The effects of food intake during hemodialysis treatments

Debbie Eggers

Articles Reviewed in This Issue:

Barakat, M.M., Nawab, Z.M., Yu, A.W., Lau, A.H., Ing, T.S., & Daugirdas, J.T. (1993). Hemodynamic effects of intradialytic food ingestion and the effects of caffeine. Journal of the American Society of Nephrology, 3(11), 1813-1818.

Grodzicke, T., Rajzer, M., Fagard, R., O’Brien, E.T, Thijs, L., Clement, D., Davidson, C., Palatini, P., Parati, G., Kocemba, J., & Staessen, J.A. (1998). Ambulatory blood pressure monitoring and postprandial hypotension in elderly patients with isolated systolic hypertension. Journal of Human Hypertension, 12(3), 161-165.

Mon, C., Vazquez, A., Sanchez, R., Fernandez-Reyes, M.J., Alvarez, U de F. (1999). Significant reduction of delivered Kt/V by food intake during hemodialysis. Journal of the American Society of Nephrology, 10, 334A.

Shibagaki, Y., & Takaichi, K. (1998). Significant reduction of the large-vessel blood volume by food intake during hemodialysis. Clinical Nephrology, 49(1), 49-54.

Yu, A.W., Nawab, Z.M., Barnes, W.E., Kai, K.N., Ing, T.S., & Daugirdas, J.T. (1997). Splanchnic erythrocyte content decreases during hemodialysis: A new compensatory mechanism for hypovolemia. Kidney International, 51, 1986-1990.

The search for the following research articles originally started an effort to understand why some of outpatients had symptomatic hypotensive episodes. We also knew when we implemented “No Eating and Drinking on Hemodialysis” in our unit, both our patients and staff needed to understand the rationale for this new policy or from the compliance perspective we would fail. When I surveyed our Renalpro listserv, the overwhelming reason for not eating or drinking on hemodialysis was for infection control purposes. The other reason mentioned was the need to protect the patients from aspiration when they vomited due to their drop in blood pressure.

As we know, there have been major technological advances in dialysis, especially in the last 10 years. Yet, we still see our patients becoming symptomatically or asymptomatically hypotensive during hemodialysis treatments. Initially, practitioners” felt this phenomenon was due to patients’ reactions to nonbiocompatible filter membranes. We now have biocompatible membranes, this being indicated by patients maintaining some residual renal function long after hemodialysis treatments start. This suggests that biocompatibility is not the complete story. Another suggestion is, maybe we are trying to remove too much fluid too quickly. This is definitely a factor, but patients who have minimal fluid removal of 1.0 to 2.0 kg have hypotensive episodes when they eat during hemodialysis treatments.

There are a number of published articles demonstrating that postprandial hypotension is prevalent in elderly nondialysis patients, and this prevalence increases with age. The observed effects of eating on dialysis have long been known. Several studies e documented significantly faster decreases in blood pressure when hemodialysis patients were given food on dialysis. It was noted that patients who ingested food on dialysis required infusions of saline for their hypotensive episodes more often than those patients who remained NPO during hemodialysis. This information led many in the dialysis community to allow some patients to eat, yet restrict others. The following articles highlight the relationship between food consumption and the redistribution of blood from the large vessels to the splanchnic organs. Extrapolating this further; if the splanchnic circulation remains contracted when our patients stay NPO, then these patients should have a better total body clearance of nitrogenous wastes as a larger volume of blood is available for filtration.

One question we needed to ask was: “Are we doing our patients any favors allowing them to eat on hemodialysis?” Are we trying so hard to improve outpatients’ nutritional intake that we feel we cannot allow 4-6 hours without nourishment 3 times per week? Maybe we should be looking at this from a different perspective. If dialysis efficiency improves, will appetite improve to the point where they can enjoy their meals in the comfort of their home? Also, hemodialysis is a physiologically stressful treatment: Are our patients receiving any nutrient value from the food they eat during the dialysis treatment?

The following journal articles try to answer some of these questions. They also highlight areas for further research and discussion. It would be interesting to perform some of these studies with larger populations of patients. With the new technology of blood volume monitoring becoming easier and less” expensive, we will be able to assess outpatients” blood volume first hand.

Summary: It has long been documented that some patients have hypotensive episodes with food ingestion during hemodialysis. The mechanisms for this have not been clear. There has been a suggestion that it could be due to decreased cardiac output. This decreased cardiac output could be due to shifting of blood volume from the central circulation to the splanchnic circulation or to the vasorelaxation of the sphanchnic vessels. The splanchnic/splenic vascular bed is composed of the blood vessels supplying the liver, intestines, and the spleen.

It has also been demonstrated that caffeine blocks postprandial hypotension in the elderly with autonomic insufficiency in the nondialysis patient population. These researchers, using a double blind crossover trial, studied the effects of: placebo/no meal, placebo/meal, and caffeine/meal. Ten reasonably stable (non-hypotensive prone) chronic hemodialysis patients were studied. The researchers monitored the cardiac output of 10 hemodialysis patients who ingested a meal 1 hour into hemodialysis using thoracic electric bioimpedance. To standardize the treatments as much as possible, all ultrafiltration occurred within the first 2 hours of the treatment This also maximized the hypovolemic stress during and after the period of food ingestion. Bicarbonate dialysate was used.

