Endotoxin shock in the beagle dog JOHN

A.

MORRIS,

JOHN

P.

O’GRADY,

PATRICIA

M.D.

TOAPANTA”

EMILY

SANDOVAL*

ASHIS With

M.D.

K.

MANDAL,

the technical

JERRY JEFF

assistance

M.D. of

BROWN CHANG

JOHN

BANKHEAD

Calijornia

Los Angeles,

The hemodynamic and metabolic responses to endotoxamia were assessed in seven splenectomized, chronically instrumented, conscious but lightly sedated beagie dogs. fvfeasurements included: cardiac output (CO), right and left atrial pressures (RAP, LAP), systemic and pulmonary arterial pressures (SAP, PAP), and heart rate (HA). Arterial blood samples were measured for blood gas tensions, pli, lactate, and pyruvate. After a brief control period, 1 mg/kg en&toxin (Difco 026 : B6) was given as an intravenous bolus. Two hours later, each animal was treated with low-molecular weight dextran (LMDX), 2 ml/kg/min for 15 minutes. Et&toxin initially produced a precipitate decline in CO, HR, RAP, LAP, and SAP with concurrent pulmonary hypertension; bNh pulmonary and systemic vascular resistance increased significantly, then declined to control values as the animal partially recovered. A progressive metabolic acidosis with exoess k&ate accumulation developed. LMDX produced a significant increase in CO, SAP, PAP, and LAP with a decrease in HR; RAP increased slightly. With hydration, hemodilution was noted along with relief of the metabolic acidosis and the oxygen debt. We conclude (1) neither pulmonary nor systemic vasconstriction persisted in the shocked dog, (2) the response of the pulmonary and systemic vascular beds to endotoxin was qualitatively similar, and (3) oncotic fluid therapy appeared to restore the hemodynamic and metabolic parameters to preshock values. (AM. J. OBSTET. GYNEGOL. 134:120,

1979.)

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The Memorial Foundation Award Thesis, presented by invitation at the Forty-fifth Annual Meeting of the Pacific Coast Obstetrical and Gynecological Society, Gleneden Beach, Oregon, September 26-30, 1978. Reprint requests: Dr. John A. Morris, Division of Reproductive Sciences, Department of Obstetrics and Gynecology, Charles R. Drew Postgraduate Medical School, Los Angeles, California. *Minority students. 120

Biomedical

Support

Program

Undergraduate

shock, much

tionable tificiality

From the Division of Reproductive Sciences, the Department of Obstetrics and Gynecology and the Department of Surgery, Charles R. Drew Postgraduate Medical School. Supported by Grant No. 5 SO6 RR01840from the National Heart, Lung and Blood Institute, Department Health, Education, and Welfare.

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@ 1979 The C. V. Mosby

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Volume Number

Endotoxin shock in beagle dog

134 2

Fig. 1. Schematic illustration

of surgical preparation

tally instrumented, conscious population of beagle dogs. The response of this population of control animals will be used to contrast the responses of a similar population of animals treated before and after shock with various vasoactive amines and humoral modifiers.

Material and methods Beagle dogs of either sex, 6 to 7 months of age, and of uniform weight (average 8.0 kg) were obtained from a supplier* and evaluated carefully over the next 4 weeks in a certified experimental animal facility for anemia, parasitic infestations, intercurrent disease, or other processes which might interdict their use. Thereupon, each animal was prepared in two stages. Stage 1 included a left lateral thoracotomy and pericardiotomy under general anesthesia (1.5% halothane and a 50/50 mixture of nitrous oxide and oxygen) utilizing a Bennet BA-4 respirator. The pulmonary artery I(PA) was dissected free of the aortic arch and a precalibrated electromagnetic flow meter transducer? of appropriate size was placed about the PA to measure cardiac output. A precalibrated 3.5 mm outside diameter micropressure transducer4 was secured *Marshall Beagles for Research, North Rose, New York. tMicron Induistries, Los Angeles, California. SKonigsberg [ndustries, Pasadena, California.

