Management of Acute Post-Op Pain (Grass)

Question 1

What are eventual and adverse effects of untreated pain?

Answer 1

CV stress

Autonomic hyperactivity

Tissue breakdown

Pulmonary dysfunction

Hypercoagulability

Water retention

Immune dysfunction

Constipation

Chronic pain

Question 2

What is the neural gateway for all our pain sensations that gets afferent and efferent input?

Answer 2

Thalamus

Question 3

What are two chemicals released by our cells in response to injury that are precursors to eventual pain signal transduction?

Answer 3

Bradykinin precursors

Arachidonic acid (after modification by phospholipase A2)

Question 4

In the spinal cord, where do pain signal transduction occur?

Answer 4

They run through the dorsal root ganglia which eventually congregate at the dorsal horns (carries signals up to the sensory cortex)

Question 5

Describe the axonal tracts of neurons involved in pain signal transmission in the spinal cord.

Answer 5

Nociceptive-specific and WDR (wide dynamic-range) neurons send their axons up the dorsal horn and ant-lat spinothalamic tract.

These tracts synapse on 3rd order neurons in the contralateral thalamus (opposite side).

3rd order neurons project to the somatosensory Cx.

Note: 1st order neuron = initial pain signal, 2nd order neuron = the nociceptive-specific and WDR neurons aforementioned

Question 6

3 classes of NT cmds integral to pain transmission

List and give examples.

Answer 6

Excitatory amino acids (glutamate, aspartate)

Excitatory neuropeptides (substance P, neurokinin A)

Inhibitory amino acids (glycine,GABA)

Question 7

Are NMDA receptors involved in pain transmission?

Answer 7

Yes. This is why ketamine has analgesic properties.

Question 8

What are traits of dynamic pain?

Answer 8

Pt can move

Relief provides improved outcome

Question 9

What are the characteristics that describe pain (general)?

Answer 9

Location

Pattern

Quality

Question 10

List 3 non-opioid systemic analgesics.

Answer 10

• Salicylates
• Acetaminophen
• NSAIDs

Question 11

What is the analgesia ceiling effect?

Answer 11

Dose at which analgesia is maximized.

Beyond that, side effects increase (greater toxicity) without any additional benefits to the patient.

Question 12

What is the does for adults and childre for acetaminophen?

Answer 12

Adults: 1 g QID

Children: 10-15 mg/kg

Question 13

Studies of COX inhibitors have demonstrated improved post-op analgesia with up to X percent reduction in opioid analgesia requirements. What number(s) = X?

Answer 13

30-40%

Question 14

What are anesthetic benefits of NSAID as shown by research?

Answer 14

Reduced pain with movement

Reduced bladder spasm pain

Opioid sparing (up to 40%)

Earlier recovery of GI function

Question 15

Describe the dosing of Ketorolac.

Answer 15

>50 kg: 30 mg IV q6

<50 kg: 15 mg IV q6

Children: 0.5 mg/kg q6

Limit dosing to < 5 consecutive days

Question 16

What are complications of NSAIDs? Is there a special age group we need to worry about?

Answer 16

GI bleeding

Operative site bleeding (bigger issue for cranial and ENT procedures)

Acute renal failure

Hypersensitivity reactions

**These risks are shown to be much more significant in pts > 75 y/o

Question 17

Describe the mechanism of current NSAIDs.

Answer 17

They inhibit COX activation of prostaglandins.

COX = cyclo-oxygenase (comes from arachidonic acid)

Prostaglandins support renal and platelet functions, protect gastric mucosa, and lead to inflammation + pain.

Question 18

Why were COX 2 inhibitors developed?

Answer 18

COX 1 (constitutive) was known to mediate effects on GI, renal, and plt systems.

COX 2 (inducible) was known to mediate effects on inflammatory sites.

Therefore, inhibition of COX 2 would theoretically avoid all the negative effects of non-selective COX inhibitors.

Question 19

Describe what research has found out about our current COX 2 selective inhibitors.

Answer 19

• Similar analgesic effects to non-selective COX inhibitors
• Improved GI safety
• No plt effects
• Renal side effects still present
• Possible adverse CV and neuro effects with long-term use

Question 20

What is a commonly seen COX-2 inhibitor? Describe dosing.

Answer 20

Celecoxib (Celebrex)

100-200 mg PO q12

No need to withold. Dose pre-op or immediately post-op

Question 21

Does tolerance, physiologic dependence, and withdrawal from opioids indicate addiction?

Answer 21

Nope.

Question 22

Characteristics of opioid agonists include…

Answer 22

Full mu-receptor binding

No analgesic ceiling

Equianalgesic doses = equivalant efficacy

Similar side effects profiles

Different metabolites and elimination profiles

Effects on pain are highly patient variable!

Question 23

Traits of opioid agonist-antagonist combinations include…

Answer 23

• Kappa agonism + partial/full mu antagonism
• Respiratory depression ceiling (although this ceiling is pretty high [~20 mg morphine], so still a concern)
• Analgesic ceiling
• Acute withdrawal with mu-agonists
• Psychomimetic side effects

Question 24

Approximate differences between peak-plasma levels and time-to-peak levels between IV and IM opioids are.. (give me a multiple)

Answer 24

Compared to IV opioids, IM opioids:

Peak plasma levels: 2-5 x lower

Time to peak: 3-7 fold higher

*Peaks and troughs in plasma levels rather than a steady plasma peak as in IV opioids

Note: HIGHLY patient variable

Question 25

Are IM opioids safe?

