Insufflation pressure required for thoracoscopic surgery and its influence on respiratory and cardiovascular parameters

Thoracoscopy is usually performed with one lung ventilation using a double lumen endotracheal tube. These surgeries can also be performed with a single lumen tube and double lung ventilation and the use of a capnothorax to cause a partial lung collapse. Lung collapse and capnothorax can cause adverse respiratory and cardio-vascular effects. Therefore the insufflation pressure needs to be safe and minimum.


Diagnostic
9][10][11] During thoracoscopic surgery it is necessary to create a space in the thoracic cavity in order to identify the anatomy of the structures and for instrumentation for dissection of tissues.Providing access in the thoracic cavity for thoracoscopic surgery is challenging.Thoracoscopy is usually performed under general anesthesia with one lung ventilation using a double-lumen endotracheal tube or endobronchial blocker to collapse one lung to obtain the space.It is necessary to insufflate a certain volume of CO 2 initially to collapse the lung which does not need to be continued.In our unit some surgeries are performed with a conventional single lumen endotracheal tube with double lung ventilation.In this instance capnothorax is used to cause the initial partial lung collapse and the capnothorax needs to be maintained throughout the surgery with continuous insufflation.Causing a lung collapse and maintenance of a capnothorax are known to cause adverse respiratory and cardiovascular effects.The physiological homeostatic responses try to compensate to minimize possible resultant hypoxia and the reduction of pre load by maintaining the cardiac output.
Hence the CO 2 insufflation pressures in both lung ventilator situations need to be safe and minimum.
At our unit a wide range of thoracoscopic procedures are performed with varying degrees of complexity.We reviewed all the cases to evaluate a CO 2 insufflation pressure that is adequate to provide a satisfactory lung collapse and to report any complications.

Material and Methods
The thoracoscopic surgeries were performed using both single and double lung ventilation.At the beginning of the series procedures involving less dissection such as sympathectomy, splanchnicectomy, lymph node biopsy and lung biopsy were done with double lung ventilation.Complex procedures like oesophagectomy and thymectomy were done with single lung ventilation.However later in the series all procedures were done with double lung ventilation.
After anaesthesia patients were placed supine for anterior and superior mediastinal procedures and prone for posterior mediastinal procedures.Initial insufflation pressure of 4mmHg was selected.The camera was inserted and the lung was observed for collapse.Then the working ports were introduced under vision.Adequacy of lung collapse was observed when there was clear vision of the lesion and the related anatomy to be dissected.The adequacy of the space provided for instrumentation was noted.The positioning used helped to retract the lung away from the field of dissection with the aid of gravity.
During the procedure respiratory and haemodynamic parameters were closely monitored and recorded.In double lung ventilation if the lung collapse was not found to be adequate the insufflation pressure was increased.The final insufflation pressure required was noted.

Results
A total number of 65 procedures were performed.The average insufflation pressure used was noted to be 6-8mmHg.

Table 2 Respiratory parameters
There was no reduction of oxygen saturation or significant rise of end tidal CO 2 .There was no significant deviation of the peak airway pressure from baseline.

Table 3 Haemodynamic parameters
All systolic and diastolic blood pressure changes were within a range of 10-20 % recording no major change.No significant changes of heart rate was noted.

Discussion
Lung can be collapsed during thoracoscopy by single lung ventilation.To promote the collapse initially CO 2 has to be introduced in to the pleural cavity by insufflation.Continuous insufflation is not required if the bronchus is successfully blocked.While the lung is being ventilated, a partial lung collapse can also be obtained by the creation of a capnothorax.In this situation continuous CO 2 insufflation was used not only to promote the initial collapse but to maintain the collapse.Looking at the results it is seen that in single lung ventilation the required insufflation pressure was 6mmHg.With double lung ventilation insufflation pressure had to be maintained at 8mmHg.In both situations the lung collapse obtained was adequate to visualize the anatomy and perform a safe dissection.The completeness of the dissection with minimal blood loss, in acceptable time, and having no conversions to thoracotomy can be considered as a surrogate for the adequacy of the space created.
In the range of 6-8mmHg insufflation pressure there were no adverse respiratory or cardiovascular complications inferring the safety of the pressure in the thorax.

Conclusion
With an insufflation pressure of 6-8mmHg an adequate lung collapse can be obtained for thoracoscopy.This pressure did not have any adverse respiratory or cardiovascular effects.

Table 1
Procedural details