Asian Cardiovasc Thorac Ann 1999;7:9-12
© 1999 Asia Publishing EXchange Pte Ltd
Low-Dose Dopamine in Coronary Artery Bypass Patients with Preoperative Renal Dysfunction
Suchart Chaiyaroj, MD,
James Tatoulis, FRACS
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Department of Cardiothoracic Surgery Royal Melbourne Hospital Victoria, Australia
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For reprint information contact: Suchart Chaiyaroj, MD Tel: 66 2 282 8826 Fax: 66 2 259 5555 email: wynn{at}loxinfo.co.th Bhumibol Adulyadej Hospital, 23 Samsen 6, Bangkok 10200, Thailand.
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Abstract
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Fifty-two patients undergoing coronary artery bypass surgery with preoperative renal dysfunction were studied to evaluate the effects of low-dose dopamine on renal function during the postoperative period. Patients were randomly assigned to the dopamine-treated group or an untreated control group. The treatment period was 24 hours commencing on induction of anesthesia. Serum creatinine levels were followed up for 6 days postoperatively. The degree of preoperative renal dysfunction was higher in the dopamine group but the pattern of change in the creatinine levels was similar in both groups, with an initial fall and a rise to maximum levels at 48 to 72 hours postoperatively, followed by a fall on day 6. We could not demonstrate any beneficial effect of low-dose dopamine in patients with preoperative renal dysfunction undergoing coronary artery bypass surgery.
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Introduction
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Impaired renal function increases the risk of morbidity and mortality in cardiac surgery patients especially because of the potential life-threatening complication of renal failure.1–4 The reported incidence of renal dysfunction following cardiac surgery ranges from 2% to 40% and mortality rates of 40% to 70% have been reported with established renal failure.5–9 Factors important in maintaining good perioperative renal perfusion include optimization of renal perfusion pressure and renal blood flow, myocardial protection and myocardial performance post-bypass, and minimizing the duration of cardio-pulmonary bypass.3,4 Diuretic administration, although increasing urine volume, may be associated with accelerated renal failure in the presence of contracted blood volume or low cardiac output.1–4
Dopamine is a renal vasodilator that increases renal blood flow without decreasing the mean arterial blood pressure.10,11 There have been several reports of the effects of low-dose dopamine in cardiac surgical patients and in other critically ill populations, with no demonstrated benefit.4 A study by Myles and colleagues12 did not show any improvement in renal function resulting from routine low-dose dopamine in patients with normal renal function preoperatively who underwent elective coronary artery bypass surgery. Another study by Costa and colleagues13 in patients undergoing cardiac surgery showed the effect of dopamine in increasing the patient's ability to eliminate water and sodium during cardiopulmonary bypass in comparison to a control group but there was no demonstrable difference in renal function.
The aim of this study was to evaluate any possible benefit of low-dose dopamine used prophylactically intra-operatively and postoperatively in patients with pre-operative renal impairment undergoing elective coronary bypass graft surgery because previous studies had been carried out in patients with normal renal function.
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Patients and Methods
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Assuming an expected deterioration in renal function of more than 30%, a sample size of 50 was considered appropriate.12 Fifty-two consecutive patients with preoperative renal dysfunction who underwent coronary artery bypass graft surgery were entered into this blinded prospective randomized study from June 1992 to July 1993. Renal dysfunction was defined as a serum creatinine level greater than 0.11 mmol•L–1. Three patients were known to have chronic renal disease. The patients were randomly assigned to one of two groups according to odd or even unit registry numbers; one group served as a control while patients in the other group were treated with dopamine. Two patients were excluded from the study because of unstable hemodynamics following cardiopulmonary bypass; one required an adrenaline infusion and the other had an intraaortic balloon pump postoperatively to maintain circulation. Medications such as gentamicin, cephalothin, and indomethacin, which have an effect on renal function, were not used. Medications that influence dopaminergic function, including metoclopramide, chlorpromazine, and haloperidol were similarly avoided.
All patients underwent coronary artery bypass graft surgery that included at least one internal mammary artery bypass graft in combination with other arterial and venous grafts. Cardiopulmonary bypass with mild hypothermia (28°C) was required in all patients. A membrane oxygenator was used in all cases. The bypass prime consisted of 2 L Plasma-Lyte-148 (Baxter Co., Sydney, NSW, Australia), an electrolyte solution of 294 mOsmol•L–1. The mean arterial pressure was maintained at 70 mm Hg. Sodium nitroprusside infusion was used for vasodilatation and metaraminol was used for vasoconstriction. The flow was maintained at a target rate of 70 mL•kg–1•min–1. Antegrade intermittent blood cardioplegia was delivered by the aortic root every 15 to 20 minutes at a temperature of 15°C for myocardial protection. The dopamine infusion solution was prepared by adding 600 mg dopamine hydrochloride to 100 mL of 5% dextrose (final dopamine concentration 6 mg•mL–1). The infusion rate was 200 to 300 µg•min–1 (3 µg•kg–1•min–1) delivered by an infusion pump from the time of induction of anesthesia up to 24 hours thereafter. Serum creatinine levels were measured to evaluate renal function as this was the most readily available reproducible and routine parameter.
