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CCN > Mechanical Ventilation > Flashcards

Mechanical Ventilation Flashcards

1
Q

What are some clinical objectives of mechanical ventilation?

A

Reverse hypoxemia, resp acidosis, prevent / reverse atelectasis, allow for sedation with NMBAs, decrease ICP by controlling pCO2, decrease myocardial and systemic O2 demand

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2
Q

What is normal pCO2?

A

35-45 mmHg

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3
Q

What is normal paO2?

A

80-100 mmHg

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4
Q

What is normal blood pH?

A

7.35 - 7.45

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5
Q

Why does tachypnea cause respiratory alkalosis? What is impact on brain?

A

Too much CO2 being blown off, cerebral vessels constrict if < 35 pCO2, therefore resp alkalosis causes worsened cerebral perfusion

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6
Q

What are the types of mechanical ventilation?

A

1) Negative pressure –> Iron lung, vacuum pressure draws back the chest wall to allow passive inspiration
2) Positive pressure –> Mechanical drive mechanism to force gas into lungs
3) ECMO –> Blood is run through an oxygenator then returned to the pt

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7
Q

How do positive pressure ventilators maintain a closed system?

A

Filter and artificial humidifier cleans and warms/humidifies gas as it exits medic air port before it reaches the inspiratory port. Gas is exhaled into the filter before released into the atmosphere

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8
Q

How does a long term humidifier work and what are the cons?

A

Humidifier is built into the vent circuit to warm/humidify gas before entering the inspiratory port.

Frequent disconnection of circuit required to clean it / change it / empty water buildup which can cause VAP for pts and aerosolization for caregivers

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9
Q

How does a short term humidifier work and what are the cons?

A

HME filter attached to y junction at the inspiratory and expiratory ports. Traps heat and warmth from pt’s own body during exhalation and uses it to humidify inspirations.

Secretions buildup can block the filter and cause VAP / frequent changes. Therefore not used for chronic vents with lots of secretions.

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10
Q

What are the 4 types of positive pressure ventilators?

A

1) Volume cycled
2) Pressure cycled
3) Flow cycled
4) Time cycled

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11
Q

What is volume cycled ventilation and which pts can get it?

A

Volume is guaranteed, pressure changes depending on lung compliance (Peak airway pressure fluctuates)
Pressure can be too high causing barotrauma
Used on pts with compliant lungs

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12
Q

What is pressure cycled ventilation and which pts can get it?

A

Pre-set pressure, volume (Vt) fluctuates as once pressure is reached the machine stops flow of gas
Safer for pts with non-compliant lungs
Number of breaths can be increased to make up for lost Vt (pressure and time can be cycled together)

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13
Q

What is flow cycled ventilation?

A

Inspiration ends at preset flow rate (less commonly used)

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14
Q

What is time cycled ventilation?

A

Preset time interval for inspiration (set resp rate)

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15
Q

What is lung compliance? What is the normal?

A

How easily lung can accept a volume of gas, is relationship between pressure (Paw) and volume (Vt)

Normal compliance is 15 - 25cm H20

Increased pressures indicate deterioration, > 45 risks barotrauma

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16
Q

What factors can decrease lung compliance?

A

1) Stiffening of lungs (pneumonia, fibrosis)
2) Chest wall distensibility (abdominal pressure)
3) Conditions occupying intrathoracic space (pneumothorax, pleural effusion)

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17
Q

What is the ideal tidal volume for a person?

A

6-8ml / kg of body weight

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18
Q

What are ideal standards for FiO2 for a vented pt?

A

Maintain PO2 > 60, SaO2 > 90, FiO2 < 0.6 to avoid oxygen toxicity

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19
Q

How is minute volume calculated?

A

MV = f x Vt

If MV is too large, need to decrease f to avoid blowing off CO2

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20
Q

What is the normal inspiration : expiration ratio?

A

1 : 2 spontaneously

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21
Q

What is PEEP, pros, and what is normal physiologic PEEP?

A

Pressure left in lungs at the end of expiration, allows for alveoli to stay open and prevent collapse, increase SA for ventilation, allows PO2 to be maintained at less FiO2

Physiologic = 2.5 cm H20

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22
Q

What is alveolar recruitment strategy?

