Desflurane vapor pressure depression

Veterinary Anaesthesia and Analgesia, 2005, 32, 1–19

Abstracts presented at the American College of Veterinary Anesthesiologists 29th Annual Meeting, Phoenix, Arizona, 19–25 October 2004

Comparison of tramadol and morphine for pre-medication of dogs undergoing general anesthesia for orthopedic surgery AGP Guedes, CC Natalini, EP Rude, RX Faria University of Minnesota, St Paul, MN, USA

Tramadol is a centrally acting analgesic with opioid and monoaminergic actions. Its clinical effects have been well characterized in humans, where it has been in use for many years, but little is known for veterinary species. This study evaluated the sedative, emetic, thiopental-sparing and intraoperative respiratory and hemodynamic effects of tramadol in comparison to morphine for pre-medication of dogs undergoing orthopedic surgery under halothane anesthesia. Sixteen adult, healthy, mixed breed dogs (8.0 ± 2.6 kg) were studied. Eight dogs were premedicated with tramadol (1.0 mg kg-1 IM) and the other eight with morphine (1.0 mg kg–1 IM). After 20 minutes, anesthesia was induced with thiopental and subsequently maintained with halothane in oxygen using a Bain system, with spontaneous respiration. Degree of sedation and occurrence of emesis were evaluated after pre-anesthetic medication. Dose of thiopental necessary for tracheal intubation was compared between the two groups. Arterial blood gas analyzes were done before premedication and at 60 minutes of anesthesia. Heart rate and noninvasive arterial blood pressure were recorded before pre-medication and every 10 minutes during anesthesia. Observer was blinded of the treatment given for each dog. Tramadol produced no visible sedation and no vomiting, while morphine induced a moderate degree of sedation in all dogs and vomiting in 62% of them. Dogs premedicated with tramadol required significantly more thiopental (17 ± 3.8 mg kg–1) for induction of anesthesia than those pre-medicated with morphine (12 ± 1.8 mg kg–1). Pre-medication with morphine was associated with significantly higher PaCO2 and lower pH at 60 minutes of anesthesia.

The remaining respiratory parameters and the hemodynamic variables were similar between the two groups. In conclusion, dogs pre-medicated with tramadol at 1 mg kg–1 IM do not become visibly sedated and require a greater amount of thiopental for induction of anesthesia than pre-medication with morphine. As intraoperative respiratory function is better preserved with tramadol, it may be useful for pre-medication of respiratory compromised patients.

Desflurane vapor pressure depression RJ Brosnan, BH Pypendop University of California, Davis, CA, USA

Due to its high vapor pressure and low boiling point, desflurane requires a specially designed, electronically controlled, temperature and pressure compensated vaporizer to regulate agent delivery to the anesthetic circuit. However, if the vapor pressure and boiling point were decreased, desflurane could be used in any conventional variable bypass vaporizer. Raoult’s Law states that the vapor pressure of a liquid is proportional to its molar fraction in a solution. Accordingly, propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Desflurane boiling point increased and vapor pressure decreased as a nonlinear function of dilution, but these changes were less than predicted by Raoult’s Law. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in-circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved a 11.5 ± 1.0% (mean ± SD) circuit desflurane concentration with a 5.2 ± 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog 1

attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L min–1. Anesthesia was maintained for over two hours at a mean vaporizer setting of 6.2 ± 0.4, yielding mean inspired and end-tidal desflurane concentrations of 8.7 ± 0.5% and 7.9 ± 0.7%, respectively. Within 5 minutes after cessation of anesthesia, the dog was awake, extubated and standing. In clinical practice, propylene glycol may not prove an ideal solvent for desflurane due to its instability in solution and substantial positive deviation from Raoult’s Law. However, rather than alter the vaporizer to suit physical properties of anesthetic agents, this study demonstrates that it may also be possible to alter anesthetic agents to suit physical properties of the vaporizer.

from baseline) and 13.9 ± 5.8 ng mL–1, respectively. The CRI produced increased vFT at plasma concentrations >30 ng mL–1, when compared to saline controls (p < 0.05). Targeted plasma concentrations were inconsistent at higher infusion rates, suggesting the PK of morphine may change during CRI. The actual mean ± SD CRI plasma concentrations (ng ml–1) were 10.8 ± 3.0, 22.7 ± 7.4, 32.4 ± 13.9, 35.7 ± 16.9. Morphine dosing protocols should be re-evaluated, as sufficient analgesia may not be obtained from published dosages. Intravenous boluses may be more predictable than CRI.

Evaluation of veterinarian and veterinary student knowledge and clinical use of pulse oximetry Pharmocokinetic and pharmacodynamic evaluation of intravenous morphine in dogs

EH Hofmeister, MR Read, BM Brainard University of Georgia, Athens, GA, USA

B KuKanich, BDX Lascelles, MG Papich North Carolina State University, Raleigh, NC, USA

We hypothesized that veterinarians and veterinary students may lack key knowledge about pulse oximetry, which may result in this type of patient monitor not being used on appropriate patient populations or to its full capabilities. A questionnaire was developed to assess an individual’s knowledge and understanding of pulse oximetry. Residents and specialists in anesthesiology and critical care at several academic institutions were surveyed first to assess the questionnaire for clarity and to serve as a control group. General veterinary practitioners (GPs) attending continuing education courses at the University of Georgia were surveyed over a 24-month period. Students entering their senior year anesthesiology rotation at the University of Georgia were also surveyed. Residents and specialists (69% correct responses) scored significantly higher than senior students (46%), who scored significantly higher than GPs (34%). Only 15% of GPs and 21% of senior students reported that they had received training in pulse oximetry in school. Those who had received training scored significantly higher than those who did not. Many GPs did not report using a pulse oximeter on their critical patients under anesthesia, a group that would be expected to benefit from its use. Veterinarians have a poor understanding about how pulse oximetry works, the information provided by pulse oximetry, and how to best apply it to their patients. Furthermore, the respondents did not use pulse oximeters in a

Morphine is considered the prototypical opiate analgesic. Despite the common use of morphine in dogs, ideal dosing strategies have not been formulated due to the difficulty in assessing its analgesic effects. The purpose of this study was to: 1) evaluate a noninvasive mechanical threshold device (von Frey device) to measure antinociceptive responses (pharmacodynamics) of opiates in dogs and 2) evaluate the pharmacokinetics (PK) and pharmacodynamics (PD) of intravenous (IV) morphine in dogs. Six healthy Beagle dogs were used. The von Frey threshold (vFT) response was evaluated hourly for 8 hours in each dog to examine the effect of repeated testing (controls). PK and PD (vFT) measurements were then made following a 1 mg kg–1 IV bolus of morphine sulfate. A two way blinded crossover consisted of an 8 hour IV constant rate infusion of saline or morphine with hourly PD measurements. The individual CRI was based on individual PK data and adjusted every 2 hours to attain targeted plasma concentrations of morphine of 10, 20, 30, and 40 ng mL–1. Blood samples were taken hourly in all phases, except the controls. No significant (p > 0.05) intraindividual changes in vFT occurred in the controls over 8 hours. The morphine bolus produced increased vFT at 1, 2, 3, and 4 hours post injection (p < 0.05). The EMAX and EC50 following the IV bolus were 213 ± 104% (increase 2


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manner that would derive the most information and result in the greatest benefit to the patient relative to the cost of the instrument. Didactic training in veterinary curricula and during continuing education opportunities continues to be necessary in order to produce veterinarians, who have an understanding of the technologies available that can be used to improve patient care.

with minimal cardiovascular adverse effects in these awake, healthy dogs. The plasma histamine levels obtained may be associated with significant hemodynamic changes in patients with limited cardiovascular reserve and reduced sympathetic tone.

VCARS – veterinary computerized anesthetic record system Evaluation of histamine release during constant rate infusion of morphine in dogs

JE Ilkiw, CM Brandt University of California, Davis, CA, USA

AGP Guedes, EP Rude, MA Rider University of Minnesota, St Paul, MN, USA

VCARS, the Veterinary Computerized Anesthetic Record System, has been developed to capture pre-, peri- and post-anesthetic data using Tablet PCs, 802.11b wireless networks, and a web-based database. Patient demographics, anticipated procedures and anesthetist, service information and hematologic and chemistry values are imported from the Veterinary Medical Teaching Hospital patient information system. Using a wireless Tablet PC, pre-anesthetic examination findings are recorded and an anesthetic plan including anesthetic drugs and anesthetic and monitoring equipment is developed. During induction and maintenance of anesthesia, physiologic variables, drug, fluid, anesthetic gas and oxygen administration, laboratory values, patient location, and important events can be charted with the simplicity of a paper anesthetic record. This information can be manipulated for display in a variety of ways depending on the specific needs of the case. Tools for calculating optimal fluid rates and drug dosages are incorporated into the design. The anesthetic records from multiple cases can be viewed simultaneously using a centrally-located monitor. Detailed audit trails ensure data integrity. A high-end search engine will allow rapid and complete retrieval of patient and anesthetic information. Macromedia flash is used to allow temporary disconnection from the wireless network without losing the ability to view, add, or edit data. The initial stages of software development are nearing completion, a wireless network is in place and hardware is being purchased. A pilot study will be conducted using manual entry of physiologic data prior to integration of automatically captured patient physiological variables. It is anticipated that this system will drastically improve the accuracy of data collection and retrieval and will provide important information about anesthetic management allowing improvement in overall patient care.

