Visualisation and quantification of the effects of surgical humidification on intestinal perfusion and viability in a porcine model

Abstract

Cold and poorly oxygenated tissues are known to increase the risk of surgical site infection and anastomotic leaks in gastrointestinal surgery. Especially during laparotomy, the abdominal cavity is exposed to the cold dry operating theatre which may contribute to surgical site evaporative cooling, tissue desiccation, and reduced oxygenation. Surgical humidification, the intraoperative insufflation of warm humidified carbon dioxide into the laparotomy wound, is a local intervention designed to prevent the evaporative cooling and desiccation effects of laparotomy. In this study, we present the first data from a large animal model to visualise and quantify the effects of surgical humidification on intestinal tissue viability and oxygenation during open surgery. Our results demonstrated that surgical humidification significantly improved core and local intestinal temperature. In addition, intestinal local capillary lactate levels used as a surrogate of local tissue oxygenation demonstrated a significant improvement with surgical humidification. Further, surgical humidification showed a significant protective effect against peritoneal and intestinal tissue damage. The use of surgical humidification improved local tissue oxygenation as confirmed with perfusion biomarkers, as well as maintaining core and local temperature repetition. Surgical humidification may help to improve outcomes of abdominal open surgery. Further confirmatory clinical trials are needed.

Keywords: Humidification; Laparotomy; Surgery; Surgical site infection.

Fig. 1

Experimental Timeline. Difference between each timepoint is one hour. Animal anesthesia started at T-2. At T-1 the surgical incision was made, and the intestines exposed, surgical humidification (SH) was also turned on at T-1 if the animal was randomized to the intervention group. Arterial oxygen saturation (SaO₂), respiratory rate (RR), operating room (OR), tissue oxygen saturation (StO₂), tissue water index (TWI), local capillary lactate (LCL). Exposure of the open abdominal cavity was continued from T-1 to T6 for a total exposure time of 7 h. Total experiment time was 8 h.

Fig. 2

Core and intestinal temperature (°C) with and without surgical humidification (SH) over time. (A) Core temperature changes over time are significantly different between the groups. Statistical analyses performed via linear regression and slope comparison p = 0.0007, mean and standard error of the mean at each timepoint displayed. (B) Core temperature difference from the start to the end (T0–T6) of surgery, differences between the groups assessed via an independent t-test. Individual pig data is represented by dots with the mean and standard error of the mean are displayed. Local (C) jejunum and (D) duodenum temperature both show significant differences between groups (p < 0.0001 and p = 0.0005 respectively). Statistical analyses for C, and D performed via Two-way repeated measures ANOVA followed by Šídák’s multiple comparisons tests, *p < 0.05, **p < 0.01, and ***p < 0.001. Note that core temperature has been added as a X symbol at timepoint T-2 for graphs C and D to show the instantaneous effect of surgical humidification on local temperature when turned on at T-1. For all graphs blue: control group (no insufflation); red: surgical humidification group (SH), *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001.

Fig. 3

Local capillary lactate (intestinal) and systemic lactates (mmol/L) with and without surgical humidification over time. Local capillary lactate (intestinal) and systemic lactates were lower in the surgical humidification group however mixed effects statistical analysis (mean ± standard error) showed that only the (A) jejunum showed a statistically significant difference between the groups p = 0.0273, whereas the (B) duodenum p = 0.0867, and (C) systemic p = 0.1002 did not (Mixed Effect analysis). For all graphs blue: control group (no insufflation); red: surgical humidification group (SH, insufflation of warm humidified CO2), *p ≤ 0.05.

Fig. 4

Over time evolution of superficial oxygen tension (StO2%) and tissue water index (TWI) in the intestine with and without surgical humidification. StO2 imaging provides a quantification of the oxygenated hemoglobin within the visible light wavelength at the different ROIs. The TWI computes the tissue water content. Both hyperspectral imaging parameters showed a significant increase with time (p < 0.05 for all parameters) but mixed effects statistical analysis did not show an effect of surgical humidification on local StO2 or TWI. Data presented are mean ± standard error of the mean.

Fig. 5

Peritoneal histological analysis. (A) H&E staining showed increasing tissue damage with time in surgery and a protective effect of humidifier use. (B) SEM pictures of control and humidifier groups of the peritoneum. (C) Semi-quantification of the histological analysis, data are presented as mean ± standard error. and compared with unpaired t-tests to the controls at each timepoint. (A) The histology scores showed a significant increase in peritoneal damage with time. (D) Duodenum histology and the relative semi-quantification of the histological analysis. (D) Jejunum histology and the relative semi-quantification of the histological analysis. Both duodenum and jejunum show an improved quality and integrity of the tissue with humidifier use, marked by a reduced presence of inflammatory elements. Statistical analyses for D and E were Two-Way ANOVA with multiple comparison via Šídák test. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001.