AU7018800A

AU7018800A - Improvements relating to catheter positioning

Info

Publication number: AU7018800A
Application number: AU70188/00A
Authority: AU
Inventors: Simon Andrews; Robert Mcnair; Aws Nashef; Ted Vander Wiede; Stephen Wilson
Original assignee: Aortech International PLC
Current assignee: Omega Critical Care Ltd
Priority date: 1999-08-26
Filing date: 2000-08-25
Publication date: 2001-03-19
Also published as: MXPA02002088A; WO2001013789A1; NZ517437A; EP1207783A1; CA2382222A1

Description

WO 01/13789 PCT/GBOO/03266 1 1 IMPROVEMENTS RELATING TO CATHETER POSITIONING 2 3 The present invention relates to improvements for the 4 positioning of catheters monitoring cardiac output 5 data. 6 7 US 5509424 describes a catheter having a heat transfer 8 device near its distal end for use in monitoring 9 cardiac output within an artery. The apparatus 10 determines cardiac output using selected features 11 derived from a temperature difference signal based on 12 measurement of average native blood temperature 13 detected at a proximal temperature sensor from the 14 temperature of a heating coil detected by a distal 15 temperature sensor. 16 17 An important consideration in the use of such catheters 18 is the importance of the location of the catheter and 19 its heat transfer device. The main pulmonary artery of 20 a human is generally only about five centimetres long, WO 01/13789 PCT/GBOO/03266 2 1 and it is important to have the catheter positioned 2 correctly in order to obtain the correct cardiac output 3 (CO) information. 4 5 According to a non published study in 60 patients, the 6 tip of a catheter, after normal flotation of the 7 catheter into the main pulmonary artery (PA), could be 8 between 0-8 cm in the left or right main branch of the 9 PA. In the case of a catheter that relies on thermal 10 dilution for the determination of cardiac output (CO), 11 this positioning is acceptable. However, in the case 12 of a catheter as described in US 5509424 which relies 13 on the heat transfer principle for measurement of 14 cardiac output, the position of the heat transfer 15 element (HTD) is critical. If the HTD is located in a 16 branch, then it will sense part of the flow giving a 17 lower CO. Also if the HTD is near high turbulence, for 18 example, near a valve or bifurcation, it would give 19 higher CO. Hence it is important to control the 20 position of HTD in order to improve the overall 21 accuracy of CO determination. 22 23 One design of a cathater according to US 5509424 has a 24 heat transfer device located at 7.5 cm from the distal 25 tip (figure 1). This will ensure, based on the 26 clinical study mentioned above, that the HTD would not 27 be in a branch in 95% of the cases. However, based on 28 one clinical study in 20 patients, there appeared to be 29 a position influence in about 20-30% of the time (CO 30 determined by heat transfer was significantly lower 31 than CO determined by thermal dilution). 32 WO 01/13789 PCT/GBOO/03266 3 1 It is an object of the present invention to provide 2 apparatus and method for a catheter for positional 3 information. 4 5 According to one aspect of the present invention, there 6 is provided a catheter which includes means to measure 7 local pressure at two or more points along the catheter 8 body. 9 10 The points are preferably located in two different 11 pressure areas. The catheter preferably has a heat 12 transfer device thereon, more preferably at or near its 13 distal end. 14 15 The pressure measuring means may be fluid filled lumens 16 which allow transmission of a pressure waveform to a 17 pressure transducer which may be located outside the 18 patient. Alternatively, pressure transduction means 19 may be located at these points and the signal 20 transmitted via electrical cables, fluid or fibre 21 optic. The transduction means itself may be optical, 22 semiconductor or some other means. The pressure 23 measuring means may be identical or different. The 24 transmission could pass along only one lumen. 25 26 The measuring means is preferably two or more pressure 27 measuring devices such as diaphragms located along the 28 length of the catheter body. The information from the 29 different pressure measuring means can be referenced 30 and calculated to indicate the position of the 31 catheter, more particularly the catheter tip and any 32 heat transfer device, in a blood vessel, organ or 33 similar. The catheter could use an existing lumen or WO 01/13789 PCT/GBOO/03266 4 1 includes an additional lumen to relay the information 2 from the pressure measuring means to its proximal end. 3 4 According to a second aspect of the present invention, 5 there is provided a method of gauging the positional 6 location of a catheter in a blood vessel, organ or 7 similar, the catheter having means to monitor the local 8 pressure at two or more points along the catheter body, 9 wherein the catheter is located along two different 10 pressure areas, and the pressure differential 11 measurements between the points in the two different 12 areas is indicative of the location of the catheter. 13 14 The pressure detecting means of the present invention 15 could be located across a valve in a blood vessel, 16 organ or similar, eg the heart. In one embodiment of 17 the present invention, one pressure detecting means is 18 located in the pulmonary artery, and one pressure 19 detecting means is located in an adjoining ventricle. 20 The known different pressures of the blood in the 21 pulmonary artery and the ventricle will create a 22 pressure differential, and with knowledge of the artery 23 pressure at the valve, the pressure differential 24 information can be used to ensure that the catheter tip 25 and heat transfer device is located where desired, eg 26 whether the tip is in the atrium, the ventricle or in 27 the pulmonary artery. 28 29 Typically a catheter according to the present invention 30 will have means to locate pressure points so that the 31 heat transfer device is in the centre of the main 32 pulmonary artery. 33 WO 01/13789 PCT/GBOO/03266 5 1 According to a third aspect of the present invention, 2 there is provided a method of gauging the positional 3 location of a catheter in a blood vessel, organ or 4 similar, the catheter having means to monitor the local 5 pressure at a point along the catheter body, wherein 6 the catheter is located in a first position in the 7 vessel, organ or similar, and the local pressure 8 measured, and the catheter is then moved to a second 9 position in the vessel, organ or similar, and the local 10 pressure measured, and the pressure measurements at the 11 first and second locations are indicative of the 12 location of the catheter. 13 14 This method would use only one pressure measuring means 15 to detect the pressure waveforms. This allows 16 minimising the size of a catheter for applications 17 requiring the least possible outer diameter, for 18 example in paediatric or neonatal cardiovascular 19 system. The catheter would be moved forward until the 20 indicative pressure waveform (measured by the pressure 21 measuring means) changed indicating that the sensor had 22 crossed a valve. The catheter could then be withdrawn 23 until the valve is crossed again, to confirm the 24 position. In this way any part of the catheter at 25 fixed, known distances from the pressure sensing means 26 can have location known relative to the position of the 27 valve. 