JOURNAL
OF SURGICAL
Potential
RESEARCH
18,
611-614 (1975)
Difference
as an Estimate
of Intestinal
Viability
NELSON J. GURLL, MAJ, MC, AND GUY BRAXTON, PFC Walter Reed Army Institute of Research, Washington, D.C. 20012 Submitted for publication September 10, 1974
The surgeon is often faced with the critical potentiometer (Keithley Electrometer, decision to resect or save intestine of ques- Model 602). The PD of each loop of ileum tionable viability involved by strangulation was continuously monitored throughout the obstruction or mesenteric vascular insuffi- experiment. By convention a positive PD inciency. The traditional signs of color, peri- dicated that the mucosal side of the intestine stalsis, and pulse may not be completely reli- was negative with respect to blood. Rectal able. Recourse to available experimental temperature was continuously monitored techniques is cumbersome and time- with a probe and telethermometer (Yellow consuming. Robinson has shown that bowel Springs Instrument Co., Yellow Springs, ischemia abolishes all intestinal transport OH). Thirty to 60 min were allowed for stacapacity, including sodium absorption [ 10, bilization. The ischemic loop was then II]. This sodium transport results in a clamped using a rubber-shod intestinal charge difference between mucosal and se- clamp to occlude the lumen and blood suprosa1 sides of the intestine. Since the trans- ply (Fig. 1). The clamped loop was released mural electrical potential difference (PD) is at 60 or 120 min (and at 3 and 5 hr, respecquite sensitive to hypoxia, we examined the tively, in two rabbits) and observations possibility of using PD to predict intestinal continued for another 30 min. The intestinal viability. stab wounds were closed with interrrupted inverting sutures of 5-O silk at the end of the MATERIALS AND METHODS experiment. The peritoneal cavity was then Seventeen New Zealand white rabbits of irrigated and closed. The animal was either sex weighing between 2 and 4 kg were returned to its cage and allowed food and lightly anesthetized with Innovar-Vet (Pit- water ad lib. The rabbits were sacrificed at 7 days or were autopsied if they died before man-Moore, Ft. Washinton, PA) 0.5 cc kg-’ intramuscularly. The abdomen was opened that time. Statistical analyses were by Student’s t in the midline and two lZin.-long loops of distal ileum were selected for study, a test for paired experiments. The absolute proximal ischemic loop and a distal control values of PD were used in calculations of loop. A PD bridge (PE 190 tubing filled with mean and standard error. saturated KCl, 4% agar) was placed into RESULTS each loop through a stab incision in the bowel wall. The bridge was fixed in place 1. Survival with a purse-string suture of 4-O silk so that Ten of the 17 rabbits died postoperatively the intestinal mucosa was in constant from infarction of the intestine. There were contact with the open end of the bridge. A two rabbits that died of sepsis related to a PD bridge was also fixed in the iliac vein to leak from the site of the intestinal stab serve as a serosal reference potential. The wound (for the PD bridge). These two rabends of the 50-cm-long bridges were im- bits would probably have survived save for mersed in beakers of saturated KC1 solution this technical problem and were added to the containing balanced calomel electrodes five surviving animals to constitute the (Orion 90-01) which were connected to a noninfarcted group. 611 Copyright o 1975by Academic Press, Inc. All rights of reproduction in any form reserved.
612
JOURNAL
OF SURGICAL
RESEARCH VOL. 18, NO. 6, JUNE 1975
3. Clinical Estimate Compared to PD
12” Ischemic Loop of Ileum
FIG. 1. Experimental preparation. Potential difference across ischemic (PD,) and control (PD,) ileal loops of rabbit.
2. PD in infarcted vs Noninfarcted
Groups
Before clamping of the intestine there was no significant difference between the potential difference across the bowel wall of ischemic loops (PDO and control loops (PD,) in either the infarcted or noninfarcted group. In the infarcted group, however, PD, was significantly less than PD, at 60 and 120 min and 30 min after release of the intestinal clamp. On the other hand, no difference between PD, and PD, was noted at any time in the noninfarcted group. These data are presented in Table 1.
