Discussion
At the end of this study we determined that the creatinine levels of diabetic patients receiving insulin medication with normal creatinine and microalbuminuria increased significantly on the post-op 3rd day, when compared to the patients having oral antidiabetic medication.
It is known that cardiac surgery, which has been performed for many years in the world, is a risky and difficult discipline in mortality and morbidity compared to other surgical disciplines (16). Diabetes mellitus is accepted as an independent risk factor especially for coronary atherosclerosis, which concerns a wide age group(17). It is known that diabetes alone increases mortality and morbidity in coronary artery disease, both at younger ages and with more widespread involvement(18), and in coronary artery bypass operations(19). The following can be considered as main reasons for poor prognosis during and after surgery due to diabetes: Severe cardiac disease, subclinical insufficiency in renal functions in accompany, dehydration and electrolid disorders due to hyperglycemia, arrhythminogenic, and increased fatty acids that decrease myocardial oxygen demand(20,21). Since the effect of diabetes on coronary bypass surgery is known to increase mortality and morbidity, in our study, we aimed to investigate on type 2 diabetic patients using insulin and taking oral antidiabetics in terms of kidney functions and morbidity.
Today, most of the coronary artery bypass surgeries are performed on-pump. We have done all the operations we have performed on-pump. It is known that on-pump coronary artery bypass operations alone cause an increase in renal functions and are an important cause of morbidity(22). Loss of renal functions causes cardiac dysfunction, lung function impairment, wound healing problems, and prolongation of stay intensive care and hospital stays(23).
While microalbuminuria is seen as a marker of complications that develop in diabetic patients, it is considered a sign of diabetic nephropathy(24) and it is also known to increase early mortality in these patients(25). It is accepted as a marker of atherosclerosis, which is the cause of ischemic heart diseases in patients without diabetes(26).
While clinical studies investigating the effects of microalbuminuria on mortality and heart failure in cardiovascular diseases were previously conducted we aimed to investigate diabetic patients using insulin and taking oral antidiabetics(27). Studies on patients who had undergone coronary artery bypass surgery were generally compared on patient groups with and without microalbuminuria(28). In a study conducted by Kristina S. and al. in 2015, patients with microalbuminuria who have type 2 diabetes were compared with non-diabetic patients(29). In our searches we did not find a previous study comparing type 2 diabetes patients receiving insulin medication and taking oral antidiabetics.
In our study, we aimed to compare patients who underwent coronary artery bypass surgeries with type 2 diabetes patients receiving insulin treatments and patients taking oral antidiabetics all with normal creatinine values of microalbuminuria, which is one of the poor prognostic factors.
According to the results we obtained there were no statistically significant difference between the preoperative demographic data, preoperative microalbuminuria levels and perioperative cross clamp times, total pump times and bypass numbers of both groups.
When the postoperative durations of stay on the ventilator compared, there was no statistically significant difference between the groups although the durations were longer in the diabetic group receiving insulin treatment. There was no statistically significant difference between the amount of drainage. When the length of stay in intensive care unit and hospital stays were compared, there was no statistically significant difference, although the average of the diabetic group receiving insulin treatment was high.
No postoperative early mortality observed in both patient groups.
Mediastinitis developed in one patient who was in the diabetic group receiving insulin treatment. Mediastinitis is generally seen with a rate of 1-4%, and it is known that rates of non-healing wounds and mediastinitis are higher in diabetic patients receiving insulin treatment (30). In our study, the rate of mediastinitis was calculated as 1.25%. When only the group receiving insulin treatment was considered, the rate was found as 2.38%. When we evaluated this result, we thought that diabetes treatment with insulin may have a facilitating role for mediastinitis rather than microalbuminuria.
When the postoperative data are examined, it is seen that the most important difference is on renal functions. The mean preoperative creatine level of diabetic group taking oral antidiabetics was 0.88 ± 0.16, and the mean creatine level was 1.01 ± 0.18 on the postoperative 3rd day. The increase in between was found to be statistically significant (P <0.001). The mean preoperative creatine levels of diabetic group receiving insulin treatment were 0.93 ± 0.21, the mean postoperative day 3 creatine levels were found to be 1.33 ± 0.46, and the increase in creatine levels was also statistically significant (P <0.001). These two data showed that there was a significant increase in creatine levels after on-pump coronary artery bypass surgery of the type 2 diabetes patients using insulin and taking oral antidiabetics, with microalbuminuria.
When the preoperative creatinine values of both groups were compared, there was no statistically significant difference. When the increases in creatinine levels on the postoperative 3rd day were compared between the groups, there was a much higher increase in the diabetic group using insulin compared to the diabetic group taking oral antidiabetics, which was statistically significant (P <0.001). Acute renal failure developed in only one patient in the diabetic group using insulin who returned to normal with the treatment, without any need for dialysis. This shows us that creatine levels of diabetic patients receiving insulin treatment with microalbuminuria have a significant increase when compared to ones taking oral antidiabetics, and these patients even have the risk of acute renal failure.
As the conclusion of this study, we think that the presence of microalbuminuria in patients causes impairment in renal functions in the early postoperative period of on-pump coronary artery bypass operations, and this deterioration is much more severe in type 2 diabetes patients receiving insulin treatment. In addition, we think that the surgery of patients with microalbuminuria can be performed safely, since there is no difference between the durations of stay on the ventilator, the length of stay in intensive care unit and hospital stay, and the impairment of kidney functions can be treated with an effective intensive care treatment without the need for dialysis.
The number of patients included seems to be sufficient because only the patient group with microalbuminuria was determined as the target for our study however, we think that a larger patient group should be studied and the results should be compared with another study including patients with low ejection fraction.