28 29 In a preferred embodiment, the catheter could have 30 calibrated distance markings on its outer surface to 31 assist in accurate determination of insertion and 32 withdrawal distances. 33 WO 01/13789 PCT/GBOO/03266 6 1 According to a fourth aspect of the present invention 2 there is provided a catheter which includes internal 3 fluid piping whose fluid pressure is relatable to the 4 general pressure of surrounding fluid external to the 5 catheter, and at least one means to measure the fluid 6 pressure in the internal piping. 7 8 The piping could directly use a portion of the fluid 9 surrounding the catheter. Alternatively, the piping 10 could relay information from an external pressure 11 measuring means such as a diaphragm. The catheter 12 preferably has a heat transfer device at or near its 13 distal end. 14 15 Embodiments of the present invention are shown by way 16 of example only in the accompanying diagrammatic 17 drawings in which; 18 19 Figure 1 is a cross-sectional view through part of a 20 first catheter according to the present invention; 21 22 Figure 2 is a cross-sectional view through a part of a 23 second catheter according to the present invention; and 24 25 Figure 3 shows R.V. and PA traces provided by the 26 catheter shown in Figure 2. 27 28 Figure 4 illustrates positioning of a Pulmonary Artery 29 Catheter. 30 31 Referring to the drawings, Figure 1 is a cross 32 sectional view of a section of a first catheter 2, 33 having an internal fluid piping 4. Each end of the WO 01/13789 PCT/GBOO/03266 7 1 piping 4 is covered by a diaphragm 6 aligned with the 2 catheter outer wall 8. The piping 4 is filled with a 3 fluid 10 such as a sterile saline solution or gel. The 4 fluid should be non-toxic and bio-compatible. 5 6 In the middle of the piping 4 is a third diaphragm 11 7 connected to a pressure sensor (not shown) at the end 8 of a lumen 14. 9 10 In use, this section of the catheter 2 is intended to 11 be located across a differential pressure boundary 12 (dashed line A-A) such as a heart ventricle valve, such 13 that the pressure on one of the end diaphragms 6 of the 14 piping 4 is different to that on the other. The 15 different pressures on the end diaphragms 6 will result 16 (through the internal fluid 10) in movement of the 17 intermediate diaphragm 11, and movement of this 18 diaphragm 11 can be measured by the pressure sensor. 19 20 With knowledge of the blood pressure at and around the 21 heart, positive confirmation of the correct location of 22 the catheter 2 can be provided by waiting for the 23 desired pressure measurement to be sensed, confirming 24 the location of the piping 4 across a valve. The 25 precise position of the catheter tip and any associated 26 heat transfer device can then be confirmed, also 27 allowing correct determination of information relating 28 to the heat transfer device. 29 30 Figure 2 shows a second catheter body 12 which has two 31 measuring means 13, 14, with respective waveform 32 transmissions means 13a, 14a. The dashed line BB 33 indicates a pulmonary valve. The pressure waveform WO 01/13789 PCT/GBOO/03266 8 1 trace measured at position 13 would be as shown in 2 Figure 3; the waveform indicative of the right 3 ventricle, R.V. Similarly, position 14 would show the 4 waveform indicative of the pulmonary artery PA also 5 shown in Figure 3. When the catheter 12 was so 6 positioned as to give these respective waveforms the 7 user would know the location of the pressure measuring 8 means 13, 14 and hence the location of any other part 9 of the catheter 12 which is a fixed distance along the 10 catheter from those means. For example, if the distal 11 tip 16 was 10 cm from point 14, then the user would 12 know that the tip was approximately 10 cm from the 13 pulmonary valve. Similarly for a heat transfer device 14 15, located for example 1cm from point 14. 15 16 Figure 4 illustrates positioning of a pulmonary artery 17 catheter. The catheter (2) extends through the 18 Superior Vena Cava (17), into the Right Atrium (18), 19 into the Right Ventricle (19), into the Main Pulmonary 20 Artery (20) and into the Right Pulmonary Branch (21). 21 Use of pressure detecting means allows the heat 22 transfer device to be positioned in the main pulmonary 23 artery. 24 25 The present invention provides two approaches for 26 actual clinical practice; 27 28 Approach 1 29 30 Provide a separate lumen for pressure monitoring. A 31 current catheter according to US Patent No 5509424 has 32 a cross section having 6 lumens described as follows: 33 WO 01/13789 PCT/GBOO/03266 9 1 The proximal injectate lumen terminates at a port 2 located 30 cm from the distal tip. When the 3 distal tip is located in the pulmonary artery, the 4 proximal injectate port resides in the right 5 atrium or vena cava, allowing for bolus cardiac 6 output injections, right arterial pressure 7 monitoring, blood sampling, or infusion of 8 solutions. 9 10 The pulmonary artery (PA) distal infusion lumen 11 terminates at the distal tip. During insertion, 12 this port is used to monitor catheter location, 13 via transitional pressure measurements. At full 14 insertion, this port resides in the pulmonary 15 artery, (allowing for pulmonary artery and 16 pulmonary capillary wedge pressure measurements) 17 or mixed venous blood sampling. This port also 18 allows for infusion of solutions, pressure 19 monitoring or blood sampling. 20 21 The distal and proximal thermistor lumens contain 22 the electrical leads for the thermistors, which 23 are positioned on the catheter surface, 24 approximately 7.5 cm and 11 cm respectively from 25 the distal tip. The thermistors are used to 26 measure temperatures and in conjunction with the 27 thermal coil, generate data used to calculate 28 cardiac output. The distal thermistor is located 29 immediately below the thermal coil. 30 31 The thermal coil lumen contains leads for the 32 thermal coil, which is located 7.5 cm from the 33 distal tip. The thermal coil generates heat WO 01/13789 PCT/GBOO/03266 10 1 necessary for maintenance of a constant 2 temperature differential between the proximal and 3 distal thermistors. The energy required to 4 maintain the fixed temperature differential, is 5 used to calculate cardiac output continuously. 6 7 The balloon inflation lumen has a one-way stopcock 8 at its proximal end and terminates in a latex 9 balloon at the distal tip. When the catheter is 10 properly positioned in the pulmonary artery, the 11 balloon is inflated intermittently for the 12 measurement of pulmonary artery wedge pressure. 13 The balloon is inflated by a volume restricted 14 syringe. 15 16 By combining the two thermistors and coil wires in one 17 lumen, two lumens become available to be used for 18 pressure monitoring. 19 20 In the first approach there is a slot (PC1) at 3cm 21 below the heat transfer device (HTD), in one of the two 22 vacated lumens, and another slot (PC2), in the second 23 vacated lumen, at 2 cm above HTD. When the catheter is 24 floated in place, the trace of PC1 should be PA 25 waveform, and PC2 should be the right ventricular (RV) 26 waveform if the HTD is located in mid PA. Manipulation 27 of catheter position to achieve these traces ensures 28 always locating the HTD in the right place. 29 30 Approach 2 31 32 Another approach would be to vacate only one lumen to 33 use only one slot either below or above the HTD.

