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Anesthesiology > Mechanical Ventilation > Flashcards

Mechanical Ventilation Flashcards

1
Q

How does anesthesia affect ventilation?

A
  1. Alters CO2 sensitivity
  2. Relaxes respiratory muscles
  3. Develops atelectasis
  4. Worsens V/Q match issues
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2
Q

How can ventilation affect anesthesia?

A
  1. Uptake depends on ventilation

2. Controlled ventilation facilitates reliable uptake and smooth plane of anesthesia

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3
Q

What is ventilation defined by?

A

PaCO2

Patient should have normal resp rate, rhythm and effort

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4
Q

What is oxygenation?

A

Process of oxygenation of arterial blood

Defined by PaO2

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5
Q

What is oxygenation monitored by?

A

Arterial blood gas or pulse oximetry

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6
Q

What does oxygenation depend on?

A

Inspired O2%

100% O2 typically insures good oxygenation

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7
Q

What are the two phases of respiration?

A

Inspiration and expiration

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8
Q

What does resistance do?

A

Limits flow

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9
Q

What does compliance do?

A

Limits volume

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10
Q

Indications for mechanical ventilation?

A
  1. Need to decrease PaCO2
  2. Need to increase PaO2
  3. Need to decrease respiratory effort (mostly ICU)
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11
Q

Indication for mechanical ventilation during anesthesia

A
  1. Control of respiratory function
  2. Prolonged anesthesia
  3. Maintain stable anesthesia plane
  4. Neuromuscular blockade
  5. Thoracic surgery, chest wall, hernia
  6. Obesity, increased abdomen pressure
  7. head down positioning
  8. Laparoscopy
  9. Control ICP
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12
Q

Side effects of MV

A
  1. Impairs venous return and cardiac output
  2. May cause hypotension especially in hypovolemic patients
  3. Pneumothorax and lung injury
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13
Q

Direct effects of hypercapnia

A
  1. Peripheral vasodilation
  2. Decreased myocardial contractility
  3. Bradycardia and possible arrest
  4. Increased ICP
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14
Q

Indirect effects of hypercapnia

A
  1. Tachycardia, arrhythmias
  2. Increased myocardial contractility
  3. Increased blood pressure
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15
Q

CO2 narcosis levels

A

> 95 mmHg progressive narcosis

>245 mmHg complete narcosis

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16
Q

What may happen if not ventilating properly?

A

CO2 accumulation, hypoxemia, sudden death

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17
Q

Should horses be ventilated?

A

Debated issue

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18
Q

Types of ventilation

A 
Spontaneous- patient breathing
Assisted- patient timed, machine assists
Mandatory/Controlled- ventilator controls
Manual- bag
Mechanical- machine driven
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19
Q

Ventilation modes

A

Volume controlled

Pressure controlled

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20
Q

What can result from volume ventilation?

A

Pneumothorax if compliance is decreased

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21
Q

Which ventilation mode is preferred if lung volume changes during a procedure?

A

Pressure controlled

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22
Q

Which ventilation mode is preferred if trans-pulmonary pressure changes during a procedure?

A

Volume controlled

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23
Q

Which ventilation mode works well for all patient sizes?

A

Pressure controlled

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24
Q

Classification of ventilators

A
  1. Source of driving power
  2. Control variable
  3. Cycle variable
  4. Trigger variable
  5. Limit variable
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25
Q

Source of driving power

A
  1. Electronically driven

2. Pneumatically driven (pressurized gas)

26
Q

Which source of driving power is more common?

A

Pneumatically driven

27
Q

Control variables

A
  1. Flow- delivers constant flow

2. Pressure- delivers constant patient

28
Q

Cycle variables

A

Triggers expiration when a set value is reached

  1. Volume
  2. Pressure
  3. Time
  4. Flow- diminishing flow
29
Q

What is flow variable useful for?

A

Pressure support ventilation- helps accommodate the patients breathing pattern

30
Q

Trigger variable

A

Triggers inspiration when a set value is reached

  1. Pressure- negative pressure
  2. Flow- inpiratory flow
31
Q

Trigger variables are used during what ventilation modes?

