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

2

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.

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

4

Causes of Hypoxia (NEW!)

Low partial pressure of oxygen Hypoventilation Impaired diffusion Shunt Increased dead space ventilation Abnormal hemoglobin binding Abnormal mitochondrial usage

5

Remember

Alveolar-arterial gradient (REVIEW)

A Alveolar oxygen = PAO2 = (PB – PH2O) x %FiO2 - PACO2/R

a arterial oxygen = measured with arterial blood gas

Normal ValuesPB ~ 760 mmHg (at sea level)PH2O = 47 mmHgPACO2 = PaCO2 (from blood gas)PAO2 = 100 mmHgPaO2 = 80 mmHgA-a gradient = 0 (perfect lungs)

< 20 mmHg (clinical medicine)

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 Respiratory muscles Chest wall Lung

Tracheobronchial tree Alveoli

Pulmonary vasculature Heart and the peripheral vasculature

Load

Competence

9

Load versus Neuromuscular Competence

Load

NeuromuscularCompetence

Depressed DriveDrug OverdoseBrainstem LesionSleep Disordered Breathing

Impaired N-M TransmissionPhrenic Nerve InjurySpinal Cord LesionNeuromuscular BlockersMyasthenia GravisALS

Muscle WeaknessFatigueElectrolyte DerangementMalnutritionMyopathy

Resistive LoadsBronchospasmAirway edemaOSA

Lung Elastic LoadsAlveolar edemaInfectionAtelectasis

Chest Wall Elastic LoadsPleural EffusionChest wall traumaObesityAbdominal Distention

Minute Volume LoadsSepsisPulmonary Embolus

Adapted from Murray and Nadel, 1995

Detection of Respiratory Failure

Examine the patient Oximetry Blood Gas

René Laennec

11

“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

Patient Exam

CPR Annie

12

Needed: Finger / Forehead Light

Red light (660nm) Infrared light (910nm)

Pulse Detection of pulse is how

the oximeter subtracts out venous/tissue absorption

How do we measure saturation?The Pulse Oximeter

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!

16

An ABG measures: 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

Would an ABG be better?ABG Machine (not to scale)

CO-oximetry absorption

17

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

Final Check of Oxygen Delivery - Lactate

J Exp Biol 208 4561 2005

Hospital mortality increases with increasing lactate

Lactate production in health

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%

20

Advantages and Disadvantages of the Nasal Cannula

Advantages: Comfortable Able to communicate Patient can eat and

take oral medications Easy to use at home

Disadvantages: 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

22

Rebreather Mask

Flow set to 15 LPM Bag should remain 1/3-

1/2 full after the patient takes a deep breath

Partial Rebreather No valves Delivers 60%-80%

oxygen

Non-Rebreather Valves in place Delivers 90-100%

oxygen…maybe

No Valves

Valves

Treatment of Respiratory Failure

Hypoxemic Supplemental oxygen

Hypercapnic Decrease production CO2

Decrease ventilatory load Improve neuromuscular competence

Hypoxemia / Hypercapnia Positive-pressure ventilation

Reduce feverAttention to nutrition

Treatment of Respiratory Failure

Hypoxemic Supplemental oxygen

Hypercapnic Decrease production CO2 Decrease ventilatory load Improve neuromuscular competence

Hypoxemia / Hypercapnia Positive-pressure ventilation

25

Load versus Neuromuscular Competence

Load

NeuromuscularCompetence

Depressed DriveDrug OverdoseBrainstem LesionSleep Disordered Breathing

Impaired N-M TransmissionPhrenic Nerve InjurySpinal Cord LesionNeuromuscular BlockersMyasthenia GravisALS

Muscle WeaknessFatigueElectrolyte DerangementMalnutritionMyopathy

Resistive LoadsBronchospasmAirway edemaOSA

Lung Elastic LoadsAlveolar edemaInfectionAtelectasis

Chest Wall Elastic LoadsPleural EffusionChest wall traumaObesityAbdominal Distention

Minute Volume LoadsSepsisPulmonary Embolus

Adapted from Murray and Nadel, 1995

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 Inability to protect airway THIS GUY/GAL IS SICK…

* All values are relative

Positive Pressure Ventilation

Machine CPAP – helps oxygenation BiPAP – helps oxygenation and ventilation “Ventilator” – one stop shop for Respiratory Failure

Home CPAP machine

Hospital BiPAP machine

Hospital Ventilator

Positive Pressure Ventilation

Interface Mask

Awake patient, easily removable Endotracheal Tube

Patient can be sedated Can be difficult to place

Tracheotomy Permanent airway

Face Masks

“Trach” patient

Sedated, mechanically ventilated patient with ET tube

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

Respiratory Failure Quiz

Questions / Comments / Suggestions

If you look like this at the end of lecture, go back and restart the slides…

Please email me:matthew.exline@osumc.edu

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