Kidney Overview
location of kidneys
retroperitoneal between T12 -L4
right slightly caudal (lower) to accommodate the liver
What is AKI? causes? hallmark sign
failure to excrete nitrogenous waste products to maintain fluid/electrolyte homeostasis
caused by hypotension, hypovolemia, nephrotoxins
Azotemia: build-up of nitrogenous waste products (Cr, Urea)
anesthesia + volume & blood loss decrease RBF
BUN:Cr > 20:1
reversible
tx= restore RBF (fluids, mannitol, diuretics, pressers, maintain MAP
leading cause of CKD
anesthesia concerns
stability of ESRD
body weight pre/post dialysis
glucose management, BP management
aspiration risk
pressors
uremic bleeding - desmopressin
cardiac output of the kidneys
20% receiving 1-1.25L/min
outer= cortex receives 85-90% RBF
inner = medulla most vulnerable to necrosis during hypotension
RF for AKI
pre-existing renal disease, advanced age, CHF, PVD, DM, sepsis, jaundice, IV contrast, surgery
intrarenal AKI
Decrease GFR late symptoms
decreased urea reabsorption - decreased BUN, decreased filtration of creatine - increased serum creatinine
BUN: Cr < 15:1
stages of CKD
Stage 1 - > 90
Stage 2 - 60- 89
Stage 3 - 30-59
Stage 4 - 15-29
Stage 5 - <15
GFR decreases by 10 per decade starting at age 20
drug considerations
best NMB for CKD
many anesthetic agents are lipid soluble
reabsorbed by renal tubular cells
avoid active metabolites - demerol, morphine
cisatracurium not dependent on renal elimination
function of the kidney (7)
Regulate ECF volume, osmolarity, composition.
regulate BP (RAAS, ANP)
Excrete toxins/metabolites
Maintain acid/base balance (excretion/reabsorption of H+/HCO3-)
produce hormones (calcitrol, renin, epo, prostaglandins)
blood glucose homeostasis (gluconeogenesis, filtration/reabsorption of glucose)
AKI diagnosic criteria
Increase serum Cr 0.3 mg/dL in 48 hr.
Increase serum Cr by 50% in 7 days.
decreased creatinine clearance by 50%
abrupt oliguria is not always seen
physical symptoms: asymptomatic, malaise, hypotension, hypovolemia/hypervolemic
post renal AKI
outflow obstruction
increased nephron tubular hydrostatic pressure
reversibility inverse to duration
remove obstruction - persistent obstruction damages the tubular epithelium
CKD CV effects
systemic HTN (1st line thiazide diuretics/ACE-I/ARB)
dysipidemia (MI risk)
lipid insoluble drugs?
thiazide diuretics, loop diuretics, digoxin, many ABX
prolonged duration - eliminated unchanged in urine
renal function Labs
GFR 125-140 mL/min - influenced by hydration
creatinine clearance 115-140 mL/min - most reliable measure of GFR
serum creatinine 0.6-1.3 mg/dL - influenced by high-protein intake, muscle breakdown, supplements (inverse of GFR)
BUN 10-20 mg/dL - influenced by hydration, protein diet
BUN:Cr ratio 10:1 - BUN(reabsorbed):Cr (not reabsorbed) - hydration
proteinuria < 150 mg/dL (>750 mg/dL indicates UTI or glomerular injury)
specific gravity 1.001- 1.035 - measures ability to concentrate urine
complications of AKI - neuro/heme
uremic encephalopathy, mobility disorders, neuropathies, myopathies, seizures, stroke
Anemia - decreased EPO production & platelet dysfunction
*vWF disrupted by uremia - DDVAP (increase vWF and Factor VIII)
correct fluid/electrolyte/acid-base imbalances
NS preferred - albumin
MAP within 20% of baseline
Vasopressin (efferent arteriole), alpha agonists (afferent arteriole)
prophylactic NaHCO3
dialysis??
Acidosis metabolic
Electrolyte (hyperK+)
Intoxications (active metabolites accumulation)
Overload - fluid
Uremic encephalopathy
HD is more effective than PD
can cause rapid fluid shifts -- hypotension most commo
infection leading cause of death
drugs that excreted renally
-induction, muscle relaxants, cholinesterase, CV drugs, antimicrobials
induction - phenobarbital, thiopental
muscle relaxants - pancuronium, vecuronium
cholinesterase - neostigmine, edrophonium
CV drugs - milrinone, digoxin, atropine, hydralazine, glycopyrrolate antimicrobials - aminoglycosides, cephalosporin, PCN, vancomycin
volume status/monitors
orthostatic pressure changes, decreased base excess, increased lactate
A drop in UOP is a late sign of volume loss
UOP - 30 mL/hr or 0.5-1 mL/kg/hr; oliguria < 500 mL/day
US to assess IVC collapse
CVP, RAP,
LAP, PCWP - powerful stimuli for renal vasoconstriction
PAP
SVV - assumes vented patient/SR
complications of AKI CV/metabolic
systemic HTN, LV Hypertrophy, CHF, pulmonary edema, uremic cardiomyopathy, arrhythmia
hyperK+, water/Na+ imbalances, hypoalbuminemia, metabolic acidosis, malnutrition, hyperparathyroidism
low threshold for invasive hemodynamic monitoring
Prefer preop dialysis/possibly postop dialysis if cannot clear drugs
tailored drug dosing
avoid drugs with active metabolites, drugs that decrease RBF and renal toxins
CKD hematologic effects
responsive to exogenous EPO
target Hgb 10
platelet dysfunction
K+ < 5.5 on elective surgery
Dialysis before surgery
aspiration precautions
Anesthesia and surgery decrease RBF and GFR
blood loss activates baroreceptors increasing SNS outflow (constricting afferent arteriole)
longer periods of hypotension (cross-clamping, hemorrhage, sepsis) decrease RBF