Previous studies have reported increased plasma histamine levels after single intravenous injections of morphine in dogs. The goals of this study were to evaluate histamine release and selected physiologic parameters during constant rate infusion (CRI) of morphine in dogs. Five adult healthy, conscious, intact female dogs were studied. Using a Latin square, repeated-measures design, dogs were randomly assigned to three treatment groups to receive either a loading dose of morphine at 0.3 mg kg–1 IV followed by a CRI of 0.17 mg kg– 1 hour–1 IV (LM) or 0.6 mg kg–1 IV followed by a CRI of 0.34 mg kg–1 hour–1 IV (HM) or a bolus and a CRI of saline (SAL). Dogs received each of the three treatments at intervals of at least 7 days. Plasma histamine concentrations, skin flushing, edema and wheals, heart rate and rhythm and noninvasive arterial blood pressure were measured before and at 1, 2, 5, 15, 30, 60, 120, 180 and 240 minutes during the CRI or at the time of occurrence. Observer was blinded to the treatment given. Results showed that the highest histamine release occurred in the HM group at 1 minute after the loading dose (median 10.6 ng mL–1), which was significantly different from the LM (median 1.85 ng mL–1) and the SAL (median 0.26 ng mL–1) groups. By comparison, no other significant differences in plasma histamine were seen for the remaining time points, although during the CRI, plasma histamine levels were numerically highest in the LM group. One dog that developed hypotension for two minutes after the loading dose in the HM group and one dog showed occasional ventricular premature contractions during both morphine CRIs, otherwise cardiovascular parameters were similar among the three treatment groups. In conclusion, both doses of morphine induced variable histamine release
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The influence of transdermally administered fentanyl on isoflurane requirements in normothermic and hypothermic dogs D Wilson, GR Pettifer, G Hosgood Louisiana State University, Baton Rouge, LA, USA

Intraoperative reductions in serum fentanyl concentrations during transdermal fentanyl (TDF) administration in dogs with induced moderate hypothermia have been reported. The impact of these reductions on any anesthetic sparing effect has not been evaluated in dogs. The objective of this investigation was to determine whether the minimum alveolar concentration (MAC) of isoflurane is altered in the presence of transdermal fentanyl in normothermic and hypothermic dogs. Six mature, healthy, mixed breed dogs were anesthetized on four separate occasions, and received each of the four following treatments in random order: (i) Sham patch-normothermia (CNORM), (ii) Sham patch-hypothermia (C-HYPO), (iii) TDF-normothermia (F-NORM), 4. TDF-hypothermia (F-HYPO). Twenty-four hours prior to induction of anesthesia, a sham or a 75 lg hour–1 fentanyl patch was applied. Following induction with isoflurane, the dogs were intubated and mechanically ventilated. Animals in the hypothermia group were cooled to 34.5 C; normothermia was maintained in the other group. MAC determinations were performed using a current (50 cycles second–1, 6.5 milliseconds duration, 40 volts) applied to needle electrodes placed 4 cm apart in the buccal mucosa of the lower jaw of the dog. The MAC (±SD) for C-NORM, C-HYPO, F-NORM and F-HYPO was 1.196 ± 0.167, 0.855 ± 0.183, 0.763 ± 0.097, and 0.830 ± 0.172, respectively. MAC for C-NORM was significantly higher than the other groups. There was a significant difference between C-NORM and F-NORM. There was no significant difference between C-HYPO, F-NORM, and F-HYPO. TDF in hypothermic dogs appears to provide no greater anesthetic sparing effect than that associated with moderate hypothermia. These findings suggest that reductions in serum fentanyl concentrations seen with moderate hypothermia are the result of a decrease of drug uptake rather than a shift of the active drug to the biophase. Effect of metoclopramide on gastroesophageal reflux in anesthetized dogs DV Wilson, AT Evans, W. Mauer Michigan State University, East Lansing, MI.

Administration of morphine before anesthesia leads to gastro-esophageal reflux (GER) in over 50% of 4

dogs during the subsequent anesthetic. This GER is clinically silent but can lead to aspiration pneumonitis, esophagitis and esophageal stricture. In this prospective clinical study we aimed to determine the effect of metoclopramide on gastro-esophageal reflux (GER) in dogs undergoing elective orthopedic surgery. Dogs were admitted to the study if they were healthy, and had no history of vomiting or dysphagia. Dogs were fasted for an average of 18.2 ± 4.3 (mean ± SD) hours prior to induction of anesthesia. Anesthesia in all dogs included acepromazine, morphine, thiopental and isoflurane in oxygen. By random allocation, half the dogs received metoclopramide (M) as an IV bolus (0.4 mg kg–1) and then infusion (0.3 mg kg–1 hour–1), the others received equivalent volumes of saline (S). To measure esophageal pH a sensortipped catheter was placed with the tip 5–7 cm cranial to the lower esophageal sphincter, and connected to a computer for continual data collection. The pH of any fluid running from the mouth or nose was measured. Gastro-esophageal reflux was defined as a decrease in esophageal pH below 4 or an increase above 7.5. Fisher’s Exact test was used to test significance of differences in incidence between groups. Separate multivariable logistic regression models were created for each outcome to assess the effects of risk factors on outcome. There were seven cases of GER in 16 dogs receiving M and 8/14 in those receiving S. There were no significant differences between M and S treated dogs in age, weight, duration of anesthesia and fasting, thiopental dose or incidence of vomiting. The administration of metoclopramide at this dose did not significantly reduce the incidence of GER in these anesthetized dogs.

Effects of intravenous lidocaine on the minimum alveolar concentration of isoflurane in cats BH Pypendop, JE Ilkiw University of California, Davis, CA, USA

Lidocaine has been reported to decrease the minimum alveolar concentration (MAC) of inhalation anesthetics in several species and has been used clinically to reduce the requirements for other anesthetic drugs. This study examined the effects of intravenous lidocaine on isoflurane MAC in cats. Six cats were studied. In experiment 1, the MAC of isoflurane was determined. An intravenous bolus of lidocaine 2 mg kg–1 was then administrated and
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venous plasma lidocaine concentrations measured to determine pharmacokinetic values. In experiment 2, lidocaine was administered to achieve target plasma concentrations between 1 and 11 lg mL–1 and the MAC of isoflurane was determined in triplicate at each lidocaine plasma concentration, using the tail-clamp method. End-tidal isoflurane concentration was determined using a calibrated infrared analyzer. Systolic blood pressure (Doppler), SpO2 and end-tidal PCO2 (calibrated Raman spectrometer) were measured prior to each MAC determination. Body temperature was maintained between 38.5 and 39.5 C by supplying external heat as needed. MAC values at the different lidocaine plasma concentrations were analyzed by a repeated measures ANOVA, using the Huynh–Feldt correction. The MAC of isoflurane in these cats was 2.21 ± 0.17. For the target concentrations of 1, 3, 5, 7, 9, and 11 lg mL–1, the actual lidocaine plasma concentrations was 1.06 ± 0.12, 2.83 ± 0.39, 4.93 ± 0.64, 6.86 ± 0.97, 8.86 ± 2.10, and 9.84 ± 1.34 lg mL–1, respectively. At these target concentrations, the MAC of isoflurane was 2.14 ± 0.14, 1.88 ± 0.18, 1.66 ± 0.16, 1.47 ± 0.13, 1.33 ± 0.23, and 1.06 ± 0.19%, respectively. Lidocaine, at target plasma concentrations of 1, 3, 5, 7, 9, and 11 lg mL–1, linearly decreased isoflurane MAC by –6 to 6, 7 to 28, 19 to 35, 28 to 45, 29 to 53, and 44 to 59%, respectively. Lidocaine significantly dose-dependently and linearly decreases the requirements for isoflurane in cats. No ceiling effect was observed within the range of plasma concentrations studied.

Effect of pre-anesthetic meperidine on gastro-esophageal reflux in anesthetized dogs DV Wilson, AT Evans, W. Mauer Michigan State University, East Lansing, MI, USA

Meperidine has been shown to decrease lower esophageal sphincter tone in monkeys and people, to have little effect in cats, and to physically increase it in dogs. We hypothesized that administration of meperidine to dogs before anesthesia would decrease the probability of GER during the subsequent anesthetic. In this randomized, prospective clinical trial we aimed to determine the incidence of GER in dogs undergoing elective orthopedic surgery and receiving either meperidine or morphine prior to anesthesia. Dogs were admitted to the study, if they were healthy, with no history of vomiting or
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dysphagia. Dogs were fasted overnight. Dogs were received either morphine (0.66 mg kg–1 IM) or meperidine (8.8 mg kg–1 IM) with acepromazine. Anesthesia in all dogs included thiopental and isoflurane in oxygen. To measure esophageal pH a sensor-tipped catheter was placed with the tip 5– 7 cm cranial to the lower esophageal sphincter, and connected to a computer for continual data collection. Dogs were observed for vomiting after premedication, and the pH of any fluid running from the mouth or nose during anesthesia was measured. Gastro-esophageal reflux was defined as a decrease in esophageal pH below 4 or an increase above 7.5 for greater than 15 seconds. One-way ANOVA was used to test significance of differences between groups in parametric variables. Fisher’s Exact test was used to test significance of differences in incidence between groups. In dogs receiving meperidine the incidence of vomiting was 0, and of GER was 31% (4/13), compared to 60% (6/10) and 60% (6/10), respectively in dogs receiving morphine. In this preliminary study, the administration of pre-anesthetic meperidine was associated with a 29% reduction in the absolute risk of GER compared to morphine.

Hemodynamic effects of intravenous lidocaine in isoflurane anesthetized cats BH Pypendop, JE Ilkiw University of California, Davis, CA, USA

Lidocaine dose-dependently decreases the minimum alveolar concentration (MAC) of isoflurane in cats. The purpose of this study was to determine the hemodynamic effects of six lidocaine plasma concentrations in isoflurane anesthetized cats. Six cats were studied. After instrumentation, end-tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration (MAC), which was determined in a previous study. Lidocaine was administered intravenously to target pseudo-steady state plasma concentrations of 0, 3, 5, 7, 9, and 11 lg ml–1, and isoflurane concentration was reduced to an equipotent concentration, determined in a previous study. Cardiovascular variables; blood gases; PCV; total protein and lactate concentrations; and lidocaine and monoethylglycinexylidide concentrations were measured at each lidocaine target concentration, before and during noxious stimulation. Derived variables were calculated. Data were analyzed using a repeated measures ANOVA, followed by a Tukey test for 5

pairwise comparisons where appropriate. One cat was excluded from analysis because the study was aborted at 7 lg ml–1 due to severe cardiorespiratory depression. Heart rate, cardiac index, stroke index, right ventricular stroke work index, total protein concentration, mixed-venous PO2 and hemoglobin oxygen saturation, arterial and mixed-venous bicarbonate concentrations, and oxygen delivery were significantly lower during lidocaine administration than when no lidocaine was administered. Mean arterial pressure, central venous pressure, pulmonary artery pressure, systemic and pulmonary vascular resistance indices, PCV, arterial and mixed-venous hemoglobin concentrations, lactate concentration, arterial oxygen concentration, and oxygen extraction ratio were significantly higher during administration of lidocaine than when no lidocaine was administered. Most changes were significant at lidocaine target plasma concentrations of 7 lg ml–1 and above. Noxious stimulation did not significantly affect most variables. Despite significantly decreasing in inhalant requirements, when combined with isoflurane, lidocaine produces greater cardiovascular depression than an equipotent dose of isoflurane alone. The use of lidocaine to reduce isoflurane requirements is not recommended in cats.