WO 01/13789 PCT/GBOO/03266 11 1 2 A. For example, if the pressure slot is located 3-4 3 cm below the HTD, the catheter can be advanced 4 until this pressure slot shows a PA trace, then it 5 is withdrawn slightly (e.g. 1 cm increments) until 6 an RV trace is obtained. The HTD will then be in 7 the main PA just after the pulmonic valve. 8 9 B. Or, the slot is placed 2 cm above the HTD. When 10 the catheter is in place, withdraw catheter until 11 an RV trace is observed, then advance 4 cm into 12 PA. The HTD is then in the main PA above the 13 pulmonic valve. 14 15 16 The present invention can be used to more accurately 17 have knowledge of the position of the catheter in a 18 blood vessel, organ or similar. Where the catheter 19 includes a heat transfer device, the position of the 20 heat transfer device can be more accurately calculated, 21 and thus the nature of the heat measurements and 22 associated cardiac information can be more accurately 23 determined. 24 25 Particular applications for this invention include: 26 27 ensuring that a component is located in the 28 pulmonary artery 29 30 ensuring that a component is located in the right 31 ventricle 32 WO 01/13789 PCT/GBOO/03266 12 1 ensuring that the distal tip of a product is not 2 more than a certain distance beyond the pulmonary 3 valve. 4 5 The last point is relevant to any pulmonary artery 6 catheter. It is important for the wellbeing of 7 patients that the tip of any pulmonary artery catheter 8 is not allowed too far beyond the pulmonary valve. 9 10 The novel apparatus and methods of the present 11 invention could also be used in non-medical fields 12 requiring accurate positioning of elongate tubing and 13 the like in remote locations. Such fields include 14 aeronautics, any fluid flow analysis, food and drink 15 processing and monitoring, water and sewerage 16 management, chemical engineering, fuel supply to 17 engines, etc. Indeed, the present invention is also 18 applicable to any device required to be placed beyond a 19 one-way valve in a fluid flow situation, and/or any 20 fluid flow situation which exhibits a pressure 21 differential.

