GB2607307A

GB2607307A - Paediatric regurgitation monitoring system and method

Info

Publication number: GB2607307A
Application number: GB2107814.2A
Authority: GB
Inventors: Andrew Sutton John
Original assignee: Andrew Sutton
Current assignee: Andrew Sutton
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2022-12-07
Also published as: GB202107814D0

Abstract

A paediatric regurgitation monitoring system 300 and method is configured to detect stomach acid in the oesophagus 101 of a neonatal patient comprises: a first electrode 302a and a second electrode 302b, at least one of which is connected to an electrical power source 301. Both electrodes are attachable to the skin of the neonatal patient such that the electrical power source is operable to cause a current to flow along an internal current path between the first electrode and the second electrode, the internal current path including a portion passing through the oesophagus. An electrical parameter determination module 306 is configured to determine a baseline value of a first electrical parameter and, subsequently, a test value or derived test value of the first electrical parameter. A processor 305 is configured to compare the test value or derived test value of the first electrical parameter with the baseline value of the first electrical parameter, wherein if the processor determines that the test value or derived test value of the first electrical parameter deviates from the baseline value of the first electrical parameter by at least a threshold amount, the processor is configured to generate a signal indicating that stomach acid is present in the oesophagus of the neonatal patient.

Description

PAEDIATRIC REGURGITATION MONITORING SYSTEM AND METHOD

FIELD OF THE INVENTION

The present invention relates to a system and method for detecting gastric malfunction in infants. In particular, the present invention relates to a system and method for detecting stomach acid in the oesophagus of an infant, and in particular in the oesophagus of a neonate.

BACKGROUND

Some infants suffer from gastric malfunction. There is considerable incidence of gastric malfunction in neonates. This can cause acid from the stomach to regurgitate into the mouth where it can be inhaled and cause a fatal pneumonia. Existing systems used to detect acid in the oesophagus of neonates depend upon the unpleasant and occasionally damaging procedure of placing a pH probe in the neonate's oesophagus. This procedure itself risks some regurgitation and even acid inhalation.

A non-invasive system for detecting and monitoring acid reflux in neonates would be highly beneficial. A non-invasive method for obtaining information about acid levels in the oesophagus of a neonatal patient would be beneficial.

SUMMARY OF THE INVENTION

Accordingly, broadly speaking, the present invention is directed towards a system operable to non-invasively detect the presence of stomach acid in the oesophagus of a neonate by measuring the value of a first electrical parameter, such as impedance or conductivity, associated with an internal current path, the internal current path including a portion through the oesophagus of the patient.

Stomach acid has different electrical properties from the tissues which make up the oesophagus, and the tissues which lie around the oesophagus, in particular the typically air-filled lungs. For example, stomach acid includes hydrochloric acid (HCl) and so is highly conductive, whereas the soft tissues around the oesophagus have low conductivities; this is especially true of the lungs. Therefore, the presence of stomach acid in the oesophagus of a neonate can be detected by determining the value of a first electrical parameter of an internal current path, the internal current path including a portion through the oesophagus, as this value will vary depending on whether stomach acid is present in the oesophagus.

Specifically, the presence of acid in the oesophagus of a neonate may be associated with a marked decrease in the overall impedance across the chest or neck, or, correspondingly, a marked increase in the overall conductivity. Systems according to the present invention exploit the detection of such a change to detect when stomach acid is present in the oesophagus of the neonate. For example, if the first electrical parameter value is less than the threshold value, there may be stomach acid present and if the first electrical parameter value is greater than the threshold value, there may be no stomach acid present.

Accordingly, a first aspect of the present invention provides a system for detecting acid in the oesophagus of a neonatal patient, the system comprising: a first electrode and a second electrode, at least one of the first electrode and the second electrode connected to an electrical power source, wherein the first electrode and the second electrode are attachable to the skin of the neonatal patient such that the electrical power source is operable to cause a current to flow along an internal current path between the first electrode and the second electrode, the internal current path including a portion through the oesophagus of the neonatal patient; an electrical parameter determination module configured to determine a baseline value of a first electrical parameter and, subsequently, a test value or derived test value of the first electrical parameter; and a processor configured to compare the test value or derived test value of the first electrical parameter with the baseline value of the first electrical parameter, wherein if the processor determines that the test value or derived test value of the first electrical parameter deviates from the baseline value of the first electrical parameter by at least a threshold amount, the processor is configured to generate a signal indicating that stomach acid is present in the oesophagus of the neonatal patient.

