Christine Marie Egger DVM

Physiologic and antinociceptive effects following intramuscular administration of xylazine hydrochloride in combination with tiletamine-zolazepam in llamas

R Seddighi et al. — Fri, 03 May 2013 06:55:35 PDT

Objective-To evaluate antinociceptive and selected effects associated with IM administration of xylazine hydrochloride in combination with tiletamine-zolazepam in llamas. Animals-8 adult male llamas. Procedures-Each llama received tiletamine-zolazepam (2 mg/kg) combined with either xylazine (0.1, 0.2, or 0.4 mg/kg) or saline (0.9% NaCl) solution IM (treatments designated as TZ-Xy0.1, TZ-Xy0.2, TZ-Xy0.4, and TZ-Sal, respectively) at 1-week intervals. Selected cardiorespiratory variables were assessed during lateral recumbency and anesthesia, and recovery characteristics were recorded. Duration of antinociception was evaluated by clamping a claw every 5 minutes. Results-Interval between treatment administration and lateral recumbency for TZ-Xy0.4 was shorter than that for TZ-Xy0.1 or TZ-Sal. Mean ± SEM duration of antinociception was longer for TZ-Xy0.4 (51.3 ± 7. 0 minutes), compared with findings for TZ-Xy0.2 (31.9 ± 6.0 minutes), TZ-Xy0.1 (8.1 ± 4.0 minutes), and TZ-Sal (0.6 ± 0.6 minutes). Interval between treatment administration and standing was longer for TZ-Xy0.4 (112 ± 9 minutes) than it was for TZ-Xy0.2 (77 ± 9 minutes) or TZ-Sal (68 ± 9 minutes). Mean heart and respiratory rates during the first 30 minutes for TZ-Sal exceeded values for the other treatments. Administration of TZ-Xy0.2 and TZ-Xy0.4 resulted in Pao2 < 60 mm Hg at 5 minutes after llamas attained lateral recumbency, and values differed from TZ-Sal findings at 5, 10, and 15 minutes; Paco2 was greater for TZ-Xy0.2 and TZ-Xy0.4 than for TZ-Sal at 5, 10, 15, and 20 minutes. Conclusions and Clinical Relevance-Xylazine (0.2 and 0.4 mg/kg) increased the duration of antinociception in llamas anesthetized with tiletamine-zolazepam.

Repeated Administration of Tribromoethanol in C57BL/6NHsd Mice

William Allen Hill et al. — Fri, 03 May 2013 06:55:33 PDT

We evaluated the effect of repeated intraperitoneal administration of tribromoethanol on various parameters in C57BL/6NHsd mice. Mice (n = 68) were randomly assigned to 1 of 7 groups to receive tribromoethanol (500 mg/kg IP) on day 0 or days 0 and 8; vehicle (tert-amyl alcohol in sterile water) only on day 0 or days 0 and 8; sterile water injection on day 0 or days 0 and 8; or no treatment. A single dose of tribromoethanol failed to produce loss of pedal reflex and had no effect on median food and water consumption but altered median body weight on days 1 through 4 when compared with that in mice that received vehicle only or no treatment. Median body weight did not differ between mice that received a single dose of tribromoethanol and those that received an injection of water. Among mice given 2 doses of tribromoethanol, induction time, anesthetic duration, and recovery time varied widely. Repeated administration of tribromoethanol had no effect on median food and water consumption or body weight compared with those in controls. Median liver weight was significantly greater in mice that received 2 doses compared with a single dose of tribromoethanol. Median liver weight did not differ between untreated mice and those that received tribromoethanol. No significant organ or tissue pathology was observed in any study animal. Although tribromoethanol did not produce morbidity, mortality, or pathologic changes in treated animals, we urge caution in use of tribromoethanol in C57BL/6NHsd mice due to its variable anesthetic effectiveness.

Effect of nitrous oxide on the minimum alveolar concentration for sevoflurane and the minimum alveolar concentration derivatives that prevent motor movement and autonomic responses in dogs.

