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Epidural anesthesia and splanchnic perfusion

To the Editor:

Piper et al. reported that during and after aortic surgery, gastric intramucosal pH (pHi) showed a similar decrease from baseline in patients with and without epidural anesthesia. CO₂-gap was also comparable between groups.¹

These findings are in disagreement with the majority of studies on the effects of epidural anesthesia on splanchnic perfusion during abdominal surgery. Most studies reported beneficial effects of epidural anesthesia, resulting in increased regional blood flow or gastric pHi.^1–3

Experimental work using intravital microscopy also demonstrated that thoracic epidural anesthesia increases gut mucosal blood flow.⁴ Others reported that during lumbar epidural blockade, intestinal vasoconstriction resulted due to a compensatory increase in splanchnic sympathetic activity.⁵ Therefore, beneficial changes in gastrointestinal mucosal blood flow (and pHi, or CO₂ gap) cannot be expected if the epidural results in anesthesia outside the area of interest.

Usually, investigators who demonstrated evidence for improved splanchnic blood flow during epidural anesthesia performed measurements inside the anesthetized region.^2–4 In the study by Piper et al., epidural catheters were inserted at L3–4.¹ Therefore, the anesthetic block did not include those sympathetic nerves that supply the gastric wall. The site of pHi measurement and the location of epidural anesthesia were different, thus explaining why epidural anesthesia failed to produce beneficial effects on gastric intramucosal pHi, or CO₂ gap.

Obviously, the authors missed this important point. With all their patients having received lumbar epidural anesthesia only, the conclusion that epidural bupivacaine has no effect on splanchnic microvascular hemodynamics and pHi was inappropriate.

References

1 Piper SN, Boldt J, Schmidt CC, Maleck WH, Brosch C, Kumle B. Hemodynamics, intra-mucosal pH and regulators of circulation during perioperative epidural analgesia. Can J Anesth 2000; 47: 631–7.[Abstract/Free Full Text]

2 Kapral S, Gollmann G, Bachmann D, et al. The effects of thoracic epidural anesthesia on intraoperative visceral perfusion and metabolism. Anesth Analg 1999; 88: 402–6.[Abstract/Free Full Text]

3 Müller M, Schück R, Erkens U, Sticher J, Haase C, Hempelmann G. Influence of lumbar peridural anaesthesia on tissue-pO2 in the human colon. (German) Anästhesiol Intensivmed Notfallmed Schmerzther 1995; 30: 108–10.

4 Sielenkämper AW, Eicker K, Van Aken H. Thoracic epidural anesthesia increases mucosal perfusion in ileum of rats. Anesthesiology 2000; 93: 844–51.[Medline]

5 Hogan QH, Stekiel TA, Stadnicka A, Bosnjak ZJ, Kampine JP. Region of epidural blockade determines sympathetic and mesenteric capacitance effects in rabbits. Anesthesiology 1995; 83: 604–10.[Medline]

Ludwigshafen, Germany

Sielenkämper et al. criticize two aspects of our study: firstly, that the results with respect to gastric pH were foreseeable and thus our study was superfluous. Secondly, they assume that we concluded that "epidural bupivacaine has no effect on splanchnic microvascular hemodynamics and pHi" and they emphasized that this conclusion is inappropriate.

Concerning their first comment, they base their argument on theoretical assumptions on the effect of lumbar vs thoracic epidural anesthesia (EA) on splanchnic perfusion and on four studies, of which two were done in sham- operated animals and two during intestinal surgery in humans. These studies are definitely different from the aortic surgery setting (where patients present with vascular pathology and undergo aortic cross-clamping) and, consequently, cannot be used to predict the results of our trial. Furthermore our study did not focus on gastric pH, but analysed regulators of circulation and hemodynamic responses as well. Publications on EA and regulators of circulation in aortic surgery are rare.^1–4 At the time the trial was designed, no study on the influence of EA on gastric pH in aortic surgery had been published. A single other article has focussed on these patients since then.⁵ Väisänen et al. reported similar results concerning the inability of thoracic EA to influence gastric pH.

Concerning their second criticism, Sielenkämper et al. misquote us. We wrote: "It is concluded that perioperative administrated bupivacaine (0.125%) had no benefit in ... splanchnic perfusion, ... in patients undergoing abdominal aortic surgery." We measured only endothelin, ANP, renin, epinephrine, norepinephrine and ADH. These remained almost unchanged in patients receiving EA. It is not implied that EA is unable to optimize splanchnic perfusion in patients without vascular pathology and in other types of surgery that do not require aortic cross-clamping. Also, we did not suggest that EA is worthless in aortic surgery as it optimizes postoperative pain therapy. There surely was an intraoperative analgesic effect of our lumbar catheters, as shown by a significantly lower fentanyl consumption in the epidural group.

Finally, we would like to add that although thoracic EA is used for several procedures at our institution, we do not consider it appropriate for abdominal aortic surgery where the need for intraoperative iv heparin may increase the rate for neurological complications.

References

1 Smeets HJ, Kievit J, Dulfer FT, van Kleef JW. Endocrine-metabolic response to abdominal aortic surgery: a randomized trial of general anesthesia versus general plus epidural anesthesia. World J Surg 1993; 17: 601–7.[Medline]

2 Gold MS, deCrosta D, Rizzuto C, Ben-Harari RR, Ramanathan S. The effect of lumbar epidural and general anesthesia on plasma catecholamines and hemodynamics during abdominal aortic aneurysm repair. Anesth Analg 1994; 78 :225–30.[Abstract]

3 Brinkmann A, Seeling W, Wolf CF, et al.. Einfluß der thorakalen Epiduralanästhesie auf die Pathophysiologie des Eventerationssyndroms. Anaesthesist 1994; 43: 235–44.[Medline]

4 Norman JG, Fink GW. The effects of epidural anesthesia on the endocrine response to major surgical stress: a randomized prospective trial. Am Surg 1997; 63: 75–80.[Medline]

5 Väisänen O, Parviainen I, Ruokonen E, et al. Epidural analgesia with bupivacaine does not improve tissue perfusion after aortic reconstruction surgery. Br J Anaesth 1998; 81: 893–8.[Abstract/Free Full Text]

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