Cardiopulmonary effects of intravenous fentanyl infusion in dogs during isoflurane anesthesia and with concurrent acepromazine or dexmedetomidine administration during anesthetic recovery.

OBJECTIVE: To evaluate the cardiopulmonary effects of IV fentanyl administration in dogs during isoflurane anesthesia and during anesthetic recovery with or without dexmedetomidine or acepromazine. ANIMALS: 7 sexually intact male purpose-bred hound-type dogs aged 11 to 12 months. PROCEDURES: Dogs received a loading dose of fentanyl (5 µg/kg, IV) followed by an IV infusion (5 µg/kg/h) for 120 minutes while anesthetized with isoflurane and for an additional 60 minutes after anesthesia was discontinued. Dogs were randomly assigned in a crossover design to receive dexmedetomidine (2.5 µg/kg), acepromazine (0.05 mg/kg), or saline (0.9% NaCl) solution (1 mL) IV after anesthesia ceased. Cardiopulmonary data were obtained during anesthesia and for 90 minutes after treatment administration during anesthetic recovery. RESULTS: Concurrent administration of fentanyl and isoflurane resulted in significant decreases in mean arterial blood pressure, heart rate, and cardiac index and a significant increase in Paco2. All but Paco2 returned to pretreatment values before isoflurane anesthesia was discontinued. During recovery, dexmedetomidine administration resulted in significant decreases in heart rate, cardiac index, and mixed venous oxygen tension and a significant increase in arterial blood pressure, compared with values for saline solution and acepromazine treatments. Acepromazine administration resulted in significantly lower blood pressure and higher cardiac index and Po2 in mixed venous blood than did the other treatments. Dexmedetomidine treatment resulted in significantly lower values for Pao2 and arterial pH and higher Paco2 values than both other treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl resulted in transient pronounced cardiorespiratory effects when administered during isoflurane anesthesia. During anesthetic recovery, when administered concurrently with an IV fentanyl infusion, dexmedetomidine resulted in evidence of cardiopulmonary compromise and acepromazine transiently improved cardiopulmonary performance.

Cardiopulmonary and sedative effects of the peripheral α2-adrenoceptor antagonist MK 0467 administered intravenously or intramuscularly concurrently with medetomidine in dogs.

OBJECTIVE: To evaluate the cardiopulmonary and sedative effects of the peripheral α(2)-adrenoceptor antagonist MK 0467 when administered IM or IV concurrently with medetomidine in dogs. ANIMALS: 8 adult dogs. PROCEDURES: Dogs received 20 µg of medetomidine/kg, IM, alone or concurrently with MK 0467 (0.4 mg/kg, IM), and 10 µg of medetomidine/kg, IV, alone or concurrently with MK 0467 (0.2 mg/kg, IV), in a randomized crossover study. Sedation characteristics were scored and hemodynamic measurements and arterial and mixed-venous blood samples for blood gas analysis were obtained before (time 0; baseline) and for 90 minutes after treatment. RESULTS: Heart rate (HR), mixed-venous partial pressure of oxygen (Pvo(2)), and cardiac index (CI) were significantly lower and mean arterial blood pressure (MAP), systemic vascular resistance (SVR), and oxygen extraction ratio (ER) were significantly higher after administration of medetomidine IM or IV, compared with baseline values. Administration of medetomidine and MK 0467 IM caused a significantly higher heart rate, CI, and Pvo(2) and significantly lower MAP, SVR, and ER for 60 to 90 minutes than did IM administration of medetomidine alone. Administration of medetomidine and MK 0467 IV caused a significantly higher CI and Pvo(2) and significantly lower MAP, SVR, and ER for 45 to 90 minutes than did IV administration of medetomidine alone. There was no significant difference in sedation scores among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, MK 0467 administered concurrently with medetomidine IV or IM reduced the cardiovascular effects of medetomidine but had no detectable effect on sedation scores.

Effects of hypercapnia, hypocapnia, and hyperoxemia on brain morphometrics determined by use of T1-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.

