Subarachnoid hemorrhage

Last updated: September 20, 2023

Summarytoggle arrow icon

Subarachnoid hemorrhage (SAH) refers to bleeding into the subarachnoid space. While SAH is often caused by trauma, 5–10% of cases are nontraumatic or spontaneous, in which case they are often due to the rupture of an aneurysm involving the circle of Willis (aneurysmal SAH). Nontraumatic SAH typically manifests with sudden and severe headache, which may be accompanied by nausea, vomiting, signs of meningism, and/or acute loss of consciousness. The best initial diagnostic test is a head CT without contrast, in which acute subarachnoid bleeding can be seen as hyperdensities in the subarachnoid space. If a head CT is negative for SAH, this diagnosis can be ruled out in many patients. However, if clinical suspicion remains high, it may be necessary to perform a lumbar puncture or CT angiography. Once SAH is confirmed, angiography is always necessary in order to identify the source of bleeding (e.g., aneurysms or other vascular abnormalities) and plan definitive treatment. The management of traumatic and nontraumatic SAH consists mostly of neuroprotective measures (e.g., control of blood pressure) to prevent secondary brain injuries. In aneurysmal SAH, microsurgical clipping or endovascular coiling of the aneurysm is indicated to prevent potentially fatal rebleeding. Aneurysmal SAH has a high mortality rate as a result of complications such as rebleeding and delayed cerebral ischemia.

See also “Overview of stroke” and “Traumatic brain injury” for more information.

Definitiontoggle arrow icon

Epidemiologytoggle arrow icon


Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

Classificationtoggle arrow icon

There is no universally accepted grading scale for SAH, but the scales presented here are among the most commonly used and have some value in predicting the neurological outcome (probability of death and expected level of disability). They have been created for the assessment of aneurysmal SAH and are usually not validated for use in traumatic SAH. [10][11][12]

Clinical classification

Clinical severity should be graded at the time of presentation.

Hunt-Hess classification of aneurysmal SAH [12][13]
Grade Symptoms and level of consciousness Neurological exam

Do not use the Hunt-Hess scale to predict the likelihood of a diagnosis of SAH, but rather to estimate the prognosis of patients with confirmed SAH. [14]

World Federation of Neurological Surgeons (WFNS) grading scale for SAH [15]
Grade GCS Motor deficit








May be present


May be present

Radiological classification

In addition to scales for clinical severity, the radiological appearance of SAH can also be graded. The most reliable tool is the modified Fisher scale, which is used to predict the incidence of delayed cerebral ischemia. [11]

Modified Fisher scale [11][16]
Grade Subarachnoid hemorrhage Intraventricular hemorrhage




2 Present


4 Present

Clinical featurestoggle arrow icon

Maintain a high index of suspicion for SAH in patients with isolated headache or cranial nerve palsy, as they are more often misdiagnosed, resulting in poor outcomes due to delayed diagnosis and interventions. [14]


Spontaneous SAHtoggle arrow icon

The following information applies to the diagnostic workup of suspected SAH in patients without a history of trauma. See “Management of traumatic SAH” for the treatment of patients with SAH due to head trauma.

Diagnosticstoggle arrow icon

Approach [10][18][19][20]

Since a missed diagnosis of SAH can have devastating consequences, clinicians should maintain a high index of suspicion when deciding whether to pursue testing.

  • Common indications for testing
  • Best initial test: immediate head CT without contrast [19][21]
    • Confirmation of SAH: Obtain angiography to confirm source of bleeding and plan treatment.
    • Nondiagnostic head CT but persisting suspicion: Perform second-line diagnostic tests.
    • Nondiagnostic CT in the first 6 hours in a neurologically intact patient: SAH unlikely; consider other differential diagnoses. [21]
  • Second-line tests: lumbar puncture (LP) or CT angiography (CTA) ; [18][21]
    • Lumbar puncture
      • LP positive: Identify the source of bleeding with angiography (e.g., CTA, DSA) and plan intervention.
      • LP negative; : SAH can be ruled out in most cases. If suspicion remains high, obtain CTA.
    • CTA (alternative)
      • CTA positive: Consider if additional angiographic imaging is necessary (e.g., DSA, MRA) and plan intervention.
      • CTA negative: SAH can be ruled out; consider other diagnoses. If suspicion remains high (which is rare), consider additional imaging (e.g., DSA, MRA).
  • Additional studies: Obtain CBC, BMP, coagulation panel, and type and screen.