The first aspect of the present invention therefore overcomes the disadvantages of the prior art systems by its ability to non-invasively carry out the detection of stomach acid in the oesophagus of a neonate. It should be noted that the term "derived test value" is defined later in the application.

The system carries out stomach acid detection without the need for complicated processing of the first electrical parameter value data; a meaningful result may be obtained simply by comparing a first electrical parameter value with a baseline value, also determined by the system. It is important to note that characteristic values of the first electrical parameter may vary from individual to individual, so it is advantageous first to determine a baseline and then to compare a test value (or derived test value) with this baseline, rather than setting an absolute threshold. Herein, the processor may be configured to generate the signal when the test value (or derived test value) differs from the baseline value, or the inverse of the test value (or derived test value) differs from the baseline value, by more than 5%, more than 10%, more than 20%, more than 30%, more than 40%, more than 50%, more than 60%, more than 70, more than 80, more than 90, more than 95, or more than 99% of the value of the baseline value.

The large difference in the electrical properties of stomach acid and the tissues which make up the oesophagus, and surrounding tissues mean that the system can be highly sensitive.

Optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention. The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

The first electrode may be attachable to the front of the neonate's chest and the second electrode may be attachable to the back of the neonate's chest, or vice versa. In such cases, the distance between the first and second electrodes may be between 10cm and 20cm. In alternative implementations, the first electrode may be attachable to one side of the neonate's chest and the second electrode may be attachable to the other side of the neonate's chest. In such cases, the distance between the first and second electrodes may be between 20cm and 30cm. Alternatively, in other arrangements, the first electrode may be attachable to the front of the neonate's neck, and the second electrode may be attachable to the back of the neonate's neck, and vice versa. In such cases, the distance between the first and second electrodes may be 10cm to 20cm.

In all these cases, it will be appreciated that the distance between the electrodes is small, which enables the system to be highly sensitive. Without wishing to be bound by theory, it is believed that sensitivity of impedance methods is greatly influenced by distance (impedance believed to vary like the 4th power of the radius). The present invention is therefore particularly effective over the small dimensions associated with neonatal patients.

In preferred implementations of the present invention, the first electrical parameter is impedance. Alternatively, the first electrical parameter may be conductance, which is the inverse of impedance. Stomach acid has a relatively low impedance, and the tissue of the oesophagus and the tissue surrounding the oesophagus has a relatively high impedance. Therefore, the presence of stomach acid in the oesophagus will cause a marked, and therefore detectable reduction in the impedance measured along the internal current path.

Accordingly the baseline value of the first electrical parameter may be a baseline impedance, and the test value of the first electrical parameter may be a test impedance. Then, if the test impedance value falls below the baseline impedance value by at least a threshold amount, the processor determines that there is stomach acid present in the oesophagus of the neonatal patient. Since the impedance of stomach acid is much less than the impedance of the tissues which make up the oesophagus, and the tissues which lie around the oesophagus, the system can be highly sensitive. For example, since the lungs are large air-filled cavities, they can provide a highly impedic background, which contrasts with highly conductive stomach acid. This means that a change in the impedance of the internal current path can be detected, even when stomach acid is present only in small amounts. The system may comprise further pairs of electrodes connected to the electrical power source and attachable to the skin of the patient, in addition to the first electrode and the second electrode. The electrical power source is operable to cause a current to flow along an internal current path between a first electrode and a second electrode in each pair of electrodes, each internal current path including a portion through the oesophagus of the neonatal patient. In the present application, one of the first electrode and the second electrode may be referred to as an input electrode, and the other may be referred to as a detector electrode. This may be the case of each of a plurality of pairs of electrodes.

The system may further be configured to detect how far up the oesophagus stomach acid travels. Specifically, in implementations including a plurality of pairs of electrodes each defining a respective internal current path between a first electrode of that pair and a second electrode of that pair, the electrical parameter determination module may be configured to determine a baseline value of a first electrical parameter and a test value or derived test value of the first electrical parameter. Then, for each pair of electrodes, the processor may be configured to compare the determined baseline value of the first electrical parameter and the test value or derived test vale of the first electrical parameter, and to determine that stomach acid is present in the portion of the oesophagus between the first electrode and the second electrode of that pair if the test value or derived test value of the first electrical parameter deviates from the baseline value of the first electrical parameter by at least the threshold amount. Each pair of electrodes may have a respective threshold amount, which may be different for each pair of electrodes. The processor may be configured to generate a signal indicating for which pairs of electrodes the deviation is at least the threshold amount, thereby indicating that stomach acid is present in the portion of the oesophagus between that pair of electrodes.

