Oxygen consumption and circulatory arrest

Brit. J. Anaesth. (1971), 43, 1113

OXYGEN CONSUMPTION DURING CARDIOPULMONARY BYPASS WITHMODERATE HYPOTHERMIA IN MAN

BY

E. A. HARRIS, EVE R. SEELYE AND A. W. SQUIRE

SUMMARY

Oxygen consumption was measured during hypothermic total body perfusion in twenty-seven patients undergoing cardiac operations. In nine patients it was also measuredimmediately before induction of anaesthesia. Fourteen patients were kept at normaltemperature for from 5 to 17 minutes after bypass began; the rest were cooledimmediately to 30 °C. Oxygen consumption during bypass at normothermia, whetherbefore or after cooling, was 84 per cent of the pre-anaesthesia value, due possibly tothe effects of muscle relaxation. During hypothermia, patients who were cooledimmediately had an oxygen consumption which was about 15 per cent lower than thatfound in the patients with delayed cooling. Even in the latter group, oxygen con-sumption during hypothermia probably did not quite meet requirements, since it wasshown to be positively correlated with blood flow.

The adequacy of perfusion in all regions of thebody during extracorporeal circulation and hypo-thermia is variously judged by arteriovenousoxygen-content difference, by mixed venous oxy-gen pressure and by the concentration of lactate,"excess lactate" or lactate/pyruvate ratio in theblood. The reliability of any such criterion muststand or fall by its correlation with an independentcriterion of the adequacy of tissue perfusion. Inthe last analysis, the only available referencevalue is the whole-body oxygen consumption inrelation to the prevailing oxygen requirement ofthe tissues.

We have measured whole-body oxygen con-sumption under a variety of conditions in patientsduring cardiac operations with cardiopulmonarybypass, with the objects of (1) gaining informationon the relation between oxygen consumption andoxygen requirement and (2) obtaining data againstwhich other criteria of tissue perfusion can beassessed. In this paper we report our results onoxygen uptake (a) before anaesthesia, (b) duringbypass, both normothermic and hypothermic, withimmediate or delayed cooling and with varyingpump flow, and (c) in relation to body size.

METHODS E A . HARMS, M.D., PH.D., M.R.C.P., F.R.A.C.P.; EVE R.Twenty-seven patients were studied. Clinical and S E E L Y E > B.A., M.B., F.F.A.R.OS.; A W. SQUIRE, M.B.,

, \ .. v , . , , ™T » , F.F.A.R.A.C.S.; Department of Clinical Physiology, Greenother details are shown in table I. They formed Lane Hospital, Auckland, 3, New Zealand.

part of three successive experimental series whichdiffered in design.

Series I. Patients 1-7 have been described pre-viously (Harris, Seelye and Barratt-Boyes, 1970,patients 20, 16, 13, 12, 9, 8 and 5). Patients 1 and2 were kept at normal temperature, for 5 and 7minutes respectively, after cardiopulmonary by-pass was started, and were then cooled to 30° C.Patients 3-7 were cooled immediately. Duringhypothermia, flow was kept roughly constant ineach case at 2.0 l./min/m2 or more. These patientscould be described as having perfusions with"warm" or "cold" starts and constant flow.

Series II. Patients 8-18 all had "warm starts"lasting up to 17 minutes. During hypothermia,except in patient 18, pump flow was deliberatelyvaried at 20-minute intervals; each patient wasperfused at either two or three rates (around 50,60 and 75 ml/kg body weight/min). The orderof flow rates was varied (see table I). All but oneof the patients in this series thus had "warmstarts" and varied flows.

Series III. These studies were similar to thoseof series I except that a duplicate measurement ofoxygen uptake was made, in each patient, in a

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1114 BRITISH JOURNAL OF ANAESTHESIA

TABLE I

Clinical data on patients studied.

PatientNo.

