Acid-Base Lecture Flashcards
Normal metabolism produces ___ meq/L of non volatile (H ) acid together with volatile acid (CO2) daily.
1 meq/L
body fluid pH is tightly maintained at…
7.40
norm= 7.38-7.42
weak base
*levels regulated by kidneys and maintained for buffering
HCO3
Where is the bicarbonate buffer system located?
extracellular space
Total venous CO2 can be estimated by looking at….
HCO3 levels
Primary respiratory disorders effect….
pCO2
Primary metabolic disorders effect…
HCO3
Do compensatory changes totally correct the pH?
NO! …they move towards normal but do not fully compensate/correct
pH decreased, PCO2 increased, HCO3 increased (comp.), acute and chronic forms.
Respiratory acidosis
pH increased, PCO2 decreased, HCO3 decreased (comp.), acute and chronic forms.
Respiratory alkalosis
pH decreased, HCO3 decreased, PCO2 decreased (comp.)
Metabolic acidosis
pH increased, HCO3 increased, PCO2 increased (comp.)
Metabolic alkalosis
Compensatory mechanism includes:
*increase ventilatory drive, which will blow off more CO2 gas, causing a shift back towards normal pH
Metabolic acidosis
Compensatory mechanism: decrease ventilatory drive to hold onto CO2
Metabolic alkalosis
Primary defect is increased PCO2 as a result of decreased alveolar ventilation.
Respiratory acidosis
Trouble getting rid of CO2 gas in…
Respiratory acidosis
CO2 +H2O ⇔ H2CO3 ⇔ H + HCO3
which way will this equation shift in Respiratory acidosis?
Towards right
due to increase in CO2 gas
Conditions associated with decreased ventilation: severe COPD; asthmatic who tires; drug OD with suppression of ventilatory drive, neuromuscular diseases.
Symptoms: somnolence, confusion (CO2 narcosis), coma, resp. arrest.
Respiratory Acidosis
CO2 narcosis
somnolence
confusion
*seen in respiratory acidosis
first 24 hours of respiratory acidosis, what do HCO3 levels look like?
*when does compensation start
Normal in 24 hrs
*over about 3 days, HCO3 levels will increase..leading to compensation
Acute – the pH decreases 0.08 units for every 10mmHg increase in PCO2**
Respiratory acidosis
In ACUTE respiratory acidosis, every 10 mmHg increase in PCO2 leads to a decrease in pH of….
0.08 units
Chronic - HCO3 ↑1.1-3.5 mEq/liter per ↑10 mmHg PCO2; pH will move towards normal
Respiratory acidosis
Little Billy got into some of dad’s pain meds (oxycodone). He suffers a significant depression of mental status and respiration. You see him in the ED 3 hours after ingestion. He is somnolent with a respiratory rate of 4. A blood gas is obtained: pH- 7.16, PCO2- 70mmHg, HCO3- 24 meq/L
UNCOMPENSATED respiratory acidosis
*bicarb levels haven’t started to rise yet, so you know its uncompensated
(tx=ventilate and rapidly reverse effects of narcotics)
Ventilatory support until the underlying disorder can be corrected
*Narcotic antagonist if applicable
Tx for Respiratory Acidosis
Narcotic OD leading to decreased respirations can lead to….
Respiratory Acidosis
Increase in CO2 levels due to a decrease in respirations….
Respiratory acidosis
Primary defect is decreased PCO2 as a result of increased alveolar ventilation.
Respiratory alkalosis
Decreased CO2 levels due to increase in ventilation
Respiratory alkalosis
CO2 +H2O ⇔ H2CO3 ⇔ H + HCO3
Which direction does this equation move in Respiratory alkalosis?
Left!
bc decrease of CO2 in body during Respiratory alkalosis
Hyperventilation: anxiety, panic attacks, sepsis, CNS insult, cirrhosis, salicylates, progesterone, mechanical over ventilation, etc.
**Symptoms- lightheadedness, paresthesias, tetany.
Respiratory alkalosis
Address the underlying cause; most cases of anxiety-hyperventilation syndrome are self-limited→respiratory muscle fatigue.
**When acute anxiety is a factor, re-breathing into a paper bag may be useful (short term fix only).
Respiratory alkalosis
Most common acid-base disturbance?
Metabolic acidosis
Primary measured defect is decreased HCO3 (combines with increased H ions to buffer) with resultant drop in pH.
