Spontaneous pneumothorax is a common clinical condition, mostly caused by the rupture of pulmonary blisters or tiny subpleural blisters and the entry of air into the pleural cavity. According to the presence or absence of primary disease in the lung, spontaneous pneumothorax is usually divided into two types: idiopathic (primary) and secondary. Primary spontaneous pneumothorax refers to the pneumothorax occurring in people with no obvious lesions found on lung imaging, and is most likely to occur in men aged 30-40 years with a long and lean body type.
I. Pathogenesis
It is generally believed to be caused by the rupture of subpleural pulmonary blisters or microscopic blisters, the formation of which is associated with nonspecific inflammatory scarring or congenital dysplasia of elastic fibers, and can be divided into:1 subpleural blisters, located in the extra-alveolar pneumothorax between the dirty pleura and the lung parenchyma, protruding outside the dirty pleura, with the outer wall composed of dirty pleura and normal basal lung tissue, mostly located at the pulmonary apex, and in a few patients may be combined with old pulmonary tuberculosis, CT shows as a smooth inner layer without trabecular air sac structure, this type of pulmonary blister is easy to rupture and develop into spontaneous pneumothorax; 2 intra-parenchymal pulmonary blister, which is an abnormally enlarged air cavity formed in the lung parenchyma due to degeneration and destruction of alveolar tissue, CT shows that the inner layer of the blister in the lung parenchyma contains trabecular structures, and is divided into two types according to the presence or absence of obstructive lung lesions in the lung parenchyma around the blister.
Type I: clearly demarcated, single and confined, with basal implantation in the lung parenchyma, often located at the lung apex.
Type II: older, mostly secondary to chronic obstructive pulmonary disease or emphysema, with multiple blisters of varying size, which can occur bilaterally, with a wide base implanted in the lung parenchyma, this type is also known as emphysema herpetiformis.
Smoking increases the risk of primary spontaneous pneumothorax. Secondary pneumothorax is caused by the formation of emphysema, pulmonary blister or direct pleural injury on the basis of pre-existing lung disease. Chronic obstructive pulmonary disease and tuberculosis are common causes of secondary pneumothorax 25% of patients with severe COPD are prone to pneumothorax. Cystic fibrosis, bronchial asthma, nodular disease, idiopathic interstitial pulmonary fibrosis, eosinophilic granuloma, acute bacterial pneumonia (e.g. Pneumocystis aureus), and AIDS combined with Pneumocystis carinii pneumonia are common causes of secondary pneumothorax. The causes of pneumothorax secondary to lung cancer, especially metastatic lung cancer, are: tumor obstruction of fine bronchi, resulting in limited emphysema; obstructive pneumonia, which further develops into pulmonary sepsis and finally breaks down into the chest cavity; tumor itself invades or destroys the dirty pleura.
Preferred site
When a person is in standing position, the pressure gradient of the pleura from the lung tip to the lung base is 6.25pxH2O/cm, that is, the negative pressure of the thoracic cavity at the lung tip is higher than that at the lung base. The left side of the chest cavity is more occupied by the heart, so that the upper left chest cavity has higher negative pressure, and when the intrapulmonary pressure increases, the left upper lung is more likely to form a pulmonary blister and rupture than the right side.
The symptoms of spontaneous pneumothorax are mainly chest pain, chest tightness and dyspnea, and the signs are not obvious when a small amount of pneumothorax is present. When pneumothorax is complicated by emphysema, the diminished breath sounds on the diseased side are more obvious. When the amount of pneumothorax >30%, the diseased side of the thorax is full and the intercostal space is inflated, the respiratory movement is weakened, the percussion is drumming, the heart or liver turbid boundary disappears, and the speech fibrillation and breath sounds are weakened or disappeared. In case of massive pneumothorax, the trachea and mediastinum may be displaced to the healthy side. Tension pneumothorax can be seen with thoracic bulge and elevated blood pressure on the sick side. In elderly patients, especially in combination with COPD, whether the trachea is centered and whether the breath sounds of both lungs are symmetrical is a very important sign.
