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Canadian Journal of Anesthesia 47:631-637 (2000)
© Canadian Anesthesiologists' Society, 2000
Reports of Investigation

Hemodynamics, intramucosal pH and regulators of circulation during perioperative epidural analgesia

S.N. Piper, MD, J. Boldt, MD, C.C. Schmidt, MD, W.H. Maleck, ARZT, C. Brosch, MD and B. Kumle, MD

From the Department of Anaesthesiology and Intensive Care Medicine, Klinikum der Stadt Ludwigshafen, Akademisches Lehrkrankenhaus der Universität Mainz, D-67063 Ludwigshafen a. Rh., Germany.

Address correspondence to: Dr. Swen N. Piper, Department of Anaesthesiology and Intensive Care, Klinikum Ludwigshafen, Bremserstraße 79, D-67063 Ludwigshafen, Germany. Phone: 49-621-503-3000; Fax: 49-621-503-3024.


   Abstract
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 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Purpose: To evaluate the effects of perioperative epidural analgesia on hemodynamics, splanchnic perfusion and regulators of circulation.

Methods: Twenty patients undergoing aortic surgery were randomised into two groups: epidural analgesia group (EAG): epidural analgesia with bupivacaine (15 ml, 0.125%) was started before surgery. Eight and 16 hr postoperatively 10 ml bupivacaine 0.125% and 1 mg morphine were given. Control group (COG): patients received no epidural catheter. Monitoring included pulmonary artery catheter and gastric tonometer. Norepinephrine, epinephrine, renin, ADH, ANP and endothelin were measured: before epidural analgesia (T0), before aortic clamping (T1), 20 min after aortic clamping (T2), after declamping the first leg (T3), at end of surgery (T4), one hour (T5) and 24 hr postoperatively (T6).

Results: At T5 mean arterial blood pressure decreased in EAG compared with baseline (86 ± 16 to 75 ± 8 mmHg) and compared with COG (75 ± 8 vs 84 ± 11 mmHg). At T2 pulmonary capillary wedge pressure and cardiac index increased and at T6 decreased in both groups. Systemic vascular resistance decreased at T1 and at T3-T5 in EAG compared with COG and at T1 and T3-T6 to baseline (1472 ± 448 to 1027 ± 184 dyn• sec•cm–5• m–2 ). In EAG and in COG, pHi decreased compared with baseline but without group differences. In both groups, epinephrine, norepinephrine, renin, and ADH levels increased from baseline. Endothelin and ANP levels showed no changes.

Conclusions: Perioperatively administrated epidural bupivacaine has no beneficially effects on hemodynamics, pHi or release of regulators of circulation.


   Introduction
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 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
PERIOPERATIVE circulatory stability is of major importance for patients outcome during major surgery.1,2 Deterioration in systemic and regional perfusion may be of particular importance for postoperative complications.3,4 The risk of developing gut ischemia and multiple organ failure (MOF) has been recognised in patients undergoing major surgery.5 The systemic hemodynamic effects of infrarenal aortic cross-clamping during abdominal aortic surgery are unfavourable,6–8 because clamping increases myocardial work and reduces cardiac output.9 In addition, the splanchnic region appears to play a pivotal role in the development of MOF in patients undergoing major surgery.10 Patients who suffer perioperative splanchnic ischemia have a poor outcome.5 The central role of the gastrointestinal tract in the development of MOF suggests that outcome can be improved if gut ischemia is prevented by techniques which improve splanchnic blood flow.11 It has been demonstrated that epidural anesthesia has a beneficial effect on bowel function.12 Lumbar and thoracic epidural analgesia may be associated with an increase in splanchnic perfusion due to sympathetic blockade.5,13,14 In the perioperative period systemic and local humoral regulators for controlling blood flow appear to be of importance for sufficient tissue perfusion.5 These substances may be influenced either by the technique of anesthesia and analgesia or by altered release and metabolism. Humoral substances which are known to regulate circulatory blood flow include vasopressin, renin, epinephrine and norepinephrine.3,15 Atrial natriuretic peptide (ANP) has been suggested as a mediator of vascular tone and fluid balance release,16 due to potent natriuretic, vaso-relaxant, and aldosterone-inhibiting properties.17 Among the substances released from the endothelium to maintain hemostasis and circulatory homeostasis is 21-amino acid endothelin-1.3,18 This endothelin is the most active pressor substance yet discovered, with a potency ten times that of angiotensin II.19 Increased endothelin plasma concentrations have been observed in pathophysiologic states associated with increased vascular resistance, vasospasm, vascular injury, including myocardial infarction, shock, hypertension and surgical stress.18 The interactions between these and others vasoactive substances ultimately determine systemic and regional blood flow.20

