Veterinary technicians are the backbone of the veterinary practice. Technicians fill many roles, such as phlebotomist; animal restrainer; customer service specialist; radiology, laboratory, pharmacy, and surgery technician; anesthetist; and, most important, patient care advocate. The veterinary technician often spends more time with patients than does the attending veterinarian. While veterinarians are seeing appointments or performing medical and surgical procedures, technicians provide moment-to-moment care for hospitalized patients. This is a vital role because technicians must be able to properly assess individual patients, be aware of changes in a patient’s medical status, and discuss any concerns with the veterinarian.
Because technicians play such an integral role in patient care, they must feel comfortable having open discussions about potential changes or additions in management strategies. The veterinary technician and veterinarian should be able to work together to achieve the best care possible for the patient. To help accomplish this task, technicians must be able to have thoughtful and intelligent discussions with the veterinarian and feel comfortable making suggestions for patient care when needed.
I find that technicians often feel intimidated or worried about discussing potential treatment plans. They feel that their ideas may be dismissed as uninformed. Knowledge is power. By having a solid understanding of common techniques and drugs, how they work, and why they are used, technicians can participate in effective discussions. Although veterinary technicians cannot prescribe drugs for pain management, they can accurately assess pain and work with the veterinarian to come up with a protocol.
Information on pain management and assessment in veterinary patients has grown tremendously over the past few decades. As our understanding grows, so should the techniques used to combat pain. Common pharmaceuticals range from opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) to α2-agonists, gabapentin, amantadine, ketamine, and local anesthetics. A list of common drugs and dosages used at UC Davis Veterinary Medical Teaching Hospital is available here.
More advanced multimodal techniques should also be considered when appropriate; these include epidural injections and catheters, local blockades, and constant-rate infusions (CRIs). Although beyond the scope of this article, other methods of pain management include weight management, acupuncture, laser therapy, nutraceuticals, corticosteroids, thermal therapy, and physical therapy techniques.
Nociception can be described as the detection of potential or actual trauma to the tissue by the nervous system. Nociceptors detect noxious stimuli caused by mechanical, chemical, or thermal mechanisms. Recognition is generally rapid. For example, a dog running to catch a ball steps on a nail. The peripheral nociceptors sense the trauma of the nail penetrating the skin and send a signal to the peripheral nerves. This pain sensation is sent through the dorsal root ganglion to the dorsal horn of the spinal cord and up to the brain. The body recognizes the sensation of pain and reacts: the dog pulls the foot away from the painful stimulus.
Many different terms are used to classify types of pain: acute, chronic, visceral, somatic, idiopathic, neuropathic, inflammatory, maladaptive, adaptive, and physiologic. Animals can experience more than one type of pain at a time, and some pain can morph from one type to another. Understanding what each term means is important in being proactive in pain assessment and improving overall nursing care.
PAIN SCALES AND ASSESSMENT
Pain should be assessed in all patients, ideally when they come into the hospital for an appointment and before and after any procedures (this helps to develop a baseline for that individual patient). Patients being maintained on analgesics should also be assessed regularly to help ensure pain medications are administered at proper intervals. Signs of pain can vary by species; therefore, it is important to understand the differences among animals commonly seen in the practice. Common signs of pain can include hunching or tucking up of the abdomen, vocalization, increased heart rate, increased respiratory rate, increased temperature, inability to find a comfortable position, restlessness, guarding the painful area, aggression, shaking, inappetence, anorexia, bruxism, and chewing and/or licking at the site of pain.
Being able to recognize and interpret signs of pain is crucial in patient care. Several pain scales are available for use, such as the visual analog scale, the grimace scale (rats, rabbits, and mice), Colorado State Canine Acute Pain Scale, Colorado State Feline Acute Pain Scale, numeric pain scale, and Glasgow Composite Pain Scale. I prefer the Colorado State scales for canine and feline patients (see Canine Pain Scale and Feline Pain Scale) because they contain both images and descriptions.
COMMON ANALGESIC DRUGS
Dexmedetomidine is the α2-agonist most commonly used in small animal medicine. α2-Agonists are not controlled, provide some analgesia, and are reversible. They are potent sedatives that can be used alone or with other drugs, such as opioids or tranquilizers. When they are combined with opioids or tranquillizers, they have a synergistic or additive effect. Dexmedetomidine is effective when given at IV microdoses for patients experiencing a rough recovery from anesthesia.
