure (TEC). Rescue analgesia with fentanyl was administered at 2 µg/kg IV if nociception corresponding to a 20% increase of any cardiorespiratory variables was noted. Postoperative pain assessment was performed using a modified composite Glasgow pain scale along the first 6 hours following the end of surgery. Numeric data were compared using ANOVA for repeated measures followed by Tukey test and ovarian ligament relaxation was analyzed using chi-square test under 5% significance. No differences were found on FR among times or groups, although HR showed significant differences between GM and GD at TSI, TOP1, TOP2, TSC and TEC and between GM and GDM at TEA and TSI (significantly lower HR values recorded in dexmedetomidine groups). Differences among time points were found on HR between TB and TEA in GD and on PAS between TOP1 and TSC in GM and between TOP1 and TUC in GDM (p<0.05). Ovarian ligament relaxation was significantly more present in groups using dexmedetomidine, although the number of rescue analgesia administrations did not differ among groups. Kaplan-Meyer analysis failed to show significant differences on time of rescue analgesia administration among groups (p>0.05). In conclusion, the combination of epidural dexmedetomidine and morphine is a more interesting choice for elective ovariohysterectomy in bitches for producing analgesia comparable to that of each drug alone, with noticeable relaxation of ovarian ligaments and lesser cardiovascular consequences.

Ketamine-dexmedetomidine combined with local anesthesia, with or without different doses of atipamezole in the postoperative period, for orchiectomy in cats

OBJECTIVE

To evaluate the anesthetic and cardiopulmonary effects of ketamine-dexmedetomidine combined with local anesthesia, associated or not in the postoperative period with different doses of atipamezole, for orchiectomy in cats.

ANIMALS

24 healthy cats.

PROCEDURES

Cats received ketamine (7 mg/kg) combined with dexmedetomidine (10 µg/kg) IM, and 1 mL of saline (group KDSAL), 25 µg/kg (group KDAT25), or 50 µg/kg (group KDAT50) of atipamezole IV, postoperatively. All cats received local anesthesia (2 mg/kg of lidocaine) intratesticular and SC. Physiologic variables were recorded at baseline and at time points during anesthesia. Ketamine rescue dose (1 mg/kg) was recorded. The quality of recovery, the degree of sedation, and side effects were evaluated postoperatively.

RESULTS

2 cats received a single additional bolus of ketamine to perform local anesthesia. Heart rate was lower in KDSAL, KDAT25, and KDAT50 during anesthesia, compared with baseline. Hypertension was observed intraoperatively in all groups. The time to head up, pedal reflex regained time, time to sternal recumbency, and time to standing were shorter in KDAT25 and KDAT50 compared to KDSAL. Lower sedation scores were assigned sooner to KDAT25 and KDAT50 than KDSAL. All groups resulted in low recovery quality scores and no side effects.

CLINICAL RELEVANCE

At the doses used, ketamine-dexmedetomidine combined with local anesthesia allowed the performance of orchiectomy. Rescue dose of ketamine for performing local anesthesia may be required. This combination can result in hypertension. Both atipamezole doses shortened the anesthetic recovery, without differences among them, and side effects.

Effect of Dexmedetomidine Low Doses with or without Midazolam in Cats: Clinical, Hemodynamic, Blood Gas Analysis, and Echocardiographic Effects

Objectives

The aim of the study is to compare the sedative, cardiorespiratory, echocardiographic, and blood gas effects of dexmedetomidine and methadone associated or not with midazolam for restraint chemistry in cats.

Methods

Eighteen healthy young cats (4.06 ± 0.48 kg) were randomly sedated with two protocols, through the intramuscular route: dexmedetomidine (5 µg.kg-1), methadone (0.3 mg. kg-1) and midazolam (0.3 mg. kg-1) (DMTM, n = 9), or dexmedetomidine (7.5 µg.kg-1) and methadone (0.3 mg. kg-1) (DMT, n = 9). The cardiorespiratory parameters were measured at baseline, 5 and 10 minutes after pharmacological latency. The sedation, analgesia, and muscle relaxation scores were assessed before and 5 minutes after pharmacological latency, while arterial blood gas analysis and echocardiography were assessed before and after 10 or 15 minutes, respectively.

Results

There was no difference between the protocols regarding the cardiorespiratory, blood gas, and echocardiographic parameters used. The scores for sedation, analgesia, and muscle relaxation also did not differ between the protocols, with the degree of sedation, analgesia, and myorelaxation considered satisfactory in both groups. A significant decrease in heart rate (HR) was observed after administration of the sedative protocols, reaching a maximum reduction at T10 (46% and 53% reduction in the DMT and DMTM groups, respectively). The reduction in HR had an impact on echocardiographic parameters such as CO, which decreased 53% and 56% in the DMT and DMTM groups, respectively. There was a significant reduction in PaO2, SaO2, ejection fraction, and fractional shortening in both protocols. SpO2 decreased significantly after 5 minutes of sedation in the DMT group, but with a minimum mean SpO2 of 92% in T5. The respiratory rate decreased significantly at 5 and 10 minutes in the DMTM group, while PaCO2 increased in both groups, indicating respiratory depression caused by the drugs. Conclusions and Relevance. The study pointed out that both sedative protocols can be recommended for clinical sedation of young and healthy cats in the doses used. However, both protocols resulted in cardiorespiratory depression in cats and also the particularities of the animals should be evaluated regarding reducing cardiac output by more than 50%.

