Haemodialysis

BTM – Blood Temperature MonitorImproved quality of haemodialysis

as a result of individualised temperature control

Contents

Intradialytic complications – still a problem today? 4

Hypovolaemia and body temperature 6

How does the BTM register and regulate individually body temperature? 8

The use of the BTM in clinical practice 10

Recirculation 12

A brief overview of the operation of the BTM 13

Thermal energy and temperature regulation with the BTM 13

Recirculation measurement 15

Use of the BTM in other modes and situations 16

Frequently asked questions 17

References 18

Intradialytic complications – still a problem today?

Even today, the dialysis treatment is fre-quently interrupted by hypotensive events.Such events occur during up to 20 % of alltreatments, in some cases even more fre-quently [1, 2]. Moreover, patients complain ofcramps, nausea and dizziness and somepatients may even lose consciousness duringtreatment (Fig. 1).

The measures which are then requiredinclude, e.g. discontinuation of ultrafiltrationor the administration of hypertonic solutions:it may even become necessary to prema-turely terminate the dialysis session.

These undesirable effects and the inter-ventions required not only interfere with theoperation of the dialysis unit, butalso increase material requirements.

Such events are even more serious from thepoint of view of the patient, as they not onlyinvolve considerable impairment of thequality of treatment, with symptoms such asnausea or tiredness expanding also into theinterdialytic interval. Moreover, all interventionsundertaken, such as the reduction of bloodflow or premature discontinuation of treat-ment, also mean that the aims of treatment –detoxification and fluid removal – are placedat risk. Discontinuation of ultrafiltration andadministration of hypertonic solutions make itdifficult to achieve specified dry weight andcan have long term hypertensive effects.

In addition, there can be long term conse-quences if hypotensive episodes occurfrequently, such as damage to cardiac andneural tissue, acceleration of the loss of resi-dual renal function and possibly an increasedrisk of morbidity and mortality [1, 3].

Although the technical improvements intro-duced in recent decades have led to areduction in the frequency of hypotensiveepisodes during haemodialysis, the problemis still present today. One reason for this isthat in the group of dialysis patients, as in thepopulation as a whole, the average age andthe proportion of individuals with cardio-vascular disorders are constantly increasing.

Fig. 1: Hypotensive episodes, cramps and other symptoms canoccur in up to 50 % of dialysis sessions [2]

Treatment without interventions 48 %

Lightheadedness 13 %Crampings 15 % Hypotension 24 %

Fig. 2: Patient and therapy related factors contribute to thedevelopment of intradialytic hypotension

Waterquality

Biocompa-tibility

VascularCompliance

Fluidstatus Heart Sympathetic

response

Anti-hypertensivemedication

Bloodvolume

Dialysatetemperature

Electrolyteconcentrations

HYPOTENSION

4

In addition to these factors, there are thepathophysiological problems characteristic ofpatients with renal insufficiency and thevarious parameters relating to the haemo-dialysis treatment which need to be takeninto account (Fig. 2).

It has been demonstrated in epidemiologicaland clinical studies that there is an increasedrisk of hypotensive episodes during dialysisparticularly in patients of advanced age,patients with accompanying cardiovasculardisorders (such as cardiac arrhythmia, hypo-tension, left ventricular hypertrophy, diastolicdysfunction) or diabetes mellitus (peripheraland autonomic neuropathy), patients in whomthere is an interdialytic increase in weight ofmore than 3 % of dry weight and in anephricpatients [3].

Fluid removal is the main factor that can causehypotension during dialysis. At a haematocritvalue of 33 %, an average blood volume of4.5 litres is equivalent to approximately 3 litresof plasma. Assuming an average weight gaincorresponding to 1.5 litres per day or approxi-mately 3 litres over 2 days, the volume removedduring a dialysis session is equivalent to thetotal plasma volume. This removal of fluid iscompensated by plasma refilling from theinterstitial tissues, which is determined byvarious factors, such as the extent of over-hydration or the sodium concentration in thedialysate and, in consequence, in the blood.As the plasma refilling does not occur at thesame rate as the removal of fluid by thedialyser, hypovolaemia is induced. In order toensure that a stable blood pressure ismaintained under these circumstances, thebody has developed various compensatoryregulatory mechanisms which generally allowdialysis treatment to be completed withoutproblems arising.