A

High level of PEEP for about 20 secs to recruit collapsed alveoli short term

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23
Q

What are disadvantages of high PEEP?

A 
Pneumothorax
Decrease preload (pressure on inferior vena cava leads to decreased venous return, preload)
Increased ICP (decreased venous return from superior vena cava)
24
Q

What is CPAP and what sort of pts get it?

A

Constant Positive Airway Pressure.

Both inspiratory and expiratory pressures are above atmospheric pressures, used to increase functional residual capacity for a spontaneously breathing pt.

25
Q

What is BIPAP and what sort of pts get it?

A

Bi-level positive airway pressure.

2 levels of positive pressure (at inspiration and expiration), with inspiratory pressure usually higher. Tight seal required to keep pressures, used for pts who have issues with spontaneous breathing such as acute emergency, pulmonary edema related to CHF, neuromuscular disease

26
Q

What are contraindications to CPAP / BIPAP?

A

Not for hemodynamically unstable pts, impaired gastric emptying, pts cannot get fed as stomach must be empty, not for pregnant pts, requires full pt cooperation

27
Q

What is high flow nasal cannula?

A

High flow O2 with heated humidification, sustained by special prongs and tubing to handle increased flow. Ordered as flow and FiO2 rather than pressure.

Flow pushes air into lungs but not with pressure, can be used with traches

28
Q

What are the types of invasive ventilation?

A

1) Pressure support (PSV)
2) Assist Control / Volume Control (ACVC)
3) Assist Control / Pressure Control (ACPC)
4) Synchronized intermittent mandatory volume (SIMV)
5) Pressure regulated volume control (PRVC)

29
Q

What is pressure support ventilation and what are pros / cons?

A

Spontaneous breathing mode with pressure support, pre-set positive pressure in the inspiratory port (at least 5cm H2O to overcome resistance of ETT), preset FiO2 and PEEP to augment pt own spontaneous resps

Preset mandatory rate + volume incase of apneic period

Pros: Keeps resp muscles toned, good for weaning
Cons: Vt and MV not guaranteed, risk of hypoventilation, pt needs to be spontaneously breathing

30
Q

What is ACVC and what are the pros / cons?

A

Assist Control / Volume Control

Preset f and Vt, pt can trigger own breaths which will give the preset volume (assisted breaths)

Pros: Good for short term ventilation
Cons: Promotes laziness of resp muscles, risk of resp alkalosis with hyperventilation if pt triggers too much, all breaths are positive pressure and can decrease CO, risk of high Paw, barotrauma

31
Q

How much deviation is acceptable between Vte and set Vt?

A

+- 75 mls

32
Q

What is SIMV and what are pros / cons?

A

Synchronized Intermittent Mandatory Volume

Preset f, Vt except when pt triggers the vent the assisted breath depends on pt effort.

Pros: Allows assessment of resp muscle tone, during weaning resps can be taken away to allow more spont triggers
Cons: Cannot respond to increased demand, pt will end up taking more breaths leading to increased WOB

33
Q

What is ACPC and what are pros / cons?

A

Assist Controlled Pressure Controlled

Preset f, Pip, FiO2, PEEP, but Vt fluctuates
Preset max inspiratory pressure and time = safety mechanism against barotrauma for pts with poor lung compliance. Pt will end of triggering additional breaths because Vt will be low

Pros: For pts with poor compliance
Cons: Highly uncomfortable, if pt resists or “fights” the vent it will cut him off due to high pressure. Cannot be used to wean

34
Q

What is PRVC and what are pros / cons?

A

Pressure regulated volume control

Preset f, Pip, Vt BUT there is no guarantee the pt will get the max Vt because it is time cycled with preset duration of inspiration. As Vt enters lungs, velocity of gas slows down so Paw is 5cm away from set max Pip. Aim to give whole Vt by increasing I:E ratio making inspiration longer. Pt can still trigger above set rate.

Pros: Much better for non-compliant lungs than ACPC because pts get better Vt
Cons: Limited by software

35
Q

What are the 4 methods of weaning?

A

1) SBT
2) PSV Wean
3) SIMV with PS
4) Prolonged mechanical ventilation wean

36
Q

What is SBT and how is it assessed?

