Propofol versus Propofol and Ketamine for MRI
Rita Agarwal MF, FAAP, FASA
If you’re like me, you’ve done many, many anesthetics for MRIs in children and have developed your own preferred cocktail, so reading about someone else’s technique isn’t particularly compelling. However, today’s PAAD by Bang et.al caught my eye because it looked at pulmonary atelectasis as a result of anesthetics used.1 There are so many articles of various combinations of medications and techniques that can be used for anesthesia for MRI, and most are safe, relatively effective, and have few side effects. A lot of what we end up using comes down to personal preference, institutional policies, and/or convenience (who wants to draw up 2 infusions, when we can just use one)? Bang et. al1 give us at least one reason to consider adding ketamine to propofol.
But first a word from our friendly radiologist Dr. Glaucomflecken
Original article
Bang YJ, Kim J, Gil NS, Sim WS, Ahn HJ, Park MH, Lee SM, Kim DJ, Jeong JS. Pulmonary Atelectasis After Sedation With Propofol vs Propofol-Ketamine for Magnetic Resonance Imaging in Children: A Randomized Clinical Trial. JAMA Netw Open. 2024 Nov 4;7(11):e2433029. doi: 10.1001/jamanetworkopen.2024.33029. PMID: 39485355; PMCID: PMC11530935.
This was a single center, randomized, double blind study performed at the Samsung Medical Center in Seoul, Korea. It included 107 ASA I and II patients aged 3-12 undergoing sedation/anesthesia for MRI. Patients were excluded if they had pulmonary pathology of any sort, respiratory tract infection, uncontrolled hypertension or seizures, or allergies/contraindications to the study drugs. Interestingly (and not explained if this was part of the study or routine practice), all the patients had a chest x-ray within 7 days of the MRI, and all of them received 4 mcg/kg glycopyrrolate 3 minutes prior to entering the MRI suite. The control group received only propofol (Group P) in a dose of 2 mg/kg, followed by an infusion of 200 mcg/kg/minute. The group that received ketamine in addition to propofol received 1 mg/kg propofol and 1 mg/kg of ketamine (Group KP), followed by an infusion of 100 mcg/kg/min propofol and 20 mcg/kg/min ketamine. Additional boluses of propofol were administered as needed. Standard monitors were used, and patient BP, HR, snoring, movement, need to interrupt the scan, respiratory complications and duration of scan were recorded, After the MRI, the patients were immediately taken to the PACU and underwent lung U/S to evaluate for evidence of consolidation and B lines by 2 experienced anesthesiologist ultrasonographers. Each patient underwent scans in 14 predefined of their lungs, as well as their bilateral diaphragms to evaluate excursion during spontaneously breathing.2 Each area was recorded for 10 seconds and independently scored by 2 masked (blinded?) anesthesiologists. The Scores were based on the results from a previous study that validated the efficacy of transthoracic lung ultrasound for diagnosing anesthesia induced atelectasis.2 They looked for juxta-pleural consolidation and the presence or absence of B lines.
So what did they find? Demographics were mostly comparable, with a median age of 5 in both groups, BMI of 16, and a similar distribution of male and female participants. They did not mention the diagnosis leading to the MRI, but did list the types of scans performed (brain, spine, abdomen/pelvis etc). One thing that I thought was interesting, but not commented upon in the paper was that a higher number of patients in the KP group received whole spine or whole body MRIs which in my institution is a much longer scan, but in this study the median time for all scans was 34 mins. At my institution there is almost no scan that is as short as 34 minutes!
The most important finding here was that 88.9% of patients in the P group had atelectasis based on lung ultrasound, while only 58.5% of patients in the KP group did. There were the usual minor other side effects such as more transient hypertension in the KP group, more hypotension in the P group and more spontaneous movement in the KP group. One patient in the propofol group stayed hypotensive for 25 minutes and required pharmacologic treatment. Time to emergence was faster in the KP group and more families reported cough, fever and sputum production after PACU discharge in the P group. There was no difference in the quality of the scans, number of interruptions, or incidence of respiration complications.
