I can’t talk about these meds without first showing a quick slide on acute pain process.
This is one of the areas where we as anesthesiologists, anesthesia providers have an important role in minimizing opioids and doing what we can to enhance patient recovery/well-being. So, today, I will discuss few of the medications that are a crucial part of this process including lidocaine,magnesium, and ketamine. Ketamine:my fav drug, saved best for last
This slide demonstrates the sites of action for a variety of analgesics used in multi-modal analgesia. We’ll focus on ketamine and see that it acts on the dorsal horn of the spinal cord.
As we already know narcotics may lead to resistance and patients can end up having tolerance, hyperalgesia, and allodynia. These are precisely the types of adverse effects we are trying to prevent, and ketamine has been shown in multiple studies to decrease the incidence of all of these side effects. Before moving on, let me define these terms. Tolerance is self explanatory. Hyperalgesia refers to an increased sensitivity to pain, which may be due to injury to nociceptors or peripheral nerves. Allodynia means patients have pain from a stimuli that is not normally known to cause pain. For example temperature or physical stimuli may lead to allodynia and patients complain of having a burning sensation.
Lidocaine acts peripherally and centrally. Peripherally: it decreases the release of inflammatory mediators. Centrally: acts by modifying neuronal responses in the dorsal horn. Define Hyperalgesic and Nociceptic: receptors that exist to feel any and all pain. The other type of pain is neuropathic (direct injury to the nerve itself)
Lidocaine infusion: shortens postoperative ileus because it may reduce postsurgical peritoneal irritation and suppress the inhibitory gastrointestinal reflexes.
Prolonged surgery: decrease the rate of lidocaine continuous infusion by 50% every 6hours. Watch for signs fo toxicity
Think of this gradation as peripheral, central, and systemic as it increases in severity. If you are planning on using lidocaine, know where your intralipid is located and how to dose it. Have an anesthesia pager on hand. Place patient on monitor if you plan to continue it on the floor and watch for EKG changes. Low dose is best, and most often all that’s needed. EKG changes w/toxicity: wide QRS and prolonged PR interval
Mg ion cannot cross the BBB to reach the CSF: hence, IV admin maybe limited
Albrecht et al: U of Washington in conjunction with University of Toronto did a meta-analysis: Peri-operative intraveous administration of magnesium sulphate and postoperative painDr. Shin et al from South Korea: Magnesium suphate attenuates acute postoperative pan and increased pain intensity after surgical injury in staged bilateral totatl knee arthroplasty: a randomized, double-blinded, placebo-cotrolled trail.
Dosing varis by institution. Our institution, 2g magneisum appears to be beneficial
I do give a bolus, and I really try to keep the numbers simple for calculation purposes. So, I usually keep my infusion at 5mg/kg/hr.
Accessed from google images 12/4/2016
Only avail anesthetic that has amnestic, analgesic, and hypnotic properties
NMDA:: N-Methyl-D-aspartate receptor. It is a glutamate receptor and ion channel protein found in nerve cells which is activated when glutamate and glycine bind to it. Ketamine has an important role in pain processing.
2 enantiomers: S and R. Binds to the phencyclidine sites on postsynaptic channels and decreases frequency and opening time of ion channels. NMDA blockade mechanism:
How does one dose this drug? Today we are talking about intravenous route. P.O: 10-25 mg q8(up to 0.5-1 mg/kg q8H (max=200mg q6H)Transdermal: 5-15%SC: 10-25 mg PRN (or 0.2-0.5 mg/kg)
How does the Dissociative State happen: due to disconnection of thalamoneocortical and limbic systems at high doses and also salivation at high doses.
Affects affective aspect of pain. What does affective pain mean? It is one of the four levels of pain, and it refers to a patient’s emotional reaction to pain.
4 levels of Pain: 1. sensory-motor 2. affective 3. Imaginative 4. Linguistic narrative
When can we as anesthesia providers use subanesthetic ketamine?
Like etomidate and thiopental, ketamine has been implicated in exacerbation of porphyria. When those with porphyria are given ketamine, neurologic and gastrointestinal symptoms may arise.
I included this review because it was one of the first of its kind to exclude all studies that used neuraxial or regional anesthesia. So, they looked at studies that were more homogenous in their parameters.
At this point in our practice we have developed a protocol for postoperative infusion, and we are continuing it for 24 hours. Other centers such as UPMC and Mayo Jacksonville have also instituted continuous postoperative infusions in cases where ketamine is deemed appropriate.
