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Acid Base Disorders
Transcript of Acid Base Disorders
Check Arterial pH
Check Anion Gap
= Na - (Cl + HCO3)
- Acute lung dx
- Chronic lung dx (COPD)
- Opioids, narcotics,
sedatives > Hypoventilation
- Weakening of Respiratory muscles
- Alveolar Hyperventilation
- Pulmonary Embolism, pneumonia, asthma
- Mechanical Ventilation
- Liver disease
- Salicylate toxicity
- Antacid use
Increased Anion Gap
Normal Anion Gap (8-12 mEq/L)
Methanol (formic acid)
Paraldehyde or Phenytoin
Intoxication, Iron tablets, Isoniazid
- Glue sniffing
- Renal tubular acidosis
Is it Acidosis? Metabolic? Anion Gap? Compensated? Corrected?
What are the normal values?
pH = 7.40
pCO2 = 40
HCO3 = 24
pO2 = 100-.25(age)
What are the clinical effects?
- Right shift in oxygen-hemoglobin dissociation curve diminishes the affinity of hemoglobin for oxygen. (Increased oxygen delivery to tissues)
- Depresses CNS
- Decreases pulmonary blood flow
- Impairs myocardial function
- Decreases cerebral blood flow
- Left shift in oxygen-hemoglobin dissociation curve increases the affinity of hemoglobin for oxygen (so decreases oxygen delivery to tissues)
- Tetany, seizures
YoungKey Chung, MSIII
Wayne State University School of Medicine
Acute or Chronic Respiratory Acidosis?
Immediate compensation elevation of HCO3-
Increase of 1 mmol/L for every 10 mmHg increase in PaCO2
Kidneys will slowly adapt
HCO3- increase of 4 mmol/L for every 10 mmHg increase in PaCO2
Acute or Chronic Respiratory Alkalosis?
For every 10 mm Hg decrease in PaCO2, plasma HCO3 decreases by 2 mEq/L
pH increases by 0.08 mEq/L
For each 10 mmHg decrease in paCo2, plasma HCO3- decreases by 5-6 mEq/L
Blood pH decreases by 0.02 mEq/L
WHAT DOES THIS MEAN?
1. Lactate is added
2. H+ from acid is buffered by the bicarbonate system
3. Co2 is formed and removed by the lungs
H+ + HCO3- <-> H2CO3- <-> H2O + CO2
4 .HCO3- levels decrease in the ECF
5. Kidneys reabsorb more HCO3- to maintain pH
DIFFERENT VARIATIONS CAN ARISE:
1. Change in anion gap = Change in HCO3-
1. You add acid, then anion gap increases proportionately!
2. Change in AG is less than HCO3- change
"Normal AG Acidosis + High AG Acidosis"
2. You started with low HCO3-. That is why when you added acid, the HCO3- is lower than the predicted value.
3. Change in AG is greater than HCO3- change
"Metabolic alkalosis + High AG Acidosis"
3. When you have a high AG, the acid is buffered by HCO3-. So, HCO3- decreases. If it doesn't, then you had a lot of HCO3- to start with.
ANION GAP = Na - (Cl + HCO3)
Normal AG = 12 +/- 4
Homeless Man with Altered Mental Status, with a positive UDS:
Na: 158 mEq/L
Ethanol level:0 mg/dL
pCO2: 30 mmHg
pO2: 95 mmHg
% O2 sat: 98%