Effects of various doses of sodium dichloroacetate on hyperlactatemia in fed ischemic rats

ORIGINAL CONTRIBUTION hyperlactatemia; sodium dichloroacetate

Effects of Various Doses of Sodium Dichloroacetate on Hyperlactatemia lschemic Rats In shock, the presence of hyperlactatemia is prognostic of a failure to survive. An experimental model of stroke that combines bilateral carotid ligation and bleeding to a mean arterial pressure of 50 mm Hg induces hyperlactatemia like that associated with tissue hypoperfusion of hemorrhagic shock. In previous nonsurvival studies with this model, postischemic treatment of fed rats with 25 mg/kg of sodium dichloroacetate JDCA) was effective in lowering brain tissue lactate but did not significantly affect the ischemia-induced increase in serum lactate measured after 30 minutes of ischemia followed by 30 minutes of reperfusion. Investigators using other animal models treated hyperlactatemia associated with tissue hypoperfusion successfully with a DCA dose of more than 25 mg/ kg. Our goal was to determine the effect of a higher dose of DCA on serum lactate in the model of cerebral ischemia with systemic hypotension that we had used in previous studies. The previously unstudied dose-response also was evaluated in our study Rats that had been fed ad libitum were assigned randomly to either a real or sham (control) ischemic group. Immediately after 30 minutes of ischemia and subsequent reinfusion of blood or after 30 minutes of sham ischemia, rats received DCA (0, 25, 50, 100, 200, or 300 mglkg). Comparisons were made of blood values measured at the end of equilibration before ischemia, after 30 minutes of ischemia, and after 30 minutes of reperfusion. All ischemic rats were hyperlactatemic. Serum lactate levels were not correlated to blood glucose elevation during ischemia. After treatment in both control and ischemic rats, the percentage decrease in serum lactate varied as a logarithmic function of the DCA dose administered. Glucose levels and pH were not affected by DCA treatment at any dose. Because acidemia decreases lactate uptake by the liver, values for acidotic rats were compared with those for nonacidotic rats. Whereas lactate in acidotic rats decreased significantly only when treated with DCA, nonacidotic rats evidenced this decrease regardless of whether they received DCA. We discuss the relationship of these findings to the peak levels of lactate achieved, the resolution of hyperlactatemia, and factors that affect the interpretation of data in therapeutic studies using DCA. [Dimlich RVW Kaplan f, Timerding BL, Van ligten PF: Effects of various doses of sodium dichloroacetate on hyperlactatemia in fed ischemic rats, Ann Emerg Med November 1989;18:11621171.]

in Fed

RVW Dimlich, PhD*d J Kaplan, MD* BL Timerding, MD* PF Van Ligten, MD* Cincinnati, Ohio From the Departments of Emergency Medicine* and Anatomy and Cell Biology,+ University of Cincinnati College of Medicine, Cincinnati, Ohio. Received for publication 1987. Revision received Accepted for publication Presented Assembly Emergency November

November 23, January 19, 1989. July 28, 1989.

in part at the Scientific of the American College of Physicians in San Francisco, 1987.

This study was funded in part by NIH Grant NS-25635 (Dimlich), Smith Kline & French/Emergency Medicine Foundation Research Fellowships Awards (1985-1986, Kaplan) (1986.1987, Van Ligten) (1987-1988, Timerding), and University of Cincinnati Emergency Medicine Resident Research Fund. Address for reprints: Ruth VW Dimlich, PhD, Department of Emergency Medicine, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267.0769.

INTRODUCTION Since hyperlactatemia, or the elevation of serum lactate above normal levels (ie, > 5 yM/mL),l has been inversely correlated with survival in shock,2,s there has been great interest in finding a therapy that would effectively lower dangerously elevated lactate levels. One drug that has been used experimentally and clinically to successfully treat hyperlactatemia of type B lactic acidosis (eg, in association with diabetic ketoacidosis) is sodium dichloroacetate (DCA). 4,s As summarized (Table l), DCA also has been used experimentally to treat hyperlactatemia of oxygen deprivation (type A) lactic acidosis (eg, acidosis associated with hypoxia or shock).“-1” With one exception, these studies demonstrated an effectiveness of DCA in a variety of species under different experimental conditions, such as animal nutrition, method of oxygen deprivation, drug dosing, and treatment regimen. The exception was noted in our previous study on the ef18.11 November

1989

Annals

of Emergency

Medicine

1162151

HYPERLACTATEMIA Dimlich et al

TABLE 1. Summary of previous studies of the effects of DCA on elevated serum lactate and decreased

pH due to oxygen deprivation

Species (Nutrition)

Model DCA (Conditions of Dose Time of (mg/kg) Treatment Experiment)

Rat (fasted)

Hypotension (30 min, 50 mm Hg) Rat (fasted) Hypotension (30 min, 50 mm Hg) Rat (fed) Hypotension (30 min, 50 mm Hg) Dog (fasted) Hypoxia (90 rain)

Rat (fed)

Time of Analysis Reported

Change in Serum lactate (mean, mmol/L)

Change in pH (mean)

Citation

25

Preinsuit (15 min)

After 30 min Decrease of reperfusion (9 to 6)

Decrease (7.37 to 7.29)

References 6-9

25

Postinsult (3 min) (15 rain) Postinsult (3 min)

After 30 min After 15 rain of reperfusion After 30 min of reperfusion

Decrease (7.48 to 7.34) (7.42 to 7.25) Decrease (7.39 to 7.09)

Reference 9

For 20 min starting after 30 min of a 90-min insult During 20-min induction of hypoxia During hypoxia when lactate at 7 For 10 min after hemorrhage

For 120 min after starting DCA

25

150

Hypoxia (60 min, 7.5% 02) Dog (fasted) Hypoxia (8% 02)

300

Dog (fasted) Hemorrhagic shock (50% total vol over 60 min)

100

100

After 60 min of hypoxia

Decrease (18 to 8) 22 to 13) No significant decrease (12 to 17) Decrease moderately for 45 min, then to below control levels over next hour Untreated (4.8) vs DCA (2.4)

Decrease over 45 Reference 11 min, then slight increase over next hour Untreated (7.18) Reference 12 vs DCA (7.24)

60 min after DCA started

Decrease* (7 to 6)

Increase (7.16 to 7.21)

References 13 and 14

30 and 60 min after hemorrhage

At 60 min, untreated (6.96) vs DCA (2.07)

At 30 min, bicarbonate untreated (16) vs DCA (20)

Reference 15

Reference 10

*Lactate production by gut and muscle decreased by 58%. Rate of lactate extraction by the liver increased from 4.8% to 7.9% of filtered load.

fect of D C A on excessive brain lactate after cerebral i s c h e m i a in the fed rat. 10 T h e 25 m g / k g dose of D C A that lowered brain and s e r u m lactate in fasted rats 6 9 did n o t reduce this m e t a b o l i t e in the s e r u m of fed rats. l° Because in laboratory studies using other animal models, hyperlact a t e m i a was a m e l i o r a t e d in fed animals w i t h a D C A dose of m o r e than 25 mg/kg, n 15 the hypothesis of this study was that a D C A dose of m o r e than 25 m g / k g w o u l d effect a significant decrease in s e r u m lactate in fed rats in an established m o d e l of stroke that combines cerebral ischemia w i t h h e m o r r h a g i c h y p o t e n s i o n . Because n o n e of the p r e v i o u s studies used more than one dose, our study also used a iange of doses to investigate the p o t e n t i a l d o s e - r e s p o n s e effect of this agent.

