Renal Physiology and Anesthesia

Effects of Anesthesia and Surgery

• General: Reversible decreases in RBF, GFR, urinary flow, and sodium excretion occur during both regional and general anesthesia. Such changes are less pronounced during regional anesthesia. These effects can be partially overcome by maintenance of adequate intravascular volume and a normal blood pressure.

• Cardiovascular effects: Most intravenous and inhalational agents cause some degree of cardiac depression or vasodilation and therefore are capable of decreased systemic blood pressure. Neuraxial anesthesia can produce similar drops in systemic blood pressure. These blood pressure changes cause adverse effects on renal function if outside the limits of autoregulation.

• Neural effects: Heightened sympathetic activity increases renal vascular resistance and reduces RBF, GFR, and urine output.

• Endocrine effects: Catecholamines, ADH, and angiotensin II all reduce RBF by inducing renal arterial constriction. Aldosterone enhances sodium reabsorption in the distal tubule and collecting tubule, resulting in expansion of the extracellular compartment. The endocrine response to surgery is at least partly responsible for transient postoperative fluid retention seen.

• Volatile agents: Decrease renal vascular resistance. Compound A, a breakdown product of sevoflurane at low flows, has been shown to cause renal damage in laboratory animals.

• NSAIDs: Prevent prostaglandin synthesis and may result in AKI.

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