Respiratory Failure
in less than 30 minutes
or your lecture is free*
Matthew Exline, MD MPH
* Just kidding you still have to pay tuition
Learning Objectives
 Define the mechanisms of hypoxemia.
 Use A-a gradient to differentiate the cause of
hypoxemia in the clinical setting.
 Recognize depressed respiratory drive,
inadequate neuromuscular competence and
excessive respiratory system load as causes of
ventilatory failure.
 Describe clinical treatment strategy to improve
oxygen delivery based on the oxygen delivery
equation.
 Describe the use of Positive Pressure Ventilation
in the treatment of respiratory failure.
2
What is respiratory failure?
 Hypoxemic:
Failure to maintain
adequate oxygenation
of tissue (Type I
Failure)
 Hypercapnic
Failure to remove
carbon dioxide from
tissue (Type 2 Failure)
 May be acute,
chronic, or acute on
chronic
Causes of Hypoxia (NEW!)
 Low partial pressure
of oxygen
 Hypoventilation
 Impaired diffusion
 Shunt
 Increased dead space
ventilation
 Abnormal hemoglobin
binding
 Abnormal
mitochondrial usage
4
Alveolar-arterial gradient (REVIEW)
Remember
A Alveolar oxygen = PAO2 = (PB – PH2O) x %FiO2 - PACO2/R
a arterial oxygen = measured with arterial blood gas
Normal Values
PB ~ 760 mmHg (at sea level)
PH2O = 47 mmHg
PACO2 = PaCO2 (from blood gas)
PAO2 = 100 mmHg
PaO2 = 80 mmHg
A-a gradient = 0 (perfect lungs)
< 20 mmHg (clinical medicine)
5
Causes of Hypercapnia
Causes of Hypercapnia (simple version)
 Inhalation of CO2
 Increased production CO2
 Fever
 Increased calories
 Pump Failure
 Competence - not
enough effort
 Load – too much work
Apollo 13 Carbon Dioxide Scrubbers
“I suggest you gentlemen invent a way to
put a square peg in a round hole. Rapidly.”
Pump Failure? Can you expand on that?
 CNS (medulla)
 Peripheral nervous system
Competence
 Respiratory muscles
 Chest wall
 Lung
 Tracheobronchial tree
 Alveoli
 Pulmonary vasculature
 Heart and the peripheral vasculature
Load
Load versus Neuromuscular Competence
Neuromuscular
Competence
Resistive Loads
Bronchospasm
Airway edema
OSA
Depressed Drive
Drug Overdose
Brainstem Lesion
Sleep Disordered Breathing
Impaired N-M Transmission
Phrenic Nerve Injury
Spinal Cord Lesion
Neuromuscular Blockers
Myasthenia Gravis
ALS
Muscle Weakness
Fatigue
Electrolyte Derangement
Malnutrition
Myopathy
Adapted from Murray and Nadel, 1995
9
Lung Elastic Loads
Alveolar edema
Infection
Atelectasis
Load
Chest Wall Elastic Loads
Pleural Effusion
Chest wall trauma
Obesity
Abdominal Distention
Minute Volume Loads
Sepsis
Pulmonary Embolus
Detection of Respiratory Failure
 Examine the patient
 Oximetry
 Blood Gas
René Laennec
Patient Exam
 “How’s your breathing?”
 Evaluate mental status
 Work of breathing
 Respiratory rate
 Accessory Muscle Use
 General signs of
distress
 Abnormal heart rate
 Abnormal blood
pressure
 Oxygen Saturation
11
CPR Annie
How do we measure saturation?
The Pulse Oximeter
 Needed:
 Finger / Forehead
 Light
 Red light (660nm)
 Infrared light (910nm)
 Pulse
 Detection of pulse is how the
oximeter subtracts out
venous/tissue absorption
12
When can oximeter lead me astray?
 Apnea
 Increased work of
breathing
 Inadequate oxygen
content
 Anemia
 Abnormal hemoglobin
binding
 Methemoglobinemia
 Carboxyhemoglobin
Work of Breathing
 Keep in mind we are
exquisitely sensitive
to our respiratory load
 Straw-breathing
 Patients with airway
obstruction may
maintain oxygenation
until respiratory
collapse
 Laryngeal edema
 Tracheal stenosis
Tracheal Stenosis
Normal Trachea
What to I really care about? (REVIEW)
 Remember oxygen content (CaO2) is a more
important management measure than PaO2
 ([Hb] * %Sat * 1.34 ml/g) + (PaO2 * 0.003)
 Oxygen delivery the key parameter
 CaO2 * Cardiac output (CO)
 Always correlated your oxygenation status
with your clinical picture!
Would an ABG be better?
