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 endtidal
isoflurane MAC with or without administration of
dobutamine (1 to 3 µg/kg/min, IV). 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. (Am J Vet Res 2005;66:1639–1645).
Objective—To evaluate the cardiopulmonary and sedative effects of the peripheral α2-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 (Pvo2), 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 Pvo2 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 Pvo2 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.
Objective—To determine the pharmacokinetics and
toxic effects associated with IV administration of lithium
chloride (LiCl) to conscious healthy horses.
Animals—6 healthy Standardbred horses.
Procedure—Twenty 3-mmol boluses of LiCl (0.15
mmol/L) were injected IV at 3-minute intervals (total
dose, 60 mmol) during a 1-hour period. Blood samples
for measurement of serum lithium concentrations
were collected before injection and up to 24 hours
after injection. Behavioral and systemic toxic effects
of LiCl were also assessed.
Results—Lithium elimination could best be described
by a 3-compartment model for 5 of the 6 horses.
Mean peak serum concentration was 0.561 mmol/L
(range, 0.529 to 0.613 mmol/L), with actual measured
mean serum value of 0.575 mmol/L (range, 0.52 to
0.67 mmol/L) at 2.5 minutes after administration of the
last bolus. Half-life was 43.5 hours (range, 32 to 84
hours), and after 24 hours, mean serum lithium concentration
was 0.13 ± 0.05 mmol/L (range, 0.07 to
0.21 mmol/L). The 60-mmol dose of LiCl did not produce
significant differences in any measured hematologic
or biochemical variables, gastrointestinal motility,
or ECG variables evaluated during the study period.
Conclusions and Clinical Relevance—Distribution
of lithium best fit a 3-compartment model, and clearance
of the electrolyte was slow. Healthy horses
remained unaffected by LiCl at doses that exceeded
those required for determination of cardiac output.
Peak serum concentrations were less than steadystate
serum concentrations that reportedly cause
toxic effects in other species. (Am J Vet Res 2001;
Objective—To evaluate cardiopulmonary effects of
glycopyrrolate in horses anesthetized with halothane
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, IV).
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 µg/kg, IV) was administered
at 10-minute intervals until heart rate (HR) increased
at least 30% above baseline or a maximum cumulative
dose of 7.5 µg/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 µg/kg, whereas 1 horse
received 7.5 µg/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. (Am J Vet Res 2004;65:456–463)
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 yintercept
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. (Am J Vet Res 2002;63:1048–1052)
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.
Objective—To assess the sedative and cardiopulmonary effects of medetomidine and xylazine and their reversal with atipamezole in 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 PaO2 decreased, whereas central venous pressure, PaCO2, 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.
Objective—To evaluate the cardiorespiratory and
intestinal effects of the muscarinic type-2 (M2) antagonist,
methoctramine, in anesthetized 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, IV) 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 µg/kg, IV) until
heart rate (HR) increased at least 30% above baseline
values or until a maximum cumulative dose of 30
µg/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 µg/kg to 4 horses, whereas 2 horses
received 10 µg/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. (Am J Vet Res 2004;65:464–472)
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.
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 µg/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. (Am J Vet Res 2005;66:1430–1436)