- 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 and is principally due to intrinsic myogenic responses of the afferent glomerular arterioles to blood pressure changes.
- 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. Acute kidney injury is less likely if an adequate intravascular volume and a normal blood pressure are maintained.
- The endocrine response to surgery and anesthesia is at least partly responsible for transient fluid retention seen postoperatively in many patients.
- Compound A, a breakdown product of sevoflurane, has been shown to cause renal damage in laboratory animals. Its accumulation in the breathing circuit is favored by low flow rates. No clinical study has detected significant renal injury in humans during sevoflurane anesthesia; nonetheless, some regulatory authorities recommend fresh gas flow of at least 2 L/min with sevoflurane to prevent this theoretical problem.
- The pneumoperitoneum produced during laparoscopy causes an abdominal compartment syndrome-like state. The increase in intraabdominal pressure typically produces oliguria (or anuria) that is generally proportional to the insufflation pressures. Mechanisms include central venous compression (renal vein and vena cava); renal 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 renal physiology and renal function, and may lead to perioperative fluid overload, hypovolemia, renal insufficiency, and kidney failure, which are major causes of perioperative morbidity and mortality.
Diuretics are frequently used in the perioperative period. Diuretics are commonly administered on a chronic basis to patients with cardiovascular disease, including hypertension and chronic heart failure, and to patients with liver and kidney disease. Diuretics may be 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 (the renal corpuscle, composed of a glomerulus and a Bowman’s capsule), an ultrafiltrate of blood is formed, and as this fluid passes through the nephron, its volume and ...