Andre Shih

Continual systemic infusion of lidocaine provides analgesia in an animal model of neuropathic pain.

&NA; We examined whether continual constant‐rate infusion of lidocaine would provide analgesia during the initial post‐injury phase in the chronic constriction injury model of neuropathic pain. Male Sprague–Dawley rats were divided into control and ligated groups and infused with saline or lidocaine (0.15, 0.33, 0.67, and 1.3 mg/kg/h) via subcutaneously implanted Alzet® osmotic minipumps. Thermal withdrawal latencies were obtained prior (Day 0) and 3 days after loose sciatic ligation and pump implantation surgery. Ligated animals receiving lidocaine at 0.67 or 1.3 mg/kg/h exhibited no change in withdrawal latency on Day 3 after surgery, indicating that lidocaine at these doses prevented the development of thermal hyperalgesia as a sign of neuropathic pain. In contrast, ligated animals treated with saline or lidocaine at 0.15 or 0.33 mg/kg/h exhibited hyperalgesia on Day 3 after surgery, indicating that these lower doses of lidocaine failed to provide analgesia. Control animals treated with saline or any of the lidocaine doses exhibited no change in withdrawal latencies between Day 0 and Day 3. In a separate group of ligated animals, lidocaine infusion (0.67 mg/kg/h) that was started 24 h after sciatic ligation surgery reversed the already present thermal hyperalgesia. Average plasma lidocaine concentrations were 0.11, 0.36, and 0.45 &mgr;g/ml for animals receiving 0.33, 0.67 and 1.3 mg/kg/h of lidocaine, respectively. These results suggest that continual systemic infusion of lidocaine prevents or reverses the development of neuropathic pain following chronic constriction injury. These results add to the increasing body of evidence supporting the therapeutic value of preemptive and post‐operative lidocaine administration for the relief of neuropathic pain.

Evaluation of an indirect oscillometric blood pressure monitor in normotensive and hypotensive anesthetized dogs

OBJECTIVE To determine the accuracy and precision of an oscillometric noninvasive blood pressure device as a predictor of invasive direct blood pressure in healthy anesthetized hypotensive and normotensive dogs. DESIGN Prospective observational study. SETTING University teaching hospital. ANIMALS Eight crossbred adult dogs. INTERVENTIONS Anesthesia was induced with propofol and maintained with isoflurane. A catheter was placed in the dorsal pedal artery to record systolic, mean, and diastolic arterial blood pressures (aSAP, aMAP, and aDAP, respectively). The noninvasive blood pressure device cuff was placed around the contralateral front limb to record noninvasive systolic, mean, and diastolic blood pressure (nSAP, nMAP, and nDAP). Two states of blood pressure (BP) were studied: baseline state was established by keeping end-tidal isoflurane concentration at 1.2+/-0.1%. The hypotensive state was achieved by maintaining the same isoflurane concentration while withdrawing approximately 40% of the animals blood volume until aMAP was stable at approximately 40 mm Hg. At the end of the study, blood was returned to the animal and it was allowed to recover from anesthesia. MEASUREMENTS AND MAIN RESULTS Agreement between the direct and indirect BP measurements was determined by the Bland-Altman method. The SAP and MAP but not DAP bias varied significantly between each BP state. Normotensive absolute biases (mean [SD]) for SAP, MAP, and DAP were -14.7 mm Hg (15.5 mm Hg), -16.4 mm Hg (12.1 mm Hg), and -14.1 mm Hg (15.8 mm Hg), respectively. Absolute biases during the hypotensive state for SAP, MAP, and DAP were -32 mm Hg (22.6 mm Hg), -24.2 mm Hg (19.5 mm Hg), and -16.8 mm Hg (17.2 mm Hg), respectively. CONCLUSION The oscillometric device was not reliably predictive of intra-arterial BP during hypotension associated with acute hemorrhage.

Comparison between the analgesic effects of morphine and tramadol delivered epidurally in cats receiving a standardized noxious stimulation

This study compared the analgesic effects of epidural tramadol versus morphine in six healthy cats. Under general anesthesia, each cat received an epidural injection of saline 0.22 ml/kg (control treatment, CT), tramadol 1 mg/kg (tramadol treatment, TT), or morphine 0.1 mg/kg (morphine treatment, MT). After cats had recovered from anesthesia a simple descriptive scale (SDS), visual analog scale (VAS) and physiological parameters (respiratory and heart rate) were used to assess analgesia level to a noxious stimulus (base of the tail skin fold clamping) at 1, 2, 3, 4, 6, 8, 10, and 12 h post-epidural. Group TT had a higher SDS and VAS score when compared to MT at 8, 10 and 12 h post-epidural. CT had higher SDS and VAS score at all time points when compared to TT and MT. In conclusion both morphine and tramadol provided analgesia in this model for the first 6 h; with epidural morphine resulting in longer lasting analgesia when compared to tramadol.