Series I1234567

Series II89

101112131415161718

Series III192021222324252627

MSVHAVRTofFASVTA

Age,sex

27 M52 M54 M42 F66 M59 F42 F

64F61 M48 M56 M

M64 M60 M17 F39 M53 M33 M

57 M66 M67 M40 F54 M36 M27 M35 F66 M

Mitral

Operation

MSVHAVHAV, MSVHAV, MSVHAVHAVHAV

HAVHAVHPV (M)HAVHAVHAVHAVHAVRTofFHAVHAV

HAV, MV, TAHAVASVHPV(M)HAV (M)HAVHAVHPV (M), TAHAV

Starr valve.Homograft aortic valve.RepaiiAortic

Dura-tion ofwarmstart(min)

57-——_-

1112141513171312111212

12—-————-—

: Tetralogy of Fallot.Starr valve.

Tricuspid annuloplasty.

Dura-tion ofhypo-

thermia(min)

7550

137162719299

6666666071464132645068

707133725068264855

Measure-ments Dura-during tion ofhypo- bypass

thermia (min)

4256554

64565343654

642437233

HPV(M)

HAV(M)

MV

186121190224126134158

14516512212012910310386

136114132

16011175

12012211376

116108

Homograft

Lowesttemper-

ature

Flowduringhypo-

thermia(°C) (ml/kg/min)

30.029.830.032.030.030.030.0

28.031.030.029.829.830.130.130.030.030.029.8

30.030.029.932.132.128.830.132.130.0

pulmonaryplacing mitral valve.Homograftmitral valve

aortic valve

Mitral valvotomy.

57535255515452

50, 60, 7550,6049, 58,4950, 60, 7051,60,7561,5060,5259,5050,75, 5977, 50, 6050

614959576053526354

valve re-

: replacing

calm or drowsy state just before the induction ofanaesthesia. Patient 19 was perfused with a "warmstart" lasting 12 minutes. In the remainder, cool-ing to 30° C was started as soon as bypass began.Arterial pump flow, during hypothermia, was keptroughly constant in each case at 2.0 l./min/m2

or more.The procedure used for perfusion and details

of laboratory methods have been described (Bar-ratt-Boyes, 1965; Harris, Seelye and Barratt-Boyes, 1970). Oxygen consumption was measured,pre-operatively in series III, by the standardDouglas-bag method and Lloyd-Haldane analysisof expired gas. During bypass, oxygen consump-

tion was calculated from the flow rate of the cali-brated arterial pump and the arteriovenous oxygencontent difference; blood samples were drawnfrom the venous line before the blood reachedthe venous reservoir and from the arterial outflowfrom the pump oxygenator. Blood oxygen contentwas calculated from haemoglobin concentration,oxygen saturation and oxygen partial pressure,using a Huffner factor of 1.36 and the solubilitycoefficient appropriate to the patient's tempera-ture, as recorded from a thermistor in the naso-pharynx.

In series II, oxygen consumption was measuredon bypass before cooling, during hypothermia 10

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OXYGEN CONSUMPTION DURING CARDIOPULMONARY BYPASS 1115

and 20 minutes after each change of flow, andagain after rewarming but while still on full by-pass. In series I and series III the measurementswere made less regularly; "warm start" patientsall had one measurement before cooling; all hadat least one measurement after rewarming, andfrom two to seven measurements during hypo-thermia, depending on the duration of this phase.

Calculations.According to the Arrhenius equation, the loga-

rithm of the rate of a chemical reaction is inverselyrelated to the reciprocal of the absolute tempera-ture. Over a small range of temperature (37-30° C;31O-3O3°A) this relationship is almost equallywell described by stating that the logarithm of thereaction rate is directly related to the temperature.In this form, it finds expression in van't Hoff'slaw, which states that a rise in temperature of10 °C increases the reaction rate by between twoand three times. This proportional increase (or,in cooling, decrease) is usually denoted by thesymbol Q10. We have therefore considered thelogarithm of oxygen consumption in relation totemperature and have expressed this relationshipin terms of the Q lo.

