Arterial Blood Gas

Question 1

External vs internal respiration

Answer 1

External: gas moving across the lung membrane
Internal: movement of gas between tissue and capillaries

Question 2

Partial pressure of oxygen (PaO2)

Answer 2

Available oxygen for diffusion into cells

60 = adequate

Question 3

Oxygen transport in the blood

+ what affects tissue oxygen supply

Answer 3

• 3% in plasma, 97% bound to Hb

Affected by:
* Hb level
* Hb saturation
* O2 dissociation
* Perfusion pressure

Question 4

Oxyhaemoglobin dissociation curve

Factors that impact, left vs right shift

Answer 4

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

Question 5

Carboxyhaemoglobin (HbCO)
Methaemoglobin (MetHb)

+ causes

Answer 5

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

Question 6

Acidosis & alkalosis pH

Answer 6

• Acidosis pH < 7.35
• Alkalosis pH > 7.45

Question 7

Body systems that regulate acid-base balance

Answer 7

• Respiratory: within minutes
• Renal: metabolic regulation, hours to days

Question 8

Buffer system equation

Answer 8

CO2 + H2O - H2CO3 - HCO3 + H

Question 9

Buffer system components

Answer 9

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)

Question 10

2 Types of respiratory imbalances

Answer 10

• Insufficient CO2 removal (low RR)
• Excessive removal (high RR)

Question 11

2 Types of metabolic imbalances

Answer 11

• H ion production > urinary elimination or chemical buffering (diarrhoea)
• Urinary excretion > H production (polyuria)

Question 12

Respiratory acidosis

pH&CO2, cause, symptoms, treatment

Answer 12

• pH < 7.35, CO2 > 45mmHg
• Due to hypoventilation
• SS: headache, blurred vision, breathlessness, restlessness, disorientation
• Tx: increase RR

Question 13

Respiratory alkalosis

pH&CO2, cause, symptoms

Answer 13

• pH > 7.45, CO2 < 35
• C: hyperventilation
• SS: dizziness, confusion, parenthesis, convulsions, coma

Question 14

Metabolic acidosis

pH, cause, symptoms, treatment

Answer 14

• pH < 7.35
• C: excessive H production exceeding removal (acute kidney injury, DKA, insufficient buffer production - LF)
• T: sodium bicarbonate supplements

Question 15

Metabolic alkalosis

pH, cause, symptoms

Answer 15

• pH > 7.45
• C: excessive loss of H (polyuria, vomiting), or excessive production/absorption of bicarbonate (during constipation)
• SS: weakness, muscle cramps, confusion, tetany

Question 16

Compensation

Answer 16

Renal and respiratory adjustments that result in pH returning to normal

Question 17

Normal ABG values

pH, PaCO2, PaO2, HCO3, SaO2

Answer 17

pH: 7.35-7.45
PaCO2: 35-45 mmHg
PaO2: 80-100 mmHg
HCO3: 22-26 mmol/L
SaO2: 94-100%