METHODS T h e e x p e r i m e n t a l m o d e l we u s e d was described by Rehncrona and cow o r k e r s 16 and used in our p r e v i o u s e x p e r i m e n t s . 6-Io It c o m b i n e s b i l a t eral carotid ligation and bleeding to a 52/1163

m e a n arterial pressure (MABP) of 50 m m Hg for 30 m i n u t e s followed by 30 m i n u t e s of reperfusion. Hyperlact a t e m i a o c c u r s in t h i s m o d e l as it does in m a n y clinical conditions associated with tissue hypoperfusion (eg, h e m o r r h a g i c shock6qo). It also t y p i f i e s c e r e b r a l i s c h e m i a b y inducing a b u i l d u p of excessive cerebral lactate. 6-10 To sample brain tissue for lactate and other metabolites, t h e s e a n i m a l s w e r e k i l l e d after 30 m i n u t e s of reperfusion. Because, as we r e p o r t e d previously, e x p e r i m e n tally brain levels of lactate are n o t related to s e r u m levels, 7 an observation t h a t h a s b e e n n o t e d c l i n i c a l l y as well,17 the dose effect of D C A on cerebral lactate is addressed in a companion a r t i c l e J 8 We used 87 m a l e Wistar rats (290450 g) that were fed ad libitum in our study. T h e s e rats were d i v i d e d rand o m l y into two e x p e r i m e n t a l groups, an ischemic group and a shamischemic, control group. Each group was s u b d i v i d e d i n t o six t r e a t m e n t groups, one for each D C A dose administered. The animal groupings Annals of Emergency Medicine

and analyses times are listed (Table 2). T h e p r o t o c o l for this s t u d y was a p p r o v e d by the U n i v e r s i t y of Cinc i n n a t i I n s t i t u t i o n a l A n i m a l Care and Use C o m m i t t e e . All rats were anesthetized with h a l o t h a n e (2.5%) in n i t r o u s oxide {70% N 2 0 - 30% 0 2 ). Surgery, equilib r a t i o n , i s c h e m i a , and r e p e r f u s i o n occurred as described in our previous studies. 6-1o Briefly, both carotid arteries were isolated, and halothane (0.6%) in 70% N 2 0 - 30% 02 was adm i n i s t e r e d by t r a c h e o s t o m y throughout the surgical preparation. Femoral arteries were c a n n u l a t e d for the meas u r e m e n t of MABP and blood withdrawal. O n e f e m o r a l v e i n was prepared for drug or carrier administrat i o n a n d t h e r e p l a c e m e n t of s h e d blood. A rectal probe was inserted for the c o n t i n u o u s m e a s u r e m e n t of body t e m p e r a t u r e . T u b o c u r a r i n e chloride (0.4 m g / k g ) a n d h e p a r i n (50 units) were given IV. After surgery, halothane was withdrawn, and the rats were continued on c o n t r o l l e d v e n t i l a t i o n of 70% N 2 0 - 30% 02. After 30 m i n u t e s of 18:11 November 1989

TABLE 2. Diagrammatic representation of experimental groups (sham-ischemic control and ischemic), DCAtreatment groups (0, 25, 50, 100, 200, and 300 mg/kg DCA doses), and times at which parameters were measured (before ischemia [0 min], at the end of ischemia [30 min], and after 30 minutes of recirculation [60 min]) Experimental Group Sham-lschemic, Control (mg/kg DCA)

.... Time of Analysis (min)

Ischemic (mg/kg DCA)

0 0

25 0

50 0

100 0

200 0

300 0

0 0

25 0

50 0

100 0

200 0

300

30

30

30

30

30

30

30

30

30

30

30

30

0

60 60 60 60 60 60 60 60 60 60 60 60 Solid lines indicate statistical comparisons that were made among times within each treatment group using ANOVA. Broken lines indicate statistical comparisons that were made based on percentage change during ischemia (ie, 0 to 30 minutes) and during reperfusion after treatment (ie, 30 to 60 minutes). Statistical comparisons of these percent changes then were made between treatment groups within each experimental group using the KruskaI-Wallis test.

1000

80.

I--1 Control 1771 I=¢hemi¢

•

f

O .-I

E

;3 L

0q ,-

@ W

o

60. 40 20 ¢1=¢

~

O,

b,d -20 25

50

100

200

300

Do=a of DCA ( m g / k g )

equilibration, the carotid arteries of rats to be m a d e i s c h e m i c w e r e clamped, and blood yeas withdrawn to a MABP of 50 m m Hg. In 30 minutes, the clamps were removed, and the shed blood was reinfused as a bolus injection. Nonischemic rats were maintained for 30 minutes of sham ischemia..Rats were treated immediately after sham or real ischemia with either DCA or an equal volume of carrier (ie, sterile water [2 mL/kg]). Rats were killed 30 minutes after termination of sham or real ischemia. MABP and t e m p e r a t u r e were recorded every 15 minutes throughout the experiment. Blood (0.8 mL) for glucose, serum lactate, hematocrit, 18:11 November 1989

and arterial blood gases was drawn just before the insult (0 minutes), immediately before reinfusion of shed blood (30 minutes), and at the end of recirculation (60 minutes). To ensure appropriate Pao 2 (> 70 m m Hg) and Paco2 (< 50 m m Hg) before surgery, blood (0.2 mL) also was drawn in the middle of equilibration (15 minutes), and the ventilator was adjusted if necessary. Arterial pH, Pco2, and Po 2 were determined, and as done routinely in clinical and experimental laboratories, bicarbonate ion (HCO 3 was calculated from pH and Pco2 with a blood gas machine (IL 513 Blood Gas Analyzer, Fisher Scientific Co, PittsAnnals of Emergency Medicine