The aim of this study was to investigate whether epidural analgesia alters splanchnic perfusion and regulators of circulation in patients undergoing surgery of the abdominal aorta.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After obtaining approval from our local Human Ethics Committee, and obtaining informed consent, 20 patients undergoing elective infrarenal aortic bypass surgery were studied. Randomisation was performed with closed envelopes containing the study assignment opened after inclusion in the study. Patients were allocated randomly to one of two groups: epidural analgesia group (EAG; n=10): an epidural catheter was inserted at L3–4 or one segment below, and 15 ml bupivacaine 0.125% were given as a bolus at the beginning of surgery. Eight and 16 hr postoperatively 10 ml bupivacaine 0.125% and 1 mg morphine were administraded via the lumbar epidural catheter. Postoperative analgesia was given on demand by bupivacaine and morphine. Control group (COG ; n=10): patients received no epidural catheter. Postoperative analgesia was achieved by patient controlled analgesia (PCA) using piritramide.

All patients received premedication with 0.02 mg•kg–1 lorazepam 30–45 min before surgery. Induction of general anesthesia was standardised including 3 µg•kg–1 fentanyl, 5 mg•kg–1 thiopental, and 0.4 mg•kg–1 atracurium. Anesthesia was maintained with a mixture of isoflurane, 0.4–1.5%, nitrous oxide, 50%, and oxygen 50%. Mechanical ventilation was used in all patients with positive endexpiratory pressure (PEEP) = 5 mbar. Atracurium and fentanyl were given as needed to supplement general anesthesia and relaxation. Intraoperative fluids (crystalloid, gelatin) were infused in all patients to keep central venous pressure (CVP) between 7–12 mmHg, mean arterial pressure (MAP) between 60–80 mmHg, and heart rate (HR) < 100•min–1. Packed red blood cells (PRBC) were administered when hemoglobin was < 9 g•dl–1. Patients who received perioperative catecholamines were excluded. Postoperatively all patients were admitted to intensive care unit and their lungs were mechanically ventilated for at least one hour, but < 24 hr.

After induction of anesthesia a pulmonary-artery-catheter was inserted via the right internal jugular vein. A tonometer-catheter (Trip®, NGS-catheter, Tonometrics, Helsinki, Finland) was placed in the stomach by the nasogastric route and connected to a Tonocap®-system (Datex-engstrom, Helsinki, Finland). Its position was verified by auscultation over the epigastrium. Intraoperatively the correct position of the tonometry-catheter was rechecked by the surgeon by touching the stomach. Before use the catheter was calibrated. The tonometer end-tidal CO2 was measured with a line next to the endotracheal tube. Gastric intramucosal pH (pHi) and mucosal-arterial CO2-difference (CO2-Gap) were measured closely following the guideline of the manufacturer. The Tonocap® calculates pHi = pHa – log [arterial bicarbonate / regional PCO2 • 0.03 ]. The PCO2 was measured using the blood-gas analyser Ciba 865® (Ciba-Corning Diagnostics Corp., Medfield, MA 02052, USA). No patient received a H2-antagonist throughout the study period.

Heart rate (HR), mean arterial blood pressure (MAP), central venous pressure (CVP), mean pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), cardiac output (CO, thermodilution technique), cardiac index (CI), oxygen delivery (DO2), oxygen consumption (VO2), temperature, PrCO2, pHi and CO2–Gap were measured, as calculated from standard formulas. Measurements were made after induction of anesthesia, before bupivacaine 0.125% was administrated (T0), before aortic clamping (T1), 20 min after aortic clamping (T2), after declamping the first leg (T3), at the end of surgery (T4), one hour postoperatively (T5) and 24 hr postoperatively (T6).

Arterial blood samples were withdrawn at the same data points and the following regulators of circulation were measured: endothelin (measured by radioimmunnoassay [RIA]; Nichols, Bad Nauheim, Germany; the sensitivity of the assay is 2 pg•ml–1, the coefficient of variation 4.5%), vasopressin (by RIA Nichols, Bad Nauheim, Germany; the sensitivity of the assay is 1.3 pg•ml–1, the coefficient of variation 6.9%), renin (by RIA Nichols, Bad Nauheim, Germany; the sensitivity of the assay is 1.4 µU•ml–1, the coefficient of variation 2.5%), atrial natriuretic peptide (ANP) (by RIA Nichols, Bad Nauheim, Germany; the sensitivity of the assay is 7.5 pg•ml–1, the coefficient of variation 7.7%), epinephrine (the sensitivity of the assay is 10 ng•l–1, the coefficient of variation 5.4%) and norepinephrine (the sensitivity of the assay is 10 ng•l–1, the coefficient of variation 5.8%) (both measured by high-pressure liquid chromographic [HPLC]-technique with electrochemical detection).

