Coronary artery bypass graft, or CABG, carries serious risks for all your body systems. After surgery, critical care nurses closely monitor your vital signs and lab work while continuously assessing your body systems, including urine output from the kidneys. Depending on the type of CABG performed, your kidneys will have a greater or lesser chance of failure.
Basics
One type of heart bypass surgery calls for your heart to be stopped during the procedure while a heart and lung machine circulates and oxygenates your blood; another type allows your heart to continue to beat while the surgeons work around it. In the first case, after the new blood vessel grafts are sewn into place on your arteries, your heart is restarted. In both surgeries, if everything goes well, you are wheeled into the hospital's coronary critical care unit and monitored closely for signs of distress. A strong indicator of a successful surgery is urine output by your kidneys.
Urine Quantity and Characteristics
Critical care nurses monitor your lab values, including the blood urea nitrogen level, or BUN. If a spike occurs, it indicates that your kidneys are compromised or beginning to shut down. The color of your urine is also a big indicator that the kidneys cannot filter out the medications as well as they should. The darker and more concentrated the urine, the more likely the kidney compromise. While you probably would not produce your usual amount of urine immediately after surgery due to pre-surgical fluid restrictions, you should still produce about 30 ml or roughly 2 tbsp. of urine an hour, states Meg Gulanick in her book, "Nursing Care Plans." If your urine produced falls below this these numbers for a couple of hours, the nurse will notify your surgeon.
Effects
Other factors will also indicate that your kidneys are not functioning optimally. As fluids cannot be flushed out of your body, they back up in your tissues. Your arteries fill up with more fluid, which causes your blood pressure to rise. Another factor to watch for is edema, or swelling from retained fluids, which can occur in your feet, legs and hands. Initially, your heart rate may speed up as your heart tries to combat the extra fluid that the kidneys cannot clear from the body; the heart will pump more vigorously.
Stress of Heart Restart
When the heart is restarted after bypass, any stagnant blood left in the heart rushes to the kidneys. This blood may contain medications, such as blood thinners and anti-hypertensive drugs. When that blood is combined with fresher blood and more of those same IV medications, it can overwhelm the kidneys' filtering capabilities. The good news is that while you are still in the critical care unit, you can receive a quick one-time kidney dialysis to offer some help to the kidneys' filtering functions.
Speculation
The University of Chicago Medical Center reports that CABG surgery performed while your heart beats, instead of stopping the heart and using the traditional heart and lung pump, may lower your risk of kidney failure. A Nov. 2009 report by ABC News showed that some doctors prefer off-pump surgery if their patients already have compromised kidney function. When it comes time for you to choose between off-pump or on-pump surgery, make sure you discuss all the risks and benefits with your doctor.
References
- University of Chicago Medical Center: Beating Heart, Off-Pump Coronary Artery Bypass Surgery
- "Nursing Care Plans, Nursing Diagnosis and Intervention"; Meg Gulanick, Ph.D., R.N., Judith L. Myers, M.S.N., R.N., 2003
- "Critical Care Nursing"; Judith A. Schilling McCann, RN, MSN; 2007
- ABC News: Beating Heart Bypass Surgery May Be Riskier