Obviously there are several major limitation to this study, starting with the fact that the patients were from a homogenous population in one institution, were healthy, and the scan times were (at least compared to my institution) surprisingly short. BUT it did make me stop and think. There are several papers in the literature touting the benefits of ketamine/propofol infusion versus propofol alone in sedation/anesthesia for MRIs.3 Others have looked at dexmedetomidine in various combinations and have mostly focused on vital signs and emergence. 4,5 One recent study showed that a dose of 1 mg/kg of ketamine bolused at the start of case decreases airway collapsibility in patients undergoing MRI,6 which may lend support to the findings of the study by Bang et al in today’s PAAD.
I tend to use dexmedetomidine and propofol for my patients getting anesthesia for MRI. I think the dexmedetomidine allows me to use less propofol and I generally see less hypotension. Ketamine would do the same thing, but one of the reasons I don’t use much ketamine is quite frankly the fact that until recently the ketamine in our institution came in large vials and we would have to waste so much drug for each patient. We now have prepackaged syringes in smaller doses, which makes it a little less wasteful, but since it is a controlled substance, it is still more hassle to waste than propofol or dexmedetomidine. In sicker patients or those with underlying respiratory concerns in whom I want or plan to use a natural airway, the addition of ketamine might make sense.
What do you do in your practices? Does anyone routinely use ketamine and propofol for patients undergoing MRI? How about transthoracic ultrasound to evaluate for atelectasis? Do you use it routinely? If not routinely, when would you use it?Please send any thoughts or responses to Myron and he will print then in the Friday Reader’s Response.
PS from Myron: atelectasis (and V/Q mismatch) in anesthetized patients breathing spontaneously with any anesthetic agent, including the vapor anesthetics is well known and has been well known since the dawn of modern anesthetic practice. That’s one of the reasons minimum FiO2s of 30% are routine and why positive end-expired pressure is so commonly used.
References
1. Bang YJ, Kim J, Gil NS, et al. Pulmonary Atelectasis After Sedation With Propofol vs Propofol-Ketamine for Magnetic Resonance Imaging in Children: A Randomized Clinical Trial. JAMA network open 2024;7(11):e2433029. (In eng). DOI: 10.1001/jamanetworkopen.2024.33029.
2. Acosta CM, Maidana GA, Jacovitti D, et al. Accuracy of transthoracic lung ultrasound for diagnosing anesthesia-induced atelectasis in children. Anesthesiology 2014;120(6):1370-9. (In eng). DOI: 10.1097/aln.0000000000000231.
3. Schmitz A, Weiss M, Kellenberger C, et al. Sedation for magnetic resonance imaging using propofol with or without ketamine at induction in pediatrics-A prospective randomized double-blinded study. Paediatric anaesthesia 2018;28(3):264-274. (In eng). DOI: 10.1111/pan.13315.
4. Usher AG, Kearney RA, Tsui BC. Propofol total intravenous anesthesia for MRI in children. Paediatric anaesthesia 2005;15(1):23-8. (In eng). DOI: 10.1111/j.1460-9592.2004.01390.x.
5. Tosun Z, Akin A, Guler G, Esmaoglu A, Boyaci A. Dexmedetomidine-ketamine and propofol-ketamine combinations for anesthesia in spontaneously breathing pediatric patients undergoing cardiac catheterization. Journal of cardiothoracic and vascular anesthesia 2006;20(4):515-9. (In eng). DOI: 10.1053/j.jvca.2005.07.018.
6. Bhardwaj P, Panneerselvam S, Rudingwa P, et al. Comparison of airway collapsibility following single induction dose ketamine with propofol versus propofol sedation in children undergoing magnetic resonance imaging: A randomised controlled study. Indian journal of anaesthesia 2024;68(2):189-195. (In eng). DOI: 10.4103/ija.ija_287_23.