The effect of autonomic manipulation on heart rate variability in dogs AM McCoig, JR Dodam, AW Spier, HL Shafford University of Missouri-Columbia, Columbia, MO, USA

Beat-to-beat variation of heart rate is reflective of autonomic balance and has been used to assess pain and stress in human beings. The purpose of this investigation was to pharmacologically manipulate the autonomic nervous system and to determine the effect of these manipulations on heart rate variability (HRV) in dogs. Four adult male hound dogs (27 ± 1 kg) were used in the investigation. Each dog was given five treatments: Parasympathetic blockade (glycopyrrolate; 0.01 mg kg–1 IV and 0.01 mg kg–1 IM), parasympathetic stimulation (phenylephrine; 0.005 mg kg–1 IV + 0.05 mg kg–1 hour–1), sympathetic blockade (propranolol; 0.11 mg kg–1 IV), sympathetic stimulation propranolol; 0.01 lg kg–1 minute–1), and saline control. At least 48 hours were allowed between treatments. ECG recordings were obtained using an ambulatory ECG monitor. A 5-minutes period of continuous recording obtained ~30 minutes after initiation of 6

drug administration was used for data analysis. Changes in HRV were evaluated by time and frequency-domain analysis. The standard deviation of normal R-R intervals (SDNN), as well as the standard deviation of successive differences in RR intervals (SDSD) were assessed for each treatment. Low frequency (LFP; 0.05–0.15 Hz), high frequency (HFP; 0.15–0.35 Hz), and total (TP; 0.017–0.5 Hz) spectral power were also determined. The LFP:HFP ratio was also evaluated. A two-way ANOVA with a Tukey’s test was used to detect differences (p < 0.05). Administration of glycopyrrolate or isoproterenol increased HR and decreased SDNN and SDSD below control levels. Phenylephrine or propranolol administration were without effect. LFP was diminished by glycopyrrolate and isoproterenol, but was unaffected by phenylephrine and propranolol. HFP, TP, and LFP:HFP were unaffected by treatment. Both branches of the autonomic nervous system influence SDNN and LFP. SDSD, in contrast, is altered primarily by parasympathetic activity. Thus, it appears that parasympathetic activity modulates HRV in the resting dog, as either withdrawal of parasympathetic influence or accentuated sympathetic activity led to significant changes in these measures of HRV. Conversely, augmentation of parasympathetic activity or withdrawal of sympathetic tone minimally affected HRV.

Effect of intravenous lidocaine and ketamine on isoflurane minimum alveolar concentration in goats MA Redua, T Doherty, P Castro-Queiroz, BW Rohrbach University of Tennessee, Knoxville, TN, USA

This study evaluated the effects of IV lidocaine (L) and ketamine (K), alone and in combination (LK), on the isoflurane MAC (ISOMAC) in goats. It was hypothesized that L and K would reduce ISOMAC and that the effect of LK would be additive. Eight adult goats (24–51 kg) were used in the study. Each goat was studied on four occasions, at weekly intervals, using a randomized crossover design. Anesthesia was induced with isoflurane (ISO) in O2 and goats were intubated and ventilated to normocapnia. Endtidal ISO (ETISO) and CO2 were monitored with a calibrated infrared analyzer. Body temperature was maintained in the normal range using a heating pad. Approximately 45 minutes after intubation, and with the ETISO having been held constant for at least 20 minutes, determination of the baseline MAC (MACB) was initiated. A noxious stimulus,
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which consisted of clamping a claw between the jaws of a 10-inch Vulsellum forceps, was administered for 60 seconds or until purposeful movement occurred. If purposeful movement occurred, the ETISO was increased by 0.1 vols% otherwise it was decreased by 0.1 vols% and the stimulus was reapplied following a 20 minute equilibration period. Following MACB determination treatments were administered as a loading dose (Ld) in 10 mL 0.9% NaCl over 3 minutes followed by a constant rate infusion to a final volume of 60 mL hour–1 in 0.9% NaCl, as follows: L (Ld 2.5 mg kg–1 + 100 lg kg–1 minutes–1); K (Ld 1.5 mg kg–1 + 50 lg kg–1 minutes); LK or 0.9% NaCl. Post-treatment MAC (MACT) determination began 45 minutes after the start of the loading dose. MACB and MACT were determined in triplicate and the mean value was used for data analysis. Difference in percent change in MAC was tested using a mixed-model ANOVA. Means separation among levels of treatment was tested using the Tukey-Kramer method. The mean MACB for all treatments was 1.13 ± 0.03 vols%. L, K and LK reduced (p < 0.05) MACB by 19%, 49% and 69%, respectively. No change (p > 0.05) occurred with saline. It was concluded that L and K caused clinically significant decreases in ISOMAC; however, the percent MAC reduction with L was less than expected given the MAC reduction reported with L for other species. The combination (LK) caused a profound decrease in ISOMAC and this effect was additive.

dose of morphine (0.5 mg kg–1 IM) was administered at extubation. Time domain analysis of HRV was performed on 5 minutes epochs of artefact- and arrhythmia-free ECG data obtained at 12 noon and 12 midnight on each of the seven experimental days. Mean RR interval, standard deviation of normal R-R intervals (SDNN), and the standard deviation of successive differences in RR intervals (SDSD) were compared to baseline for ANES and ANSX. Pain scores obtained during the day were also evaluated. Significance was set at p < 0.01. There were no differences between groups for any baseline data. Mean RR interval did not differ from baseline on days 1–6 in ANES or ANSX. SDNN and SDSD values at noon were not different from baseline on days 1–6 in ANES or ANSX. At midnight on days 1 and 2, SDNN was significantly decreased from baseline in ANSX, and on day 1 a significant difference between groups existed. ANSX values of SDSD at midnight were significantly decreased from baseline and ANES on day 1. Pain scores for ANSX were significantly greater than baseline on days 1–3, and different from ANES on days 1–5. These results suggest that HRV is decreased following anesthesia plus surgery, and that changes in HRV may be associated with pain.

Constant rate infusion of ketamine reduces minimal alveolar concentration of isoflurane in alpacas JW Schlipf Jr, K Eaton, P Fulkerson, TW Riebold, C Cebra Oregon State University, Corvallis, Oregon

The effect of anesthesia and surgery on heart rate variability in dogs HL Shafford, JR Dodam, AW Spier University of Missouri –Columbia, Columbia, MO, USA

Heart rate variability (HRV) may be useful for objective assessment of stress and pain in animals. The objective of this study was to describe the effect of anesthesia and surgery on HRV in dogs. We hypothesized that surgery would decrease HRV to a greater degree and for a longer duration than anesthesia alone. Four healthy male dogs (29 ± 2 kg) were instrumented for ambulatory ECG monitoring. Continuous ECG data was obtained for 1 day prior to, and 6 days following anesthesia alone (ANES) or anesthesia plus unilateral stifle arthrotomy (ANSX). The anesthetic protocol included xylazine (0.5 mg kg–1 IM), morphine (0.5 mg kg–1 IM), atropine (0.04 mg kg–1 IM), thiopental (10 mg kg–1 IV) and isoflurane in oxygen. A single
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Ketamine is a rapid acting, potent, nonspecific, noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist commonly used for inducing general anesthesia and for providing post-operative pain management and may possibly lessen the need for other potentially harmful or contraindicated analgesics in camelids, such as nonsteroidal antiinflammatory drugs. Prior to determining the effectiveness of CRI ketamine for analgesia, a safe, sub-anesthetic dose was established that did not produce untoward side effects, sedation or alter normal behavior. Six healthy male alpacas (40– 90 kg) were used for the trial and each acted as its own control. Each alpaca was randomly assigned to receive ketamine at 20 and 40 lg kg–1 minute–1 in 500 mL saline. A blinded observer recorded heart rate, respiratory rate, and body temperature hourly, and behavior for 8 hours. There was a 72-hour washout period between each dosing regime. An 7

equal volume saline CRI without ketamine was used as a control. Each alpaca was allowed a one-week washout prior to being anesthetized with isoflurane using mask induction. After achieving a stable plane of anesthesia, the MAC value for isoflurane was determined. Ketamine was infused at 40 lg kg–1 minute–1 after MAC was determined for each alpaca and new MAC values for isoflurane were established after a 30-minute equilibration period. Data were analyzed with a paired t-test. No significant difference (p < 0.05) in normal behavior frequency and no untoward effects were observed between groups and controls. The mean MAC value for isoflurane was 1.158 ± 0.074%. The mean MAC value during administration of ketamine by CRI at 40 lg kg– 1 minute–1 was 0.733 ± 0.233%. There was a mean reduction of MAC value for isoflurane of 37.3 ± 16.38%. Ketamine CRI at 40 lg kg–1 min–1 ute may provide analgesia in alpacas as demonstrated by a reduction in isoflurane MAC values. Use of ketamine in a pain model will be necessary to assess true analgesic properties of ketamine CRI in alpacas, however based on the effectiveness in other species it is reasonable to assume that ketamine CRI in alpacas does provide analgesia. Whether ketamine CRI will be effective in alpacas with pre-existing pain is unknown, but for elective procedures, preemptive analgesia using ketamine CRI in alpacas may be beneficial.