From consideration of critical oxygen tensionsin tissues (Stainsby, 1966) the oxygen uptake (Vo2)might also be expected to vary with pump-flow(Q) independently of temperature. Clowes andassociates (1958) published a curve for dogswhich, on analysis, shows a correlation of 0.997between log Vo2 and log Q, both corrected forbody weight; Vo2 varied directly as the power0.524 of <J. In considering flow we have there-fore postulated a log-log relationship with oxygenconsumption, and in averaging data within andbetween individuals (see below) we have usedgeometric means for both oxygen uptake and flow.Temperatures have been averaged arithmetically.Regression analyses and tests of significance havefollowed standard procedures (Davies, 1961).

RESULTS

(1) Correction of oxygen consumption forbody size.

The basal oxygen consumption measured justbefore anaesthesia in the nine patients in seriesIII, and in two patients not otherwise includedin this paper, has been correlated with body

weight, surface area, weight to the power 0.6 (Hill,1966) and weight to the power 0.75 (Kleiber,1947). The correlation coefficients were respect-ively 0.770, 0.732, 0.769 and 0.769. By z-trans-formation these correlations do not differ signifi-cantly. For present purposes, therefore, oxygenconsumption has been corrected to a standardbody weight of 65 kg by multiplying it by thefactor 65/body weight in kg.

(2) Effects of varying temperature andflow on oxygen consumption.

These were assessed in the following manner.Single values for weight-corrected oxygen uptake(Vo2

65), flow in ml/kg/min (Q) and temperature(t) were obtained for each patient in each temper-ature state: thus, a set of three values was obtainedin each of three states for the "warm start"patients (precooling, hypothermic and rewarmed)and in each of two states for the "cold start"patients (hypothermic and rewarmed). In eachcase, geometric means were taken for Vo2

65 andQ, and an arithmetic mean for t. The averageddata were arranged as follows:

(a) Cold to warm ("cold start" patients)(b) Warm to cold(c) Cold to warm j

("warm start" patients)

A multiple-regression analysis for (a), (b) and (c)was then carried out of log Vo2

65 on t and log Qaccording to the hypothetical equation

log Vo265 = a + fc,t + b2 log Q

where £>, and fc2 are the partial regression co-efficients on t and log Q respectively. Partial cor-relations, r, and r2, were also calculated. Theresults are shown in table II.

It can be seen that in neither group of patientsdid flow appear to affect oxygen consumption.The correlations with temperature were, however,highly significant. In the "cold start" group, theslope of log Vo2

65 on t was 0.04339, correspondingto a Q10 of 2.72. The "warm start" slopes of0.02311 and 0.01942, for cooling and warmingrespectively, were not significantly different fromeach other (0.3>2P>0.2) but were significantlydifferent from the slope for the "cold start"patients (2P<0.001). The mean slope for the"warm start" patients, 0.02127, corresponds to aQ10 of 1.63.

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TABLE II

Partial regressions (b) and correlations (r) of log Po2K on temperature (b, and rt) and on log

(b2 and r2).Patients

1 "Cold start"Cold to warm

72 = 26

2 "Warm start"(a) Warm to cold

n = 28(b) Cold to warm

w = 283 Series II

Hypothermia(individual data)

n=47

b.

0.04339(Q,o 2.72)

0.02311(Q,o 1-70)0.01942

(Q,o 1-56)

0.06280

r,

0.6010.01>2P>0.001

0.5540.01>2P>0.001

0.5250.01>2P>0.001

0.510

2P<0.001

b,

-0.36499

0.20673

0.33026

0.21997

r,

-0.1102P>0.1

0.1122P>0.10.195

2P>0.1

0.330

0.05>2P>0.01

Since series I, II and III had been studied inthat sequence over a period of 2-3 years, it wasthought that the difference in Q lo between"warm" and "cold" starts might be due to asystematic technical error. Against this was thefact that most of the "warm start" patients werein series II and were thus studied in the middleof the period. To test the postulate further, themean slopes of Vo2

05 on temperature for the "coldstart" patients in series I and series III werecalculated separately and were not found to differsignificantly (0.7>2P>0.6).

