Blood Gas Interpretation Flashcards
What is the primary purpose of obtaining blood gas values in neonates?
To determine whether the patient has adequate ventilation and perfusion
Blood gas values also facilitate analysis of oxygenation and acid-base status.
What are the normal arterial blood gas values for pH?
7.35 – 7.45
What does an elevated pH (> 7.45) indicate?
Alkalosis
What does a pH < 7.35 indicate?
Acidosis
What does PaO2 measure?
The amount of O2 dissolved in the serum – 3% of the total O2 content
What is the reliability of capillary PaO2 compared to arterial specimens?
The value is lower than with an arterial specimen
What does an increase in PaCO2 indicate?
A decrease in the pH (respiratory acidosis)
What is HCO3 and its role in blood gas analysis?
Bicarbonate; it is a base that affects pH levels
What causes metabolic alkalosis?
Increased bicarbonate (HCO3 > 26) and pH > 7.45
What are some causes of respiratory alkalosis?
- Iatrogenic – excessive mechanical ventilation
- Hypoxemia – Increase in alveolar ventilation
- CNS irritation
- Aspirin overdose
What defines metabolic acidosis?
A decreased pH (< 7.35) caused by decreased base (HCO3) or increased acid (CO2, lactic acid)
What indicates respiratory acidosis?
PaCO2 > 45 and pH < 7.35
What is the significance of the pH being normal in blood gas interpretation?
The blood gas is normal or full compensation has occurred
What does compensated acidosis mean in terms of pH?
pH 7.35-7.39
What are the three key questions to ask when evaluating blood gases?
- Is the pH normal?
- Is the pCO2 normal?
- Is the HCO3 normal?
What is the organ of oxygen exchange for the fetus?
The placenta
What does umbilical cord compression simulate in terms of respiratory function?
Breath holding (or strangulation)
What causes respiratory acidosis during labor?
Increased CO2 from lack of exchange
What is the effect of anaerobic metabolism on blood gases?
Increased production of H+ primarily from lactic acid
What does a low pH and normal pCO2 indicate in blood gas evaluation?
Metabolic acidosis
What is the base deficit in a case of metabolic acidosis?
Higher base deficit
What happens to pH during complete occlusion of the cord?
pH falls ~ 0.04/minute
How quickly does metabolic acidosis develop in response to cord occlusion?
Changes occur slowly in other situations
What distinguishes arterial from venous blood gases in terms of metabolic acidosis?
The venous and arterial pH values are similar as the placenta cannot correct the HCO3 rapidly
What is the pH range for umbilical artery blood gases?
7.28 +/- 0.05
What is the role of the umbilical cord in fetal oxygen conveyance?
It is equivalent to the windpipe
What causes an increase in lactic acid production leading to acidosis?
Decreased tissue perfusion/anaerobic metabolism
What does a high pCO2 in arterial gases indicate?
Respiratory acidosis
