Untitled Quiz

Renal Anatomy

• Kidneys are retroperitoneal organs located between T12 and L4
• The right kidney is slightly lower than the left kidney
• The nephron is the functional unit of the kidney
• The kidneys receive innervation from the sympathetic and parasympathetic nervous systems
  • Sympathetic innervation originates from T8-L1
  • Parasympathetic innervation is provided by the vagus nerve (CN X) and the pudendal nerve (S2-S4)
  • At least a T10 epidural or ESP is needed for a nephrectomy

Renal Functions

• The kidneys maintain extracellular fluid (ECF) composition by regulating ionic composition and osmolality
  • Osmolality is the concentration of sodium
• Conserve non-ionic components like glucose and amino acids
• Excrete waste products
• Regulate arterial blood pressure
• Endocrine function includes the renin-angiotensin-aldosterone system (RAAS), erythropoietin production, and vitamin D activation
  • Activated vitamin D increases calcium absorption from the gastrointestinal tract
  • Erythropoietin stimulates red blood cell production
  • Chronic renal disease can lead to anemia due to erythropoietin deficiency and hypocalcemia due to impaired calcium absorption

Assessment of Renal Function

• Glomerular filtration rate (GFR) is the best overall measure of renal function
  • GFR is determined by the surface area for filtration (Kf), the difference in hydrostatic pressure across the membrane (ΔP), and the difference in osmotic pressure across the membrane (ΔΠ)
  • Prerenal failure can decrease Kf and ΔP
  • GFR typically mirrors cardiac output
  • Normal GFR is 125-140 mL/min, decreasing by 8 mL/year after age 30
  • GFR < 60 mL/min indicates chronic kidney disease (CKD)
• Creatinine is freely filtered and a good indicator of GFR
  • Normal creatinine level is 0.6-1.3 mg/dL
• Creatinine clearance is the most reliable measure of GFR
  • Normal creatinine clearance is 110-140 mL/min
  • Creatinine clearance < 30 mL/min contraindicates drugs that rely on renal clearance (e.g., sugammadex)
• Blood urea nitrogen (BUN) is another indicator of renal function
  • Normal BUN level is 10-20 mg/dL
• Proteinuria is an indicator of glomerular damage
  • Normal protein excretion is < 150 mg/day
• Renal tubular function can be assessed using urine specific gravity, fractional excretion of sodium (FENa), and urinalysis
  • Specific gravity should be < 1.018 in the absence of diuretics, glycosuria, or proteinuria
  • FENa < 1% suggests prerenal disease
  • FENa > 2% indicates tubular dysfunction
  • Urinalysis can detect protein, blood, glucose, hemoglobin, leukocytes, and toxins

Acute Kidney Injury (AKI)

• AKI is a rapid deterioration of renal function over hours to days, leading to failure to excrete waste products and maintain fluid homeostasis
• Affects up to 20% of hospitalized patients and 50% of ICU patients
• Most common cause is hypotension and hypovolemia
• Symptoms can be asymptomatic, malaise, weight loss, orthostatic hypotension, volume overload, dyspnea
• Diagnosis based on creatinine increase (0.3 mg/dL in 48 hours or 1.5x baseline within 7 days) and decreased urine output (< 0.5 mL/kg/hr or < 500 mL/day)
• AKI can be oliguric or nonoliguric

Etiology of AKI

• Prerenal AKI: caused by inadequate renal perfusion, often seen in CHF, liver dysfunction, or sepsis
  • Most common type of AKI
  • Rapidly reversible
  • Induction of anesthesia or poor hemodialysis management can lead to prerenal AKI
• Intrarenal AKI: caused by injury to the kidney itself, affecting the glomerulus, tubules, interstitium, or renal vasculature
  • Can be caused by toxic drugs like aminoglycosides or vancomycin, NSAIDs
  • Can have nephritic (hematuria) or nephrotic (proteinuria) patterns
• Postrenal AKI: caused by obstruction of the urinary flow tract, often due to prostatic hypertrophy, stones, or tumor bulk
  • Least common, but most easily reversible type
  • Recovery potential is inversely related to the duration of obstruction

Complications of AKI

• Complications arise from impaired fluid balance and electrolyte homeostasis
• Volume overload is common
• Neurological complications include confusion, somnolence, and seizures

