Effect of topically administered atropine on tear production in dogs.

Baseline tear production values were established for both eyes of 19 dogs, using the Schirmer tear test. Atropine sulfate, 1% solution, was administered topically in the left eye of each dog once daily for 14 days. Tear production was then determined for both eyes at 15, 30, 60, 120, 180, 240, and 300 minutes, and 3, 6, 9, 12, and 15 days. A final Schirmer tear test reading was obtained for each eye 5 weeks after the last atropine treatment to check for the possibility of prolonged effect. Both eyes had statistically significant (P less than 0.05) decrease in tear production that was most marked at 120 minutes after atropine instillation, then returned to baseline values by 300 minutes after instillation. Although atropine was placed in the left eye only, statistically significant difference was not apparent in Schirmer tear test values between the left and right eyes. Tear production continued to decrease in both eyes over time, becoming statistically significant (P less than 0.05) on day 9. However, on days 12 and 15, tear production in the untreated eye plateaued, but that in the treated eye continued to decrease. Five weeks after the last treatment with atropine, both eyes still had a statistically significant (P less than 0.05) decrease in tear production, although Schirmer tear test values had increased from day-15 values and appeared to be returning to baseline. Association was not evident between age or body weight and magnitude of response to topically applied atropine.     

Effect of metoclopramide on gastro-esophageal reflux in anesthetized dogs

Administration of morphine before anesthesia leads to gastro-esophageal reflux (GER) in over 50% of dogs during the subsequent anesthetic. This GER is clinically silent but can lead to aspiration pneumonitis, esophagitis and esophageal stricture. In this prospective clinical study we aimed to determine the effect of metoclopramide on gastro-esophageal reflux (GER) in dogs undergoing elective orthopedic surgery. Dogs were admitted to the study if they were healthy, and had no history of vomiting or dysphagia. Dogs were fasted for an average of 18.2 ± 4.3 (mean ± SD) hours prior to induction of anesthesia. Anesthesia in all dogs included acepromazine, morphine, thiopental and isoflurane in oxygen. By random allocation, half the dogs received metoclopramide (M) as an IV bolus (0.4 mg kg^–1) and then infusion (0.3 mg kg^–1hour^–1), the others received equivalent volumes of saline (S). To measure esophageal pH a sensor-tipped catheter was placed with the tip 5–7 cm cranial to the lower esophageal sphincter, and connected to a computer for continual data collection. The pH of any fluid running from the mouth or nose was measured. Gastro-esophageal reflux was defined as a decrease in esophageal pH below 4 or an increase above 7.5. Fisher's Exact test was used to test significance of differences in incidence between groups. Separate multivariable logistic regression models were created for each outcome to assess the effects of risk factors on outcome. There were seven cases of GER in 16 dogs receiving M and 8/14 in those receiving S. There were no significant differences between M and S treated dogs in age, weight, duration of anesthesia and fasting, thiopental dose or incidence of vomiting. The administration of metoclopramide at this dose did not significantly reduce the incidence of GER in these anesthetized dogs.     

Effect of pre-anesthetic meperidine on gastro-esophageal reflux in anesthetized dogs

Meperidine has been shown to decrease lower esophageal sphincter tone in monkeys and people, to have little effect in cats, and to physically increase it in dogs. We hypothesized that administration of meperidine to dogs before anesthesia would decrease the probability of GER during the subsequent anesthetic. In this randomized, prospective clinical trial we aimed to determine the incidence of GER in dogs undergoing elective orthopedic surgery and receiving either meperidine or morphine prior to anesthesia. Dogs were admitted to the study, if they were healthy, with no history of vomiting or dysphagia. Dogs were fasted overnight. Dogs were received either morphine (0.66 mg kg^–1 IM) or meperidine (8.8 mg kg^–1 IM) with acepromazine. Anesthesia in all dogs included thiopental and isoflurane in oxygen. To measure esophageal pH a sensor-tipped catheter was placed with the tip 5–7 cm cranial to the lower esophageal sphincter, and connected to a computer for continual data collection. Dogs were observed for vomiting after pre-medication, and the pH of any fluid running from the mouth or nose during anesthesia was measured. Gastro-esophageal reflux was defined as a decrease in esophageal pH below 4 or an increase above 7.5 for greater than 15 seconds. One-way anova was used to test significance of differences between groups in parametric variables. Fisher's Exact test was used to test significance of differences in incidence between groups. In dogs receiving meperidine the incidence of vomiting was 0, and of GER was 31% (4/13), compared to 60% (6/10) and 60% (6/10), respectively in dogs receiving morphine. In this preliminary study, the administration of pre-anesthetic meperidine was associated with a 29% reduction in the absolute risk of GER compared to morphine.     

