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ELECTIVE SURGERY FOR SMALL ABDOMINAL AORTIC ANEURYSMS
909
Point of View ELECTIVE SURGERY FOR SMALL ABDOMINAL AORTIC ANEURYSMS
JACK COLLIN Nuffield Department of Surgery, John Radcliffe Hospital, Oxford OX3 9DU THE
majority of patients
with
abdominal
aortic
aneurysms experience no symptoms until the aneurysm ruptures and causes death. Elective surgery to replace an aneurysm with an arterial graft can usually be justified only if the risk of death or disability from surgery is less than that expected from the natural history of the disease. The factors to be considered when deciding on management are the size of the aneurysm, the patient’s age and general state of health,
and the
prevailing operative mortality
safer surgery and slower, more scientific anaesthesia with maintenance of intravascular volume. In the best centres the operative mortality is now less than 5%.9-11 Elderly patients with small aneurysms are the group most likely to be rejected for elective surgical replacement of an aortic aneurysm. What is the likely outcome for such patients with and without elective surgery? In men aged 80-84 years known to have aortic aneurysms of 4-6 cm diameter, approximately 19% would be dead after 12 months without any surgical treatment. If the same men received elective surgery 18% would be dead 13 months after surgery, if we assume an operative mortality of 5%. The breakeven point for operative versus non-operative management of this apparently unpromising group of patients is therefore less than 12 months, after which an increasing advantage in life expectation accrues to patients who have had elective surgery. The increase in life expectation provided by early elective surgery is greater the younger the patient at the time of diagnosis. It is now no longer acceptable for a patient of any age with an abdominal aortic aneurysm of more than 4 cm in diameter to be casually denied the life-saving routine elective operation of aneurysm replacement. accurate
for elective aortic-
aneurysm surgery.
In general, the larger the external diameter of the aneurysm the greater is the risk of rupture. Consequently, all vascular surgeons would recommend elective surgery for an otherwise healthy man with a symptomless aneurysm greater than 6 cm in diameter, in the happy knowledge that the chances of his still being alive a year later are better with surgery than without. For small aneurysms of 4-6 cm diameter, there is uncertainty whether elective surgery or continued observation offers patients the best chance of survival.1 Information on the natural history of abdominal aortic aneurysms comes from three types of study. In patients with aneurysms discovered for the first time at necropsy at the Massachusetts General Hospital, 23-4% of those measuring 41-5-0 cm in diameter had caused death.2 For aneurysms known to,be present before death but measured at necropsy, 35-5% of those less than 6 cm diameter caused death.3 Neither type of study addresses the crucial clinical question. What is the subsequent risk of rupture of an aneurysm known to be less than 6 cm in diameter at the time of diagnosis? Cronenwett4 has attempted to answer this question by a follow-up study on a group of patients rejected for surgery either because the aneurysm was thought to be too small or because their general health was too poor. The mean diameter of the aneurysms at the time of entry to the study was 39 cm. In the 3 years of follow-up the annual rate of aneurysm rupture (6%) was the same as the mortality rate from all other causes. Aneurysms do not stay the same size; the mean growth rate of aortic aneurysms less than 6 cm in diameter is 05 cm per year.4-{) The continuing risk of rupture therefore increases with time. The patient’s age and general physical condition are the -other factors affecting the probability of death from an aneurysm. The annual death rate from all causes increases progressively from 2-2% for men aged 60-64 years to 13% for men aged 80-84 years. If we take Cronenwett’s figure4of a 5% annual death rate from rupture of a small aneurysm, we can see that the presence of an untreated small aneurysm raises the expected annual death rate by 230 % for men aged 60-64 years and 38% for men aged 80-84 years. Elective surgery for replacement of aortic aneurysms has become progressively safer since the operation was first carried out in 1951.8 Mortality has been reduced by faster,
REFERENCES
Cooley DA, Carmichael MJ. Abdominal aortic aneurysm. Circulation 1984; 70 (suppl 1): 5-6. 2. Darling RC, Messina CR, Brewster DC, Ottinger LW. Autopsy study of unoperated abdominal aortic aneurysms. Cardiovasc Surg 1976; 56 (suppl 2 Circ): 161-64. 3. Szilagyi DE, Smith RF, DeRusso FJ, Elliott JP, Sherrin FW. Contribution of abdominal aortic aneurysmectomy to prolongation of life. Ann Surg 1966; 164: 1.
678-99.
