Reversal of pentobarbital anesthesia with 4-aminopyridine and yohimbine in cats pretreated with acepromazine and xylazine

In 2 separate experiments, groups of atropinized cats (6 cats/group) were given acepromazine (0.25 mg/kg of body weight) or xylazine (2.2 mg/kg) IM and anesthetized with pentobarbital. The mean dose of pentobarbital was decreased approximately 36% by acepromazine, and approximately 80% by xylazine, compared with published doses. Anesthetized cats were given IV saline solution (control groups) or were given the antagonists 4-aminopyridine (4-AP; 0.5 mg/kg), yohimbine (0.4 mg/kg), or 4-AP + yohimbine (0.5 mg/kg and 0.4 mg/kg, respectively). In acepromazine-treated cats, 4-AP + yohimbine was the most effective antagonist; arousal and walking occurred in an average of 10.4 minutes and 91.7 minutes, respectively. Yohimbine enhanced the antagonistic effects of 4-AP. In xylazine-treated cats, yohimbine was an effective antagonist; arousal and walking occurred in an average of 2.8 minutes and 12.8 minutes, respectively. Yohimbine did not enhance the antagonistic effects of 4-AP. Mean respiratory rates were decreased by acepromazine, but were increased by xylazine. Thus, respiratory rate depression by pentobarbital was not as marked with xylazine as it was with acepromazine. Changes in mean heart rate were not remarkable with either sedative, and cardiac irregularities were not palpated or auscultated. In healthy cats, the duration of pentobarbital anesthesia can be controlled by 4-AP + yohimbine (acepromazine-pretreated cats) or by yohimbine alone (xylazine-pretreated cats).     

Cardiovascular effects of a high dose of romifidine in propofol-anesthetized cats

OBJECTIVE: To determine the hemodynamic effects of IM administration of romifidine hydrochloride in propofol-anesthetized cats. ANIMALS: 15 adult domestic shorthair cats. PROCEDURE: Cats were randomly assigned to receive romifidine (0, 400, or 2,000 microg/kg, IM). Cats were anesthetized with propofol and mechanically ventilated with oxygen. The right jugular vein, left carotid artery, and right femoral artery and vein were surgically isolated and catheterized. Heart rate; duration of the PR, QRS, and QT intervals; mean pulmonary artery pressure; mean right atrial pressure; systolic, diastolic, and mean arterial pressures; left ventricular systolic pressure; left ventricular end-diastolic pressure; and cardiac output were monitored. Systemic vascular resistance, rate of change of left ventricular pressure, and rate pressure product were calculated. Arterial and venous blood samples were collected anaerobically for determination of pH and blood gas tensions (Po2 and Pco2). RESULTS: Administration of romifidine at 400 and 2,000 microg/kg, IM, decreased heart rate, cardiac output, rate of change of left ventricular pressure, rate pressure product, and pH. Arterial and pulmonary artery pressures, left ventricular pressure, left ventricular end-diastolic pressure, and right atrial pressure increased and then gradually returned to baseline values. Arterial blood gas values did not change, whereas venous Pco2 increased and venous Po2 decreased. Significant differences between low and high dosages were rare, suggesting that the dosages investigated produced maximal hemodynamic effects. CONCLUSIONS AND CLINICAL RELEVANCE: Romifidine produces cardiovascular effects that are similar to those of other alpha2-agonists. High dosages of romifidine should be used with caution in cats with cardiovascular compromise.     

Hemodynamic effects of xylazine in the calf

The hemodynamic effects of sedative level doses of xylazine in five chronically instrumented calves were studied. These effects included immediate and prolonged reductions in heart rate, cardiac output, arterial blood pressure, and left ventricular dp/dt max. Stroke volume showed an initial decrease in value with a return in 15 minutes to base-line values. Total peripheral resistance, end-diastolic left ventricular pressure, end-diastolic left ventricular volume, and left ventricular residual fraction were increased after drug administration. The results indicate that a depressed myocardium results from xylazine administration. With one exception (the absence of a hypertensive response), these effects largely parallel, both quantitatively and qualitatively, those seen with this drug in other species. Sedation by xylazine is produced in cattle at doses which are small compared to those which is required for sedation in other species. These same small doses in cattle also cause hemodynamic changes.     

