Dr SD Maasdorp

Introduction Primary function of respiratory system: Supply O 2 to blood Remove CO 2 from blood

Introduction cont… Adequate gas exchange require: Ventilation Perfusion Diffusion Ventilation-perfusion matching

Definitions Respiratory failure: Failure of lungs to oxygenate arterial blood adequately and/or prevent CO 2 retention Not a primary disease, but syndrome caused by many different diseases

Respiratory failure Type 1 (Hypoxemic) Type 2 (Hypercapnic) AcuteChronicAcuteChronic

Definitions cont… Acute: – Develops in minutes to hours Chronic: – Develops over several days or longer Types: – Type 1(hypoxemic): PaO 2 < 60 mmHg, PaCO 2 N/ ↓ – Type 2(hypercapnic): PaO 2 50 mmHg (Acute – pH ↓, Chronic – pH normal)

Causes of ↓PaO 2 1. Decreased inspired PO 2 2. Hypoventilation 3. Diffusion impairment 4. Shunt 5. Ventilation-perfusion mismatch

Causes of ↑PaCO 2 Hypoventilation Ventilation-perfusion inequality

Hypoventilation A: Impaired respiratory drive: Peripheral and central chemoreceptors: Carotid body dysfunction Metabolic alkalosis Brainstem respiratory neurons: Pharmacologic eg narcotic or sedative overdose Structural eg meningoencephalitis, localized tumors, vascular abnormalities of medulla, strokes affecting medullary control centres Metabolic eg myxedema, hepatic failure, uremia

B: Defective respiratory neuromuscular system: Spinal cord and peripheral nerves: High cervical trauma Poliomyelitis Motor neuron disease Guilain-Barré syndrome Respiratory muscles: Myasthenia gravis Myopathy

C: Impaired ventilatory apparatus: Chest wall: Kyphoscoliosis Ankylosing spondylitis Obesity hypoventilation Airways and lungs: Laryngeal and tracheal stenosis COPD

Clinical features Hypoxia : Dyspnoea Central cyanosis Agitation Restlessness Confusion Hypercapnia : Headache Peripheral Vasodilatation Tremor / flap Bounding pulse Drowsiness Coma

Acute on Chronic respiratory failure COPD = most common cause Chronic CO 2 retention → renal HCO 3 2+ retention → normal pH (compensated respiratory acidosis) Hypoxia is main stimulus for ventilation New insult eg acute exacerbation → sudden ↑PaCO2 and acidemia → drowsiness and coma. Aim of management: Airway protection Controlled O 2 therapy to improve oxygenation without removing hypoxic respiratory drive completely Treat specific precipitating cause

Approach to patient with ↓PaO 2 PaCO 2 ↑ ? Hypoventilation PAO 2 – PaO 2 ↑ ? Hypoventilation alone Hypoventilation + another mechanism PAO 2 – PaO 2 ↑ ? ↓ FIO 2 Is low PO 2 correctable with O 2 ? ShuntV/Q mismatch YesNo Yes NoYes NoYes

Management of respiratory failure Depends on the cause: Ensure open airway O2 via face mask or nasal cannulae – 35-55% O2 Venturi mask – controlled delivery of 24 or 28% O 2 Mask with reservoir bag – delivers almost 100% O2 Mechanical ventilation – invasive or non-invasive

Cor Pulmonale Right ventricular hypertrophy or failure as a result of pulmonary hypertension caused by diseases affecting the lung or its vasculature Acute and life threatening or chronic and slowly progressive

Possible mechanisms: Pulmonary vasoconstriction (secondary to alveolar hypoxia or blood acidosis) Anatomic reduction of pulmonary vascular bed (emphysema, pulmonary emboli) Increased blood viscosity (polycythemia, sickle-cell disease) Increased pulmonary blood flow

Clinical features Symptoms: Dyspnea on exertion Fatigue Lethargy Chest pain Syncope on exertion Cough Hempotysis Anorexia Right upper quadrant discomfort

Signs: Pulmonary hypertension S2 loud, palpable, narrowly split Systolic ejection murmer Diastolic PR murmer RV hypertrophy Prominent A wave of JVP Right-sided 4 th heart sound Left parasternal heave RV failure Elevated JVP Prominent V-wave Right ventricular 3 rd heart sound TR murmer Hepatomegaly Other Peripheral edema

Chest X-ray

ECG

Echocardiography

Management of cor pulmonale Oxygen therapy for hypoxemic patients Relieves pulmonary vasoconstriction Diuretics Improve function of both right and left ventricles by reducing preload and right ventricular filling pressure Caution: Excessive volume depletion can reduce cardiac output Metabolic alkalosis can suppress ventilation Phlebotomy If hct > 55% and patient symptomatic

Case studies A mountain climber is 5800m above sea-level (barometric pressure = 380 mmHg). He has headache, looks disoriented and is hyperventilating. An ABG reveals a PaO2 of 40 mmHg and PaCO2 of 25 mmHg. Why is he hypoxic?

After passing the recent grade 12 exams, a young female experienced with narcotics and accidentally took and overdose of heroin. She is brought to casualty comatose. ABG reveals PaO2 of 50 mmHg and PaCO2 of 80 mmHg with pH 7.0 Why is she hypoxic?

A 24 year old university student presents at casualty with recent onset of severe fever, coughing and dyspnea. ABG reveals a PaO2 of 35 mmHg and PaCO2 of 25 mmHg. After giving him 40% via facemask, his PaO2 improves to 70 mmHg. Why is he hypoxic?