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

TypesType 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.

- 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?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.

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 .