Reza Seddighi DVM, MS, PhD, Dip ACVA, cVMA et al. — Wed, 18 Apr 2012 12:04:43 PDT

OBJECTIVE: To investigate the effects of the concurrent administration of 70% N(2)O on the minimum alveolar concentration (MAC) for sevoflurane in dogs, the MAC derivative that blocks motor movement (MAC(NM)), and the MAC derivative that blocks autonomic responses (MAC(BAR)). ANIMALS: 7 adult sexually intact male mixed-breed dogs. PROCEDURES: For each dog, anesthesia was induced with sevoflurane delivered via a face mask. Initially, the baseline MAC, MAC(NM), and MAC(BAR) for sevoflurane were determined by use of a noxious stimulus (50 V, 50 Hz, and 10 milliseconds) applied subcutaneously over a midulnar region. Nitrous oxide (70%) was added to the breathing circuit, and MAC, MAC(NM), and MAC(BAR) were determined again. Percentage changes from the respective baseline concentrations for MAC, MAC(NM)' and MAC(BAR) were calculated after the administration of N(2)O. RESULTS: Baseline median values for the MAC, MAC(NM), and MAC(BAR) for sevoflurane were 1.75%, 2.00%, and 2.50%, respectively. Addition of 70% N(2)O significantly decreased MAC, MAC(NM), and MAC(BAR) by 24.4%, 25.0%, and 35.2%, respectively, and these values did not differ significantly from each other. CONCLUSIONS AND CLINICAL RELEVANCE: Supplementation with 70% N(2)O caused a clinically important and significant decrease in the MAC, MAC(NM)' and MAC(BAR) for sevoflurane in dogs.

The effect of midazolam on the end-tidal concentration of isoflurane necessary to prevent movement in dogs

Reza Seddighi et al. — Fri, 02 Sep 2011 12:54:07 PDT

OBJECTIVE: To determine the possible additive effect of midazolam, a GABA(A) agonist, on the end-tidal concentration of isoflurane that prevents movement (MAC(NM) ) in response to noxious stimulation. STUDY DESIGN: Randomized cross-over experimental study. ANIMALS: Six healthy, adult intact male, mixed-breed dogs. METHODS: After baseline isoflurane MAC(NM) (MAC(NM-B) ) determination, midazolam was administered as a low (LDS), medium (MDS) or high (HDS) dose series of midazolam. Each series consisted of two dose levels, low and high. The LDS was a loading dose (Ld) of 0.2 mg kg(-1) and constant rate infusion (CRI) (2.5 μg kg(-1) minute(-1)) (LDL), followed by an Ld (0.4 mg kg(-1)) and CRI (5 μg kg(-1) minute(-1)) (LDH). The MDS was an Ld (0.8 mg kg(-1)) and CRI (10 μg kg(-1) minute(-1)) (MDL) followed by an Ld (1.6 mg kg(-1)) and CRI (20 μg kg(-1) minute(-1)) (MDH). The HDS was an Ld (3.2 mg kg(-1)) and CRI (40 μg kg(-1) minute(-1)) (HDL) followed by an Ld (6.4 mg kg(-1)) and CRI (80 μg kg(-1) minute(-1)) (HDH). MAC(NM) was re-determined after each dose in each series (MAC(NM-T)). RESULTS: The median MAC(NM-B) was 1.42. MAC(NM-B) did not differ among groups (p > 0.05). Percentage reduction in MAC(NM) was significantly less in the LDS (11 ± 5%) compared with MDS (30 ± 5%) and HDS (32 ± 5%). There was a weak correlation between the plasma midazolam concentration and percentage MAC(NM) reduction (r = 0.36). CONCLUSION AND CLINICAL RELEVANCE: Midazolam doses in the range of 10-80 μg kg(-1) minute(-1) significantly reduced the isoflurane MAC(NM) . However, doses greater than 10 μg kg(-1) minute(-1) did not further decrease MAC(NM) indicating a ceiling effect.