If patients are unstable or have signs of increased ICP, diagnostics should not delay stabilizing and neuroprotective measures.

The Ottawa SAH clinical decision rule [21][22]

The Ottawa SAH clinical decision rule can be used as a tool to exclude SAH in selected patients presenting to the emergency department with acute headache.

  • Inclusion criteria (all of the following need to be fulfilled):
    • Age > 15 years
    • Neurologically intact and alert (GCS 15)
    • New, nontraumatic, severe headache, reaching maximum intensity in < 1 hour
  • Risk features
  • Interpretation [22]
    • Presence of 0 risk features: SAH ruled out
    • Presence of ≥ 1 risk feature: SAH cannot be ruled out

CT head without contrast [11][18][23]

If there is a high index of suspicion for SAH, a negative CT head does not exclude the diagnosis and second-line tests are necessary. [18]

Lumbar puncture (LP) [21][27][28]

  • Indication: history and/or examination that is concerning for SAH, but negative CT head [29]
  • Opening pressure: normal or elevated
  • The following may be evaluated to identify cerebrospinal fluid (CSF) features suggestive of SAH:
    • CSF color
      • Early findings: pink to red blood-tinged discoloration [30][31]
      • Late findings: xanthochromia; , which is the presence of bilirubin in the CSF secondary to the breakdown of RBCs, resulting in yellow discoloration [20]
    • Cell count (normal RBC:WBC ratio)
      • RBC count: elevated (no specific threshold) [30] [19][32]
      • WBC count: may be mildly elevated
    • Glucose: normal
    • Protein: elevated

Concerns for elevated ICP (e.g., on physical examination or CT scan) or coagulopathy are relative contraindications for LP.

Neurovascular imaging [10][18][19][33]

  • CT angiography (CTA)
    • Indications [33][34][35]
      • Patients with SAH identified on CT head without contrast
      • First-line imaging in patients with suspected SAH and ≥ 2 first-degree relatives with known aneurysmal SAH
      • Patients with a negative CT head who decline or have contraindications to LP
    • Benefits
    • Findings [37]
      • Visualization of aneurysms (accumulation of contrast)
      • May detect extravasation of contrast in the case of active bleeding
        • No blood visualized or a perimesencephalic SAH blood pattern: No further imaging is required. [38]
        • Diffuse or peripheral SAH blood pattern: Proceed to catheter-directed angiography with DSA. [18][33][39]
      • May detect vascular abnormalities (e.g., AVM)
  • Digital subtraction angiography (DSA): gold standard for cerebral vessel imaging ; [11]
    • Indications
      • Detection of small aneurysms in selected patients with a negative CT
      • To plan interventions (when CTA is insufficient)
    • Invasive imaging modality
    • Findings: similar to CTA
  • MRI and/or MR angiography [11][18][36][40]

CTA has poor sensitivity for detecting aneurysms < 3 mm in size and aneurysms that overlie bone (e.g., at the skull base). [18][33][39]

Managementtoggle arrow icon

The initial management of all patients with spontaneous SAH is similar, but further management depends on the underlying etiology. While aneurysmal hemorrhage can be treated with endovascular coiling or microsurgical clipping, there are few specific definite treatment options for nonaneurysmal SAH.

Initial management [11][18][20]

Primary measures should be initiated urgently in the ED. The goal is to stabilize the patient and prevent early rebleeding and secondary brain injury.

Rebleeding is a life-threatening complication that most commonly occurs in the first 6 hours after SAH. Start measures to prevent rebleeding immediately. [11][18]

Generally avoid nitrates for blood pressure control in brain injury, as they may elevate ICP. Consider alternative agents (e.g., titratable nicardipine or labetalol). [18]

Treatment of aneurysmal SAH [18][43]

All aneurysmal SAHs require definitive endovascular or microsurgical aneurysm repair as early as possible. Patients should be admitted to critical care for further management to prevent and treat secondary brain injury and systemic complications.