During the treatments accompanied by ultrafiltration where food was ingested, the blood pressures were found to drop sooner and to a greater extent when compared to the smaller blood pressure drops when food was not ingested (e.g., at 30 minutes after food ingestion, percent change in mean arterial pressure [MAP] was -12.4 + 1.8 mmHg versus -2.4 + 3.5 mmHg when food was not ingested). Essentially, the mechanism for food ingestion-related hypotension was related to a drop in systemic vascular resistance (SVR). The caffeine pretreatment of 200 mg resulted in intradialytic plasma caffeine levels of 4 micrograms/mL at the time of food ingestion. The caffeine appeared to have no effect on food-associated drops in blood pressure or SVR. The researchers felt the results suggested that food ingestion during hemodialysis caused hypotension mainly due to the decrease in SVR. The ingestion of caffeine did not appear to have any effect on either the MAP or SVR during the hemodialysis treatment.

Commentary: This article evaluated the effects of caffeine on postprandial hypotension in dialysis patients. It has been shown thai caffeine can block the postprandial effects in elderly nondialysis patients through its theoretical vaso-constrictive activity. In hemodialysis patients, caffeine failed to block the accelerated drop in MAP following food ingestion and did not block the SVR observed following food ingestion during their treatments. The researchers did wonder if sufficient caffeine may have been dialyzed out in the first 2 hours of dialysis, leaving insufficient caffeine to exert an effect. It appears that the ingestion of food during dialysis caused an accelerated fall in blood pressure. This study showed that the fall in MAP was due to a decrease in SVR. The results of this research confirmed the results of earlier studies by Sherman, Tortes, and Cody (1988) and Zoccali, Mallamaci, Ciccarelli, mad Maggiore (1989). The results also demonstrated that the mechanism for the hypotensive episodes was related to a decrease in SVR.

Summary: These researchers monitored postprandial changes in blood pressure using ambulatory BP monitoring (ABPM) in elderly subjects with only isolated systolic hypertension (ISH) seen on conventional measurement. The sample consisted of 530 subjects, with a median age of 70. Essentially, the researchers found that the mean systolic BP and diastolic BP decreased and reached their lowest points 2 hours after the meal, while the pulse did not alter.

In conclusion, the descriptive analysis of the meal-induced changes in ABPM in elderly subjects with ISH showed that in everyday circumstances most experienced decreases in both SBP and DBP within 2 hours after a meal.

Commentary: This article was interesting as it demonstrated that nondialysis elderly subjects with hypertension are subject to postprandial BP drops within 2 hours of eating. Registry data indicate that our dialysis population is aging and the majority of these patients have hypertension. These patients need to be protected from the possibility of symptomatic hypotensive events.

Moll, C., Vazquez, A., Sanchez, R., Fernandez Reyes, M.J., Alvarez, U de F. (1999). Significant reduction of delivered Kt/V by food intake during hemodialysis, Journal of the American Society of Nephrology, 10, 334A,

Summary: Other researchers have demonstrated that food intake during hemodialysis has been related to postprandial hypotension. This study looked at the relationship between food intake and measurement of Kt/V. The question asked by the researchers was: “Is there a relation between food intake during HD and changes of Kt/V?”

Fourteen subjects (8 males and 6 females) with a mean age of 60 years (range 46 to 79 years) were studied. The subjects received hemodialysis three times a week. Session length ranged between 210 to 240 minutes, dialysate flow was 500 ml/min, and blood flow was between 350-400 ml/min. All the subjects were clinically stable. The principle causes of chronic renal failure were: chronic glomerulonephritis (6), interstitial nephritis (6), hypertension (1), and polycystic kidney disease (1).

The researchers measured Kt/V (using the Gotch formula, Sargent formula, and Daugirdas formula), urea reduction ratio (URR), time averaged urea concentration (TAC), protein catabolic rate (PCR), intradialytic weight gain (IWG), cramps, and symptomatic hypotension in the second section of the week, with and without food intake during hemodialysis. The time between sets of measures was 1 week. Predialysis blood was drawn from the arterial needle prior to connecting and postdialysis blood was drawn by slowing the blood pump to 50 ml/min and then obtaining the blood sample 2 minutes later. Each meal con mined 20 grams of protein. Statistical analysis was performed using paired t-test and Wilcoxon test. A p value less than 0.05 was regarded as significant.

There was no significant change in PCR, TAC, IWG, and URR (p = 0.057) levels. However, there was a significant change in levels of Kt/V. Kt/V using the Gotch formula with food intake was mean: 1.28 + 0.2, Kt/V; no food intake, [bar.X] = 1.35 + 0.22 (p = 0.021); Kt/V using Daugirdas formula with food intake, [bar.X] = 1.54 + 0.29; no food intake, [bar.X] = 1.65 + 0.35 (p = 0.037). These subjects did not report symptomatic hypotension and cramps in any session.

The results of this study indicated that food intake during hemodialysis changed clearance. A possible explanation given for this finding was the redistribution of the blood from the large vessels to the splanchnic organs transiently during food intake.