Prognostic indicators for dogs and cats with cardiopulmonary arrest treated by cardiopulmonary cerebral resuscitation at a university teaching hospital

Christine Marie Egger — Fri, 02 Sep 2011 12:50:23 PDT

OBJECTIVE: To determine the association among signalment, health status, other clinical variables, and treatments and events during cardiopulmonary cerebral resuscitation (CPCR) with the return of spontaneous circulation (ROSC) for animals with cardiopulmonary arrest (CPA) in a veterinary teaching hospital. DESIGN: Cross-sectional study. ANIMALS: 161 dogs and 43 cats with CPA. PROCEDURES: Data were gathered during a 60-month period on animals that had CPA and underwent CPCR. Logistic regression was used to evaluate effects of multiple predictors for ROSC. RESULTS: 56 (35%) dogs and 19 (44%) cats had successful CPCR. Twelve (6%) animals (9 dogs and 3 cats) were discharged from the hospital. Successfully resuscitated dogs were significantly more likely to have been treated with mannitol, lidocaine, fluids, dopamine, corticosteroids, or vasopressin; had CPA while anesthetized; received chest compressions while positioned in lateral recumbency; and had a suspected cause of CPA other than hemorrhage or anemia, shock, hypoxemia, multiple organ dysfunction syndrome, cerebral trauma, malignant arrhythmia, or an anaphylactoid reaction and were less likely to have been treated with multiple doses of epinephrine, had a longer duration of CPA, or had multiple disease conditions, compared with findings in dogs that were not successfully resuscitated. Successfully resuscitated cats were significantly more likely to have had more people participate in CPCR and less likely to have had shock as the suspected cause of CPA, compared with findings in cats that were not successfully resuscitated. CONCLUSIONS AND CLINICAL RELEVANCE: The prognosis was grave for animals with CPA, except for those that had CPA while anesthetized.

Anesthesia case of the month. Multiform ventricular premature contractions and nonsustained ventricular tachycardia during anesthesia

L C. Love et al. — Fri, 02 Sep 2011 12:47:18 PDT

Survey of academic veterinarians' attitudes toward provision of cardiopulmonary-cerebral resuscitation and discussion of resuscitation with clientele

E H. Hofmeister et al. — Fri, 02 Sep 2011 12:32:50 PDT

Objective: To examine the impact of stress on veterinarians resulting from both the provision of cardiopulmonary-cerebral resuscitation (CPCR) and the discussion of CPCR and do not attempt resuscitation (DNAR) with affected clients. Design: Descriptive cross-sectional with survey methodology. Setting: Eight colleges of veterinary medicine in the United States. Subjects: Two hundred and one academic veterinarians. Interventions: The survey was distributed by the authors to small animal faculty, residents, and interns. Demographic variables and Likert-style questions about comfort discussing and performing CPCR and affective impact of CPCR events were included. Multiple linear regression models were constructed to determine the effect of the questions on different target variables of interest. Measurements and Main Results: Ninety-six percent of veterinarians experienced stress when performing CPCR and reported that positive emotions after a successful CPCR were statistically greater than the negative emotions of an unsuccessful CPCR. Veterinarians trained in CPCR reported lower scores for stress and negative emotional impact from a failed CPCR. Conclusions: Veterinarians experience stress during CPCR and when discussing CPCR and DNAR choices with owners. Steps can be taken to reduce the likelihood of having a negative affect from CPCR efforts, such as improved training of CPCR supervisors and increased competence of CPCR supervisors.

Dobutamine-induced bradycardia in a dog

E H. Hofmeister et al. — Fri, 02 Sep 2011 12:20:37 PDT

An otherwise healthy 8-year-old neutered male, mixed breed dog was anesthetized for surgical removal of multiple uroliths. Pre-anesthetic medication was midazolam, glycopyrrolate, and morphine. Anesthesia was induced with propofol and maintained with isoflurane in oxygen. One hour after induction, the patient moved and propofol was administered. Subsequently, the patient developed hypotension. Dobutamine administered at this time produced a rapid and profound decrease in heart rate that was treated successfully with atropine. The bradycardia in this case may be the result of the Bezold-Jarisch reflex, an intracardiac parasympathetic nervous reflex. Discontinuation of dobutamine and/or administration of a parasympatholytic drug should be performed if bradycardia occurs during dobutamine infusion.