Intracranial aneurysm repair [18]

Intracranial aneurysm repair [10][18][29]
Endovascular coiling Microsurgical clipping
  • Minimally invasive
  • Higher risk of incomplete obliteration and recurrent bleeding
  • More invasive
  • Higher rate of complete aneurysm occlusion
  • Lower risk of recurrent bleeding
  • Insertion of a catheter under fluoroscopic guidance
  • Placement of metal coils in the aneurysm lumen to interrupt blood flow and induce thrombotic occlusion

Further management [43]

Only administer nimodipine orally or via enteral tube; Parenteral administration is associated with significant adverse effects (e.g., severe hypotension and cardiac arrest).

Treatment of nonaneurysmal SAH

Depending on the etiology, some specific measures may help improve the outcome.

Acute management checklisttoggle arrow icon

Traumatic SAHtoggle arrow icon

Typically, patients present with a clear history of trauma, and the diagnosis of SAH is then made based on imaging. See also “Management of trauma patients” and “Initial management of traumatic brain injury” (TBI).



Traumatic SAH is common in severe head injuries. CT head detects SAH in up to 33% of patients during the initial scan and in up to half of patients when subsequent imaging is included. [34]


There is no specific surgical or interventional treatment for traumatic SAH. Management is mostly supportive, with the goal of preventing secondary brain injury. If there are associated lesions, surgical intervention may be required.

  • Mild TBI with isolated SAH [47][48][49][50]
    • Typically, no surgical intervention is required and outcomes are good.
    • Consider neurosurgical and critical care consult if red flags for mTBI are present.
    • Repeat neuroimaging in the case of clinical deterioration or based on individual evaluation.
    • See the article on “Mild TBI” for additional information.
  • Moderate or severe TBI with SAH [51]
  • SAH with other pathologic radiographic findings [49]
    • Regardless of the initial GCS, these patients are at a higher risk of deterioration.
    • Admit the patient to a critical care unit.
    • Surgical intervention (e.g., hematoma evacuation) may be required.
    • See also “Treatment” in “SDH,” “EDH,” and “ICH.”

Complicationstoggle arrow icon


We list the most important complications. The selection is not exhaustive.

Prognosistoggle arrow icon

  • Approx. 30% mortality rate in the U.S. within the first 30 days [18]
  • Survivors: increased rates of neurologic impairment (e.g., cognitive, mood changes, functional, epilepsy) and increased risk of recurrent SAH

