Lecture 31 - Mechanical Ventilation

Question 1

2 forms of respiratory failure?

Answer 1

1. Hypercapnic

2. Hypoxic

Question 2

Causes of hypercapnic respiratory failure?

Answer 2

1. Depressed drive

2. Overloaded muscles (excessive loads or weakened muscles)

Question 3

Causes of hypoxic respiratory failure?

Answer 3

1. Gas exchange abnormalities
2. Low perfusion states

Aka: 5 physiologic causes of hypoxemia

Question 4

Example of an excessive load causing the respiratory muscles to be overloaded?

Answer 4

Obstructive lung diseases that increase airway resistance, like asthma

Question 5

2 ways of adjusting oxygenation on a mechanical ventilator?

Answer 5

1. FiO2 (except for shunt)

2. PEEP

Question 6

How does PEEP increase oxygenation?

Answer 6

Increases surface area of gas exchange as more alveoli are open at FRC

Question 7

What 4 settings need to be set on a mechanical ventilator?

Answer 7

1. FiO2
2. Respiratory rate
3. TV
4. PEEP

Question 8

At what FiO2 do we usually start patients who need a mechanical ventilator? Why?

Answer 8

100% FiO2 to avoid any hypoxic injury to the brain (unless patient needs ventilator because of a seizure)

Question 9

How to determine what to set TV at to start?

Answer 9

Based on ideal body weight

Question 10

How to determine what to set RR at to start?

Answer 10

Normal rate: 10-12 breaths/min

Question 11

How to determine what to set PEEP at to start?

Answer 11

Start at physiologic PEEP of 5 cm of H2O

Question 12

Way of adjusting PaCO2 levels on a mechanical ventilator?

Answer 12

Minute ventilation through RR

Question 13

What will happen if the TV is kept constant on someone with a restrictive lung disease?

Answer 13

As time goes by, the lung will lose more and more compliance (more diseased lung, less healthy lung), and the TV will become too high for the lung which could get damaged unless the TV is adjusted

Question 14

How to adjust RR to adjust minute ventilation and therefore PaCO2? Under what conditions in this equation valid?

Answer 14

°VeCO2 x 0.86 / (1- Vd/ Vt) = PA/a CO2 x °Ve

1- Vd/Vt = percent of volume that is alveolar
°VeCO2 = minute ventilation of CO2 = volume of CO2 being expired/min

Conditions: as long as minute production of CO2 (°VeCO2) and ratio of dead space to tidal volume (Vd/Vt) is constant

Question 15

If a patient is on a ventilator at constant TV and °Ve, and the PaCO2 increased, what happened?

Answer 15

One of 2 things:

1. Either the CO2 production rose = hypercatabolic state
2. Or the volume of physiological dead space increased

Question 16

Can you adjust PaCO2 by adjusting TV?

Answer 16

NOPE, only RR

Question 17

What do volume targeted ventilators do?

Answer 17

Most common mode in which every breath you give the patient is the same volume with
pressure dependent on compliance

Question 18

What do pressure targeted ventilators do?

Answer 18

Ventilator mode in which the pressure given is constant and the volume will depend on compliance

Question 19

What 4 factors will cause peak pressure to increase?

Answer 19

1. Decrease compliance
2. Increased airway resistance
3. Large tidal volume
4. Higher flow

Question 20

If volume on a pressure targeted ventilator goes up, what are the 2 possible causes?

Answer 20

1. Increased compliance

2. Decreased airway resistance

Question 21

If peak P on a volume targeted ventilator goes up, what are the 2 possible causes?

Answer 21

1. Decreased compliance

2. Increased airway resistance

Question 22

How to obtain plateau pressure on a mechanical ventilator? What is the plateau pressure equal to?

Answer 22

Program a one second inspiratory pause

Plateau pressure = end alveolar distending pressure

Question 23

What pressure should never go over 30-35 cm H2O?

Answer 23

Plateau pressure = end alveolar distending pressure

Question 24

2 factors affecting plateau pressure?

Answer 24

1. Compliance

2. TV

Question 25

2 possibilities if compliance is decreasing?

Answer 25

1. Decreasing lung compliance

2. Decreasing chest wall compliance

Question 26

What is alveolar space synonymous with?

Answer 26

Respiratory zone

Question 27

What does somulent mean?

Answer 27

Abnormally drowsy

Question 28

When given baseline and new values for arterial blood gas, how to determine acute from chronic respiratory acidosis/alkalosis?

Answer 28

1. Calculate pH change compared to PaCO2 change from baseline to new values
2. Calculate pH change compared to PaCO2 change from baseline to standard values

=> Could have an acute disorder on top of a chronic state

Question 29

What happens right after you put a patient in chronic respiratory acidosis/alkalosis on a ventilator to fix his PaCO2? What happens once this goes away?

Answer 29

Short period of time during which the patient will be in metabolic acidosis/alkalosis that was there to compensate the respiratory primary disorder

Once the metabolic compensatory mechanisms dissipates, if all of the ABG values go back to STANDARD normal and the patient is extubated… There will be an issue!

Since we got rid of the metabolic compensation and we stabilized him at standard normals instead of his own, the patient goes right back into hypercapnic failure with acute respiratory acidosis/alkalosis

Question 30

What are cc?

Answer 30

mL

Question 31

What is tachypnea?

Answer 31

Abnormally rapid breathing = hyperventilation

Question 32

What is the diagnosis if a patient has acute respiratory alkalosis and once fixed with 100% O2 the patient is still tachypneic?

Answer 32

Pulmonary embolism causing a V/Q imbalance (VD/VT has doubled) where the blood clot is and the patient is breathing fast to exhale all of the CO2 through one of the 2 lungs to maintain normal °VeCO2 => he needs to double his RR to maintain a constant PaCO2