Data are shown as mean ± SD. The distribution of all variables was tested for normality using the one-sample Kolmogorov-Smirnov test. Differences between demographic data, between perioperative management and differences from baseline and between the groups were evaluated by one and two-way analysis of variance for repeated measures (ANOVA, followed by Scheffe test). Additionally, Mann-Whitney-U test was used to analyse nonparametric demographic data, and categoric variables were analysed using the chi-square test (differences for gelatin or cristalloid infusion.) A P < 0.05 was considered the minimum level of significance.


   Results
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 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
The cumulative number of excluded patients was 3; 2 in the control and 1 patient in the epidural group. The two groups did not differ with regard to demographic, intra- and perioperative data, but there was lower intraoperative fentanyl consumption in the EAG (0.8 ± 0.38 mg) than in the control group (1.2 ± 0.19 mg) [Table IGo]. There was no significant group difference concerning ventilation time; furthermore, in all patients the tracheas were extubated after four hours and before 24 hr.


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  		TABLE I Demographic and perioperative data
 
After declamping, MAP decreased in EAG compared with baseline (86 ± 16 to 75 ± 8 mmHg) and with the COG-patients (75 ± 8 vs 84 ± 11 mmHg). Pulmonary arterial pressure did not differ between the groups and decreased at the 1st postoperative day in both groups compared with baseline values. During aortic clamping PCWP increased and at T6 decreased in both groups compared with baseline but there were no differences between the two groups (Table IIGo). Cardiac index showed a similar course in both groups: it decreased during aortic clamping and increased at the 1st postoperative day (Table IIGo). At T1 and T3-T5, SVR was lower than in COG (Table IIGo). During aortic clamping SVR increased significantly in both groups compared with baseline values (Table IIGo). Central venous pressure and PVR did not differ between the groups, as well as compared with baseline values throughout the study period. We detected no differences between the groups in oxygenation parameters (SaO2, SvO2, PaO2, PvO2, PaCO2, DO2, VO2).


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  		TABLE II Changes in mean arterial blood pressure (MAP), heart rate (HR), mean pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), systemic vascular resistance (SVR), cardiac index (CI), intramucosal pH (pHi) and CO2-Gap.
 
The PrCO2 was comparable at baseline in both groups and did not differ between the two groups throughout the study period. Intramucosal pH (pHi) showed a similar decrease from baseline data in both groups (Table IIGo). CO2-Gap did not also differ between the two groups throughout the study period (Table IIGo).

Plasma concentrations of ADH (vasopressin), norepinephrine and epinephrine increased from baseline in both groups but there were no differences between the groups until the end of the study period (Figure 1Go). Renin plasma levels increased from baseline in the EAG (48.8 ± 37.6 to 97.2 ± 73.3) and in the COG (45.8 ± 30.2 to 91.4 ± 45.5 µU•ml–1, respectively) (Figure 2Go). Endothelin and ANP plasma concentrations showed no changes throughout the study period in either group (Figure 2Go).



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  		FIGURE 1 Changes of plasma levels of epinephrine (normal range: 30 to 85 ng•–1), norepinephrine (normal range: 185 to 275 ng•ml–1) and ADH (normal range: 1.3 to 8.0 pg•ml–1)

+ P < 0.05 different vs baseline value

* P < 0.05 different vs the other group

 


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  		FIGURE 2 Changes of plasma levels of endothelin (normal range: 2.5 to 5.3 ng•l–1), ANP (normal range: 22 to 65 pg•ml–1) and renin (normal range: 5 to 47 µU•ml–1)

+ P < 0.05 different vs baseline value

* P < 0.05 different vs the other group

 

   Discussion
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
We found no hemodynamic intergroup differences except for a lower MAP and SVR in the EAG. In both groups pHi decreased compared with baseline without group differences. Likewise the regulators of circulation showed no intergroup differences; endothelin and ANP did not even change when compared with baseline.

