Aggressive positive pressure mechanical ventilation in patients with unilateral lung disease [1,2] or in situations of significant difference in compliance between the two ventilated lungs [3,4] were previously described as causes of unilateral malignant hyperinflation of the more compliant lung. In this situation, hypoxemia and hypoventilation are induced and further aggravated by increasing inspiratory volumes or pressures, or by increasing the end-expiratory pressure. We report a case of acute intraoperative hypoxemia and hypoventilation caused by malignant hyperinflation of the nondependent lung during surgery for the resection of a lung tumour.
A 72-year-old man was admitted for elective left lung lower lobectomy for the removal of a lung tumour incidentally identified in a chest radiograph performed before elective inguinal hernioplasty. The patient’s past medical history included 60 pack years of smoking until 4 years before surgery, and tuberculosis of the right upper lung. The patient had no limitations on daily physical activities, and did not complain of a productive cough. A computerized tomographic (CT) scan of the chest demonstrated a tumour in the left lower lobe and interstitial fibrotic changes in the right upper lobe. Lung function tests indicated moderate airway obstruction: forced vital capacity 3.9 L (84% of predicted), forced expiratory volume in the first second of 2 L (66% of predicted), peak expiratory flow of 8.4 L s–1 (107% of predicted), and forced expiratory flow 25/75 1.31 L s–1 (43% of predicted). A good response to bronchodilators was demonstrated. The patient was premedicated with diazepam 10 mg orally 1 h prior to surgery. Induction of anaesthesia was with midazolam 2 mg, thiopental 350 mg and fentanyl 0.2 mg intravenously (i.v.); vecuronium 8 mg i.v. was given for muscular paralysis. Orotracheal intubation using a 39 French gauge right-sided Mallinckrodt double lumen tube was performed and the position confirmed with both auscultation and fibreoptic bronchoscopy in the supine as well as the right decubitus position.
A few minutes from right thoracotomy and the commencement of one-lung ventilation, a significant decrease in lung compliance (from 20 to 7 mL cmH2O–1), oxygenation (PaO2/FiO2 from 40 to 7 kPa), and ventilation (PaCO2 increased from 5.3 to 8 kPa) were noted. The oxygenation and ventilation did not improve with oxygen supplementation or continuous positive airway pressure (CPAP) application to the nondependent lung, or with bilateral lung ventilation. Fibreoptic bronchoscopy revealed correct positioning of the orotracheal tube, with increased secretions and bronchial plugging of the dependent lung. After failure to improve oxygenation by bronchoalveolar lavage, surgery was interrupted and the patient was turned to the supine position and the right-sided double lumen tube was changed to a Portex single lumen tube. No improvement in the degree of hypoxemia was noted. A chest radiograph performed in this stage demonstrated an acute massive hyperinflation of the left lung (Figure 1).
At this stage, a left-sided Mallinckrodt double lumen tube was inserted and differential lung ventilation initiated. Both lungs were ventilated in the pressure-controlled mode using two Smartvent (Versamed, Israel) lung ventilators. The left lung ventilated with a peak inspiratory pressure (PIP) of 18 cmH2O, respiratory rate (RR) 14 breaths min–1, FiO2 0.7, positive end-expiratory pressure (PEEP) of zero; the right lung with PIP 25 cmH2O, over PEEP 7 cmH2O, RR 18 breaths min–1, and FiO2 0.7.
After aggressive physiotherapy and bronchial washing, the patient’s condition improved, and oxygen saturation returned to the preoperative value. A repeat chest radiograph (Figure 2) showed significant improvement and reduction of the left lung hyperinflation. The patient was turned to right decubitus position and the operation continued. At the end of surgery the patient was transferred to the postanaesthesia care unit, ventilated in the differential lung ventilation mode and was extubated within an hour.
Double lumen orotracheal tube insertion and one-lung ventilation are routinely used during surgery for lung resection. Turning the patient into the lateral position, opening of the chest and using positive pressure mechanical ventilation, produce disturbances of lung physiology. As approximately 70% of the perfusion is directed to the dependent lung, the matching of ventilation in this lung is important for adequate gas exchange . The use of general anaesthesia and muscle relaxants, pressure of abdominal contents, compression by the weight of mediastinal structure, and suboptimal positioning on the operating table are common reasons for ventilation impairment . Other factors that may contribute to the impairment of optimal ventilation to the dependent lung include absorption atelectasis, accumulation of secretions, and the formation of a fluid transudate in the dependent lung [6,7].
In our patient, hypoxemia and hypoventilation developed shortly after instituting one-lung ventilation of the dependent right lung. The common practices of treating hypoxemia during one-lung ventilation were taken. The position of the double lumen tube was confirmed with a fibreoptic bronchoscope. The application of continuous positive pressure to the nondependent lung not only failed to improve oxygenation but rather caused significant deterioration. Surprisingly, even turning to two-lung ventilation caused the patient’s condition to deteriorate with life threatening hypoxemia and hypoventilation. Only a radiograph performed at this stage of the surgery demonstrated the uncommon mechanism of hypoxemia in this patient, namely malignant hyperinflation of the compliant left lung in the presence of a noncompliant right lung due to airway obstruction by secretions.
The selection of the initial ventilatory mode and form of therapy in a situation of different lung compliance is a most important problem [8,9]. Conventional ventilatory modes apply the same pressure and flow to both lungs. The lung with lower compliance receives less of the delivered tidal volume regardless of the mode employed. In problematic cases, as in our patient, this results in failure to achieve the desired gas exchange, particularly acceptable levels of oxygenation. Application of PEEP in this situation may result in overinflation of the more compliant uninvolved lung with a resultant decrease in perfusion to those lung units and a redistribution of blood flow to affected lung. This exacerbates gas exchange problems by worsening the ventilation–perfusion mismatch and increasing the pulmonary shunt. Attempts to address the deteriorating gas exchange by increasing minute ventilation and PEEP may further exacerbate the situation by hyperexpanding the uninvolved lung and producing increased maldistribution of ventilation and perfusion while increasing the risk of barotrauma [1,2,7]. For resolving this problem, the use of different lung ventilation with different tidal volumes, FiO2, PIP and PEEP was recommended. Thomas and Bryce  considered some systems of therapy of unilateral lung disease refractory to conventional treatment. The systems includes CPAP application to each limb of the double lumen tube with spontaneous ventilation, differential ventilation and PEEP applied with a single ventilator, independent ventilation with two synchronized or asynchronized ventilators, and a combination of different modalities.
In the presented patient, unilateral malignant lung hyperinflation, developed due to positive pressure ventilation in a patient with different lung compliance, appeared on account of bronchial obstruction and atelectasis of dependent lung demanded an emergency resolution of this life-threatening problem. We used intensive physiotherapy and different lung ventilation with two independent asynchronous ventilators in the pressure-controlled mode. While the high compliant left lung was ventilated with low inspiratory pressure and no PEEP, the low compliant lung was ventilated with high PEEP and a higher inspiratory pressure, which avoided many serious problems and saved the life of our patient.
In conclusion, this case demonstrates the option of malignant hyperinflation of the nondependent lung as a differential diagnosis for hypoxemia during thoracic surgery, and the usefulness of different lung ventilation in this situation.
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