Comparison of surgical variables in cats undergoing single‐incision laparoscopic ovariectomy using a LigaSure or extracorporeal suture versus open ovariectomy

OBJECTIVE To evaluate the applicability of single-incision laparoscopic ovariectomy (SILOVE) in cats using a single-incision laparoscopic port (SILP); to compare surgical time, complications, and postoperative pain after SILOVE using a LigaSure (SILOVE-LS) or extracorporeal suture (SILOVE-ECS), and open ovariectomy (open-OVE). STUDY DESIGN Randomized, blinded, prospective study. ANIMALS Healthy, domestic female cats (n = 24). METHODS Cats underwent physical examination, packed cell volume, total solids and blood urea nitrogen analysis. Cats were randomly assigned to 1 of 3 groups: SILOVE-LS (n = 8), SILOVE-ECS (8) or open-OVE (8). Surgical time, complications, and postoperative pain scores were recorded. RESULTS Single-incision laparoscopic ovariectomy was successful in (n = 8) SILOVE-LS cats and (n = 5) SILOVE-ECS cats. Surgical time was significantly longer for the SILOVE-ECS group compared with the SILOVE-LS (P < .0001) and open-OVE (P < .0001) groups, which were not different (P = .55). Complications were more frequent in the SILOVE-ECS group and removal of the SILP was required to complete ovariectomy in 3 cats. Cumulative 4-hour pain scores were not different between groups. CONCLUSIONS Single-incision laparoscopic ovariectomy using a SILP is a feasible method for OVE in cats. Single-incision laparoscopic ovariectomy using an extracorporeal suture is more time consuming and associated with more complications than either the SILOVE-LS or open-OVE methods.Objective To evaluate the applicability of single-incision laparoscopic ovariectomy (SILOVE) in cats using a single-incision laparoscopic port (SILP); to compare surgical time, complications, and postoperative pain after SILOVE using a LigaSure (SILOVE-LS) or extracorporeal suture (SILOVE-ECS), and open ovariectomy (open-OVE). Study Design Randomized, blinded, prospective study. Animals Healthy, domestic female cats (n = 24). Methods Cats underwent physical examination, packed cell volume, total solids and blood urea nitrogen analysis. Cats were randomly assigned to 1 of 3 groups: SILOVE-LS (n = 8), SILOVE-ECS (8) or open-OVE (8). Surgical time, complications, and postoperative pain scores were recorded. Results Single-incision laparoscopic ovariectomy was successful in (n = 8) SILOVE-LS cats and (n = 5) SILOVE-ECS cats. Surgical time was significantly longer for the SILOVE-ECS group compared with the SILOVE-LS (P < .0001) and open-OVE (P < .0001) groups, which were not different (P = .55). Complications were more frequent in the SILOVE-ECS group and removal of the SILP was required to complete ovariectomy in 3 cats. Cumulative 4-hour pain scores were not different between groups. Conclusions Single-incision laparoscopic ovariectomy using a SILP is a feasible method for OVE in cats. Single-incision laparoscopic ovariectomy using an extracorporeal suture is more time consuming and associated with more complications than either the SILOVE-LS or open-OVE methods.

Assessment of cardiac output measurement in dogs by transpulmonary pulse contour analysis.

