Monday, April 2, 2007

fMRI & the PVS; Opioids & respiratory depression

1) Neurology has an interesting article about using functional MRI to, perhaps, differentiate between a minimally conscious state (MCS) & a persistent vegetative state (PVS). It looks at 12 severely brain injured people (mostly traumatic; 7 clinically assessed as being in vegetative states and 5 MCS; most in the 2-6 month range post-injury). Patients had fMRI scanning while their own name was being spoken to them (the assumption is that this is a powerfully meaningful stimulus). Most of the PVS patients demonstrated activity (if any at all) isolated to the auditory cortex (as you'd expect). Two of them, however, had activity in 'higher order associative temporal' lobe regions--all the MCS patients did as well (the article is quite neurologically technical but basically this is taken as evidence of some higher cortical functioning). Very interesting is that these two patients, within a few months, had clinically improved had been reassessed as being in MCS (both were 4 months out from their injury at the time of scanning). The authors' gloss on this is that these two patients were probably were in an MCS but just outwardly appeared (at least temporarily) to be vegetative.

At this point it's too early to know what to make of all of this, but it seems likely that functional imaging is going to be incorporated in the diagnosis of these, and similar conditions. It's long been recognized that a few people in prolonged vegetative states eventually make some recovery (&, depending on who you ask, one should wait 6 months to a year before concluding that a persistent VS is a permanent PVS, particularly in the setting of traumatic head injuries). Hopefully techniques such as the above will be helpful in better prognosticating this. None of this changes the fact however that most people wouldn't want to be kept alive artificially in a MCS either and going from a PVS to an MCS is no real improvement in the big scheme of things. Indeed, the authors of this article noted that none of the MCS patients improved during the months of monitoring after scanning. The chances of recovering from an MCS to a decent level of function are much higher than a VS but still dismal; for me the priority is figuring that out.

(Thanks to Tom Quinn for letting us know about this article.)
(Image cribbed from fMRI's Wikipedia page).

We usually don't post much about articles published in the major palliative care journals but I thought I'd comment on the recent trial looking at respiratory depression and opioid dose titration in Palliative Medicine. It's an interesting trial from the Cleveland Clinic and--while not a hot topic for the average palliative provider--concern for respiratory depression is a major fear amongst clinicians less familiar/comfortable with opioids. The study asks What happens to respiratory function during IV opioid titration for cancer inpatients with severe pain? Basically, it follows the 'natural history' of respiratory function as these patients were getting their pain treated by the palliative service. It looks at 30 patients (median age 60, most with ECOGs of 3-4, none on oxygen or delirious) admitted with severe pain who were put on parenteral opioid infusions. They excluded patients on oxygen because they wanted a "purer" look at oxygen saturation and end-tidal CO2. Most patients were chronically on opioids (median daily oral morphine dose of 73mg). Basically the patients were admitted, baseline data were taken, they received parenteral opioid dosing per the palliative service's routine practice, and follow-up data were gathered. They measured pain, respiratory rate, oxygen saturation, and end-tidal CO2 (basically exhaled C02 tension). These patients seemed to have received good pain control (mean pain decreased from 6.8/10 to 1.9/10), and the mean morphine dose equivalent more than doubled during the study (to 169mg).

The results were as expected. Mean ET-CO2 didn't change (went from 33.3 to 34.7 mmHg) across the study (they compared baseline to when pain was controlled); no patients manifested clinically significant respiratory depression; and oxygen saturation remained >92% throughout the study in all patients. That said, there were a couple transient episodes in 2 patients of low respiratory rate (<10/minute). style="font-style: italic;">background evidence but probably wouldn't change too many minds.

Pallimed | Blogger Template adapted from Mash2 by Bloggermint