Risk Factors for AKI

• High-risk surgical procedures
• Advanced age
• Preexisting renal insufficiency
• CHF
• Diabetic neuropathy
• Liver failure
• Pregnancy-induced hypertension (preeclampsia)
• Sepsis/shock

Treatment of AKI

• Goal is to limit further renal injury and correct fluid, electrolyte, and acid-base imbalances
• Fluid resuscitation and vasopressor therapy are universal treatments
  • Balanced salt solutions and Lactated Ringer's solution are preferred
  • 0.9% NaCl can lead to hyperchloremic metabolic acidosis and hyperkalemia
• Norepinephrine and vasopressin are used to maintain mean arterial pressure (MAP) between 65-70 mmHg
• Dopamine use is not supported by literature to treat or prevent AKI
• Fenoldopam is a D1 agonist that increases renal perfusion but has no proven benefit in AKI treatment
• Loop diuretics can be used in hypervolemic, non-anuric AKI
• N-acetylcysteine and mannitol can decrease contrast dye-induced injury
• Blood glucose management is essential
• Continuous renal replacement therapy (CRRT) may be necessary

Pharmacology in AKI

• Ideal to select drugs that do not rely on renal excretion
• Drug doses rarely need alteration if creatinine clearance is > 30 mL/min
• Loading doses may not require adjustments unless volume status alters distribution
• Dosing intervals should be increased
• Avoid drugs with toxic or active metabolites
• Nephrotoxins like NSAIDs, aminoglycosides, vancomycin, and contrast dyes should be avoided
• Avoid drugs that decrease renal perfusion like ACE inhibitors, ARBs, NSAIDs, and diuretics

Anesthetic Management of AKI

• Only lifesaving surgery should be performed in patients with AKI due to high mortality and morbidity
• Anesthetic goals: maintain adequate systemic blood pressure and cardiac output, and avoid further renal insults
• Preoperative evaluation: EKG, blood chemistries, CBC, coagulation assessment, urine indices, chest radiograph if respiratory issues, preop dialysis for high-risk patients, DDAVP for platelet dysfunction
• Intraoperative management: large bore IVs (≥18g), avoid succinylcholine in hyperkalemia, correct anemia, maintain intravascular volume, avoid morphine, tramadol, and meperidine

Chronic Kidney Disease (CKD)

• Progressive, irreversible deterioration of renal function due to various diseases
• Leading causes are diabetes mellitus and hypertension
• Large racial disparity: ESRD rate in African Americans is 3.6x higher than Caucasians, Native Americans 1.8x higher
• ~15% of the US population has CKD
• Half of Americans will develop CKD in their lifetime
• Diagnosed when GFR < 60 mL/min for > 3 months
• GFR < 25 mL/min progresses to end-stage renal disease (ESRD) requiring dialysis or transplantation
• Stages of CKD are categorized by GFR and albuminuria excretion rate:

Cardiovascular Effects of CKD

• Systemic hypertension increases the risk of left ventricular hypertrophy, CHF, CAD, and cerebrovascular disease
• Hypertension accelerates the progression of ESRD

Anesthetic Management of CKD

• Induction: patients often respond as if hypovolemic, requiring careful titration of induction drugs to prevent hemodynamic fluctuations
  • RSI is often necessary
  • Succinylcholine is safe in CKD, but rocuronium is often preferred
• Maintenance: general anesthesia with a balanced technique is safe and effective
  • Use volatile agents sparingly, as they can lead to fluoride toxicity or compound A production
  • TIVA with EEG monitoring is an option
  • Cerebral oximetry can be useful in high-risk patients
  • Hemodynamics are labile, so a defibrillator should be readily available
  • Neuromuscular blockade should be avoided when possible
  • Rocuronium and vecuronium have reduced clearance
  • Laudanosine can cause seizures
  • Neostigmine and edrophonium have reduced clearance, so risk of re-curarization is low
  • Sugammadex is safe and effective in CKD with creatinine clearance > 30 mL/min
  • Opioids can reduce the need for volatile anesthetics
  • M6G can accumulate
• Regional anesthesia: brachial plexus block is useful for vascular access for hemodialysis
  • Assess and document for uremic neuropathies before regional
  • Neuraxial anesthesia is possible, with a T4-T10 sympathetic block potentially improving renal function
  • All types of regional are possible, but consider vascular access location and future placement needs