Influence of anesthetic regimen on the frequency of seizures after cervical myelography in the dog

We examined the influence of various anesthetic drug combinations on the frequency of seizures in dogs after cervical myelography with metrizamide. Over a 12-month period, 78 dogs admitted to the teaching hospital for cervical myelography were assigned randomly to 1 of 6 anesthetic protocols. Myelography was performed, and the dogs were observed for signs of seizure activity after recovery from anesthesia. The person making the decision as to whether or not a dog had had a seizure was unaware of the anesthetic protocol that had been used. Preanesthetic treatment with pentobarbital (5.0 mg/kg) and maintenance of anesthesia with methoxyflurane significantly reduced the frequency of seizures (P less than 0.05). No reduction in seizure frequency was seen with any anesthetic protocol using halothane as the maintenance agent.     

Effect of intravenous administration of dextrose or lactated Ringer's solution on seizure development in dogs after cervical myelography with metrizamide

The effect of fluid (5% dextrose in water or lactated Ringer's solution) administered intravenously on the development of seizures after cervical myelography with metrizamide was studied in 10 dogs. In a crossover experimental design, 8 dogs were used twice. Urine output was measured during the second part of the study to determine whether diuresis was a factor affecting seizure development. Dogs given 5% dextrose in water had significantly (P less than 0.05) fewer seizures than did dogs given lactated Ringer's solution. This was attributed to an increase in CSF glucose concentration and was not associated with diuresis.     

COMPLICATIONS OF METRIZAMIDE MYELOGRAPHY IN THE DOG: A SUMMARY OF 107 CLINICAL CASE HISTORIES

The case histories of 107 dogs undergoing metrizamide myelography at two veterinary hospitals were reviewed. Twenty-three variables, including body weight, injection site, dose of contrast medium, and medical complications during and after recovery from anesthesia, were submitted to statistical analysis by computer. Partial or generalized seizures were the most common medical complications, occurring in 54 percent of the dogs weighing more than 29 kg. Other less frequent medical complications were exacerbation of neurologic signs the day following myelography (11 percent), transient apnea during contrast medium injection (9 percent), vomiting (5 percent), hyperesthesia (3 percent), pyrexia (1 percent), and death (1 percent). The incidence of medical complications associated with metrizamide myelography in this study is higher than in previous reports. The most likely variables associated with seizures were high injection volumes and metrizamide injection at the cisterna magna. The preanesthetic administration of intramuscular pentobarbital did not significantly reduce seizure incidence. Seizures were controlled by anticonvulsant medication.     

A COMPARISON OF IOPAMIDOL AND METRIZAMIDE FOR CERVICAL MYELOGRAPHY IN THE DOG

Cervical myelography using iopamidol, a new nonionic contrast medium, was studied in nine dogs. Postmyelographic seizure activity, motor evoked potentials, and rectal temperatures were monitored, and myelographic quality was subjectively evaluated. The results were compared with data from eight dogs that had metrizamide myelography. The iopamidol group had fewer seizures ( p < 0.01) but exhibited no difference in motor evoked potential or rectal temperature recordings. Myelographic quality was similar for iopamidol and metrizamide. The study suggests that iopamidol was less neurotoxic than metrizamide for canine cervical myelography.     

Complications associated with the use of iohexol for myelography of the cervical vertebral column in dogs: 66 cases (1988-1990).

Medical records of 66 dogs that had undergone myelography, using iohexol (240 mg of iodine/ml, 0.3 to 0.5 ml/kg of body weight) during a 2-year period, were reviewed. In 3 dogs, myelography was performed twice during different anesthetic procedures. Neurologic abnormalities were more pronounced the day after myelography in dogs with caudal cervical spondylomyelopathy (P less than 0.01), meningitis (P less than 0.01), or extradural tumors (P less than 0.05). Neither anesthetic regimen nor duration of anesthesia significantly affected the frequency of complications. Seizures occurred after myelography in 6 dogs, and 1 dog had seizures after each of 2 myelographic procedures. The frequency of seizures was significantly greater in male Doberman Pinschers afflicted with caudal cervical spondylomyelopathy. Male dogs (P less than 0.01) and Doberman Pinschers (P less than 0.001) had higher prevalence of seizures. Caudal cervical spondylomyelopathy was associated with higher prevalence of seizures, compared with all other diagnoses (P less than 0.001). Seizures were significantly more prevalent when body weight was greater than or equal to 29 kg (P less than 0.001), when greater than or equal to 2 injections of contrast medium were administered (P less than 0.016), or when 2 injections of contrast medium were given at the cisterna magna (P less than 0.015). The 10% prevalence of seizures after myelography with iohexol in the study reported here is greater than in previous reports, but is lower than that reported after myelography using metrizamide.     

