Interpretation of Traumatic Lumbar Punctures in the Setting of Possible Subarachnoid Hemorrhage: Who Can Be Safely Discharged?
Interpretation of Traumatic Lumbar Punctures in the Setting of Possible Subarachnoid Hemorrhage: Who Can Be Safely Discharged?
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可能发生蛛网膜下腔出血时外伤性腰椎穿刺的解读：谁可以安全出院？
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发表时间：
2007
期刊：
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通讯作者：
T. Newton
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作者：
J. Gorchynski;Jennifer A. Oman;T. Newton
腰椎穿刺（LP）是一种常见的急诊科（ED）手术，常用于诊断蛛网膜下腔出血（SAH）。虽然LP是一个相对简单的测试，但当针头造成的创伤导致蛛网膜下腔出血时，诊断的不确定性就会显著增加。这通常被称为“创伤性穿刺”。据估计，创伤性LP的发生率为常规LP的10-30%，尽管真实频率尚不清楚，并取决于如何定义创伤性LP。目前，对于什么是外伤性LP还没有达成共识。经LP检测脑脊液中血液的灵敏度被认为接近100%。然而，考虑到大约20%的外伤性tap发生率，特异性仅为80%左右。2
The lumbar puncture (LP) is a common Emergency Department (ED) procedure often used in the diagnosis of subarachnoid hemorrhage (SAH). Although the LP is a relatively simple test, significant diagnostic uncertainty can arise when trauma from the needle causes bleeding into the subarachnoid space. This is usually referred to as a “traumatic tap”. Traumatic LPs are estimated to occur in 10–30% of routine LPs, although the true frequency is unknown and depends on how a traumatic LP is defined. 1 At present, there is no consensus as to what constitutes a traumatic LP. The sensitivity of detecting blood in the cerebrospinal fluid (CSF) via LP is considered to approach 100%. Given an approximate 20% traumatic tap incidence, however, the specificity is only about 80%. 2
Distinguishing a traumatic LP from SAH is critical for the emergency physician. SAH is a devastating condition with high morbidity and mortality; roughly two-thirds of untreated SAH patients die or have serious neurologic disabilities as a consequence. 3 Depending on their neurologic status at initial clinical presentation, many patients with SAH can do well with early diagnosis and treatment. 4 Consequently, low-grade SAHs, often referred to as “sentinel leaks,” that are quickly diagnosed may have excellent outcomes. Conversely, those patients with traumatic LPs who are incorrectly presumed to have SAH are exposed to unnecessary, expensive, and potentially harmful procedures such as angiography.
The usual method of diagnosing SAH begins with computed tomography (CT) of the head without contrast. If this study is negative or equivocal, an LP is performed. 5 CT scan has a sensitivity of 98% within the first 12 hours of the ictus and 93% within 24 hours. Sensitivity decreases to approximately 80% at 72 hours and 50% at 1 week. CT scan findings are positive in 92% of patients who have SAH. Sensitivity is lower when using older second or first-generation scanners. Most North American hospitals have been using third-generation scanners since the mid 1980s. 6
There is consensus in the literature that an LP should be performed when strong clinical suspicicon of SAH exists in the setting of a negative or equivical CT or when CT is not available. 7 The presence of red blood cells (RBCs) in the CSF is diagnostic for SAH. However, there is no consensus in the literature on the number of RBC per cubic millimeter (mm3) needed to make the diagnosis. 8 Although most counts range from a few thousand to a million or more, there are case reports of SAH diagnosed by LP with RBC counts in the low hundreds. 9, 10 Thus, the ability to differentiate between SAH and traumatic LP is crucial even at low numbers of RBCs.
SAH often can be distinguished from traumatic LP by comparing the RBC counts of the first and last tubes of CSF. However, this is not always reliable, especially at higher numbers of RBCs. Theoretically the RBC count will not decrease between the first and last tubes in the setting of SAH; however, multiple case reports of this phenomenon do exist. The method of comparing the first and last tubes of CSF for RBCs has never been validated in a study. 11 Some authors suggest that a decrease in RBC count of more than 30% between the first and last tubes of CSF is diagnostic of a traumatic LP, although this has never been verified. 12
A potentially more reliable method of differentiating SAH from a traumatic LP is to spin down the CSF and examine the supernatant fluid for the presence of xanthochromia, a pink or yellow coloration of the CSF supernatant caused by the breakdown of RBCs and subsequent release of heme pigments. However, this method is sensitive and specific only when spectrophotometry (rather than the naked eye) is used to identify xanthochromia. 13 Unfortunately, many laboratories do not have the capability to identify xanthochromia with spectrophotometry. In addition, although xanthochromia is present 12 hours after the bleed in nearly 100% of patients with an SAH, it typically will not appear until up to 4 hours after the ictus.
The lack of consensus on how to differentiate a traumatic LP from one diagnostic for SAH creates a diagnostic dilemma for the emergency department physician. When there is a low suspicion for SAH, which patients can be safely sent home without extensive and expensive workups? Finding a lower limit of RBCs in the CSF and determining the necessary degree of RBC clearance in consecutive tubes would be useful in excluding a clinically significant SAH and diagnosing a traumatic LP. The goal of this study is twofold. The first aim is to determine whether a CSF RBC cutoff value exists that may safely exclude a radiographically detectable SAH. The second goal is to compare the RBC clearance from tubes 1 and 4 in LPs of subjects identified as positive for SAH to those of radiographically normal subjects.