ROLE OF VENOUS PRESSURE AND ARTERIAL PRESSURE IN DETECTION OF NEEDLE DISLODGEMENT
Venous pressure:
All dialysis machines must be equipped with a functioning venous pressure alarm, which stops the blood pump and clamps the blood lines in case of a venous pressure outside the alarm limits.
An acute decrease in dialysis venous pressure should theoretically be there rapidly after dislodgement of the venous needle from the access and trigger a pressure alarm to alert the dialysis nurse.
However, the venous alarm monitor on HD machines is affected by not only the intra-access pressure but also, the dialysis blood flow, blood viscosity, AVF Vs AVG, flow resistance of the extracorporeal tubing, and the height difference between the access and venous drip chamber. A VND/ ABLS will not always cause a change in the baseline venous pressure. It is therefore difficult for the staff to set the alarm limits so that high sensitivity is assured without also causing numerous false alarms. The alarm limits are set manually.
Ideally, to ensure early detection of blood loss, the venous pressure alarm would be set 10 mmHg below the baseline dialysis venous pressure. However, the venous pressure varies by 30–40 mmHg during a typical dialysis session due to patient position (reclining versus sitting) and movement of the access extremity. To prevent triggering multiple false pressure alarms during each dialysis session, the pressure monitor is usually set below that threshold. As a consequence, the dialysis staff may have a false sense of security when, in fact, a substantial blood leak may occur before the venous pressure drops by 40 mm Hg and triggers the pressure alarm.
Arterial pressure
Arterial pressure monitoring is not available in all blood lines.
The pressure in the inflow blood line is negative (below zero) because
- The blood pump pulls blood into the circuit at 200–600 mL/min
- The resistance to flow at the “arterial” opening of the vascular access catheter or “arterial” needle
Intensity of negative pressure depends on
- Blood flow rate
- Blood viscosity (which increases with hematocrit)
- Size of the inflow catheter lumen or needle
- Whether the end of the arterial needle or catheter is partially obstructed by nearby tissue from the inside wall of the vascular access
Circuit disruption between access and pump leads to high arterial pressure alarm. In such a case, after the line separates, the resistance to inflow will be suddenly reduced, and the negative pressure may rise above −50 mm Hg, triggering the alarm.
But even after a line separation this pressure may remain in range. For example, if there is a partial blockage in the inflow line after line separation, or if an arterial needle pulls out from the access, continued resistance to inflow by the needle may keep pressure in the set range; then the alarm may not sound, and the blood pump will keep on pumping air into the circuit.
To understand pressure alarms and blood circuit in detail read
https://glomindia.com/blood-circuit-for-hemodialysis-drjigarshrimali/
ROLE OF SENSORS IN DETECTION OF NEEDLE DISLODGEMENT
Various sensors can detect blood leaks during VND. Some were initially developed to detect moisture related to enuresis but later, used for detection of VND by some dialysis units. It consists of an alarm unit connected by an optical fibre to a sensor patch; the sensor patch has an absorbent patch in the centre. The patch is placed over the venous needle, with the absorbent area placed directly over the needle entry point.
In the event of VND or significant blood leakage, the blood comes in contact with the optical sensor that is embedded within the patch and generates a continuous alarm.
Although blood sensors are considered for additional safety in high-risk patients and patients on home HD. However, sensors should never replace an appropriate stepwise protocol to prevent VND.
ROLE OF DIALYSIS TECHNICIANS IN PREVENTION AND TREATMENT OF NEEDLE DISLODGEMENT
Practice recommendations to prevent VND and ABLS include:
Pre-dialysis assessment of patient risk factors
We need to check for high-risk patients and need to keep them close to the nursing station.
Also, we need to have frequent rounds for these patients.
Proper needle, catheter and bloodline securement
1)Preparing for cannulation and taping needles
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| 1) Insertion of needle after sterile technique. Special care to be taken for making the insertion side dry. | 2) A thick piece of tape is placed across the needle and wing to totally secure it. |
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| 3) Chevron to prevent dislodging needle. It provides extra support | 4) Another tap to secure the needle further. |
Only certain types of tape to be used to anchor the needles (Micropore is the preferred tape to use for this).
2)Securing CVC connections
Luer lock of access and tubing connection to be kept tight.
3)Securing bloodlines
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| Blood lines are taped onto the bed | Blood lines are taped onto the arm |
Blood lines are taped onto the arm or bed and then secured loosely onto your machine, so that some movement is allowed with minimal risk of line being pulled out.
Tape technique and replacing tape following intradialytic intervention
Skin preparation, use of correct taping techniques, and replacement of tape whenever needles are repositioned are important measures in the prevention of VND.
Most adhesives stick best to clean, dry surfaces so try to minimize moist conditions as much as possible. After the access is initially disinfected, it must be allowed to dry thoroughly. Touch the sticky surface of the tap as little as possible. Obtain full contact between the tape and the skin or tubing so that moisture cannot slip between the two and loosen the tape. Cover adequate surface area so that the tape can support the tubing or dressing. Remove substances that contain emollients or oils, such as most moisturizers and adhesive tape removers. If the skin is very oily, use a mild soap and water to remove the excess oil. An alcohol wipe may also be used to remove the excess oil, but since it is very drying, it should be used with care.
If the dialysis needles need to be adjusted, then tape should be replaced and not reapplied.
This statement is important due to reapplied tape losing some of its adhesive capability.
Understanding safety alarm capabilities
Haemodialysis machines are equipped with standard arterial and venous pressure alarms but may it not detect all VND or ABLS that we need to keep in mind. So, technicians and nurses must monitor all individuals during their 4 to 6-hour dialysis session. Each patient must have their face, vascular access site, and bloodline connections visible by a staff member throughout the haemodialysis treatment to prevent accidental needle dislodgement or line separation.
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| Correct method of keeping blood line visible | Incorrect method where bloodline is hidden under cloth |
Intradialytic monitoring and interventions
This includes proper taping of access needle, adequate tightening of luer lock at all connections, and ensuring that all blood- lines are loosely looped to prevent accidental dislodgement.
The access site should always be examined whenever the venous pressure monitor suggests a drop-in pressure, even if the blood leakage detector does not generate an alarm.
Ideally, haemodialysis machine placement would be on the same side of the AVF/AVG/CVC, allowing for more dialysis bloodline available for line securement to the patient. This placement avoids bloodlines crossing over the patient, which can restrict the bloodline length, causing the line to be pulled taut, pulling on the dialysis needles, and possibly leading to needle dislodgement.
ROLE OF PATIENT IN PREVENTION OF NEEDLE DISLODGEMENT
Patient should be very careful when he moves around during dialysis and should be conscious of where your lines are.
If possible, leave your fistula arm visible and free from blankets, as your dialysis nurse won’t need to disturb you to check your needles if you are sleeping.
PREVENTION OF NEEDLE DISLODGEMENT DURING HOME HEMODIALYSIS
Before the patient starts dialysis at home the dialysis technician will show the correct method for taping your needles and lines, to reduce the risk of venous needle dislodgement. They will also advise patients how often to check your needle sites while you are dialysing.
If a patient is doing solo dialysis your dialysis technician will give sensors. These sensors have a small sensor, which is placed directly over your needle site. If blood leaks from the needle site onto the sensor the machine will alarm, to let you know there is a problem.
Article Courtesy – Dr. Jigar Shrimali
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