Comparison of metrizamide and iohexol for cisternal myelographic examination of dogs

A double-blind study, using metrizamide, iohexol, or Ringer's solution (control) as cisternal myelographic agents, was performed on 25 dogs. Before myelographic examination was done, each dog was subjected to physical, clinical pathologic, and neurologic examinations, as well as examinations by electroencephalography and computerized tomography. These were repeated 24 hours after completion of the myelographic examination. The group of dogs given metrizamide (group II) had a significantly greater occurrence of seizure activity (6 of 10) than did the control dogs (group I; 0 of 5) or dogs given iohexol (group III; 0 of 10; P less than 0.003). In group II, the CSF microprotein concentration was significantly greater 24 hours after myelography was done than were the values in groups I and III (P less than 0.003). Myelograms of the group II dogs (metrizamide) and group III dogs (iohexol) had similar diagnostic qualities. At 24 hours after myelographic examination was done, computerized tomography scan revealed that each dog given metrizamide and iohexol had myelographic contrast material in the brain and cervical spinal cord parenchyma. Seemingly, iohexol has good diagnostic quality, but is less epileptogenic than metrizamide when used in cervical myelographic examinations of dogs.     

Prevention of postmetrizamide myelographic seizures in dogs, using 5% dextrose solution

Diuresis by IV administration of 5% dextrose in a balanced electrolyte solution (BES) reduced the frequency of occurrence of postmyelographic seizures in dogs. In the first study, a single myelogram was obtained in 8 dogs without dextrose diuresis. Two of these dogs weighed greater than 15 kg and both had seizures after metrizamide myelography. The remaining 6 dogs weighed less than 15 kg and only 2 had seizures. Greater body weight may have increased the risk of postmyelographic convulsions. In a crossover study, myelograms were obtained in 12 dogs weighing 20 to 31 kg. Six dogs were given 5% dextrose in BES (20 ml/kg of body weight/hr [diuresed]) and 6 were given BES alone (10 ml/kg/hr [not diuresed]). When myelography was repeated 10 days later, the 6 dogs that had been given 5% dextrose in BES were given BES only and the 6 dogs that had been given BES alone were given 5% dextrose in BES. The frequency of convulsions after metrizamide myelography was lower when dogs were given dextrose (33%) than when they were not (100%).     

Influence of halothane, isoflurane, and sevoflurane on gastroesophageal reflux during anesthesia in dogs

OBJECTIVE: To determine whether maintenance of anesthesia with halothane or sevoflurane is associated with a lower incidence of gastroesophageal reflux (GER) than the use of isoflurane in dogs undergoing orthopedic surgery. ANIMALS: 90 dogs. PROCEDURES: Dogs were evaluated during elective orthopedic surgery. Dogs with a history of vomiting or that had received any drugs that would alter gastrointestinal tract function were excluded from the study. The anesthetic protocol used was standardized to include administration of acepromazine maleate and morphine prior to induction of anesthesia with thiopental. Dogs were allocated to receive halothane, isoflurane, or sevoflurane to maintain anesthesia. A sensor-tipped catheter was placed to measure esophageal pH during anesthesia. Gastroesophageal reflux was defined as an esophageal pH < 4 or > 7.5. RESULTS: 51 dogs had 1 or more episodes of acidic GER during anesthesia. Reflux was detected in 14 dogs receiving isoflurane, 19 dogs receiving halothane, and 18 dogs receiving sevoflurane. In dogs with GER, mean +/- SD time from probe placement to onset of GER was 36 +/- 65 minutes and esophageal pH remained < 4 for a mean of 64% of the measurement period. There was no significant association between GER and start of surgery or moving a dog on or off the surgery table. Dogs that developed GER soon after induction of anesthesia were more likely to regurgitate. CONCLUSIONS AND CLINICAL RELEVANCE: Maintenance of anesthesia with any of the 3 commonly used inhalant agents is associated with a similar risk for development of GER in dogs.     