OBJECTIVE: To evaluate the effects of various combinations of PaCO2 and PaO2 values on brain morphometrics. ANIMALS: 6 healthy adult dogs. PROCEDURES: A modified Latin square design for randomization was used. Dogs were anesthetized with propofol (6 to 8 mg/kg, IV), and anesthesia was maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). Three targeted values of PaCO2 (20, 40, and 80 mm Hg) and 2 values of PaO2 (100 and 500 mm Hg) were achieved in each dog, yielding 6 combinations during a single magnetic resonance (MR) imaging session. When the endpoints were reached, dogs were given at least 5 minutes for physiologic variables to stabilize before T1-weighted MR images were obtained. Total brain volume (TBV) and lateral ventricular volume (LVV) were calculated from manually drawn contours of areas of interest by use of a software program, with each dog serving as its own control animal. Three blinded investigators subjectively evaluated the lateral ventricular size (LVS) and the cerebral sulci width (CSW). Brain morphometric values were compared among the target blood gas states. RESULTS: No significant differences in TBV were found among target states. The LVV was significantly greater during hypocapnia, compared with hypercapnia at the same PaO2 value. With regard to the subjective evaluations, there were no significant differences among evaluators or among combinations of PaO2 and PaCO2 values. CONCLUSIONS AND CLINICAL RELEVANCE: The changes observed in LVV during hypocapnia and hypercapnia may serve as a potential confounding factor when neuromorphometric evaluations are performed in anesthetized dogs.

Effects of hypercapnia, hypocapnia, and hyperoxemia on blood oxygenation level-dependent signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.

OBJECTIVE: To assess the effects of alterations in PaCO(2) and PaO(2) on blood oxygenation level-dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs. ANIMALS: 6 healthy dogs. PROCEDURES: In each dog, anesthesia was induced with propofol (6 to 8 mg/kg, IV) and maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). During 1 magnetic resonance imaging session in each dog, targeted values of PaCO(2) (20, 40, or 80 mm Hg) and PaO(2) (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO(2), 40 mm Hg; PaO(2), 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of >or= 5 minutes before susceptibility-weighted imaging was performed. Signal intensity was measured in 6 regions of interest in the brain, and data were analyzed by use of an ANCOVA and post hoc Tukey-Kramer adjustments. RESULTS: Compared with control condition findings, BOLD signal intensity did not differ significantly in any region of interest. However, signal intensities in the thalamus and diencephalic gray matter decreased significantly during both hypocapnic conditions, compared with all other conditions except for the control condition. CONCLUSIONS AND CLINICAL RELEVANCE: In isoflurane-anesthetized dogs, certain regions of gray matter appeared to have greater cerebrovascular responses to changes in PaCO(2) and PaO(2) than did others. Both PaO(2) and PaCO(2) should be controlled during magnetic resonance imaging procedures that involve BOLD signaling and taken into account when interpreting findings.

Cardiopulmonary effects of diazepam-ketamine-isoflurane or xylazine-ketamine-isoflurane during abdominal surgery in foals.

OBJECTIVE: To evaluate cardiopulmonary effects of anesthetic induction with diazepam and ketamine or xylazine and ketamine, with subsequent maintenance of anesthesia with isoflurane, in foals undergoing abdominal surgery. ANIMALS: 17 pony foals. PROCEDURES: Foals underwent laparotomy at 7 to 15 days of age and laparoscopy 7 to 10 days later. Foals were randomly assigned to receive diazepam, ketamine, and isoflurane (D/K/Iso; n = 8) or xylazine, ketamine, and isoflurane (X/K/Iso; 9) for both procedures. RESULTS: During anesthesia for laparotomy, cardiac index, and mean arterial blood pressure ranged from 110 to 180 mL/kg/min and 57 to 81 mm Hg, respectively, in the D/K/Iso group and 98 to 171 mL/kg/min and 50 to 66 mm Hg, respectively, in the X/K/Iso group. Cardiac index, heart rate, and arterial blood pressures were significantly higher in the D/K/Iso group, compared with the X/K/Iso group. During anesthesia for laparoscopy, cardiac index and mean arterial blood pressure ranged from 85 to 165 mL/kg/min and 67 to 83 mm Hg, respectively, in the D/K/Iso group, and 98 to 171 mL/kg/min and 48 to 67 mm Hg, respectively, in the X/K/Iso group. Heart rates and arterial blood pressures were significantly higher in the D/K/Iso group, compared with the X/K/Iso group. There were no significant differences between groups during either experimental period for percentage end-tidal isoflurane, arterial blood gas partial pressures, or pH values. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthesia of foals for abdominal surgery with D/K/Iso was associated with less hemodynamic depression than with X/K/Iso.

