VOL: 103, ISSUE: 8, PAGE NO: 30-31
Leanne Llewellyn, BSc, RN
Sister, paediatric intensive care unit, King’s College Hospital NHS Foundation Trust, London
Llewellyn, L. (2007) Changing inotropes in the PICU: double pumping or switching technique? www.nursingtimes.net
Inotrope infusions are commonly used in paediatric intensive care units to achieve cardiovascular stability in critically ill patients. These infusions are administered as a continuous infusion and require frequent changeover. Various methods are used in practice when changing the infusions, none of which are evidence based. An audit was conducted to determine which method of changeover caused the least cardiovascular compromise to patients. The results of the audit will inform development of a guideline on which method of change over should be used.
Inotropes and vasoactive drugs, such as adrenaline and noradrenaline, are commonly used in the paediatric intensive care unit (PICU) for children with cardiovascular instability. Vasoactive medications improve cardiac output and vascular tone and help achieve cardiovascular stability (Morrice et al, 2004; Craig et al, 2001) and continuous inotrope infusions are administered to children experiencing cardiovascular instability.
All infusions must be changed regularly, but inotropes infusions particularly frequently because the half-life of most inotropes used in the PICU is only 2-3 minutes (Arino et al, 2004). It is essential that a continuous supply of these drugs be achieved to prevent fluctuations in cardiac function that may lead to a child becoming haemodynamically compromised.
There are two common methods of changing infusions - the double pumping technique and the switching technique. Double pumping involves running both infusions simultaneously, starting the new one at a lower rate and titrating both until the new infusion is at full rate and old infusion stopped. Switching involves running the new infusion at the same rate as the old and connecting it to the patient while turning the old infusion off.
Although both methods ensure that drug flow to the patient is not interrupted, their use can cause an increase or decrease in the patient’s mean arterial blood pressure(MABP) and neither method is evidence based. It was therefore decided that an audit project would be undertaken to assess which method of changeover resulted in the least cardiovascular compromise to the patient.
Inotrope infusions are used for improving oxygen delivery and cardiovascular function in the critically ill (Arino et al, 2004; Trim and Roe, 2004). Careful assessment of the cardiovascular variables will determine the need for inotrope support and the appropriate agent to use (Stanford, 1991).
Up to 80% of patients admitted to hospital receive IV therapy (Workman, 1999) and safe administration requires knowledge and skills in the application of equipment (containers, administration sets and infusion pumps), cannulation, drug calculations, potential adverse effects and how to prevent them (Williams and Lefever, 2000; Workman, 1999).
Most inotrope infusions are delivered via an infusion pump to ensure a continuous supply (Morrice et al, 2004). Although pumps vary between hospitals, the principles around safe use are the same. When a syringe pump is started, there is typically a delay before fluid delivery to the patient commences (Amoore et al, 1998) because of the time required to take up the mechanical slack in the pump-syringe system, both in the pump’s driving mechanism and in the fitting of the syringe into the pump.
When a syringe is loaded into many models of syringe pumps the syringe can be moved back and forth 1-2mm while the syringe flange is in the pump groove but before clamping the plunger. If the plunger clamp is then loosely dropped over/applied to the plunger, it will often still be possible to move the syringe back and forth.
The pump takes up the slack by moving the whole syringe - plunger and barrel - forward. During this period there is little, if any, movement of the plunger in relation to the barrel, and hence little or no fluid flow. The slower the flow rate set, the longer the time required to take up the slack and the longer the start-up time (Quinn, 2000; Amoore et al, 1998).
The start-up delay has two main implications for infusion device therapy. First, it delays the delivery of medication to the patient and, because the half-life of inotropic drugs is very short (Morrice et al, 2004), a delay in delivery to the patient may result in an adverse effect, such as a drop in MABP. In addition there will be a difference between the volume recorded as delivered by the pump’s totaliser and that read from the barrel of the syringe, which is the volume actually delivered. Most infusion devices do not measure fluid delivery - they measure the movement of the pumping mechanism. It is therefore difficult to document the total inotropic requirement for the patient receiving it.
The start-up delay can be reduced with most pumps by using the prime facility on the pump if it has one, or purging/bolus the pump once the syringe is fitted but before connecting it to the patient. This helps with the uptake of the mechanical back slack (Quinn, 2000; Amoore et al, 2001) and ensures drug delivery to the patient once connected. It is therefore recommended that the infusion device be purged/bolus/primed before connection to a patient to ensure continuous infusion of inotrope (Morrice et al, 2004; Arnio et al, 2004; Trim and Roe, 2004).
It is also recommended that infusion devices are primed and then programmed at the same rate as the infusion to be changed because of the risk of mechanical back slack. The infusion should run for between 10 minutes to 1 hour (Morrice et al, 2004; Trim and Roe, 2004) before being connected to the patient, or the drug might not be delivered to patient immediately. The drug can be safely switched in this way because the infusion device will be at full speed and functioning correctly (Morrice et al, 2004).
