Temperature Maintenance Is the Prime Consideration for the Effective and Safe Handling

ABSTRACT:

Temperature maintenance is the prime consideration for the effective and safe handling of the patient. Mistakes regarding to it can lead to life-threatening condition for the patient. The normal body temperature of human is 37.5 deg. Celsius. The blood from blood bank is at lower temperature.It is dangerous to directly infuse cool blood in patient .To avoid hypothermic adverse effects in the patient body while transfusion,real time comparision of blood bag temperature and patient body temperature and accordingly heating is provided to IV line upto themal equilibrium. Thermistor is a very suitable temperature sensor with NTC (Negative temperature co-efficient) is the heart of the WARMER FOR BLOOD INFUSION and is in form of bridge configuration.The device can be hand-held or fixed on IV panel near the patient bed. Blood warmer has advantages of no contamination,easy manipulation,portability ,clear digital temperature indication, with fast result.As being a recent concept based device-it has also limitations and challenges like inability to cool the heated blood and restriction on use i.e. must with doctors prescription.Here is a model which has the same function with use of electronic circuitry at beginner level to better understand the above stated concept of warming of blood. With the latest electronic circuitry comprising of PID programmed microcontroller,and audible alarm system the blood infusion warmer can be made more dynamic but more costly. Undoubtedly, the actual device is altogether different with the aspects of component specifications, accuracy, dynamicity and appearance.We are taking water or dextrose in stead of blood. But, this project is sufficient to provide functional simulation to the actual real-time warmer for blood infusion.

1. Introduction

BLOOD INFUSION WARMER is an advanced device which is aimed to warm the blood prior to transfusion therapy with use of latest technology in place of earlier , insufficient, conventional methods i.e. hot bath.

The main concept behind this project is use of temperature difference signal for proportional heating of the cold blood. This difference is of 2 temperatures.1.of patient body and 2. Of blood bag.

As, sensing range of thermistor is in microvolts, directly the error signal can be given as input to the heating circuit because it will provide insufficient heat production.So,it is required to be properly amplified.So,the block diagram is designed taking into account this matter.

It is not the actual design but at the beginning phase with almost simulation of basic function of the warmer.So,the component specifications may differ from the actual one.

1. Requirement of project

The normal body temperature of human is 37.5 deg.Celcius. The blood stored at lower temperature to lower the metabolic rate and bacterial growth.Now,if it is directly infused in the patient body,it leads to a life-threatening situation due to adverse reaction of normal blood and transfused blood named as “Hypothermia.”The result is shearing of blood cells,slow metabolism due to hypodynamia,ague,spasm of blood vessel,arthrosisache,stomachache,platelet dysfunction, increase in blood viscocity,disturbed CVS function.

To avoid it,BLOOD INFUSION WARMER is used.This device heats the blood of the blood bag till it equals to the body temperature by detecting the temperature difference between both.

Thus it is very needy instrument in operation theatres,I.C.U.s or in other environment which needs transfusion therapy to prevent mishaps related with low temperature blood transfusion.

1. Generalized block diagram:

• 3.1 EACH BLOCK IN BRIEF………

1. Power supply to give d.c.supply to ICs and other devices
2. Temperature sensor with bridge for blood bag temperature.(B)
3. Temperature sensor with bridge for patient body temperature (P)
4. Instrumentation amplifier for channel-1.i.e.B-channel
5. Instrumentation amplifier for channel -2 i.e.-channel
6. Differential amplifier for obtaining temperature difference.
7. Voltage to Current converter to make compatible electrical signal for the heating coil
8. Power amplifier (Optional):to strengthen the V-I output.
9. Heating element i.e. coil coated with mica wound on fabricated steel tube.

• 3.2 BLOCKS CAN BE ADDED AS SORT OF MODIFICATION

ADC- Analog-to- Digital Converter, Microcontroller ,Audible alarm circuit

4. DETAILED DESCRIPTION OF EACH BLOCK:

4.1 BLOCK-0:POWER SUPPLY

This is the main block in any of the electronic as well as biomedical project.Its

main function is to provide electrical excitation.

COMPONENTS USED:

-IC 7812,7912(+12V,-12 V)

-IC 7805,7905(+5V,-5V)

-IC of bridge rectifier

-capacitors of 1000 micro farads,25 volts(2)

-capacitors of 0.1 micro farads(2*4)

-center tapped transformer 12-0-12

CIRCUIT DIAGRAM:

WORKING OF CIRCUIT:

The working of this circuit is so simple .Mains supply is given to the 12-0-12 center-tapped transformer.Output of secondary winding is given to the bridge rectifier IC .Then to get peak-to-peak output voltage signal, capacitors are used.In lab-application,variable power supplies are preferred.

