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.
2.Definition • Respiratory failure 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.
3.Classification • acute respiratory failure • chronic respiratory failure • Type Ⅰrespiratory failure • Type Ⅱrespiratory failure • Central respiratory failure • peripheral respiratory failure
Classification :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.
Classification : 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.
Pathogenesis • we have known that the lungs’ ability is gas exchange. The gas exchange involves not only oxygenation but also carbon dioxide elimination.
Pathogenesis • Respiratory failure is mainly associated with pulmonary gas exchange and pulmonary ventilation.
1. pulmonary gas exchange is mainly determined by 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
Any of the factors influenced the ratios may mainly cause hypoxemia respiratory failure. For example, V/Q>0.8, including emphysema,pulmonary embolism.(无效腔） V/Q<0.8, including atelectasis, severe COPD.（动静脉分流）
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.
restrictive hypoventilation • Some diseases influenced central nervous system, peripheral nervous system, chest wall respiratory muscles and pulmonary compliance may all cause restrictive hypoventilation. • Such as brain stem lesion, altered neuromuscular transmission(guillain-barre syndrome), muscle weakness(malnutrition, shock, hypoxemia, hypokalemia), decreased lung compliance(infection, atelectasis, interstitial fibrosis, acute lung injury), decreased chest wall compliance(chest wall trauma, pleural effusion, pneumothorax).
obstructive hypoventilation. • COPD and asthma are the most common disease associated to obstructive hypoventilation. • Increased airway resistance(upper airway obstruction, increased bronchial secretions and edema),
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.
V/Q mismatch hypoxic Diffuse ability . restrictive hypoventilation • hypercapnic-hypoxic. • obstructive hypoventilation.
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.
Pathophysiology • The unbalance of acid-alkalose metabolic and dielectric abnormality are usually exist in the course of respiratory failure.
Clinical manifestations • Clinical signs include not only symptoms associated with primary diseases but also those caused by hypoxic and hypercapnic-hypoxic respiratory failure.
Clinical manifestations of hypoxia and hypercapnia HYPOXEMIA HYPERCAPNIA Tachycardia Somnolence Tachypnea Lethargy Anxiety Restlessness Altered mental status Slurred speech Confusion Headache Cyanosis Asterixis Hypertension Papilledema Hypotension Coma Bradycardia unbalance of acid-alkalose metabolic Seizures Lactic acidosis
Diagnosis • According to history, clinical manifestations, physical examination and blood gas analysis, we can diagnose respiratory failure. Especially arterial blood gas analysis may reveal hypoxemia and hypercapnia.
Diagnosis standard • 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.
Treatment • The principle of treatment includes • primary disease treatment • airway maintenance • correction of hypoxemia and hypercapnia • management of symptoms caused by hypoxemia and hypercapnia.
(1)Airway maintenance and enhance the volume of ventilation • Assurance of an adequate airway is key in the patient with respiratory failure. • correctly use of bronchodilators • In severe cases intubation and mechanical ventilation may be used.
To most of the chronic respiratory failure, correctly use of bronchodilators is very important. Table 2. Bronchodilators Route Dose salbutamol MDI and spacer 400-600g q1-4h Aerosol solution 2.5-7.5mg q1-4h Ipratropium MDI and spacer 80-120g q4-6h Aerosol solution Theophylline IV 5.6mg/kg 0.3-0.6mg/kg/hr oral
Mechanical ventilation The aim of mechanical ventilation is to improve hypoxemia and to prevent hypercapnia. When do you select mechanical ventilation? This is a question we always meet in our clinical work. 1.progressive elevation in PaCO2>70-80mmHg 2.severe hypoxemia, after oxygen therapy, PaO2<40mmHg 3.respiratory rates>35 per minute or severe breathlessness 4.severe metabolic acidosis or pulmonary encephalopathy
How to select artificial airway? face mask or nasal noninvasive intermittent positive pressure ventilation are delivered to augment alveolar ventilation and reducing the work of breathing. If hypoventilation can not be effectively reverses by noninvasive methods, intubation must be adopted. When artificial ventilation is required for more than 2 weeks, a tracheotomy is often required. Tracheotomy carries some risk of bleeding, pneumothorax, and local infection and incidence of aspiration.