Effects of sodium nitroprusside after load reduction and/or atropine pre-treatment prior to dexmedetomidine administration on cardiovascular variables in dogs RD Keegan, SA Greene, BC McKusick Washington State University, Pullman, WA, USA

The purpose of this study was to determine the cardiovascular effects of sodium nitroprusside (SNP)-induced after load reduction in dogs administered dexmedetomidine (DEX). Using a randomized crossover design and allowing at least 2 weeks between treatments 12 adult hound dogs of either sex weighing 22 ± 1.7 SD kg were anesthetized by face mask administration of 2.9% ET sevoflurane to facilitate instrumentation prior to administration of treatment drugs. Dogs were intubated and instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures, mean pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), pulmonary 8

arterial temperature (TEMP), and cardiac output (CO). Systemic (SVR) and pulmonary vascular resistances were calculated. Following completion of instrumentation dogs were allowed to recover for 40 minutes. After collection of baseline data, dogs were administered one of four treatments at T– 10 minutes prior to injection of DEX (500? g M–2 IM): 1) saline (SAL); 2) atropine (ATR, 0.02 [n = 6] or 0.04 [n = 6] mg kg–1 IM); 3) SAL + SNP (infused at 1–10 ?g kg–1 minute–1, IV as needed to maintain MAP between 90–110 mm Hg; or 4) ATR + SNP. Cardiovascular data were collected at T-20 minutes prior to administration of DEX, T-5 and at 5, 10, 20, 30, 40, and 60 minutes following DEX. Data were analyzed using ANOVA for repeated measures with post hoc differences between means identified using Bonferroni’s method (p < 0.05). Differences in ATR dose were not found to be significant and thus results for ATR dose groups were pooled. Administration of SAL (dexmedetomidine alone) was associated with decreases in HR and CO and increases in SAP, MAP, DAP, CVP, and SVR. Administration of ATR was associated with an increase in HR and CO compared with SAL. Administration of SNP was associated with an increase in HR and CO and a decrease in SVR, MAP and CVP compared with SAL. Administration of SNP + ATR was associated with effects similar to that of SNP or ATR alone and resulted in an additive increase in CO. We conclude that SNP-induced afterload reduction with or without atropine is effective in mitigating DEX-induced impairment of cardiovascular function.

Cardiovascular effects of butorphanol in isoflurane-anesthetized alpacas F Garcia Pereira, SA Greene, R Keegan, A Tibary, MM McEwen Washington State University, Pullman, WA, USA

Butorphanol has been used clinically to provide analgesia in alpacas, but cardiovascular effects have not been reported. Using a randomized cross-over design, eight healthy, young adult female alpacas (3 ± 1 SD years) weighing 64 ± 9 SD kg were anesthetized with isoflurane by mask followed by tracheal intubation and maintenance of anesthesia with 1.75% et (isoflurane) in oxygen. Two treatments, butorphanol (0.1 mg kg–1 IV) and control (saline, IV) were assigned to the animals in a randomized manner allowing a minimum of two weeks between treatments. While anesthetized, animals were instrumented for measurement of
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cardiovascular variables including systolic, diastolic, and mean arterial blood pressure, pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure, cardiac output (CO) and pulmonary temperature (TEMP). CO was measured via thermodilution using 5 mL of iced 5% dextrose and recording the average of three replicate measurements. Cardiac index, systemic vascular resistance (SVR) and pulmonary vascular resistance were also calculated. Arterial and mixed venous blood samples were collected for blood gas analysis [pH, pO2, pCO2, (HCO3)), BE, Hbsat]. Variables were collected at baseline (time 0) and at 5, 10, 15, 30, 45, and 60 minutes following injection. Variables were analyzed by ANOVA for repeated measures with post-hoc differences between means identified using the Bonferroni comparison (p < 0.05). SVR decreased five minutes after administration of butorphanol (Huynh Feldt corrected p = 0.045) and remained decreased for 60 minutes. TEMP decreased with time in both groups (Huynh Feldt corrected p = 0.000027), but groups were not different between each other. Other cardiovascular and blood gas variables were not different between groups. We conclude that butorphanol (0.1 mg kg–1 IV) had minimal effects on the cardiovascular system of these alpacas, causing a mild decrease in SVR.

The cardiovascular effects of dexmedetomidine given by continuous infusion during isoflurane anesthesia in dogs PJ Pascoe University of California, Davis, California, CA, USA

In a previous study we showed that the MAC of isoflurane was decreased by 18 ± 12% and 59 ± 7% by constant rate infusions of dexmedetomidine at 0.5 and 3 lg kg–1 hour–1. The purpose of this study was to document the cardiovascular changes associated with these infusions of dexmedetomidine at 1.3 MAC isoflurane/ dexmedetomidine. Dogs were anesthetized with isoflurane in oxygen given by mask. A cephalic venous catheter, a dorsal pedal arterial catheter and a balloon tipped, Swan–Ganz, pulmonary arterial catheter were placed percutaneously. After instrumentation the dogs were maintained at 1.3 MAC isoflurane for 60 minutes. At this time a set of measurements was made including, heart rate, respiratory rate, core body temperature, pulmonary and systemic arterial
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blood pressures (SAP, MAP, DAP, CVP, SPAP, MPAP, DPAP and PAOP), cardiac output and arterial and mixed venous blood samples were collected for the measurement of blood gases, pH, hemoglobin concentration, PCV and total protein. Calculated variables included base excess (BE), (HCO3)), cardiac index, systemic and pulmonary vascular resistance indices, oxygen delivery, oxygen consumption, oxygen utilization ratio and shunt fraction. After these measurements to dogs were randomly assigned to receive a loading dose of 0.5 or 3 lg kg–1 of dexmedetomidine given over 6 minutes followed by an infusion of 0.5 (LD) or 3 lg kg–1 hour–1 (HD), respectively. The concentration of isoflurane was reduced by the above percentages, respectively, to maintain 1.3 MAC. Full sets of measurements were repeated at 10, 30, 60, 90, 120, 150 and 180 minutes after the start of the loading dose. Measured and calculated variables were compared with baseline using an ANOVA and a post-hoc Tukey’s test. Significance was set at p = 0.05 and results are given as mean ± SD. The initial concentration of isoflurane was 1.73 ± 0.02% and was reduced to 1.41 ± 0.02 and 0.72 ± 0.09% for the LD and HD, respectively. Heart rate decreased with both doses but no other parameter changed significantly with the LD. With the HD there were significant changes in SAP, MAP, DAP, CVP, MPAP, PAOP, CI, SVRI, PCV, DO2 and shunt fraction. The LD appeared to have minimal effect on the cardiopulmonary values measured, whereas the HD caused typical changes expected with an alpha-2 agonist.

Effects of 2.0% end-tidal isoflurane with and without atropine prior to dexmedetomidine administration on cardiovascular variables in dogs RD Keegan, SA Greene, BC McKusick Washington State University, Pullman, WA, USA

The purpose of this study was to determine the cardiovascular effects of 2.0% end-tidal isoflurane in dogs administered dexmedetomidine (DEX). Using a randomized crossover design and allowing at least 2 weeks between treatments 12 adult hound dogs of either sex weighing 22 ± 1.7 SD kg were anesthetized by face mask administration of either sevoflurane or isoflurane to facilitate instrumentation prior to administration of treatment drugs. Dogs were intubated and instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP) and 9

diastolic (DAP) arterial pressures, mean pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), and cardiac output (CO) via thermodilution using 5 mL of 5% dextrose, and recording the average of three replicate measurements. Cardiac index (CI) and systemic (SVR) and pulmonary vascular resistances were calculated. Following completion of instrumentation, dogs were allowed to recover for 40 minutes. After collection of baseline data, dogs were administered one of four treatments at T10 minutes prior to injection of DEX (500? g M–2 IM): 1) saline (SAL); 2) atropine [ATR, 0.02 (n = 6) or 0.04 (n = 6) mg kg–1 IM]; 3) ISO (2.0% end tidal concentration); or 4) ISO + ATR. Cardiovascular data were collected at T-20 and T-5 minutes prior to administration of DEX, and at 5, 10 , 20, 30, 40, and 60 min following DEX. Data were analyzed using ANOVA for repeated measures with post-hoc differences between means identified using Bonferroni’s method (p < 0.05). Differences in ATR dose were not found to be significant and thus results for ATR dose groups were pooled. Administration of SAL (dexmedetomidine alone) was associated with decreases in HR and CO and increases in SAP, MAP, DAP, CVP, and SVR. Administration of ATR was associated with an increase in HR and CO compared with SAL. Administration of ISO was associated with an increase in HR and a decrease in SVR, MAP and CVP compared with SAL. Administration of ISO + ATR was associated with effects similar to that of ISO or ATR alone. We conclude that administration of ISO reduces the increase in SVR associated with administration of DEX and does not adversely affect CO.

An effective buprenorphine analgesic protocol increases post-operative adhesions in rats after laparotomy LS Peck, SE Blenden, M Michelis, EP Goldberg University of Florida, Gainesville, FL, USA

The use of analgesics in post-operative adhesion (POA) research is problematic due to POA-inhibiting effects of anti-inflammatory agents and bowel motility-inhibiting effects of opioids, which may increase adhesion formation. This study was conducted to assess a buprenorphine (BUP) protocol for analgesic efficacy and its effects on POA formation in a rat cecal abrasion model. The protocol was approved by the University of Florida’s Institutional 10

Animal Care and Use Committee (IACUC). Forty-one female Sprague-Dawley rats were randomized into two groups (n = 20 or 21 group). Body weight, food and water intake were recorded daily from 2 days before until 7 days after surgery. Treatment rats received 0.05 mg kg–1 BUP SQ at anesthesia induction and 0.3 mg kg–1 BUP orally in flavored gelatin 6 hours after surgery. Control rats received saline placebo injection and plain gelatin. All rats underwent laparotomy and controlled cecal abrasion. At 3, 6 and 24 hours post-operatively rats were individually observed in 10-minutes periods for pain related behavior incidence: ‘twitch’ (contraction of muscles along dorsum and/or head), ‘back arch’ (cat-like position with front legs extended and pushing backward), ‘writhe’ (flank contraction), and ‘stagger/fall’ (momentary loss of balance while grooming or ambulating), using the method of Roughan and Flecknell (Pain 2001,90, 65–74). On post-op day seven rats were euthanized by CO2 inhalation and POA evaluated (0 to 4 scale; 3 Grade 2 = clinically significant.) BUP treated rats had lower mean pain scores than control rats at 3 hours (1.6 ± 1.7 versus 20.3 ± 13.5 (mean ± SD); p < 0.001) and 6 hours (2.1 ± 2.7 versus 23.7 ± 12.9; p < 0.001) but not 24 hours (1.5 ± 1.3 versus 4.9 ± 6.6; p = 0.35) post-operatively. Predominant pain behavior was ‘writhe’ (flank contraction) in contrast to ‘twitch,’ ‘back arch,’ and ‘stagger/fall’ reported as most common pain indicators in other rat strains. BUP rats had greater mean adhesion incidence (2.4 ± 1.7 versus 1.4 ± 1.8; p < 0.03) and severity (90% 3 Gr.2 versus 65% of controls; p < 0.05). The BUP protocol appeared to provide effective analgesia for at least 24 hours post-operatively. Strain of rat may affect pain related behavior. BUP should be used with caution after abdominal surgical procedures having high risk of POA formation.