The difference between the two groups ofpatients is illustrated in figures 1 and 2. In figure1 the mean Vo2

65 for the "cold start" patients ofseries III is seen, at each temperature, to be in-significantly different from that for the "cold start"patients in series I and III combined. The Vo2

65

measured before the induction of anaesthesia inseries III is, however, significantly higher than therewarmed Vo2

05 in either or both series. Figure2 shows the results in the "warm start" patients.The mean Vo2

65 before cooling was not signifi-cantly different from that after rewarming, andboth were insignficantly different from the meanVo2

65 in the "cold start" series III patients afterrewarming. On the other hand, when cooled, the"warm start" patients showed a significantlysmaller reduction of Vo2

65 in relation to temper-ature than the "cold start" patients of series III.

(3) Effect of flow on oxygen consumption atuniform temperature.

It seems possible that the multiple-regressionanalysis of all three series might have obscured a

small effect of flow on oxygen consumption, since(a) the varying flows of series II were confoundedwith the much more uniform flows of series I and

I

a.

u

225

200

175

150

125

100

BYPASS WITH IMMEDIATE COOLING 1

Series

n •

- Q1Cc

Series

n "

-

-r

•

1

•

1 • 3 • •

13

2 7

3 • - - -« and X J7/

'/I236 / /

;

-

7^ i VQr, - Geometric meanst2SEm

Temperature - means1 j2SEm'

30 35 37TEMPERATURE - C

FIG. 1Geometric means of weight-corrected oxygen con-sumption, and arithmetic mean of temperature werecalculated for each "cold-start" patient in series I andIII; these means were then averaged in the same wayfor series III and for series I and III combined. Thebars show 2 standard errors of the mean, on each sideof the mean, for each variable. The pre-operativemeasurements of oxygen consumption and temperature

in the patients of series III are shown at X.

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225

200

&175

c

125

z

lOO

BYPASS WTTH NORMOTHERMC START

O Before cooling

• typothermic and after rewarming

n .14

0,0-163

(Series 3-—•and X;

•"' V ^ - Geometric means* 2SEm

Temperature - means t 2SEm

30 35 37

TEMPERATURE - C

FIG. 2Procedure as for fig. 1, showing the "warm start"patients (2 from series I, 11 from series II, and 1 fromseries III) in comparison with the 8 "cold start" patientsof series III, for whom the pre-ooerative data are shown

atX.

Ill, and (b) the range of temperature might havebiased the correlations in favour of temperature.To test this possibility, the individual data forthe hypothermic state in series II patients wereconsidered separately; this procedure reduced thetemperature range and relatively increased therange of flow. The result is shown in table II.Vo2

65 is now seen to be related directly to thepower 0.220 of flow (fc2), with a significant cor-relation (r2). In this test the significance of thecorrelation is, of course, enhanced by the largernumber of data (47) compared with the analysisof means for each patient in the upper part oftable II.

(4) Comparison of basal Vo265 with the Vo,65

during normothermic perfusion.Basal Vo2

65 was measured pre-operatively inonly the nine patients of series III, eight of whomhad a "cold start"; it is thus impossible from thepresent data to make a direct comparison of oxy-

gen uptakes before anaesthesia and immediatelyafter the start of bypass at normal temperature.However, inspection of figures 1 and 2 shows thatthe mean Vo2

65 during normothermic perfusion isnot significantly different in the "warm start"group (whether before cooling or after rewarming)and the "cold start" group. It is thus reasonableto compare the pre-operative Vo,65 with the meannormothermic Vo2

65 for all patients. The differ-ence was significant (0.02>2P>0.01) and indi-cated a fall of 16 per cent in Vo2

65 between thepre-anaesthesia measurement and that made dur-ing normothermic perfusion. The difference inmean temperature, 0.26° C, was inconsiderable(0.3>2P>0.2).

