Seminar 2 - respiratory function monitoring

Question 1

what information do rate monitors and aoniea alarms give us, what are some negatives?

Answer 1

• tells us patient is breathing, thermistor place in patient airway, change in resistance as warmed gases pass over thermistor is converted to electrical system
• machine beeps with each expiration, alarm if no breath
• relatively expensive
• gives no info on adequacy of ventilation i.e. depth, how much o2 in etc..

Question 2

what does spirometry measure?

Answer 2

• tidal volume

- minute ventilation

Question 3

what is the physiological range of oxygen and carbon dioxide within the blood?

Answer 3

PO2 = >80mmHg in arterial blood 
PCO2 = b/w 35 - 45 mmHg in arterial blood

Question 4

what are the pros and cons of arterial blood gas analysis

Answer 4

most accurate measure of rest function
PaCO2 <35 = hyperventilation, >45 = Hypoventilation
cons: difficult and invasive to sample

Question 5

what is pulse oximetry?

Answer 5

combines oximetry and plethysmography

2 components - light emitting diode and photodiode detector (beer lambart law)

Question 6

what are the two wavelengths of pulse oximetry and describe their importance

Answer 6

1. 940 nm
2. 660 nm
   oxyhemoglobin absorbs infrared light at 940, deoxyghymoglobin absorbs infrared light at 640.

Question 7

what are some limitations with use of pulse oximetry?

Answer 7

sensitive to hypoxia
sensitive to movement
sensitive to ambient lighting
pigments - doesn’t work on dark pigments

Question 8

what are some common hypoxaemia causes?

Answer 8

low inspired oxygen concentration
hypoventilation
venous admixture: ventilation/ perfusion mismatch, shunt, diffusion impairement.

Question 9

what is capnography and what does it measure

Answer 9

plots a continuous trace of CO2 in resp gases against time, gives an indication of adequacy of ventilation

Question 10

what are some pros of capnography

Answer 10

characteristic traces can be produced
non-invasive
EtCO2 correlates with PaCO2

Question 11

what is the normal range for EtCO2

Answer 11

35 mmHg > EtCO2 < 45 mmHg
< 35 = hyperventilation: pain, awakening during anaesthetic
> 45 = hypoventilation: getting deeper, re-breathing

Question 12

what will appear on capnography with rebreathing?

Answer 12

increased baseline

Question 13

what causes increased or decreased CO2 during anasethia?

Answer 13

1. CNS depression due to aesthetic, opiates
2. resp muscle weakness
3. restricted airflow
4. movement of ribs restricted - external pressure ie/ surgeon.

Question 14

what do you do if the patient isn’t ventilating well? and how quickly do you act

Answer 14

manually ventilate: IPPV
PaCO2 > 60mmHg
PaO2 < 80 mmHg