Ventilation and Oxygenation

Question 1

High PaCO2

Answer 1

Hypoventilation; hypercarbia

Question 2

Low PaCO2

Answer 2

Hyperventilation; hypocarbia

Question 3

Normal arterial CO2

Answer 3

~35-45mmHg

Question 4

What causes hypercarbia?

Answer 4

1. Inadequate elimination (hypoventilation)
2. Increased metabolism (malignant hyperthermia)

Make sure the equipment is working properly!!!

Question 5

What causes hypocarbia?

Answer 5

1. Hyperventilation

2. Hypothermia

Question 6

T/F: CO2 is the main stimulus to breathing.

Answer 6

True, controlled by medullary centers of the brain stem

Question 7

T/F: all anesthetics are respiratory depressants

Answer 7

True, more profound depths of anesthesia have more respiratory depression by increasing the CO2 stim threshold

Question 8

What else can contribute to respiratory depression

Answer 8

1. Mechanical obstruction (obesity, pregnancy, mass)

2. Positional (head down/butt up position

Question 9

What causes decreased compliance in the lungs?

Answer 9

Pneumothorax, pulmonary edema, rigid chest wall

Anything that prevents the chest the expand

Question 10

What does a respirometer measure?

Answer 10

Volume that is exhaled

Question 11

Is it better to measure CO2 or RR as an assessment of adequate ventilation?

Answer 11

CO2

Breathing rate can be slow if the depth of breath is increased

Question 12

What is the standard for measuring CO2 levels?

Answer 12

Capnometry

Question 13

T/F: ETCO2 is a good approximation of the PaCO2.

Answer 13

True

Question 14

Two types of capnometry

Answer 14

1. Sidestream- sensor and display are diverted from airway

2. Mainstream- sensor is in line with the airway

Question 15

Advantages of mainstream capnometry

Answer 15

Not as affected by dilution with fresh gaas

Question 16

Disadvantages of mainstream capnometry

Answer 16

More expensive if cuvette is damaged

Adds dead space

Question 17

Advantages of sidestream capnometry

Answer 17

Tubing less expensive

Less added dead space

Question 18

Disadvantages of sidestream capnometry

Answer 18

Large underestimation in small patients due to gas dilution

Tubing collects a lot of moisture and needs to be replaced more often

Question 19

What is the target EtCO2 in a healthy patient?

Answer 19

up to 50-60mmHg usually acceptable but should be kept below 60mmHg

Question 20

Is EtCO2 typically higher or lower than PaCO2?

Answer 20

Lower; usually ~3-7mmHg but can be much larger

Question 21

Consequences of high PCO2

Answer 21

1. Respiratory acidosis
2. Hypoxia
3. Sympathetic activation
4. Unconsciousness, coma, hypotension
5. Atelectasis

Question 22

Why is keeping PCO2 low especially important for neurologic patients?

Answer 22

Increased CO2 can lead to dilation of the cerebral pressure and increased ICP

Should be kept 2540mmHg

Question 23

Consequences of low PCO2

Answer 23

1. Respiratory alkalosis and metabolic acidemia

Question 24

When EtCO2 is low there is less/more circulation to the lungs.

Answer 24

Less

Question 25

T/F: EtCO2 is a good predictor for recovery during CPR.

Answer 25

True; if EtCO2 is low, it is unlikely the animal will recover

Question 26

T/F: It is normal to find small depressions in the capnograph.

Answer 26

True; cardiac oscillations pushing against the lungs

Question 27

Rebreathing capnograph

Answer 27

Wave does not return to baseline

Question 28

What does pulse oximetry tell us

Answer 28

HR, O2 saturation%

Question 29

What does pulse oximetry estimate?

Answer 29

Hemoglobin-O2 saturation

Question 30

Transmission probes

Answer 30

LED light passes through tissues and transmitted light is measured

Question 31

Reluctance probe

Answer 31

Both LEDs on the same side and reflected light is measured

Question 32

What is a normal SpO2

Answer 32

>97% Horses

Question 33

Causes of hypoxemia

Answer 33

1. Pulmonary dysfunction (decreased perfusion or atelectasis) 2. Pneumo- or hemothorax 3. Respiratory depression with no O2 supplementation

Question 34

Why do we use pulseox?

Answer 34

Monitor oxygen levels especially for at-risk patients

Question 35

Limitations of pulseox

Answer 35

1. Vasoconstriction 2. Fur/pigmentation 3. Movement 4. Usually over estimates at low end and under estimates at high end 5. Cannot distinguish from other types of hemoglobins 6. Ambient light may interfere

Question 36

Does anemia effect the SpO2?

Answer 36

Shape of the curve stays the same but the O2 content is reduced

Question 37

Does inspired O2% effect SpO2?

Answer 37

No, it has a profound effect on PaO2 but hypoxemia is more likely if breathing room air