Hence, cardiovascular reactions, such as anincrease in heart rate, increased contractilityof the cardiac muscle and/or an increase inperipheral resistance can, to a limited extent,counteract the effects of hypovolaemia andprevent the development of hypotension. Un-fortunately, the accompanying cardiovascularcomplications in many patients mean thatthese regulatory mechanisms are impaired,so that the risk of hypotensive episodes isfurther increased [1].

Pathophysiological factors affectingdialysis patients, but also the use ofinadequate treatment parameters,can lead to hypotension duringdialysis.

5

Hypovolaemia and body temperature

The body’s thermoregulatory mechanisms,however, are superimposed on the physiologi-cal reactions to volume reduction. The purposeof thermoregulation is to maintain a constantcore body temperature. Excessive heat canbe removed from the body if peripheral vas-cular resistance is reduced to increase bloodperfusion in the capillary vessels of the skin.In the opposing situation, in hypothermia, thereis an increase in peripheral vascular resis-tance in order to reduce the blood perfusionof the skin and thus the release of thermalenergy.

In the case of dialysis patients, thermal energycan also be released or taken up by theextracorporeal circulation (Fig. 3).

These processes of temperature regulationare, however, superimposed by volume regu-lation. The body reacts to volume reductionas a result of fluid removal with increasedperipheral vascular resistance in order tostabilise central blood volume and bloodpressure. The reduction of cutaneous bloodflow means that the radiation of thermalenergy from the skin is also reduced.

Not only as a result of this, but also becauseof increased metabolic production of thermalenergy and the potential supply of thermalenergy via the dialysate during haemodialysis,there is an increase in core temperature [4].

When this increase reaches a critical point,the body reacts by dilating skin vessels inorder to eliminate the excessive heat from thebody by increasing peripheral blood flow.This sudden reduction in peripheral vascularresistance can very frequently trigger a fall inblood pressure.

Early studies demonstrated that the bodywas very sensitive to even slight shifts in tem-perature. The standard range of temperaturefor dialysis fluids (37–37.5°C) frequently causesan increase in body temperature of 0.3–0.5°C[5, 6, 7, 8]. This can be a particular problemwhen hypothermal patients (body tempera-ture prior to dialysis <36.5 °C) are exposed to“standard dialysate temperatures” of 37°C [9].Even a very slight increase in temperature hasled to a marked drop of blood pressure (Fig. 4)and an increase in the frequency of staff inter-ventions (Fig. 5), in contrast to treatments inwhich body temperature was maintained at aconstant level or was slightly reduced by useof a cooled dialysate (Fig. 4, 5) [7, 10].Fig. 3: During dialysis thermal energy can be lost or

supplied via the extracorporal circulation

Skin Dialysis treatment

Heatproductionby the body

Energy lossto the environment

Supply or lossof thermal energy

Fig. 4: A slight increase of the core body temperature can cause a marked blood pressure drop [5]

Core body temperature in thecourse of treatment

Chan

ge o

f mea

n ar

teria

l blo

od

pres

sure

(mm

Hg)

0

- 5

- 10

- 15

- 20

- 25+ 0.8 ºC +/- 0 ºC

6

With an increase in body temperature of lessthan 1°C, the fall in blood pressure was doublethat recorded during treatments in which bodytemperature was kept constant [5]. This sensi-tivity to temperature is particularly pronouncedin patients known to be prone to hypotension[11].

In view of these observations, it is clear thatthe stabilisation of core body temperature isone of the basic requirements of haemo-dialysis treatment. Excessive body heat,which can be eliminated via the skin only to alimited extent due to volume-induced vasocon-striction, should thus be eliminated by meansof the extracorporeal blood circulation. This isdependent, however, on the temperature

difference between blood and the dialysateand can vary considerably, as there can begreat differences in predialysis body tempera-ture, not only between individual patients, butalso from one treatment to another. Manypatients are hypothermal at start of dialysis,i.e. their body temperature is less than 37 °C.The lower the body temperature on initiationof dialysis, the greater the increase in tem-perature during treatment (Fig. 6) [12]. Inaddition, there are very wide variations in heatproduction and body temperature duringdialysis between individual cases.

Active regulation of body temperature is notpossible merely by use of a dialysate at aspecific fixed temperature. What is required isa regulation of temperature that takes intoaccount the predialytic body temperature ofthe individual patient, and the course of bodytemperature related to volume regulation, andthat variably and automatically adjusts to theactual temperature development during treat-ment (Fig. 7). Such regulation is possible usingthe Blood Temperature Monitor (BTM).