121

(see text for details).

in the left atrium to measure left atria1 pressure. The chest wound was repaired after exteriorizing the silicone rubber-invested wire leads; these were buried subcutaneously. The spleen was then exposed thrdugh a midline incision in the upper abdomen,. decompressed by the injection of 0.1 ml of a 1: 1,000 epinephrine solution into the splenic artery, then removed. The animal was allowed to recover over the next 2 to 3 weeks. In Stage 2 each dog was premeditated with morphine sulfate, 1 mg . kg-’ body weight. An endotracheal tube was inserted to ensure an adequate airway. The femoral artery was exposed under local anesthesia and cannulated with a polyvinyl catheter in order to measure systemic arterial pressure and to collect arterial blood samples. The electromagnetic flow meter and micropressure terminals were exposed and connected to a physiologic amplifier.* A triple-lumen 7 Fr. Swan Ganz balloon catheter was floated down on the exposed jugular vein into the pulmonary artery. Location was assured by monitoring the characteristic pulsatile waveform. Pulmonary arterial pressure and pulmonary artery wedge pressure were obtained through the distal port. The proximal port, 20 cm from the distal port, lay within the right atrium *Electronics for Medicine VR-6, White Plains, New York.

122

Morris et al.

hemodynamic parameters. Pulmonary artery flow Fig. 2. Analogue. signal display of six simultaneous jQp,4), SAP, PAP, and LAP, all have a common zero baseline; RAP zero centered 50 mm r. Scaiar values reflect

on right-hand respiratory

ordinate appear rate. Pulsatile and

for each parameter. Phasic swings in electrocardiogram electronically average signals are displayed.

and it was connected to another pressure transducer to measure the right atria1 pressure. This pressure was considered the hydrodynamic equivalent of central venous pressure. The zero reference level for systemic arterial, pulmonary, and right atria1 pressures was assumed to be the animal’s midsternum as it lay in the lateral recumbent position. Finally, a standard limb Lead I electrocardiograph was attached. The complete preparation is illustrated in Fig. 1. After a 30 minute control period, each animal was shocked with the intravenous boius administration of 1 mg . kg-’ E. coli lipopolysaccharide (Difco 026: B6, lot 613872); the toxin was administered over a 1.5 second interval. A continuous recording of the changes in flow, pressure, heart rate, and electrocardiogram was made over the next 5 minutes. Another set of values were made at 15 and 30 minutes after the toxin had been administered and thereafter at 30 minute intervals for a total elapsed time of 2 hours. Thereupon, a 10% solution of low-molecular weight dextran (Rheomacrodex, LMDX-40) in saline was administered through a forelimb vein at a rate of 2 ml . kg- I . min-’ over a 15 minute interval. Hemodynamic data were measured at the end of the infusion and again 45 minutes later. The animal was killed with a supersaturated solution of potassium chloride and the electromagnetic flow meter transducer and micropressure transducer were recovered; the relative position of the Swan Ganz catheter in the heart was ascertained. Arterial blood samples were obtained during the control period, again at 1 and at 2 hours after administration of the toxin, and just prior to terminating the experiment. Blood gas tensions (0, and COz) and blood pH were measured*; hematocrit was also measured. Base excess was calculated from the SiggaardAndersen nomogram. Arterial lactate and pyruvate *Model IL, No. 213 digital pH blood gas analyzer, Lexington, Massachusetts.

signal

were measured using standard kits” and excess tactate. a measure of oxygen debt, was calculated by the method of Huckabee.’ Both pulsatile and electronically averaged (mean) pressure and flow signals were displayed and allowed simultaneous measurement of systemic arterial pressure (SAP), right and left atria1 pressures (RAP, LAP), pulmonary artery pressure (PAP), and, intermittently, pulmonary artery wedge pressure (PAWP), as well as heart rate (HR) and cardiac output. Total pulmonary vascular resistance (TPR) and total systemic resistance (‘TSR) were derived from standard formulas wherein resistance is the quotient of pressure (in millimeters of mercury) x 100 divided by flow (in ml . min-I). Resistance was expressed as Green’s’ peripheral resistance units.