Effect of administering dexmedetomidine with or without atropine on cardiac troponin I level in isoflurane-anesthetized dogs

We aimed to determine whether dexmedetomidine administration with or without atropine increases cardiac troponin I (cTnI) level in healthy dogs. We hypothesized that 10 µg/kg dexmedetomidine + atropine increases the cTnI level, whereas 5 µg/kg dexmedetomidine + atropine does not. Eighteen healthy, pet dogs that underwent an orthopedic surgery or ovariohysterectomy were included in this study. The dogs were randomly assigned to atropine (0.02 mg/kg)–dexmedetomidine (10 µg/kg), saline–dexmedetomidine (10 µg/kg), and atropine (0.02 mg/kg)–dexmedetomidine (5 µg/kg) groups. Each dog was premedicated with atropine or saline intramuscularly (IM). After 10 min, they were IM injected with dexmedetomidine (10 or 5 µg/kg)–morphine (0.5 mg/kg)–midazolam (0.2 mg/kg). Following this, anesthesia was induced after 10 min with propofol and maintained with isoflurane in 100% oxygen. The median plasma cTnI level at 6, 12 and 24 hr after premedication was significantly higher than that at baseline. The cTnI level in the atropine–dexmedetomidine (10 µg/kg) group was significantly higher than that in the saline–dexmedetomidine (10 µg/kg) and atropine–dexmedetomidine (5 µg/kg) groups at 6 and 12 hr after premedication. The cTnI level returned to normal within 72 hr after premedication in all groups. The administration of atropine in combination with 10 µg/kg dexmedetomidine increased the cTnI level, indicating subclinical myocardial damage.

Hyperinsulinemia/euglycemia and intravenous lipid emulsion therapy for the management of severe amlodipine toxicosis in a cat

Calcium-channel blockers (CCBs) are widely used in people and animals. Overdose can result in cardiovascular collapse and death. Hyperinsulinemia/euglycemia therapy (HIET) and intralipid therapy (ILT) are reported treatment options in people. This is the first report describing HIET and ILT as treatments for amlodipine toxicosis in a cat.

Reversal effects of atipamezole, flumazenil, and 4-aminopyridine on bradycardia and increases in blood pressures induced by medetomidine, midazolam, and ketamine in isoflurane-anesthetized cats

OBJECTIVE

To investigate the effects of a fixed dose of atipamezole (AT), flumazenil (FL), and 4-aminopyridine (AP), both alone and in combination, on changes in arterial blood pressure and heart rate induced by medetomidine (ME), midazolam (MI), and ketamine (KE) under isoflurane anesthesia with controlled ventilation in healthy cats.

DESIGN

Prospective experimental study.

SETTING

University animal research facility.

ANIMALS

Healthy adult mixed-breed cats were used for 8 investigation groups (6 cats per group), with ≥2 weeks between interventions.

INTERVENTIONS

Cats were anesthetized with an end-tidal isoflurane concentration of 2% under controlled ventilation. A catheter was inserted into the right or left femoral artery for arterial pressure monitoring and blood gas sampling, and ECG electrodes were placed. Upon completed preparations, cats were administered a mixture of ME (0.05 mg/kg) and MI (0.5 mg/kg), followed 10 minutes later by intramuscular KE (10 mg/kg). Twenty minutes after KE injection, the cats received IV injection with either a physiological saline solution at 0.1 mL/kg (control), or 1 of 7 variations of experimental drugs, alone or in combination: AT (0.2 mg/kg), FL (0.1 mg/kg), AP (0.5 mg/kg), AT+FL, FL+AP, AT+AP, and AT+FL+AP. Arterial blood pressure and heart rate were continuously measured over 120 minutes after administration of potential antagonists.

MEASUREMENTS AND MAIN RESULTS

ME+MI+KE induced an increase in blood pressure and bradycardia. Potential antagonists alone or in combination did not significantly alter the bradycardia. FL, AP alone, and FL+AP did not significantly alter the changes in blood pressures induced by ME+MI+KE. Meanwhile, administration of AT alone or in combination reversed the increase in blood pressure induced by ME+MI+KE but transiently caused excessive hypotension.

CONCLUSION

These results revealed that AT alone or in combination is effective for antagonizing hypertension induced by ME+MI+KE; however, attention should be paid to temporary hypotension in cats anesthetized with isoflurane.

Sedative effects of acepromazine in combination with nalbuphine or butorphanol, intramuscularly or intravenously, in healthy cats: a randomized, blinded clinical trial

OBJECTIVES

The aim of this study was to compare the sedative effects in cats administered acepromazine-nalbuphine and acepromazine-butorphanol, intramuscularly (IM) and intravenously (IV), and the occurrence of adverse cardiorespiratory effects.

