Sunday, November 23, 2014
Blood Chemistry and Anesthesia
My 17-yr. old son is monitored by a nephrologist for hypertension and a kidney condition (Thin Basement Membrane). He has basic labs done every 6 months, his hypertension is well-controlled with medication, and his kidney function is very good. My question is this - when he goes for surgery w/general anesthesia (as he just did yesterday), what is most important for the anesthesiologist to know regarding kidney function? Yesterday the anesthesiologist was interested in my son`s creatine level and, fortunately, I had the latest labwork (from the nephrologist) with me, but it got me wondering what the most important values are to the anesthesiologist. Knowing this will allow us to best prepare for future surgeries. Thank you!
Thanks for the great question.
As you've realized, your anesthesiologist has an important role to play in maintaining the function of all your key organ systems - before, during and after surgery. Major surgery is a stress on those organ systems, including the kidneys. The kidneys are key players in the regulation and maintenance of the circulation, of electrolytes, of blood. Patients with poor kidney function, or kidney failure, tend to be among the sickest patients in a hospital, an operating room or an ICU, and the most at risk for unsatisfactory outcomes of surgery.
In general terms, when a patient has a medical condition and comes to the hospital for anesthesia and surgery, we need to know the cause of the problem or condition, its effects, the treatment for the condition, and the effects of the treatment.
So your anesthesiologist will want to know the exact cause of the kidney condition (thin basement membrane disease), the extent to which kidney function has decreased, the medications that are being taken, and whether those medications or treatments have had the desired beneficial effects, or expected or unintended side-effects.
Kidney function is usually estimated based on "BUN" (urea) and creatinine values measured in the blood, which reflect the kidney's abilities to clear waste from the body. These values can give you an estimated "creatinine clearance", a number which can also be more accurately determined by collecting urine and measuring the creatinine in the urine over a defined time period. Patients with kidney failure may produce little or no urine. In such cases, we have to be very careful not to unnecessarily administer large amounts of fluid. Kidney patients may also have abnormal values of calcium, phosphate, magnesium and potassium. An increased potassium can be extremely dangerous and is one of the things we almost always check immediately before anesthesia and surgery, along with blood glucose concentration, as many kidney failure patients have diabetes. Because of the circulation effects of kidney disease an electrocardiogram (ECG/EKG) is also commonly done.
Patients who are on dialysis normally should have a session of dialysis the day before their surgical procedure. The frequency and schedule of dialysis is important for the anesthesiologist to know, and ideally this information is accompanied by previous laboratory results to get a sense of what is normal for that patient. We also need to examine the patient's dialysis access, which may be a fistula or shunt, or a special intravenous line. These sites and devices must be carefully protected during and after surgery.
Knowing a person's kidney function helps the anesthesiologist to decide on which drugs to administer and in what doses. Not only anesthetic drugs but antibiotics and other medications. Kidney disease also influences the type and intensity of monitoring that is used, the potential need for blood transfusion, and postoperative care that may best be provided initially in the intensive care unit.
Just as important as the blood and other tests is a general physical examination and a comprehensive medical history that covers all the body systems. For that, you need to talk to your anesthesiologist ahead of the procedure or be seen in a preoperative clinic of some sort, or have your information sent to the hospital to be reviewed beforehand.
Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University