Pain

Question 1

MOA of intrathecal opioids

Answer 1

Main site of action is Laminae I and II
Bind to G-protein linked opioid receptors both pre and post synaptically
Presynaptic receptors
* K+ channel opening ad Ca2+ channel closure
* reduction of intracelluar calcium
* reduction in release of excittatoty neurotransmitters e.g. glutamate
Postsynaptic receptors
* K+ channel opening
* Increase in inhibitory descending pathway activation
Other effects:
* possible effects similar to LA on C-fibers
* increase adenosine concentration» open K channels»_space; hyperpolarisation

Question 2

S/E of intrathecal opioids

Answer 2

1. Respiratory depression
2. Pruritis
3. N&V
4. Urinary retenstion
5. Sedation
6. Thermoregulation dysfunction
7. Viral reactivation
8. CNS excitation

Question 3

Which factors incresae risk of respi depression with intrathecal opioids?

Answer 3

• Elderly
• Pulmonary disease
• OSA
• Use o sedative drugs
• PPV
• Cephalad spread (esp drugs with lower lipid solubility > slower binding > spread)