Claims

1. A catheter having a catheter body, wherein the body includes means to measure local pressure at two or more points along the catheter body.

2. A catheter as claimed in Claim 1 wherein the measuring means comprises two or more pressure measuring devices located along the length of the catheter body.

3. A catheter as claimed in Claim 2 wherein the pressure measuring devices are diaphragms.

4. A catheter as claimed in Claim 1 wherein the means comprises one or more fluid- filled lumens or piping.

5. A catheter as claimed in Claim 4 having one or more intermediate diaphragms across the or each lumen or piping.

6. A catheter as claimed in any one of the preceding Claims which includes a pressure transduction means.

7. A catheter as claimed in Claim 6 which includes signal transmission means able to transmit local pressure information from one or more points along the catheter body to the proximal end of the catheter.

. A catheter as claimed in 7 wherein the signal is transmitted via one or more electrical cables, fluid or fibre optic.

9. A catheter as claimed in any one of the preceding Claims wherein pressure measurement information is passed along the catheter through one or more lumens in the catheter body.

10. A catheter as claimed in any one of the preceding Claims which includes one or more heat transfer devices.

11. A method of gauging the positional location of a catheter in a blood vessel, organ or similar, the catheter having means to monitor the local pressure at two or more points along the catheter body, wherein the catheter is located along two different pressure areas, and the pressure differential between the points in the two different areas is indicative of the location of the catheter.

12. A method as claimed in Claim 11 wherein the pressure monitoring means is located across a valve in a blood vessel organ or similar.

13. A method as claimed in Claim 12 wherein the pressure monitoring means is located across a valve in the heart.

14. A method of gauging the positional location of a catheter in a blood vessel, organ or similar, the catheter having means to monitor the local pressure at a point along the catheter body, wherein the catheter is located in a first position in the vessel, organ or similar, and the local pressure measured, and the catheter is then moved to a second position in the vessel organ or similar, and the local pressure measured, and the pressure measurements at the first and second locations are indicative of the location of the catheter.

15. A method as claimed in Claim 14 for a paediatric or neo-natal catheter.

16. A method as claimed in Claim 14 or Claim 15 wherein the catheter is located in a first position on one side of a valve, and in the second position on the other side of the valve.

17. A method as claimed in any one of Claims 14-16 wherein the catheter has calibrated distance markings on its outer surface.

18. A catheter which includes internal fluid piping whose fluid pressure is relatable to the general pressure of surrounding fluid external to the catheter, and at lest one means to measure the fluid pressure in the internal piping.

19. A catheter as claimed in Claim 18 wherein the piping uses a portion of the fluid surrounding the catheter.

20. A catheter as claimed in Claim 18 wherein the piping relays information from an external pressure measuring means.

21. A catheter as claimed in Claim 20 wherein the external pressure measuring means is a diaphragm.

22. A catheter as claimed in any one of Claims 18-21 which includes a heat transfer device at or near its distal end.

23. A catheter as claimed in any one of Claims 1 to 10 and 18-22 for use in any one of: aeronautics, fluid flow analysis, food and drink processing and monitoring, water and sewage management, chemical engineering, fuel engine supply.