Vents and airway pressures

Question 1

Ventilator hazards

Answer 1

Leaks and disconnects: check connections, cracks (ETCO2 is most sensitive) -> set hi and low values for alarm
Excessive positive pressure -> risk of barotrauma
Excessive negative pressure -> excessive suction
Discrepancies between settings and actual delivery: leaks, circuit compliance
No flow states: leak, disconnections, obstruction

Question 2

General principles of ventilator

Answer 2

Most are driven by O2
- driving gas circuit: provides driving force for ventilator bellows and machine
- patient gas circuit: gas supply to patient
Inspiration: pressurized O2 for driving circuit fills space inside container and bellow empties
- inspiratory time is determined by TV, flow, and rate
Exhalation: bellow ascends during exhalation, descending bellow hangs during exhalation
Fresh gas flow: inspiration -> reservoir bag, expiration -> bellow fills from reservoir

Question 3

Discrepancies between machine settings and delivered tidal volumes

Answer 3

Leaks, breathing circuit complications, gas compression

Question 4

No flow states on ventilator

Answer 4

Disconnection/obstruction of tubing or ETT

Question 5

Ventilator Alarms

Answer 5

Disconnect - low PIP, low exhaled tidal volume, low ETCO2

High PIP, high PEEP, sustained airway pressure, negative pressure, low O2

Question 6

Airway pressure

Answer 6

Airway resistance + alveolar pressure

Question 7

PIP

Answer 7

Highest pressure in circuit during inspiration

Question 8

Plateau pressure

Answer 8

Pressure during inspiratory pause

Question 9

Causes of increased PIP and Plateau Pressure

Answer 9

1-pulmonary edema
2-pleural effusion
3-tension ptx 
4-endobronchial intubation
5-pneumonia
6-intra-abdominal gas insufflation
7-intra-abdominal packing
8-trendelenburg
9-ascites

Question 10

Causes of increased PIP and unchanged Plateau Pressure

Answer 10

1-kinked ETT
2-airway compression
3-foreign body
4-vocal cord paralysis
5-tracheal mass
6-bronchospasm
7-secretions

Question 11

Management of Increased airway pressures

Answer 11

Inspiratory pressures >40 cm H2O should be treated as abnormal
-check equipment and airway

Question 12

Systematic Approach for Increased Airway Pressure

Answer 12

1. Equipment: check O2 and all connections, hand-ventilate patient to see if difficult ->can be obstruction at airway or patient
2. Airway Device: ascertain whether airway kinked/obstructed
   - can suction to clear
3. Patient: observe chest expansion with breaths
   - fiber optic scope to assess airway

Question 13

Pulse Oximetry

Answer 13

Noninvasive continuous means of assessing arterial O2 saturation

• 2 light emitting diodes @ 660 nm and 940 mm
• SaO2 = O2Hb% and Hb% are calculated from ratio of light absorbed
• Accuracy unaffected by fetal hemoglobin, sickle, and polycythemia

Question 14

Capnography

Answer 14

Continuous display of exhaled CO2 waveform

-2 assumptions: all CO2 product of tissue metabolism, PaCO2 is 5-10 mmHg>PACO2=ETCO2

Question 15

Capnography provides following info:

Answer 15

Adequacy of ventilation and perfusion
Presence of airway obstruction
Positioning of double-lumen tubes

Question 16

Capnography - causes of abrupt ETCO2 decreases

Answer 16

Esophageal intubation
Kinked, obstructed, or disconnected airway
Low cardiac output (PE, arrest)

Question 17

Capnography- causes of abrupt ETCO2 increases

Answer 17

Hypoventilation
Hyperthermia
Rebreathe get

Question 18

4 phases of typical capnogram

Answer 18

1. Gas exhaled from anatomic dead space
2. CO2 rich alveolar and dead space gas leads to increased exhaled CO2
3. Steady [ ] of CO2 is exhaled from all lung regions
4. True “end-tidal” CO2 tension at very end of exhalation