Hemodialysis Research Paper

Sodium, Hypertension, and an Explanation of "Lag Phenomenon" in Hemodialysis Patients
Author: Zbylut Twardowski, MD, PhD

I. INTRODUCTION

Healthy kidneys clean your blood by removing excess fluid, minerals, and wastes. They also make hormones that keep your bones strong and your blood healthy. When your kidneys fail, harmful wastes build up in your body, your blood pressure may rise, and your body may retain excess fluid and not make enough red blood cells. When this happens, you need treatment to replace the work of your failed kidneys. (National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health, 2011). When kidney disease progresses, it may eventually lead to kidney failure, which requires dialysis or a kidney transplant to maintain life. (National Kidney Foundation, 2012).

When you have chronic kidney disease, you need to
make changes in your diet, including: limiting fluids, eating a low-protein diet (this may be recommended), restricting salt, potassium, phosphorous, and other electrolytes, and getting enough calories if you are losing weight. Your recommended diet may change over time if your kidney disease gets worse, or if you need dialysis. Reducing sodium in your diet helps you control high blood pressure, keeps you from being thirsty, and prevents your body from holding onto extra fluid. You will probably need to eat a low-salt diet. (U.S. National Library of Medicine, National Institute of Health, September 2011).

II. DISCUSSION

Sodium balance is precisely regulated by intake and output. The kidneys are responsible for adjusting sodium excretion to maintain balance at varying intakes. Our distant ancestors were herbivores. Their diet contained little sodium, so they developed powerful mechanisms for conserving sodium and achieving low urinary excretion. About 10,000 years ago, early humans became villagers and discovered that food could be preserved in brine. This led to increased consumption of salt. High salt intake increases extracellular volume (ECV), blood volume, and cardiac output resulting in elevation of blood pressure. High ECV induces release of a digitalis-like immunoreactive substance and other inhibitors of Na(+)-K(+)-ATPase. As a consequence, intracellular sodium and calcium concentrations increase in vascular smooth muscles predisposing them to contraction. Moreover, high ECV increases synthesis and decreases clearance of asymmetrical dimethyl-l-arginine leading to inhibition of nitric oxide (NO) synthase. High concentration of sodium and calcium in vascular smooth muscles, and decreased synthesis of NO lead to an increase in total peripheral resistance. Restoration of normal ECV and blood pressure are attained by increased glomerular filtration and decreased sodium reabsorption. In some individuals, the kidneys have difficulty in excreting sodium, so the equilibrium is achieved at the expense of elevated blood pressure. There is some lag time between reduction of ECV and normalization of blood pressure because the normal levels of Na(+)-K(+)-ATPase inhibitors and asymmetrical dimethyl-l-arginine are restored slowly. In dialysis patients, all mechanisms intended to increase renal sodium removal are futile but they still operate and elevate blood pressure. The sodium balance must be achieved via dialysis and ultrafiltration. Blood pressure is normalized a few weeks after ECV is returned to normal, i.e., when the patient reaches dry body weight. This is called the "lag phenomenon."

III. RELEVANCE

Dr. Twardowski elegantly detailed the complex interplay among sodium intake, fluid overload, hypertension, and the "lag phenomenon" in maintenance hemodialysis patients. It is well-known that excessive sodium intake in hemodialysis patients with negligible or absent renal function can bring about hypervolemia, hypertension, cardiac dysfunction and a resultant high mortality (1). In addition, excessively fast ultrafiltration during hemodialysis has been demonstrated to lead to transient hypovolemia, hypotension as well as an array of harmful manifestations (2). The great benefits of salt restriction and proper ultrafiltration were also aptly emphasized by Dr. Twardowski in the present communication. Analysis of USRDS Waves 3 and 4 showed that weight gain between hemodialysis sessions of greater than 4.8% (ie, 3.4 kg in a 70-kg person), a reflection of excessive sodium and water intakes, was accompanied by an increased mortality rate (3). A longer dialysis treatment time and a slower ultrafiltration rate have also been found to be associated with a reduced mortality (4). Strict limitation of daily sodium intake to less than 5 grams of sodium chloride (ie, 2 grams or 85 millimoles of sodium) has been recommended in hemodialysis patients [exceptions being those patients who lose a substantial amount of sodium in their urines and/or via extrarenal routes] by the KDOQI hemodialysis adequacy guidelines (5). Similar sodium restriction approaches have long been championed by Scribner (6), Shaldon (7), Charra (8) and many others. (Ing, 2012).

IV. IMPLICATION OF THE STUDY, CONCLUSION, GENERALIZATION

Hemodialysis is the most common method used to treat advanced and permanent kidney failure.
Since the 1960s, when hemodialysis first became a practical treatment for kidney failure, we 've learned much about how to make hemodialysis treatments more effective and minimize side effects. In recent years, more compact and simpler dialysis machines have made home dialysis increasingly attractive. But even with better procedures and equipment, hemodialysis is still a complicated and inconvenient therapy that requires a coordinated effort from the whole health care team, including a nephrologist, dialysis nurse, dialysis technician, dietitian, and social worker. The most important members of the health care team are the patient and his family. Nurses, as a member of the health care team, should be able to reinforce to the patients the importance of compliance to treatment regimen especially on sodium restrictions. Reinforcing and making the aware about it will enable them to work with the health care team to give themselves the best possible results, and they can lead themselves to a full, active
life.

REFERENCES: 1. National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health. December 2011. NIH Publication No. 07-4666. Retrieved from http://kidney.niddk.nih.gov/kudiseases/pubs/hemodialysis/ 2. National Kidney Foundation. 2012. Retrieved from http://www.kidney.org/kidneydisease/aboutckd.cfm 3. Lin HY., U.S. National Library of Medicine, National Institute of Health. September 2011. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/002442.htm 4. Twardowski ZJ., (2008). Sodium, hypertension, and an explanation of "lag phenomenon" in hemodialysis patients. Hemodial Int. 2008;12(4):412-25. Retrieved from http://ishd.net/abstracts.php?article=20090128 5. National Kidney Foundation: KDOQI clinical practice guidelines and clinical practice recommendations for hemodialysis adequacy, 2006 updates (Guideline 5. Control of volume and blood pressure). Am J Kidney Dis. 2006;48, No 1, Suppl 1:S1-90. 6. Blumberg A, Nelp WB, Hegstrom RM, Scribner BH. Extracellular volume in patients with chronic renal disease treated for hypertension by sodium restriction. Lancet. 1967;2(7506):69-73. 7. Shaldon S, Ozkahya M, Ok F, Basci A, Dornhout Mees EJ. The long forgotten salt factor. Kidney Int. 2008;76:759-64. 8. Charra B, Chazot C. The neglect of sodium restriction in dialysis patients: A short review. Hemodial Int. 2003;7:342-7. 9. Ing, TS. International Society for Hemodialysis. July 2012. Retrieved from http://ishd.net/abstracts.php?article=20090128