L. Chris Sanchez

Factors associated with survival of neonatal foals with bacteremia and racing performance of surviving Thoroughbreds: 423 cases (1982-2007).

OBJECTIVE To identify factors associated with short-term survival in bacteremic neonatal foals, evaluate the racing performance of Thoroughbred survivors, and evaluate changes in causative organisms and their antimicrobial susceptibility. DESIGN Retrospective case series. ANIMALS 423 bacteremic foals. PROCEDURES Medical records of foals that were hospitalized in 1982 through 2007 were reviewed, and those with bacteremia were included in the study. Data retrieved included signalment, physical examination and clinicopathologic findings at admission, localized infections, concurrent illnesses, duration of hospitalization, and outcome (survival to discharge from the hospital vs nonsurvival). The number, identity, and antimicrobial susceptibility of organisms isolated from blood samples were also obtained. Racing records for surviving Thoroughbred foals and maternal siblings were examined. RESULTS Of 423 bacteremic foals, 254 survived. Odds of survival were negatively associated with age at admission, septic arthritis, band neutrophil count, and serum creatinine concentration and positively associated with year of admission, diarrhea, rectal temperature, neutrophil count, and arterial blood pH. Overall, microbial culture of blood samples yielded 554 isolates; Escherichia coli was consistently isolated most frequently. Percentage of isolates susceptible to enrofloxacin, but no other antimicrobial, decreased over time. Surviving Thoroughbred foals did not differ from siblings with regard to percentage of starters, percentage of winners, or number of starts; however, surviving foals had significantly fewer wins and total earnings. CONCLUSIONS AND CLINICAL RELEVANCE During the study period, microbial resistance to antimicrobials commonly used to treat bacteremic foals did not develop. Surviving bacteremic Thoroughbred foals were as likely to start races as their siblings but earned less money.

Effect of detomidine on visceral and somatic nociception and duodenal motility in conscious adult horses

OBJECTIVE To evaluate the effects of detomidine on visceral and somatic nociception, heart and respiratory rates, sedation, and duodenal motility and to correlate these effects with serum detomidine concentrations. STUDY DESIGN Nonrandomized, experimental trial. ANIMALS Five adult horses, each with a permanent gastric cannula weighing 534 +/- 46 kg. METHODS Visceral nociception was evaluated by colorectal (CRD) and duodenal distension (DD). The duodenal balloon was used to assess motility. Somatic nociception was assessed via thermal threshold (TT). Nose-to-ground (NTG) height was used as a measure of sedation. Serum was collected for pharmacokinetic analysis. Detomidine (10 or 20 microg kg(-1)) was administered intravenously. Data were analyzed by means of a three-factor anova with fixed factors of treatment and time and random factor of horse. When a significant time x treatment interaction was detected, differences were compared with a simple t-test or Bonferroni t-test. Significance was set at p < 0.05. RESULTS Detomidine produced a significant, dose-dependent decrease in NTG height, heart rate, and skin temperature and a significant, nondose-dependent decrease in respiratory rate. Colorectal distension threshold was significantly increased with 10 microg kg(-1) for 15 minutes and for at least 165 minutes with 20 microg kg(-1). Duodenal distension threshold was significantly increased at 15 minutes for the 20 microg kg(-1) dose. A significant change in TT was not observed at either dose. A marked, immediate decrease in amplitude of duodenal contractions followed detomidine administration at both doses for 50 minutes. CONCLUSIONS AND CLINICAL RELEVANCE Detomidine caused a longer period of visceral anti-nociception as determined by CRD but a shorter period of anti-nociception as determined by DD than has been previously reported. The lack of somatic anti-nociception as determined by TT testing may be related to the marked decrease in skin temperature, likely caused by peripheral vasoconstriction and the low temperature cut-off of the testing device.

