CSII: benefits and drawbacks

Most patients with Type 1 Diabetes are managed with multiple daily doses of insulin (MDI), a combination of short acting analogue insulin with meals, and a long acting analogue to provide a basal insulin. Insulin pump therapy, or continuous subcutaneous insulin infusion (CSII) is an alternative method of delivery of this insulin, which more closely resembles physiological insulin delivery. CSII is indicated in certain situations as advised by the National Institute for Health and Clinical Excellence (NICE) in the UK. These recommendations are summarised below:

NICE recommendations for initiation of insulin pump therapy.[1]

CSII is recommended as a possible treatment for patients with Type 1 DM over the age of 12 if

  • Attempts to reach target haemoglobin A1c (HbA1c) levels with multiple daily injections result in the person having ‘disabling hypoglycaemia' or significant fear of hypoglycaemia, or
  • HbA1c levels have remained high (8.5% or above) with multiple daily injections (including using long-acting insulin analogues if appropriate) despite the person and/or their carer carefully trying to manage their diabetes.
  • For children aged less than 12 – CSII can be considered if MDI is considered impractical

The Mechanics of Insulin Pump Therapy

An insulin pump is a mechanical device that delivers a constant small infusion of insulin which can vary hour by hour to meet individualised physiological needs. A short acting analogue insulin such as Novorapid, Humalog or Apidra is contained in a reservoir within the pump. The insulin is most commonly delivered via a flexible tube and a cannula which is inserted subcutaneously. This cannula remains in situ for up to 72 hours. There are alternative methods to deliver the insulin which are explained in sections below.

The continuous small amount of insulin delivered hour by hour is termed the basal rate and provides a background of insulin to prevent ketosis and maintain steady glucose levels in the fasted state . In addition to this basal rate, additional bolus insulin is delivered via the pump in the circumstances shown in the table below. [2]

Table 1: Situations requiring injection of additional bolus insulin.

Table 1
Meal Times An amount of insulin is delivered depending on the amount of carbohydrate contained in the food.
Correction Doses An amount of insulin is delivered via the pump to correct a person's blood glucose back to the normal range

The insulin pump itself is around the size of a pack of playing cards. There are various insulin pumps available for use for patients. Most commonly in the UK patients use an insulin pump connected to the patient via a flexible cannula. A comparison between available insulin pumps is shown in the table below.

Table 2: A comparison of available insulin pumps

Name of Pump: Accu-Chek Insight Insulin Pump Minimed 640G OmniPod Animas Vibe
Tubeless No No Yes No
Wireless or bluetooth CBG Meter Yes Yes Yes No
Wireless or Bluetooth Control Yes No Yes No
Waterproof No No Yes Yes
On-board bolus calculator Yes Yes Yes Yes
CGM Augmentation* No Yes No Yes
Downloadable at Home by Patients Yes Yes Yes Yes

*Continuous glucose monitoring (CGM) augmentation is an additional feature that can be added to certain pumps.

The Advantages of Insulin Pump therapy

Studies have demonstrated that insulin pump therapy is associated with sustained reductions of HbA1c of 6 mmol/mol (0.5%). Greater reductions than this are often seen in the first 6 months of pump initiation. This reduction is associated with reduced glucose variability and reduced severity and frequency of hypoglycaemia. Recent long term observational studies have demonstrated a continued improvement in overall diabetes control over many years versus MDI therapy.

Insulin pumps have a number of advanced features that enable them to more closely mimic normal pancreatic physiology such as bolus calculators, extended and dual wave bolusing, and temporary basal rates.

All of the available insulin pumps have on-board bolus calculators. These use input from the wearer to calculate the insulin dose required for a particular circumstance. This is shown in the diagram below. As part of the onboard bolus calculator the pump calculates the amount of active insulin from any previous insulin which is bloused (known as the active insulin). This amount of active insulin decreases the greater the time from the bolus dose, and can be adjusted for each individual patient.

All patients who use insulin pumps should be proficient in carbohydrate counting and should have received a structured education programme for type 1 diabetes. It is routine clinical practice that patients will undergo intensification of standard multiple daily injections prior to initiation. By entering the carbohydrate value of the meal into the on-board calculator with the current blood glucose level prior to a meal the pump calculator will be able to accurately determine the insulin dose required as it is pre-programmed with an individual's insulin sensitivity. This reduces the maths skills needed to calculate an insulin bolus dose and improves accuracy of matching insulin requirements.[2][3]

Required Insulin Dose

  • (Units)
  • Insulin Correction Dose
  • (Insulin Sensitivity Factor)
  • Insulin to cover any
  • carbohydrate eaten
  • (Insulin:Carbohydrate ratio)

= +/-

All pumps also have the ability to extend insulin boluses. Not all carbohydrate is absorbed at the same rate, and absorption depends on a number of factors including size of meal, and complexity of carbohydrate. This is difficult to manage in a patient with MDI without asking them to inject an additional dose of short acting insulin. With Insulin pumps the bolus insulin can be adjusted so that some is delivered as an initial bolus whilst a portion of it is delivered over a prolonged period.

