GB2075683A - Method and apparatus for facilitating central venous pressure measurements - Google Patents

Abstract

A height indicating device for use with a central venous pressure manometer comprises a liquid filled U-tube 8 one end of which is attached to a patient 1, and the other to a scale 10. A pointer 9 is set to indicate a datum corresponding to the initial height of the part of the patient to which the end is attached. Any change in height is then read on the scale and used to correct manometer readings. <IMAGE>

Description

SPECIFICATION Method and apparatus for facilitating central venous pressure measurements.

This invention relates to a method of and means for facilitating central venous pressure measurements by means of a manometer.

A central venous pressure manometer reading has to be taken in relation to a reference or zero point related to the horizontal level of a predetermined zone on the patient. This level is normally that of the right atrium. This requirement often complicates the taking of pressure measurements. The posture of the patient or the height or attitude of the support on which the patient is lying may have period- ically to be altered for medical or surgical reasons.

It is difficult to make correct compensation for such changes when taking readings and the alternative procedure of restoring the patient to the correct predetermined position is time consuming and may be harmful.

According to the present invention there is provided a method of measuring central venous pressure by means of a manometer characterised in that use is made of a patient position indicating device comprising a flexible U-tube containing liquid which maintains a common level in the tube limbs, one of such limbs being associated with a vertical scale so that the magnitude of variations of the liquid level from a zero or reference level can be noted, and such magnitude is used as a compensating factor to derive actual venous pressure or pressure variations from the manometer reading.

The said magnitude constituting the compensating factor may of course in any given instance be zero. This will be the case if the patient's posture or spatial position effectively corresponds with a predetermined one such that the liquid level in the U-tube coincides with a zero or reference point.

The vertical scale can be any suitable units.

Preferably the scale is calibrated in volume or pressure units which can be directly added to or subtracted from the values read from the manometer scale. Preferably one and the same scale is used for the manometer and position indicator readings. This can easily be done by disposing the distal limb of the Utube and the manometer riser in adjacent parallel relationship in association with a common scale.

Preferably use is made of a small bore flexible U-tube containing mercury. The use of such an indicator is very advantageous from the point of view of sensitivity. A tube with a very small or capillary bore, e.g. of about 1 mm diameter, is very suitable.

In carrying out the invention the proximal limb of the U-tube is advantageously attached to the patient in the area of the manubrium and the tube is set up so that the liquid level is at the horizontal level of the right atrium.

The proximal limb is attached to the patient in such manner that is allows the attachment zone on the patient's body to move through certain angles in vertical and horizontal planes without necessitating objectionable changes in the orientation of the attached part of the tube or in the spatial relationship between that part and said attachment zone such as would falsify the compensating factor represented by changes in the common liquid level. The foregoing will be the normal manner of use but other arrangements are possible and can be adopted if circumstances so require, provided a viable reference level is established with which subsequent liquid level readings can be compared.In the said normal use the liquid level when the tube is set up as referred to can be taken as the zero level and recorded as such e.g. by setting the zero point of a movable scale against the liquid level and/or by means of a suitable marker such as a cursor or other slidable member.

The invention includes a reference level indicating device for use in carrying out the method hereinbefore defined. Thus the invention includes a reference level indicating device for use in conjunction with a central venous pressure manometer said device comprising a flexible hermetically sealed tube which contains liquid and can be supported in the form of a U in the opposed limbs of which the liquid maintains a common level, said tube permitting inspection of the liquid level through its wall; and said device also comprising means for attaching a limb of the U when so formed to a patient so that changes in the horizontal level of the point of attachment to the patient can be measured in terms of variations in said liquid level.

Preferably the liquid in the tube is mercury.

The tube should be sealed at negative internal pressure.

Preferably at least one of the tube ends is sealed by means of a collapsible end comporient which can serve as a reservoir for receiving liquid from the tube. Such end component(s) is or are preferably of bulbous form, like a balloon. The presence of at least one said collapsible end component affords a number of important advantages. The device can be packaged, stored and transported with the liquid held in the or one of the reservoirs if it has adequate capacity, which is preferably the case. Secondly, when setting up the device, squeezing of the collapsible end component(s) not only expels liquid into the tube but assists in ensuring that an uninterrupted column of liquid is established within the U-tube.Furthermore the presence of said collapsible end component(s) prevents the required liquid level changes from being interferred with by the retarding effect of internal negative pressure variations above the liquid.

Preferably there is a said collapsible end member at each end of the tube.

In preferred embodiments of the invention the tube and/or any said collapsible end member is/are enclosed by an outer envelope with a protective function. In the event of rupture of the tube containing the liquid or of a said collapsible end member spillage of liquid from the device is prevented. The liquid is retained by the outer envelope. This protective measure is of course highly desirable when using mercury as the filling liquid, as is preferred.

