Postoperative pain and delirium is a common concern and currently approached by different interventions. There is some evidence suggesting that ketamine given intra-operatively might have an influence on postoperative pain and delirium. Some anaesthetists commonly give a single dose of ketamine intra-operatively for exactly this reason.
Thumbs up for Ket
Ketamine has kept its fascination in various settings, from retrieval medicine onto the the care of critically ill patients in the ICU. Ketamine reduces postoperative markers of inflammation, is a rapid-acting antidepressant drug with an effect lasting for several days and might have neuroprotective properties.
Ketamine also has become increasingly popular as an adjunct to other sedatives in the ICU. There is evidence showing that ketamine used in the ICU has the potential to reduce cumulative opioid consumption after surgery (Asad E. et al. J Intensive Care Med December 8 2015 ).
Even better: It does not cause any kidney injuries, preserves laryngeal protective reflexes, lower airway resistance and much more...
And: Ketamine is cheap and has been used safely for over 50 years by anaesthetists!
The Dark Side of Ket
But there's the other side of ketamine making all of this a little more complicated. After all, Ketamine is a psychoactive drug and has well known hallucinogenic properties. Developed in the 1960s as a dissociative anaesthetic agent it started to appear on the street in the early 1970s and made its way to the 1980s as Special K, Acid and Super C (Dotson JW et al. J of Drug Abuse, Vol 25, Issue 4, 1995).
From a medical point of view there are some worries that these psychotomimetic effects, which are of concern in the critically ill patient, might predispose to delirium (Erstad BL, J Crit Care, Oct 2016, Vol 35, p 145-149).
The PODCAST Trial
On the background of all this facts this trial revealed some interesting findings. Avidan et al. performed a
multicentre, international randomised trial
in which they randomly assigned
672 patients undergoing major cardiac and non-cardiac surgery under general anaethesia
into three groups to either receive a bolus of
placebo (normal saline), low-dose ketamine (0·5 mg/kg), or high dose ketamine (1·0 mg/kg) after induction of anaesthesia, before surgical incision.
Participants, clinicians, and investigators were blinded to group assignment. They found
NO difference in in the incidence of postoperative delirium among these groups
significantly more postoperative hallucinations and nightmares with increasing ketamine doses compared to placebo
This trial seems well performed with an acceptable sample size. The application of a single dose of ketamine before surgery neither prevented delirium nor induced it. With this sample size it seems safe to say that even if ketamine does prevent delirium, its effect would be rather small.
Furthermore, postoperative pain was not influenced by giving a single dose of ketamine and this is in contrast to previous findings and current guidelines. Importantly, most of the previous studies are smaller than this trial, making these findings remarkable.
But what really drew my attention was the fact that the appearance of hallucinations and night-mares was increased for at least 3 days after surgery.
So if ketamine has no influence on postoperative delirium or pain but does induce hallucinations and nightmares, even 3 days after surgery, current guidelines might have to be revised.
The Bottom Line
- The application of a subanaesthetic dose of ketamine during surgery to tackle postoperative pain and delirium does not seem to be as effective as previously assumed
- The usage of ketamine in this setting even seems to have undesirable side-effects like hallucinations and nightmare - and this effect might even last for up to 3 days!
- This trial provides good reasons to look for other options to prevent postoperative delirium!
(Like dexmedetomidine? The answer to this question has just been answered: READ HERE!)
Ketamine - a drug with various actions and just as many opinions on it. One concern often mentioned is that ketamine might cause a raise in intracranial pressure (ICP) and therefore is often avoided in this group of patients. In May's Journal of Anaesthesia Wang et al. looked at the existing evidence on this topic. They ended up with 5 trials meeting their inclusion criteria on administration of ketamine and the ICP levels within the first 24h as a primary outcome.
To make it short: Ketamine does not increase ICP in comparison to opioids. They conclude that ketamine should not be discouraged on the basis of ICP-related concerns.
Wang et al. J Anaesth. 2014 May 24