Position Statement: 2003 Nov 22

AANS Position Statement On Recent Literature Correlating Volume to Outcome

Heather L Monroe

(Reaffirmed, November 2009)

(Statement Approved by the AANS Board of Directors on 11/22/03)

An inverse relationship between hospital and/or surgeon case volume and morbidity and mortality has been documented in the literature for a number of complex medical and surgical conditions. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Because of the complexity and heterogenicity of neurosurgical care, such analysis has not been done until recently for specific neurosurgical conditions. Carotid endarterectomy has been analyzed in this manner for a number of years; however, only a minority of operations in these studies were performed by neurosurgeons [8,18,19].

Several articles have appeared recently in the neurosurgical literature relating hospital and/or surgeon volume (number of cases of that particular condition treated per year) to outcome. Generally mortality rate and in some cases, either length of stay or discharge destination (home vs. extended care facility) have been used as the only outcome measures. The specific neurosurgical conditions analyzed so far are craniotomoy for brain tumors [20,21], overall care of patients with subarachnoid hemorrhage [22,23], surgical treatment of intracranial aneurysms [24,25,26,27,28], and surgical treatment specifically for unruptured intracranial aneurysms [29]. In general, these studies have found that mortality and morbidity appear to be lower in high volume centers and/or when the surgeon that performs the operation does a high volume of such operations per year.

Two recent editorials have pointed out the limitations of these specific neurosurgical studies [30,31]. In addition to the retrospective uncontrolled nature of these studies, their authors have used state, regional or national databases that, although offering some data on co-morbidities, do not offer specific data on the initial (on admission or pre-operative) neurological condition; for example, admission grade of patients with subarachnoid hemorrhage and the severity or complexity of the condition to be treated (severity of the subarachnoid hemorrhage, size or location of the tumor or size or location of the aneurysm). Additionally, although mortality is a clear end point in these databases, morbidity cannot be analyzed except by using indirect measures such as length of stay and/or destination of the patient after discharge from the initial hospital, as indicated before.

To balance these studies, at least one careful, though smaller, study has documented that excellent results can be achieved in aneurysm surgery by well trained neurosurgeons who perform a relatively small number of such operations in relatively "small volume" community hospitals [32].

The AANS Executive Committee and Board of Directors have carefully analyzed this issue and reviewed the studies alluded to above. We do not dispute the validity of the statistical analysis used in these studies and we accept the fact that it is possible that indeed, their conclusions are correct. However, given the limitations imposed on these studies by the databases used, we conclude that at this time, a mandate for regionalization of neurosurgical care would be premature and potentially harmful to some patients whose definitive neurosurgical care is delayed pending transfer. In addition, we conclude that the evidence available so far does not justify holding a hospital or a neurosurgeon legally liable simply because a patient with a bad outcome was treated at a hospital where only a low volume of such cases are treated yearly and/or by a neurosurgeon who treats only a limited number of such patients a year. It is clear that well-trained neurosurgeons can achieve excellent results in a "low volume" hospital even if they treat a limited number of patients with a particular condition [32]. Likewise, it is a fact that high volume is not always associated with superior outcomes.


