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OBJECTIVE To determine the onset, duration, and extent of regional nerve blocks performed by administration of lidocaine or lidocaine-bupivacaine into the infraorbital canal in dogs.
ANIMALS 6 healthy hound-type dogs.
PROCEDURES Under general anesthesia, stimulating needles were inserted into the gingiva dorsolateral to both maxillary canine (MC) teeth and the maxillary fourth premolar (MPM4) and second molar (MM2) teeth on the treatment side. A reflex-evoked muscle potential (REMP) was recorded from the digastricus muscle after noxious electrical stimulation at each site. After baseline measurements, 1 mL of 2% lidocaine solution or a 2% lidocaine-0.5% bupivacaine mixture (0.5 mL each) was injected into the infraorbital canal (at approx two-thirds of the canal length measured rostrocaudally). The REMPs were recorded for up to 7 hours. The REMP data for the contralateral (untreated control) canine tooth were used to normalize results for all stimulation sites.
RESULTS With both treatments, nerve block for MC teeth on the treated side was achieved by 5 (n = 5 dogs) or 10 (1) minutes after injection, but nerve block for ipsilateral MPM4 and MM2 teeth was successful for only 3 dogs and 1 dog, respectively. Mean duration of nerve blocks for MC teeth was 120 and 277 minutes following injection of lidocaine and lidocaine-bupivacaine, respectively.
CONCLUSIONS AND CLINICAL RELEVANCE Local anesthesia, as performed in this study, successfully blocked innervation of MC teeth, but results for MPM4 and MM2 teeth were inconsistent. This specific technique should not be used during tooth extractions caudal to the MC teeth.
Objective—To compare cardiovascular effects of equipotent infusion doses of propofol alone and in combination with ketamine administered with and without noxious stimulation in cats.
Procedure—Cats were anesthetized with propofol (loading dose, 6.6 mg/kg; constant rate infusion [CRI], 0.22 mg/kg/min) and instrumented for blood collection and measurement of blood pressures and cardiac output. Cats were maintained at this CRI for a further 60 minutes, and blood samples and measurements were taken. A noxious stimulus was applied for 5 minutes, and blood samples and measurements were obtained. Propofol concentration was decreased to 0.14 mg/kg/min, and ketamine (loading dose, 2 mg/kg; CRI, 23 µg/kg/min) was administered. After a further 60 minutes, blood samples and measurements were taken. A second 5-minute noxious stimulus was applied, and blood samples and measurements were obtained.
Results—Mean arterial pressure, central venous pressure, pulmonary arterial occlusion pressure, stroke index, cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, oxygen delivery index, oxygen consumption index, oxygen utilization ratio, partial pressure of oxygen in mixed venous blood, pH of arterial blood, PaCO2, arterial bicarbonate concentration, and base deficit values collected during propofol were not changed by the addition of ketamine and reduction of propofol. Compared with propofol, ketamine and reduction of propofol significantly increased mean pulmonary arterial pressure and venous admixture and significantly decreased PaO2.
Conclusions and Clinical Relevance—Administration of propofol by CRI for maintenance of anesthesia induced stable hemodynamics and could prove to be clinically useful in cats. (Am J Vet Res 2003;64:913–917)
Objective—To determine the incidence and type of alterations in heart rate (HR), peak systolic blood pressure (PSBP), and serum biochemical variables (total bilirubin, BUN, and creatinine concentrations) associated with IV administration of ionic-iodinated contrast (IIC), nonionic-iodinated contrast (NIC), and gadolinium dimeglumine (GD) contrast media in anesthetized dogs.
Animals—280 anesthetized dogs undergoing cross-sectional imaging.
Procedures—HR and PSBP were recorded at 5-minute intervals for 20 minutes for untreated control dogs and dogs that received IIC, NIC, or GD contrast medium. The development of an HR of < 60 beats/min or > 130 beats/min that included a ≥ 20% change from baseline was considered a response. The development of PSBP of < 90 mm Hg or > 160 mm Hg that included a ≥ 20% change from baseline was considered a response. Pre- and postcontrast serum biochemical values were recorded.
Results—Of dogs receiving IIC medium, 3% (3/91) had a response in HR and 4% (4/91) had a response in PSBP at ≥ 1 time points. None of the dogs receiving NIC medium had a response in HR; 1 of 16 had a response in PSBP. Of dogs receiving GD contrast medium, 1% (1/92) had a response in HR and 4% (4/92) had a response in PSBP. Of control dogs, 2% (2/81) had a response in HR and 4% (3/81) had a response in PSBP. No serum biochemical alterations were observed.
Conclusions and Clinical Relevance—IV administration of contrast media in anesthetized dogs caused moderate bradycardia, tachycardia, hypotension, or hypertension.
