pilbeams ch 5 Flashcards
About 75% of patients receiving invasive PPV are intubated
95% with an oral ET and 5% with a nasal ET. Tracheostomy tubes are used in the remaining 25% of patients receiving invasive PPV.
There are two methods of providing noninvasive positive pressure ventilator support
• Continuous positive airway pressure (CPAP) • Noninvasive positive pressure ventilation (NIV)
, CPAP and NIV are most commonly administered
via a face or nasal mask. Ensuring that the mask fits properly will minimize patient discomfort and help prevent air leaks.
Patients with COPD often have trouble generating the pressure difference between the alveoli and the mouth to begin inspiratory gas flow.
The air trapped in the lungs creates a positive alveolar pressure. If the pressure in the lungs is positive at end exhalation, the pressure must drop below the pressure at the mouth to start gas flow into the lungs for inspiration.
Externally applied CPAP can help overcome the
pressure difference between the mouth and the alveoli when flow limitation is the cause of auto-peep. The patient then does not have to work as hard to drop their alveolar pressure. CPAP can decrease inspiratory work.
NIPPV/CPAP Candidates
Impending respiratory failure OSA COPD patients Neuromuscular weakness Chest wall deformities Cardiogenic pulmonary edema Post extubation difficulties Asthma Post –Op complications Pneumonia * Can reduce the need for mechanical ventilation in 60-75% of these cases
In which of the following situations would NIV be tried?
1 Patient in whom blood pressure is 65/35, heart rate is 150 beats/min, and respiratory frequency is 34 breaths/min
2 Patient who nearly drowned who has copious amounts of white, frothy secretions
3 Patient with chronic obstructive pulmonary disease (COPD) and right lower-lobe pneumonia with respiratory acidosis and increased work of breathing (WOB)
4 A 5-year-old child who has aspirated a piece of chicken and is having trouble breathing
3 Patient with chronic obstructive pulmonary disease (COPD) and right lower-lobe pneumonia with respiratory acidosis and increased work of breathing (WOB)
A high percentage of patients who need mechanical ventilation
require invasive positive pressure ventilation via an artificial airway.
Full ventilatory support (FVS)
Ventilator provides all the energy necessary to maintain effective alveolar ventilation Rates > 8 breaths/min Adequate VT for patient Preset volume or pressure Allows patient to rest and recover
Partial ventilatory support (PVS)
Patient participates in the work of breathing (WOB)
Rates < 6 breaths/min
Avoid if pt has increased WOB
2 types of Targeted control variables
Volume
Pressure
3 types of Timing of breath delivery
Continuous mandatory ventilation (CMV)
Intermittent mandatory ventilation (IMV)
Continuous spontaneous ventilation (CSV)
Mandatory breath
Ventilator controls: timing, tidal volume or inspiratory pressure
Spontaneous breath
Patient controls: the timing and the tidal volume
Volume and/or Pressure is based on patient demand and the patient’s lung characteristics
Assisted breath
Has characteristics of both mandatory and spontaneous
All or part of the breath is generated by the ventilator, which does part of the WOB for the patient
A patient receives a breath that is patient triggered, volume targeted, and time cycled. What type of breath is it?
Assisted
It is a patient controlled machine breath. The Vt is delivered by the ventilator and the ventilator cycles the breath.
Targeting Volume as the Control Variable
Volume is constant, pressure based on patient’s lung characteristics
Advantages
Guarantees a specific volume delivery and volume of expired gas
The goal of volume-controlled ventilation is to maintain a certain PaCO2
Disadvantages
Evident when lung condition worsens
High pressures
Flow and sensitivity settings
Watch for patient-ventilator asynchrony if volume/flow isn’t adequate
Targeting Pressure as the Control Variable
Pressure is set as the independent variable
Volume delivery changes as lung characteristics change, therefore volume delivery must be closely monitored
Considered a lung protective strategy
May be more comfortable for the spontaneously breathing patient
Advantages and Disadvantages of Pressure-Controlled Ventilation
Advantages
Allows a set max pressure
Set pressure reduces the risk of overdistention
Decelerating flow pattern
Disadvantages
Volume delivery varies with the patient’s lung characteristics
Clinicians may be less familiar with pressure-control ventilation
VT and expired volume per minute (VE) decrease when lung characteristics deteriorate
Pressure control ventilation and volume control ventilation are
are equally beneficial in patients who are not spontaneously breathing when a targeted flow pattern is used
. In spontaneously breathing patients,
pressure-controlled ventilation may lower the WOB and improve patient comfort to a greater extent than volume-controlled ventilation, thereby reducing the need for sedatives and neuromuscular blocking agents.
Continuous mandatory ventilation (CMV)
Time- or patient-triggered
Intermittent mechanical ventilation (IMV)
Patient receives a set number of mandatory breaths
Can breath spontaneously breaths between mandatory breaths
Continuous spontaneous ventilation (CSV)
All breaths are spontaneous
Patient-triggered
CMV-All breaths are mandatory
and can be volume or pressure targeted. Breaths can be time triggered or patient triggered
When breaths are time triggered,
they are described as controlled ventilation
When breaths are patient triggered
they are described as assisted ventilation.