The individual differences in bodytemperature at start and during dia-lysis require flexible adjustment of thetemperature of the dialysate, as ispossible using the Blood TemperatureMonitor.

Fig. 5: A slight decrease of the core body temperature reducesthe frequency of hypotensive episodes [10]

Fig. 7: Factors requiring individual and physiologicaltemperature control

Sensitivity of the patientto slight temperature

changes

Intra- and interpatientvariability of body

temperature

Excess of thermal energyin the course of the

treatment, dependingfrom UF volume

Variability of delivereddialysate temperature

Active and individual control of body temperature

Postdialytic change of body temperature [°C]

Predialytic body temperature [°C]

Data of individual sessionsLinear regression

2

1.5

1

0.5

0

-0.5

-1

-1.5

-235 35.5 36 36.5 37 37.5

Fig. 6: The lower the body temperature at start of dialysis, the higher the increase of body temperature during the treatment [12]

Core body temperature in thecourse of the treatment

Freq

uenc

y of

trea

tmen

ts w

ith s

taff

inte

rven

tions

(%)

50

40

30

20

10

0+ 0.3 °C - 0.2 °C

7

The dialyser, in which blood and dialysatecirculate in a counterflow, is an ideal heatexchanger. Dependent on the temperature of the blood and the dialysate, the blood in the dialyser either releases or takes upthermal energy. Measurements have shownthat the blood absorbs thermal energy whenthe dialysate temperature is 37 °C with a con-sequent rise in body temperature by an aver-age of 0.3 °C, while with a dialysate at atemperature of 34 °C, the patient releasesthermal energy with a reduction in bodytemperature by 0.7 °C [6]. The increase inbody temperature which is observed withdialysates at standard temperatures has anunfavourable effect on cardiovascular stability.One way of avoiding this increase in tem-perature is to reduce the temperature of thedialysate, but when this method is usedpatients frequently complain of a sensation ofcoldness. Cold-induced shivering may evenoccur, a physiological reaction to maintainbody temperature by increasing metabolismand heat production [6, 9, 13].

The situations described above are undes-irable. It should thus be ensured that the leastpossible effects on body temperature occurduring dialysis treatment.

Active control of blood temperature is easy tobe performed with the Blood TemperatureMonitor (Fig. 8). The device has two sensorswhich non-invasively monitor arterial andvenous blood temperature in the extra-corporeal circulation. On the basis of theserecordings the corresponding fistula tem-peratures are calculated. Arterial bloodtemperature is determined by body tempe-rature, venous temperature by the tem-perature of the dialysate.

By altering the temperature of the dialysate,the temperature of the venous blood re-entering the fistula can be adjusted by meansof heat transfer. The higher the venoustemperature in comparison with arterialtemperature and the higher the actual bloodflow rate, the greater the amount of thermalenergy transferred to the blood per time unit.The required dialysate temperature is calcu-lated on the basis of the results of tempera-ture measurement, actual blood flow rate andseveral other constants.

The BTM provides two basic methods ofthermal regulation (Fig. 9).

With the one option, thermal energy control(E control), it is possible to control the supply

of thermal energy to andfrom the extracorporealcirculation. If a neutraltemperature balance isrequired, thermal energyshould neither be suppliednor removed and themeasured temperaturesof the arterial and venousfractions of the extra-corporeal blood circulationshould be identical.

How does the BTM register and re-gulate individually body temperature?

QB (Effective blood flow)

Fig. 8: Blood Temperature Monitor

Calculation of dialysate temperature

Adjustment ofdialysatetemperature

T art

T ven

T dial

Adjustment of control function

8

In order to achieve this, the dialysis machinecontinuously adjusts the temperature of thedialysate to the temperature recorded by thearterial sensor. As the arterial temperature in-creases during dialysis, it is not possible tocontrol body temperature using this method.

From the therapeutic pointof view, E control at asetting of 0 kJ/h isadvisable if it is desirableto exclude influencingthermal energy balance inthe extracorporeal circu-lation.

In clinical practice, how-ever, thermal energyregulation is generallyless important than bodytemperature control (Tcontrol) with the BTM.

This option allows activeregulation of body tem-perature. This is moreadvantageous in physio-logical terms, as anyincrease in temperatureinduced by hypovolaemia,and thus the risk of hypo-tension, can be avoided.