Evaluation of diphenhydramine as a sedative for dogs

E Hofmeister et al. — Fri, 02 Sep 2011 12:17:44 PDT

OBJECTIVE: To determine and compare levels of sedation achieved by IM administration of diphenhydramine, saline (0.9% NaCl) solution, and acepromazine in dogs. DESIGN: Prospective randomized study. ANIMALS: 56 dogs. PROCEDURE: Dogs were randomly assigned to receive diphenhydramine at 2, 4, or 8 mg/kg (0.9, 1.8, or 3.6 mg/lb, respectively) i.m.; acepromazine at 0.1 mg/kg (0.05 mg/lb) i.m.; or saline solution at 0.05 mL/kg (0.02 mL/lb) i.m. Sedation was assessed by use of a 6-category descriptive system based on observation and interaction. RESULTS: Dogs in the acepromazine group had significantly higher sedation scores than did dogs in the saline solution or diphenhydramine groups at 30 minutes. Dogs in the diphenhydramine groups did not have significantly different sedation scores from dogs in the saline solution group at any time point. CONCLUSIONS AND CLINICAL RELEVANCE: Diphenhydramine did not cause clinically appreciable sedation in healthy dogs. Diphenhydramine is not suitable as a sole sedative prior to general anesthesia in dogs.

Anesthesia case of the month. Tachycardia

E H. Hofmeister et al. — Fri, 02 Sep 2011 12:14:43 PDT

Helical computed tomographic portography in ten normal dogs and ten dogs with a portosystemic shunt

P Frank et al. — Fri, 02 Sep 2011 12:10:33 PDT

Contrast enhanced helical computed tomography (CT) of the liver and portal system is routinely performed in human patients. The purpose of this project is to develop a practical protocol for helical CT portography in the dog. Ten clinically normal dogs were initially evaluated to develop a protocol. Using this protocol, ten dogs with confirmed portosystemic shunts (PSS) were then evaluated. Each patient was anesthetized, and a test dose of sodium iothalamate (400 mg I/ml) at 0.55 ml/kg was injected. Serial images were acquired at the level of T12-13 or T13-L1. The time to maximum enhancement of the portal vein was determined. This time period was used as the period between the second injection (2.2 ml/kg) and the start of the helical examination of the cranial abdomen. Delay times for normal dogs ranged from 34.5 s-66.0 s (median: 43.5 s) or 1.41 s/kg-4.12 s/kg (median: 2.09 s/kg). For patients with a PSS, the delay times were 16.5-70.5 s (median: 34.5 s) or 1.47-19.17 s/kg (median: 3.39 s/kg). The aorta, caudal vena cava, portal vein, shunt vessels, and their respective branches were well visualized on the CT images. Clinical case results were surgically confirmed. The surgeons reported that the information gained from the CT portography resulted in a subjective decrease in surgical time and degree of dissection necessary compared with similar surgeries performed without angiographic information. We believe that helical CT portography in the dog will be a useful adjunct in the diagnosis of PSS. The use of helical CT portography may allow clinicians to give clients a more accurate prognosis prior to surgery and will allow patients with lesions that are not surgically correctable to avoid a costly and invasive procedure.

Plasma fentanyl concentrations in awake cats and cats undergoing anesthesia and ovariohysterectomy using transdermal administration

