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Anesthesiology > Mechanical Ventilation > Flashcards

Mechanical Ventilation Flashcards

1
Q

What is happening physiologically during inspiration?

A
  • Contraction of diaphragm and intercostal mm +/- abd mm
  • Enlargement of chest cavity > drop in pleural pressure = drop in alveolar pressure
  • Air moves from atmosphere to alveoli
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2
Q

What is happening physiologically during expiration?

A
  • Contraction of resp mm ceases
  • Elastic recoil of chest wall and lungs incr alveolar pressure over the atm pressure
  • Air moves from alveoli to atm
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3
Q

During spontaneous ventilation, as transpulmonary pressure and alveolar pressure drop, the alveolar volume ______

A

Increases

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4
Q

Describe the work of breathing

A
  • Energy required by resp mm to produce an inspiration - under normal conditions expiration is passive (No WOB)
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5
Q

Work of breathing is needed to do what 3 things?

A
  1. To expand lungs against elastic forces
  2. To overcome the viscosity of the lung and chest wall structures
  3. To overcome airway resistance
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6
Q

Airway resistance has to do with what?

A

Atm P - Alveolar P

Volume of airflow

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7
Q

Define tidal volume

A

Volume of air inspired or expired with each normal breath; 10-20 ml/kg

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8
Q

Define minute ventilation (Vm)

A

Total amount of new air moved into the resp passages each minute

Vm = TV x RR

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9
Q

Define alveolar minute ventilation (Va)

A

Total volume of new air entering the alveoli each minute

Va = RR x (TV - anatomical dead space volume)

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10
Q

What are the normal FiO2 and FiN2 of atmospheric air?

A

FiO2 = 21% (159 mmHg)

FiN2 = 78% (590 mmHg)

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11
Q

What is the PaCO2 and PaO2 (arterial) during normal alveolar ventilation? PvCO2 and PvO2?

A

PaCO2 = 40 mmHg; PaO2 =100 mmHg

PvCO2 = 50 mmHg; PvO2 = 40 mmHg

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12
Q

What 4 things cause CNS depression and affect spontaneous ventilation? What is the effect of these on spontaneous ventilation?

A

general anesthesia, sedatives, opioids, CNS dz; decr alveolar ventilation and reduce central drive

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13
Q

What types of thoracic abnormalities affect spontaneous ventilation?

A

Open chest, pneumothorax, pleural effusion, external pressure on the chest, obesity

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14
Q

What things cause increased intra-abdominal pressure that affect spontaneous ventilation? What is the effect of these on spontaneous ventilation?

A

Pregnancy, GDV, abdominal fluids, large abd masses, pneumoperitoneum, obesity; decr alveolar ventilation, reduce compliance

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15
Q

Define compliance

A

Measure of lung’s ability to stretch and expand; is the change in the volume for any given applied pressure

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16
Q

What are the two main effects on spontaneous ventilation we are concerned about with hypoventilation?

A

Hypoxemia (unless high FiO2 is provided) and hypercapnea

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17
Q

What are four causes of hypoxemia?

A
  1. Hypoventilation - inability of resp system to maintain a normal alveolar ventilation = CO2 not eliminated adequately
  2. Diffusion limitation
  3. Shunt
  4. Venilation-perfusion inequality

*plus low FiO2

18
Q

What are situations where ventilatory support is mandatory?

A
  • Open chest sx
  • Use of neuromuscular blocker agents
  • Resp arrest
  • Lung dz where normoxemia is not maintained by supplementing O2
  • Hypercapnia
  • Patients that cannot tolerate incr in CO2 (ie. brain tumors)
19
Q

What are situations where ventilatory support is highly recommended?

A
  • Low lung/chest compliance
  • Obese
  • GDV
  • Pregnant
  • Horses
  • Laparoscopic sx

*these animals are prone to severe hypoventilation therefore ventilatory support can become mandatory!

20
Q

What are situations where ventilatory support is beneficial?

A

Dorsal recumbency

Any patient under general anesthesia

21
Q

During positive pressure ventilation, positive pressure is generated in the breathing system producing movement of air into the alveoli. Therefore, during inspiration the alveolar pressure is _______ compared to the atmospheric pressure (as opposed to spontaneous ventilation).

A

Positive

22
Q

What is a demand valve?

A

Provides high flow of oxygen (up to 160 L/min); used in large animals before connecting to anesthetic machine or in the process of weaning from the ventilator

23
Q

What is the name of the bag used for manual positive pressure ventilation in small animals?

