Respiratory Failure

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Respiratory Failure

• Saad Lahri
• Registrar
• Dept Of Emergency Medicine
• UCT / University of Stellenbosch

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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)

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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.

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Mechanisms of respiratory failure

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

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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

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• Blood gases are
• PCO2
• PO2 decreased (lt8KPa). (Compensatory
  hyperventilation reduces or maintains PCO2 but is
  less effective at increasing PO2)

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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

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Management

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

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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.

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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

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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 lt8KPa) with hypercapnia (PaCO2
  gt6KPa)

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

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Management

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

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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

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

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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 ABGs.

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References

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