Respiratory Failure 呼吸衰竭

3.Classifications

Generally both acute and chronic respiratory failure may be divided into two main categories:
Type Ⅰrespiratory failure


Type Ⅰrespiratory failure is also called hypoxic respiratory failure, which means that severely reduces arterial oxygen tension(PaO2<60mmHg), CO2 retention is not exist. This type of respiratory failure is caused by a failure of gas exchange.


COPD and asthma are the most common disease associated to obstructive hypoventilation. In our clinical work, multifactors involve in the course of respiratory failure. For example, a COPD patient with severe pulmonary infection, his pulmonary gas exchange ability and pulmonary ventilation are all abnormal.
2.Definition


Respiratory failure is functional acute or chronic disorder caused by any condition that affects the lung’s ability to maintain arterial oxygenation or carbon dioxide(CO2) elimination. It is defined as a condition in which this gas exchange deteriorates below the usual level, so that arterial oxygen tension decreases, with or without an abnormal rise in arterial carbon dioxide tension.
Pathogenesis

Respiratory failure is mainly associated with pulmonary gas exchange and pulmonary ventilation.
1. pulmonary gas exchange is mainly determined by
Lethargy
Restlessness Slurred speech Headache Asterixis Papilledema Coma
Diagnosis

According to history, clinical manifestations,physical examinations and blood gas analysis, we can diagnose respiratory failure. Especially arterial blood gas analysis may reveal hypoxemia and hypercapnia.
Some common conditions that may cause ventilatory failure with hypercapnea

These conditions include brain stem lesion, altered neuromuscular transmission(guillain-barre syndrome), muscle weakness(malnutrition, shock, hypoxemia, hypokalemia),increased airway resistance(upper airway obstruction, increased bronchial secretions and edema), decreased lung compliance(infection, atelectasis, interstitial fibrosis, acute lung injury), decreased chest wall compliance(chest wall trauma, pleural effusion, pneumothorax).
Type Ⅱrespiratory failure



Type Ⅱrespiratory failure is also meant that hypercapnic-hypoxic respiratory failure. Arterial blood gas values shows that arterial carbon dioxide tension is more than 50 mmHg and arterial oxygen tension is less than 60 mmHg Type Ⅱrespiratory is mainly caused by hypoventilation.
Respiratory Failure
1.Abstracts


Respiratory failure, whether acute or chronic, is a frequently faced problem and a major cause of death in our country. For example, mortality from COPD, which ends in death from respiratory failure, continues to increase. More than 70% of the deaths in patients with pneumonia are attributed to respiratory failure.
Clinical manifestations


Clinical signs include not only symptoms associated with primary diseases but also those caused by hypoxic and hypercapnichypoxic respiratory failure. Hypoxemia and hypercapnia mainly influence the function of important organs, including respiratory system, central nervous system, cardiovascular system, digestive system, renal functions.

Diffuse ability Diffusion abnormality mainly influence oxygen exchange.
2.Pulmonary hypoventilation


It may cause hypercapnic-hypoxic respiratory failure. Pulmonary hypoventilation includes restrictive hypoventilation and obstructive hypoventilation. Some diseases influenced central nervous system, peripheral nervous system, chest wall respiratory muscles and pulmonary compliance may all cause restrictive hypoventilation.
Pathogenesis

Mainly discuss chronic respiratory failure we have known that the lungs’ ability is gas exchange. The gas exchange involves not only oxygenation but also carbon dioxide elimination.
Diagnosis


The diagnosis standard include: Type Ⅰ respiratory failure:PaO2 <60mmHg Type Ⅱrespiratory failure:PaCO2 >50mmHg, PaO2 <60mmHg. In the condition of oxygen therapy, PaO2/Fi O2<300mmHg indicates respiratory failure.


Any of the factors influenced the ratios may mainly cause hypoxemia respiratory failure. For example, V/Q>0.8, including emphysema,pulmonary embolism. V/Q<0.8, including atelectasis, severe COPD.
ventilation-perfusion(V/Q) ratios and diffuse ability

V/Q mismatch: An effective lung gas exchange needs not only sufficient lung ventilation and lung blood volumes but also an adequate V/Q ratios. Usually, the volume of ventilation is 4 liters/min. The volume of lung blood is 5 liters/min. So the ratios is 0.8
Pathophysiology

Hypoxia and hypercapnic may influence functions of many important organs and systems, including respiratory system, cardiovascular system, central nerve system,blood system and digestive system and renal function.
Clinical manifestations of hypoxia and hypercapnia
HYPOXEMIA Tachycardia HYPERCAPNIA Somnolence
Tachypnea
Anxiety Altered mental status Confusion Cyanosis Hypertension Hypotension Bradycardia Seizures nbalance of acid-alkalose metabolic and dielectric abnormality are usually exist in the course of respiratory failure. Table 1. Clinical manifestations of hypoxia and hypercapnia.