In T control, the devicemeasures the currenttemperatures of arterialand venous blood in thesensor heads and cal-culates the correspondingfistula temperatures, ta-king into account thepotential loss of thermalenergy in the blood tu-bing system. In order todetermine core bodytemperature, the bloodrecirculation must alsobe taken into account.This is measured usingthe BTM thermodilutiontechnique.

The body core temperature at start of thetreatment, which is used as the targettemperature for active regulation, is calcu-lated on the basis of total blood recirculationand various system parameters (actual bloodflow rate, assumed ambient temperature set usually at 23 ºC, thermal conductivity of the blood tubing system and the distancebetween the patient and the sensor).Measurement and calculation are continuallyrepeated during treatment and the tem-perature of the dialysate is adjusted if bodytemperature rises or falls to ensure that thepreset core body temperature is maintained.Although in most cases maintenance of aconstant core temperature will be required(�T = 0 °C), it is also possible to achieve anincrease or reduction of core temperaturewithin certain limits, e.g. in case of hypo-thermia or high fever.

Heat exchange in the extracorporealcirculation and thus body tempera-ture can be actively controlled usingthe BTM.

The limits of temperature regulation

The BTM can regulate the temperature of thedialysate only within a narrow physiologicalrange, generally 35 – 38 °C. This avoids therisk of undercooled or overheated bloodbeing supplied to the patient. It also meansthat an unexpected change in the bodytemperature of the patient, such as develop-ment of fever, does not remain undetected. Insuch a case, the BTM would possibly beunable to achieve the set target (e.g.maintenance of a constant body tempera-ture), but dialysate temperature would remainwithin a physiological range.

Temperature alarm limits (set to temperaturesoutside the upper and lower limits of the BTM itself) which have been installed in thedialysis machine also prevent the patientbeing exposed to dialysate at inappropriatetemperatures.

Fig. 9: Control of thermal energyflow and body temperaturewith the Blood TemperatureMonitor (Tb: body temperature; R: Recirculation)

Part of the system undercontrol of the BTM

Standard HD

HD with control of thermal energy balance

HD with control of bodytemperature

Dialysate temperature higher than Tart, increase of Tven

Dialysate temperature, Tart and Tven identical

Dialysate temperature lower than Tart, decrease of Tven

Tb?

Tb?

Tb

R

9

As numerous studies have shown, an in-crease in body temperature during dialysishas unfavourable effects on the cardiovas-cular stability of the haemodialysis patient.

The effects of active control of core bodytemperature on cardiovascular stability usingthe BTM, which prevents undesirable rises orfalls in temperature, have been investigatedin several clinical studies [10, 14].

This aspect was investigated in a multicentrestudy conducted in 27 European dialysiscentres [14]. A total of 95 patients, whofrequently suffered hypotensive episodesduring dialysis, received either dialysis withconstant body temperature regulation (in Tcontrol: temperature difference; �T = 0 °C) orwith neutral energy balance in the extra-corporeal circulation (E control: �E=0kJ/h, i.e.with identical arterial and venous tempera-ture) for a period each of 4 weeks.

The results of this study confirmed that it wasnecessary to reduce the temperature of thedialysate during treatment and thus eliminatethermal energy from the patient in order tomaintain the body temperature measured bythe BTM at start of treatment (T control) (Figs.10, 11, 12a).

When in the extracorporeal circulation onlythe supply or removal of thermal energy wasregulated (E control), however, there was anincrease in body temperature (Fig. 12b), whichwas accompanied by increasing dialysatetemperature.

This means that body temperature increasesirrespective of whether thermal energy issupplied via the extracorporeal circulation –probably as a result of the vasoconstrictioninduced by volume reduction and theresultant decrease in heat dissipation fromthe skin.

The use of the BTM in clinical practice

Fig. 10: Course of dialysate temperature in HD withcontrol of thermal energy flow and with control of bodytemperature by the BTM

Treatment time (min)

Dial

ysat

e te

mpe

ratu

re (°

C)

HD with control of thermal energy flow

HD with control of body temperature

Fig. 11: Thermal energy has to be removed duringdialysis to control and to maintain body temperature

Fig. 12a: Course of arterial and venous blood temperatureduring HD with control of body temperature

Treatment time (min.)

