deck_1297508 Flashcards
What is the % of CO that is partitioned to renal blood flow?
20-25% via the renal artery
The renal cortex gets what % of the RBF?
80% (extracts very little O2)
The renal juxtamedullary gets what % of the RBF?
10-15%
What area of the renal system is most sensitive to ischemia?
The medulla: which uses high metabolic activity for solute absorption and requires low blood flow to maintain osmotic gradients.
What MAP is appropriate to maintain autoregulation in the kidneys?
MAP of 75-160mmHg
A MAP below _____ % can be associated with impaired filtration.
<70
Filtration ceases at a MAP less than ______%.
<40-50
Your 2 kidneys are comprised of 2 regions called the _______ and the ________.
cortex and medulla
What is the functional unit of the kidney? How many are there?
nephron; approx. 1.25 million per kidney
What is the function of the nephron?
functional unit of the kidney; it holds filtrate that is filtered by blood, excretes waste, and absorbs important substances such as water and bicarbonate
What does renal fraction mean?
renal fraction is the portion of the blood that passes through the kidney
What is the renal fraction of the CO? and in mL?
20-25%; 1100-1200mL per minute
What is the glomerulus?
It is a high pressure capillary bed formed by the afferent arterioles.
In what two ways is RBF regulated?
intrinsic autoregulation and neural regulation
What is neural regulation and the effect of SNS stimulation on the RBF?
afferent and efferent arterioles are innervated by the sympathetic nervous system, stimulation of the SNS causes vasoconstriction….. and thus a decrease in RBF
What are the main functions of the kidney?
maintenance of ECF composition and volume, endocrine functions (erythropoietin, RAA system, vitamin D), regulation of arterial BP
What is the significance of erythropoietin, the RAA, and vitamin D?
erythropoietin stimulates the production of RBCs; RAA regulates BP, K, and Na excretion; kidney converts vitamin D into its active form to absorb Ca from the intestine… so a deficiency in vitamin D results in hypocalcemia
What does one nephron consist of and what are its 4 main functions?
consists of the glomerulus (bowmans capsule), proximal and distal convoluted tubule (in the cortex), and the loop of henle and collecting tubule (in the medulla); functions include glomerular filtration, tubular reabsorption, tubular secretion, and excretion (byproduct of the previous 3 functions)
What are the 2 types of nephrons? Describe.
cortical nephrons (extend only partially into the medulla) and juxtamedullary (lie deep in the cortex and extend deep into the medulla); 1/5 to 1/3 are juxtamedullary—> play an important role in the concentration of urine.
What is the name of the peritubular capillaries of the loop of Henle?
vasa recta
What is the difference between reabsorption and secretion?
reabsorption is when a substance is transported from the tubule to the capillary….. secretion is when a substance is transported from the capillary to the tubule
What part of the medulla is most vulnerable to ischemia?
outer medulla (top of the loop of Henle)
What is the % and mL/min value for GFR?
20% RBF (125mL/min)
The release of what substance causes RAA activation?
renin
What % of the approximately 125mL/min of filtrate is reabsorbed from the renal tubules while the remainder is excreted as urine?
99%
Why does glucose get excreted in urine when past a certain concentration?
some substances like glucose have a maximum reabsorption value after which the remainder is excreted.
What factors can increase the GFR?
increased renal blood flow, dilation of the afferent arteriole, and increased resistance in the efferent arteriole increases GFR
Describe the activation and process of the RAA.
SNS stimulation and decreased delivery of sodium and chloride to the macula densa cause the juxtaglomerular cells to release renin—> renin clears angiotensinogen from the liver to form angiotensin I—> in the lung, angiotensin I is changed into angiotensin II under the influence of a converting enzyme—> in addition to having a generalized vasoconstriction effect, angiotensin II causes constriction of the efferent arteriole—> this causes pressure in the glomerulus to increase and the GFR to return to normal
What is the short description for the proximal tubule?
