Unit 3 Day 3 (Thur 4/23)

Question 1

Define Henderson-Hasselbalch Equation for Bicarbonate/CO2

Answer 1

pH is defined as –log [H+] which gives:

-log [H+] = -log Ka- log [HA]/[A-]

or

pH = pKa + log[A-][HA]

Question 2

Normal arterial blood gas values for pH, PaCO2, and [HCO3]

Answer 2

• pH: 7.4(little higher in Denver)
• PaCO2: 40mm Hg
• HCO3: 24 mEq/L

Question 3

Four Major Acid-Base Disorders

Answer 3

• respiratory acidosis
• respiratory alkylosis
• metabolic acidosis
• metabolic alkalosis

Question 4

Respiratory Acidosis Causes

Answer 4

• common cause:
• -acute: CNS depressants (opiates, benzos, alcohol), respirator muscle fatigue (inc. work of breathing)
• -chronic: central hypoventilation (obesity hypoventilation syndrome), neuromuscular disease (ALS), chronic lung diseases (emphysema, bronchiectasis), hypothyroidism

Question 5

Respiratory Alkalosis Causes

Answer 5

• acute causes: pain, anxiety/panic attack, fever, mechanical ventilation
• chronic causes: living at altitude, brain injury, chronic salicylate toxicity, pregnancy

Question 6

Metabolic Acidosis Causes

Answer 6

• anion gap: methanol, uremia, DKA, propylene glycol, INH, lactate, ethylene glycol, salicylates (mud piles)
• non-anion gap: GI losses (diarrhea), renal losses (RTA), too much IV saline (inc. Cl- with loss of bicarb)

Question 7

Metabolic Alkalosis Causes

Answer 7

• vomiting or NG tube suction (loss of gastric acid)
• ingestion of NaHCO3
• ingestion of other alkali
• hypovolemia, so called contration alkalosis
• diuretics

Question 8

Respiratory Acidosis Compensation

Answer 8

•acute change in PaCO2 of 10 Torr pH changes about 0.08 •PaCO2 of 1 Torr change in [HCO3–]of 0.4 meq/L in the same direction

Question 9

Respiratory Alkalosis Compensation

Answer 9

• acute change in PaCO2 of 10 Torr pH changes about 0.08

* PaCO2of1Torrchangein [HCO3–]of 0.4 meq/L in the same direction

Question 10

Metabolic Acidosis Compensation

Answer 10

Expected pCO2 = 1.5[HCO3-] + 8± 2

Question 11

Respiratory Acidosis Acid-Base Disturbancs

Answer 11

• pH dec.
• pCO2 inc.
• HCO3- no change/small inc.

Question 12

Metabolic Alkalosis Compensation

Answer 12

Increase [HCO3-] of 1mEq/L increases PaCO2 by 0.7 Torr

Question 13

Respiratory Alkalosis Acid-Base Disturbances

Answer 13

• pH inc.
• pCO2 dec.
• HCO3- no change/small dec.

Question 14

Metabolic Acidosis Acid-Base Disturbances

Answer 14

• pH dec.
• pCO2 dec.
• HCO3- dec.

Question 15

Metabolic Alkalosis Acid-Base Disturbances

Answer 15

• pH inc.
• pCO2 inc.
• HCO3 inc.

Question 16

Anion Gap

Answer 16

anion gap = [Na] - ([Cl] +[HCO3-])

• normally 12-14
• the difference in the measured cations and the measured anions in serum, plasma, or urine.

Question 17

Winter’s Formula

Answer 17

expected pCO2 = 1.5 [HCO3-] + 8 +/- 2

• compare to given PCO2
• compensation rule
• if within range, it is compensated/probably chronic

Question 18

A-a Gradient

Answer 18

PAO2 = (630-47) x FiO2 - (PCO2/0.8) - PaO2

• useful in determining the source of hypoxemia
• isolates the location of the problem as either intrapulmonary or extrapulmonary
• normal is between 5 - 20
• an inc. A–a gradient suggests a defect in diffusion, V/Q mismatch, or right-to-left shunt.