Canine Gastric Acid Secretion and Blood Flow Measurement in Hemorrhagic Shock

GASTROENTEROLOGY

73:75-78, 1977

Vol. 73, No.1

Copyright © 1977 by the American Gastroenterological Association

Printed in U.S A .

CANINE GASTRIC ACID SECRETION AND BLOOD FLOW MEASUREMENT IN HEMORRHAGIC SHOCK SIROOS S. SHIRAZI, M.D., THOMAS M . MUELLER, M.D., AND BRUCE M. HARDY, M.D.

Departments of Surgery and Cardiovascular Center, Department of Internal Medicine , University of Iowa College of Medicine, Iowa City, Iowa

In 5 anesthetized and 5 conscious dogs, gastric blood flow was measured with 15-JL labeled microspheres. Acid secretion and regional flow under control conditions (mean blood pressure (BP) = 100 mm Hg), after 1 hr of hemorrhagic shock (mean BP = 40 mm Hg), and 60 min after retransfusion of shed blood (mean BP = 100 mm Hg) were measured. Results are expressed as mean milliequivalents per hour for acid secretion and milliliters per minute x 100 g of tissue for blood flow. Condition Control Shock Transfusion

Anesthetized dogs

Conscious dogs

H+ secretion

Fundus

Antrum

H + secretion

Fundus

Antrum

0.63 0.18 0.21

34 9" 13

39 15a 18

2.10 0.11" 0.90"

94 23" 42

126 20" 97

" P < 0.05 compared to control.

These results indicate that (1) acid secretion and regional blood flow are significantly higher in conscious dogs; (2) hemorrhagic shock caused a significant reduction of acid secretion and blood flow within the gastric tissue; (3) blood flow to fundic mucosa decreases more than antral mucosa (P < 0.05) in anesthetized dogs; and (4) although retransfusion increased regional blood flow, it was not restored to preshock level. Because the perfusion offundic mucosa is more sensitive to hemorrhagic shock, this may partially explain the propensity of stress ulcers to be located in the fundus of the stomach. various stressful systemic conditions are unknown, this study was designed to evaluate the effect of hemorrhagic shock on total and regional gastric blood flow in anesthetized and consious dogs and to assess the effectiveness of retransfusion on restoring the blood flow to the stomach.

Since Curling's first report in 1842 of gastric ulceration after burns, many other clinical conditions, such as shock, sepsis, trauma, and central nervous injury, have been found to predispose of acute gastric mucosal ulceration. The vascular embolic theory of stress ulceration was first proposed by Virchow. 1 • 2 This theory has been supported by Freisen's observations3 that hemoconcentration with stasis and low blood flow, resulting from bums, precedes infarction and ulceration of the gastric mucosa by several hours. Skillman et al. 4 and Harjola and Sivula5 have reported that rabbits subjected to hypotension develop superficial fundic erosions. They concluded that stress ulcerations were attributable to low mucosal blood flow secondary to arteriovenous shunting of blood away from the mucosa after shock. Studies in our laboratory have implicated the reflux of bile into the stomach as an etiological factor. This is not an isolated factor, however, as the presence of HCl and a period of hypotension appear to be necessary to produce mucosal lesions typical of stress ulcer. 6 • 7 Because the changes in gastric microcirculation during

Materials and Methods Experiments were carried out in anesthetized dogs in group 1 and in conscious dogs in group 2. Protocols. In group 1, 5 healthy fasted mongrel dogs (average weight 20 kg) were anesthetized with sodium pentobarbital, 30 mg per kg, and ventilated with a Harvard respirator (Harvard Apparatus Company, Inc., Millis, Mass.). Through a short neck incision the right carotid artery was cannulated and an 8 Fr polyurethane catheter was advanced into the left ventricle and left in place for subsequent microsphere injections. The right femoral artery was then cannulated with a similar catheter, and continous blood pressure recording was carried out by connection to a Statham P 23b pressure transducer (Statham Instruments, Oxnard, Calif.) coupled with a Beckman dynograph recorder (Beckman Instruments, Inc., Fullerton, Calif.) . The right femoral vein was cannulated with a 10 Fr polyvinyl catheter left in place for measurement of venous pressure and for later blood withdrawal. Through a short midline abdominal incision an atraumatic clamp was then placed across the pylorus to facilitate gastric acid collection and prevent bile reflux. A 20 Fr orogastric tube

Received December 14, 1976. Accepted January 28, 1977. Address requests for r eprints to: Dr. Siroos S. Shirazi , Depart· ment of Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242. 75

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SHIRAZI ET AL.