Cerebrospinal fluid response following metrizamide myelography in normal dogs: effects of routine myelography and postmyelographic removal of contrast medium

The effect of metrizamide myelography on 90-minute postmyelographic cerebrospinal fluid (CSF) samples was evaluated in a paired crossover study in 16 normal dogs. Each dog received a routine cervical myelogram (nonwithdrawal myelography) and a myelogram followed by contrast medium removal via aspiration from the subarachnoid space (withdrawal myelogram). Following nonwithdrawal myelography, the CSF was characterized by mild inflammation with a mixed pleocytosis and increased protein concentration. Compared with the nonwithdrawal CSF samples, the postmyelographic CSF of the withdrawal dogs had a more severe inflammatory response with significant increases (p < 0.05) in absolute numbers of neutrophils, monocytoid cells, eosinophils, lymphocytes, and protein concentration. The withdrawal procedure may have contributed an additional mechanical effect on the leptomeninges producing the more severe inflammatory response in the withdrawal dogs. Although seizure data are not reported here, postmyelographic seizures were more frequent following non-withdrawal myelography as compared with withdrawal myelography (p < 0.05), suggesting a decrease in metrizamide-induced neurotoxicity for the withdrawal dogs.     

Risk factors associated with development of seizures after use of iohexol for myelography in dogs: 182 cases (1998)

OBJECTIVE: To determine prevalence of seizures after use of iohexol for myelography and identify associated risk factors in dogs. DESIGN: Retrospective study. ANIMALS: 182 dogs that received iohexol for myelography in 1998. PROCEDURE: Medical records were reviewed for age, breed, sex, weight, dose and total volume of iohexol, injection site, number of injections, lesion type and location, total duration of anesthesia, duration from time of iohexol injection to recovery, presence and number of seizures, and whether surgery followed the myelogram. RESULTS: 39 (21.4%) dogs had at least 1 generalized seizure during or after myelography. Injection site was strongly associated with prevalence of seizures, and risk of seizure was significantly higher after cerebellomedullary injections, compared with lumbar injections. Mean total volume of iohexol administered to dogs that had seizures was significantly higher, compared with that administered to dogs that did not have seizures, although dosage did not differ between groups. Weight was significantly correlated with risk of seizure, and dogs that weighed > 20 kg (44 lb) had higher prevalence of seizures than dogs that weighed < 20 kg. CONCLUSIONS AND CLINICAL RELEVANCE: It is preferential to administer iohexol via the L5-6 intervertebral space to minimize the risk of seizures. Higher prevalence of seizures in large dogs, compared with smaller dogs, may be caused by administration of larger total volumes of contrast agent per volume of CSF.     

Cardiorespiratory responses and plasma cortisol concentrations in dogs treated with medetomidine before undergoing ovariohysterectomy

OBJECTIVE: To evaluate effects of medetomidine on anesthetic dose requirements, cardiorespiratory variables, plasma cortisol concentrations, and behavioral pain scores in dogs undergoing ovariohysterectomy. DESIGN: Randomized, prospective study. ANIMALS: 12 healthy Walker-type hound dogs. PROCEDURE: Dogs received medetomidine (40 micrograms/kg [18.2 micrograms/lb] of body weight, i.m.; n = 6) or saline (0.9% NaCl) solution (1 ml, i.m.; 6) prior to anesthesia induction with thiopental; thiopental dose needed for endotracheal intubation was compared between groups. Ovariohysterectomy was performed during halothane anesthesia. Blood samples were obtained at various times before drug administration until 300 minutes after extubation. Various physiologic measurements and end-tidal halothane concentrations were recorded. RESULTS: In medetomidine-treated dogs, heart rate was significantly lower than in controls, and blood pressure did not change significantly from baseline. Plasma cortisol concentrations did not increase significantly until 60 minutes after extubation in medetomidine-treated dogs, whereas values in control dogs were increased from time of surgery until the end of the recording period. Control dogs had higher pain scores than treated dogs from extubation until the end of the recording period. CONCLUSION AND CLINICAL RELEVANCE: Administration of medetomidine reduced dose requirements for thiopental and halothane and provided postoperative analgesia up to 90 minutes after extubation. Dogs undergoing ovariohysterectomy by use of thiopental induction and halothane anesthesia benefit from analgesia induced by medetomidine administered prior to anesthesia induction. Additional analgesia is appropriate 60 minutes after extubation.     