Commentary: This article suggests that more research could be very useful in order to improve dialysis efficiency. During food ingestion, the dialysis efficiency is diminished as there was less blood available at a given time to be filtered. In other words, the dose of the treatment was altered during this period of time as a large amount of blood was diverted into the splanchnic circulation.

One notable outcome of this study was that there was no measurable difference in PCRs between the eating and noneating group of subjects. Another outcome of this study demonstrated that subjects who did not eat on dialysis achieved higher levels of Kt/V (when measured by the Gotch, Sargent, or Daugirdas formula) than subjects who did eat on dialysis.

Shibagaki, Y., & Takaichi, K. (1998). Significant reduction of the large-vessel blood volume by food intake during hemodialysis. Clinical Nephrology, 49(1), 49-54.

Summary: The principle mechanisms of postprandial hypotension are felt to be due to the reduction in systemic vascular resistance and the shifting of circulating blood to the splanchnic organs. This leads to a decrease in the blood volume to the large vessels, hence a decrease in cardiac output. The researchers set out to monitor changes in blood volume by monitoring the subjects’ hematocrits (Hcts). The Hct of the large vessels is expected to increase with ultrafiltration and peripheral shift of the blood because Hct of the peripheral vessels is much less than the Hct of the large vessels.

Twenty-one clinically stable subjects were chosen for this study. To analyze the effects of food intake during hemodialysis on blood volume (BV) of the large vessels quantitatively, the researchers monitored Hct of the arteriovenous shunt blood continuously in the subjects treated with hemodialysis regularly and estimated BV using the following equation: BV/initial BV = initial Hct/Hct. The rate of ultrafiltration was kept constant during the study. The reduction rate of BV was expressed as a percentage of the initial BV per hour (delta BV). The researchers looked at the effect of eating on dialysis in both the supine and sitting positions.

The researchers concluded that food intake during hemodialysis decreases the blood volume of the large vessels transiently but significantly. They also found that the effects of food intake on blood volume were nitre severe when the meal was taken in a sitting position than those when the meal was taken in a supine position.

Commentary: This article is consistent with a means of monitoring that a nonresearch funded dialysis unit could use to see the effects of eating on dialysis, as BV monitoring is increasingly more affordable.

In our dialysis unit, we trialed a machine with BV monitoring before we introduced our “No eating and drinking policy.” We chose one of our patients who we knew was sensitive to eating on dialysis and on whom it was also very difficult to remove fluid. All of a sudden, in the first half-hour of his run, we noticed a significant drop in his BV as displayed by graft on the machine (BP still maintained at this stage). The patient admitted to eating a muffin when we were otherwise occupied. Our patient took an immediate interest in this event such that for the next few runs we all varied the food and fluids. All ingested items had a similar effect. The only time he had a slow and stable decrease in BV was when he did not ingest any food.

Summary: These researchers studied the changes hi the splanchnic/splenic venous capacity during hemodialysis, with and without fluid removal. They also studied the integrity of the autonomic nervous system (ANS) associated with splanchnic blood pooling by focusing on the parasympathetic activity as measured by die spontaneous variations of the R-R interval during deep inspiration and by the Valsalva ratio. Subjects chosen for this study were not expected to have ANS dysfunction. A decrease in sphanchnic capacity during hypovolemia in a variety of clinical conditions is known to occur, either by a reduced inflow or too active vasoconstriction. The spleen can contract on a change in position from supine to upright and during exercise, helping to maintain central blood volume mid hence cardiac output. Eight nondiabetic, nonhypotension-prone patients were studied. The researchers tagged erythrocytes with technetium to follow the movement of the venous blood volume in dialysis associated with and without fluid removal. This study demonstrated that the splanchnic radioactivity decreased only during dialysis associated with fluid removal. Splenic radioactivity did not have a statistically significant decrease. Subjects also appeared to have intact autonomic reflexes controlling their heart rates.

Commentary: This article examined the splanchnic vascular bed response to ultrafiltration compared to nonultrafiltration dialysis. The results suggested that patients maintain their central blood volume, hence cardiac output and BP during ultrafiltration. This is achieved by the con traction of the sphanchnic vascular bed (and possibly the splenic vascular bed), forcing more erythrocytes into the central circulation.

Summary

Most of the above studies have one major weakness: the number of patients studied was very small or in statistical terms the samples are small. The studies appear to support the idea that dialysis patients, notably the elderly, would have better overall outcomes if they did not have food on dialysis.

Additional References

Sherman, R.A., Tortes, F., & Cody, R.P. (1988). Postprandial blood pressure changes during hemodialysis. American Journal of Kidney Diseases, 12(1), 37-39.

Zoccali, C., Mallamaci, F., Ciccarelli, M., & Maggiore, Q. (1989). Postprandial alterations in arterial pressure control during hemodialysis in uremic patients. Clinical Nephrology, 31(6), 323- 326.

Debbie Eggers, BSc, BScN, RN, CNeph(C), is a Patient Care Specialist, Hemodialysis/Renal Health Clinic, Kelowna, British Columbia, Canada.

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