Referencestoggle arrow icon

  1. Lee et al.. Comprehensive Assessment of Isolated Traumatic Subarachnoid Hemorrhage. JOURNAL OF NEUROTRAUMA. 2014: p.595-609.doi: 10.1089/neu.2013.3152 . | Open in Read by QxMD
  2. Daroff RB, et al.. Bradley's Neurology in Clinical Practice. Elsevier
  3. Feigin VL, Lawes CM, Bennett DA, Barker-Collo SL, Parag V. Worldwide stroke incidence and early case fatality reported in 56 population-based studies: a systematic review. The Lancet Neurology. 2009; 8 (4): p.355-369.doi: 10.1016/s1474-4422(09)70025-0 . | Open in Read by QxMD
  4. Louis et al.. Merritt's Neurology. Wolter Kluwers ; 2015
  5. Behari S, Bhaisora K, Godbole C, Phadke R. Traumatic aneurysms of the intracranial and cervical vessels: A review. Neurol India. 2016; 64 (7): p.14.doi: 10.4103/0028-3886.178032 . | Open in Read by QxMD
  6. Keedy A. An overview of intracranial aneurysms.. McGill Journal of Medicine. 2006; 9 (2): p.141-6.
  7. Macdonald RL, Schweizer TA. Spontaneous subarachnoid haemorrhage. The Lancet. 2017; 389 (10069): p.655-666.doi: 10.1016/s0140-6736(16)30668-7 . | Open in Read by QxMD
  8. Chalouhi N, Hoh BL, Hasan D. Review of Cerebral Aneurysm Formation, Growth, and Rupture. Stroke. 2013; 44 (12): p.3613-3622.doi: 10.1161/strokeaha.113.002390 . | Open in Read by QxMD
  9. Etminan N, Rinkel GJ. Unruptured intracranial aneurysms: development, rupture and preventive management. Nature Reviews Neurology. 2016; 12 (12): p.699-713.doi: 10.1038/nrneurol.2016.150 . | Open in Read by QxMD
  10. Lawton MT, Vates GE. Subarachnoid Hemorrhage. N Engl J Med. 2017; 377 (3): p.257-266.doi: 10.1056/nejmcp1605827 . | Open in Read by QxMD
  11. Muehlschlegel S. Subarachnoid Hemorrhage. CONTINUUM. 2018; 24 (6): p.1623-1657.doi: 10.1212/con.0000000000000679 . | Open in Read by QxMD
  12. Rosen DS, Macdonald RL. Subarachnoid Hemorrhage Grading Scales: A Systematic Review. Neurocrit Care. 2005; 2 (2): p.110-118.doi: 10.1385/ncc:2:2:110 . | Open in Read by QxMD
  13. Hunt WE, Hess RM. Surgical Risk as Related to Time of Intervention in the Repair of Intracranial Aneurysms. J Neurosurg. 1968; 28 (1): p.14-20.doi: 10.3171/jns.1968.28.1.0014 . | Open in Read by QxMD
  14. Ois A, Vivas E, Figueras-Aguirre G, et al. Misdiagnosis Worsens Prognosis in Subarachnoid Hemorrhage With Good Hunt and Hess Score. Stroke. 2019; 50 (11): p.3072-3076.doi: 10.1161/strokeaha.119.025520 . | Open in Read by QxMD
  15. [No authors listed]. Report of World Federation of Neurological Surgeons Committee on a Universal Subarachnoid Hemorrhage Grading Scale. J Neurosurg. 1988; 68 (6).doi: 10.3171/jns.1988.68.6.0985 . | Open in Read by QxMD
  16. Frontera JA, Claassen J, Schmidt JM, et al. Prediction of Symptomatic Vasospasmafter Subarachnoid Hemorrhage: The Modified Fisher Scale. Neurosurgery. 2006; 59 (1): p.21-27.doi: 10.1227/01.neu.0000218821.34014.1b . | Open in Read by QxMD
  17. Singer RJ, Ogilvy CS, Rordorf G. Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated: September 26, 2013. Accessed: March 1, 2017.
  18. Connolly ES, Rabinstein AA, Carhuapoma JR, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association. Stroke. 2012; 43 (6): p.1711-1737.doi: 10.1161/STR.0b013e3182587839 . | Open in Read by QxMD
  19. Singer RJ, Ogilvy CS, Rordorf G. Treatment of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated: October 7, 2014. Accessed: February 14, 2017.
  20. Marcolini E, Hine J. Approach to the Diagnosis and Management of Subarachnoid Hemorrhage. Western Journal of Emergency Medicine. 2019; 20 (2): p.203-211.doi: 10.5811/westjem.2019.1.37352 . | Open in Read by QxMD
  21. Kim SM, Woo HG, Kim YJ, Kim BJ. Blood pressure management in stroke patients. J Neurocrit Care. 2020; 13 (2): p.69-79.doi: 10.18700/jnc.200028 . | Open in Read by QxMD
