HEMODYNAMIC-EFFECTS OF INTRADIALYTIC FOOD INGESTION AND THE EFFECTS OF CAFFEINE

Although the hypotensive effects of food ingestion during hemodialysis have been documented, the hemodynamic mechanism is unclear. It could be decreased cardiac output due to splanchnic sequestration or decreas ed vascular resistance due to splanchnic vasorelaxation. Also, the eff ects of caffeine, which block postprandial hypotension in the elderly, have not been studied in a dialysis setting. Central hemodynamics wer e monitored by thoracic electric bioimpedance in 10 dialysis patients who ingested a test meal 1 h into dialysis. All ultrafiltration was do ne during the initial 2 h. Bicarbonate dialysate was used. Each patien t was studied three times in a double-blind (with respect to placebo/c affeine) cross-over trial: placebo/no meal, placebo/meal, and caffeine /meal. Blood pressure decreased sooner and to a greater extent in the treatments in which food ingestion accompanied ultrafiltration (e.g., at 30 min after food ingestion, percent change in mean arterial pressu re was -12.4 +/- 1.8 versus -2.4 +/- 3.5 mm Hg when food was not inges ted; P < 0.05). The hemodynamic mechanism of food-associated hypotensi on was found to be a fall in systemic vascular resistance (SVRI). Caff eine pretreatment (200 mg), which resulted in intradialytic plasma caf feine levels of about 4 mug/mL at time of food ingestion, had no effec t on food-associated reductions in blood pressure or SVRI. The results suggest that food ingestion during dialysis causes hypotension primar ily because of decreased SVRI. The effects of food ingestion on mean a rterial pressure and SVRI are not attenuated by the ingestion of 200 m g of caffeine 1 h before dialysis.