Insulin pumps offer further advantages under other conditions such as exercise, stress, illness and around a female's menstrual cycle. Correct set up and programming of the pumps allows a reduction or increase in the basal rate using a feature termed a temporary basal rate which is a change to the basal rate by a set percentage for a given amount of time. Temporary, or alternative basal rates can be used when large changes in glycaemia can be predicted, such as at a quiet weekend when compared with a busy weekday, premenstrually in females, or if unwell and under times of stress. Use of many of these and other advanced features can be particularly useful in exercise which can be challenging to manage as changes in blood glucose are dependent upon a number of factors including type, timing , duration and intensity of activity.

Some of the modern insulin pumps are integrating with continuous glucose monitoring systems (CGMS) as a prelude to the artificial pancreas which is seen by many as the apogee of modern type 1 diabetes management. CGMS and sensor augmented pump therapy has many perceived advantages over insulin pump therapy alone such as further reduction in hypoglycaemia, further reduced glucose variability, improved quality of life but it is not routinely funded by the NHS in the UK currently.

One of the key advantages to insulin pump therapy is the increased flexibility in lifestyle, and more freedom with food because of the advanced pump functions above. Insulin pump therapy can be beneficial both to reduce episodes, and severity of hypoglycaemia, improved hypoglycaemia awareness and also to reduce glucose variability. This is often a reason why CSII is started, and favoured by patients. Many patients see a 30-40% reduction in insulin dose on commencement of CSII which can help with weight management.

Lipohypertrophy and atrophy, as recognised complications of injectable therapy in diabetes, can lead to poor absorption and may be indications for CSII. Cannula changes for insulin infusion therapy are required every 48-72 hours, depending on the device, to ensure consistent flow and delivery rates. This often facilitates resolution of difficulties with absorption of insulin at injection sites and also may provide an alternative for people with severe needle phobia.[3][4][5]

The Disadvantages of Insulin Pump Therapy

There are some disadvantages to insulin pump therapy. Initiation of insulin pump therapy takes significant time and effort on the part of both the person with diabetes and the healthcare team. Accessibility to specialist diabetes teams with experience in this therapy remains a postcode lottery and funding may still be difficult to procure. Pump therapy is not suited to everyone and a multidisciplinary approach involving the team of physician, specialist nurses, dieticians and psychologist is required to assess and counsel anyone considering pump therapy to ensure realistic expectations and goals. It may be a challenge initially and often takes a concerted effort to adjust basal rates, insulin sensitivity and behaviours around diabetes before ideal goals are achieved. Some patients feel “attached” to a machine all of the time and this can raise significant psychological body image barriers and some consider it as an intrusion as they can never "escape" their diabetes. Despite the pumps being small, and a number of different methods of attaching or hiding the pump this can be difficult to overcome.

In early studies there was a perceived increased risk of diabetic ketoacidosis (DKA) due to either pump failure, or problems with the infusion set as people would be rendered insulin deficient within 2-4 hours after failure of the device. However, the technology has progressed over time and pump failure is an uncommon occurrence. A safety mechanism of multiple alarms alerts the wearer in case of device failure or occlusions. This initial risk of DKA is now thought to have been over-estimated and in fact current experience suggests a reduced incidence of DKA for patients on insulin pump therapy.[3][5][6]

The advantages and disadvantages of CSII are summarised in the table below.

Table 3: Advantages and Disadvantages of Insulin Pump Therapy

Advantages Disadvantages
Increased Lifestyle Flexibility Increased time and effort at insulin pump start
Reduced Hypoglycaemia Attachment to a machine 24 hours a day
Increased hypoglycaemia awareness A visual acknowledgement that you have diabetes
Reduced Glucose Variability Risk of mechanical failure
Useful in Patients with Lipohypertrophy Infusion site reactions -adhesive or cannula
Needle phobia Cost
Benefits for exercise Availability of experienced team


CSII is a more physiological method of insulin delivery that has some clinical, and personal advantages to certain patient groups. It may be considered in a number of patient groups, but particularly those with disabling hypoglycaemia.


  1. ^ National Institute for health and care excellence (2004) Type 1 Diabetes: Diagnosis and management of type 1 diabetes in children, young people, and adults. [CG15] London: National Institute for Health and Care Excellence.

  2. ^ Walsh J, Roberts R. Pumping insulin: Everything you need for success on a smart insulin pump. Torey Pines Press. 2006

  3. ^ Maynard D. Pros and cons of pumping. Accessed online www.insulin-pumpers.org.uk 21/05/2014.

  4. ^ Cummins E, Royle P, Snaith A, Greene A, et al. Clinical Effectiveness and cost-effectiveness of continuous subcutaneous insulin infusion for diabetes: systematic review and economic evaluation. NIHR Health Technology Assessment programme. 2010

  5. ^ Pickup J. Insulin Pump Therapy for Type 1 Diabetes Mellitus. NEJM 2012;366:1616-24

  6. ^ Hanas R, Ludvigsson J. Hypoglycemia and ketoacidosis with insulin pump therapy in children and adolescents. Paediatr Diabetes 2006;7(Suppl 4):32-38


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