Acid/Base Phys Flashcards
LO 1. Define the Henderson-Hasselbalch Equation for Bicarbonate/CO2.
H2O + CO2 H2CO3 H+ + HCO3- pH = 6.1 + log [HCO3] / 0.03xPCO2 For a normal bicarbonate concentration of 24 mM (at sea-level) and an arterial PCO2 of 40 Torr, the Henderson-Hasselbalch equation gives arterial blood pH of 7.40.
What is normal human pH?
normal pH is 7.4 (7.38-7.43, perhaps a bit higher here in Denver)
What are the 2 major types of buffers?
intracellular and extracellular
What are the intracellular buffers?
organic phosphates, proteins, ESPECIALLY hemoglobin
What are the extracellular buffers?
phosphate, ESPECIALLY bicarbonate and plasma proteins (mostly albumin)
pH = pK + log [A-] [HA]
Henderson-Hasselbalch Equation
For humans, the best buffer ought to be close to what pH?
7.4
______ is the conjugate base of carbonic acid.
Bicarbonate
Bicarbonate is the conjugate base of _______.
carbonic acid
Why is bicarbonate the most important buffer in the body?
- It is present in relatively high concentration (higher than phosphate)
- The pK is relatively close to arterial pH
- The conjugate acid, CO2, is readily controlled via ventilation by the lungs
_______ has a pK of 7.9.
Deoxyhemoglobin
Deoxyhemoglobin has a pK of _____.
7.9
Carbon dioxide can then diffuse into red blood cells, where it is rapidly converted to bicarbonate and the protons are buffered by _______.
deoxyhemoglobin
Carbon dioxide can then diffuse into red blood cells, where it is rapidly converted to ______ and the protons are buffered by deoxyhemoglobin.
bicarbonate
The acid/base status of normal arterial blood can be altered in two general ways: (a) ________, or (b) by too much or too little acid, resulting in a metabolic disturbance.
by altering PCO2 resulting in a respiratory disorder
The acid/base status of normal arterial blood can be altered in two general ways: (a) by altering PCO2 resulting in a respiratory disorder or (b) ______.
by too much or too little acid, resulting in a metabolic disturbance
Too much acid in the blood is referred to as ______, and too much base in the blood is referred to as ______.
academia; alkalemia
Because CO2 can be regulated by the _______ and bicarbonate can be regulated by the _______, the body will attempt to compensate for any acid-base disturbance to try and correct the pH back towards normal.
lungs; kidneys
What is respiratory acidosis?
an increase in arterial PCO2, leading to a decrease in pH
This is an increase in arterial PCO2, leading to a decrease in pH.
respiratory acidosis
What can lead to chronic respiratory failure?
- emphysema
- chronic bronchitis (COPD)
- bronchiectasis
- Central hypoventilation disorders (obesity hypoventilation)
- neuromuscular diseases (e.g. ALS, AKA Lou Gehrig’s disease)
What causes acute respiratory failure?
- drugs (opiates, benzos, EtOH) 2. muscle fatigue
Which compensatory mechanism is slow, taking 2-3 days to complete?
bicarbonate conservation in the kidneys
What is respiratory alkalosis?
a decrease in arterial PCO2, leading to an increase in pH
This is a decrease in arterial PCO2, leading to an increase in pH.
respiratory alkalosis
What are the most common causes of chronic alveolar hyperventilation?
- high altitude
- neuro disorders
- chronic salicylate (aspirin) toxicity
What are the most common causes of acute alveolar hyperventilation?
- pain/anxiety
- mechanical ventilation
Compensation of respiratory alkalosis takes place through the ______, which increase the excretion of bicarbonate and lower the pH toward its normal value.
kidneys
Compensation of respiratory alkalosis takes place through the kidneys, which increase the excretion of ______ and ______ the pH toward its normal value.
bicarbonate; lower
What is metabolic acidosis?
a primary addition of an acid other than CO2 leading to a reduction in bicarbonate
The major cation in serum is ______ and the major anions are ______ and ______.
sodium; chloride, bicarbonate
What is the anion gap (AG)?
other substances in the blood that lead to a difference between sodium concentration and the two major anions AG = Na+ - (Cl- + HCO3-) = 12 ± 2 under normal circumstances
What are the most common causes of anion gap metabolic acidosis?
