Vascular access monitoring device

1. A monitoring device for continuously monitoring the presence of an unattended skin piercing vascular access device, the monitoring device comprising:

an ultrasonic transmitter configured to transmit an ultrasound signal pulse;

a sensing section having an ultrasonic receiver configured to receive a reflected ultrasound signal;

attachment means for attaching the monitoring device to a patient adjacent a vascular access point such that, in use, a vascular access device entering the patient at the vascular access point passes underneath the sensing section of the monitoring device; and

control electronics configured so that, in use, the control electronics activate the transmitter to transmit the ultrasound signal pulses, and monitor an amplitude of the reflected ultrasound signal received by the receiver to determine whether the received reflected ultrasound signal was reflected only by the patient's body tissue or, alternatively, was reflected by both the patient's body tissue and the vascular access device that has been inserted underneath the sensing section;

wherein, when the vascular access device is underneath said sensing section, the ultrasound signal pulses transmitted by said transmitter pass through the patient's skin and are reflected by the patient's body tissues and by the vascular access device, and when the vascular access device is not underneath said sensing section, the ultrasound signal pulses transmitted by said transmitter pass through the patient's skin and are reflected by the patient's body tissue only;

wherein the determination by the control electronics of whether the ultrasound signals received by the receiver were reflected only by the patient's body tissue consists essentially of comparing the amplitude of the reflected ultrasound signals across a frequency spectrum received by the receiver to a control signal, and detecting whether there is a difference in amplitude between the reflected ultrasound signals received by the receiver and the control signal; and

wherein, if the difference is detected, the control electronics automatically take appropriate action as a consequence of dislodgement of the vascular access device; and

wherein the appropriate action comprises at least one of generating a warning signal that the vascular access device has become dislodged and stopping a medical procedure using the vascular access device.

2. The device according to claim 1 , wherein the control electronics are configured so that, in use, the ultrasonic signal pulses transmitted by the ultrasonic transmitter are transmitted periodically.

3. The device according to claim 1 , wherein:

the control electronics monitor the reflected ultrasound signals received by the receiver within a particular time window, that time window being based on a maximum and minimum expected time of flight of the ultrasound signal pulses from the transmitter, to the vascular access device and back to the receiver.

4. The device according to claim 3 , wherein: the particular time window exceeds an expected window, between the minimum expected time of flight and the maximum expected time of flight, by a factor relating to a margin of error.

5. The device according to claim 1 , wherein the control signal is an ultrasound signal previously received by the receiver.

6. The device according to claim 1 , wherein the control signal is an ultrasound signal transmitted by the transmitter.

7. The device according to claim 1 , wherein the control signal is a model signal.

8. The device according to claim 1 , further comprising:

an ultrasonic coupling means for, in use, ultrasonically coupling the device to the patient's skin.

9. The device according to claim 8 , wherein:

the ultrasonic coupling means comprises a coupling gel encapsulated in a flexible pack.

10. The device according to claim 9 , wherein:

the flexible pack has a thin outer membrane such that, in use, the outer membrane conforms substantially to contours of the patient's skin, thereby substantially filling any space between the monitoring device and the patient's skin.

11. The device according to claim 1 , wherein the attachment means comprises a strap to pass around a section of the patient's body.

12. The device according to claim 1 , further comprising:

an electrical connection for connecting the monitoring device to a medical apparatus.

13. The device according to claim 1 , further comprising:

a wireless transceiver for wireless communication with a medical apparatus.

14. The device according to claim 1 , wherein the appropriate action comprises the generating of the warning signal indicating that the vascular access device has become dislodged.

15. The device according to claim 1 , wherein:

the control electronics are configured to periodically receive an interrogation to perform a self diagnosis check, to carry out the self diagnosis check, and to signal the device is working properly.

16. The device according to claim 1 wherein:

the ultrasonic transmitter is a piezo transmitter.

17. The device according to claim 1 , wherein:

the transmitter and receiver comprise a single transceiver.

18. The device according to claim 1 , further comprising:

a power source.

19. The device according to claim 18 , wherein:

the power source is a re-chargeable battery.

20. The device according to claim 19 , wherein:

the re-chargeable battery is wirelessly re-chargeable and is fully encapsulated within the monitoring device.

21. A kit comprising:

a monitoring device in accordance with claim 1 for continuously monitoring the presence of an unattended skin piercing vascular access device; and

an ultrasonic coupling gel, encapsulated within a flexible membrane to form a thin flexible gel pack; and

wherein the flexible membrane allows passage of ultrasound therethrough.

22. A kit according to claim 21 , wherein:

the flexible membrane comprises two planar sides of flexible membrane material joined around their edges.

23. A kit according to claim 21 , wherein a side of the flexible membrane intended to be placed adjacent the patient's skin comprises thin flexible membrane material that, in use, conforms substantially to contours of the patient's skin.

24. A kit according to claim 21 , wherein:

the flexible membrane has a thickness equal to, or less than one third of, a wavelength of the ultrasound signal pulse transmitted from the ultrasonic transmitter.

25. A kit according to claim 21 , wherein:

the ultrasonic coupling gel is characterised in that it has a transmission frequency optimised to be substantially that of a transmission frequency of the ultrasound signal pulse transmitted by the ultrasonic transmitter.

26. A kit according to claim 25 , wherein:

the ultrasonic coupling gel has an optimum transmission frequency in a range of 100 kHz to 2 MHz.

27. A kit according to claim 21 , wherein:

the flexible membrane prevents evaporation of water therethrough.

28. A kit according to claim 21 , wherein:

the flexible membrane is semi permeable, and permits slow evaporation of water therethrough.

29. A kit according to claim 28 , further comprising:

a sealed outer package in which the gel pack is provided, the outer package preventing evaporation from the ultrasonic coupling gel.

30. A kit according to claim 29 , wherein:

the flexible membrane retards evaporation such that, after removal from the outer package, the gel pack retains sufficient ultrasonic coupling gel therein to function fully for at least 12 hours before its ultrasonic coupling properties become diminished to an extent that coupling performance is affected.