Respiratory insufficiency / failure
Transcription
Respiratory insufficiency / failure
Respiratory insufficiency / failure Katalin Veres MD, PhD 3rd Department of Internal Medicine Respiratory failure the goal of breathing is to fill the blood with the sufficient amount of oxygen necessary for the tissues and clear the blood of carbon dioxide RF = the insufficiency of the breathing to fulfill the above task - that is insufficient respiratory performance of the lungs Definition a functional acute or chronic disorder severely affects the lungs’ ability to maintain arterial oxygenisation or carbon dioxide elimanation frequently encountered medical problem major cause of death in the US Respiratory failure Physiologic definition inability of the lungs to meet the metabolic demands of the body can’t take in enough O2 or can’t eliminate CO2 fast enough to keep up with production Alveolar phase of breathing Oxygen consumption Resting oxygen consumption + work load (physical + metabolic) requirements Hypoxia: Hypoxemic – – – reduction of FIO2 (mountain sickness) Ventilation/diffusion failure Shunting - anatomic R→L shunts circulation without ventilation = atelectasis!!! Stagnation - mixed SatvO2↓ Ischemic Anemic Histotoxic CO2 elimination arterial CO2 level (PaCO2) depends on the metabolic production rate (VCO2) and the alveolar clearing = alveolar ventilation (VA) PaCO2 = k VCO2/VA under normal circumstances these values are relatively constant Classification failure of gas exchange – hypoxemia Hypoxemic respiratory failure (failure of oxygenation: PaO2<60 mmHg) failure of ventilation – hypercapnia Hypercapnic-hypoxemic respiratory failure (failure of ventilation: PaCO2>50 mmHg) Classification according to ventilatory pump–function: partial or global according to time length (duration): chronic or acute according to origin: obstructive or restrictive Classification Acute/ chronic respiratory failure + acute exacerbation of a chronic process Partial or total (global) ARI (hypoxia alone or + hypercapnia) Ventilation/ Diffusion/ Perfusion abnormalities Obstructive or restrictive RI Causes of ventilation problems Central: CNS – spinal cord Neurologic, neuromuscular, muscular failures Thoracic cage – rib fractures, burns, scars, … Compression of the lungs – hydrothorax, hemothorax, pneumothorax Airway obstruction E.g. myasthenia gravis, GuillainBarré sy., muscle relaxants Mechanical causes Injuries Drug action - e.g. opioids! Upper airway obstruction – foreign body, stenosis, … Lower airways – bronchospasm, asthma, ... Problems in the lung-parenchyma itself Clinical signs of respiratory insufficiency dyspnoea use of ventilatory accessory muscles cyanosis progressive elevation of the resp. rate tachycardia agitation, confusion, somnolentia, coma Diagnosis Inspection – dyspnoea, thoracic movements, etc. Respiratory rate, (VC, FEV?) Pulsoximetry (capnography?) Blood gases (arterial, venous) – repeated! – Reaction to oxygen inhalation? Asthma: peak flow Further investigations: Chest X ray?, CT, MRI Sputum - bacteriology, serology Laboratory testing ECG, US (TEE?) Hypoxic respiratory failure any condition that severely reduces arterial oxygen tensio (<50 mmHg) and cannot be corrected by increasing the inspired O2 concentration to > 50% (FiO2 > 50%) low PaO2 is due to a large right-to-left shunt in well-perfused but poorly oxygenated lung tissue anatomic features: edema, atelectasis or consolidation, hyaline membranes O2 reserve is minimal and patients become symptomatic Clinical manifestations arterial hypoxemia increases ventilation by stimulating carotid body chemoreceptors activity of the sympathetic nervous system tachycardia, tachypnea, anxiety, diaphoresis, altered mental status, confusion, cyanosis, hyper/hypotension, bradycardia, seizures, lactic acidosis Acute hypoxemic respiratory failure Shunt disease - intracardiac or intrapulmonary Severe V/Q mismatch - asthma, PE Venous admixture due to low cardiac output states, severe anemia coupled with shunt and/or V/Q mismatch Features of hypoxemic acute respiratory failure medical history: hypertension, heart disease present illness: acute shortness of breath temporally related to some serious event physical examination: evidence of acute illness, tachypnea, tachycardia, hypotension, diffuse crackles, signs of consolidation CXR, ECG, laboratory Hypercapnic-hypoxemic respiratory failure life-threatening condition with inadequate CO2 excretion (PaCO2 > 55 mmHg) a rise in the PaCO2 level signifies reduced alveolar ventilation or hypoventilation mechanism for the failure in CO2 excretion varies, usually associated with severe airflow obstruction (e.g. COPD, asthma) hypercapnia may also occur in normal lungs: the control of breathing is altered (e.g. sedative drug overdose) or the neuromuscular apparetes is inadequte Clinical manifestations hypercapnia