Pain Flashcards
Opioid Agonist-Antagonists advantages
analgesia
limited depression of ventilation
Low potential for physical dependence
Ceiling effect prevents additional responses
Ceiling effect
Higher dose = no higher effect/ wont OD.
Pentazocine receptors
Agonist effects on δ and κ receptors with weak antagonist activity
Pentazocine potency
1/5th as potent as Nalorphine (morphine)
Pentazocine Excretion
Glucoronide conjugates = urine
Pentazocine Elimination half-time
2-3 hr
Pentazocine Moderate Chronic Pain Dose
10 to 30 mg IV or 50 mgs PO (equivalent to Codeine 60 mgs)
Pentazocine analgesia sedation and depression of ventilation
20 to 30 mgs IM: analgesia sedation and depression of ventilation similar to 10 mgs of Morphine
Pentazocine S/E
S/E: sedation, diaphoresis, dizziness, dysphoria (high doses), increased HR, BP, PA bp, LVEDP.
Crosses placental barrier fetal depression
Butorphanol potency
Agonist 20x and antagonist 10x to 30x > Pentazocine
more potent than morphine
Butorphanol Receptors
low affinity for µ receptors to produce antagonism
moderate affinity for κ receptors to produce analgesia and anti-shivering effects
minimal affinity for σ receptors so dysphoria is low
Butorphanol dose comp to morphine
2 to 3 mg IM = 10 mg Morphine (depression of ventilation)
Rapidly & completely absorbed with IM.
Butorphanol Elimination half-time
2.5 to 3.5 hours
Butorphanol caution
difficult to use with another opioid agonist
What receptor has a moderate affinity for Butorphanols effects to mitigate shivering and produce analgesia
Kappa
Butorphanol Elimination site
Bile > urine
Nalbuphine potency
equally potent to Morphine
1/4th as potent as Nalorphine
Nalbuphine receptor
µ receptors agonist
Nalbuphine on cv
no increase in BP, PA BP, HR, or atrial filling pressures ->√√√ cardiac catheterization patients
Nalbuphine Elimination half-time
3 to 6 hours
Buprenorphine potency
µ receptors agonist affinity is 50x > Morphine
Analgesic potency 0.3 mg IM = 10 mg Morphine
Buprenorphine onset and duration
Onset: 30 mins
Duration: 8 hours
Buprenorphine and naloxone
prolonged resistance to Naloxone
Nalorphine
Equally potent with Morphine
Not used clinically: high incidence of dysphoria (σ receptors)
Bremazocine
κ receptors 2x potent > Morphine
Naloxone = not effective as reversal (could be other receptors)
Dezocine
δ & µ: analgesia, no CV
0.15 mg/kg IM= Morphine
10 to 15 mg IM rapid absorption
Onset: 15 mins.
Meptazinol
mu1 receptors
100 mg = 8 mg Morphine
Rapid onset
Duration: < 2 hrs
Protein binding: 25%
Which opioid agonist- antagonist is more potent than morphine
Buprenorphine
Naloxone, Naltrexone, and Nalmefene receptor
Pure µ opioid receptor antagonists
Naloxone moa
Nonselective antagonist with all 3 opioid receptors
Naloxone dose
1 to 4 µg/kg IV
Naloxone continuous infusion
5 µg/kg IV
Naloxone shock dose
> 1 mg/kg IV
Naloxone for Epidural S/E
0.25 µg/kg/hour IV
Naloxone Duration of action
30 to 45 minutes
give slow
Naloxone Elimination half-time
60-90 min
Naloxone S/E
reversal of analgesia*, N/V**, increased SNS (HR, BP, pulmonary edema, cardiac dysrhythmias [v-fib])
Naltrexone
More effective PO
Duration: 24 hours
Uses: alcoholism
Nalmefene
Equipotent to naloxone
Dose: 15 to 25 µg IV (q 2 to 5 mins) -> 1 µg/kg
Elimination half-time: 10.8 hours
Methylnaltrexone
Highly ionized (quarternary): peripheral
Promotes gastric emptying and antagonizes N/V
No alteration in centrally mediated analgesia
Alvimopan
Newer, µ-selective PO peripheral opioid antagonist
Uses: post op ileus
Metabolism: gut flora
Limitations: long term use -> CV events
Fentanyl effect on MAC
3 µg/kg IV 25 to 30 minutes before surgical incision = decreased Minimum Alveolar Concentration (MAC) of Iso or Desflurane to 50%
Sufentanyl on MAC
