Mechanical Ventilation Flashcards
Resistance
- How hard is it to get air in?
- The difficulty of a tube to carry gas
- opposition to airflow
- “airway resistance”
Difference between PIP and Plateau. The closer the plateau to PIP the lower the pressure loss
Compliance
- How difficult is it to inflate?
- Characteristics of the lung to make it strechy
- “static compliance”
- Balloon
Mandatory breath
- the start or end (or both) of the breath is determined by the ventilator, independent of the pt
Plateau pressure
- end inspiratory alveolar pressure attained during mechanical ventilation
- <30
Adaptive pressure control
A volume feedback mechanism for pressure-controlled or pressure supported breaths, the desired tidal volume is set and the vent adjusts the inspiratory pressure to deliver the minimal tidal volume
Flow triggering
A alternate to pressure triggering in mechanical vent, in which the vent responds to a change in flow rather than pressure drop
Mean airway pressure (MAP)
- Average airway pressure during a breathing cycle.
- directly related to insp time, RR and peak insp pressure and end- exp pressure
- <12
- associated with oxygenation
Positive end-expiratory pressure
PEEP
- Baseline pressure applied during exhalation with mech vent
- reestablished FRC and makes it easier for the pt to breath
Volume control
Vent controls the inspiratory flow and tidal volume;
tidal volume in this mode is delivered regardless of resistance or compliance
Pressure control
Airway pressure set and remains constant regardless of resistance or compliance
Auto-PEEP
End expiratory alveolar pressure that is greater than the pressure at the proximal airway, which results from high airway resistance and a short expiratory time
AKA air trapping
Breath stacking
Indications for mechanical ventilation
apnea
Acute ventilatory failure
Impending ventilatory failure
OD
Goals of mechanical ventilation
Provide adequate oxygenation
Provide adequate alveolar oxygenation
Avoid autoPEEP
Pulmonary barotrauma
Excessive pressure and volume delivery to the lung and is a consequence of alveolar overdistention to the point of rupture
Lung protective ventilator strategy
Vent technique where the target tidal volume is 6mL/kg of predicted body weight, the plateau pressure is kept below 30 cm H2O and PEEP is applied to maintain alveolar recruitment
Phases of a breath
- Initiation of inspiration
- Inspiration
- End of inspiration
- Expiration
assisted breath
A breath during which all or part of inspiratory (or expiratory) flow is generated by the ventilator doing work for the patient
What is the cycle?
The signal that ends the inspiratory phase of breathing
elastic load
a component of the patient-ventilator interaction, describing the elastance of the respiratory system (lungs and chest wall) and the volume of flow as a function of time
Equation of motion
Pvent(t) = EV(t) + R
What factors increase resistance?
- Bronchospasm
- Mucous
- Airway inflammation
- tumor
Any factors that decrease airway radius increase the resistance
associated with size and patency of airways as well as turbulence of airflow
what is normal resistance
- spontaneously breathing adult 1-3 cmH2O/LPM
- Intubated adult ( increase resistance due to tube): 4-7 cm of H2O/LPM
Peak Inspiratory Pressure
PMax, PIP, PAW
- highest pressure produced during the inspiratory phase
Volume control pros and cons
Cons
- risk of barotrauma
- machine controls flow (more asynchrony)
- pressure changes with changes in Raw and Cst
Pro
- Min vent guaranteed
Pressure control pros and cons
Pro:
- less risk for barotrauma
- patient controls flow
Con
- volume changes with changes in Raw and Cst
- minute vol not guaranteed
What is the P/F ratio?
- PaO2/FiO2 ratio quantifies ventilator-induced lung injury
- normal P/F is > 300
What is the P/F for ALI?
200-300
What is the P/F for ARDS?
Less than 200
What causes Ventilator-associated pneumonia?
A result of the aspiration of contaminated oral and gastric secrections
What are factors that help prevent VAP?
- 30o head up
- good airway cuff seal, subglottic ET
- good oral hygiene
- maintain gastric acidity
What are the potential adverse effects of mechanical ventilation?
- increased intrathoracic pressure
- decreased CO
- Decreased urine output
- Gastrointestinal ischemia
- increased intracranial pressure (ICP)
- Increased Deadspace
- increased shunt
- ventilator-induced lung injury
- VAP
- Psychological stress/sleep disturbances
What can cause increased airway resistance?
- Bronchospasm
- aspiration
- secretions
- obstruction
- small ETT
What can cause a decreased compliance?
- atelectasis
- Auto-PEEP
- pneumothorax
- pulmonary edema
what are the advantages of volume control?
Disadvantages?
Advantages: guaranteed minute volume
Disadvantages:
- risk of barotrauma
- machine controls the inspiratory flow
- pressure change with changes in compliance and resistance
What are the advantages of pressure control?
Disadvantages?
Advantages:
- Less risk of barotrauma
- patient can control flow (and so can we)
- improved synchrony
Disadvantages
- Minute volume changes with changes in compliance and resistance
- minute volume is not guaranteed
