RESPIRATORY FAILURE Michael Kelly, MD Division of Pediatric Critical Care Dept. of Pediatrics
What talk is he giving? DO2= CO * CaO2 CO = HR * SV CaO2 = (Hgb* SaO2 * 1.34) + (PaO2 * 0.003)
Sound familiar?? Net result of any process is inability of pulmonary system to meet demands of tissues..compensatory mechanisms are often the same.increased drive leads to increased rate and effort.
RESPIRATORY FAILURE
Work of Breathing Work = volume x pressure Compliance = Δvolume /Δ pressure Resistance = Δ pressure /Δ flow Resistance: Inversely proportional to radius to the 4 th power
Work of Breathing Move gas into lungs overcome airway resistance Increase the volume of the lungs overcome the elastic recoil of the lungs and chest Inertance of the gas Tissue resistance
Get moving Dissipative forces are needed to overcome the resistance of gas to flow (gas wants to stick to walls) and loss of energy when flow becomes turbulent Nondissipative forces include pressures needed to overcome elastic recoil and inertial forces (negligible in normal breathing)
Don t be a baby Infants chest wall is more compliant thus they retract with less degree of distress Infant s closing volume is above the FRC thus they are prone to atelectasis
Like the garbage. P a CO 2 = VCO 2 / MV a * k MV= RR * TV TV a = TV dead space Anatomic MV a = RR * TV a Physiologic
All there is.. Hypoventilation V/Q Mismatch PaCO2
Scotty and O Brien Carbon Dioxide Bicarbonate Hemoglobin Dissolved Oxygen Hemoglobin Dissolved More soluble Higher MW Less soluble Lower MW
Oxygen Transfer Alveolar Gas Equation (Atmospheric pressure water vapor)*f i O 2 (P a CO 2 /RQ) = P A O 2 A-a Gradient = P A O 2 -P a O 2 Normal gradient is 5-15 mmhg due to bronchial veins and thespian veins that return to LA and V/Q mismatch
Hypoxemia Absent flow of fresh gas to alveolus Hypoventilation Absent flow of blood to lungs Cardiac Shunt ( true shunt ) Inability to get across alveolus Diffusion Ventilation not matched to perfusion V/Q mismatch (waste)
Yes, Virginia Low V/Q units waste perfusion so they contribute to hypoxemia and hypercarbia High V/Q units that waste ventilation have less of an adverse impact on gas exchange
Still kinda simple PaO2
Always a good choice V/Q Mismatch we all have some can be due to wasted ventilation or wasted perfusion usually blunted by hypoxic vasoconstriction
RESPIRATORY FAILURE
Hypoventilation Central Motor pathways Spinal Cord Anterior Horn Cell (SMA) PNS (GBS) NMJ (MG, botulism) Muscle Nares Pharynx Larynx Trachea Bronchioles Hypoventilation does not change the A-a gradient
New Taxes Restrictive Lung Disease Increased elastic work Obstructive Lung Disease Increased resistive work
Restrictive Lung Disease Decreased thoracic compliance Elastic work is increased Higher pressure for same volume Reduced Vital Capacity Small resting lung volumes Normal Resistance FRC is decreased
Restrictive Diseases Lung Fibrosis Pleura Pneumothorax; Effusion Chest Wall Scoliosis Neuromuscular SMA
Obstructive Lung Disease Resistive work is increased resistance of airways increases exponentially as diameter decreases (obstruction worsens)
Obstructive Processes Extrathoracic Intrathoracic
Extrathoracic Inspiratory stridor Increased inspiratory effort Use of accessory muscles Retractions Tachypnea (with worsening of process)
Extraspecial - not Croup Epiglottitis Bacterial Tracheitis Retropharyngeal Abscess Obstructive Sleep Apnea
Here s looking at you..
More problems yet.. Foreign Body Esophageal/trachea Wheezing on exhalation Inhalation Injury Thermal Caustic Masses Neoplasms Hemangiomas papillomatosis Airway Abnormalities Laryngomalacia Tracheomalacia Bronchomalacia Vocal cord dysfunction
Intrathoracic Expiratory flow limitation wheeze Increased respiratory effort Use of accessory muscles Retractions Tachypnea Hyperinflation
Problems in the depths. Bronchiolitis Reactive Airway Disease Foreign Body Anaphylaxis Airway Edema Extrinsic Mass
Treatment Reverse the obstruction Remove the obstruction Supplemental oxygen Relieve the work of breathing Positive Pressure In early stages are hypoxemic secondary to V/Q mismatch; hypercarbia is late finding
V/Q Mismatch Alveolar Collapse Pneumonia Atelectasis Edema Loss of surfactant Decreased blood flow Thrombus Vasoconstriction Decreased cardiac output Shunt Decreased Ventilation
Just play it loud Reverse/Treat underlying cause Restore volume Reverse/ remove obstruction Recruit volume (PEEP) Supplemental oxygen Support respiratory effort Positive pressure Negative pressure
Not a good short cut Shunt Intrapulmonary ARDS, pneumonia, atelectasis Extrapulmonary Congenital heart disease Can t be corrected with 100% oxygen Shunt Equation Q S /Q T = C co 2 C ao2 / C co2 C mvo2
Get past it Diffusion Increased distance between alveolus and RBC & hemoglobin Seen with fibrosis Pulmonary Edema Time Reserve
RESPIRATORY FAILURE Venous Admixture Decreased mixed venous PO 2 Low Cardiac Output Low hemoglobin Increased Oxygen Consumption
RESPIRATORY FAILURE Vascular Pulmonary Hypertension Embolus
Ma Ma Ma Bell
Looking at a failure
Age Related Considerations Respiratory Rate Infants depend far more on their respiratory rate to maintain minute ventilation Chest Wall Compliance Infants have a more compliant chest wall, increasing work of breathing even when well Closing Volume Closing volume in infant is often higher than FRC, predisposing to collapse Airway Diameter Airways are smaller, thus greater susceptibility to increase in resistance with occlusion Obligate nasal breathers
Still under Consideration Tongue Relatively larger tongue; tends to flop backwards Tonsils Enlarged, making it easier for them to obstruct; also more friable Diaphragm Inserts at a more horizontal orientation Less type I fibers Larynx Higher in neck ( anterior ) Head Larger occiput in infants can cause natural flexion of airway
Indications for Intubation Relieve hypoxemia Relieve hypercarbia Relieve work of breathing Divert cardiac output from respiratory muscles Secure the airway
Remember Importance of compliance Importance of hemoglobin dissassociation curve V/Q mismatch Positive pressure
ABP 2. Respiratory failure a. Recognize the clinical and laboratory manifestations associated with respiratory failure of various etiologies b. Plan appropriate management for respiratory failure of various etiologies