Tem

pera

ture

(°C)

Venous fistula temperatureArterial fistula temperature

Fig. 12b: Course of arterial and venous blood temperatureduring HD with control of thermal energy flow

Treatment time (min.)

Tem

pera

ture

(°C)

Venous fistula temperatureArterial fistula temperature

Control of thermalenergy flow

Control of bodytemperature

10

In the prephase to this study, in whichpatients received treatment using dialysatesat the temperatures routinely employed at thecentres, and in the phase in which the ex-change of thermal energy in the extracorporealcirculation only was regulated, hypotensiveepisodes requiring treatment occurred onaverage in 50 % of dialysis treatments. This ratewas significantly reduced to 25 % with activetemperature regulation and maintenance of aconstant core temperature using the tempera-ture control function of the BTM (Fig. 13).

At the same time, blood pressure and heartrate were more stable when body tempera-ture remained constant as a result of activetemperature regulation.

It was also demonstrated in this study andothers, that the dialysis dose, measured asKt/V, was not influenced by temperaturecontrol [10, 14].

Targeted regulation of core body temperatureimproves cardiovascular stability withoutreducing the dialysis dose. The procedure iswell tolerated by patients, as the rapidcooling of blood is avoided, a phenomenon

which can occur when an inappropriately lowtemperature of the dialysate is selected forthe individual patient. There is thus a majorimprovement in the quality of treatment for thepatient. As interventions are less frequentlyrequired, patient care is simplified and theuse of additional therapeutic materials, suchas hypotonic solutions, is reduced.

Targeted regulation of core bodytemperature significantly improvescardiovascular stability and thus alsothe quality of treatment of the patient.

Fig. 13: The frequency of treatments with symptomatichypotension can be reduced by active control of bodytemperature with the BTM

Standard HD(without BTM)

% o

bser

ved

trea

tmen

ts

HD with control ofthermal energy flow

HD with control ofbody temperature

p<0.001

11

Recirculation

If the blood flow to the fistula is lower than theblood flow rate set for the extracorporealcirculation, it is possible that purified venousblood may pass back through the fistula inthe opposing direction and re-enter theextracorporeal circulation. As this means thatthe blood does not pass through the capillarysystem of the body, it will not be loaded withuraemic toxins. As a result, the toxin concen-tration in the blood reaching the dialyser andhence the purification efficiency of the treat-ment are reduced. The dialysis dose achievedwith each treatment is reduced and, over thelong term, this can result in increased morbi-dity in the patient.

In addition to fistula recirculation, cardiopul-monary recirculation can also occur. In thiscase, the right ventricle, lung and leftventricle represent the recirculation pathwayof the purified blood. Cardiopulmonaryrecirculation also leads to a reduction ofclearance.

Using the BTM, it is possible to determine theextent of recirculation by means of a non-invasive temperature bolus technique (seepage 15). This method can be used to detectboth fistula recirculation and cardiopulmonaryrecirculation. The value for recirculation deter-mined by the BTM (given in %) reflects totalrecirculation and is equivalent to the percen-tage of extracorporeal blood recirculating inthe fistula or cardiopulmonary circulation.

If the value for recirculation is low (<10 %),this is probably attributable to unavoidablecardiopulmonary recirculation only.

If the value for recirculation is high (>20 %),there is probably considerable fistula recircu-lation. In this case, it should be ensured thatthe cannulas are appropriately positionedand that the tubes have not been incorrectlyconnected. If there are no such errors, thefistula should be examined for the presenceof any possible stenoses.

If recirculation is in the range 10 – 20 %, itis possible that the patient has a very highrate of cardiopulmonary recirculation or thatthere is fistula recirculation. In order todetermine which of these two alternativesapplies, the blood flow should be increasedor reduced by 100 ml/minute, and therecirculation re-measured. If there is only aslight change in recirculation, cardiopul-monary recirculation is probably the cause. If,on the other hand, there is a marked changein recirculation (>10%), it is more likely thatfistula recirculation is present.

It should be borne in mind wheneverrecirculation is determined that the efficiencyof dialysis is reduced and it is advisable toconsider prolongation of treatment.

Using the BTM, it is possible tomeasure total blood recirculation witha non-invasive technique and thusdetect vascular problems which couldreduce the efficacy of dialysis.

12

The BTM is easy to operate (Fig. 14a, b) andrequires only a few parameters to be set forroutine dialysis treatment. No special con-sumables are required for operation.