  22. Steiner T, Juvela S, Unterberg A, Jung C, Forsting M, Rinkel G. European Stroke Organization Guidelines for the Management of Intracranial Aneurysms and Subarachnoid Haemorrhage. Cerebrovasc Dis. 2013; 35 (2): p.93-112.doi: 10.1159/000346087 . | Open in Read by QxMD
  23. Diringer MN, Bleck TP, Claude Hemphill J, et al. Critical Care Management of Patients Following Aneurysmal Subarachnoid Hemorrhage: Recommendations from the Neurocritical Care Society’s Multidisciplinary Consensus Conference. Neurocrit Care. 2011; 15 (2): p.211-240.doi: 10.1007/s12028-011-9605-9 . | Open in Read by QxMD
  24. Grasso G, Alafaci C, Macdonald Rl. Management of aneurysmal subarachnoid hemorrhage: State of the art and future perspectives. Surg Neurol Int. 2017; 8 (1): p.11.doi: 10.4103/2152-7806.198738 . | Open in Read by QxMD
  25. Ahmadian A, Mizzi A, Banasiak M, et al. Cardiac manifestations of subarachnoid hemorrhage.. Heart, lung and vessels. 2013; 5 (3): p.168-78.
  26. Zhang L, Zhang B, Qi S. Impact of echocardiographic wall motion abnormality and cardiac biomarker elevation on outcome after subarachnoid hemorrhage: a meta-analysis. Neurosurg Rev. 2018; 43 (1): p.59-68.doi: 10.1007/s10143-018-0985-6 . | Open in Read by QxMD
  27. Al-Mufti F, Stein A, Damodara N, et al. Decision-Making for Patients With Cerebral Arteriovenous Malformations. Cardiol Rev. 2020; 29 (1): p.10-14.doi: 10.1097/crd.0000000000000342 . | Open in Read by QxMD
  28. Derdeyn CP, Zipfel GJ, Albuquerque FC, et al. Management of Brain Arteriovenous Malformations: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke. 2017; 48 (8).doi: 10.1161/str.0000000000000134 . | Open in Read by QxMD
  29. Mensing LA, Vergouwen MDI, Laban KG, et al. Perimesencephalic Hemorrhage. Stroke. 2018; 49 (6): p.1363-1370.doi: 10.1161/strokeaha.117.019843 . | Open in Read by QxMD
  30. Meurer WJ, Walsh B, Vilke GM, Coyne CJ. Clinical Guidelines for the Emergency Department Evaluation of Subarachnoid Hemorrhage. J Emerg Med. 2016; 50 (4): p.696-701.doi: 10.1016/j.jemermed.2015.07.048 . | Open in Read by QxMD
  31. Godwin SA, Cherkas DS, Panagos PD, et al. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Acute Headache. Ann Emerg Med. 2019; 74 (4): p.e41-e74.doi: 10.1016/j.annemergmed.2019.07.009 . | Open in Read by QxMD
  32. Perry JJ, Stiell IG, Sivilotti ML, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013; 310 (12): p.1248-55.doi: 10.1001/jama.2013.278018 . | Open in Read by QxMD
  33. Heit JJ, Iv M, Wintermark M. Imaging of Intracranial Hemorrhage.. Journal of stroke. 2017; 19 (1): p.11-27.doi: 10.5853/jos.2016.00563 . | Open in Read by QxMD
  34. Barreau X, Marnat G, Gariel F, Dousset V. Intracranial arteriovenous malformations. Diagn Interv Imaging. 2014; 95 (12): p.1175-1186.doi: 10.1016/j.diii.2014.10.004 . | Open in Read by QxMD
  35. Seehusen, et al. Cerebrospinal Fluid Analysis. American Family Physician. 2003.
  36. Long D, Koyfman A, Long B. The Thunderclap Headache: Approach and Management in the Emergency Department. J Emerg Med. 2019; 56 (6): p.633-641.doi: 10.1016/j.jemermed.2019.01.026 . | Open in Read by QxMD
  37. Gorchynski J, Oman J, Newton T. Interpretation of traumatic lumbar punctures in the setting of possible subarachnoid hemorrhage: who can be safely discharged?. Cal J Emerg Med. 2007; 8 (1): p.3-7.
  38. China M, Matloob SA, Grieve JP, Toma AK. The value of repeated lumbar puncture to test for xanthochromia, in patients with clinical suspicion of subarachnoid haemorrhage, with CT-negative and initial traumatic tap. Br J Neurosurg. 2021: p.1-4.doi: 10.1080/02688697.2021.1875398 . | Open in Read by QxMD