“coarse control”: reabsorbs the bulk of glomerular filtrate (65-75%); NaCl, water, bicarb, glucose, protein, amino acids, potassium, magnesium, calcium, phosphates, uric acid, urea; also produces ammonia; has active (at the cost of metabolic energy d\t electrochemical gradient) and passive (movement of substances across concentration gradients) transport
Describe the differences in permeability of the descending and ascending limb of the loop of Henle.
descending is highly permeable to water but not actively transport sodium and chloride–> this leaves the remaining fluid in the descending limb concentrated; ascending retains water within the tubule, while the countercurrent exchange begins in the thick ascending limb with the active transport of sodium and chloride out of the tubular lumen and into the medullary interstitium—> since it is impermeable to water the tubular fluid becomes hypoosmotic (dilute) and the intertitium hyperosmotic
Describe the blood flow through the nephron.
afferent arteriole–> glomerulus–> unfiltered blood to efferent arterioles–> peritubular capillaries–> venous system
What happens to the ultrafiltrate once it leaves the glomerulus?
travels from the glomerulus through tubules for reabsorption/secretion; reabsorption–> goes into the interstitium and returns to systemic vasculature
Differentiate between the ECF effects of aldosterone and ADH.
aldosterone: ECF volume via sodium reabsorption (water follows NaCl) and controls K+ secretion.; ADH: ECF osmolality via H2) reabsorption/secretion (to dilute osmolality, conserve H20)
Describe the “fine tuning” that occurs in the kidney.
(actions via hormones): distal tubule: aldosterone (Na reabsorption/K+ secretion; Na reabsorption/H secretion—- acid base buffering); collecting tubule: ADH (adjusts permeability to H20 dependent on osmolality)
What is the end product when ADH is present vs not present?
ADH present—– water is reabsorbed so there is a small volume of concentrated urine; ADH not present—– water stays in tubules so there is a large volume of dilute urine
What can prompt the activation of the RAA system?
low glomerular flow, SNS stimulation (vasoconstriction=decreased renal blood flow), decreased NaCl concentration at the site of macula densa (part of the JGA which is next to the glomerulus)
What is angiotensin II and what countermeasures does it take?
it is a potent vasoconstrictor but also releases protective prostaglandins (vasodilate) to protect renal blood flow
What is the anhydrase equation?
acid-base balance via Na/H ion exchange; H + HCO3–> H2CO3–> H2O + CO2; Na is exchanged for H…. excess H requires for HCO3
What is the effect of hyperkalemia? Give common treatments.
hyperexcitability b\c the resting membrane potential is closer to threshold potential; Ca++ will help stabilize the membrane potential (decrease excitability by spreading potentials further from each other), HCO3, insulin, albuterol (to shift K+ back into the cell)
What should you do for the hypoosmolar state?
free water overload or water intoxication: hyponatremia, so restrict free H20 and give hypertonic saline
What is the anion gap utilized for?
for differential diagnosis of metabolic acidosis; it is the difference between the primary measured cations (Na and K+) and the primary measured anions (Cl- and HCO3-) in serum
How do you calculate anion gap?
normal anion gap= Na-Cl-HCO3= 8-12 mM
Where is atrial natriuretic factor synthesized and what is its action on the kidneys?
it is a peptide hormone synthesized, stored, and secreted in the cardiac atria; acts on the kidney to increase urine flow and sodium excretion, and it may enhance renal blood flow and GFR; it enhances both the release and end-organ effects of renin, aldosterone, and ADH; the stimulus for ANF is atrial distention, stretch, or pressure; one of the most potent diuretics known
What stimulates the release of ANF?
atrial distention, stretch, or pressure
Name two loop diuretics and their function.
lasix and bumex; stops reabsorption of ions in ascending loop of Henle–> decreases osmololity and increases water excretion—> fluid volume deficit; they act by binding with the Na-K-Cl symporter to inhibit the reabsorption of these ions from the asc loop…. water will follow the Na…. so since ion reabsorption is inhibited….. often results in hypokalemia…. also triggers release of prostaglandins from the kidneys which cause venodilation and decrease in BP d\t decrease preload.