Treatment
1.Oxygen inhalation
The importance of oxygenation in the management of pneumothorax is often overlooked. The absorption rate of pneumothorax without oxygen is about 1.25% per day, and it takes about 20 days for 25% of pneumothorax to be completely absorbed. In contrast, the absorption rate can be increased 3-4 times with oxygen, and the increase in absorption rate is more obvious when the pneumothorax volume is large. Because oxygen inhalation increases the gas pressure gradient between the chest cavity and the tissue, it promotes the absorption of oxygen and other gases in the chest cavity at the same time. In addition, the occurrence of pneumothorax may be accompanied by ventilation/perfusion ratio imbalance, anatomical shunt and dead space, and the ventilation/perfusion ratio may temporarily deteriorate after drainage, and it takes 30-90 min to improve, which emphasizes the necessity of oxygen therapy. Therefore, oxygen inhalation should be the basic measure of pneumothorax treatment, usually 3L/min. small pneumothorax with no respiratory distress and less than 15% of pneumothorax volume can be simply observed and wait for its self-absorption.
2.Simple pumping
Pneumothorax with 15%-30% of pneumothorax volume can be treated by simple suction. After local disinfection and anesthesia, a small catheter is placed between the 4th and 5th ribs in the anterior axillary line, connected with a tee connector, and pumping is performed until the gas cannot be pumped out or when a sudden cough occurs. The catheter is removed at the end of the operation. This treatment can be considered first in all cases of primary spontaneous pneumothorax with a unilateral pneumothorax volume of more than 15%]. The advantages are simplicity and low cost. Since the failure rate of simple suction treatment is high, 25% and 63% for primary and secondary spontaneous pneumothorax, respectively, and it is difficult to predict the outcome of treatment, its clinical application is relatively limited.
3.Chest tube drainage
Closed chest drainage is simple and easy to perform, and it is suitable for primary spontaneous pneumothorax and most secondary spontaneous pneumothorax patients whose pneumothorax volume is greater than 30% or who have failed to be treated by simple suction, and it is the most commonly used method for treating various pneumothoraxes at present.
(1) Success rate of chest tube drainage and chest tube retention time: the chest tube is connected to closed drainage, and negative pressure is gradually applied to 2.5 kPa 20-30 minutes after surgery, and the longest chest tube is retained for 10 days, and the air leakage is judged by observing the bubbles, stopping suction and closed tube observation for 24 hours after the bubbles disappear, and discharging from the hospital after 1 day of observation if there is no pneumothorax on chest film review. If pneumothorax still exists after 10 days, surgery or treatment by thoracoscopic spraying of talcum powder is performed.
Traditionally, it is advocated that negative pressure suction should be continued for 5-7 days after drainage when the air leak does not persist or the lung fails to reopen. However, some studies have shown that when the duration of air leak is greater than 48 hours, it is difficult to stop the air leak even if the chest tube drainage and suction time are prolonged, regardless of whether it is secondary or primary spontaneous pneumothorax. Therefore, more aggressive treatment measures are taken when the air leak has not stopped after 48-72 hours of chest tube drainage. In order to detect the cessation of air leak as early as possible so that the chest tube can be removed in time, a suction pump capable of detecting a decrease in air leak by only 0.01 L has been designed, thus reducing the suction time from 8.1 days to 4.8 days and the hospital stay from 10 days to 6.5 days. The benefit came from accurate grasp of the air leak, overcoming the shortcomings of clamping the chest tube before the air leak had stopped or performing ineffective drainage even after the air leak had stopped.
(2) Size of chest tube: The size of the selected chest tube depends on several factors, including the likelihood of a persistent air leak, the size of the leak, and whether ventilation therapy is applied or intended. Mechanical ventilation can increase the volume of pneumothorax. Although successful treatment with small diameter chest tubes smaller than 14 gauge has been reported, small diameter chest tubes have disadvantages such as easy blockage, dislodgement, and poor drainage in larger pneumothorax volumes, and are only indicated for non-exudative pleural effusion cases with small air leaks that are not mechanically ventilated and prone to catheter blockage. Preparation for mechanical ventilation should be done with large diameter chest tubes greater than or equal to 28 gauge.
Devices connected to the chest tube: If the air leak persists after placement of the chest tube and the lung does not reopen, a drainage device should be connected. Usually drainage is performed first, and then negative pressure suction is connected if the air leak does not stop.
