Respiratory Failure

A-a Gradient is the difference between the Alveolar PO2 (A) and arterial PO2 (a). The a-a gradient indicates how well O2 is equilibrating across the blood air barrier. 

B i.e. Respiratory failure

Type II respiratory failure, which occurs d/t hypoventilation (i.e. failure of ventilation) is characterized by hypoxemia with hypercapnia (CO₂) retention but normal (not increased) alveolar-arterial oxygen gradient IP                                            1

Aa02,

Hypercapnia (hypercarbia or CO₂ retention) is defined as an elevation in arterial partial pressure of carbon dioxide (Pco₂). It characteristically occurs secondary to inadequate alveolar ventilation (hypoventilation), in type II respiratory failure.   –

–              Type II respiratory failure (or alveolar hypoventilation = alveolar ventilatory failure = hypercapnia = hypercarbia = CO₂ retention = respiratory acidosis) or normal PA-a02 is seen in reduced compliance of chest like kyphoscoliosisQ, reduced lung compliance like pulmonary (alveolar) edetnaQ, obstructive lung disease like COPDQ, weakness of respiratory muscle (like bulbar poliomyelitisQ), bronchospasm and decreased central respiratory drive. Drowning may cause bronchospasm & pulmonary edema & so CO₂ retention.

–   Type I respiratory failure results from failure in exchange (diffusion) of respiratory gases at the alveolar-capillary junction as a result of disease of lung parenchyma (like pneumonia), or vasculature (like right to left shunt), and ventilation-perfusion mismatchQ. It is characterized by increased alveolar-arterial oxygen gradient (PA-ao2)Q, hypoxemia and normal or low PaCO2.

–  At high altitudes alveolar CO₂ decreases b/o hyperventilation.

Respiratory failure is defined as a disorder wherein lung function is inadequate to meet the metabolic demands of the individual and is unable to maintain normal arterial cas level in the blood.

Ans. is ‘d^‘ i.e., Respiratory failure 

Death is usually due to complications arising from respiratory dysfunction.

        Paralytic polio

o In less than I% of infections.

o Paralysis is characterized as :

I. Descending                    4. Non progressive                     6. No autonomic disturbance

2. Asymmetrical                5. No sensory involvement         7. Lower motor neuron type

3. Proximal muscles > distal muscles

o Most common muscle affected —> Quadriceps

o Most common muscle undergoes complete paralysis Tibialis anterior

o Most common muscle affected in hand —> Opponens pollicis.

o M.C. cause of death -4 Respiratory paralysis

Following signs can be elicited :

1. Tripod sign                                 —>       Child is asked to sit up unassisted. He assumes tripod posture.

2. Kiss the knee Test                     —>          The child cannot kiss his knees due to spine stiffness.

3. Head drop sign                       —>           Hand is placed under the patients shoulder and the trunk is raised. The head lags behind simply.

Answer is D (Normal A-a gradient)

This type is caused by conditions which affect oxygenation, like:

• Parenchymal diseases (V-Q mismatch)
• Diseases of vasculature/shunts

Examples:

– Pneumonia Q

– ARDS Q

– Emphysema ^Q

–  Right to left shunts ^Q

This type is caused by conditions causing hypoventilation as in:

• Obstructive lung disease: COPD, F. body
• Decreased central respiratory drive e.g. CNS disorders like : Brain injury, Meningitis
• Weakness of respiratory muscle e.g.

–   Peripheral N.S. disorders like: M. gravis.

–   Interstitial lung disease. Q

–   MS disorders like polymyositis.

– Rib cage disorders : Kyphoscoliosis

Answer is B (Low PO₂ and high PCO₂):

Type I Respiratory failure
Hypoxemia with decreased PaCO₂

Type II Respiratory failure
Hypoxemia with increased PaCO₂

Ans. B i.e. COPD

Respiratory failure

Type I:

–  Parenchymal disease,

–  ARDS,

–  Pneumoniae,

Emphysema

Type II:

– COPD,

– Flail chest etc.

Type III:

–  Atelectasis

Ans: A: Flail chest

Hypercapnic respiratory failure (type II) is characterized by a PaCO2 of more than 50 mm Hg. Hypoxemia is common in patients with hypercapnic respiratory failure who are breathing room air. The pH depends on the level of bicarbonate, which, in turn, is dependent on the duration of hypercapnia.

Type I (Oxygenation) respiratory failure:

–        Adult respiratory distress syndrome (ARDS)

–        Asthma

–        Pulmonary oedema

–        Chronic obstructive pulmonary disease (COPD)

–        Interstitial fibrosis
Pneumonia

–        Pneumothorax

–        Pulmonary embolism

–        Pulmonary hypertension

Type II Respiratory Failure:

• Disorders affecting central ventilatory drive

–        Brain stem infarction or haemorrhage

–        Brain stem compression from supratentorial mass

–        Drug overdose, Narcotics, Benzodiazepines, Anaesthetic agents etc.

• Disorders affecting signal transmission to the respiratory muscles

–        Myasthenia Gravis

–        Amyotrophic lateral sclerosis

–        Gullain-Barre syndrome

–        Spinal -Cord injury Multiple sclerosis

–        Residual paralysis (Muscle relaxants)

• Disorders of respiratory muscles or chest-wall

–        Muscular dystrophy

–        Polymyositis

–        Flail Chest

Type Ill respiratory Failure:

–        Occurs as a result of lung atelectasis

Type IV respiratory Failure:

It occurs due to hypoperfusion of respiratory muscle in a patient with shock.

Ans. D: ARDS

Ans. D: Low PaO₂ and high PaCO₂

Type II Respiratory Failure (Ventilatory Failure: Arterial Hypercapnia): Partial pressure of CO2 in the arterial blood reflects the efficiency of ventilatory mechanism that clears (washes out) CO2 produced during tissue metabolism. Type II failure can be caused by any disorder that decreases central respiratory drive, interferes with the transmission of signals from the central nervous system, or impedes the ability of respiratory muscles to expand the lungs and chest wall.

Type II failure is characterized by an abnormal increase in the partial pressure of CO2 in the arterial blood (PaCO2 > 46 mm Hg), and is accompanied by simultaneous fall in PAO2 and Pa02, therefore PAO2 – Pa02 difference remains unchanged.

Ans. C: COPD

Causes of type II (hypercapnic) respiratory failure:

Chronic causes: COPD, sleep apnea, kyphscoliosis, myopathies/ muscular dystrophies, ankylosing spondylitis;

Acute causes: Acute severe asthma (NOT acute asthma), acute exacerbation of COPD, upper airway obstruction, narcotic drugs etc.

Type II respiratory failure:

• Reduced PaO₂
• Increased PaCO₂
• Normal P(A-a)O₂
• Hypoxemia with increased PaCO₂

Type I respiratory failure:

• Reduced PaO₂
• Normal/ decreased PaCO₂
• INcreased P(A-a)O₂
• Hypoxemia with decreased PaCO₂

Ans. is ‘a’ i.e., Post-operative atelectasis