In alternative cases, there may be a single input electrode (e.g. a driven electrode), and a plurality of detector electrodes. In that case, the pairs of electrodes may each include the single input electrode, and a different respective detector electrode. The position of stomach acid in the neonatal patient's oesophagus may then be monitored in the way as discussed in the previous paragraph.

The electrical parameter deternination module may include: a first sensor configured to measure the value of a second electrical parameter; and a calculation module configured to calculate a value of the first electrical parameter from the value of the second electrical parameter. The first sensor and the calculation module may be employed in the determination of both the baseline value of the first electrical parameter, and the test value of the first electrical parameter.

Specifically, the first sensor may be configured to measure a baseline value of the second electrical parameter, and the calculation module may be configured to deteluLLine the baseline value of the first electrical parameter from the baseline value of the second electrical parameter. And, the first sensor may be configured to measure a test value of the second electrical parameter, and the calculation module may be configured to determine the test value of the first electrical parameter from the test value of the second electrical parameter. The processor may comprise the calculation module.

The electrical parameter determination module may be configured to determine the baseline value of the first electrical parameter by determining a plurality of values of the first electrical parameter and by deriving a statistical parameter from the plurality of values of the first electrical parameter, preferably a mean value. Alternatively, a median or mode value may be taken. In some cases, a calculation module (which may be part of the processor) may he configured to derive the statistical parameter. The electrical parameter determination module may be configured to determine each value of the plurality of values at regular time intervals. The electrical parameter determination module may be configured continuously to monitor the value of the baseline value of the first electrical parameter. This may be achieved by e.g. determining a moving average value of the first electrical parameter over a predetermined number of samples. Alternatively, the baseline value of the first electrical parameter may be updated as each new value is determined.

In some cases, the first sensor of the electrical parameter determination module may be configured to measure a plurality of values of the second electrical parameter. As above, the plurality of values may be measured at regular time intervals. Then, the calculation module may be configured to derive a statistical parameter from the plurality of values (preferably a mean, but alternatively a median or mode), and to determine the baseline value of the first electrical parameter from the derived statistical parameter. Alternatively, the calculation module may be configured to determine a respective value for the first electrical parameter for each of the measured values of the second electrical parameter, and to derive a statistical parameter from the plurality of determined values of the first electrical parameter, the derived statistical parameter being the baseline value of the first electrical parameter.

After the baseline value of the first electrical parameter has been determined, or initially determined (in cases where it is continuously updated), the electrical parameter determination module may be configured to determine the test value of the first electrical parameter. In preferred cases, the system is a monitoring system, and the electrical dete ination module may be configured to determine a plurality of test values of the first electrical parameter, preferably at regular intervals, for example every second. Then, the calculation module may be configured to derive a statistical parameter from the plurality of test values (preferably a moving average), which may be referred to herein as a derived test value, and to compare the derived test value with the baseline value (in addition to, or instead of, an individual test value). In this way, any anomalous increases or decreases in the first electrical parameter may be ironed out, and not cause generation of a signal when there is no stomach acid present in the oesophagus.

Specifically, the first sensor may measure a plurality of second electrical parameter values. The first sensor may continually measure second electrical parameter values. The calculation module may be configured to calculate a plurality of test values of the first electrical parameter values from a corresponding plurality of second electrical parameter values.

In some cases, the calculation module may be configured to derive a statistical parameter from the plurality of measured second electrical parameter values, or a subset thereof, and to determine the derived test value of the first electrical parameter based on the derived test value.

The time interval between measurements of second electrical parameter values from which respective first electrical parameter values are calculated may be as set out below. For example, second electrical parameter values may be continually measured, but first electrical parameter values may be calculated from a selection of second electrical parameter values, each second electrical parameter value in the selection being measured at intervals as proposed below apart.

In the cases mentioned in the previous three paragraphs, the time intervals may be no less than 10 seconds, no less than 5 seconds, no less than 2 seconds, or no less than 1 second. A time interval of 1 second is preferable.