Dexmedetomidine and midazolam interaction is synergistic with isoflurane and additive with halothane in terms of MAC reduction E Rioja, M Santos, F Martı´nez, FJ Tendillo Universidad Complutense de Madrid and Hospital Universitario Puerta de Hierro, Spain

Dexmedetomidine and midazolam have synergistic interaction for the sedative/hypnotic and analgesic effects. The purpose of this study was to assess the type of interaction between dexmedetomidine and
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midazolam for the immobilizing effect in terms of MAC reduction of either halothane (HAL) or isoflurane (ISO). Fifty-six rats were randomly allocated into one of eight groups (n = 7): SAL + HAL group received saline solution and halothane, SAL + ISO group received saline solution and isoflurane, DEX + HAL group received an intravenous continuous infusion of dexmedetomidine (0.25 lg kg–1 minute–1) and halothane, DEX + ISO group received an intravenous continuous infusion of dexmedetomidine (0.25 lg kg–1 minute–1) and isoflurane, MID + HAL group received an intravenous bolus of midazolam (1 mg kg–1) and halothane, MID + ISO group received an intravenous bolus of midazolam (1 mg kg–1) and isoflurane, DEX + MID + HAL group received dexmedetomidine (0.25 lg kg–1 minute–1), midazolam (1 mg kg–1) and halothane and DEX + MID + ISO group received dexmedetomidine (0.25 lg kg–1 minute–1), midazolam (1 mg kg–1) and isoflurane. The tail clamp method was used for MAC determination. Heart rate, invasive arterial blood pressure, respiratory rate and rectal temperature were continuously monitored. Arterial blood gases were analyzed at the end of each experiment. Data were analyzed using a one-way ANOVA and a Tukey-Kramer test for multiple comparisons. A p < 0.01 value was considered statistically significant. MAC values were adjusted to the barometric pressure at sea level. Control MACbar values expressed as mean ± SD were 1.31 ± 0.11% for HAL and 1.46 ± 0.05% for ISO. Percentages of MAC reduction were 72 ± 17% for HAL and 43 ± 14% for ISO in DEX groups, 26 ± 11% for HAL and 20 ± 9% for ISO in MID groups, and 90 ± 5% for HAL and 78 ± 5% for ISO in DEX + MID groups. The interaction between dexmedetomidine and midazolam in terms of MAC reduction can be described as additive with halothane and synergistic with isoflurane.

Serum concentrations across time after subcutaneous administration of liposomeencapsulated or standard oxymorphone in Rhesus macaques LJ Smith, L Krugner-Higby University of Wisconsin, Madison, WI, USA

Our lab has developed a slow-release liposomal formulation of oxymorphone (LEOx). The purpose of this study was to compare serum concentrations of oxymorphone after administration of LEOx and standard oxymorphone (STDOx) to healthy female
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rhesus macaques. At baseline, 1 mL of blood was drawn from the femoral vein with the animal in a restraint cage. Primates were divided into two groups: (i) LEOx 1.0 mg kg–1(n = 4); 2) STDOx 0.1 mg kg–1(n = 4). Unloaded liposomal vehicle (0.5 mL) was used as a control (n = 2). All treatments were given subcutaneously in a shaved area proximal to the right ileal wing. Femoral venous blood was drawn and serum concentrations of drug were measured at 0.5, 1, 2, 4, 8, 12, 24, 48, 72, 96, and 120 hours. Serum concentrations were measured with ELISA. Serum concentrations were compared between groups and within groups across time with ANOVA. Drug was not detected at any time point in the control group. While sedation was not objectively measured, no animal appeared overly sedate after either treatment. All animals willingly accepted treats and did not appear nauseated or somnolent. Serum concentrations of drug were not significantly different between the two treatment groups from 0 to 2 hours. From 4 hours through 72 hours, however, serum concentrations were significantly higher (p < 0.05) in the animals that received LEOx. By 12 hours, serum concentrations of drug fell below the limit of detection (1.5 ng mL–1) in animals that received STOx. In animals that received LEOx, serum concentrations at 72 hours were comparable to those measured at 4 hours in animals that received STOx. These results suggest that subcutaneous administration of liposomal oxymorphone yields extended serum levels of drug. These results also suggest that liposomal oxymorphone may provide therapeutic (i.e. analgesic) serum concentrations of drug for 2–3 days after a single subcutaneous administration. Further studies are warranted to assess analgesic efficacy and pharmacokinetics of lipsomal oxymorphone in primates.

Effects of diazepam, ketamine, and their combination on intraocular pressure in normal dogs EH Hofmeister, CB Mosunic, BT Torres, AG Ralph, PA Moore, MR Read University of Georgia, Athens, GA, USA

Ketamine has been implicated as causing increases in intraocular pressure. The purpose of this study is to document the effects of ketamine, diazepam, and their combination on intraocular pressure (IOP) in normal, unpremedicated dogs. Random-source dogs were assigned to one of five groups of 10 dogs each: 11

ketamine 5 mg kg–1 (KET5), ketamine 10 mg kg–1 (KET10), diazepam 0.5 mg kg–1 (VAL), ketamine 10 mg kg–1 with diazepam 0.5 mg kg–1 (KETVAL), saline 0.1 mL kg–1 (SAL), all given intravenously. A baseline IOP was measured before injection, immediately after injection, and at 5, 10, 15, and 20 minutes following injection. IOP was increased over baseline immediately after injection in the KET5, KET10, and KETVAL groups; at 5, 10, and 15 minutes in the KET5 group; and at 20 minutes in the KETVAL group. The mean IOP change compared to SAL increased immediately after injection and at 5 minutes in the KET5, KET10, and KETVAL groups; at 10 and 15 minutes in the KET5 group, and at 20 minutes in the KETVAL group. The mean IOP increased up to 5.7, 3.2, and 3.1 mm Hg over mean baseline in the KET5, KET10, and KETVAL groups, respectively. All dogs in the KET5 group and the majority in the KETVAL and KET10 groups had an increase in their IOP over baseline. Ketamine caused a clinically and statistically significant elevation in IOP over baseline and compared to SAL. The concurrent addition of diazepam did not blunt this increase. Ketamine should be avoided in dogs with corneal trauma, glaucoma, or in those undergoing intraocular surgery.

Sedative effects and serum concentrations across time after subcutaneous administration of liposome-encapsulated or standard oxymorphone in healthy dogs LJ Smith, L Krugner-Higby University of Wisconsin-Madison, WI, USA

Our lab has developed a slow-release liposomal formulation of oxymorphone (LEOx). The purpose of this study was to compare sedative effects and serum concentrations of oxymorphone after administration of LEOx and standard oxymorphone (STDOx) to dogs. At baseline, 1 mL of blood was drawn from the cephalic vein and sedation score was recorded. Dogs were divided into four groups (n = 6): (i) LEOx 1.0 mg kg–1; (ii) LEOx 0.5 mg kg–1; (iii) STDOx 0.1 mg kg–1; (iv) STDOx 0.05 mg kg–1. Unloaded liposomal vehicle (0.5 mL) was used as a control (n = 2). All treatments were given subcutaneously between the scapulae. Sedation score and serum concentration of drug were recorded at 0.5, 1, 2, 4, 8, 12, 16, 24 hours and daily for 5 days. Serum concentrations were measured with ELISA. At all time points, drug was not detected and sedation score was 0 in the control group. Sedation score for group 1 12

was significantly higher (p < 0.05) at 1 hour than for groups 2,3, and 4. There was no difference in sedation score between treatment groups at any other time. Serum concentrations of drug were significantly higher (p < 0.05) for group 1 at all time points measured after baseline. In groups 2, 3, and 4, serum concentrations of drug fell below the limit of detection (1.5 ng mL–1) by 24 hours. Serum concentrations after 0.1 mg kg–1of STDOx were 11.1 ± 3.6 ng mL–1at 4 hours, which is the recommended time for redosing and presumably reflects the lower end of a therapeutic serum concentration. Serum concentrations were comparable after 1.0 mg kg–1 of LEOx (10.5 ± 2.4 ng mL–1) 48 hours after administration. These results suggest that liposomal oxymorphone may provide therapeutic serum concentrations of drug for 2 days after a single subcutaneous administration without undue sedation or other deleterious effects in healthy dogs. Further studies are warranted to assess analgesic efficacy and pharmacokinetics of lipsomal oxymorphone in dogs.