What is the effect of thiazides and K+ sparing diuretics like spironolactone?
work on distal tubule of the nephron to inhibit sodium reabsorption, thereby again decreasing water reabsorption… spironolactone competitively inhibits aldosterone increasing sodium excretion and promotes sodium retention; aldosterone is an important regulator of K+
What is diamox and its function?
it is a carboxic-anhydrase inhibitor; inhibits the action of carbonic anhydrase in the proximal tubule of the kidney—> inhibits bicarb reabsorption (more bicarb is left in the interstitium to bind with H); sodium reabsorption also decreases–> diuresis and hyperchloremic metabolic acidosis results
What is Mannitol and its effects?
it is an osmotic diuretic; agent that is impermeable to the renal tubule exerts an osmotic pulling force decreasing the reabsorption of water leading to increased water excretion; hypokalemia can result (secondary to increased distal tubule flow)
What are some considerations for patients taking ACE inhibitors or ARBs?
these drugs block protective effects of RAA system leading to hypotension that is often refractory to our commonly used adrenergic agonists (neo and ephedrine); often more responsive to fluid resuscitation and vasopressin administration (bolus dose of 0.2-0.4 units/kg of vasopressin may be effective….2-4 units of vasopressin usually given); can also consider albumin (do not exceed 250g in 48hr)
How do you decide between 5% and 25% albumin?
depends if patient requires primarily volume (5%) or primarily protein/oncotic pressure (25%); 5%= hypovolemic shock, burns, hypoproteinemia, cardiopulmonary bypass, acute liver disease; 25%: acute nephrosis, acute liver failure, ARDS, burns, cardiopulmonary bypass, hypoproteinemia, renal dialysis, hypovolemic shock, hemolytic disease of newborn, hepatic surgery/transplant
What is refractory hypotension?
it is blocking action of angiotensin II, a powerful vasoconstrictor; blocks release of aldosterone and ADH
Name the normal values of Na, K, Ca, and Magnesium.
Na: 135-145, K: 3.5-4.5, Ca: 9.9-10.5, Magnesium: 1.7-2.5
What electrolytes control the following: 1) resting membrane potential (-90mV) and 2) threshold (-60mV)?
K+ controls the resting membrane potential; Ca+ controls the threshold
What is the most common electrolyte disturbance with renal failure?
hyperkalemia
How do you treat hyperkalemia and what are the effects?
calcium: move threshold away from resting membrane potential (stabilizes); Na HCO3 and hyperventilation: decrease concentration of H+ in plasma….. H+ from ICF to ECF, K back inside; beta-2 agonist (albuterol) and insulin: stimulate Na-K pump, drives K back into cells, give dextrose to prevent hypoglycemia
The incidence of surgery related acute renal failure is ____ to _____ %.
18-47%
How do you calculate allowable blood loss?
EBVx (start Hct-target Hct)/ start Hct
What is the mL/kg to calculate obese patients estimated blood volume?
45-55mL/kg
Urine specific gravity > ______ shows that the kidneys are concentrating urine adequately.
> 1.018
What is the normal values for GFR?
125-140 mL/min; decreases 1% per year after the age of 20
What test is considered the NEST measure of renal function?
GFR
What is the normal range for serum creatinine?
0.6-1.0 mg/dL in women and 0.8-1.3 mg/dL in men
What is creatinine?
a waste product of muscle metabolism; not reabsorbed by the kidneys
What is the normal value for BUN?
5-20 mg/dL; increases can be seen in high protein diets
What are the normal values for specific gravity?
1.005-1.030; assesses renal tubular function by measuring the urine concentrating ability
What marker may turn out to be a better indicator of GFR than creatinine, but costs more money?
cystatin C; produced by all nucleated cells in the body and not influenced by muscle mass, gender, or age
What is the difference in acute kidney injury, nephritic disease, and renal tubular dysfunction?