METHODS

Forty-six cats were randomly divided into four groups and administered acepromazine (0.05 mg/kg) combined with nalbuphine (0.5 mg/kg) or butorphanol (0.4 mg/kg), IV (ACP-NALIV and ACP-BUTIV groups, respectively) or IM (ACP-NALIM and ACP-BUTIM groups, respectively). Sedation scores, ease of intravenous catheter placement (simple descriptive scale [SDS] scores), physiologic variables, venous blood gases and the propofol dose required for anesthetic induction were recorded.

RESULTS

Mild sedation was observed in all groups approximately 30 mins after treatment administration (timepoint T1, prior to propofol administration). Sedation scores at T1 increased above baseline in all groups (P <0.05), but no significant difference was observed among groups. Dynamic interactive visual analogue scale sedation scores (range 0-100 mm) recorded at T1 were (median [interquartile range]): ACP-NALIM, 12 (10-12); ACP-NALIV, 11 (6-16); ACP-BUTIM, 11 (7-14); and ACP-BUTIV, 12 (7-19). Overall, SDS scores did not change from baseline at T1 and there was no significant difference among groups. The propofol dose did not differ among groups. Blood gases remained within the reference intervals for cats. Significant decreases from baseline were detected for all groups in systolic arterial pressure (SAP). Mean ± SD values at T1 were (mmHg): ACP-NALIM, 108 ± 13; ACP-NALIV, 102 ± 10; ACP-BUTIM, 97 ± 13; and ACP-BUTIV, 98 ± 21. Arterial hypotension (SAP <90 mmHg) was recorded at T1 in 0/11, 1/13, 4/11 and 5/11 cats in groups ACP-NALIM, ACP-NALIV, ACP-BUTIM and ACP-BUTIV, respectively, and was further exacerbated after the induction of anesthesia with propofol.

CONCLUSIONS AND RELEVANCE

In healthy cats administered acepromazine-nalbuphine and acepromazine-butorphanol, IM and IV, the degree of sedation was mild regardless of the protocol and the route of administration. The main adverse effect observed was a reduction in arterial blood pressure.

Comparison of intraperitoneal ropivacaine and ropivacaine-dexmedetomidine for postoperative analgesia in cats undergoing ovariohysterectomy

OBJECTIVE

To investigate the intraperitoneal (IP) administration of ropivacaine or ropivacaine-dexmedetomidine for postoperative analgesia in cats undergoing ovariohysterectomy.

STUDY DESIGN

Prospective, randomized, blinded, positively controlled clinical study.

ANIMALS

A total of 45 client-owned cats were enrolled.

METHODS

The cats were administered intramuscular (IM) meperidine (6 mg kg^-1) and acepromazine (0.05 mg kg^-1). Anesthesia was induced with propofol and maintained with isoflurane. Meloxicam (0.2 mg kg^-1) was administered subcutaneously in all cats after intubation. After the abdominal incision, the cats were administered one of three treatments (15 cats in each treatment): IP instillation of 0.9% saline solution (group Control), 0.25% ropivacaine (1 mg kg^-1, group ROP) or ropivacaine and dexmedetomidine (4 μg kg^-1, group ROP-DEX). During anesthesia, heart rate (HR), electrocardiography, noninvasive systolic arterial pressure (SAP) and respiratory variables were monitored. Sedation and pain were assessed preoperatively and at various time points up to 24 hours after extubation using sedation scoring, an interactive visual analog scale, the UNESP-Botucatu multidimensional composite pain scale (MCPS) and mechanical nociceptive thresholds (MNT; von Frey anesthesiometer). Rescue analgesia (morphine, 0.1 mg kg^-1) IM was administered if the MCPS ≥6. Data were analyzed using the chi-square test, Tukey test, Kruskal-Wallis test and Friedman test (p < 0.05).

RESULTS

HR was significantly lower in ROP-DEX compared with Control (p = 0.002). The pain scores, MNT, sedation scores and the postoperative rescue analgesia did not differ statistically among groups.

CONCLUSIONS AND CLINICAL RELEVANCE

As part of a multimodal pain therapy, IP ropivacaine-dexmedetomidine was associated with decreased HR intraoperatively; however, SAP remained within normal limits. Using the stated anesthetic protocol, neither IP ropivacaine nor ropivacaine-dexmedetomidine significantly improved analgesia compared with IP saline in cats undergoing ovariohysterectomy.

Assessment of hydromorphone and dexmedetomidine for emesis induction in cats

OBJECTIVE

To compare the efficacy of hydromorphone and dexmedetomidine at inducing emesis in cats.

DESIGN

Prospective, blinded, randomized crossover study.

SETTING

Veterinary university teaching hospital.

ANIMALS

12 healthy purpose-bred cats.

INTERVENTIONS

Cats were randomly assigned to receive hydromorphone (0.1 mg/kg, subcutaneously) or dexmedetomidine (7 μg/kg, IM). Following administration, the incidences of emesis, number of emetic events, signs of nausea (hypersalivation, lip licking), temperature, heart rate, respiratory rate, and sedation score were recorded for 6 hours.