(2)Antiinfectious therapy • Repeated bronchial and pulmonary infection is a major cause of chronic respiratory failure. • About 90% of COPD patients with respiratory failure is caused by acute bronchial or pulmonary infection. • Infection may also increase bronchial secretion and CO2 production. • So antiinfectious therapy is an important method to treat respiratory failure.
Select effective antibiotics According to sputum culture, we can select sensitive antibiotics • Using combined antibiotics Because of multibacteria infection, it needs several kind of antibiotics. For example, we may combine second or third generation cephalosporin to aminoglycoside or fluoroguinolone.
(3)Oxygen therapy • The goal of oxygen therapy is to improve PaO2. It makes PaO2>60mmHg. • In general, the lowest FiO2 achieving adequate oxygenation. sometimes, arterial oxygen saturation>90% should be used.
The methods of oxygen therapy: nasal prongs 1-3L/min to chronic respiratory failure venti mask 1-3L/min For type 1 respiratory failure, we can elevate the percentage of oxygen to maintain the PaO2. We can use higher inspirated fration of oxygen in type 1 respiratory failure oxygen therapy. But in type 2 respiratory failure we must select lower inspirated fration of oxygen .
(4)Acid-base and electrolytes disturbance • There are many factors lead to acid-base and electrolytes disturbance. • These factors include severe pulmonary infection, hypoxemia or (and) hypercapnia. So airway maintenance, antibiotic therapy and use of bronchodilators are beneficial to treat it.
The acid-base disorder types in respiratory failure • Usually the disorders are compound types. • It is difficult to judge the type of disorder according to the clinical symptoms and signs. Arterial blood gas analysis is the major method to judge the type of disorder.
How to judge the acid-base disorder the acid-base index. • PH • PaCO2 • HCO3- the index of respiratory the metabolism
Treatment of acid-base disorders • looking for the etiology of the disorder is the most important .
Respiratory acidosis • It is most commonly encountered in clinical practice of respiratory diseases.(COPD) • It is essential to improve alveolar ventilation, while alkaline supplement is not necessary. • For example: PH:7.32;PCO276mmHg; PO276mmHg SO2%94% BE13.9 HCO3- 41mmol/L
Respiratory acidosis complicated with metabolic acidosis • First of all, the cause of metabolic acidosis should be clarified and treated, such as severe hypoxia may lead to increase in lactic acid or it is due to renal dysfunction or diabetic ketoacidosis. • If the level of PH is less than 7.2, alkaline drugs should be treated. • 5%NaHCO3(ml)=[normal HCO3-(mmol/L)-actual HCO3-(mmol/L)] ×0.2×weight(Kg)
Respiratory acidosis complicated with metabolic acidosis • Arterial gas analysis: PH:7.20;PCO276mmHg; PO256mmHg SO2%86% BE-7; HCO3- 20mmol/L
Respiratory acidosis complicated with metabolic alkalosis • PH:7.28;PCO276mmHg; PO266mmHg SO2%92% BE5.1; HCO3- 33.8mmol/L
(6)Corticosteroids • Methyprednisone is usually used to reduce the airway inflammation, and to improve FEV!. The treatment is recommended in all patients but it is not used for a longer time.
(7)Gastrointestinal bleeding treatment Because of hypoxemia, hypercapnia and by using corticosteroids, gastrointestinal bleeding always be happened. The treatment mathod include correct hypoxemia and hypercapnia, use of H2-blocker and some block bleeding drugs.
1.Definition • ARDS, which is a from of acute lung injury often seen in previously healthy patients, • It is characterized by rapid respiratory rates and a sensation of profound shortness of breath, and accompanied by severe arterial hypoxemia.
2.Pathogenesis • ARDS can result from many disorders, including systemic or pulmonary infection,(viral, bacterial, fungal, ect.), aspiration, inhalation of toxins, metabolic disorders and severe sepsis or septic shock. • The initial insult cause release of cytokines, mediators from cell membranes and activation of a number of cascades with injury to the pulmonary endothelium.