Anesthesia and Renal Disease Flashcards
What are the main perioperative factors to consider with the kidney?
The effect of anesthetic drugs on renal function
The effect of renal disease on anesthetic drug metabolism
The effect of renal disease on fluid and electrolyte balance
Ins need to equal outs
What is the principle function of the kidneys?
Regulate water and electrolytes balance, excrete hydrogen ions and nitrogenous waste
25% of CO
GFR=20% renal plasma flow
0.5-1 ml/kg/hr
What else does the kidney do besides make urine?
Target organ for various hormones
The kidney metabolize and secrete regulatory substances, such as insulin, renin, prostaglandin, and erythropoietin
How does anesthesia and surgery affect glomerular filtration?
Release of neurohumoral substances Factors include: Changes in arterial blood pressure Release of catecholamines Production of ADH, endothelin, nitric oxide, prostaglandins Aldosterone-renin-angiotensin system
How is renal blood flow regulated?
RBF and GFR are autoregulated at 60-160 mmHg in conscious patients
UO is not subjected to autoregulation, but decreases with MAP
How are perfusion pressure and renal output related?
Decreaed perfusion reduces hydrostatic pressure in the glomerular capillaries and decreases filtration
What does SNS stimulation due to surgery do and how does it affect perfusion pressure?
Causes renal artery vasoconstriction which decreased RBF and GFR despite maintenance of perfusion pressure within the range of autoregulation
What do hemorrhage, hypovolemia, and dehydration do to filtration pressure?
Decrease it
What does a decrease in RBF do?
Initiates renin release, which, combine with release of catecholamines, can further decrease RBF
Are anesthetics nephrotoxic?
All anesthetics are functional nephrotoxins
How do anesthetics affect the kidney?
Generalized reduction of measurable renal function secondary to anesthetic-induced hypotension and reduced CO or secondary to drug or stress-induced renal vasoconstriction
What can dexmedetomidine protect against?
Acute kidney injury following ischemia-reperfusion injury
How do injectable anesthetic agents acutely affect renal function?
Most injectable anesthetics do not directly affect the kidney, but hypotension that is related may reduce RBF and GFR
How do inhalant anesthetic agents acutely affect renal function?
No direct effect, but indirectly reduce GFR and RBF through their depressant effects on cardiac function and BP
What can the effect of inhalant anesthetics be attenuated by?
Reducing the inhaled anesthetic concentration; maintaining MAP >60 mmHg
How long do anesthetic agents affect renal function?
Transient
Limited to the anesthetic period
Usually clinically insignificant as long as metabolites are inactive
Can anesthetic agents cause delayed nephrotoxicity?
Delayed nephrotoxicity can occur secondary to biotransformation of the fluoride-containing inhalant anesthetics to oxalate and free fluoride ion
What enhances the nephrotoxic effect of other druds?
Methoxyflurane
What about nephrotoxicity with other fluoride-containing inhaled anesthetics?
Sevoflurane is transformed in the presence of soda lime in the CO2 absorber of the anesthetic circuit to the fluoride-containing substance known as compound A
Compound A is unlikely to build to toxic concentrations during routine semi-closed administration of sevoflurane
What kind of renal failure patients are likely to be anesthetized?
Animals with an acute postrenal problem
Animals with chronic kidney disease where anesthesia is require to facilitate an unrelated problem
What is the best lab test for clinical evaluation of renal function?
Combinations of GFR and renal tubular function tests
Also, hematocrit, acid-base status, and circulating Na and K levels
What are GFR tests?
Blood urea nitrogen
Plasma creatinine
Creatinine clearance
What are renal tubular fucntion tests?
Urine specific gravity
Urine osmolarity
When does clinical evidence of renal failure occur?
After >70% of nephrons are nonfunctional
What is the best way to anesthetize a patient in acute postrenal failure?
Pre-surgical stabilization, including peritoneal dialysis, treatment of electrolyte and acid-base
disturbances, and volume replacement
Isotonic saline IV up to 10 ml/kg/hr
Anesthetized after stabilization
What would be on an ECG with mild K increase (6.0-6.5 mEq/L)?
T waves tall and peaked; HR and P waves normal
What would be on an ECG with moderate K increase (6.5-7.0 mEq/L)?
HR slows, P waves flatten
What would be on an ECG with high K increase (>/= 7.5 mEq/L)?
Bradycradia, atrial standstill, T wave may or may not be large
Cardiac arrest may occur at any time when K >/= 9.5 mEq/L
True or False: patients with a K >5.5-6.0 mEq/L should be anesthetized for elective procedures.
False
What is the treatment for acute hyperkalemia?
Prior to anesthesia, calcium salts are initially administered to counteract hyperkalemic bradycardia. Once a stable HR is achieved, therapy is subsequently directed to drive extracellular K intracellularly
What is the best way to anesthetize a patient in chronic renal failure?
Maintain RBF, avoid hypovolemia, hypotension, and renal vasoconstriction
Fluid administration at maintenance rates (ins=outs)
Giving fluids at high rates to “promote diuresis” isn’t effective during anesthesia and generally leads to interstitial edema and dilution of
plasma proteins WITHOUT improving urine production
My patient is oliguric. What should I do to restore urine production?
If prerenal, try isotonic crystalloid fluid bollus challenge of 5-10 ml.kg IV
If due to low CO, 1st restore recirculating volume the start inotropes
Diuretics can be administered in oliguric, normovolemic patients, but not hypovolemic
What about using a low-dose dopamine infusion to stimulate low-dose dopamine infusion to stimulate renal dopaminergic receptors and improve renal output?
Low dose dopamine has been advocated to increase RBF and GFR, increase urine output, and sodium excretion and to decrease renal vascular resistance
Can I safely administer an NSAID for analgesia during anesthesia and surgery?
Okay to use in clinically normal dogs undergoing anesthesia and surgery
Limit to well-hydrated patients with normal renal function where MAP is monitored and IV fluids administered during anesthesia and surgery
Should MAP be maintained above 60 mmHg in neonatal/pediatric patients?
Probably not
MAP increases with physiological age and does not reach adult values until 6-9 months old
Target BP at 80% of the awake baseline pressure
