Improvements in or relating to neonatal sensor devices
The invention relates to devices for monitoring the condition of neonates. In neonates, and especially in premature neonates or other neonates requiring special clinical care, it is common for an umbilical arterial catheter to be introduced into the neonate via the umbilical cord to permit the delivery into the neonate of nutrient solutions, drugs and other solutions and removal of blood samples for remote laboratory tests.
In a known sensor device for use in neonates, the sensor device includes an elongate probe which can be advanced along a previously introduced catheter and can monitor the concentration of various analytes, in particular dissolved oxygen, carbon dioxide and hydrogen ions, as oxygen partial pressure (p02) , carbon dioxide partial pressure (pC02) and pH, in the neonatal blood. That known device permits information relevant to the neonate' s condition to be obtained without the need for insertion of any additional access device. Furthermore, the data is available substantially continuously and without frequent withdrawal of blood samples, offering considerable advantages over the intermittent readings that are available from samples taken for laboratory analysis.
It is known to site a blood pressure measurement device in an umbilical arterial catheter. In that case, if the sensor device described above is also present, it is necessary for the sensor to be of a size such that the catheter can be subjected to a continuous flush of heparinised solution with the sensor in situ, to retain patency and facilitate blood pressure transduction. The sensor probe must, as a result, be of small diameter, for example, 500μm. The sensor probe can be introduced through the catheter and advanced to a position at which its tip is beyond the open end of the catheter. The tip of the sensor is provided with a radio-opaque marker to enable its position to be confirmed by x-ray examination. The known sensor has a pressure monitoring port to which a pressure monitoring line can be attached, and pressure measurement relies upon a transducer which is located externally of the patient. The invention provides a sensor device for use in a neonate, comprising an elongate flexible probe for insertion into a blood vessel of the neonate, the elongate flexible probe comprising a distal portion comprising an optical analyte sensor for monitoring an analyte in neonatal blood and a proximal portion which can communicate with an interrogation device for interrogating said analyte sensor, the probe further comprising an elongate flexible housing extending along said proximal or distal portions and enclosing said analyte sensor, the housing being permeable to said analyte for permitting access thereof to said sensor, wherein the elongate flexible housing further comprises an aperture and a lumen communicating with said aperture and enclosed within said housing for delivery of fluids into or withdrawal of fluids from the blood vessel in use of the device.
Advantageously, the device further comprises a pressure sensor.
In another aspect, the invention provides a sensor device for use in a neonate, comprising an elongate flexible probe for insertion into a blood vessel of the neonate, the elongate flexible probe comprising a distal portion comprising an optical sensor for monitoring an analyte in neonatal blood and a proximal portion which can communicate with an interrogation device for interrogating said optical sensor, the probe further comprising an elongate flexible housing extending along said proximal and distal portions and enclosing said analyte sensor, the housing being permeable to said analyte for permitting access thereof to said sensor, wherein the probe further comprises a pressure sensor. Advantageously, the pressure sensor is housed within the elongate flexible housing. Advantageously, the pressure sensor is housed within the distal portion of the probe. Advantageously, the proximal portion of the housing may incorporate kink-resisting means. Advantageously, the pressure sensor is located at or in the vicinity of a distal end of the probe. Where the pressure sensor is enclosed within the elongate housing, the probe should be so arranged that pressure externally of the probe can be detected by the pressure sensor inside the housing and, with that in mind, a region of the housing in the vicinity of the pressure sensor may be arranged to permit transmission of external pressure to the interior of the housing. For example, a region of the housing in the vicinity of the pressure sensor may be microporous. Advantageously, the pressure sensor is a pressure transducer. Any suitable form of pressure sensor may, however, be used. For example, the pressure sensor may be a strain-gauge.
Advantageously the pressure sensor is connected to a fibre-optic cable for permitting optical interrogation of the pressure sensor. Where appropriate, the pressure sensor can be connected to an electrically conductive cable for transmission of the measured pressure data.
Advantageously, the device comprises a connector, the proximal portion of the probe being attached to the connector for communication of data from the analyte sensor and the pressure sensor to the connector. Preferably, the connector is arranged to permit connection of the sensor device to a base unit for communication of the data to the base unit. Advantageously, the analyte sensor is an optical sensor suitable for determining an analyte selected from p02, pC02 and pH. Preferably, there is at least a second analyte sensor, for determining a second analyte. More preferably, the sensor device is suitable for determining p02, pC02 and pH. Preferably, the or each analyte sensor is an optical sensor.
In practice, the device may advantageously comprise three or more analyte sensors, and especially a first optical sensor for p02, a second optical sensor for pC02 and a third optical sensor for pH. Suitable optical sensors include, but are not limited to, those comprising an optical waveguide containing a plurality of cells containing an indicator sensitive to the gas to be measured, such as the absorption indicator-based pC02 and pH sensors and fluorescence indicator-based p02 sensor of the device known as Paratrend made by Diametrics Medical Limited of High Wycombe, England.
Advantageously, the sensor device further comprises a temperature measurement device, for example, a thermocouple.