Objective—To determine the incidence and type of alterations in heart rate (HR), peak systolic blood pressure (PSBP), and serum biochemical variables (serum total bilirubin, BUN, and creatinine concentrations) associated with IV administration of ionic-iodinated contrast (IIC), nonionic-iodinated contrast (NIC), and gadolinium (GD) contrast media in anesthetized cats.
Animals—220 anesthetized cats undergoing cross-sectional imaging.
Procedures—HR and PSBP were recorded at 5-minute intervals for 20 minutes for untreated control cats and cats that received IIC, NIC, or GD contrast medium. The development of HR < 100 beats/min or > 200 beats/min that included a ≥ 20% change from baseline was considered a response. The development of PSBP of < 90 mm Hg or > 170 mm Hg that included a ≥ 20% change from baseline was considered a response. Pre- and postcontrast serum biochemical values were recorded.
Results—Of cats receiving IIC medium, 2% (1/60) had a response in HR at ≥ 1 time point. Of cats receiving IIC medium, 7% (4/60) had a response in PSBP. None of the cats receiving NIC medium had a response in HR; 2 of 12 had a response in PSBP. Of cats receiving GD contrast medium, 6% (5/83) had a response in HR and 8% (7/83) had a response in PSBP. None of the control cats had a response in HR or PSBP. No serum biochemical alterations were observed.
Conclusions and Clinical Relevance—IV administration of iodine and GD contrast media in anesthetized cats was associated with changes in HR and PSBP.
To compare the efficacy and duration of desensitization of oral structures following injection of various volumes of lidocaine-bupivacaine via an infraorbital approach in dogs.
6 healthy adult hound-type dogs.
In a randomized crossover study, each dog received 1, 2, and 3 mL of a 2% lidocaine-0.5% bupivacaine mixture (50:50 vol/vol) injected within and near the caudal aspect of the infraorbital canal with a 14-day washout period between treatments. Dogs were anesthetized, and each treatment was administered through a 22-gauge, 4.5-cm-long catheter, which was fully inserted through and then withdrawn 2 cm to the caudal aspect of the infraorbital canal. The reflex-evoked motor potential was measured for the maxillary canine tooth (MC), fourth premolar tooth (MPM4), second molar tooth (MM2), and hard palate mucosa ipsilateral to the injected treatment and for the contralateral MC (control) at predetermined times before and for 6 hours after treatment administration or until the block was no longer effective. For each oral structure, the proportion of dogs with desensitization (efficacy) and time to onset and duration of desensitization were compared among the 3 treatments (injectate volumes).
Treatment was not associated with efficacy, time to onset, or duration of desensitization. Regardless of treatment, MC and MPM4 were more frequently desensitized and mean durations of desensitization for MC and MPM4 were longer, compared with those for MM2 and the hard palate.
CONCLUSIONS AND CLINICAL RELEVANCE
The volume of local anesthetic used for an infraorbital nerve block had no effect on block efficacy or duration.
To compare efficacy and duration of desensitization of oral structures with a lidocaine-bupivacaine mixture administered via a lateral percutaneous or modified infraorbital approach.
6 healthy adult hound-type female dogs.
In this crossover study, dogs were randomized for side (left or right) and maxillary nerve approach (lateral percutaneous or infraorbital), with a 2-week washout period. Dogs were anesthetized, and a 2-mL mixture of 2% lidocaine and 0.5% bupivacaine (50:50 [vol/vol]) was administered with a 22-gauge, 4.5-cm-long catheter inserted through the infraorbital canal (infraorbital approach) or with a shielded stimulating needle to the maxillary nerve (percutaneous approach). Reflex-evoked motor potentials were measured for the maxillary canine tooth, fourth premolar tooth, second molar tooth, and hard palate mucosa ipsilateral to the injected mixture and for the contralateral maxillary canine tooth (control) at three 10-minute intervals before injection (baseline) and at predetermined times after injection for up to 6.7 hours. For each oral structure, the proportion of dogs with desensitization (efficacy) and time to onset and duration of desensitization were compared between approaches.
The proportion of dogs with successful nerve blockade did not significantly differ between infraorbital and percutaneous approaches and among the 4 oral structures. Time to onset of desensitization did not differ between approaches, but duration was significantly longer with the infraorbital approach.
CONCLUSIONS AND CLINICAL RELEVANCE
A modified infraorbital approach with the lidocaine-bupivacaine mixture had similar effects to a lateral percutaneous approach but provided a longer duration of desensitization. Neither approach was universally successful at desensitizing all oral structures.
Objective—To determine the minimum infusion rate (MIR50) for propofol alone and in combination with ketamine required to attenuate reflexes commonly used in the assessment of anesthetic depth in cats.