Results Resolution of surgical and technical pr&lems. Almost two thirds (19/33) of the dogs suffered major surgical and postoperative complications (hemorrhage, sepsis, wound disruption, and death). Much of this was the result of surgical inexperience and improper implantation of the atria1 micropressure transducer as well as not allowing the animals sufficient time to recover from the earlier surgery. More recent experiments have been successful and we have complete data on seven dogs. Detailed statistical analysis is pending completion of an additional three animals. Possibly the most troublesome biophysical signal was that obtained from the micropressure transducer in the left atrium. Zero baseline shift and drift were observed which were compensated for during the control period by using the PAWP as the reference standard to which the mean left atria1 pressure was matched. No future adjustments in LAP signal were made thereafter as any *Sigma Chemical Co., St. Louis, Missouri.

Volume

134

Endotoxin

shock

in

beagle dog

123

Number 2

discrepancies in the shock interval were considered physiologic and not artifactual. Fig. 2 depicts the typical analogue signals obtained with the VR-6 physiologic recorder. All signals were calibrated from a common zero to a 100 mm full-scale deflection except for (1) the unquantified electrocardiogram display and (2) the RAP zero, which was arbitrarily placed in the center of the strip (i.e., 50 mm up from the common zero). Pulsatile and electronically averaged signals were displayed. Changes i!l hemodynamics. The changes in both mean cardiac output (equal to pulmonary artery flow) and heart rate are illustrated in Fig. 3. The changes from control status, over the next 5 minutes following the injection of endotoxin and over the next 2 hours as well as the response to low-molecular weight dextran, are plotted. The profound fall in cardiac output was accompanied by a fleeting tachycardia whereupon the heart gradually decelerated (-20 bpm). The nadir of the response was invariably reached in the first 5 minutes. Thereafter the animal partially recovered so that 75 to 90 minutes later cardiac output had been partially restored to preshock levels and a significant tachycardia was evident; cardiac output then began to decline while HR remained elevated. A dramatic increase in cardiac output and a concomitant fall in HR characterized the response to the infused dextran. Fig. 4 illustrates the changes in mean systemic and pulmonary pressure in this same group of seven dogs. Delta (A) SAP, the net pressure across the systemic vascular bed, was derived from the mathematical difference of SAP minus RAP. Since RAP is a relatively trivial value when compared to SAP, ASAP is not significantly different from mean SAP. The change in SAP was characteristic: A profound hypotension occurred initially, with little evidence ‘of recovery, then a persistent hypotension developed which was corrected dramatically with the dextran. In contrast dextran barely increased RAP (~6 mm Hg); mean atria1 pressure was still well with’in the physiologic range. APAP, the net pressure across the pulmonary vascular bed, equal to mean PAP minus LAP, is similarly depicted in Fig. 4. Pulmonary hypertension developed immediately after the injection of endotoxin and was associated with a significant fall in LAP. The changes persisted for another 45 to 60 minutes, then returned toward preshock values. The dextran initially produced a sharp increase in PAP and LAP but the former was not persistent, returning to preinfusion levels. A comparison of the changes in systemic and pulmonary vascular resistances is depicted in Fig. 5. The resistance calculations assume that left ventricular output is

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124

Morris

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the peak TSR. Both resistances returned to control values about 60 minutes later, with the TSR falling below control levels during the relapsing phase. The response to the volume overload was striking and cunsistent in each animal: a significant fall in TSR with little change in TPR. The extent to which this fall in TSR reflects an alteration in blood viscosity and rheology rather than an inhibition of peripheral sympathetic activity in response to baroreceptor stimulation3 is speculative. Nonetheless, the dissimilarity in the two vascular beds is noteworthy. While a comparison of the changes in vascular resis-

