Ventilation and Oxygenation Flashcards
High PaCO2
Hypoventilation; hypercarbia
Low PaCO2
Hyperventilation; hypocarbia
Normal arterial CO2
~35-45mmHg
What causes hypercarbia?
- Inadequate elimination (hypoventilation)
- Increased metabolism (malignant hyperthermia)
Make sure the equipment is working properly!!!
What causes hypocarbia?
- Hyperventilation
2. Hypothermia
T/F: CO2 is the main stimulus to breathing.
True, controlled by medullary centers of the brain stem
T/F: all anesthetics are respiratory depressants
True, more profound depths of anesthesia have more respiratory depression by increasing the CO2 stim threshold
What else can contribute to respiratory depression
- Mechanical obstruction (obesity, pregnancy, mass)
2. Positional (head down/butt up position
What causes decreased compliance in the lungs?
Pneumothorax, pulmonary edema, rigid chest wall
Anything that prevents the chest the expand
What does a respirometer measure?
Volume that is exhaled
Is it better to measure CO2 or RR as an assessment of adequate ventilation?
CO2
Breathing rate can be slow if the depth of breath is increased
What is the standard for measuring CO2 levels?
Capnometry
T/F: ETCO2 is a good approximation of the PaCO2.
True
Two types of capnometry
- Sidestream- sensor and display are diverted from airway
2. Mainstream- sensor is in line with the airway
Advantages of mainstream capnometry
Not as affected by dilution with fresh gaas
Disadvantages of mainstream capnometry
More expensive if cuvette is damaged
Adds dead space
Advantages of sidestream capnometry
Tubing less expensive
Less added dead space
Disadvantages of sidestream capnometry
Large underestimation in small patients due to gas dilution
Tubing collects a lot of moisture and needs to be replaced more often
What is the target EtCO2 in a healthy patient?
up to 50-60mmHg usually acceptable but should be kept below 60mmHg
Is EtCO2 typically higher or lower than PaCO2?
Lower; usually ~3-7mmHg but can be much larger
Consequences of high PCO2
- Respiratory acidosis
- Hypoxia
- Sympathetic activation
- Unconsciousness, coma, hypotension
- Atelectasis
Why is keeping PCO2 low especially important for neurologic patients?
Increased CO2 can lead to dilation of the cerebral pressure and increased ICP
Should be kept 2540mmHg
Consequences of low PCO2
- Respiratory alkalosis and metabolic acidemia
When EtCO2 is low there is less/more circulation to the lungs.
Less
T/F: EtCO2 is a good predictor for recovery during CPR.
True; if EtCO2 is low, it is unlikely the animal will recover
T/F: It is normal to find small depressions in the capnograph.
True; cardiac oscillations pushing against the lungs
Rebreathing capnograph
Wave does not return to baseline
What does pulse oximetry tell us
HR, O2 saturation%
What does pulse oximetry estimate?
Hemoglobin-O2 saturation
Transmission probes
LED light passes through tissues and transmitted light is measured
Reluctance probe
Both LEDs on the same side and reflected light is measured
What is a normal SpO2
> 97%
Horses
Causes of hypoxemia
- Pulmonary dysfunction (decreased perfusion or atelectasis)
- Pneumo- or hemothorax
- Respiratory depression with no O2 supplementation
Why do we use pulseox?
Monitor oxygen levels especially for at-risk patients
Limitations of pulseox
- Vasoconstriction
- Fur/pigmentation
- Movement
- Usually over estimates at low end and under estimates at high end
- Cannot distinguish from other types of hemoglobins
- Ambient light may interfere
Does anemia effect the SpO2?
Shape of the curve stays the same but the O2 content is reduced
Does inspired O2% effect SpO2?
No, it has a profound effect on PaO2 but hypoxemia is more likely if breathing room air