Effect of acepromazine, butorphanol, or N-butylscopolammonium bromide on visceral and somatic nociception and duodenal motility in conscious horses

OBJECTIVE To evaluate effects of butorphanol, acepromazine, and N-butylscopolammonium bromide (NBB) on visceral and somatic nociception and duodenal motility in conscious, healthy horses. ANIMALS 6 adult horses. PROCEDURES Visceral nociception was evaluated by use of colorectal distention (CRD) and duodenal distention (DD) threshold. Somatic nociception was evaluated via thermal threshold (TT). Nose-to-ground height, heart rate, and respiratory rate were also measured. Each horse received each treatment in randomized order; investigators were not aware of treatments. Butorphanol was administered IV as a bolus (18 microg/kg) followed by constant rate infusion at 13 microg/kg/h for 2 hours, whereas acepromazine (0.04 mg/kg), NBB (0.3 mg/kg), and saline (0.9% NaCl) solution (2 mL) were administered IV as a bolus followed by constant rate infusion with saline solution (10 mL/h) for 2 hours. Variables were measured before and for 3 hours after treatment. Data were analyzed by use of a 3-factor ANOVA followed by a Bonferroni t test for multiple comparisons. RESULTS Nose-to-ground height decreased after acepromazine. Respiratory rate decreased after acepromazine and increased after butorphanol. Heart rate increased briefly after NBB. Some horses had an increase in TT after butorphanol and acepromazine, but there was not a significant treatment effect over time. Drug effect on DD or motility was not evident. The CRD threshold increased significantly at 5, 65, 155, and 185 minutes after acepromazine and from 5 to 65 minutes after NBB. CONCLUSIONS AND CLINICAL RELEVANCE Each drug caused predictable changes in sedation and vital signs, but consistent anti-nociceptive effects were not evident.

Effect of fentanyl on visceral and somatic nociception in conscious horses.

BACKGROUND Transdermal fentanyl is used clinically in horses based on pharmacokinetic data and antinociceptive effects documented in other species. HYPOTHESIS Fentanyl IV administration increases both visceral and somatic nociceptive threshold in conscious horses. ANIMALS Six clinically normal horses, each fitted with a permanent gastric cannula. METHODS Visceral nociception was evaluated with 2 methods of threshold detection--olorectal distention and duodenal distention. Somatic nociception was assessed by measurement of thermal threshold. Fentanyl was administered as an increasing stepwise infusion followed by a continuous-rate infusion for a total of 2 hours. There were 4 doses of fentanyl and 1 dose each of saline and xylazine administered to each horse. Serum fentanyl concentrations were measured and the resulting data were used to determine pharmacokinetic parameters for each horse. All data were analyzed by means of a 3-factor analysis of variance followed by either a simple t test or a Bonferroni t test for multiple comparisons. RESULTS Fentanyl administration did not result in significant changes in duodenal or colorectal distention threshold. Thermal threshold showed an increased trend at the 15-minute time point for the highest fentanyl group only, with a corresponding mean serum fentanyl concentration of 7.82 +/- 2.10 ng/mL. Two horses in this group became agitated and tachycardic during the first 15 minutes of the infusion. CONCLUSIONS AND CLINICAL IMPORTANCE Fentanyl did not produce a significant antinociceptive effect at the doses used, 2 of which resulted in serum concentrations above the nociceptive threshold in other species.

Systemic and anti-nociceptive effects of prolonged lidocaine, ketamine, and butorphanol infusions alone and in combination in healthy horses

