It may take 700 LPs to find a subarachnoid hemorrhage, but it’s a needle-in-a-haystack worth finding. Dr. Klauer challenges Dr. David Newman’s cost-effective approach in the SAH workup.
I’m proud to be a card-carrying member of the “700 Club,” as David Newman put it in last month’s issue. In his bi-monthly column, Newman dug into the numbers behind diagnosing subarachnoid hemorrhage (SAH), explaining that it takes 700 LPs to find one. In the end, he argued that the risks associated with these 700 LPs outweighed the benefits of finding the one needle in the haystack.
David is a smart man, and I do respect his thoughts and opinions. However, in this case, I believe the academic discussion of NNT could distract us from the reality that subarachnoid hemorrhage is a life-threatening disease and standard CT and LP is the best testing combination we have for ruling it out. In fact, a negative CT and negative LP provides an absolute answer that a subarachnoid hemorrhage is not present. One study reported a negative likelihood ratio of 0 when both tests are negative, making this a very effective testing combination1. Academic discussions focusing on statistical analyses, such as the NNT, are often difficult to translate to clinical practice. Is it time to quit performing LPs for patients with headaches suspicious for SAH? Probably not. It is a crucial element of the evaluation.
So, somebody please tell me why we should be surprised by an NNT of 700? Subarachnoid hemorrhage is a rare entity; it always has been. Based on that fact alone, a lot of people must be tested to find those that have a SAH. This is not a new concept. With approximately 136 million U.S. ED visits annually and 5% of ED patients presenting with headache as their chief complaint, finding the 30,0002 subarachnoid hemorrhages reported annually in the U.S. was, and will always be, selectively looking for the needle in the medical haystack.
The variability of the history patients provide and the wide array of headache presentations seen in the emergency department make accurate patient selection for LP very, very difficult. The test isn’t the problem. Risk stratification and patient selection are, as physicians are challenged in assessing the baseline risk for SAH among various populations. “Is this the worst headache of your life?” Are you kidding me? Is this our primary tool for deciding who needs a work up for SAH and who doesn’t? Until we come up with a better strategy for identifying those at greatest risk, and conversely, those not at risk, we should recruit more members to the “700 Club,” not less. The reality is that if we start doing fewer LPs, we will begin missing SAHs. Yes, admittedly, the number will be small. However, we should look at this disease from a purist’s perspective and not a medical economist’s perspective (e.g. avoiding misses as opposed to performing fewer tests). How many SAHs are you willing to miss so that you don’t have to do a bunch of LPs? I don’t know what others are comfortable with. My answer is 0! The likely outcome of a missed SAH is death or severe disability. Twenty-five percent of subarachnoid hemorrhages are misdiagnosed at the time of their initial evaluation and 48% deteriorate or re-bleed before they are able to return3. Omitting the LP will only increase the risk of delayed or misdiagnosis.
I challenge the assertion that significant dangers exist with the performance of a lumbar puncture when it is performed correctly, with the appropriate training, technique and equipment. The vast majority of LP complications are not life threatening, with back pain and post dural puncture headache being the most common, 25% and 22% respectively4.
Spinal headache is not uncommon. However, it must be recognized that with meta-analysis or systematic review of LP complications, it is impossible to avoid factoring in bad practice with the good. The data is clear. If you use an atraumatic needle, the spinal headache rate is substantially lowered. In fact, the postdural puncture headache rate using a 22 gauge Quincke (cutting needle) has been reported to be 15.2%, compared to 4.2% with the Whitacre (atraumatic needle)5. So, much of the concern raised by Dr. Newman about complications of LP, likely includes those not performing the procedure optimally with known techniques to avoid the most common complications.
I‘m “all in” on the NNT discussions on antibiotics and dog bites and rapid strep screening. Often, these items are, in aggregate, costly and offer little to no value to the care provided. Whether we perform them or not, the patient won’t be exposed to serious risks such as death or severe morbidity, like that of SAH. If we are going to use NNT to guide management, aren’t we better served applying this data to disease entities that can be missed without risk? For example, antibiotics are often prescribed for strep throat due to the concern for rheumatic fever. The NNT to avoid this complication is 4,0006. Treating 4,000 to benefit one is an unreasonable proposition.
It would be enlightening to calculate the NNT for obtaining an electrocardiogram for chest pain. The number of ECGs performed, compared to AMIs detected, must be astronomical and would likely produce an NNT much greater than 700. Although there is no risk associated with performing ECGs, LPs are also very safe. Both cast a wide net to look for life-threatening diseases. Testing many to look for the few is a reasonable approach when the outcomes of misdiagnosis are devastating.
We have to be careful with how we apply the NNT. Let’s apply this concept to the entire work up for SAH (CT and LP), and every other rare disease we can think of. The result could easily be, “Why bother.” In other words, in every uncommon disease, the absolute risk reduction will be low, resulting in a NNT that will be high for the diagnostic evaluation. Despite the low yield, I don’t think we are ready to abandon the search for these needles in the high-risk haystack.
As a risk manager, my goal is to improve patient safety while reducing provider liability. Miss a subarachnoid hemorrhage and I can almost guarantee that you are at serious risk of looking down the smoking barrel of a policy limits claim. In fact, in many of these cases, you may be lucky to resolve the claim without tendering your policy limits; plaintiff demands in such cases are often far north of $1 million.
Those sitting in the comfort of their armchair, ready to Monday morning quarterback, will likely say that these cases are defensible or that the demands can be negotiated down to policy limits or below. This may be true. However, that is an extremely cavalier position to take from the comfort of your Barcalounger. Ask anyone who has experienced the painful process of a lawsuit – even if it never reaches the courtroom. It takes months of the provider’s life. It consumes them emotionally and often destroys their confidence. I suspect that they’d be happy to perform a few, or a lot more, LPs to find the one patient that will benefit from it.
I caution those who choose to perform fewer LPs due to this NNT analysis. Perhaps the strongest rationale for doing fewer LPs due to the NNT of 700 is that in uncommon disease, you have luck on your side. With uncommon disease, good and bad practice are just as likely to result in negative workups. However, if you want to find a SAH, good practice, CT and LP, is still the best approach.
1. Perry JJ, et al. Is the combination of negative computed tomography result and negative lumbar puncture result sufficient to rule out subarachnoid hemorrhage? Ann Emerg Med. 2008 Jun;51(6):707-13.
2. Bederson et al. Guidelines for the Management of Aneurysmal SAH: Stroke 2009;40:994-1025
3. Mayer. Misdiagnosis of symptomatic cerebral aneurysm. Stroke 1996.
4. Ruff RL, Dougherty JH Jr Complications of lumbar puncture followed by anticoagulation. Stroke. 1981;12(6):879.
5. Hatfield, M.K., et al. Blood Patch Rates After Lumbar Puncture With Whitacre Versus Quincke 22- And 20-Gauge Spinal Needles, Am J Roent 190(6):1686, June 2008.
6. Worall GH. Acute Sore Throat. Canadian Family Physician; Vol 53:november 2007.
Kevin Klauer, DO, EJD is Editor-in-chief of Emergency Physicians Monthly, CMO of Emergency Medicine Physicians, Vice Speaker of the ACEP Council.