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KEY CONCEPTS

KEY CONCEPTS

  • Image not available. The combined blood flow through both kidneys normally accounts for 20% to 25% of total cardiac output.

  • Image not available. Autoregulation of renal blood flow normally occurs between mean arterial blood pressures of 80 and 180 mm Hg and is principally due to intrinsic myogenic responses of the afferent glomerular arterioles to blood pressure changes.

  • Image not available. Renal synthesis of vasodilating prostaglandins (PGD2, PGE2, and PGI2) is an important protective mechanism during periods of systemic hypotension and kidney ischemia.

  • Image not available. Dopamine and fenoldopam dilate afferent and efferent arterioles via D1-receptor activation.

  • Image not available. Reversible decreases in renal blood flow, glomerular filtration rate, urinary flow, and sodium excretion occur during both neuraxial and general anesthesia. Acute kidney injury is less likely to occur if adequate intravascular volume and normal blood pressure are maintained.

  • Image not available. The endocrine response to surgery and anesthesia is at least partly responsible for the transient fluid retention often seen postoperatively.

  • Image not available. Compound A, a breakdown product of sevoflurane, causes acute kidney injury in laboratory animals. Low fresh gas flow rates promote its accumulation in the anesthesia machine breathing circuit. No clinical study has detected significant kidney injury in humans as a consequence of sevoflurane anesthesia; nonetheless, some authorities recommend a fresh gas flow of at least 2 L/min with sevoflurane to minimize the risk of this theoretical problem.

  • Image not available. Pneumoperitoneum produced during laparoscopy causes an abdominal compartment syndrome–like state. The increase in intraabdominal pressure often produces oliguria or anuria that is generally proportional to insufflation pressure. Mechanisms include vena cava and renal vein compression; kidney parenchymal compression; decreased cardiac output; and increases in plasma levels of renin, aldosterone, and antidiuretic hormone.

The kidneys play a vital role in regulating the volume and composition of body fluids, eliminating toxins, and elaborating hormones, including renin, erythropoietin, and the active form of vitamin D. Factors directly and indirectly related to operative procedures and to anesthetic management frequently have a physiologically significant impact on kidney physiology and function, and may lead to perioperative fluid overload, hypovolemia, and acute kidney injury, which are major causes of perioperative morbidity and mortality.

Diuretics are frequently used in the perioperative period. They are commonly administered on a chronic basis to patients with hypertension or chronic heart failure, and to patients with liver or kidney disease. Diuretics may be used intraoperatively, typically during neurosurgical, cardiac, major vascular, ophthalmic, and urological procedures. Familiarity with the various types of diuretics and their mechanisms of action, side effects, and potential anesthetic interactions is therefore essential.

THE NEPHRON

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. In the renal corpuscle, a structure at its proximal end composed of a glomerulus and a Bowman’s capsule, an ultrafiltrate of blood is formed which flows through the nephron’s tubules. During ...

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