MEASUREMENT OF DIAPHRAGMATIC DYSFUNCTION AND PHRENIC NERVE PALSY IN PATIENTS UNDERGOING THORACIC SURGERY FOR LUNG- OR ESOPHAGEAL CANCER

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<h3>Introduction and Objective</h3> Thoracic surgery carries a substantial risk of postoperative pulmonary complications. Recent studies have shown that the risk of postoperative pulmonary complications is significantly higher in patients suffering from postoperative diaphragmatic dysfunction. Diaphragmatic dysfunction may be accompanied by phrenic nerve palsy. However, the extent of phrenic nerve palsy and its association with diaphragmatic dysfunction following thoracic surgery is unknown. Therefore, we aimed to quantify changes in diaphragmatic function and phrenic nerve conductance in patients undergoing thoracic surgery for lung- or esophageal cancer using ultrasonographic measures and phrenic nerve conduction studies. <h3>Design and Methods</h3> This was a prospective observational study including patients scheduled for pulmonary lobectomy or esophageal resection. Examinations were carried out the day prior to surgery and respectively 3 days and 10-14 days after surgery. Endpoints for diaphragmatic function included ultrasonographic measurements of diaphragmatic excursion of the posterior part of the right hemidiaphragm, excursion of the hemidiaphragmatic top point, change in intrathoracic area and diaphragmatic thickening fraction. Ultrasonographic measurements were recorded during a standardized respiration cycle. Endpoints for phrenic nerve conductance included baseline-to-peak amplitude, peak-to-peak amplitude and transmission delay of the diaphragmatic compound muscle action potential (CMAP). Measurements for both diaphragmatic- and phrenic nerve recordings were assessed for both the surgical side and the non-surgical side of the thorax and thus measured over time. <h3>Results</h3> We included 40 patients of which 13 had pulmonary lobectomies and 27 had esophageal resections performed. Significant reductions in diaphragmatic excursion were seen on the surgical side of the thorax for all excursion measures (posterior part of the right hemidiaphragm, p < 0.001; hemidiaphragmatic top point, p < 0.001; change in intrathoracic area, p < 0.001) (Figure 1). Conversely, all ultrasound excursion measures did not change significantly on the non-surgical side. Diaphragmatic thickening fraction did not change significantly on either side. For phrenic nerve measures, significant reductions were seen for both CMAP amplitude measures on the surgical side (baseline-to-peak, p < 0.001; peak-to-peak, p < 0.001) and non-surgical side (baseline-to-peak, p < 0.001; peak-to-peak, p < 0.001). Transmission delay also changed significantly between assessments on both the surgical (p =0.041) and the non-surgical side (p =0.021) (Figure 2). <h3>Conclusion</h3> Thoracic surgery caused a significant unilateral reduction in diaphragmatic excursion on the surgical side of the thorax, whereas the contralateral hemidiaphragm's excursion did not decrease significantly. Diaphragmatic compound muscle action potential amplitude was reduced significantly bilaterally. Therefore, our findings show that a postoperative reduction in diaphragmatic excursion is accompanied by partial phrenic nerve palsy, which may be a contributing factor in the pathogenesis of postoperative pulmonary complications.