α2-Agonists can have substantial cardiovascular side effects. These drugs should be given only to healthy patients and are generally avoided in geriatric, diabetic, pregnant, pediatric, or sick animals. Common adverse effects include profound hypertension, bradycardia, and a reduction in cardiac output. Administration of an anticholinergic to treat bradycardia is generally contraindicated. Anticholinergics are not always effective and can increase the workload of the heart and exacerbate hypertension. It is often better to reverse the drug than to treat the bradycardia. Dexmedetomidine is usually reversed with atipamezole.
Dexmedetomidine can be also be used as a CRI or can be administered in an epidural or as part of a local blockade.
Opioids are commonly used as part of a balanced premedication protocol. These drugs can be administered as a premedication, intraoperatively as a bolus, postoperatively to help manage pain, as a CRI, or as part of an epidural or local blockade (FIGURE 1). Different intensities of analgesia are obtained according to the type of opioid chosen. Few negative effects are associated with administration of opioids, and they are generally considered safe in pediatric, geriatric, and sick or critical patients. Respiratory depression and bradycardia can occur and are most severe with higher doses of opioids.
A complete discussion of opioid types and uses is not within the scope of this article, but current anesthesia and analgesia textbooks often have chapters dedicated to opioids. I recommend the BSAVA Manual of Canine and Feline Anaesthesia and Analgesia, 3rd edition, as a valuable source of more detailed information about the drugs mentioned below.
Common full mu opioids include hydromorphone, morphine, oxymorphone, fentanyl, remifentanil, and methadone. These drugs can be used for mild, moderate, or severe pain.
Fentanyl and remifentanil are most commonly used for anesthetic induction and CRI infusions.
Morphine can cause a histamine release when administered via the IV route; therefore, if given this way, it should be administered slowly. Morphine has a long onset of action compared with the other full mu opioids and can take about 30 to 40 minutes to become fully effective after SC or IM injection. Morphine should not be used in patients where vomiting is contraindicated because this drug is most likely to cause emesis. Among the full mu opioids, morphine will also likely cause the most sedation, which can be beneficial in rambunctious patients.
Oxymorphone and hydromorphone have similar sedative properties and times to effect. Both may cause emesis and may be contraindicated in patients for which vomiting is not ideal.
Methadone is the only full mu opioid with which emesis is extremely unlikely. Sedation is often mild to moderate with this drug. Because it has activity on the N-methyl-d-aspartate (NMDA) receptor, it may be beneficial for patients experiencing neuropathic or “wind-up” pain.
Buprenorphine is a partial mu agonist opioid and is suggested for use in mild to moderate pain control. Traditional buprenorphine has a long onset of action; it takes about 15 minutes to become effective when given via the IV route and about 40 minutes when given via the IM route. Traditional buprenorphine can also be given via a transmucosal route in cats. This may provide a good option for owners who find it hard to give injections to their pets. Buprenorphine can also be administered in an epidural or as part of a local blockade.
Long-acting buprenorphine, such as Simbadol (zoetisus.com), is similar to traditional buprenorphine but is administered via the SC route at a much higher dose. This formulation is suggested for use in cats only and can be given once daily for up to 3 days. It should be used for mild to moderate pain management and is useful for feline patients that are difficult to medicate.
Butorphanol is a kappa agonist, mu antagonist opioid best used for sedation or mildly painful procedures in canine and feline patients. In avian patients that are known to have more kappa receptors than mu receptors, butorphanol is considered more effective for moderate to severe pain. Butorphanol is very short acting in most species but can be used as a CRI in some avian species if longer periods of pain relief are needed.
Tramadol, a centrally acting opioid analgesic, is generally well tolerated in most patients. It acts on the mu receptor and inhibits serotonin and noradrenaline uptake, which, in turn, may contribute to a reduction in nociceptive transmission within the spinal cord. There have been recent discussions on the actual efficacy of analgesia provided to some species, but more research is needed in this arena.
Ketamine can be used as both a premedication and an induction agent (often used in combination with a benzodiazepine). Ketamine produces a trancelike anesthesia often termed dissociative anesthesia or catalepsy. Common responses after administration include strong palpebral reflexes, increased muscle and jaw tone, central eye position, and an apneustic breathing pattern (patient holding breath for several seconds between a short and quick breath). Unlike most anesthetic drugs, ketamine does not decrease heart rate or depress myocardial function. Most animals exhibit tachycardia and vasoconstriction, which increase blood pressure.
Ketamine should be used with caution in patients with cardiac arrhythmias, hyperthyroidism, or cardiomyopathy. Until recently, ketamine was mostly avoided in patients with brain trauma or space-occupying masses because it can contribute to increased intracranial pressure. Some argue that ketamine may benefit this patient population because it can increase cerebral perfusion, but I generally avoid ketamine in these patients. If ketamine is necessary, small doses are chosen and titrated to effect.