Volume Number

Endotoxin shock in beagle dog

134 2

Table I. Changes in arterial blood pH, blood gases (oxygen and carbon dioxide), hematocrit base excess (B.E), and selected metabolic parameters (arterial lactate, pyruvate, and computed in the shocked dog and after volume therapy Parameter

pHa (units) Pao, (ton) Pace, (torr) Hct (vol ‘%) BE (mEq/L) Arterial Lactate (mg/ 100 ml) Arterial Ilyruvate (mg/ 100 ml) Excess lactate (mg/ 100 ml)

Control 7.35

109 51 38

+1.4 11.2 1.04 -

(Hct), excess lactate)

S + 60

s + 120

D + 60

7.30 75 42 42 -5.5

7.33 98 36

7.34 82 45 27

25.1 1.76 6.70

41 -6.3 27.7

1.43 10.3

S + 60 and S + 120 denote time in minutes after 1 mg kg-’ of an intravenous bolus of E. coli lipopolysaccharide the time in minutes after administration of LMDX-40, 2 ml . kg-’ min-’ x 15 minutes. tance does suggest a qualitative similarity, the true assessment of the quantitative disparity is reflected by expressing the resistance changes as a percentage of control. Percent changes in TSR are shown (in Fig. 5) in the left-hand ordinate and those for TPR are in the right-hand ordinate. The scalar changes in TPR are tenfold those of the TSR. The increased sensitivity of the pulmonary vascular bed to endotoxin when compared to the systemic vascular bed is re-emphasized. Exactly how different components of the systemic vascular bed (i.e., liver, kidneys, gut, and muscle) behave cannot be derived from this experiment. Metabolic changes. The metabolic indices and response to shock and to volume therapy are summarized in Table I. The occurrence of a progressive metabolic acidosis and of lactate accumulation, reflecting an increasing oxygen debt, is demonstrated. The hemodilution secondary to volume therapy may have contributed to the a@urent reduction in metabolic acidosis and oxygen debt but also may well reflect improved tissue perfusion, oxygenation, and aerobic metabolism.

Comment This study, still in progress, was designed to establish a uniform experimental animal model for the study of endotoxic shock in which the usual variables of acute surgery, i.e., anesthesia, ventilatory support, vasoactive drug (barbiturates), heparinization to maintain catheter patency, uncontrolled blood sampling, and the like, are minimized. That objective appears to have been accomplished so that our next goal-to determine what role the prostaglandins play in the pathophysiology of endotoxic shock-can be approached. Recent studies suggest that the genesis of pulmonary hypertension in septic shock in the dog,4-B cat,’ and sheep8 is mediated by the prostaglandins. While it would have been tempting to use, as a control population, the findings reported93 lo several years ago by one of us (J. A. M.)l in an acutely instrumented,

125

-1.4 19.3 1.54 2.62 and D + 60 is

anesthetized, and artificially ventilated population of mongrel dogs with intact spleens, we elected instead to revalidate that report with the present model. Surprisingly, perhaps, the current findings are comparable except in two regards. First, pulmonary hypertension and pulmonary vascular resistance appeared to be persistent and biphasic in the mongrel dog. While both parameters increased in a similar manner immediately after the administration of endotoxin in both groups of dogs, PAP and PVR were reported93 lo to be sustained in the mongrel dog and did, in fact, appear to increase again as the animal relapsed. No such persistent or biphasic effect has been noted in the beagle dog. The genesis of the pulmonary changes is still speculative and has been attributed to a variety of stimuli, i.e. (1) a reflex neurogenic vasoconstrictor response to microembolization (platelet aggregation?) and (2) the release of humoral vasoactive substances (histamine, serotonin, prostaglandins). Whatever the stimulating factor(s), the present studies do not suggest that the alterations in the pulmonary and systemic vascular beds are dissimilar except in a quantitative manner with the former seemingly more intense. Second, whereas hemoconcentration developed in the mongrel after shock, such was not the case in the beagle. Earlier it was thought that the hemoconcentration developed as plasma leaked across damaged endothelium.‘O The data in the splenectomized beagle do not support that premise, at least not during the 2 hour shock interval. Most likely, the postshock increase in hematocrit observed previously was due to splenic contraction whereby 8 ml . kg-’ . body weight of red blood cells may be added to the circulation. The genesis of the acute reduction in cardiac output, heart rate, and SAP along with a marked increase in pulmonary and systemic vascular resistance is unknown. Seemingly, a large volume of blood is trapped peripheral to the heart in either the pulmonary vascular tree (increased central blood volume) and/or the