Evaluation of transpulmonary thermodilution as a method to measure cardiac output in anesthetized cats.

The objectives of this study were to evaluate the use of a transpulmonary thermodilution (Trans) technique for the measurement of cardiac output, and to determine the agreement between Trans and conventional thermodilution (TD) in anesthetized cats. Using each technique, cardiac output was measured in 5 mature cats (weights 2.4 to 5.6 kg) anesthetized with isoflurane. To induce different levels of cardiac output in each cat, anesthesia was maintained at > 1.5x end-tidal minimum alveolar concentration (MAC) of isoflurane, and at 1.3x end-tidal isoflurane MAC with and without administration of dobutamine. At least 2 comparisons between TD and Trans values were made at each cardiac output rate. Thirty-two of the 42 recorded comparisons were analyzed. Linear regression analysis (TD vs Trans) yielded an r(2) value of 0.83. The mean bias (TD-Trans) was -3.7 mL/kg/min with limits of agreement of -35.9 to 28.5 mL/kg/min. The concordance coefficient was 0.91. The Trans method showed good relationship and good agreement with TD in anesthetized cats. The Trans method is a relatively noninvasive, practical, and safe method to measure cardiac output in anesthetized cats.

Effects of a peripheral alpha2 adrenergic-receptor antagonist on the hemodynamic changes induced by medetomidine administration in conscious dogs.

OBJECTIVE: To evaluate the effects of administration of a peripheral alpha(2)-adrenergic receptor antagonist (L-659,066), with and without concurrent administration of glycopyrrolate, on cardiopulmonary effects of medetomidine administration in dogs. ANIMALS: 6 healthy adult dogs. PROCEDURES: Dogs received saline (0.9% NaCl) solution (saline group), L-659,066 (group L), or L-659,066 with glycopyrrolate (group LG). These pretreatments were followed 10 minutes later by administration of medetomidine in a randomized crossover study. Hemodynamic measurements and arterial and mixed-venous blood samples for blood gas analysis were obtained prior to pretreatment, 5 minutes after pretreatment, and after medetomidine administration at intervals up to 60 minutes. RESULTS: After pretreatment in the L and LG groups, heart rate, cardiac index, and partial pressure of oxygen in mixed-venous blood (PvO2) values were higher than those in the saline group. After medetomidine administration, heart rate, cardiac index, and PvO2 were higher and systemic vascular resistance, mean arterial blood pressure, and central venous pressure were lower in the L and LG groups than in the saline group. When the L and LG groups were compared, heart rate was greater at 5 minutes after medetomidine administration, mean arterial blood pressure was greater at 5 and 15 minutes after medetomidine administration, and central venous pressure was lower during the 60-minute period after medetomidine administration in the LG group. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of L-659,066 prior to administration of medetomidine reduced medetomidine-induced cardiovascular changes in healthy dogs. No advantage was detected with concurrent administration of L-659,066 and glycopyrrolate.

Cardiopulmonary effects of anesthetic induction with thiopental, propofol, or a combination of ketamine hydrochloride and diazepam in dogs sedated with a combination of medetomidine and hydromorphone.

OBJECTIVE: To evaluate the cardiopulmonary effects of anesthetic induction with thiopental, propofol, or ketamine hydrochloride and diazepam in dogs sedated with medetomidine and hydromorphone. ANIMALS: 6 healthy adult dogs. PROCEDURES: Dogs received 3 induction regimens in a randomized crossover study. Twenty minutes after sedation with medetomidine (10 microg/kg, IV) and hydromorphone (0.05 mg/kg, IV), anesthesia was induced with ketamine-diazepam, propofol, or thiopental and then maintained with isoflurane in oxygen. Measurements were obtained prior to sedation (baseline), 10 minutes after administration of preanesthetic medications, after induction before receiving oxygen, and after the start of isoflurane-oxygen administration. RESULTS: Doses required for induction were 1.25 mg of ketamine/kg with 0.0625 mg of diazepam/kg, 1 mg of propofol/kg, and 2.5 mg of thiopental/kg. After administration of preanesthetic medications, heart rate (HR), cardiac index, and PaO(2) values were significantly lower and mean arterial blood pressure, central venous pressure, and PaCO(2) values were significantly higher than baseline values for all regimens. After induction of anesthesia, compared with postsedation values, HR was greater for ketamine-diazepam and thiopental regimens, whereas PaCO(2) tension was greater and stroke index values were lower for all regimens. After induction, PaO(2) values were significantly lower and HR and cardiac index values significantly higher for the ketamine-diazepam regimen, compared with values for the propofol and thiopental regimens. CONCLUSIONS AND CLINICAL RELEVANCE: Medetomidine and hydromorphone caused dramatic hemodynamic alterations, and at the doses used, the 3 induction regimens did not induce important additional cardiovascular alterations. However, administration of supplemental oxygen is recommended.

