Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)

Algorithm Steps

1. ▶

   Start

   START: Suspected SAH

   Sudden severe headache (thunderclap)

   1. ●

      Action

      Clinical Assessment

      High-risk features

      • Thunderclap headache (max intensity <1 min)
      • Worst headache of life
      • Neck stiffness/meningismus
      • Loss of consciousness, syncope
      • Focal neurologic deficit
      • Seizure at onset
      • Age >40 increases risk
      1. ●

         Action

         Ottawa SAH Rule

         Clinical decision tool

         • Consider SAH investigation if ANY present:
         • - Age ≥40
         • - Neck pain or stiffness
         • - Witnessed LOC
         • - Onset with exertion
         • - Thunderclap headache
         • - Limited neck flexion
         • 100% sensitive (validation ongoing)
         1. ●

            Action

            Non-Contrast CT Head

            First-line imaging

            • Sensitivity 95-100% within 6 hours
            • Decreases to 85% at 24h, 50% at 1 week
            • Modern CT scanners highly sensitive if interpreted by expert
            • Look for: Blood in cisterns, sulci, ventricles
            1. ◆

               Decision

               CT Result?

               Interpret findings

               1. ⚠

                  Warning

                  CT Positive for SAH

                  Blood identified on CT

                  • Confirm SAH
                  • Neurosurgery consult immediately
                  • CTA to identify aneurysm source
                  • Admit to ICU
                  1. ●

                     Action

                     CT Angiography

                     Identify aneurysm

                     • 95-98% sensitivity for aneurysms >3mm
                     • Identifies aneurysm location and morphology
                     • May miss small aneurysms (<3mm)
                     • DSA if CTA negative but high suspicion
                     1. ●

                        Action

                        SAH Management

                        Immediate interventions

                        • ICU admission
                        • BP control (SBP <160 before aneurysm secured)
                        • Nimodipine 60mg PO q4h x 21 days (reduces vasospasm)
                        • Secure aneurysm: Coiling vs clipping (within 24-72h)
                        • Monitor for vasospasm, hydrocephalus, rebleeding
               2. ◆

                  Decision

                  CT Negative - LP Needed?

                  Depends on timing and clinical suspicion

                  • CT <6h + low suspicion: Some evidence LP may be deferred
                  • CT >6h or high suspicion: LP recommended
                  • Institutional protocols vary
                  1. ●

                     Action

                     Lumbar Puncture

                     CSF analysis

                     • Collect 4 tubes
                     • RBC count Tube 1 vs Tube 4 (traumatic tap clears)
                     • Xanthochromia (visual or spectrophotometry)
                     • Xanthochromia takes 12 hours to develop
                     • Send for cell count, protein, glucose
                     1. ◆

                        Decision

                        LP Result?

                        Interpret CSF

                        • POSITIVE: RBCs not clearing + xanthochromia
                        • NEGATIVE: No RBCs, no xanthochromia
                        • EQUIVOCAL: RBCs clearing, no xanthochromia (may need CTA)
                        1. ⚠

                           Warning

                           LP Positive for SAH

                           SAH confirmed

                        2. ●

                           Action

                           LP Negative

                           SAH unlikely

                           • No RBCs, no xanthochromia
                           • Consider alternative diagnoses
                           • Migraine, tension headache
                           • Cervical artery dissection (consider CTA if suspicious)
                           1. ✓

                              Outcome

                              Discharge with Precautions

                              SAH ruled out

                              • Headache treatment
                              • Strict return precautions
                              • Return if: Worse headache, fever, neuro symptoms
                              • Primary care follow-up