Diagnosis and
Management of Acute
Respiratory Failure
Steven B. Leven, M.D., F.C.C.P.
Clinical Professor, Pulmonary/Critical Care
Medicine UCI
Director MICU and Respiratory Therapy,
UCI Medical Center
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Objectives
• Understand the causes of hypoxia and
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hypercapnea
Know the clinical manifestations of
respiratory failure
Be familiar with various oxygen delivery
systems
Know indications and contraindications to
noninvasive positive pressure ventilation
Know indications for endotracheal intubation
Be familiar with basic modes of mechanical
ventilation
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CASE # 1
J.T. is a 68-kg, 42-yr old
female admitted after a
drug overdose
complicated by emesis
and aspiration.
Intubation and
mechanical ventilation
are initiated in the
emergency department.
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CASE # 1
• Mechanical
ventilation
– AC (volume)
mode
– Tidal volume 750
mL
– 16 breaths/min
– FIO2 1.0
– PEEP 5 cm H2O
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CASE # 1
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Peak airway pressure 52 cm H2O
Inspiratory plateau pressure (IPP) 48 cm H2O
pH 7.38, PaCO2 36 PaO2 57
Sinus tach at 166, BP 75/50, no urine output
Patient very “agitated” and “fighting vent”
What would you do?
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CASE #2
L.W. is a 62-yr-old, 52-kg
female with severe
emphysema. For 2 days
she has had
progressive dyspnea
and was found
unresponsive. ABG on
5liters NC pH 7.07
pCO2 87 pO2 62.
She required intubation
and initiation of
mechanical ventilation.
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CASE #2
ICU ventilator settings
• AC, rate 12
breaths/min
• Tidal volume 500 mL
• FIO2 100%
• PEEP 5 cm H2O
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CASE #2
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RR 24
I:E ratio = 1:1.5
Peak pressure 50 cm H2O, IPP 35 cm H2O
End expiratory pressure is 20 cm
pH 7.20, PaCO2 60, PaO2 215
Sinus tach 157
BP 78/45
No urine output
Patient very agitated
What would you do?
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CASE #3
• 37 year old healthy malpractice
plaintiff attorney presents to ER with
24 hour history of generalized
weakness. Last week he had a mild
bout of gastroenteritis after eating
under cooked chicken. He could
walk with difficulty when he arrived
at ER 8 hours ago. Now he needs
help to reposition himself in bed and
he coughs when he attempts to
drink.
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CASE #3
• Exam normal
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except weakness
Chemistries and
CBC normal
RA ABG pH 7.41
pCO2 41 pO2 84
Vital Capacity
840cc (12cc/Kg)
CXR at left
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CASE #3
• Where should this patient be cared
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for? ICU? Tele? Ward? Home?
Should this patient be fed?
Should he be advised to call a
lawyer?
Would you put him on BiPAP?
Anything else you would do?
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Case # 4
• A 25-year-old lady, Miss. Poor Compliance,
is rushed into your Emergency Department.
She is an asthmatic who on arrival is sitting
forward in the tripod position, using her
accessory muscles to breath. She is
tachypneic, diaphoretic, agitated and unable
to talk. During a nebulizer tx with albuterol
she becomes dusky and poorly responsive.
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Case # 4
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Plan of care?
• Get ABG?
• Start BiPAP?
• Discuss patient’s “feelings” about
being ill?
• Get advice from resident (oops, he is
running a code)
• Other?
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Acute Respiratory Failure
• Hypoxemic
–Room air PaO2  50 torr
• Hypercapneic
–PaCO2  50 torr
• Acute vs chronic
• Often Multifactorial
ARF 15
Pathophysiology of Hypoxemia
• Ventilation/perfusion mismatch
• Shunt effect (intracardiac or
intrapulmonary)
• Decreased diffusion of O2
• Alveolar hypoventilation
• FIO2 < 21% (eg. High altitude)
ARF 16
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Pathophysiology of
Hypercapnea
• Alveolar ventilation is the prime
determinant of CO2 exchange during
mechanical ventilation
• VA ~ 1/pCO2
• VA=(VT-VD)f
• Change in any variable affects pCO2
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Causes of Hypercapnea
• Inability to sense elevated PaCO2
• Inability to signal respiratory
muscles
• Inability to effect a response from
respiratory muscles
• Increased dead space
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Inability to effect adequate
response from respiratory
muscles
• Imbalance between demand for
respiratory muscle work and the
ability to supply that work
• Examples of increased demand:
bronchospasm, fever, low lung
compliance, pleural effusion
• Decreased supply: poor cardiac
output, malnutrition, deconditioning
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Increased Dead Space
(wasted ventilation)
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Hypovolemia
Low cardiac output
Pulmonary embolus
High airway pressures
Short-term compensation by increasing
tidal volume and/or respiratory rate
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Manifestations of Respiratory Distress
• Altered mental status – especially anxiety!!!
