Optimizing Working-space in Laparoscopy: the Effect of Pre-stretching of the Abdominal Wall in a Porcine Model

John Vlot, MD, Rene Wijnen, Prof, Robert Jan Stolker, Prof, Klaas Bax, Prof

Erasmus MC Sophia, Depts. of Pediatric Surgery and Anesthesiology

Introduction
Adequate working space is a prerequisite for safe and efficient minimal access surgery (MAS). In a research line with a porcine model investigating the effect of various interventions aimed at increasing working space we noticed a positive effect of brief abdominal insufflation (pre-stretching) up to a (relatively) high intra-abdominal pressure (IAP).

Methods and procedures
Twenty female 20kg pigs were studied. Eight animals received mechanical bowel preparation (MBP) in the context of other investigations. Anesthesia was strictly protocolized with volume-controlled ventilation and continuous monitoring of cardiorespiratory parameters. No neuromuscular blocking agents were used. An electronic CO2 insufflator was attached to an abdominal trocar. End-expiratory CT-scans were made at stepwise increased IAPs of 0, 5, 10 and 15mm Hg. At each pressure level a 5 minutes stabilization period was taken into account before CT scanning. After desufflation of the abdomen, the abdomen was insufflated again up to an IAP of 5mm Hg and scans were repeated. Intra-abdominal CO2 volume for all pressure-levels was calculated from reconstructed CT-images. Data were analyzed using SPSS version 20 and volumes were compared using a paired-samples T-test.

Results
One animal died unexpectedly during instrumentation before the start of the actual experiment. Data from three other animals were incomplete, leaving 16 animals for analysis. An increase in the CO2 pneumoperitoneum volume at repeat insufflation up to an IAP of 5mm Hg was seen in all but one animal. The mean volume at an IAP of 5mm Hg increased by pre-stretching from 1507ml to 1821ml, a 21% increase (SD 209ml). This increase was highly significant (p<0.01). There was no difference between MBP and no MBP animals

Conclusion
A 21% increase in the CO2 pneumoperitoneum volume at an IAP of 5mm Hg was found after short pre-stretching of the abdominal wall up to an IAP of 15mm Hg. The practice of short pre-stretching offers an opportunity for increasing working space in MAS without the disadvantages of long lasting high IAP. Further experiments are needed to examine the sustainability of this effect.