20-Feb-16Respiratory failure1 Pathophysiology of Respiratory Failure

20-Feb-16Respiratory failure2 Respiratory Failure  Severe impairment of gas exchange  May be categorized Hypercapnic Hypercapnic Hypoxaemic Hypoxaemic  Either may arise Acutely or chronically Acutely or chronically

20-Feb-16Respiratory failure3 Hypercapnic Respiratory Failure  Pa CO2 > 45 mm Hg Upper limit of normal Pa CO2 Upper limit of normal Pa CO2

20-Feb-16Respiratory failure4 Hypoxaemic Respiratory Failure  Defined as clinically Significant hypoxaemia Significant hypoxaemia  Despite therapy with high O 2 Pa O2 < 55 mm Hg Pa O2 < 55 mm Hg

20-Feb-16Respiratory failure5 Components of Respiratory System  The normal gas exchange depend on Integration of several components  CNS  Chest cavity  Nerves  Muscles  Chest wall  The airways  Alveolar gas-exchange unit CNS Chest cavity Airways Alveoli

20-Feb-16Respiratory failure6 Components of Respiratory System  CNS Monitor levels of P O2 & P CO2  These determine Level & pattern of ventilation CNS Chest cavity Airways Alveoli

20-Feb-16Respiratory failure7 Components of Respiratory System  Lung inflation & deflation cause Gas flow in and out of gas exchange unit  Passive diffusion Of O 2 & CO 2 across  Alveolar-capillary membrane CNS Chest cavity Airways Alveoli

20-Feb-16Respiratory failure8 Components of Respiratory System  Pump failure refers to Dysfunction of  CNS  Chest bellows or airways CNS Chest cavity Airways Alveoli

20-Feb-16Respiratory failure9 Components of Respiratory System  Lung failure refers to Dysfunction of  Alveoli  Pulmonary capillaries  Alveolar – capillary membrane CNS Chest cavity Airways Alveoli

20-Feb-16Respiratory failure10 Ventilatory Supply  Factors that affect ventilatory supply  Abnormal respiratory mechanics Airflow obstruction Airflow obstruction  Asthma  Chronic obstructive pulmonary diseases (COPD)

20-Feb-16Respiratory failure11 Ventilatory Supply Chest wall deformities Chest wall deformities  Kyphoscoliosis Loss of lung volume Loss of lung volume  Pneumonia

20-Feb-16Respiratory failure12 Ventilatory Supply   Respiratory muscle strength & endurance Nerve lesions Nerve lesions NMJ abnormalities NMJ abnormalities Muscle abnormalities Muscle abnormalities  Atrophy  Weakness

20-Feb-16Respiratory failure13 Failure of CNS  Blood gas changes Respiratory acidosis Respiratory acidosis   Pa CO2   In pH   Pa O2

20-Feb-16Respiratory failure14 Failure of CNS  Following can cause CNS depression & respiratory failure Overdose with sedatives Overdose with sedatives  Barbiturates  Opiates Anesthetic agent Anesthetic agent  Hypoxia, hypercapnia

20-Feb-16Respiratory failure15 Failure of CNS  Diseases of medullary respiratory control center Encephalitis Encephalitis Haemorrhage Haemorrhage Trauma Trauma Tumours Tumours

20-Feb-16Respiratory failure16 Failure of Chest Bellows  Disorders of motor nerves UMN innervating respiratory muscles UMN innervating respiratory muscles  Trauma above C 3-4  Interfere with phrenic nerve

20-Feb-16Respiratory failure17 Failure of Chest Bellows  Fracture dislocation Lower cervical vertebra Lower cervical vertebra  Respiratory muscle paralysis  Weakness of respiratory muscle

20-Feb-16Respiratory failure18 Failure of Chest Bellows  The fall in respiratory muscle strength

20-Feb-16Respiratory failure19 Failure of Chest Bellows  Changes in arterial blood gases Similar to those in CNS failure Similar to those in CNS failure Respiratory acidosis Respiratory acidosis   Pa CO2   In pH   Pa O2

20-Feb-16Respiratory failure20 Airway Diseases Causing Failure  Airways diseases impose Severe limitation in ventilatory supply Severe limitation in ventilatory supply  ventilatory demand  ventilatory demand

20-Feb-16Respiratory failure21 Airway Diseases  Limitation of ventilatory supply Arise from narrowing of airways Arise from narrowing of airways Lead to diminished Lead to diminished  Expiratory rate  Inspiratory rate  Exhaled volume (FEV 1 )

20-Feb-16Respiratory failure22 Failure of Gas Exchange  Failure of alveolar gas exchange Leads to hypoxaemic respiratory failure Leads to hypoxaemic respiratory failure

20-Feb-16Respiratory failure23 Gas Exchange Failure  Causes Disorders which cause Disorders which cause  Diffuse alveolar diseases  Emphysema  Pneumonia

20-Feb-16Respiratory failure24 Gas Exchange Failure  In both cases  Diffusing capacity of the lung  Diffusing capacity of the lung  Ability of the lung to  Ability of the lung to  Oxygenate blood  Remove CO 2