FIGURE 1. Percent decrease in serum lactate in control and ischemic fed rats treated after 30 minutes of real or sham ischemia with various doses of DCA (25, 50, 100, 200, and 300 mg/kg) and a s u b s e q u e n t survival period of 30 minutes. Note that the percent decrease was greater in control rats treated with 200 and 300 mg/kg than in those rats that were untreated (a and c, P < .05, Dunn's) or given 25 mg/kg (b, P < .05 for 200 mg/kg; d, P < .06 for 300 mg/kg, Dunn's). In ischemic rats, the percent decrease was significantly greater in rats receiving 200 mg/kg (e, P < .05, Dunn's) and 300 mg/kg (f, P < .08, Dunn's) than in rats treated with 25 mg/kg DCA. The dose-response (25 to 300 mg/kg) for both control and ischemic rats was logarithmic (r = .91 a n d . 95, respectively). burgh, Pennsylvania). Blood glucose was m e a s u r e d using D e x t r o s t i x s ® and an Accu-Check BG Monitor (Biodynamics Co, Boehringer-Manheim Co, Indianapolis, Indiana). Blood was spun down by microcapillary centrifugation and read in a h e m a t o c r i t reader. Serum for lactates was collected, frozen, and later measured spectrophotometrically by the Clinical Chemistry Laboratory at the University of Cincinnati Medical Center. As depicted by the solid lines (Table 2), statistical comparisons were made between values at each time indicated within a single experimental group (ie, at 0, 30, and 60 rain1164/53

HYPERLACTATEMIA D i m l i c h et al

TABLE 3. Values for control rats Control Experimental Condition T i m e M A B P (mg/kg) (N) (min) (mm Hg)

Hematocrit PO 2 (%) (mm Hg)

Pco 2

(mm Hg)

HC03-

pH

Blood Glucose (mg/dL)

Serum Lactate (#mol/mL)

0 (13)

0 30 60

124 ± 131 _+ 130 ±

6 5 3

41 ± 1 40 _+ 1 39 + 1

108 _+ 117 ± 119 _+

5 5 5

39 _+ 1 38 +_ 1 38 _+ 1

20 ± 1 20 _+ 0 19 _+ 1

7.33 _+ .02 7.35 _+ .01 7.31 _+ .02

192 _+ 11 208 _+ I 6 209 _+ 14

4.3 _+ .3 4.3 ± .4 4.3 ± .6

25 (4)

0 30 60

134 _+ 11 134 +_ 9 132 _+ 8

44 _+ 2 42 _+ 1 38 _+ 3

106 _+ 106 +_ 111 _+

5 8 9

38 -+ 1 37 ± 1 35 _+ 2

21 _+ 1 20 _+ 1 18 _+ 1

7,36 + .03 7.35 _+ .02 7.33 _+ .02

175 +_ 15 190 + 27 182 _+ 20

5.9 _+ 1 5.7 _+ 1 5.5 + .8

50 (4)

0 30 60

119 _+ 13 126 _+ 7 131 _+ 8

39 _+ 2 36 -+ 2 37 _+ 2

111 _+ 7 118 ± 13 131 +_ 10

34 +_ 4 32 + 2 32 _+ 3

19 + 1 18 + 1 17 ± 0

7.38 _+ .04 7,36 _+ .03 7.33 + .03

182 ± 13 172 ± 16 184 + 14

5.6 + .7 4.8 _+ .7 4.2 + .9

100 (4)

0 30 60

138 + 10 134 _+ 8 129 ± 10

38 + 3 37 _+ 3 36 _+ 2

100 + 3 118 +_ 9 105 ± 14

35 _+ 6 36_+ 7 37 _+ 5

19 _+ 0 20 +_ 2 18 _+ 2

7.40 _+ .05 7.38 _+ .04 7.32 _+ .04

182 + 16 226 + 42 258 _+ 59

4,7 _+ 1 4.8 ± ,7 4.5 + 1

200 (4)

0 30 60

135 +_ 130 _+ 129 ±

5 0 2

44 _+ 1 42 _+ 2 42 ± 1

95 +- 7 97 _+ 4 99 -+ 5

32 _+ 2 30 _+ 1 34 + 1

22 _+ 1 20 _+ 0 19 + 2

7.44 +_ .02 7.44 _+ .02 7.40 _+ .02

165 _+ 12 160 _+ 11 187 ± 9

4.4 ± .2* 4.3 + .3* 2.5 ± .1"

300 (8)

0 30 60

129 _+ 131 _+ 126 _+

4 6 5

42 _+ 0 40 _+ 1 39 _+ 1

36_+ 1 37 _+ 2 37 + 3

20 _+ 0 19 _+ 1 18 _+ 2

7.34 _+ .02 7.33 _+ .01 7.30 ± .01

182 _+ 17 182 _+ 14 197 + 14

5.8 +- .4* 5.9 ± .4* 3.6 + .3*

115 _+ 115 _+ 119 _+

6 6 7

*P < .01 by Duncan's. Physiologic and biochemical parameters (mean +_ SEM) in fed rats just before (0 min) and immediately after 30 minutes of sham ischemia (30 min) and 30 minutes of sham recirculation (60 min). Note that serum lactate was significantly lower in rats treated with 200 and 300 m g / k g DCA when c o m p a r e d with baseline (0 min) and postsham ischemic (30 min) levels.

utes). A one-way analysis of variance (ANOVA) was used to compare these values. As depicted by the dotted lines (Table 2), percent changes were calculated in values between times indicated to correct for variation in baseline values between treatment groups (ie, from 0 to 30 minutes [during isc h e m i a before treatment] and from 30 to 60 minutes [during reperfusion after treatment]). This standardization allowed for a statistical comparison to be m a d e a m o n g t r e a t m e n t groups within each experimental group (sham ischemic and ischemic) using a nonparametric test appropriate to c o m p a r e p e r c e n t a g e s (ie, Kruskal-Wallis test)J 9 All significance was determined at P less than or equal to .05.19 When using A N O V A or Kruskal-Wallis, if t h e r e w e r e s i g n i f i c a n t differences among more than two groups, Duncan's multiple-range test z0 or Dunn's m u l t i p l e - c o m p a r i s o n p r o c e d u r e 19 was used, respectively, to determine w h i c h of the g r o u p s w e r e significantly different. Statistical calculations were performed w i t h a c o m p u t e r p r o g r a m (STATPAK, N o r t h west Analytical, Inc, Portland, Oregon). D o s e - r e s p o n s e data w e r e 54/1165

tested by a c a l c u l a t o r curve-fitting program (Hewlett-Packard 41C Stat Pac, H e w l e t t - P a c k a r d , Inc, Sunnyvale, California). A previous study indicated that the response of serum lactate and blood glucose to D C A in fasted rats might be affected by the acidotic state of the rat. 7 Therefore, parameters in ischemic rats that were acidotic (ie, pH < 7.2, H C O 3 <~ 10, or both) (11 rats} at the end of ischemia (30 m i n u t e s ) were compared w i t h values in rats that were not acidotic (17). Excess lactate is taken up and metabolized by the liver. Fed rats contain more hepatic glycogen than fasted rats. Because glycogen is a ready source of the glucose substrate necessary for the anaerobic production of lactate, extra glycogen m i g h t influence lactate metabolism in the liver and, subsequently, the serum lactate response. Therefore, results with fed rats also were c o m p a r e d w i t h the data from a previous study with fasted rats. 7

