Bupivacaine 0.25% and methylene blue spread with epidural anesthesia in dog

ObjectiveTo evaluate the extent sensory and motor blocks produced by the epidural injection of different volumes of 0.25% bupivacaine (Bu) with methylene blue (MB), in dogs.Study designProspective experimental trial.AnimalsTwenty healthy adult mongrel dogs, weighing 9.9 ± 1.9 kg.MethodsDogs were randomly allocated into one of four groups that received 0.2, 0.4, 0.6 or 0.8 mL kg^?1 of an epidural solution containing 0.25% Bu and MB. Sensory block was evaluated against time by pinching the tail, hind limb interdigital web, toenail bases and the skin over the vertebral dermatomes. Motor block was assessed by ataxia, hind limb weight-bearing ability and by loss of muscle tone of the tail and pelvic limbs. Data were collected at 2, 5, 10, 15 and 30 minutes after the end of epidural injection. After the final time point, dogs were euthanatized and laminectomies were conducted to expose the extent of the dural dye staining.ResultsThe volumes 0.2, 0.4, 0.6 and 0.8 mL kg^?1 of 0.25% Bu and MB blocked a mean of 5, 14.2, 20.2 and 21 dermatomes, respectively. The extent of the senory block increased up to a volume of 0.6 mL kg^?1. Motor block was longer-lasting and more intense than sensory block. Complete dyeing of the spinal cord with MB was achieved in some dogs at 0.4 mL kg^?1 and all dogs at 0.6 mL kg^?1.ConclusionsThe volume of anesthetic injected into the epidural space plays an important role in the quality of the epidural anesthesia. At 0.25%, bupivacaine provided an efficient sensory block at 0.6 mL kg^?1.Clinical relevanceRelatively high volumes (0.6 mL kg^?1) of 0.25%, BU and MB were needed to produce an effective sensory and motor block caudal to the umbilicus, but all spinal cord segments were reached by MB at this dose.     

Effect of contrast and local anesthetic on dye spread following transversus abdominis plane injection in dog cadavers

ObjectiveTo determine whether the addition of bupivacaine or contrast medium to methylene blue dye would affect dye distribution following ultrasound (US)-guided transversus abdominis plane (TAP) injections.Study designProspective, randomized, blinded cadaveric study.AnimalsA total of 29 fresh Beagle dog cadavers.MethodsEach hemiabdomen (n = 58) was randomized into one of three groups: group M, 1% methylene blue; group MB, 50:50 mixture of 1% methylene blue and 0.5% bupivacaine; group MC, 25:75 mixture of 1% methylene blue and contrast agent (iohexol). TAP injections (0.5 mL kg^–1) were performed bilaterally by a trained individual followed by dissection of the abdominal walls. Craniocaudal and dorsoventral spread along tissue planes was measured. Staining of branches of the thoracic and lumbar spinal nerves was considered successful when dye on the nerve was >10 mm. One-way anova with post hoc Tukey test was used to compare craniocaudal and dorsoventral spread and Kruskal–Wallis test to compare incidence of nerve staining among groups.ResultsTAP injections were successful in 52 out of 58 hemiabdomens. Dorsoventral spread was greater for group M (60 ± 10 mm) compared with MC (49 ± 9 mm; p = 0.01) but not MB (52 ± 9 mm; p = 0.09). No difference was found in craniocaudal spread or number of nerves stained among groups.Conclusion and clinical relevanceThe significant difference found in spread of tissue staining between methylene blue alone and methylene blue mixed with contrast in the TAP blocks should be kept in mind when interpreting dye-based cadaveric regional anesthesia studies.     

Distribution of new methylene blue injected into the dorsolumbar epidural space in cows

Objective To describe the effect of injection volume and anatomy on the spread of new methylene blue (NMB) injected into the epidural space between the first and second lumbar vertebrae in cows. Study Design Prospective experimental study. Sample Population Thirteen nonpregnant cows. Methods Cows were randomly assigned to two groups. Group 1 received 5 mL and Group 2 received 10 mL of 0.12% NMB in 0.9% saline. The injection was made into the first interlumbar epidural space using a dorsal approach. The extent of cranial and caudal migration of the dye, as manifested by the staining of the epidural fat and dura mater, was measured. Results Mean ± SEM number (range) of stained vertebrae was significantly greater in the 10‐mL group than in the 5‐mL group, 4.4 ± 0.6 (T11 to L5) and 3.0 ± 0.2 (T12 to L3), respectively (p < 0.05). Linear regression analysis showed that the volume was significantly correlated with the number of stained vertebrae (R² = 0.42, p = 0.016). In the dorsal and lateral aspect of the spinal cord, there were two types of distribution of NMB along the surface of the epidural fat: between the periosteum and epidural fat; and between the epidural fat and dura mater. Migration under the spinal cord occurred along the two longitudinal epidural veins. Conclusions and Clinical Relevance The larger the volume of solution injected into the first interlumbar epidural space, the greater the spread. Intrinsic anatomic factors, such as characteristics of epidural fat and veins, influence the epidural spread of injected solution and, consequently, epidural analgesia.     