connected to an intermittent suction machine was then placed in the stomach and the incision was closed. The 5 fasted mongrel dogs of group 2 underwent laparotomy 2 weeks before experiments. At that time an 8 Fr polyethylene catheter was placed arund the pylorus with the catheter ends brought through a stab wound in the anterior abdominal wall and sutured subcutaneously. Before the experiments, the dogs were trained to tolerate orogastric tubes flxed to bite blocks while in Pavlov stands. On the day of the experiment, arterial and venous lines as described for group 1 were placed using only local anesthesia (12 to 20 ml of 1% lidocaine). The pyloric catheter was retrieved from its subcutaneous location and tracted in order to occlude the pylorus. The efficacy of this technique in prevention of acid loss or bile reflux has been tested in our laboratory. Dogs were then placed in Pavlov stands and a 20 Fr orogastric tube, secured to a bite block was placed in the stomach. The experimental procedure was otherwise identical in both groups. After rinsing of the stomach with 25-ml aliquots of normal saline, continous aspiration through the orogastric tube for 30 min was used to empty the stomach completely. Two 15-min control collections of gastric juice were obtained. Between these collections a microsphere injection was carried out for measurement of control gastric blood flow rate (mean arterial pressure 100 mm Hg). Shock was then induced by slow exsanguination (45 to 60 min) into citrated plastic bags from the cannulated femoral vein to a mean arterial pressure of 40 to 50 mm Hg; this was monitored continuously (mean volume of blood removed was 435 ml for anesthetized dogs and 500 ml for conscious dogs) . After a period of stabilization, another flow measurement was obtained by injection of labeled microspheres and two 15-min gastric collections were made. Then the blood was retransfused over a period of 30 to 35 min. Additional intravenous normal saline was necessary to sustain the blood pressure and left ventricular pressure at preshock level (100 mm Hg). After the blood pressure was returned to preshock level and stabilized for 10 min, two 15-min gastric collections of gastric juice and flow measurement were again performed. Blood flow measurement. Microspheres, 15 ± 5 J.L in diameter, labeled with 1 ~ 1 Ce , 8 :;Sr, and ~Hsc, were used. For each flow measurement approximately 2 x 10n microspheres suspended in dextran were injected as a bolus into the left ventricle, and the cannula was then immediately flushed with 5 ml of saline at room temperature. Before injection, the vial containing the microspheres and 1 drop of Tween 80 was vigorously agitated mechanically for at least 4 min. Starting 1 min before injection and continuing until 3 min after injection, blood was withdrawn from the distal aorta at 2.06 ml per min with a Harvard pump. After the study, the animals were killed with an injection of potassium chloride. The stomach was excised, and, with sharp TABLE

dissection, mucosa and submucosa were separated from muscular and serosal layers. Each of them was subdivided into fundic and antral portions. They were weighed (to the nearest milligram) , cut in small pieces, placed in glass tubes, and counted for 2 min in a 3-inch well type sodium iodide scintillation counter. The reference blood samples were divided into aliquots so that their counting geometry was similar to that of the gastric samples. Energy windows utilized were ~ 6 Sc, 700 to 1500 kev; a;sr, 400 to 600 kev; 141 Ce, 126 to 175 kev. Isotope separation was performed utilizing standard techniques. i The blood flow was calculated using the following formula: BF = (C x RBF)/Cr, when BF = blood flow in milliliters per 100 g per min, C = tissue counts per minute per 100 g of stomach tissue, RBF = reference blood flow (rate of withdrawal from reference artery), and Cr = total counts in reference blood. Statistics. Student's t-test for paired and unpaired data or analysis of variance was used where appropriate to assess the statistical significance of the observed differences. All results are expressed as the mean ± SE .

Results Results of acid secretion are tabulated in table 1. Hydrogen ion (:fi+) secretion dropped significantly, from 0.63 ± 0.01 to 0.18 ± 0.02 mEq per hr in anesthetized dogs and from 2.1 ± 0.5 to 0.11 ± 0.01 in conscious dogs when shock was induced. Retransfusion of blood increased the rate of acid secretion in both groups; the degree of increase was not significant in the anesthetized group. Fundic mucosal blood flow (FMBF) was 35 ± 1.9 ml per min x 100 g of tissue for the control period in anesthetized dogs and FMBF was 94 ± 10 ml per min for conscious dogs. The flow dropped to 9 ± 1.8 ml per min in anesthetized dogs and to 23 ± 8 ml per min in conscious dogs with induction of shock. The control FMBF was significantly higher in conscious dogs than in anesthetized dogs. FMBF was also significanty higher in conscious dogs during shock period than during the same period in anesthetized dogs (P < 0.05). In anesthetized dogs the drop in resting antral mucosa blood flow (AMBF), from 30 ± 5.1 to 15 ± 2 ml per min for the shock period, was less than occurred in the fundic mucosa, and the difference between FMBF and AMBF for the shock period was significant (P < 0.05). Retransfusion of blood increased the flow rate in both groups of dogs but did not restore it to resting levels. AMBF of conscious dogs was significantly higher than FMBF after retransfusion (table 1). Muscularis blood