  39. Czuczman AD, Thomas LE, Boulanger AB, et al. Interpreting Red Blood Cells in Lumbar Puncture: Distinguishing True Subarachnoid Hemorrhage From Traumatic Tap. Acad Emerg Med. 2013; 20 (3): p.247-256.doi: 10.1111/acem.12095 . | Open in Read by QxMD
  40. American College of Radiology ACR Appropriateness Criteria® Cerebrovascular Diseases-Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage. Updated: January 1, 2021. Accessed: December 2, 2021.
  41. Walls R, Hockberger R, Gausche-Hill M. Rosen's Emergency Medicine. Elsevier Health Sciences ; 2018
  42. Whitehead MT, Cardenas AM, Corey AS, et al. American College of Radiology ACR Appropriateness Criteria® Headache. J Am Coll Radiol. 2019.doi: 10.1016/j.jacr.2019.05.030 . | Open in Read by QxMD
  43. Maher M, Schweizer TA, Macdonald RL. Treatment of Spontaneous Subarachnoid Hemorrhage. Stroke. 2020; 51 (4): p.1326-1332.doi: 10.1161/strokeaha.119.025997 . | Open in Read by QxMD
  44. Kobata H, Sugie A, Yoritsune E, Miyata T, Toho T. Intracranial extravasation of contrast medium during diagnostic CT angiography in the initial evaluation of subarachnoid hemorrhage: report of 16 cases and review of the literature. SpringerPlus. 2013; 2 (1).doi: 10.1186/2193-1801-2-413 . | Open in Read by QxMD
  45. Agid R, Andersson T, Almqvist H, et al. Negative CT angiography findings in patients with spontaneous subarachnoid hemorrhage: When is digital subtraction angiography still needed?. AJNR Am J Neuroradiol. 2010; 31 (4): p.696-705.doi: 10.3174/ajnr.A1884 . | Open in Read by QxMD
  46. ACR–ASNR–SIR–SNIS Practice parameter for the performance of diagnostic cervicocerebral catheter angiography in adults. Updated: October 1, 2021. Accessed: December 2, 2021.
  47. Mitchell P, Wilkinson ID, Hoggard N, et al. Detection of subarachnoid haemorrhage with magnetic resonance imaging. J Neurol Neurosurg Psychiatry. 2001; 70 (2): p.205-11.doi: 10.1136/jnnp.70.2.205 . | Open in Read by QxMD
  48. Cooper SW, Bethea KB, Skrobut TJ, et al. Management of traumatic subarachnoid hemorrhage by the trauma service: is repeat CT scanning and routine neurosurgical consultation necessary?. Trauma Surg Acute Care Open. 2019; 4 (1): p.e000313.doi: 10.1136/tsaco-2019-000313 . | Open in Read by QxMD
  49. Quigley MR, Chew BG, Swartz CE, Wilberger JE. The clinical significance of isolated traumatic subarachnoid hemorrhage. J Trauma Acute Care Surg. 2013; 74 (2): p.581-584.doi: 10.1097/ta.0b013e31827d6088 . | Open in Read by QxMD
  50. Witiw CD, Byrne JP, Nassiri F, Badhiwala JH, Nathens AB, da Costa LB. Isolated Traumatic Subarachnoid Hemorrhage. Crit Care Med. 2018; 46 (3): p.430-436.doi: 10.1097/ccm.0000000000002931 . | Open in Read by QxMD
  51. Phelan HA, Richter AA, Scott WW, et al. Does Isolated Traumatic Subarachnoid Hemorrhage Merit a Lower Intensity Level of Observation Than Other Traumatic Brain Injury?. J Neurotrauma. 2014; 31 (20): p.1733-1736.doi: 10.1089/neu.2014.3377 . | Open in Read by QxMD
  52. Armin SS, Colohan ART, Zhang JH. Traumatic subarachnoid hemorrhage: our current understanding and its evolution over the past half century. Neurol Res. 2006; 28 (4): p.445-452.doi: 10.1179/016164106x115053 . | Open in Read by QxMD
  53. Westerlaan HE, van Dijk JM, Jansen-van der Weide MC, et al. Intracranial aneurysms in patients with subarachnoid hemorrhage: CT angiography as a primary examination tool for diagnosis--systematic review and meta-analysis.. Radiology. 2011; 258 (1): p.134-45.doi: 10.1148/radiol.10092373 . | Open in Read by QxMD
  54. Perry JJ, Alyahya B, Sivilotti MLA, et al. Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study. BMJ. 2015; 350 (feb18 8): p.h568-h568.doi: 10.1136/bmj.h568 . | Open in Read by QxMD

Icon of a lockAccess full content

Sign up and get unlimited access.
 Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer