Bicarbonate attenuates intracellular acidosis

Acta Anaesthesiol Scand 2002; 46: 579–584 Printed in Denmark. All rights reserved

Copyright C Acta Anaesthesiol Scand 2002 ACTA ANAESTHESIOLOGICA SCANDINAVICA

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Bicarbonate attenuates intracellular acidosis H. B. NIELSEN2, L. HEIN2, L. B. SVENDSEN2, N. H. SECHER2 and B. QUISTORFF1 1

NMR Center, the Panum Institute and 2the Copenhagen Muscle Research Center, Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark

Background: 'This study was prompted by concern that administration of bicarbonate for correction of lactate acidosis aggravates a low intracellular pH (pHi). In healthy subjects we evaluated skeletal muscle pHi using 31P-magnetic resonance spectroscopy during 5-minute rhythmic handgrip to provoke intracellular acidosis. Methods: Subjects were randomized to treatment with bicarbonate or saline infused intravenously in a cross-over study design with 1 h between trials. Results: In response to rhythmic handgrip, muscle venous O2 hemoglobin saturation decreased from 51 ∫ 4% to 36 ∫ 2% and lactate increased from 1.0 ∫ 0.1 to 4.9 ∫ 0.5 mmol/l with a reduction in pH from 7.43 ∫ 0.01–7.23 ∫ 0.01 (P⬍0.05). pHi decreased from 7.06 ∫ 0.02–6.36 ∫ 0.08 (P⬍0.05). Infusion of bicarbonate increased the arterial blood concentration from 26 ∫ 1 to 39 ∫ 1 mmol/l (P⬍0.05). The arterial CO2 partial pressure decreased from 5.6 ∫ 0.2 to 5.2 ∫ 0.3 kPa during rhythmic handgrip, whereas it increased to 5.9 ∫ 0.2 kPa (P⬍0.05) during infusion of

bicarbonate. Bicarbonate treatment also increased pH of arterial and venous blood (7.55 ∫ 0.01 vs. 7.44 ∫ 0.02 and 7.31 ∫ 0.01 vs. 7.23 ∫ 0.02, respectively; P⬍0.05). In the last min of rhythmic handgrip the decrease in pHi was attenuated by the administration of bicarbonate (6.60 ∫ 0.11 vs. 6.40 ∫ 0.12; P⬍0.05). Conclusion: During exercise-induced metabolic acidosis, intravenous administration of bicarbonate increased the buffering capacity of blood and attenuated the decrease in intracellular muscle pH, although there was a small increase in the arterial carbon dioxide pressure.

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cm [median with range]) participated in the study as approved by the Ethics Committee of Copenhagen (KF 01-276/99).

develops when O2 delivery by the circulation of blood does not meet the tissue demand (1). Such metabolic acidosis may be corrected by intravenous infusion of sodium bicarbonate to enhance the buffering capacity of blood. However, treatment with bicarbonate has been speculated to aggravate intracellular acidosis (2) depending on the adequacy of the circulation versus elimination of CO2 by ventilation. Intense muscular work is associated with lactate production and the subsequent reduction in muscle pH (pHi) can be determined non-invasively by nuclear magnetic resonance (3, 4). Using phosphorus-31 nuclear magnetic resonance (31P-MRS), we assessed pHi of the forearm flexor muscles during rhythmic handgrip with and without infusion of bicarbonate. ACTIC ACIDOSIS

Methods Nine healthy male students (age 24 (20–29) years, bodyweight 76 (72–82) kg, and height 183 (177–194)

Received 18 June, accepted for publication 13 December 2001

Keywords: bicarbonate; buffer; intracellular acidosis. c Acta Anaesthesiologica Scandinavica 46 (2002)

Protocol Intracellular muscle acidosis was established during rhythmic handgrip. Prior to the main study, subjects performed rhythmic handgrip at different percentages of the maximal voluntary contraction force (MVC) without infusion of bicarbonate or saline (Fig. 1) to familiarize the subjects with the experimental procedures and to establish the intensity that would elicit a significant decrease in pHi. These pilot studies demonstrated that 5-minute rhythmic handgrip for 2 s at 40% MVC followed by 1 s of relaxation caused a significant drop in pHi. Also it was demonstrated that the reduction in pHi was consistent and reproducible when the protocol was repeated after 1 h. Thus, this work intensity was chosen for the main study. Muscle contractions were performed using a modi-

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fied pneumatic ergometer with automatic return of the handle to the resting position. A non-magnetic strain gauge dynamometer connected to a transducer (PFN Teknik, Copenhagen, Denmark) determined the force of the handgrip. The subjects remained seated with their arm fully extended, whereby the flexor group was covered by the MRS coil. Maximal voluntary contractions were performed three times separated by about 30 s and the largest contraction was chosen to represent MVC. Thereafter, the subjects performed rhythmic handgrip and the protocol was repeated after a recovery period of 1 h.

Bicarbonate On the day of the experiment, the subjects were randomized in a single blinded fashion to receive a sodium-bicarbonate solution (1 mol/l) or a similar volume of saline (1 mol/l). It was difficult to establish an adequate dose of bicarbonate for all subjects due to different body size and also because pHi did not decrease to the same extent during rhythmic handgrip in all subjects. Furthermore, severe hypercapnia might influence the results. Therefore, one subject was admitted to an infusion rate of 10 ml/min during exercise, one subject received 20 ml/min and seven subjects 30 ml/min. A priming dose of half the infusion rate during exercise started 2 min before rhythmic handgrip and the initial infusion rate was maintained in the first 5 min of the recovery. Thereafter, infusion of bicarbonate or saline was stopped. The arm re-

mained in the magnet for an additional 5 min to allow for 31P-MRS measurements. 31

P-MRS

A Vivospec spectrometer (Otsuka Electronics, Japan) was interfaced to an 80-cm long, 26 cm bore, 2.9-T superconducting magnet (Magnex Scientific, Abingdon, UK) and homogeneity of the magnetic field was secured (4). Line width before experiments was ⬍0.5 parts per million. The 31P spectra were obtained at 49.83 MHz by single-pulse excitations (65 ms), and pulse power and width were optimized by the height of the phosphocreatinine peak. Data were collected in 2K points over 205 ms at a 6-second interpulse delay. Data acquisition was performed for 3 min at rest prior exercise, during exercise and 10 min into the recovery after exercise. All spectra were analyzed by applying exponential line broadening and muscle pHi was calculated according to Taylor et al. (5).

Blood sampling On the day of the experiment, a catheter (1.0 mm i.d.; 19 gauge) was inserted in the radial artery of the nondominant non-working arm and a second catheter was inserted retrograde into a cubital vein of the working dominant arm. A venous catheter was placed in the non-dominant arm for administration of bicarbonate or saline. Samples for blood gas variables and lactate in arterial and venous blood believed to drain the flexor muscle group were obtained at rest and during each min of rhythmic handgrip, as well as each min during the first 5 min of the recovery and 10 min after cessation of exercise. All blood samples were stored on ice and analyzed immediately thereafter using ABL-615 apparatus (Radiometer, Copenhagen, Denmark).

Statistics Data are expressed as mean with standard error. Comparisons among multiple samples were evaluated by the Friedman analysis of variance (SYSTAT, Evanston, IL). This test included the effect of rhythmic handgrip and comparisons between the two trials. Significant effects resulted in a Wilcoxon test by rank for locating pair-wise differences and a Pⱕ0.05 was considered to be statistically significant. Fig. 1 Pilot evaluation of different workloads (square, 20% of maximal voluntary contraction (MVC); triangle, 30% MVC; circle, 40% (MVC) on magnetic resonance spectroscopy determined pH of the forearm flexor group (pHi) at rest and during termination of rhythmic handgrip for 5 min. Each symbol represents one subject.

