Renal Disease and Anesthesia

Renal Disease and Anesthesia

• Normal kidney function is vital for excreting anesthetics and medications, balancing fluid and acid-base levels, and regulating hemoglobin during the perioperative period.

Importance of Kidneys

• Regulates body fluid volume and composition
• Eliminates toxins
• Produces hormones like renin and erythropoietin, and the active form of vitamin D

Impact of Operative Procedures

• Factors related to surgery and anesthesia can significantly affect kidney physiology and function leading to perioperative fluid overload, hypovolemia, and acute kidney injury
• These increase perioperative morbidity, mortality, hospital stay length, and costs

Kidney Anatomy

• The kidneys are located in the posterior abdominal wall and are positioned behind the 11th and 12th ribs and diaphragm
• Each kidney measures 10 cm in length, 5 cm in width, and 3 cm in thickness

Renal Blood Flow (RBF)

• Renal function is closely related to renal blood flow (RBF)
• Kidneys are the only organs where oxygen consumption is determined by blood flow
• Combined blood flow through both kidneys accounts for 20% to 25% of total cardiac output
• Approximately 80% of RBF goes to cortical nephrons and 10% to 15% goes to juxtamedullary nephrons
• Autoregulation of RBF occurs with blood pressures between 80 - 180 mm Hg, due to afferent glomerular arterioles responding to blood pressure changes
• Within these limits, RBF and Glomerular Filtration Rate (GFR) remain relatively constant through arteriolar adjustments
• Glomerular filtration typically stops when mean systemic arterial pressure drops below 40 to 50 mm Hg

Kidney Functions

• Regulates ions such as sodium, potassium, calcium, chloride, and phosphate in the blood
• Regulates blood volume by adjusting blood volume or eliminating water in urine
• Regulates blood pH by excreting hydrogen ions in the urine and conserving bicarbonate (HCO3) ions
• Produces hormones such as calcitriol for calcium hemostasis, erythropoietin for RBC production, and renin for blood pressure control
• Excretes waste products, including urea, creatinine, ammonia, amino acids, and drugs

Evaluating Kidney Function

• Impaired kidney function can result from glomerular or tubular dysfunction, or urinary tract obstruction
• Traditional Acute Kidney Injury (AKI) diagnosis relies on serum creatinine and urine output, refined to include an increase in serum creatinine of 0.3 mg/dL or more within 48 hours, or a 1.5-fold or greater increase from baseline within 7 days
• Kidney excretory function assessment via serum creatinine and urine output overlooks endocrine, metabolic, and immunological kidney functions

Serum Creatinine

• Creatine is a product of muscle metabolism converted to creatinine
• Daily creatinine production is relatively constant and related to muscle mass, averaging 20 to 25 mg/kg in men and 15 to 20 mg/kg in women
• Creatinine is filtered but not reabsorbed in the kidneys
• Creatinine production rate and its distribution volume are often abnormal in critically ill patients, single serum creatinine measurement may not accurately reflect GFR
• Normal serum creatinine concentration is 0.8 to 1.3 mg/dL in men and 0.6 to 1 mg/dL in women

Creatinine Clearance

• Measurement is the most accurate method for assessing GFR
• Measurements typically take over 24 hours however 2-hour creatinine clearance determinations are reasonably accurate and easier to perform
• Creatinine clearances less than 25 mL/min indicate overt kidney failure

Blood Urea Nitrogen: Creatinine Ratio

• Low renal tubular flow rates increase urea reabsorption without affecting creatinine excretion
• Serum BUN to serum creatinine ratio increases to more than 10:1
• Decreased tubular flow results from reduced kidney perfusion or urinary tract obstruction
• BUN: creatinine ratios greater than 15:1 indicate volume depletion or edematous disorders linked to decreased tubular flow (e.g., congestive heart failure, cirrhosis, nephrotic syndrome), as well as obstructive uropathies
• Increased protein catabolism can also increase this ratio

Effects of Anesthesia & Surgery on Kidney Function

Acute Kidney Injury

• Acute kidney injury (AKI) occurs in 1% to 5% of all hospitalized patients and approximately 50% of ICU patients
• AKI is a systemic disorder involving fluid and electrolyte imbalances, respiratory failure, cardiovascular events, weakened immune response, altered mental status, hepatic dysfunction, and gastrointestinal hemorrhage
• AKI is a major cause of chronic kidney disease (CKD)
• Preoperative risk factors include preexisting kidney disease, hypertension, diabetes mellitus, liver disease, sepsis, trauma, hypovolemia, multiple myeloma, and age over 55 years
• Risk of perioperative AKI increases with exposure to nephrotoxic agents like NSAIDs, radiocontrast agents, and antibiotics
• Clinicians must understand the risks of AKI, its differential diagnosis, and evaluation strategy
• AKI contributes to increased hospital stay, morbidity, mortality, and cost
• Patients can develop AKI and kidney failure secondary to intrinsic kidney disease

AKIN Criteria

• Definition and staging of acute kidney injury

• Risk factors for AKI in the perioperative setting include preexisting kidney impairment, diabetes mellitus, cardiovascular disease, hypovolemia, and nephrotoxic medications in older adults

