Pharmacological options for intra-operative and early postoperative analgesia: an update

Transversus abdominis plane block in rats: Preliminary cadaveric studies

The transversus abdominis plane (TAP) block is an ultrasound guided regional anaesthetic technique used to provide analgesia to the abdominal wall. Research in humans and cats has demonstrated that TAP blocks reduce pain and post-operative opioid requirements after abdominal surgery. To date TAP blocks have not been described in rats. The optimal technique to employ when performing TAP blocks is controversial with single point injection techniques failing to reliably provide adequate coverage of the cranial abdominal wall. It has been suggested that performing a two point injection may provide more reliable coverage of the cranial abdominal wall.The objective of this study was to determine the feasibility of performing ultrasound guided TAP blocks in rat cadavers and to evaluate whether performing a two point technique provides greater spread of injectate than a one point technique when administering the same total volume of methylene blue solution.Twenty-three, four-month-old, female Sprague Dawley rat cadavers weighing 506 ± 78 g were used. TAP blocks were performed using a total of 1 ml/kg of methylene blue solution.Overall success rates for injections were 21.7% (13.6-32.8%). Single point injection area of spread was 87.8 ± 32 mm² compared with 102.4 ± 17 mm² for the two point injection technique.Due to the low success rate the use of TAP blocks using the current technique cannot be recommended. Two point injection technique appears to provide greater spread; however, additional data is required to draw meaningful conclusions.

Pain in Pets: Beyond Physiology

Animals do not speak a language humans understand, making it easy to believe that they do not experience pain the way humans do. Despite data affirming that companion animals can and do experience pain much as do humans, there remains a gap between companion animal acute pain management knowledge and its execution. Companion animal pain is not simply a physiological issue. Veterinary clinicians can and should embrace the foundational principles of clinical bioethics-respect for autonomy, nonmaleficence, beneficence, and justice-translated from human medicine for the benefit of their patients. By reframing companion animal pain as a bioethical issue, as described in this paper, veterinarians affirm their commitment to closing the gap between what is known and what is done for painful companion animals. This takes pet pain beyond physiology.

The effect of splash block on the need for analgesia in dogs subjected to video-assisted ovariectomy

Objectives

The present study aimed to demonstrate the efficacy of splash block using lidocaine to provide additional analgesia during ovariectomy in bitches. To identify an acute intraoperative nociceptive response, three clinical parameters were used: increased blood pressure, heart rate and respiratory rate.

Material and Methods

Forty healthy bitches were randomly assigned to receive 2% lidocaine (L group) topical application (splash block) on both ovaries (2 mg/kg each), or an equal volume of NaCl 0.9% at the same sites (C group). A fentanyl bolus (2 µg/kg) was administered intraoperatively in response to an increase in blood pressure, heart rate or respiratory rate during surgery (> 30% compared with the pre‐incisional values).

Results

Local lidocaine administration significantly reduced the need for supplementary fentanyl. Dogs in the L group showed greater intraoperative hemodynamic stability and lower surgical pain than those in the C group. In addition to the routine anaesthetic protocol, the local anaesthesia used in the present study was safe and caused no cardiopulmonary suppression. In addition, it significantly reduced the need for mandatory systemic or rescue analgesia.

Clinical Significance

Ovariectomy is a common surgical procedure in bitches. Analgesia during this procedure is important because intraoperative pain can cause negative effects that prevent patient recovery. This study aimed to demonstrate the analgesic efficacy of lidocaine splash block in video‐assisted ovariectomy in dogs. The results showed that splash block improved surgical analgesia during canine laparoscopic ovariectomy. Considering its relative simplicity, low cost, and safety, splash block could be used in daily clinical practice.