Effect of adenosine infusion on isoflurane MAC in dogs. M Asakawa, JW Ludders, B Badgley, HN Erb, LP Posner, RD Gleed Cornell University, Ithaca, NY, USA

Adenosine is a potent analgesic in people and reduces the MAC of halothane in dogs. The purpose of this study was to determine whether adenosine reduces the MAC of isoflurane in dogs. Seven beagles (four males and three females) were anesthetized and randomly assigned to receive adenosine (0.3 mg kg–1 minute–1; 6 mL kg–1 hour–1, IV) or saline (0.9%, 6 mL kg–1 hour–1IV). After an interval of ‡7 days, each dog was reanesthetized and treated with the alternate infusion. Anesthesia was induced and maintained with isoflurane in oxygen. Dogs were intubated and instrumented for measurement of mean systemic arterial blood pressure and airway concentration of isoflurane and endtidal partial pressure of carbon dioxide. The MAC for isoflurane was determined using the tail-clamp technique. Baseline MAC values were 1.25 (1.15, 1.35)% [median (minimum, maximum)] and 1.25 (1.05, 1.45)% before the saline and adenosine treatments, respectively. After 2 hours of infusion with saline or adenosine, MAC values were not different (p = 0.156) and were 1.25 (0.95, 1.35)% and 1.05 (1.00, 1.25)%, respectively. Two hours
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following the end of each infusion, the MAC values for saline and adenosine treatment groups differed significantly (p = 0.015), but by no more than the normal variation inherent in this study, and were 1.15 (1.15, 1.35)% and 1.05 (1.05, 1.25)%, respectively. Mean arterial blood pressure was 93 (74, 123) mm Hg for saline treated dogs and 67 (52, 72) mm Hg (p = 0.008) during adenosine infusion. End-tidal carbon dioxide was not different between the two treatment groups. We conclude that adenosine administered at 0.3 mg kg–1 min–1 ute had no effect on isoflurane MAC in dogs, but decreased mean arterial blood pressure.

Confirmation of epidural needle placement using nerve stimulation in dogs

was considered to be successful in 19/20 dogs. In only 9/20 dogs, needle placement would have been correct based on using ‘classic’ indicators alone (‘pop’ as enter epidural space, loss of resistance to injection). The results of this study suggest that nerve stimulation may be useful in confirming correct epidural needle placement prior to drug administration.

Comparison of noninvasive cardiac output measurements by transthoracic bioimpedance, partial carbon dioxide rebreathing, and transesophageal echocardiography with the thermodilution technique in beagle dogs

MR Read Veterinary Emergency Clinic, Toronto, ON, Canada

K Yamashita, R Igarashi, T Kushiro, Y Ueyama, K Miyoshi, MA Umar, WW Muir Rakuno Gakuen University, Ebetsu, Hokkaido, Japan.

Caudal epidural anesthesia is useful when anesthesia of the lumbar and sacral dermatomes is needed. Its success relies on the proper placement of the needle in the epidural space. However, accurate positioning of the needle can be difficult in certain patients (i.e.obesity). The purpose of this preliminary study was to document the use of nerve stimulation as a means of confirming accurate needle positioning in the epidural space prior to drug administration. Twenty large breed dogs undergoing hindlimb or perineal surgery were enrolled. Following induction of general anesthesia, patients were prepared for routine epidural drug administration. A 17 ga, 3.5’’ shielded Tuohy needle was used and was connected to a peripheral nerve stimulator set to deliver a current at 1 Hz, with a pulse width of 0.2 m sec. Initial current was set at 1.2 mA as the needle was advanced into position. Confirmation of epidural needle placement was confirmed when twitches were observed in the hindlimbs and/or tail. Current setting was then decreased incrementally by 0.2 mA until no further twitches were observed. Success of epidural drug placement was confirmed subjectively by motor blockade to the blocked dermatomes and clinical signs of balanced anesthesia (lack of sympathetic response to surgical stimulation while maintained at light plane of anesthesia). Lowest mean (range) current to elicit hindlimb twitches was 0.72 mA (0.4–1.0 mA). Lowest mean (range) current to elicit tail twitches was 0.58 mA (0.4– 1.0 mA). Tail twitches were reliably lost at mean current of 0.37 mA (0.2–0.8). Epidural anesthesia

Most methods for determining cardiac output (CO) have limited application in clinical practice due to the invasive techniques required. This study compared the thermodilution technique (TDCO) with three noninvasive methods for determining CO in anesthetized dogs: transthoracic bioimpedance (BICO), partial CO2 rebreathing (NICO), and transesophageal echocardiography (TEECO). TDCO was compared to BICO, NICO, and TEECO in six adult sevoflurane anesthetized beagle dogs (9.1–13.0 kg). All dogs were administered midazolam [0.3 mg kg)1, intravenously (IV)] and butorphanol (0.1 mg kg)1 IV), followed by ketamine (5.0 mg kg–1 IV) and sevoflurane in nitrous oxide (1 L minute–1) and oxygen (1 L minute–1) and mechanically ventilated. Dogs were maintained at 2.2% end-tidal sevoflurane (ETsev) concentration for instrumentation and baseline measurements. Low (5.0% ETsev), intermediate (3.3% ETsev), and high cardiac output values were achieved by varying the end-tidal sevoflurane concentration and the administration of dobutamine (3–10 g kg–1 minute–1 and 2.2% ETsev). A minimum of thirty data sets was obtained for each comparison. The correlation coefficients when compared to TDCO were 0.684 for BICO (p < 0.0001), 0.883 for NICO (p < 0.0001), and 0.991 for TEECO (p < 0.0001). Cardiac output values ranged 50–444 mL kg–1 minute–1 for TDCO, 100–253 mL kg–1 minute–1 for BICO, 64– 214 mL kg–1 minute–1 for NICO, and 52– 401 mL kg–1 minute–1 for TEECO. The differences when compared to TDCO ranged – 62–235 mL kg)1 minute)1 for BICO, 18–220 mL kg)1 minute)1 for


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NICO, and – 35–32 mL kg–1 minute–1 for TEECO. Differences were maximum at the highest CO in BICO and NICO. In conclusion, this study demonstrated that BICO and NICO underestimate CO in sevoflurane anesthetized dogs. TEECO is a viable noninvasive method for determining CO in sevoflurane anesthetized dogs.

Compliance in the administration of prescribed analgesics to critically ill dogs and cats. EA Armitage,1 LA Wetmore,1 DL Chan,1 JC Lindsey1,2 1 Tufts University, N. Grafton, MA, USA; 2 Harvard University School of Public Health, Boston, MA, USA

There is a wide discrepancy between the prescription and administration of analgesics, to critically ill people. The purpose of this study was to investigate the administration of prescribed analgesics to critically ill dogs and cats. The treatment orders for patients in the Tufts University Foster Small Animal Hospital intensive care unit (ICU) over a 2-month period were reviewed daily and the ordered and administered analgesics recorded. 351 patients were hospitalized in the ICU over the study period, for durations between 1–15 days. On average, 39% of the patients were prescribed analgesics, the most common being hydromorphone. A greater percentage of dogs were prescribed analgesics (46%) compared to cats (25%). This difference was not statistically significant after adjusting for primary complaint however following trauma, cats tend to be prescribed analgesics less frequently (67%) than dogs (89%) (p = 0.251). 64% of the patients received their analgesics exactly as ordered. The most frequent variation from patient orders was withholding an analgesic dose. Other variations included prolonged dosing interval, doses administered early, and changes in the drug dose administered. Doses were decreased or given late more frequently (34 patients) than they were increased or given early (20 patients). When analgesics were administered early, reasons cited included obvious patient pain and agitation. Fewer cats (5%) received early or additional analgesics compared to dogs (15%). Reasons listed for late or missed doses included excessive sedation and hypotension. The incidence of late or missed analgesics did not correlate with higher patient number in the ICU. Approximately half (46%) of the changes made to dosing regimens had no reason recorded. Critically ill 14

dogs and cats frequently receive analgesic doses differing from those ordered, in many cases because of observers’ perceptions of drug side effects. Within the ICU, cats may be treated differently to dogs with respect to analgesic administration.

The use of concentrated bovine serum albumin in canines. CAE Mosley, KA Mathews University of Guelph, ON, Canada

In humans it has been estimated that for each 2.5 g L–1 decrease in serum albumin, risk of death increases by 24–56%. Clinical impression suggests this may be similar in veterinary patients. Speciesspecific albumin (plasma) is often unavailable and concentrated solutions are not. Our experience using 25% human serum albumin (HSA) in critically ill dogs suggests a positive effect (results submitted), however it is expensive. Bovine serum albumin (BSA) may be a more cost effective and readily available alternative. The purpose of this study was to assess the immediate and long-term safety of an intravenous dose (500 mg kg–1) of bovine albumin administered to healthy dogs. Ten mature dogs (eight males, two females, 28 ± 6 kg) were to receive BSA (250 mg mL–1) twice (BSA1 and BSA2) with 14 days between treatments. Temperature, blood pressure, and pulse and respiration rate were continuously monitored to identify a reaction to BSA. All dogs received BSA1. One dog immediately developed mild urticaria and pruritus, otherwise the infusion was well tolerated. No immediate reaction was noted in the other nine dogs. Two dogs received BSA2. One dog developed a mild immediate reaction similar to that occurring with BSA1, and one dog (the dog immediately reacting to BSA1) developed a severe anaphylactic reaction. Due to these reactions, no other dogs received BSA2. During a two-week observation of the remaining eight dogs given BSA1, five developed a mild or severe generalized type-III hypersensitivity reaction. The dog experiencing a mild reaction during BSA2 administration also developed a generalized type-III hypersensitivity reaction. Delayed reactions occurred 15 ± 2.7 days after BSA exposure. Three dogs did not develop a reaction. All reacting dogs recovered fully. The severity of reactions, and the number of dogs affected, suggests prior (natural) exposure and immunological sensitization to bovine albumin.
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Bovine serum albumin is not suitable for therapeutic use in dogs.

