Effect of dexmedetomidine added to retrobulbar blockade with lignocaine and bupivacaine in dogs undergoing enucleation surgery

OBJECTIVE

To investigate the effect of the addition of dexmedetomidine (BLD) to retrobulbar blockade with combined lignocaine and bupivacaine on nociception.

ANIMALS

A total of 17 eyes from 15 dogs.

METHODS

Prospective, randomized, masked clinical comparison study. Dogs undergoing unilateral enucleation were randomly assigned into two groups; a retrobulbar administration of lignocaine and bupivacaine in a 1:2 volume ratio combined with either BLD or 0.9% saline (BLS). The total volume of the intraconal injection was calculated at 0.1 mL/cm cranial length. Intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO2 (EtCO2 ) arterial blood pressure (BP), and inspired isoflurane concentration (ISOinsp). Pain scores, heart rate and RR were recorded postoperatively.

RESULTS

Dogs receiving BLD (n = 8) had significantly lower intraoperative RR (p = 0.007), and significantly lower ISOinsp (p = 0.037) than dogs in the BLS group (n = 9). Postoperatively heart rate was significantly lower in the BLD group at 1 min (p = 0.025) and 1 h (p = 0.022). There were no other significant differences in intraoperative or postoperative parameters, or in postoperative pain scores (p = 0.354). Dogs receiving BLD had a higher rate of anesthetic events of bradycardia and hypertension (p = 0.027). Analgesic rescue was not needed in either group.

CONCLUSIONS

The addition of BLD to retrobulbar anesthesia did not result in a detectable difference in pain scores relative to blockade with lignocaine and bupivacaine alone. Dogs receiving retrobulbar BLD had a significantly lower intraoperative RR and isoflurane requirement and an increased incidence of intraoperative bradycardia and hypertension.

Safety and accuracy of blind vs. ultrasound‐guided dorsal retrobulbar nerve blocks in horses—A cadaveric study

OBJECTIVE

There is limited knowledge regarding the safety and accuracy of ultrasound-guided retrobulbar nerve blocks in horses. The aim of this study was to compare these parameters between blind and ultrasound-guided injection techniques for the dorsal retrobulbar nerve block in horses.

METHODS

Equine cadaver heads were used to inject the retrobulbar space with contrast medium (CM). Injections were performed either blindly based on anatomic landmarks (blind group, n = 44) or under ultrasonographic guidance (US-group, n = 44), equally divided between an experienced and unexperienced operator. Needle position and distribution of CM were assessed with computed tomography imaging and evaluated by a board-certified veterinary diagnostic imager blinded to the technique. Safety and accuracy of both techniques were compared.

RESULTS

Ocular penetration was observed in two cases (n = 2/44) in the blind group but not in the US group (n = 0/44). No intrathecal, intraneural, or intravascular injections were seen in either group. Safety was significantly improved in the US group (p = .026). There was no statistically significant difference between the groups regarding the accuracy of the injection. Excellent accuracy was achieved more often with the ultrasound-guided technique (n = 11/22) than with the blind technique (n = 7/22) when performed by the unexperienced operator, but this difference was not statistically significant.

CONCLUSION

To prevent globe-threatening complications and improve the safety of the injection, we recommend using the ultrasound-guided injection technique for the dorsal retrobulbar nerve block.

A computed tomography-based method for the assessment of canine retrobulbar cone volume for ophthalmic anaesthesia

OBJECTIVE

To develop a comprehensive formula for calculating the volume of local anaesthetic solution used for retrobulbar anaesthesia in dogs with different skull morphologies.

STUDY DESIGN

Retrospective cohort imaging study.

ANIMALS

Skull computed tomography (CT) images of 188 dogs of different breeds collected between January 2009 and December 2017.

METHODS

Anatomical integrity of the orbit and adjacent structures, presenting complaint, clinical signs and CT findings were verified to exclude ocular abnormalities. The volume of the retrobulbar cone of 376 eyes was calculated using CT scans of the dogs' skulls. Additional data recorded included morphology of the skull, body weight, sex and size of the dogs, all of which were matched for possible association to the retrobulbar cone volume through univariable and multivariable linear regression models. Results of linear regression models were expressed as estimated beta coefficients with the corresponding 95% confidence intervals (95% CIs).

RESULTS

Using univariate analysis, the retrobulbar cone volume was positively associated with weight and male sex. In addition, brachycephalic and dolichocephalic dogs showed a larger retrobulbar cone volume than mesocephalic dogs, while sex was no longer significantly associated with the retrobulbar cone volume. In multivariate analysis, when considering all variables in the model, weight emerged as the strongest predictor (beta coefficient: 0.062 mL kg^-1, 95% CI: 0.056-0.067 mL kg^-1, p < 0.001).

