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.