Animal Bowen (the Bowen technique adapted for animals): use of a gentle hands-on therapy for chronic musculoskeletal pain in dogs LS Peck, C Bennett Gainesville, FL and Durango, CO, USA

The Bowen Technique is a unique hands-on therapy developed by Tom Bowen of Australia in the 1950s–60s and adapted for use in animals by Carol Bennett in 1997. It consists of a specific sequence of gentle, precise rolling moves done with thumb and fingers over muscle and tendon edges, across the direction of tension. A short waiting period follows each set of moves. Definitive mechanism(s) of action remains to be identified; however, autonomic nervous system modulation (heart rate variability studies) has been documented in humans. The technique has also been reported effective for back, hip, neck, and shoulder pain in human studies. Five geriatric dogs (13–16 years old) of various breeds were presented in a case series at a small animal clinic for primary complaints of stiffness, poor ambulation, and difficulty lying down/getting up. Four had hindlimb proprioceptive deficits; three had arthritic changes to coxofemoral joints and/or lumbar spine; three showed active indicators of pain (chronic pacing/panting; irritability; social withdrawal). All were on NSAID and/or nutritional therapy with unsatisfactory results. One dog had acupuncture weekly for over 1 year but no longer tolerated the needles. Treatment consisted of Animal Bowen at weekly or biweekly intervals. Three dogs were pain scored [0–10; average starting score 6.7 ± 0.6 (mean ± S.D.); range 6–7] by owner before and after treatment. All five dogs showed significant positive changes in attitude, and four had notable improvement in ease of ambulation, after the first treatment. Improvement was progressive over treatment course. Average post-treatment score was 2.3 ± 2.1 (0, 3, 4); average pain score reduction was 4.3 ± 1.5 (range 3–6) after two to six treatments for the three dogs scored. One dog had complete resolution of hindlimb lameness of 5 years duration after three sessions. Animal Bowen, used alone or in conjunction with standard analgesics and other treatments, can be an effective therapy for chronic musculoskeletal conditions in dogs.
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Pre-hospital low-volume resuscitation with hemoglobin-glutamer-200 (Hb-200) in a canine hemorrhagic shock model B. Driessen,1 L Zarucco,1 PM Burns,1 R Boston,1 RA Gunther,2 AT Cheung2 1 University of Pennsylvania, Kennett Square, PA, USA 2 University of CA, Davis, CA, USA

Recently, hypotensive small volume fluid resuscitation has been advocated for early treatment of hemorrhagic shock to avoid aggravating further blood loss and to minimize hemodilution. Our objective was to study whether a hemoglobin-based O2 carrier is more efficacious than crystalloids for prehospital treatment of severe hemorrhage. Effects of Hb-200 (Oxyglobin) on systemic hemodynamic and oxygenation functions and on muscle blood flow (MBF), muscle O2 tension (PMO2) and debt (O2DebtM), as well as on systemic lactate levels were studied during the early post-hemorrhage resuscitation period (pre-hospital). Dogs were anesthetized, instrumented and then splenectomized. After baseline recordings, they were hemorrhaged (~50 mL kg–1) over 30 minutes to a mean arterial pressure (MAP) of 45 mm Hg and kept at that level for 30 minutes. Then they received 8.3 mL kg–1 of either 0.9% saline (SAL; n = 5) or 50% Hb-200 (n = 5) over 60 minutes. Recordings were then repeated. Data analysis included robust regression modeling (p < 0.05). Hemorrhage was associated with characteristic changes in both groups. Heart rate and systemic and pulmonary vascular resistances increased, and MAP, cardiac output, systemic O2 delivery (DO2), MBF, and PMO2 decreased (p < 0.05). As a result, systemic O2 extraction and O2DebtM increased and lactic acidosis developed (p < 0.05). Low volume resuscitation with Hb-200 was as efficacious as with SAL in improving most hemodynamic variables. However, Hb-200 increased systemic and pulmonary vascular resistances, which resulted in significantly greater increases in MAP and mean pulmonary arterial pressure compared to the SAL group (p < 0.05). SAL and Hb-200 resuscitation increased DO2 and PMO2 by 43 and 88%, and 33 and 149%, respectively (p < 0.05). Neither aO2ct nor DO2 or PMO2 were significantly higher after Hb-200 than SAL resuscitation. Acid-base parameters post resuscitation improved similarly in both groups. In conclusion, Hb-200 may be a better choice than SAL for low volume resuscitation only if immediate strong pressor support is needed post hemorrhage to prevent imminent cardiac arrest as it improves tissue oxygenation despite its vasoconstrictive action. 15

Effect of sequential NSAID therapy on the upper gastrointestinal tract in dogs KL Dowers, S Rayroux, PW Hellyer, K Mama, JS Gaynor Colorado State University, Fort Collins, CO, USA

It is unknown whether overlapping or sequential use of nonsteroidal anti-inflammatory (NSAIDs) results in an increased risk for gastrointestinal (GI) ulceration. The purpose of this pilot study was to evaluate the GI effects of various combinations of an injectable NSAID followed by an oral NSAID, a scenario often employed clinically for management of the pre- and post-operative canine patient. Six healthy Walker hounds received four treatment regimens in a randomized, cross-over design with a 2 week washout period between each treatment week: carprofen (4 mg kg–1, SQ) followed by placebo (PO, q24 · 4 days); placebo (SQ) followed by deracoxib (3–4 mg kg–1, PO, q24 · 4 days); carprofen (4 mg kg–1, SQ) followed by carprofen (4 mg kg–1, PO, q24 · 4 days); carprofen (4 mg kg–1, SQ) followed by deracoxib (3–4 mg kg–1, PO, q24 · 4 days). Weekly bloodwork (CBC, biochemistry panel, fecal evaluation, fecal occult blood) and daily clinical scoring (TPR, vomiting, diarrhea, appetite) were obtained. GI endoscopy was performed on days –2, 1, 2, 5, and 11 days post treatment of each treatment period and lesions scored using a previously reported 6-point scale. Data was analyzed using a mixed ANOVA for repeated measures. There were no significant differences in clinical or clinicopathologic data between groups. Within the carprofen-carprofen and carprofen-deracoxib groups, lesions worsened by Day 5 (1 day after last oral dose) for the fundic and antral regions (p < 0.05). Fundic, antral and lesser curvature lesions improved by Day 5 in the carprofen-placebo group and lesser curvature lesions improved in the placebo-deracoxib group (p < 0.05). No significant within-group differences were noted for the esophagus, cardia or duodenum. The small number of dogs precludes general conclusions about the safety of sequential NSAID use, but these results suggest that a larger scale study is warranted.

Colloid oncotic pressure and total protein changes in horses during anesthesia fluid therapy P Boscan, Z Watson, TB Farver and EP Steffey University of California, Davis, California, CA, USA

According to Starling forces, colloid oncotic pressure COP is an important determinant of fluid 16

distribution between the vascular and extra-vascular space. The influence of common anesthetic management on plasma COP has not been reported in horses. It is necessary to seek this information preliminary to more in depth study of systemically ill horses. In this study we measured direct COP and total plasma protein concentration (TP) changes before and during routine anesthetic management of 12 adult healthy horses presented for elective surgery. Horses were fasted overnight before anesthesia. Xylazine 0.39 ± 0.13 mg kg–1 IV was administered 5–15 minutes prior to anesthetic induction with IV ketamine 1.86 ± 0.29 mg kg–1, diazepam 0.05 ± 0.01 mg kg–1 and guaifenesin 39 ± 11.2 mg kg–1. Anesthesia was maintained with isoflurane as required (1.4 ± 0.2% end tidal). Blood samples were taken before premedication, immediately following induction and every 30 minutes thereafter for 2.5 hours. Direct COP was measured with a colloid osmometer and TP by refractometry. Peri-anesthetic fluid therapy consisted of commercial Lactate Ringer’s solution (LRS) at a rate of 11 ml kg–1 hour–1 (total LRS at 2.5 hours was 13.5 ± 2.7 L). Before anesthesia COP and TP was 22.22 mm Hg and 6.9 ± 0.4 g dl–1 respectively. Within 15 minutes of anesthetic induction, COP and TP decreased significantly (19.9 ± 1.9 mm Hg and 6.3 ± 1.9 g dl–1 respectively; p < 0.01). Over the 2.5 hours course of uneventful anesthesia the COP and TP decreased in a linear fashion (for COP R2 = 0.96 and TP R2 = 0.97). The COP and TP were 15 ± 1.3 mm Hg and 5.1 ± 0.2 g dl–1 at 2.5 hours of anesthesia. The Pearson correlation coefficient for COP versus TP was 0.705. In conclusion, the data indicates that COP, like TP decreases over the course of relatively routine anesthetic management of horses.

Anesthesia and pain management in Russia CE Short University of Tennessee, Knoxville, TN, USA

There was only limited emphasis on anesthesia and pain management in veterinary colleges in Russia until the last ten years. There is now great interest in improvement by Russia practitioners. This effort is hampered by the lack of approved and available medications and limited instructions. At this time, the small animal practitioners have tranquilizers, alpha2 agonists local anesthetics and NSAID’s for their use. Propofol is available through pharmacies
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and efforts are being made for veterinarians to use ketamine. Only a few practices have inhalant anesthetic units and halothane. During a recent lecture tour of Russia, general clinical principles and specific anesthetic and pain management protocols were taught. The audience, primarily young and progressive veterinarians, actively participated and showed great desire to practice quality anesthesia and pain management for their patients. Teaching young veterinarians how to manage their cases without the availability of opioids, ketamine advanced anesthetic equipment and monitors was indeed challenging. Protocols for perioperative management consisting of medetomidine with or without local anesthesia followed by carprofen for post-operative pain is an improvement. We sometimes spend so much time discussing which of many drug combinations we will use but seldom consider what we would do if we were practicing our specialty in parts of the world where we would have to modify dosages and combinations to achieve humane care with few drug choices.

(t1/2k2,0) half-lives were 1.3 and 12.0 hours, respectively. The bHb molecules in OXY are not of uniform size and vary substantially in molecular weight (MW). Of the OXY molecules 53% were eliminated in C1, which represented the smaller MW molecules and 47% in C2, which represented the larger MW bHb. The maximal 0-time plasma concentration was 662.0 lg/mL and declined to 97.1 lg mL–1 at 24 h. The area below the plasma concentration-time curve was 5143 lg h–1 mL–1. The volumes of C1 and C2 were 86.9 and 63.9 mL kg–1, respectively. Oxyglobin was not detected in urine. This study shows the detection and quantification in equine plasma of a HBOC following IV infusion and demonstrates the short half-life of about 50% of infused bHb molecules.