Effect of lacrimal punctal occlusion on tear production and tear fluorescein dilution in normal dogs

OBJECTIVE: To evaluate effects of lacrimal punctal plugs positioned in either the upper, lower, or combination of upper and lower lacrimal canaliculi on plug retention and tolerance; tear production, as measured by the Schirmer tear test; and the dilution of fluorescein within the tear film in normal dogs. MATERIAL AND METHODS: Lacrimal punctal plugs were positioned in the lower, upper, or combination of lower and upper plugs in six laboratory-quality Beagles under topical anesthesia. Retention of plugs was evaluated daily from 8 to 23 days by visual inspection and slit-lamp biomicroscopy. Schirmer tear tests (STT 1 without topical anesthesia) were performed at 48-h intervals. Dilution of fluorescein was determined at 5- and 45-min post-fluorescein instillations once weekly. RESULTS: Lacrimal punctal plugs of 0.4 and 0.6 mm in diameter were retained for 14 (lower plugs: 100%) and 23 days (75%), and for the upper plugs at 8 days less often (75%), and were infrequently locally nonirritating. Combination of lower and upper plugs seemed to adversely affect retention of either plug. When loss of the plugs occurred, a next larger size plug was necessary suggesting some stretching of the lacrimal canaliculi occurred. Pre- and postplug placement STT results indicated no change with lower and combination lacrimal punctal plugs, but decreased levels following upper lacrimal punctal plugs. Tear fluorescein levels at 5 and 45 min in control eye (no punctum plugs) were 3.39% and 0.14%, respectively. With lower, upper, and the combination of lower and upper lacrimal puncta plugs, tear fluorescein levels at 45 min were higher than the controls (lower: 0.76%; upper: 0.45%, and combination 0.56%). CONCLUSION: Lacrimal punctal silicone plugs are retained for 8-23 days in the lower, upper, and combined lower and upper canaliculi at high rates. Effects on STT levels appear limited. Fluorescein within the tear film persists longer with all different positioned lacrimal punctum plugs than in the control eyes.     

Effects of atropine, isoprenaline, neostigmine and practocol on cardiac arrhythmias induced by potassium in anesthetized dogs

Either atropine, isoprenaline, neostigmine or practolol was given intravenously in therapeutic doses to dogs anesthetized with pentobarbitone sodium. Cardiac arrhythmias were induced by potassium chloride intravenously as a bolus injection in a dose of 0.3 mmol/kg. The standard electrocardiographic lead II was recorded continuously. pH, Po2 and Pco2 were checked from arterial blood samples before and after the injection. The isoprenaline treated dogs showed the smallest amount of arrhythmias and all the dogs survived. More severe arrhythmias were seen in the neostigmine and practolol treated dogs and the most severe occurrences were encountered in the atropine treated dogs.     

The cardiovascular sparing effect of fentanyl and atropine, administered to enflurane anesthetized dogs.

Cardiovascular effects of high dose opioid together with low dose inhalant were compared with inhalant alone to determine whether opioid/inhalant techniques were less depressant on the cardiovascular system. The effects of positive pressure ventilation and increasing heart rate to a more physiological level were also studied. Cardiovascular measurements recorded during administration of enflurane at 1.3 minimum alveolar concentration (MAC; 2.89 +/- 0.02%) to spontaneously breathing dogs (time 1) and during controlled ventilation [arterial carbon dioxide tension at 40 +/- 3 mmHg (time 2)] were similar. At time 2, mixed venous oxygen tension and arterial and mixed venous carbon dioxide tensions were significantly decreased, while arterial and mixed venous pH were significantly increased compared to measurements at time 1. After administration of fentanyl to achieve plasma fentanyl concentration of 71.7 +/- 14.4 ng/mL and reduction of enflurane concentration to yield 1.3 MAC multiple (0.99 +/- 0.01%), heart rate significantly decreased, while mean arterial pressure, central venous pressure, stroke index, and systemic vascular resistance index increased compared to measurements taken at times 1 and 2. Pulmonary arterial occlusion pressure was significantly increased compared to measurements taken at time 2. After administration of atropine until heart rate was 93 +/- 5 beats/min (plasma fentanyl concentration 64.5 +/- 13.5 ng/mL) heart rate, mean arterial pressure, cardiac index, oxygen delivery index, and venous admixture increased significantly compared to values obtained at all other times.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of short-term diphenhydramine administration on aqueous tear production in normal dogs

