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Factors influencing time to computed tomography in emergency department patients with suspected subarachnoid haemorrhage
  1. Maryam Khan1,
  2. Marco L A Sivilotti2,
  3. Michael J Bullard3,
  4. Marcel Émond4,
  5. Jane Sutherland5,
  6. Andrew Worster6,
  7. Corinne M Hohl7,
  8. Jacques S Lee8,
  9. Mary Eisenhauer9,
  10. Merril Pauls10,
  11. Howard Lesiuk11,
  12. George A Wells12,
  13. Ian G Stiell1,
  14. Jeffrey J Perry1
  1. 1Departments of Emergency Medicine, University of Ottawa, Ottawa, Ontario, Canada
  2. 2Departments of Emergency Medicine and of Biomedical & Molecular Sciences, Queen's University, Kingston, Ontario, Canada
  3. 3Department of Emergency Medicine, University of Alberta, Edmonton, Alberta, Canada
  4. 4Department of Family and Emergency Medicine, Université Laval, Quebec City, Quebec, Canada
  5. 5Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
  6. 6Division of Emergency Medicine, McMaster University, Hamilton, Ontario, Canada
  7. 7Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada
  8. 8Division of Emergency Medicine, University of Toronto, Toronto, Ontario, Canada
  9. 9Division of Emergency Medicine, University of Western Ontario, London, Ontario, Canada
  10. 10Department of Emergency Medicine, University of Manitoba, Winnipeg, Manitoba, Canada
  11. 11Division of Neurosurgery, University of Ottawa, Ottawa, Ontario, Canada
  12. 12School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, Ontario, Canada
  1. Correspondence to Dr Jeffrey J Perry, Clinical Epidemiology Unit, F647, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario K1Y 4E9, Canada; jperry{at}


Background CT has excellent sensitivity for subarachnoid haemorrhage (SAH) when performed within 6 hours of headache onset, but it is unknown to what extent patients with more severe disease are likely to undergo earlier CT, potentially inflating estimates of sensitivity. Our objective was to evaluate which patient and hospital factors were associated with earlier neuroimaging in alert, neurologically intact ED patients with suspected SAH.

Methods We analysed data from two large sequential prospective cohorts of ED patients with acute headache undergoing CT for suspected SAH. We examined the time interval from headache onset to CT, both overall and subdivided from headache onset to hospital registration and from registration to CT.

Results Among 2412 patients with headache, 194 had SAH, with 178 identified on unenhanced CT. Of these, 91 (51.1%) were identified by CT within 6 hours of headache onset and 87 after 6 hours. Patients with SAH had a shorter time from headache onset to hospital presentation (median 4.5 hours, IQR 1.7–22.7 vs 9.6 hours, IQR 2.8–46.0, p<0.001) and were imaged sooner after headache onset (6.4 hours, IQR 3.5–27.1 vs 12.6 hours, IQR 5.5–48.0, p<0.001) compared with those without SAH. The median time from in-hospital registration to CT scan was significantly shorter in those patients with SAH although this difference was less than 1 hour (1.9 hours, IQR 1.2–2.8 vs 2.5 hours, IQR 1.5–3.9, p<0.001). Arrival by ambulance (OR 3.1, 95% CI 1.94 to 4.98, p<0.001) and higher acuity at triage (OR 1.39, 95% CI 1.02 to 1.88, p=0.032) were among the factors associated with having CT imaging within 6 hours of headache onset.

Conclusions Time from headache onset to imaging is moderately associated with positive imaging for SAH. Delay to hospital presentation accounts for the largest fraction of time to imaging, especially those without SAH. These findings suggest limited opportunity to reduce lumbar puncture rates simply by accelerating in-hospital processes when imaging delays are under 2 hours, as diagnostic yield of imaging decreases beyond the 6-hour imaging window from headache onset.

  • CT/MRI
  • emergency department

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