Respiratory Failure Dr. Nick Weatherley Respiratory Registrar

Aims Control of breathing review Classification of respiratory failure Causes of respiratory failure Treatment options

Question 1 Annie is a 65 year old lady with a long history of heavy smoking. She feels breathless and wheezy. You perform an arterial blood gas.

pH: 7. 31 (7. 35 - 7. 45) paO2: 7. 5 kPa (10 – 14) paCO2: 7. 2 kPa (4 pH: 7.31 (7.35 - 7.45) paO2: 7.5 kPa (10 – 14) paCO2: 7.2 kPa (4.5 – 6.0) HCO3: 27 mmol/L (22 – 26)

What type of respiratory failure does this represent? What is the cause of this event? What treatment will you initiate?

Control of breathing

CO2 + H2O <--> HCO3- + H+

What is the partial pressure of oxygen at 4000 ft? ~ 16kPa (vs. 19.5kPa at ground level) How long can you hold your breath underwater? Try holding your breath with an O2 sats monitor – your spO2 won’t fall!

Classification of respiratory failure

Type 1 : low paO2, normal (or low) paCO2, normal or high A-a gradient Limitation of ventilation, perfusion or diffusion Type 2 : low paO2, high CO2, usually normal A-a gradient (acute or chronic) Alveolar hypoventilation CO2 enters alveoli, but not removed

CO2 CO2 CO2

Signs of hypercapnoea: Bounding pulse Flapping tremor Confusion Drowsiness Reduced conciousness

Causes of respiratory failure Failure to maintain patent airway (obstruction) – type 1 (if severe type 2) Failure to ventilate alveoli – type 1 or 2 Failure to diffuse oxygen into blood – type 1 Perfusion – usually type 1

1. Airflow Obstruction

Obstructive sleep apnoea Relaxation of pharynx during sleep Occlusion causes stimulation and wakening

2. Alveolar hypoventilation

CO2 CO2 CO2

CO2 + H2O <--> HCO3- + H+

Radiopaedia

Obesity hypoventilation Chest wall deformity Neuromuscular weakness Myaesthenia gravis Motor neurone disease Guillan-Barre syndrome

Volume Time Inspiratory Reserve Volume (IRV) Vital Capacity (VC) Tidal (TV) Volume Total Lung Capacity (TLC) Expiratory Reserve Volume (ERV) Functional Residual Capacity (FRC) Residual Volume (RV) Residual Volume (RV) Time

3. Diffusion limitation

Interstitial lung disease Emphysema Interstitial lung disease IPF Sarcoidosis Pneumoconiosis etc. Drug-induced lung disease (bleomycin, methotrexate)

O2 CO2 O2 CO2

4. V/Q (mis)matching

Obstruction Hypo-ventilation Diffusion Perfusion Asthma COPD (emphysema) IPF Pulmonary embolism COPD Neuromuscular weakness Other ILDs Cardiac failure OSA Obesity (OHS) Emphysema Shunt (e.g. VSD) Pneumonia Chest wall deformity Pulmonary hypertension Reduced drive (e.g. narcotics)

Treatment Underlying cause E.g. bronchodilators for COPD, antibiotics for pneumonia Specific treatments for ventilation support

CPAP (Continuous positive airways pressure) Acutely : Pulmonary oedema Chronic: Obstructive sleep apnoea Expanding into other areas

BIPAP (Bi-level positive airways pressure Causes of type two respiratory failure e.g. Acute: COPD exacerbation Chronic: Motor neuron disease / OHS

Spontaneous CPAP Bipap Pressure Time

Question 1 Annie is a 65 year old lady with a long history of heavy smoking. She feels breathless and wheezy. You perform an arterial blood gas.

pH: 7. 31 (7. 35 - 7. 45) paO2: 7. 5 kPa (10 – 14) paCO2: 7. 2 kPa (4 pH: 7.31 (7.35 - 7.45) paO2: 7.5 kPa (10 – 14) paCO2: 7.2 kPa (4.5 – 6.0) HCO3: 27 mmol/L (22 – 26)

What type of respiratory failure does this represent? What is the cause of this event? What treatment will you initiate?

pH: 7. 31 (7. 35 - 7. 45) paO2: 7. 5 kPa (10 – 14) paCO2: 7. 2 kPa (4 pH: 7.31 (7.35 - 7.45) paO2: 7.5 kPa (10 – 14) paCO2: 7.2 kPa (4.5 – 6.0) HCO3: 27 mmol/L (22 – 26) Type 2 – note the low O2 and high CO2 The low pH suggests an acute event, though it may be an acute on chronic process given slightly high HCO3-

What type of respiratory failure does this represent? What is the cause of this event? What treatment will you initiate?

Obstruction Hypo-ventilation Diffusion Perfusion Asthma COPD (emphysema) IPF Pulmonary embolism COPD Neuromuscular weakness Other ILDs Cardiac failure OSA Obesity (OHS) Emphysema Shunt (e.g. VSD) Pneumonia Chest wall deformity Pulmonary hypertension Reduced drive (e.g. narcotics) Almost certainly alveolar hypoventilation given type 2 RF Probably COPD given history

What type of respiratory failure does this represent? What is the cause of this event? What treatment will you initiate?

Bronchodilators, steroids Cautious oxygen to maintain spO2 88-92%. Consider BIPAP (NIV) or invasive ventilation

Summary Break down causes into broad categories – all may cause type 1 RF Alveolar hypoventilation may lead to type 2 RF ABG crucial for determining type and chronicity

n.weatherley@sheffield.ac.uk