🎚️ EVD Settings

Leveling, drainage systems, and bedside setup principles

The EVD setting represents the pressure threshold (cm H₂O) above which CSF will drain.

Common Settings

Important

How the setting relates to the drainage system: The flushless transducer is zeroed at the external auditory meatus (EAM), approximating the foramen of Monro. The CSF collecting chamber sits at a height above the EAM that corresponds to the EVD setting — for example, a +20 cm H₂O setting means the chamber is raised 20 cm above the EAM reference point. CSF only drains into the chamber once ICP exceeds that height, so CSF output depends directly on the relationship between the patient’s ICP and the chamber height set at the bedside.

evdSettings = {
  const { initializeApp, getApps, getApp } = await import("https://www.gstatic.com/firebasejs/10.14.1/firebase-app.js");
  const { getFirestore, collection, onSnapshot } = await import("https://www.gstatic.com/firebasejs/10.14.1/firebase-firestore.js");

  const firebaseConfig = {
    apiKey: "AIzaSyD1FLnIrd86qOsFPLi5y1q_EIU0lhL5gxc",
    authDomain: "evdtoolkit.firebaseapp.com",
    projectId: "evdtoolkit",
    storageBucket: "evdtoolkit.firebasestorage.app",
    messagingSenderId: "1002374431151",
    appId: "1:1002374431151:web:fe3724bb1f39eb4744af5a"
  };

  const app = getApps().length ? getApp() : initializeApp(firebaseConfig);
  const db = getFirestore(app);

  return Generators.observe(notify => {
    const unsubscribe = onSnapshot(collection(db, "EVDSettings"), snapshot => {
      notify(snapshot.docs.map(d => d.data()).sort((a, b) => (a.order ?? 0) - (b.order ?? 0)));
    });
    return unsubscribe;
  });
}

evdSettings.length === 0
  ? html`<div class="fs-empty">Loading…</div>`
  : html`<div class="fs-grid">${evdSettings.map(s => `
      <div class="fs-card">
        <img class="fs-card-image" src="${s.imageURL ?? ""}" onerror="this.style.display='none'" onclick="fsOpenLightbox(this.src)" onload="fsClassifyImage(this)" />
        <div class="fs-card-body">
          <h4 class="fs-card-title">${s.title ?? "Untitled"}</h4>
          <p class="fs-card-desc">${s.description ?? ""}</p>
          ${s.source ? `<span class="fs-source">📎 ${s.source}</span>` : ""}
        </div>
      </div>
    `).join("")}</div>`

Note

Further reading: Lele AV, Prabhakar H, Lin V, et al. External Ventricular Drain Management in Aneurysmal Subarachnoid Hemorrhage: Perspectives and Practices From Low-Income and Middle-Income Countries. Cureus. 2025 Apr. PMID: 40453290

Weaning

EVD weaning generally follows one of two approaches:

• Rapid weaning: +10 cm H₂O → clamp trial for 24–48 hours.
• Gradual weaning: +10 cm H₂O → +20 cm H₂O → clamp, with each change occurring at 24-hour intervals.

Note

Further reading — rapid vs. gradual weaning:

Ebel F, Lichter E, Mariani L, et al. Rapid Versus Gradual Weaning of External Ventricular Drain: A Systematic Literature Review and Meta-analysis. Neurocritical Care. 2023 Aug. PMID: 37308728

Brown GW, Lisitsyna A, Ashraf M, et al. Rapid versus gradual weaning of external ventricular drains in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Journal of Neurosurgical Sciences. 2026 Apr. PMID: 41949294

Clinical Model

• EVD behaves like a pressure-regulated valve
• ICP must exceed the setting for drainage
• Setting, ICP, and CSF output are interdependent

Tip

Clinical Pearl: Always interpret ICP in the context of the EVD setting.

CSF Output (mL/hr)

• High output → low setting OR elevated ICP
• Low output → high setting, low ICP, or obstruction
• Trend matters more than single values

Clamp Status

• Open: CSF drains if ICP exceeds setting
• Clamped: No drainage → ICP reflects true pressure

Warning

Critical: Interpretation changes completely when the EVD is clamped.

Leveling

• Reference point = external auditory meatus
• Small height errors → large pressure errors
• Always confirm before interpreting ICP

Common Errors

• Ignoring EVD setting
• Not checking clamp status
• Misinterpreting CSF output
• Failure to confirm leveling