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1、Respiratory Failure,Dr. Sat Sharma Univ of Manitoba,RESPIRATORY FAILURE,“inability of the lung to meet the metabolic demands of the body. This can be from failure of tissue oxygenation and/or failure of CO2 homeostasis.”,RESPIRATORY FAILURE,Definition Respiration is gas exchange between the organism
2、 and its environment. Function of respiratory system is to transfer O2 from atmosphere to blood and remove CO2 from blood. Clinically Respiratory failure is defined as PaO2 50 mmHg.,Respiratory system includes:,CNS (medulla) Peripheral nervous system (phrenic nerve) Respiratory muscles Chest wall Lu
3、ng Upper airway Bronchial tree Alveoli Pulmonary vasculature,Potential causes of Respiratory Failure,HYPOXEMIC RESPIRATORY FAILURE(TYPE 1),PaO2 60mmHg with normal or low PaCO2 normal or high pH Most common form of respiratory failure Lung disease is severe to interfere with pulmonary O2 exchange, bu
4、t over all ventilation is maintained Physiologic causes: V/Q mismatch and shunt,HYPOXEMIC RESPIRATORY FAILURE CAUSES OF ARTERIAL HYPOXEMIA,1. FiO2 2. Hypoventilation ( PaCO2) Hypercapnic 3. V/Q mismatch Respiratory failure (eg.COPD) 4. Diffusion limitation ? 5. Intrapulmonary shunt - pneumonia - Ate
5、lectasis - CHF (high pressure pulmonary edema) - ARDS (low pressure pulmonary edema),Causes of Hypoxemic Respiratory failure,Caused by a disorder of heart, lung or blood. Etiology easier to assess by CXR abnormality: - Normal Chest x-ray Cardiac shunt (right to left) Asthma, COPD Pulmonary embolism,
6、Hyperinflated Lungs : COPD,Causes of Hypoxemic Respiratory failure (contd.),Focal infiltrates on CXR Atelectasis Pneumonia,An example of intrapulmonary shunt,Causes of Hypoxemic Respiratory Failure (contd.),Diffuse infiltrates on CXR Cardiogenic Pulmonary Edema Non cardiogenic pulmonary edema (ARDS)
7、 Interstitial pneumonitis or fibrosis Infections,Diffuse pulmonary infiltrates,Hypercapnic Respiratory Failure (Type II),PaCO2 50 mmHg Hypoxemia is always present pH depends on level of HCO3 HCO3 depends on duration of hypercapnia Renal response occurs over days to weeks,Acute Hypercapnic Respirator
8、y Failure (Type II),Acute Arterial pH is low Causes - sedative drug over dose - acute muscle weakness such as myasthenia gravis - severe lung disease: alveolar ventilation can not be maintained (i.e. Asthma or pneumonia) Acute on chronic: This occurs in patients with chronic CO2 retention who worsen
9、 and have rising CO2 and low pH. Mechanism: respiratory muscle fatigue,Causes of Hypercapnic Respiratory failure,Respiratory centre (medulla) dysfunction Drug over dose, CVA, tumor, hypothyroidism,central hypoventilation Neuromuscular disease Guillain-Barre, Myasthenia Gravis, polio, spinal injuries
10、 Chest wall/Pleural diseases kyphoscoliosis, pneumothorax, massive pleural effusion Upper airways obstruction tumor, foreign body, laryngeal edema Peripheral airway disorder asthma, COPD,Clinical and Laboratory Manifestation (non-specific and unreliable),Cyanosis - bluish color of mucous membranes/s
11、kin indicate hypoxemia - unoxygenated hemoglobin 50 mg/L - not a sensitive indicator Dyspnea - secondary to hypercapnia and hypoxemia Paradoxical breathing Confusion, somnolence and coma Convulsions,ASSESSMENT OF PATIENT,Careful history Physical Examination ABG analysis -classify RF and help with ca
12、use 1) PaCO2 = VCO2 x 0.863 VA 2) P(A-a)02 = (PiO2 - PaCO2) PaO2 R Lung function OVP vs RVP vs NVP Chest Radiograph EKG,Clinical & Laboratory Manifestations Circulatory changes - tachycardia, hypertension, hypotension Polycythemia - chronic hypoxemia - erythropoietin synthesis Pulmonary hypertension
13、 Cor-pulmonale or right ventricular failure,Management of Respiratory Failure Principles,Hypoxemia may cause death in RF Primary objective is to reverse and prevent hypoxemia Secondary objective is to control PaCO2 and respiratory acidosis Treatment of underlying disease Patients CNS and CVS must be