MEASUREMENTS AND MAIN RESULTS

Emesis was successful in 9 of 12 (75%) cats when treated with hydromorphone and in 7 of 12 (58%) cats when treated with dexmedetomidine (P = 0.67). Dexmedetomidine was more likely to cause sedation than hydromorphone (P < 0.001). Heart rate in cats was significantly decreased at 1 and 2 hours post-hydromorphone (P = 0.003, 0.014, respectively) and at 1, 2, 3, 5, 6 hours post-dexmedetomidine (P = 0.001, 0.003, 0.038, 0.013, 0.001, respectively). Cats were more likely to develop an increase in body temperature with hydromorphone administration although this was not clinically significant.

CONCLUSIONS

Results of the present study indicate that hydromorphone is an effective alternative to dexmedetomidine for the induction of emesis in cats. Hydromorphone appears to cause less sedation and less decrease in heart rate. Further investigation into the most adequate dose of hydromorphone for optimizing emesis is warranted.

Thermal antinociceptive, sedative and cardiovascular effects of Governing Vessel 1 dexmedetomidine pharmacopuncture in healthy cats

OBJECTIVE

To compare the antinociceptive, sedative and cardiovascular effects of dexmedetomidine pharmacopuncture at Governing Vessel 1 (GV 1) with dexmedetomidine intramuscular (IM) administration.

STUDY DESIGN

Randomized, masked crossover design.

ANIMALS

A group of eight healthy female cats.

METHODS

Cats were randomly administered either dexmedetomidine (0.005 mg kg^-1; Dex-IM) IM or at acupuncture point GV 1 (Dex-P) separated by 1 week. Prior to and up to 120 minutes posttreatment, skin temperature (ST), thermal threshold (TT), heart rate (HR), respiratory rate (f_R), sedation, muscle relaxation and auditory response scores were recorded. Parametric data were analyzed using a two-way repeated measures anova followed by Tukey's test for multiple comparisons. Nonparametric data were analyzed using a Friedman test followed by Dunn's multiple comparisons test, and Wilcoxon signed-rank test with Bonferroni correction for multiple comparisons. Significance was set at p ≤ 0.05.

RESULTS

There were no differences within or between treatments for ST, f_R and auditory response. TT was significantly higher at 30-90 minutes in Dex-P (p ≤ 0.0285) than baseline. TT was significantly higher at 60-90 minutes for Dex-P than for Dex-IM (p ≤ 0.0252). HR was significantly lower at 10-75 minutes in Dex-P (p ≤ 0.0378) and at 5-75 minutes in Dex-IM (p ≤ 0.0132) than baseline. Compared with baseline, sedation scores were higher at 25 minutes (p = 0.0327) and 30 minutes (p = 0.0327), and muscle relaxation scores were higher at 25 minutes (p = 0.0151) and 35 minutes (p = 0.0151) in Dex-P. There were no differences in HR, sedation and muscle relaxation scores between treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Dex-P increased thermal antinociception compared with Dex-IM at the same dose of dexmedetomidine in cats. This antinociceptive effect must be evaluated under clinical situations.

The effect of aquapuncture at Pericardium 6 (PC-6) on dexmedetomidine-induced nausea and vomiting in cats

OBJECTIVE

To determine the effect of aquapuncture at acupuncture point Pericardium 6 (PC-6) on the incidence of dexmedetomidine-induced vomiting and nausea in cats.

STUDY DESIGN

Randomized, prospective, crossover study.

ANIMALS

A group of 22 cats, 14 females and eight males, aged 1-12 years and weighing 3.8-5.9 kg.

METHODS

Each cat was administered treatments in random order at ≥1 week intervals. For treatment (DEX-A), cats were administered PC-6 stimulation by aquapuncture (0.25 mL/250 μg vitamin B12 injection subcutaneously at PC-6). After 30 minutes, dexmedetomidine (10 μg kg^-1) was administered intramuscularly (IM). For control treatment (DEX), cats were administered only dexmedetomidine (10 μg kg^-1) IM. Incidence of vomiting, number of vomiting episodes and time to first vomiting were recorded by an observer unaware of treatment allocation. At 30 minutes after dexmedetomidine administration, atipamezole (0.1 mg kg^-1) was injected IM. Behavior was video recorded and later scored by two observers for clinical signs of nausea. A regression model (analysis of covariance) was used to detect the influence of aquapuncture on vomiting and nausea. Significance was set at p < 0.05.

RESULTS

Of 21 cats, 18 (85%) and 16 cats (76%) vomited in DEX-A and DEX, respectively. There was no significant difference in the incidence of vomiting (p = 0.55), number of vomiting episodes (p = 0.55), mean time to vomit (p = 0.88) or nausea score (p = 0.51) between DEX-A and DEX.

CONCLUSIONS AND CLINICAL RELEVANCE

PC-6 aquapuncture did not reduce the incidence of dexmedetomidine-induced vomiting or severity of nausea in cats.

AAFP Feline Anesthesia Guidelines

AIM

The overarching purpose of the AAFP Anesthesia Guidelines (hereafter referred to as the 'Guidelines') is to make anesthesia and sedation safer for the feline patient. Scope and accessibility: It is noteworthy that these are the first exclusively feline anesthesia guidelines authored by an expert panel, making them particularly useful as an extensively referenced, practical resource for veterinary practice teams. Because much of the key content is presented in tabular or visual format, the Guidelines have a high level of accessibility and convenience that invites regular usage. While the recommendations in the Guidelines focus primarily on client-owned cats, the content is also applicable to community-sourced animals with an unknown medical history.

