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Abstract

Objective—To determine the effects of nitrous oxide (N2O) on the speed and quality of mask induction with sevoflurane or isoflurane in dogs.

Animals—7 healthy Beagles.

Procedure—Anesthesia was induced with sevoflurane or isoflurane delivered in 100% oxygen or in a 2:1 mixture of N2O and oxygen via a face mask. Each dog received all treatments with at least 1 week between treatments. Initial vaporizer settings were 0.8% for sevoflurane and 0.5% for isoflurane (0.4 times the minimum alveolar concentration [MAC]). Vaporizer settings were increased by 0.4 MAC at 15-second intervals until settings were 4.8% for sevoflurane and 3.0% for isoflurane (2.4 MAC). Times to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and cardiopulmonary variables were measured.

Results—Administration of sevoflurane resulted in a more rapid induction, compared with isoflurane. However, N2O had no effect on induction time for either agent. Heart rate, mean arterial blood pressure, cardiac output, and respiratory rate significantly increased and tidal volume significantly decreased from baseline values immediately after onset of induction in all groups. Again, concomitant administration of N2O had no effect on cardiopulmonary variables.

Conclusions and Clinical Relevance—Administration of N2O did not improve the rate or quality of mask induction with sevoflurane or isoflurane. The benefits provided by N2O attributable to concentrating and second gas effects appear minimal in healthy dogs when low solubility inhalation agents such as isoflurane and sevoflurane are used for mask induction. (Am J Vet Res 2001;62:1727–1733).

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize the effects of medetomidine- midazolam, midazolam-butorphanol, or acepromazine- butorphanol as premedicants for mask induction of anesthesia with sevoflurane in dogs.

Animals—10 healthy Beagles.

Procedure—The following premedicants were administered intramuscularly: medetomidine-midazolam (20 µg/kg and 0.3 mg/kg, respectively), midazolambutorphanol (0.1 and 0.2 mg/kg, respectively), and acepromazine-butorphanol (0.05 and 0.2 mg/kg, respectively). Saline (0.9% NaCl) solution (0.1 ml/kg) was administered intramuscularly as a control. Anesthesia was induced in each dog with sevoflurane in a 100% O2 at a flow rate of 4 L/min developed by a facemask. Vaporizer settings were increased by 0.8% at 15-second intervals until the value corresponding to 4.8% sevoflurane was achieved. Time to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and the cardiopulmonary variables were measured.

Results—Mask induction with sevoflurane in dogs that received each premedicant resulted in a shorter induction time and milder changes in heart rate, mean arterial blood pressure, cardiac output, and respiratory rate, compared with mask induction without premedicants. Treatment with medetomidine-midazolam resulted in a shorter and smoother induction, compared with acepromazine-butorphanol or midazolambutorphanol treatment, whereas the cardiovascular changes were greater. Cardiopulmonary variables of dogs during induction following treatment with acepromazine- butorphanol or midazolam-butorphanol were maintained close to the anesthetic maintenance values for sevoflurane, with the exception of mild hypotension that was observed in dogs following acepromazine-butorphanol treatment.

Conclusion and Clinical Relevance—In dogs use of premedicants provides a smoother and better quality mask induction with sevoflurane. (Am J Vet Res 2002;63:1022–1028)

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether heartworm (HW) extract-induced shock in dogs is consistent with anaphylactic shock by examining the role of histamine.

Animals—6 mixed-breed dogs (3 without and 3 with HW infections) and 4 specific pathogen-free (SPF) Beagles.

Procedure—Four experiments were performed as follows: 1) 6 mixed-breed dogs were treated IV with 2 ml of HW extract, and plasma histamine concentrations were determined; 2) 4 SPF dogs were treated IV with 2 ml of HW extract and examined for shock; 3) sera from 6 dogs of experiment 1 and from 4 SPF dogs of experiment 2 that were obtained before HW extract treatment were tested for heterologous passive cutaneous anaphylaxis (PCA), using rabbits during a sensitization period of 48 to 72 hours; and 4) mast cell degranulation by HW extract was tested, using rat mesentery and canine cultured mast cells.

Results—Experiment 1: 6 dogs developed shock, and plasma histamine concentrations increased significantly from 0.3 ± 0.2 (mean ± SD) ng/ml before HW extract treatment to 44.6 ± 68.9 ng/ml at the onset of shock; experiment 2: all SPF dogs developed shock and had an increase in plasma histamine concentrations; experiment 3: sera from mixed-breed dogs without HW infection and from SPF dogs had negative PCA reactions; experiment 4: HW extract degranulated rat mesentery mast cells and released histamine directly from canine mast cells.

Conclusions and Clinical Relevance—Results of our study indicate that an unknown mast cell-degranulating substances contained in HW extract may degranulate mast cells directly, consequently releasing histamine that may participate in the onset of shock in HW extract-induced shock in dogs. (Am J Vet Res 2001;62:770–774)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize respiratory reflexes elicited by nasal administration of sevoflurane (Sevo), isoflurane (Iso), or halothane (Hal) in anesthetized dogs.

