Fisher Grading Scale for Subarachnoid Hemorrhage (SAH)

Why Use

Angiographic vasospasm occurs in at least 50% of patients with aSAH and often results in DCI, which occurs in up to 46% of all patients with aSAH and can cause devastating neurological consequences and/or death ( Claassen 2001 ). Because vasospasm typically occurs between 4 and 14 days (“vasospasm window”) after the onset of aSAH, the Fisher scale may allow timely preventative treatment for vasospasm and DCI to be initiated ( Fisher 1983 ). Despite its well-documented shortcomings, the Fisher grading scale remains widely used and well-known in critical care and neurocritical care communities.

When to Use

Patients with aSAH .

Formula

Pearls / Pitfalls

The Fisher Grading Scale was originally designed to predict risk of cerebral arterial vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH) based on radiographic distribution of subarachnoid hemorrhage. The Fisher scale is entirely radiographic and typically determined at presentation. Variable rates of vasospasm corresponding to each Fisher grade have been reported in studies; therefore, the scale should not be used to quote an exact probability of vasospasm or delayed cerebral ischemia (DCI). The Fisher scale should also NOT be used as the sole clinical data point to make decisions on medical management or goals of care. Points to Keep in Mind: The Fisher scale has a number of shortcomings: It does not consider the effect of thick cisternal subarachnoid blood or intraventricular hemorrhage (IVH), which are both known risk factors for vasospasm (Claassen et al 2001, Wilson et al 2012). For this reason, the Modified Fisher Grading Scale is often preferred by many neurocritical care providers. Higher Fisher scale grades do not necessarily correlate with increasing probability of vasospasm. Studies show little to no difference between grades 1 and 2 ( Claassen 2001 ), and that grade 4 is associated with a lower rate of clinical vasospasm than grade 3 (Fisher 1980 & 1983 , Smith 2005 , Frontera 2006 , Kramer 2008 ). The original Fisher scale was developed based on measurements on paper printouts from a low-resolution EMI CT scanner, which was not reflective of true SAH thickness. In reality, most SAH is >1 mm thick, so Grades 1 and 2 are rare. ( Rosen 2005 ) The scale does NOT apply to SAH due to trauma, arteriovenous malformations, cavernous angiomas, dural arteriovenous fistulae, cortical or sinus venous thromboses, mycotic aneurysms, or septic emboli with hemorrhagic transformation.

Advice

Immediate neurological and neurosurgical consultation should be obtained for patients with evidence of any SAH on imaging or lumbar puncture, even if the SAH is likely to be non-aneurysmal in nature. Computed tomographic angiography (CTA) of the head is helpful to determine the presence of a lesion suitable for surgical or endovascular intervention. The need for obtaining cerebrovascular imaging, such as CTA of the head or catheter angiography, should be discussed with a neurological or neurosurgical consultant first. Similarly, the decision to start medications that have been shown to alter outcomes in aSAH (such as nimodipine and/or aminocaproic acid) should be deferred to the neurological or neurosurgical consultant.

More Information

Score interpretation: Fisher grade Blood on CT* Risk of vasospasm I No SAH detected Low (range 0-21%) II Diffuse or vertical layer of subarachnoid blood < 1mm thick Low (range 0-25%) III Localized clot and/or vertical layer within the subarachnoid space > 1mm thick Low to high (range 23-96%) IV ICH or IVH with diffuse or no SAH Low to moderate (range 0-35%) *Measurements were made on printed EMI CT scans. The measurements were not scaled to the actual thickness.