Distribution of new methylene blue injected into the lumbosacral epidural space in cats

OBJECTIVE: To determine the effects of injection volume and vertebral anatomy on the spread of new methylene blue (NMB) injected into the lumbosacral epidural space in cats. STUDY DESIGN: Prospective experimental study. SAMPLE POPULATION: Sixteen cats. METHODS: Cats were randomly assigned to four groups and received from 0.1 to 0.4 mL kg(-1) of 0.12% NMB in 0.9% saline. Injection was made into the lumbosacral epidural space using a dorsal approach with the cats in sternal recumbency. The extent of cranial migration of the dye as indicated by the staining of epidural fat and dura mater was measured. RESULTS: The mean +/- SD (range) number of stained vertebrae in the 0.3 and 0.4 mL kg(-1) groups, were 11.5 +/- 1.5 (T7-T11) and 12.4 +/- 1.8 (T6-T10), respectively. This was significantly greater than the number in the 0.1 and 0.2 mL kg(-1) groups, 4.3 +/- 0.6 (L3-L4) and 6.0 +/- 0.7 (L1-L2) vertebrae, respectively (p < 0.001). Linear regression analysis showed that the volume injected correlated significantly with the number of stained vertebrae (R2 = 0.83, p < 0.001). In the dorsal and lateral aspect of the spinal cord, NMB solution distributed between epidural fat and dura mater. Migration under the spinal cord occurred along the two longitudinal epidural veins. CONCLUSIONS AND CLINICAL RELEVANCE: The larger the volume of solution injected into the lumbosacral epidural space in cats, the greater the spread.     

Cardiovascular effects following epidural injection of romifidine in isoflurane‐anaesthetized dogs

ObjectiveTo investigate the cardiovascular effects of epidural romifidine in isoflurane-anaesthetized dogs.Study designProspective, randomized, blinded experiment.AnimalsA total of six healthy adult female Beagles aged 1.25 ± 0.08 years and weighing 12.46 ± 1.48 (10.25–14.50) kg.MethodsAnaesthesia was induced with propofol (6–9 mg kg^?1) and maintained with 1.8–1.9% end-tidal isoflurane in oxygen. End-tidal CO₂ was kept between 35 and 45 mmHg (4.7–6.0 kPa) using intermittent positive pressure ventilation. Heart rate (HR), arterial blood pressure and cardiac output (CO) were monitored. Cardiac output was determined using a LiDCO monitor and the derived parameters were calculated. After baseline measurements, either 10 μg kg^?1 romifidine or saline (total volume 1 mL 4.5 kg^?1) was injected into the lumbosacral epidural space. Data were recorded for 1 hour after epidural injection. A minimum of 1 week elapsed between treatments.ResultsAfter epidural injection, the overall means (± standard deviation, SD) of HR (95 ± 20 bpm), mean arterial blood pressure (MAP) (81 ± 19 mmHg), CO (1.63 ± 0.66 L minute^?1), cardiac index (CI) (2.97 ± 1.1 L minute^?1 m^?2) and stroke volume index (SI) (1.38 ± 0.21 mL beat^?1 kg^?1) were significantly lower in the romifidine treatment compared with the overall means in the saline treatment [HR (129 ± 24 bpm), MAP (89 ± 17 mmHg), CO (3.35 ± 0.86 L minute^?1), CI (6.17 ± 1.4 L minute^?1 m^?2) and SI (2.21 ± 0.21 mL beat^?1 kg^?1)]. The overall mean of systemic vascular resistance index (SVRI) (7202 ± 2656 dynes seconds cm^?5 m^?2) after epidural romifidine injection was significantly higher than the overall mean of SVRI (3315 ± 1167 dynes seconds cm^?5 m^?2) after epidural saline injection.ConclusionEpidural romifidine in isoflurane-anaesthetized dogs caused significant cardiovascular effects similar to those reportedly produced by systemic romifidine administration.Clinical relevanceSimilar cardiovascular monitoring is required after epidural and systemically administered romifidine. Further studies are required to evaluate the analgesic effects of epidural romifidine.     

