Arterial Blood Gas Flashcards
External vs internal respiration
External: gas moving across the lung membrane
Internal: movement of gas between tissue and capillaries
Partial pressure of oxygen (PaO2)
Available oxygen for diffusion into cells
60 = adequate
Oxygen transport in the blood
+ what affects tissue oxygen supply
- 3% in plasma, 97% bound to Hb
Affected by:
* Hb level
* Hb saturation
* O2 dissociation
* Perfusion pressure
Oxyhaemoglobin dissociation curve
Factors that impact, left vs right shift
Describes the relationship between available oxygen and amount of oxygen carried by Hb
Factors:
* Temp, pH, CO2, DPG levels (lowers Hb affinity for O2)
Left shift: reduce dissociation
Right shift: increase dissociation, low PaO2 but SaO2 might be high
Carboxyhaemoglobin (HbCO)
Methaemoglobin (MetHb)
+ causes
HbCO: CO2 bound to Hb that prevents O2 binding, caused by chemical exposure (exhaust, tobacco) - blood is cherry red
MetHb: oxidisation of iron, caused by nitrate meds and cyanide poisoning - blood is dark blue/brown
Acidosis & alkalosis pH
- Acidosis pH < 7.35
- Alkalosis pH > 7.45
Body systems that regulate acid-base balance
- Respiratory: within minutes
- Renal: metabolic regulation, hours to days
Buffer system equation
CO2 + H2O - H2CO3 - HCO3 + H
Buffer system components
Chemical buffers: rapid, bind to a&b to balance H
Resp: lower h2CO3 by dissociating then removing CO2 (rapid but limited)
Protein: Hb bind with H to buffer CO2
Renal: reabsorb HCO3, also produce H2CO3 so that H & HCO3 can be excreted (slower but buffer largers loads)
2 Types of respiratory imbalances
- Insufficient CO2 removal (low RR)
- Excessive removal (high RR)
2 Types of metabolic imbalances
- H ion production > urinary elimination or chemical buffering (diarrhoea)
- Urinary excretion > H production (polyuria)
Respiratory acidosis
pH&CO2, cause, symptoms, treatment
- pH < 7.35, CO2 > 45mmHg
- Due to hypoventilation
- SS: headache, blurred vision, breathlessness, restlessness, disorientation
- Tx: increase RR
Respiratory alkalosis
pH&CO2, cause, symptoms
- pH > 7.45, CO2 < 35
- C: hyperventilation
- SS: dizziness, confusion, parenthesis, convulsions, coma
Metabolic acidosis
pH, cause, symptoms, treatment
- pH < 7.35
- C: excessive H production exceeding removal (acute kidney injury, DKA, insufficient buffer production - LF)
- T: sodium bicarbonate supplements
Metabolic alkalosis
pH, cause, symptoms
- pH > 7.45
- C: excessive loss of H (polyuria, vomiting), or excessive production/absorption of bicarbonate (during constipation)
- SS: weakness, muscle cramps, confusion, tetany