AKI is a blanket term that can be applied to most any acute renal disease; nephritic disease covers diseases involving inflammation of the nephrons; renal tubular dysfunction is established by demonstrating the kidneys do not produce appropriately concentrated urine in the presence of physiologic stimulus for release of ADH
Define oliguria and non-oliguric.
urine output 400cc/day
What are some causes of AKI?
systemic diseases (cardiogenic shock, sepsis, hepatic failure, vasculitis), drugs (aminoglycosides, NSAIDS, ACE inhibitors, solvents such as ethylene glycol, heavy metals such as mercury), interventional therapies (radiographic contrast dyes, aortic or renal artery clamping)
What are 3 classifications of AKI?
pre-renal, intra-renal, post-renal
What is pre-renal azotemia?
azotemia is characterized by abnormally high levels of nitrogen-containing compounds, such as urea, creatinine, various body waste compounds, and other nitrogen-rich compounds in the blood; pre-renal azotemia implies the problem lies somewhere proximal to the kidney itself, so there is nothing structurally wrong with the kidney. rapidly reversible if the underlying cause is treated—– if not treated—> ischemia induced acute tubular nephrosis—> intrarenal problem
What are some examples of pre-renal azotemia?
hemorrhage, GI fluid loss, trauma, surgery, burns, cardiogenic shock, sepsis, hepatic failure, aortic or renal clamping, thromboembolism
Among hospitalized patients, what are common causes of pre-renal azotemia?
CHF, liver dysfunction, septic shock
Where does intra-renal azotemia occur?
name implies that its cause lies within the parenchyma of the kidney itself
How is intra-renal azotemia categorized?
according to the primary site of injury: glomerulus, renal tubules, interstitium, renal vasculature
Why can injury to the kidneys occur during reperfusion?
d\t an influx of inflammatory cells, cytokines, and oxygen-free radicals; ischemia and toxins combine to cause AKI in severely ill patients with conditions such as sepsis or AIDS.
What are some causes of intra-renal azotemia?
acute interstitial nephritis most often caused by allergic reactions to drugs, glomerulonephritis, renal artery emboli, renal vein thrombosis, and vasculitis
What is post-renal azotemia?
AKI when urinary outflow tracts are obstructed; can use renal ultrasonography
What are s\s of post-renal azotemia?
generalized malaise, fluid overload (dyspnea, edema, and HTN), lethargy, nausea, confusion, accumulation of protein and amino acid metabolites, encephalopathy
Oliguria is defined as < ______mL/day or < _______ cc/kg/hr.
<0.5cc/kg/hr
Anuria is defined as < _______cc/day.
100; complete anuria is very unusual
What are AKI complications seen in central nervous system, cardiovascular, hematologic, and GI systems?
CNS: confusion, asterixis, somnolence, seizures, polyneuropathy—all are ameliorated by dialysis; CARDIO: systemic HTN, CHF, pulmonary edema, uremic pericarditis, peaked T waves and widened QRS (hyperkalemia), dysrhythmias—-ameliorated by dialysis; HEMAT: anemia (Hct as low as 20-30% d\t hemodilution and decreased erythropoietin production), coagulopathy (uremia induced platelet dysfunction; also give DDAVP–1-desamino-8-D-arginine vasopressin– to temporarily increase concentrations of vWF and factor VIII to improve circulation); GI: anorexia, N/V, paralytic ileus, GI bleed, gastroparesis
What are some treatments for AKI?
no specific treatments; limit further renal injury and correct fluid, electrolyte, and acid-base derangement; treat underlying cause; maintain MAP 65— no evidence that higher MAP and CO is better outcome
What fluids are preferred in patients with renal impairment and why?
0.9% Saline d\t lack of K+, but too much can cause hyperchloremic metabolic acidosis which secondarily causes hyperkalemia; no evidence to support use of colloids over crystalloids
What is the role of dopamine in treatment of AKI?
useless and associated with a number of undesirable side effects.
What is the overall concern with the use of vasopressors with AKI?
vasoconstriction may exacerbate tubular injury
Regardless of the cause, a decrease in GFR < _____ mL/min generally requires dialysis or renal transplant.