First electrical parameter values may be determined in real time.

In addition to detecting the presence of stomach acid in the oesophagus of the patient, the system of the present invention may be configured to determine additional parameters based on e.g. the test value of the first electrical parameter, or preferably a plurality of test values of the first electrical parameter. For example, the processor may be configured to determine the duration of time over which stomach acid is present in the oesophagus. This may be achieved by determining the number of consecutive test values which deviate from the baseline value by at least the threshold amount. In some cases, the processor may only he configured to generate the signal when there have been a predetermined number of consecutive determinations that the test value (or derived test value) deviates from the baseline value by the threshold amount. In this way, movement artefacts can be discarded.

The processor may be configured to determine the volume of regurgitated stomach acid based on the same.

The system may be configured to determine the frequency of first electrical parameter values which result in a determination that stomach acid is present in the oesophagus.

The system may further comprise a memory, the memory being configured to store first electrical parameter values and/or second electrical parameter values. When the memory is configured to store second electrical parameter values, the calculation module may be configured to calculate the first electrical parameter values after the second electrical parameter values are measured.

The electrical power source may be a constant current power source operable to cause a constant current to flow along the internal current path. A constant current source is a term known in the art to mean source which generates a current with a magnitude which does not change with input voltage and output load. The magnitude of the constant current output by the power source may be in the range of 1 mA to 10 mA to avoid risk of injury to the neonatal patient. Alternatively, the electrical power source may be a constant voltage power source, or a power source which has neither a constant voltage nor a constant current.

The electrical power source may be an alternating current (AC) constant current source. In this case, the system may further comprise second electrical parameter amplifier means tuned to the frequency of the AC constant current source and configured to amplify measured second electrical parameter values measured by the first sensor.

The first sensor of the electrical parameter determination module may be a voltage sensor configured to measure a voltage value across the internal current path. In this case, the second electrical parameter is voltage. A voltage sensor may comprise a pair of voltage sensing electrodes, the pair of voltage sensing electrodes being a first voltage sensing electrode and a second voltage sensing electrode, attachable to the skin of the neonatal patient. In some cases, one or both of the first voltage sensing electrode and the second voltage sensing electrode may be the same as one or both of the first and second electrodes.

The first and second voltage sensing electrodes may be attachable to the skin of the patient such that they measure the voltage across a portion of the internal current path. The first and second voltage sensing electrodes may be attachable to the skin of the patient such that they measure the voltage across the entire internal current path.

The first voltage sensing electrode may be attachable to the front of the patient's chest and the second voltage sensing electrode may be attachable to the back of the patient's chest.

The first voltage sensing electrode may be attachable to one side of the patient's chest and the second voltage sensing electrode may be attachable to the other side of the patient's chest. The first voltage sensing electrode may be attachable to the front of the patient's neck and the second voltage sensing electrode may be attachable to the back of the patient's neck.

The voltage sensor may comprise least two pairs of voltage sensing electrodes for each first and second electrode connected to the electrical power source.

When the electrical power source is a constant voltage source, the first sensor of the electrical parameter determination module may be a current sensor configured to measure the magnitude of a current through the internal current path. In this case, the second electrical parameter is current. The first sensor of an electrical parameter determination module may be a power sensor, which may comprise a voltage sensor and a current sensor, configured to measure the power through the internal current path. In this case, and the second electrical parameter is power.

The first electrical parameter may be impedance when the electrical power source is a constant current source, and the first sensor is a voltage sensor. In this case, the calculation module calculates an Impedance value using the equation Z = V/I, where Z is the impedance of the internal current path, V is the measured voltage across the internal current path, and I is the magnitude of the constant current through the current path. The magnitude of the constant current output by the power source may be 1 mA to 10 mA as discussed above. The electrical power source may be an alternating current (AC) constant current source. In this case, the system may further comprise a voltage amplifier means tuned to the frequency of the AC constant current source for amplifying voltage values measured by the voltage sensor.

The first electrical parameter may be impedance with an alternative electrical power source and an alternative first sensor. For example, the electrical power source may be a constant voltage power source, and the sensor may be a current sensor.

The first electrical parameter may be a parameter which is not impedance when the electrical power source is a constant current source, and the first sensor is a voltage sensor. For example, the first electrical parameter may be conductance.

