Effects of intravenous nitroglycerin and noradrenaline on gastric microvascular perfusion in an experimental model of gastric tube reconstruction

Introduction

Esophagectomy with gastric tube reconstruction is the surgical treatment for cancer of the esophagus. The perfusion of the distal part of the gastric tube depends exclusively on the microcirculation, making it susceptible to hypoperfusion and ischemia. It is unknown whether an increased perfusion pressure can exert a beneficial effect on gastric tissue perfusion.

Methods

For this purpose we performed a gastric tube reconstruction in 12 pigs, mean bodyweight 32 ± 1 kg (mean ± SE). Besides systemic hemodynamic parameters, the gastric microvascular blood flow (MBF) was assessed on pylorus, corpus and fundus with laser Doppler flowmetry and gastric microvascular HbO₂ saturation (mHbSO₂) and hemoglobin concentration (mHbcon) with spectrophotometry. Animals were evenly randomized over two groups: in both groups the mean arterial pressure was increased from 50 to 110 mmHg with infusion of noradrenaline; however, in the nitroglycerin (NTG) group the central venous pressure was maintained below 10 mmHg throughout the entire experiment with intravenous NTG. In this way, we aimed to increase the perfusion pressure gradient over the gastric tube tissue.

Results

Central venous and pulmonary capillary wedge pressures were lower in the NTG group. Although the systemic circulation tended to be more dynamic in the NTG group at baseline, all systemic hemodynamic parameters were similar in both groups throughout the experiment. Baseline MBF was all-over higher in the NTG group. Following surgery, in both groups the MBF decreased severely especially in the upper gastric tube. At higher mean arterial pressure (MAP), MBFs tended to be higher than at the lowest MAP levels. Overall, MBFs were higher in the NTG group. mHbcon levels increased significantly with the initial decreases in flow and remained lower in the NTG group. mHbSO₂ values were no different between groups and did not change accordingly at different MAP levels.

Conclusion

In our experimental model, tissue perfusion is severely compromised following formation of the gastric tube; this effect is aggravated by systemic hypotension independent from cardiac output. Venous congestion might contribute to this effect and can be prevented with continuous intravenous administration of NTG. Clinical studies will have to demonstrate an effect on anastomotic healing and outcome.