A short overview of the operation of the BTMis provided below. Please note that the BTMshould only be used in practice after theoperator’s manual has been studied in detailand the operator has received appropriateinstruction.

Thermal energy andtemperature regulationwith the BTM

Connection of blood lines and initiation of treatment

As the sensor heads are flexible to someextent, blood tubing systems with an externaldiameter of 6.5 – 7.05 mm can be used withthe BTM. It is important to ensure that botharterial and venous blood lines are of thesame diameter.

The arterial line is inserted into the upper,arterial sensor head and then connected tothe arterial blood pump and to the dialyserand dialysis machine as usual.

Similarly, the venous line from the venousbubble trap is inserted into the lower venoussensor. The length of tube between sensorhead and fistula should be approximately 1.5 m(including the tube length used to connect tothe fistula needle). It should be ensured thattubes are not covered e.g. by bed sheets.

Prior to setting a regulation mode, the requireddialysate temperature is set in the dialysismachine in accordance with manufacturer’sinstructions. When the BTM is operative, itregulates temperature in accordance with theselected mode; if there is a malfunction of theBTM or the operation of the BTM is pre-maturely terminated, the temperature settingof the dialyser is automatically used.

Regulation of thermal energy balance in the extracorporeal circulation

In order to set the BTM to regulate thermalenergy balance in the extracorporeal circu-lation, press “E Set” . The energy flow rate(in kJ/h) is set to the required value using thearrow keys . The energy flow rate can beset within a range of –500 to +200 kJ/h. If apositive value is selected, thermal energy issupplied to the patient, if the value is set to 0,the BTM maintains a neutral thermal energybalance in the extracorporeal circulation,while at a negative value, thermal energy iswithdrawn from the patient. Confirm with the“Enter” key .

The value for thermal energy displayedshould be reset to “0” by pressing both arrowkeys so that the energy balance of eachdialysis treatment can be exactly measured.

When the “Enter” key is pressed ,regulation of extracorporeal thermal energybalance is initiated. An LED on the “E Set”key lights up to confirm that this mode isoperational.

Thermal energy balance regulation can beended at any time by again pressing the key“E Set” .

A brief overview of the operation of the BTM

Fig. 14a: Operating elements of BTM

Display

Operating keys fordisplay functions

Arterial sensor head

Venous sensor head

Operating keys forcontrol programmesand recirculation test

13

Regulation of body temperature

In order to set the BTM to regulate bodytemperature, press “T Set” . Bodytemperature adjustment (in °C/h) is set to therequired value using the arrow keys andthe setting is confirmed by pressing the“Enter” key . Body temperature adjust-ment can be set within a range of –0.50 to+0.25 °C/h. At a positive value, body tempe-rature is increased, at a negative setting,body temperature is decreased. If the value isset to “0”, body temperature is maintained ata constant level.

If only the thermal energy balance of the on-going dialysis treatment is to be measured inthis mode, the value for the energy balancedisplayed should also be reset to “0” bypressing the two arrow keys .

When the “Enter” key is pressed ,regulation of body temperature is initiated. AnLED on the “T Set” key lights up to con-firm that this mode is operational.

Body temperature regulation can be ended atany time by again pressing the key “Select Tmode” . In this case, the system auto-matically switches over to the dialysatetemperature previously set at the dialysismachine.

Display of thermal data

Various thermal data can be displayed usingthe keys of the upper row of the panel.

T Art: Arterial fistula temperature in °C, i.e.the temperature of the blood at the entry fromthe fistula to the arterial needle.

T Ven: Venous fistula temperature in °C, i.e.the temperature of the blood in the venousneedle directly prior to re-entry into the fistula.

E: Thermal energy flow rate in kJ/h, i.e.the quantity of thermal energy supplied to orwithdrawn from the patient via the extra-corporeal blood circulation per time unit.

E: Total thermal energy balance in kJ, i.e.the quantity of thermal energy supplied orwithdrawn from the patient since the com-mencement of treatment or resetting of theenergy balance. A negative value means thatthermal energy has been withdrawn from thepatient.

Result (press twice): Current core bodytemperature (displayed for 5 seconds) ascalculated by the BTM. This can only bedisplayed if recirculation has been previouslydetermined. In temperature control mode,this occurs automatically (at start, then athourly intervals and whenever there are largervariations in blood flow). In thermal energyregulation mode, this must be initiatedmanually.

