Acute Pain Targets
This post has been inspired by an excellent article by @anaestricks (Dr. Gavin Doolan http://anaestricks.tumblr.com ) entitled Acute Pain Targets.
Here Gavin drew a simple diagram of the nociceptive pain pathway with analgesic targets and corresponding drugs responsible at each level.
I have become obsessed with this, thinking about it during all my GA’s and sharing it with my patients, to motivate and educate them to take their regular paracetamol, NSAIDS and GABA’nergic medication.
As a GP anaesthetist I didn’t need to delve deep into the depths of pharmacology but rather I did an apprenticeship over a year, using perioperative and acute pain regimes based on what we were thought and what we saw as useful.
Thinking about pain diagrammatically in the form of receptor targets is not new but a great way for GPA’s to know pharmacologically what how they should be managing acute, perioperative and chronic pain.
Here are a few examples from my past week of anaesthetics to help illustrate this point.
Nociceptor transduction blockade (inflammatory mediator inhibition): Paracoxib 40mg IV + Dexamethasone 8mg iv
Peripheral Nerve Transmission: 20ml 0.75% Ropivacaine infiltration by surgeon
Spinal Cord Modulation: Ketamine 50mg (induction) +30mg + 30mg, Tramadol 100mg iv + Morphine 15mg
Brain transmission: Paracetamol 1gm iv, Tramadol 100mg iv
Post operatively I relied on
Ibuprofen 400mg TDS
Paracetamol 1gm QUID
Fentanyl PCA (20mcg 5min lock out)
Later that day, she was happy and in relative comfort. This is very different from her last hysteroscopy/laparoscopy where she needed 28mg of morphine, 2 hours in recovery and a ketamine infusion for 24hours together with her Fentanyl PCA.
20yo well woman for a 3rd molar extraction day case.
Nociceptor Blockade: Paracoxib 40mg iv + dexamethasone 8mg iv
Peripheral Nerve Conduction: Alveloar block + Local infiltration by surgeon
Spinal Cord Transmission: Fentanyl 150mcg on induction (blunt sympathetic response to laryngoscopy + perioperative analgesia)
Brain perception: Paracetamol 1gm iv
Simple case but well illustrates effective blockade at each level so that she woke up comfortable and pain free.
The winner in this case is the local anaesthetic infiltration by the surgeon, after that block takes effect, the patient effectively “relaxes” physiologically on the monitor, less tachycardic/hypertensive. This works beautifully post operatively too, together with the long acting Cox-2 inhibition and regular paracetamol.
50yo medically well man with chronic back pain from osteoarthritis, hip OA, on the waitlist for a THR, seen in the rooms.
Debilitated by pain with difficulty mobilizing and preforming ADL’s. He was only taking Tramadol SR 150mg BD.
He had not wanted to take tablets in the past but now was ready to listen to some options.
With using the pain targets diagram, we agreed on the following plan.
Nociceptor Blockade: Celecoxib 100-200mg BD
Spinal Cord Transmission: Fentanyl patch (12-25mcg/hr)
Brain perception: Paracetamol 1330mg SR TDS (Considering Amitryptiline/Gabapentin/Pregabalin in the future on follow up)
I am hoping that this regime will work but with an understanding of analgesic targets, we are not stabbing in the dark and hoping for the best with our patient’s pain. We have options with dosages and different targets at each level.
This may be teaching most of you to suck eggs but this simple way that Gavin has outlined will help your anaesthetic and GP patients.
Hope that was helpful!
Maybe this is pedantic (OK it’s definitely pedantic) shouldn’t there be a transition from 2nd to 3rd order nerurone through the thalamus in there? And i thought that’s precisely where ketamine was thought to act? (i always describe ketamine to students as “unplugging the thalamus” – i may be totally wrong so please let me know!!!)