DISCUSSION

Measurement of temperature and oxygenconsumption.

The correlation of Vo2 with temperature de-pends, in the first place, on how accurately eachcan be measured.

(a) Temperature. It is well established thattemperature gradients exist throughout the body,even in the normal state, that different regionscool at different rates, and that the pattern ofcooling rates varies with the method of coolingused. Our own experience, for example, confirmsthat nasopharyngeal temperature is above muscletemperature, before cooling, by an average of1.7°C (0.005>2P>0.001 by paired (-test); ataround 30°C, muscle is warmer than nasopharynxby an average of 1.4°C (0.02>2P>0.01); afterrewarming the nasopharynx is again the warmerby an average of 2.9°C (2P<0.001). Our use ofnasopharyngeal temperature in the present studiesis, therefore, open to immediate criticism on thegrounds that it is unrepresentative of the wholebody, but we know of no way in which this ob-jection can be met.

(b) Oxygen consumption. The measurement ofVo2 during perfusion, from pump flow and arterio-venous oxygen-content difference, cannot bechecked by an independent measurement. Lackingthis, we have examined the difference betweentwo successive measurements of Vo2 10 and 20minutes after changing flow at the same temper-ature, in the patients of series II. The secondmeasurement was, on average, 0.48 per cent higherthan the first, a difference which was not signifi-

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cant (0.9>2P>0.8). While it cannot be assumed,a priori, that there should not have been anydifference between these "duplicate" measure-ments, we conclude that this method for deter-mining Vo2 on full bypass is probably satisfactory.

Oxygen consumption during normothermicperfusion.

Our results indicate that oxygen consumptionis the same, during normothermic perfusion, be-fore cooling and after rewarming. In each case itis, on average, 84 per cent of the pre-operativeoxygen uptake in the premedicated patient.

Theye and Tuohy (1964) measured oxygen con-sumption during light halothane anaesthesia, with-out premedication, and compared it with predic-ted (not measured) values for basal oxygen con-sumption. If a relaxant drug had not been giventhe values were the same. After tubocurarine,Vo2 fell to 84 per cent of the predicted basal value.

We conclude that the fall in Vo2 between ourpre-operative measurement and that made duringnormothermic perfusion was probably due to theeffects of muscular relaxation, and that the meas-ured Vo2 in each case probably represents theprevailing oxygen requirement.

Oxygen consumption during hypothermicperfusion.

The fall in Vo2 observed after cooling appearedto depend, in the present studies, on the manner

in which cooling was effected. If the perfusionbegan with a normothermic phase, Q,o was 1.63;if the patient was immediately perfused withcooled blood, Q l0 was 2.72. It would seem that,at least in the latter group, oxygen availability fellshort of requirement in the cooled state. It remainsto consider whether, even in the patients who hadan initial normothermic phase, oxygen require-ment was being met at 30 °C.

Table III shows Q!0 values obtained by otherworkers under various conditions. It can be seenthat apart from the value of 1.51 observed in dogsby Clowes and his colleagues (1958), all valuesare higher than the 1.63 of our "warm start"patients. It is perhaps especially notable thatShapiro and Stoner (1966) obtained a value of1.93 in two healthy subjects who were heated to39.9°C; the peripheral vasodilatation due to heat-ing would presumably ensure that uptake of oxy-gen kept pace with requirement. In the light ofthese data we conclude that in those of ourpatients whose perfusion had a normothermicstart, oxygen consumption in the hypothermicstate was probably a fair reflection of requirement.Since the Q,o in these patients was relativelylow, the question indeed arises as to whether Vo2

may have somewhat exceeded current require-ment, as it might have done were an oxygen debt,incurred during the cooling phase, being repaid.