Sedative and cardiopulmonary effects of medetomidine hydrochloride and xylazine hydrochloride and their reversal with atipamezole hydrochloride in calves.

OBJECTIVE: To assess the sedative and cardiopulmonary effects of medetomidine and xylazine and their reversal with atipamezole in calves. ANIMALS: 25 calves. PROCEDURES: A 2-phase (7-day interval) study was performed. Sedative characteristics (phase I) and cardiopulmonary effects (phase II) of medetomidine hydrochloride and xylazine hydrochloride administration followed by atipamezole hydrochloride administration were evaluated. In both phases, calves were randomly allocated to receive 1 of 4 treatments IV: medetomidine (0.03 mg/kg) followed by atipamezole (0.1 mg/kg; n = 6), xylazine (0.3 mg/kg) followed by atipamezole (0.04 mg/kg; 7), medetomidine (0.03 mg/kg) followed by saline (0.9% NaCl; 6) solution (10 mL), and xylazine (0.3 mg/kg) followed by saline solution (10 mL; 6). Atipamezole or saline solution was administered 20 minutes after the first injection. Cardiopulmonary variables were recorded at intervals for 35 minutes after medetomidine or xylazine administration. RESULTS: At the doses evaluated, xylazine and medetomidine induced a similar degree of sedation in calves; however, the duration of medetomidine-associated sedation was longer. Compared with pretreatment values, heart rate, cardiac index, and PaO(2) decreased, whereas central venous pressure, PaCO(2), and pulmonary artery pressures increased with medetomidine or xylazine. Systemic arterial blood pressures and vascular resistance increased with medetomidine and decreased with xylazine. Atipamezole reversed the sedative and most of the cardiopulmonary effects of both drugs. CONCLUSIONS AND CLINICAL RELEVANCE: At these doses, xylazine and medetomidine induced similar degrees of sedation and cardiopulmonary depression in calves, although medetomidine administration resulted in increases in systemic arterial blood pressures. Atipamezole effectively reversed medetomidine- and xylazine-associated sedative and cardiopulmonary effects in calves.

Postoperative effects of anesthesia and surgery on resting energy expenditure in horses as measured by indirect calorimetry.

In this study, we aimed to define the effects of anesthesia and surgery on the resting energy expenditure of horses in experimental conditions. Six horses were used in a longitudinal study with 2 study periods: before and after anesthesia and surgery. Every horse underwent a standard 90-min ventral midline exploratory laparotomy. Oxygen uptake (VO2) and carbon dioxide output (VCO2) were measured, with the use of a closed-circuit spirometry system, on 5 consecutive days immediately before and after the surgery. In 3 consecutive 5-min periods each day, the expired air was collected in a Collins spirometer. Samples of the expired gas were drawn from the spirometer through a drying column into O2 and CO2 analyzers. Resting energy expenditure was calculated as [(VO2 STPD*3.94) + (VCO2 STPD*1.11)]*1.44. This study showed that anesthesia and ventral midline exploratory laparotomy in experimental conditions increase the postoperative caloric demand in horses by an average of 1.0 Mcal/d, which represents approximately a 10% increase (P = 0.03). Additional studies in critically ill horses after surgery are needed to determine their caloric needs and to optimize their nutritional management.

Comparison of hemodynamic, clinicopathologic, and gastrointestinal motility effects and recovery characteristics of anesthesia with isoflurane and halothane in horses undergoing arthroscopic surgery.