Intra-articular use of analgesic/antinflammatory drugs in dogs and horses

Joint pain is a major cause of lameness in animals such as horses and dogs, and it may affect their athletic performance and quality of life. The intra-articular administration of analgesic/antinflammatory drugs is a common practice in veterinary medicine, for both lameness diagnosis and joint pain management. It is used either perioperatively, such as in animals undergoing arthroscopy/arthrotomy, and in osteoarthritic animals. However, evidence regarding efficacy and safety of each drug is limited, and controversies persist in these areas. In particular, it is often uncertain whether a defined treatment is effective by simply relieving the symptomatic pain associated with the joint disease, or whether it has a positive effect on the joint environment. Moreover, there is still much hesitation about treatments for joint diseases, related to the time of their application for the best outcome, and to any possible deleterious side effects. This article includes a review of the literature concerning the main analgesic/antinflammatory drugs used intra-articularly for managing acute and chronic joint pain/inflammation in dogs and horses. Three main issues for each class of drugs are considered, including clinical efficacy, pharmacokinetics, and local cytotoxic effects.

Clinical utility of a targeted smartphone application to aid veterinary students in calculating constant rate infusions and perioperative fluid drip rates

BACKGROUND

To compare the utility of a targeted smartphone application (TSPA) with a non-programmable calculator (NPC) when calculating fluid drip rates (FDR) and constant rate infusions (CRIs).

METHODS

In a prospective randomised clinical study, 48 fourth-year veterinary students entered one of four parallel groups involving two mock scenarios: fentanyl calculation using an NPC followed by lidocaine calculation using a TSPA, fentanyl (TSPA) followed by lidocaine (NPC), lidocaine (NPC) followed by fentanyl (TSPA) or lidocaine (TSPA) followed by fentanyl (NPC). Students calculated volume of drug added to maintenance fluids and drops/second that correctly administered the drug dose and FDR. Time to completion was assessed using an analysis of variance. A Fisher's exact test assessed the effect of study period, scenario and device in the proportion of correct/incorrect answers.

RESULTS

Participants took longer to complete the scenarios in period 1 and 2 with the NPC (380.7±195.6 seconds and 488±154.8 seconds, respectively) than the TSPA (247.5±88.8 seconds and 224±94.2 seconds, respectively) (P<0.0031 and P<0.0001). Participants were more likely to complete the scenarios incorrectly with the NPC (n=32) when compared with the TSPA (n=7) (P<0.0001).

CONCLUSIONS

TSPAs are more efficient and accurate when calculating CRIs and FDR compared with conventional methods. Medical mathematics must be emphasised during the veterinary curriculum.

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.

Evaluation of intraoperative analgesia provided by incisional lidocaine and bupivacaine in cats undergoing ovariohysterectomy

Objectives The objective of this study was to assess the intraoperative analgesic effect of preoperative infiltration of the incision site with lidocaine or a mixture of lidocaine with bupivacaine in cats undergoing ovariohysterectomy (OHE). Methods This was a prospective, randomised clinical study. Healthy female intact cats (n = 75) undergoing OHE under medetomidine-ketamine-buprenorphine anaesthesia were assigned randomly into three treatment groups (n = 25 per group) to receive one of two local anaesthesia protocols or placebo preoperatively in the midline incision: lidocaine 1.5 mg/kg (group GL) or mixture of lidocaine 1 mg/kg and bupivacaine 1 mg/kg (group GLB) or sodium chloride 0.9% (control group). Blood pressure, heart and respiratory rate, temperature, muscle tonus and pupillary reflex were registered during surgery. During recovery, the cats were observed for side effects. Postoperative analgesia was provided with meloxicam (0.2 mg/kg). Most cats were rechecked 2 weeks postoperatively to remove skin sutures. Results There was no significant difference between groups regarding breed, age, body weight, surgical time and postoperative complication rate. The majority of the cats (60%) included in the control group received a supplemental bolus of propofol during surgery, when compared with 43% and 44% of the cats included in the GL and GLB groups, respectively. Heart rate was significantly higher ( P <0.05) in the control group at the time of excision of the second ovary and the uterine body. Mean arterial pressure (MAP) was stable in both treatment groups; in contrast, it tended to increase in the control group. Heart rate and MAP were similar between treatment groups. Conclusions and relevance Preoperative incisional block with only lidocaine or combined with bupivacaine seems to produce a similar intraoperative analgesia in cats undergoing OHE. Despite the similar intraoperative analgesic effect between treatment groups, the combination of lidocaine and bupivacaine reduced the required doses, and had a faster onset of action and prolonged effect.