Objective To perform a randomized, placebo‐controlled, masked clinical trial using a cross‐over design to determine the effect of oral diphenhydramine on aqueous tear production in normal dogs. Animals studied Seventeen dogs with normal ophthalmic examinations. Procedures Baseline tear production was established for each dog by performing Schirmer tear test I (STT I). Dogs received 20‐day treatment courses of both oral diphenhydramine and placebo solutions with a 10‐day washout period between treatment periods. Each dog was randomly assigned to receive diphenhydramine or placebo at the outset of the study. Measurements of STT I values were measured at regular intervals during the study and were conducted at the same time of day throughout the study to control for diurnal variations in tear production. The significance of the impact of diphenhydramine treatment on the quantity of aqueous tear production, as determine by STT results over time, was evaluated using regression analysis with appropriate transformation. Results Statistical comparisons at each measurement time, including baseline measurements between control and treatment groups, revealed no significant differences. Mean STT I levels also did not differ significantly at any measurement time compared to baseline for treatment or control groups. Conclusions Short‐term administration of oral diphenhydramine does not result in a significant decrease in aqueous tear production in normal dogs.     

Effect of topical tropicamide on tear production as measured by Schirmer's tear test in normal dogs and cats

Objective To evaluate the effect of a single dose of topical 1% tropicamide on tear production as measured by the Schirmer tear test (STT) in the normal dog and cat. Material and methods Twenty‐eight dogs and 32 cats received 50 µl : l of 1% tropicamide in one eye and the opposite eye served as the control. STTs were performed immediately before instillation of tropicamide and then at 1, 4, 8 and 24 h post drug instillation. STT results were compared between the control and treated eyes at the different times. Results Aqueous tear production in dogs, measured by STT, was not significantly reduced. The mean ± SEM STTs for the baseline time for control and tropicamide‐treated eyes were 19.9 ± 0.8 and 20.3 ± 0.8 mm wetting/min, respectively. For the control eyes, the subsequent mean ± SEM STT levels were 20.3 ± 0.9 (1 h), 21.1 ± 0.8 (4 h), 20.1 ± 0.9 (8 h), and 18.7 ± 0.7 (24 h). For the tropicamide‐treated eyes, the subsequent mean ± SEM STT levels were 19.4 ± 0.9 (1 h), 19.3 ± 0.9 (4 h), 20.0 ± 0.9 (8 h), and 18.4 ± 0.8 (24 h). Aqueous tear production of both eyes was significantly reduced in cats at 1 h but returned to baseline by 4 h post tropicamide instillation. The mean ± SEM STT levels for the baseline time in cats for control and tropicamide‐treated eyes were 14.9 ± 0.8 and 14.7 ± 0.8 mm wetting/min, respectively. Subsequent mean ± SEM STT levels for the control eyes were 6.4 ± 1.1 (1 h), 11.9 ± 1.0 (4 h), 13.9 ± 0.8 (8 h), and 16.4 ± 1.0 (24 h). For the tropicamide‐treated eyes, the subsequent mean ± SEM STT levels were 5.3 ± 0.8 (1 h), 10.2 ± 0.8 (4 h), 14.7 ± 1.0 (8 h), and 16.6 ± 1.0 (24 h). Conclusion Single dose 1% tropicamide does not significantly lower tear production rates, as measured by the STT, in normal dogs. However, in normal cats single doses of 1% tropicamide in one eye cause significant reductions in tear production of both eyes at 1 h that recovered to baseline levels by 4 h.     

Effect of atropine sulfate on tear production in the cat when used with ketamine hydrochloride and acetylpromazine maleate

Schirmer I tear tests were done on 10 cats before and during anesthesia induced with ketamine hydrochloride in combination with acetylpromazine maleate, with and without atropine sulfate as a preanesthetic agent. Use of atropine sulfate alone decreased tear production from a mean base-line value of 16.9 +/- 3.7 mm/min to 8.2 +/- 4.9 mm/min, 10 minutes after its subcutaneous administration. Tear production continued to decrease from 8.2 +/- 4.9 mm/min to a mean of 2.3 +/- 2.5 mm/min at 30 minutes after the administration of the ketamine hydrochloride and acetylpromazine maleate combination.     