(3) Timing of chest tube removal: Usually the chest tube is clamped 24 hours after the cessation of air leak, and the chest tube is removed after 24 hours of chest film review. However, some people closed the tube 4 hours after stopping the air leak for observation, and no adverse consequences occurred. Another person compared the removal of chest tube after 6 hours or 48 hours after stopping the air leak and found that the percentage of pneumothorax occurred in the 6-hour group after removal of chest tube was as high as 25%, while there was no pneumothorax recurrence in the 48-hour group. The best time to remove chest tube has yet to be studied prospectively.
(4) The significance of chest tube drainage alone in preventing pneumothorax recurrence: chest tube drainage alone does not prevent pneumothorax recurrence. A 7-year study showed that the percentage of pneumothorax recurrence after chest tube drainage alone was 34% and 30% for primary and secondary spontaneous pneumothorax, respectively. Another study showed that the recurrence rate after pneumothorax treatment was 49% for bed rest, 40% for bed rest followed by chest tube drainage, and 38% for chest tube drainage alone.
(5) Chest tube drainage and recurrent pulmonary edema: The incidence of recurrent pulmonary edema can be as high as 25% and the morbidity and mortality rate is 19%. Most of them occur on the diseased side, occasionally on both sides or even on the healthy side. The mechanism of its occurrence is complex and not fully understood. It may be related to oxygen radical formation, increased capillary permeability after reopening, decreased production of surface active substances, production of various substances in the diseased lung that can cause increased local or systemic capillary permeability, and mechanical lung injury. Younger patients with extensive pulmonary atelectasis are most likely to develop it, with 21-39 years being the high-risk age group and less frequently in those 40 years and older. Longer duration of atelectasis is another high-risk factor. Resuscitated pulmonary edema can occur within 3 days after surgery, but mostly occurs in the immediate postoperative period and may be related to too rapid reopening. When it occurs, supportive therapy is usually used, and timely detection and treatment with continuous positive airway pressure ventilation via mask is of clinical importance.
4.Surgical treatment
After the first episode of spontaneous pneumothorax is treated by simple thoracotomy or closed drainage, the recurrence rate is up to 20% or more, and the recurrence rate of two and three episodes of spontaneous pneumothorax is up to 50% and 80% respectively, therefore, surgery is the best way to treat spontaneous pneumothorax.
Surgical method: general anesthesia with built-in double-lumen trachea, single-lung ventilation on the healthy side, and healthy-side lying position. A small axillary incision is made in the axilla, the anterior border of the latissimus dorsi muscle is freed and pulled backward with a small pull hook, and the anterior serratus muscle fibers are followed, bluntly separated to the surface of the intercostal muscle, and the intercostal muscle is incised through the 4th or 5th superior border of the rib to enter the chest. The other two operating holes are selected according to the initial exploration, usually small incisions are made in the anterior axillary line between 4-5 ribs and in the posterior axillary line between 5-6 ribs to form a triangular operating channel. First, electrocautery and pure separation of pleural cavity adhesions, adhesion cords with bleeding if electrocoagulation is not easy to stop bleeding can be titanium clips to stop bleeding, aspiration of fluid, sequential examination of the lung surface, looking for large herpes and rupture, to explore the site and scope of the lesion, and then make the appropriate treatment.
Compared with conventional open-chest surgery, the axillary incision is concealed, does not cut the pectoral muscle, and meets the requirements of minimally invasive surgery, which is safe and reliable. Since most of the pneumothorax lesions are located in the apical segment of the upper lobe or the dorsal segment of the lower lobe, it can be the surgical option for most of the spontaneous pneumothorax. Small axillary incision surgery is better than conventional open-chest surgery cases in terms of operation time, drainage tube retention time and postoperative recovery time. However, due to the narrow field of view of the axillary incision, it is more difficult to operate in cases with multiple lesions and heavy intrathoracic adhesions. Meanwhile, the axillary incision has heavy intercostal pulling and easy to damage the thoracic dorsal nerve, and the postoperative pain is heavier compared with VATS.
Compared with small incision surgery, thoracoscopy has similar surgical results and the recurrence rate is about 4-10%. VATS surgery is less invasive and does not damage the muscles and nerves of the chest wall. With the improvement of equipment, the scope of lens observation can satisfactorily explore the lesions in various parts of the body, which can be converted into clear TV images through endoscopy, with little patient pain and fast postoperative recovery. It is now widely used in clinical practice and has become the method of choice for the surgical treatment of spontaneous pneumothorax.