OBJECTIVE: To compare hemodynamic, clinicopathologic, and gastrointestinal motility effects and recovery characteristics of halothane and isoflurane in horses undergoing arthroscopic surgery. ANIMALS: 8 healthy adult horses. PROCEDURE: Anesthesia was maintained with isoflurane or halothane (crossover study). At 6 intervals during anesthesia and surgery, cardiopulmonary variables and related derived values were recorded. Recovery from anesthesia was assessed; gastrointestinal tract motility was subjectively monitored for 72 hours after anesthesia. Horses were administered chromium, and fecal chromium concentration was used to assess intestinal transit time. Venous blood samples were collected for clinicopathologic analyses before and 2, 24, and 48 hours after anesthesia. RESULTS: Compared with halothane-anesthetized horses, cardiac index, oxygen delivery, and heart rate were higher and systemic vascular resistance was lower in isoflurane-anesthetized horses. Mean arterial blood pressure and the dobutamine dose required to maintain blood pressure were similar for both treatments. Duration and quality of recovery from anesthesia did not differ between treatments, although the recovery periods were somewhat shorter with isoflurane. After isoflurane anesthesia, gastrointestinal motility normalized earlier and intestinal transit time of chromium was shorter than that detected after halothane anesthesia. Compared with isoflurane, halothane was associated with increases in serum aspartate transaminase and glutamate dehydrogenase activities, but there were no other important differences in clinicopathologic variables between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with halothane, isoflurane appears to be associated with better hemodynamic stability during anesthesia, less hepatic and muscle damage, and more rapid return of normal intestinal motility after anesthesia in horses undergoing arthroscopic procedures.

Evaluation of a lithium dilution cardiac output technique as a method for measurement of cardiac output in anesthetized cats.

OBJECTIVE: To evaluate the use of a lithium dilution cardiac output (LiDCO) technique for measurement of CO and determine the agreement between LiDCO and thermodilution CO (TDCO) values in anesthetized cats. ANIMALS: 6 mature cats. PROCEDURE: Cardiac output in isoflurane-anesthetized cats was measured via each technique. To induce different rates of CO in each cat, anesthesia was maintained at > 1.5X end-tidal minimum alveolar concentration (MAC) of isoflurane and at 1.3X end-tidal isoflurane MAC with or without administration of dobutamine (1 to 3 microg/kg/min, i.v.). At least 2 comparisons between LiDCO and TDCO values were made at each CO rate. The TDCO indicator was 1.5 mL of 5% dextrose at room temperature; with the LiDCO technique, each cat received 0.005 mmol of lithium/kg (concentration, 0.015 mmol/mL). Serum lithium concentrations were measured prior to the first and following the last CO determination. RESULTS: 35 of 47 recorded comparisons were analyzed; via linear regression analysis (LiDCO vs TDCO values), the coefficient of determination was 0.91. The mean bias (TDCO-LiDCO) was -4 mL/kg/min (limits of agreement, -35.8 to + 27.2 mL/kg/min). The concordance coefficient was 0.94. After the last CO determination, serum lithium concentration was < 0.1 mmol/L in each cat. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated a strong relationship and good agreement between LiDCO and TDCO values; the LiDCO method appears to be a practical, relatively noninvasive method for measurement of CO in anesthetized cats.

Comparison of arterial pressure waveform analysis with the lithium dilution technique to monitor cardiac output in anesthetized dogs.

OBJECTIVE: To assess agreement between arterial pressure waveform-derived cardiac output (PCO) and lithium dilution cardiac output (LiDCO) systems in measurements of various levels of cardiac output (CO) induced by changes in anesthetic depth and administration of inotropic drugs in dogs. ANIMALS: 6 healthy dogs. PROCEDURE: Dogs were anesthetized on 2 occasions separated by at least 5 days. Inotropic drug administration (dopamine or dobutamine) was randomly assigned in a crossover manner. Following initial calibration of PCO measurements with a LiDCO measurement, 4 randomly assigned treatments were administered to vary CO; subsequently, concurrent pairs of PCO and LiDCO measurements were obtained. Treatments included a light plane of anesthesia, deep plane of anesthesia, continuous infusion of an inotropic drug (rate adjusted to achieve a mean arterial pressure of 65 to 80 mm Hg), and continuous infusion of an inotropic drug (7 microg/kg/min). RESULTS: Significant differences in PCO and LiDCO measurements were found during deep planes of anesthesia and with dopamine infusions but not during the light plane of anesthesia or with dobutamine infusions. The PCO system provided higher CO measurements than the LiDCO system during deep planes of anesthesia but lower CO measurements during dopamine infusions. CONCLUSIONS AND CLINICAL RELEVANCE: The PCO system tracked changes in CO in a similar direction as the LiDCO system. The PCO system provided better agreement with LiDCO measurements over time when hemodynamic conditions were similar to those during initial calibration. Recalibration of the PCO system is recommended when hemodynamic conditions or pressure waveforms are altered appreciably.