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Anxiety is a result of respiratory distress,
almost NEVER the cause.
Increased work of breathing
– Tachypnea, nasal flaring
– Accessory muscle use, retractions,
paradoxical breathing pattern, respiratory
alternans
Catecholamine release
– Tachycardia, diaphoresis, hypertension
Abnormal ABG – not always!!!
Neuromuscular failure is different from above
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Oxygen Supplementation
low flow systems 1-10 LPM
• 100% O2 mixes with room air to determine FIO2 -
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definition
FIO2 varies with patient’s breathing pattern
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Rapid inspiration entrains more room air
Deep breaths entrain more room air
Rapid respiratory rate entrains more room air
Patients in more distress get lower FIO2
• FIO2 is unknown since amount of entrainment is
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unknown
Any humidity in gas comes from entrained air- wall O2
has 0% relative humidity
Low flow devices
Simple Nasal Cannulas
Simple masks
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High Flow O2 Devices > 20 - 60 lpm
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Device provides 100% of gas to patient - definition
No entrainment of room air if mask fits
FIO2 is known and exact
Relative humidity depends on the device
High flow devices:
– High flow nasal cannula
– Venturi mask
– Aerosol mask – heated or cool
– Nonrebreather mask – some characteristics of
both high and low
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O2 Devices
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Aerosol O2 devices
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BiPAP or NPPV
• Contraindications
– Cardiac or respiratory arrest
– Inability to cooperate, protect the airway, or clear
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secretions
– Nonrespiratory organ failure, esp shock
– Facial surgery, trauma, or deformity
– Prolonged duration of mechanical ventilation
anticipated
– Recent esophageal anastomosis
A need for emergent intubation is an absolute
contraindication to NPPV
Set inspiratory pressure (IP) and exp pressure (PEEP)
Mean pressure determines oxygenation
IP – PEEP determines ventilatory assist
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Endotracheal Intubation
“….An opening must be attempted in
the trunk of the trachea, into which a
tube or cane should be put; You will
then blow into this so that lung may
rise again….And the heart becomes
strong….”
-Andreas Vesalius
(1555)
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Indications for
Endotracheal Intubation
• Airway protection (outside ICU?)
• Relief of airway obstruction
• Respiratory failure or impending
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respiratory failure
– Hypoxic or
– Hypercapneic or both
Need for hyperventilation - ICP
Unsustainable work of breathing
Facilitate suctioning/pulmonary toilet
• Shock !!!!!!!!!!!
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Decision to intubate
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Clinical decision-not based on ABG
Error on the side of patient safety
What is the safest way to navigate illness?
Intubation is not an act of weakness
Think ahead- if need to intubation is
expected in next 24hr, intubate now
Endotracheal tubes are not a disease and
ventilators are not an addiction i.e.
Intubation does not cause ventilator
dependence
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Modes of Mechanical
Ventilation
Point of Reference:
Spontaneous Ventilation
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Continuous Positive
Airway Pressure (CPAP)
• No machine breaths delivered
• Allows spontaneous breathing at
elevated baseline pressure
• Patient controls rate and tidal volume
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Assist-Control Ventilation
• You set tidal volume and minimum rate
• Additional breaths delivered with minimal
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inspiratory effort - pt sets actual rate
Advantages: reduced work of breathing;
allows patient to modify minute ventilation
Most patients should start with this mode
Rate 12, TV 8-10 cc/kg, FiO2 100% PEEP 5
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Synchronized Intermittent
Mandatory Ventilation (SIMV)
• Volume cycled breaths at a preset rate
• Additional spontaneous breaths at tidal
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volume and rate determined by patient
Invented as weaning mode
Best weaning mode is sink or swim
Best use is to mitigate AutoPEEP
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Pressure-Support Ventilation
• Pressure assist during spontaneous
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inspiration with flow-cycled breath
Pressure assist at constant pressure
continues until inspiratory effort
decreases
Delivered tidal volume dependent on set
pressure, inspiratory effort and
resistance/compliance of lung/thorax
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Inspiratory Plateau Pressure
• Airway pressure measured at end of inspiration with
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no gas flow present
Estimates alveolar pressure at end-inspiration
IPP is best indicator of alveolar distension
PIP – IPP ~ airway resistance
Peak pressure
Inspiration
Plateau pressure
Expiration
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Inspiratory Plateau Pressure
• High inspiratory plateau pressure – stiff
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lungs
– Barotrauma - no
– Volutrauma – yes – pneumothorax, etc
– Decreased cardiac output
Methods to decrease IPP
– Decrease tidal volume
– ??? Decrease PEEP
Goal IPP usually  30 cm H2O
ARDS protocol: tidal volume 6 cc/kg IBW
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Auto-PEEP - common
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Occurs in setting of severe COPD or asthma
Very uncomfortable for patient - agitation
Can be measured on most ventilators
Increases peak, plateau, and mean airway pressures
Hypotension – impaired venous return
Suspect in setting of COPD or asthma pt who is
agitated or hypotensive – this is common!!!
