Types of Respiratory Failure

 

Criteria for respiratory failure: decreased PaO2 (< 60 mm Hg)

	Type I	Type II
PaCO2	< 50 mm Hg	>= 50 mm Hg

 

where:

• The cutoff above is simplified. The actual criteria would be the upper limit of normal for age and gender. Adult males have an upper limit of normal of 48 mm Hg and adult females 45 mm Hg. Infants have an upper limit of normal of 41 mm Hg.

 

Additional Features	Type I	Type II
pH		decreased (respiratory acidosis)
alveolar to arterial blood oxygen difference (gradient)	increased	decreased

 

Additional features of Type I respiratory failure:

(1) pH normal or elevated (respiratory alkalosis)

(2) alveolar to arterial blood oxygen gradiation increased

 

Type I respiratory failure may be seen with:

(1) impaired diffusion of oxygen across the alveolus

(2) right-to-left shunt

(3) other causes of ventilation-perfusion mismatch

(4) low oxygen in inspired air (high altitude, other)

(5) alveolar hypoventilation (may progress to Type II RF)

 

Type II respiratory failure may be seen with:

(1) COPD (chronic bronchitis and/or emphysema)

(2) asthma

(3) suffocation

(4) decreased breathing effort (injury to respiratory center in brainstem, medications, etc)

(5) neuromuscular disease affecting respiratory muscles

(6) chest and spine deformities (flail chest, kyphoscoliosis, anklyosing spondylitis)