Equations

Question 1

Free Water Clearance

Answer 1

CH2O = V {urine flow rate} - Cosm {osmolar clearance}

CH2O = V - ([Uosm * V] / Posm)

Uosm = Urinary osmolarity
Posm = Plasma osmolarity

Question 2

Filtered Load

Answer 2

FL = GFR * Plasma [ ] * % Filterability

FL = (([Ux] {urinary concentration of ‘x’} * V {urine flow rate}) / [Px] {plasma concentration of ‘x’}) * Plasma [ ] * % Filterability

Question 3

Anion Gap

Answer 3

Anion Gap = [Na+] - ([Cl-] + [HCO3-])

Question 4

Henderson-Hasselbach Equation

Answer 4

pH = pka +log ([Base/Acid])

Question 5

Henderson Hasselbach Equation for Bicarbonate buffer system

Answer 5

pH = 6.1 + log ([HCO3-]/[H2CO3])

pH = 6.1 + log ([HCO3-]/[0.03 * Pco2 {plasma CO2 concetration}]

Question 6

Net Acid Excretion

Answer 6

NAE = [(Unh4+ * V) + (Uta+ * V) - (Uhco3- * V)]

Unh4+ = Urinary NH4+

Uta+ = Urinary titratable acids (phosphate salts and creatinine)

Uhco3- = Urinary HCO3-

V = Urine flow rate

Question 7

How to determine whether you have Chronic Respiratory Acidosis?

Answer 7

[HCO3-] = 24 + (0.4 * (PaCO2 - 40))

Question 8

How to determine whether you have acute Respiratory Acidosis?

Answer 8

[HCO3-] = 24 + (0.1 * (PaCO2 - 40))

Question 9

How to determine whether you have Chronic Respiratory Alkalosis?

Answer 9

[HCO3-] = 24 - (0.5 * (40 - PaCO2))

Question 10

How to determine whether you have Acute Respiratory Alkalosis?

Answer 10

[HCO3-] = 24 - (0.2 * (40 - PaCO2))

Question 11

When are you concerned about anion gap?

Answer 11

When you have metabolic acidosis

Question 12

When are you concerned with using the [HCO3-] equations?

Answer 12

When you have respiratory acidosis/alkalosis and are looking for acute/chronic diagnosis

Question 13

When are you concerned with Cl-responsiveness?

Answer 13

Metabolic alkalosis