Effects of sedation with dexmedetomidine and buprenorphine on echocardiographic variables, blood pressure and heart rate in healthy cats

Objectives Sedative agents are occasionally used to enable echocardiographic examination when screening cats for heart disease, such as hypertrophic cardiomyopathy (HCM). Owing to their haemodynamic effects, sedative agents may alter echocardiographic measurements. The aim of the study was to evaluate the effects of the sedative combination dexmedetomidine and buprenorphine on echocardiographic variables, blood pressure (BP) and heart rate (HR) in healthy cats. Methods Fifty healthy, client-owned cats were prospectively recruited and included after physical examination. Cats were sedated intramuscularly with dexmedetomidine and buprenorphine, according to body weight. Blood pressure and HR measurements, echocardiographic and Doppler examinations were performed prior to sedation and repeated once cats had achieved acceptable sedation. Results Left ventricular internal diameter at end-diastole and systole, right ventricular internal diameter at end-diastole, left atrium (LA), pulmonary artery (PA) deceleration time, and systolic, diastolic and mean arterial blood pressure increased after sedation ( P ⩽0.022). Aortic and PA maximum velocity, fractional shortening, PA acceleration/deceleration time and HR decreased after sedation ( P <0.0001). Interventricular septum at end-diastole and systole, left ventricular posterior wall at end-diastole and systole, aortic diameter (Ao), left atrial/aortic diameter (LA/Ao) and pulmonic acceleration time did not change. Conclusions and relevance Blood pressure increased and HR decreased post-sedation. While wall thickness and LA/Ao were not affected by sedation, indices of LA and left ventricular size increased. Further studies are needed using cats with HCM to assess the effect of this sedative combination on HCM screening results.

Hemodynamic effects of low-dose atipamezole in isoflurane-anesthetized cats receiving an infusion of dexmedetomidine

Objectives The objective of this study was to evaluate the cardiovascular effects of low-dose atipamezole administered intravenously to isoflurane-anesthetized cats receiving dexmedetomidine. We hypothesized that atipamezole would increase heart rate (HR) and reduce arterial blood pressure in isoflurane-anesthetized cats receiving dexmedetomidine. Methods Six healthy adult domestic shorthair cats were anesthetized with isoflurane and instrumented for direct arterial pressures and cardiac output (CO) measurements. The cats received a target-controlled infusion of dexmedetomidine (target plasma concentration 10 ng/ml) for 30 mins before administration of atipamezole. Two sequential doses of atipamezole (15 and 30 μg/kg IV) were administered at least 20 mins apart, during dexmedetomidine administration. The effects of dexmedetomidine and each dose of atipamezole on HR, mean arterial blood pressure (MAP), CO and systemic vascular resistance (SVR) were documented. Results Dexmedetomidine reduced the HR by 22%, increased MAP by 78% (both P ⩽0.01), decreased CO by 48% and increased SVR by 58% (both P ⩽0.0003). Administration of atipamezole 15 and 30 μg/kg intravenously increased HR by 8% ( P = 0.006) and 4% ( P = 0.1), respectively. MAP decreased by 39% and 47%, respectively (both P ⩽0.004). Atipamezole 30 μg/kg returned CO and SVR to baseline values. Conclusions and relevance Low doses of atipamezole (15 and 30 μg/kg) administered intravenously to anesthetized cats decreased arterial blood pressure with only marginal increases in HR. Atipamezole 30 μg/kg restored CO and SVR to baseline values before dexmedetomidine administration.

Avaliação da dexmedetomidina e do tramadol, associados ao midazolam, em gatas anestesiadas com isoflurano e submetidas à ovário-histerectomia

RESUMO Objetivou-se comparar as alterações cardiorrespiratórias e a analgesia pós-operatória promovidas pela dexmedetomidina e pelo tramadol, quando associados ao midazolam, em felinas. Para tal, foram selecionadas 18 gatas hígidas, divididas em dois grupos randomizados: GDM, tratadas com dexmedetomidina (10µg/kg) e GTM, tratadas com tramadol (2mg/kg), ambos associados a midazolam (0,2mg/kg,) IM. Após 15 minutos, procedeu-se à indução anestésica com propofol (1,46±0,79mL), mantendo-se a anestesia com isoflurano. As felinas foram submetidas à ovário-histerectomia, registrando-se as variáveis cardiorrespiratórias 15 minutos após a MPA (M0), 15 minutos após a indução (M15) e sequencialmente a cada cinco minutos, até o término do procedimento cirúrgico (M20, M25, M30, M35 e M40). A avaliação da dor iniciou-se 30 minutos após o término do procedimento cirúrgico (MP30) e sequencialmente em intervalos de 30 minutos (MP60, MP90, MP120). A partir do MP120, as avaliações foram registradas a cada hora (MP180, MP240 e MP360). A associação dexmedetomidina-midazolam infere diminuição inicial de frequência cardíaca (FC) sem significado clínico e está relacionada à sedação mais pronunciada, à analgesia menor e menos duradoura e a episódios de êmese, quando comparada à associação tramadol-midazolam. Ambos os protocolos denotaram estabilidade cardiorrespiratória e podem ser considerados seguros em felinas submetidas à ovário-histectomia.