Cardiopulmonary effects of romifidine/ketamine or xylazine/ketamine when used for short duration anesthesia in the horse.

The cardiovascular changes associated with anesthesia induced and maintained with romifidine/ketamine versus xylazine/ ketamine were compared using 6 horses in a cross over design. Anesthesia was induced and maintained with romifidine (100 microg/kg, IV)/ketamine (2.0 mg/kg, IV) and ketamine (0.1 mg/kg/min, IV), respectively, in horses assigned to the romifidine/ ketamine group. Horses assigned to the xylazine/ketamine group had anesthesia induced and maintained with xylazine (1.0 mg/kg, IV)/ketamine (2.0 mg/kg, IV) and a combination of xylazine (0.05 mg/kg/min, IV) and ketamine (0.1 mg/kg/min, IV), respectively. Cardiopulmonary variables were measured at intervals up to 40 min after induction. All horses showed effective sedation following intravenous romifidine or xylazine and achieved recumbency after ketamine administration. There were no significant differences between groups in heart rate, arterial oxygen partial pressures, arterial carbon dioxide partial pressures, cardiac index, stroke index, oxygen delivery, oxygen utilization, systemic vascular resistance, left ventricular work, or any of the measured systemic arterial blood pressures. Cardiac index and left ventricular work fell significantly from baseline while systemic vascular resistance increased from baseline in both groups. The oxygen utilization ratio was higher in the xylazine group at 5 and 15 min after induction. In conclusion, the combination of romifidine/ketamine results in similar cardiopulmonary alterations as a xylazine/ketamine regime, and is a suitable alternative for clinical anesthesia of the horse from a cardiopulmonary viewpoint.

Effects of glycopyrrolate on cardiorespiratory function in horses anesthetized with halothane and xylazine.

OBJECTIVE: To evaluate cardiopulmonary effects of glycopyrrolate in horses anesthetized with halothane and xylazine. ANIMALS: 6 horses. PROCEDURE: Horses were allocated to 2 treatment groups in a randomized complete block design. Anesthesia was maintained in mechanically ventilated horses by administration of halothane (1% end-tidal concentration) combined with a constant-rate infusion of xylazine hydrochloride (1 mg/kg/h, i.v.). Hemodynamic variables were monitored after induction of anesthesia and for 120 minutes after administration of glycopyrrolate or saline (0.9% NaCl) solution. Glycopyrrolate (2.5 microg/kg, i.v.) was administered at 10-minute intervals until heart rate (HR) increased at least 30% above baseline or a maximum cumulative dose of 7.5 microg/kg had been injected. Recovery characteristics and intestinal auscultation scores were evaluated for 24 hours after the end of anesthesia. RESULTS: Cumulative dose of glycopyrrolate administered to 5 horses was 5 microg/kg, whereas 1 horse received 7.5 microg/kg. The positive chronotropic effects of glycopyrrolate were accompanied by an increase in cardiac output, arterial blood pressure, and tissue oxygen delivery. Whereas HR increased by 53% above baseline values at 20 minutes after the last glycopyrrolate injection, cardiac output and mean arterial pressure increased by 38% and 31%, respectively. Glycopyrrolate administration was associated with impaction of the large colon in 1 horse and low intestinal auscultation scores lasting 24 hours in 3 horses. CONCLUSIONS AND CLINICAL RELEVANCE: The positive chronotropic effects of glycopyrrolate resulted in improvement of hemodynamic function in horses anesthetized with halothane and xylazine. However, prolonged intestinal stasis and colic may limit its use during anesthesia.

Effects of a muscarinic type-2 antagonist on cardiorespiratory function and intestinal transit in horses anesthetized with halothane and xylazine.