All clinical signs were normal in the animals surviving or dying of a gastrointestinal leak. In the infarcted group, absenceof pulse and peristalsis were more reliable than abnormal color as indicators of nonviability (Table 2). Only one animal died of bowel infarction when all the clinical signs of bowel viability were present (Rabbit 5). In this animal, PD, was much less than PD (+0.9 mV vs +5.0 mV) 30 min after revascularization. During the procedure mean body temperature fell from 33.7 f 0.2”C to 30.2 + 0.4”C but there was no difference in temperature between those animals that survived and those that did not. DISCUSSION Many of the experimental techniques used to assess viability are extensions of the clinical triad of color, peristalsis, and pulse. A persistence of electromyographic evidence of slow wave activity is a good index of viability [ 1, 4, 121. An increase in serosal temperature [l, 61 and mucosal reactive hyperemia (as measured by ggmTc)[8, 151 are also reliable. Recently, ultrasound has been employed to help detect pulses in the mesentery and bowel wall and correlates with intestinal viability [ 141. Purely biochemical and biophysical techniques have also been applied to the question
TABLE I Comparison of Infarcted and Noninfarcted Groups in Potential Difference of Ischemic (PDr) and Control (PD,) Loops
I. Infarcted PDc PDi
P NC II. Noninfarcted PDc PDi
P N
Before clamped
Clamped 60 min
Clamped 120 min
30 min after unclamped
4.1 * 0.4a 4.0 * 0.4 Nsb 10
5.2 + 0.9 2.1 +_0.6
OF SURGICAL
Potential
RESEARCH
18,
611-614 (1975)
Difference
as an Estimate
of Intestinal
Viability
NELSON J. GURLL, MAJ, MC, AND GUY BRAXTON, PFC Walter Reed Army Institute of Research, Washington, D.C. 20012 Submitted for publication September 10, 1974
The surgeon is often faced with the critical potentiometer (Keithley Electrometer, decision to resect or save intestine of ques- Model 602). The PD of each loop of ileum tionable viability involved by strangulation was continuously monitored throughout the obstruction or mesenteric vascular insuffi- experiment. By convention a positive PD inciency. The traditional signs of color, peri- dicated that the mucosal side of the intestine stalsis, and pulse may not be completely reli- was negative with respect to blood. Rectal able. Recourse to available experimental temperature was continuously monitored techniques is cumbersome and time- with a probe and telethermometer (Yellow consuming. Robinson has shown that bowel Springs Instrument Co., Yellow Springs, ischemia abolishes all intestinal transport OH). Thirty to 60 min were allowed for stacapacity, including sodium absorption [ 10, bilization. The ischemic loop was then II]. This sodium transport results in a clamped using a rubber-shod intestinal charge difference between mucosal and se- clamp to occlude the lumen and blood suprosa1 sides of the intestine. Since the trans- ply (Fig. 1). The clamped loop was released mural electrical potential difference (PD) is at 60 or 120 min (and at 3 and 5 hr, respecquite sensitive to hypoxia, we examined the tively, in two rabbits) and observations possibility of using PD to predict intestinal continued for another 30 min. The intestinal viability. stab wounds were closed with interrrupted inverting sutures of 5-O silk at the end of the MATERIALS AND METHODS experiment. The peritoneal cavity was then Seventeen New Zealand white rabbits of irrigated and closed. The animal was either sex weighing between 2 and 4 kg were returned to its cage and allowed food and lightly anesthetized with Innovar-Vet (Pit- water ad lib. The rabbits were sacrificed at 7 days or were autopsied if they died before man-Moore, Ft. Washinton, PA) 0.5 cc kg-’ intramuscularly. The abdomen was opened that time. Statistical analyses were by Student’s t in the midline and two lZin.-long loops of distal ileum were selected for study, a test for paired experiments. The absolute proximal ischemic loop and a distal control values of PD were used in calculations of loop. A PD bridge (PE 190 tubing filled with mean and standard error. saturated KCl, 4% agar) was placed into RESULTS each loop through a stab incision in the bowel wall. The bridge was fixed in place 1. Survival with a purse-string suture of 4-O silk so that Ten of the 17 rabbits died postoperatively the intestinal mucosa was in constant from infarction of the intestine. There were contact with the open end of the bridge. A two rabbits that died of sepsis related to a PD bridge was also fixed in the iliac vein to leak from the site of the intestinal stab serve as a serosal reference potential. The wound (for the PD bridge). These two rabends of the 50-cm-long bridges were im- bits would probably have survived save for mersed in beakers of saturated KC1 solution this technical problem and were added to the containing balanced calomel electrodes five surviving animals to constitute the (Orion 90-01) which were connected to a noninfarcted group. 611 Copyright o 1975by Academic Press, Inc. All rights of reproduction in any form reserved.
612
JOURNAL
OF SURGICAL
RESEARCH VOL. 18, NO. 6, JUNE 1975
3. Clinical Estimate Compared to PD
12” Ischemic Loop of Ileum
FIG. 1. Experimental preparation. Potential difference across ischemic (PD,) and control (PD,) ileal loops of rabbit.
2. PD in infarcted vs Noninfarcted
Groups
Before clamping of the intestine there was no significant difference between the potential difference across the bowel wall of ischemic loops (PDO and control loops (PD,) in either the infarcted or noninfarcted group. In the infarcted group, however, PD, was significantly less than PD, at 60 and 120 min and 30 min after release of the intestinal clamp. On the other hand, no difference between PD, and PD, was noted at any time in the noninfarcted group. These data are presented in Table 1.
All clinical signs were normal in the animals surviving or dying of a gastrointestinal leak. In the infarcted group, absenceof pulse and peristalsis were more reliable than abnormal color as indicators of nonviability (Table 2). Only one animal died of bowel infarction when all the clinical signs of bowel viability were present (Rabbit 5). In this animal, PD, was much less than PD (+0.9 mV vs +5.0 mV) 30 min after revascularization. During the procedure mean body temperature fell from 33.7 f 0.2”C to 30.2 + 0.4”C but there was no difference in temperature between those animals that survived and those that did not. DISCUSSION Many of the experimental techniques used to assess viability are extensions of the clinical triad of color, peristalsis, and pulse. A persistence of electromyographic evidence of slow wave activity is a good index of viability [ 1, 4, 121. An increase in serosal temperature [l, 61 and mucosal reactive hyperemia (as measured by ggmTc)[8, 151 are also reliable. Recently, ultrasound has been employed to help detect pulses in the mesentery and bowel wall and correlates with intestinal viability [ 141. Purely biochemical and biophysical techniques have also been applied to the question
TABLE I Comparison of Infarcted and Noninfarcted Groups in Potential Difference of Ischemic (PDr) and Control (PD,) Loops
I. Infarcted PDc PDi
P NC II. Noninfarcted PDc PDi
P N
Before clamped
Clamped 60 min
Clamped 120 min
30 min after unclamped
4.1 * 0.4a 4.0 * 0.4 Nsb 10
5.2 + 0.9 2.1 +_0.6
