Perioperative Lung Injury

Abstract

Traditional patterns of mechanical ventilation with large (e.g., 10–12 mL/kg) tidal volumes and without positive end-expiratory pressure (PEEP) cause a subclinical injury in healthy lungs in proportion to the duration of ventilation. Perioperative acute lung injury becomes clinically important when injurious ventilation patterns are used in patients who have other concomitant lung injuries such as large pulmonary resection, cardiopulmonary bypass, or transfusion-related lung injury. Lung-protective patterns of mechanical ventilation, using more physiologic tidal volumes and appropriate PEEP, reduce the severity of this lung injury. A recent decrease in the incidence of lung injury after pulmonary resection is primarily due to a decrease in the frequency of pneumonectomies.

Clinical Case Discussion

A 68-year-old 70 kg male presents with bronchogenic carcinoma of the right middle and lower lobes. The patient is a smoker (30 pack-year) with good exercise tolerance. Preoperative FEV1 is 80% predicted and DLCO is 70% predicted. V/Q scan shows 50% ventilation and perfusion to the right lung. The patient has an uncomplicated 3 h right pneumonectomy. During the procedure, he receives 1.5 L of crystalloid and is ventilated with a tidal volume of 700 mL, FiO₂ 1.0, during both two- and one-LV. Postoperatively, the patient is stable in the recovery room (see Fig. 10.15) with thoracic epidural analgesia and is discharged to the thoracic surgical floor.

Fig. 10.15

Immediate postoperative chest X-ray of a 68-year-old male following a right pneumonectomy. This is normal post-pneumonectomy film

On postoperative day 3, the patient complains of increasing dyspnea. The patient’s oximetry saturation is 85% on air and 93% with FiO₂ 0.4 mask. His pulse is sinus rhythm at 104 and blood pressure 130/80. A repeat chest X-ray is taken (see Fig. 10.16).

• What is the differential diagnosis?

• How can the diagnosis be confirmed?

Fig. 10.16

Chest X-ray on postoperative day 3 of the same patient in Fig. 10.15. The patient has gradually become more dyspneic and has significant arterial oxygen desaturation breathing air. Chest X-ray shows signs of increased lung interstitial markings suggestive of pulmonary edema

The differential diagnosis should include post-thoracotomy ARDS, pulmonary embolus, congestive heart failure and/or myocardial ischemia, aspiration, and pneumonia. ARDS in this setting is a diagnosis of exclusion. A perfusion lung scan should be obtained to rule out emboli and an electrocardiogram to rule out subclinical ischemia, which is unlikely in the absence of a prior history of coronary heart disease or diabetes. A transthoracic echocardiogram should be performed to rule out myocardial dysfunction. Major aspiration is unlikely without a history of a decreased level of consciousness. Pneumonia is a possibility, but unlikely without signs of sepsis or an elevated white blood cell count, sputum for culture and sensitivity should be obtained. If other common possibilities of postoperative respiratory failure are ruled out, the provisional diagnosis is ARDS.

• What therapy is indicated?

The patient should be transferred to an intensive care unit. All therapy is basically palliative with the aim to support respiratory function and minimize any exacerbation of the lung injury pending spontaneous resolution. Initially respiratory support should begin with noninvasive ventilation and minimizing the FiO₂ to maintain normal physiologic oxygen saturations. Attempts to reduce the pulmonary vascular pressures with inhaled nitric oxide or prostacyclin are logical although not proven and are unlikely to cause harm. The same applies to inhaled β-adrenergic agents. The benefit of corticosteroids is uncertain. If gas exchange deteriorates, then mechanical ventilation using the principles of lung protection will need to be added. In severe ARDS, unresponsive to conventional therapy, the use of extracorporeal lung support should be considered (see also Chap. 55).