Ketamine also increases intraocular pressure and is often considered contraindicated in patients with glaucoma or in procedures that may affect intraocular pressure. I generally avoid ketamine in these patients as well.
Ketamine provides good analgesia for skin and limb pain but is a poor analgesic for visceral pain. Ketamine helps combat neuropathic or “wind-up” pain and should be considered for use as a CRI when appropriate.
Amantadine is an NMDA antagonist originally developed for use as an antiviral. It is generally used as an adjunct with other drugs, such as NSAIDs, tramadol, or opioids, for both acute and longer-term, chronic pain.
Gabapentin was developed as an anticonvulsant drug but is often used for its analgesic properties. It is effective for management of neuropathic pain and can be used in both cats and dogs. The most common side effect is sedation.
Many NSAIDS are available in oral and injectable formulations. Most current NSAIDs preferentially inhibit cyclo-oxygenase (COX)-2 or are COX-1 sparing to varying degrees. COX-2 generates prostaglandins involved with inflammation, and COX-1 synthesizes prostaglandins needed for gastrointestinal and renal function. NSAIDs are commonly used to treat acute pain after trauma, postoperative pain, and chronic pain (eg, from osteoarthritis). These drugs can be used with other analgesic drugs and are not suggested for use in patients with moderate to severe kidney and/or liver disease. They should also be avoided in patients being administered corticosteroids. NSAIDs commonly used in veterinary medicine include carprofen, deracoxib, meloxicam, robenacoxib, and firocoxib.
Lidocaine has many uses, including free radical scavenging, systemic analgesia when administered as a CRI, regional anesthesia when administered as a local block, reducing neuropathic pain, providing minimum alveolar concentration (MAC) reduction (ability to reduce vaporizer settings), anti-inflammatory properties, promoting gastrointestinal motility as a prokinetic, and working as an antiarrhythmic. Lidocaine is safe when given at appropriate doses but is generally considered contraindicated for IV use in cats because of the potential for severe cardiac depression.
ADVANCED ANESTHETIC TECHNIQUES
Epidural anesthesia/analgesia, local blockades, and CRI of analgesic drugs are extremely effective for managing pain in several different types of medical and surgical procedures as well as after surgery. The species, type of procedure, and status of the patient must be considered before administration of any drug or drug combination.
Epidural Anesthesia and Analgesia
An epidural should be considered for patients requiring painful procedures of the hindlimbs, abdomen, thorax, and potentially even forelimbs. Epidural placement can be performed in as little as 5 minutes, thereby adding little time to the total time under anesthesia. Drugs commonly used for epidural administration include preservative-free morphine, lidocaine, bupivacaine, buprenorphine, and dexmedetomidine. Epidural anesthesia/analgesia should not be administered if the patient is septic or has signs of pyoderma or a skin infection around the epidural site.
Standard Epidural Procedure
A 25- or 22-gauge spinal needle is generally used for this procedure, with a length ranging from 1 inch to 3 inches depending on patient size. While a hypodermic needle can be used, a spinal needle is usually preferred because it contains a stylet. The stylet helps prevent tissue from clogging the lumen of the needle.
- Position the patient in sternal recumbency. (Lateral recumbency is an option.)
- Palpate the wings of the ilium. The lumbosacral space can be palpated between vertebral bodies L7 and S1.
- Shave and aseptically prepare the area as for a sterile surgical procedure. Wear sterile gloves when administering the epidural injection (FIGURE 2).
- Place the needle on the midline and slowly insert it through the skin and into the epidural space. A “pop” will be felt as the needle passes through the ligamentum flavum and enters the epidural space. If the needle touches bone, you have gone too far and need to back the needle out slightly.
- Determine correct placement with the loss-of-resistance or hanging drop technique. For the former, place a sterile glass syringe containing a small amount of air (1 to 2 mL) on the spinal needle and inject it into the space. If the air injects easily, you are in the correct spot. If there is a vacuum on the syringe, you are not in the correct space and need to reposition.1 For the hanging drop technique, place a drop of saline onto the opening of the spinal needle. If the drop is sucked into the hub of the spinal needle, you are in the correct space. If the drop of saline is not sucked into the spinal needle, you may or may not be in the correct spot. The hanging drop technique works much better in larger animals than in smaller patients.