Christine Marie Egger et al. — Fri, 02 Sep 2011 12:07:30 PDT

OBJECTIVE: To measure the plasma fentanyl concentrations achieved over time with transdermal fentanyl patches in awake cats and cats undergoing anesthesia and ovariohysterectomy. STUDY DESIGN: Randomized prospective experimental study. ANIMALS: Twenty-four purpose-bred cats. METHODS: Cats were randomly assigned to three groups for Part I of a larger concurrent study. Group P received only a 25 micro g hour-1 transdermal fentanyl patch. Group P/A received the patch and anesthesia. Group A received only anesthesia. After a minimum 1-week washout period, the cats were randomly reassigned to two groups for Part II of the larger study. Group P/A/O received the patch, anesthesia and ovariohysterectomy. Group A/O received anesthesia and ovariohysterectomy. Patches were left in place for 72 hours and plasma samples were obtained for fentanyl analysis while the patches were in place, and for 8 hours after patch removal for cats in Group P, P/A, and P/A/O. RESULTS: The 25 micro g hour-1 transdermal fentanyl patches were well tolerated by the cats in this study (mean body weight of 3.0 kg) and no overt adverse effects were noted. Mean plasma fentanyl concentrations over time, mean plasma fentanyl concentrations at specific times (8, 25, 49, and 73 hours after patch placement), time to first detectable plasma fentanyl concentration, time to reach maximum plasma fentanyl concentration, maximum plasma fentanyl concentration, mean plasma fentanyl concentration from 8 to 73 hours, elimination half-life, and total area under concentration (AUC) were not statistically different among the groups. CONCLUSIONS: Halothane anesthesia and anesthesia/ovariohysterectomy did not significantly alter the plasma fentanyl concentrations achieved or pharmacokinetic parameters measured, when compared with awake cats. There was a high degree of individual variability observed both within and between groups of cats in parameters measured. CLINICAL SIGNIFICANCE: The high degree of variability observed suggests that careful observation of cats with fentanyl patches in place is required to assess efficacy and any potential adverse effects. Anesthesia and anesthesia/ovariohysterectomy do not appear to alter plasma fentanyl concentrations achieved by placement of a 25 micro g hour-1 transdermal fentanyl patch when compared to cats not undergoing these procedures.

Open-heart correction of tetralogy of Fallot in an acyanotic dog

L J. Lew et al. — Fri, 02 Sep 2011 12:03:31 PDT

Tetralogy of Fallot was diagnosed in an acyanotic 11-month-old dog. Predicted pressure gradient across the pulmonic valve, as assessed by use of continuous wave Doppler echocardiography, was 94.5 mm Hg. Bidirectional shunting was identified by means of selective angiography. Open-heart correction was performed, using a transatrial approach with limited ventriculotomy and cardiopulmonary bypass. The hypertrophied infundibulum was resected, the ventricular septal defect was closed primarily, and a transannular pericardial patch graft was applied. Pressure gradients across the pulmonic valve were 52.9 and 22.8 mm Hg 2 weeks and 4 months after surgery, respectively. Advances in cardiopulmonary bypass, anesthetic management, and use of the transatrial approach may improve the success of open-heart correction of tetralogy of Fallot in dogs.

Cardiopulmonary effects of propofol infusion in llamas

T Duke et al. — Fri, 02 Sep 2011 11:53:40 PDT

OBJECTIVE: To evaluate selected cardiopulmonary responses to propofol 2 infusion rates in nonpretreated llamas breathing room air. ANIMALS: 5 adult llamas (3 males, 2 females) with mean +/- SD body weight of 135 +/- 17.7 kg. PROCEDURE: After anesthesia induction with propofol (2 mg/kg of body weight, IV), llamas received either propofol infusion 0.2 mg/kg/min (group 1) or 0.4 mg/kg/min (group 2) for 60 minutes. Measurements, taken before anesthesia induction and at regular intervals during infusion were: direct blood pressures, heart and respiratory rates, cardiac output, and arterial blood gas tensions. Systemic and pulmonary vascular resistance, cardiac and stroke indices, and plasma bicarbonate and base excess concentrations were calculated. RESULTS: At 3 to 60 minutes after either dosage of propofol, PaCO2 and heart rate increased in all llamas; at the same time, PaO2 and arterial pH decreased. Mean pulmonary artery and central venous pressures, and stroke index decreased at 3 to 60 minutes after either dosage of propofol. Mean arterial pressure decreased at 30 to 60 minutes after infusion of 0.4 mg of propofol/kg/min; pulmonary arterial wedge pressure decreased at 20 to 40 minutes and 3 to 60 minutes after infusion of 0.2 and 0.4 mg of propofol/kg/min, respectively. Mean time from termination of infusion to sternal recumbency was 7 (group 1) and 13 (group 2) minutes. Standing was achieved in a mean 11 (group 1) and 22 (group 2) minutes. CONCLUSION: Propofol infusion rate of 0.2 mg/kg/min was considered too low to maintain a suitable depth of anesthesia, but 0.4 mg/kg/min was considered sufficient for noninvasive procedures with minimal cardiopulmonary depression.

