The Impact Of Pneumothorax And Hemothorax On The Pathophysiology Of Flail Chest

Objective: Flail chest, the severe form of blunt chest wall injury, accounts for 10-20 percents of blunt trauma mortality. The pathophysiology of flail chest remains unclear so far. Furthermore, flail chest is often complicated by hemothorax and pneumothorax. To assess the impact of hemothorax and pneumothorax on the pathophysiology of flail chest, an experimental study is conducted in animal models.Methods: Eighteen adult, healthy mongrel dogs weighing between 15 to 22 kg were randomly assigned to three groups: isolate flail chest (FC, n=6); FC complicated by pneumothorax (n=6) and FC complicated by hemothorax (n=6). The preoperative respiratory rate, intrapleural pressure, arterial blood gases and circulation values were considered as control values. After intravenously anesthetized, using electrocautery and blunt dissection, the right sixth to tenth ribs were exposed. Each rib was arbitrarily fractured (1cm) near to the dorsal and anterior attachments. Then the muscles and skin were sutured. At the first and fourth hour post operation, the parameters were measured in the conditions of flail chest.When studying the group of the flail chest complicated by pneumothorax, the above parameters were measured before and after operation of flail chest. Then through the minor catheter of the Peripherally Inserted Central Catheter (PICC) by injecting air from a 50ml syringe into the right pleural cavity of dogs to produce pneumothorax volume of 100ml. Thirty minutes later, the same parameters were measured. The same measuring methods were done when pneumothorax volume were 200ml, 300ml, 400ml and 500ml.When studying the group of the flail chest complicated by hemothorax, the above parameters were measured before and after operation of flail chest. Then though the minor catheter of PICC by injecting mixed liquor of blood from a 50ml syringe into the right pleural cavity of dogs to produce hemothorax volume of 100ml. Thirty minutes later, the same parameters were measured. The same measure methods were done when hemothorax volume were 200ml, 300ml and 400ml. Statistical analysis: Statistical Data are expressed as mean±standard deviation (SD). Differences among groups were determined by analysis of variance (ANOVA) followed by the Student-Newman-Keuls'(SNK) test. P < 0.05 was considered statistically significant.Result: Flail chest was accompanied by paradoxical motion during respiration that the flail segment collapsed during inspiration and expanded during expiration post operation. The mean area of flail chest was 8.3cm²/kg.A significant (P <0.05) decreased in left ventricular end-diastolic pressure (LVEDP) (22.36±4.27 to 10.71±2.28 mmHg), maximal rate of left ventricular pressure (LVP) rise (+dp/dt_max) (3899.69±677.03 to 3022.41±628.48 mmHg/s) and the values of the PaO₂(89.83±10.87 to 70.83±11.51 mmHg) were noted. And increase in respiratory rates (about increase 50%).The breathing rates and heart rates (133.33±26.70 beats/min to 172.17±19.56 beats/min) increased significantly immediately after pneumothorax, and were even greater when the pneumothorax increased, as well as the levels of PaCO₂ (31.48±2.42 to 44.02±2.52 mmHg) and superior vena caval pressure ( 7.02±1.14 cmH₂O to 9.02±1.03cmH₂O). In contrast, pneumothorax complicated by flail chest was followed by a progressive reduction in left ventricular systolic pressure (LVSP) (129.07±20.12 mmHg to 107.72±12.13 mmHg), maximal rate of LVP fall (-dp/dt_max) (2865.27±464.67 to 2267.31±371.09 mmHg/s), LVEDP, +dp/dt_max and the level of PaO₂.Respiratory rates, heart rates, superior vena caval pressure and the level of PaCO₂ increased in hemothorax group and were raised ingraded increments when hemothorax volumes increased. Hemothorax produced a reduction in the levels of PaO₂, LVEDP, +dp/dt_max, -dp/dt_max and artery diastolic blood pressure(90.75±13.70 mmHg to 80.98±5.30mmHg).Conclusion: Flail chest can impair normal lung function and circulation. Flail chest complicated by pneumothorax can aggravate the pathophysiology of flail chest. When hemothorax volumes increase, flail chest complicated by hemothorax can aggravate the pathophysiology of flail chest. Experiment suggests that the above three diseases require emergent surgical management promptly.