An important application of the present invention is for monitoring neonatal patients, in order to ensure that any regurgitation of stomach contents can be dealt with rapidly and safely. Accordingly, the system may include an alarm configured to generate a visible or audible output.

Specifically, the alarm is preferably configured to receive the signal from the processor, and to emit the visible, haptic or audible output in response to receiving the signal. In this way, a clinician's attention can be attracted immediately in response to detection of stomach acid in a neonatal patient's oesophagus.

Broadly speaking, the present invention is also directed to a method of non-invasively obtaining information about acid levels in the oesophagus of a neonatal patient by measuring the value of a first electrical parameter associated with of an internal current path, the internal current path including a portion through the oesophagus of the patient.

Accordingly, a second aspect of the invention provides a method of obtaining information about acid levels in the oesophagus of a neonatal patient, the method comprising: providing a first electrode and a second electrode, at least one of the first electrode and the second electrode connected to an electrical power source; attaching the first electrode and the second electrode to the skin of the neonatal patient such that the electrical power source is operable to cause a current to flow along an internal current path between the first electrode and the second electrode, the internal current path including a portion through the oesophagus of the neonatal patient; providing an electrical parameter determination module configured to determine the value of a first electrical parameter associated with the internal current path; and; operating the electrical power source such that the internal current path flows; comparing the value of the first electrical parameter with a predetermined threshold value; and, determining whether acid is present in the oesophagus of the neonatal patient based on the comparison.

The system used to carry out this method may have any one, or any combination insofar as they are compatible of the optional features set out with reference to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: -Figure 1 shows a cross section of a human chest.

- Figure 2 is a demonstrative plot to show that the presence of stomach acid in the oesophagus may cause a decrease in the impedance measured across an internal current path.

- Figures 3A and 3B each show a schematic diagram of an embodiment of a system according to the present invention.

- Figure 4 shows an embodiment of a processor according to the present invention.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference Figure 1 shows a diagram of the cross section of a human chest (102). The oesophagus (101) can be seen in to lie next to the lungs (103). The stomach (104) lies at the end of the oesophagus (101). The impedance of the oesophagus tissue (101) and of the lungs and lung tissue (103) is high. The impedance of stomach acid is low. Therefore, the presence of stomach acid in the oesophagus (101) will cause a reduction in the impedance of a current path which passes through the oesophagus.

Figure 2 shows a schematic example of a plot of the impedance of a current path through the oesophagus over time. Stomach acid is present in the oesophagus at point 201. No stomach acid is present in the oesophagus at points 202a, 202b.

Figure 3A shows an embodiment of a system (300) for determining whether stomach acid is present in the oesophagus (101) of a neonatal patient by determining the impedance across an internal current path, the internal current path including a portion through the oesophagus (101) of the patient.

The system comprises a first electrode (302a) and a second electrode (302b) connected to an electrical power source (301). The first electrode (302a) and the second electrode (302b) are shown attached to the front and back of the chest (102) of a neonatal patient.

The electrical power source (301) is an AC constant current power source (301) operable to cause a constant current to flow along an internal current path between the first electrode (302a) and the second electrode (302b), the internal current path including a portion through the oesophagus (101) of the neonatal patient.

The system (300) further comprises an electrical parameter determination module (306), for determining the impedance across the internal current path.

The electrical parameter determination module (306) comprises a voltage sensor (303) for measuring the voltage across the internal current path. The voltage sensor (303) comprises a pair of voltage sensing electrodes (303a, 303b). A first voltage sensing electrode (303a) is shown attached to the front of the patient's chest and the second voltage sensing electrode (303b) is shown attached to the back of the patient's chest. The system (300) also comprises a voltage amplifier means (304) tuned to the frequency of the AC constant current source for amplifying voltage values measured by the voltage sensor (303).

The electrical parameter determination module (306) further comprises a processor (305) which comprises a calculation module (401) for calculating the impedance of the internal current path from the voltage measured by the voltage sensor (303).

The calculation module (401) calculates an impedance value using the equation Z = V/I, where Z is the impedance of the internal current path, V is the measured voltage across the internal current path, and I is the magnitude of the constant current through the current path.

The processor (305) is further configured to compare the value of the calculated impedance with a predetermined threshold impedance value and determine whether acid is present in the oesophagus of the neonatal patient based on the comparison; if the calculated impedance is greater than the threshold impedance, stomach acid is not present, if the calculated impedance is less than the threshold impedance, stomach acid is present.