Result (pressfivetimes): Current tempera-ture of the dialysate (displayed for 5 seconds).

Termination of thermal energy ortemperature regulation

The BTM automatically recognises thecompletion of the dialysis treatment; at thispoint, the regulation function is ended andany on-going recirculation measurement isterminated.

If it is necessary to prematurely terminateBTM operation (e.g. at the wish of thepatient), this can be accomplished simply bypressing “T Set” or “E Set” asappropriate, or removing the blood lines fromthe sensor heads. This is automaticallyrecognised by the BTM which then switchesover to the dialysate temperature setting ofthe dialysis machine.

Fig. 14b: Operating keys of the BTM

14

Fig. 15a: Course of arterial (Ta), venous (Tv) and dialysatetemperature (Td) during recirculation measurement

Fig. 15b: Recirculation measured by thermodilution

T a

REC T d

T v

Recirculationmeasurement

For the purpose of recirculation measure-ment, the BTM induces a brief (positive ornegative) temperature bolus, characteristi-cally in the range ±2.5°C, for 2.5 minutes viathe dialysate (Fig. 15). This temperature bolusis transferred to the venous blood and hencevia the venous sensor head to the fistula. Thisbolus is partially transported, via cardiopul-monary and fistula recirculation to the arterialline, where the attenuated bolus is detectedby the arterial sensor head. The relation of thetemperature boluses measured by arterialand venous sensor heads is equivalent to thepercentage recirculation of blood flow.

A recirculation measurement can be initiatedat any time during the dialysis session. Theregulation mode selected for the operation ofthe BTM is briefly interrupted and automaticallyrestarted on completion of the recirculationmeasurement.

To start recirculation measurement, press thekey REC % . When the measurement iscompleted, the percentage recirculation is dis-played for 30 seconds. The result can be redis-played in the following 30 minutes using thekey Result (press once). Recirculation meas-urement requires on average 5 – 6 minutes.

15

Use of the BTM in other treatment modalities

Online Clearance Monitoring OCM®

All functions of the BTM can be used in combination with the option OCM®. Both measure-ment cycles of the BTM and OCM® are synchronised, thus permitting an optimal monitoringon the efficacy of the running treatment.

Blood Volume Monitor BVM

The BTM can be used simultaneously with the BVM, offering an automatic and individuallyadapted control of body temperature and blood volume in order to prevent the occurence of Symptomatic Hypotension.

Single-Needle dialysis

It is not possible to use the BTM during Single-Needle dialysis.

On-line Haemodiafiltration

The BTM can be used during on-line haemodiafiltration with the ONLINEpplluussTM system,irrespective of whether a pre- or post-dilution treatment is provided.

Online Haemofiltration / isolated ultrafiltration

As there is no countercirculation of blood and dialysate during these procedures, it is notpossible to regulate extracorporeal thermal energy balance or body temperature with the BTM. However, fistula temperatures can be measured and the thermal energy balancecalculated on this basis.

Sodium profiles and UF profiles

The BTM can be used in combination with all Sodium and UF profiles.

Central venous catheter

As a certain heat exchange can occur along double lumen central venous catheters, theBTM should only be used in patients with central venous catheters when two separatecannulas are used.

16

Can temperature regulation with the BTM beinterrupted during on-going treatment?

The temperature regulating functions of theBTM can be stopped at any time during on-going treatment. However, it is then notpossible to continue with temperature regu-lation after a restart, as the BTM uses thetemperature at restart as the baseline fortemperature regulation. Hence, the currenttemperature rather than the original tempera-ture on commencement of treatment is takenas target temperature by the BTM after arestart. Thermal energy regulation can becontinued, as this is controlled on the basis ofthe current arterial and venous temperaturesmeasured by the sensor heads.

Can I change the BTM settings duringoperation?

It is possible to adjust set target parametersduring operation, i.e. for thermal balance in theextracorporeal circulation or control of bodytemperature, however, in the latter case, anongoing regulation is interrupted.

Can patients eat or drink during operation ofthe BTM?

It is known that eating and drinking duringdialysis can increase the risk of hypotensiveepisodes, so that dialysis patients withunstable blood pressure are advised not todo so. As during active temperature regu-lation with the BTM the cardiovascularstability may be improved, it could be testedunder close monitoring whether patientstolerate nutritional intake better under theseconditions.

Is it possible to detect fever if the BTM iscounteracting the temperature regulationmechanisms of the body?

