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* From the Department of Intensive Care Medicine (Drs. van Haren and Rozendaal), Jeroen Bosch Hospital, s-Hertogenbosch; and Department of Intensive Care Medicine (Dr. van der Hoeven), University Medical Hospital St. Radboud, the Netherlands.
Correspondence to: Frank M. P. van Haren, MD, Department of Intensive Care Medicine, Jeroen Bosch Hospital, PO Box 90153, 5200 ME s-Hertogenbosch, the Netherlands; e-mail: fvharen{at}planet.nl
| Abstract |
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Design: Prospective clinical study.
Setting: ICU in a teaching hospital.
Patients: Eleven consecutive patients with documented septic shock who remained hypotensive despite norepinephrine infusion at a rate
0.2 µg/kg/min.
Interventions: Insertion of a gastric tonometry catheter, and continuous infusion of vasopressin 0.04 U/min during 4 h.
Measurements and main results: Difference between gastric and arterial CO2 partial pressure (P[g-a]CO2 gap), mean arterial pressure, and cardiac index were recorded at baseline and after 15 min, 30 min, 60 min, 120 min, and 240 min.
Results: The median P(g-a)CO2 gap increased from 5 mm Hg at baseline to 19 mm Hg after 4 h (p = 0.022). Mean arterial pressure increased from 61 ± 13 mm Hg at baseline to 68 ± 9 mm Hg after 4 h (p = 0.055). No significant changes in cardiac index were noted.
Conclusions: In norepinephrine-dependent patients in septic shock, continuous infusion of low-dose vasopressin results in a significant increase of the P(g-a)CO2 gap compatible with GI hypoperfusion.
Key Words: catecholamines GI tonometry intensive care prospective study sepsis septic shock splanchnic circulation vasopressin
| Introduction |
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Patients with septic shock, compared to other forms of shock, have low levels of circulating endogenous vasopressin.1 2 3 This may be related to depletion of vasopressin stores in the neurohypophysis.4 In experimental septic shock, release of vasopressin is inhibited by central nitric oxide production arising from the inducible nitric oxide synthase pathway.5 Other experimental data indicate that sepsis also causes cytokine-mediated downregulation of vasopressin V(1A) receptors.6
Vasopressin is a potent vasoconstrictor in patients with septic shock. Vasopressin increases BP, improves some measures of renal function, and decreases catecholamine requirements.7 8 9 10 Terlipressin, a long-acting vasopressin analog, also restores BP in patients with catecholamine-resistant septic shock.11
Despite its favorable effect on global hemodynamics in patients with septic shock, few clinically relevant data are available on the effect of vasopressin on the splanchnic circulation.12 In patients with bleeding esophageal varices, vasopressin leads to vasoconstriction of the splanchnic circulation and may stop the bleeding.13
The aim of our study was to investigate the effect of vasopressin infusion on the splanchnic circulation in patients with septic shock. We hypothesized that vasopressin, being a potent vasoconstrictive agent, decreases GI blood flow and therefore may be potentially harmful.
| Patients and Methods |
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70 mm Hg despite norepinephrine infusion at a rate
0.2 µg/kg/min. Exclusion criteria were age < 18 years, pregnancy, and myocardial ischemia or infarction < 6 months prior to the study.
Interventions
A gastric tonometry catheter (Tonometrics-catheter, TONO-16F; Datex-Ohmeda Division; Helsinki, Finland) was inserted in the stomach. Calibration was performed according to the guidelines of the manufacturer. Enteral feeding was discontinued, and all patients received omeprazole, 40 mg IV, 1 h before the first measurements. After data collection at baseline, patients received vasopressin, 0.04 U/min, by continuous central venous infusion for 4 h. Catecholamine doses were not changed during the study period unless mean arterial pressure dropped below 50 mm Hg despite fluid resuscitation. Vasopressin was continued after 4 h in case of persistent hypotension, based on the judgment of the treating physician.
Measurements
We recorded demographic data as well as the severity of illness using APACHE (acute physiology and chronic health evaluation) II (first 24 h of admission to the ICU) and sequential organ failure assessment (SOFA) scores (24 h prior to inclusion in the study). Partial pressure of CO2 in the stomach was measured by automated air tonometry using an equilibration time of 10 min. PaCO2 was measured simultaneously with a blood gas analyzer (Bayer; Meijdrecht, the Netherlands), and the difference between gastric and arterial CO2 partial pressure (P[g-a]CO2 gap) was calculated. BP and cardiac index were also recorded. Plasma levels of vasopressin were measured with a radioimmunoassay kit (Wizard gamma counter; Nichols; Wallac, Finland). All measurements were performed at baseline and after 15 min, 30 min, 60 min, 120 min, and 240 min. Data on hospital mortality were collected after completion of the study.