JL, Murphy TF, Zelenock GB, et al. Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985; 98: 472-83. Delin A, Ohlsen H, Swedenborg J. Growth rate of abdominal aortic aneurysms as measured by computed tomography. Br J Surg 1985; 72: 530-32. Bernstein EF, Dilley RB, Goldberger LE, Gosink BB, Leopold GR. Growth rates of small abdominal aortic aneurysms. Surgery 1976; 80: 765-73. Mortality Statistics Cause. Office of Population Censuses and Surveys, England and Wales. London: HM Stationery Office, 1984: series DH2, 11. DuBost C, Allary M, Oeconomos N. Resection of an aneurysm of the abdominal aorta. Arch Surg 1952; 64: 405-08. Crawford ES, Saleh SA, Babb JW, Glaeser DH, Vaccaro PS, Silvers A. Infrarenal abdominal aortic aneurysm. Factors influencing survival after operation performed over a 25 year period. Ann Surg 1981; 193: 699-709. Castleden WM, Mercer JC. Abdominal aortic aneurysms in Western Australia: descriptive epidemiology and patterns of rupture Br J Surg 1985; 72: 109-12. Campbell WB, Collin J, Morris PJ. The mortality of abdominal aortic aneurysm. Ann R Coll Surg Engl 1986; 68: 275-78.
4. Cronenwett
.
5. 6. 7. 8. 9.
10
11.
care should be taken by those who wish scientists to be socially responsible. Do they really believe that scientists have special skills which will enable them to make, what are, in essence, ethical and social decisions? Do they really wish to give up to the scientists their right to participate in the decision-making process? Would they be prepared to leave to scientists decisions as to what defence systems to build? To make the scientist so powerful would
"Great
more
be
a mistake. "But there is clearly considerable anxiety about genetic engineering. I have asked many people what is their worst fear of the outcome of genetic engineering and, while responses vary considerably, there is undoubtedly considerable distaste for tampering with nature together with a fear of monsters being created. The image of Dr Frankenstein looms large. I think this reflects the ignorance of the nature of the science involved. For the further these fantasies are explored the less likely they become. If we are a society that restricts abortion, bans euthanasia, and is very sensitive about vivisection, how is it conceivable that we will breed a race of apelike slaves? Who would bear clones? Each case followed in detail turns out, I believe, to be implausible. Whereas problems of abortion and euthanasia are low-level technology, the very term genetic engineering makes for alienation and implies a technology which most people think they cannot understand."-L. WOLPERT. Science and Antiscience. Lloyd-Roberts Lecture, 1986. J R Coll Phys Lond 1987; 21: 159-65.
Point of View ELECTIVE SURGERY FOR SMALL ABDOMINAL AORTIC ANEURYSMS
JACK COLLIN Nuffield Department of Surgery, John Radcliffe Hospital, Oxford OX3 9DU THE
majority of patients
with
abdominal
aortic
aneurysms experience no symptoms until the aneurysm ruptures and causes death. Elective surgery to replace an aneurysm with an arterial graft can usually be justified only if the risk of death or disability from surgery is less than that expected from the natural history of the disease. The factors to be considered when deciding on management are the size of the aneurysm, the patient’s age and general state of health,
and the
prevailing operative mortality
safer surgery and slower, more scientific anaesthesia with maintenance of intravascular volume. In the best centres the operative mortality is now less than 5%.9-11 Elderly patients with small aneurysms are the group most likely to be rejected for elective surgical replacement of an aortic aneurysm. What is the likely outcome for such patients with and without elective surgery? In men aged 80-84 years known to have aortic aneurysms of 4-6 cm diameter, approximately 19% would be dead after 12 months without any surgical treatment. If the same men received elective surgery 18% would be dead 13 months after surgery, if we assume an operative mortality of 5%. The breakeven point for operative versus non-operative management of this apparently unpromising group of patients is therefore less than 12 months, after which an increasing advantage in life expectation accrues to patients who have had elective surgery. The increase in life expectation provided by early elective surgery is greater the younger the patient at the time of diagnosis. It is now no longer acceptable for a patient of any age with an abdominal aortic aneurysm of more than 4 cm in diameter to be casually denied the life-saving routine elective operation of aneurysm replacement. accurate
for elective aortic-
aneurysm surgery.
