Renal Physiology Lesson 7 PDF

Kidneys = paired organs located in the retroperitoneal cavity against the abdominal wall Each kidney has 1 million nephrons Hilus = where nerves and arteries exit organ Kidneys receive 20-25% of CO Renal blood flow (RBF) and glomerular filtration are autoregulated i.e. RBF and GFR remain constan...

Kidneys = paired organs located in the retroperitoneal cavity against the abdominal wall Each kidney has 1 million nephrons Hilus = where nerves and arteries exit organ Kidneys receive 20-25% of CO Renal blood flow (RBF) and glomerular filtration are autoregulated i.e. RBF and GFR remain constant between 60-150 mmHg Positioning affects kidney position -- think steep T in robot surgery BP will be higher in the head/arm and lower in the kidney Functions of the kidney - Filter blood - Maintain proper sodium water balance - Maintain/regulate electrolyte homeostasis (primarily calcium and phosphorous) - Ca and Phos are antagonists - Bone metabolism - Erythropoiesis -- kidneys make EPO - EPO creates RBCs - RBCs transport oxygen via Hgb - Control of systemic BP - RAAS - Renin secreted by the kidneys - Renin angiotensinogen by liver angiotensin 1 converted to angiotensin 2 by ACE in lungs - Angiotensin 2 is a vasoconstrictor - ACEI = Angiotensin converting enzyme inhibitor works in lungs - ARBS = angiotensin receptor blocker works in blood vessels - Aldosterone is secreted by the adrenal glands and causes kidneys to reabsorb sodium and water into the blood to increase BP - Macula densa stops secretion of aldosterone once enough sodium and water reabsorbed Adrenal glands secrete -- salt, sugar, sex Anatomy & Physiology: GFR determinants \| ditki medical & biological sciences - Urine output - Daily output 400-500 is required to excrete nitrogenous waste - Preference is 1 mL/kg/hr - Oliguria = less than 0.5 mL/kg/hr - In absence of renal disease, low renal perfusion and decreased GFR is due to hypovolemia and renal vasoconstriction - Innervation of the kidney - Via autonomic NS - PSNS input comes from vagus nerve - SNS Increases in renal sympathetic nerve activity regulate the functions of the nephron, the vasculature, and the renin-containing juxtaglomerular granular cells - Sympathetic tone of the kidneys - Little sympathetic tone in non-stressed state - Mild-moderate stress = RBF decreases, efferent arterioles constrict to maintain GFR - Severe stress and high dose epi and NE = decrease in RBF and GFR - Severe stress e.g. hypovolemia, hypoxia, hypercarbia, trauma - Why do we care about kidney perfusion relating to medications? Many medications are metabolized by the liver and excreted renally. Impairment could affect both active metabolites and overall excretion of medications resulting in prolonged duration of action - Afterload and SVR are not synonymous - In healthy pts, they are - In temporary aortic clamp, afterload can be elevated but SVR won't be - Acute renal failure (ARF) - Significant decrease in GFR over 2 weeks or less - Incidence in aortic surgery = 8% - Supraceliac (most involved) and suprarenal clamps are above the kidney - Cardiopulmonary bypass decreases RBF by 30% - Infrarenal AKI results in least amount of change - Prevention - Diuretics - Renal dose dopa - Nitroglycerin to dilate capacitance vessels - At risk for ARF - Pre-existing renal disease - CHF - Advanced age - Prolonged renal hypoperfusion e.g. hypovolemia, hypotension - High risk surgery e.g. abdominal aneurysm, cardiopulmonary bypass - Extensive burns - Sepsis - Jaundice - Chronic renal failure = progressive decrease in number of functioning nephrons - Patients with 60% of nephrons are asymptomatic - Renal insufficiency = 15-40% functioning nephrons - Renal failure = less than 15% functioning nephrons - Chronic renal failure characteristics -- think CAFÉ - CAFÉ = coagulopathy, anemia, fluids, electrolytes - Coagulopathy - Thrombocytopenia - Impaired platelet function - Metabolic acidosis affects coagulation factors III and VIII - Assess pt's bleeding time with creatinine levels 6mg/dL - Bleeding time can be reversed with hemodialysis - Pt's other labs can be normal (e.g. CBC , PT, and APTT) but not show platelet function - Pt's should have hemodialysis within 24 hours of surgery to be optimized - Anemia - Urea that is not secreted causes decreased production of EPO - Decreased half life of RBCs by 50% - Hgb 6-7 g/dL - Fluids - Fluid overload can lead to pulmonary edema and CHF - Strict fluid control via buritrol, microdrip sets, dial-a-flow - Replace blood loss with blood at 1:1 ratio - Do not use LR because it contains potassium - Use NS or D5W - Electroyltes - Renal patients have problems regulating electrolytes - You will see hyperkalemia, hypermagnesemia, and hypocalcemia - Potassium levels control resting membrane potential (RMP) across cell membrane - RMP is the starting point for action potentials - Hyperkalemic - Acidosis will lead to increase in H+ and therefore hyperkalemia - ECG changes = peaked T waves, prolonged PR, wide QRS, heart block, ventricular fibrillation - Treatment for hyperkalemia - K\> 6.5 mEq/L - Ventilation -- hyperventilation to reduce H+ - Albuterol -- Stimulating beta 2-adrenergic receptors, Increasing intracellular potassium uptake - Insulin/dextrose - Bicarbonate - Dialysis - Magnesium plays a role in muscle/nerve function, protein synthesis, stabilize RMP - Risk factors for hypermagnesemia = antacid and laxative use - Hypermagnesemia can cause hypotension - Calcium - Impaired ability of kidney to activate vitamin D from the GI tract - Calcium is a clotting factor - Increased parathyroid activity via increased parathyroid hormone secretion due to hypocalcemia = secondary hyperparathyroidism - Parathyroid hormone increases calcium by increasing breakdown of bone via osteoclasts - Signs and symptoms = tetany, paresthesias, prolonged QT, muscle cramping, stridulous breathing due to prolonged contraction of respiratory and laryngeal muscles - GI = anorexia, adynamic ileus, hypersecretion of gastric acid (peptic ulcers), delayed gastric emptying secondary to autonomic neuropathy will predispose pt to aspiration - Asterixis - Chvostek's sign = cheek twitching when tapped - Trousseau's sign = BP cuff on arm inflated greater than SBP for 3 mins should cause spasm of arm - Autonomic and peripheral neuropathies - What is dry weight? Weight post dialysis - Anesthetic considerations for the patient with renal disease - Get labs - Treat coagulopathy with DDADP - CMP -- K should be \