Ventilation Flashcards
what are the 3 different ways ventilation may be achieved during anaesthesia?
spontaneous
manual
mechanical
what pressures are involved in spontaneous ventilation?
negative pressure
what is an example of negative pressure ventilation?
spontaneous ventilation
what pressures are involved in mechanical and manual ventilation?
positive pressure
what happens within the lungs during negative pressure ventilation?
air drawn into the lungs by creating of negative pressure by diaphragm and intercostal muscles
how does air move into the lungs during positive pressure ventilation?
system pushes gas into the lungs
what is the ideal method of ventilation during anaesthesia?
spontaneous
why is spontaneous ventilation the preferred type?
most physiologically normal
what are the 3 overriding factors which affect spontaneous ventilation?
physiological/anatomical
external
internal restriction
what are the main physiological/anatomical factors which affect spontaneous ventilation?
airway obstruction
stenotic nares
excess tissue around the airway
hypoplastic trachea
obesity and associated pressure on the diaphragm
what are the main external factors which affect spontaneous ventilation?
ET tube too small
external restriction (surgeon applying pressure / sandbags)
why can external factors effect spontaneous ventilation?
prevent the thorax from expanding
what are the main internal restriction factors which affect spontaneous ventilation?
effusions
what are the indications for assisted ventilation?
reduced drive to ventilate
inability to ventilate or ventilate effectively
what can decreased respiratory drive be caused by?
anaesthetic drugs
CNS disease
raised ICP
encephalopathy
hypothermia
what can cause an inability to ventilate?
open thoracic cavity
muscle failure
nerve failure
external factors affecting lung inflation
why will an open thoracic cavity lead to an inability to ventilate?
no negative pressure
what types of muscle failure can lead to an inability to ventilate?
NMBA (peri and post)
myasthenia gravis
what nerves may fail leading to an inability to ventilate?
intercostal
diaphragmatic
what are the external factors affecting lung inflation that can lead to an inability to ventilate?
sandbag positioning
surgeon
what can you use to identify if a patient requires ventilation?
ventilatory pattern
tidal or minute volume
blood gases
EtCO2
pulse oximitry
how can a patients ventilatory pattern be assessed?
watching the chest
how can tidal or minute volume be assessed?
spirometry
what is the most useful method for assessing patient ventilation?
looking at the chest