EFFECTS OF METRIZAMIDE MYELOGRAPHY ON CEREBROSPINAL FLUID ANALYSIS IN THE DOG

The effect of metrizamide myelography on the composition of cerebrospinal fluid (CSF) was studied. Seven dogs received an intracisternal injection of metrizamide. An intracisternal puncture was performed in three additional dogs that did not receive metrizamide. CSF was collected before myelography and 24, 72, and 144 hours after myelography from all dogs. A significant increase in the percentage of neutrophils (p<0.05) and a pleocytosis noted 24 hours after myelography (p<0.02) were attributed to the effect of metrizamide. Significant increases in total protein concentration (p<0.001) and erythrocyte count (p<0.05), and a decrease in the percentage of small mononuclear cells (p<0.01) were attributed to repeated intracisternal puncture. No significant changes were observed for CSF creatine phosphokinase activity or the percentage of large mononuclear cells.     

Incidence of seizures associated with iopamidol or iomeprol myelography in dogs with intervertebral disk disease: 161 cases (2000–2002)

Objective – To compare the incidence of seizures in dogs with intervertebral disk disease after iopamidol or iomeprol myelography, and to assess whether the incidence of seizures differed between the 2 agents when severity of neurological deficits, location of cord compression, duration of anesthesia, site of myelogram, volume of contrast, and concentration of contrast were evaluated. Design – Retrospective study. Setting – Veterinary teaching hospital. Animals – One hundred and sixty‐one client‐owned dogs with intervertebral disk disease. Interventions – Subarachnoid injection of contrast medium. Measurements and Main Results – One hundred and sixty‐one dogs with intervertebral disk disease were subjected to myelography using iopamidol (n=74) or iomeprol (n=87). Cranial myelography was performed in 31 dogs, caudal myelography in 125 and both cranial and caudal myelography in 5. Seizures occurred in 23 of 161 (14%) dogs. There was no significant difference overall between iopamidol and iomeprol myelography. However, in dogs with thoracolumbar disk extrusion and paraplegia, seizures occurred more frequently after caudal myelography using iopamidol compared with iomeprol. Conclusions – Both iomeprol and iopamidol are suitable for myelography in dogs. Iomeprol is recommended for caudal myelography in paraplegic dogs with thoracolumbar disk extrusion due to the higher incidence of seizures in this group when iopamidol was used.     

Clearance of nasal mucus in nonanesthetized and anesthetized dogs

Clearance rates for nasal mucus in the maxillary turbinate region were measured in 8 Beagle dogs. 99mTc Macroaggregated albumin (10 microliters) was instilled in the nasal maxillary region of dogs under general anesthesia. A gamma camera was used to detect movement of the 99mTc macroaggregated albumin in the nose for 1 hour after it was instilled. Velocity of mucus was measured in the 8 dogs each under 3 conditions of anesthesia: anesthesia with pentobarbital given IV (20 mg/kg of body weight), anesthesia with halothane gas, and no anesthesia. Mean velocities (+/- SD) were 3.7 +/- 1.4 mm/min in dogs anesthetized with pentobarbital, 4.3 +/- 2.5 mm/min in dogs anesthetized with halothane, and 3.4 +/- 1.7 mm/min in awake dogs. The differences between the 3 anesthetic conditions were not significant at the P less than 0.05 level. Use of anesthesia at a light surgical plane provides a controlled method for measurement of clearance of nasal mucus with minimal alterations from the nonanesthetized state.     

EFFECTS OF POSTMYELOGRAPHIC REMOVAL OF METRIZAMIDE IN DOGS

Using a paired crossover trial, the effects of postmyelographic removal of metrizamide injected via the cerebellomedullary cistern were studied in 16 normal dogs. Each animal received a routine and a withdrawal myelogram. Seizure activity, changes in spinal evoked motor potentials and body temperature were measured following each myelogram. The amount of metrizamide removed was determined by densitometrically analyzing radiographs of cerebrospinal fluid/metrizamide aliquots recovered during the withdrawal procedure. There was a significant decrease in the number of seizures for withdrawal versus nonwithdrawal myelography (p < 0.01). The mean amount of metrizamide withdrawn per dog was 29% of the total injected.     