Comparison of Intravenous Dexmedetomidine and Midazolam for Bispectral Index-Guided Sedation During Spinal Anesthesia

Background

Despite the high frequency of hypotension during spinal anesthesia with proper sedation, no previous report has compared the hemodynamic effects of dexmedetomidine and midazolam sedation during spinal anesthesia. We compared the effects of bispectral index (BIS)-guided intravenous sedation using midazolam or dexmedetomidine on hemodynamics and recovery profiles in patients who underwent spinal anesthesia.

Material/Methods

One hundred and sixteen adult patients were randomly assigned to receive either midazolam (midazolam group; n=58) or dexmedetomidine (dexmedetomidine group; n=58) during spinal anesthesia. Systolic, diastolic, and mean arterial pressures; heart rates; peripheral oxygen saturations; and bispectral index scores were recorded during surgery, and Ramsay sedation scores and postanesthesia care unit (PACU) stay were monitored.

Results

Hypotension occurred more frequently in the midazolam group (P<0.001) and bradycardia occurred more frequently in the dexmedetomidine group (P<0.001). Mean Ramsay sedation score was significantly lower in the dexmedetomidine group after arrival in the PACU (P=0.025) and PACU stay was significantly longer in the dexmedetomidine group (P=0.003).

Conclusions

BIS-guided dexmedetomidine sedation can attenuate intraoperative hypotension, but induces more bradycardia, prolongs PACU stay, and delays recovery from sedation in patients during and after spinal anesthesia as compared with midazolam sedation.

COMPARISON BETWEEN DEXMEDETOMIDINE-S-KETAMINE AND MIDAZOLAM-S-KETAMINE IN IMMOBILIZATION OF ONCILLA (LEOPARDUS TIGRINUS)

Established immobilization protocols are required for safe procedures on wildlife and zoo animals. This study evaluated the cardiovascular, respiratory, and anesthetic effects of dexmedetomidine (40 μg/kg) with S-ketamine (5 mg/kg) and midazolam (0.5 mg/kg) with S-ketamine (5 mg/kg) in 12 specimens of oncilla (Leopardus tigrinus) at Quinzinho de Barros Municipal Zoo Park in Sorocaba, São Paulo, Brazil, between January and March 2010. Each animal underwent both protocols, totaling 24 anesthetic procedures. The dexmedetomidine-S-ketamine group (DK) showed a decrease in heart rate compared to initial values and significantly lower heart rate and oxyhemoglobin saturation values compared to Midazolam-S-Ketamine Group (MK). Four animals in DK had episodes of sinus pauses. Systemic blood pressure, respiratory frequency, and rectal temperature showed no significant differences between groups. The dexmedetomidine-S-ketamine group showed a greater degree of muscle relaxation and allowed for more thorough and longer oral evaluations. The dexmedetomidine-S-ketamine group had a shorter period of recumbency, longer period to return of muscle tone, and shorter recovery time. Two animals in MK did not reach recumbency. The dexmedetomidine-S-ketamine group had better qualities of induction and recovery. It may be concluded that both protocols can be safely used in oncillas. Midazolam-S-ketamine promotes effective chemical restraint for quick and minimally invasive procedures and dexmedetomidine-S-ketamine promotes effective chemical restraint for prolonged and more invasive procedures.

Accidental alfaxalone overdose in a mature cat undergoing anaesthesia for magnetic resonance imaging

Case summary This case report describes the clinical signs and treatment of an alfaxalone 10 times overdose in a 12-year-old cat undergoing anaesthesia for MRI. The cat was discharged from hospital following a prolonged recovery including obtunded mentation and cardiorespiratory depression for several hours following cessation of anaesthesia. The cat received supportive therapy that included supplemental oxygen via a face mask, intravenous crystalloid fluids and active rewarming. The benefits of using alfaxalone for maintenance of anaesthesia, its pharmacokinetics and previously reported lethal doses are discussed. Strategies for reducing the incidence of medication errors are presented. Relevance and novel information An unintentional overdose of alfaxalone by continuous rate infusion has not been reported previously in a cat. Treatment is supportive and directed towards maintenance of the cardiorespiratory systems. Whenever possible, smart pumps that have been designed to reduce human error should be used to help prevent medication errors associated with continuous rate infusions.

Effects of intramuscular sedation with alfaxalone and butorphanol on echocardiographic measurements in healthy cats

OBJECTIVES

The aim of the study was to evaluate the effects of intramuscular (IM) injections of alfaxalone combined with butorphanol on echocardiographic (ECG) measurements in cats.

