Pain Management for the Forgotten Minority (Medical Pain)
World Small Animal Veterinary Association World Congress Proceedings, 2014
Bonnie Wright, DVM, DACVAA

Text from: Guidelines for recognition, assessment and treatment of pain. J Small Anim Pract. 2014, with permission http://onlinelibrary.wiley.com/doi/10.1111/jsap.12200/abstract

Perceived Level of Pain Associated with Various Conditions

The designation of conditions into categories below is intended to serve only as a guide. Pain may vary according to the patient and the condition. Each patient should be assessed individually.

Severe-to-Excruciating

 Central nervous system infarction/tumors or meningitis

 Fracture repair where extensive soft-tissue injury exists

 Spinal surgery

 Ear canal ablation

 Burn injury

 Articular or pathological fractures

 Limb amputation

 Necrotizing pancreatitis or cholecystitis

 Thrombosis/ischemia

 Bone cancer

 Hypertrophic osteodystrophy

 Aortic saddle thrombosis

 Neuropathic pain (nerve entrapment/inflammation, acute intervertebral disc herniation)

 Inflammation (extensive e.g., peritonitis, fasciitis - especially streptococcal, cellulitis)

Moderate-to-Severe (Varies with Degree of Illness or Injury)

 Immune-mediated arthritis

 Panosteitis

 Capsular pain due to organomegaly

 Hollow organ distension

 Traumatic diaphragmatic rupture

 Pleuritis

 Trauma (i.e., orthopaedic, extensive soft tissue, head)

 Frostbite

 Ureteral/urethral/biliary obstruction

 Glaucoma

 Corneal abrasion/ulceration

 Uveitis

 Early or resolving stages of soft-tissue injuries/inflammation/disease

 Intervertebral disc disease

 Mesenteric, gastric, testicular or other torsions

 Peritonitis with septic abdomen

 Mucositis

 Oral cancer

 Mastitis

 Dystocia

 Extensive resection and reconstruction for mass removal and corrective orthopaedic surgery (osteotomies; cruciate surgery; open arthrotomies)

Moderate

 Soft-tissue injuries (i.e., less severe than above)

 Urethral obstruction

 Ovariohysterectomy

 Cystitis

 Diagnostic arthroscopy and laparoscopy

 Osteoarthritis

Mild-to-Moderate

 Dental disease

 Otitis

 Superficial lacerations

 Mild cystitis

 Chest drains

 Abscess lancing

 Castration

Emergency and Critical Care

In addition to analgesia for pain control, many injured or ill animals will require analgesia to facilitate restraint, diagnostic and emergency procedures. As each animal will present with varying levels of injury or illness and be experiencing different degrees of pain, individual drug selection, and dosing to effect is essential, rather than considering a standard regimen for all patients. Painful animals may also be aggressive and chemical restraint is required to protect staff and the patient from further (self-inflicted or iatrogenic) injury and to facilitate a physical examination. These animals may appear stable even with severe injury or illness (especially cats) due to the 'fight or flight' response. Where blood or fluid loss may be present or suspected, fluid therapy is commenced prior to careful titration of the opioid to avoid potential adverse effects with standard dosing. Detailed guidelines for analgesia, restraint and performing minor procedures, can be found at www.wsava.org.

The use of NSAIDs in the emergency patient should be withheld until the volume, cardiovascular and renal status of patients is determined to be within normal limits and with no potential for deterioration. NSAIDs should never be administered to patients with evidence of/potential hemorrhage.

Due to the variability of diagnoses, animals admitted for ongoing critical care experience a variable degree of pain, which contributes to a catabolic state in these patients. In addition to the primary problem, there are the additive effects of pain due to placement/presence of IV, urinary, thoracic, and abdominal catheters and drains. Many patients undergo frequent manipulations and procedures also contributing to the overall pain experienced. When considering analgesic selection, potential adverse effects should be minimized due to the often compromised organ function of these patients. Opioid analgesics and ketamine can still be used in patients with renal and hepatic insufficiency. Initial low dosing of the analgesic titrated to effect is required to reach therapeutic levels and avoid adverse effects; however, ongoing dosing with adjustments will be dependent on the individual patient as metabolism and excretion will be reduced (see below). Analgesia must be withdrawn slowly to avoid an abrupt return to a hyperalgesic state, should pain still be present. Where the re-appearance of pain is identified, return to the previous dose for several more hours followed again by slow withdrawal. Analgesia and the induction of restful sleep are the goals. Continuous rate infusions are useful to achieve this. The following drugs, approximate dosages and combinations, are suggested for moderate to severe pain. Initially, start with a lower dose of an opioid. Should further analgesia be required, add lidocaine (not cats) or ketamine if needed. Where drug availability is limited, select a regimen from the following based on availability:

Drug

Approx loading dose: titrate to effect

Approx CRI/time period based on loading dose

Fentanyl

2–5+ μg/kg

3–5 μg/kg/h

Hydromorphone

0.04–0.05+mg/kg

0.01–0.015 mg/kg/h

Methadone

0.2–1.0 mg/kg

0.05–0.2 mg/kg/h

Morphine

0.3 mg/kg

0.1 mg/kg/h

Ketamine

0.2–2 mg/kg

0.2–2 mg/kg/h

Lidocaine
(Dogs only)

2 mg/kg

1–2 mg/kg/h

For severe pain, opioids alone will not be sufficient and higher dosages than those in the Table above may be required. Should adverse effects begin but pain is still not controlled, introduce ketamine. Add lidocaine if ketamine cannot control the pain.