BackgroundProlonged drug infusions are used to treat horses with severe signs of pain, but can be associated with altered gastrointestinal transit. The purpose of this study was to determine the effects of prolonged constant rate infusions (CRI) of lidocaine (L), butorphanol (B), and ketamine (K) alone and in combination on gastrointestinal transit, behavior, and thermal nociceptive threshold in healthy horses.MethodsEight healthy adult horses were used in a randomized, cross-over, blinded, prospective experimental trial. Interventions were saline, L, K, B, LK, LB, BK, and LBK as an intravenous CRI for 96 hours. Drugs were mixed or diluted in saline; following a bolus, CRI rate was 0.15mL/kg/hr with drug doses as follows: L – 1.3 mg/kg then 3 mg/kg/hr; B – 0.018 mg/kg then 0.013 mg/kg/hr; K – 0.55 mg/kg then 0.5 mg/kg/hr. Two-hundred plastic beads were administered intragastrically by nasogastric tube immediately prior to the bolus. Feces were collected every 2 hours, weighed, and beads manually retrieved. Behavior was scored every 2 hours, vital parameters every 6 hours, and thermal nociceptive threshold every 12 hours for 96 hours. Drug concentrations in the LBK solution were tested every 6 hours for 72 hours.ResultsFour of 64 trials (3 LBK, 1 BK) were discontinued early due to signs of abdominal discomfort. There were no apparent differences between groups in vital parameters or thermal threshold. Transit time was delayed for LB and LBK with a corresponding decrease in fecal weight that was most severe in the final 24 hours of infusion. Significant changes in behavior scores, vital parameters, or thermal threshold were not observed. The concentration of each drug in the combined solution declined by less than 31% over the sampling period.ConclusionsDrug combinations containing butorphanol cause an apparent delay in gastrointestinal transit in healthy horses without substantially affecting somatic nociception at the doses studied. Combinations of lidocaine and ketamine may have less impact on gastrointestinal transit than infusions combined with butorphanol. Further work is needed to determine the effects of these drugs in painful or critically ill patients.

Treatment of Visceral Pain in Horses

Identification and alleviation of visceral pain is a frequent concern for the equine owner and veterinarian. This article discusses sources, methods for identification and quantitation, and options for treatment of visceral pain in horses.

Determination of cardiac output in neonatal foals by ultrasound velocity dilution and its comparison to the lithium dilution method.

OBJECTIVE To compare cardiac output (CO) measured by use of lithium dilution (LiDCO) and ultrasound velocity dilution (UDCO) in conditions of high, intermediate, and low CO in anesthetized foals. DESIGN Original prospective study. SETTING University teaching hospital. ANIMALS Six foals 1-3 days of age (38-45 kg). INTERVENTIONS Neonatal foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. The CO was measured by use of LiDCO and UDCO techniques. Measurements were obtained from each foal at baseline and during low, intermediate, and high CO states. Measurements were converted to cardiac index (cardiac index=CO/body weight) values for statistical analysis. Agreement between the 2 methods was determined using Bland and Altman analysis and concordance correlation coefficients. MEASUREMENTS AND MAIN RESULTS LiDCO determinations of CO ranged between 4.0 and 14.0 L/min resulting in cardiac index ranging between 75.5 and 310 mL/kg/min. There was no significant effect of blood pressure variation on bias or relative bias (P=0.62 and 0.93, respectively). The mean bias and relative bias of UDCO (+/-SD) compared with LiDCO were -20.1+/-39.2 mL/kg/min and -7.7+/-23.4%, respectively. Concordance correlation coefficient between LiDCO and UDCO was 0.833. CONCLUSIONS When compared with LiDCO, the UDCO technique has acceptable clinical utility for measuring CO in healthy anesthetized newborn foals.

Accuracy of calculated arterial saturation in oxygen in neonatal foals and effects of monitor, sensor, site of sensor placement, and degree of hypoxemia on the accuracy of pulse oximetry.