Advantageously, the device comprises a lumen extending along the elongate probe within said elongate flexible housing and having an aperture in a lateral wall of the housing through which fluid may be delivered into or withdrawn from the neonate. Advantageously, the probe comprises a housing which is an elongate flexible tube, which is preferably closed at the distal end of the probe. Advantageously, the elongate flexible housing is microporous at least in the region of the or each analyte sensor and the pressure sensor. Advantageously, the housing is porous over a length of 15 to 30 mm. The housing is advantageously a monolithic structure of which a portion has been rendered microporous. The pores may be of diameter of, for example, from 0.1 to lOμm.
Preferably, the pores are of diameter from 0.1 to 5μm. The elongate flexible tube may be of any suitable material. Suitable materials are biocompatible, especially biocompatible polymeric materials, for example, polyurethane and silastic polymers. Advantageously, the probe has an external diameter of not more than 1.2mm.
It will be appreciated that the dimensions of the pores will be selectable having regard to the species to which they are desired to be permeable. It will often be desirable selectively to control the permeability of the housing by filling the pores with a filling material that is selectively permeable to the desired species, for example, blood gas. Advantageously, the analyte sensor (s) within the housing will be surrounded by a matrix which is permeable to the analyte to be detected.
At least a region of the housing in the vicinity of the sensors is microporous. The sensor probe is advantageously from 30 to 40 cm in length.
It will be appreciated that references herein to an "elongate flexible probe" or to an "elongate flexible housing" are to be understood as referring to probes and housings which are sufficiently flexible to be introduced into a neonatal blood vessel without causing clinically unacceptable interference with the material, structure or functioning of that blood vessel. The term "flexible" is not to be taken as implying uniform flexibility of the probe or housing along the length thereof and, indeed, it may in certain circumstances be desirable for a minor proportion of the probe to be relatively inflexible provided that the flexibility of the probe or housing as a whole does not lead to clinically unacceptable interference with the material, structure or functioning of that blood vessel.
The invention also provides a method of monitoring a neonate, comprising inserting into a blood vessel of said neonate a sensor device comprising at least one optical analyte sensor housed within an elongate flexible housing, permitting a blood analyte to permeate through said housing to said sensor, and introducing fluid into and or withdrawing fluid from the blood vessel through a lumen within said housing. Advantageously, two or more analytes are measured. Preferably, the pressure is measured using a pressure transducer or gauge. Advantageously, data relating to the pressure is transmitted optically to a monitoring device. Advantageously, data relating to the pressure is transmitted electrically to a monitoring device.
Moreover, the invention provides a method of monitoring a neonate, comprising inserting into a blood vessel of said neonate a sensor device comprising an analyte sensor, housed within an elongate flexible housing, and a pressure sensor, permitting a blood analyte to permeate through said housing to said analyte sensor and monitoring pressure and the concentration of one or more analytes in the blood of the neonate . One illustrative embodiment of the invention will now be described in detail with reference to the accompanying drawings, of which:
Fig. 1 is a plan view of a device according to the invention; Fig. 2 is a schematic view of distal portion of the device of Fig. 1;
Fig. 3 is a longitudinal section of the distal portion of the device.
Referring to Fig. 1, the sensor device 1 has an elongate probe portion 2 which has a distal portion 3 terminating at distal end 4 and a proximal portion 5 which is attached at proximal end 6 to a bifurcated connector 7. Connector 7 communicates with a sample withdrawal lumen 8 and an electro- optical cable 9. Electro-optical cable 9 terminates at electro-optical connection 10, which is suitable for connection to suitable data processing means, not included in Fig. 1.
The probe portion 2 has an elongate cylindrical housing 11 which is closed at distal end 4 and open at proximal end 6. The cylindrical housing is formed from a polyurethane catheter in which a closure is formed at distal end 4. The closure at the distal end 4 is smoothly curved to permit an even flow of blood around it in use. Any suitable housing may, however, be used. For example, the housing may comprise a silastic material laid down on a kink free wire coil 12 (see Fig. 2) . The kink free wire coil, where present, may extend from proximal end 6 towards distal end 4, but will terminate at a point spaced from distal end 4 and in particular will not be present in the region of the probe portion in which the sensing means are located.
Fig. 2 shows schematically a distal portion 3 of the device 1. Analyte sensors for determining p02, pC02 and pH, a thermocouple and a pressure sensor are located within the distal portion 3, enveloped by the housing 11. A microlumen 12 extends from an access opening 13, provided laterally in housing 11, along the probe portion 2 to proximal end 6, from which it communicates with sample withdrawal lumen 8. The internal diameter of microlumen 12 is about lOOμm. Kink free wire coil 12 terminates at a point 14 approximately 2.5cm from distal end 4 and the analyte sensors, thermocouple junction and pressure sensor are all located between the point 14 and distal end 4. In that region, the polyurethane housing 11 is microporous, comprising a multiplicity of laser machined holes of diameter 5μm which are substantially uniformly spaced at a spacing of 62μm between adjacent pore centres. The sensors are integrated within the housing 11 in the sense that they form a unitary structure therewith so that there is substantially no relative movement, in use, between the sensors and the housing 11. The overall diameter of the probe 2 is 1.2mm, and the length of the probe is about 35cm.