CONCLUSIONS

and clinical relevance In the veterinary literature, there is no agreement on the precise volume of local anaesthetic solution that should be used to achieve intraconal retrobulbar anaesthesia in dogs. Here we suggest a formula to calculate the retrobulbar cone volume and, accordingly, the injection volume of local anaesthetic solution for effective retrobulbar anaesthesia.

Analgesic effects of a retrobulbar block with 0.75% ropivacaine in dogs undergoing enucleation

OBJECTIVE

To assess the analgesic effects of a retrobulbar block with ropivacaine in dogs undergoing enucleation.

STUDY DESIGN

Prospective, randomized, masked placebo-controlled trial.

ANIMALS

A total of 23 client-owned dogs.

METHODS

Dogs were randomized to be administered a preoperative inferior-temporal palpebral retrobulbar injection of either ropivacaine 0.75% (1 mL 10 kg^-1; group RG) or equivalent volume of 0.9% saline (control; group CG). Intraoperative variables recorded to detect a response to noxious stimuli included heart rate (HR) and mean arterial pressure (MAP). Three observers assessed and recorded pain using a numerical rating pain scale and visual analog scale (VAS) before anesthesia (baseline) and postoperatively at 0, 0.5, 1, 2, 3, 4, 5, 6 and 24 hours after extubation. Rescue analgesia was administered if intraoperative HR or MAP increased by ≥ 20% from the previously recorded surgical time point, average postoperative pain scores totaled ≥ 9/20, scored ≥ 3/4 in any one category with VAS ≥ 35/100, or if VAS was ≥ 35/100 with a palpation score > 0/4.

RESULTS

Intraoperatively, there was no significant difference in HR or MAP between groups. Rescue analgesia was administered intraoperatively to four and one dogs and postoperatively to five and seven dogs in groups CG and RG, respectively, with no significant difference between groups. VAS scores were significantly lower in ropivacaine dogs at extubation (p = 0.02), but not at other postoperative time points. Adverse events were not observed in either group.

CONCLUSIONS AND CLINICAL RELEVANCE

Preoperative retrobulbar 0.75% ropivacaine injection (1 mL 10 kg^-1) provided analgesia in dogs following enucleation at extubation; however, intraoperative and postoperative pain control did not differ from a placebo injection with saline. Lack of differences between groups may have been influenced by sample size limitations.

Analgesic effects of intraorbital insertion of an absorbable gelatin hemostatic sponge soaked with 1% ropivacaine solution following enucleation in dogs

OBJECTIVE

To evaluate analgesic effects and complications associated with intraorbital insertion of an absorbable gelatin hemostatic sponge (AGHS) soaked with 1% ropivacaine solution following enucleation in dogs.

ANIMALS

20 client-owned dogs undergoing enucleation.

PROCEDURES

Dogs were randomly assigned to receive an AGHS soaked with 1% ropivacaine solution (n = 10) or saline (0.9% NaCl) solution (control group; 10) inserted intraorbitally prior to skin closure following enucleation. Carprofen (2 mg/kg [0.9 mg/lb]) was administered SC once after orotracheal extubation and then PO twice a day for 5 days. During the postoperative recovery period, apparent pain level was scored at various points with a modified short-form Glasgow Composite Pain Scale (score range, 0 to 19), and methadone was administered for rescue analgesia if any score was ≥ 5. After dogs returned home, owners recorded their behavior and apparent pain level for the first 3 days following enucleation.

RESULTS

At extubation, the median (range) pain score was significantly higher in the control group (8 [2 to 14]) versus the ropivacaine group (3 [1 to 7]). A greater proportion of dogs in the control group received methadone (7/10 vs 1/10) and had crying or attention-seeking behavior on the first day following enucleation (7/10 vs 1/10). No complications were observed in either group.

CONCLUSIONS AND CLINICAL RELEVANCE

Addition of intraorbital insertion of a ropivacaine-soaked AGHS to the analgesic protocol for dogs undergoing enucleation provided better analgesia than was achieved without this treatment as measured immediately and the first day after surgery, with no noted adverse effects.

Retrospective analysis of complications associated with retrobulbar bupivacaine in dogs undergoing enucleation surgery

OBJECTIVE

To investigate complications associated with, and without, bupivacaine retrobulbar local anesthesia in dogs undergoing unilateral enucleation surgery.

STUDY DESIGN

Retrospective, observational study.

ANIMALS

A total of 167 dogs underwent unilateral enucleation surgery via a transpalpebral approach.

