Positive end-expiratory pressure attenuates positional effect after thoracotomy

Abstract

Context: Thoracotomy is a common procedure. However, thoracotomy leads to lung atelectasis and deteriorates pulmonary gas exchange in operated side. Therefore, different positions with operated side lowermost or uppermost may lead to different gas exchange after thoracotomy. Besides, PEEP (positive end-expiratory pressure) influence lung atelectasis and should influence gas exchange.

Aims: The purpose of this study was to determine the physiological changes in different positions after thoracotomy. In addition, we also studied the influence of PEEP to positional effects after thoracotomy.

Materials and methods: There were eight pigs in each group. Group I received left thoracotomy with zero end-expiratory pressure (ZEEP), and group II with PEEP; group III received right thoracotomy with ZEEP and group IV with PEEP. We changed positions to supine, LLD (left lateral decubitus) and RLD (right lateral decubitus) in random order after thoracotomy.

Results: PaO2 was decreased after thoracotomy and higher in RLD after left thoracotomy and in LLD after right thoracotomy. PaO2 in groups II and IV was higher than in groups I and III if with the same position. In group I and III, PaCO2 was increased after thoracotomy and was higher in LLD after left thoracotomy and in RLD after right thoracotomy. In groups II and IV, there were no PaCO2 changes in different positions after thoracotomy. Lung compliance (Crs) was decreased after thoracotomy in groups I and III and highest in RLD after left thoracotomy and in LLD after right thoracotomy. In groups II and IV, there were no changes in Crs regardless of the different positions.

Conclusion: There were significant changes with regards to pulmonary gas exchange, hemodynamics and Crs after thoracotomy. The best position was non-operated lung lowermost Applying PEEP attenuates the positional effects.

Keywords: Positive end-expiratory pressure; position; pulmonary gas exchange; thoracotomy.

Figure 1

Gas exchange after thoracotomy There was significant decrease in PaO2 after thoracotomy in all groups. There were also significant PaCO2 changes after thoracotomy in groups I and III (with ZEEP) but not in groups II, IV (with PEEP). * Comparison of baseline and after thoracotomy, P < 0.05

Figure 2

Respiratory mechanics after thoracotomy In group I, there was significantly decreased Crs after thoracotomy. However, in group II, there were no significant changes in Crs after thoracotomy. The Crs changes were similar in right thoracotomy (groups III, IV). However, there were increased Raw after right or left thoracotomy in all groups. * Comparison of baseline and after thoracotomy, P < 0.05

Figure 3

Systemic, pulmonary hemodynamics and extra-vascular lung water index after thoracotomy There were no significant changes in systemic hemodynamics (MAP, CI, SVRI), cardiac performance (GEF) and preload parameter (GEDI) after thoracotomy. There were significantly increased MPAP, PVRI and EVLWI after thoracotomy in all groups. * Comparison of baseline and after thoracotomy, P < 0.05

Figure 4

Changes of PaO₂ in different positions after thoracotomy In group I, the PaO2 was higher in RLD than in supine and LLD after left thoracotomy. In group II, the PaO2 was still higher in RLD than in supine or LLD. However, the PaO2 in group II was higher than group I in LLD and supine. There were similar changes of PaO2 in different positions after right thoracotomy (III and IV). * Significantly different from control, P < 0.05; †Significantly different from RLD, P < 0.05; #Comparison of the same positions between groups I vs. II and groups III vs. IV, P < 0.05

Figure 5

Changes of PaCO2 in different positions after thoracotomy In group I, the PaCO₂ was significantly higher in LLD than in RLD and supine. In group II, there were no prominent PaCO2 changes in different positions. The PaCO2 changes were similar in right thoracotomy (groups III and IV). *Significantly different from control, P < 0.05; †Significantly different from RLD, P < 0.05; #Comparison of the same positions between groups I vs. II and groups III vs. IV, P < 0.05

Figure 6

Changes of respiratory system compliance in different positions after thoracotomy In group I, there were significant higher Crs in RLD than in supine and LLD. However, in group II, there were no significant changes in Crs in different positions. The Crs changes were similar in right thoracotomy (groups III, IV). *Significantly different from control, P < 0.05; †Significantly different from RLD, P < 0.05; #Comparison of the same positions between groups I vs. II and groups III vs. IV, P < 0.05