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Results Before exercise, blood gas variables (Table 1 and Fig. 2) and pHi (Fig. 3) were similar in both trials. During

Muscle pH and bicarbonate

rhythmic handgrip, muscle venous O2 hemoglobin saturation and O2 pressure became reduced (Table 1). Also base excess decreased (Table 1), while venous PCO2 increased and PaCO2 decreased only in the last min of rhythmic handgrip (Fig. 2). Venous HCO3– decreased during rhythmic handgrip and remained low into the recovery period (Fig. 2). Arterial HCO3– became reduced after rhythmic handgrip (Fig. 2). The concentration of lactate increased, whereby venous pH decreased with no significant change in arterial pH although it did become reduced after rhythmic handgrip (Fig. 2). The pHi demonstrated a progressive decrease to a lowest level in the last min of exercise (Fig. 3). One subject was able to work with a pHi below 6 through the last min of rhythmic handgrip and established a lowest value of 5.63. In the recovery period, pHi remained low in the first min and then increased progressively to establish the pre-exercise level 10 min after cessation of rhythmic handgrip (Fig. 3). Infusion of bicarbonate increased its concentration in both arterial and venous blood and increased the arterial CO2 pressure (Fig. 2). The venous CO2 pressure increased and reached similar values as in the control trial (Fig. 2). This was the case also for the arterial concentration of lactate, and venous lactate was significantly higher than with saline only in the last min of rhythmic handgrip (Fig. 2). During infusion of bicarbonate arterial pH increased and remained high even after the infusion was stopped (Fig. 2). Furthermore, the infusion prevented venous pH from becoming significantly reduced during rhythmic handgrip and it maintained venous pH above that in the control trial (Fig. 2). For pHi, taken as an average throughout rhythmic handgrip, there was no significant effect of bicarbonate. However, in the last min of rhythmic handgrip

the decrease in pHi was attenuated (Fig. 3). The recovery kinetic was similar in both trials.

Discussion This study demonstrates that during spontaneous ventilation in healthy subjects, appropriate use of bicarbonate for the treatment of lactate acidosis during rhythmic handgrip does not aggravate intracellular acidosis. Rather with the development of a low pHi, infusion of bicarbonate tended to increase pHi as was the case for pH of blood. This was the case with a small increase in the arterial carbon dioxide pressure. A clinical concern is that with infusion of bicarbonate an increase in PaCO2 may increase intracellular CO2 partial pressure and thereby reduce pHi. This may be the case in particular if the treatment of acidosis is accompanied by an inadequate increase in ventilation. We aimed at a model where tissue becomes ischaemic due to a combination of a high level of O2 demand and a limited O2 supply. During rhythmic handgrip we combined a two-second intense static muscle contraction with one-second relaxation and subjects repeated this cycle for five min. By doing so O2 consumption of muscle increases and with a limited supply of O2 anaerobic metabolism made pHi decrease (6). Infusion of bicarbonate attenuated the decrease in pHi at the end of the rhythmic handgrip protocol where pHi was the lowest. The concentration of bicarbonate increased by almost 15 mmol/l and although the drop in pHi at the initial stages of rhythmic handgrip followed a similar decline in bicarbonate and control trials, the plateau tended to be higher during exercise with infusion of bicarbonate. We ensured that the subjects maintained the same rhythmic handgrip

