Intrathecal Narcotics for Post-operative Analgesia

Posted by e-Medical PPT Wednesday, June 6, 2012
Thoracic and Upper Abdominal Procedures
Elective Total Hip Arthroplasty
350,000 Procedures per year in the US
+ 5 min to consent
+ 15 min for procedure

Anatomy, Physiology & Pharmacology
Drug disposition depends primarily on lipid solubility
Any drug rapidly redistributes
 opioid is detectable in the cisterna magna within 30 min of lumbar intrathecal administration

Lipophilic opioids
Rapidly traverse the dura; sequestered in epidural fat (and enter systemic circulation)
Rapidly penetrate the spinal cord and bind receptors and nonspecific sites

Hydrophilic opiods
Limited binding to epidural fat and nonspecific receptors
Slower transfer to systemic circulation
Higher CSF concentrations accounting for rostral spread

Complications
Pruritus
Mechanism unclear – likely opiod receptor mediated (not histamine)
Incidence 30-100%
Rx:  Antihistamines, 5-HT3 antagonist, opiod antagonists (or agonist-antagonists), propofol

Urinary Retention
Not dose dependent
Can last 14-16 hours
Most frequent with Morphine
35 % incidence
Mechanism related to sacral parasympathetic outflow inhibition
Allows increase in maximal bladder capacity

Nausea and Vomiting
Incidence 30 %
Most profound with Morphine
Likely due to cephalad migration of drug to area postrema

Respiratory Depression
Incidence is dose dependent
Very Rare 0.09% to 0.4%
Likely no more clinically relevant than for IV narcotics
Monitoring for 18-24 hours when using lipophilic opiods

PDPH
Age, Gender, History of PDPH, Obesity
Multiple dural puncture, Needle size, Needle design

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