British Journal of Surgery 1994,81, 31-32

Hyperamylasaemia in ruptured aortic aneurysm: incidence and prognostic implications J. S. BAGLEY, M. P. H. TYLER and G. G. COOPER

Department of Vascular Surgery, Aberaken Royal Infirmary. Foresterhill. Aberdeen A M 2ZB. UK Correspondence lo: Mr G. G. Cooper

A study was carried out to determine the incidence of had an uncomplicated postoperative recovery (P<O.O5). increased serum amylase activity in patients with ruptured There was a correlation between preoperative serum aortic aneurysm during the 48 h after presentation and to amylase activity and length of stay in the intensive care unit assess its clinical signiflcance. In a prospective series of 25 atkr operation (rs=0.78 (95 per cent confidence interval patients, hyperamylasaemia occurred in ten and was @54-090), P< 0.002). Serum amylase activity may be useful significantly associated with poor outcome (P=O-OoS). In as a prognostic indicator in patients with ruptured aortic patients who died or had a major complication, serum aneurysm. amylase activity was significantly higher than in those who

It has been recognized for many years that patients with ruptured abdominal aortic aneurysm ( A M ) may have increased serum amylase activity both before and after emergency surgery'-3. Hyperamylasaemia has also been noted after a wide range of operative procedures including coronary artery bypass grafting4-' and gastrectomy'. Isoamylase analysis has shown that such increases in serum amylase activity may originate from the pancreas or the salivary glands4v6. Postulated causes have included hypotension, hypoxia, thromboemboli, local trauma to the pancreas and No study to date has focused on patients with ruptured AAA. The aim of the present study was to determine the incidence of increased serum amylase activity in patients with this condition and to assess its clinical significance.

Patients and methods Between August 1990 and August 1992,25 patients with ruptured aortic aneurysm were admitted prospectively to the study. Blood was taken for measurement of serum amylase activity, creatinine and urea concentration on admission and on the first and second days alter surgery. Samples were analysed in the hospital routine laboratory where normal amylase activity is defined as that less than 340 units/l; amylase isozyme analysis was not available. Findings at operation, the length of intensive care unit stay, total hospital stay and death within 30 days of operation were recorded.

Patients were divided into two outcome groups: those in group 1 survived without complication; the remainder (group 2) either died or survived with a major complication. Major complications encountered were gut ischaemia, renal failure, respiratory failure and myocardial infarction. Gut ischaemia was defined as that requiring resection at the time of operation or at a later operation within the follow-up period, or necrotic bowel at autopsy. Renal failure was defined as reduced renal function requiring temporary or permanent dialysis. Respiratory failure was defined as that requiring mechanical ventilation for more than 7 days after operation in the absence of other major organ failure. Myocardial infarction was diagnosed by serial electrocardiographic changes and appropriate rises in cardiac enzyme activity.

Statistical analysis

The data were not normally distributed. Comparison between groups was performed using the Mann-Whitney U test and Fisher's exact test

Paper accepted 25 May 1993

as appropriate, within the BDMPstatistical package(BDMP Statistical Software, Berkeley, California, USA). The Spearman rank correlation test was performed using the BDMP package, and partial correlation was calculated using the Spearman correlation coefficient as described by Altman'. Significance was assumed at the 5 per cent level.

Results The 25 patients recruited included two women. The mean age was 70 years and the mortality rate at 30 days was 32 per cent (eight of 25). Two patients died during operation, one before graft insertion, as a result of haemorrhagic shock. The post- operative complications documented were renal failure (six patients), gut ischaemia (three), myocardial infarction (one) and respiratory failure (one).

The incidence of hyperamylasaemia in any one of the three samples taken was 40 per cent. Four patients were hyper- amylasaemic on admission to hospital, values ranging from 379 to 667 units/l. Fourteen patients made an uncomplicated recovery (group 1) and, of the remaining 11 (group 2), eight died and three survived after recovering from one or more of the complications defined above. Only three of the eight deaths were followed by autopsy; the pancreas appeared normal in all cases. Hyperamylasaemia occurred in eight patients in group 2 and two in group 1. This difference was highly significant (P= 0005, Fisher's exact test).

A sigdicantly higher amylase activity was found in patients in group 2 after each of the three measurements, most notably on the first day after operation (P=@002, Mann-Whitney U test) (Table I ) . Whereas serum amylase activity remained

Table 1 Serum amylase activity ~

Serum amylase activity (units/l)

Day 1 Day 2 Admission after surgery after surgery

Group 1 (n= 14) 207 (146-324) 174 (88-419) 161 (70-485) Group 2 ( n = l l ) 319 (157-667) 449 (167-1561) 402 (140-1323) P 0-07 0-002 002

~ ~

Values are median (range). "Mann-Whitney U test

31

32 J. S. BAGLEY, M. P. H. TYLERand G. G. COOPER

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0 5 10 15 20 Stay in intensive care (days)

Fig. 1 Prcopcralibc serum amylase activity and length of stay in thc intcnsivc c ‘ m uiiil for thc 23 patients who survived operation. 0. ,Aliw ;it 30 ikiys: 0. dead iit 30 days. r,=0.78

constant in patients in group 1, there was a significant rise in amylase activity in those in group 2 on the first day after surgery.

The preoperative serum amylase activity was significantly correlated with length of intensive care in the study group (rs=0.78 (95 per cent confidence interval Q54-0.90), P<O-002) (Fig. I). This remained significant when corrected for the serum creatinine concentration using partial correlation. The two subsequent amylase analyses did not correlate significantly with length of stay in the intensive care unit.

Discussion The lack of specificity of a moderate increase in serum amylase activity in patients with acute abdominal pain is well recognized, and it is perhaps not surprising that four of the 25 patients with ruptured aortic aneurysm were hyperamylasaemic at presentation. It is of interest, however, that ten of these patients exhibited hyperamylasaemia in the 48 h after admission and that this was significantly associated with postoperative mortality and morbidity rates. In addition, there was a correlation between serum amylase activity at the time of admission and length of the subsequent stay in intensive care that was independent of renal functional impairment.

Amylase isozyme analysis was not performed and therefore the origin of the increased serum amylase activity could not be determined. From studies of patients developing hyper- amylasaemia in the course of critical illness or major surgery,

other investigators have found that salivary or pancreatic isozymes may be responsible. Morrissey er al.’ reported 28 patients undergoing abdominal surgery in whom there were four cases of hyperamylasaemia, three of the pancreatic subtype (one following routine AAA repair) and one of the salivary subtype. Following coronary artery bypass, the salivary subtype is found almost ex~ lus ive ly~~~ . In an autopsy study of patients who died after surgery for ruptured aortic aneurysm, Warshaw and OHarag found that 18 of 63 patients (29 per cent) had evidence of acute inflammatory pancreatitis, pancreatic necrosis or pancreatic abscess. In the subgroup of 30 patients with evidence of acute tubular necrosis, 15 had pancreatic disease. It is therefore possible that the pancreas was the more important source of hyperamylasaemia in the present series of patients.

Irrespective of the isozyme responsible, hyperamylasaemia was common and significantly associated with a complicated postoperative course. As estimation of serum amylase activity is an inexpensive and widely available biochemical test, serial estimations in patients with ruptured AAA might be considered worthwhile as an indicator of prognosis.

Acknowledgements The authors thank Mr I. Engeset for permission to include patients under his care and the Department of Medical Illustration for drawing Fig. 1.

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