Respiratory failure&

Cor Pulmonale

Dr SD Maasdorp

IntroductionPrimary function of

respiratory system:Supply O2 to bloodRemove CO2 from

blood

Introduction cont…Adequate gas

exchange require:VentilationPerfusionDiffusionVentilation-

perfusion matching

Definitions

Respiratory failure:Failure of lungs to oxygenate arterial blood

adequately and/or prevent CO2 retentionNot a primary disease, but syndrome caused by

many different diseases

Respiratory failure

Type 1 (Hypoxemic)

Type 2 (Hypercapnic)

Acute Chronic Acute Chronic

Definitions cont…• Acute:

– Develops in minutes to hours• Chronic:

– Develops over several days or longer• Types:

– Type 1(hypoxemic): • PaO2 < 60 mmHg, PaCO2 N/↓

– Type 2(hypercapnic): • PaO2 < 60 mmHg, PaCO2 > 50 mmHg (Acute – pH

↓, Chronic – pH normal)

Causes of ↓PaO2

1. Decreased inspired PO2

2. Hypoventilation3. Diffusion impairment4. Shunt5. Ventilation-perfusion mismatch

Causes of ↑PaCO2

HypoventilationVentilation-perfusion inequality

HypoventilationA: 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 featuresHypoxia :

DyspnoeaCentral

cyanosisAgitationRestlessnessConfusion

Hypercapnia :HeadachePeripheral VasodilatationTremor / flapBounding

pulseDrowsinessComa

Acute on Chronic respiratory failureCOPD = most common causeChronic CO2 retention → renal HCO3

2+ retention → normal pH (compensated respiratory acidosis)

Hypoxia is main stimulus for ventilationNew insult eg acute exacerbation → sudden

↑PaCO2 and acidemia → drowsiness and coma.Aim of management:

Airway protectionControlled O2 therapy to improve oxygenation without

removing hypoxic respiratory drive completelyTreat specific precipitating cause

Approach to patient with ↓PaO2

PaCO2 ↑ ?

Hypoventilation

PAO2 – PaO2 ↑ ?

Hypoventilation alone

Hypoventilation + another

mechanism

PAO2 – PaO2 ↑ ?

↓ FIO2

Is low PO2 correctable with O2?

Shunt V/Q mismatch

Yes No

No Yes

NoYes

No Yes

Management of respiratory failureDepends on the cause:

Ensure open airwayO2 via face mask or

nasal cannulae – 35-55% O2

Venturi mask – controlled delivery of 24 or 28% O2

Mask with reservoir bag – delivers almost 100% O2

Mechanical ventilation – invasive or non-invasive

Cor PulmonaleRight 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 featuresSymptoms:

Dyspnea on exertionFatigueLethargyChest painSyncope on exertionCoughHempotysisAnorexiaRight 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 4th heart sound Left parasternal heave

RV failure Elevated JVP Prominent V-wave Right ventricular 3rd heart sound TR murmer Hepatomegaly

Other Peripheral edema

Chest X-ray

ECG

Echocardiography

Management of cor pulmonaleOxygen therapy for hypoxemic patients

Relieves pulmonary vasoconstrictionDiuretics

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

PhlebotomyIf hct > 55% and patient symptomatic

Case studiesA 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?