 An ABG measures:
ABG Machine (not to scale)
 pH, pO2, pCO2
 Generally test of choice
for detecting hypercapnia
 An ABG calculates
 Bicarbonate
 Oxygen saturation
 An ABG will miss
 Carboxyhemoglobin
 Methemoglobinemia
 CO-oximetry will detect
all 4 forms of Hgb
CO-oximetry absorption
16
Final Check of Oxygen Delivery - Lactate
Lactate production in health
 Lactate produced
peripherally and
converted to pyruvate
in the liver – Cori Cycle
 Evidence of anaerobic
metabolism
 Inadequate oxygen
delivery = Respiratory
Failure
 Inadequate oxygen use
= mitochondrial
dysfunction
 Will discuss more in
Sepsis lecture
17
J Exp Biol 208 4561 2005
Hospital
mortality
increases
with
increasing
lactate
Treatment of Respiratory Failure
 Hypoxemic
 Supplemental oxygen
 Hypercapnic
 Decrease production CO2
 Decrease ventilatory load
 Improve neuromuscular competence
 Hypoxemia / Hypercapnia
 Positive-pressure ventilation
Supplemental Oxygen: Nasal Cannula
 1-6 LPM
*1L=24%
*2L=28%
*3L=32%
*4L=36%
*5L=40%
*6L=44%
**Now “High Flow” Nasal Cannula can deliver up to 15 LPM of oxygen and
estimated FIO2 of ~ 80%
Advantages and Disadvantages of the
Nasal Cannula
20
Advantages:
Disadvantages:
 Comfortable
 Able to communicate
 Patient can eat and
take oral medications
 Easy to use at home
 Nasal obstruction
may impede gas flow.
 May cause nasal
mucosal drying (can
be humidified with
sterile water)
Venturi Mask (Venti Mask)
3-15 LPM
24%-50% (set on base
of mask)
Set FIo2 with
percentage markings
on the base of mask
and adjust the
oxygen flow meter
the appropriate LPM
Rebreather Mask
 Flow set to 15 LPM
 Bag should remain 1/31/2 full after the patient
takes a deep breath
No Valves
 Partial Rebreather
 No valves
 Delivers 60%-80%
oxygen
 Non-Rebreather
 Valves in place
 Delivers 90-100%
oxygen…maybe
22
Valves
Treatment of Respiratory Failure
 Hypoxemic
 Supplemental oxygen
 Hypercapnic
Reduce fever
Attention to nutrition
 Decrease production CO2
 Decrease ventilatory load
 Improve neuromuscular competence
 Hypoxemia / Hypercapnia
 Positive-pressure ventilation
Treatment of Respiratory Failure
 Hypoxemic
 Supplemental oxygen
 Hypercapnic
 Decrease production CO2
 Decrease ventilatory load
 Improve neuromuscular competence
 Hypoxemia / Hypercapnia
 Positive-pressure ventilation
Load versus Neuromuscular Competence
Neuromuscular
Competence
Resistive Loads
Bronchospasm
Airway edema
OSA
Depressed Drive
Drug Overdose
Brainstem Lesion
Sleep Disordered Breathing
Impaired N-M Transmission
Phrenic Nerve Injury
Spinal Cord Lesion
Neuromuscular Blockers
Myasthenia Gravis
ALS
Muscle Weakness
Fatigue
Electrolyte Derangement
Malnutrition
Myopathy
Adapted from Murray and Nadel, 1995
25
Lung Elastic Loads
Alveolar edema
Infection
Atelectasis
Load
Chest Wall Elastic Loads
Pleural Effusion
Chest wall trauma
Obesity
Abdominal Distention
Minute Volume Loads
Sepsis
Pulmonary Embolus
Treatment of Respiratory Failure
 Hypoxemic
 Supplemental oxygen
 Hypercapnic
 Decrease production CO2
 Decrease ventilatory load
 Improve neuromuscular competence
 Hypoxemia / Hypercapnia
 Positive-pressure ventilation
When should I use Positive Pressure
Ventilation?
 Respiratory distress with moderate to severe
dyspnea
 use of accessory muscles of respiration, abdominal
paradox
 Increased respiratory rate (~RR 30) or work of
breathing
 Acidosis (~pH < 7.2 to 7.3)
 Inability to oxygenate (SpO2 < 90%) despite
supplemental oxygen
* All values are relative
 Inability to protect airway
 THIS GUY/GAL IS SICK…
Positive Pressure Ventilation
 Machine
 CPAP – helps oxygenation
 BiPAP – helps oxygenation and ventilation
 “Ventilator” – one stop shop for Respiratory Failure
Hospital Ventilator
Home CPAP machine
Hospital BiPAP machine
Positive Pressure Ventilation
 Interface
 Mask
Face Masks
 Awake patient, easily removable
 Endotracheal Tube
 Patient can be sedated
 Can be difficult to place
 Tracheotomy
 Permanent airway
Sedated,
mechanically
ventilated patient with
ET tube
“Trach” patient
How should I deliver ventilatory
support?
 Non-invasive (CPAP or BiPAP)
 Awake, cooperative patient
 Hemodynamically stable
 Suspected temporary condition
 COPD exacerbation, CHF exacerbation
 Use mask and either
 CPAP is purely oxygenation issue
 BiPAP if ventilatory support is needed
(hypercapnia)
How should I deliver ventilatory
support?
 Full mechanical support




Patient not protecting airway (coma)
Patient delirious, not cooperative
Hemodynamically unstable (shock)
Expected longer duration of illness > 24 to 48 hours
temporary condition
 Failure of non-invasive ventilation
 Patient will need endotracheal intubation and
mechanical ventilation (aka “life support”)
* All values are relative
What should I remember from this?
 Causes of hypoxia
 Causes of hypercapnia
 Function and utility of pulse oximeter
 Approximate FiO2 of supplemental oxygen
 When to use mechanical ventilation
Questions / Comments / Suggestions
Please email me:
matthew.exline@osumc.edu
If you look like this at the end of
lecture, go back and restart the
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