In general, the larger the external diameter of the aneurysm the greater is the risk of rupture. Consequently, all vascular surgeons would recommend elective surgery for an otherwise healthy man with a symptomless aneurysm greater than 6 cm in diameter, in the happy knowledge that the chances of his still being alive a year later are better with surgery than without. For small aneurysms of 4-6 cm diameter, there is uncertainty whether elective surgery or continued observation offers patients the best chance of survival.1 Information on the natural history of abdominal aortic aneurysms comes from three types of study. In patients with aneurysms discovered for the first time at necropsy at the Massachusetts General Hospital, 23-4% of those measuring 41-5-0 cm in diameter had caused death.2 For aneurysms known to,be present before death but measured at necropsy, 35-5% of those less than 6 cm diameter caused death.3 Neither type of study addresses the crucial clinical question. What is the subsequent risk of rupture of an aneurysm known to be less than 6 cm in diameter at the time of diagnosis? Cronenwett4 has attempted to answer this question by a follow-up study on a group of patients rejected for surgery either because the aneurysm was thought to be too small or because their general health was too poor. The mean diameter of the aneurysms at the time of entry to the study was 39 cm. In the 3 years of follow-up the annual rate of aneurysm rupture (6%) was the same as the mortality rate from all other causes. Aneurysms do not stay the same size; the mean growth rate of aortic aneurysms less than 6 cm in diameter is 05 cm per year.4-{) The continuing risk of rupture therefore increases with time. The patient’s age and general physical condition are the -other factors affecting the probability of death from an aneurysm. The annual death rate from all causes increases progressively from 2-2% for men aged 60-64 years to 13% for men aged 80-84 years. If we take Cronenwett’s figure4of a 5% annual death rate from rupture of a small aneurysm, we can see that the presence of an untreated small aneurysm raises the expected annual death rate by 230 % for men aged 60-64 years and 38% for men aged 80-84 years. Elective surgery for replacement of aortic aneurysms has become progressively safer since the operation was first carried out in 1951.8 Mortality has been reduced by faster,
REFERENCES
Cooley DA, Carmichael MJ. Abdominal aortic aneurysm. Circulation 1984; 70 (suppl 1): 5-6. 2. Darling RC, Messina CR, Brewster DC, Ottinger LW. Autopsy study of unoperated abdominal aortic aneurysms. Cardiovasc Surg 1976; 56 (suppl 2 Circ): 161-64. 3. Szilagyi DE, Smith RF, DeRusso FJ, Elliott JP, Sherrin FW. Contribution of abdominal aortic aneurysmectomy to prolongation of life. Ann Surg 1966; 164: 1.
678-99.
JL, Murphy TF, Zelenock GB, et al. Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985; 98: 472-83. Delin A, Ohlsen H, Swedenborg J. Growth rate of abdominal aortic aneurysms as measured by computed tomography. Br J Surg 1985; 72: 530-32. Bernstein EF, Dilley RB, Goldberger LE, Gosink BB, Leopold GR. Growth rates of small abdominal aortic aneurysms. Surgery 1976; 80: 765-73. Mortality Statistics Cause. Office of Population Censuses and Surveys, England and Wales. London: HM Stationery Office, 1984: series DH2, 11. DuBost C, Allary M, Oeconomos N. Resection of an aneurysm of the abdominal aorta. Arch Surg 1952; 64: 405-08. Crawford ES, Saleh SA, Babb JW, Glaeser DH, Vaccaro PS, Silvers A. Infrarenal abdominal aortic aneurysm. Factors influencing survival after operation performed over a 25 year period. Ann Surg 1981; 193: 699-709. Castleden WM, Mercer JC. Abdominal aortic aneurysms in Western Australia: descriptive epidemiology and patterns of rupture Br J Surg 1985; 72: 109-12. Campbell WB, Collin J, Morris PJ. The mortality of abdominal aortic aneurysm. Ann R Coll Surg Engl 1986; 68: 275-78.
4. Cronenwett
.
5. 6. 7. 8. 9.
10
11.
care should be taken by those who wish scientists to be socially responsible. Do they really believe that scientists have special skills which will enable them to make, what are, in essence, ethical and social decisions? Do they really wish to give up to the scientists their right to participate in the decision-making process? Would they be prepared to leave to scientists decisions as to what defence systems to build? To make the scientist so powerful would
"Great
more
be
a mistake. "But there is clearly considerable anxiety about genetic engineering. I have asked many people what is their worst fear of the outcome of genetic engineering and, while responses vary considerably, there is undoubtedly considerable distaste for tampering with nature together with a fear of monsters being created. The image of Dr Frankenstein looms large. I think this reflects the ignorance of the nature of the science involved. For the further these fantasies are explored the less likely they become. If we are a society that restricts abortion, bans euthanasia, and is very sensitive about vivisection, how is it conceivable that we will breed a race of apelike slaves? Who would bear clones? Each case followed in detail turns out, I believe, to be implausible. Whereas problems of abortion and euthanasia are low-level technology, the very term genetic engineering makes for alienation and implies a technology which most people think they cannot understand."-L. WOLPERT. Science and Antiscience. Lloyd-Roberts Lecture, 1986. J R Coll Phys Lond 1987; 21: 159-65.