Deep hypothermic low flow cardiopulmonary bypass in small dogs

L J. Lew et al. — Fri, 02 Sep 2011 11:49:39 PDT

OBJECTIVE: To evaluate the feasibility of and morbidity and mortality associated with cardiopulmonary bypass (CPB) using deep hypothermia and low flow perfusion in adult dogs weighing less than 10 kg. STUDY DESIGN: Prospective, descriptive study. ANIMALS: Two groups of three dogs underwent CPB. Group 1 dogs underwent deep hypothermia (15 to 18 degrees C), 45 minutes of low perfusion flow (20 mL/kg/min) and 1 hour of aortic cross clamp time. In group 2, ultrafiltration of perfusate before discontinuation of bypass was added to the standard treatment. Complete blood counts, serum biochemistry, urine output, ejection fraction, and cardiac output were monitored before and for 7 days after surgery. RESULTS: All dogs were successfully weaned from bypass. Four of six dogs survived, three without major complications. One dog developed and recovered from septic pleuritis. Two dogs died or were euthanatized after surgery because of respiratory or gastrointestinal complications. Minor complications included anemia, hypoproteinemia, and electrolyte disturbances. Transfusion requirements and edema formation were reduced by ultrafiltration. CONCLUSIONS: The observations in this study support the feasibility of low flow hypothermic CPB. Meticulous tissue handling, precise equipment, ultrafiltration, and aggressive postoperative potassium supplementation are recommended for smaller patients. CLINICAL RELEVANCE: Increased sensitivity to adverse sequelae of CPB may be associated with small patient size. Further evaluation is necessary before routine clinical application of low flow hypothermic CPB in this patient population.

The effect of ketamine on the MACBAR of sevoflurane in dogs

Lyda Love et al. — Mon, 29 Aug 2011 12:06:24 PDT

METHODS: Dogs were anesthetized with sevoflurane on two occasions, 1 week apart, and baseline MAC(BAR) (B-MAC(BAR)) was determined on each occasion. MAC(BAR) was defined as the mean of the end-tidal sevoflurane concentrations that prevented and allowed an increase (≥15%) in heart rate or invasive mean arterial pressure in response to a noxious electrical stimulus (50 V, 50 Hz, 10 ms). Dogs then randomly received either a low-dose (LDS) or high-dose series (HDS) of ketamine, and treatment MAC(BAR) (T-MAC(BAR)) was determined. The LDS had an initial loading dose (LD) of 0.5 mg kg(-1) and constant rate infusion (CRI) at 6.25 μg kg(-1) minute(-1), followed, after T-MAC(BAR) determination, by a second LD (1 mg kg(-1)) and CRI (12.5 μg kg(-1) minute(-1)). The HDS had an initial LD (2 mg kg(-1)) and CRI (25 μg kg(-1) minute(-1)) followed by a second LD (3 mg kg(-1)) and CRI (50 μg kg(-1) minute(-1)). Data were analyzed with a mixed-model anova and are presented as LSM ± SEM. RESULTS: The B-MAC(BAR) was not significantly different between treatments. Ketamine at 12.5, 25, and 50 μg kg(-1) minute(-1) decreased sevoflurane MAC(BAR), and the maximal decrease (22%) occurred at 12.5 μg kg(-1) minute(-1). The percentage change in MAC(BAR) was not correlated with either the log plasma ketamine or norketamine concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine at clinically relevant doses of 12.5, 25, and 50 μg kg(-1) minute(-1) decreased sevoflurane MAC(BAR), although the reduction was neither dose-dependent nor linear.