depresses central nervous system activity somnolence, lethargy, restlessness, tremor, slurred speech, headache, asterixis, papilledema, coma Features of hypercapnichypoxemic acute respiratory failure I. physiologic: COPD: hypoventilation due to marked wasted/dead space ventilation neuromuscular or overdose: hypoventilation due to decreased minute ventilation anatomic: mucus gland hyperplasia, alveolar wall destruction, hypertrophied bronchial muscle or mucous inpaction, upper airway obstruction Features of hypercapnichypoxemic acute respiratory failure II. medical history: chronic shortness of breath, history of depression, waekness and wheezing present illness: recent upper respiratory tract infection, gradual worsening of shortness of breath, increased cough, sputum and wheezing, drug ovesdose, new or increased muscle weakness physical examination: tachypnea, tachycardia, prolonged exspiration, decreased breath sounds, wheezing, pedal edema, reduced strength, altered conscionsness CXR, ECG, laboratory Acute respiratory failure Acute Lung Injury, Acute Respiratory Distress Syndrome (ALI/ARDS) Acute bronchospasm – severe asthma Acute on chronic airflow limitation acute exacerbation of COPD Severe pneumonia Pulmonary embolism Pulmonary edema Aspiration, inhalation Acute lung injury, Acute respiratory distress syndrome (ALI/ARDS) diffuse lung disease with severe hypoxia - characterized by loss of ventilated alveoli (loss of surfactant activity, edema of the lung tissue) → reduced ventilated lung-capacity → reduced compliance → severe hypoxemia (intrapulmonary shunts) ALI/ARDS ALI/ARDS diffuse bilateral infiltration caused not by LV insufficiency (Paop < 18 Hgmm) PaO2/FiO2 < 300 (ALI) or 200 (ARDS) lung compliance ↓ severe hypoxia – not reacting on oxygen inhalation ALI/ARDS Pulmonary: - infection/pneumonia - aspiration/inhalation - near drowning - contusion Extrapulmonary: - sepsis - trauma - TRALI - CPB Acute bronchospasm, severe asthmatic attack Components of the insufficiency: bronchospasmus edema of the bronchiolar mucous membranes secretion – sticky secretions obscruction of small bronchioli air trapping – exhalation incomplete the pressure never returns to zero! "dynamic hyperinflation" (TLC↑, RV↑, FRC↑) lung inflation - intrinsic or autoPEEP respiratory work elevated - exhaustion! Pneumonia Epidemiology: Infective agent: Home aquired Community aquired (CAP) Hospital aquired (HAP) Ventilator aquired (VAP) Bacterial - pneumocc., haemophylus, staphylo., mycoplasma Viral pneumonia (influenza, adenovirus, etc.) Clinical appearance: Typic pneumonia (sudden beginning, high fever, productive cough, …) Atypic pneumonia (less characteristic symptoms) Pulmonary embolism 2/3 false diagnosis non specific symptoms risk factors draw attention to the possible diagnosis potencially lethal mortality: 30%, if adequately treated: 2-8 (15)% preventable Pulmonary embolism obstruction of blood flow to one or more pulmonary arteries by thrombi usually precipitated by DVT originating in legs, pelvis, or upper extremities primary or secundary hypercoagulable states subclinical submassive: normal BP, possible RV hypokinesis or dilatation massive: BP, RV afterload, PA systolic pressure Difficulty of diagnosis – Multiple clinical presentations – Nonspecific signs and symptoms Risk factors: surgery, cancer, immobilization, trauma, oral contraceptives, pregnancy/postpartum, advanced age, prior DVT, central catheters, congestive heart failure, hypercoagulable states (inherited or acquired), polycythemia/dehydration, obesity Pulmonary edema Dynamic balance state: intravascular – interstitial – alveolar compartments Starling equation (fluid movement through semipermeable membranes): Qf = K /(Pc – Pi) – σ(Pc – Pi)/ K: filtration coefficient, σ: protein permeability, Pc, Pi: capillary + interstitial onkotic pressure Factors: alveolocapillary membrane permeability hydrostatic pressure in the capillaries onkotic pressure in the interstitium capacity of the lymph-system Common causes of pulmonary edema Cardial edema: main cause is the elevated hydrostatic pressure in the pulmonary vessels (AMI, CAD, CMP, MS, MI, hypertensive crisis…) Non cardiac causes: Chemical irritation (gases, fumes, aspiration of acidic gastric content, etc.) Fluid overload Following upper airway obstruction, near drowing Pneumothx (interstitial neg. pressure↓), re-expansion High altitude Infection, sepsis Pharmacons, toxins (sedato-hypnotica, salicylate overdose, paraquate, …) ….. Chronic respiratory failure any process that affects the airways, lung parenchyma, chest wall or neuromuscular system can evolve into chronic respiratory failure obstruction / restriction most severe cases of chronic hypoxic respiratory failure, progressive lung destruction also impairs ventilation, and hypercapnia develops supportive care lung transplantation