OBJECTIVE To determine if metatarsal artery pressure (COmet) is comparable to femoral artery pressure (COfem) as the input for transpulmonary pulse contour analysis (PiCCO) in anesthetized dogs, using the lithium dilution method (LiDCO) as a standard for cardiac output (CO) measurement. DESIGN Prospective randomized study. SETTING University research laboratory. ANIMALS Ten healthy purpose-bred mixed breed dogs were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. INTERVENTIONS The CO was measured using LiDCO and PiCCO techniques. Animals had their right femoral and left distal metatarsal artery catheterized for proximal (COfem) and distal (COmet) PiCCO analysis, respectively. Measurements were obtained from each animal during low, normal, and high CO states by changing amount of inhalant anesthetics and heart rate. Measurements were converted to CO indexed to body weigh (CI(BW) =CO/kg) for statistical analysis. Agreement was determined using Bland and Altman analysis and concordance correlation coefficients. MEASUREMENTS AND MAIN RESULTS Thirty paired measurements were taken. The LiDCO CI(BW) (± SD) was 68.7 ± 30.3, 176.0 ± 53.0, and 211.1 ± 76.5 mL/kg/min during low, normal, and high CO states, respectively. There was a significant effect of CI(BW) state on bias and relative bias with COmet (P<0.001 and P=0.003, respectively). Bias of the COmet method (± SD) was -116.6 (70.5), 20.1(76.4), and 91.3 (92.0) mL/kg/min at low, normal, and high CI(BW), respectively. Bias of the COfem (± SD) was -20.3 (19.0), 8.6 (70.9), and -2.9 (83.0) mL/kg/min at low, normal, and high CI(BW) , respectively. The mean relative bias for COfem was -6.7 ± 44% (limits of agreements: -81.2 to 67.9%). CONCLUSION Compared with lithium dilution, the pulse contour analysis provides a good estimation of CO, but requires femoral artery catheterization in anesthetized dogs.

Midazolam administration reverses thermal hyperalgesia and prevents gamma-aminobutyric acid transporter loss in a rodent model of neuropathic pain.

BACKGROUND: Loss of &ggr;-aminobutyric acid (GABA) inhibition in the spinal dorsal horn may contribute to neuropathic pain. Here we examined whether systemic administration of the benzodiazepine midazolam would alleviate thermal hyperalgesia due to chronic constriction injury (CCI) of the sciatic nerve. METHODS: Hyperalgesia was evaluated with the thermal paw withdrawal latency test before, and 3 and 7 days after CCI. Animals randomly received, via osmotic minipump infusion, midazolam (2.0 mg · kg−1 · h−1), flumazenil (0.004 mg · kg−1 · h−1), midazolam plus flumazenil at the same doses, or saline (0.01 mg · kg−1 · h−1). Four groups of sham-operated rats (surgery without nerve ligation) received matched treatments. Levels of the GABA transporter 1 (GAT-1) in the lumbar spinal dorsal horn were estimated using western immunoblots 7 days after surgery. RESULTS: Saline-treated CCI rats developed thermal hyperalgesia on Day 3 with a more pronounced effect on Day 7. Continuous midazolam infusion prevented thermal hyperalgesia on both days. The antihyperalgesic effect of midazolam was reversed by the coadministration of flumazenil. Infusion of flumazenil alone had no effect on the thermal hyperalgesia in CCI rats. Sham-operated rats treated with saline, midazolam, or midazolam plus flumazenil exhibited no thermal hyperalgesia. Unexpectedly, thermal paw withdrawal latency in sham animals treated with flumazenil alone was significantly decreased. Changes in GAT-1 levels paralleled the behavior. Midazolam prevented the CCI-associated decreases, and flumazenil reversed midazolams effect. Flumazenil alone did not modify GAT-1 levels in CCI animals but in sham animals the transporter levels were significantly reduced. CONCLUSIONS: GABA inhibition plays an important role in neuropathic pain. Continuous systemic benzodiazepine administration may prove effective in alleviating neuropathic pain.

Effects of anesthetic drugs on canine splenic volume determined via computed tomography

OBJECTIVE To evaluate effects of commonly used anesthetics administered as single bolus injections on splenic volume. ANIMALS 10 adult Beagles. PROCEDURES A randomized crossover study was conducted. Computed tomography was performed on dogs to determine baseline splenic volume and changes after IV injection of assigned drug treatments. Dogs were allowed to acclimate for 10 minutes in a plastic crate before acquisition of abdominal CT images. Treatments were administered at 7-day intervals and consisted of IV administration of saline (0.9% NaCl) solution (5 mL), acepromazine maleate (0.03 mg/kg), hydromorphone (0.1 mg/kg), and dexmedetomidine (0.005 mg/kg) to all 10 dogs; thiopental (8 mg/kg) to 5 of the dogs; and propofol (5 mg/kg) to the other 5 dogs. Splenic volume was calculated from the CT images with image processing software. A repeated-measures ANOVA was performed, followed by a Bonferroni post hoc test. RESULTS No significant difference in splenic volume was detected between the acepromazine, propofol, and thiopental treatments, but splenic volume was greater with these drugs than with saline solution, hydromorphone, and dexmedetomidine. Splenic volume was less with hydromorphone, compared with dexmedetomidine, but splenic volume with hydromorphone and dexmedetomidine did not differ significantly from that with saline solution. CONCLUSIONS AND CLINICAL RELEVANCE Administration of acepromazine, thiopental, and propofol resulted in splenomegaly. Dexmedetomidine did not alter splenic volume. Hydromorphone slightly decreased splenic volume. Propofol should not be used when splenomegaly is not desirable, whereas hydromorphone and dexmedetomidine may be used when it is best to avoid splenic enlargement.

