Chapter 31

• The combined blood flow through both kidneys normally accounts for 20–25% of total cardiac output.
• Autoregulation of renal blood flow normally occurs between mean arterial blood pressures of 80 and 180 mm Hg.
• Renal synthesis of vasodilating prostaglandins (PGD2, PGE2, and PGI2) is an important protective mechanism during periods of systemic hypotension and renal ischemia.
• Dopamine and fenoldopam dilate afferent and efferent arterioles via D1-receptor activation. Fenoldopam and low-dose dopamine infusion can at least partially reverse norepinephrine-induced renal vasoconstriction.
• Reversible decreases in renal blood flow, glomerular filtration rate, urinary flow, and sodium excretion occur during both regional and general anesthesia. These effects can be at least partially overcome by maintenance of an adequate intravascular volume and a normal blood pressure.
• The endocrine response to surgery and anesthesia is probably at least partly responsible for the transient postoperative fluid retention that is seen in many patients.
• Methoxyflurane has been associated with a syndrome of polyuric renal failure. Its nephrotoxicity is dose related and is the result of release of fluoride ions from its metabolic degradation.
• High plasma fluoride concentrations following prolonged enflurane anesthesia may also occur in obese patients and those receiving isoniazid therapy,
• Compound A, a breakdown product of sevoflurane that is formed at low flows, can cause renal damage in laboratory animals. Clinical studies have not detected significant renal injury in humans during sevoflurane anesthesia.
• Certain surgical procedures can significantly alter renal physiology. The pneumoperitoneum produced during laparoscopy produces an abdominal compartment syndrome–like state. The increase in intraabdominal pressure typically produces oliguria (or anuria). Other surgical procedures that can significantly compromise renal function include cardiopulmonary bypass, cross-clamping of the aorta, and dissection near the renal arteries.

The kidneys play a vital role in regulating the volume and composition of body fluids, eliminating toxins, and elaborating hormones such as renin, erythropoietin, and the active form of vitamin D. Surgery and anesthesia can have important effects on renal function. Failure to take these effects into consideration could result in serious errors in patient management. Fluid overload, hypovolemia, and postoperative renal failure are major causes of postoperative morbidity and mortality.

Diuretics are an important class of drugs that is frequently employed in the perioperative period. Preoperative diuretic therapy is common in patients with hypertension and with cardiac, hepatic, and renal disease. Diuretics are also used intraoperatively, particularly during neurosurgical, cardiac, major vascular, ophthalmic, and urological procedures. Familiarity with the various types of diuretics, their mechanisms of action, side effects, and potential anesthetic interactions is therefore essential.

Each kidney is made up of approximately 1 million functional units called nephrons. Anatomically, a nephron consists of a tortuous tubule with at least six specialized segments. At its proximal end (Bowman’s capsule), an ultrafiltrate of blood is formed, and as this fluid passes through the nephron, its volume and composition are modified by both the reabsorption and the secretion of solutes. The final product is ...

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