Continuous Subcutaneous Insulin Infusion

Abstract and Introduction

Continuous subcutaneous insulin infusion (CSII) is used in selected type 1 diabetic subjects to achieve strict blood glucose control. A quarter of a century after its introduction, world-wide use of CSII is increasing. We review the evidence base that justifies this increase, including effectiveness compared with modern intensified insulin injection regimens and concern about possible complications. Review of controlled trials shows that, in most patients, mean blood glucose concentrations and glycated hemoglobin percentages are either slightly lower or similar on CSII versus multiple insulin injections. However, hypoglycemia is markedly less frequent than during intensive injection therapy. Ketoacidosis occurs at the same rate. Nocturnal glycemic control is improved with insulin pumps, and automatic basal rate changes help to minimize a prebreakfast blood glucose increase (the "dawn phenomenon") often seen with injection therapy. Patients with "brittle" diabetes characterized by recurrent ketoacidosis are often not improved by CSII, although there may be exceptions. We argue that explicit clinical indications for CSII are helpful; we suggest the principal indications for health service or health insurancefunded CSII should include frequent, unpredictable hypoglycemia or a marked dawn phenomenon, which persist after attempts to improve control with intensive insulin injection regimens. In any circumstances, candidates for CSII must be motivated, willing and able to undertake pump therapy, and adequately psychologically stable. Some diabetic patients with well-defined clinical problems are likely to benefit substantially from CSII and should not be denied a trial of the treatment. Their number is relatively small, as would therefore be the demand on funds set aside for this purpose.

In 1976, we began work developing a new research tool hoped to dramatically improve metabolic control in selected type 1 diabetic subjects, thus enable testing of the links between diabetic control and complications. This technology, continuous subcutaneous insulin infusion (CSII) (often now just called "insulin pump therapy"), uses a portable electromechanical pump to help mimic nondiabetic insulin delivery, infusing short-acting insulin into the subcutaneous tissue at preselected ratesessentially a slow basal rate throughout the 24 h with patient-activated boosts at mealtimes ^[1,2,3]. Although we originally devised and developed CSII as a research procedure ^[2,4], its efficacy was quickly confirmed by many groups ^{[5,6,7,8,9,10,11,12,13,14]}, and by the early 1980s, it had been taken up in several countries as an alternative form of routine treatment in a variety of type 1 diabetic patients ^[15].

A quarter of a century after its introduction, CSII is widely used in clinical practice; there are now estimated (largely from pump sales) to be >200,000 diabetic subjects worldwide using CSII for their everyday treatment, with >130,000 in the U.S. alone ^[16]. However, there are major variations in usage: in some countries, such as the U.K., there are only a few hundred pump users but growing pressure from diabetic patients to increase its availability.

Patient reactions to CSII have been largely enthusiastic and the discontinuation rates low ^{[15,17,18,19]}. Good control is achieved without compromising quality of life ^[20,21]. But enthusiasm from some is mixed with uncertainty from others, who are concerned about the possible complications of pump therapy ^[22] or intensive insulin therapy in general ^[23].

The advantages and disadvantages of CSII are particularly pertinent in the atmosphere of cost containment and the need for the most appropriate use of expensive technology, which has affected all health care systems in recent decades. The purpose of this article is twofold: to review the evidence base for the expanding use of CSII, in the light of its efficacy and possible side effects, and to initiate a debate about the need for clinical guidelines on the most suitable patients for pump therapy.

Throughout this review, we use the terms "optimized insulin injection regimen" or "intensive insulin injection therapy" to mean modern intensive management of type 1 diabetes, with multiple daily insulin doses given in a basal-bolus mode (with or without an insulin pen), with adjustment according to diet, exercise, and frequent blood glucose self-monitored values and full diabetes educational input. We have not reviewed the use of CSII in type 2 diabetes, where the present evidence base is small.

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