OBJECTIVE: To evaluate the cardiorespiratory and intestinal effects of the muscarinic type-2 (M2) antagonist, methoctramine, in anesthetized horses. ANIMALS: 6 horses. PROCEDURE: Horses were allocated to 2 treatments in a randomized complete block design. Anesthesia was maintained with halothane (1% end-tidal concentration) combined with a constant-rate infusion of xylazine hydrochloride (1 mg/kg/h, i.v.) and mechanical ventilation. Hemodynamic variables were monitored after induction of anesthesia and for 120 minutes after administration of methoctramine or saline (0.9% NaCl) solution (control treatment). Methoctramine was given at 10-minute intervals (10 microg/kg, i.v.) until heart rate (HR) increased at least 30% above baseline values or until a maximum cumulative dose of 30 microg/kg had been administered. Recovery characteristics, intestinal auscultation scores, and intestinal transit determined by use of chromium oxide were assessed during the postanesthetic period. RESULTS: Methoctramine was given at a total cumulative dose of 30 microg/kg to 4 horses, whereas 2 horses received 10 microg/kg. Administration of methoctramine resulted in increases in HR, cardiac output, arterial blood pressure, and tissue oxygen delivery. Intestinal auscultation scores and intestinal transit time (interval to first and last detection of chromium oxide in the feces) did not differ between treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Methoctramine improved hemodynamic function in horses anesthetized by use of halothane and xylazine without causing a clinically detectable delay in the return to normal intestinal motility during the postanesthetic period. Because of their selective positive chronotropic effects, M2 antagonists may represent a safe alternative for treatment of horses with intraoperative bradycardia.

The echocardiographic effects of romifidine in dogs with and without prior or concurrent administration of glycopyrrolate.

OBJECTIVE: To determine the cardiopulmonary response to romifidine (RO) in the dog with or without prior or concurrent administration of glycopyrrolate. STUDY DESIGN: Randomized, cross-over experimental study. ANIMALS: Six (three male, three female) cross-bred dogs weighing 23 +/- 2.4 kg. METHODS: Two-dimensional guided M-mode echocardiography was performed in conscious dogs simultaneously with measurement of systolic arterial blood pressure (SBP) and heart rate (HR). Dimensions of the left ventricle (LVID), interventricular septum (IVS), and left ventricular free wall (LVFW) were obtained in systole (S) and diastole (D). Amplitude of motion (Amp) of the IVS and LVFW were also measured. From these, measures of wall stress (WS) and fractional shortening (FS) of the left ventricle were derived. Baseline echocardiographic measurements were recorded, following which one of the five treatments was administered. Glycopyrrolate (G) 0.01 mg kg-1, or saline (S) 0.5 mL, was administered IM as pre-medication (Gp or Sp), or G was administered concurrently (Gc) with romifidine (RO). Treatments were: T1, Sp + RO (40 micro g kg-1); T2, Gp + RO (40 micro g kg-1); T3, Sp + RO (120 micro g kg-1); T4, Gp + RO (120 micro g kg-1); and T5, Sp + Gc +RO (120 micro g kg-1). Romifidine or RO + Gc was administered SC 20 minutes after pre-medication (time 0), and further measurements were taken 10, 20, 30, 60, and 90 minutes after RO. RESULTS: Echocardiographic indices of cardiac systolic function (LVID-S, FS, Amp-LVFW) and HR were decreased in RO-sedated dogs (p < 0.0001). The magnitude of change in cardiac indices was least with low-dose RO. At most sampling times, high-dose RO produced significantly more alteration in cardiac indices. Systolic blood pressure increased in all treatment groups, with the greatest increases in those groups receiving G. Glycopyrrolate significantly increased HR; however, cardiac indices were further reduced. Wall stress significantly increased, with a more dramatic increase in groups receiving G. CONCLUSIONS: Indices of LV systolic function were reduced in RO-sedated dogs in a dose-related manner. Glycopyrrolate further reduced these indices and dramatically increased measurements of wall stress in dogs sedated with RO. CLINICAL RELEVANCE: Use of low-dose RO minimizes cardiac dysfunction; however, it should still be used cautiously in dogs with cardiomyopathy or heart failure. The routine use of G is not recommended to alleviate the bradycardia associated with RO in conscious dogs.

Effect of background serum lithium concentrations on the accuracy of lithium dilution cardiac output determination in dogs.