Comparison of Plasma Fentanyl Concentrations by Using Three Transdermal Fentanyl Patch Sizes in Dogs

Christine Marie Egger et al. — Fri, 05 Aug 2011 09:34:03 PDT

Objective—To compare plasma fentanyl concentrations attained after the application of three transdermal fentanyl patch sizes (50, 75, and 100 μg/hour) in dogs.

Design—Repeated Latin square controlled study.

Animals—Six intact, mixed-breed adult dogs (2 males, 4 females) weighing 19.9 ± 3.4 kg.

Methods—Each dog was randomly assigned to receive each of three treatments: 50 (P50), 75 (P75), or 100 (P100) μg/hour transdermal patches. Patches were left in place for 72 hours. Jugular venous blood was collected at 1,2, 4, 8, 12, 24, 36, 48, 60, and 72 hours after patch application and for 1, 2, 4, 8, and 12 hours after patch removal. Plasma fentanyl concentrations were measured using a radioimmunoassay technique. After a 96-hour washout period, each dog was moved to another treatment group and received a different patch size.

Results—The following results were obtained (mean ± SD): average plasma fentanyl concentration from 24 to 72 hours, 0.7 ± 0.2 ng/mL (P50), 1.4 ± 0.5 ng/mL (P75), 1.2 ± 0.5 ng/mL (P100); the total area under the concentration versus time curve (0 hours to infinity), 46 ± 12.2 ng/h/mL (P50), 101.2 ± 41.4 ng/h/mL (P75), 80.4 ± 38.3 ng/h/mL (P100); and the apparent elimination half-life, 3.6 ± 1.2 hours (P50), 3.4 ± 2.7 hours (P75), and 2.5 ± 2.0 hours (P100). There was a high degree of variability in plasma fentanyl concentrations achieved. Plasma fentanyl concentrations declined rapidly after patch removal.

Conclusions—The attainment of steady-state plasma concentrations takes up to 24 hours, and there is a great deal of variability in the final concentrations reached in different individuals. In this study, the 100 μg/hour patches did not provide statistically increased plasma concentrations when compared with the 50 μg/hour patches.

Clinical Relevance—Because of the interindividual and intraindividual variation in plasma fentanyl concentrations, patches should be applied 24 hours before the anticipated time that analgesia will be required. Adequacy of analgesia and potentially deleterious side effects, such as sedation and respiratory depression, should be monitored while the patches are in place. Skin reactions may occur, and the patches should be removed if such skin irritation is seen. After the patch is removed, it is expected that analgesia will wane rapidly because of the brief elimination half-life.

Analgesic Effect of the Transdermal Fentanyl Patch During and After Feline Ovariohysterectomy

Leigh E. Glerum et al. — Fri, 05 Aug 2011 09:34:02 PDT

Objective— To evaluate the efficacy of the transdermal fentanyl patch in relieving perioperative pain and stress associated with ovariohysterectomy in cats.

Study Design— Prospective laboratory trial.

Animals— Twenty-four female, purpose-bred cats.

Methods— Each cat was randomly assigned to groups 1–3. Group 1 received a 25-μg/h transdermal fentanyl patch only. Group 2 received the patch and anesthesia. Group 3 received anesthesia only. Patches were left in place for 72 hours. Rectal temperature, heart rate, respiratory rate, indirect blood pressure, blood glucose, serum cortisol concentration, plasma fentanyl concentration, pain score, and excitement/sedation score were monitored at prescribed intervals over an 81-hour period. Cats from groups 1–3 were reassigned to groups 4 and 5. Group 4 received the patch, anesthesia, and an ovariohysterectomy. Group 5 received anesthesia and an ovariohysterectomy only. The study period and monitored parameters were the same as for groups 1–3.

Results— Serum cortisol concentrations were significantly lower in group 4 than group 5 during the surgical and early postsurgical time periods. A similar effect was noted in blood glucose concentrations during the surgical period. Rectal temperature was significantly higher in group 2 when comparing all anesthetized groups during the early postsurgical period. Pain scores were significantly higher in groups 4 and 5 than in groups 2 and 3 during the early postsurgical period. There was no significant difference in pain scores between groups 4 and 5 during this period, however.

