Introduction

Renal function in the peri-operative period is often misunderstood. It is considered synonymous with the patient making “good urine”. Treatment of renal dysfunction is also centered on methods to make urine appear. Understanding renal dysfunction requires a more analytic and physiologic approach to the patient, that is even more important in the morbidly obese patient who has other anatomical and physiologic variations.

We will review basic renal physiology and pathophysiology and its alterations in both the non-obese and obese patient as they relate to renal ischemia, pre-operative risk factors for developing post-operative acute renal failure (ARF), and finally, non-dialytic and dialytic modalities.

Basic renal physiology and pathophysiology

The kidney primarily functions to maintain internal homeostasis by regulating effective arterial blood volume (EABV), osmolality and ionic composition, and to concentrate and excrete the daily endogenous and exogenous load of nitrogenous waste. These actions are achieved by a complex interplay between glomerular filtration, tubular reabsorption and tubular secretion. The kidney also plays a vital role as an organ of endocrine function, regulating both red blood cell mass by the production of erythropoietin, and calcium and phosphorus homeostasis through the synthesis of vitamin D to its most active form, 1,25-dihydroxycholecalciferol.