<25
What are the two general patterns of glomerular disease?
nephritic (inflammation and an active urine sediment containing red and white blood cells) and nephrotic (marked by proteinuria and relatively inactive urine sediment) patterns
What are some complications of nephrotic syndrome?
less circulating protein d\t proteinuria; result in higher circulation of highly protein-bound drugs d\t hypoalbuminemia—> need diuretics to offset kidneys propensity to retain sodium—> diruese slowly because abrupt natriuresis can cause hypovolemia and AKI
What is a renal problem characterized by inflammation of the renal pelvis (collecting ducts) and the kidney itself?
pyelonephritis; treated with antibiotics….. if infection ascends high enough, glomeruli are damaged
Are there any anesthetics we administer that have negative renal effects?
enflurane and sevoflurane, when in high doses, can potentially cause renal toxicity
What are ways to partially overcome renal impairment during anesthesia?
maintain adequate intravascular volume and normotension
Are renal effects more or less with regional vs. general anesthesia?
generally less
What are some indirect effects on the renal system during anesthesia caused by cardiac, neural, and endocrine effects?
most inhalation and IV anesthetics cause some degree of cardiac depression or vasodilation and can decrease arterial BP; sympathectomy caused by regional; decreases in BP below autoregulation can decrease RBF, GFR, urinary flow, and sodium excretion; neural effects such as sympathetic activation (DL, light anesthesia, tissue trauma) can cause increases in renal vascular resistance and activate hormonal systems— both tend to decrease GFR, RBF, and UO; endocrine effects: stress response to surgical stimulation, CV depression, hypoxia, or acidosis…. increases in catecholamines, ADH, and angiotensin II all reeice RBF by inducing renal arterial constriction….aldosterone enhances Na+ reabsorption
Why is Ketorolac (Toradol) not a good choice in most patients with renal impairment?
NSAID inhibits prostaglandin synthesis preventing renal production of vasodilatory prostaglandins in patient with high levels of angiotensin II and norepinephrine….. this attenuation of normal protective response can decrease GFR and produce renal dysfunction in some patients
What are some potential problems for the kidneys associated with ACE inhibitors?
these drugs block protective effects of angiotensin II and may result in additional reductions in GFR during surgery
What are some drugs that could cause renal artery vasospasm, direct cytotoxic injury, or renal tubular obstructions?
aminoglycosides, immunosuppressive agents (cyclosporins, tacrolimus), radiocontrast dyes
What are complications for the kidneys during aortic cross-clamping and CPB?
regardless of clamp position the RBF is decreased by 50%, clamp release causes increase RBF but GFR is impaired to only 2/3 normal for up to 24h, tubular functions (concentrating ability, sodium, and water conservation), mannitol—dopamine—-fenoldopam for renal protection
What lab values decrease in presence of renal failure?
calcium, albumin, red cell production/erythrpoietin/anemia
What lab values are increased in presence of renal failure?
potassium, phosphate, magnesium, uric acid
Why should cautionary use of PEEP be considered in renal patients?
studies found that 15cmH2O PEEP depressed CO, RBF, GFR, and urine volume by 20-30% and was associated with increases in renin and aldosterone
What are the effects of pneumoperitoneum, CPB, and pelvic surgery on renal function?
Pneumoperitoneum-(or even PEEP) abdominal compartment syndrome-like- state d/t renal vein and vena cava compression. Leads to increases in renin, aldosterone, and ADH. Cardiopulmonary bypass- non pulsatile flow, production of free radicals, and decreased renal perfusion at cross clamp time. Pelvic surgery- compression of the bladder by retractors, ligation of ureters, trendelenberg position impeding emptying of the bladder
Release of fluoride ions from VAA metabolic degradation with plasma concentrations > _____ micromol/L have been associated with renal toxicity.
> 50 micromol/L; fluoride production is greatest with prolonged use of enflurane and sevoflurane (compound A)…. but overall safe with impaired renal function
How does the body compensate to increase cardiac output?