A comparison of noninvasive cardiac output measurement by partial carbon dioxide rebreathing with the lithium dilution technique in anesthetized foals A Valverde S Giguere, TE Morey, E Bucki University of Florida, Gainesville, FL, USA

Pharmacokinetics of hemoglobin-based oxygen carrier hemoglobin-glutamer-200 bovine (oxyglobin) in the horse LR Soma,1 F Guan,1 CE Uboh,1,2 Y Luo,2 PJ Moate,1 and B Driessen1 1 University of Pennsylvania, Kennett Square, PA, USA; 2 West Chester University, West Chester, PA, USA

Oxyglobin (OXY) is a hemoglobin-based oxygen carrier (HBOC) made of glutaraldehyde-polymerized bovine hemoglobin (bHb). Products similar to OXY are under development for use as temporary blood substitutes in trauma, shock and anemia. Since they all may increase blood O2-carrying capacity and thus, possibly tissue oxygenation, they may also be used to enhance performance of both equine and human athletes. That is why HBOCs are banned from use in athletic competition. Our goal was to determine the pharmacokinetics of OXY after intravenous (IV) infusion to horses. Blood and urine samples were collected from adult horses that received an IV dose of 32.5 g of OXY. Concentrations of OXY in plasma and urine were quantified using a newly developed LC/Q-TOF-MS/MS detection technique. Level of quantification (LOQ) was 50 lg mL–1. The decline of the plasma concentration-time curve of the HBOC was described by a 2compartment model (C1 and C2). The median distribution alpha (t1/2k1,0) and elimination beta
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Newer techniques for cardiac output (Q) determinations that are minimally invasive remain to be validated in neonatal foals against other accepted techniques such as the lithium technique (LiDCO). This study compares Q determinations using the partial CO2 rebreathing technique (NICO) with LiDCO in anesthetized neonatal foals. Ten foals were instrumented for NICO and LiDCO determinations. For each foal low, intermediate and high levels of cardiac output were achieved in that order using an end-tidal isoflurane (ETI) concentration of 1.3 – 2.1% for the lowest rate; an ETI of 0.85–1.4% and a constant-rate infusion of dobutamine (1–3 ?g/ kg/min) for the intermediate rate; and an ETI of 0.83–1% and dobutamine (2–6 ?g/kg/min) for the highest rate. Four foals also received IV intermittent doses (total cumulative dose of 1.1–1.7 mg) of phenylephrine at the highest rate of Q. The measurements were obtained in duplicate or triplicate for each Q technique after achieving a stable hemodynamic plane for at least 15 minutes at each rate of Q. For the lithium technique, all foals received 1.1–1.9 mL (0.16–0.28 mmol) of lithium. A BlandAltman analysis was used to compare the bias and precision of the two techniques. Eighty seven comparisons were determined between the two techniques. Eight were excluded due to more than 20% variation between the LiDCO determinations or 17

technical errors at the time of determination. The correlation coefficient between the two methods was 0.67 for all Q determinations. Mean LiDCO and NICO values from 79 measurements were 130 ± 40 mL–1 kg minute–1 (range, 68– 237) and 152 ± 31 mL–1 kg minute–1 (89 – 209), respectively. The mean ( mL–1 kg minute–1) of the differences of LiDCO – NICO was = –0.7248 + 0.8602 NICO. The precision (1.96 SD) of the differences between LiDCO and NICO was 58.9 mL–1 kg minute–1 (–80.9–+36.9) with a mean difference of –22 mL–1 kg minute–1 (bias; 95% CI – 15.2 to 28.7). In conclusion, given the small bias compared to the limits of agreement, the NICO technique for determining Q deserves further consideration for adoption into clinical practice in neonatal foals.

The use of vascular access ports in nonanesthetized green iguanas (iguana iguana) to collect baseline arterial blood gas parameters. JC Hess, KA Grimm, GJ Benson, WA Tranquilli, R Sarr University of Illinois, Urbana, IL,USA

The green iguana, Iguana iguana, is used as a model in reptile anesthesia research because of its size, availability, and the body of knowledge characterizing its physiology. Arterial blood gas values in nonanesthetized green iguanas have not been determined because of the technical difficulty involved. Vascular access port (VAP) placement to facilitate blood sampling has been described in other species, but not lacertilians. This abstract describes the technique for placement of VAPs and the values for arterial blood gas parameters in seven 1 kg adult green iguanas. Using sterile technique, a 1.5 cm incision was made on the lateral side of the neck. Blunt dissection ventral to the external jugular vein revealed the internal and external carotid arteries near their bifurcation. The catheter was inserted into the internal carotid artery and then guided to the common carotid artery. The other end of the catheter was tunneled below the skin to a subcutaneous location, caudal-dorsal to the ispsilateral scapula. The skin was closed and the port was flushed twice a week with heparinized saline. Postoperatively, the VAPs were well tolerated by the iguanas. Difficulties included port disconnection (n = 1), inability to aspirate blood after a few weeks (n = 2), and infection (n = 1). The iguanas were breathing room air prior to and during blood collection. From the five functional VAPs, the blood 18

pH, PCO2, PO2, HCO3- , and BE (measured at 37 C) were 7.45 ± 0.06; 37.5 ± 7.0 mm Hg, 99.0 ± 16.6 mm Hg, 25.4 ± 2.5 mmol L–1, and 1.5 ± 2.4 mmol L–1 respectively (mean ± SD). VAPs can be successfully used to facilitate collection of arterial blood gas samples in green iguanas. These values are similar to those reported for most mammalian species. This technique should facilitate research in anesthesiology and respiratory physiology of iguanas and other lacertilians.

Total intravenous anesthesia with ketamine–medetomidine–propofol in horses MA Umar, K Yamashita, T Kushiro, WW Muir Rakuno Gakuen University, Ebestu, Hokkaido, Japan.

Propofol is a potentially useful intravenous anesthetic agent for total intravenous anesthesia (TIVA) in horses. The purpose of this study was to compare the anesthetic and cardiorespiratory effects of TIVA following the administration of propofol alone(P– TIVA) and ketamine–medetomidine–propofol (KM– P–TIVA) in adult horses. The carotid artery was translocated to a subcutaneous position during TIVA with P–TIVA (n = 6) or KM–P–TIVA (n = 6). All horses were premedicated with medetomidine [0.005 mg kg–1, intravenously (IV)]. Anesthesia was induced with midazolam (0.04 mg kg–1 IV) and ketamine (2.5 mg kg IV). All horses were orotracheally intubated and breathed 100% oxygen. The KM drug combination (ketamine 40 mg mL–1 and medetomidine 0.05 mg mL–1) was infused at a rate of 0.025 mL kg–1 hour–1. Subsequently, a loading dose of propofol (0.5 mg kg–1, bolus IV) was administered to all horses; surgical anesthesia (determined by horse response to incision and surgical manipulation, positive response being purposeful or spontaneous movement of limbs or head) was maintained by varying the propofol infusion rate as needed. Arterial blood pressure and HR were also monitored. Both methods of producing TIVA provided excellent general anesthesia for the surgical procedure. Anesthesia time was 115 ± 17 (mean ± SD) and 112 ± 11 minutes in horses anesthetized with KM–P–TIVA and P–TIVA, respectively. The infusion rate of propofol required to maintain surgical anesthesia with KM–P–TIVA was significantly less than for P–TIVA (mean infusion rate of propofol during anesthesia; KM–P–TIVA 0.15 0.02 P–TIVA 0.23 ± 0.03 mg kg–1 minute–1, p = 0.004). Apnea
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occurred in all horses lasting 1–2 minutes and intermittent positive pressure ventilation was started. Cardiovascular function was maintained during both methods of producing TIVA. There were no differences in the time to standing after the cessation of anesthesia (KM–P–TIVA 62 ± 10 minutes versus P–TIVA 87 ± 36 minutes, p = 0.150). The quality of recovery was good in KM–P–TIVA and satisfactory in P–TIVA. KM–P–TIVA and P–TIVA produced clinically useful general anesthesia with minimum cardiovascular depression. Positive pressure ventilation was required to treat respiratory depression. Respiratory depression and apnea must be considered prior to the use of propofol in the horse.

Clinical evaluation of balanced anesthesia using infusion of midazolam–ketamine– medetomidine in combination with inhalation of sevoflurane (MKM–OS anesthesia) in horses T Kushiro, K Yamashita, MA Umar, Y Izumisawa K Taguchi, WW Muir Rakuno Gakuen University, Ebetsu, Hokkaido, Japan

MKM–OS anesthesia provides general anesthesia with minimum cardiovascular depression in experimental horses. The purpose of this study was to evaluate the effect of MKM–OS anesthesia in clinical cases. Sixty-eight horses were anesthetized with MKM–OS anesthesia for selective or emergency surgery. The horse physical status was categorized based upon the American Society of Anesthesiologists (ASA) classification scheme. Forty-four horses were classified as ASA I or II (low-risk; 30 soft tissue, eight ophthalmic, and six orthopedic surgeries) and 24 horses were classified as ASA III to V


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(high-risk; 24 emergency colic surgeries). All horses were administered medetomidine (0.005 mg kg–1 IV) as premedication and anesthetized with ketamine (2.5 mg kg–1 IV) and midazolam (0.04 mg kg–1 IV). The horses were orotracheally intubated and connected to a large animal breathing circuit that delivered oxygen-sevoflurane and administered the midazolam (0.8 mg mL–1)-ketamine (40 mg mL–1)-medetomidine (0.05 mg mL–1) drug combination at a rate of 0.025 mL kg–1 hour–1. Surgical anesthesia was maintained by controlling the dial setting of the sevoflurane vaporizer and achieved by delivering 1.6–1.8% of end-tidal sevoflurane concentration. All horses were mechanically ventilated during anesthesia. Hypercapnia and hypoxia were not sufficiently improved in high-risk horses (PaCO2; low-risk 45–53 mm Hg versus highrisk 56–60 mm Hg, p < 0.01: PaO2 low-risk 248– 388 mm Hg versus high-risk 95–180 mm Hg, p < 0.01). Heart rate was significantly higher in high-risk horses (low-risk 37–42 bpm versus highrisk 44–73 bpm, p < 0.01). Dobutamine infusion was required in five low-risk (11%) and 17 high-risk horses (68%) to maintain mean arterial blood pressure >70 mm Hg. Eleven high-risk horses died during the perioperative period (three euthanized during surgery, two died during recovery, six died after recovery). The quality of recovery was good in low-risk horses and good to satisfactory in high-risk horses. MKM–OS anesthesia provided excellent surgical anesthesia with minimal to mild cardiovascular depression in low risk-horses and mild to moderate cardiovascular depression in high riskhorses. The possibility of preserve cardiovascular function could be the advantage of MKM–OS anesthesia in high-risk horses.

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