I am not sure if this is the proper forum.Please transfer it if just in case.

My question is regarding the setting of the maximum occlusion pressure on a syringe pump.Other than to be able to detect kinks on the tubing perhaps,will this setting have any effect on the patient in case it is too high?
Why am I asking this? Well if you inject a patient manually there is NO CONTROL whatsoever on the occlusion pressure the hand exerts on the the syringe,so why bother to set it for a pump?

Bonski
If you administer manually to a conscious adult and the needle is not properly located, the patient will probably tell the person administering the drug to stop. (The hand is also a very sensitive device for moitoring pressure)

We set occlusion pressures (especially on neonatal pumps) to reduce the effect of tissuing injuries (if they occur). An unconscious neonate will not cry out when something is wrong - so it must be right.

The use of a bolus-push i.e. manual delivery by hand is not suitable for all infusions - particularly of drugs at relatively high concentrations that need to be delivered consistently and accurately over extended periods - to neonates for example. When it is appropriate the manual method is used, hopefully, by a skilled practitioner trained to do so. With regard to pressure; the difference with a manual bolus-push and an automated infusion is that much higher, potentially damaging, pressures can be applied to the patient without the clinician or, possibly, the patient being aware at all.

In this case no one is in a position to intervene and damage can occur if attention is not drawn to the problem - the case of an automated infusion without appropriate occlusion alarm thresholds being set. Besides the risk of tissuing, possibly infiltration and extravasion, high occlusion pressure alarm thresholds at low infusion rate give a loss of delivery if there is a restriction in the line/site/cannula - thus in the case of delivery of short half-life drugs a rapid onset of adverse effects may occur quickly for example. In any case the time for the occlusion alarm to occur, indicating a problem, is longer with higher occlusion alarm thresholds and the bolus of the drug built-up in the line is potentially greater depending upon infusion rate of course.

If the problem with the non-patent line/site/cannula is then cleared, carelessly, without releasing the accumulated pressure into the syringe then it is likely this bolus of drug will then be released into the patient. Particularly dangerous with the groups of drugs used to regulate blood pressure for example where the release may cause the reverse effects to that caused by the loss of delivery. Low occlusion alarm settings on syringe drivers can be used to indicate when there is increase in backpressure in the line above the pressure associated with a patent line under normal conditions.

When the line pressure is trended by the pump then operators can see trends in pressures and alter occlusion alarm thresholds as appropriate to prevent nuisance alarms. Low occlusion alarm thresholds limit potential bolus delivery, reduce time to alarm after occlusion, so limit loss of delivery of drug if the line becomes non-patent for whatever reason. It's quite important to configure occlusion alarm settings on infusion pumps appropriately for the application they are to be used in so that there is a balance struck between clinically significant events affecting the line e.g. alarms occurring due to restriction of the cannula by the wall of the blood vessel and nuisance alarms caused by slight arm-movement of a patient with a peripheral line connected for example.

Richard,
Very well explained. If we have the facility, lets train the users to maximise the benefits.

I don't think the operators are that interested John; especially where I work at the moment - training is a good idea but only if it's integrated into a package for them that's recognised (of use when looking to progress in their career) and also mandatory (they have to attend) - I think I'll keep on fixing things, as required, for now.

Richard,
I think it changes from place to place. We set default values, but teach the users to adjust if required. We also do a lot of fixing.

We have a ticklish problem regarding the Graseby 3200. Our nursing staff wish to introduce an anti-syphonage valve into the line as was recommended several years ago. Under normal operating conditions the iv runs fine until they wish to give a bolus. Bolus rate is 200ml/hr. When this is initiated an occlusion alarm sounds. The answer would be to increase the mechanical setting in the pump but that means pulling several hundred of these units throughout the hospital and carrying out the adjustment, a long and laboreous task. The downside to this adjustment would be higher occlusion pressure leading to a longer time to occlusion alarm particularly at low flow rates, increase in bolus size, increase risk to patient from extravasation damage.

It will be a compromise reduce the risk from free flow increase the risk of tissue damage etc.

These pumps incidentally are used in general ward areas, ITU, CCU, HDU but not in neonatal areeas.

Any answers?

No answer to the Graseby 3200 problem I'm afraid but I was interested in 2 things:
What is the occlusion alarm limit set at?
Why do you think an increased occlusion alarm is going to increase the risk of extravasation? This is a common fear, in Paediatric nurses in particular but I can't find anything to back it up. In fact what I have read seems to suggest it doesn't.

I agree SaraS- extravasion (involving a vesicant drug) or infiltration are cases where infusate is delivered into the interstitial space, or tissues, outside the blood vessel causing damage around the infusion site as far as I am aware. They are not the major potential cause of occlusion type alarms - however not all the literature I've read discounts this as a source of occlusion problems.

Some studies indicate that occlusion alarms are not initiated in these cases - however there are others that indicate there could be issues with occlusion alarms. Certainly if a vessel is in spasm or the cannula is placed against a tissue restriction then there will likely be problems with delivery.

Joe - we have had similar issues, in the past, with 3300 syringe drivers set-up to the manufacturers occlusion specification (4.5-5.5kgf). With a BD 50 syringe, anti-syphon, line, etc, stat rate of 200ml/hr.

