Critical care Flashcards
Mechanical ventilation
MV replaces the function of the inspiratory muscles by delivering gas under positive pressure to the lungs.
Respiratory pump= the abdominal and thoracic structures that contribute to the expansion and contraction of the lungs
Either patient or ventilator triggers ventilation
What is compliance?
Compliance reflects ability to change the shape of a structure when mechanical load is applied.
So lung compliance is the ability of the alveoli and lung tissue to expand on inspiration.
Compliance varies on: elasticity and surface tension of the lung (stiffer the lung the less compliant= harder to MV)
Why ventilate
Respiratory failure
Prolonged post op recovery
altered conscious level
inability to protect airway
Respiratory failure= inadequate gas exchange as reflected in ABGs
What is type 1 failure
hypoxaemia- failed oxygenation Pa02 (<8kpa) due to failure of the gas exchanging function of the respiratory system
what is type 2 respiratory failure
Hypoxaemia and hypercapnia- failed ventilation paCO2 >6.7 with hypoxaemia Pa02 <8kpa.
Raised CO2 is caused by failure of the respiratory pump
Can be acute or chronic
What is PEEP?
Positive end expiratory pressure- pressure maintained in the alveoli at the end of expiration to prevent alveolar and airway collapse
What is volume controlled ventilation
ventilator delivers a pre set TV
Pre set: inspiratory time, pause time and RR
Airway pressure rises slowly as the ventilator reaches the desired volume
Peak airway pressure will vary from breath to breath as the mode is volume controlled and the ventilator will deliver its set volume irrespective of how hard that might be because of variations in lung compliance and resistance to flow
Pressure controlled ventilator
Flow is delivered to pre-set target limit during inspiration
Pre set: RR and inspiratory time
Pressure is constant and set so the volume can change from breath to breath depending on lung compliance.
Better lung compliance leads to larger volume & vice versa
Main advantage is pressure can be controlled reducing the risk of barotrauma in patients with stiff lungs
Dual control
combination of both types avoids barotrauma and maintain good lung volumes.
delivers a pre set volume with the lowest possible pressure- if volume falls below, pressure increases
If upper pressure limit is reached before full volume= sound alarm
Pressure support or AKA assisted spontaneous breath
A spontaneous mode- so the patient must trigger the machine or there will be no breath given and provides a set pressure to boost each breath
Volume support
A spontaneous mode- a set TV is delivered with different pressure support from the ventilator depending on patient effort
Biphasic positive airway pressure (bi-level, bi-vent)
Pressure controlled mode giving the patient unrestricted opportunities for spontanous breathing at pre-set high and low pressure levels
Uses 2 shifting pressure levels- IPAP and EPAP
automode
interactive mode, allows patient to receive a supported breath if triggered or a mandatory breath if not
allows for weaning
CPAP
Continuous positive airway pressure- provides positive pressure but with no mandatory breaths so the patient has to breathe spontaneously.
It increases FRC improving gas exchange by splinting open alveoli
Unlike BIPAP- CPAP delivers the same flow of gas through inspiration as expiration
Continous monitoring of vital signs
RR, SPO2, BP, HR
