I've always wondered why we use magnesium to deal with many arrhythmias (at least as an adjunct) and have to say that all the doctors I've asked here don't actually know. Anyway today I was reading one of the USMLE books and it says that MgSO4 decreases calcium influx, thus reducing the early afterdepolarizations that perpetuate many arrhythmias. The paragraph was in relation to dig toxicity but I'm guessing the reason applies across the board. Was so excited to finally find the reason for magnesium. :-)
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Thursday, September 27, 2012
Friday, September 21, 2012
Pupillary responses
Looking at the pupils can sometimes be helpful, particularly in an unconscious patient. There are many causes of dilated pupils but if you're lucky and a patient comes in with constricted pupils then this narrows down the possible causes significantly.
A constricted pupil is one that is less than 2mm under normal lighting conditions. Note that the pupils will constrict if you shine a torch into them!
Bilateral pinpoint pupils
- Opiates (Heroin, Fentanyl, Codeine, Methadone, Morphine) stimulate the parasympathetic side of the autonomic nervous system causing pupil constriction. Look for track marks and a past history of drug use.
- Pontine hemorrhage (brain stem)
- Organophosphate chemicals (pesticides, Sarin gas). Look for SLUDGE presentation (salivation, lacrimation, urination, defecation, emesis)
- Other drugs (neuroleptics, EtOH, benzos, isopropryl alcohol, lithium)
Bilateral dilated pupils
- Anticholinergic drugs (TCA)
- Adrenergic drugs (cocaine, amphetamines) - but these don't usually lead to coma unless complicated by seizures or cerebrovascular events.
- Other drugs (quinine, baclofen, barbiturates, other sedatives like carbamazepine)
- Raised ICP
- Brain death
References I used:
1) http://theemtspot.com/2009/04/23/rapid-diagnosis-pinpoint-pupils/
2) http://curriculum.toxicology.wikispaces.net/Pupil+Size+and+Reaction
There is also an online teaching syllabus for toxicology at WikiTox.
A constricted pupil is one that is less than 2mm under normal lighting conditions. Note that the pupils will constrict if you shine a torch into them!
Bilateral pinpoint pupils
- Opiates (Heroin, Fentanyl, Codeine, Methadone, Morphine) stimulate the parasympathetic side of the autonomic nervous system causing pupil constriction. Look for track marks and a past history of drug use.
- Pontine hemorrhage (brain stem)
- Organophosphate chemicals (pesticides, Sarin gas). Look for SLUDGE presentation (salivation, lacrimation, urination, defecation, emesis)
- Other drugs (neuroleptics, EtOH, benzos, isopropryl alcohol, lithium)
Bilateral dilated pupils
- Anticholinergic drugs (TCA)
- Adrenergic drugs (cocaine, amphetamines) - but these don't usually lead to coma unless complicated by seizures or cerebrovascular events.
- Other drugs (quinine, baclofen, barbiturates, other sedatives like carbamazepine)
- Raised ICP
- Brain death
References I used:
1) http://theemtspot.com/2009/04/23/rapid-diagnosis-pinpoint-pupils/
2) http://curriculum.toxicology.wikispaces.net/Pupil+Size+and+Reaction
There is also an online teaching syllabus for toxicology at WikiTox.
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