Sufentanyl decreases MAC with Enflurane by 70 to 90%
Alfentanyl on MAC
up to 70% decrease in MAC
Remifentanyl on MAC
50 to 91% decrease
Neuraxial opioids Receptors
Opioid Receptors in substantia gelatinosa (lamina 2) of spinal cord
Epidural dose
Dose is 5 to 10x more because the drug still needs to diffuse through the duramatter
Diffusion of drugs across the dura -> systemic absorption
Epidural on morphine
slower onset, but longer duration
Epidural systemic Uptake
Epidural venous plexus = systemic absorption
Intervention: Add epinephrine
Epidural Lipid solubility
Fentanyl
Fentanyl (800x > morphine)
Peak: 20 mins
Epidural Uptake Lipid solubility
Sufentanil
Sufentanil (1,600x > morphine)
Peak 6 mins
EPIDURAL ADMIN/
CSF PEAK
fent
20 MIN
EPIDURAL ADMIN/
CSF PEAK
SUFENTANIL
6 MIN
EPIDURAL ADMIN/
CSF PEAK
MORPHINE
1-4 hrs
EPIDURAL
ADMIN/
PLASMA PEAK
Fent
5-10 min
EPIDURAL
ADMIN/
PLASMA PEAK
Sufent
< 5 min
EPIDURAL
ADMIN/
PLASMA PEAK
morphine
10-15 min
INTRATHECAL/CSF/
CERVICAL LEVELS
morphine
1-5 hrs
Neuraxial Opioids Depression of Ventilation
Early: within 2 hours
Delayed: 6 to 12 hours after
Most reliable sign: depressed LOC secondary to hypercarbia
Treatment: Naloxone (0.25 µg/kg/hour IV) is effective in attenuating the side effects (nausea and vomiting, pruritus)
What is the emphasis of multimodal anesthesia for general anesthesia includes these two aspects
short acting anesthetic agents
opioid sparing
Gabapentin MOA
Structural analogue of GABA
No activity in GABA neurotransmission
Binds voltage gated Ca++ channels
Enhances descending inhibition
Inhibits excitatory neurotransmitter release
What medications can be given in both preop and post op
gabapentin and acetaminophen
Gabapentin’s Preemptive Analgesia dose
300-1200 mg PO; 1 to 2 hrs prior to OR
Gabapentin’s C/I
MG and myoclonus; reduce dose in elderly.
Gabapentin S/E
Abrupt withdrawal in seizure pts: seizures
COX-1
ubiquitous
“physiologic”
Inhibition is responsible for many adverse affects
COX-2
“pathophysiologic”
Expressed at sites of injury
Not protective…oncogenic processes
Sensitization, “wind-up”
COX-2 Selective
vs.
Nonspecific Inhibitors
Comparable analgesia
Lack effects on platelets
May be assoc. with ↓ GI effects
Possible ↑ in MI and CVA
Dosage ceiling
-↑ in side effects
Celecoxib (Celebrex) dose
200 to 400 mg PO QD
Celecoxib (Celebrex) dose
200 to 400 mg PO QD
Celecoxib (Celebrex) Peak
3 hours
Ofirmev dose
1000 mg IV Q4-6H; max 3000-4000 mg QD
Ofirmev Peak PO and IV
PO: 1-3 hours
IV: 30 mins to 1 hour
Ofirmev Duration
6-8 hours
Ofrimev MOA
Reduces prostaglandin metabolites
Ofirmev C/I
Hepatic Dysfunction
Ketorolac (Toradol) MOA
inhibits PG synthesis by inhibiting COX 1 and 2
Ketorolac (Toradol) C/I
Severe renal impairment, significant risk for bleeding, CAD, CABG, pregnancy; decrease dose in. elderly, NSAID allergy
Ketorolac (Toradol) Peak
45 to 60 mins IV
Ketorolac (Toradol) dose
15-30 q6H (1/2 dose in elderly): Max 60-120 mg QD
Ibuprofen MOA
anti-inflammatory, analgesic, and antipyretic; inhibits COX 1 and 2.
Ibuprofen Dose
200 to 800 IV over 30 mins Q6H PRN (3200 mg/day max).
Ibuprofen peak
1 to 2 hours
Lidocaine dose initial
1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
Lidocaine gtt dose
1 to 2 mg/kg/hour
terminated 12 - 72 hours
Mag MOA
N-methyl-D-aspartate (NMDA) receptor antagonist
MagnesiumDose
50mg/kg IV preop, then …
8 mg/kg/hr intraoperatively
Ondansetron Duration/Plasma ½ life
4 hrs
Ondansetron dose
4 mg IV (up to 8 mgs)
Pediatrics: 0.1 mg/kg IV
Corticosteroids moa for nausea
Glucocorticoid receptors in nucleus tractus solitarius
Increase effectiveness for 5 HT3 antagonists and droperidol
Dexamethasone (Decadron) dose
8-10 mgs
Dexamethasone (Decadron) efficacy persists for
24 hrs
onset = 2 hr delay