cliot (version 1.0.0)

fisher_sah_grade: Fisher Grading Scale for Subarachnoid Hemorrhage (SAH)

Description

Calculates the Fisher Grade for patients with subarachnoid hemorrhage based on initial CT scan findings. The scale predicts the risk of cerebral vasospasm. Note that Grade 3 (Thick clot) carries the highest risk, higher than Grade 4 (ICH/IVH).

Usage

fisher_sah_grade(sah_present, ich_ivh_present, clot_thickness_ge_1mm)

Value

A list containing:

Fisher_Grade

The calculated grade (1-4).

CT_Findings

The description of the grade.

Vasospasm_Risk

Estimated percentage risk of developing vasospasm.

Arguments

sah_present

Numeric (0 or 1). Is subarachnoid blood detected on CT? (1 = Yes).

ich_ivh_present

Numeric (0 or 1). Is there an intracerebral (ICH) or intraventricular (IVH) clot? (1 = Yes). Note: In the original Fisher scale, this finding (Grade 4) defines the category regardless of SAH thickness, though clinically Grade 3 implies higher vasospasm risk.

clot_thickness_ge_1mm

Numeric (0 or 1). Are localized clots or vertical layers >= 1mm thick present? (1 = Yes).

References

Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by computerized tomographic scanning. Neurosurgery. 1980;6(1):1-9. doi:10.1227/00006123-198001000-00001

Examples

# Example 1: Highest Risk (Grade 3)
# SAH present, No ICH/IVH, Thick clot
fisher_sah_grade(1, 0, 1)

# Example 2: Grade 4
# SAH present, ICH present (overrides thickness in classification logic)
fisher_sah_grade(1, 1, 0)