RESULTS The criteria for exclusion included an i n a d e q u a t e h y p e r g l y c e m i c response during ischemia (glucose, < 75% of baseline), Pao 2 less than 70 Annals of Emergency Medicine

m m Hg, or Pa¢o2 more than 50 m m Hg at any t i m e during the experim e n t and MABP less than 80% of value after reinfusion. Based on these criteria, 19 rats were excluded from our study. In the remaining 68 rats, body temperature was stable at 37 -+ 1.3 C t h r o u g h o u t the experiment. In control rats (38), MABP, h e m a t o c r i t , blood gases, H C O 3 , and pH did not c h a n g e s i g n i f i c a n t l y d u r i n g either sham ischemia or recirculation (Table 3). In ischemic rats (30), MABP and hematocrit decreased as dictated by experimental design (Table 4). In these rats, Pco2, H C O 3 , and pH also decreased during ischemia (Table 4). After recirculation, MABP remained low in untreated and 25 mg/kg-DCA treated rats (Table 4). In all treatment groups, pH remained unchanged and P c o 2 increased (Table 4). After recirculation, in contrast to treated rats, H C O 3- in untreated rats was not significantly different from the initial value (Table 4). There was no significant change after sham ischemia (30 minutes) in any treatment group (Table 3). Controls showed a significant decrease in lactate after D C A treatment (60 minutes) with 200 and 300 mg/kg (Dun18:11 November 1989

TABLE 4. Values for ischemic rats Ischemic Experimental Condition T i m e M A B P (mg/kg) (N) (min) (mm Hg)

Hematocrit PO 2 (%) (mm Hg)

Pco 2

(mm Hg)

HCO~

pH

Blood Glucose (mg/dL)

Serum Lactate (~mol/mL)

0 (5)

0 30 60

132 -452 + 120 _+

5* 1 3*

41 _+ 1 28 + 2 38 _+ 1

110 + 12 123 _+ 14 103 _+ 7

34 _+ 3 27 ± 2 42 _+ 3

21 ± 2 11 _+ 2 16 _+ 2

7,41 _+ .01" 7.19 _+ .06 7.20 + .07*

165 _+ 6 537 ± 47 304 +_ 26

4.4 _+ .7t 26.6 _+ 5* 13.3 ± 5

25 (5)

0 30 60

130 ± 51 ± 110 _+

4t 2 7t

41 + 1 34 _+2 38 -+ 2

108 _+ 9 I 2 3 -4- 17 104 +_ 15

30 _+ 4 28 ± 3 34 ± 3

20 ± 1" 10 + 2 12 ± 2*

7.42 _+ .04t 7,15 _+ .07 7.16 -+ .05t

164 _+ 14 454 + 93 262 _+ 39

4.8 _+ .7* 22,1 -+ 6* 13,4 _+ 4

50 (4)

0 30 60

132 _+ 10 54 _+ 1 132 ± 9

41 _+ 1 31 _+ 2 42 ± 1

93 + 13 138 _+ 7 97 -+ 9

33 _+ 2 25 ± 3 36 _+ 2

19 _+ 1" 11 _+ 1 16 _+ 0*

7.38 ± .02t 7.26 ± .02 7.28 -+ .02t

152 -+ 9 397 _+ 50 248 ± 44

3.8 _+ .1" 18.8 _+ 4* 7.4 -+ 2*

100 (6)

0 30 60

132 _+ 53 _+ 126 -4-

4 1 2

41 -+ 1 30 -+ 1 40 ± 1

97 _+ 12 124 _+ 15 99 + 13

29 _+ 2 27 ÷ 2 33 _+ 2

20 ± 0 t 12 _+ 1 16 -+ I t

7.45 _+ .03t 7.28 _+ .02 7.29 + .02t

162 _+ 7 450 _+ 60 318 _+ 47

4.8 ± .4t 17.9 -4- 2 t 6.8 ± 2 t

200 (5)

0 30 60

128 + 57 _+ 122 _+

7 4 7

44 ± 1 29 ÷ 1 42 _+ 1

97 _+ 10 124 -4- 5 104 ± 13

34 + 1 27 _+ 3 40 + 2

21 _+ 0 t 11 + 1 17 ± I t

7.40 _+ .01t 7.23 _+ ,03 7,25 _+ .02t

176 _+ 10 562 _+ 49 312 _+ 36

4,7 + .4t 21.4 + l * t 5,2 ± .6t

300 (8)

0 30 60

132 + 8 50 ÷ 0 121 ± 11

41 _+ 1 28 -+ 2 38 _+ 3

107 -+ 15 118 -+ 11 92 + 9

36 -+ 1 26 ± 1 41 _+ 2

21 _+ 1" 10 + 1 15 _+ 2*

7.38 _+ .01t 7.17 ± .04 7.16 ± .06t

165 +_ 6 407 _+ 55 184 _+ 22

4.4 _+ .4t 23.2 _+ 2 t 5,2 _+ .6t

*P < .05 by Duncan's. t p < .01 by Duncan's. Physiologic and biochemical parameters (mean ± SEM) in fed rats just before (0 min), immediately after 30 minutes of ischemia (30 min), and after 30 minutes of recirculation (60 rain). Except where indicated, MABP, hematocrit, blood gases, pH, blood glucose, and serum lactate recovered to preischemic levels (0 min).

can's). In all i s c h e m i c - t r e a t m e n t groups, lactate was increased significantly at the end of i s c h e m i a (30 minutes) (Table 4). After t r e a t m e n t and reperfusion (60 minutes), lactate was decreased s i g n i f i c a n t l y in all ischemic-treatment groups except for rats t r e a t e d w i t h 25 m g / k g D C A (Table 4). To explore a possible dose-response effect, percent changes within treatm e n t g r o u p s were c a l c u l a t e d and comparisons were made among treatment groups. From 0 to 30 minutes, in b o t h c o n t r o l and i s c h e m i c rats, there were no significant differences in t h e p e r c e n t c h a n g e in l a c t a t e among different t r e a t m e n t groups. After treatment, there were significant differences in the p e r c e n t decrease from 30 to 60 minutes among treatment groups in both the control and i s c h e m i c groups (Figure 1). For control and ischemic rats, the percent decrease in lactate was greatest in rats treated with 200 and 300 rag/ kg (Figure 1). Mean percent changes in lactate among dose groups in both control and i s c h e m i c rats were related logarithmically to dose (r = .91 and .95, respectively). There was no effect from the anes18:11 N o v e m b e r 1989

thetic, surgical procedures, sham ischemia, or D C A t r e a t m e n t at any dose on blood glucose in the controls (Table 3). Blood glucose in ischemic rats increased significantly (P < .01, ANOVA) in response to shock (Table 4). With or w i t h o u t treatment, glucose dropped and was not significantly different from baseline (0 minutes) in all ischemic groups except the 100 and 200 m g / k g t r e a t m e n t groups (Table 4). There were no differences in percent changes in either control or ischemic rats a m o n g all doses of DCA. At the end of i s c h e m i a , 12 rats were acidotic. In the two untreated acidotic rats, pH increased in one and decreased in the other. Of the ten acidotic rats treated with DCA, pH increased in six and decreased in four. Of the 18 nonacidotic ischemic rats, two of four evidenced an increase in pH; in the other two, pH continued to decrease. In the 14 nonacidotic ischemic rats that received DCA, pH increased in eight and decreased in six. Overall, these results indicated that approximately 50% of acidotic and 50% of nonacidotic rats showed an i n c r e a s e in pH, r e g a r d l e s s of whether treated with DCA. Annals of Emergency Medicine

