Ventilatory failure hypoxia
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Applied Sciences Lecture Course. Ventilatory Failure & Hypoxia. Mahesh Nirmalan MD, FRCA, PhD Consultant, Critical Care Medicine Manchester Royal Infirmary. Objectives. Respiratory failure is one of the commonest manifestations of acute illness Hypoxia and CO 2 retention

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Ventilatory failure hypoxia

Applied Sciences Lecture Course

Ventilatory Failure & Hypoxia

Mahesh Nirmalan MD, FRCA, PhD

Consultant, Critical Care Medicine

Manchester Royal Infirmary


Objectives

Objectives

  • Respiratory failure is one of the commonest manifestations of acute illness

  • Hypoxia and CO2 retention

  • Failure of oxygen transfer

  • Failure of effective alveolar ventilation

  • Pathophysiology

  • Differences in management approach


Respiration or breathing

Ventilation

Moving an adequate volume of air

Minute ventilation

Alveolar ventilation

Oxygenation

Transfer of O2 across the alveoli

Dusky colour

Cyanosis

Low SpO2

Low arterial PaO2

Respiratory rate

Tidal volume or chest expansion

Arterial PaCO2

Respiration or Breathing


Respiratory failure

Type 2

Type 1

Mixed

Hypoxia

&

Hypercarbia

Hypercarbia

PaCO2>7kPa

Hypoxia

PaO2<8kPa

Respiratory Failure


Treatment of respiratory failure

Treatment of Respiratory failure

  • Type 1

    • Cause

    • O2 supplementation

    • PEEP

  • Type 2

    • Cause

    • Ventilatory assistance

      • Pharmacological

      • Mechanical: IPPV

  • Mixed


Ventilatory failure hypoxia

FRC


Lung volumes

Lung volumes

FRC is a balance between two forces

Reduced compliance

Reduced FRC

Increased compliance

Increase in FRC


Low compliance and low frc

Inflammation and oedema within the lung parenchyma

Low compliance and low FRC


Ventilatory failure hypoxia

Hepatisation

Fibrinous exudate

H’ge


Histological changes reduced lung compliance

Hyaline.membrane

Normal lung

Interstitial oedema

Organising oedema

Alveolar oedema

Haemorrhage

Neutrophil infiltartion

Histological changes: reduced lung compliance


Reduced compliance

Reduced compliance

  • Pulmonary oedema

  • Pneumonia

  • ARDS and ALI

  • Fibrosis

Tachypnoea

Increased work of breathing

Hypoxia


Extensive pneumonia reduced lung compliance frc

Extensive pneumonia: Reduced lung compliance→↓FRC


Pneumonia lung compliance

Pneumonia: ↓lung compliance


Decreased lung compliance

Decreased lung compliance

  • Early stages: Interstitial oed

  • Tendency for the alveoli to collapse

  • May involve large parts of the lung

  • Reduction in FRC is an important factor

  • Alveolar oedema & consolidation

  • Increased work of breathing

  • Common cause for failure in oxygenation

  • Type 1 respiratory failure


Increased lung compliance

Loss of elastic tissue within the lung parenchyma

Increased lung compliance


Copd increase in compliance frc

COPD: Increase in compliance→↑FRC


Increased lung compliance increased frc

Increased lung compliance: Increased FRC

Hyper-inflation

Low set diaphram

Reduced lung markings


Lung volumes1

Lung volumes


Hypoxia failure in oxygenation

Hypoxia: Failure in oxygenation


Hypoxia failure of tissue oxygenation

Hypoxia: failure of tissue oxygenation

  • Hypoxic hypoxia: Pulmonary oxygen transfer

  • Stagnant hypoxia: Poor blood flow

  • Anaemic hypoxia: poor oxygen carriage

  • Histotoxic hypoxia: Sepsis, Cyanide


Oxygen cascade in an ideal lung

Oxygen cascade in an ideal lung

Diffusion, shunt, ventilation perfusion mismatch

High Altitude

Hypoventilation


Pathophysiology of hypoxia

Pathophysiology of hypoxia

Venous blood

Oxygenated blood


Pathophysiology of hypoxia1

Pathophysiology of hypoxia

Venous blood

Venous blood


Ventilation perfusion or v q mismatch

Ventilation/perfusion or V/Q mismatch

Partially oxygenated

blood

Venous blood


Shunt and v q mismatch

Shunt and V/Q mismatch

Alveolar oedema

Shunt: blood that goes through unventilated lung units

V/Q mismatch: Blood going through poorly ventilated units


Causes of hypoxia

Causes of Hypoxia

Clinically how does one distinguish between shunt and V/Q mismatch?

Effect of increasing FiO2

Hypoventilation

Diffusion defects

Ventilation-perfusion mismatch

Shunts


45 years old male breathless pyrexial unwell breathing 50 o 2 pulse oximetry 90 saturation

45 years old male: Breathless, pyrexial, unwell, (breathing 50% O2)Pulse oximetry: 90% saturation

  • pH=:7.15

  • PCO2: 3.3 kPa

  • PO2: 13.47kPa

  • HCO3-: 17 mmol.l-1

  • Hb: 10.8 g.dl-1

  • Glucose: 12.8mmol.l-1

  • Lactate: 0.9mmol.l-1

Shunt and V/Q mismatch


Ventilatory failure co 2 retention

Ventilatory failure: CO2 retention


Physiological dead space

Physiological dead space

Wasted ventilation

Extension of dead space

Ventilated but not perfused alveolar units

Physiological dead space

Dead space ventilation does not clear CO2

Extension of dead space will lead to CO2 retention


Copd increase in compliance frc1

COPD: Increase in compliance→↑FRC


Pulmonary embolism

Pulmonary embolism:

Typically increase in Physiological dead space

When large also causes significant V/Q mismatch

Hypoxia and CO2 retention


Ventilatory failure hypoxia

Most organic parenchymal diseases:Increase in V/QSome shuntingIncrease in physiological dead space


Ventilatory failure

Ventilatory Failure

  • Hypoventilation

    • Depression of respiratory centre: opiates

    • Pain: upper abdominal surgery, Rib fractures

    • Prolonged increase in work of breathing

      • Tachypnoea

      • Reduced lung compliance

      • Severe asthma

  • Extension of physiological dead space

    • COPD


  • Copd 25 o 2

    COPD: 25% O2

    pH=:7.15

    PCO2: 12.3 kPa

    PO2: 13.47 kPa

    HCO3-: 32mmol.l-1

    Hb: 18.8 g.dl-1

    Glucose: 9.8mmol.l-1

    Lactate: 0.9mmol.l-1


    Treatment of respiratory failure1

    CO2 retention: Ventilatory failure

    Treat the cause: Opiates, pain, airway obstruction

    Ventilatory support:

    Non-Invasive: BiPAP

    Invasive: Mechanical ventilation

    OXYGENATION: HYPOXIA

    Treat the cause: Infection, oedema

    ↑FiO2

    PEEP

    Treatment of respiratory failure


    Summary

    Summary

    Failure of oxygenation

    • Hypoventilation

    • Diffusion

    • Shunt and V/Q mismatch

  • Treat the cause

  • Supplemental oxygenation & PEEP

    Failure of ventilation

    • Respiratory depression

    • Increase in physiological dead space

  • Treat the cause

  • Ventilatory assistance


  • Ventilatory failure hypoxia

    ??


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