Answer 25

Not really. Erratic absorption means severe respiratory depression can occur spontaneously. No advantage over oral route\* (more erratic)

Question 26

Describe the elimination of Morphine. (Active metabolites, excretion)

Answer 26

Active metabolite = M6G 90% renal excreted

Question 27

Any contraindications to morphine that we commonly see? What's a good long-acting alternative opioid we commonly give?

Answer 27

Yes: renal dysfunction due to active metabolite and predominantly renal excretion Hydromorphone: 6x as potent as morphine; good alternative

Question 28

What is the best opioid agent to use in pts with renal dysfunction? Describe this drugs relative potency, onset, and duration to morphine.

Answer 28

Fentanyl. 80-100x more potent than morphine Quicker onset Shorter duration

Question 29

Compare meperidine with morphine. When is this opioid usually used?

Answer 29

Its 1/10th as potent as morphine Has active metabolites (normeperidine) that provide no analgesic properties like M6G. Contraindicated in renal dysfxn, siezures, MAOIs Its pretty much used only if pt is intolerant to all other opioid agonists.

Question 30

Give me the equianalgesic doses with 10 mg morphine for Dilaudid and fentanyl.

Answer 30

10 mg morphine = 1.5 mg hydromorphone = 100 mcg fentanyl

Question 31

Is opioid consumption for pain correlated better with weight or age?

Answer 31

Age. Very little correlation with weight (shallow slope)

Question 32

Whhat very negative adverse effects can acute reversal of opioids cause?

Answer 32

Due to acute reversal of analgesia, reversing opioids too rapidly with Naloxone can cause **acute MI, seizures,** or **pulmonary edema**!

Question 33

How should Naloxine be dosed?

Answer 33

Titrate 40 mcg q2-3 min to RR \> 12/min Infusion (due to spinals or IM overdose): hourly rate = load/3 For full respiratory arrest: 0.2 mg increments Note: at MHTMC and most other places, comes in 0.4 mg bottles (titrate into a 10 cc syringe)

Question 34

Risk factors for respiratory depression with PCA include..

Answer 34

Advanced age Advanced pulmonary disease Concurrent administration of sedatives/hypnotics (avoid benzos) OSA Background infusions

Question 35

When should you use PCA with a basal/background infusion of more opioids? If used, what limit should be placed on the rate of basal infusions?

Answer 35

Opioid tolerant patients Children 5-12 y/o Extreme extreme pain Keep BI \< 50% of total consumption possible that hour (titrate)

Question 36

What is the dose of morphine for intrathecal/spinal and epidural analgesia?

Answer 36

Intrathecal = 0.1-0.5 mg Epidural = 2-5 mg

Question 37

Compare the use of bupi with ropi in epidurals (general pain mngmt)

Answer 37

Bupi causes differential sensory blockade Ropi causes less motor blockade (lumbar)

Question 38

When we give epidural opioids, where's the site of action we hope they get to exert their effects most?

Answer 38

Dorsal horn of the spinal cord to block pain signals presynaptically

Question 39

What are hydrophilic opioids? Lipophilic opioids? What difference does it make in spinals?

Answer 39

Hydrophilic = morphine, Dilaudid Lipophilic = fentanyl, sufentanil, etc. Hydrophilic = slow onset, long duration, **extensive CSF spread**, more side effects, delayed respiratory depression Lipophilic = fast onset, short duration, **minimal CSF spread**, lower side effects profile

Question 40

What are advantages of epidurals/spinals?

Answer 40

Synergistic analgesia Superior pain relief Decreased DVT and graft occlusions Earlier return of bowel function Less pulmonary complications

Question 41

Unlike lipophilic opioids, the administration of hydrophilic opioids can cause two (rather than one) phases of respiratory depression. Why do these two phases occur?

Answer 41

FIrst phase is an acute phase due to systemic absorption (equivalent to same dose given IM) Second dose is due to cephalad CSF spread (lipophilics don't spread as much or last as long) This second phase peaks in 8-10 hours and plateaus for \>18 hours. Occurs in 0.1-0.6% pts. Treat with naloxone load + **infusion**.

Question 42

What are some common analgesic adjuncts?

Answer 42

Ketamines Benzodiazepines Hydroxyzine (first gen anti-histamine with multiple antagonistic effects, not well studied) Clonidine (or other alpha 2 agonists) TCA Gabapentin (Neurontin)

Question 43

What is Gabapentin used for?

Answer 43

Used as an antisiezure drug. Effective in treating neuropathic pain, comeplx regional pain syndrom Can block development of hyperalgesia Due to ability to effect nociceptive processes involving central sensitization

Question 44

What kind of surgeries have been implicated to be the most likely predictor of chronic pain outcome?

Answer 44

Limb amputations (Followed by thoracotomies and breast surgeries)

Question 45

What are some predictive factors for chronic pain?

Answer 45

Pre-op: repeat surgery, psychologic vulnerability, worker's comp (lol) Intraop: nerve damage risk in surgery Post-op: radiation Rx, chemo Rx, depression, psychologic vulnerability, anxiety, neuroticism