Nathir Obeidat University of Jordan RESPIRATORY FAILURE Nathir Obeidat University of Jordan

Definitions Hypoxemia is reduction in the oxygen content in the arterial system. Tissue hypoxia is reduction in the oxygen delivery to the tissue, caused by reduction oxygen content and or reduction in cardiac output.

Respiratory Failure Types Type 1 Hypoxemic Respiratory failure Type 2 Hypercapnic Respiratory failure

Respiratory failure Is failure to maintain adequate arterial blood gas tensions. 1- PaO2 <60 mm Hg 2- PaCO2 >50 mm Hg Assume 1) breathing room air 2) awake and at rest

Classification: 1) Lung Failure 2) Pump Failure 3) Defects of respiratory control

Lung Failure Hypoxemic respiratory failure due to lung pathology Lung Failure Hypoxemic respiratory failure due to lung pathology. - Affects gas transfer and ventilation /perfusion relationships. - Refractory arterial hypoxemia despite O2 therapy.

2) Respiratory pump failure : Is hypercapnic respiratory failure. Affects the respiratory pump. PCO2 > 50 mm Hg

3) Defects of respiratory control - Affects . Regulation of gas exchange. . The respiratory pump.

Pathophysiology of ARF Mechanisms which cause acute Hypoxemic respiratory failure 1) Hypoventilation 2) Ventilation/Perfusion mismatch 3) Shunt 4) Diffusion limitation 5) Low FiO2

BLOOD GAS MEASURMENTS Only became available in 1950s - respiratory failure can only be reliably diagnosed by measuring arterial blood gases. Respiratory failure and dyspnea are not synonymous .There may be no symptoms with ARF, or the reverse is true

Indirect measurment of gas Tension Oximetry : Direct measurement of the arterial oxygen saturation from arterialised blood in ear lobe or finger. The Technique based on differential absorption of red and infra red light by haemoglobin molecule - Measure only saturation , not partial pressure - Useful in ICU, Sleep labs and ER. - Less sensitive in range 94-100%.

Alveolar Hypoventilation Causes 1- Neuromuscular diseases 2- Neurological diseases 3- Diseases of respiratory control 4- Drug overdose 5- Sleep apnea

Continue …Alveolar hypoventilation Characteristics Hypercapnia Respiratory acidosis PaCO2 = (VCO2/AV) .K - Associated with hypoxemia due to reduced PAO2 - If hypoventilation is the only cause for hypoxia then the PA-a O2 gradient will be normal (5-15 mmHg)

What is PA-aO2 PA-aO2 = PA O2 –PaO2 PaO2 is taken from ABGs PA O2 = FiO2(atmosph pressure –H2O pressure) – PaCO2/k Room Air FiO2= o.21 Atmosph Pressure = 760 at sea level 680 at JUH. Water Pressure = 47 PaCO2= is taken from ABG K is constant value = 0.8

Ventilation Perfusion mismatch Characteristics - It is the major mechanism of hypoxia by which lung disease causes hypoxemia. - PaCO2 either normal or increased. - A-a gradient is increased. - Hypoxia is caused by under ventilated alveoli with respect to their blood flow. - Within a lung region : decrease PAO2 and increased PACO2 always occurs.

- Good areas cannot compensate for bad areas of V/Q mismatch. - Hypoxemia usually corrected by relatively small increase in FiO2. This is because hypoventilated airways are open and alveolar O2 can be increased SO Increased PAO2 lead to increased PaO2

Why in some case PaCO2 is normal Why in some case PaCO2 is normal? Because of hyperventilation in other normal lung region.

Diseases causes V/Q mismatch Air Way Diseases Bronchial Asthma, COPD, Bronchiectasis, Bronchiolitis Obliterans. Intestitial Lung diseases Pulmonary embolism

SHUNT It is an extreme of V/Q mismatch No ventilation but blood flow continues, so venous blood reaches arterial circulation without being oxygenated. It causes high A-a gradient PaCO2 low because of hyperventilation of normal well perfused areas.

Small increase in FiO2 have no effect on PaO2 It needs very high FiO2 to improve PaO2 - Usually associated with : -cardiac shunt - collapsed or fluid filled the alveoli CXR usually shows pulmonary infiltrate. PEEP may improves PaO2 by - opening collapsed lung units - keeping lung units at higher lung volume and allowing some ventilation

Diagnosis Of Acute Respiratory Failure 1- Clinical Suspicion that ARF might be present 2- Confirmation by ABG analysis that ARF is present. 3- Diagnostic steps to identify specific etiology of ARF

Clinical suspicion: Pre-existing chronic respiratory disease Acute illness with high incidence of ARF Symptoms of disease process - any respiratory symptoms - Hypoxaemia :cyanosis Signs : tachypnea, use of accessory muscles

Signs of hypoxaemia and acidosis CNS signs anxiety,restlessness,confusion,seizures, coma and cerebral edema Confirmatiomn CXR ,ABG

Signs of Hypercapnia Tachycardia. Asterixis Signs of Hypercapnia Tachycardia . Asterixis. Distension of forearm veins. Clouding of consciousness. Pupil edema.

PRINCIPLES OF MANAGEMENT 1) Maintain an adequate Airway 2) Correct inadequate oxygenation 3) Correct Respiratory acidosis 4) Maintain Cardiac output and Tissue 02 Delivery 5)Treate underlying condition by definitive management . 6) Avoid preventable complications

Correction of Oxygenation Goal Of Therapy Improve PaO2 while avoiding O2 toxicity In COPD aim for PaO2 60 mmHg or O2 sat of 90% In trauma aim for PaO2 80mmHg

OXYGEN TOXICITY In COPD, excess O2 may cause: increase hypercapnia and hypercapnic acidosis Parenchymal lung injury due to high levels of o2 , it is related to dose and duration So keep FiO2 to lowest level that achieves adequate PaO2

Supplemental O2 Delivery Methods If slight increase in PaO2 is required - Nasl canula - Venturi mask (0.24, 0.28, 0.31, 0.35, 0.40, 0.50) Always check with repeat ABG

Measures to Correct Respiratory Acidosis GOAL - Avert life threatening acidosis - Not to correct PaCO2 - Partial correction usually suffices PHARMACOLOGY THERAPY - Bicarbonate administration may lead to metabolic alkalosis

MECHANICAL VENTILATION Non Invasive Ventilation Non-invasive ventilation refers to the ability to deliver ventilatory support without establishing an endotracheal airway. CPAP BiPAP Invasive Ventilation Needs intubation

Treatment of Under lying Disease Bronchodilatation Removal of Secreations Antibiotics .