Animals—8 healthy Beagles.

Procedure—A permanent tracheostomy was created in each dog. Two to 3 weeks later, dogs were anesthetized by IV administration of thiopental and α-chloralose. Nasal passages were isolated such that inhalant anesthetics could be administered to the nasal passages while the dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of each anesthetic at 1.2 and 2.4 times the minimum alveolar concentration (MAC) and the full vaporizer setting (5%) were recorded. Reflexes in response to administration of 5% of each anesthetic also were recorded following administration of lidocaine to the nasal passages.

Results—Nasal administration of Sevo, Iso, and Hal induced an immediate ventilatory response characterized by a dose-dependent increase in expiratory time and a resulting decrease in expired volume per unit of time. All anesthetics had a significant effect, but for Sevo, the changes were smaller in magnitude. Responses to administration of each anesthetic were attenuated by administration of lidocaine to the nasal passages.

Conclusions and Clinical Relevance—Nasal administration of Sevo at concentrations generally used for mask induction of anesthesia induced milder reflex inhibition of breathing, presumably via afferent neurons in the nasal passages, than that of Iso or Hal. Respiratory reflexes attributable to stimulation of the nasal passages may contribute to speed of onset and could promote a smoother induction with Sevo, compared with Iso or Hal. (Am J Vet Res 2001;62:311–319)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize and determine the sensory innervation of respiratory reflexes elicited by nasal administration of halothane to dogs.

Animals—10 healthy Beagles.

Procedure—Dogs underwent permanent tracheostomy and, 2 to 3 weeks later, were anesthetized with thiopental and α-chloralose administered IV. The nasal passages were functionally isolated so that halothane could be administered to the nasal passages while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of halothane at concentrations of 1.25, 1.75, and 2.5 times the minimum alveolar concentration (MAC), and 5% (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of 5% halothane were also recorded following transection of the infraorbital nerve, transection of the caudal nasal nerve, and nasal administration of lidocaine.

Results—Nasal administration of halothane induced an inhibition of breathing characterized by a dosedependent increase in expiratory time and a resultant decrease in expired volume per unit time. Effects were noticeable immediately after the onset of halothane administration and lasted until its cessation. Reflex responses to halothane administration were attenuated by transection of the caudal nasal nerve and by nasal administration of lidocaine, but transection of the infraorbital nerve had no effect.

Conclusions and Clinical Relevance—Nasal administration of halothane at concentrations generally used for mask induction of anesthesia induces reflex inhibition of breathing. Afferent fibers in the caudal nasal nerve appear to play an important role in the reflex inhibition of breathing induced by halothane administration. (Am J Vet Res 2000;61:260–267)

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE

To evaluate the feasibility of buccal mucosal graft urethroplasty for repairing complete urethral rupture in cats.

ANIMALS

15 male domestic shorthair cats with traumatic complete urethral rupture.

PROCEDURES

In each cat, a section of buccal mucosa was harvested, sutured, and formed into a tubule by use of an 8F indwelling catheter as support. This tubular graft was connected to both ruptured ends of the urethra to renew the urinary passage. The catheter was left in place until the absence of leakage was confirmed by positive contrast retrograde urethrography. After spontaneous urination was confirmed, cats were discharged from the hospital. Six months later, urethrography was repeated and owners were asked to score their cats’ urinary function and quality of life.

RESULTS

13 cats recovered well following surgery, with no complications in the oral cavity or surgical site and no signs of difficulty or discomfort when urinating. Urethrography 2 weeks and 6 months after surgery revealed no stricture or leakage in the abdominal cavity. The 2 remaining cats developed a urethral stricture and underwent second surgery with a successful outcome. At the 6-month follow-up, 14 cats had only mild urinary signs, and 1 cat had incontinency. Owners indicated they were delighted (n = 14) or pleased (1) with their cats’ quality of life.

CLINICAL RELEVANCE

Buccal mucosa was found to be a good source of graft tissue for performance of urethroplasty in male cats, yielding satisfactory outcomes with few postoperative complications. The described technique may be suitable for severe and complicated cases of urethral rupture in male cats.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To develop an IM administrable anesthetic combination for pigs.

Design

Use of a combination of atropine, medetomidine, butorphanol, and ketamine (MB-K) was evaluated as an anesthetic regimen and compared with that of a combination of atropine, xylazine, butorphanol, and ketamine (XB-K). Cardiorespiratory effects of MB-K combination and use of atipamezole as a means of reversing anesthesia induced by MB-K were examined.

Animals

18 castrated, mixed-breed, specific-pathogen- free pigs, aged 8 to 15 (mean, 12.1) weeks and weighing 14.5 to 26.0 (mean, 19.6) kg, were studied.

Procedure

Dosages of drugs used in this study were atropine, 25 µg/kg of body weight; medetomidine 80 µg/ kg; xylazine, 2 mg/kg; butorphanol, 200 µg/kg; ketamine, 10 mg/kg; and atipamezole, 240 µg/kg.

