NEW YORK (Reuters Health) – For children and very lean adults who use a 5 mm insulin needle, angling the injection into a pinched skin fold reduces pain and increases efficacy, researchers reported online June 28th in Diabetes Care.
“These are the most popular needles in children,” lead author Dr. Paul L. Hofman of the University of Auckland, New Zealand, told Reuters Health by e-mail. “Longer and wider bore needles are often used in adults,” he added, “and these are definitely more painful.”
A successful injection technique should reliably deposit insulin into subcutaneous fat without inadvertently putting the needle into muscle.
More than 250 patients – 122 children and adolescents and 137 adults – agreed to help Dr. Hofman and his colleagues establish the best approach with a 5 mm needle. Each subject received eight injections of sterile air (given by a diabetes nurse specialist) corresponding to 20 IU of insulin, either perpendicularly or at 45 degrees, in the abdomen and thigh, and with or without a pinched skin fold.
The research team used ultrasonography to determine the depth and site of the injected air (intradermal, subcutaneous, or intramuscular).
Each patient also received four injections of an insulin-free diluent (equivalent to 20, 40 and 60 U of insulin) using the FlexPen (Novo Nordisk). Again, the injections were perpendicular or angled, with a pinched skinfold, into either the abdomen or lateral thigh. The injection area was wiped with a tissue, which was weighed to determine spillage.
None of the injections in the study produced bleeding, bruising, or any other adverse effect.
Overall, the majority of injections were subcutaneous: 5.5% were intramuscular and 0.5% intradermal in children, and 1.3% were intramuscular and 0.6% were intradermal in adults. Subcutaneous fat thickness was the main factor associated with intramuscular injections.
“In children, injecting into fat can be difficult as they are thinner and injecting into muscle occurs much too frequently,” Dr. Hofman said. “This alters the release of many insulins, increasing the risk of major low glucoses.”
The outcomes varied by the site and technique of the injection. Among the children, for example, rates of intramuscular injections with angled and vertical needle insertion, respectively, were 1.6% vs 9.8% in the thigh and 7.4% vs 8.2% in the abdomen – when the skin wasn’t pinched. With pinched skin, however, angled and vertical injections went into thigh muscles in 2.5% vs 1.6%, respectively, and into abdominal muscles in 8.2% and 4.9%.
“In most adults all injection techniques were fine — except in the very thin,” Dr. Hofman added. “In children and very thin males, an angled approach with pinching — creating a skinfold — resulted in the majority of insulin being injected into fat and not muscle.”
There was also minimal leakage in both adults and children.
A third of all patients reported no pain during insulin injection, and no overall difference in pain between the angled and perpendicular injections. The younger group had more discomfort in general, however, and more of the painful intramuscular injections.
“These needles inject reliably when used as we recommend and result in less pain and discomfort” compared to larger needles, Dr. Hofman concluded.
At any rate, he believes, “Doctors should try all the needles their patients have to use!”
Defining the ideal injection techniques when using 5-mm needles in children and adults
Diabetes Care 2010.