Echocardiographic assessment of cats anesthetized with xylazine-sodium pentobarbital.

Left ventricular echocardiographic parameters in cats were recorded, measured and analyzed to study the effects of a combination of xylazine and sodium pentobarbital on left ventricular function. The depressant effects of a combination of xylazine and sodium pentobarbital on the left ventricular dimension at end diastole, the percent change in minor diameter and the velocity of circumferential fibre shortening were compared to echocardiographic values of unanesthetized cats. No change in heart rate was noted. Stroke volume and cardiac output were depressed.     

Effects of xylazine butorphanol on cecal arterial blood flow, cecal mechanical activity, and systemic hemodynamics in horses

A chronic model with an ultrasonic transit time blood flow probe and strain gauge force transducers implanted on the cecum was used to evaluate cecal mechanical activity and cecal arterial blood flow in 4 conscious adult horses. Intravenous administration of xylazine (1.1 mg/kg of body weight) significantly decreased heart rate and cardiac output, but significantly increased diastolic pulmonary arterial pressure, mean pulmonary arterial pressure, carotid arterial pressure, and central venous pressure. Lateral cecal arterial blood flow after xylazine administration was decreased substantially more than was cardiac output, suggesting that xylazine caused constriction of the cecal vasculature. This effect of xylazine may have resulted from either a direct effect of xylazine on the cecal vasculature or from reflex vasoconstriction attributable to reduced cardiac output. Intravenous administration of butorphanol tartrate (0.1 mg/kg) did not significantly alter the hemodynamic responses to xylazine. Cecal mechanical activity, as measured by the motility index, was decreased for 120 minutes after administration of xylazine and for 150 minutes after administration of xylazine/butorphanol.     

Comparison between invasive hemodynamic measurements and noninvasive assessment of left ventricular diastolic function by use of Doppler echocardiography in healthy anesthetized cats

OBJECTIVE: To compare Doppler echocardiographic variables of left ventricular (LV) function with those obtained invasively via cardiac catheterization under a range of hemodynamic conditions. ANIMALS: 7 healthy anesthetized cats (1 to 3 years of age). PROCEDURE: Cats were anesthetized and instrumented to measure the time constant of isovolumic relaxation (tau [tau]), LV end-diastolic pressure (LVEDP), peak negative and positive rate of change of LV pressure, arterial blood pressure, and cardiac output. Echocardiographic variables of diastolic function (isovolumic relaxation time [IVRT], early LV flow propagation velocity [Vp], transmitral and pulmonary venous flow velocity indices, and LV tissue Doppler imaging indices) were measured simultaneously over a range of hemodynamic states induced by treatments with esmolol, dobutamine, cilobradine, and volume loading. Correlation between invasive and noninvasive measures of LV filling was determined by univariate and multivariate regression analyses. RESULTS: Significant correlations were found between tau and IVRT, peak Vp, peak late transmitral flow velocity, and peak systolic pulmonary venous flow velocity. A significant correlation was found between LVEDP and early diastolic transmitral flow velocity (peak E) and the ratio of peak E to peak Vp, but not between LVEDP and peak Vp. CONCLUSIONS AND CLINICAL RELEVANCE: IVRT and Vp can be used as noninvasive indices of LV relaxation; Vp was independent of preload and heart rate in this study. The E:Vp ratio may be useful as an indicator of LV filling pressure.     