Na retention and activation of renin-angiotensin system
What are considerations for induction of patients with renal disease?
slow and steady wins the race, RSI vs. standard d\t possible delayed gastric emptying, choice of agents
What are some considerations for intra-op maintenance of patients with renal disease?
focus on normotension, avoid hypoventilation (K, acidosis, etc) or hyperventilation (shift left)
Is morphine good for patients with renal disease?
not generally; morphine accumulation has been found to prolong respiratory depression in patients with renal failure; demerol has active metabolites associated with seizures
What is the NMB drug of choice for renal patients?
cisatricurium, atracurium, or mivacurium d\t ester hydrolysis and Hofmann elimination
What is the NMB drug of choice for renal patients?
cisatricurium, atracurium, or mivacurium d\t ester hydrolysis and Hofmann elimination
When can succinylcholine be safely administered to renal patients?
When serum K is <5meQ/L
When can succinylcholine be safely administered to renal patients?
When serum K is <5meQ/L
What are some renal considerations for vecuronium and rocuronium?
Vec is 20% eliminated in urine; prolongation of NMB with Rocuronium has been seen with severe renal disease
What are some renal considerations for vecuronium and rocuronium?
Vec is 20% eliminated in urine; prolongation of NMB with Rocuronium has been seen with severe renal disease
What is mannitol and its effects?
osmotic diuretic (6 carbon sugar); may activate intra-renal synthesis of vasodilating prostaglandins, increase, RBF, and act as a free radical scavenger
What is mannitol and its effects?
osmotic diuretic (6 carbon sugar); may activate intra-renal synthesis of vasodilating prostaglandins, increase, RBF, and act as a free radical scavenger
What is the danger in rapid correction of hyponatremia?
associated with demyelinating lesions in the pons resulting in serious permanent neurological conditions
What is the danger in rapid correction of hyponatremia?
associated with demyelinating lesions in the pons resulting in serious permanent neurological conditions
What is the effect of hypernatremia on anesthesia?
increases MAC for inhaled anesthetics in animal studies….. if related to hypovolemia, cardiac depressant and vasodilatory effects of these drugs will be enhanced leading to hypotension and hypoperfusion of tissues; less volume of distribution of IV medications and more rapid uptake of VAA because of decreased CO
What is the effect of hypernatremia on anesthesia?
increases MAC for inhaled anesthetics in animal studies….. if related to hypovolemia, cardiac depressant and vasodilatory effects of these drugs will be enhanced leading to hypotension and hypoperfusion of tissues; less volume of distribution of IV medications and more rapid uptake of VAA because of decreased CO
What is a cardiac consideration for patients with low calcium?
potentiation of negative inotropic effects of barbs and VAAs will be seen
What is a cardiac consideration for patients with low calcium?
potentiation of negative inotropic effects of barbs and VAAs will be seen
If a patient has magnesium imbalances, how does this effect anesthesia?
high: dosages of NDMBs should be decreased by 25-50%; low: cardiac arrythmias
If a patient has magnesium imbalances, how does this effect anesthesia?
high: dosages of NDMBs should be decreased by 25-50%; low: cardiac arrythmias
What are considerations during a TURP?
prostate is resected and large amounts of irrigation fluid are used; slightly hypotonic/non-electrolyte solutions are used d\t cautery; open venous sinuses in prostate and pressure of irrigation fluid allow systemic absorption of this irrigation fluid (2L or more); intra-op: arrthymias/hypotension; post-op: confusion, dyspnea, seizures; height of irrigation and length of procedure is KEY
What are considerations during a TURP?
prostate is resected and large amounts of irrigation fluid are used; slightly hypotonic/non-electrolyte solutions are used d\t cautery; open venous sinuses in prostate and pressure of irrigation fluid allow systemic absorption of this irrigation fluid (2L or more); intra-op: arrthymias/hypotension; post-op: confusion, dyspnea, seizures; height of irrigation and length of procedure is KEY