A protective envelope for a collapsible tube end member must of course itself be collapsible to permit the end member to be collapsed by squeezing its envelope. The envelope of the liquid-holding tube must itself be flexible to allow the tube and its envelope to be supported in U-configuration.

The means for attaching the tube to a patient may comprise a fastening member with a contact face for seating against the patient's body e.g. at the region of the manubrium and a tie member, preferably a flexible tie member, for connecting said fastening member to the tube near one end thereof. The fastening member may of course be permanently connected to the tube. The fastening member may carry a contact adhesive for enabling it to be adhesively secured to the patient's skin. The fastening member may for example be in the form of a pad of the general form and size of an E.C.G. electrode and in fact such an electrode of standard form can be used. The tie may be connected to the fastening member by a swivel joint permitting the remote end of the tie to move freely around the fastening member without twisting of the tie.The tie should be short enough to hold the connected end of the tube near to the fastening zone of the patient's body. A tie length of less than 10 cm, most preferably less than 8 cm, is recommended. It is often advantageous for the length of tie to be such that its point of connection to the tube remains near the periphery of the fastening member whose contact face is secured against the patient's body.

The invention includes a central venous pressure measuring apparatus which comprises a central venous pressure manometer installed in association with a refernce level indicating device according to the invention as hereinbefore defined. In particular the invention includes such an association of appliances wherein a common scale or twin scales in like units is or are used for reading the liquid level in the tube of the indicating device and the liquid level in the manometer. In the latter circumstances correction of the manometer reading to compensate for changes in patient position involves nothing more than the addition or substraction of the magnitude of a scale interval representing change in liquid level in the indicating device, to or from the value of the manometer reading.

Various of the optional features hereinbefore described and various other advantageous optional features are referred to in the following description of an embodiment of the invention, selected by way of example, which is illustrated in the accompanying diagrammatic drawings.

In these drawings: Figure 1 is a diagrammatic representation of a central venous pressure manometer in use in association with a reference level indicating device according to the invention; Figure 2 is a more detailed view of part of the said level-indicating device; Figure 3 is a detail of the proximal end of the level-indicator tube; and Figure 4 is a view of a modified proximal tube end construction and shows an attached fastening device.

Fig. 1 represents a patient 1 recumbant on a support 2. An intravenous drip line 3 is in position for saline feed from a bottle 4 supported by a stand 5. The line 3 incorporates a switch valve 6 by which the drip feed can be shut off at the same time placing the line to the patient in communication with a manometer column 7 in which the liquid level is visible against a scale (not shown) for reading venous pressure. The illustrated apparatus as so far described is in accordance with known practice.

For carrying out the present invention there is provided a patient position indicating device comprising a flexible U-tube 8 (only part of which is shown) one end of which is attached to the upper sternum zone of the patient and the other end of which is supported by the stand 5, parallel with the manometer column 7. The term U-tube used herein is of course used loosely to denote any arrangement of a tube such that it has opposed portions in which the liquid finds a common level under gravity. It is not excluded that either or both of the opposed portions may have a horizontal part as in the case represented in the figure.

The tube is set up so that the common liquid level coincides with the horizontal level of the right atrium. That level of the liquid can be noted from the scale. Should the support 2 be, raised or lowered or should the posture of the patient be changed, for example should he moved onto one of his sides, involving change in the horizontal level of the right atrium, the mercury level in the tube 8 will undergo a corresponding change. The change from the initial pre-set position noted on the scale (called "zero" position) can be measured on the scale and the value can be used as a correction factor to correct the pressure reading on the manometer.

Fig. 2 shows part of the same apparatus in more detail. The zero level position which coincides with the fastening zone X on the patient can be recorded on the tube by a marker 9 which is slidable along the tube 8. A scale 10 is adhesively or otherwise secured onto the stand 5 with its zero mark coincident with the marker. The same scale can be used for the manometer readings if the manometer apparatus is set up on the stand in the correct manner.

The proximal end of the tube 8 i.e. the end nearer the patient, is sealed by a collapsible bulb.

A suitable sealing arrangement is shown in Fig. 3 in which the proximal end of tube 11 which contains mercury and which may for example be made of polyethylene is sealed by a collapsible bulb or balloon 12. The balloon may be made of silicone or latex for example.

The mouth of the bulb may for example be secured around the end of the tube 11 by means of a silk filament. The tube 11 may for example have a length of 1.75 metres and have a bore of 1 mm.

A similar collapsible balloon may be used for sealing the distal end of the tube 11, as diagrammatically suggested for the tube 8 in Fig. 1.