OBJECTIVES To (1) assess the agreement between calculated values for arterial hemoglobin saturation of oxygen (SaO2 ) and values obtained by co-oximetry, (2) assess the accuracy of 2 pulse oximetry monitors for measurement of SaO2 in foals, and for each monitor, and (3) determine the optimal combination of sensor type and site of sensor placement for SaO2 monitoring. DESIGN Prospective experimental study. SETTING University teaching hospital. ANIMALS Six neonatal foals. INTERVENTIONS Foals were anesthetized with isoflurane and SaO2 was manipulated by varying the inspired fraction of oxygen. SaO2 was calculated from oxygen tension or measured by pulse oximetry using 2 monitors equipped with transmission or reflectance sensors attached to the foals tongue, lip, ear, or inserted rectally (reflectance sensor only). SaO2 values measured by co-oximetry were used as the gold standard to calculate bias. MEASUREMENTS AND MAIN RESULTS Mean (±SD) SaO2 determined by co-oximetry was 65.2% ± 11.8%, 85.4% ± 2.5%, and 97.2% ± 0.4% at the low, intermediate, and high SaO2 level, respectively. Sensors attached to the ear failed to provide SaO2 readings for most attempts. Reflectance sensors placed on the lip or rectally gave significantly larger biases at low SaO2 (-17.0% and -23.6%, respectively) than at higher levels. Bias of all other combinations of monitors, sensors, and sites (-1.8 to -4.1%) was not significantly influenced by the level of SaO2 or different from each other. The bias of calculated saturation was similar to that of pulse oximetry. CONCLUSIONS Transmission sensors placed on the lip or tongue or reflectance sensors placed on the tongue give the most accurate assessment of SaO2 in anesthetized neonatal foals. Calculated saturation is not more accurate than pulse oximetry to estimate SaO2 .Objectives To (1) assess the agreement between calculated values for arterial hemoglobin saturation of oxygen (SaO2) and values obtained by co-oximetry, (2) assess the accuracy of 2 pulse oximetry monitors for measurement of SaO2 in foals, and for each monitor, and (3) determine the optimal combination of sensor type and site of sensor placement for SaO2 monitoring. Design Prospective experimental study. Setting University teaching hospital. Animals Six neonatal foals. Interventions Foals were anesthetized with isoflurane and SaO2 was manipulated by varying the inspired fraction of oxygen. SaO2 was calculated from oxygen tension or measured by pulse oximetry using 2 monitors equipped with transmission or reflectance sensors attached to the foals tongue, lip, ear, or inserted rectally (reflectance sensor only). SaO2 values measured by co-oximetry were used as the gold standard to calculate bias. Measurements and Main Results Mean (±SD) SaO2 determined by co-oximetry was 65.2% ± 11.8%, 85.4% ± 2.5%, and 97.2% ± 0.4% at the low, intermediate, and high SaO2 level, respectively. Sensors attached to the ear failed to provide SaO2 readings for most attempts. Reflectance sensors placed on the lip or rectally gave significantly larger biases at low SaO2 (−17.0% and −23.6%, respectively) than at higher levels. Bias of all other combinations of monitors, sensors, and sites (−1.8 to −4.1%) was not significantly influenced by the level of SaO2 or different from each other. The bias of calculated saturation was similar to that of pulse oximetry. Conclusions Transmission sensors placed on the lip or tongue or reflectance sensors placed on the tongue give the most accurate assessment of SaO2 in anesthetized neonatal foals. Calculated saturation is not more accurate than pulse oximetry to estimate SaO2.

Removal of ureteral calculi in two geldings via a standing flank approach

CASE DESCRIPTION Two geldings, aged 11 and 17 years, were examined for treatment of ureteroliths located approximately 10 cm proximal to the bladder. CLINICAL FINDINGS Ureteral obstruction was an incidental finding in 1 horse that was referred because of urinary tract obstruction and a cystic calculus. This horse did not have clinical or laboratory evidence of renal failure, although severe hydronephrosis was evident on transabdominal ultrasonography. The second patient had a serum creatinine concentration of 6.3 mg/dL (reference range, 0.8 to 2.2 mg/dL) and mild hydronephrosis of the affected left kidney. TREATMENT AND OUTCOME In both patients, the obstructed ureter was exteriorized through a flank incision as a standing procedure, and the calculus was crushed and removed with a uterine biopsy forceps introduced through a ureterotomy approximately 25 cm proximal to the calculus. The cystic calculus was removed through a perineal urethrostomy by lithotripsy, piecemeal extraction, and lavage. The horse without azotemia developed pyelonephritis in the affected kidney and was euthanatized because of complications of a nephrectomy 13 months later. In the horse with azotemia, the serum creatinine concentration decreased after surgery, and the horse returned to its intended use. However, it was euthanatized approximately 2 years after surgery because of progressive renal failure, and a large nephrolith was found in the previously unobstructed right kidney. CLINICAL RELEVANCE The technique used for ureterolith removal was successful in both horses in this report, did not require sophisticated equipment, and could be effective in the early stages of ureteral obstruction as a means of restoring urine flow and renal function. The outcome in the horse with advanced unilateral renal disease without azotemia would suggest that nephrectomy should be considered as a treatment in such patients.