MUDPILES = Methanol Uremia Diabetic ketoacidosis (and other causes of ketoacidosis such as starvation and alcoholism) Propylene glycol Isoniazid Lactate Ethylene glycol Salicylates
What is anion gap metabolic acidosis?
a metabolic acidosis from additional unmeasured acids in the blood with an anion gap larger than usual
If the anion gap is not elevated but the pH is low, then a _______ exists.
non-gap metabolic acidosis
If the anion gap is _______ but the pH is low, then a non-gap metabolic acidosis exists.
not elevated
What causes a non-gap metabolic acidosis?
GI or renal losses; giving large amounts of normal saline to pts
Compensation for a metabolic acidosis is ________.
increased ventilation
What causes metabolic alkalosis?
- base additions (antacids, baking soda)
- vomiting
- hypovolemia
Compensation for the increase in pH leads to a ______ in ventilation and a/an ________ in PCO2.
decrease; increase
For respiratory disturbances, an acute change in PaCO2 of ______ yields a pH change of about _____ (increased PaCO2 leads to decreased pH).
10 Torr; 0.08
For respiratory disturbances, an acute change in ______ of 10 Torr yields a _____ change of about 0.08.
PaCO2; pH
For _______, a change in PaCO2 of 1 Torr should lead to compensatory change in [HCO3–] of 0.4 meq/L in the same direction (e.g., increases in [HCO3–] for increases in pCO2) to bring the pH back to normal.
chronic respiratory disturbances
For chronic respiratory disturbances, a change in PaCO2 of _____ should lead to compensatory change in [HCO3–] of ______ in the same direction (e.g., increases in [HCO3–] for increases in pCO2) to bring the pH back to normal.
1 Torr; 0.4 meq/L
For chronic respiratory disturbances, a change in _____ of 1 Torr should lead to compensatory change in ______ of 0.4 meq/L in the same direction to bring the pH back to normal.
PaCO2; [HCO3–]
For _______, a decrease in [HCO3–] of 1 meq/L should result in a decrease in PaCO2 of 1.3 Torr and an increase in [HCO3-] of 1mEq/L should result in an increase in PaCO2 of 0.7 Torr to bring the pH back to normal.
metabolic disturbances
For metabolic disturbances, a decrease in (a)______ of 1 meq/L should result in a decrease in (b) _____ of 1.3 Torr and an increase in (a) of 1mEq/L should result in an increase in (b) of 0.7 Torr to bring the pH back to normal.
(a) [HCO3–]; (b) PaCO2
For metabolic disturbances, a decrease in [HCO3–] of ______ should result in a decrease in PaCO2 of _____ and an increase in [HCO3-] of 1mEq/L should result in an increase in PaCO2 of 0.7 Torr to bring the pH back to normal.
1 meq/L; 1.3 Torr
For metabolic disturbances, a decrease in [HCO3–] of 1 meq/L should result in a decrease in PaCO2 of 1.3 Torr and an increase in [HCO3-] of ______ should result in an increase in PaCO2 of _____ to bring the pH back to normal.
1mEq/L; 0.7 Torr
Normal blood gas values
- pH = 7.40±0.02
- PaCO2 = 36±2 Torr
- [HCO3–] = 22±2 meq/L
- PaO2 = 70-80 Torr
Low pH combined with an increase in PaCO2 tells you right away that the primary disturbance is ______.
a respiratory acidosis
_____ combined with ______ tells you right away that the primary disturbance is a respiratory acidosis.
Low pH; an increase in PaCO2
pH is elevated with an elevated PaCO2 and the [HCO–] is also elevated so this is a _____.
metabolic alkalosis
The high pH with a low PaCO2 means this is a ______.
respiratory alkalosis