Table 1 Blood variables during rhythmic handgrip. Infusion of saline

BE (a) mmol/l BE (v) mmol/l SaO2 % SvO2 % PaO2 kPa PvO2 kPa

Infusion of bicarbonate

Rest

Exercise

Recovery

Rest

Exercise

Recovery

3.4 ∫ 1.1 3.7 ∫ 1.1 97.8 ∫ 0.4 50.7 ∫ 4.3 14.0 ∫ 0.5 4.1 ∫ 0.4

1.9 ∫ 1.2* 0.4 ∫ 1.1* 98.2 ∫ 0.3 35.8 ∫ 2.3* 15.5 ∫ 0.8* 3.5 ∫ 0.1*

0.8 ∫ 1.2* ª1.2 ∫ 1.1 97.4 ∫ 0.3 74.3 ∫ 3.7* 13.8 ∫ 0.5 6.0 ∫ 0.4*

2.6 ∫ 1.5 0.2 ∫ 0.7† 97.8 ∫ 0.0 47.1 ∫ 3.0 14.3 ∫ 0.3 3.6 ∫ 0.2

14.2 ∫ 1.0*† 9.4 ∫ 1.2*† 98.6 ∫ 0.0* 34.3 ∫ 2.2* 15.7 ∫ 0.5* 3.2 ∫ 0.1*

15.1 ∫ 1.7*† 9.1 ∫ 1.6*† 98.2 ∫ 0.0 64.1 ∫ 6.0* 14.0 ∫ 0.5 4.7 ∫ 0.5*

Values are means ∫ SEM. Blood is obtained at rest, in the last min of exercise and 5 min into the recovery period where infusion of bicarbonate was stopped. a, arterial blood; BE, base excess; PO2, oxygen partial pressure; SO2, oxygen saturation of haemoglobin; v, venous blood. *, different from rest; †, different from trial without bicarbonate; Pⱕ0.05.

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Fig. 2 Arterial (left panels) and venous (right panels) blood carbon dioxide pressure (PCO2), concentration of bicarbonate (HCO3–), lactate, and pH at rest, during and after rhythmic handgrip at 40% of maximal voluntary contraction with (filled circle) and without (open circle) intravenous infusion of bicarbonate. Values are mean with SEM. *, different values to rest; †, different from the trial with no infusion of bicarbonate, Pⱕ 0.05. Open circle, control; filled circle, bicarbonate.

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dium-free solution of tromethamine (THAM [12–14]); and another is a sodium bicarbonate and carbonate solution named Carbicarb (15). Both solutions limit CO2 generation and increase both the extra- and intracellular pH (2, 16, 17). However, in both intra- and extracellular compartments buffering following bicarbonate infusion may be more effective than with THAM (18). The present study demonstrates that infusion of bicarbonate also increases pHi even in the face of a small increase in the arterial CO2 pressure. Bicarbonate serves the purpose of enhancing the buffer capacity of blood to attenuate pH of the intracellular environment during exercise-induced metabolic acidosis.

References Fig. 3 Magnetic resonance spectroscopy determined pH of the forearm flexor group (pHi) at rest and during and after rhythmic handgrip at 40% of maximal voluntary contraction with (filled circle) and without (open circle) intravenous infusion of bicarbonate. Values are mean with SEM. †, different from the trial with no infusion of bicarbonate, PΩ 0.05. pHi decreased in response to rhythmic handgrip in both trials and remained reduced below the resting level throughout the recovery.

intensity in both trials and the pre-exercise level of pHi and pH of blood was not significantly different in the two trials. Intense rhythmic handgrip does not challenge the cardiopulmonary system in healthy subjects although infusion of bicarbonate induced a small increase in arterial PCO2. This may be related to a combination of a non-significantly elevated venous CO2 pressure and increased blood bicarbonate. It is considered that the dose of bicarbonate administered to the subjects is higher than that normally recommended to be infused to patients threatened by acidosis (7). In that case, ventilation may not be inadequate and also the circulation is affected. The mechanism by which an increase in the extracellular bicarbonate concentration attenuates a decrease in pHi is not known. The release of lactate from cells is partly by a pH sensitive lactate-proton translocation where a low pH supports its release from the muscle and the uptake by, e.g. erythrocytes, kidney, liver, muscle and brain (8). However, this mechanism may be dominated by lactate efflux that appears to be accelerated by an increase in the external buffer capacity as induced by the administration of bicarbonate (9–11). In the clinical setting, concern about decreasing pHi by infusion of bicarbonate has led to the use of alternative alkalinizing agents. One such agent is a so-