The BTM adjusts dialysate temperature onlywithin a very narrow range, generally 35–38°C.Hence, there is no masking of any markedincrease in body temperature e.g. due to apyrogenic reaction while the BTM is active.On the other hand, this might mean that theBTM does not achieve the set target of tem-perature regulation or energy balance.

Do patients experience a sensation ofcoldness during temperature regulation withthe BTM?

There have been only very rare reports ofpatients experiencing a sensation of coldnessduring temperature regulation and stabilisationof body temperature with the BTM. In contrastwith systems in which a dialysate cooled to afixed temperature is used, there is no abruptcooling of the blood, but blood temperature ismaintained at a constant level due to theindividual adjustment of the temperature ofthe dialysis fluid.

Can the BTM also be used during hotweather?

The BTM is preset to operate at a roomtemperature of 23 °C. The device uses thistemperature when calculating the potentialloss of thermal energy along the blood linesbetween sensor head and fistula. The effectsof variations in room temperature of ±2 °C are negligible. If there are consistently largerdeviations in ambient temperature, a differentstandard temperature should be selected forBTM operation in the set-up menu.

Why is there an increase in the extent ofrecirculation during treatment?

During treatment, there is usually a reductionof relative blood volume and thus a decreasein cardiac output. This can lead to an increasein the value determined for recirculation duringtreatment. It is thus advisable to conductmeasurement of recirculation during the first30 minutes of a dialysis treatment.

How frequently should recirculation bemeasured?

It is advisable to measure recirculation asfrequently as possible: if necessary, duringeach treatment. This allows close control ofthe dialysis procedure, so that treatmentduration can be adjusted as necessary toachieve the optimum dialysis dose.

Frequently asked questions

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References

[1] Daugirdas JT: Pathophysiology of dialysis hypotension: An update. Am J Kidney Dis 2001;38 (Suppl. 4): S11-S17.

[2] Steuer RR, Conis JM: The incidence of hypovolemic morbidity in hemodialysis.Dial&Transplant 1996; 25: 272-281.

[3] Schreiber MJ: Clinical dilemmas in dialysis: Managing the hypotensive patient- setting thestage. Am J Kidney Dis 2001; 38 (Suppl. 4): S1-S10.

[4] Bergström J: Why are dialysis patients malnourished? Am J Kidney Dis 1995; 26: 229-241.

[5] Maggiore Q, Pizzarelli F, Sisca S et al.: Blood temperature and vascular stability duringhemodialysis and hemofiltration. Trans Am Soc Artif Intern Organs 1982; 28: 523-527.

[6] Provenzano R, Sawaya B, Frinak S et al.: The effect of cooled dialysate on thermal energybalance in hemodialysis patients. Trans Am Soc Artif Intern Organs 1988; 34: 515-518.

[7] Yu AW, Ing TS, Zabaneh RI, Daugirdas JT: Effect of dialysate temperature on centralhemodynamics and urea kinetics. Kidney Int 1995; 48: 237-243.

[8] Van Kuijk WHM, Hillion D, Saviou C, Leunissen KLM: Critical role of extracorporeal bloodtemperature in the hemodynamic response during hemofiltration. J Am Soc Nephrol 1997;8: 949-955.

[9] Fine A, Penner B: The protective effect of cool dialysate is dependent on patients’predialysis temperature. Am J Kidney Dis 1996; 28: 262-265.

[10] Kaufman AM, Morris AT, Lavarias VA et al.: Effects of controlled blood cooling onhemodynamic stability and urea kinetics during high-efficiency hemodialysis. J Am Soc Nephrol 1998; 9: 877-883.

[11] Jost CMT, Agarwal R, Khair-El Din T, Grayburn PA, Victor RG, Henrich WL: Effects ofcooler temperature dialysate on hemodialysis stability in “problem” dialysis patients.Kidney Int 1993; 44: 606-612.

[12] Tattersall J; 1993, unpublished.

[13] Sherman RA, Rubin MP, Cody RP, Eisinger RP: Amelioration of hemodialysis-associated hypotension by the use of cool dialysate. Am J Kidney Dis 1985; 5:124-127.

[14] Maggiore Q, Pizzarelli F, Santoro A et al.: The effects of control of thermal balance onvascular stability in hemodialysis patients: Results of the European randomized clinicalstudy, Am J Kidney Dis 2002; 40 (Suppl.2): 280-290.

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