Before the audit was undertaken, all intensive and high-dependency care centres involved in delivering care to children in the UK were contacted by letter to ask which was their preferred technique for changing inotrope infusions. The response rate was poor, with only 10 centres replying. All 10 of these centres stated that they used a switching technique when changing inotropes, but admitted that the evidence to support their preferred technique was limited. The responses were written by three practice development nurses, two ward managers and five ward sisters.
An audit was then carried out over a four-week period in which all staff involved in the changeover of inotrope infusions were asked to complete a simple questionnaire. The questionnaire aimed to find out which technique had been used to change over the infusion and what effect (if any) this had had on the patient’s MABP.
A total of 30 questionnaires (recording 30 changeovers) were completed and analysis of the results showed three techniques were used to change infusions. The double pumping technique was used for 43% of the changeovers, the switching technique for 53% and, in 4% of cases, the old infusion was stopped before the new one commenced. Observational charts of inpatients revealed that 76 infusions were changed over that month, so the audit response rate was poor (39%).
None of the responses reported a fall in blood pressure, 29 reported a rise in MABP and one reported no change. A stop/start technique had been used for this patient but the drug involved was milrinone which has a half life of 2-6 hours.
The results showed that the method of changing the infusion had different effects on the patient MABP. Sixteen questionnaires documented the use of the switching technique when changing inotrope infusions; 11 stated there was a rise in patient MABP between 0-5mmHg, four observed a rise of 5-10mmHg and one stated an increase of 15-20mmHg (Fig 1).
One questionnaire completed showed no change in patient MABP when infusion was stopped, changed and then recommenced. In this case the drug being changed over was milrinone, which has a half life of 2-6 hours, so no immediate change in MABP would be identified.
No drop in MABP was documented in the questionnaires. Rises in MABP were observed with the use of both techniques and the double pumping method was associated with the greatest rises, with considerably more patients experiencing rises of up to 20mmHg than with the switching technique.
Limitations of the audit
Changes to the patient’s MABP were recorded by the person changing the inotropes rather than another individual, so it is possible that transient changes in blood pressure might have been missed because the respondent was concentrating on undertaking the changeover.
The audit was very specific to the PICU and did not consider other risk factors associated with the use of inotrope infusions. For example, when starting an inotrope infusion, there may be a delay before the medication reaches the patient (Amoore and Adamson, 2003; Amoore et al, 2001; Medical Devices Agency, 1998). This can be overcome by purging the infusion pump before attaching the infusion to the patient, but this was not covered in the audit.
Occlusion of the central venous line may occur during infusion and, if this happens, the line may need to be flushed and the inotrope infusion stopped while this takes place (Davies, 2001). However, flushing the line can result in a bolus of drug being administered to the patient which will consequently cause a rise in MABP. The audit did not ascertain whether the venous line had to be flushed in any of the patients included.
In addition, the audit did not assess the duration of increases in MABP and whether the rise had a detrimental effect on patients’ cardiovascular status. No assessment was made of whether there was any rebound drop in MABP after the initial increase.
User knowledge is essential when changing inotrope infusions as the nurse has to be confident not only in making up the drug correctly but also with the equipment needed to administer it (Crisp, 2002; Whyte, 2001). However, the audit did not analyse the experience of the nurse administering the inotrope and whether this had any effect at changeover.
It may also have been beneficial to identify which inotropes were used to see whether the type had any correlation with the differences in increase in MABP. As half-lives of inotropes vary, it is possible that certain types might have caused a larger rise in MABP than others at changeover.
The delivery devices used in the PICU were standard and there were no documented variations in the syringe drivers used.
Although the audit was limited, it was felt by the team that the switching method should be adopted when changing inotrope infusions in the PICU because increases in MABP associated with this technique were lower than increases associated with double pumping. The findings of the audit supported the replies received from 10 ICUs in the UK which highlighted switching as the favoured technique.
There is no guidance on which changeover method should be adopted for inotrope infusions, so the method adopted by staff is usually based on how they were taught and their previous experiences of various methods. Senior staff are responsible for the training and development of junior staff regarding this skill, and it is likely that they demonstrate the double pumping method because that was the method that they were used to. The switching technique is now used more frequently than it was in the past. Old infusion devices were not as reliable modern ones, so it was considered safer to titrate a new infusion alongside one ready for change in case the infusion device failed. This is no longer necessary, as infusion devices are able to deliver at their set rate immediately.
A guideline is being produced to give staff members in the PICU straightforward instructions of which method to adopt when changing over inotrope infusions and how this switching process should be undertaken. Once this guideline has been in place for three months, another audit will be undertaken to establish what impact the use of the guideline has had on patients’ cardiovascular status during change-over of infusions.
It is evident that there is insufficient research on changing of inotrope infusions and the area of requires further investigation to further develop the guideline and enable evidence-based practice.
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