Transcript Building a Solid Understanding of Mechanical Ventilation

Building a Solid
Understanding of
Mechanical Ventilation
By Chris Kallus, RRT, MEd
Nursing2009, June 2009
2.5 ANCC contact hours
Online: www.nursingcenter.com
© 2009 by Lippincott Williams & Wilkins. All world rights reserved.
Mechanical ventilation

More patients who are mechanically
ventilated are on general units

Follow facility’s procedures and protocols

Assess patient first when problems arise

Obtain physician orders as appropriate

Work with respiratory therapists when
making ventilator changes
Relationship between ventilator
settings and arterial blood gas

Step 1: Evaluate pH and PaCO2

Step 2: Evaluate PaO2 and FIO2

Step 3: Determine the solution
Step 1: Evaluate pH and PaCO2



Hypoventilation causes patient’s pH to
drop and PaCO2 to rise
Hyperventilation, pH is >7.45; PaCO2 is
<35 mmHg
Changing “minute ventilation” setting will
help get values back to normal
Step 1: Evaluate pH and PaCO2

“Minute ventilation” is determined by
multiplying tidal volume by ventilator rate;
expressed as Ve

Tidal volume is based on patient’s ideal
body weight (IBW)

Normal tidal volume is between 10 and 12
mL/kg of IBW

Large tidal volumes can cause ventilatorinduced lung injury
Calculating IBW

Patients of different weights can have
same lung size; calculating IBW (in lbs)
helps choose right tidal volume

Men: 106 + 6(height in inches-60)

Women: 105 + 5(height in inches-60)
Lungs under pressure


Best indicator of alveolar overdistension
(too much pressure from mechanically
delivered breaths) is peak alveolar
pressure, which can be assessed by
measuring plateau pressure, or pressure
applied to small airways and alveoli during
inspiration
Following delivery of tidal volume, you’ll
see a number on ventilator called PIP, or
amount of pressure it takes to deliver that
volume. This number shouldn’t be used
for trending or evaluation
Lungs under pressure


If you set ventilator to achieve a breath
hold following delivery of tidal volume, you
should see pressure drop from peak to a
holding pressure (the plateau pressure;
should be 30 cm H2O or less)
If value is higher, overdistension is likely.
Every time you perform ventilator check,
assess plateau pressure. If value is
trending upward or exceeds 30 cm H2O,
talk to respiratory therapist about
alternative, lung-protective strategies
Lungs under pressure


Alternative strategies include permissive
hypercapnia, airway pressure release
ventilation, changing the mode to
pressure control ventilation
If patient’s peak inspiratory pressure (PIP)
is increasing but plateau stays the same,
reason for pressure increase is in
ventilator tubing or patient’s
tracheobronchial tree
Lungs under pressure


If patient’s PIP is 35 cm H2O and plateau
pressure is 25 cm H2O and an hour later
peak pressure is 65 cm H2O but plateau
pressure is still 25 cm H2O, patient isn’t in
danger of lung damage because reason for
high PIP is an increase in airway
resistance
Patient may be biting on ET tube or need
an inline bronchodilator treatment or
suctioning; this is why plateau pressure is
more important ventilator pressure to
monitor
Lungs under pressure


Transairway pressure is difference
between PIP and the plateau pressure; is
typically <10 cm H2O. Investigate any
pressure above this level
For example, a sudden increase means an
ET tube may be occluded; a more gradual
increase may mean patient is developing
bronchoconstriction and may need an
inline bronchodilator
Step 2: Evaluate PaO2 and FIO2

Oxygenation status is evaluated by
calculating P/F ratio

P/F ratio = PaO2 divided by FIO2

>300 is considered normal

Lung injury and values <200 indicate
refractory hypoxemia
Step 2: Evaluate PaO2 and FIO2



FIO2 is always expressed as a decimal
(ex., FIO2 of 1.0 = 100% oxygen)
Only reason to keep FIO2 above 100% is
in treating carbon monoxide poisoning
As delivered, FIO2 increases, PaO2 should
increase; if not, patient has refractory
hypoxemia
Step 2: Evaluate PaO2 and FIO2


P/F ratio is good indicator of how much
oxygen patient is breathing (FIO2) and
how much is moving into circulation (PaO2)
In critically ill patients, 3 common causes
of refractory hypoxemia:
- pneumothorax
- atelectasis
- pulmonary edema
3 Common causes of refractory
hypoxemia



Pneumothorax - rapid deterioration in
patient condition, absent breath sounds,
high pressure ventilator alarm
Atelectasis – gradual, usually identified on
chest X-ray
Pulmonary edema - may occur in patients
with history of heart failure, decreasing
SpO2 accompanied by fine crackles in lung
bases
3 Common causes of refractory
hypoxemia


HCP will rule out pneumothorax first as
increasing ventilator volume will worsen
pneumothorax
If atelectasis or pulmonary edema, PEEP
will be added
PEEP


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Restores or maintains lung volume
Using PEEP also lets you use lower FIO2 to
reach a target PaO2
Generally, to reduce the risk of oxygen
toxicity, FIO2 should be below 0.5 provided
PaO2 is OK and SpO2 is 92% or higher
Step 3: Determine the solution


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Goal is PaO2 60 to 100 mmHg
Pulse oximetry values are best used for
trending rather than spot-checking
oxygenation
Follow facility protocol and work with
respiratory therapist to make ventilator
changes
Ventilator modes


Assist/control - tidal volume delivered in
response to every patient effort; can be
used in most patients except those with
COPD due to risk of hyperinflation of lungs
SIMV - delivers tidal volume only at a set
time interval; patient can breathe in
between, suitable for all patients,
including COPD
Ventilator modes

Continuous positive airway pressure
(CPAP) - can be used for ventilator
weaning, and patients with sleep apnea;
basically, PEEP with 10 breaths per minute
Ventilator strategies to deliver
tidal volume


Volume control ventilation - sets tidal
volume so patient receives same tidal
volume with each mechanical breath; also
called volume target, volume cycled,
volume limited
ABGs remain constant with this strategy
Ventilator strategies to deliver
tidal volume


Pressure support ventilation (PSV) - sets
PIP; monitor patient for risk of
hypo/hyperventilation
Pressure support ventilation (PSV) - addon strategy for patients with low tidal
volume and mild respiratory distress; adds
pressure boost on inspiration, decreases
work of breathing