Volume-targeted CMV (also called volume-controlled continuous mandatory ventilation [VC-CMV])
All breaths are mandatory
If patient triggered, it is called assisted
Once thought to minimize the WOB during mechanical ventilation
However, studies have shown that patients receiving this mode of ventilation may actually perform 33% to 50% or more of the work of inspiration
Pg. 66, Fig 5-4
This is true when inspiration is active and the set flow does not match the patient’s inspiratory flow demand. If the pressure does not rise smoothly and rapidly to peak during inspiration, flow is inadequate.
Pressure-targeted CMV is also called pressure-control continuous mandatory ventilation (PC-CMV) or simply pressure-control ventilation (PCV)
All breaths are time or patient triggered, pressure targeted, and time cycled
The ventilator provides a constant pressure to the patient during inspiration
PC-CMV
The operator sets:
the length of inspiration, the pressure level, and the backup rate of ventilation
The VT delivered by the ventilator is influenced by the compliance and resistance of the patient’s lungs, patient effort, and the set pressure
Several studies have shown that the decelerating ramp flow curve may improve gas distribution and allows the patient to vary inspiratory gas flow during spontaneous breathing efforts
A patient on PC-CMV has widely fluctuating changes in Raw because of secretions and bronchospasm. The low tidal volume alarm is activated every few hours; the set pressure is 18 cm H2O. The physician is concerned about consistency in ventilation. What would you recommend? A. Increase the set pressure B. Sedate the patient C. Switch to VC-CMV D. Switch to PSV
C. Switch to VC-CMV
VC-IMV and PC-IMV
Involves periodic volume- or pressure-targeted breaths that occur at set intervals (time triggering)
The patient can breathe spontaneously between mandatory (i.e., machine) breaths at the desired baseline pressure without receiving a mandatory breath
Most ventilators can also provide pressure support for spontaneous breaths
Spontaneous breathing
Patients can breathe spontaneously through a ventilator circuit without receiving any mandatory breaths (T-piece
Continuous positive airway pressure (CPAP)
Helpful for improving oxygenation in patients with refractory hypoxemia and a low FRC
Pressure support ventilation (PSV)
The ventilator provides a constant pressure during inspiration once it senses that the patient has made an inspiratory effort
Additional PSV Settings
Important that the ventilator deliver an appropriate flow at the beginning of inspiration
Current ICU ventilators allow the operator to adjust the slope of the pressure and flow curves during inspiration
Flow acceleration percent, inspiratory rise time, inspiratory rise time percent, and slope adjustment
Inspiratory cycle percent, inspiratory flow termination, and expiratory flow sensitivity
Rise Time-refers to the time required for the ventilator to rise to the set pressure at the beginning of inspiration
In which of these four circumstances is it appropriate to select PSV?
1 As a method of weaning
2 To overcome the WOB through the endotracheal tube and circuit
3 For patients on PSV using the SIMV mode
4 For long-term patient support
1, 2, and 3
2, 3, and 4
1, 3, and 4
1, 2, 3, and 4
1, 2, 3, and 4
1 As a method of weaning
2 To overcome the WOB through the endotracheal tube and circuit
3 For patients on PSV using the SIMV mode
4 For long-term patient support
Pressure augmentation
Dual-control mode that provides pressure-limited ventilation with volume delivery targeted for every breath
Patient triggered, pressure targeted breath, but targets the set volume
Will deliver additional flow if needed
Another term is volume-assured pressure support (VAPS)
Pressure-regulated volume control
Volume-targeted, pressure control breath
Volume-support ventilation
Basically pressure support with a volume target
No backup rate
A patient with severe tetanus needs ventilatory support. Which of the following modes would you recommend?
A. Paralyze and sedate the patient; control ventilation using volume control (VC-CMV)
B. PC-CMV
C. VC-IMV
D. PSV with CPAP.
A. Paralyze and sedate the patient; control ventilation using volume control (VC-CMV)
Airway Pressure-Release Ventilation (APRV)
Designed to provide two levels of CPAP and to allow spontaneous breathing at both levels when spontaneous effort is present
High CPAP level is interrupted intermittently to allow pressures to drop very briefly
Expiratory flow generally is not permitted to return to baseline (zero); therefore auto-PEEP is intentionally present
Both pressure levels are time triggered and time cycled
Proportional Assist Ventilation (PAV)
Pressure, flow, and volume delivery are proportional to the patient’s spontaneous effort
Amount of pressure the ventilator produces depends on two factors:
1 the amount of inspiratory flow and volume demanded by the patient’s effort
2 the degree of amplification selected by the clinician (which determines the extent of ventilator response to patient effort)
PAV is a positive feedback system
Which of the following modes would be used for a trauma victim with crushed chest injuries?
1 Negative-pressure ventilation
2 Pressure-cycled ventilator
3 Volume controlled–continuous mandatory ventilation (VC-CMV)
4 NIV
3 Volume controlled–continuous mandatory ventilation (VC-CMV)
