Vascular access monitoring device
A vascular access monitoring device for monitoring characteristics of a skin piercing vascular access device comprising: an acoustic sensor operable to detect an acoustic emission created by flow through said vascular access device and produce an electrical signal indicative of said emission; electronics processing means for processing and monitoring said electrical signal, and to determine, by identifying a change of characteristic of said signal, the possibility that the vascular access device has become dislodged from its normal working position.
1. A vascular access monitoring device fbr monitoring characteristics of a skin piercing vascular access device, the monitoring device comprising:
an acoustic sensor operable to detect an acoustic emission created by flow through said vascular access device and produce an electrical signal indicative of said emission; and
an electronic monitor that monitors said electrical signal and processes it to determine, by identifying a change of characteristic of said signal, the possibility that the vascular access device has become dislodged from its normal working position;
wherein the electronic monitor comprises an electrical input that, in use, receives a signal from an extracorporeal blood pump; and
wherein said extracorporeal blood pump is arranged for intermittent pumping and the electronic monitor receives a signal indicative of a pumping cycle of said extracorporeal blood pump.
2. The monitoring device according to claim 1 , wherein:
the electronic monitor is phase locked with the pumping cycle of the extracorporeal blood pump and wherein said electronic monitor compares the electrical signals on successive cycles of the extracorporeal pump as it induces flow through said vascular access device.
3. The monitoring device according to claim 1 wherein:
the electronic monitor monitors background noise and subtracts the background noise from the signal indicative of the acoustic emission.
4. The monitoring device according to claim 3 , wherein:
the background noise includes noise created by a patient's heartbeat.
5. The monitoring device according to claim 4 , further comprising: a second acoustic sensor located on a patient's body, remote from said vascular access device, for measuring the background noise.
6. The monitoring device according to claim 1 , wherein:
the monitoring device monitors background noise in between pumping cycles of the extracorporeal blood pump.
7. The monitoring device according to claim 6 , wherein:
the acoustic sensor comprises a single acoustic sensor that is used for creating a signal indicative of acoustic noise due to flow through the vascular access device and indicative of the background noise.
8. The monitoring device according to claim 1 , further comprising:
a second monitoring device for monitoring presence of the skin piercing vascular access device, the second monitoring device including:
a mount having an ultrasonic transmitter and an ultrasonic receiver therein,
attachment means for attaching the mount to a patient adjacent a vascular access point such that, in use, the vascular access device entering a patient at the vascular access point, passes underneath a sensing section of the mount, and
control electronics to monitor an ultrasonic signal received at the receiver;
wherein when the vascular access device is underneath said sensing section, ultrasound produced by said transmitter passes through a patient's skin and is reflected by a patient's body tissues and by the vascular access device, and when the vascular access device is not underneath said sensing section, ultrasound produced by said transmitter passes through a patient's skin and is reflected by a patient's body tissue only, and
wherein the control electronics detect, the presence of a vascular access device by performing a comparison on the received ultrasonic signal.
9. The device according to claim 8 , wherein:
the transmitter of the second monitoring device periodically emits an ultrasonic pulse and the receiver receives a reflected ultrasonic pulse.
10. The device according to claim 8 , wherein:
the control electronics monitor the received signal from the receiver of the second monitoring device received within in a particular time window, that time window being based on a maximum and minimum expected time of flight of an ultrasonic pulse from the transmitter, to the vascular access device and back to the receiver.
11. The device according to claim 10 , wherein:
the time window exceeds an expected window by a factor relating to a margin of error.
12. The device according to claim 8 , wherein:
the control electronics of the second monitoring device are configured to identify ultrasonic reflections from first and second surfaces, one of which is the vascular access device, and the control electronics detect a change in the received signal.
13. The device according to claim 8 , wherein:
when the vascular access device is located beneath the sensing section of the second monitoring device, the received signal shows altered characteristics.
14. The device according to claim 13 , wherein:
by comparing subsequent received signals received from the receiver of the second monitoring device, a change in the received signal can be identified by the control electronics and a warning can be raised that the vascular access device has become dislodged.
15. The device according to claim 13 , wherein:
by comparing the received signal to a transmitted signal, characteristics of the received signal can be identified by the control electronics of the second monitoring device and a warning can he raised when the vascular access device becomes dislodged.
16. The device according to claim 13 , wherein:
by comparing the received signal from the receiver of the second monitoring device to a model received signal, characteristics of the received signal can be identified by the control electronics of the second monitoring device and if they deviate from the model signal more than a prescribed amount, a warning can be raised that the vascular access device has become dislodged.
17. The device according to claim 8 , wherein:
an amplitude of at least a part of the received signal received by the receiver of the second monitoring device changes dependent on the presence of the vascular access device.
18. The device according to claim 8 , further comprising:
an ultrasonic coupling means configured for, in use, ultrasonically coupling the second monitoring device to a patient's skin.
19. The device according to claim 8 , further comprising:
means for connection to a medical apparatus.
20. The device according to claim 19 , wherein:
when dislodgement of the vascular access device is sensed, the control electronics send a control signal indicative of that to the medical apparatus, the control signal forming a part of a control algorithm for the medical apparatus.
21. The device according to claim 19 , wherein:
the control electronics are configured to periodically receive an interrogation from the medical apparatus to perform a self diagnosis check, to carry out a self diagnosis check and to send a confirmation signal to the medical apparatus indicative that the diagnosis check was successful and the second monitoring device is working properly.