SEM2WK2 O2 AND BLOOD GAS ANALYSIS

Question 1

PaO2 define and normal values

Answer 1

• This is the partial pressure of oxygen found dissolved in arterial plasma
• A normal Pa02 is 80-100mmHg

Question 2

SaO2 define

Answer 2

• % of Hb that is fully saturated with oxygen
• In most clinical situations the SaO2 will be the same as the SPO2 (carbon monoxide poisoning is the exception)

Question 3

CaO2

Answer 3

• This is the total oxygen content of the body
• Probably the best way to measure the overall oxygen status of the patient

Question 4

what is 23DPG

Answer 4

is a competitive binder for Hb against oxygen. Sort of like carbon monoxide. 2-3DPG is a side effect of aerobic respiration, its created in situations like exercise and “pushes” oxygen off Hb to distribute in the tissues and binds to Hb as a result.

Question 5

diffusion gradiant of molecules is affected by

Answer 5

• Concentration gradient (greater the difference in partial pressures results in a faster exchange of gases) (slower diffusion at higher altitudes)
• Temperature
• Mass and solubility
• Surface area, thickness of membrane and distance travelled (900mls of blood can participate in gas exchange at any given time.)

Question 6

causes of hypoxaemia

Answer 6

• Low PO2
• Hypoventilation
• V/Q mismatch
• Shunt
• Diffusion impairment

Question 7

causs of hypercapnia

Answer 7

• Hypoventilation (reduced V/Q ratio)
• Increased CO2 production where there is inadequate respiration compensation

Question 8

causes of resp acidosis

Answer 8

Caused by hypoventilation
* CNS depression leading to decreased respiratory drive
* Neuromuscular disorders
* Decreased chest wall compliance
* Loss of chest wall integrity
* Increased airway resistance
* Decreased lung compliance

Question 9

causes of respiratory alkalosis

Answer 9

• Hypoxaemia (increase in Mv to compensate for low oxygen)
• PE
• Pulmonary disease
• Anxiety
• Pain
• Mechanical ventilation

Question 10

causes metabolic acidosis

Answer 10

Caused by an increase in H+ or decreased in HCO3-
4 main mechanisms
* Increased acid production
* Decreased excretion of acid
* Acid ingestion
* Renal or GI bicarbonate losses

Question 11

causes metabolic alkalosis

Answer 11

Causes
Loss of H+
* Via stomach (vomiting, NG suctioning)
* Via kidneys (loop or thiazide diuretics, Cushing’s disease)
Increase of HCO3-
* Sodium bicarbonate administration
* Sodium citrate administration
* Impaired renal excretion