- Once you are in the correct space, place the syringe containing the drugs onto the spinal needle. It is important to aspirate the syringe to ensure no blood or spinal fluid is present. If blood is aspirated, remove the needle and start over. If spinal fluid is aspirated, you should deliver only about one-fourth of the initial calculated dose.
Coccygeal Epidural Procedure
Coccygeal epidural injections can be used to provide analgesia and/or anesthesia for surgery or medical procedures involving the more caudal portions of the body (eg, pelvis, tail, genitals, perineal area). I find this block especially useful for providing local anesthesia to blocked cats. These patients are often in very critical condition and general anesthesia may be contraindicated. When the coccygeal epidural injection is done correctly, a urinary catheter can be passed without the need for inhalant anesthetics.
- Aseptically prepare the injection site. Palpate the sacrococcygeal space, which is found just cranial to the first coccygeal vertebrae. Wear sterile gloves during this procedure.
- Slowly insert a 25-gauge spinal needle or hypodermic needle at approximately a 30° to 45° angle into the injection site along the midline of the back. A “pop” will be felt as the needle passes through the ligamentum flavum.
In my opinion, the hanging drop technique does not work well at this site, especially in smaller patients. Therefore, the loss-of-resistance technique is used to ensure correct placement into the epidural space. After confirming proper needle placement, attach the drug syringe to the hub of the needle and aspirate it. If blood or cerebral spinal fluid enters the syringe, remove the needle and insert a new needle into the epidural space. Relaxation of the rectum and the tail indicates proper epidural placement.
Delivering a CRI before, during, or after general anesthesia is an excellent way to provide additional analgesia. BOX 1 provides examples of CRI calculations for administration via syringe pump and fluids. Common drugs used for analgesic CRIs include ketamine, dexmedetomidine, lidocaine, hydromorphone, morphine, and fentanyl. Using one or a combination of these drugs not only helps provide additional analgesia, but, depending on the species, may also help reduce the percentage of gas anesthesia (MAC reduction) needed. Reducing the amount of gas anesthesia has many benefits, including helping reduce the hypotension commonly experienced with inhalants (e.g., isoflurane, sevoflurane). If an opioid is used as a CRI at higher “anesthetic” doses, the patient should be intubated and placed on intermittent positive-pressure ventilation (manual or mechanical) because full mu opioids can cause moderate to severe respiratory depression.
In many instances, analgesic CRIs require a loading dose given at the onset of CRI delivery. A loading dose will quickly increase the drug plasma concentration levels, enabling the low-dose CRI to become effective quickly.2
LOCAL ANESTHETIC TECHNIQUES
Local and regional anesthetic techniques are the only way to provide a complete blockade of peripheral nociceptive input; therefore, they are the most effective method of preventing sensitization of the central nervous system and development of pathologic pain. The onset and duration of local anesthetics vary based on the drug chosen. However, the preoperative use of local anesthetics reduces inhalant anesthetic requirements and often helps patients have a smoother and less painful recovery. Lidocaine has a quick onset but a short duration of action, whereas bupivacaine has a longer onset and longer duration of action. Lidocaine will become effective in as little as 1 to 2 minutes and will last about 1 to 2 hours or more. Bupivacaine will become effective in about 10 to 20 minutes and last about 4 to 6 hours or more.
Some people advocate mixing local anesthetics, such as lidocaine and bupivacaine, to achieve the quicker onset of action provided by lidocaine and the longer duration of action provided by bupivacaine. Generally, mixing these two drugs shortens their duration of action compared to using bupivacaine alone. Studies have shown that the onset of action stays the same or actually is delayed when these two drugs are mixed.3
Topical anesthetics, such as 2.5% lidocaine and 2.5% prilocaine, can be applied to skin for minor procedures, such as IV and arterial catheter placement. It is advisable to shave the area of interest, spread a thin layer of cream, and place an occlusive dressing over the area of application for at least 10 minutes. I especially like this technique for placing arterial catheters in the auricular arteries of rabbit’s ears.
Local anesthetics can be administered into existing wounds or open surgical sites. This is usually accomplished by “splashing” the local anesthetic into the open wound before surgical closure.4
Infiltration of Local Anesthetics
Local anesthetics are commonly used to provide additional anesthesia and analgesia for such procedures as minor laceration repair, skin biopsies, and removal of small tumors located just under the skin. Local anesthetics, such as lidocaine and bupivacaine, can be injected into the tissue, preferably around the nerve of interest.
