External insulin infusion pumps

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Continuous subcutaneous insulin infusion pumps (CSII) are small programmable devices, about the size of a pager, with a reservoir filled with insulin. Insulin is delivered through a catheter, inserted under the abdomen, to the subcutaneous tissue. The device allows programming of different pre-selected rates (basal rate) as well as bolus doses. CSII allows the user to program different pre-selected basal rates of insulin infusion based on patterns of perceived needs. The device also allows the diabetic user to select from several types of mealtime boluses. The earliest insulin infusion pumps received FDA approval in the late 1980's. Since then a number of different pumps continue to be cleared through the 510(k) regulatory approval process as class II devices. To date, over 35 external insulin infusion pumps have been cleared [13]. Most recently, technological advancement has allowed the pump to incorporate communication software via an infrared interface allowing the user and the physician to transfer (download) data stored in the pump to a personal computer (PC) for display or print. The communication will also allow the user to program the pump via PC with selected pump settings for basal or bolus infusion.

The number of pump users increased after the publication of the DCCT, which showed that achieving and maintaining tight blood glucose control prevented or slowed the progression of microvascular complications in type 1 diabetics. Based on devices sales information, it is estimated that there are about 450,000 pump users globally. In the US, about 250,000 diabetics currently use the device. It is also estimated that 5-10% of these pump users discontinue use for various reasons [14].

Advantage of Insulin Pumps

Efficacy of Glycemic control Pump therapy is effective in achieving long-termblood glucose control in type 1 diabetic patients. The DCCT also showed that both CSII and MDI injection therapy are effective means of achieving normoglycemia in the insulin-requiring patient. Since the DCCT, a number of studies have compared the effectiveness of CSII with optimum MDI. A meta-analysis of 12 randomized control trials concluded that glycemic control was slightly better with CSII when compared with "optimized" injection therapy [15]. The same study concluded that the difference in control between the two insulin delivery methods were small but significant. The analysis also showed that daily insulin usage is less with CSII. A number of studies enrolling smaller numbers of patients have also demonstrated that CSII is effective compared to MDI [16,17,18].

In 2000, FDA approved new long acting insulin Lantus (glargine) for once a day, bed time injection [19]. Lantus has a slower, more prolonged absorption and a relatively constant concentration/time profile over 24 hours without the pronounced peaks seen with other long acting insulin. Because of these constant serum concentration, Lantus is occasionally referred to as the ''poor man's pump''[20]. However, there are no long term studies comparing Lantus with CSII. A short-term, 16-week study of pediatric patients comparing insulin analogs for MDI with CSII showed lower HbA1c were achieved with CSII than with glargine-based MDI treatment [21]. There are a number of factors other than effectiveness to consider when choosing a pump. Some of these factors will be discussed below.

Hypoglycemia Initial studies raised concerns of severe hypoglycemia in patients using an insulin pump [22]. The incidence of hypoglycemia was noted to be about three times higher in the intensive therapy group (CSII and MDI) in the DCCT, and as a result, there was some reluctance to use CSII. However, a number of trials have suggested that when the pump is properly used the rate of hypoglycemic episodes are no more frequent, or are even less common, compared to MDI [23,24,25]. The decrease in hypoglycemic events is accompanied by an increase in self-reported warning symptoms of hypogly-cemia, as well as by an increase in counter regulatory hormonal responses to hypogly-cemia. Because of the reported lower incidence of hypoglycemia with pump therapy, some experts are now recommending hypoglycemia unawareness as an indication for pump use [26].

Pump therapy has also been recommended for certain conditions and for special subsets of the diabetic populations. CSII can help improve blood glucose control in patients with the 'dawn phenomenon', in which blood glucose is elevated before breakfast [27]. Pump users who experience the dawn phenomenon can program their pump to increase night time basal insulin infusion to counter pre-breakfast blood glucose elevation. Experts also have suggested that the dosing flexibility of CSII may aid in reducing gastroparesis. In addition, erratic blood glucose control, and optimization of glycemic control during pregnancy [28] are additional indications by some medical community practice for CSII use. For those who chose CSII, improved lifestyle flexibility due to better control during exercise, eating out, or travel is cited as one of the most important reasons for choosing the pump. The ability to change dosing from moment to moment, and living with different dosing flexibility may be another reason for the increased pump usage observed recently. The evidence on quality-of-life is limited to testimonies from those patients who have had a positive experience with CSII.

Disadvantages of CSII

Short acting insulin used with CSII has no depot, as opposed to the subcutaneously used longer acting insulin. In addition, subcutaneous insulin delivered via injection is cleared at a much slower rate compared to insulin delivered via CSII. Therefore, any interruption of insulin flow from CSII can result in rapid hyperglycemia and DKA. In addition, even though hypoglycemia is less common with CSII use, the proper use of an insulin pump requires a highly motivated patient who is able to monitor blood glucose frequently, operate the device, and work with a diabetes team. Infrequent blood glucose monitoring, poor cooperation with the patent's treatment team, and inability to program the device properly can result in severe adverse events including hypoglycemia, hyperglycemia or DKA.

Device-related safety issues may involve clogging of catheters, bleeding at the site, hematomas, and catheter-related infections at the insertion site. Catheter-related infection is the most commonly reported complication to the FDA through Medical Device Reports [29]. A number of manufacturing-related and device specific malfunctions may also occur. Some reports of water ingress resulting in over-perfusion, leakage of insulin due to cracks in the pump, and other malfunctions have also resulted in device failures and recall of the device [30]. For some patients, cost and having to wear a device may be a barrier to choosing the pump over MDI.

In summary, CSII is as effective as or more effective than MDI in achieving and maintaining tight blood glucose levels. The key to successful use of the device depends on the appropriate selection of diabetics and pumps. A patient who is motivated to monitor daily blood glucose levels frequently, skilled at operating the device, and willing to work with a health team is required.

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