Discussions for Module 7 : Accidental Subdural Injections

Questions are answered by module author: Sharon Davies MD FRCPC

 

Question:

I had recently a poor result with a labour epidural for a patient on maintenance methadone treatment for a prior opioids addiction. Any thought about managing such patients?

Dr. Davies replies:

In regards to your question, Collier has described the phenomena of poor epidural pain relief in patients on methadone. Although one might expect opioid tolerance for epidural administered narcotic medications, the decreased response to local anesthetics is a bit of a mystery. Collier has suggested that it may be a competitive block at the spinal cord receptors but I don’t believe he really knows for sure either.

As for managing such a patient, my only suggestion would be to try much higher concentrations of local anesthetics than we typically use today. Many anesthesiologists have not been accustomed to 0.25 -0.5% bupivicaine that we used in the “old days” when I was first a resident (we used 8-10 ml of  0.5% bupivicaine to initiate the block and then ran them on pumps of 0.25% - so you have a fair amount of leeway in your dosing). Obviously in those days their legs were very heavy!!! We certainly have come a long way! Anyways, I would just titrate these higher concentrations to effect in order to get some reasonable level of pain relief, albeit, it may not ever be perfect. 2% lidocaine might also be added for patchiness and one might even add epinephrine to the lidocaine, just as you do for Cesarean Sections. I have certainly used lidocaine with epinephrine for patients with poor back and sacral analgesia, particularly with posterior presentations or for forcep deliveries with a lot of perineal discomfort.

 

Question:

Is there higher incidence of subdural injections with CSE compared to epidural?

Nov. 10, 2005 at 12:39, U.T.

Dr. Davies replies:

Good question! Intuitively one might expect that it might be increased. However, to my knowledge, I do not believe that anyone has ever studied that.

 

Question:

How do the pharmacokinetics and pharmacodynamics of opioids placed in the subdural space compare to placement in the epidural and subarachnoid spaces?

Nov. 10, 2005 at 12:39, J.T.

Dr. Davies replies:

I do not have the answer to your question. Since subdurals are not an intended outcome and are generally a clinical diagnosis, there are no studies that have addressed this issue. I suspect that there never will be any literature on this. What we do know is how radiographic dye travels through this space, but nothing else. With the epidurograms we have assumed that any fluid injected into the space would follow the same cource as the dye but even that is an assumption. However, clinical manifestations of subdurals confirmed on epidurogram suggest that this assumption is true. On the other hand, pharmacodynamics of drugs,as you well know, depends on many characteristics of the drug (eg, lipid soluability) as well as the distribution in the space.

 

Question:

I wonder if there is any difference in incidence of unintentional subdural catheter placement with LOR to saline vs. air.

Nov. 10, 2005 at 12:38, H.F.

Dr. Davies replies:

This is an interesting question since some authors (Stride & Cooper 1993) have suggested that LOR to saline is associated with less dural punctures.If this indeed the case ( and there is not much in the literature) then we would expect that inadvertent subdurals would also be less as the dura needs to be punctured in order to get a subdural. However, I am not aware of any literature that has specifically addressed this issue in relation to subdurals. Also,since subdurals are a clinical diagnosis in most cases and frequently are not recognised, collecting data on the incidence between these techniques is difficult. We would need to randomize the patients to the two techniques and do epidurograms on all cases where a subdural is suspected in order to answer the question. This would be a very difficult study; therefore I'm not sure that it would ever be feasible.

 


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