Lactates after ischemia were higher in acidotic compared with nonacidotic rats. After 30 minutes of reperfusion, l a c t a t e s in n o n a c i d o t i c rats were at baseline (0 minutes) regardless of whether they had been treated with D C A (Figure 2). In contrast, acidotic rats treated with D C A had significantly lower lactates than in untreated acidotic rats (Table 5). Levels of lactate in acidotic rats approached t h o s e in n o n a c i d o t i c rats o n l y at higher doses of D C A (Figure 2). Percent decreases in lactate of acidotic and nonacidotic ischemic rats were logarithmically related to dose (r = .95) (Figure 3). In the previous study, fasted rats were t r e a t e d o n l y w i t h 25 m g / k g DCA; 7 therefore, this comparison includes only data from fed rats treated with 25 mg/kg. When fed rats were compared with fasted rats, there was no difference in the percent change in lactate during ischemia in those that were acidotic (Table 5). N o n acidotic fed rats evidenced a greater increase in lactate than did nonacidotic fasted rats (Table 5). W i t h o u t treatment, changes in lactate in fed and fasted rats were variable, correlating with the acidotic rather than 1166/55

HYPERLACTATEMIA Dimlich et al

FIGURE 2. Comparison of serum lactate '(~mol/mL) after 30 m i n u t e s of r e p e r f u s i o n in a c i d o t i c a n d nonacidotic fed rats after treatment with D C A (0, 25, 50, 100, 200, and 300 mg/kg) after 30 m i n u t e s of ischemia. Note that levels in fed acidotic rats were higher after ischemia and res p o n d e d m o r e to changes in dose than fed nonacidotic rats. FIGURE 3. Percent decrease in ser u m l a c t a t e in a c i d o t i c a n d nonacidotic ischemic fed rats treated after 30 m i n u t e s of i s c h e m i a w i t h D C A (25, 50, 100, 200, and 300 rag~ kg) that was followed by 30 m i n u t e s of reperfusion. Note that the percent d e c r e a s e in n o n a c i d o t i c was less than in acidotic rats; however, the responses for D C A doses (25 to 300 m g / k g ) were l o g a r i t h m i c in both cases (r = .95). the nutritional state of the rat (Table 5). In fed rats, the percent decrease was unaffected by D C A t r e a t m e n t (Table 5). In fasted rats, D C A induced a significantly increased reduction in lactate in rats that were acidotic and a significantly decreased reduction in nonacidotic rats (Table 5). Changes in blood glucose in acidotic and nonacidotic rats depended on w h e t h e r they were fed or fasted (Table 6). In fed rats, the p e r c e n t changes in blood glucose during ischemia were significantly greater in acidotic than in nonacidotic rats (Table 6). This relationship was reversed in fasted rats where blood glucose decreased in acidotic and increased in nonacidotic rats (Table 6). Treatment with D C A did not affect the glucose response of fed or fasted rats regardless of whether they were acidotic or nonacidotic (Table 6). DISCUSSION In 1925, Clausen reported that children in h y p o v o l e m i c shock exhibit an increase in serum lactate. 2~ The clinical relevancy of this observation became apparent when in 1964 it was noted that there was a high inverse correlation b e t w e e n arterial blood lactate levels and survival. 2 Because the degree of hyperlactatemia, regardless of carbon dioxide tension, ref l e c t s the s e v e r i t y of t i s s u e hypoxia, 22 the level of serum lactate is a valuable prognosticator of survival for those clinical states associated with a perfusion deficit. 23 Survival 56/1167

40 Nonaoldotio t77] Acidotic

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does n o t appear to c o r r e l a t e w i t h blood pressure or pH. However, ser u m lactate and serial determinations of arterial blood lactate have been c o n s i d e r e d i m p o r t a n t n o t o n l y in prognosticating survival but also in evaluating the effectiveness of treatment. 22 It is unclear w h e t h e r peak concentration or the ability to clear lactate progressively during therapy is the important determinant for this prognosis. 23 A l t h o u g h this s t u d y did n o t analyze survival, several observations were made regarding peak concentrations and the clearance of lactate from the serum that are applicable to the performance and interpretation of Annals of Emergency Medicine

future studies on the treatment and survival of shock. Other influences on o u t c o m e (ie, the degree of acidosis, drug dose, regimen, mechanism, and temporal and interspecies variability) also are discussed. In our study, the increase in serum lactate did not correlate with the increase in blood glucose (ie, substrate availability). The degree of elevation of serum lactate can be variable and depend on the presence and extent of underlying pathology (eg, liver disease), type and degree of shock, and substrate availability. ~3 With the use of h e a l t h y rats, it is a s s u m e d that there was no underlying pathology. However, the effect of the degree of 18:11 November 1989

TABLE 5. Percent changes (mean) in serum lactate after ischemia with and

without DCA treatment (25 mg/kg) in ,fed and fasted, acidotic and nonacidotic rats

Ischemic Experimental Subgroups

% Change With Ischemia (0 to 30 min) (N)

Fed acidotic Fasted acidotic* Fed nonacidotic Fasted nonacidotic* *Data from previous study.7 tp < .05 by Dunn's.

+446 +414 +381t +2251-

(11) (18) (17) (14)

% Change Without Treatment (30 to 60 min) (N) -36 -35t -66 -45t

(2) (6) (4) (5)

% Change With DCA Treatment (30 to 60 min) (N) -33 -63t 50 -131-

(2) (5) (4) (3)

TABLE 6. Percent changes (mean) in blood glucose after ischemia with and

without DCA treatment (25 mg/kg) in fed and fasted, acidotic and nonacidotic rats

Ischemic Experimental Subgroups

% Change With Ischemia (0 to 30 min) (N)

Fed acidotic + 2 0 9 t (12) Fasted acidotic* - 2 6 t (12) Fed nonacidotic + 172t (18) Fasted nonacidotic* +141- (14) *Data from previous study.7 tp < .05 by Dunn's.

shock on s e r u m lactate levels was ilIustrated. Before s h a m or real ischernia, s o m e l a c t a t e s w e r e at or j u s t above n o r m a l (ie, > 5 ~ m o l / m U ) . This s l i g h t e l e v a t i o n p r o b a b l y w a s due to t h e stress (shock) of surgery because t h e s e v a l u e s i n c o n t r o l s dropped during s h a m i s c h e m i a and sham reperfusion. The effect of substrate availability on lactate p r o d u c t i o n is discerned by comparing results in fasted rats from previous studies 7 w i t h those in ad libitum fed r.ats from our study. After ischemia, blood glucose was significantly h i g h e r in fed t h a n in fasted rats. However, acidotic rats, b o t h fed with elevated blood glucose and fasted w i t h n o n e l e v a t e d blood glucose, exhibited h y p e r l a c t a t e m i a . These results s u b s t a n t i a t e the i n a p p r o p r i a t e use of blood glucose as an indicator of substrate availability for attainable 18:11 November 1989

