Experimental study of delivery of humidified-warm carbon dioxide during open abdominal surgery

Abstract

Background: The aim of this study was to monitor the effect of humidified-warm carbon dioxide (HWCO₂ ) delivered into the open abdomen of mice, simulating laparotomy.

Methods: Mice were anaesthetized, ventilated and subjected to an abdominal incision followed by wound retraction. In the experimental group, a diffuser device was used to deliver HWCO₂ ; the control group was exposed to passive air flow. In each group of mice, surgical damage was produced on one side of the peritoneal wall. Vital signs and core temperature were monitored throughout the 1-h procedure. The peritoneum was closed and mice were allowed to recover for 24 h or 10 days. Tumour cells were delivered into half of the mice in each cohort. Tissue was then examined using scanning electron microscopy and immunohistochemistry.

Results: Passive air flow generated ultrastructural damage including mesothelial cell bulging/retraction and loss of microvilli, as assessed at 24 h. Evidence of surgical damage was still measurable on day 10. HWCO₂ maintained normothermia, whereas open surgery alone led to hypothermia. The degree of tissue damage was significantly reduced by HWCO₂ compared with that in controls. Peritoneal expression of hypoxia inducible factor 1α and vascular endothelial growth factor A was lowered by HWCO₂ . These effects were also evident at the surgical damage sites, where protection from tissue trauma extended to 10 days. HWCO₂ did not reduce tumorigenesis in surgically damaged sites compared with passive air flow.

Conclusion: HWCO₂ diffusion into the abdomen in the context of open surgery afforded tissue protection and accelerated tissue repair in mice, while preserving normothermia. Surgical relevance Damage to the peritoneum always occurs during open abdominal surgery, by exposure to desiccating air and by mechanical trauma/damage owing to the surgical intervention. Previous experimental studies showed that humidified-warm carbon dioxide (HWCO₂ ) reduced peritoneal damage during laparoscopic insufflation. Additionally, this intervention decreased experimental peritoneal carcinomatosis compared with the use of conventional dry-cold carbon dioxide. In the present experimental study, the simple delivery of HWCO₂ into the open abdomen reduced the amount of cellular damage and inflammation, and accelerated tissue repair. Sites of surgical intervention serve as ideal locations for cancer cell adhesion and subsequent tumour formation, but this was not changed measurably by the delivery of HWCO₂ .

Figure 1

Laparotomy set‐up using four retractors, intubation tube, PhysioSuite® monitor and rectal probe: a control mouse and b mouse with carbon dioxide diffuser (arrow). Humidified‐warm carbon dioxide is delivered via the diffuser throughout the 1‐h procedure

Figure 2

Core temperature monitoring over time in control (no carbon dioxide) and humidified‐warm carbon dioxide (HWCO₂) groups (18 in each group). Normal body temperature range for mice shown by dotted lines. Values are mean(s.d.). P < 0·001 for mean temperature of both cohorts (2‐way ANOVA)

Figure 3

Percentage perfusion at the mouse paw in control (no carbon dioxide) and humidified‐warm carbon dioxide (HWCO₂) groups (18 in each group). Values are plotted for each animal and mean(s.d.) values are also shown. P = 0·002 (2‐way t test)

Figure 4

a Illustration depicting a normal peritoneal cell with cellular junctions (orange and blue) along with normal microvilli (black arrow). Damaged microvilli (blue arrow) and delaminating/bulging mesothelial cells (red arrow) are also illustrated, and exposure of the basement membrane (BM). b Representative scanning electron microscopic (SEM) images of peritoneal surface at 24 h after laparotomy in control (no carbon dioxide) and humidified‐warm carbon dioxide (HWCO₂) groups (scale bar 20 μm). c Higher‐power SEM images in both groups; cell bulging was apparent in the control group (scale bar 10 μm). d,e Quantification of retracted and/or bulged mesothelial cells (d) and structural defects in microvilli (e). Values are mean(s.d.) extent of damage (9 per group). *P < 0·050 (2‐way t test)

Figure 5

Effect of humidified–warm carbon dioxide (HWCO₂) on simulated surgery damage at 24 h after laparotomy. a Scanning electron microscopic (SEM) images from both groups; mesothelial bulging and delamination was reduced by the use of HWCO₂ (scale bar 20 μm). b Higher‐magnification SEM images of peritoneal surface in both groups (scale bar 10 μm). c,d Quantification of retracted and/or bulged mesothelial cells (c) and structural defects in microvilli (d). Values are mean(s.d.) (9 per group). *P < 0·050 (2‐way t test)

Figure 6

Effect of humidified‐warm carbon dioxide (HWCO₂) on markers of hypoxia at 24 h after laparotomy. a–c Matched immunohistochemical (IHC) images showing expression of nuclear hypoxia inducible factor (HIF) 1α (a) and cyclo‐oxygenase (COX) 2 expression (b) in the peritoneum, and vascular endothelial growth factor (VEGF) A staining of damaged peritoneum (c) in control (no carbon dioxide) and HWCO₂ groups (scale bar 50 μm). d–f Histological scores (H‐scores) for IHC staining of HIF‐1α, (d) COX‐2 (e) and VEGF‐A (f). Dotted lines indicate basal expression of each marker in mice subjected to anaesthesia but no surgery. Values are mean(s.d.) (9 per group). *P < 0·050 (2‐way t test)

Figure 7

Sustained tissue changes assessed at 10 days after laparotomy in control (no carbon dioxide) and humidified‐warm carbon dioxide (HWCO₂) groups in the absence or presence of damage caused by simulated surgery: a retracted and/or bulged mesothelial cells and b structural defects in microvilli. Values are mean(s.d.) (9 per group). *P < 0·050 (2‐way t test)