Subcutaneous rehydration therapy (SCRT), also known as hypodermoclysis, is a method of fluid replacement first described in the 1880s as a proposed treatment for cholera in India.1 It involves the infusion of fluids into the subcutaneous space where it slowly diffuses into the circulation.2 This method was widely used for rehydration until the 1950s until it was superseded by the intravenous (IV) route.3 This was due to reports of serious adverse events that were most likely caused by improper choice of fluids for SCRT (e.g., shock secondary to osmotic shift caused by infusion of hypertonic or electrolyte-free fluids).4 Subsequent studies have confirmed the safety and efficacy of hypodermoclysis.
SCRT offers many advantages over IV hydration. It is often much easier to obtain and maintain access in patients who may be dehydrated with collapsible veins, agitated, at risk of pulling out IV lines. Nursing time to obtain subcutaneous access is less than with IV access.5 SCRT does not cause thrombophlebitis and there is less risk of fluid overload than with IV fluid administration.6 The popularity of SCRT is once again increasing in geriatrics, palliative care, and limited-resource environments. Its use remains unfamiliar to and overlooked by many Emergency Physicians.
ANATOMY AND PATHOPHYSIOLOGY
Hyaluronidases are enzymes that break down hyaluronic acid, a compound found in the intercellular matrix responsible for stabilizing the structure of the connective tissue.1 They are commonly used for subcutaneous hydration, extravasation of hyperosmolar radiologic contrast, and eye surgery.
Hyaluronidases are divided into three groups or classes (Figure 140-1).7 These include the β-endoglucuronidases (found in hookworms and leeches), endo-β-N-acetyl-d-hexosaminidases (found in ants, bees, hornets, mammalian testicles, wasps, and yellow jackets), and the hyaluronic acid lyases (found in bacteria). They all are responsible for the hydrolysis of bonds in hyaluronic acid. These enzymes are responsible for insect venom spreading and causing allergic reactions. There are numerous forms that are available for human use (Table 140-1). Hyaluronidase is inactivated by blood.
The action of various classes of hyaluronidases. (Used from reference 7.)
TABLE 140-1The Characteristics of Various Hyaluronidase Preparations ||Download (.pdf) TABLE 140-1 The Characteristics of Various Hyaluronidase Preparations
| ||Available for use ||Source ||U/mL |
|Hylenex ||Yes ||Human recombinant ||150 |
|Vitrase ||Yes ||Sheep testis ||200 |
|Wydase ||Not since 1999 ||Cow testis ||150 |
|Hydase ||Not since 2008 ||Cow testis ||150 |
|Amphadase ||Not since 2010 ||Cow testis ||150 |
Hyaluronidase temporarily breaks down the extracellular matrix and allows infused fluid to be absorbed up to five times more rapidly, decreasing the amount of localized edema, and increasing efficiency of SCRT.8 The matrix will rebuild itself within 24 to 48 hours after the injection of hyaluronidase. ...