Infiltration of local anesthetics is generally easy and relatively quick. Shave and aseptically prepare the area before administering any drugs. Aseptic technique helps prevent contamination of the tissues with skin bacteria when the local anesthetic is injected. In most cases, use a small, 25- to 27-gauge needle attached to a 1-mL or 6-mL syringe to prevent tissue damage and allow for more precise administration of the drug (FIGURE 3). The volume of drug to be administered varies according to the area of interest and size of patient. If the patient is very small and the volume to be delivered is tiny, it may be necessary to dilute the local anesthetic before administration. Sodium chloride 0.9% is the most common fluid used for dilution. Always remember to aspirate the syringe before giving the injection. If blood is aspirated, reposition and start over (this is true for any injection of a local anesthetic).
Dental Nerve Blocks
Common dental nerve blocks include the maxillary, infraorbital, inferior alveolar, and mental blocks. Blocking these nerves provides excellent anesthesia for extractions and facial surgery. The maxillary nerve block provides anesthesia for the caudal portion of the maxilla. The infraorbital nerve block provides anesthesia for the rostral portion of the maxilla. The inferior alveolar nerve block provides anesthesia to the caudal portion of the mandible, while the mental nerve block provides anesthesia to the rostral portion of the mandible. It is ideal to use an insulin syringe with attached needle for very small patients. A 1- to 3-mL syringe with a 25- to 22-gauge needle attached can be used for larger dogs.
Brachial Plexus, Intercostal, Testicular, and Limb Blocks
Blockade of the brachial plexus is generally used to manage perioperative pain of the forelimb. The best technique is to block the nerves of the brachial plexus at C6 to T1. It is ideal to block the nerves close to the intervertebral foramina rather than the axillary space. This procedure is not benign. The phrenic nerve can become blocked, anesthetizing a portion of the diaphragm; thus, a brachial plexus block should be performed only unilaterally. Other complications include pneumothorax and IV and intrathecal injection. A nerve stimulator and insulated needle should be used to increase the success rate of this block.
Intercostal nerve blocks can be used for patients with fractured ribs or those undergoing a lateral thoracotomy. To provide complete blockade of the affected area, inject the local anesthetic not only at the caudal border of the rib at the fracture or incision site but also at the 2 to 3 ribs on either side of the fracture or incision site.
Testicular blocks are a cost-effective and easy way to provide MAC reduction and additional pain relief during and after castration. Blocks can be done in most species. Before injection, aseptically prepare the testicle. This block is generally performed in two steps. First, insert the needle into the caudal pole of each testicle, cranially toward the spermatic cord. Second, perform an incisional block at the anticipated surgical site.
Distal limb blocks are effective for procedures involving the lower extremity and digits. Examples include dewclaw removal, cat declawing, and mass removal (FIGURE 4). The local anesthetic is injected around the nerve via the SC route and caudal to the surgical site. Common sites include the radial, ulnar, and median nerves.
Soaker catheters are used for such procedures as large wound repairs, mass removals, and limb amputations. These catheters are aseptically placed by the surgeon just before closure of the surgical site. Soaker catheters are available commercially but can also be easily made by using a rubber feeding tube. To make a soaker catheter, set up a sterile barrier drape and remove the feeding tube from the package using aseptic technique. Use a sterile large-bore needle or scalpel blade to make several holes along the length of the tube. Inject sterile saline through the tube to ensure the holes are patent before handing the soaker catheter to the surgeon. Once the catheter has been sutured in place, a bolus of local anesthetic can be administered. In some cases, a CRI may be used to infuse small volumes of drug over a specific time frame. In general, soaker catheters are used for 24 to 48 hours after surgery (FIGURES 5 and 6).
Local anesthetics can also be infused into chest tubes to relieve postoperative pain. In general, inject a bolus of bupivacaine into the chest tube just before anesthetic recovery and incrementally as needed during the recovery period (usually every 6 hours if the patient’s actions indicate pain). Local anesthetic can cause pain on injection; therefore, sodium bicarbonate is often added to the bupivacaine just before injection into the chest tube. The sodium bicarbonate acts as a buffer, making the injection more tolerable for the patient. To prevent aspiration and removal of the drugs, first aspirate the chest tube to remove any fluid or air. After achieving negative pressure, insert the drugs through the tube.
Veterinary technicians play an integral role in pain assessment and management. Do not be afraid to make suggestions and ask questions. It is important that technicians feel comfortable alerting veterinarians to changes in patient status and are able to offer suggestions to the treatment plan when warranted. The entire veterinary team can work more harmoniously together when the technician is armed with the knowledge of how drugs work, when drugs are most appropriately used, how various combinations of drugs work together, and when advanced techniques could be added to a procedure. Advocating for the patient will in turn improve overall patient care.