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- Author or Editor: Francisco J. Teixeira-Neto x
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Objective—To evaluate cardiopulmonary effects of glycopyrrolate in horses anesthetized with halothane and xylazine.
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)
Objective—To evaluate the effects of a dexmedetomidine constant rate infusion (CRI) and atropine on changes in global perfusion variables induced by hemorrhage and volume replacement (VR) in isoflurane-anesthetized dogs.
Animals—8 adult dogs.
Procedures—Each dog was anesthetized twice, with a 2-week interval between anesthetic sessions. Anesthesia was maintained with 1.3 times the minimum alveolar concentration of isoflurane with and without dexmedetomidine (1.6 μg/kg, IV bolus, followed by 2 μg/kg/h, CRI). Dogs were mechanically ventilated and received an atracurium neuromuscular blockade during both sessions. During anesthesia with isoflurane and dexmedetomidine, atropine was administered 30 minutes before baseline measurements were obtained. After baseline data were recorded, 30% of the total blood volume was progressively withdrawn and VR was achieved with an equal proportion of autologous blood.
Results—Following hemorrhage, cardiac index, oxygen delivery index, and mixed-venous oxygen saturation were significantly decreased and the oxygen extraction ratio was significantly increased from baseline. The anaerobic threshold was not achieved during either anesthetic session. When dogs were anesthetized with isoflurane and dexmedetomidine, they had a significantly lower heart rate, cardiac index, and mixed-venous oxygen saturation during VR than they did when anesthetized with isoflurane alone. Plasma lactate concentration, mixed venous-to-arterial carbon dioxide difference, base excess, and anion gap were unaltered by hemorrhage and VR and did not differ between anesthetic sessions.
Conclusions and Clinical Relevance—Results indicated that the use of a dexmedetomidine CRI combined with atropine in isoflurane-anesthetized dogs that underwent volume-controlled hemorrhage followed by VR did not compromise global perfusion sufficiently to result in anaerobic metabolism.
Objective—To evaluate the correlation between the bispectral index (BIS) and end-tidal isoflurane (ET ISO ) concentration and compare the use of 3 BIS sensor positions in dogs.
Animals—6 adult dogs.
Procedures—Mechanically ventilated dogs received pancuronium, and depth of anesthesia was altered by increasing ET ISO concentration from 1.5% to 2.3% and 3.0%. The BIS, suppression ratio (relative percentage of isoelectric electroencephalographic waveforms), and signal quality index (SQI) were recorded at each ET ISO concentration for each of 3 BIS sensor positions (frontal-occipital, bifrontal, and frontal-temporal positions).
Results—The BIS and ET ISO concentration were poorly correlated; regardless of sensor positioning, mean BIS values did not change significantly as ET ISO was increased. At 3% isoflurane, regardless of sensor positioning, there was an increase in suppression ratio coincident with BIS < 40 in some dogs, whereas paradoxic increases in BIS (> 60) were recorded in others. Furthermore, at 3.0% isoflurane, the SQI was significantly lower for the bifrontal sensor position (compared with values for the other positions), but low SQI values prevented recording of BIS values from the frontal-occipital sensor position in 2 dogs. Overall, BIS values derived from the 3 sensor positions did not differ.
Conclusions and Clinical Relevance—In dogs, BIS values may not reflect changes in depth of isoflurane anesthesia in the absence of noxious stimulation. Of the 3 sensor positions, frontal-temporal positioning provided better correlation with changes in depth of anesthesia induced via changes in isoflurane concentrations. However, the sensor placements yielded similar results at SQI values > 50.
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 investigate the effects of buprenorphine on cardiopulmonary variables and on abdominal auscultation scores in horses.
Animals—6 healthy adult horses.
Procedures—Horses were restrained in stocks and allocated to 2 treatments in a randomized crossover design, with 1-week intervals between each treatment. Saline (0.9% NaCl) solution was administered IV as a control, whereas buprenorphine (10 μg/kg, IV) was administered to the experimental group. Cardiopulmonary data were collected for 120 minutes after buprenorphine or saline solution administration. Abdominal auscultation scores were monitored for 2 and 12 hours after drug administration in the control and experimental groups, respectively.
Results—Following control treatment, horses remained calm while restrained in the stocks and no significant changes in cardiopulmonary variables were observed throughout the study. Buprenorphine administration caused excitatory phenomena (restlessness and head shaking). Heart rate, cardiac index, and arterial blood pressure were significantly increased after buprenorphine administration until the end of the observational period (120 minutes). Minimal changes were found in arterial blood gas tensions. Abdominal auscultation scores decreased significantly from baseline for 4 hours after buprenorphine administration.
Conclusions and Clinical Relevance— Buprenorphine induced excitement and hemodynamic stimulation with minimal changes in arterial blood gas tensions. These effects may impact the clinical use of buprenorphine in horses. Further studies are indicated to investigate the effects of buprenorphine on gastrointestinal motility and fecal output.
Objective—To evaluate the effects of epidural administration of 3 doses of dexmedetomidine on isoflurane minimum alveolar concentration (MAC) and characterize changes in bispectral index (BIS) induced by nociceptive stimulation used for MAC determination in dogs.