Statistical and Data Analysis
Data are presented as mean ± 1 SD or as median (25 to 75th percentile) depending on their distribution. Changes over time were analyzed by analysis of variance. All statistics were done using SPSS version 10.0 (SPSS; Chicago, IL).
| Results |
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| Discussion |
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We found that vasopressin infusion leads to an immediate and important increase in P(g-a)CO2 gap in a dose-dependent fashion. This P(g-a)CO2 gap is a reliable measure of GI hypoperfusion. In animal experiments, increased levels of circulating vasopressin in different states of shock have been shown to contribute to redistribution of blood from the peripheral to the cerebral circulation.15 Although low concentrations of vasopressin have been shown to have vasodilatory effects in selected organs,2 the results of the only placebo-controlled trial16 that has been conducted with vasopressin in patients with septic shock show that vasopressin treatment results in peripheral vasoconstriction. Our study shows that vasopressin probably also leads to vasoconstriction of the splanchnic vasculature. This finding is consistent with studies17 in human gastroepiploic arteries that demonstrate a concentration-dependent vasoconstriction effect starting at levels that are lower than those obtained in our study. An increase in gastric PCO2 indicating splanchnic vasoconstriction has also been shown in patients who received ornipressin (a vasopressin agonist specific for the V1 receptor) to reverse the hypotension associated with combined general/epidural anesthesia.18 In animal experiments, endogenous release of vasopressin during endotoxin administration has been associated with gastric, duodenal, and jejunal microcirculatory and mucosal injury.19 Several studies20 21 22 23 24 25 26 have demonstrated that GI hypoperfusion, reflected by a low gastric intramucosal pH, is a good predictor of poor outcome. Gut intramucosal hypoxia is thought to be important both as an indicator of inadequate resuscitation and as a mechanism by which multiorgan failure may occur; however, resuscitation based on the results of gastric tonometry has failed to show improvement in outcome.27
Other vasoconstrictive agents used in septic shock do not share the apparent detrimental effect of vasopressin on the GI perfusion. In one study,28 for example, both epinephrine and the combination of norepinephrine and dobutamine in septic shock patients increased gastric mucosal perfusion. GI hypoperfusion can be reversed by infusion of prostacyclin.29 In our study, all patients acquired gastric hypoperfusion despite standard use of low-dose vasodilating agents.
There are several limitations to this study: the number of patients studied is small, but an increase in the P(g-a)CO2 gap was seen in 10 of 11 patients. Furthermore, the patients included in this study were severely ill, which makes generalization to all patients with septic shock difficult. Although hospital mortality was unusually high, the study design permits no further speculations to be made on this observation.
Because all patients received high-dose norepinephrine infusion as well as vasopressin, interaction between these two vasoconstrictive agents cannot be ruled out. Several studies17 30 31 indicate that subconstricting doses of vasopressin are able to potentiate the constricting effects of catecholamines. In a recent study, 32 low-dose terlipressin without administration of other catecholamines increased ileal microcirculation in fluid-challenged endotoxic rats. It is possible, therefore, that the effect of vasopressin observed in our patients reflects the potentiating effect of vasopressin to infused and endogenous catecholamines.
Finally, the vasopressin dose administered to the patients may have been too high. We showed that higher levels of vasopressin led to more profound gastric hypoperfusion in a dose-dependent fashion. Landry et al3 showed in six patients with septic shock that administration of vasopressin at a lower infusion rate of 0.01 U/min resulted in plasma concentrations expected for the level of hypotension (approximately 30 pg/mL), with an increase of systolic arterial pressure from 83 to 115 mm Hg.
In this prospective study, infusion of low-dose vasopressin in patients with severe septic shock resulted in a rapid increase in P(g-a)CO2 gap compatible with GI hypoperfusion. In our view, vasopressin treatment of patients with septic shock should be limited to controlled clinical trials until its effect on clinical outcome such as organ failure and mortality has been clarified.
| Acknowledgements |
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| Footnotes |
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Received for publication December 10, 2002. Accepted for publication April 16, 2003.
| References |
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