The data were collected serially on the preoperative day, 30 minutes after completion of the operation, 6, 12, 48, and 72 hours postoperatively, and on the 6th postoperative day. The preoperative and postoperative data are summarized in Tables 1 and 2
. Data are reported as mean ± standard deviation or as proportions. Data were processed using Statistical Package for Social Sciences software for personal computer, Version 3.0 (SPSS, Inc., Sydney, NSW, Australia). Groups were compared using the unpaired Student t test or chi-squared test as appropriate. Continuous data were analyzed using one-way analysis of variance. Multivariate analysis of variance was used in the analysis of repeated measurements. Results were considered significant if the p value was less than 0.05.
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Results
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After exclusion of the 2 patients with unstable hemo-dynamics immediately postoperatively, the dopamine and control groups comprised 25 patients each. The baseline data in the control group and the dopamine group were similar except for systolic blood pressure and the preoperative creatinine level, which were both higher in the dopamine group. The left atrial pressure (mean in the first 24 hours postoperatively) was also higher in the dopamine group. The mean cardiac index in the first 24 hours and the 24-hour urine output were similar in both groups. In both groups, values were within the normal range for adequate tissue perfusion and volume status (Table 1
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The mean preoperative serum creatinine level in the dopamine group was higher than that of the control group (Table 2). In the dopamine group, there were 10 patients with preoperative serum creatinine levels above 0.16 mmol•L–1 and 4 of these patients had levels of 0.2 mmol•L–1 or greater. In the control group, only 2 patients had a preoperative creatinine level of more than 0.16 mmol•L–1. There was a significant difference in the creatinine levels (p < 0.005) between the control group and the dopamine group in the preoperative and postoperative measurements at all the time intervals (Table 2). However, sequential comparisons of serum creatinine levels within each group were not statistically significant. The pattern of change of the creatinine level was similar in both the dopamine group and the control group. Serum creatinine decreased to its lowest level immediately postoperatively, then gradually increased to its highest level at 48 to 72 hours postoperatively, falling back to the preoperative level by day 6 (Figure 1). No episode of acute renal failure or irreversible deterioration of preoperative renal dysfunction was observed.
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Discussion
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The incidence of renal impairment and renal failure after coronary bypass surgery is now low but the associated mortality in the event of renal failure remains very high.5 Preoperative renal impairment was found to be a risk factor associated with higher morbidity and mortality.6 There are many causes of renal impairment after cardiac surgery including cardiopulmonary bypass with potentially lower mean perfusion pressures, nonpulsatile flow, prolonged duration of cardiopulmonary bypass, and the presence of free hemoglobin due to hemolysis induced by cardiopulmonary bypass.4,5 However, cardiovascular instability with a low renal perfusion pressure and low renal blood flow are the main factors. Anecdotally, low-dose dopamine infusions have produced an improvement in renal function (resolution of oliguria) with no deleterious hemodynamic effect in cardiac patients who manifested postoperative combined left ventricular dysfunction and oliguria.14,15 Nevertheless, there is no evidence supporting the use of perioperative low-dose dopamine to maintain renal function in patients undergoing cardiac surgery.12,13
It is common for creatinine clearance to be used for assessing renal function although serum creatinine levels are dependent on muscle mass and state of dehydration as well as renal function. However, for practical purposes, we used serum creatinine levels because they are routinely available, inexpensive, and form part of the standard assessment protocols for our patients undergoing cardiac surgery.
Although our patients were consecutive and randomized, there was a significant difference in the preoperative serum creatinine levels between the dopamine group (higher) and the control group, which made it more difficult to prove any benefit of a low-dose dopamine infusion. When patients with preoperative creatinine levels of 0.2 mmol•L–1 or greater were excluded, there was no statistically significant difference between the two groups at all time intervals. The pattern of change in the creatinine levels was similar in both groups. Initially, there was a fall in the serum creatinine following cardiopulmonary bypass and hemodilution. The creatinine levels then gradually rose so that they were almost identical to the preoperative levels at the 12th hour postoperatively. The rise in serum creatinine peaked at 48 to 72 hours and fell to the preoperative level by the 6th postoperative day.
We concluded that in patients with mild renal impairment (serum creatinine 0.12 to 0.24 mmol•L–1), dopamine infusion was of no benefit in the maintenance of renal function. It is possible that there may be a role for dopamine in patients with more severe levels of renal dysfunction preoperatively (creatinine levels greater than 0.2 mmol•L–1). It would seem that renal function may be protected to a large degree during cardiac surgery by attention to the maintenance of excellent perfusion pressure and circulation, optimum volume loading, and adequate cardiac output both during and after the operation. Because the causes of renal dysfunction in cardiac surgical patients are multifactorial, all methods of maintaining renal function are important and need to be considered individually.
Thus far, no reports have been able to show that dopamine improves renal function or prevents renal failure in patients undergoing cardiac surgery, either with normal preoperative renal function or with mild to moderate preoperative renal impairment. Hence the use of low-dose dopamine infusion to maintain renal function or prevent significant renal dysfunction or renal failure in patients undergoing cardiac surgery remains unclear but its role in patients with greater levels of renal dysfunction needs to be explored.
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Acknowledgments
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We thank Charuwan Kangkagate for her assistance with the statistics.
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References
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Abstract
Introduction