% Change Without Treatment (30 to 60 min) (N) -18 +14 -51 +14

(2) (6) (4) (5)

% Change With DCA Treatment (30 to 60 min) (N) -43 +26 -32 +8

(3) (5) (2) (3)

peak lactate concentration. These data are in agreement w i t h the finding that only one third of the l a c t a t e p r o d u c e d in a c a n i n e shock m o d e l can be traced to the anaerobic b r e a k d o w n of b l o o d g l u c o s e . 24 Instead, the m a j o r i t y of s e r u m lactate in h y p o x i c a c i d o s i s is s u p p l i e d by s k e l e t a l m u s c l e 2 4 , 25 a n d g u t . 2s Therefore, except possibly under conditions of e x t r e m e depletion (eg, starvation), the availability of blood glucose as s u b s t r a t e does n o t s e e m to play a major role in the degree of elev a t i o n of s e r u m l a c t a t e a c h i e v e d in shock. A t a n y dose, D C A did n o t affect t h e g l y c e m i c l e v e l s (ie, s u b s t r a t e a v a i l a b i l i t y ) in o u r s t u d y . P r e v i o u s studies w i t h D C A in d i a b e t i c 2 6 y or f a s t e d r a t s 28,29 r e s u l t e d i n h y p o g l y c e m i a that apparently was due to an i n h i b i t o r y action of this drug 3o or

Annals of Emergency Medicine

its m e t a b o l i t e s 3~ on h e p a t i c glucon e o g e n e s i s . R a t s in o u r p r e v i o u s s t u d y were n o t fasted long e n o u g h for D C A to h a v e t h i s effect. 7 T h e lack of effect of DCA, even at higher doses, on blood glucose in fed rats in o u r s t u d y is i n a g r e e m e n t w i t h results from numerous other studies 3°,32 and suggests that no dose of D C A decreases lactate by affecting t h e g l u c o s e s u p p l y in t h i s experiment. O n e o b s e r v a t i o n in this s t u d y as well as in our p r e v i o u s s t u d y 7 was t h a t o n l y s o m e of t h e h y p e r l a c t a t e m i c i s c h e m i c rats were acidotic. Because the degree of elevation of ser u m lactate a m o n g i s c h e m i c rats in this study was variable and not dep e n d e n t on blood glucose availability, was it related to the degree of aci d e m i a t h a t developed? A f t e r ischemia, lactate was higher in rats that w e r e a c i d o t i c t h a n in n o n a c i d o t i c rats (except for t w o rats). T h i s acidosis was metabolic, not respiratory, b e c a u s e v e n t i l a t i o n was c o n t r o l l e d during this e x p e r i m e n t and the only change in P c o 2 was a decrease that returned toward n o r m a l during reperfusion. ~ Therefore, this e x p e r i m e n t a c t u a l l y was designed to i n c l u d e a m e t a b o l i c acidosis and prevent a respiratory acidosis. The observation that acidotic rats a l m o s t always had the highest s e r u m lactates confirms the success of this e x p e r i m e n t a l design. Our study showed that D C A doses of 50 m g / k g or m o r e induce a m o r e p r o f o u n d decrease in s e r u m l a c t a t e than no t r e a t m e n t or 25 m g / k g DCA. T h e c l i n i c a l r e l e v a n c y of t h e s e results is that a d m i n i s t r a t i o n of higher doses reduced m e a n s e r u m lactate to values that were closer to the critical t h r e s h o l d of 5 ~xmol/kg t h a n w h e n there was no t r e a t m e n t or a dose of 25 mg/kg. T h i s suggests t h a t D C A doses of more than 25 m g / k g m a y be beneficial in survival because s e r u m lactates have been shown to correlate directly w i t h that parameter. 2 Although the mean values were lower for rats receiving D C A doses of m o r e than 25 rng/kg, they were not s t a t i s t i c a l l y lower. However, as previously discussed, the degree of elevation in lactate during i s c h e m i a was variable in our study. Could that variation in elevated values be m a s k ing a m o r e d r a m a t i c response? W h e n e x a m i n i n g o u t c o m e , if the s t a r t i n g values (ie, baselines) are variable, the

1168/57

HYPERLACTATEMIA Dimlich et al

differences in measured values with time m a y not be as revealing as percent change differences. In fact, in a recent clinical study, the percent decrease in lactate correlated with survival. 33 Therefore, for our study, the drug effect also was analyzed by calculating percent change over time. S t a t i s t i c a l a n a l y s i s of p e r c e n t changes s h o w e d t h a t the effect of D C A was significant at the higher doses of 200 and 300 m g / k g w h e n compared with a dose of 25 m g / k g and that the dose-response was typical for drugs (ie, logarithmic in nature). Because there was a relationship between acidemia and lactatemia, it was logical to explore possible effects of acidemia on the clearance of lactate in our study. In untreated acidotic rats, the percent reduction in lactate was approximately half that in untreated nonacidotic rats. This m a y be related to the fact that lactate uptake by the liver is inhibited by a low pH.34, 35 However, the difference in the percent decrease between the two groups was not as pronounced in rats receiving DCA, especially at doses of more than 25 mg/kg. The higher the dose of DCA, the lower the lactate and the greater the percent response. DCA, by some u n k n o w n m e c h a n i s m that also is dose-dependent, m a y offset the adverse effect that pH has on lactate clearance. With the limited number of acidotic rats and nonacidotic rats that were treated with higher doses in our present study, we cannot be certain but, based on these preliminary data, can suggest that higher doses of D C A are more effective in acidotic t h a n in n o n a c i d o t i c rats. As M i z o c k states and as we show in this study and in our previous study, failure to stratify a patient 23 or experimental population 7 may result in some variability in peak lactate concentrations, 23 in response to therapy, and, therefore, in the interpretation of results. These factors must be considered when interpreting experimental data and m a y be the reason for controversial results a m o n g s o m e of the t h e r a p y studies. 23 The failure of a dose of 25 mg/kg D C A to evoke a significant change substantiated our previous results in fed rats. 7 An inability to resolve elevated levels of serum lactate m o s t c o m m o n l y results from underuse of lactate or related metabolites, espe58/1169