Small-volume resuscitation with hypertonic saline solution in hypovolemic cats

We evaluated the hemodynamic effects of IV and intraaortic (aortic root) administration of 7.5% NaCl solution on hemodynamics in anesthetized cats with severe hypovolemia. Hypovolemic shock was induced by exsanguinating cats to a mean arterial blood pressure of 50 mm of Hg, which was maintained for 30 minutes prior to treatment. Shed blood volume was 38.4 +/- 2.1 ml/kg of body weight. The cats were treated with a small volume (4 ml/kg) of 0.9% NaCl solution IV, 7.5% NaCl solution IV, or 7.5% NaCl solution administered into the aortic root. The IV administration of 0.9% NaCl solution did not improve hemodynamics. The IV administration of 7.5% NaCl solution induced rapid restoration of arterial blood pressure, aortic blood flow, and cardiac contractility. Total peripheral vascular resistance decreased. The administration of 7.5% NaCl solution into the aortic root induced a further deterioration in hemodynamics resulting in death in 3 cats and a marked improvement in hemodynamics similar to that observed after IV administration of 7.5% NaCl solution in 2 cats. The duration of the beneficial hemodynamic effects after IV or intra-aortic administration of 7.5% NaCl solution did not exceed 60 minutes. Results of these studies suggested that either the IV or intra-aortic administration of 7.5% NaCl solution in cats can induce beneficial hemodynamic effects that may be of value in the field resuscitation of hypovolemic patients.     

The effect of 7.2% hypertonic saline solution with 6% dextran 70 on cardiac contractility as observed by an echocardiography in normovolemic and anesthetized dogs

We studied the effect of a small volume of 7.2% hypertonic saline solution (HSS) or HSS with 6% dextran 70 (HSD) on hemodynamic status, especially on cardiac contractility, in anesthetized dogs using the left ventricular end-systolic volume index (ESVI) and ejection fraction (EF), which can be obtained in noninvasive echocardiography. In the present study, the mean values of ESVI were unaffected by HSS and HSD infusion, whereas the left ventricular end-diastolic volume index (EDVI) was markedly and significant increased. As a result of the changes in EDVI but not in ESVI, EF increased transiently and significantly in the HSS and HSD group, whereas no such significant change was observed in the dogs that received isotonic saline solution. In addition, as a result of the increases in cardiac index but not arterial pressure, system vascular resistances (SVR) decreased transiently and significantly in the HSS and HSD groups, whereas no such significant change was observed in the ISS group. Therefore, the positive inotropic effects of HSS and HSD may be attributable to the increase in left ventricular preload and decreases in SVR rather than direct changes in myocardial contractility.     

The effects of a hemoglobin-based oxygen carrier (HBOC-301) on left ventricular systolic function in anesthetized dogs

OBJECTIVE: To evaluate the effects of a hemoglobin-based oxygen carrier (HBOC-301) on left ventricular preload, afterload, contractility, and ventriculo-arterial coupling in anesthetized dogs. STUDY DESIGN: A prospective experimental study. ANIMALS: Seven adult male dogs weighing 2.3 to 2.7 kg. METHODS: The study was performed on intact, closed-chest, chloralose-anesthetized dogs. Heart rate, left ventricular end-systolic and end-diastolic volume and pressure, cardiac output, stroke volume, blood resistivity, mean arterial pressure (MAP), dP/dtmax, end-systolic elastance (Ees), systemic vascular resistance (SVR), effective arterial elastance (Ea), left ventricular-arterial coupling (Ees/Ea), and myocardial oxygen consumption (MVO2) were determined during a 90-minute infusion of 30 mL/kg (20 mL/kg/h) of HBOC-301 and for 90 minutes thereafter. RESULTS: The administration of HBOC-301 significantly decreased packed cell volume, blood resistivity, heart rate, cardiac output, and dP/dtmax and significantly increased left ventricular end-diastolic and end-systolic pressure, MAP, and SVR. The Ea, Ees, Ees/Ea and MVO2 did not change. CONCLUSIONS: HBOC-301 produced insignificant changes in load independent indexes of cardiac performance (Ees, E, Ees/Ea) in anesthetized dogs. The collective directional changes in these variables, however, in conjunction with significant increases in SVR were most likely responsible for a decrease in cardiac output. Increases in SVR and the volume load (30 mL/kg) contributed to increases in left ventricular end-diastolic pressure. CLINICAL RELEVANCE: HBOC-301 infusion should be monitored and administered cautiously to dogs with poor ventricular function.     