State of the art analgesia-Recent developments pharmacological approaches to acute pain management in dogs and cats: Part 2

There has been considerable interest in the area of acute pain management over recent years, focusing on pain assessment, pharmacological and non-pharmacological interventions. The evidence base for our clinical decision making and treatment of patients is ever increasing and becoming more robust. There is still a tendency to base some aspects of pain management on poor quality evidence and this requires further input in years to come. With new literature come new ideas and this review will detail the current knowledge base behind pharmacological management of acute pain in dogs and cats. The known mechanisms of action of each analgesic and its evidence will be considered. The second part of this review will consider the non-traditional analgesics, describing their component drugs individually, thereby focusing on their mechanisms of action and the current evidence for their use in acute pain management.

The lack of analgesic use (oligoanalgesia) in small animal practice

Oligoanalgesia is defined as failure to provide analgesia in patients with acute pain. Treatment of pain in emergencies, critical care and perioperatively may influence patient outcomes: the harmful practice of withholding analgesics occurs in teaching hospitals and private practices and results in severe physiological consequences. This article discusses the prevalence, primary causes, species and regional differences and ways to avoid oligoanalgesia in small animal practice. Oligoanalgesia may be addressed by improving education on pain management in the veterinary curriculum, providing continuing education to veterinarians and implementing pain scales.

Comparison of Morphine, Morphine-Lidocaine, and Morphine-Lidocaine-Ketamine Infusions in Dogs Using an Incision-Induced Pain Model

We aimed to compare antinociceptive effects of IV infusions of morphine (M), morphine-lidocaine (ML), or morphine-lidocaine-ketamine (MLK) combined, in a mild-to-moderate pain model in dogs. Eighteen adult hounds were heavily sedated with IV morphine (0.2 mg/kg) and dexmedetomidine to undergo thoracic skin incisions. After reversal, dogs were randomly assigned to receive loading doses of lidocaine and ketamine (MLK), lidocaine and saline (ML), or equivalent volume of saline (M), followed by 18 hr constant infusions of morphine (0.12 mg/kg/hr), lidocaine (3 mg/kg/hr) and ketamine (0.6 mg/kg/hr); morphine (0.12 mg/kg/hr) and lidocaine (3 mg/kg/hr); or morphine (0.12 mg/kg/hr), respectively. Pain was assessed with Short Form Glasgow Composite Measure Pain Scale and mechanical nociception with von Frey filaments (VFFS). Data were analyzed with linear mixed model on ranks. Independently of treatment, Short Form Glasgow Composite Measure Pain Scale was significantly higher than baseline for 24 hr (p < .0001), while VFFS was significantly lower than baseline for 48 hr post-recovery (p < .0001), with no difference between MLK and M groups. The ML group recorded significantly lower VFFS (p = .02) than the M group for the entire study. In conclusion, there was no significant analgesic difference between MLK and M alone.

Fentanyl-induced asystole in two dogs

Fentanyl is used in small animals for perioperative analgesia during anaesthesia. Severe bradycardia and asystole were observed on bolus administration of a 3 µg/kg loading dose of fentanyl in two dogs under isoflurane anaesthesia. Premedication with 10 µg/kg glycopyrrolate did not prevent asystole in the first case; and although bradycardia was treated with 5 µg/kg glycopyrrolate administered intravenously in the second case, the heart rate continuously decreased and asystole subsequently developed. Asystole in both cases was quickly corrected by intravenous administration of 0 · 04 mg/kg atropine and closed chest compressions. This case report describes asystole induced by fentanyl administration in isoflurane anaesthetised dogs. Atropine was more effective than glycopyrrolate in the treatment of fentanyl-induced asystole.