Cardiovascular effects of epidural administration of methadone, ropivacaine 0.75% and their combination in isoflurane anaesthetized dogs

ObjectiveTo compare the cardiovascular effects of four epidural treatments in isoflurane anaesthetised dogs.Study designProspective, randomized. experimental study.AnimalsSix female, neutered Beagle dogs (13.3 ± 1.0 kg), aged 3.6 ± 0.1 years.MethodsAnaesthesia was induced with propofol (8.3 ± 1.1 mg kg^?1) and maintained with isoflurane in a mixture of oxygen and air [inspiratory fraction of oxygen (FiO₂) = 40%], using intermittent positive pressure ventilation. Using a cross-over model, NaCl 0.9% (P); methadone 1% 0.1 mg kg^?1 (M); ropivacaine 0.75% 1.65 mg kg^?1 (R) or methadone 1% 0.1 mg kg^?1 + ropivacaine 0.75% 1.65 mg kg^?1 (RM) in equal volumes (0.23 mL kg^?1) using NaCl 0.9%, was administered epidurally at the level of the lumbosacral space. Treatment P was administered to five dogs only. Cardiovascular and respiratory variables, blood gases, and oesophageal temperature were recorded at T-15 and for 60 minutes after epidural injection (T0).ResultsMean overall heart rate (HR in beats minute^?1) was significantly lower after treatment M (119 ± 16) (p = 0.0019), R (110 ± 18) (p < 0.0001) and RM (109 ± 13) (p < 0.0001), compared to treatment P (135 ± 21). Additionally, a significant difference in HR between treatments RM and M was found (p = 0.04). After both ropivacaine treatments, systemic arterial pressures (sAP) were significantly lower compared to other treatments. No significant overall differences between treatments were present for central venous pressure, cardiac output, stroke volume, systemic vascular resistance, oxygen delivery and arterial oxygen content (CaO₂). Heart rate and sAP significantly increased after treatment P and M compared to baseline (T-15). With all treatments significant reductions from baseline were observed in oesophageal temperature, packed cell volume and CaO₂. A transient unilateral Horner’s syndrome occurred in one dog after treatment R.Conclusions and clinical relevanceClinically important low sAPs were observed after the ropivacaine epidural treatments in isoflurane anaesthetised dogs. Systemic arterial pressures were clinically acceptable when using epidural methadone.     

The effect of epidural injection speed on epidural pressure and distribution of solution in anesthetized dogs

ObjectiveTo determine the effect of injection speed on epidural pressure (EP), injection pressure (IP), epidural distribution (ED) of solution, and extent of sensory blockade (SB) during lumbosacral epidural anesthesia in dogs.Study designProspective experimental trial.AnimalsTen healthy adult Beagle dogs weighing 8.7 ± 1.6 kg.MethodsGeneral anesthesia was induced with propofol administered intravenously and maintained with isoflurane. Keeping the dogs in sternal recumbency, two spinal needles connected to electrical pressure transducers were inserted into the L6-L7 and the L7-S1 intervertebral epidural spaces for EP and IP measurements, respectively. Bupivacaine 0.5% diluted in iohexol was administered epidurally to each dog via spinal needle at L7-S1 intervertebral space, at two rates of injection (1 and 2 mL minute^?1 groups), with a 1-week washout period. Epidural distribution was verified with computed tomography, and SB was evaluated after arousal by pinching the skin with a mosquito hemostatic forceps over the vertebral dermatomes. The results were analyzed according to each injection speed, using paired t- and Wilcoxon signed-rank tests.ResultsMean ± SD of baseline EP and IP values were 2.1 ± 6.1 and 2.6 ± 7.1 mmHg, respectively. Significant differences were observed between 1 and 2 mL minute^?1 groups for peak EP (23.1 ± 8.5 and 35.0 ± 14.5 mmHg, p = 0.047) and peak IP (68.5 ± 10.7 and 144.7 ± 32.6 mmHg, p <0.001). However, the median (range) of the ED, 11.5 (4–22) and 12 (5–21) vertebrae, and SB, 3.5 (0–20) and 1 (0–20) dermatomes, values of the two groups were not related to injection speed.Conclusions and clinical relevanceThe EP profile during injection was measured by separating the injection and pressure monitoring lines. The increase in epidural injection speed increased the EP, but not the ED or the SB in dogs.     