Cardiac performance in cats after administration of xylazine or xylazine and glycopyrrolate: echocardiographic evaluations

Cardiac performance was evaluated in 9 healthy cats sedated with xylazine. Each cat was evaluated echocardiographically before and after the administration of xylazine or xylazine and glycopyrrolate. Each cat was echocardiographically evaluated during manual restraint only (control value), after IM administration of 0.55 mg of xylazine/kg of body weight, after IM administration of 2.2 mg of xylazine/kg, and after IM administration of 0.011 mg of glycopyrrolate/kg followed 10 minutes later by IM administration of 2.2 mg of xylazine/kg. Echocardiographic indices of cardiac performance (fractional shortening, left ventricular wall amplitude, aortic amplitude, mitral valve E point septal separation) indicated a significant decrease (P less than 0.05) in the left ventricular function and heart rate after the small (0.55 mg/kg) and large (2.2 mg/kg) dosages of xylazine. With the administration of glycopyrrolate, the bradycardia was minimized, but cardiac performance was not improved. After administration of glycopyrrolate, cardiac performance decreased, but the decrease was not significant when compared with the ventricular performance of the cats after administration of the large dosage of xylazine. Compared with control values, the reduction in left ventricular function values associated with administration of xylazine or xylazine and glycopyrrolate was independent of the heart rate. Therefore, the alpha-2 adrenergic agonist xylazine has a marked depressive effect on cardiac performance in the cat, and premedication with glycopyrrolate may not completely alleviate the undesirable bradycardia, but may actually be detrimental to the cardiovascular system.     

Hemodynamics in the guinea pig after anesthetization with ketamine/xylazine

The resting hemodynamics were determined in 8 guinea pigs after they were anesthetized with ketamine/xylazine. Measurements were made of blood pressure, heart rate, cardiac output, arterial blood gases, and pH. These measurements were obtained initially at 4 to 5 hours after an injection (IM) of ketamine HCl (25 mg) and xylazine (0.15 mg) was given to anesthetize the animals for catheterization (period 1), again 5 days after the operation (period 2), and finally 4 to 5 hours after a 2nd injection of ketamine/xylazine (period 3). There were no differences in heart rates, respiratory rates, or cardiac outputs among the 3 study periods. However, arterial blood pressure was slightly, but significantly, lowered after, and presumably due to, instrumentation (62 +/- 4 mm of Hg, P less than 0.05) when compared with the 5-day postoperative period (67 +/- 7 mm of Hg) or after the readministration of anesthetics (66 +/- 7 mm of Hg). The partial pressure of carbon dioxide in the arterial blood was slightly lower (4 mm of Hg, P less than 0.05) in both acutely postanesthetic periods (period 1 and period 3) than in the same animals at postoperative day 5 (period 2). This study has demonstrated that resting hemodynamics measured shortly after this anesthesia with ketamine/xylazine are not largely different from those in chronically instrumented animals.     

Absence of sensitization to epinephrine-induced cardiac arrhythmia and fibrillation in dogs and cats anesthetized with CI 744.