METHODS

Records from 167 dogs that underwent unilateral enucleation surgery that did (RB) or did not (NB) include retrobulbar bupivacaine anesthesia were reviewed, including anesthetic record, daily physical examination records, surgery report, patient discharge report and patient notes within 14 days of the surgery. Specific complications and severity were compared between RB and NB using the Wilcoxon rank-sum test. A 'complication burden' (0-5) comprising five prespecified complications was assigned and tested using rank-sum procedures. Statistical significance was set to 0.05.

RESULTS

Group RB included 97 dogs and group NB 70 dogs. Dogs in NB had a 17.0 percentage points (points) greater risk for a postoperative recovery complication (38.6% versus 21.6%; 95% confidence interval: 3.0-30.6 points; p = 0.017). There was inconclusive evidence that dogs in group RB had a lower risk of requiring perioperative anticholinergic administration (12.4% versus 22.9%; 10.5 points; p = 0.073). Other complications were similar between groups RB and NB with risks that differed by <10 points. The risk of hemorrhage was similar between groups RB (22.7%) and NB (20.0%) with no significant difference in the level of severity (p = 0.664).

CONCLUSIONS AND CLINICAL RELEVANCE

In this retrospective study, the use of retrobulbar bupivacaine for enucleation surgery in dogs was not associated with an increased risk of major or minor complications.

A preoperative bupivacaine retrobulbar block offers superior antinociception compared with an intraoperative splash block in dogs undergoing enucleation

PURPOSE

Investigate nociception differences in dogs undergoing enucleation administered bupivacaine either via preoperative retrobulbar block (pRB) or intraoperative splash block (iSB).

METHODS

Prospective, randomized, double-masked, clinical comparison study. Dogs undergoing unilateral enucleation were randomized to two groups: one received bupivacaine pRB and saline iSB of the same volume, and the other received saline pRB and bupivacaine iSB. The following intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO₂ (EtCO₂ ); systolic, mean, and diastolic arterial blood pressure (SAP, MAP, and DAP respectively); inspired end-tidal isoflurane concentration (EtISOIns), and expired end-tidal isoflurane concentration (EtISOExp). Pain scores were recorded pre- and postoperatively. Analgesic rescue was documented. Surgical hemorrhage and postoperative bruising and swelling were graded subjectively by the surgeon (HDW) and study coordinator (AEZ).

RESULTS

A significant (P = .0399) increase from baseline in overall mean heart rate was recorded in iSB bupivacaine patients (n = 11) compared with pRB bupivacaine patients (n = 11), with no significant differences in other intraoperative physiologic parameters, or pain scores. More analgesic rescue events occurred in iSB bupivacaine patients compared to pRB bupivacaine patients. A near-significant increase in intraoperative bleeding (P = .0519), and a significant increase in bruising (P = .0382) and swelling (P = .0223) was noted in the iSB bupivacaine group.

CONCLUSIONS

Preoperative retrobulbar block bupivacaine is more effective than an iSB bupivacaine at controlling both intraoperative and postoperative nociception in dogs undergoing enucleation. Additionally, iSB causes more postoperative bruising and swelling and may be associated with increased intraoperative hemorrhage.

Locoregional Anesthesia of the Head

Locoregional (local and regional) anesthesia is used routinely during surgical procedures of the head. The goal of this article is to provide a practical guide for the clinician to safely perform different techniques in dogs and cats and to minimize the risk of complications associated with locoregional anesthesia.

A surgical approach for extensive orbital exenteration in dogs; a description of technique and its application in 4 cases

OBJECTIVE

To describe a surgical approach for preplanned orbital exenteration.

ANIMALS STUDIED

Indications included intraconal orbital mass lesions. Four dogs were included, 3 with neoplasia and one with retro bulbar nodular fasciitis.

PROCEDURE

To facilitate complete removal of lesions, exenteration was performed by a new procedure for wide access. The frontalis and temporalis muscles were elevated and retracted through a single U-shaped skin incision. Zygomatic arch osteotomy was performed, followed by a 360-degree peritomy and zygomatic process osteotomy. The eyelids were divided from each other through the lateral cantus and then folded forward to expose the globe. The orbit was exenterated by blunt and sharp dissection. Osteotomies were closed with cerclage wires, soft tissues closed and the skin wound sutured in a T-shape.

RESULTS

The present exenteration procedure gave excellent access to remove orbital contents flush with the optic foramen and orbital fissure. Postoperative swelling and pain were limited and healing uneventful. Two of the 3 neoplasia cases experienced tumor recurrence involving the brain at 18 and 20 months postoperatively, respectively. Both of these had optic canal or intracranial tumor extension preoperatively. Long-term complications included mild concavity of the operated side of the face.

CONCLUSIONS

The present approach for preplanned exenteration offers excellent access for complete removal of orbital contents to the level of the optic foramen. Complications due to the surgical method are few and limited.