126

Morris

et al.

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REFERENCES 1. Huckabee, W. E.: Relationship of pyruvate and lactate during anaerobic metabolism. II. Exercise and formation of O2 debt, J. Clin. Invest. 37:255, 1958. 2. Green, H. D.: Circulatory system: Physical principles, ztl Glasser, O., editor: Medical Physics, Chicago, 1950, vol. 2. Year Book Medical Publishers, Inc., p. 228. 3. Green, J. H., and Heffron, P. F.: Studies upon the relationship between baroreceptor and sympathetic activity, Q. J. Exp. Physiol. 53:23, 1968. 4. Kadowitz, P. J., and Hyman, A. L.: Influence of a prostaglandin endoperoxide analogue on the canine pulmonary vascular bed, Circ. Res. 40~282, 1977. 5. Flynn, J. T., and Lefter, A. M.: Beneficial effects of arachidonic acid during hemorrhagic shock in the dog, Circ. Res. 40~424, 1977. 6. Fitzpatrick, T. M., Alter, I., Corey, E. P., Ramwell, P. W.. Ros’e, J. C., and Kot, P. A.: Cardiovascular responses to PGI+ (Prostacvclin) in the doz. Circ. Res. 42:192, 1978. 7. Parr‘&, J. R.,‘and’Sturgess, E. M.: The possible roles of histamine, 5-HT and prostaglandin Fp as mediators of the acute pulmonary effects of endotoxin, Br. J. Pharmacol. 60:209, 1977.

8. Cefalo, R. C., Lewis, P., Fletcher, R., and Ramwell, I’.: Prostaglandins and pulmonary hypertension, presented at the Twenty-sixth Annual Clinical Meeting of the American College of. Obstetricians and Gynecologists. Anril 10. 1978. Anaheim. California. 9. Mbrris, j. A., Smith, R. w., and Assali, N. S.: Hemodynamic action of vasopressor and vasodepressor agents in endotoxin shock, AM. J. OBSTET. GYNECOL. 91:491, 1965. J, A.: Bacteremia shock in obstetrics, irt Marcus, 10. Morris, S. L., and Marcus, C. C., editors: Advances in Obstetrics and Gynecology, Baltimore, 1967. vol. 1, Thr Williams & Wilkins Co., pp. 150-161. 11 Guntheroth, W. G., and Kawabori, 1.: ‘The contribution of splanchnic pooling to endotoxin shock in the dog. Circ. Res. 41:467, 1977. 12 Morris, J. A.: Right ventricular dynamics and pulmonary vascular dynamics in experimental endotoxin shock, presented to the Society for Gynecologic Investigation, Phoenix, Arizona, 197 1. 13. Brisman, R., Parks, L. C., and Benson, D. W.: Pitfalls in the clinical use of central venous pressure, Arch. Surg. 95902, 1967.

Endotoxin shock in the beagle dog.

Endotoxin shock in the beagle dog JOHN A. MORRIS, JOHN P. O’GRADY, PATRICIA M.D. TOAPANTA” EMILY SANDOVAL* ASHIS With M.D. K. MANDAL, t...
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