Ci 744 (20 mg/kg, given intramuscularly (IM) produced a reliable level of surgical anesthesia in both dogs and cats. Animals anesthetized in this way did not have an increased sensitivity to cardiac fibrillation after they were given epinephrine. Epinephrine-induced ventricular arrhythmia observed in C1 744-anesthetized animals was eliminated in cats and was markedly reduced in dogs by bilateral vagotomy. Myocardial fibrillation was not produced by epinephrine (0.1 to 100 mug/kg, intravenously (IV) in dogs and cats anesthetized with C1 744 alone. Pentobarbital anesthesia, like C1 744 anesthesia, did not sensitize the heart, whereas a significant number of thiamylal-halothane-anesthetized animals died from cardiac fibrillation after they had been given epinephrine. Additional dogs were anesthetized with C1 744 or pentobarbital and given a series of pressor and depressor agents (isoproterenol, epinephrine, tyramine, 1, 1-dimethyl-4-phenylpiperazium iodide (DMPP) plus bilateral carotid occlusion) before and after vagotomy. The responses with either anesthetic were similar with the exception that the reflex bradycardia to pressor agents was more evident in C1 744- than in pentobarbital-anesthetized dogs.     

Hemodynamic effects of carbon dioxide during intermittent positive-pressure ventilation in horses

The hemodynamic effects of high arterial carbon dioxide pressure (PaCO2) during anesthesia in horses were studied. Eight horses were anesthetized with xylazine, guaifenesin, and thiamylal, and were maintained with halothane in oxygen (end-tidal halothane concentration = 1.15%). Baseline data were collected while the horses were breathing spontaneously; then the horses were subjected to intermittent positive-pressure ventilation, and data were collected during normocapnia (PaCO2, 35 to 45 mm of Hg), moderate hypercapnia (PaCO2, 60 to 70 mm of Hg), and severe hypercapnia (PaCO2, 75 to 85 mm of Hg). Hypercapnia was induced by adding carbon dioxide to the inspired gas mixture. Moderate and severe hypercapnia were associated with significant (P less than 0.05) increases in aortic blood pressure, left ventricular systolic pressure, cardiac output, stroke volume, maximal rate of increase and decrease in left ventricular pressure (positive and negative dP/dtmax, respectively), and median arterial blood flow, and decreased time constant for ventricular relaxation. These hemodynamic changes were accompanied by increased plasma epinephrine and norepinephrine concentrations. Administration of the beta-blocking drug, propranolol hydrochloride, markedly depressed the response to hypercapnia. This study confirmed that in horses, hypercapnia is associated with augmentation of cardiovascular function.     

Postoperative Catecholamine Response to Onychectomy in Isoflurane-anesthetized Cats Effect of Analgesics

Twenty-four healthy adult cats were anesthetized with isoflurane in oxygen. Six cats (group 1) served as controls; onychectomy of the forefeet was performed in the other three groups. Saline was administered intravenously to group 1, and morphine, xylazine, and salicylate were administered to groups 2, 3, and 4, respectively. Mixed venous blood samples were drawn for catecholamine analysis before induction of anesthesia, after recovery from anesthesia, and 30 minutes and 60 minutes after administration of the analgesic agent. Plasma catecholamine concentrations were determined by high performance liquid chromatography. Isoflurane anesthesia alone induced a transient increase in epinephrine concentration. Norepinephrine and epinephrine concentrations increased significantly after onychectomy. Morphine and xylazine significantly decreased postoperative norepinephrine and epinephrine concentrations; salicylate did not.     

Changes in the myocardial performance index during dobutamine administration in anesthetized cats

OBJECTIVE: To investigate the relationship between myocardial performance index (MPI; also known as the Tei index) and cardiac function in anesthetized cats administered dobutamine. ANIMALS: 6 adult cats. PROCEDURES: Cats were anesthetized by administration of propofol (6 mg/kg, IV), and anesthesia was maintained by administration of isoflurane. Heart rate and systolic arterial pressure (SAP) were monitored. Stroke volume, cardiac output, and aortic blood flow (ABF) were measured by use of transesophageal ultrasonography. Left ventricular fractional shortening (LVFS), mitral E-wave velocity-to-A-wave velocity (E:A) ratio, and ejection time were measured by use of transthoracic echocardiography. Dobutamine was administrated via a cephalic vein at rates of 2.5, 5.0, and 10 microg/kg/min. RESULTS: Heart rate, SAP, cardiac output, and ABF increased with dobutamine administration, whereas stroke volume significantly decreased. The LVFS significantly increased, and the E:A ratio significantly decreased. Total isovolumic time and the MPI significantly decreased. The MPI was negatively correlated (r=-0.63) with LVFS. Conversely, the MPI was positively correlated with the E:A ratio (r=0.47), stroke volume (r=0.66), and total isovolumic time (r=0.95). However, the MPI was not significantly correlated with heart rate, SAP, cardiac output, or ABF. CONCLUSION AND CLINICAL RELEVANCE: Analysis suggested that the MPI provides a sensitive clinical assessment of cardiac response to medication in cats, which may be similar to the usefulness of the MPI reported in humans.     

