Post-Operative+Pain


 * Treatment of Acute Post-op Pain**

-relieves suffering and leads to earlier mobilization -shortened hospital stay, reduced hospital costs, and increased patient satisfaction -ideally individualized to medical, psychological, physical conditions -age, level of fear or anxiety, surgical procedure, personal preference, response to agents -minimize the dose of meds (lessen side effects) but provide adequate analgesia -multimodal and preemptive -team approach, eg) acute pain service -inflammation from tissue trauma (surgical incision, dissection, burns) vs. direct nerve injury (transection, stretching, compression)
 * Why**:
 * Goals**:
 * Surgical Pain Mechanism:**

-afferent pain pathway -Tissue trauma à local inflammatory mediators à hyperalgesia and allodynia -Other mechanisms contributing to hyperalgesia and allodynia: sensitization of the peripheral pain receptors (primary hyperalgesia) and increased excitability of central nervous system neurons (secondary hyperalgesia )

-targeting central mechanisms involved in perception of pain (opioids) -direct block of pain receptor activity (eg, [|lidocaine] ) -indirect via anti-inflammatory agents (eg,aspirin, NSAIDs) à diminish the local hormonal response to injury -target the activity of neurotransmitters à inhibit or augment their activity (eg, [|ketamine], [|clonidine] ) -better approach: use several agents, each acting at different sites of the pain pathway, lessens the dependence on a given medication and mechanism (synergism) -Synergism between meds à decreases the dosages needed and helps avoid the unwanted effects associated with the higher doses that would be required if only a single agent was used
 * Mechanism of Therapy:**

-administration of analgesics prior to onset of noxious stimuli -modifies peripheral and central nervous system processing of noxious stimuli à reducing hyperalgesia and allodynia -reduces postoperative opioid use and opioid side effects -use multiple pharmacological agents to reduce nociceptor (pain receptor) activation by blocking or decreasing receptor activation, and inhibiting the production or activity of pain neurotransmitters -three essential principles à (1)adequate depth to block all nociceptive stimuli during surgery (2)include the entire surgical field (3) duration including surgical and postsurgical periods
 * Pre-emptive analgesia**:

- swift and potent when administered IV -most common à morphine, hydromorphone, fentanyl
 * Opioids:**

-relative quick onset, peak effect 1-2 hours, plasma half life 2 hours -duration of action closer to 4-5 hours -hepatic glucuronidation to morphine-6-glucuronide(active metabolite) and morphine-3-glucuronide; both cleared renally -Morphine-6-glucuronide à responsible for side effects drowsiness, nausea and vomiting, coma, and respiratory depression -Morphine-3-glucuronide à agitation,myoclonus, delirium, and hyperalgesia. -bolus with 2mg slowly over 4-5 mins, titrated up to 1-2mg q1-3h -continuous à 2-5mg then 1mg/hr -IM à 5-10mg q3-4h prn
 * Morphine**:

-100 times more potent than morphine -more lipid-soluble à more rapid onset of action -shorter half-life of two to three hours -continuous IV infusions in ICU setting -no histamine-releasing properties à perferred in presence of hemodynamic instability and bronchospasm - extensively metabolized in liver to norfentanyl and other inactive metabolites à excreted in urine and bile, therefore suitable for pts with renal failure -IV, SQ, transdermal, transmucosal, neuraxial -moderate post-op pain à 25-100mcg over 1-2 min -severe pain à loading dose of 50 to 200mcg then continuous intravenous infusion of 25 to 50 mcg per hour, with titration to adequate analgesia.
 * Fentanyl:**

-semisynthetic opiate agonist -oral, rectal,parenteral, and neuraxial administration -bioavailability via SQ is 78% -biotransformed in the liver -compared to morphine à more rapid onset of analgesia (within 30 minutes) and a shorter half-life (2.4 hours) - moderate to severe pain à 0.2 to 0.6 mg bolus q2-3h
 * Hydromorphone****(Dilaudid):**

-somnolence, depression of brainstem control of respiratory drive -hypotension (more common in hypovolemic patients and following rapid injection) -urinary retention -emesis due to direct stimulation of the chemoreceptor trigger zone -Histamine release(mostly morphine) à tachycardia, hypotension, pruritus, and bronchospasm
 * Opioid Side effects**:

Ketorolac -NSAIDs useful in reducing amount of opiates requested by the patient, thus decreasing opioid side effects -adjuncts to other agents à epidural analgesia -IV for pre-emptive analgesia -reduces narcotic consumption 25-45% -usual dose 30mg IV
 * NSAIDs**:

-exact mechanism unknown -reduce undesirable physiological and psychological effects of opioid withdrawal -PO [|clonidine] à 150 to 200 mcgs preop à perioperative hemodynamic stability and reduce the requirement of postoperative analgesics
 * Alpha-2 receptor agonists:**

-reduces hyperalgesia and prevents opioid tolerance à lowering [|morphine] consumption and its side effects -acts as a bronchodilator -limited due to potential for hallucinations and dissociative mental state -infusion dose starting at 0.1 mg/kg/hr up to 0.3 mg/kg/hr
 * Ketamine:**
 * -**noncompetitive inhibitor of the N-methyl-D-aspartate (NMDA)

-wide range of oral pain medications to choose from - [|acetaminophen] (325 to 1000 mg PO or rectally q4-6h max dose 4g/d) - [|ibuprofen] (300 to 800 mg 3-4 times per day) -narcotics ( [|codeine] 15 to 60 mg orally every four to six hours, [|oxycodone] 5 to 30 mg orally every four to six hours)
 * Post-Op Oral analgesics:**

-epidural catheter at lumbar or low thoracic level for surgical anesthesia; or placed post specifically for analgesia -continued until patient tolerates oral meds -combination of local anesthetic and opioid à via patient-controlled epidural pump (PCEA); lowers dose requirements for each drugs, lowers the frequency of side effects - [|bupivacaine] (0.125 percent) or [|ropivacaine] (0.2 percent) plus [|fentanyl] (2 mcg/mL) or [|hydromorphone] (20 mcg/mL) Obese patients: -history of sleep apnea, susceptible to respiratory depression by parenteral narcotics -consider using local anesthetics alone for epidural Monitoring: -assess for adequacy of pain relief, level of activity tolerated, presence of motor blockade, presence of side effects -side effects à nausea, pruritis, infection (erythema, tenderness, swelling, discharge) -Hypotension à common after major abdominal surgery, assess fluid balance and other causes before implicating epidural infusion as source -Nausea or severe pruritus à remove opioid -nursing protocol à RR q2h, maintain IV access, ephedrine and naloxone available, notify MD if analgesia inadequate, RR <8, SBP<80, motor blockade, temp>101.5 twice in 8h
 * Neuraxial Analgesia: Postop epidural analgesia with local anesthetics and opioids:**