This question is difficult to answer. We havepreviously shown (Harris, Seelye and Barratt-

Author(s)Bigelow et al. (1950)

Fuhrman (1956)

Linder (1958)Clowes et al. (1958)Benazon (1964)

Brewin (1964)

Shapiro and Stoner (1966)Lunding and Rygg (1968)

TABLE III<2,0 values from previous studies.

Temperature inhypothermia

CO281810

3030282510302015

5403328.523

SourceDogsDogsOrgan slices:

kidney, liver, heart, brain,muscle

ManDogs"Values are similar in tissue

slices, in whole animals andin man"

Man

Man (heating)

Man

Q, .

2.402.83

2.0-3.0

2.771.512.382.732.351.852.262.372.551.933.182.082.26

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Boyes, 1970) that in this "warm start" group ofpatients the blood lactate concentration rose al-most twice as rapidly, during the hypothennicphase, as in the "cold start" patients, and thatthis difference was, statistically, highly significant.This observation would hardly, at first sight,suggest that the patients in the "warm start"group were paying off an oxygen debt at the sametime, but this is quite conceivable. Elsewhere(Seelye et al., 1971) we have presented clear evi-dence of oxygen debt repayment in babies at atime when "washout" lactic acidosis was increas-ing very rapidly indeed. At present we are re-luctant to call upon evidence derived from "excesslactate" or lactate/pyruvate ratio, since this wouldbeg the question of whether these indices providereliable evidence of oxygen availability or not.There remains a possible indication that oxygenrequirement was not in fact being fully met inour cooled "warm start" patients, and this will beconsidered below in connection with changes re-lated to pump flow.

By contrast, the Q10 for the "cold start" per-fusions was, at 2.72, considerably higher than theheating Q10 of Shapiro and Stoner (1966), andlies in the upper part of the range shown in tableIII. It seems almost certain that during hypo-thermia in this group the oxygen availability fellshort of requirement by as much as 15 per cent.The provision of a "warm start" lasting up to 15minutes or so would therefore seem to assure thetissues of a better oxygen supply during the hypo-thermic phase. In most cases this advantage isprobably of minor consequence, and the "warmstart" technique certainly adds to the hazards, atthis stage of the operation, in patients with aorticreflux whose hearts suddenly fibrillate before theheart is cool or the coronary arteries have beencannulated. In some instances, however, it maypossibly be a desirable means of reducing themetabolic insult to which the patient is exposed.

Oxygen consumption in relation to pump flow.The data for series II shown in table II sug-

gest a positive correlation between Vo2 and flowover the range 50-75 ml/kg/min. From theobserved relationship that log Vo2 varies as 0.220log Q, it may be deduced that Vo2 increased by10 per cent as flow increased from 50 to 75ml/kg/min. For a 65-kg man of 1.7 m2

surface area, the commonly accepted minimalflow of 2.0 l./m2/min at 30° C is equivalentto 52 ml/kg/min. It would appear that higherflows may confer some advantage in more effectivetissue perfusion. If this be so, it cannot be heldthat the mean hypothennic Vo2 in the "warmstart" patients of series II represented the pre-vailing oxygen requirement, since many of theVo2 measurements were made at the lower twoflow rates.

CommentsIn the absence of continuous, accurate measure-

ment of oxygen consumption and exact know-ledge of the mass of lactate released and excreted,the oxygen requirement can never be preciselyknown. It is virtually certain that most estimatesin the literature, of oxygen consumption duringhypothermic bypass, represent not what thetissues need so much as what they can get. If onecan be reasonably sure that requirement is metunder a certain set of conditions, then the Q10

offers a guide as to what effect a change oftemperature has had, other conditions remainingessentially unchanged. The lower the Q,o duringcooling the more likely it is that oxygen needsare being supplied. Presumably there is, theoreti-cally, a limiting value at which one can say thatoxygen supply is just sufficient, and we havesomewhat arbitrarily taken the "heating" Q10 ofShapiro and Stoner (1966) as being near thislimit. Unfortunately, any attempt at precision isprobably doomed to failure by the impossibilityof measuring "body temperature". The presentstudies, nevertheless, form a possible basis forfurther consideration of venous P02, arteriovenousoxygen difference, and pyruvate and lactate con-centrations as indices of adequate perfusion.