cially pyruvate3, ~3 Kidney and liver are major sites for lactate u s e J Other than at very high blood levels when a significant a m o u n t may be excreted in the urine, the sole method of removing lactate is by the oxidation to its precursor, pyruvate. 36 In fact, lactic acidosis can be considered a disorder of pyruvate metabo l i s m ) This s t a t e m e n t is the theoretical basis for the use of D C A in the t r e a t m e n t of h y p e r l a c t a t e m i a that is a marker for lactic acidosis.1 DCA, by s t i m u l a t i n g the p y r u v a t e dehydrogenase enzyme complex (PDHC), increases the flux of lactate t h r o u g h p y r u v a t e i n t o t h e tric h l o r o a c e t i c a c i d (TCA) c y c l e . 31 However, this flux is dependent on aerobic c o n d i t i o n s t h a t w o u l d be limited during hypoxia 31 or poor tissue oxygenation as a result of inadequate blood f l o w ) This i m p o r t a n t factor m u s t be considered when int e r p r e t i n g data f r o m s t u d i e s w i t h D C A because it m a y be the reason for controversial results among some of these experiments. 37,38 In this study, w h e r e reperfusion was allowed and the tissue was not deprived entirely of its oxygen supply, D C A at higher doses was effective in l o w e r i n g s e r u m l a c t a t e to levels below those attained with no treatment or a dose of 25 mg/kg. This s t u d y s h o w e d a log-related, dose-dependent, D C A - m e d i a t e d decrease in s e r u m lactate in fed rats that was the same under either control or ischemic conditions. This response also was l o g a r i t h m i c in isc h e m i c rats w h e t h e r they were acidotic or nonacidotic. The logarithmic nature of this response is consistent with a receptor-mediated event and is similar to the response of PDHC to D C A in rat brain. 39 Because the doseresponse of s e r u m lactate to D C A was logarithmic in both acidotic and nonacidotic rats, a low pH did not appear to adversely influence the effect of D C A on PDHC. A l t h o u g h brain, hepatic, kidney, and m u s c l e P D H C a c t i v i t y were n o t m e a s u r e d in our study, these results suggest that the dose-response effectiveness is mediated through the enzymatic activity of PDHC (ie, the metabolism of lactate in at least one if not all of these organs). T h e r e t u r n of blood pressure to baseline values in the rats treated with D C A doses of more than 25 mg/ kg suggests a possible role for higher Annals of Emergency Medicine

doses of D C A in blood pressure stabilization. Because the pressure in all rats was more than 70 m m Hg, this difference m a y not be clinically significant. However, it is a positive effect and m a y relate to other studies that noted improvements in cardiac index, MABP, or both.ll,]2,15,33, 4° T h e lack of effect at 25 m g / k g in these e x p e r i m e n t s agrees w i t h our previous studies 6-1o and m a y relate to the data from other studies that have reported that neither cardiac index nor MABP was i n f l u e n c e d by D C A treatment33,14 Again, part of the controversy in results m a y be due to an interpretation of the data. D C A affects m a n y s y s t e m s , b o t h d i r e c t l y and indirectly. 36 In the cardiovascular system, D C A may improve cardiac muscle f u n c t i o n directly. 12 I n d i r e c t l y , this could i m p r o v e h e m o d y n a m i c s and, thereby, increase tissue perfusion, decrease anaerobic metabolism, and facilitate lactate uptake and use by the liver u-13 (ie, offset the low pH inhibition of lactate clearance). It is difficult to assign a clinical or i n v i v o response to a specific mechan i s m u n l e s s the specific effect is m e a s u r e d in t h a t s y s t e m . In this study, MABP was the only parameter m e a s u r e d . MABP does n o t necessarily correlate with cardiac perform a n c e 2s or reflect changes in myocardial pH or function. Because card i a c i n d e x , m y o c a r d i a l p H , or enzyme analyses were not performed in this study, effects of D C A on myocardial performance and hemodynamics cannot be ruled out by the results of this study. Another possible influence on cardiac f u n c t i o n w o u l d be the osmolarity of D C A solutions. Hyperosmolar solutions up to 400 m o s m / m L m a y improve left ventricular performance. 41 The osmolarity of D C A (/> 50 mg/kg) is more than 400 m o s m / m L ( u n p u b l i s h e d data, R u t h VW Dimlich) and, therefore, probably unrelated to the effects observed. In addition, because osmolarity is directly p r o p o r t i o n a l to c o n c e n t r a t i o n , expected dose effects due to osmolarity m i g h t be correlated in a linear, not logarithmic, fashion. D C A also s t i m u l a t e s significant n a t r i u r e s i s and diuresis, and improved hemodynamics could sustain this effect. 12 At high blood levels, the k i d n e y n o r m a l l y can excrete large a m o u n t s of lactate; 36 therefore, the 18:11 November 1989

influence of D C A on renal salt handling in t h i s s t u d y c a n n o t be excluded. With the apparent species variability in the p h a r m a c o k i n e t i c s and pharmacodynamics of DCA, 42,43 it is d i f f i c u l t to c o m p a r e d o s e e f f e c t s among species. However, s o m e corr e l a t i o n s a p p e a r to e x i s t . In o u r study, the percent change at 50 m g / kg D C A was 20% m o r e than a dose of 25 mg/kg. D C A was tested in 11 healthy, fasted h u m a n subjects w i t h the same results. 32 In a study of the dose effect of D C A on P D H C a c t i v i t y in the b r a i n t h a t t e s t e d a range of doses s i m i l a r to ours, t h e p e r c e n t change o v e r t h e e n t i r e r a n g e w a s 30% 39 compared w i t h our change of 40%. The narrow range of percent increase in effect (20% to 40%) over the entire dose range in these studies suggests that there is a l i m i t to the degree of change that can be elicited by an increase in drug concentration. T h a t r e s p o n s e is t y p i c a l of a n e n z y m e - m e d i a t e d r e a c t i o n in w h i c h a m a x i m a l portion of the e n z y m e is a l r e a d y in its a c t i v e s t a t e , w h i c h limits a further increase in its activity. In contrast to oral dosage, 44 IV adm i n i s t r a t i o n of D C A p r o d u c e s o n l y mild c o m p l a i n t s in h u m a n beings 4° with no evidence of t o x i c i t y 33 and no effects w h e n given in high doses to rats. 44 Therefore, IV a d m i n i s t r a t i o n of D C A has been deemed safe 4° and has been used in recent experiments, both clinical 4o and laboratory, 32 that have tested this drug. The analysis of the effectiveness of DCA appears to rely on not only h o w but w h e n it was administered, especially as it relates to oxygen availability. For example, in cases where DCA has been effective in lowering the h y p e r l a c t a t e m i a of e n d o t o x i n shock a n d i m p r o v f n g s u r v i v a l , t h e subjects were pretreated. 4s4z However, w h e n t r e a t m e n t was a d m i n i s tered before hemorrhagic shock, there was no effect on the extent of lactate elevation or acidemia achieved6, 37 u n t i l after r e p e r f u s i o n had b e e n e s t a b l i s h e d . 6 , s , 10 In t w o studies where D C A had no effect on survival, good t i s s u e p e r f u s i o n was never reestablished in one, 4s and animals were treated during severe h e m orrhage 49 w h e n oxygen a v a i l a b i l i t y would be l i m i t e d in the other. M u l t i p l e - t r e a t m e n t regimens need appropriate s i n g l e - t h e r a p y controls. 18:11 November 1989