METHODS

Client-owned adult domestic shorthair cats younger than 5 years of age were recruited. All cats that were considered healthy on the basis of physical examination, blood work, urinalysis, blood pressure measurement and baseline ECG underwent a second ECG under sedation. Cats were sedated with two separate IM injections of butorphanol at 0.2 mg/kg and alfaxalone at 2 mg/kg. ECG variables were analysed using a linear mixed model, and sedation scores were analysed using an ordinal mixed logistic model. The significance level was set at α = 0.05 and adjusted at α = 0.0017 for multiple comparisons of the ECG measurements.

RESULTS

Ten healthy cats were included. Sedation was uneventful, and recovery was smooth and quick for all cats. The mean duration of lateral recumbency was 36.3 ± 4.37 mins. Reduction in heart rate following sedation approached statistical significance (P = 0.002). The thickness of the interventricular septum, the thickness of the left ventricular free wall, and the left ventricular internal dimensions in diastole and systole were not affected by the sedation. The changes in left atrium/aortic ratio and shortening fraction were statistically significant. Although the peak velocity of early diastolic transmitral flow (E) and late diastolic transmitral flow (A), the peak early diastolic (Ea) mitral valve annulus velocity, and the peak late diastolic (Aa) mitral valve annulus velocity changed after sedation, the ratios E/A, E/Ea and Ea/Aa were not significantly different after sedation.

CONCLUSIONS AND RELEVANCE

IM injections of alfaxalone and butorphanol induced rapid, deep and short-lasting sedation. The mean differences after sedation were not clinically significant for most echocardiographic measurements.

Serum aldosterone and cortisol concentrations before and after suppression with fludrocortisone in cats

Primary hyperaldosteronism is an increasingly recognized syndrome in cats, and diagnosis can be difficult. A potential diagnostic method has been reported, utilizing oral fludrocortisone administered twice daily for 4 days followed by collection of urine. In the current study, we sought to determine if blood sampling and a shorter dosing period would provide a possible means to test for primary hyperaldosteronism. Also, cortisol concentrations were measured to assess the potential of fludrocortisone to act as a glucocorticoid in cats. In phase I, 8 healthy laboratory cats were studied in a placebo-controlled, crossover design. Serum aldosterone and cortisol concentrations were measured before and on the second, third, and fourth day of treatment and compared within groups. In phase II, based on the results obtained in phase I, 8 healthy client-owned cats were administered 3 doses of fludrocortisone or placebo. Serum aldosterone and cortisol concentrations were compared before and after treatment within groups. In both phases, serum aldosterone and cortisol concentrations were significantly suppressed in fludrocortisone-treated cats. Thus, it was determined that oral administration of fludrocortisone causes suppression of serum aldosterone in healthy adult cats after only 3 doses. Further research is needed to determine the effects of oral fludrocortisone in cats with primary hyperaldosteronism and cats with other disorders causing hypertension and/or hypokalemia to determine if this protocol can be used as a tool for the definitive diagnosis of primary hyperaldosteronism.

Relationship between plasma dexmedetomidine concentration and sedation score and thermal threshold in cats

OBJECTIVE

To characterize the relationship between plasma dexmedetomidine concentration and the temperature difference between the thermal threshold and skin temperature (ΔT) and between plasma dexmedetomidine concentration and sedation score in healthy cats.

ANIMALS

5 healthy adult spayed female cats.

PROCEDURES

Cats received IV administrations of saline (0.9% NaCl) solution, dexmedetomidine (5, 20, or 50 μg/kg), or acepromazine (0.1 mg/kg). Blood samples were collected and thermal threshold and sedation score were determined before and at various times up to 8 hours after drug administration. In addition, cats received an IV infusion of dexmedetomidine that targeted a concentration achieving 99% of the maximum effect on ΔT.

RESULTS

No change in ΔT over time was found for the saline solution and acepromazine treatments; ΔT increased for 45 minutes when cats received dexmedetomidine at 5 and 20 μg/kg and for 180 minutes when cats received dexmedetomidine at 50 μg/kg. No change in sedation score over time was found for saline solution. Sedation score increased for 120 minutes after cats received acepromazine and for 60, 120, and 180 minutes after cats received dexmedetomidine at 5, 20, and 50 μg/kg, respectively. The plasma dexmedetomidine concentration-effect relationships for the effect on ΔT and sedation score were almost identical. The plasma dexmedetomidine concentration after infusion was lower than targeted, and ΔT was not significantly affected.

CONCLUSIONS AND CLINICAL RELEVANCE

Dexmedetomidine administration to cats resulted in thermal analgesia and also profound sedation. These data may be useful for predicting the course of thermal analgesia and sedation after dexmedetomidine administration to cats.

Pharmacokinetics of dexmedetomidine after intravenous administration of a bolus to cats

OBJECTIVE

To characterize the pharmacokinetics of dexmedetomidine after IV administration of a bolus to conscious healthy cats.

ANIMALS

5 healthy adult spayed female cats.

PROCEDURES

Dexmedetomidine was administered IV as a bolus at 3 doses (5, 20, or 50 μg/kg) on separate days in a random order. Blood samples were collected immediately before and at various times for 8 hours after drug administration. Plasma dexmedetomidine concentrations were determined with liquid chromatography-mass spectrometry. Compartment models were fitted to the concentration-time data by means of nonlinear regression.