1. Acid secretion and gastric regional blood flow in anesthetized and conscious dogs during hemorrhagic shock and after retransfusion a

A+ Group

H + secretion

F Muc BF

A Muc BF

0.63 ± 0.10 0.18 ± 0.02" 0.21 ± 0.01 "

35.0 ± 1.9 9.0 ± 1.8" 14.0 ± 2.0"

30.0 ± 5.1 15.0 ± 2.2 18.0 ± 2.5b

2.10 ± 0.50 0.11 ± 0.01 b 0.90 ± 0.02

94 ± 10 23 ± 8" 42 ± 9"

126 ± 21 20 ± 8" 97 ± 10~>

mEq/hr

Anesthetized dogs Control Shock Retransfusion Conscious dogs Control Shock Retransfusion

F Mus BF mill 00 g of tissue

A Mus BF

TMBF

14.0 ± 7.2 6.0 ± 2.2 9.0 ± 6.0

9.0 ± 1.6 5.0 ± 1.0 4.0 ± 0.8

34.0 ± 1.74 11.0 ± 1.70 14.0 ± 1.72

19 ± 3 4 ± 2" 15 ± 6

19 ± 4 23 ± 3" 21 ± 4

99 ± 9 23 ± 3" 51 ± 8"

" F Muc BF = fundic mucosal blood flow; A Muc BF = antral mucosal blood flow; F Mus BF = fundic muscular blood flow; A Mus BF = antral muscular blood flow; TMBF = total mucosal blood flow. 1 ' P < 0.05 compared to control.

July 1977

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GASTRIC BLOOD FLOW IN SHOCK

flow for fundic and antral portions of the stomach dropped with induction of shock, and retransfusion increased the flow but not the resting level. Discussion Acute gastrointestinal ulceration may occur with a variety of systemic conditions. Harnza and DenBesten·' have shown that dogs subjected to hemorrhagic shock develop stress ulcers when canine bile, taurocholic acid, or a combination of taurocholic acid and HCl is instilled into the distally occluded stomach. Because no ulcers developed in shocked animals when the duodenum was occluded to prevent bile reflux, they concluded that bile salts were etiologically related to stress ulcer formation after shock. In an effort to clarify the role ofH+ and bile salts in the etiology of stress ulcers, one of us 6 in a subsequent experiment showed that three factors, the presence of H +, increased mucosal permeability to H+ (induced by agents such as bile salts), and altered mucosal blood flow (secondary to shock), are all necessary for the development of stress ulcerations in that experimental model. The importance of these three factors has been reported by Ritchie. 9 We have shown in our laboratory that elimination of any of these three factors will prevent stress ulceration in our models, 7• 8 but the exact role of shock in altering total and regional gastric perfusion has not been investigated. In this experiment the gastric blood flow is markedly greater in awake animals than in those under barbiturate anesthesia. There is a regional distribution of gastric blood flow, with mucosa better perfused than serosa and muscularis. With shock there is a marked decrease in gastric blood flow, with significant difference between antral and fundic mucosal flow in anesthetized dogs. Although shock decreases acid secretion, H+ secretion still occurs during shock, and although retransfusion partially restores flow, the gastric blood flow remains below control level. Sales et al., 10 by using microsphere technique in piglets, have also shown a decrease in the mean blood flow to the fundus and the antrum with anesthesia and a marked drop of blood flow to the stomach after hemorrhagic shock. Cheung and Moody 11 have demonstrated a significant fall in gastric mucosal blood flow during hemorrhagic shock in isolated chambered gastric mucosa. Davenport et al. 12 have also noted a fall in blood flow to gastric pouches by using aminopyrine clearance technique. Of the several techniques devised to measure regional blood flow, one of the most successful methods is the use of radioactive microspheres. This is based on the premise that microspheres injected into the central arterial system mix evenly with blood and are entrapped in the microcirculatory bed in direct proportion to the blood flow. The advantages of this technique are that it can be used with intact organs, regional distribution of flow can be determined, the indicator is accurate over great ranges of blood flow, and several determinations of gastric blood flow can be made in any one animal. Rudolph and Hayman 13 quantitated regional flow in the sheep fetus by multiplying the fraction of total body radioac-