4.2 BLOCK-1:TEMPERATURE SENSING CIRCUIT (OF BLOOD-BAG)

This block senses the temperature of the blood bag by thermistor as a sensor.Themistor are most commonly used for moderate temperature range (ofcourse not for very high temperatures).They have negative temperature co-efficient.Thermistors are temperature sensitive resistors.Thermistors are constructed of semiconductor material with a resistivity that is especially sensitive to temperature. However, unlike most other resistive devices, the resistance of a thermistor decreases with increasing temperature. That's due to the properties of the semiconductor material that the thermistor is made from.That’s why it is called NTC(Negative Temperature Co-efficient)temperature sensors.Thermistor used here is in form of bridge configuration so as to provide temperature compensation and the circuit for it is given below.

In this bridge circuit, three resistors are constant, Ra, Rb, and Rc, while the resistive sensor, Rs, varies depending upon some physical variable - like temperature, light level, etc. That's where the thermistor can be used.

The thermistor can be placed anywhere in the bridge with three constant resistors, but different placements can produce different behavior in the bridge. For example, different placements might cause the output voltage to go in different directions as the temperature changes.

COMPONENTS USED:

Thermistor

resistors of 10k (2)

Variable resistor (pot) of 22k.

5 V D.C. power supply.

CIRCUIT DIAGRAM:

WORKING OF CIRCUIT:

This is temperature sensing bridge. Firstly, temperature of interest is sensed and manually bridge balance condition i.e. null output is obtained by varying the pot. Now as the ambient temperature is changed, accordingly change in the output (shown in fig. by encircled v.)This output is further given as input to the instrumentation amplifier1.

4.3 BLOCK-2:TEMPERATURE SENSING CIRCUIT (OF PATIENT)

This block senses the temperature of the patient body by thermistor as a sensor.So it is obvious that all the details regarding to sensor will be same to that given in the description i.e. circuit diagram,components used etc. on the previous block.

NOTE: For sake of simplicity and to reduce complexity of temperature circuitry, both the bridge channels are mounted on same GPB.

Thermistor specifications:

NTC-Negative Temperature Co-efficient

Value of co.eff.-,,

Temperature(Degree Celsius) / Ohm
20 / 134.52
40 / 149.79
60 / 165.9
80 / 182.84
100 / 200.64

4.4 BLOCK-3: INSTRUMENTATION AMPLIFIER1 (B CHANNEL)

This block provides sensor output signal the sufficient amplification so as to drive further circuits properly and without loading.Generally 3 Op-Amp instumentation amplifier is employed in biomedical projects.”B channel” refers to the blood-bag channel. As thermistor senses in range of microvolts,we have to amplify it in 2 stages of 1000 gain.

Instrumentation amplifiers are actually made up of 2 parts: a buffered amplifier OP1, OP2 and a basic differential amplifier OP3. The differential amplifier part is often essential when measuring sensors. Because a sensor produces a signal between its terminals.The buffered amplifier OP1 and OP2 not only provides gain, but prevents the sensor resistance from affecting the resistors in the op amp circuit, and vice-versa! The gain can be calculated by:

where R1=R3 and R5/R4 = R7/R6.(R5=RF).

Gain calculations:

Gain(A)= (1+(2*(R1/R2))*(RF/R4)

Taking A=1000 & diving 1000 as 500*2,

1+2R1/R2=2

2R1/R2=1

2R1=R2

Taking R2=2K ,R1 =1K.

Now,RF/R4=500K

R4=1K ,RF=500K

=1MOhm || 1MOhm

=(1000000*1000000)/(1000000+1000000)

=500 K.

COMPONENTS USED

IC OP07(3)

Resistors of 1K (4 no.s)

Resistors of 2K (2 no.s)

Resistors of 1Mohm(2 no.s)

Power supply of 12 V.d.c.

CIRCUIT DIAGRAM:

WORKING OF CIRCUIT:

The instrumentation amp offers two useful functions: amplify the difference between inputs and reject the signal that’s common to the inputs. The latter is called Common Mode Rejection (CMR).OP1 and OP2 are the two input amp’s and connected in the non-inverting follower configuration.It is the solution for the high gain and high input impedance.

Note:This is of high gain circuit so before soldering it on GPB, connectivity check of all the components as per circuit diagram twice on bread-board is advisable.There may chances of unpredictable o/p due to IC saturation.

4.5 BLOCK-5:INSTRUMENTATION AMPLIFIER (P CHANNEL)

The circuit diagram,component specifications,working of the circuit,other details will be remaining same as block-4 except the change in channel.Here “P Channel”refers to Patient-channel.Ofcouse,to reduce complexity,direct IC for it is available & can be used.(for above block also.)

