Indications for mechanical ventilation in patients with chest trauma are listed in Table 19-1. None of these indications are absolute, and each is dependent on the corresponding level of respiratory failure. Flail chest with paradoxical chest movement was once considered an absolute indication for positive pressure ventilation. However, many cases of flail chest are now managed effectively without intubation and mechanical ventilation. ARDS is a common complication of chest trauma, and may occur without associated chest contusion. When ARDS occurs in association with chest trauma, its management is similar to that with other causes of ARDS. Pain control is an issue in many patients with chest trauma. If large doses of narcotic pain control are required, respiratory depression may occur and mechanical ventilation may be necessary. Epidural narcotics, patient-controlled analgesia, and intercostal nerve blocks are used to control pain without associated respiratory depression.
Table 19-1Indications for Mechanical Ventilation in Patients With Chest Trauma ||Download (.pdf) Table 19-1 Indications for Mechanical Ventilation in Patients With Chest Trauma
• Flail chest with paradoxical chest movement that results in tachypnea, hypoxemia, hypercarbia
• Pulmonary contusion with tachypnea and severe hypoxemia ( < 60 mm Hg) breathing 100% O2
• Rib fractures with chest pain requiring large doses of narcotics for pain control
• Postoperative thoracotomy
• Hemodynamic instability, particularly with marginal respiratory reserve (eg, hypoxemia and tachypnea)
• Severe associated injuries (eg, head trauma)
• Failed noninvasive ventilation
Mask CPAP and Noninvasive Ventilation
The use of NIV has become increasingly common in the patient with chest trauma. The early use of NIV in patients with chest trauma facilitates stabilization of the chest, promotes recruitment of collapsed lung regions, and significantly reduces mortality and intubation rate without increasing complications. Some of these patients are managed with 8 to 12 cm H2O CPAP and Fio2 adjusted to maintain the Pao2 more than 60 mm Hg. In some patients, NIV is indicated due to increased work-of-breathing. However, the patient who is requiring increasing levels of CPAP, Fio2, or ventilatory support should be considered for invasive ventilation. Intubation is usually required if the patient is also hemodynamically unstable.
Recommendations for initial ventilator settings in patients with chest trauma are listed in Table 19-2. Initially, full ventilatory support using volume control or pressure control is frequently used (Figure 19-1). However, some patients who are well managed for pain and are hemodynamically stable do well on pressure support.
Table 19-2Initial Mechanical Ventilation Settings in Patients With Chest Trauma ||Download (.pdf) Table 19-2 Initial Mechanical Ventilation Settings in Patients With Chest Trauma
|Setting ||Recommendation |
|Mode ||A/C (CMV) |
|Rate ||15-25/min |
|Volume/pressure control ||Pressure or volume |
|Tidal volume ||6-8 mL/kg IBW provided that plateau pressure ≤ 30 cm H2O; 4-8 mL/kg IBW with ARDS |
|Inspiratory time ||≤ 1 s |
|PEEP ||5 cm H2O; none with severe air leaks; appropriately titrated if ARDS |
| ||1.0 |
An algorithm for mechanical ventilation of the patient with chest trauma.
Oxygenation is dependent on Fio2, PEEP, the extent of pulmonary dysfunction, and hemodynamic stability. The initial Fio2 should be set at 1, and then titrated to the desired level of arterial oxygenation using pulse oximetry. Generally, the initial PEEP level should be set at 5 cm H2O. If the patient has significant barotrauma (eg, subcutaneous emphysema, pneumothorax, air leaks from chest tubes), then it may be desirable to set the initial PEEP at 0 cm H2O. If the patient has significant pulmonary shunt, a trial of higher PEEP is appropriate. In patients with chest trauma, however, caution must be exercised when increasing airway pressure because barotrauma is common. As the result of blood loss, hemodynamic instability may result when PEEP is increased, and increasing PEEP may increase intracranial pressure in patients with associated head trauma. If a unilateral pulmonary contusion is present, care must also be exercised when increasing PEEP. With unilateral lung disease, PEEP may result in shunting of blood from higher compliance lung units to low-compliance nonventilated areas, which will result in increasing shunt and hypoxemia. With unilateral pulmonary contusion, lateral positioning with the contused lung up may be more beneficial than increasing PEEP.
With either volume ventilation or pressure ventilation, the plateau pressure should be kept below 30 cm H2O. In trauma patients with satisfactory lung compliance (eg, postoperative thoracotomy), tidal volumes of 6 to 8 mL/kg of ideal body weight can be used with plateau pressure of less than 30 cm H2O. Patients with pulmonary contusion and ARDS may require tidal volumes of 4 to 8 mL/kg to keep plateau pressure less than 30 cm H2O. An initial respiratory rate of 15 to 25/min is often adequate. Respiratory rate is increased if required to establish a desired Paco2. Permissive hypercapnia is generally well tolerated in chest trauma patients, provided that there is no accompanying head trauma with increased intracranial pressure. An inspiratory time less than or equal to 1 second is usually adequate in patients with chest trauma.
Monitoring the mechanically ventilated chest trauma patient is similar in many aspects to that with any mechanically ventilated patient (Table 19-3). Air leak is more likely in patients with chest trauma, and signs of air leak must be assessed frequently. Pneumothorax should be considered following any rapid deterioration of the mechanically ventilated chest trauma patient. Chest trauma patients should be ventilated at the lowest peak alveolar pressure and PEEP level that produces adequate arterial oxygenation. Auto-PEEP must be avoided. Pulmonary embolism is also common in these patients, and should be considered if clinical status rapidly deteriorates. As is the case with many surgical patients, fluid overload frequently occurs and is associated with shunting and decreased lung compliance. With prolonged mechanical ventilation, nutritional support is necessary to facilitate healing and weaning from mechanical ventilation.
Table 19-3Monitoring of the Mechanically Ventilated Patient With Chest Trauma ||Download (.pdf) Table 19-3 Monitoring of the Mechanically Ventilated Patient With Chest Trauma
• Pneumothorax and extra-alveolar air
• Auto-PEEP, mean airway pressure
• Peak alveolar pressure
• Pulmonary embolism
• Fluid volume status
• Nutritional status
Discontinuation of mechanical ventilation can occur early and quickly in many chest trauma patients, such as those ventilated postoperatively following repair of a penetrating chest injury. Many of these patients have no previous cardiopulmonary disease and recover rapidly if there are no associated problems (eg, head trauma, ARDS). Those who have severe pulmonary contusion and ARDS may have a long mechanical ventilation course that may be complicated with pulmonary infection, empyema, sepsis, and pulmonary embolism. Ventilator liberation may be difficult in some of these patients, particularly if they develop multisystem failure. These patients may require prolonged weaning with periodic spontaneous breathing trials. Weaning may also be difficult in patients with severe chest wall injury or diaphragmatic injury. For patients who are difficult to wean, the goals should be treatment of injuries and preexisting medical conditions, bronchial hygiene (eg, secretion removal), nutritional support, and strengthening and conditioning of respiratory muscles (ie, periods of spontaneous breathing at subfatiguing loads).