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Flashcards in Mechanical Ventilation Deck (55)
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What are some clinical objectives of mechanical ventilation?

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


What is normal pCO2?

35-45 mmHg


What is normal paO2?

80-100 mmHg


What is normal blood pH?

7.35 - 7.45


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

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


What are the types of mechanical ventilation?

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


How do positive pressure ventilators maintain a closed system?

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


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

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


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

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.


What are the 4 types of positive pressure ventilators?

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


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

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


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

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)


What is flow cycled ventilation?

Inspiration ends at preset flow rate (less commonly used)


What is time cycled ventilation?

Preset time interval for inspiration (set resp rate)


What is lung compliance? What is the normal?

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


What factors can decrease lung compliance?

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


What is the ideal tidal volume for a person?

6-8ml / kg of body weight


What are ideal standards for FiO2 for a vented pt?

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


How is minute volume calculated?

MV = f x Vt

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


What is the normal inspiration : expiration ratio?

1 : 2 spontaneously


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

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


What is alveolar recruitment strategy?

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


What are disadvantages of high PEEP?

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


What is CPAP and what sort of pts get it?

Constant Positive Airway Pressure.

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


What is BIPAP and what sort of pts get it?

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


What are contraindications to CPAP / BIPAP?

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


What is high flow nasal cannula?

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


What are the types of invasive ventilation?

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)


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

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


What is ACVC and what are the pros / cons?

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