Mechanical Ventilation Flashcards
How does pressure controlled ventilation?
Pressure is selected and duration of inflation is set to deliver the tidal volume
How does volume controlled ventilation?
Tidal volume is preselected
What is the peak airway pressure in volume controlled ventilation?
It is the pressure needed to overcome the resistive forced in the airway and elastic forces of the lungs and chest wall
What is Pres a function of?
Resistance to flow in the airways and the inspiratory flow rate
What is Pel a function of?
Elastic recoil of the lungs and chest wall
What is the plateau pressure in the volume ventilation mode?
It is the same as the peak pressure at the alveoli at the end of inspiration
Is there airflow at the end of inspiration in pressure controlled ventilation?
Yes
What is the end expiratory pressure?
The minimum pressure in the alveoli during a ventilatory cycle
What is ZEEP.
In a normal lung, there is no airflow at the end of expiration. Therefore the pressure in the alveoli is equivalent to the atmospheric pressure
What is applied PEEP?
Added via a pressure sensitive valve in the expiratory limb - stops the flow of air in expiration once the pressure drops below a threshold to be able to keep distal airways open
Which mode is the air movement at the end of inspiration?
Volume control
What is the peak alveolar pressure a reflection of in volume control?
Alveolar volume at the end of inspiration
What does the plateau pressure in the volume control mode need to be to decrease the risk of ventilator induced lung injury?
It represents the peak alveolar pressure so it must be kept less than 30 cm H2O
What is the advantage of volume control?
You can give a constant tidal volume despite changed in the mechanical properties of the lungs and airways
What is the disadvantage to volume control?
Uneven alveolar filling
Patient distress if inspiratory flow isn’t adequate
Which mode is inspiratory flow rate decelerating?
Pressure control
What is the peak alveolar pressure equivalent to in pressure control?
It is equivalent to end inspiratory airway pressure because there is no airflow at the end of inspiration in pressure control
What is the major advantage to pressure control?
The ability to control the peak alveolar pressure
More comfortable for the patient
What is the disadvantage to pressure control?
A decrease in alveolar volume when there is a change in the mechanics of the airways or lungs
What is pressure regulated volume control?
It provides a constant tidal volume but limits end inspiratory pressure.
Monitors mechanics of lungs and calculates lowest pressure needed to achieve the desired tidal volume
What is assist control ventilation?
Allows the patient to take a breath, but also gives patient breaths at a desired rate
What are the triggers in assist control ventilation?
- Generate a negative pressure of 2-3mmhg (double what it takes in quiet breathing though)
- Flow rate
Why is flow rate trigger easier for patients on ACV?
It involves little to no pressure change and volume.
Need flow rate of 1-10 l/min
How can you increase the I:E ratio?
- Increasing the inspiratory flow rate
- Reducing the tidal volume
- Decreasing the inspiratory time
What is intermittent mandatory ventilation?
Allows patient to take their own breaths while still delivering breaths
How does IMV work?
Has unidirectional valve that opens in the circuit to allow spontaneous breath when ventilator breath is not delivered
What are the adverse effects of IMV.
- Increased work of breathing
2. Decreased cardiac output
When is IMV used?
Rapid breathing with incomplete exhalation
Who is IMV not advised for?
Patients with respiratory muscle weakness or LV dysfunction
What is pressure support ventilation?
Allows patient to terminate the lung inflation and therefore tidal volume and inspiratory time
When does the pressure augmentation terminate in PSV?
When inspiratory rate falls below 25% of peak
When is pressure support used?
During weaning to reduce the work of breathing without augmenting tidal volumes (5-10 mmHg)
Noninvasive ventilation
To augment tidal volumes (15-30)
What is the closing pressure?
The transpulmonary pressure at which distal air spaces start to collapse
What is a normal closing pressure?
3 cm H2O
In what conditions is the closing pressures elevated?
Obstruction (COPD)
Reduced lung compliance
What is the purpose of PEEP?
To keep the airway pressure above closing pressure
What does PEEP do to the peak alveolar pressure and mean alveolar pressure?
Increases them proportionately
What does the change in peak alveolar pressure influence?
The risk of lung injury from overdistention and volutrauma
What does the change in mean airway pressure determine?
The influence of PEEP on cardiac output
What do high levels of PEEP do?
Recruit alveoli
How can you tell if PEEP is recruiting alveoli versus overdistending?
- Increasing lung compliance
- Increasing PAO2/FiO2
- Increasing O2 saturation
How should you calculate a tidal volume?
8 mL/kg using predicted body weight
What should you do to the tidal volume over the next 2 hours?
Reduce to 6 mL/kg
Where should the peak alveolar pressure be kept?
Less than 30 cm H2O
What should you set the inspiratory flow rate at if the patient is breathing quietly or not at all?
60 L/min
When should higher inspiratory flow rates be used?
When patient is in distress
What should you set the respiratory rate for if the patient isn’t breathing?
Set it to their minute ventilation just prior to intubation
What should the initial PEEP be set at?
5 cm H2O
When may PEEP be required to increase?
- FiO2 over 60%
2. Refractory hypoxemia
What does PEEP do to preload?
Decreases it by:
- Decreasing the intrathoracic pressure gradient for venous inflow into the thorax
- Decreases the transmural pressure during diastole which impairs ventricular filling
- Increases pulmonary vascular resistance - impede RV stroke volume and therefore LV filling
What is ventricular interdependence?
When the right ventricular septum bulges into the LV from back up of blood causing LV dysfunction due to RV dysfunction
What does PEEP do to afterload?
It decreases afterload because it decreases the transmural pressure on the heart
What does PEEP do to intra abdominal pressure?
Increases it so maintains venous inflow into the thorax
How does PEEP act as a ventricular assist?
By decreases the transmural pressure across the heart and helping with systole (especially in failing heart which operates on flat part of starling curve)
What is essential during positive pressure ventilation to avoid deficits in CO?
Maintaining volume status (preload)
What is the most common organism to cause VAP in the first 48 hours of ventilation?
MSSA
Others include: Klebsiella, Enterobacter, Proteus, S. Pneumo, H. Flu
What are the bugs associated with late onset VAP?
MRSA
Pseudomonas
Acinetobacte
