The Effects of Phenylephrine and Norepinephrine On Tissue Oxygenation in an Experimental Gastric Conduit Model As Measured By Optical Fiber Spectroscopy

Erin W Gilbert, MD, Vincent L Harrison, MD, Vivan V Hou, MD, James P Dolan, MD, Brett C Sheppard, MD, Steven L Jacques, PhD, John G Hunter, MD, Dan Gareau, PhD. Department of Surgery, Oregon Health & Science University, Portland, OR, Department of Anesthesiology, Oregon Health & Science University, Portland, OR, Department of Dermatology &Biomedical Engineering, Oregon Health & Science University, Portland, OR

INTRODUCTION: Anastomotic oxygenation of the gastric conduit following esophagectomy is largely dependent on microcirculation which makes the gastro-esophageal anastomosis susceptible to ischemia. Ischemia is known to contribute to significant postoperative complications. In addition, many patients require hemodynamic support in the peri-operative period which may further influence microcirculation and tissue oxygenation. Optical fiber spectroscopy (OFS) has been shown to reliably assess tissue oxygenation in both human and animal models. We hypothesize that OFS can effectively measure changes in oxygenation during gastric conduit creation and during vasopressor administration in an experimental animal model.

METHODS: A gastric conduit was constructed in a swine model. OFS was used to measure tissue oxygenation (OSat) and blood volume fraction at the antrum, the serosal surface and the mucosal surface of the future anastomotic site during and after conduit creation. Next, continuous OFS measurements were obtained at the future anastomotic site while administering increasing doses of the vasopressors norepinephrine and phenylephrine. Comparisons of OFS data were made using Student’s t-test and analysis of variance (ANOVA.)

RESULTS: Following conduit creation observed OSat increased in the antrum (p<0.001) and decreased in the mucosa (p<0.001) and serosa (p=0.006) at the proposed site of anastomosis [figure 1]. In addition, mean decrease in OSat was particularly pronounced at the mucosal surface as compared to the serosal surface (62% vs. 36% respectively, p<0.001.) Bolus administration of norepinephrine led to a uniform sustained rise in OSat (avg. increase 19%) despite escalating doses (min. dose 2.5 μg, max. dose 10 μg) [figure 2].
Bolus administration of low dose (50 μg) phenylephrine resulted in an initial increase in OSat over baseline (48% to 63%, p<0.001.) However, with increasing doses (200 μg and 400 μg) there was a sustained decrease in OSat (62% to 52% and 53% to 47% respectively, p<0.001 in each instance) [figure 3].

CONCLUSION: During and after creation of a gastric conduit, both the serosal surface, and to a greater extent the mucosal surface of the future anastomotic site have decreased oxygen saturation as compared to baseline values. Administration of norepinephrine resulted in uniformly increased tissue oxygenation in the gastric conduit while administration of phenylephrine did not result in a reliable increase in tissue oxygenation. Taken together, our data indicates that norepinephrine administration increases tissue oxygenation of the gastric conduit in this model system.