Referring to Fig. 3, the polyurethane catheter may be coated with a thin coating of modified heparin (not shown) . The distal portion 3 encloses in the vicinity of distal end 4 three analyte sensors 15, 16, 17. Analyte sensors 15, 16, 17 are optical sensors of known construction. Analyte sensor 15 is a pH sensor comprising an optical fibre 18 through a distal sensing portion of which extends a helical array of apertures, which are so arranged that all parts of the cross sectional area of the fibre are interrupted by at least one of the apertures. Each of the apertures is filled with a pH sensitive indicator, for example phenol red in a gel. The optical fibre 18 also has an optical transmission portion (not shown in Fig. 3) extending from the distal sensing portion to connector 7 by means of which it can be connected via electro-optical cable 9 to a light source and a data collection and/or processing device. A mirror is provided embedded in the distal end of the fibre 18. Optical radiation transmitted along fibre 18 is reflected by the mirror and passes back along the fibre 18. The transmitted and reflected light passes through the indicator-containing apertures and the amount of light absorbed gives an indication of the pH of the medium in which the sensor is located. Analyte sensor 16 is of similar construction to sensor 15 except that it contains an indicator sensitive to oxygen, for example, a fluorescent indicator such as ruthenium dye in a silicone matrix.
Analyte sensor 17 is a pC02 sensor which is of broadly similar construction to sensor 15 except that the indicator is suitable for detection of C02. For example, the indicator may be phenol red in a solution which is a source of bicarbonate ions. Sensor 17 is enveloped by a tubular membrane of C02-permeable polymer, for example polyethylene. Analyte sensors of the kind described above are present, for example, in the sensor devices described in US 5 596 988.
A pressure sensor 20 is located adjacent to the distal end 4 and close to the microporous region of housing 11 by means of which the pressure in the immediate vicinity of the sensor device can equilibrate with the pressure of the interior of the device where it can be measured by the sensor 20. The sensor 20 is a pressure sensor of the kind made by RADI Medical and known as the Pressure Wire O (trade mark) . That sensor uses essentially a strain gauge piezo-resistance technique, using a pressure sensitive diaphragm of micro- machined silicon. The sensor 20 has an input 21 and an output 22 which are connected via electrical wires (not shown in Fig. 3), extending along the probe 2, to connector 7 for the input of electrical current and output of a measurement signal corresponding to the pressure.
Other suitable sensors include fibre-optic sensors, for example, a fibre-optic pressure transducer of the kind made by FISO Technologies, which has a diameter of 550μm. The fibre-optic sensor can be connected via an optical fibre and the electo-optical cable 9 to a source of light by means of which the sensor can be interrogated using white light interferometry .
The sensor device also includes a thermocouple 23.
With reference to Fig. 1, the elongate sensor probe 2 is connected at its proximal end to connector 7 which in turn can be connected via electro-optical cable 9 to a light source from which light of wavelengths suitable for interrogation of the sensors may be transmitted to the optical fibres 18, and to a data processing unit from which the data received from those optical fibres, optionally after analysis, may be transmitted to a display device, for example, a monitor.
As may be seen from Fig. 3, the analyte sensors 15, 16, 17, the pressure sensor 20 and the thermocouple 23 are embedded in polyacrylamide gel 24, which fills the interior of the distal portion 3 of the sensor probe 2 and maintains the sensors 15, 16, 17, 18 and thermocouple 23 substantially in their relative positions within the housing 11.
The device may be manufactured by any suitable method. By way of example, the housing 11, for example of polyurethane, incorporating kink free wire 12 may be preformed as a continuous tube having lengths of wire-free tube at suitable intervals. Pores may be formed by any suitable method. For example, where the housing is of polyurethane, the pores may be formed by laser machining in the wire-free portions . Suitable lengths of the tube may then be cut, terminating with a wire-free portion. The sensors and the sample lumen may then be threaded into the tube, which can then be backfilled with polyacrylamide gel to fix the sensors in position and provide a permeable matrix around the sensors and lumen. The end closure may then be formed and the lumen access opening located by locating the lumen onto a pin and thermoforming the tip of the tube into the desired smooth configuration, with the desired location of the lumen access laterally of and to the rear of the tip 4.
In use, the probe 2 of the sensor device may be introduced into the vasculature of the neonate via the umbilical cord, and the distal end 4 advanced and positioned in a desired location, for example, the descending aorta. Once in place, and following a short time in which the pressure within the sensor probe can equilibrate with the external pressure, the pressure sensor 20 is interrogated using a suitable frequency current. The analyte sensors 15, 16, 17 are similarly interrogated using respective appropriate light sources. The analyte and pressure measurements may be exhibited on any suitable display device, for example, a monitor. Fluids, for example, drugs or nutrients may be introduced into the neonate or blood samples withdrawn via the microlumen 12 and sample withdrawal lumen