32
Q

Limit Variable

A

When value is reached, inspiration will be terminated

  1. Volume limit
  2. Pressure limit
33
Q

What does a pressure limit prevent?

A

Barotrauma if ventilator is set inappropriately

34
Q

How can volume controlled ventilation be achieved?

A

Flow controlled, time cycled ventilator
OR
Flow controlled, volume limited, time cycled ventilator

35
Q

How can pressure controlled ventilation be achieved?

A
  • Pressure controlled, time cycled ventilator
  • Pressure controlled, pressure cycled ventilator
  • Flow controlled, pressure cycled ventilator
36
Q

I:E Ratio

A

Ratio of inspiratory/expiratory times

37
Q

What does the I:E ratio define?

A

Tidal volume (Vt)

38
Q

Does the RR affect inspiratory time and Vt?

39
Q

PIP

A

Peak inspiratory pressure- inflates alveoli

40
Q

PEEP

A

Positive end expiratory pressure- keeps alveoli open

41
Q

Indications for PEEP

A
  1. Open thorax
  2. Lung parenchymal disease
  3. Following alveolar recruitment maneuver
42
Q

Should PEEP be used during routine anesthesia?

A

Benefits are questionable

43
Q

IMV

A

Intermittent mandatory ventilation- allowed to breath freely between mechanical breaths

44
Q

SIMV

A

Synchronized IMV- each spontaneous breath is assisted

45
Q

PSV

A

Pressure Support Ventilation- patient is breathing freely but supported with pressure

Flow termination, better synchrony than SIMV

46
Q

CPAP

A

Continuous Positive Airway Pressure- assisted ventilation mode when both insp/exp pressures are positive

47
Q

Ventilating healthy lung values

A 
Tidal volume : 10-15mL/kg
RR: 10-15 bpm
Inspiratory time: 1-2sec
PIP: 10-20 cmH2O
PEEP: 0-2 cmH2O
48
Q

Ventilating sick lungs

A 
Tidal volume : 4-8mL/kg
RR: up to 60 bpm
Inspiratory time: may be increased but watch expiration
PIP: 35-60max cmH2O
PEEP as needed: 5-20 cmH2O
49
Q

Which lung typically collapses during anesthetic procedures?

A

The most dependent one very rapidly after induction

50
Q

Can a collapsed lung persist for hours/days after surgery?

51
Q

What is cyclic recruitment?

A

Opening and collapse of alveoli with each breath, may lead to lung injury

52
Q

Mechanisms of atelectasis formation

A
  1. Compression
  2. Absorption
  3. Lack of surfactant
53
Q

Alveolar recruitment maneuver (ARM)

A

Therapeutic maneuver aiming to open lung atelectasis and improve oxygenation

54
Q

Types of ARM

A

CPAP and Cycling

Should be followed by PEEP

55
Q

Open Lung concept

A

Therapeutic approach aiming to reverse atelectasis, prevent cyclic recruitment, and ventilator inducted lung injury

ARM followed by optimal PEEP

56
Q

Clinical application of ARM

A

Safe airway pressures are highly individual variation

Should only be performed if you have sufficient monitoring/equipment and clinical indication

57
Q

Patient-ventilator asynchrony

A

Patient attempts to breath out of phase with the ventilator

58
Q

Common causes of patient-ventilator asynchrony

A

Inadequate anesthetic depth
Inadequate lung volume or tidal volume

ICU: pneumothroax, atelectasis, hypotension, hyperthermia

59
Q

Treatment for patient-ventilator asynchrony

A

Treat underlying cause; may cause rapid deterioration of oxygenation and ventilation

60
Q

Weaning from ventilator after surgery

A

If a normal healthy animal it’s simple

Decrease ventilator setting or continue ventilating until fully awake

May use opioid antagonists if necessary

61
Q

Weaning from ventilator in the ICU

A

More difficult since lungs are probably not healthy

Spontaneous ventilation trials may be used

Anesthesiology (27 decks)

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