Metabolic acidosis
Compensatory response to Metabolic Acidosis is decreased…
pCO2
hyper-ventilation
Lactic acidosis
Diabetic ketoacidosis
Most common causes of metabolic acidosis
Na - (HCO3 + Cl) = 4-10
anion gap
most metabolic acidosis increases anion gap bc HCO3 levels go down
Most metabolic acidosis _____ the anion gap
increases
bc HCO3 levels go down
Lactic Acidosis (cardiogenic shock or arrest). Lactate (unmeasured anion) prod. due to inadequate tissue perfusion or hypoxia.
Metabolic acidosis
increased anion gap
DKA-Hyperglycemia with metabolic acidosis; increased production of ß-hydroxybutyric & acetoacetic acids (ketoacids→hyperketonemia).
Metabolic acidosis
increased anion gap
Toxins- Ethylene glycol, salicylates, methanol. Uremia (severe renal failure)- endogenous acids.
Metabolic acidosis
increased anion gap
pH
increased anion gap metabolic acidosis
Hallmark is acidosis, decreased HCO3 and hyperchloremia.
GI HCO3 losses from pancreatic or small bowel contents.
Normal anion gap metabolic acidosis
massive (secretory) diarrhea with volume contraction (NaCL and K loss as well); HCO3 secretion in small/large intestine is accompanied by Cl generation/absorption (countertransport); volume contraction leads to NA and Cl retention in the kidney.
Normal anion gap metabolic acidosis
Renal tubular acidosis is an example of…
Normal anion gap acidosis
JR has had intermittent vomiting and severe diarrhea for 4 days. He has been unable to keep fluids down and has not urinated in 8 hours. He has a cardiomyopathy with compensated HF.
PE: P-90, BP-90/70 with postural changes. He appears lethargic and cool to touch with a prolonged capillary refill time. His arterial blood gas reveals: pH=7.30, PCO2=28mmHg, HCO3=14meq/L.
Na-136meq/L, K-3.0meq/L, Cl-110meq/L
Compensated metabolic acidosis
Hallmark: High HCO3 with increased pH.
Metabolic alkalosis
excessive lost of gastric contents (i.e. vomiting)
*results in loss of Na, Cl, volume and H+
Metabolic alkalosis
Severe vomiting or continuous NG suction: HCl and NaCl losses from stomach initiate the alkalosis and volume contraction. Cl loss (and ↓total body stores) sustains the alkalosis because ↑renal Na reabsorption from volume contraction is accompanied by HCO3 reabsorption (most available anion with Cl depleted).
Metabolic alkalosis
What happens to the anion gap during metabolic acidosis? (HCO3 is loss)
Increase in anion gap!
*a loss of HCO3 leads to an increase in the anion gap
To drop pCO2 (blow off CO2) you….
breathe faster!
in respiratory acidosis (increase in pCO2), there can either be no compensation (no HCO3 change) OR compensation (increased HCO3) because….
the kidneys take time to compensate
*compensation (increase in HCO3) takes time!
if the pH and pCO2 are going in the same direction, it is what kind of process?
Metabolic
if the pH and pCO2 are going in the opposite direction, it is what kind of process?
Respiratory
ROME
Respiratory
Opposite
Metabolic
Equal
When HCO is loss..what happens to the anion gap?
Anion gap increases
Na - (Cl + HCO3) = 12
Normal anion gap
anion gap and HCO3 concentration are ____ related
inversely
*anion gap increases when HCO3 concentration decreases
GI HCO3 losses from pancreatic or small bowel contents
Non anion gap acidosis (NAGA)
massive (secretory) diarrhea with volume contraction (NaCL and K loss as well); HCO3 secretion in small/large intestine is accompanied by Cl generation/absorption (countertransport); volume contraction leads to NA and Cl retention in the kidney.
Non anion gap acidosis (NAGA)
seen with extracellular volume contraction and hypokalemia. Responds to saline administration.
Metabolic alkalosis
Severe vomiting or continuous NG suction: HCl and NaCl losses from stomach
Metabolic alkalosis
Activation of the RAA system to maintain volume results in hypokalemia (↑Na/K/H exchange in distal tubule) and additional H losses.
Occurs with metabolic alkalosis
Massive diarrhea (NAGA) Renal tubular (NAGA) Lactic Acidosis (increased AG) DKA (increased AG) Toxins, uremia (increased AG)
Metabolic acidosis
When HCO3 combines with H+, there is what kind of acidosis
anion gap
non anion gap acidosis is when HCO3 is just loss
Entire sequence is rapidly corrected by administering 0.9% saline* (isotonic) with supplemental KCL. The process will self perpetuate until adequate amounts of Na/K/Cl and H2O are available.
Metabolic alkalosis tx
For metabolic compensation..
pCO2 increases 0.5-1.0 mmHg per increase in ___ mEq/L HCO3
1
