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					Respiratory Failure
Sa’ad Lahri Registrar Dept Of Emergency Medicine UCT / University of Stellenbosch

Introduction
• Most common reason for admission to ICU is to provide airway and ventilator care to critically ill patients. • Primary functions of lung and thorax is to oxygenate arterial blood and to eliminate CO2. • Dysfunction may occur in oxygenation (intrapulmonary gas exchange by which mixed venous blood releases CO2 and becomes oxygenated) or in ventilation (the movement of gases between the environment and the lungs)

Clinical Recognition
The patient with resp failure may be recognised early if they are:

• • • • • •

Dyspnoeic/tachypnoeic Unable to speak in complete sentences Using accessory muscles of respiration Centrally cyanosed Sweaty and tachycardic Showing a decrease in level of consciousness.

Mechanisms of respiratory failure
• Acute respiratory failure can be divided into two broad types: • Ventilation perfusion mismatch (type I) • and ventilation failure (type II)

Ventilation – perfusion mismatch
• Overall ventilation is adequate but blood passing through the lungs is not fully oxygenated.

• Caused by parenchymal lung disease: lung contusion pneumonia Pulmonary oedema ARDS Atelectasis Pulmonary embolism

• Blood gases are: • PCO2 • PO2 decreased (<8KPa). (Compensatory
hyperventilation reduces or maintains PCO2 but is less effective at increasing PO2)

Detecting failure of simple oxygen therapy
• • • • • • • You must be alert! May be indicated by: Increasing respiratory rate Increasing distress/dyspnoea/confusion Oxygen sats of 80% or less (late sign) PaO2 less than 8kPa PaCO2 greater than 7kPa

Management
• Depends on the cause: Treat it! • Increase inspired oxygen • Use CPAP or mechanical ventilation with PEEP

What is PEEP?
• Positive pressure applied during expiration. • Prevents collapse of alveoli at end-expiration leading to an increased FRC. • End –result is improved ventilation perfusion mismatching in the pulmonary circulation improving circulation. • On the Flip-side: can induce barotrauma, diminish venous return to the heart and raise Intracranial pressure.

CPAP
• Employed in patients with acute resp failure to correct hypoxamia. Permits higher inspired oxygen concentration, increases mean airway pressure and improves ventilation to collapsed areas of lung. • Main indication is to correct hypoxaemia!!!!!! • A tight – fitting mask with a range of expiratory valves that do not open until a pressure of 2.5 to 10cm H2O is applied to the patient with a high flow source of oxygen enriched air • As patient expires against the valve or gas flows into the patient during inspiration the pressure in the airways should not drop to below that of the valve. This opens up any alveoli that may be closed and prevents their collapse on expiration

Ventilation failure (type II)
• Lungs are normal but not enough air is moving in and out. • Carbon dioxide accumulates and Oxygen decreases in alveoli but there is normal gas exchange across the alveolar capillary interface. • “hypoxia (PaO2 <8KPa) with hypercapnia (PaCO2 >6KPa)”

• Caused by an interference with respiratory mechanics, partial airway obstruction, depression of resp centre. • Blood Gases: PCO2 PO2

Management
• Remove the cause • Mechanical ventilation • (be careful: only increasing the inspired O2 may mask the rising PCO2.

Non – invasive ventilation by mask
• If type II resp failure develops, This mode should be considered. • The level of CPAP is alternated between a high and a low level at a fixed frequency. This may be termed BiPAP mask ventilation. • The higher CPAP level is set around 20 at inspiration and the lower level at 5 during expiration. • This pressure difference will generate gas flow into the lungs during inspiration

• • • • • •

Not effective in all patients. Inappropriate for : Cardiovascular unstable Decreased LOC Severe metabolic acidosis Must be in control of their own airway and be cooperative • NIV should not be used as a substitute for tracheal intubation and invasive ventilation when the latter is clearly more appropriate.

Conclusions:
• Routine Assessment is predominately clinical and aims to identify the patient who is deteriorating. • Treat the cause of the failure as well as the hypoxia/hypercarbia. • Continously reassess your clinical signs, pulse oximetry and most importantly ABG’s.

References:
• Emergency Medicine Secrets 4th Edition • Oxford Handbook of Trauma for Southern Africa. • Care of the Critically ill surgical Patient – Ian Anderson.


				
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