Figure 33 shows an alternative embodiment of a system (300') for determining whether stomach acid is present in the oesophagus (101) of a neonatal patient. In this embodiment, the first voltage sensing electrode (403a') and the second voltage sensing electrode (403a') are the same as the first electrode (302a') and second electrode (302b). Similar reference numerals are used to refer to corresponding features in Fig. 3A.

The processor (305, 305') of the embodiment shown in Figs. 3A and 3B is shown in more detail in Fig. 4. The processor (305, 305') comprises the calculation module (401) , a module (402) to compare the value of the calculated impedance with a predetermined threshold value, and a module (403) to determine whether acid is present in the oesophagus of the neonatal patient based on this comparison.

The system (300, 300') overcomes the disadvantages of the prior art systems by its ability to non-invasively carry out the detection of stomach acid in the oesophagus (101) of a neonate.

The features disclosed in the description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise" and "include", and variations such as "comprises", "comprising", and "including" will be understood to imply the inclusion of a stated integer cr step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means for example +/-105%.

All references referred to above are hereby incorporated by reference.

Claims

CLAIMS1. A paediatric regurgitation monitoring system configured to detect stomach acid in the oesophagus of a neonatal patient, the system comprising: a first electrode and a second electrode, at least one of the first electrode and the second electrode connected to an electrical power source, wherein the first electrode and the second electrode are attachable to the skin of the neonatal patient such that the electrical power source is operable to cause a current to flow along an internal current path between the first electrode and the second electrode, the internal current path including a portion passing through the oesophagus of the neonatal patient; an electrical parameter determination module configured to determine a baseline value of a first electrical parameter and, subsequently, a test value or derived test value of the first electrical parameter; and a processor configured to compare the test value or derived test value of the first electrical parameter with the baseline value of the first electrical parameter, wherein if the processor determines that the test value or derived test value of the first electrical parameter deviates from the baseline value of the first electrical parameter by at least a threshold amount, the processor is configured to generate a signal indicating that stomach acid is present in the oesophagus of the neonatal patient.
2. A paediatric regurgitation monitoring system according to claim 1, wherein: the first electrical parameter is the impedance of the internal current path.
3. A paediatric regurgitation monitoring system according to claim 2, wherein, either: the first electrode is attachable to the back of the chest of the neonatal patient and the second electrode is attachable to the front of the chest of the neonatal patient; the first electrode is attachable to a first side of the chest of the neonatal patient and the second electrode is attachable to a second side of the chest of the neonatal patient, the second side being opposite from the first side; the first electrode is attachable to the back of the neck of the neonatal patient and the second electrode is attachable to the front of the neck of the neonatal patient; the first electrode is attachable to a first side of the neck of the neonatal patient and the second electrode is attachable to a second side of the neck of the neonatal patient, the second side being opposite from the first side.
4. A paediatric regurgitation monitoring system according to any one of claim 1 to 3, wherein: the electrical parameter determination module is configured to determine the baseline value of the first electrical parameter by determining a plurality of values of the first electrical parameter and deriving a statistical parameter from the plurality of values of the first electrical parameter.
5. A paediatric regurgitation monitoring system according to any one of claims 1 to 4, wherein: the electrical parameter determination module includes: a first sensor configured to measure the value of a second electrical parameter; and a calculation module configured to calculate a value of the first electrical parameter from the measured value of the second electrical parameter.
6. A paediatric regurgitation monitoring system according to claim 5, wherein: the first sensor is configured to measure a plurality of values of the second electrical parameter; and the calculation module is configured to: derive a statistical parameter from the plurality of measured values of the second electrical parameter; and determine the baseline value of the first electrical parameter from the derived statistical parameter.
7. A paediatric regurgitation monitoring system according to claim 5, wherein: the first sensor is configured to measure a plurality of values of the second electrical parameter; and the calculation module is configured to: determine a respective value for the baseline value of the first electrical parameter for each of the measured values of the second electrical parameter; and derive a statistical parameter from the plurality of baseline values of the first electrical parameter, the derived statistical parameter being the determined value of the first electrical parameter.
8. A paediatric regurgitation monitoring system according to any one of claims 1 to 5, wherein: the electrical parameter determination module is configured to determine a plurality of test values of the first electrical parameter.
