Mechanical Ventilation Flashcards
Difference between the 2 types of non-invasive venilation
CPAP (continuous positive airway pressure) - no ventilatory assistance; just improves oxygenation by opening the alveoli and improves hemodynamics by decreasing afterload/preload to improve LV function
BiPAP: continuous positive airway pressure + set inspiratory pressure to assist the ventilatory muscles in their effort to generate inspiratory flow, decreasing the WOB
Indications for CPAP?
OSA
Cardiogenic pulmonary edema
Acute on chronic respiratory failure (i.e. COPD exacerbation)
Indications for BiPAP?
Acute on chronic respiratory failure (i.e., COPD exacerbation)
Other forms of ventilatory failure (neuromuscular disease)
Onc/bone marrow transplant patients w/pneumonia
Acute pulmonary edema (while diuresis works)
Contraindications to non-invasive ventilation?
Significant secretions
Facial trauma/burns/other anatomic problems w/mask seal
Aspiration risk
NNT w/non-invasive ventilation to avoid intubation?
2
Indications for MV?
Anyone who looks like they will die without intubation in the next few minutes
Ventilatory problems (apnea, impending respiratory muscle fatigue, etc.)
Oxygenation problems (hypoxia, etc.)
Protection of the airway
Secretions
List the 4 most commonly used modes of MV.
ACVC
ACPC
SIMV
PS
What 3 things does the mode determine?
How the ventilator initiates the breath (trigger)
How the breath is delivered (limit)
When the breath is terminated (cycle)
ACVC - trigger, limit, cycle?
Trigger: patient or time (negative airway pressure or inspiratory flow)
Limit: flow rate and pattern (constant = square vs. decelerating = ramp)
Cycle: volume (flow lasts until the set TV is delivered)
Compare square vs. ramp
Square: minimize inspiratory time to maximize expiratory time (i.e., obstructive lung disease)
Ramp: ventilate a heterogenous lung (i.e., ARDS)
Purpose of PEEP?
Prevent atelectasis
Decrease inspiratory WOB
Improve gas exchange
Advantages to ACVC
Low work of breathing - every breath is supported, TV is guaranteed
Disadvantages to ACVC
Tachypnea can lead to hyperventilation and respiratory alkalosis
Breath stacking can occur when the patient initiates a second breath before exhaling the first, leading to high volumes and pressures (can overcome w/optimal settings and sedation)
Compare SIMV and ACVC.
Like AC, SIMV delivers a minimum number of fully assisted breaths per minute that are synchronized w/patient effort. However, off-cycle breaths are not assisted.
Identical modes in patients who are not breathing spontaneously due to heavy sedation or paralysis
In SIMV, set a ___ RR to limit the opportunity for spontaneous breathing.
High
Advantage of SIMV?
“exercise” the respiratory musculature
Disadvantage of SIMV?
May increase WOB and cause respiratory muscle fatigue
What is set in ACPC?
RR, peak inspiratory pressure (PIP), inspiratory time (machine pushes in flow until PIP is hit and holds it for the inspiratory time)
What is ACPC commonly used for and why?
ARDS, because it allows for more time for gas exchange
Disadvantages to ACPCP?
Risk of barotrauma
Very uncomfortable
Frequently requires paralysis
PS - trigger, limit, cycle?
Trigger: patient
Limit: pressure
Cycle: flow
Set PIP (patient sets RR and TV)
Inspiratory pressure is added to spontaneous breaths to overcome the resistance of the ETT or to increase the volume of spontaneous breaths
Advantages of PS?
Reduce the risk of barotrauma, more comfortable
Disadvantages of PS?
No back-up, cannot be used when comatose, sedated, or fluctuating mental status
Typical vent settings?
Mode: ACVC RR: 12 TV: 8-10 mL/kg IBW FiO2: 60% or lower is non-toxic PEEP: 5 cm H2O
Regardless of mode, you always have to set FiO2 and PEEP
Techniques to improve tissue oxygenation while on MV?
Increase FiO2
Increase PEEP
Extend inspiratory time fraction
Bronchodilation
Decubitus, upright, or prone positioning
Decrease O2 requirements, improve O2 delivery
Remove pulmonary vasodilators
Settings that affect PaCO2?
MV -> RR x TV
Compliance = ?
TV/(Plateau pressure - PEEP total)
Normal compliance in MV?
60-80 mL/cm H2O
<20 is stiff
Causes of low compliance?
Pulmonary edema ILD Hyperinflation Pleural disease Obesity Ascites Pneumothorax Atelectasis Pneumonia Bronchial intubation
Resistance = ?
(Peak inspiratory pressure - plateau pressure) / flow
If flow is 60L/min = 1L/sec, remove from exation
Normal <15
DDx - increased airway resistance
Kinking or plugging of ETT
Secretions
Bronchospasm
Sedation options on ventilator?
PRN and opiate-based
Strategies to improve hypoxemia in ARDS
- Rx the cause
- Increase FiO2
- Diuresis (theoretically less capillary leakage)
- Increase PEEP
- Low TV (permissive hypercapnia)
- Optimize PmVO2
- Prone positioning
- ECMO
DDx - ARDS
Sepsis or infection (especially pneumonia) Aspiration/near drowning Trauma Burns Blood transfusion S/p transplant of lungs, bone marrow Drugs, alcohol SIRS, including pancreatitis
3 most common - sepsis, pneumonia, aspiration
Strategies to reduce auto-PEEP?
Signaled by persistent expiratory flow at the time the next breath is delivered
Measure by performing expiratory hold maneuver
- Prolong expiratory time (decrease RR, increaase inspiratory flow rate)
- If severe, disconnect from ventilator and manually decompress the thorax
Requirements for extubation?
- Rx underlying cause that lead to ventilation
- Off pressors
- <40% FiO2, 5 or less of PEEP
- Neuro function intact
- Any impending doom?
Weaning parameters (isolated measure of respiratory muscle strength)?
Rapid Shallow Breathing Index (RSBI): RR/TV (in L)
-you want <104
Negative Inspiratory Force (NIF)
-you want more negative than -60 cm H2O (-20 to 0 is weak)
Cause of HTN following intubation?
Stress
Cause of hypotension following intubation?
Most commonly due to decreased venous return due to PPV
Clinical criteria for ARDS?
Acute (w/in 7 days of known clinical insult or new/worsening respiratory symptoms)
Hypoxia (PO2/FiO2 <300)
Diffuse bilateral CXR opacities
No clinical hint of heart failure/fluid overload
Type of respiratory failure in ARDS?
Type 1 (non-ventilatory) - hypoxemia +/- hypercapnia; disease in the lung itself
Type of respiratory failure in COPD?
Type 2 (failure of alveolar ventilation) - decrease in MV or increase in dead space
Mechanism of hypoxemia in ARDS?
Shunting; does not respond to supplemental O2