A

Spontaneous breathing trial, daily transient reduction in vent support to assess resp function

Pt safety screen done by RT, if pt meets criteria then positive pressure decreased to 0 and pt is left to spontaneously breathe with minimal FiO2

2 mins post SBT started, calculate RSBI and assess distress, sats, hemodynamics, blood gasses

37
Q

What makes a pt eligible for SBT?

A

Able to have spontaneous effort, P/F ratio > 200, FiO2 < 0.5, PEEP < 10, at most 1 vasoactive drug (levo must be < 0.2mcg/kg/min), stable neurological condition

RSBI (Rapid Shallow Breathing Index): f/Vt if > 110 pt is breathing too much and not enough tidal volume

P/F ratio: PaO2/FiO2: If ratio < 200, pt needs to much FiO2

38
Q

What causes a pt to fail SBT?

A

RR > 35 and signs of distress > 5 mins
Sustained SpO2 < 88% for > 2 mins
Increase / Decrease baseline BP / HR > 25%

39
Q

How is pressure support wean done?

A

Pt spontaneously breathing on vent with no preset Vt or f

Gradually decrease positive pressure in inspiratory port

40
Q

How is SIMV with PS weaning done?

A

Bring down SIMV set f, pt will take over more spontaneous breaths with pressure support according to effort. Eventually pt is 100% spontaneously breathing, now decrease PS to 5cm H20

41
Q

How is prolonged mechanical ventilation (PMV) weaning done?

A

Pts have a psychological dependence on the vent and less confidence with spontaneous breathing.
MD may order T-piece or trach mask wean. Pt gets periods of vent support with short periods of spont breathing via T-piece or trache. Can increase spont breathing with consistent rest time.

42
Q

What is important to remember with PMV weans?

A

Must stay with pt during weaning time, pt will be +++ anxious, important to bolster confidence. Pt may have complications post weaning, must be monitored a few days before sending to floor and coordination must be done

43
Q

What are the complications of O2 therapy?

A

1) O2 toxicity
2) Absorption atelectasis
3) Carbon dioxide retention

44
Q

What is O2 toxicity?

A

Free radicals generated when O2 is metabolized, usually neutralized by enzymes but too much O2 causes acute lung injury.

SS: Chest pain, dry cough, sore throat, atelectasis

45
Q

What is absorption atelectasis?

A

Nitrogen keeps alveoli open, so excess O2 “washes out” the alveolar nitrogen causing alveolar collapse. Can occur within 30 mins of FiO2 1.0

46
Q

What is carbon dioxide retention and why is it happen with hyperoxia?

A

Can be due to hypoxic drive or ventilation perfusion mismatch where hyperoxia causes vasodilation to increase blood flow to alveoli. However due to atelectasis, more Co2 gets brought to alveoli than is able to be blown off causing retention.

Could be due to increased O2 binding to hemoglobin leaving less space for CO2 to bind to be excreted.

47
Q

What are the two types of respiratory failure?

A

1) Hypoxic

2) Hypercapnic

48
Q

What is the benefit of oropharyngeal airway? Cons?

A

Keeps tongue out of the way, helps to bag pt until intubation.

Highly uncomfortable, induces gagging, pt either comatose or sedated

49
Q

What is the benefit of naso-pharyngeal airway? Cons?

A

Provides method for frequent suctioning, better for alert pts. Watch for skin breakdown

50
Q

What are nasal ETTs used for?

A

Pts with jaw or neck injury, neck cannot hyperflex.

Difficult insertion, smaller airway, increases WOB, harder to suction

51
Q

What is a normal cuff pressure?

A

< 20mm Hg

52
Q

What is the purpose of ETT cuff?

A

Ensure movement of Vt and pressure

Prevent aspiration

Keep ETT in place

53
Q

What is minimal cuff leak technique?

A

Inject air until no longer hear turbulent air at trachea, then pull back 0.1 cc of air to create minimal leak

54
Q

What is minimal occlusive volume technique?

A

Inflate cuff until no turbulent flow is heard at peak inspiration

55
Q

What are complications of ETT suctioning?

A

Hypoxemia
Atelectasis (neg pressure)
Bronchospasm (stimulation of airways, pull back 1-2 cm)
Cardiac arrythmias (stimulation of vagus nerve)
Hemodynamic changes
Airway tissue trauma

CCN (27 decks)

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