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  3. Glasgow RE, Mulvihill SJ: Hospital volume influences outcome in patients undergoing pancreatic resection for cancer. West J Med 165: 294-300, 1996.
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  5. Jollis JG, Peterson ED, deLong ER et al: The relation between the volume of coronary angioplasty procedures at hospitals treating Medicare beneficiaries and short-term mortality. N Eng J Med 331: 1625-1629, 1994.
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  8. Wennberg DE, Lucas FL, Birkmeyer JD et al: Variation in carotid endarterectomy mortality in the Medicare population: trial hospitals, volume, and patient characteristics. JAMA 279: 1278-1281, 1998.
  9. Begg CB, Cramer LD, Hoskins WJ et al: Impact of hospital volume on operative mortality for major cancer surgery. JAMA 280: 1747-1751, 1998.
  10. Nathens AB, Jurkovich GJ, Maier EV et al: Relationship between trauma center volume and outcomes. JAMA 285: 1164-1171, 2001.
  11. Tu JV, Austin PC, Chan BT: Relationship between annual volume of patients treated by admitting physicians and mortality after acute myocardial infarction. JAMA 285: 3116-3122, 2001.
  12. Hannan EL, Radzyner M, Rubin D, Dougherty J, Brennan MF: The influence of hospital and surgeon volume on in-hospital mortality for colectomy, gastrectomy and lung lobectomy in patients with cancer. Surgery 131: 6-15, 2002.
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  14. Flood AB, Scott WR, Ewy W: Does practice make perfect? Part II - The relation between volume and outcomes and other hospital characteristics. Med Care 22: 115-125, 1984.
  15. Gordon TA, Burleyson GP, Tielsch JM, Cameron JL: The effects of regionalization on cost and outcome for one general high-risk procedure. Ann Surg 221: 43-49, 1995.
  16. Lieberman MD, Kilburn H, Lindsey M, Brennan MF: Relation of perioperative deaths to hospital volume among patients undergoing pancreatic resection for malignancy. Ann Surg 222: 638-645, 1995.
  17. Hillner BE, Smith TJ, Desch CE: Hospital and physician volume or specialization and outcomes in cancer treatment: Importance in quality of cancer care. J Clin Oncol 18: 2327-2340, 2000.
  18. Cebul RD, Snow RJ, Pine R et al: Indications, outcomes and provider volumes for carotid endarterectomy. JAMA 279: 1282-1287, 1998.
  19. Karp HR, Flanders WD, Shipp CC et al: Carotid endarterectomy among Medicare beneficiaries: a statewide evaluation of appropriateness and outcome. Stroke 29: 46-52, 1998.
  20. Cowan JA, Dimick JB, Leveque CJ, Thompson GB, Upchurch GR, Hoff JT: The impact of provider volume on mortality after intracranial tumor resection. Neurosurg 52: 48-54, 2003.
  21. Long DM, Gordon T, Bowman H, Etzel A, Burleyson G, Betchen S, Garonzik I, Brem, H: Outcome and cost of craniotomy performed to treat tumors in regional academic referral centers. Neurosurg 52: 1056-1065, 2003.
  22. Cross DT, Tiirschwell DL, Clark MA, Tuden D, Derdeyn CP, Moran CJ, Dacey RG: Mortality rates after subarachnoid hemorrhage: variations according to hospital case volume in 18 states. J Neurosurg 99: 810-820, 2003.
  23. Bardach NS, Zhao S, Gress DR, et al: Association between subarachnoid hemorrhage outcomes and numbers of cases treated at California hospitals. Stroke 33: 1851-1856, 2002.
  24. Cowan JA,,Dimick JB, WainessRM, Upchurch GR, Thompson GB: Outcomes after cerebral aneuurysm clip occlusion in the United States: the need for evidence-based hospital referral. J Neurosurg 99: 947-952, 2003.
  25. Chayatte D, Porterfield R: Functional outcome after repair of unruptured intracranial aneurysms. J Neurosurg 94: 417-421, 2001.
  26. Solomon RA, Mayer SA, Tarmey JJ: Relatiohship between the volume of craniotomies for cerebral aneurysm performed at New York state hospitals and in-hospital mortality. Stroke 27: 13-17, 1996.
  27. Bardach NS, Zhao S, Gress DR, Lawton MT, Johnston SC: Association between subarachnoid hemorrhage outcomes and number of cases treated at California hospitals. Stroke 33: 1851-1856, 2002.
  28. Johnston SC: Effect of endovascular services and hospital on cerebral aneurysm treatment outcomes. Storke 31: 111-117, 2000.
  29. Barker FG, Amin-Hanjani S, Butler WE, Ogilvy CS, Carter BS: In-hospital mortality and morbidity after surgical treatment of unruptured intracranial aneurysms in the United States, 1996-2000: The effect of hospital and surgeon volume. Neurosurg 52: 995-1009, 2003.
  30. Heros RC: Editorial: Case volume and outcome. J Neurosurg 99: 945-946, 2003.
  31. Heros RC: Editorial: Case volume and mortality. J Neurosurg 99: 805-806, 2003.
  32. Naso WB, Rhea AH, Poole A: Management and outcomes in a low-volume cerebral aneurysm practice. Neurosurg 48: 91-100, 2001.

Article ID: 20039
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