Analgesic Administration Techniques and Reassessment Cadence

Administration Routes and Techniques

The route of analgesic delivery determines onset, duration, controllability, and patient suitability. Selection depends on the procedure, the patient's hydration and cardiovascular status, the species, and the available equipment.

Bolus Injection (IV, IM, SQ)

Bolus injection is the simplest route and is appropriate for short procedures, premedication, and breakthrough pain. IV gives the fastest onset (minutes) and is titratable, ideal for intraoperative top-ups. IM and SQ are practical for premedication and clinic-side administration when IV access is not yet established. Morphine should be given IM/SQ (histamine release if IV); methadone and hydromorphone can be given IV.

Constant Rate Infusion (CRI)

A CRI delivers a drug at a steady rate, maintaining a therapeutic plasma concentration and avoiding the peaks (toxicity) and troughs (breakthrough pain) of intermittent boluses. CRIs are standard of care for moderate-to-severe postoperative pain, major abdominal or orthopedic surgery, and critical care.

Equipment: syringe pump (preferred — accurate, small volumes, easy to adjust) or a buretrol/IV bag mixed to a known concentration. The technician calculates the dose (μg/kg/min or mg/kg/h) and the flow rate. Examples:

CRIs require a dedicated line, accurate calculation, and frequent monitoring. A technician error in the math is one of the most common causes of analgesic overdose or underdose — double-check the calculation and the pump setting. Label the bag with the drug, concentration, dose, patient weight, time started, and initials.

Transdermal — Fentanyl Patches

A fentanyl transdermal patch delivers fentanyl continuously over ~72 hours. Use cases: anticipated moderate-to-severe postoperative pain, or amputation/orthopedic surgery where oral opioids are limited.

Caveats:

• Slow onset (12–24 h to reach therapeutic levels) — apply BEFORE surgery to have effect by recovery; never rely on a patch for immediate analgesia.
• Heat affects absorption — warming blankets, fever, or shaving close to the patch increase absorption and risk overdose.
• Variable absorption between patients — monitor for both dysphoria (overdose) and breakthrough pain (underdose).
• Dysphoria can occur with high plasma levels; have naloxone available.
• Drug diversion concern — fentanyl patches are Schedule II controlled substances; log application, removal, and disposal of used patches (which retain drug).
• Skin reaction at the site is possible; rotate sites between applications.

Local and Regional Blocks

Local anesthetic blocks are the cornerstone of preemptive analgesia because they completely block nociceptive transmission for the duration of the drug.

• Infiltration / line block / splash block — lidocaine or bupivacaine infiltrated along the incision line or splashed on a wound; simple, no special equipment.
• Dental nerve blocks — infraorbital, maxillary, mandibular, mental; performed during dental procedures to numb specific quadrants; reduces intraoperative anesthetic requirement and postoperative pain from extractions.
• Ring block — circumferential around a digit for distal limb procedures.
• Brachial plexus block — for forelimb surgery.
• Epidural — injection into the epidural space (L7–S1 in dogs; cats similar). Provides analgesia of the hindlimbs, pelvis, perineum, and caudal abdomen. Combinations like morphine + bupivacaine (preservative-free morphine) are common. Strict asepsis is mandatory. Complications: urinary retention (catheterize if needed), pruritus (opioid), hypotension from sympathetic block (with local anesthetic), and rare spinal cord injury. Contraindicated with coagulopathy, skin infection at the site, or sepsis.

Oral At-Home Administration

For discharge, transition to oral formulations the owner can administer:

• NSAIDs: carprofen, meloxicam (single dose cat), robenacoxib, grapiprant — once or twice daily with food.
• Gabapentin: 100–300 mg per dog/cat, q8–12h — capsules or suspension; especially for neuropathic or chronic pain.
• Tramadol: cats metabolize it well; less reliable in dogs.
• Amantadine: once daily, usually with an NSAID for chronic OA.
• Buprenorphine transmucosal: cats — owners apply to the buccal mucosa; useful short-term post-op at home.
• Fentanyl patch: may remain in place at discharge; schedule a removal/recheck.

Preemptive and Preventive Analgesia

Preemptive analgesia is analgesia delivered before the nociceptive stimulus, preventing central sensitization and wind-up from ever establishing. Examples: NSAID given as premedication; local block placed before incision; opioid premedication 20–30 minutes before first surgical stimulus.

Why it matters: Once central sensitization has been established, dorsal horn neurons are easier to keep sensitized than to return to baseline. Studies show that patients who receive the same analgesic drug regimen but with the local block placed before vs after incision have lower post-op pain scores and require fewer rescue analgesics. The technician's role is to make sure the analgesic plan is in place before the first cut, not after.

Preventive analgesia extends this concept to the entire perioperative period, blocking nociceptive input from before incision through the inflammatory healing phase, to prevent chronic post-surgical pain.

Reassessment Cadence

Pain is dynamic — it changes with the surgical stage, the inflammatory phase, and the time since last dose. A single intraoperative or immediate post-op score is never enough. The standard reassessment cadence is:

• Every 4–6 hours for hospitalized post-operative patients at minimum; every 2 hours for severe pain, epidural patients (urinary retention check), or those on CRIs.
• Same observer and same scale when possible, so trends are comparable. Different observers using different scales introduce noise.
• Document the score in the medical record at each assessment — the charted score is the basis for dose adjustment and the legal record of analgesia adequacy.
• Treat to a target — typically a target of "mild or none" on the chosen scale. A static moderate or severe score, or any rising trend, triggers intervention (rescue dose, change drug class, adjust CRI, add an adjunct).
• Combine with physiologic monitoring — HR, RR, BP, temperature — but remember that physiologic parameters can normalize even with significant pain; behavioral scales are more sensitive.
• Before, during, and after any painful procedure (bandage change, drain removal, repositioning) — pre-medicate with a short-acting opioid, then score after.

Discharge and Client Education

Before discharge:

• Confirm the oral at-home plan is filled, labeled, and dosed correctly for the patient's weight.
• Educate the owner on dosing schedule, with-food guidance, side effects to watch (vomiting, melena, anorexia, lethargy, yellow sclera for NSAIDs), and warning signs requiring a call (no eating >24 h, persistent vomiting, dark/tarry stool).
• Schedule a recheck call at 24–48 h and a recheck visit. Many surgical complications and pain escalations are caught at the follow-up call.
• Do not discharge a patient still scoring moderate or severe pain — transition to oral, demonstrate comfort, then discharge.

Common Technician Pitfalls

• Treating only when pain is obvious — by the time a stoic animal vocalizes, pain is severe.
• Using one opioid dose as a substitute for a plan — single-dose analgesia without reassessment leads to untreated trough periods.
• Skipping documentation — "patient comfortable" without a numeric score is not actionable across shifts.
• Forgetting the NSAID + steroid trap at the medication reconciliation step.
• Failing to catheterize after an epidural — urinary retention is common and must be monitored.
• Discharging without an at-home plan — the in-hospital analgesia ends at discharge; the inflammatory pain does not.