Conclusions— The transdermal fentanyl patch affects biochemical markers of perioperative pain and stress associated with ovariohysterectomy in cats, attenuating rises in serum cortisol and blood glucose concentrations during the surgical and early postsurgical periods.

Clinical Relevance— The transdermal fentanyl patch is effective in alleviating perioperative pain and stress associated with ovariohysterectomy in cats as evidenced by attenuated rises in cortisol and blood glucose concentrations in cats that were operated on and treated with the patch.

The Effects of Pre-anesthetic Administration of Xylazine on the Cardiovascular Responses to Dobutamine in Halothane Anaesthetized Horses

Christine Marie Egger — Fri, 05 Aug 2011 09:34:01 PDT

Studies evaluating the effects of dobutamine in horses do not consistently report increases in cardiac output despite increases in arterial blood pressure. The concurrent administration of the α₂ agonist clonidine, in people, inhibited the chronotropic effects of dobutamine and increased left ventricular stroke work (Zimpfer et al. 1982). Our study was performed to determine if pre-medication with an α₂ agonist affects the response to dobutamine in anaesthetized horses.

Eleven horses were anaesthetized on four separate occasions for one of four randomly assigned treatments; (I) no xylazine, no dobutamine (II) xylazine, no dobutamine (III) no xylazine, dobutamine, and (IV) xylazine, dobutamine. Horses received 0.02 mg kg⁻¹ of butorphanol IV 10 minutes prior to anesthetic induction. Two minutes prior to induction, groups II and IV received 0.5 mg kg⁻¹ of IV xylazine. Anaesthesia was induced with 6–7 mg kg⁻¹ of thiopental and maintained with halothane. End-tidal halothane concentrations were maintained between 1.1 and 1.2% in groups I and III, and 0.9–1.0% for groups II and IV. Heart rate, cardiac output, right atrial pressure, and systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure were recorded 30 minutes after beginning halothane anaesthesia (T10). Cardiac output was estimated using Lithium dilution (Linton et al. 2000). Baseline measurements were repeated twice, at 5-minute intervals (T5 and T0). At time 0 (T0), an IV infusion of either saline (100 mL hour⁻¹) or dobutamine (0.001 mg kg⁻¹ minute⁻¹) was started and data recorded at 5-minute intervals for 30 minutes (T5 – T30). Stroke volume and systemic vascular resistance (SVR) were calculated. Data were analysed using repeated measures anova (p < 0.01 significant) and Newman–Keuls for multiple comparisons.

Cardiac output and stroke volume increased over time in groups III and IV. Cardiac index was higher in groups III and IV than in groups I and II from T10 until completion of the study. Estimates of cardiac index at T30 for groups I–IV were 45 ± 9, 46 ± 11, 71 ± 11, and 78 ± 19 mL kg⁻¹ minute⁻¹, respectively (mean ± SD). Stroke index was higher in groups III and IV than in groups I and II from T15 to T30. Values for stroke index at T30 for groups I–IV were 0.98 ± 0.19, 1.11 ± 0.18, 1.46 ± 0.21, 1.74 ± 0.33 mL kg⁻¹. Heart rate decreased from T10–T30 in groups I and II. Heart rate was greater in groups I and III than in groups II and IV at T5 and T0. Values for heart rate at T0 for groups I–IV were 48 ± 5, 42 ± 5, 50 ± 4, 43 ± 4 beats minute⁻¹. Systolic arterial pressure, DAP and MAP were higher in groups III and IV than in groups I and II from T5 to T30. There were no differences in SVR between groups.

Dobutamine at 0.001 mg kg⁻¹ minute⁻¹ increased cardiac output, blood pressure, and stroke volume. Premedication with xylazine at 0.5 mg kg⁻¹ did not appear to affect the response to dobutamine.

Treatment of severe atopicpyodermatitis with TCVM. Case Report

Christine Marie Egger — Fri, 05 Aug 2011 09:33:59 PDT