Chronic Kidney Disease

• CKD is defined as either kidney damage or a GFR less than 60 mL/min for 3 months or more
• Kidney damage is a pathologic abnormality or markers in blood, urine, or imaging studies
• Oliguria isn't evident until late in the disease, and is an unreliable marker
• A confirmed fluid overload and cardiac disease in laboratory testing is a marker
• Proteinuria & urinary sediment are helpful for diagnosis

Classification of Chronic Renal Disease

• Stage 1: Kidney damage with normal or GFR (≥90 ml/min)
• Stage 2: Kidney damage with mild GFR (60-89 ml/min)
• Stage 3: Moderate GFR (30-59 ml/min)
• Stage 4: Severe GFR (15-29 ml/min)
• Stage 5: Kidney failure with GFR

Causes of Renal Failure

• Diabetes Mellitus 25%
• Glomerulonephritis 14%
• Hypertension 8%
• Polycystic kidney disease 6%
• Pyelonephritis 6%
• Renal vascular disease 6%
• Others 17%
• Uncertain 15%

Systemic Effects of Renal Failure

• Cardiovascular: Left ventricular hypertrophy, Atherosclerosis, Hypertension
• Respiratory: Pulmonary edema
• Metabolic acidosis
• Coagulopathy
• Autonomic neuropathy
• Fluid and electrolyte: Volume overload, Hyperkalemia

Altered Kidney Function & Effects of Anesthetic Agents

Intravenous Agents

• Propofol & Etomidate: minimally affected by impaired kidney function, hypoalbuminemia may enhance etomidate's pharmacological effects
• Barbiturates. Patients with kidney disease exhibit increased sensitivity, free barbiturate levels increase, which can be exacerbated by acidosis
• Ketamine pharmacokinetics are minimally altered by kidney disease
• Some active hepatic metabolites are dependent on renal excretion and can potentially accumulate in kidney failure
• Benzodiazepines. They undergo hepatic metabolism; increased sensitivity may be seen in patients with hypoalbuminemia, diazepam and midazolam should be administered cautiously due to potential accumulation of active metabolites

Opioids

• Most are inactivated by the liver and excreted in urine, remifentanil pharmacokinetics remain unaffected by kidney function
• Morphine and meperidine can accumulate, prolonging respiratory depression, increased normeperidine levels may promote seizure activity
• The pharmacokinetics of opioid agonist-antagonists remain unaffected by kidney failure

Inhalation Agents

• Volatile agents. Ideal for patients with kidney disease, minimal direct effects on kidney blood flow, accelerated induction and emergence may be seen in anemic patients with chronic kidney failure, avoid sevoflurane and low gas flows for lengthy procedures
• Nitrous Oxide. Some clinicians totally omit this agent to maintain FiO2 in anemic patients with end-stage kidney disease, may be justified with hemoglobin less than 7 g/dL to increase arterial oxygen content

Muscle Relaxants

• Succinylcholine: Safe during kidney failure without hyperkalemia, but it should be avoided with high serum potassium levels. Prolongation of neuromuscular blockade using succinylcholine is rare even with decreased plasma cholinesterase levels
• Cisatracurium & Atracurium are preferred drugs: They undergo degradation via plasma ester hydrolysis and Hofmann elimination
• Vecuronium & Rocuronium: Hepatic elimination, effects of vecuronium are modestly prolonged, rocuronium prolongation is reported in severe kidney cases, use with neuromuscular monitoring
• Pancuronium: dependent on renal excretion, monitor neuromuscular function closely, if used
• Reversal Agents: Renal excretion is principal route for edrophonium, neostigmine, pyridostigmine. Half-lives are prolonged

Anesthetic Considerations

Pre-operative Assessment

• Routine anesthetic assessment with special attention to renal functions
• Hypertension and ischemic heart disease are commonly seen in chronic renal failure
• Proteinuria and hypoalbuminemia predispose to edema
• Urinalysis is a cheap, readily available, informative laboratory test
• Complete blood count may reveal anemia or other causes
• A chest X-ray and ECG may be required

Summary of Pre-operative Assessment

• Optimize patients preoperatively, manage hypertension with anti-hypertensives, provide antibiotics for urinary infections
• Routine transfusion is not recommended, electrolytes should be corrected, and dialysis may be needed
• Pre-medications and antacids may be considered

Intra-operative

• General anesthesia with positive pressure ventilation and muscle relaxation for open or laparoscopic renal surgery
• Rapid sequence intubation in patients with chronic renal failure
• Induction with intravenous and inhalational agents
• Maintenance with inhalational agents
• Propofol is preferred due to hepatic metabolism
• Atracurium preferred due to Hoffman degradation
• Large-bore intravenous line needed due to bleeding risk
• Do not use limbs with arteriovenous fistulas for infusions

Monitoring

• Routine standard monitoring is essential, CVP monitoring may be required, temperature monitoring is also essential.

Fluid therapy

• Patients may be dehydrated, use appropriate fluid resuscitation to avoid hypotension, maintain urine output with crystalloid fluid

Post-operative pain relief

• Significant pain is expected, utilize multimodal analgesia
• Epidural analgesia should be used unles is contraindicated
• Fentanyl and short-acting opioids are useful
• Nonsteroidal anti-inflammatory drugs are contraindicated
• Paracetamol is safe and a good adjuvant