14、 monitored and treated,Oxygen Therapy,Supplemental O2 therapy essential titration based on SaO2, PaO2 levels and PaCO2 Goal is to prevent tissue hypoxia Tissue hypoxia occurs (normal Hb & C.O.) - venous PaO2 60 mmHg(SaO2 90%) or venous SaO2 60% O2 dose either flow rate (L/min) or FiO2 (%),Risks of O
15、xygen Therapy,O2 toxicity: - very high levels(1000 mmHg) CNS toxicity and seizures - lower levels (FiO2 60%) and longer exposure: - capillary damage, leak and pulmonary fibrosis - PaO2 150 can cause retrolental fibroplasia - FiO2 35 to 40% can be safely tolerated indefinitely CO2 narcosis: - PaCO2 m
16、ay increase severely to cause respiratory acidosis, somnolence and coma - PaCO2 increase secondary to combination of a) abolition of hypoxic drive to breathe b) increase in dead space,MECHANICAL VENTILATION,Non invasive with a mask Invasive with an endobronchial tube MV can be volume or pressure cyc
17、led For hypercapnia: - MV increases alveolar ventilation and lowers PaCO2, corrects pH - rests fatigues respiratory muscles For hypoxemia: - O2 therapy alone does not correct hypoxemia caused by shunt - Most common cause of shunt is fluid filled or collapsed alveoli (Pulmonary edema),POSITIVE END EX
18、PIRATORY PRESSURE (PEEP),PEEP increases the end expiratory lung volume (FRC) PEEP recruits collapsed alveoli and prevents recollapse FRC increases, therefore lung becomes more compliant Reversal of atelectasis diminishes intrapulmonary shunt Excessive PEEP has adverse effects - decreased cardiac out
19、put - barotrauma (pneumothorax, pneumomediastinum) - increased physiologic dead space - increased work of breathing,PULMONARY EDEMA,Pulmonary edema is an increase in extravascular lung water Interstitial edema does not impair function Alveolar edema cause several gas exchange abnormalities Movement
20、of fluid is governed by Starlings equation QF = KF (PIV - PIS ) + ( IS - IV ) QF = rate of fluid movement KF = membrane permeability PIV & PIS are intra vascular and interstitial hydrostatic pressures IS and IV are interstitial and intravascular oncotic pressures reflection coefficient Lung edema is
21、 cleared by lymphatics,Adult Respiratory distress Syndrome (ARDS),Variety of unrelated massive insults injure gas exchanging surface of Lungs First described as clinical syndrome in 1967 by Ashbaugh & Petty Clinical terms synonymous with ARDS Acute respiratory failure Capillary leak syndrome Da Nang
22、 Lung Shock Lung Traumatic wet Lung Adult hyaline membrane disease,Risk Factors in ARDS,Sepsis 3.8% Cardiopulmonary bypass 1.7% Transfusion 5.0% Severe pneumonia 12.0% Burn 2.3% Aspiration 35.6% Fracture 5.3% Intravascular coagulopathy 12.5% Two or more of the above 24.6%,PATHOPHYSIOLOGY AND PATHOGE
23、NESIS,Diffuse damage to gas-exchanging surface either alveolar or capillary side of membrane Increased vascular permeability causes pulmonary edema Pathology: fluid and RBC in interstitial space, hyaline membranes Loss of surfactant: alveolar collapse,CRITERIA FOR DIAGNOSIS OF ARDS,Clinical history
24、of catastrophic event Pulmonary or Non pulmonary (shock, multi system trauma) Exclude chronic pulmonary diseases left ventricular failure Must have respiratory distress tachypnea 20 breath/minute Labored breathing central cyanosis CXR- diffuse infiltrates PaO2 O.6 Compliance 50 ml/cm H2O increased s
25、hunt and dead space,ARDS,MANAGEMENT OF ARDS,Mechanical ventilation corrects hypoxemia/respiratory acidosis Fluid management correction of anemia and hypovolemia Pharmacological intervention Dopamine to augment C.O. Diuretics Antibiotics Corticosteroids - no demonstrated benefit early disease, helpful 1 week later Mortality continues to be 50 to 60%,