Procedure—Propofol infusion started at 0.05 to 0.1 mg/kg/min for propofol alone or 0.025 mg/kg/min for propofol and ketamine (low-dose [LD] constant rate infusion [CRI] of 23 µg/kg/min or high-dose [HD] CRI of 46 µg/kg/min), and after 15 minutes, responses of different reflexes were tested. Following a response, the propofol dose was increased by 0.05 mg/kg/min for propofol alone or 0.025 mg/kg/min for propofol and ketamine, and after 15 minutes, reflexes were retested.
Results—The MIR50 for propofol alone required to attenuate blinking in response to touching the medial canthus or eyelashes; swallowing in response to placement of a finger or laryngoscope in the pharynx; and to toe pinch, tetanus, and tail-clamp stimuli were determined. Addition of LD ketamine to propofol significantly decreased MIR50, compared with propofol alone, for medial canthus, eyelash, finger, toe pinch, and tetanus stimuli but did not change those for laryngoscope or tail-clamp stimuli. Addition of HD ketamine to propofol significantly decreased MIR50, compared with propofol alone, for medial canthus, eyelash, toe pinch, tetanus, and tail-clamp stimuli but did not change finger or laryngoscope responses.
Conclusions and Clinical Relevance—Propofol alone or combined with ketamine may be used for total IV anesthesia in healthy cats at the infusion rates determined in this study for attenuation of specific reflex activity. ( Am J Vet Res 2003;64:907–912)
Objective—To determine whether opioids with varying interactions at receptors induce a reduction in minimum alveolar concentration (MAC) of isoflurane in cats.
Animals—12 healthy, female, spayed cats.
Procedure—Cats were anesthetized with isoflurane and instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Each drug was studied separately, and for each drug cats were randomly allocated to receive 2 doses. The drugs studied were morphine (0.1 or 1.0 mg/kg), butorphanol (0.08 or 0.8 mg/kg), buprenorphine (0.005 and 0.05 mg/kg), and U50488H (0.02 and 0.2 mg/kg). All drugs were diluted in 5 ml of saline (0.9% NaCl) solution and infused IV for 5 minutes. The MAC of isoflurane was determined in triplicate, the drug administered, and the MAC of isoflurane redetermined for a period of 3 hours.
Results—All drugs had a significant effect on MAC over time. With morphine only, the effect on MAC over time was different between doses. The greatest mean (± SD) reductions in MAC of isoflurane in response to morphine, butorphanol, buprenorphine, and U50488H administration were 28 ± 9, 19 ± 3, 14 ± 7, and 11 ± 7%, respectively.
Conclusions and Clinical Relevance—Morphine (1.0 mg/kg) and butorphanol (0.08 and 0.8 mg/kg) induced significant reductions in MAC of isoflurane that were considered clinically important. Although significant, reductions in MAC of isoflurane induced by morphine (0.1 mg/kg), buprenorphine (0.005 and 0.05 mg/kg), and U50488H (0.02 and 0.2 mg/kg) were not considered clinically relevant because they fell within the error of the measurement technique. Administration of morphine or butorphanol decreases the need for potent inhalant anesthetics in cats and could potentially be beneficial in combination with inhalants. (Am J Vet Res 2002;63:1198–1202)
Case Description—Acute severe systemic reactions developed during IV administration of an ionic iodinated contrast agent (iothalamate meglumine) in 2 dogs undergoing contrast-enhanced computed tomography.
Clinical Findings—Both dogs developed marked changes in heart rate and systolic arterial blood pressure during or immediately after IV administration of the contrast agent. The first dog became profoundly hypertensive and bradycardic with poor oxygenation, apparent bronchospasm, and prolonged diarrhea. The second dog became hypotensive and tachycardic with erythema on the ventral aspect of the abdomen and pelvic limbs, periocular edema, and diarrhea.
Treatment and Outcome—Both dogs were treated for shock by means of IV fluid administration, and anesthesia was discontinued. The first dog was placed on a ventilator to improve oxygenation but was hypertensive and unresponsive for 6.5 hours following contrast agent administration. Bloody diarrhea persisted once consciousness was regained. The dog was discharged 3 days after contrast agent administration, and diarrhea resolved 15 days later. The second dog responded to phenylephrine administration, but urine output appeared low immediately following recovery from anesthesia. Urine output was normal the following day, and the dog was released 36 hours after contrast administration with no residual adverse effects.
Clinical Relevance—Findings highlighted the potential risk for severe reactions associated with IV administration of ionic iodinated contrast agents in dogs. Both hypertensive and hypotensive responses were seen. Supportive care for systemic manifestations was effective in these 2 dogs, and extended hospitalization was not necessary.