ACKNOWLEDGEMENTS

We are grateful to Sir Brian Barratt-Boyes and MrD. S. Cole for the opportunity to study patients undertheir care, and for their equanimity in the operatingtheatre during our investigations. We also wish to thankMrs C. Ford, B.sc, Mrs M. Barron, B.SC., and Mrs A.Kenyon, B.SC., for laboratory assistance. This workwas supported by successive grants from the AucklandMedical Research Foundation, the Golden Kiwi LotteryFund, and the Medical Research Council of NewZealand.

REFERENCES

Barratt-Boyes, B. G. (1965). A method for preparingand inserting a homograft aortic valve. Brit. J.Surg., 52, 847.

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Benazon, D. B. (1964). Profound hypothermia. Int.Anesth. Clin., 2, 941.

Bigelow, W. G., Lindsay, W. K., Harrison, R. C ,Gordon, R. A., and Greenwood, W. F. (1950).Oxygen transport and utilization in dogs at lowbody temperatures. Amer. J. Physiol., 160, 125.

Brewin, E. G. (1964). Physiology of hypothermia. Int.Anesth. Clin., 2, 803.

Clowes, G. H. A., Neville, W. E., Sabga, G., andShibota, Y. (1958). The relationship of oxygen con-sumption, perfusion rate and temperature to theacidosis associated with cardiopulmonary circula-tory bypass. Surgery, 44, 221.

Davies, O. L. (1961). Statistical Methods in Researchand Production. Edinburgh: Oliver and Boyd.

Fuhrman, F. A. (1956). Oxygen consumption of mam-malian tissues at reduced temperatures; in ThePhysiology of Induced Hypothermia, Publ. 451,50, Nat. Acad. Sci., Washington.

Harris, E. A., Seelye, E. R., and Barratt-Boyes, B. G.(1970). Respiratory and metabolic acid-basechanges during cardiopulmonary bypass in man.Brit. J. Anaesth., 42, 912.

Hill, J. R. (1966). The effects of hypoxia on the cardio-respiratory system and on energy metabolism inthe neonatal period. Proc. int. Symp. cardiovasc.respir. Effects Hypoxia, 266. Basle and New York:Karger.

Kleiber, M. (1947). Body size and metabolic rate.Physiol. Rev., 27, 511.

Linder, F. (1958); cited by Thauer, von R., andBrendel, W. (1962). Hypothermie. Progr. Surg.(Basel), 2, 73.

Lunding, M., and Rygg, I. H. (1968). Evaluation of thesufficiency of tissue oxygenation during cardio-pulmonary bypass and hypothermia using Rygg/Kyvsgaard pump oxygenator. Scand. J. thorac.cardiovasc. Surg., 2, 169.

Seelye, E. R., Harris, E. A.3 Squire, A. W., andBarratt-Boyes, B. G. (1971). Metabolic effects ofdeep hypothermia and circulatory arrest in infantsduring cardiac surgery. Brit. J. Anaesth., 43, 449.

Shapiro, H., and Stoner, E. K. (1966). Body temper-ature and oxygen uptake in man. Ann. phys. Med.,8, 250.

Stainsby, W. N. (1966). Some critical oxygen tensionsand their physiological significance. Proc. int.Symp. cardiovasc. respir. Effects Hypoxia, 29. Basleand New York: Karger.

Theye, R. A., and Tuohy, G. F. (1964). Oxygen up-take during light halothane anesthesia in man.Anesthesiology, 25, 627.