Cardiac Output Monitoring in Horses

Cardiac output (CO) is the volume of blood pumped out by the heart in 1 minute. Monitoring of CO can guide therapy and improve clinical outcome in critically ill patients and during anesthesia. Although there is increasing research into clinically useful methods of monitoring CO in equine patients, there are limitations to the available methods. There are 4 basic methods of measuring CO: (1) indicator methods, (2) a derivation of the Fick principle, (3) arterial pulse wave analysis, and (4) imaging diagnostic techniques. This article discusses the importance of CO, available technology, and challenges of monitoring CO in equine medicine.

Cardiopulmonary effects of a new inspiratory impedance threshold device in anesthetized hypotensive dogs.

OBJECTIVE To compare the hemodynamic and respiratory effects of an inspiratory impedance threshold device (ITD) in anesthetized normotensive and hypotensive dogs. STUDY DESIGN Prospective randomized study. ANIMALS Ten adult dogs. METHODS Dogs were anesthetized with propofol followed by isoflurane. During spontaneous ventilation, tidal volume (.VT), systolic (SAP), mean (MAP) and diastolic arterial blood pressure, central venous pressure, gastric PCO(2) as an indicator of gastric perfusion, subcutaneous oxygen tension, subcutaneous blood flow, cardiac index (CI), systemic vascular resistance and blood lactate were monitored. To monitor respiratory compliance (RC) and resistance (ResR), animals were briefly placed on mechanical ventilation. Dogs were studied under four different conditions: 1) normotension (MAP > 60 mmHg) with and without the ITD and 2) hypotension (target MAP = 40 mmHg) with and without ITD. These four conditions were performed during one anesthetic period, allowing for stabilization of parameters for each condition. Data were analyzed by anova repeated measure mixed models. RESULTS No cardiovascular changes were detected between no ITD and ITD in the normotensive state. During hypotension, CI was higher with the ITD (5 +/- 1.0 L minute(-1) m(-2)) compared with no ITD (4 +/- 1.3 L minute(-1) m(-2)). During hypotension, SAP was increased with ITD (80 +/- 14 mmHg) versus without ITD (67 +/- 13 mmHg). There was an increase in ResR and decreased RC with the ITD in both normotensive and hypotensive state. CONCLUSION AND CLINICAL RELEVANCE Impedance threshold device in dogs during isoflurane-induced hypotension improved CI and SAP but had negative effects on RC and ResR.

Evaluation of electric neurostimulation to confirm correct placement of lumbosacral epidural injections in dogs

OBJECTIVE To determine the minimal electric threshold (MET) of neurostimulation in and out of the lumbosacral epidural space necessary to cause muscle contraction of the hind limb or tail, determine an MET cutoff value that indicates epidural needle placement, and compare predictability of epidural needle placement attained by use of neurostimulation versus the standard technique that uses loss of resistance in dogs. ANIMALS 96 healthy Beagles. PROCEDURES Dogs received nonionic contrast medium (90 mg/kg) either in or out of the epidural space. Correct placement of the needle was evaluated by use of neurostimulation and loss of resistance of injection and confirmed by use of epidurography. RESULTS With the neurostimulator test, MET was significantly lower in dogs with needle placement in the epidural space (mean +/- SEM, 0.30 +/- 0.07 mA) than those with needle placement out of the epidural space (1.2 +/- 0.13 mA). When an electric current cutoff of < or = 0.28 mA for the neurostimulator test was used to suggest correct needle placement in the lumbosacral epidural space, sensitivity and specificity were 74% and 93%, respectively. The loss of resistance test had sensitivity of 63% and specificity of 90%. The combination of both tests yielded a sensitivity of 89% and specificity of 83%. CONCLUSIONS AND CLINICAL RELEVANCE Neurostimulation is a useful tool to suggest correct lumbosacral epidural needle placement in dogs.