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 = P A O 2 = (P B – P H2O ) x %Fi O2 - P A CO 2 /R a arterial oxygen = measured with arterial blood gas Normal Values P B ~ 760 mmHg (at sea level) P H2O = 47 mmHg P A CO 2 = P a CO 2 (from blood gas) P A O 2 = 100 mmHg P a O 2 = 80 mmHg A-a gradient = 0 (perfect lungs) < 20 mmHg (clinical medicine)

Causes of Hypercapnia

Causes of Hypercapnia (simple version)  Inhalation of CO 2  Increased production CO 2  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 Neuromuscular Competence 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 Resistive Loads Bronchospasm Airway edema OSA Lung Elastic Loads Alveolar edema Infection Atelectasis Chest Wall Elastic Loads Pleural Effusion Chest wall trauma Obesity Abdominal Distention Minute Volume Loads Sepsis Pulmonary 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 (CaO 2 ) is a more important management measure than PaO 2  ([Hb] * %Sat * 1.34 ml/g) + (PaO2 * 0.003)  Oxygen delivery the key parameter  CaO 2 * Cardiac output (CO)  Always correlated your oxygenation status with your clinical picture!

16  An ABG measures:  pH, pO 2, pCO 2  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 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 % oxygen…maybe No Valves Valves

Treatment of Respiratory Failure  Hypoxemic  Supplemental oxygen  Hypercapnic  Decrease production CO 2  Decrease ventilatory load  Improve neuromuscular competence  Hypoxemia / Hypercapnia  Positive-pressure ventilation Reduce fever Attention 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 Neuromuscular Competence 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 Resistive Loads Bronchospasm Airway edema OSA Lung Elastic Loads Alveolar edema Infection Atelectasis Chest Wall Elastic Loads Pleural Effusion Chest wall trauma Obesity Abdominal Distention Minute Volume Loads Sepsis Pulmonary 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

Questions / Comments / Suggestions If you look like this at the end of lecture, go back and restart the slides… Please me:

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