OBJECTIVES: To assess the effect of increasing serum lithium concentrations on lithium dilution cardiac output (LiDCO) determination and to determine the ability to predict the serum lithium concentration from the cumulative lithium chloride dosage. ANIMALS: 10 dogs (7 males, 3 females). PROCEDURE: Cardiac output (CO) was determined in anesthetized dogs by measuring LiDCO and thermodilution cardiac output (TDCO). The effect of the serum lithium concentration on LiDCO was assessed by observing the agreement between TDCO and LiDCO at various serum lithium concentrations. Also, cumulative lithium chloride dosage was compared with the corresponding serum lithium concentrations. RESULTS: 44 paired observations were used. The linear regression analysis for the effect of the serum lithium concentration on the agreement between TDCO and LiDCO revealed a slope of -1.530 (95% confidence interval [CI], -2.388 to -0.671) and a y-intercept of 0.011 (r2 = 0.235). The linear regression analysis for the effect of the cumulative lithium chloride dosage on the serum lithium concentration revealed a slope of 2.291 (95% CI, 2.153 to 2.429) and a y-intercept of 0.008 (r2 = 0.969). CONCLUSIONS AND CLINICAL RELEVANCE: The LiDCO measurement increased slightly as the serum lithium concentration increased. This error was not clinically relevant and was minimal at a serum lithium concentration of 0.1 mmol/L and modest at a concentration of 0.4 mmol/L. The serum lithium concentration can be reliably predicted from the cumulative lithium dosage if lithium chloride is administered often within a short period.

The cardiopulmonary effects of romifidine in dogs with and without prior or concurrent administration of glycopyrrolate.

OBJECTIVE: To determine the electrocardiographic and cardiopulmonary effects of romifidine with and without prior or concurrent administration of glycopyrrolate. STUDY DESIGN: Randomized crossover experimental study. ANIMALS: Six (three male, three female) cross-bred dogs weighing 23 ± 2.4 kg. METHODS: Baseline cardiopulmonary measurements were obtained in conscious dogs and one of five treatments was administered. Glycopyrrolate (G) 0.01 mg kg-1, or saline (S) 0.5 mL, were administered IM as premedication (Gp or Sp), or G was administered concurrently (Gc) with romifidine (RO). Treatments were as follows T1, Sp + RO 40 µg kg-1; T2, Gp + RO (40 µg kg-1); T3, Sp + RO 120 µg kg-1; T4, Gp + RO (120 µg kg-1); T5, Sp + Gc + RO (120 µg kg-1). Romifidine or RO + Gc was administered subcutaneously 20 minutes after premedication (time 0), and further measurements were taken 10, 20, 30, 60 and 90 minutes after RO. The main treatment effect was evaluated using two-way anova for repeated measures, followed by one-way anova and a post-hoc least squares difference test with a modified Bonferroni correction (p < 0.02). A Student's t-test was used to compare the effect of romifidine at 20 and 60 minutes versus baseline values (p < 0.05). RESULTS: Both low- and high-dose RO (T1, T3) significantly decreased heart rate (HR), respiratory rate (RR), cardiac index (CI) and stroke volume index, and increased arterial blood pressure (SAP), systemic vascular resistance (SVR), pulmonary arterial occlusion pressure (PAOP) and central venous pressure. High-dose RO produced greater increases in SVR and SAP measurements. Neither dose of RO produced an alteration in blood gas values or the alveolar to arterial oxygen gradient. Glycopyrrolate significantly increased HR and CI from 10 to 90 minutes between T1/T2 and T3/T4. Increases in SAP were dose related with significant differences between T1/T3 and T2/T4 at 90 and 10 minutes, respectively, and were highest in animals receiving Gp or Gc. High-dose RO groups (T3, T4) had higher values for SVR than low-dose RO groups (T1, T2), unrelated to G administration. There was an increase in PAOP in all treatments. The oxygen extraction ratio was increased with all treatments: larger increases were observed in T1, T3 and T4 compared with only minimal changes in T2. Concurrent G administration was associated with an increased frequency of high-grade second-degree atrioventricular heart block with variable conduction at 10 and 20 minutes. CONCLUSIONS: Romifidine produced effects consistent with other selective α2-adrenoreceptor agonists. Glycopyrrolate offset the decrease in HR and partially offset the decrease in CI associated with RO administration. Glycopyrrolate premedication produced an initial tachycardia and added to the increase in SAP associated with RO. Concurrent G administration was associated with a higher frequency of dysrhythmias and is not recommended. Despite the decrease in RR, RO sedation did not alter blood gas values. CLINICAL RELEVANCE: It appears likely that G administration prior to or concurrent with RO produces an increase in myocardial workload and oxygen demand suggesting that this combination should not be used in dogs with cardiomyopathy or heart failure. The improvement in oxygen extraction ratio with T2 suggests that G may be beneficial with lower doses of RO, nevertheless, the use of G and RO in cardiovascularly compromised patients is not advised.