4.6 BLOCK-6: DIFFERENTIAL AMPLIFIER

This block provides error signal by detecting temperature difference of both channels.As mentioned earlier,to get conversion of main sensor signal(without process) from microvolts to volts,2 phasic amplification is done.Phase-1 is given by instrumentation amplifier (mv) and remaining is given by this block.

Expressions of o/p of differential amplifier of gainA,i/p v1 and v2 is given by:

Vo=A(v1-v2) and A= -RF/R1.

COMPONENTS USED:

-IC 741(1)

-resistors of 10k (3)

-resistor of 10 ohm(1)

-15 v.d.c.supply

CIRCUIT DIAGRAM:

WORKING OF CIRCUIT:

There are 2 inputs in each teminal of op-amp.1)from B-Channel instrumentation amplifier.2)from P-channel instrumentation amplifier.Now as name suggests,It amplifies the difference between i/p 1&2 by gain 1000.So,finally the thermistor initial o/p is converted into volts.

4.7 BLOCK-7: VOLTAGE TO CURRENT CONVERTER

This block provides conversion of the output of differential amplifier to the correspoing value of current that a heating coil is capable to handle.

COMPONENTS USED:

resistors of 1k(4)

resistor of 1 megaohms(1)

5V D.C.supply,15V D.C.supply.

IC 741

CIRCUIT DIAGRAM:

This circuit is known as V-I converter with the grounded load.The other configuration that can be used is V-I converter with floating load.

WORKING OF CIRCUIT:

The main working is based on the well-known Ohm’s law.Acoording to this law,in the given conditions,voltage and current are directly proportional.It is given by

V=IR(R is constant of proportionality called Resistance-a property of material to oppose the current flow.)

I=(V/R)

thus here I=5/1000=5 mA.

4.8 BLOCK-8: HEATING ELEMENT

This is the block which performs heating operation on the cold blood of the blood bag equal to the patient body temperature.A very thin coil of mica is wound on the grooved surgical stainless steel tube. This typical design requires the fabrication. As the no. of turns increases the heating efficiency is increased. One has to take care about heating path.i.e. there should be no overlapping of coil. If so,it will lead to the damage of the coil material due to excessive heating.the dimensions and design of this block is in the schematic given below.

SCHEMATIC OF HEATING TUBE:

5. The Blood Warmer Model At a glance………..

Figure: Blood Infusion Warmer Model Schematic

6.Applications of Blood Infusion Warmer:

In health care centers

In transfusion therapy room

In anaesthesia

In blood bank……

7.Technical Specifications of Actual Device:

Device: Blood and infusion warmer

Type designation: Protherm II

Voltage: 230 V, 50–60 Hz

Power consumption: 1200 W

Current: 6 A

Type of protectionagainst electric shock: I

Degree of protectionagainst electric shock: B

Degree of protectionagainst ingress of liquids: IPX4 splash proof

Temperature selection: 37°C to 41°C in 0.5°C increments

Safety features: multiple independent cut-off from 42°C

Warm up time: 40 sec. max

Dimensions: 390 x 278 x 96 mm

Weight: 5 kg

Type of operation: continuous operation

Degree of pre-heat: less than 2 minits

8. Cost of the Project :

9.Advantages:

• Liquid warmed gently by three independently controlled

heat zones

• Permanently running self-tests and error display

• Easy to service with serial interface

• Ergonomic design makes it easily transportable and mountable

on all commercially available infusion stands

• Low cost disposables

• Quick readiness for operation

• Low temperature alarm

• Automatic adaption of the heating control system to various media

• Simple,user-friendly,fast operation
• No requirement of external heating techniques i.e.,circulating warm air,hot bath to blood bag,heating lamps,blankets,and also internal core heating techniques involving cadio-pulmonary bypass or continuous arteriovenous rewarming.

10.Limitation:

It cannot facilitate cooling of the warmed blood heated above limit to control temperature within normal physiological range.

11.Future Expansions:

Thinking with being more technological,we can also make this device as same as that available in market.This is possible by use of microcontroller based configuration and a more advanced version to that is also there –PID TYPE CONTROLLER.(PROPORTIONAL-INTEGRATE-DIFFERENTIAL)Which gives dynamic heating with elimination of overshoots and undershoots while running heating profile.

12.Conclusion:

13.References:

-

-

-

-Indian Medical Journal of Anaesthesiology,issue- August-2008.

-Analog Integrated electronics by Ramakant Gayakwad.

-Texas medical research paper on transfusion.

Created by:

Abhilash V.Nair

Khyati M.Dave

Vatsal A.Chhaya

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