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I:E Ratio during Mechanical
Ventilation
• If expiratory time too short for full exhalation
– Breath stacking
– Auto-PEEP
• Reduce auto-PEEP by reducing inspiratory
time/increasing expiratory time
– Increase peak inspiratory flow rate – 100 lpm
– Decrease respiratory rate (use IMV without
PSV) – rate of 12 usually is good
– Decrease tidal volume to 8 cc per kg IBW
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CASE # 1
J.T. is a 68-kg, 42-yr old
female admitted after a
drug overdose
complicated by emesis
and aspiration.
Intubation and
mechanical ventilation
are initiated in the
emergency department.
39
CASE # 1
• Mechanical ventilation
– AC (volume)
mode
– Tidal volume 700
ml
– 10 breaths/min
– FIO2 1.0 – always
start at 100%
– PEEP 5 cm H2O
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CASE # 1
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Peak airway pressure 52 cm H2O
Inspiratory plateau pressure (IPP) 48 cm H2O
pH 7.38, PaCO2 36 torr PaO2 57 torr
Sinus tach at 166, BP 75/50
Patient very “agitated” and “fighting vent”
What are the issues here?
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CASE # 1
• What is diagnosis?
• What are the consequences of
– FIO2 100%?
– TV 10cc/Kg?
– High inspiratory plateau
pressure?
– Hypotension and tachycardia?
– agitation and fighting vent
• What variables should be changed
to improve PaO2? BP? Protect lungs?
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ARDS
• Decreased lung compliance results
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in high airway pressures
Tidal volume goal 6cc/Kg
Maintain IPP  30 cm H2O
PEEP to improve oxygenation
Aim for FIO2 50% - O2 toxic at > 50%
Patients often need volume loading,
sometimes guided by Swan
Sedation (sometimes paralytic)
needed
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CASE #2
L.W. is a 62-yr-old, 52-kg
female with severe
emphysema. For 2 days
she has had
progressive dyspnea
and was found
unresponsive. ABG on
5 liters NC pH 7.07
pCO2 87 pO2 42.
She required intubation
and initiation of
mechanical ventilation.
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CASE #2
ICU ventilator settings
• AC, rate 12
breaths/min
• FIO2 1.0
• Tidal volume 600 ml
• Peak flow 50 l/sec
• PEEP 5 cm H2O
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CASE #2
RR 24
I:E ratio = 1:1.5
Peak pressure 50 cm H2O, IPP 35 cm H2O
End Expiratory Alveolar Pressure 20 cm
H 2O
pH 7.28, PaCO2 60 torr, PaO2 215 torr
Sinus tach 157
BP 78/45
No urine output
Patient very agitated
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CASE #2
• What is the diagnosis?
• What variable(s) should be changed to
improve the ABG ? BP? UO? Agitation?
• What are the consequences of
–change in peak flow rate ?
–change in respiratory rate ?
–change in ventilator mode?
–bronchodilators ?
–High peak pressure?
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Analysis - Patient L.W.
• Hypercapnea acceptable if pH OK
• High peak airway pressure can be OK
• Wide peak-plateau pressure difference
indicates obstructive disease
• Be alert for auto-PEEP
• Hypotension and tachycardia suggest
auto-PEEP and or inadequate preload
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Obstructive Airway
Disease
• Obstructive diseases require
adequate expiratory time
• PaCO2 should be kept at
patient’s
baseline level
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Neuromuscular Disease Case
• 37 year old healthy lawyer admitted
from ER with 24 hour history of
generalized weakness. Last week he
had a mild bout of gastroenteritis.
He could walk with difficulty when he
arrived at ER 12 hours ago. Now he
needs help to reposition himself in
bed and he coughs when he attempts
to drink.
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Neuromuscular Disease Case
• Exam normal
except weakness
• Chemistries and
CBC normal
• RA ABG pH 7.41
pCO2 41 pO2 84
• Vital Capacity
840cc (12cc/Kg)
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Neuromuscular Disease Case
• Where should this patient be cared
for? ICU? Tele? Ward? Home?
• Should this patient be fed?
• Should this patient be intubated?
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Neuromuscular Disease
• Patients do not appear to struggle
• ABG does not tell you when to
intubate
• Delay may result in aspiration and
arrest
• Follow vital capacity closely in ICU
• Intubate when VC approaches
15cc/Kg
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Case # 4
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Plan of care?
• Get ABG?
• Start BiPAP?
• Discuss patient’s “feelings” about
being ill?
• Check her health insurance
• Get advice from resident (oops, he is
running a code)
• Other?
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