1. Respiratory Failure Acute/Chronic
Dr S Bianchi

2. Outline Structure & Function Control of Breathing
Causes of Respiratory Failure
Classification of Respiratory Failure
Treatment Options in Respiratory Failure

3. Structure & Function

4. Respiratory Muscles and Work of Breathing: Health
Rhythmic pumping of gas in and out of the lungs
Inspiration mainly due to diaphragmatic function
Expiration through passive relaxation
Inspiration
Overcoming elastic recoil of lungs (very small)
Overcoming flow resistance (very small)
Expiration
Low energy expenditure

5. Respiratory Muscles and Work of Breathing: Disease
Increased muscle activation and use of accessory muscles
Inspiration
Hyperinflation (COPD/Asthma) – increased elastic work (rubber band)
Increase resistive work secondary to increased flow/respiratory rate
Expiration
Activation of expiratory muscles to overcome bronchoconstriction
Consider effect of muscle weakness/paralysis versus increased airflow resistance
Load versus capacity

6. Ventilation patterns (volunteer)
Health
Disease
Airway Obstruction (Asthma/COPD)(straw)
Expansion of ribcage, increased accessory muscle use, increased diaphragm work, inspiratory reduction in basal thoracic diameter (Hoover’s sign), increased expiratory abdominal muscle work.
Airway Restriction (Obesity/Respiratory muscle weakness)
Small amplitude chest excursion, reduced lung volumes, parameters often worse when supine.

7. Control of Breathing Beware the night! CORTEX ‘Wakefulness drive’
BRAINSTEM
Central Chemoreceptors
CAROTID SINUS
Peripheral Chemoreceptors
LUNGS
Ventilatory output
High pCO2 = +
Low pO2 = +
Awake = +
Asleep = -
CO2/O2
Negative
Feedback
loop
Beware the night!

8. Stimuli & Control of Breathing
Causes of Hypoxaemia (Pulse oximetry)
Low FiO2 (altitude)
Diffusion problems (fibrosis, COPD, heart failure, pulmonary hypertension etc.)
V/Q mismatching (pneumonia, PE, COPD etc)
Hypoventilation (muscle weakness, drugs, stroke, obesity, malnutrition etc.)
Alterations in pCO2
Secondary to alveolar ventilation only
pCO2 offers a better insight into ventilatory performance
THM: VENTILATION (NOT OXYGENATION) IS IMPORTANT

9. Considerations in Respiratory Failure
Central (brain/chemoreceptors) versus peripheral (lungs/muscles)
Increased demand (load) versus inadequate response (capacity)
Is the patient normal or is pre-existing disease present?
Acute versus Chronic: all the same except the speed at which it develops

10. Disturbance of Central Control
Cheyne-Stokes Respiration
Alternating hyper/hypoventilation (60 second cycle)
Severe cardiac disease
Secondary to slow perfusion of peripheral chemoreceptors
Agonal breathing
Pre-terminal patients or opiate poisoning
Groups of 4-8 breaths alternate with complete apnoea
Hypoventilation
OHS, hypothyroidism, respiratory muscle weakness, post sedation, REM sleep, loop diuretics causing metabolic alkalosis
Hyperventilation
Hyperthyroidism, post cortical CVA, liver cirrhosis, metabolic acidosis, anxiety and stress
Overriding of normal drives by ‘emotional centres’, reticular activation centre and sympathetic nerves

11. Normal resting ventilation
Cheyne-Stokes Respiration
Idiopathic hyperventilation
Diabetic acidosis (Kussmaul breathing)

12. Disturbance of End Organ Function
Failure of the ventilation pump
Increased load
Metabolic CO2 production (exercise/infection)
Flow resistance of airways (COPD/asthma)
Elastic recoil (COPD/Fibrosis)
Reduced capacity
Reduced central drive (opiates/CVA)
Strength & endurance of respiratory muscles
(Neuromuscular disease/Diaphragm palsy)
Sleep
LOAD
CAPACITY
LOAD ++
CAPACITY
Inc PCO2
Dec PO2
LOAD
CAPACITY --
Inc PCO2
Dec PO2

13. Classification of Respiratory Failure

14. Signs & Symptoms of Type 1 Failure
Cyanosis
Increased respiratory rate (tachypnoea)
Accessory muscle use
Tachycardia
Hypotension/peripheral shutdown
Signs of underlying disease
Confusion …

15. Symptoms & Signs of Type 2 Failure
Non-specific
Dyspnoea
Anxiety
Orthopnoea
Altered mentation
Morning headaches
Myoclonus/seizures
Drowsiness
Decompensation during sleep
Disturbed sleep
Daytime hypersomnolence
Nightmares
Witnessed apnoeas
Frequent chest infections
Impaired cough reflex
Signs
Confusion
Drowsiness
Warm peripheries
Flapping tremor
Bounding pulses
Myoclonic jerks
Papilloedema

16. Treatment Options ABC Treatment for underlying condition
Oxygen therapy
CPAP
NIV
IPPV
Others

17. Continuous Positive Airways Pressure (CPAP)
POSITIVE PRESSURE APPLIED THROUGHOUT THE RESPIRATORY CYCLE TO A SPONTANEOUSLY BREATHING PATIENT
STICK YOUR HEAD OUT OF A CAR WINDOW…..
IMPROVES OXYGENATION by improving VENTILATION and improving V/Q RATIOS
DECREASES THE WOB (think about pushing a car from stationary versus pushing an already moving car) – stops ‘complete airway collapse’
Time
Flow
CPAP
Used predominantly in Type 1 (hypoxic) respiratory failure

18. Non-Invasive Ventilation (NIV)
BI-PHASIC positive airway pressure – increases ventilation
Overcoming inspiratory resistance to flow
Unloading the inspiratory muscles
Augmenting alveolar ventilation
Improving V/Q ratio in low V/Q areas
Lowering alveolar PCO2
Increasing alveolar PO2
FLOW
TIME
EPAP
IPAP
Predominantly used in Type 2 respiratory failure

19. Other therapies Respiratory stimulants
Act via effects on brainstem respiratory centres
Only effective if adequate ventilation capacity
Doxapram – iv analeptic drug
Theophyllines – po + inotropic effect on muscles
Progesterone – acts on hypothalamus – impotence
Acetazolamide – CA inhibitor causing metabolic acidosis (via kidneys)
Protryptiline – antidepressant
Caffeine – neonates with apnoea
Rarely used in clinical practice

20. Summary Structure & Function Normal versus abnormal
Acute versus acute on chronic versus chronic
Control of Breathing
Central versus peripheral damage
Causes of Respiratory Failure
Load versus capacity
Classification of Respiratory Failure
Type 1 or Type 2
Acute versus Chronic
Treatment Options in Respiratory Failure
Treatment of underlying cause
Oxygen, Modes of ventilation, Drugs