The tube 11 enclosing the mercury is sealed under negative pressure. e.g. - 1 Ib/sq. inch.

The tube 11 and its end sealing bulbs are enclosed in an envelope. As shown in Fig. 3 the tube 11 is sheathed by an outer tube 13 which may for example be made of PVC crystal and have a bore slightly larger than the outside diameter of tube 11. In a specific instance, the outer tube 13 has a bore of 3.9 mm and the tube 11 has an outside diameter of 2 mm. The proximal end of the tube 13 is sealed by a latex outer sheath 14. A Similar collapsible sheath can be provided at the distal end so as to envelop the distal end bulb of the tube 11.

Fig. 4 shows the proximal end of a sheathed mercury-containing tube similar to that represented by Fig. 3 and corresponding parts are denoted by the same reference numerals in the two figures. Near to the distal end of the tube there is a fastening device comprising a wire or other tie 15 (6 cm in length) having one end secured to the outer tube 13 and its other end secured by a swivel joint 16 to a fastening pad 17 for fastening to the body of the patient. For this pad, use can be made of what is known as an E.C.G.

electrode but any other suitable form of fastening member can be used. Only part of the pad 17 is shown and it is represented in plan view for clarity. In practice the pad will be oriented horizontfally when secured to the patient's body and the upper end of the tube, above its point of connection to tie 15 will be in a substantially vertical orientation slightly to one side and above the swivel joint.

When the pad is secured to the patient, the proximal tube end being supported by the flexible tie as above specified, the point of connection between the tie and the tube is at the zero level, i.e. in the plane of the right atrium. The mercury will be at the same level in the other limb of the U and that level can be recorded by means of a marker as described with reference to Fig. 2 or in any other suitable manner.

Because the tie 15 is flexible and because of the swivel joint, the tie can support the proximal tube end in the described position in relation to the fastening zone on the patient, in whatever posture he or she may be placed.

The flaring of the mouth of the capilliary tube to which the collapsible balloon is sealed, as indicated by Figs. 3 and 4, is of value in ensuring that when the balloon is squeezed to expel mercury into the tube the balloon is properly evacuated and there is no residual mercury which might cause the balloon to fold over and occlude the bore of the tube.

Claims (15)

1. A method of measuring central venous pressure by means of a manometer characterised in that use is made of a patient position indicating device comprising a flexible U-tube containing liquid which maintains a common level in the tube limbs, one of such limbs being attached to the patient and the other being associated with a vertical scale so that the magnitude of variations of the liquid level from a zero or reference level can be noted, and such magnitude is used as a compensating factor to derive actual venous pressure or pressure variations from the manometer reading.

2. A method according to claim 1, wherein said vertical scale is in units which can be directly added to or subtracted from the values read from the manometer scale.

3. A method according to claim 2, wherein one and the same scale is used for the manometer and position indicator readings.

4. A method according to any preceding claim, wherein the said flexible U-tube contains mercury.

5. A method according to any preceding claim, wherein the proximal limb of the Utube is attached to the patient in the area of the manubrium and the tube is set up so that the liquid level is at the horizontal level of the right atrium.

6. A reference level indicating device for use in conjuntion with a central venous pressure manometer, said device comprising a flexible hermetically sealed tube which contains liquid and can be supported in the form of a U in the opposed limbs of which the liquid maintains a common level, said tube permitting inspection of the liquid level through its wall; and said device also comprising means for fastening a limb of the U when so formed to a patient so that changes iri the horizontal level of the point of attachment to the patient can be measured in terms of variations in said liquid level.

7. A device according to claim 6, wherein.

said liquid is mercury.

8. A device according to claim 6 or 7 wherein- at least one end of the tube is sealed by means of a collapsible end component which can serve as a reservoir for receiving liquid from the tube.

9. A device according to any of claims 6 to 8, wherein the tube and/or any said collapsible end member is/are enclosed by art outer envelope with a protective function.

10. A device according to any of claims,# to 9, wherein said fastening means has a contact face for seating against a patient's body and a tie member connecting. said fastening member to the tube at or near one end thereof.

11. A device according to claim 10, wherein said tie member is connected to the fastening member by a swivel joint.

1 2. A device according to claim 11, wherein the length of the tie is such that its point of connection to the tube remains near the periphery of the fastening member when the latter is secured against a patient's body

1 3. A central venous pressure measuring apparatus comprising a central venous pressure manometer installed in association with a reference level indicating device according to any of claims 6 to 12.

14. A reference level indicating device substantially as herein described with reference to the accompanying drawings.

15. An association of a central venous pressure measuring apparatus with a reference level indicating device substantially as herein described with reference to the accom-- panying drawings.