ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR

FOR TISSUE VIABILITY MONITORING

Dafina Tanase

Electronic Instrumentation Laboratory, Delft University of Technology, Mekelweg 4, Delft, The Netherlands

Niels Komen

Erasmus Medical Centre, Rotterdam, The Netherlands

Arie Draaijer

TNO Quality of Life, Zeist, The Netherlands

Johan F. Lange, Gert-Jan Kleinrensink, Johannes Jeekel

Erasmus Medical Centre, Rotterdam, The Netherlands

Paddy J. French

Delft University of Technology, Delft, The Netherlands

Keywords: Oxygen-tension sensor, tissue viability, colon, optical method.

Abstract: Leakage at the site of an anastomosis is the main, yet unsolved reason for mortality in abdominal surgery.

Every year, a large number of patients die due to anastomotic leakage after surgery. An objective aid to

monitor the anastomotic site pre- and postoperatively and detect leakage at an early stage, is needed.

Therefore, a miniature, wireless measurement system to detect tissue viability during and after colon

surgery (continuously for 7 days) is being developed. The complete sensor chip should include an oxygen-

saturation sensor (sO

), an oxygen-tension sensor (pO

), a carbon-dioxide tension sensor (pCO

) and a

temperature sensor. The present work focuses on the use of the oxygen-tension and temperature sensors for

animal studies. Initial in-vivo measurements were carried out on the small and large intestines of male

wistar rats. The main goal was to measure the distribution of pO

on the colon around the anastomosis and

to determine the changes in pO

during repetitive ischemia-and-reperfusion experiments on the small

intestine. The paper presents the obtained measurement results.

1 INTRODUCTION

An anastomosis is the surgical connection of two

tubular segments to restore continuity (Figure 1).

Leakage of a colorectal anastomosis is a

complication in which intestinal content leaks into

the abdominal cavity due to a “defect” in the

anastomosis. This defect can be caused by a reduced

oxygen supply and it can lead to cell death and

necrosis of the anastomosis. As a result, leakage can

occur and as a consequence, peritonitis may develop

and can lead further to sepsis, multiple-organ failure

Figure 1: A colon anastomosis.

Tanase D., Komen N., Draaijer A., F. Lange J., Kleinrensink G., Jeekel J. and J. French P. (2008).

ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR FOR TISSUE VIABILITY MONITORING.

In Proceedings of the First International Conference on Biomedical Electronics and Devices, pages 50-55

DOI: 10.5220/0001052300500055

 SciTePress

and ultimately death. Therefore, anastomotic leakage

of a colorectal anastomosis is considered a

potentially lethal complication.

The reported incidence varies between 10 % and

13 % (Kanellos, 2004; Guenaga, 2003; Peeters,

2005), with a mortality rate that can be as high as

32 % (Choi, 2006). To date, no peroperative

methods to avoid or predict anastomotic leakage, or

any validated, objective parameters for detection of

anastomotic leakage in an early postoperative phase,

exist. Current diagnostic methods include

observation of clinical signs and symptoms (fever

and pain), while confirmation is obtained by

imaging. These methods are faced with several

disadvantages. When anastomotic leakage has

progressed to a state of clinical manifestation, the

patient is already ill and treatment needs to be

initiated. Imaging modalities, more specifically

abdominal CT-scans and/with contrast enemas, are

normally used to confirm a clinical diagnosis of

anastomotic leakage, meaning the patient is already

ill (Eckmann, 2004).

At present, clinically relevant anastomotic

leakage is usually diagnosed approximately 6 to 8

days after surgery (Kanellos, 2004; Alves 1999).

Some studies report an even longer interval

(12 days) between operation and diagnosis of

anastomotic leakage (Hymann, 2007). The long

intervals between the construction of the

anastomosis and the diagnosis of anastomotic

leakage are detrimental for the prognosis, increasing

mortality rates (Macarthur, 1998).

Therefore, a biomarker reflecting the viability of

the anastomosis, could be a fast and objective

diagnostic tool in addition to current methods,

allowing diagnosis of anastomotic leakage before its

clinical presentation.

In this respect, the main goal of this research is

to develop a miniature, wireless sensor system to

monitor tissue viability pre- and postoperative,

continuously for 7 days. The complete sensor chip

should include an oxygen-saturation sensor (sO

), an

oxygen-tension sensor (pO

), a carbon-dioxide

tension sensor (pCO

) and a temperature sensor

(Figure 2).

The present work focuses on the use of the

oxygen-tension and temperature sensors for animal

studies.

2 MEASUREMENT SETUP

The measurement setup for the animal studies is

shown in Figure 3. It consists of the pO

and

temperature sensor block and a notebook for reading

and processing the data from the sensors. The

investigations were performed in the Erasmus

Medical Centre in Rotterdam, using male wistar rats,

12 weeks old. They were prepared for surgery by

shaving their abdomen and disinfecting it with 70%

alcohol.

Figure 2: Schematic of the complete sensor system for tissue viability monitoring.

ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR FOR TISSUE VIABILITY MONITORING

Figure 3: Measurement setup at Erasmus Medical Centre

in Rotterdam comprising the sensor block and the

notebook for data processing.

Afterwards, the animal undergoing surgery was

placed on a hot plate and anesthetised throughout the

intervention by administering a mixture of

isoflurane, oxygen and air (the fraction of inspired

oxygen, FiO

=66 %). Access to the internal

anatomical structures of the animals was gained by

laparotomy (surgical incision into the abdominal

wall) with an incision length of 4 cm. After opening

the abdomen and exposing the ascending colon, the

oxygen-tension and temperature sensors were fixed

together and placed at pre-defined locations along

the ascending colon, laterally (with respect to the

peritoneal membrane) and antimesenterial (opposed

to the peritoneal membrane).