A third study of irreversible hemorrhagic shock reported i m p r o v e d survival w i t h DCA; however, D C A was administered with fructose-l,6-dip h o s p h a t e {FDP), a glycolytic metabolite of glucose. 5o Because there were no t r e a t m e n t c o n t r o l groups (ie, no animals treated w i t h either D C A or FDP alone), it is i m p o s s i b l e to assign a role for each t r e a t m e n t in improving s u r v i v a l . T h e p r o b a b l e i m p o r tance of h o m e o s t a t i c control of glyc e m i a to s u r v i v a l f r o m s h o c k has b e e n d i s c u s s e d . 5~ S u p p o r t i n g t h i s concept, a r e c e n t s t u d y d e t e r m i n e d that glucose administration, when appropriately t i m e d and controlled in amount, arrests the d e c o m p e n s a t o r y phase of hemorrhagic shock and imp r o v e s s u r v i v a l , s2 T h e r e f o r e , b o t h D C A and FDP could have beneficial effects in t h e t r e a t m e n t of h e m o r rhagic shock w i t h adequate recirculation. In o u r s t u d y , a n i m a l s p r o b a b l y were not followed long enough to see an i m p r o v e m e n t in p H or H C O f . N o t only is the t i m i n g of t r e a t m e n t i m p o r t a n t but the length of t i m e that the subject is followed can be critical to w h e t h e r enough t i m e has been allowed for the effect to have occurred. In studies where h y p e r l a c t a t e m i a or the degree of hypoperfusion was not severe and the animals were followed for a longer period, t~-lS,s° D C A was effective in lowering lactate and improving pH. In a single clinical trial in w h i c h patients also were followed over a longer t i m e interval, hypotensive subjects were treated for at least 24 h o u r s w i t h s o d i u m bicarbonate, w h i c h did not effect a Correction of the acidosis or i m p r o v e blood pressure. 4o W h e n t h e s e p a t i e n t s w e r e treated w i t h DCA, lactate decreased in six of seven patients w h o were acidotic. One p a t i e n t who had an init i a l s e r u m l a c t a t e of 33 F m o l / m L survived to be discharged. The other patients died, not from the acidosis but from their underlying disease states. 4o In a subsequent study, 26 of 34 patients w i t h lactic acidosis m o s t comm o n l y due to h y p o t e n s i o n or sepsis s h o w e d a 20% d e c r e a s e in a r t e r i a l l a c t a t e w i t h i n six h o u r s after treatm e n t w i t h DCA. In the responders, l a c t a t e d e c r e a s e d f r o m 12.7 to 3.3 tLmol/mL, and H C O f and arterial p H increased from 13.9 vtmol/mL and 7.27 to 20.4 F m o l / m L and 7.42, respectively. 33 T h e l e n g t h of survival Annals of Emergency Medicine

correlated w i t h the percent change in t h e s e p a r a m e t e r s . 33 Therefore, it is necessary to follow the e x p e r i m e n t a l a n i m a l or patient long enough to allow sufficient t i m e for the expected effect of the t r e a t m e n t to occur. CONCLUSION Serum lactate levels are a result of production, m e t a b o l i s m , and disposition of that m e t a b o l i t e by several organs, including the liver, kidney, and m u s c l e . D a t a from this s t u d y indicate t h a t t h e greater a v a i l a b i l i t y of blood glucose as s u b s t r a t e does n o t play a major role in the degree of elev a t i o n of s e r u m l a c t a t e in s h o c k . T r e a t m e n t w i t h D C A at d o s e s of m o r e t h a n 25 m g / k g i n c r e a s e d the r a t e of r e s o l u t i o n of s e r u m l a c t a t e b u t n o t by l i m i t i n g b l o o d g l u c o s e availability. A l t h o u g h not necessarily r e l a t e d to c a r d i a c f u n c t i o n , b l o o d pressure had returned to p r e i s c h e m i c l e v e l s w i t h h i g h e r d o s e s of D C A . Therefore, c a r d i o v a s c u l a r effects of D C A cannot be ruled out. The same can be stated for k n o w n effects of D C A on s k e l e t a l m u s c l e and k i d n e y that were not m e a s u r e d in this study. However, the log-closerelated effect of D C A on the resolution of serum lactate over a l i m i t e d percent response range suggests that this effect p r o b a b l y is m e d i a t e d by the activation of P D H C that w o u l d p r o m o t e the m e t a b o l i s m of lactate. By some u n k n o w n m e c h a n i s m , doseresponse to D C A was m o r e profound in severely acidotic rats. Critical to proper interpretation of s t u d i e s e x a m i n i n g t h e e f f i c a c y of D C A t r e a t m e n t is an a w a r e n e s s of the degree of a c c o m p a n y i n g acidosis, success of reperfusion, and length of observation of the subject as well as the i n f l u e n c e of a d j u n c t i v e t h e r a p y and additional pathology. Equally imp o r t a n t to a fair analysis of the effect i v e n e s s of D C A t h e r a p y is k n o w l edge about the species and dose varia b i l i t y as w e l l as h o w a n d w h e n D C A was administered. High s e r u m l a c t a t e is a p r o g n o s t i c a t o r of p o o r survival in shock, and the correction of acidosis is i m p o r t a n t to m a i n t a i n adequate cardiovascular function. Therefore, future studies s h o u l d inv e s t i g a t e l o n g - t e r m effects of h i g h d o s e s of D C A on p H a n d h e m o d y n a m i c s as well as serum lactate. The authors thank Vicky Eymer for her excellent technical assistance in the labo1170/59

HYPERLACTATEMIA Dimlich et al

r a t o r y a n d J e r r i s R H e d g e s , MS, M D , FACEP, for his advice c o n c e r n i n g the statistical analyses and p r e s e n t a t i o n of these data.

17. Brown GK, Haan EA, Dirby DM, et al: "Cerebral" lactic acidosis: Defects in pyruvate metabolism with profound brain damage and minimal systemic acidosis. Eur J Pediatr 1988; 147:10-14.

1. Kreisberg RA: Lactate homeostasis and lactic acidosis. Ann Intern Med 1980;92:227-237.

18. Dimlich RVW, Timerding BL, Kaplan J, et al: Effects of sodium dichloroacetate dose. Brain metabolites associated with cerebral ischemia (abstract). Ann Emerg Med 1989;18: pp 1172-1180.

2. Peretz DI, McGregor M, Dossetor JB: Lacticacidosis: A clinically significant aspect of shock. Can Med Assoc J 1964;90:673-675.

19. Hollander M, Wolfe DA: Nonparametric Statistical Methods. New York, John Wiley and Sons, 1973.

3. Broder G, Weil MH: Excess lactate: An index of irreversibility of shock in human patients. Science 1964;143:1457-1459.

20. Duncan DB: Multiple range and multiple P tests. Biometrics 1955;11:1-42.

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Annals of Emergency Medicine

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18:11 November 1989