tivity from a region by cardiac output, which was determined by an independent method. Other investigators have simplified regional blood flow measurement by comparing tissue activity to the activity of an arterial reference sample withdrawn at a known rate during the microsphere injection. To test the validity of using microspheres to measure gastric regional flow, Archibald et al. 14 used 15-JL microspheres and compared the flow measured by two other independent methods. Total microsphere-measured flow was compared to simultaneously measured total venous flow, and mucosal flow measured by microspheres was compared to mucosal flow plasma measured by the aminopyrine clearance technique. They showed that total flow measured by venous effluent technique demonstrated close correlation with measured flow in dogs given histamine, gastrin, or isoproterenol. An interesting pecularity of stress ulcers, particularly those precipitated by trauma or hemorrhage, is the tendency of the lesions to involve only the more proximal regions of the gastric mucosal surface. This feature has been recognized in human patients and has been described more accurately in animals subjected to hemorrhagic shock: the rabbit" and the dog.7 Recently Menguy and Masters 1" · 16 have shown a decrease in energy metabolism of the gastric mucosa during shock, and they have also demonstrated that complete gastric ischemia caused a more rapid dephosphorylation of adenine nucleotides in the corpus and fundus than in the antrum. In our study, it became clear that shock significantly decreases the blood flow to the gastric mucosa. It is also interesting to see that blood flow to fundic mucosa decreases more than that to antral mucosa in the anesthetized dog. The clinical observations on the usual site of stress ulcers and the findings of Menguy and Masters may be related to our observation that antral mucosa responds differently to shock and decreased blood volume than does the mucosa of the fundus of the stomach with anesthesia. Because the perfusion of fundic mucosa during anesthesia is more sensitive to hemorrhagic shock, this may partially explain the propensity of sress ulcers to be located in the fundus of the stomach of patients who have had a period of shock before or during anesthesia. Our observations regarding acid secretion reveal that although the rate of H+ secretion decreased significantly with hemorrhagic shock, 4 it is important to note that the dogs in both groups continue to secrete acid; this is in favor of our earlier hypothesis 7 • 17 that the presence of H+ is necessary for production of stress ulcers. Elimination of bile by clamping of the duodenum in this experimental model prevents stress ulceration, as we have shown previously.7 REFERENCES 1. Virchow R: Historiches, Kritisches und positives zur lehre der unterleibsaffekktioneu. Arch Pats Anat Physiol 5:281-375, 1853

2. Virchow R: Das linfasche Chronische (Corrosie). Magengeschwur Wein Med Wochenschr 7:481-483 , 497-501 , 1857 3. Freisen SR: The genesis of gastroduodenal ulcer following burns. Surgery 28:123-158, 1950 4. Skillman JJ, Gould SA, Chung RSK , eta!: The gastric mucosal

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SHIRAZI ET AL. barrier: clinical and experimental studies in critically ill and normal man, and in the rabbit. Ann Surg 172:564-584, 1970 Harjola PT, Sivula A: Gastric ulceration following experimentally induced hypoxia and hemorrhagic shock. Ann Surg 163:2128, 1966 Hamza KN, DenBesten L: Bile salts producing stress ulcers during experimental shock. Surgery 71:161-167, 1972 Safaie-Shirazi S, DenBesten L, Hamza KN: The role ofvagotomy in preventing bile salt induced stress ulcers during hemorrhagic shock. Trauma 12:678-681, 1972 Zike WL, Shirazi S, DenBesten L: The effect of cholestyramine on stress ulceration caused by bile salt during hemorrhagic shock. J Surg Res 17:315-319, 1975 Ritchie WP Jr: Acute gastric mucosal damage induced by bile salts, acid and ischemia. Gastroenterology 68:699-707, 1975 Sales J, Norton L, Nolan P , et al: Gastric mucosal ischemia in experimental stress ulcer. J Surg Res 18:65-74, 1975 Cheung L, Moody FG: Canine gastric blood flow and its distribution during hemorrhagic shock (abstr). Clin Res 24:104A, 1976

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12. Davenport HW, Barr LL: Failure of ischemia to break the dog's gastric mucosal barrier. Gastroenterology 65:619-624, 1973 13. Rudolph AM, Hayman MA: The circulation of the fetus in utero: methods for studying distribution of blood flow , cardiac output and organ blood flow. Circ Res 21:163-184, 1967 14. Archibald LH, Moody FG, Simons M: Measurement of gastric blood flow with radioactive microspheres. J Appl Physiol 38:1051-1056, 1975 15. Menguy R, Desbaillets L , Masters YF: Mechanism of stress ulcers: influence of hypovolemic shock on energy metabolism in the gastric mucosa. Gastroenterology 66:46-55 , 1974 16. Menguy R, Master YF: Mechanism of stress ulcers: differences between antrum, corpus and fundus with respect to the effects of complete ischemia on gastric mucosa energy metabolism. Gastroenterology 66:509-516 , 1974 17. Safaie-Shirazi S, Foster LD, Hardy BM: The effect ofmetiamide, an H 2-receptor antagonist, in the prevention of experimental stress ulcers. Gastroenterology 71:421-425, 1976