The sensors were fabricated at TNO Quality of

Life, The Netherlands (Draaijer, 1999) and they

have been tested in a previous study (Tanase, 2007).

The block diagram of the sensors is shown in

Figure 4. The pO

sensor consists of a coating at the

tip of an optical fibre (3 mm diameter) and works on

the principle of dynamic quenching by oxygen of

fluorescent particles immobilized in a gas permeable

polymer. In our case, the fluorescent particle is

ruthenium, which enters an excited state caused by

the LED excitation with a wavelength of 470 nm.

The excited state of ruthenium is deactivated by the

collision process with oxygen, the particles emitting

light with a wavelength of 600 nm. The emitted

signals are detected by a photodiode (PD) and

converted to a digital signal using an on-board

analogue-to-digital (ADC) converter. The oxygen

concentration is determined by measuring the

fluorescence lifetime. In addition to the pO

sensor,

the sensor block contains the temperature sensor

(NTC type, Farnell), whose output is also converted

via an ADC. The total sequence of data sent to the

computer (via a serial connection RS 232) is BG, I1,

I2 and T (the background, the two intensities at

successive times and the temperature). From these

data, the software (LabView, National Instruments)

computes the oxygen tension and indicates the

temperature.

Figure 4: Schematic of the sensors with the LED driver

circuit, the read-out of the photodiode and of the

temperature sensor.

Figure 5 presents a photograph of the sensor block

with the two sensors and a magnified view of the

fibre tip with the oxygen-sensitive coating.

Figure 5: Photograph of the sensor block with the two

sensors and a magnified view of the fibre tip showing the

oxygen sensitive coating.

Power supply

RS 232

Temperature

sensor

Coating on fibre

senso

Sensor block

Rat undergoing surgery

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices

3 MEASUREMENT RESULTS

Initial tests were performed by placing the sensors

on the colon after the construction of the

anastomosis. Figure 6 shows the sensors at a

distance of 1 cm away from the anastomosis, while

Figure 7 presents the table and graph with the

measurement results, for different sensor locations

around the anastomosis. The sensors were placed

radial (lateral and antimesenterial) and longitudinal,

at ten different locations on both sides of the

anastomosis, as indicated in Figure 7.

Figure 6: Photograph showing the sensors on the colon,

1 cm away from the anastomosis.

The lowest oxygen-tension values are obtained

on the anastomosis (part 3 and part 8 in Figure 7).

This is an expected effect - due to local cell death,

tissue oxygenation at the site of the anastomosis is

reduced. The farther from the anastomosis we

measure, the better the oxygenation, and the higher

the oxygen-tension values. The spikes on the graph

are artefacts visible only at the moments when the

sensors are moved from one tissue location to

another, because then, for a short period of time, the

fibre is in air. The temperature changes

corresponding to tissue and air are visible on the

temperature graph.

Another series of measurements were performed

with the sensors on the small intestine (Figure 8). In

this case, the blood supply to the central part of the

small intestine was obstructed by two strings that

were fastened for ischemia and released for

reperfusion. The measurement results during the

ischemia-reperfusion experiment are shown in

Figure 9.

At the beginning of the test, the sensors were

placed on the small intestine and by fastening the

strings, the intestine was made ischemic (part 1).

The values readily decreased to 4 mmHg, indicating

total ischemia. Once the strings were released, an

overshoot was noted, showing a maximum at

202 mmHg. Two other cycles were repeated to test

the correctness of the measurement. Also in this

case, the results of the tests met our expectations.

In addition to these measurements, other tests

were performed by changing the levels of inspired

oxygen (33.4 %, 42.8 %, 66.7 % and 91 %). We

noted that the local pO

changed accordingly to the

inspired oxygen. For an even better characterisation,

a new series of tests is currently performed, during

which the animals are intubated. In this way, the

inspired oxygen can be accurately controlled, while

the rats are being continuously monitored.

4 CONCLUSIONS

The paper has presented the initial measurements

and results with an optical oxygen-tension sensor

and a temperature sensor. The performed tests have

shown that the principle of optical sensing is suitable

for tissue measurements.

The first series of measurements has shown a

significant decrease (approximately 40 mmHg) in

on the anastomosis as compared to the other

measurement sites on the colon. It was also shown

that on two points (lateral and antimesentery) of the

anastomosis, the values for the pO

were

approximately the same.

The ischemia and reperfusion experiments have

shown that the sensor system reacted as expected to

the local changes on the small intestine. When the

intestine was made ischemic, the pO

decreased and

when the obstruction was removed, the pO

increased significantly, with an overshoot.

This cycle was repeated three times to test the

correctness and repeatability of the measurement.

Sensors

Anastomosis

ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR FOR TISSUE VIABILITY MONITORING

Figure 7: The numeric results and the graphical representation of the tests performed on the colon, to determine the

distribution of the oxygen radially and longitudinally with respect to the anastomosis, at different locations.

Figure 8: An overall view and a close-up of the small intestine showing the strings (used to obstruct the blood flow) and the

sensors.

Strings

Sensors

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices

Figure 9: The graphical representation of the ischemia-reperfusion experiment on the small intestine.

Although not presented in this paper, the first

steps towards an integrated sensor system have been

taken. The sensor-system design is currently

underway and issues regarding device sterilisation

and packaging are already taken into account.

A new study is currently planned for more

detailed investigations, considering also the aspects

of biocompatibility.

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ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR FOR TISSUE VIABILITY MONITORING