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Critical Care > Renal Physiology > Flashcards

Renal Physiology Flashcards

1
Q

Definition of acidosis

A

an excess of H+ ions in the blood

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2
Q

Definition of alkalosis

A

a deficiency of H+ in the blood

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3
Q

Definition of base excess

A

the amount of acid required to restore 1L of blood to a normal pH at a pCO of 5.3kPa and at 37C

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4
Q

How to calculate the Anion Gap

A

([Na+] + [K+] ) minus ([Cl-] + [HCO3-])

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5
Q

DDx for high anion gap metabolic acidosis

A

CAT MUDPILES

C-CO, CN
A- Alcoholic ketoacidosis/ starvation ketoacidosis
T-toulene
M- metformin, methanol
U- remia
D- DKA
P- paracetamol, paraldehyde
I- isoniazid, iron
L-lactic acidosis
E- ethylene glycol
S- salicyclates

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6
Q

DDX of normal anion gap metabolic acidosis

A

A- Addison’s, hypoAldosteronism

B- bicarbonate loss (GI loss, renal loss)

C- chloride excess ( blood transfusion, NH4Cl)

D- diuretics (acetazolamide)

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7
Q

How to treat metabolic acidosis

A
  • Resuscitation
  • Organ support
  • Find and treat underlying cause
  • Give sodium bicarbonate if pH< 7.2 and hypercholeremic metabolic acidosis due to bicarbonate loss (controversial)
  • +/- dialysis
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8
Q

What is type A lactic acidosis?

A

Due to poor tissue perfusion and cellular hypoxia, resulting in anerobic metabolism, and increase production of lactate from pyruvate

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9
Q

What is type B lactic acidosis?

A

Occuring in state of normal global tissue perfusion. Can be due to drug-induced, inborn error of metabolism, localized tissue hypoxia

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10
Q

Explain mechanism behind paradoxical aciduria in GOO

A
  • GOO → hypocholeremic hypokalemic alkalosis + dehydration
  • initial attempts to maintain pH in renal tubules by preservation of H+ and excretion of HCO3- → initial alkaline urine
  • Attempts also to correct dehydration through angiotensin and aldosterone → preservation of Na+ at expense of K+
  • To maintain neutrality, Cl follows Na but due to lack of Cl, HCO3 resorption occurs instead
  • If condition not improved, and excessive loss of K+, kidneys will preserve K+ and excrete H+ leading to aciduria
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11
Q

Definition of AKI

A
  • A sudden rise in serum creatinine of 50 mmol/l, or >50% from baseline
  • Oliguria with urine output < 400 ml/day
  • Need for renal replacement therapy
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12
Q

Prerenal causes of AKI

A
  • Decrease in renal perfusion due to
    • Pump failure (MI, CHF)
    • Decrease intravascular volume
      • Hypovolemia
      • Distributive
    • Abdominal compartment syndrome
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13
Q

Renal causes of AKI

A
  • Acute tubular necrosis (80%) :
    • Ischemia
    • Nephrotoxic drugs: antibiotics, contrast, myoglobin/hemoglobin
  • Interstitial nephritis (NSAID, antibiotics)
  • Glomerular disease (glomerulonephritis, SLE, DIC
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14
Q

Post renal causes

A
  • Obstruction of outflow
    • Blocked foley catheter
    • Stones
    • Extrinsic compression by pelvic tumor
    • BPH
    • Urethral stricture/ transection from trauma
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15
Q

What investigations can help distinguish pre-renal from renal causes

A

Urinary sodium

Urinary osmolality

Urine microscopy (any tubular casts)

*kidney function is preserved in pre-renal causes

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16
Q

Indication for renal replacement therapy

A
  • Symptomatic uraemia, uraemic encephalopathy/pericarditis
  • Metabolic acidosis (pH < 7.1)
  • Severe hyperkalaemia, unresponsive to medical therapy
  • Pulmonary oedema not responding to medical treatment
  • Poisoning (dialyzable toxin)
  • High urea and creatinine (relative indication)
17
Q

Management of post-op renal failure

A
  • Rule out post-renal cause
  • Rule out pre-renal cause
  • Consider renal cause if post/pre-renal cause (renal causes mainly supportive)
  • If clinically cannot differentiate, urinalysis
18
Q

Urinalysis suggesting preserved concentrating function

A
  • Urine Na< 20
  • Urine Osmo >400
  • Specific graviy > 1.024
  • FeNa<1
19
Q

Indication of renal replacement therapy

A
  • Persistent hyperkalemia (>6mmol/L)
  • Metabolic acidosis (pH < 7.2) with negative BE
  • Fluid overload
  • Uremia with complications(pericarditis, encephalopathy)
  • Certain drug and alcohol intoxication
20
Q

Preoperative management for chronic renal failure

A
  • Establish severity of the renal failure
  • Identify coexisting conditions (CVS, DM)
  • Optimize volume status, correct electrolytes / anemia/ malnutrition
  • Adjust medication for renal impairment, avoid nephrotoxic drugs
  • Obtain baseline BW
  • For CAPD, drain abdomen before GA
  • For HD, recieve last dialysis 6-30hours before surgery
21
Q

Intraoperative management of chronic renal failure

A
  • Careful use of muslce relaxant (succinylcholine raises serum K)
  • Preserve vascular access
22
Q

Postoperative management of patient’s with chronic renal failure

A
  • Close monitoring of intravascular volume status
  • Serial monitoring of electrolytes and acid-base
  • REduce dose of narcotics to prevent respiratory distress
  • Nuritional support
  • Resume HD with low-dose heparin
23
Q

Methods of renal replacement therapy

A
  • Intermittent haemodialysis
  • Continuous renal replacement therapies
    • CVVHemofiltration
    • CVVHemoDialysis
    • CAVHD
  • Renal transplant
24
Q

Hemofiltration

A
  • blood pumped through extracorporeal system that has a semi-permeable membrane
  • driven by hydrostatic pressure of pump
  • small molecules dragged through membrane by convection
  • filtered fluid (ultrafiltrate) discarded
25
Q

Hemodialysis

A
  • blood pumped through extracorporeal system with a dialyser
  • Blood separated from dialysate with semi-permeable membrane
  • Solutes move across by diffusion
  • Dialysate flows countercurrent to maintain concentration gradient
  • If removal of water required, pressure on blood side must be increased
26
Q

Factors determining type of RRT

A
  • Size of molecules to remove(for larger molecules, filtration better than dialysate)
  • Patient’s cardiovascular status (CRRT less rapid fluid shift)
  • Resource availability
27
Q

Components of a HD circuit

A
  • Vascular access
  • Extracorporeal circuit
  • Dialysis machine
  • Roller pump
28
Q

Risk factors for contrast nephropathy

A
  • Pre-existing renal failure
  • Periprocedural volume depletion
  • Congestive heart failure
  • DM with renal impairment
  • Age > 75

Critical Care (12 decks)

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