CONSOMMATION D'OXYGENE AU COURSD'UN "BY-PASS" CARDIOPULMONAIREAVEC HYPOTHERMIE MODEREE CHEZ

L'HOMME

SOMMAIRE

La consommation d'oxygene a 6te mesuree au coursd'une circulation extra-corporelle totale sous hypo-thermie, mise en oeuvre chez 27 malades soumis a desinterventions de chirurgie cardiaque. Chez neuf malades,cette mesure a ete' aussi effectuee immediatement avantl'induction de l'anesthesie. Quatorze malades etaientmaintenus a une temperature nonnale pendant les 5 a

17 minutes qui suivirent le debut du "bypass". Lesautres malades furent immediatement places en hypo-thermie a 30°C. La consommation d'oxygene au coursdu "bypass" en normothermie, soit avant ou apresrefrigeration, correspondait a 84% de la valeur mesureeavant l'anesthesie, ce qui pouvait etre du aux effets dela myorelaxation. Au cours de l'hypothermie, lesmalades qui avaient subi immediatement la refrigerationpresentaient une consommation d'oxygene qui etaitinferieure de 15% environ a celle enregistree chez lesmalades soumis a une refrigeration retardee. Memedans ce dernier groupe, la consommation d'oxygene aucours de rhypothermie n'exigeait la mise en oeuvred'aucune mesure speciale, etant donne qu'elles'averait etre tout a fait en relation avec le flux sanguin.

SAUERSTOFF-VERBRAUCH WAHRENDCARDIOPULMONALER UBERBRUCKUNG MITMASSIGER HYPOTHERMIE BEIM MENSCHEN

ZUSAMMENFASSUNG

Bei 27 Herzoperationen wurde der Sauerstoflf-Verbrauchwahrend hypothermer Ganzkorper-Perfusion gemessen;in 9 Patienten auch kurz vor Beginn der Narkose. 14Patienten wurden von 5-17 Minuten nach dem Beginnder Oberbriickung bei normaler Temperatur gehalten,die restlichen sofort auf 30 °C unterkuhlt. Der Sauer-stoffverbrauch wahrend der Oberbruckung betrug beiden Normothermen—sowohl vor als auch nach derUnterkuhlung—84% des Wertes vor der Narkose, waswahrscheinlich auf Muskelrelaxation zuruckzufuhrenist. Wahrend der hypothermen Phase zeigten diePatienten, die sofort unterkuhlt worden waren, einenetwa 15% niedrigeren Sauerstoff-Verbrauch als diePatienten mit verzdgerter Unterkuhlung. Selbst indieser letzteren Gruppe jedoch reicht anscheinend dieSauerstoff-Versorgung wahrend der Hypothermie nichtvollig aus, wie die positive Korrelation zum Blutfluflzeigt.

CONSUMO DE OXIGENO DURANTE ELBYPASS CARDIOPULMONAR CON

HIPOTERMIA MODERADA EN EL HOMBRE

RESUMEN

El consumo de oxigeno fue medido durante la perfusi6nhipot^rmica de todo el cuerpo en veintisiete pacientessometidos a operaciones cardiacas. En nueve pacientes,tambien fu medido inmediatamente antes de la induc-ci6n de anestesia. Catorce pacientes fueron mantenidosa temperatura normal durante 5 hasta 17 minutosdespues de comenzar el bypass; los demas fueron in-mediatamente enfriados a 30 °C. El consumo de oxigenodurante el bypass con normotermia, tanto antes comodespues del enfriamiento, fue de 84 por ciento del valorpre-anestesia, probablemente a causa de los efectos delrelajamiento muscular. Durante la hipotermia, lospacientes que fueron enfriados inmediatmente tuvieronun consumo de oxigeno que era inferior en aproxi-madamente un 15 por ciento al encontrado en pacientescon enfriamiento retrasado. Incluso en este ultimogrupo es probable que el consumo de oxigeno durantela hipotermia no llego a sarisfacer completamente losrequisitos, ya que se demostr6 que estaba correlacionadopositivamente con el flujo sanguineo.

at McG

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Oxygen consumption and circulatory arrest

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