Capnography

Question 1

When would PaC02 and EtC02 not correlate?

Answer 1

Pulmonary embolism, because less CO2 is taken to the alveoli to be exhaled, the blood conc. will rise, and the lung conc. will decrease

Question 1

What is the difference between PaC02 and EtC02?

Answer 1

PaCO2is normally 3-5mmHg higher than EtCO2

Question 2

What are the effects of hypercarbia (Hypercapnia)? (6)

Answer 2

1. Respiratory acidosis (pH decreases)
   - With acidosis, catecholamines (and vasopressors) don’t work as well, and cardiac function is depressed
2. CENTRAL (pulmonary) vasoconstriction
   - Hypoventilation (elevated CO2) causes pulmonary vasoconstriction and increased pulmonary vascular resistance (PVR)
3. PERIPHERAL and CEREBRAL vasodilation
   - Increased cerebral blood flow (CBF) intracranial pressure (ICP)
   - Decreased systemic vascular resistance (SVR) (Possible decrease in BP)
4. Sympathetic response/catecholamine release
   - So, even though CO2 causes peripheral vasodilation, it can indirectly cause hypertension (via a release of epinephrine)
5. CO2 narcosis
   - Acts as sedative if >70mmHg
6. Possible death
   - CO2 becomes life threatening if >120mmHg

Question 3

What are the effects of hypocarbia (Hypocapnia)? (3)

Answer 3

1. Respiratory alkalosis (pH increases)
   –DecreasedCO2 concentration leads to decreased acid in the body, which raises pH
   –Alkalosis is associated with neuromuscular irritability and seizures
2. Central (pulmonary) vasodilation
   –Hyperventilation (decreased CO2) causes pulmonary vasodilation and decreased pulmonary vascular resistance (PVR)
3. PERIPHERAL and CEREBRAL vasoconstriction
   - Increasessystemic vascular resistance (SVR)
   - Decreasedcerebral blood flow (CBF) intracranial pressure (ICP)

Question 4

Best way to confirm tracheal intubation?

Answer 4

The most reliable confirmation that the endotracheal tube is in the trachea (and not the esophagus) is EtCO2 (NOT breath sounds, chest rise, or SpO2)

Question 5

How fast does C02 rise during apnea?

Answer 5

–After the 1st minute of apnea, PaCO2 increases 6mmHg

–After each subsequent minute of apnea, PaCO2 increases 3-4mmHg

Question 6

Phases of the EtCO2 Waveform

Answer 6

Question 7

What is a curare cleft? How do you treat it?

Answer 7

Most likely, a “curare cleft” occurs because the patient is starting to breathe over the ventilator, sometimes it is caused by the surgeon pushing on the abdomen

• *1. Suppress the patient’s respiratory drive**
• Propofol
• Re-dose paralytic or narcotic
• Increase the patient’s minute ventilation (lower their EtCO2)

2. Turn off the vent and let the patient breathe spontaneously

Question 8

First step you should take if a patient is “bucking” on the vent?

Answer 8

Remember, if a patient doesn’t just “breathe” over the vent, but rather full on starts “bucking” on the vent, remember that the first step is to always TURN THE VENT OFF before treating it with paralytic/fentanyl/propofol/more volatile agent

Question 9

What would this type of waveform indicate?

Answer 9

COPD/Emphysema

COPD patients exhibit an “upsloping” waveform, which is basically showing prolonged exhalation times (which makes sense because they have obstructive lung disease)

Question 10

What would this waveform be indicative of?

Answer 10

An esophageal intubation capnograph shows small CO2 waves that are usually washed out within a few breaths
–It’s probably due to the patient swallowing some CO2 (possibly from mask ventilation)

Question 11

What can hypocapnia be caused by?

Answer 11

1. Hyperventilation
2. Hypotension/low cardiac output
3. A loose circuit connection

Question 12

What causes this kind of waveform?

Answer 12

Cardiogenic oscillations are caused by heart contractions displace air from alveoli

–They are typically seen with low respiratory rates at the end of expiration, and they go away as the patient starts breathing faster/deeper

Question 13

What causes this waveform?

Answer 13

Exhausted C02 absorber, need to change

Question 14

What would cause this waveform?

Answer 14

Loose capnograph tubing

Question 15

What would cause this waveform?

Answer 15

Patients typically go through an irregular breathing pattern as they pass through stage II

Question 16

What is the cause of decreased C02 at the end of the expiratory phase?

Answer 16

This shows that the expiratory flow is lower than the fresh gas flow rate (at the end of expiration)

Fresh gas flow is “diluting” the expired air

Question 17

What is the point of using capnography during a sedation case?

Answer 17

Although the actual CO2 reading isn’t accurate, capnography during sedation is still extremely valuable for 2 reasons:

1. You know the respiratory rate
2. You can detect apnea

Question 18

What is the benefit of using capnography to diagnose apnea compared to pulse oximetry?

Answer 18

Capnography diagnoses apnea IMMEDIATELY
–An anesthetist can fix the problem BEFORE the patient gets hypoxic

SpO2 can’t diagnose apnea until the patient gets hypoxic
–Pulse oximeters also have a delay

Question 19

During a sedation case, you see this. What is the best course of action?

Answer 19

Start with a chin left, then a jaw thrust, then an oral airway vs. bag mask ventilation