Sometimes muggles criticize FOAM as lacking peer review, but that simply reflects a misunderstanding of the way peer review works here. FOAMed operates off a post-publication peer review system. This typically occurs mostly in the comments section of each blog or chapter (with some on twitter as well). Unlike journals, anyone is free to leave comments (not a select few, who are anointed to write letters to the editor). In this particular case, Scott Weingart sent me a review of the asthma chapter which I think makes some terrific points and deserves to be shared more broadly.
Post-publication peer review is a transparent process where the warts of a publication are dissected for all to see. It can be a bit more uncomfortable than the typical cloistered process of pre-publication review. However, having these discussions in the open allows everyone to see into the process of creating material and obtain a deeper understanding of various controversies. The ultimate goal here isn't to be right, but rather to create the best possible FOAMed to optimize our patient care.
The asthma chapter has been a bit of a saga. A few weeks ago I published a very controversial guest post by Leo Stemp. The post was intended to kick the hornets nest a bit and stir up controversy, and it sure did. Scott Weingart and I discussed these topics a few days later, including his numerous concerns about the post. These discussions helped me construct the asthma IBCC chapter here. So now that the IBCC chapter & podcast are done, Scott weighs in again with his post-publication review.
Post-publication peer review from Weingart:
I essentially agree with Scott on all of these points, so you could just listen to his recording and not read the rest of this post. However, I wouldn't be a true blogger if I didn't have some additional thoughts to add…
- Prescribing default vent settings is torture, because each review article recommends slightly different settings. I think there is a last-article bias here, where I tend to tweak these settings repeatedly while writing the chapter. The final result may be unduly influenced by the last article I read.
- The key here is really to adjust the vent settings based on the patient. Different settings will be better for various patients, depending on the severity of bronchospasm.
- Pressure control ventilation with an inspiratory pressure of 40cm and 1 sec inspiratory time is too much for most patients – so I've changed this (from 40 cm to 35 cm). However, the absolute tightest asthmatics might need more pressure to get an adequate tidal volume in. In such super-tight patients, the alveolar pressure never equilibrates with the inspiratory pressure, so the alveoli are not seeing 40cm of pressure (similar to the way in volume-cycled ventilation the peak pressure isn't transmitted to the alveoli).
- Yep, to be honest I didn't give this a ton of thought when writing the chapter. Most review articles supported IV magnesium and this is a benign therapy, so I just went with it.
- In the 3MG trial, IV magnesium administration was associated with an odds ratio for hospital admission of 0.73 with a 95% confidence interval of 0.51-1.04 (p = 0.083). This isn't statistically significant, but does trend towards favoring magnesium. It's a pretty wide confidence ratio, so it does leave the door open to having a possible beneficial effect. So this is a negative trial, but it doesn't necessarily absolutely kill IV magnesium. These asthma trials are challenging, because patients are getting lots of therapies simultaneously, which makes it difficult to exclude a small therapeutic effect from any individual intervention.
- A 2014 Cochrane review of 14 RCTs found a 25% reduction in hospital admissions with IV magnesium (OR 0.75, CI 0.6-0.92)(24865567). This is nearly the same point estimate of the OR for admission as is seen in the 3MG trial, the difference being a slightly narrower confidence interval. So you could make an argument that 3MG is consistent with this Cochrane review, it's just that 3MG was underpowered to prove a clinical improvement.
- A recent summary of evidence (including some stuff from the pediatric literature) by Stojak is here.
- Bottom line: In the initial version of the asthma chapter, IV magnesium was listed as something that folks should do. That's incorrect, so I've changed it to something that folks may want to do. I think ultimately the data here is not definitive and multiple courses of action are reasonable. Certainly this isn't a cornerstone intervention and it should not interfere with or delay other therapies.
So this has been a long walk to get here, including two posts, about 10,000 words, and about two hours of podcasts. I've learned a ton about asthma and I hope everyone else has too. If you haven't been following the saga, it might be worth it to catch up on it here:
going further: wading thru the asthma saga
- Guest post with Leo Stemp (9/25)
- Podcast with Weingart discussing the guest post (9/27)
- IBCC chapter & cast on asthma (10/8)
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