Influence of a preload of hydroxyethylstarch 6% on the cardiovascular effects of epidural administration of ropivacaine 0.75% in anaesthetized dogs

ObjectiveTo evaluate the cardiovascular effects of a preload of hydroxyethylstarch 6% (HES), preceding an epidural administration of ropivacaine 0.75% in isoflurane anaesthetized dogs.AnimalsSix female, neutered Beagle dogs (mean 13.3 ± SD 1.0 kg; 3.6 ± 0.1 years).Study designRandomized experimental cross-over study (washout of 1 month).MethodsAnaesthesia was induced with propofol and maintained with isoflurane in oxygen/air. All dogs were anaesthetized twice to receive either treatment HESR (continuous rate infusion [CRI] of 7 mL kg^?1 HES started 30 minutes [T-30] prior to epidural administration of ropivacaine 0.75% 1.65 mg kg^?1 at T0) or treatment R (no HES preload and similar dose and timing of epidural ropivacaine administration). Baseline measurements were obtained at T-5. Heart rate (HR), mean (MAP), diastolic (DAP) and systolic (SAP) invasive arterial pressures, cardiac output (Lithium dilution and pulse contour analysis) and derived parameters were recorded every 5 minutes for 60 minutes. Statistical analysis was performed on five dogs, due to the death of one dog.ResultsClinically relevant decreases in MAP (<60 mmHg) were observed for 20 and 40 minutes following epidural administration in treatments HESR and R respectively. Significant decreases in MAP and DAP were present after treatment HESR for up to 20 minutes following epidural administration. No significant within-treatment and overall differences were observed for other cardiovascular parameters. A transient unilateral Horner's syndrome occurred in two dogs (one in each treatment). One dog died after severe hypotension, associated with epidural anaesthesia.Conclusions and clinical relevanceA CRI of 7 mL kg^?1 HES administered over 30 minutes before epidural treatment did not prevent hypotension induced by epidural ropivacaine 0.75%. Epidural administration of ropivacaine 0.75% in isoflurane anaesthetized dogs was associated with a high incidence of adverse effects in this study.     

Comparison of the hanging-drop technique and running-drip method for identifying the epidural space in dogs

Objective

To compare the running-drip and hanging-drop techniques for locating the epidural space in dogs.

Preliminary observations on the effects of Meloxicam in a new model for acute intra-articular inflammation in dogs

The effects of intra-articular injection, on two occasions, 3 weeks apart, of the contrast agent Urografin on the cytological and biochemical characteristics of synovial fluid (SF) were examined in two studies in dogs. The first study provided baseline data in two non-medicated dogs. The second study used a cross-over design whereby 4 dogs received a 7-day oral treatment with either a placebo or meloxicam (0.2 mg/kg body weight daily) with a washout period of 3 weeks, in order to determine the effect of this new non-steroidal anti-inflammatory drug (NSAID) on the response to Urografin injection. SF samples were collected under general anaesthesia prior to and at 24 and 72 h after each Urografin injection. The volume, relative viscosity, white blood cell count and concentrations of protein, lactate dehydrogenase (LDH) and hyaluronic acid of these samples were determined.The results from both studies indicate that intra-articular injection of Urografin provoked a mild local transient inflammatory response, the most dramatic evidence of which was an increase in the white blood cell count in the SF after 24 h. In the second study, comparison of the synovial fluid measurements of the placebo-treated dogs at 24 h after Urografin injection with those prior to injection revealed significant increases in SF volume, white blood cell count, protein concentration and LDH activity and a significant reduction in relative viscosity. At 72 h after injection, only the white blood cell count and relative viscosity were significantly different from the pre-injection values. All of these measurements were, however, associated with high coefficients of variation, which must be taken into account in assessing the usefulness of the model for drug-testing purposes. Nevertheless, the administration of meloxicam significantly reduced the SF volume and white blood cell count at 24 h relative to the effects of concurrent placebo treatment. The general health status of the animals was not disturbed at any time as assessed by clinical and haematological observations. No adverse reactions were observed.Abbreviations LDH lactate dehydrogenase - NSAID non-steroidal anti-inflammatory drug - SF synovial fluid - WBC white blood cell count     

Effects of thoracolumbar epidural anesthesia with lidocaine on the systemic hemodynamics and hepatic blood flow in propofol anesthetized dogs