RESULTS

A 2-compartment model best fit the concentration-time data after administration of 5 μg/kg, whereas a 3-compartment model best fit the data after administration of 20 and 50 μg/kg. The median volume of distribution at steady-state and terminal half-life were 371 mL/kg (range, 266 to 435 mL/kg) and 31.8 minutes (range, 30.3 to 39.7 minutes), respectively, after administration of 5 μg/kg; 545 mL/kg (range, 445 to 998 mL/kg) and 56.3 minutes (range, 39.3 to 68.9 minutes), respectively, after administration of 20 μg/kg; and 750 mL/kg (range, 514 to 938 mL/kg) and 75.3 minutes (range, 52.2 to 223.3 minutes), respectively, after administration of 50 μg/kg.

CONCLUSIONS AND CLINICAL RELEVANCE

The pharmacokinetics of dexmedetomidine was characterized by a small volume of distribution and moderate clearance and had minimal dose dependence within the range of doses evaluated. These data will help clinicians design dosing regimens once effective plasma concentrations are established.

Effects of sedation on echocardiographic variables of left atrial and left ventricular function in healthy cats

Although sedation is frequently used to facilitate patient compliance in feline echocardiography, the effects of sedative drugs on echocardiographic variables have been poorly documented. This study investigated the effects of two sedation protocols on echocardiographic indices in healthy cats, with special emphasis on the assessment of left atrial size and function, as well as left ventricular diastolic performance. Seven cats underwent echocardiography (transthoracic two-dimensional, spectral Doppler, color flow Doppler and tissue Doppler imaging) before and after sedation with both acepromazine (0.1 mg/kg IM) and butorphanol (0.25 mg/kg IM), or acepromazine (0.1 mg/kg IM), butorphanol (0.25 mg/kg IM) and ketamine (1.5 mg/kg IV). Heart rate increased significantly following acepromazine/butorphanol/ketamine (mean±SD of increase, 40±26 beats/min) and non-invasive systolic blood pressure decreased significantly following acepromazine/butorphanol (mean±SD of decrease, 12±19 mmHg). The majority of echocardiographic variables were not significantly different after sedation compared with baseline values. Both sedation protocols resulted in mildly decreased left ventricular end-diastolic dimension and mildly increased left ventricular end-diastolic wall thickness. This study therefore failed to demonstrate clinically meaningful effects of these sedation protocols on echocardiographic measurements, suggesting that sedation with acepromazine, butorphanol and/or ketamine can be used to facilitate echocardiography in healthy cats.

Pharmacokinetics of dexmedetomidine administered intravenously in isoflurane-anesthetized cats

OBJECTIVE

To determine the pharmacokinetics of dexmedetomidine administered as a short-duration IV infusion in isoflurane-anesthetized cats.

ANIMALS

6 healthy adult domestic female cats.

PROCEDURES

Dexmedetomidine hydrochloride was injected IV (10 μg/kg over 5 minutes [rate, 2 μg/kg/min]) in isoflurane-anesthetized cats. Blood samples were obtained immediately prior to and at 1, 2, 5, 6, 7, 10, 15, 30, 60, 90, 120, 240, and 480 minutes following the start of the IV infusion. Collected blood samples were transferred to tubes containing EDTA, immediately placed on ice, and then centrifuged at 3,901 × g for 10 minutes at 4°C. The plasma was harvested and stored at -20°C until analyzed. Plasma dexmedetomidine concentrations were determined by means of liquid chromatography-mass spectrometry. Dexmedetomidine plasma concentration-time data were fitted to compartmental models.

RESULTS

A 2-compartment model with input in and elimination from the central compartment best described the disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats. Weighted mean ± SEM apparent volume of distribution of the central compartment and apparent volume of distribution at steady-state were 402 ± 47 mL/kg and 1,701 ± 200 mL/kg, respectively; clearance and terminal half-life (harmonic mean ± jackknife pseudo-SD) were 6.3 ± 2.8 mL/min/kg and 198 ± 75 minutes, respectively. The area under the plasma concentration curve and maximal plasma concentration were 1,061 ± 292 min•ng/mL and 17.6 ± 1.8 ng/mL, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats was characterized by a moderate clearance and a long terminal half-life.

Dexmedetomidine: clinical application as an adjunct for intravenous regional anesthesia

The selective α-2 adrenoceptor agonist, dexmedetomidine, has been shown to be a useful, safe adjunct in perioperative medicine. Intravenous regional anesthesia is one of the simplest forms of regional anesthesia and has a high degree of success. However, intravenous regional anesthesia is limited by the development of tourniquet pain and its inability to provide postoperative analgesia. To improve block quality, prolong postdeflation analgesia, and decrease tourniquet pain, various chemical additives have been combined with local anesthetics, although with limited success. The antinociceptive effects of α-2 adrenoceptor agonists have been shown in animals and in humans. However, less is known about the clinical effects of dexmedetomidine when coadministered with local anesthetics in patients undergoing intravenous regional anesthesia. This review examines what is currently known to improve our understanding of the properties and application of dexmedetomidine when used as an adjunct in intravenous regional anesthesia.