A

Ambu bag

24
Q

How does mechanical positive pressure ventilation differ from manual?

A

The bag is replaced by a bellow in a jar attached to a ventilator controller with high pressure oxygen flowing through

*often use O2 over room air in case there’s a hole in the bellow/jar

25
Q

Describe the concept of assisted ventilation?

A
  • To reduce the work of breathing
  • Patient is able to initiate breath
  • Tidal volume is enhanced by manual or mechanical support
26
Q

What are 2 examples of assisted ventilation modalities?

A

Synchronized intermittent-mandatory ventilation (SIMV)

Pressure Support Ventilation

27
Q

Describe controlled ventilation

A
  • Complete control of ventilation
  • Operator sets tidal volume and respiratory rate
  • Also known as IPPV (intermittent positive pressure ventilation)
28
Q

What are 2 controlled ventilation modalities?

A

Volume controlled ventilation

Pressure controlled ventilation

29
Q

Describe the process of volume controlled ventilation

A
  • The fixed delivered TV will generate a certain airway pressure (normal = 10-20 cmH2O) = peak inspiration pressure (PIP)
  • Airway pressure will depend on compliance of resp system
  • pressure is limited - safety feature of ventilators to avoid barotrauma (<30 cmH2O)
30
Q

Describe the concept of pressure controlled ventilation

A
  • The fixed PIP is set at 10-20 cmH2O and the ventilator will deliver the TV reqiuired to generate the pre-set PIP
  • TV will depend on the compliance of the resp system
  • If pulmonary compliance is reduced, the TV will be reduced, resulting in a reduced alveolar ventilation
31
Q

Define positive end expiratory pressure (PEEP)

A

PEEP maintains a positive pressure during expiration to avoid collapse of the poorly ventilated alveoli

Usually kept at 5-10 cmH2O

Reduces venous return and can have a profound CV impact on hypovolemic BP

32
Q

What are you monitoring for during controlled ventilation?

A
  1. Airway pressure:
  • avoid barotrauma, ideally PIP < 20 cmH2O
  • avoid volutrauma, ideally TV < 20 cmH2O, check PIP and compliance
  1. End tidal CO2:
    * TV, PIP, RR and I:E adjusted to maintain normocapniahigh; CO2 = hypoventilation - low CO2 = hyperventilation
  2. Compliance
33
Q

Describe the dual chamber ventilator

A
  • Driving gas compresses bellow
  • Driving gas: compressed air or O2
  • Most common in vet med
  • Ascending or descending bellow
34
Q

Describe a piston ventilator

A
  • More sophisticated
  • Advanced methods of ventilation
  • Very precise
  • Does not require driving gas
35
Q

What are the physiological consequences of positive pressure ventilation on the CV system?

A

High and sustained intrathoracic pressure > decr venous return > hypotension - esp hypovolemic patients, close monitoring CV function after initiating IPPV

36
Q

What are the physiological consequences of positive pressure ventilation on the resp system?

A

High intrathoracic pressure and volume > risk of barotrauma > always monitor airway pressure, if thoracic cavity is open, compliance is sig incr > TV and PIP should be adjusted to avoid overdistension

Risk of pneumothorax - worsening previous pneumothorax

37
Q

Patient-Ventilatory Asynchrony occurs when?

A

The timing of the ventilator cycle is not simultaneous with the timing of the patient’s resp cycle

38
Q

What are some causes of patient-ventilator asynchrony?

A

Light anesthetic plane

Nociception

Hypercapnia

Hypoxemia

Hyperthermia

39
Q

Describe how positive pressure ventilation causes diaphragmatic hernia?

A
  • In chronic cases > re-expanding the lung can lead to:
  • Repercussion injury
  • Acute resp distress syndrome
  • Use low TV and high RR to try to maintain a normal minute ventilation
  • Permissive hypercapnia (ETCO2 50-55mmHg)
40
Q

Define atelectasis and what are some causes and consequences?

A

Collapse or closure of a lung resulting in reduced or absent gas exchange

Causes: compression, absorption, decr surfactant

Consequences: V/Q mismatch, hypoxemia, risk of post-operative pulm infection

41
Q

How do you deal atelectasis?

A
  • Recruiting maneuvers (artificial sigh)
  • check CV fxn b/c CV impact may be profound esp in hypovolemic patients
  • Add PEEP after recruiting - prevents re-collapse of alveoli maintaining a positive pressure during expiration

Anesthesiology (12 decks)

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