A preliminary trial comparison of several anesthetic techniques in cats

The aim of this study was to investigate the effect of several drug combinations (atropine, xylazine, romifidine, methotrimeprazine, midazolam, or fentanyl) with ketamine for short term anesthesia in cats. Twelve cats were anesthetized 6 times by using a cross-over Latin square protocol: methotrimeprazine was combined with midazolam, ketamine, and fentanyl; midazolam and ketamine; romifidine and ketamine; and xylazine and ketamine. Atropine was combined with romifidine and ketamine, and xylazine and ketamine. Temperature, heart rate, and respiratory rate decreased in all groups. Apnea occurred in 1 cat treated with methotrimeprazine, romifidine, and ketamine, suggesting that ventilatory support may be necessary when this protocol is used. Emesis occurred in some cats treated with alpha 2-adrenoceptor agonists, and this side effect should be considered when these drugs are used.     

Hemodynamic Effects of Atropine and Glycopyrrolate in Isoflurane-Xylazine-Anesthetlzed Dogs

Alterations in parasympathetic tone are partially responsible for xylazine's hemodynamic effects. The purpose of this study was to evaluate and compare the hemodynamic changes caused by the administration of intravenous (IV) atropine or glycopyrrolate after IV xylazine in isoflurane-anesthetized dogs. Six healthy beagles (8.2 to 10.7 kg) were used in two trials separated by 7 days. Anesthesia was induced and maintained with isoflurane in 100% oxygen with controlled ventilation. Once constant end-tidal isoflurane (1.8%) and arterial partial pressure of carbon dioxide (35 to 45 mm Hg) values were reached, baseline data were recorded and xylazine (0.5 mg/kg, IV) was given. In trial 1 atropine (0.1 mg/kg, IV) was given 5 minutes after xylazine, and in trial 2 glycopyrrolate (0.025, mg/kg, IV), was given 5 minutes after xylazine. Hemodynamic variables were recorded 3 minutes after xylazine and 3 minutes after anticholinergic administration. In trial 2, bilateral vagotomies were performed 10 minutes after glycopyrrolate, and hemodynamic variables were recorded 3 minutes later. Heart rate, cardiac index, and stroke index decreased; arterial pressure and systemic vascular resistance increased after xylazine. Heart rate, cardiac index, and rate pressure product increased after anticholinergic administration. Significant differences between atropine and glycopyrrolate were not observed in any of the hemodynamic parameters. Similarly, significant differences between glycopyrrolate and bilateral vagotomy were not observed. The authors conclude that intravenous atropine and glycopyrrolate have equivalent hemodynamic actions during the increased pressure phase after IV xylazine in isoflurane-anesthetized dogs; that intravenous atropine and glycopyrrolate produce comparable increases in heart rate and that both may increase the risk of myocardial hypoxia associated with an increase in rate pressure product; and that vagal blockade produced by high-dose glycopyrrolate (.025 mg/kg, IV) is similar to that produced by bilateral vagotomy.     