Animals—6 adult dogs.
Procedures—Isoflurane-anesthetized dogs received physiologic saline (0.9% NaCl) solution (control treatment) or dexmedetomidine (1.5 [DEX1.5], 3.0 [DEX3], or 6.0 [DEX6] μg/kg) epidurally in a crossover study. Isoflurane MAC (determined by use of electrical nociceptive stimulation of the hind limb) was targeted to be accomplished at 2 and 4.5 hours. Changes in BIS attributable to nociceptive stimulation and cardiopulmonary data were recorded at each MAC determination.
Results—With the control treatment, mean ± SD MAC values did not change over time (1.57 ± 0.23% and 1.55 ± 0.25% at 2 and 4.5 hours, respectively). Compared with the control treatment, MAC was significantly lower at 2 hours (13% reduction) but not at 4.5 hours (7% reduction) in DEX1.5-treated dogs and significantly lower at 2 hours (29% reduction) and 4.5 hours (13% reduction) in DEX3-treated dogs. The DEX6 treatment yielded the greatest MAC reduction (31% and 22% at 2 and 4.5 hours, respectively). During all treatments, noxious stimulation increased BIS; but changes in BIS were correlated with increases in electromyographic activity.
Conclusions and Clinical Relevance—In dogs, epidural administration of dexmedetomidine resulted in dose-dependent decreases in isoflurane MAC and that effect decreased over time. Changes in BIS during MAC determinations may not represent increased awareness because of the possible interference of electromyographic activity.
Objective—To evaluate the effects of administration of a peripheral α2-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.
Objective—To evaluate analgesic effects of epidurally administered neostigmine alone or in combination with morphine in dogs after ovariohysterectomy.
Animals—40 healthy bitches.
Procedures—After acepromazine premedication, anesthesia was induced. Dogs randomly received 1 of the following 4 epidural treatments 30 minutes before ovariohysterectomy (n = 10/group): saline (0.9% NaCl) solution (control), morphine (0.1 mg/kg), neostigmine (10 μg/kg), or morphine-neostigmine (0.1 mg/kg and 10 μg/kg, respectively). Analgesia was assessed for 24 hours after surgery by use of a visual analogue scale (VAS; scale of 0 to 10) or numeric descriptive scale (NDS; scale of 0 to 24) and by the need for supplemental analgesia (morphine [0.5 mg/kg, IM] administered when VAS was ≥ 4 or NDS was ≥ 8).
Results—Significantly more control dogs (n = 8) received supplemental analgesia, compared with the number of neostigmine-treated dogs (1); no dogs in the remaining groups received supplemental analgesia. Compared with values for the control dogs, the NDS scores were lower for morphine-neostigmine–treated dogs (from 2 to 6 hours and at 12 hours) and for morphine-treated dogs (all time points). The NDS scores were lower for morphine-treated dogs at 3, 12, and 24 hours, compared with values for neostigmine-treated dogs. The VAS was less sensitive than the NDS for detecting differences among groups.
Conclusions and Clinical Relevance—Epidurally administered neostigmine reduced the use of supplemental analgesia after ovariohysterectomy in dogs. However, analgesic effects were less pronounced than for epidurally administered morphine or morphine-neostigmine. Adding neostigmine to epidurally administered morphine did not potentiate opioid-induced analgesia.
Objective—To compare hemodynamic effects in dogs anesthetized with remifentanilisoflurane and with isoflurane alone.
Animals—6 adult dogs.
Procedures—Mechanically ventilated, isoflurane-anesthetized dogs received increasing constant rate infusions (CRIs) of remifentanil (0.15, 0.30, 0.60, and 0.90 μg/kg/min) or physiologic saline (0.9% NaCl) solution (control treatment), with a 1-week washout interval between treatments. Each CRI of remifentanil or saline solution was maintained for 60 minutes with equipotent end-tidal isoflurane concentrations that corresponded to 1.3 times the minimum alveolar concentration. Hemodynamic measurements and plasma vasopressin concentrations were determined before and at the end of each CRI and 60 minutes after the end of the infusion regimen.
Results—Compared with the control treatment, remifentanil CRIs significantly decreased heart rate (HR) and cardiac index (CI) and significantly increased systemic vascular resistance index (SVRI) and plasma vasopressin concentration. Greatest differences in mean values between treatments were recorded for remifentanil at 0.60 μg/kg/min (HR and Cl were 55% and 47% lower, respectively, and SVRI was 91% higher than for the control treatment). Mean arterial pressure increased significantly during the highest remifentanil CRI (9% higher than for the control treatment). The increase in vascular resistance was positively correlated with increases in vasopressin concentrations (coefficient of determination, 0.65) during anesthesia with remifentanil-isoflurane.
Conclusions and Clinical Relevance—Anesthesia maintained with remifentanil-isoflurane may decrease tissue perfusion as a result of a decrease in Cl. However, hypotension may not develop because of systemic vasoconstriction. An increase in plasma vasopressin concentration was associated with the vasoconstriction observed in dogs anesthetized with remifentanil-isoflurane. (Am J Vet Res 2010;71:1133-1141)
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)