Effects of acepromazine on renal function in anesthetized dogs

OBJECTIVE: To investigate the effects of IM administration of acepromazine on indices of relative renal blood flow and glomerular filtration rate (GFR) by means of scintigraphy, as well as the effects on physiologic, hematologic, and serum biochemical variables in anesthetized dogs, compared with effects of administration of saline. ANIMAL: 6 healthy Beagles. PROCEDURE: Acepromazine (0.1 mg/kg) or physiologic saline (0.9 NaCI) solution was administered IM 30 minutes prior to induction of anesthesia with thiopentone; anesthesia was maintained with inspired isoflurane for 2.25 hours. Blood gases and circulatory and ventilatory variables were monitored. Renal function was evaluated by scintigraphic measurements of GFR and relative renal blood flow and analyses of serum and urine. Statistical analyses used ANOVA or Friedman ANOVA. RESULTS: Values of relative renal blood flow and GFR remained high despite low blood pressures. After administration of acepromazine, mean +/- SD arterial blood pressure was 66 +/- 8 mm Hg during anesthesia; this value was below the threshold (80 mm Hg) for renal autoregulation of GFR. In comparison, mean arterial blood pressure after administration of saline was significantly higher (87 +/- 13 mm Hg). However, between treatments, there were no significant differences in GFR, relative renal blood flow, or other indices of renal function. CONCLUSIONS AND CLINICAL RELEVANCE: Measurements of renal function and blood flow in dogs during anesthesia with thiopentone and isoflurane did not differ significantly between treatments, which suggested that acepromazine protects renal function despite inducing reduction in blood pressure, compared with effects of administration of saline.     

Influence of metoclopramide on gastroesophageal reflux in anesthetized dogs

OBJECTIVE: To determine the effect of 2 doses of metoclopramide on the incidence of gastroesophageal reflux (GER) in anesthetized dogs. ANIMALS: 52 healthy dogs undergoing elective orthopedic surgery. PROCEDURE: In this prospective clinical study, dogs were evaluated before and during orthopedic surgery. The anesthetic protocol used was standardized to include administration of acepromazine, morphine, thiopental, and isoflurane. Dogs were randomly selected to receive an infusion of saline (0.9% NaCl) solution, a low dose of metoclopramide, or a high dose of metoclopramide before and during anesthesia. Treatment groups were similar with respect to age, body weight, duration of food withholding before surgery, duration of surgery, and dose of thiopental administered. Dogs were positioned in dorsal recumbency during surgery. A sensor-tipped catheter was inserted to measure esophageal pH during anesthesia. We defined GER as a decrease in esophageal pH to < 4 or an increase to > 7.5 that lasted more than 30 seconds. RESULTS: The high dose of metoclopramide (bolus loading dose of 1.0 mg/kg, IV, followed by continuous infusion at a rate of 1.0 mg/kg/h) was associated with a 54% reduction in relative risk of developing GER. The low dose did not significantly affect the incidence of GER. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of metoclopramide by bolus and constant rate infusion at doses much higher than commonly used will reduce the incidence but not totally prevent GER in anesthetized dogs undergoing orthopedic surgery.     

Effect of one-lung ventilation on oxygen delivery in anesthetized dogs with an open thoracic cavity

OBJECTIVE: To evaluate effects of one-lung ventilation on oxygen delivery in anesthetized dogs with an open thoracic cavity. ANIMALS: 8 clinically normal adult Walker Hound dogs. PROCEDURE: Each dog was anesthetized and subjected to one-lung ventilation during a period when it had an open thoracic cavity. A Swan-Ganz catheter was used to measure hemodynamic variables and obtain mixed-venous blood samples. A catheter was inserted in the dorsal pedal artery to measure arterial pressure and obtain arterial blood samples. Oxygen delivery index was calculated and used to assess effects of one-lung ventilation on cardiopulmonary function. Effects on hemodynamic and pulmonary variables were analyzed. RESULTS: One-lung ventilation caused significant decreases in PaO2, arterial oxygen saturation (SaO2), mixed-venous oxygen saturation, and arterial oxygen content (CaO2). One-lung ventilation caused significant increases in PaCO2, physiologic dead space, and alveolar-arterial oxygen difference. Changes in SaO2, CaO2, and PaCO2, although significantly different, were not considered to be of clinical importance. One-lung ventilation induced a significant increase in pulmonary arterial wedge pressure, mean pulmonary artery pressure, and shunt fraction. One-lung ventilation did not have a significant effect on cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, and oxygen delivery index. CONCLUSIONS AND CLINICAL RELEVANCE: One-lung ventilation affected gas exchange and hemodynamic function, although oxygen delivery in clinically normal dogs was not affected during a period with an open thoracic cavity. One-lung ventilation can be used safely in healthy dogs with an open thoracic cavity during surgery.     