1. Gluck SL. Acid-base. Lancet 1998: 352: 474–479. 2. Adrogue´ HJ, Madias NE. Management of life-threatening acid-base disorders. First of two parts. N Engl J Med 1998: 338: 474–479. 3. Arnold DL, Matthews PM, Radda GK. Metabolic recovery after exercise and the assessment of mitochondrial function in vivo in human skeletal muscle by means of 31P-NMR. Magn Reson Med 1984: 1: 307–315. 4. Mizuno M, Secher NH, Quistorff B. 31P-NMR spectroscopy, rsEMG, and histochemical fiber types of human wrist flexor muscles. J Appl Physiol 1994: 76: 531–538. 5. Taylor DJ, Bore PJ, Styles P, Gadian DG, Radda GK. Bioenergetics of intact human muscle. A 31P nuclear magnetic resonance study. Mol Biol 1983: 1: 77–94. 6. Boushel R, Pott F, Madsen P, Rådegran G, Nowak M, Quistorff B et al. Muscle metabolism from near-infrared spectroscopy during rhythmic handgrip in humans. Eur J Appl Physiol 1998: 79: 41–48. 7. Myerburg RJ, Castellanos A. Cardiac arrest and sudden cardiac death. In: Braunwald E, ed. Heart disease – A textbook of cardiovascular medicine. Philadelphia: W. B. Saunders Company, 1997: 742–779. 8. Juel C. Lactate-proton cotransport in skeletal muscle. Physiol Rev 1997: 77: 321–358. 9. Hood VL, Schubert C, Keller U, Muller S. Effect of systemic pH on pHi and lactic acid generation in exhaustive forearm exercise. Am J Physiol 1988: 255: F479–F485. 10. Mason MJ, Mainwood GW, Thoden JS. The influence of extracellular buffer concentration and propionate on lactate efflux from frog muscle. Pflugers Arch 1986: 406: 472–479. 11. Nagesser AS, Van Der Laarse WJ, Iles RA. Lactate efflux from fatigued fast-twitch muscle fibers of Xenopus laevis under various extracellular conditions. J Physiol 1994: 481: 139–147. 12. Nahas GG, Sutin KM, Fermon C, Streat S, Wiklund L, Wahlander S et al. Guidelines for the treatment of acidaemia with THAM. Drugs 1998: 55: 191–224. 13. Nahas GG, Sutin KM, Fermon C, Turndorf H. More on acidbase disorders. N Engl J Med 1998: 339: 1005–1006. 14. Holmdal MH, Wiklund L, Wetterberg T, Streat S, Wahlander S, Sutin K et al. The place of THAM in the management of acidemia in clinical practice. Acta Anaesth Scand 2000: 44: 524–527. 15. Sun JH, Filley GF, Hord K, Kindig NB, Bartle EJ. Carbicarb: an effective substitute for NaHCO3 for the treatment of acidosis. Surgery 1987: 102: 835–839.

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H. B. Nielsen et al. 16. Bersin RM, Arieff AI. Improved hemodynamic function during hypoxia with Carbicarb, a new agent for the management of acidosis. Circulation 1988: 77: 227–233. 17. Kucera RR, Shapiro JI, Whalen MA, Kindig NB, Filley GF, Chan L. Brain pH effects of NaHCO3 and Carbicarb in lactic acidosis. Crit Care Med 1989: 17: 1320–1323. 18. Rothe KF, Diedler J. Comparison of intra- and extracellular buffering of clinically used buffer substances: tris and bicarbonate. Acta Anaesth Scand 1982: 26: 194–198.

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Address: Henning Bay Nielsen, M.D. Department of Anaesthesia 2041 Rigshospitalet Blegdamsvej 9 2100 København Ø Denmark E-mail: h.bay/dadlnet.dk