General anesthesia reduces hepatic blood flow (HBF) from circulatory depression. Total intravenous anesthesia (TIVA) is associated with decreased circulatory depression compared to inhalation anesthesia, and epidural anesthesia using local anesthetics increases blood flow by blocking the sympathetic nerves and expanding blood vessels. We investigated the effects of thoracolumbar epidural anesthesia with TIVA on HBF in dogs. Six Beagle dogs had epidural catheters placed between T13 and L1 and were anesthetized with propofol and vecuronium. Physiological saline (control) or 2% lidocaine (0.2 ml/kg, followed by 0.2 ml/kg/hr) was administered at 1–2 weeks intervals. Heart rate (HR), cardiac index (CI), mean arterial pressure (MAP), and systemic vascular resistance index (SVRI) were recorded at 10-min intervals from before epidural injections (T0) to 110 min. Indocyanine green test was used to measure HBF during the awake state and until 90 min after epidural injections. HR and CI did not differ between treatments. MAP and SVRI after lidocaine were significantly lower than those of controls, and the lowest MAP value was 65 ± 11 mmHg at T10. Compared to T0, after lidocaine treatment, HBF was significantly higher at T30, T60 and T90 (P<0.05); while, after control treatment, no significant change was evident at any time point. Despite a decrease in MAP by this technique, HBF was either maintained at pre-anesthetic levels or increased in comparison to controls, probably due to vasodilation of the hepatic artery induced by the selective blockade sympathetic ganglia.     

The use of electrical stimulation to guide epidural and intrathecal needle advancement at the L5‐L6 intervertebral space in dogs

ObjectiveTo determine the minimal electrical threshold (MET) necessary to elicit appropriate muscle contraction when the tip of an insulated needle is positioned epidurally or intrathecally at the L_5-6 intervertebral space (phase-I) and to determine whether the application of a fixed electrical current during its advancement could indicate needle entry into the intrathecal space (phase-II) in dogs.Study designProspective, blinded study.AnimalsThirteen (phase-I) and seventeen (phase-II) dogs, scheduled for a surgical procedure where L_5-6 intrathecal administration was indicated.MethodsUnder general anesthesia, an insulated needle was first inserted into the L_5-6 epidural space and secondly into the intrathecal space and the MET necessary to obtain a muscular contraction of the pelvic limb or tail at each site was determined (phase-I). Under similar conditions, in dogs of phase-II an insulated needle was inserted through the L_5-6 intervertebral space guided by the use of a fixed electrical current (0.8 mA) until muscular contraction of the pelvic limb or tail was obtained. Intrathecal needle placement was confirmed by either free flow of cerebrospinal fluid (CSF) or myelography.ResultsThe current required to elicit a motor response was significantly lower (p < 0.0001) when the tip of the needle was in the intrathecal space (0.48 ± 0.10 mA) than when it was located epidurally (2.56 ± 0.57). The use of a fixed electrical stimulation current of 0.8 mA resulted in correct prediction of intrathecal injection, corroborated by either free flow of CSF (n = 12) or iohexol distribution pattern (n = 5), in 100% of the cases.Conclusion and clinical relevanceNerve stimulation may be employed as a tool to distinguish epidural from intrathecal insulated needle position at the L_5-6 intervertebral space in dogs. This study demonstrates the feasibility of using an electrical stimulation test to confirm intrathecal needle position in dogs.     

Contrast‐enhanced voiding urosonography: A new,radiation‐free,alternative method for imaging of urinary bladder and urethra in healthy dogs

Contrast‐enhanced voiding urosonography (CE‐VUS) has been generally considered as a promising tool to diagnose vesicoureteral reflux and abnormalities in lower urinary tract in human patients, especially in children. The purpose of this prospective study is to evaluate the quality of images of the urinary bladder and urethra obtained by CE‐VUS using a second‐generation ultrasound contrast agent (SonoVue®) in healthy dogs and to investigate the safety profile of SonoVue® after intravesical administration. Eighty‐four CE‐VUS examinations with SonoVue® were successfully performed in both unsedated (39/84) and sedated (45/84) dogs. Contrast‐enhanced voiding urosonography examination of urinary bladder was technically successful in all (84/84) dogs. The image quality was not considered adequate in five (5/84) dogs including three dogs in whom layering of contrast media during filling phase was observed and two dogs with premature destruction of microbubbles. In these five dogs, the problem was readily recognized and corrected such that the procedure was still successfully undertaken. The assessment of the urethra during spontaneous micturition was successfully performed in all (84/84) dogs in whom voiding was elicited during the examination. No side effects were observed after intravesical application of SonoVue®. This study demonstrates that CE‐VUS is a feasible and valuable technique to evaluate low urinary tract morphology and function in dogs. Based on our review of the literature, there are no published reports about the use of this method in dogs.