Week 3 Mechanical Ventilation Flashcards
What are some values and signs that may indicate the need of mechanical ventilation?
- Mechanical ventilation helps protect and maintain a patent airway in unsoncious patients or those with upper airway obstruction
- Respiratory Rate >35 bpm
- Tidal volume <5ml/kg
- Vital Capacity of <10ml/kg
- PaO2 <55mmHG with supplemental oxygen
Key ventilator settings and concepts, what is Tidal Volume?
- amount/volume of air delivered with each breath
- typically set around 6-8ml/kg of ideal body weight
Key ventilator settings and concepts, what is Positive end-expiratory pressure (PEEP)?
- pressure maintained at the end of expiration to prevent alveolar collapse and improve oxygenation
Key ventilator settings and concepts, what is Respiratory Rate?
- number of breaths per minute
Normal Values: 12-16bpm
Key ventilator settings and concepts, what is Fraction of inspired oxygen (FiO2)?
- percentage of oxygen in delivered gas (can range from 21% - room air, to 100%)
Key ventilator settings and concepts, what is Peek Inspiratory Pressure (PI)?
- maximum airway pressure during inspiration, reflecting the resistance of lung/chest wall compliance
Key ventilator settings and concepts, what is Pressure Support (PS)?
- additional flow of support provided during inspiration to assist in achieving desired tidal volume
Key ventilator settings and concepts, what is Inspiration?
- Inspiration can be initiated by the patient or the machine. The machine provides a flow of gas to reach either a pre-set volume or pressure
Key ventilator settings and concepts, what is Expiration?
- expiration is passive and is the same in spontaneous breathing. Once the volume or pressure is reached the expired gas goes back into the machine.
What is Gas Mixing in MV?
- combines air and oxygen to achieve a set FiO2 - ensuring controlled oxygen delivery based on the patients needs and ventilator setting
What is Flow Pattern in MV?
- determines how gas is delivered including constant *square, decelerating, accelerating and sinusoidal flows, affecting lung filling, airway pressure, and patient ventilator synchrony.
What is involved in Assessing Adequacy of Ventilation?
It involves monitoring:
- tidal volume
- RR
- minute ventilation
- end-tidal CO2
- and blood gases
Oxygenation (PaO2 and SpO2) and patient effort are also evaluated to ensure effective gas exchange and ventilatory support.
What is Minute ventilation in Mechanical Ventilation?
- volume of gas delivered per minute
- RR x Vt
Definition: Volume of air in and out of the lungs in a minute
What is a mandatory breath?
- ventilator generated breaths delivering set volumes or pressures
What is a spontaneous breath?
breaths initiated by the patient
What is triggering and the circuit?
- Triggering is the act of the patient initiating a breath from the ventilator. It may be flow or pressure determined
- Circuit the tubing the gas travels to and from the patient
What is Controlled Mechanical Ventilation (CMV)?
- ALL breaths delivered by the ventilator at a set rate and volume/pressure
- The most basic form of ventilation and is used when the patient is NOT making any SPONTANEOUS BREATHING ATTEMPTS (uncomfortable if patient is waking or breathing up)
Settings: Vt - usually about 10ml/kg
RR - 10-20 BPM
Airway pressures:
- Inspiration terminated when a set of volume or pressure is reached, with normal airway pressure being around 20cm H2O
What is Synchronised Intermittent Mandatory Ventilation (SIMV)?
- Combines set ventilator breaths with the patients’ spontaneous breath
- Mandatory breaths synchronised with patient’s breathing effort - this ensures a minimum number of breaths per minute.
- Spontaneous breaths are supported by PS (Pressure Support)
Settings: Target RR is set
- each minute is divided into SIMV cycles
If no trigger occurs the patient is delivered a mandatory breath
Airway Pressures: Mandatory breaths can be volume or pressure cycled. Helps prevent breath stacking and reduces excessive pressure
Where is it used? Widely used in the ICU setting- transitioning from full ventilation to PS - can be applied to patients who are unconscious or conscious patients.
What is Pressure Controlled Ventilation (PCV)?
- A ventilation mode that delivers breath at a set pressure instead of a fixed volume. Reduces BAROTRAUMA and VOLUTRAUMA especially in ARDS or stiff lungs
Settings: Target pressure is set instead of a tidal volume
- Inspiratory time, rate, and PEEP are adjustable
- Tidal Volume varies based on lung compliance
Airway pressure: PIP (Positive Inspiratory Pressure) is controlled to prevent overinflation. Unlike in volume control, tidal volume is not fixed
Where is it used?
- ARDS or poor lung compliance patients. Prevents high airway pressure in lung - protective strategy. Is often combined with PS
What is Pressure support ventilation?
-Patient “controlled”, patient triggers all breaths with the ventilator providing a set pressure support. (patient triggers breath and the ventilator provides a preset pressure during inspiration. - THERE IS NO MANDATORY BREATHS
Settings: Preset pressure (Usually 10-20cmH2O) assists inspiration.
- Vt and RR is determined by the patient
- The ventilator stops PS when flow slows, passive expiration.
Airway Pressure:
- Pressure is constant during inspiration. No set Vt - this would depend on the patient effort and lung compliance
- Reduces WOB while maintaining spontaneous effort
Where is it used?
- ICU patients weaning from Ventilation. Minimises sedation needs, prevents muscle weakening, and improves patient comfort.
What is PEEP?
- an elevation of alveolar pressure above atmospheric pressure at the end of expiration imposed by a machine circuit
- This prevents all the air from being expelled, similar to PEP but PEP IS NOT A MODE OF VENTILATION on its own when used with an ETT
- Pressure maintained at the alveoli to prevent collapse and improve alveolar ventilation
How is PEEP created in a Circuit? Reistance in the expiratory circuit against the patient’s effort to breath out. Can be used in all modes of ventilation.
PEEP levels usually around 5-15cmH2O but can be up to 25cmH2O in some cases like ARDS.
What are the benefits of PEEP?
- helps the patient overcome resistance in the machine circuit
- Increases FRC
- Helps recruit collapsed lung
- Improves oxygenation
- may redistribute lung water from the alveoli to the interstitium (eg. in pulmonary oedema)
What are the side effects of PEEP?
- Hemodynamic instability - heart and lung being interrelated (an increase pressure in the lung causes an increase pressure in the heart)
- Lung damage
- Effects on ICP
- May worsen oxygenation in focal lung pathology
What is a High Pressure Alarm?
- Indicates increased resistance to Airflow. Look for/check for obstruction, secretions, or patient coughing
