AMP 31: Mechanical Ventilation (old) Flashcards
What are the two main types of respiratory failure?
oxygenation failure and ventilation failure
What does oxygenation depend on?
surface area available for gas exchange and preservation of the gas exchange barrier
What does ventilation depend on?
Fresh gas flow through alveoli removing CO2
What are the three main indications for mechanical ventilation?
- severe hypoxemia despite O2 therapy
- severe hypoventilation despite therapy
- excessive respiratory effort
What is the definition of “severe hypoxemia”?
cyanosis, PaO2 < 60 mm Hg, or SpO2 < 90%
What is the marker of “severe hypoventilation”?
PCO2 > 60 mm Hg
What does primarily control PCO2?
minute ventilation
What does “minute ventilation” mean and what are its determinants?
amount of fresh gas flow to alveoli in a minute, determined by respiratory rate and tidal volume
What are the three main ventilator breath patterns used?
- Assist control ventilation (A/C)
- Synchronized intermittent mandatory ventilation (SIMV)
- Continuous spontaneous ventilation
Describe A/C ventialtion
Assist/Control Ventilation
- all breaths are mandatory breaths (generated by the machine)
- minimum respiratory rate is set but patient can trigger additional breaths which are then generated by the machine, i.e., patient can increase the RR but all breaths are full ventilator breaths
What determines peak airway pressure in volume controled ventilation?
- tidal volume chosen
- compliance of the respiratory system
What determines the tidal volume in pressure controlled ventilation?
- level of airway pressure chosen
- compliance of the respiratory system
Describe SIMV
Synchronized Intermittent Mandatory Ventilation
- operator sets the number of full mandatory ventilator breaths
- patient can breathe spontaneously inbetween
- machine will try to synchronize mandatory and respiratory efforts
- generally used for patients with less severe disease than A/C
What are the two most common types of ventilator support for continuous spontaneous ventilation? Describe them
continuous positive airway pressure (CPAP)
- ventilator does not deliver breaths
- all breaths are spontaneous breaths/completely patient generated (rate, inspiratory time and TV all determined by patient)
pressure support ventilation (PSV)
- ventilator does not deliver breaths but tidal volume is augmented by the ventilator
- good for patients with adequate respiratory drive but inadequate ventilatory strength
- can be used alone or in conjunction with CPAP or SIMV
What is the reported normal tidal volume in dogs and cats?
10-15 ml/kg
When placing an animal on a ventilator, what is the maximum tidal volume that should be used initially
do not exceed 10 mL/kg to prevent lung injury from overdistension
What are common tidal volumes targeted in animals with severe lung disease?
6-8 mL/kg
When placing an animal on a ventilator what is a desirable initial peak airway pressure?
10-15 mm Hg
When placing an animal on a ventilator, what are reasonable trigger values to start with?
- an airway pressure drop of - 2 mm Hg
- a gas flow change of 2 L/min