62 Acid Base
62.1 What this covers
- Compensation
- Metabolic Acidosis PCO2 last 2 digits of pH PCO2
- Metabolic Alkalosis PCO2 40 + .6 (HCO3-24) aka the change in
62.2 Learning objectives
- Compensation
- Metabolic Acidosis PCO2 last 2 digits of pH PCO2
- Metabolic Alkalosis PCO2 40 + .6 (HCO3-24) aka the change in
- Respiratory Acidosis Acute: HCO3 deltaPaCO2 / 10 OR pH change
- Respiratory Alkalosis Acute: HCO3 delta PaCO2 / 10
- Stewart Approach
62.3 Bottom line / summary
- If < 22, concomitant NAGMA.
- If > 26, concomitant Met Alk
- Chronic: HCO3 (deltaPaCO2 / 10) 3.5 or pH change 0.003 CO2 Change
- Chronic: HCO3 (deltaPaCO2 / 10) 3.5
- Strong ion approach -https://journals.lww.com/ccmjournal/Abstract/2007/11000/Disordersofacidbasebalance.23.aspx
62.4 Approach
- Acidemia vs Alkalemia
- Calculate anion gap: Na - (HCO+Cl)
- Calculate the change in Anion Gap: AG - 12
- Calculate the delta delta: Change in Anion Gap + HCO3 should
- Assess if compensation is adequate.
62.5 Red flags / when to escalate
- TODO: List red flags that require urgent escalation.
62.6 Common pitfalls
- TODO: Capture common errors or missed steps.
62.7 References
- https://journals.lww.com/ccmjournal/Abstract/2007/11000/Disordersofacidbasebalance.23.aspx>
62.8 Source notes
62.9 ### Acid Base
editor_options: markdown: wrap: 72 —
63 Acid Base
Approach
- Acidemia vs Alkalemia
- Calculate anion gap: Na - (HCO+Cl)
- Calculate the change in Anion Gap: AG - 12
- Calculate the delta delta: Change in Anion Gap + HCO3 should equal 24. If < 22, concomitant NAGMA. If > 26, concomitant Met Alk
- Assess if compensation is adequate.
63.1 Compensation
63.1.1 Metabolic Acidosis PCO2 = last 2 digits of pH PCO2 =
1.5*HCO3 + 8
63.1.2 Metabolic Alkalosis PCO2 = 40 + .6 * (HCO3-24) aka the change in
bicarbonate
63.1.3 Respiratory Acidosis Acute: HCO3 = delta_PaCO2 / 10 OR pH change =
0.008 * CO2 change. (38 normal in SLC)
Chronic: HCO3 = (delta_PaCO2 / 10) * 3.5 or pH change = 0.003 * CO2 Change
63.1.4 Respiratory Alkalosis Acute: HCO3 = delta PaCO2 / 10
Chronic: HCO3 = (delta_PaCO2 / 10) * 3.5
63.2 Stewart Approach
Strong ion approach -https://journals.lww.com/ccmjournal/Abstract/2007/11000/Disorders_of_acid_base_balance.23.aspx
” In Stewart’s paradigm, H+, OH-, HCO3-, and CO32- are relegated to the status of dependent variables, i.e. they can only be formed from the differential movements and exchanges of independent strong ions (Na+, K+, Cl-) that disturb electroneutrality, which is immediately corrected by the hydrolysis of water and reaction with carbon dioxide.”
Base excess: = the amount of strong acid (complete dissociated from H+) needed to restore 1L of blood to pH of 7.4 at 40 mmHg. Used to isolate metabolic component from respiratory compensation.