Saturday, October 8, 2011

Not Long, But Short QT

Another rare channelopathy that I was not previously aware of, but that carries the same risks of sudden death as long-QT syndromes.

This is a longitudinal observational study of the European Short QT Registry - which has a grand total of 53 patients - who were followed for, on average, 5 years.  The diagnosis of short QT does not have a generally accepted definition, but typically means a QTc less than 340 or 360, and the other literature shows a high association with sudden death and QTc less than 340.  In their registry 23% had a HERG gain-of-function mutation identified, and there is also an autosomal dominant inheritance pattern identified.

Based on their follow-up for events, or for cardiac events recorded by implantable defibrillators, there was a 4.9% incidence of syncope, defibrillator shocks, or nonsustained polymorphic ventricular tachycardia.  Prophylactic treatment involves either the implantable defibrillator or daily hydroquinidine therapy to prolong QT.

Something new to look for on EKGs that you'll probably never see, but will seem really smart if you do.

"Long-term follow-up of patients with short QT syndrome"
www.ncbi.nlm.nih.gov/pubmed/21798421

Friday, October 7, 2011

Lack of IV Access, Harbinger of Death

Interesting observational study of 56,332 patients picked up in an EMS system in King County, looking at IV access and outcomes.

For reasons they don't look into in this study, they find that IV access is an independent predictor of decreased in-hospital mortality.  Not for the less-acute patients, but for patients of high-acuity, lack of IV access shows a pretty significant trend towards poor outcomes.  They don't look at fluid therapy, medication therapy, etc. as confounding variables - so we don't know what it is specifically about IV access that confers a survival advantage.

They do a brief breakdown of the systolic blood pressure and the percentage of patients receiving IV access, and, as expected, more IVs are attempted at the extremes.  This leads me to believe there are patients who were high acuity, required IV access, but had failed IV access attempts - but there's no data on that either.

This is a study that could end up telling us something, or nothing.  Interesting, nonetheless.

"Intravenous Access During Out-of-Hospital Emergency Care of Noninjured Patients: A Population-Based Outcome Study"
http://www.ncbi.nlm.nih.gov/pubmed/21872970

Wednesday, October 5, 2011

C-Collars Cannot Stabilize Unstable Injuries

This is another cautionary anatomic study that demonstrates cervical collars are not adequate immobilization devices - except in patients who already do not need them.

This is a cadaveric spinal immobilization study in which C5/C6 instability was induced, and the Ambu extrication collar, the Aspen collar, and no collar were evaluated for range of bending and rotation during a bed transfer simulation.

The results are pretty straightforward.  Before the instability was induced, patients had minimal neck movement, whether immobilized or not.  After instability was induced, the patients all had significant bending and rotation - nearly the same for the patients in the collars as in no collar at all.

This is consistent with the small amount of prior work done in actual unstable spines; most of the cervical collar data is in healthy volunteers.  The limitations of a cervical collar should be recognized, and patients should have their cervical spine evaluated and cleared or intervened on immediately.

"Cervical collars are insufficient for immobilizing an unstable cervical spine injury."
www.ncbi.nlm.nih.gov/pubmed/21397431

Tuesday, October 4, 2011

Linezolid Is Superior To Vancomycin For Pneumonia

This is consistent with prior studies and not particularly earthshaking, but if you needed more literature to support switching antibiotics in the case of treatment failure, this would be another one.

This is in pigs, and it's an animal model of MRSA ventilator-associated pneumonia.  Four groups - controls, twice-daily vancomycin, continuous vancomycin infusion, and linezolid.  Treatment was initiated after 12 hours of bacterial inoculation in ventilated pigs.  At the end of their 96 hour treatment period, 75% of controls, 11% of each vancomycin group, and 0% of linezolid pigs were BAL positive for MRSA by culture.  Likewise, pathologic sections also showed decrease inflammation and damage in the linezolid group.

Short story, linezolid is better - but not quite better enough that we can't still start with vancomycin and keep it in reserve.

Sponsored by Pfizer and Eli Lilly.

"Efficacy of linezolid compared to vancomycin in an experimental model of pneumonia induced by methicillin-resistant Staphylococcus aureus in ventilated pigs"
www.ncbi.nlm.nih.gov/pubmed/21926613

Sunday, October 2, 2011

N-acetylcysteine Overdose With Anaphylactoid Reaction and Myocardial Infarction

This is another toxicology case that illustrates a point I make (probably too often) to my residents - that every action we take has a risk of harm, whether known or unanticipated.  I'm probably the only attending who cancels their IM ketorolac orders and changes them to PO ibuprofen.  Why?  Because of cases like this.

This is an entirely appropriate therapy - N-acetylcysteine given for hydrocodone-acetaminophen overdose - gone wrong because of a mixing error resulting in 10-fold overdose (126,000mg loading dose!).  Anaphylactoid reactions are known side effects in N-acetylcysteine, and, unfortunately, this patient's reaction was more severe than most, suffering an inferior MI with a peak troponin of 658ng/mL.  He expired 17 hour after the N-acetylcysteine overdose.

I've seen epinephrine given IV instead of SQ more than once (one time resulting in an MI), many medications are tissue toxic if they extravasate, you can get sterile abscess formation from intramuscular injections, etc.  The fewer interventions and the less invasive the interventions, the less risk at which we place our patients.

"Fatal myocardial infarction associated with intravenous N-acetylcysteine error"