Flashcards in Cremo 6: Simple acid base disturbances Deck (36):
What is the difference between an -EMIA and an -OSIS? I.e. acidemia vs acidosis.
Acidemia refers to what the blood is doing.
Acidosis refers to a pathological process that causes pH to change.
What causes respiratory acidosis or alkalosis?
Pathological change in PaCO2. Often caused by abnormal function of the lung.
What causes metabolic acidosis or alkalosis?
Pathological change in [HCO3-]
pka + log(kidney/lung)
pka + log([HCO3-]/PaCO2)
pka + log(metabolic/respiratory)
What does a Davenport diagram tell you?
How blood will respond to changes in PaCO2
What does the steeper buffer line of blood reflect?
Reflects the presence of more non-volatile buffering power
What causes respiratory acidosis or alkalosis?
Pathological changes in PaCO2
In respiratory acidosis, there is a slight increase in [HCO3-] when pH decreases, but is SMALL compared to (blank)
Change in [HCO3-] during metabolic-oses
Common clinical causes of acute respiratory acidosis
-upper airway obstruction
-severe asthma attack
With respiratory alkalosis, there is a slight decrease in [HCO3-], but this is SMALL compared to (blank)
Change in [HCO3-] that occurs in metabolic-oses
Respiratory alkalosis can be caused by an increase in central drive to breathe. What variable increases?
Four conditions that act as abnormal ventilatory stimuli to increase central drive to breathe
1. arterial hypoxemia or hypoxia
2. direct stimulation of pulmonary mechano and chemo receptors by lung disease
3. chemical or physical factors that directly stimulate the medullary respiratory center
4. psychological factors
Most common pulmonary diseases can lead to (blank)
Why can hypoxemia cause respiratory alkalosis?
Think about it. Central chemoreceptors sense increase in PaCO2 in blood and respond by increasing ventilation.
The same diseases that cause respiratory alkalosis can cause respiratory acidosis. Discuss.
So, in the beginning of the disease, strength wins. Many pulmonary diseases will progress from alkalosis to acidosis if they are severe enough to decrease muscle strength and increase load enough to tip the balance.
What wins in respiratory acidosis: strength or load?
What wins in respiratory alkalosis: strength or load?
How does the blood respond to changes in addition of strong acid or base (EAP)?
[HCO3-] will increase or decrease along the isopleth! No change in PaCO2, because it is fixed.
In hypobicarbonatemia, there is a decrease in pH. What two things can cause this to occur?
Increase in EAP
Reduced net acid excretion due to renal defects
Gastrointestinal cause of acidosis?
Think diarrhea. Lots of stool, so loss of bicarb :( So, increase in HCO3- secretion by lower gut to try to compensate. This causes a concomitant increase in H+ delivered to blood. Meanwhile, blood HCO3- is consumed. Acidosis.
Hypoxia as a metabolic cause of acidosis. Discuss.
So, complete metabolism of organic acid production requires O2. During hypoxia, organic acids will build up, because they cannot be metabolized. This causes acidosis.
Vomiting causes (blank)
Recall, respiratory acidosis and alkalosis cause (blank) changes in HCO3-, while metabolic acidosis and alkalosis cause (blank) changes in HCO3-
pH down by 0.07
HCO3- up slightly (~1 mM)
Acute respiratory acidosis
pH up by 0.08
HCO3- down slightly (~2 mM)
Acute respiratory alkalosis
Purpose of any compensation, whether it be by the lung or kidney.
Return the pH toward normal. It will not go back to 7.4 as long as the disturbance is still present.
Respiratory acidosis and alkalosis can be acute or chronic, but metabolic acidosis and alkolosis cannot. Why?
Respiratory compensation to metabolic conditions is very fast.
Chronic respiratory acidosis.
In Phase 1, body buffers respond within the first ten minutes of an increase in PCO2.
Phase 2 occurs much more slowly. What does it involve?
Renal mechanisms: increase H+ excretion (new bicarb production), increase bicarb reabsorption
Primary change: fall in [HCO3-]
Rapid compensatory change: fall in PaCO2
Expected rapid compensatory response by lung during metabolic acidosis
PaCO2 = 1.5 x [HCO3-] + 8 ± 2 (Winter’s Formula)
Primary change: rise in [HCO3-]
Compensatory change: rise in PaCO2
Expected rapid compensatory response by lung during metabolic alkalosis
PaCO2 = 0.7 [HCO3-] + 20 (+/- 5)
What is the rule of thumb for determining acute respiratory alkalosis?
Rule is that for every 10 mm Hg decrease in PaCO2, there is a 0.8 increase in pH
What is the rule of thumb for determining acute respiratory acidosis?
Rule is that for every 10 mm Hg increase in PaCO2, the pH goes down by 0.07
Equation for anion gap
Gap = Na+ - (Cl- + HCO3-) where HCO3 is really the value of CO2