Anesthesia w/ Hepatic/Renal disease Flashcards
1
Q
What is the physiologic function of the kidneys?
A
- Body fluid homeostasis: extracellular & total body water
- Blood pressure regulation (RAAS)
- Electrolyte balance: calcium & phosphate
- Acid-base balance: bicarbonate & hydrogen ions
- Excretion
- Metabolic by-products: urea, uric acid, ammonia, bilirubin
- Water soluble toxins and drugs
- Reabsorption:
- Water, electrolytes, Glucose, Active form of vit D
- Endocrine
- Secretes vasoactive hormones: renin, bradykinins, prostaglandins
- Primary source of erythropoietin
2
Q
What is a nephron? what types of nephrons are there?
A
- Nephron = functional unit
- Type I - Outer cortical nephron
- present in the superficial portion of the cortex
- Short loops of Henle that reach the outer medulla
- Type II - Juxtamedullary nephron
- Present in deep regions of the cortex
- Birds and mammals
- Long LOH extend to the inner medulla
- Larger glomeruli & higher GFR
3
Q
What is different about avian and reptile kidneys?
A
- Only a few thousand nephrons
- Cannot concentrate urine in the kidneys be instead in the cloaca
- secrete uric acid, not urea
4
Q
What is the blood supply of the kidneys?
A
- Capillary Networks:
- Glomerular capillaries under high pressure for filtration
- Peritubular capillaries under low pressure
- Secretion & reabsorption
- Facilitate countercurrent mechanism
- Countercurrent Mechanisms:
- Process of using energy to generate an osmotic gradient that enables water reabsorption from the tubular fluid and production of concentrated urine
5
Q
What is the Blood flow to the kidney? % received?
A
- Receive 20-25% of total CO
- Renal blood flow is dispersed unevenly
- 80-90% RBF goes to the renal cortex
- 10% goes to the outer medulla
- 1-3% goes to the inner medulla
- Low flow helps maintain hypertonicity of filtrate
- Kidneys account for 10% of total Oxygen consumption (VO2)
- 75% of renal VO2 is due to active sodium excretion
- Medulla has highest VO2 but receives the lowest fraction of RBF
- Extracts 79% of delivered oxygen
- Medullary cells function at borderline hypoxia
- Acute tubular necrosis occurs when >40% reduction in RBF
6
Q
How is renal blood flow controlled?
A
- Autoregulation
- Maintenance of constant RBF and GFR in range of blood pressures of 80-180 mmHg
- Goal is to maintain stable GFR despite fluctuations in systemic blood pressure
- Can be over-ridden extrinsically so there is variation in RBF within the range of autoregulation
- Disruption in the normal physiological state (e.g. hemorrhagic shock, sepsis)
7
Q
What are the types of autoregulation of renal blood flow?
A
- Myogenic
- Arterial smooth muscle relaxes and contracts in response to changes in arterial vascular wall tension
- Rapid: occurs within 3-10 seconds
- Property of pre-glomerular resistance vessels
- Efferent arteriole does not respond to this mechanism
- Process:
- Increased blood pressure
- Increased arterial wall stretch
- Activation of myogenic stretch receptors
- Open voltage gated calcium channels and inward calcium influx
- Contraction of vascular smooth muscle cells
- Minimal changes in RBF and GFR
- Tubuloglomerular feedback
- Feedback mechanism that links sodium & chloride concentrations at the macula densa with control of renal arteriolar resistance
8
Q
Why is renin released?
A
- Decreased renal perfusion
- Sympathetic stimulation; mediated via B1 receptors
- Decreased tubular delivery of sodium & chloride to the macula densa
9
Q
What is the Extrinsic Neural Control of the Renal Blood Flow
A
- Sympathoadrenal axis
- Renal blood vessels supplied almost exclusively with sympathetic vasoconstrictive fibers
- Little to no basal sympathetic tone
- Vasoconstriction occurs in response to physiological stress
- I.e. excess sympathetic stimulation such as hemorrhage is ischemia
- Vasoconstriction occurs to maintain blood volume at the expense of RBF & GFR
- Minor contribution of parasympathetic fibers, which release NO to cause vasodilation
10
Q
What is the extrinsic hormonal control of renal blood flow
A
- Circulating catecholamines
- Released in response to physiologic stress
- Norepinephrine and epinephrine primarily acting at alpha1 receptors
- Vasoconstrictors
11
Q
What are the vasoconstrictors that affect renal blood flow?
A
- Arginine vasopressin
- Adenosine, endothelin, serotonin
12
Q
What are the vasodilators that effect renal blood flow
A
- Intrarenal prostaglandins
- Atrial natriuretic peptide
- Nitric oxide
13
Q
How does filtration occur across the glomerular capillary wall?
A
- Separation of an ultrafiltrate of plasm across the glomerular capillary wall
- Charge and size selection
- MW 15000 freely permeable
- MW 15000-70000 is primarily charge dependent
- more restriction to negatively charged particles
- MW 70000+ NOT filtered
- Charge and size selection
14
Q
What is the Staging of Renal Disease?
A
15
Q
How do Anesthetic drugs affect renal physiology?
A
- Acepromazine
- Maintains autoregulation
- Maintains RBF/GFR
- Alpha2 agonists (dexmedetomidine, dotomadine, etc)
- Reduce cardiac output & RBF/GFR
- Cause diuresis and hyperglycemia ⇢ avoid with post-renal obstruction
- Benzodiazepines (Midazolam, Diazepam, etc)
- Maintains RBF/GFR
- Opioids
- Morphine has active metabolites that are renally excreted
- Possible prolonged effect?
- Propofol
- Transient reduction in RBF/GFR
- Ketamine
- Maintain RBF/GFR
- Active metabolite norketamine renally excreted in dogs
- excreted unchanged in urine of cats ⇢ prolonged action possible
- Inhalants (Sevo, Iso, etc)
- Reduce RBF/GFR
18
Q
What is the anatomy of the liver?
A
- Classically 4 lobes and their subdivisions:
- Right and Left lobes
- can be divided into medial & lateral components
- Quadrate lobe
- Caudate lobe (caudate and papillary processes)
- Right and Left lobes
- Each lobe has its own arterial supply, venous drainage, & biliary system
19
Q
What is the classical functional unit of the liver
A
- Hepatic lobule
- Comprised of hepatocytes radiating out from a central vein
- Hepatic Arteriole, portal venule & bile duct comprise the portal or hepatic triad
- define the perimeter of the lobule
- Cords of hepatocytes are separated by sinusoids & bile canaliculi
20
Q
What is an acinus?
A
- Newer functional unit classification
- Cluster of hepatocytes grouped around the terminal branches of hepatic arterioles, hepatic venules, & bile ducts
- I.e. hepatocytes served by each portal triad
- In this model of the subunit, the portal triads are central
- All drainage occurs at the peripheral central vein producing a strong gradient for oxygen
21
Q
What is the blood flow of the liver?
A
- Receives 25% of CO
- ~12% of total blood volume being received at any given time
- 65% of hepatic blood flow is from the hepatic portal vein
- Portal blood supplies 50-60% of O2 used by the liver
- 35% of HBF is supplied by the hepatic artery
- Supplies 40-50% of O2 used by the liver
- Regulation of blood flow largely depends on pre-portal factors affecting portal vein blood flow
- Blood flow is usually maintained constantly and homogenously due to a semi-reciprocal relationship between portal and arterial blood flow
- Decrease in portal flow will cause arterial vasodilation
- Homogeneity flow is important because of the liver’s role in clearance and maintaining venous return
