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Eur J Cardiothorac Surg 1999;15:449-455
© 1999 Elsevier Science NL

Ventilatory muscle recruitment and work of breathing in patients with respiratory failure after thoracic surgery¹

First Department of Surgery, Osaka University Medical School, 2-2 Yamada Oka, Suita City, Osaka 565, Japan

Received 19 July 1998; received in revised form 21 December 1998; accepted 8 January 1999.

Corresponding author. Tel.: +81 6 879 3152; fax: +81 6 879 3163; e-mail: stakeda@surg1.med.osaka-u.ac.jp

Objectives: Increased work of breathing (WOB) and respiratory muscle weakness have been identified as major causes of respiratory failure after thoracic surgery. This study was undertaken firstly to characterize the mechanical impairment in patients with respiratory failure after cardio-thoracic surgery, and secondly, to determine how diaphragmatic paralysis affects deterioration in the ventilatory mechanics. Methods: We evaluated the respiratory mechanics of 24 patients following cardiac and thoracic surgery. Ten patients without respiratory problems were examined as control subjects. There were nine patients with phrenic nerve injury and five patients without phrenic nerve injury who required mechanical ventilation for more than 7 days. Phrenic nerve injury was assessed with a phrenic nerve stimulation test. We measured the respiratory variables, the esophageal, gastric and transdiaphragmatic pressure swing (Pes, Pga and Pdi, respectively), and the work of breathing during quiet tidal breathing. Results: Both the groups requiring mechanical ventilation exhibited abnormally negative Pga/Pes values, compared with the control subjects. A significant increase in WOB with the normal generation of Pdi was seen in the patients without phrenic nerve injury. In contrast, the poor generation of Pdi with a slight increase in work of breathing was noted in patients with phrenic nerve injury. Conclusions: These results demonstrated two different types of respiratory failure in thoracic surgery patients, focusing on the impact of phrenic nerve paralysis. Diaphragmatic dysfunction should not be overlooked in postoperative care, and the amelioration of this compromise in respiratory mechanics is an important aspect of good patient management.

Key Words: Respiratory failure • Respiratory muscle recruitment • Thoracic surgery • Phrenic nerve injury • Work of breathing