Occasionally there are spurious occlusion alarms despite there being no apparent problems with the line set-up or patient. There is published literature, involving issues with nuisance occlusion alarms on 3300 syringe drivers, that highlights this problem - the solution was apparently to increase the occlusion alarm threshold to prevent nuisance alarms (on the advice/guidance of the MDA I think). I have the references if you want them.

No doubt, for the 3200 running at 200ml/hr, which may have a lower occlusion alarm specification than the 3300, that this is a nuisance. The British Standard specification that syringes have to meet, for stiction in particular, is quite wide.

I have found, in the past, that check-valves/anti-syphon devices have pretty consistent characteristics (pressure gradients across them) over the range of flows. Hence I can only assume that syringe drivers with mechanical sensing rather than in-line sensing are actually sensitive to all components in the system - driver actuator friction, syringe stiction, line restrictions (rate dependent) and site problems.

My own view is that, using adult extension lines of average length, syringe stiction probably contributes most significantly to nuisance alarms since the variation is greatest in this element of the system.

Modern devices, using dedicated lines with in-line pressure sensing, monitor both line pressure and the force on the actuator i.e. they can dfferentiate between actuator problems e.g. sticking syringe actuator and site/line problems e.g. non-patent line due to restriction in-line.

They also have externally adjusted alarm thresholds. Hence the solution may be to purchase a later generation of syringe drivers to overcome the problem of nuisance alarms.

We have 3300's using a stat of 200ml/hr and using the free flow device with no probs. It just sem to be a problem with the 3200's. Units are adjusted to the factory set value.

There seems to be a bit of ambiguity regarding occlusion levels and apporpriately set prssure alarm levels. Some pundits seem to advocate setting pressure levels just above line pressure in order to have an rapid time to occlusion, others seem to advocate that it doesn't matter. Am I missing something?

Richard, Can you give me the references you are referring to. We to have a similar issue with 3200's.

Sure - I will dig them out of the in-tray on my bench.

Yes Joe - the point I made was that the 3200 occlusion specification, if the same as the 3100 (3.5Kgf- 4.2Kgf from memory), may be lower than the 3300 occlusion specification.

Unfortunately I haven't looked at a 3200 manual for years so I'm only guessing (perhaps you could tell me what the specification is and how you check compliance with it).

Anyhow what I was getting at is that if we (and others) have had problems with a similar line/syringe setup using the 3300 (200ml/hr stat rate) then problems with a 3200 at 200ml/hr using manufacturers specifications, for the occlusion threshold, are likely.

I was interested in the comments regarding tissuing and occlusion pressures.

I am sure in my own mind that tissuing will occur regardless of occlusion pressure setting if the clinical conditions exist, i.e. cannula movement, fragile vein, poor positioning etc. There are examples of tissuing occuring with gravity infusions where the in line pressures are marginally above the venous pressure to ensure positive infusate flow.

The purpose of occlusion limits as has been well descibed earlier it to prevent bolus delivery and indeed pump or disposable damage, not tissuing. The idea of trending is Ok so long as someone is there to view and interpret the data.

I know many a sales pitch has been built up on the benefits of pressure monitoring and tissuing incident reduction but I remain sceptical. I am firmly in the camp of "routine observation of the IV site" as a method of prevention. If the reply comes back that there arn't enough staff to undertake the observations, then there arn't enough staff to interpret pressure trend data either!

We have remained with the manufacturer's default setting for all infusion devices apart from those for neonates for whom we reduce the setting by 50%. Tissuing events as reported to me have been low to non existant.

Lucky? - possibly but I wait to be convinced.


Brian

I do prefer calibration of occlusion alarm thresholds, externally, rather than the tedious internal, mechanical, adjustments necessary on older generations of syringe drivers - whatever the source of alarms.

The other potential benefit of pressure monitoring/trending is that some syringe drivers use "fast start" and "backoff" features that remove actuator backlash (which causes initial loss of delivery at startup) by monitoring syringe actuator/line back-pressure and can actually remove the bolus, due to occlusion or excessive pressures in the distended line, by withdrawing ("backoff") the syringe plunger until pressures are in the normal range i.e. on alarm excessive pressure is removed from the system and bolus prevented from being delivered (if the occlusion is subsequently cleared under pressure). The pressure monitoring effectively completes a control-loop.

Brian correctly points out that there should be regular monitoring of infusion sites. However, once the operator observes colour change and swelling, damage has already occurred. In neonates particularly it is important to use devices that can measure small changes in pressure. The line pressure will vary depending on syringe size, flowrate and drug viscosity. It is therefore important to measure the line pressure for a few minutes post setup and then set a pressure window on top of that. Should a pressure increase occur, then it will be detected early before there is visible signs of tissue damage. Some syringe drivers allow this accuracy by using pressure monitoring sets. Some users choose to follow this procedure - some do not. If there is an incident and the technology was available and not used, would this be criticised? Is it not true that in the best interests of patient safety particularly in our most vulnerable patients (neonates) that pressure monitoring be carefully applied.