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Normal arterial pH?
7.35–7.45 (Midpoint = 7.4)
What is acidosis?
pH < 7.35
What is alkalosis?
pH > 7.45
What 2 systems control acid-base balance?
Lungs + kidneys
Lungs regulate?
PaCO₂
Kidneys regulate?
HCO₃⁻
Normal PaCO2 levels?
35–45 mmHg
Normal steady-state PaCO₂?
~40 mmHg
Normal HCO3?
22–26 mEq/L
Normal PaO2?
80–100 mmHg
Normal SaO2?
95–100%
Hypercapnia?
Too much CO₂/CO₂ retention
Most common reason for hypercapnia in this lecture?
Hypoventilation
Hypocapnia?
Too little CO₂/too much CO₂ blown off
Primary respiratory problem starts with a change in?
PaCO₂
Who compensates for a respiratory problem?
Kidneys/metabolic system
Primary metabolic problem starts with a change in?
HCO₃⁻
Who compensates for a metabolic problem?
Lungs/respiratory system
Does compensation make pH completely normal?
NO
Compensation moves pH where?
TOWARD normal
Metabolic acidosis ABG pattern?
↓ pH + ↓ HCO₃⁻ + ↓ PaCO₂
Main value causing metabolic acidosis?
Low HCO₃⁻
↓ pH + ↓ HCO₃⁻ = ?
Metabolic acidosis
Metabolic alkalosis ABG pattern?
↑ pH + ↑ HCO₃⁻ + ↑ PaCO₂
↑ pH + ↑ HCO₃⁻ = ?
Metabolic alkalosis
Respiratory acidosis pattern?
↓ pH, ↑ CO2
pH ↓ + CO₂ ↑ = ?
Respiratory acidosis
Respiratory alkalosis pattern?
↑ pH , ↓ PaCO₂ , HCO₃⁻
↑ pH + ↓ PaCO₂ = ?
Respiratory alkalosis
ABG QUICK RULES
First thing to look at on an ABG?
pH
pH <7.35?
Acidosis
pH >7.45?
Alkalosis
Metabolic: pH + HCO₃⁻ move how?
SAME direction
Respiratory: pH + CO₂ move how?
OPPOSITE directions
ROME?
Respiratory Opposite
Metabolic Equal
Low pH + low HCO₃⁻?
Metabolic acidosis
High pH + high HCO₃⁻?
Metabolic alkalosis
Low pH + high CO₂?
Respiratory acidosis
High pH + low CO₂?
Respiratory alkalosis
ABG: pH 7.28. Acid or alkaline?
Acid
ABG: pH 7.28 + HCO₃⁻ 16.6. Disorder?
Metabolic acidosis
Why is HCO₃⁻ important here?
It is LOW and follows the low pH
Why would CO₂ decrease with metabolic acidosis?
Respiratory compensation → lungs blow off CO₂
CASE STUDY
23-year-old with Type 1 DM + postural hypotension + tachycardia. Think?
Volume depletion
Type 1 DM + Kussmaul respirations + acetone breath. Important acid-base clue?
Metabolic acidosis pattern
What are Kussmaul respirations?
Important respiratory finding in this metabolic acidosis case
What unusual breath finding does the patient have?
Acetone-smelling breath
Chest x-ray finding?
Right lower lobe consolidation
Why is confusion important?
Neurologic changes can occur with sodium/water imbalance