Brief report
Adsorption of insulin onto infusion sets used in adult intensive care unit and neonatal care settings

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Abstract

Introduction

Insulin adsorption onto infusion equipment may affect glycaemic control.

Methods

The change in insulin concentration during delivery through tubing employed for adult ICU and neonatal patients was determined using continuous flow UV analysis.

Results

Insulin adsorption depended on tubing composition, dimensions and flow rate, being highest for neonatal polyvinylchloride tubing at low flow rates.

Conclusion

In continuous insulin therapy, we should consider the nature of the infusion set and flow rate.

Introduction

Tight glycaemic control in adult long-stay critically ill patients using intensive insulin therapy reduces absolute mortality [1], [2]. However, target glycaemia may be difficult to achieve in clinical practice [3]. A low infusion rate of insulin is used in neonatal hyperglycaemia if blood–glucose concentrations are persistently high, and in the management of neonatal diabetes [4].

Insulin adsorption onto infusion equipment may affect glucose control [5], possibly leading to hyperglycaemia [6], [7]. Adsorption may depend on infusion flow rate and concentration [7]. Over time, protein adsorption onto injecting equipment increases until binding regions reach saturation [8], with maximum adsorption occurring in the first 30–60 min [9]. The clinical significance of this in the adult ICU and neonatal settings is uncertain [8].

In this study, adsorption of insulin onto infusion sets used in the adult ICU and for neonatal insulin delivery at University College Hospital (UCH), London, at clinically relevant flow rates was analyzed. The effect of tubing composition and dimensions were also considered.

Section snippets

Methods

Soluble human insulin (Actrapid®, 100 U/ml, Novo Nordisk) was diluted to 1 U/ml in 0.9% NaCl, prepared from HPLC grade water (Fisher Scientific) and sodium chloride (Sigma–Aldrich).

The UV absorbance of insulin solutions passing through a continuous flow UV detector (Agilent Technologies 1200 Series) was measured at 210 nm. Insulin adsorption onto adult ICU infusion tubing (Cardinal Health, polyethylene (PE) 200 cm × 0.9 mm internal diameter, prime volume 1.6 ml) was determined at rates of 0.5 and 1 ml/h

Results

At a flow rate of 0.5 ml/h, insulin was adsorbed onto the PE ICU tubes, such that the concentration flowing from the tubing was 86.23% of that in the syringe after the first 30 min, and only achieved a steady state of 100% of initial concentration after approximately 600 min (Fig. 1). At 1 ml/h, the initial insulin concentration was 95.08% and took around 400 min to reach 100%. At 4 ml/h, the initial concentration was 99.06% and approximately 200 min were required to reach steady state.

For the PVC

Discussion

The relatively small loss of insulin on the syringe indicates that the majority of insulin loss observed in this study resulted from adsorption to tubing.

Maximum loss of insulin in tubing occurred at the beginning of infusion as previously described [9], with recovery of insulin increasing as adsorption sites are saturated [8]. The flow rate had a considerable effect on insulin loss. At low rates, there was greater opportunity for interaction with plastic surfaces. Comparing the two tubings at

Conflict of interest

The authors declare that they have no conflict of interest.

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