Results

MB-K combination proved to be more effective than XB-K combination as an anesthetic combination. After quick and smooth induction by IM administration, MB-K-induced anesthesia was sustained for 98.8 ± 22.5 minutes (mean ± SD, 47.4 ± 16.5 minutes by XB-K) with accompanying muscular relaxation (91 ± 18 minutes) and loss of pedal (82 ± 24 minutes) and laryngeal (75 ± 19 minutes) reflexes. Loss of these reflexes was of significantly longer duration than the loss induced by XB-K, enabled tracheal intubation, and, thus, supported major surgery for at least 30 minutes after induction. Recovery from MB-K-mduced anesthesia was smooth. MB-K combination had a slight stimulative effect on cardiovascular status, and a significant depressant effect on blood gas and acid-base status, but these effects were within biologically acceptable limits. Oxygen consumption of pigs under MB-K-induced anesthesia decreased significantly. MB-K-induced anesthesia could be effectively and quickly reversed by IM or IV administration of atipamezole.

Conclusions

The combination of medetomidine, butorphanol, and ketamine induces excellent surgical anesthesia in pigs, and results in moderate cardiorespiratory effects. A great advantage of the anesthetic regimen is that it can be effectively and quickly reversed by atipamezole.

Clinical Relevance

Medetomidine, butorphanol, and ketamine-induced anesthesia is available for short-term major surgery in pigs. (Am J Vet Res 1996;57:529–534)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate cardiopulmonary effects of sevoflurane (Sevo), compared with halothane (Hal), enflurane (Enf), and isoflurane (Iso).

Animals

24 healthy Beagles, randomly assigned to 4 groups of 6 dogs each.

Procedure

Dogs under spontaneous ventilation were anesthetized with Sevo, Hal, Enf, or Iso. After minimum alveolar concentration (MAC) of each anesthetic was determined, anesthesia was maintained at light (1 MAC), moderate surgical (1.5 MAC), and deep (2 MAC), stages and cardiopulmonary variables at conscious state (baseline) and each anesthesia stage were measured.

Results

In dogs of the Sevo group, heart rate increased significantly from the baseline value at all anesthesia stages. Systemic vascular resistance during Sevo anesthesia decreased gradually with increasing anesthesia stage, which was accompanied by dose-dependent decreases in systolic, mean, and diastolic arterial blood pressures. At 1.5 and 2 MAC Sevo, stroke index decreased slightly but significantly from the baseline value; however, cardiac index was unchanged because of the significant increase in heart rate. Respiratory rate decreased significantly at 2 MAC from that at 1 MAC Sevo. Tidal volume and dead space-to-tidal volume ratio were unchanged at all anesthesia stages of Sevo, resulting in significantly decreased expired and alveolar ventilation at 2 MAC, compared with values at 1 and 1.5 MAC Sevo. PaCO2 increased and pHa decreased significantly, depending on anesthesia stage; PaO2 increased significantly from baseline values, and remained constant because of inhalation of 100% O2.

Conclusion

Cardiovascular effects of Sevo were greater than those of Hal, similar to those of Iso, and less than those of Enf. Respiratory effects of Sevo were similar to those of Iso at all anesthesia stages, greater than those of Hal at 2 MAC, and less than those of Enf at 1.5 and 2 MAC. Up to the moderate surgical anesthesia stage, Sevo can be used safely in dogs undergoing spontaneous ventilation. (Am J Vet Res 1997;58:885–890)

Free access
in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether magnetic resonance imaging findings in dogs with paraplegia caused by thoracolumbar intervertebral disk extrusion were predictive of clinical outcome.

Design—Retrospective case series.

Animals—77 dogs.

Procedure—Medical records and magnetic resonance images were reviewed; clinical outcome was classified as successful (regained ability to walk with no more than mild neurologic deficits) or unsuccessful (severe neurologic deficits persisted). The prognostic value of magnetic resonance imaging was compared with prognostic value of deep pain perception, duration of clinical signs, and rate of onset of clinical signs.

Result—33 (43%) dogs had areas of hyperintensity of the spinal cord greater than or equal to the length of the L2 vertebral body on T2-weighted magnetic resonance images. All 44 dogs without areas of hyperintensity on T2-weighted images had a successful outcome, but only 18 of the 33 (55%) dogs with an area of hyperintensity did. Only 5 of 16 dogs with an area of hyperintensity that had also lost deep pain perception had a successful outcome. The odds ratio for an unsuccessful outcome for a dog with an area of hyperintensity (29.87) was higher than the odds ratio for a dog that had lost deep pain perception (5.24). Duration and rate of onset of clinical signs were not associated with clinical outcome.

Conclusions and Clinical Relevance—Findings suggest that results of magnetic resonance imaging can be used to predict clinical outcome in dogs with paraplegia caused by intervertebral disk extrusion. (J Am Vet Med Assoc 2005;227:1454–1460)

Full access
in Journal of the American Veterinary Medical Association