Analgesia After Lateral Thoracotomy in Dogs Epidural Morphine Vs. Intercostal Bupivacaine

One of two analgesic treatments was randomly assigned to 40 dogs undergoing lateral thoracotomy. Group E (20 dogs) received an epidural injection of morphine (0.1 mg/kg) before surgery. Group I (20 dogs) received injections of bupivacaine around five intercostal nerves when the thorax was about to be closed. All dogs were given an opioid as part of their preoperative medication (meperidine or butorphanol), followed by thiopental for induction and halothane or methoxyflurane for maintenance of anesthesia. Scores were assigned for preoperative demeanor and response to restraint and injection. Alertness, undisturbed pain behavior, and response to palpation of the wound were assessed 3, 6, 12, and 24 hours after surgery. Dogs that appeared uncomfortable were given analgesics. Blood for evaluation of arterial blood gases was obtained at 3 and 6 hours after surgery. The person scoring the dogs was blinded to the treatment given. There were no statistically significant differences between the groups. Group E contained more "nervous" dogs (12 vs. 6) and more dogs in group E received postoperative analgesics (8 vs. 2). Both techniques appeared to provide adequate analgesia for most dogs.     

THE RELATIVE SENSITIVITY OF COMPUTED TOMOGRAPHY AND MYELOGRAPHY FOR IDENTIFICATION OF THORACOLUMBAR INTERVERTEBRAL DISK HERNIATIONS IN DOGS

We compared the relative sensitivity of computed tomography (CT) and myelography for identification of disk herniation in dogs. Criteria for patient selection included presurgical CT, myelography, or both and surgical or necropsy confirmation of disk herniation between the T3 and L6 vertebral articulations. Imaging findings were described as positive or inconclusive. Adverse events such as hypotension, cardiac arrhythmias, seizures, death, and lower urinary tract infection were compared between imaging groups. One hundred and eighty-two dogs met the inclusion criteria, with 116 dogs having myelography performed as the initial diagnostic imaging modality and 66 dogs having CT performed as the initial modality. The relative sensitivity for locating the site of disk herniation was 83.6% when myelography was the first test performed and 81.8% when CT was the first test performed. CT was more sensitive than myelography at detecting lesions in chronically affected dogs ( P =0.025). Myelography was more sensitive than CT at detecting lesions in smaller dogs (<5 kg; P =0.004). Dogs that received both imaging modalities were significantly more likely to die or be euthanized compared with myelography alone ( P <0.001). Both myelography and CT are reasonable diagnostic imaging modalities for locating the site of disk herniation. CT should be considered especially in heavier, more chronically affected dogs. The major limitations of this study include lack of randomization to imaging modality and the use of surgical exploration or necropsy as the gold standard.     

Comparison of analgesic efficacy of preoperative or postoperative carprofen with or without preincisional mepivacaine epidural anesthesia in canine pelvic or femoral fracture repair

Objective— To compare analgesic efficacy of preoperative versus postoperative administration of carprofen and to determine, if preincisional mepivacaine epidural anesthesia improves postoperative analgesia in dogs treated with carprofen. Study Design— Blind, randomized clinical study. Animals— Dogs with femoral (n=18) or pelvic (27) fractures. Methods— Dogs were grouped by restricted randomization into 4 groups: group 1=carprofen (4 mg/kg subcutaneously) immediately before induction of anesthesia, no epidural anesthesia; group 2=carprofen immediately after extubation, no epidural anesthesia; group 3=carprofen immediately before induction, mepivacaine epidural block 15 minutes before surgical incision; and group 4=mepivacaine epidural block 15 minutes before surgical incision, carprofen after extubation. All dogs were administered carprofen (4 mg/kg, subcutaneously, once daily) for 4 days after surgery. Physiologic variables, nociceptive threshold, lameness score, pain, and sedation (numerical rating scale [NRS], visual analog scale [VAS]), plasma glucose and cortisol concentration, renal function, and hemostatic variables were measured preoperatively and at various times after surgery. Dogs with VAS pain scores >30 were administered rescue analgesia. Results— Group 3 and 4 dogs had significantly lower pain scores and amount of rescue analgesia compared with groups 1 and 2. VAS and NRS pain scores were not significantly different among groups 1 and 2 or among groups 3 and 4. There was no treatment effect on renal function and hemostatic variables. Conclusions— Preoperative carprofen combined with mepivacaine epidural anesthesia had superior postoperative analgesia compared with preoperative carprofen alone. When preoperative epidural anesthesia was performed, preoperative administration of carprofen did not improve postoperative analgesia compared with postoperative administration of carprofen. Clinical Relevance— Preoperative administration of systemic opioid agonists in combination with regional anesthesia and postoperative administration of carprofen provides safe and effective pain relieve in canine fracture repair.     

