Ketamine for Total Hip Arthroplasty

Bad Times in the K Hole

From: http://www.ncbi.nlm.nih.gov/pubmed/19923527
Anesth Analg. 2009 Dec;109(6):1963-71. doi: 10.1213/ANE.0b013e3181bdc8a0.

The early and delayed analgesic effects of ketamine after total hip arthroplasty: a prospective, randomized, controlled, double-blind study.

The gist: Ketamine can reduce post-op pain scores and is opioid sparing when given to patients undergoing General Anesthesia hip replacement (note this is NOT generalizable to spinal anesthesia)

Methods: Pts received IV ketamine before incision (0.5 mg/kg), and a 24-h infusion (2 microg x kg(-1) x min(-1)) or a similar blinded saline bolus and infusion. Postoperative analgesia included IV acetaminophen, ketoprofen, plus morphine/droperidol patient-controlled analgesia for 48 h

Results: Ketamine decreased morphine consumption at 24 h from 19 +/- 12 mg to 14 +/- 13 mg (P = 0.004). At Day 30, ketamine decreased the proportion of patients needing 2 crutches or a walking frame from 56% to 31% (P = 0.0035). From Day 30 to Day 180, ketamine decreased the proportion of patients with persistent pain at rest in the operated hip (P = 0.008).

Other evidence [apparently – I’m looking at you DP who never bothers to comment] shows the one time bolus 0.5mg/kg vs. infusion makes little difference in post-op pain scores… so go for the bolus!

 

 

Magnesium: a versatile drug for anesthesiologists

From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3726845/

MOA: multiple including blockade of nmda and Calcium channels 

Magnesium has multiple advantages including:

• Reduced opioid reqs post op
• Reduced Mac with tiva
• Tiva reduced remi use -> reduced hyperanalgesia post op
• Intrathecal MG prolongs labor analgesia, especially motor block and iv Mg prolongs muscle blockade when spinal wearing out 
• Potentiates Nondepolarizing blockade,  can improve incubating conditions while reducing hemodynamic response to intubation 
• Reduced post op shivering >70%

However caution:

• Reduced inh Mac questionable 
• Blunts release of NE / epi watch out in critically ill patients 
• Cardiovascular depression possible when given as bolus 

Dosing: 

loading dose of 30-50 mcg/kg followed by a maintenance dose of 6-20 mcg/kg/h (continuous infusion) until the end of surgery; alternatively 4mg bolus

Anesthesia for patients with opioid abuse and tolerance

From Anesthesiology News: http://www.anesthesiologynews.com/download/Opioid_AN0613_WM.pdf

Eval

-try to ask most use in a day, rather than average, more objective
-time of last dose, who is prescribing
-single questions alternative to CAGE-AID: How many times have you used illegal drugs in the past year?

Long term opioid therapy

Methadone
-opioid agonists, with some NMDA antagonism
-typically 30-40mg qd

Buprenorphine
-parital opioid agonist
-no high

Suboxone
-combo of buprenorphine and naloxone
-when injected, only naloxone works

Vivitrol
-extended release naltrexone
-opioid antagonist
-for etoh and opioid abuse
-monthly injection

I/O management

3 areas: manage intox, prevent/tx withdrawal, achieve effective analgesia

Antagonist reserved for life-threatening resp depression, as precipitating w/d can make management harder
If not receiving agonist therapy:
-take long-standing Rx as directed before surgery
-clonidine to tx withdrawal sx, 0.1mg bid, also tx specific sx as they arise

Multimodal pain relief
-iv tylenol, exparel
-ketamine, a2 agonists
-nsaids, regional
-pregalbin and gabapentin good for neuropathic pain

P/o

comfort and safety

opioid tolerant pts requires 2-3x more than naive patients
but still at risk from resp depression

Withdrawal happens 2/2 bolus nature of pain relief
combine long acting and pca for pain
make sure to restart methadone, divide into 3x/d dose to take advantage of analgesic properties

Post-op for Suboxone
-more complicated, buprenorphine has a celing effect (partial u agonist)
-so increasing dose intial helps, but tops out so side effects also top out, making it safer for long term management, but tought post-op
-Buprenorphine has 1000x affininty for u than morphine
–>longer half life, so persists on receptor
–>only partial agonist, so analgesia not complete
4 recs:
1. maintenance therapy continue, short-acting opioids titrate to effect
2. divide bupre into TID (if surgery not that invasive/painful)
3. d/c bupre and treat with full opioids, remember bupre can be present for up to 5 days after d/c. Be aware of withdrawal sx from bupre.
4. convert to methadone 30-40mg/day, must be written as rx for pain not withdrawal (illegal).

Post-Op for Naltrexone once monthly
-naltrex is competetive antagonist
-opioid admin is tough to predict
-depends if pt missed a dose, at end of dosing cycle etc.
-postpone elective surgery if possible until tx complete
-otherwise, multimodal with opioids