9. A paediatric regurgitation monitoring system according to claim 8, wherein: the electrical parameter determination module is configured to determine the plurality of test values of the first electrical parameter at regular intervals.
A paediatric regurgitation monitoring system according to claim 8 or claim 9, as dependent on any of claims 5 to 7, wherein: the first sensor is configured to measure a plurality of second electrical parameter values; and the calculation module is configured to calculate the plurality of test values of the first electrical parameter from the corresponding plurality of values of the second electrical parameters.
11. A paediatric regurgitation monitoring system according to claim 10, wherein: the calculation module is configured to derive a statistical parameter from the plurality of test values, referred to as the derived test value.
12 A paediatric regurgitation monitoring system according to claim 10, wherein: the calculation module is configured to derive a statistical parameter from the plurality of measured second electrical parameter values, or a subset thereof, and to determine the derived test value of the first electrical parameter based on the derived statistical parameter.
13. A paediatric regurgitation monitoring system according to any one of claims 10 to 12, wherein: the first sensor is configured to measure the plurality of second electrical parameter values at regular intervals.
14 A paediatric regurgitation monitoring system according to any one of claims 8 to 13, wherein: the processor is configured only to generate the signal when there have been a predetermined number of consecutive determinations that the test value or the derived test value deviates from the baseline value by the threshold amount.
A paediatric regurgitation monitoring system according to any one of claims 1 to 14, wherein: the electrical power source includes a constant current source operable to cause a constant current to flow along the internal current path; the second electrical parameter is a voltage across the internal current path; and the first sensor is a voltage sensor.
16. A paediatric regurgitation monitoring system according to claim 15, wherein: the constant current source is an alternating current (AC) source.
17. A paediatric regurgitation monitoring system according to claim 16, further comprising: a voltage amplifier tuned to the frequency of the AC constant current source and configured to amplify measured voltage values measured by the first sensor.
18. A paediatric regurgitation monitoring system according to any one of claims 15 to 17, wherein: the voltage sensor comprises a first voltage sensing electrode and a second voltage sensing electrode.
19. A paediatric regurgitation monitoring system according to claim 18, wherein, either: the first voltage sensing electrode is attachable to the back of the chest of the neonatal patient and the second voltage sensing electrode is attachable to the front of the chest of the neonatal patient; the first voltage sensing electrode is attachable to a first side of the chest of the neonatal patient and the second voltage sensing electrode is attachable to a second side of the chest of the neonatal patient, the second side being opposite from the first side; the first voltage sensing electrode is attachable to the back of the neck of the neonatal patient and the second voltage sensing electrode is attachable to the front of the neck of the neonatal patient; the first voltage sensing electrode is attachable to a first side of the neck of the neonatal patient and the second voltage sensing electrode is attachable to a second side of the neck of the neonatal patient, the second side being opposite from the first side.
20. A paediatric regurgitation monitoring system according to any one of claims 1 to 19, wherein: the system further comprises an alarm configured to receive the signal generated by the processor; and in response to receiving the signal, the alarm is configured to generate a visual, haptic, or audible output.
21. A paediatric regurgitation monitoring system according to any one of claims 1 to 20, wherein: the system includes a plurality of pairs of electrodes, each operable to cause a current to flow through a respective internal current path between a first electrode of that pair and a second electrode of that pair, each internal current path passing through a different respective portion of the oesophagus of the neonatal patient; for each pair of electrodes: the electrical parameter determination unit is configured to determine a baseline value of the first electrical parameter and a test value or derived test value of the first electrical parameter; the processor is configured to compare the determined baseline value of the first electrical parameter with the determined test value or derived test value of the first electrical parameter, and to determine that stomach acid is present in the portion of the oesophagus between the first electrode and the second electrode of that pair if the test value or derived test value of the first electrical parameter deviates from the baseline value of the first electrical parameter by at least a threshold amount.
22. A paediatric regurgitation monitoring method comprising: causing a current to flow along an internal current path between a first electrode and a second electrode, the internal current path including a portion passing through the oesophagus of a neonatal patient; determining a baseline value of a first electrical parameter; determining a test value or derived test value of the first electrical parameter; comparing the test value or derived test value of the first electrical parameter with the baseline value of the first electrical parameter; and if the test value or derived test value of the first electrical parameter deviates from the base line value of the first electrical parameter by at least a threshold amount, generating a signal indicating that stomach acid is present in the oesophagus of the neonatal patient.