Basic of Arteficial Ventilation

L.Dadak

CO2

O2

Ventilator

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generates a controlled flow of gas into a patient’s airways. Oxygen and air are received from cylinders or wall outlets, the gas is pressure reduced and blended according to the prescribed inspired oxygen tension (FiO2), accumulated in a receptacle within the machine, and delivered to the patient using one of many available modes of ventilation.

Positive pressure ventilation
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gas flows along a pressure gradient between the upper airway and the alveoli. The magnitude, rate and duration of flow are determined by the operator. Flow is either volume targeted and pressure variable, or pressure limited and volume variable.

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Mode of ventilation
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Control / assist Support Volume Pressure SIMV = Synchronized Intermittent Mandatory Ventilation

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Mode of vent.
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VCV = eliminate CO2
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anesthesia post-arrest

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PCV = lung problem PSV = weaning from ventilator

Getting oxygen in
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Depends on
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PAO2
– – – –

FIO2 PACO2 Alveolar pressure Ventilation

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Diffusing capacity Perfusion Ventilation-perfusion matching

Carbon dioxide out
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Respiratory rate Tidal volume Deadspace

Main determinants
Oxygen in
↑ FIO2 PEEP
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Carbon dioxide out
↑ ventilation
↑ RR ↑ tidal volume

↑ mean alveolar pressure
Re-open alveoli and ↓ shunt

Mean airway pressure
Peak Pressure

Pressure

Pressure

Mean airway pressure

Mean airway pressure

Time

Time

Mean airway pressure

Peak Pressure

Pressure

Pressure

Mean airway pressure

Mean airway pressure

Time

Time

Inspiratory time
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Set as:
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% of respiratory cycle I:E ratio Remaining time after inspiration before next breath

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Expiratory time not set
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Inspiratory time
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Increased inspiratory time
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Improved oxygenation Unnatural pattern of breathing
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Deeper sedation

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Increased risk of gas trapping

Mean airway pressure

Pressure

Pressure

Mean airway pressure

Mean airway pressure

PEEP Time Time

PEEP
Improves oxygenation
• ↑ mean alveolar pressure • ↓ shunting

Other settings
Trigger sensitivity ↑ sensitivity preferable
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Flow triggering general more sensitive than pressure triggering ↓ flow or ↓ pressure ⇒ ↑ sensitivity

Other settings

Rise time

Rise time

Pressure

Inspiratory time

Pressure

Inspiratory time

Time

Time

Respiratory complications
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Nosocomial pneumonia Barotrauma Gas trapping

Barotrauma
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High pressures (barotrauma) High volumes (volutrauma) Shear injury

Gas trapping

Gas trapping

Gas trapping

Gas trapping

Gas trapping

Gas trapping

Gas trapping

Gas traping

Gas trapping
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Predisposing factors:
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asthma or COPD long inspiratory time (⇒ expiratory time short) high respiratory rate (⇒ absolute expiratory time short) progressive hyperinflation of alveoli progressive rise in end-expiratory pressure (intrinsic PEEP)

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Effects
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Intrinsic PEEP (PEEPi)

PEEP= PEEP - PEEP i tot e
Pressure

PEEPtot PEEPe Time

Gas trapping
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Adverse effects
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Barotrauma Cardiovascular compromise

Cardiovascular effects
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Preload
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positive intrathoracic pressure reduces venous return exacerbated by
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high inspiratory pressure prolonged inspiratory time PEEP

Cardiovascular effects
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decreased afterload due to decreased LV transmural pressure

Ptm x R T = 2H

Cardiovascular effects
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decreased afterload due to decreased LV transmural pressure

PIC - Ppl

Ptm x R T = 2H

Cardiovascular effects
Overall effect depends on whether ventricular contractility is normal or abnormal ↓ contractility ● (↓ /) ↑ cardiac output
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normal contractility
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↓ cardiac output

Hypotension
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Consider
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Drug induced Gas trapping Tension pneumothorax