Mechanical Ventilation Flashcards
How does anesthesia affect ventilation?
Respiratory depression -> alter sensitivity to CO2
Relaxes respiratory muscles
Atelectasis develops
Impairs V/Q matching -> inhibits hypoxic pulmonary vasoconstriction
How can ventilation status affect anesthesia?
Uptake of inhalational anesthetics depending of ventilation
Controlled ventilation facilitates reliable uptake and smooth plane of anesthesia
How is ventilation monitored?
Arterial blood gas (PaCO2)
Capnograph
What values define oxygenation? How is it measured?
PaO2 or SpO2
Arterial blood gas or pulse oximetry
When breathing 100% O2, can oxygenation be improved more by ventilation?
Nope
How is resistance calculated?
Pressure difference/flow
How is compliance calculated?
Volume/pressure
__________ limits flow
Resistance
_____________ limits volume
Compliance
What are the stages of the respiratory cycle?
Inspiration
- inspiration flow
- inspiratory pause
Expiration
- expiratory flow
- expiratory pause
What is mechanical ventilation?
Artificial ventilation where mechanical means are used to assist/replace spontaneous breathing
Can be provided by ventilator or person
What is spontaneous ventilation?
Patient determines when and how
What is assisted ventilation?
Patient determines when and ventilator determines how
What is mandatory ventilation
Ventilator determines when and how
What is IPPV?
Intermittent positive pressure ventilation
-> positive pressure is maintained ONLY during inspiration
What is IMV?
Intermittent mandatory ventilation
Operator sets a predetermined number of positive breaths but patient can also breath freely between mechanical breaths
What is the highest pressure during inspiration called?
Peak inspiratory pressure (PIP)
What can occur at the PIP?
Pressure will inflate alveoli, opens atelectasis, or cause barotrauma
What is the PEEP?
Positive end expiratory pressure
-positive pressure that is maintained during expiration (keeps alveoli open)
What are indications for PEEP?
Open throax
Lung parenchymal disease
Following alveolar recruitment maneuver (ARM)
For intubated patients that breathing 100% O2 the main indication to ventilate is to ??
Decrease PaCO2
For patients that breathe air what are the indications for mechanical ventilation?
Hypoxemia
Decrease PaCO2
Decrease work of breathing
What are side effects of mechanical ventilation?
Hypotension (esp in hypovolemic patients)
What is the treatment of hypotension caused by MV?
Volume loading
Switch off ventilator
Decrease airway pressure
Inotropic drugs
What are the direct effects of hypercapnia?
Peripheral vasodilation
Decreased myocardial contractility
Bradycardia
Increased ICP
What are the indirect effects of hypercapnia?
Duct to catecholamine release
- tachycardia
- increased myocardial contractility
- increased BP
What is the respiratory rate for healthy lungs?
10-15 breath/min
Tidal volume of healthy lungs ?
10-15 ml/kg
When ventilating, PIP should be how much if BW <10kgs?
10 cmH2O
When ventilating, PIP should be how much if BW > 10kg?
20 cmH20
What should PEEP be when ventilating healthy lungs?
0-2 cmH2O
How is ventilation performed?
Close pop-off
Squeeze reservoir bag to desired pressure
Release bag so patient can passively expire
Open pop-off
Repeat 10times/min
What is the volume control ventilation mode?
Device sets tidal volume, pressure is a deepest variable
If compliance is decreased —> pressure would increase
Difficult to control tidal vol in small patients
What is pressure controlled ventilation mode?
Device sets the airway pressure -> tidal volume is dependent variable
Resistance increase ->volume decreases
Works regardless of body size
When is a volume controlled MV indicated?
When there are transpulmonary pressure changes
When is pressure controlled ventilation MV indicated?
When lung volume changes (eg thoracic surgery)
How do pneumatic ventilators work?
Consist of compressible bellows in a container
Pressurized drive gas in cylinder can compress bellows causing inspiration
When pressure is released, expiration happens spontaneously
An automatic pop-off valve in ventilator is controlled by the drive gas pressure
What is er variable for a pressure mode MV?
Negative pressure generative by patients breath -» tiggers assisted breath
What is the trigger variable for a flow controlled MV?
Inspiratory flow generated by patients breath
What is a limit variable for MV?
Stops inspiration when value is reached
Eg volume or pressure limit
What are common causes of patient-ventilator asynchrony during anesthesia ?
Inadequate anesthetic depth
Inadequate lung volume or tidal volume
How are normal healthy patients weaned from the ventilator after anesthesia?
Decrease ventilator setting and cause hypercapnia to stimulate breathing
Or continue ventilating until fully awake
What is cyclic recruitment?
Alveoli open and collapse with each breath (purposed mechanism of ventilator induced lung injury )
How do you ventilate an atelectasis lung?
Requires a recruitment maneuver
Increase alveolar minute ventilation —> removes more CO2
