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NP18 Nephrology
Acute Kidney Injury Toronto Notes 2019 Metabolic alkalosis (pH,HCO3)
UCl <20 mEq/L
Saline responsive
Prior diuretics
• Volume depleted
UCl >20 mEq/L
Assess volume status
GI losses
• Vomiting • NG tube
Post-hypercapnia
Volume depleted
Diuretic use
Hypertensive
• 1o hyperaldosteronism • 2o hyperaldosteronism • Cushing’s syndrome
Normal ECF volume
Saline resistant
Check blood pressure
Note: cannot use UNa to assess volume status in presence of alkalemia: HCO3 excretion, drags NaNa excretion
UCl = Urine chloride
Figure 10. Approach to metabolic alkalosis
Polyuria
Definition
Normotensive
• Exogenous alkali
• Severe hypokalemia • Bartter’s, Gitelman’s
The 2 most common causes of acute kidney injury in hospitalized patients are prerenal azotemia and ATN; remember that prerenal failure can lead to ATN
• outputgreaterthan3L/d.Distinguishfromurinaryfrequency,whereurinationoccursmultipletimes per day but the total volume over 24 h is <3 L
Etiology
• drugs(mostcommonlydiuretics)
• excessivecaffeine,alcoholintake
• increasedwaterintake(psychogenicpolydipsia,IVfluids)
• uncontrolleddiabetesmellitus(osmoticdiuresis)
• neurological:diabetesinsipidus(centralandperipheral),cerebralsalt-wastingsyndrome • genitourinary:post-obstructivediuresis,cystitis/UTI
Clinical Features
• mustdistinguishbetweentruepolyuriaandurinaryfrequency
• lookforsourcesofexternalfluidintake(IVfluids,tubefeedings)
• assessforneurologicalchanges(stroke,trauma,post-operative)(forcentraldiabetesinsipidus) • assessfordrugsthatmaycausenephrogenicdiabetesinsipidus(e.g.lithium)
• abruptonsetsuggestscentraldiabetesinsipidus
Investigation Findings
• hypernatremiasuggestsfreewaterlosssecondarytodiabetesinsipidus
■ hyponatremia suggests free water intake secondary to polydipsia
■ measure serum electrolyte/osmolality and urine osmolality after water deprivation test, see Diabetes
Insipidus, NP11 for complete workup for diabetes insipidus Treatment
• addressedtoetiology
Acute Kidney Injury
Definition
• abruptdeclineinrenalfunctionleadingtoincreasednitrogenouswasteproductsnormallyexcretedby the kidney
• formerlyknownasacuterenalfailure
Clinical Presentation
• azotemia(increasedBUN,Cr)
• abnormalurinevolume:formally<0.5ml/kg/hfor>6hbutcanmanifestasanuria,oliguria,orpolyuria