Loading Dosage

Titrate the opioid slowly to effect first; if needed add ketamine; if needed add lidocaine 2 mg/kg.

CRI

The continuous dosing regimen is based on the loading dose and expected duration of action. Clinical experience indicates that the fentanyl and ketamine loading dose can be used as the hourly infusion even though the expected duration of a single dose is ~ 30 min. For hydromorphone, methadone and morphine, the effective loading dose can then be used as the CRI dose over a 4-hour period (divide by 4 for the hourly dose) with frequent assessment and modification as duration of action may be prolonged, especially where renal or hepatic dysfunction is present. Should the patient appear overdosed at any period of time, the CRI can be stopped for 30 minutes, or less if signs subside, and reinstituted at one-half the previous dose rate. Or, careful titration of naloxone to reverse side effects (refer to Opioid Table for instructions). Where there are no contraindications/compromised organ function for NSAID use, addition is recommended where pain cannot be managed.

Where opioids are not available, lidocaine and ketamine as above, epidural anaesthesia, intrapleural or intra-abdominal local anaesthesia where indicated, diffusion catheters and various local blocks for postsurgical analgesia can be administered.

Anecdotally, acupuncture has been used as an appropriate adjunct for the critically ill patient. There are minimal risks or side effects of acupuncture, although very debilitated patients may require fewer needles.

Other modalities to include in the critically ill patient are proper use of warmth for muscle spasm or pain, cold for regions of acute injury or inflammation, gentle pressure support for appendicular regions that are painful (or sometimes for abdominal pain). Furthermore, proper padding and positioning, patient mobilization and nursing care are critical for comfort in these patients.

Medical Pain

Medical pain discussed here is a 'catch-all' for conditions not primarily associated with surgery or trauma (examples below); however, they may occur secondarily. Treating the underlying problem alleviates discomfort; however, analgesics are required during the healing process.

Abdominal, pelvic, and thoracic visceral pain occurs in conditions associated with distension and/or inflammation of hollow organs, ischemia, pulmonary thrombosis, acute enlargement of solid organs resulting in stretching of the capsule and inflammation of any organ (e.g., pancreatitis, acute kidney injury, pneumonia/pleuritis). Visceral pain tends to be diffuse in nature; however, pain can be localized to an area within the cavity when pressure is applied externally. Thoracic visceral pain may be elicited on abdominal palpation; visceral pain may also be exhibited as referred pain at a distant cutaneous site. Dermatologic diseases cause inflammation resulting in mild to excruciating pain (e.g., necrotizing fasciitis). Specific therapy to treat the underlying problem should alleviate the discomfort, but analgesics may be required to manage pain effectively.

Further examples of medical pain and their severity can be found in Section 9.

Suggested Analgesic Regimens

Opioids are the first choice drugs in many emergency and critically ill patients

Severe pain refer to critically ill above

1.  Mu agonist opioid (Table in Section 32 above) commencing at the mid-higher dosage and titrate to effect.

2.  NSAIDs, when hemodynamically stable and no contraindications, in combination with any of the opioids above

3.  Locoregional anaesthetic techniques

4.  Ketamine and/or lidocaine CRI

5.  Intrapleural and intraperitoneal blocks for visceral pain (www.wsava.org)

 

Moderate pain

1.  Low-medium dose mu agonist opioid, IV followed by CRI: fentanyl, hydromorphone, methadone or morphine. (Refer to Table in Section 32 above for dosing). If only pethidine (meperidine) opioid available: 5–10 mg/kg IM or SC; frequent IM or SC injections are painful and stressful and should be avoided where possible. Or

2.  NSAID when haemodynamically stable and no contraindications, either alone or in combination with an opioid or

3.  Buprenorphine 0.02–0.04 mg/kg IV or OTM q 4–8 h cats
0.02–0.04 mg/kg IV q 4–8 h dogs or OTM small dogs or

4.  Butorphanol 0.2–0.4 mg/kg IV q 1–2 h cats and dogs or CRI at 0.2 mg/kg/h after the loading dose

 

Mild to moderate pain (non-hospitalized or hospitalized patients)

1.  NSAID of choice where not contraindicated and/or

2.  Buprenorphine 0.02–0.04 mg/kg OTM q 6–8 h cats or
0.02–0.04 mg/kg OTM q 6–8 h small dogs

3.  Lidocaine 2% viscousa 1:1 to aluminium hydroxide 64 mg/mL, (max dose 0.4 mL/kg q 8 h) is effective in treating oral & esophageal lesionsb (personal communication, KM)

Tramadol 5 mg/kg PO q 8–12 h for dogs, or 2 mg/kg PO cats q 12 h may be of benefit, although there is little published evidence to support this.

Adjunctive Therapies (To Be Used with All Levels ff Pain Where Indicated)

 Antiemetics are indicated where nausea and vomiting are present.

 Acupuncture may be very useful for gastrointestinal and urinary cases in particular. Acupuncture may also be of benefit as an antiemetic technique.

 Medical massage and warm compress are recommended where indicated.

 Environmental enhancement to reduce stress and anxiety. Pheromonatherapy may be helpful in cats and dogs.

Endnotes

a. Lidodan 2%, Montreal, Canada (or similar product based on individual country).
b. Abrams-Ogg A. Oncologic emergencies. In: Mathews KA, ed. Emergency & Critical Care Manual. 2nd ed. Guelph, ON, Canada: Lifelearn; 2006:448.

  

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Bonnie Wright, DVM, DACVAA
USA


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