Experimental studies of the load reducing effects of nitroglycerin in heart failure

The load-reducing effect of nitroglycerin (NTG), a vasodilator, was studied in dogs with heart failure. The chordae tendineae of the mitral valve were transected to induce acute mitral regurgitation (MR) for hemodynamic evaluation. By such surgical treatment, preload indices such as left ventricular end-diastolic pressure (LVEDP) and left atrial pressure (LAP) increased significantly, and subsequent cardiac dysfunction and heart failure were indicated by another decrease in stroke volume, myocardial contractility, forward flow, and myocardial oxygen consumption. To dogs with artificially established acute MR, 3 micrograms/kg/min of NTG was administered intra-arterially by means of a continuous infusion, that resulted in decrease of LVEDP, LAP and central venous pressure (CVP). Thus, a reduction of preload was determined. Simultaneously, afterload indices such as aortic systolic pressure (Aos), aortic mean pressure (Aom) and total peripheral resistance (TPR) decreased remarkably. Afterload reduction depended on the amount of venous return; therefore, an extra-corporeal circulation system was applied in order to supply a constant venous return before NTG administration. This caused a significant decrease in aortic diastolic pressure (Aod), Aos, Aom, left ventricular systolic pressure (LVSP) and TPR, and an increase in myocardial contractility and cardiac output. This suggested that afterload reduction might be realized by the vasodilatory effect of NTG on the resistance vessels.     

Cardiovascular effects of xylazine and detomidine in horses

The cardiovascular effects of xylazine and detomidine in horses were studied. Six horses were given each of the following 5 treatments, at 1-week intervals: xylazine, 1.1 mg/kg, IV; xylazine, 2.2 mg/kg, IM; detomidine, 0.01 mg/kg, IV; detomidine, 0.02 mg/kg, IV; and detomidine, 0.04 mg/kg, IM. All treatments resulted in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index; cardiac output and cardiac index were lowest following IV administration of 0.02 mg of detomidine/kg. Mean arterial pressure was significantly reduced for various periods with all treatments; however, IV administration of 0.02 mg of detomidine/kg caused hypertension initially. Systemic vascular resistance was increased by all treatments. Indices of ventricular contractility and relaxation, +dP/dt and -dP/dt, were significantly depressed by all treatments. Significant changes were not detected in stroke volume or ejection fraction. The PCV was significantly reduced by all treatments. Respiratory rate was significantly decreased with all treatments, but arterial carbon dioxide tension did not change. Arterial oxygen tension was significantly decreased briefly with the 3 IV treatments only.     

Hemodynamic effects of ionized calcium in horses anesthetized with halothane or isoflurane

OBJECTIVES: To evaluate the effects of halothane and isoflurane on cardiovascular function and serum total and ionized calcium concentrations in horses, and to determine whether administration of calcium gluconate would attenuate these effects. ANIMALS: 6 clinically normal adult Thoroughbreds. PROCEDURE: Catheters were inserted for measurement of arterial blood pressures, pulmonary arterial blood pressures, right ventricular pressure (for determination of myocardial contractility), right atrial pressure, and cardiac output and for collection of arterial blood samples. Anesthesia was then induced with xylazine hydrochloride and ketamine hydrochloride and maintained with halothane or isoflurane. An i.v. infusion of calcium gluconate was begun 75 minutes after anesthetic induction; dosage of calcium gluconate was 0.1 mg/kg of body weight/min for the first 15 minutes, 0.2 mg/kg/min for the next 15 minutes, and 0.4 mg/kg/min for an additional 15 minutes. Data were collected before, during, and after administration of calcium gluconate. RESULTS: Halothane and isoflurane decreased myocardial contractility, cardiac index, and mean arterial pressure, but halothane caused greater depression than isoflurane. Calcium gluconate attenuated the anesthetic-induced depression in cardiac index, stroke index, and maximal rate of increase in right ventricular pressure when horses were anesthetized with isoflurane. When horses were anesthetized with halothane, a higher dosage of calcium gluconate was required to attenuate the depression in stroke index and maximal rate of increase in right ventricular pressure; cardiac index was not changed with calcium administration. CONCLUSIONS AND CLINICAL RELEVANCE: I.v. administration of calcium gluconate may support myocardial function in horses anesthetized with isoflurane.