Effect of intravenous administration of ketamine on the minimum alveolar concentration of isoflurane in anesthetized dogs

OBJECTIVE: To determine the effect of 6 plasma ketamine concentrations on the minimum alveolar concentration (MAC) of isoflurane in dogs. ANIMALS: 6 dogs. PROCEDURE: In experiment 1, the MAC of isoflurane was measured in each dog and the pharmacokinetics of ketamine were determined in isoflurane-anesthetized dogs after IV administration of a bolus (3 mg/kg) of ketamine. In experiment 2, the same dogs were anesthetized with isoflurane in oxygen. A target-controlled IV infusion device was used to administer ketamine and to achieve plasma ketamine concentrations of 0.5, 1, 2, 5, 8, and 11 microg/mL by use of parameters obtained from experiment 1. The MAC of isoflurane was determined at each plasma ketamine concentration, and blood samples were collected for ketamine and norketamine concentration determination. RESULTS: Actual mean +/- SD plasma ketamine concentrations were 1.07 +/- 0.42 microg/mL, 1.62 +/- 0.98 microg/mL, 3.32 +/- 0.59 microg/mL, 4.92 +/- 2.64 microg/mL, 13.03 +/- 10.49 microg/mL, and 22.80 +/- 25.56 microg/mL for target plasma concentrations of 0.5, 1, 2, 5, 8, and 11 microg/mL, respectively. At these plasma concentrations, isoflurane MAC was reduced by 10.89% to 39.48%, 26.77% to 43.74%, 25.24% to 84.89%, 44.34% to 78.16%, 69.62% to 92.31%, and 71.97% to 95.42%, respectively. The reduction in isoflurane MAC was significant, and the response had a linear and quadratic component. Salivation, regurgitation, mydriasis, increased body temperature, and spontaneous movements were some of the adverse effects associated with the high plasma ketamine concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine appears to have a potential role for balanced anesthesia in dogs.     

Effect of hind limb position on the craniocaudal length of the lumbosacral space in anesthetized dogs

Objective To investigate whether rostral extension of the hind limbs increases the cranio‐caudal dorsal interlaminar distance between the seventh lumbar vertebra and the sacral bone (LS distance) in sternally recumbent anesthetized dogs. Study design Prospective clinical study. Animals Eighteen dogs (eight neutered males, three intact males, six spayed females, one intact female) of various breeds, weighing 4–34 kg and ranging in age from 1 to 13 years. Methods Each dog was grouped by size: small (≤10 kg), medium (15–20 kg) or large (≥25 kg). Each dog was anesthetized and positioned in sternal recumbency. Computed tomography (CT) of the lumbosacral area was performed with the hind limbs resting on the stifle and the feet extended posteriorly, and then with the hind limbs extended rostrally. LS distance, craniocaudal dorsal interlaminar distance between sixth and seventh lumbar vertebra (L6–L7 distance), length of L7 vertebral body and lumbosacral angle (LS angle) were measured on a reconstructed mid‐sagittal CT image from the two hind limb positions. The measurements from the two hind limb positions for the whole dog population and by size were compared using Student’s T tests. Diagnostic interpretation of the CT images was performed. Results The length of L7 was taken as the reference value as it was not affected by hind limb position. LS distance, L6–L7 distance and LS angle were significantly higher when the hind limbs were extended rostrally in all three size groups. The CT images of ten dogs showed clinically undetected osteoarthrosis of the ileo‐ and lumbosacral area. Conclusions and clinical relevance Rostral extension of the hind limbs significantly increases LS and L6–L7 distance and LS angle even in dogs with clinically undetected osteoarthrosis of the ileo‐ and lumbosacral area, and may enhance the ease of lumbosacral epidural injection in sternally recumbent anesthetized dogs.     

Effects of atropine on xylazine-pentobarbital anesthesia in dogs: preliminary study

The influence of atropine on anesthesia induced by xylazine-pentobarbital administration was studied in 5 dogs. The combination of xylazine (2.2 mg/kg of body weight, IM) and pentobarbital (14.0 mg/kg, IV) caused anesthesia with the duration of absence of the pedal reflex, duration of anesthesia, and the time from return of consciousness to ambulation to be 107.4, 123.4, and 59.2 minutes, respectively. Bradycardia and short-term respiratory depression were observed. An IM injection of atropine sulfate (0.045 mg/kg) did not significantly change the durations of absence of the pedal reflex and of anesthesia, the time from return of consciousness to ambulation, or the pattern of respiration in the anesthetized dogs. The PaO2 increased gradually in both groups; however, atropine caused a marked tachycardia and increased the PaCO2. Fifteen minutes after pentobarbital injection, administration of atropine sulfate caused a slight but significant (P less than 0.01) decrease in arterial pH. Although atropine sulfate antagonized xylazine bradycardia, the data indicated that it may have caused increased respiratory depression in dogs anesthetized with xylazine and pentobarbital.