Aortic cross-clamping is accompanied by an increase in impedance to aortic flow (increased SVR) with subsequent increase in left ventricular end-systolic volume and a decrease in ejection fraction and CI.7,8,21 Beside the hemodynamic sequel, aortic cross-clamping causes tissue hypoxia and an oxygen debt. Aortic declamping results in reperfusion of the ischemic tissue with possible derangement in physiological homeostasis and in repayment of the oxygen debt.22 In patients undergoing abdominal aortic surgery hemodynamic stability appears to be a prerequisite to avoid postoperative organ dysfunction. Gastric tonometry is a minimally-invasive method of assessing splanchnic perfusion.23 By measuring intramucosal CO2 [PrCO2] and calculating the intramucosal pH (pHi), tonometry can monitor changes in mucosal oxygenation24 and is an early indicator of effectiveness of therapy in patients who suffer a hemorrhagic shock.25 The conditions wherein gastric tonometic variables proved prognostically significant for the development of MOF and subsequent death are: acute pancreatitis, trauma, sepsis, mechanical ventilation, cardiopulmonary bypass and other types of major, emergency vascular surgery.26 An approach to improve splanchnic perfusion in patients undergoing major surgery may be the use of perioperative epidural anesthesia. In patients undergoing aortic surgery Seeling et al. described lower blood pH-levels after declamping in patients with general anesthesia compared to patients with continuous epidural plus general anesthesia.27 Johansson and colleagues studied the effects of epidural bupivacaine on intestinal blood flow with laser doppler flowmetry in patients during large bowel resection.13 They recognised an increase of blood flow in 13 patients and concluded that epidural bupivacaine has a favourable effect on intestinal blood flow during colorectal surgery.13 Another study suggests that thoracic epidural anesthesia prevents the decrease of pHi during major abdominal surgery, most likely due to beneficial effects on perfusion.14 Müller and co-workers found that spinal nerve block produced an increase of colon tissue oxygen pressure in patients undergoing elective colorectal surgery.28 The present study was designed to evaluate the effects of epidural analgesia on splanchnic perfusion as measured by gastric tonometry and its influence on regulators of circulation.

The lower fentanyl consumption intraoperatively is indicative of an analgesic effect of epidural bupivacaine. The decrease of MAP and SVR secondary to the sympatholytic effects after epidural bupivacaine application is well established. The other hemodynamic parameters were not different from those in untreated patients. This is in accordance with other publications.29–31 We did not see a beneficial effect of epidural anesthesia on pHi- and CO2 difference of gastric mucosa. Likewise Väisänen et al.,32 who evaluated the effect of epidural anesthesia on splanchnic blood flow and gastric and sigmoid mucosal pH in 20 patients undergoing abdominal aortic surgery, found that epidural anesthesia did not improve splanchnic blood flow or tissue oxygenation. Epidural anesthesia did not affect pH or pCO2 measured from gastric or mucosal mucosa.32 In contrast, Sutcliffe et al. found that fewer patients with epidural blockade developed gastric intramucosal pH-values < 7.32 postoperatively than did control patients undergoing major surgery.5 We have administrated a low dose of bupivacaine (15 ml, 0.125%), because of the decrease in blood pressure secondary to the sympathetic blockade.33 In an investigation using higher doses of bupivacaine no improvement of splanchnic perfusion was found.32 Whether continuous administration of bupivacaine or supplementation with another substance (e.g. clonidine) would have more beneficial effects on splanchnic perfusion needs further investigations.

Systemic and local control mechanisms are responsible for tissue perfusion and oxygenation. Renin and vasopressin (ADH) are vasoconstrictors, reducing renal and splanchnic blood flow.17,34 The renin and vasopressin plasma concentrations were not different between epidural group and control group, but we recognised increases compared with baseline in both groups. This is in accordance to De Lasson et al. who found an increase in patients undergoing infrarenal aortic surgery.35 Endothelin release is stimulated by hypoxia, shear stress, hypotension, and low cardiac output.21 In our investigation a decrease of MAP in the EAG did not cause a counter-regulatory release of endothelin. Endothelin plasma concentrations were similar in both groups, as we found no differences to baseline in both groups. Atrial natriuretic peptide is known to increase glomerular filtration, renal vascular resistance, and filtration fractions and possesses also direct vasodilatory effects. The ANP release is stimulated by distension of the atria.17,19,36 The ANP levels showed no significant differences. There was no increase from baseline in either group. Epinephrine and norepinephrine concentrations were increased from baseline in both groups but there were no differences between the groups. This increase in catecholamine levels reflects the magnitude of the sympathetic nervous system response.

It is concluded that perioperative administrated bupivacaine (0.125%) had no benefit in hemodynamics, oxygenation, splanchnic perfusion, in releasing regulators of the micro- and macrocirculation in patients undergoing abdominal aortic surgery.

Accepted for publication April 1, 2000.


   References
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 Introduction
 Methods
 Results
 Discussion
 References
 
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