Transient leakage across the blood-cerebrospinal fluid barrier after intrathecal metrizamide administration to dogs

Cerebrospinal fluid samples from 9 dogs given 84 mg of metrizamide/kg of body weight intrathecally were collected at intervals from 3 hours to 30 days after treatment and were compared with CSF samples collected before metrizamide treatment (base line) and with samples taken at similar intervals from 2 nontreated control dogs. Increased CSF albumin (mean 19.2 mg/dl) and immunoglobulin (Ig) G (mean 5.91 mg/dl) concentrations occurred 1 day after myelography, compared with base-line concentrations (6.15 and 1.24 mg/dl, respectively) and with concentrations from controls. Immunoglobulin M and IgA concentrations also were increased in some of these samples. However, immediately after myelography (3 hours after treatment) CSF albumin and IgG concentrations were comparable with those of controls, and these values returned to base line within 5 days of myelography and remained so for 30 days. A high correlation between albumin and IgG concentrations of individual CSF samples indicated the likelihood that leakage across the blood-CSF barrier was the origin of the increased values. A transient increase in CSF leukocytes, consisting of mononuclear cells and neutrophils, was also noticed 1 day after treatment but not at other times and not in controls. Nonsuppurative, predominately histiocytic meningitis of decreasing intensity was noticed in dogs euthanatized at 1 or 5 days, but not in dogs euthanatized at 10, 20, or 30 days after treatment. The meningeal cells stained intensely with periodic acid-Schiff stain and intracellular contrast medium was ultrastructurally apparent in phagolysosomes. Control dogs killed after 30 days did not have these changes. The intrathecal administration of metrizamide resulted in transient leakage of serum components into CSF and an accompanying transient meningitis.     

Analgesic effects of epidurally administered levogyral ketamine alone or in combination with morphine on intraoperative and postoperative pain in dogs undergoing ovariohysterectomy

OBJECTIVE: To evaluate the analgesic and adverse effects of epidurally administered levogyral (S[+]) ketamine alone or in combination with morphine on intraoperative and postoperative pain in dogs undergoing ovariohysterectomy. ANIMALS: 30 dogs scheduled for ovariohysterectomy. PROCEDURE: Dogs were randomly allocated to 1 of 3 groups. Dogs in group 1 received S(+) ketamine (1 mg/kg), dogs in group 2 received S(+) ketamine (0.5 mg/kg) and morphine (0.05 mg/kg), and dogs in group 3 received S(+) ketamine (1 mg/kg) and morphine (0.025 mg/kg). The skin was incised 15 minutes after epidural administration of analgesics. Heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), oxygen saturation as measured by pulse oximetry, and arterial blood gases were obtained before anesthesia, 15 minutes after epidural administration of analgesics, 15 and 30 minutes after initiation of surgery, and at the end of surgery. During the intraoperative period, an increase of > or =20% in baseline values for HR, RR, and SBP was considered a sign of intraoperative pain. Signs of pain and adverse effects were assessed at 2, 4, and 8 hours postoperatively. RESULTS: There were no significant differences in intraoperative or postoperative measurements among the 3 groups. No dogs had intraoperative signs of pain. Mean postoperative pain assessment scores were <3.5 in all 3 groups. Salivation was the most frequent adverse effect in dogs in groups 1 and 3, and sedation occurred more frequently in dogs in groups 2 and 3. CONCLUSIONS AND CLINICAL RELEVANCE: All 3 analgesic regimens provided good respiratory and cardiovascular stability intraoperatively and adequate postoperative analgesia with minimal adverse effects.