Hypodermoclysis, the subcutaneous infusion of fluids, has been practiced for almost a century. Despite its successful use, hypodermoclysis remains an underrecognized and underused method of rehydration. In this issue of American Family Physician, Shvartzman and Sasson¹ provide a practical overview of this useful rehydration technique.

Hypodermoclysis fell out of favor during the 1950s after several case reports detailed complications related to its use.² Many of these complications, however, were the result of inappropriately high infusion rates or the use of hypertonic solutions that caused excessive fluid shifts and cardiovascular compromise.² During the 1980s, hypodermoclysis made a comeback after several articles described its potential benefits when properly administered. In 1996, Rochon and colleagues conducted a systematic review of the literature on this topic.²

Hypodermoclysis is frequently part of palliative care.^1,3 The treatment of dehydration in this setting is controversial. Some experts argue that terminally ill patients should not receive invasive rehydration therapy for a variety of clinical and ethical reasons; others counter that maintaining hydration using hypodermoclysis can prevent the occurrence of agitated delirium. One advantage of hypodermoclysis in the palliative care setting is that it can be used to administer certain analgesics (e.g., morphine and hydromorphone) to patients who are no longer able to take these drugs orally. In some cases, palliative care patients who are intolerant of oral narcotics prefer the subcutaneous administration of narcotics.⁴ Studies^5,6 comparing intravenous with subcutaneous administration of narcotics have demonstrated similar pain control with both methods.

Hypodermoclysis has been proved valuable in treating dehydration in older adults in long-term care institutions. Older adults often get acute intercurrent illnesses in which fluid replacement is an important component of treatment. If administering intravenous therapy for rehydration is not possible in a long-term care setting, which is nearly always the case, patients are transferred to an acute-care hospital for intravenous rehydration. Such a transfer can be a traumatic experience for a frail older patient. Hypodermoclysis performed in long-term care settings can be a convenient and cost-effective alternative to hospitalization.

As described in detail by Shvartzman and Sasson,¹ subcutaneous fluid infusion requires much of the same equipment used in intravenous therapy. The needle of a small-gauge catheter can be inserted into tissue at various sites including the thighs, abdominal wall, back, thorax and arms. Fluids are efficiently absorbed into the vasculature. The infusion volume at a single site should be limited to approximately 1.5 L during a 24-hour period. The infusion rate should be maintained above 20 mL per hour to prevent clogging of the line and below 75 mL per hour to prevent localized swelling.

It is important to discuss the composition of the fluids used in hypodermoclysis. Isotonic or electrolyte-containing hypotonic solutions should be used. The use of hypertonic or electrolyte-free solutions and rapid infusion rates can precipitate cardiovascular collapse, as was reported in the 1950s. Whether or not hyaluronidase should be added to subcutaneous fluids is debated, as Shvartzman and Sasson¹ discuss. Hyaluronidase is an enzyme that, theoretically, facilitates diffusion of fluids in the interstitium. Although radioisotope studies have shown that hyaluronidase may increase the rate of absorption of subcutaneous fluid,⁷ this finding does not translate into clinical benefits.² Furthermore, hyaluronidase can produce allergic reactions.

Subcutaneous therapy has several potential advantages over intravenous therapy. Subcutaneous administration of fluids is easier to set up, less invasive and often better tolerated. In patients who might try to pull the catheter out, hypodermoclysis can be administered at sites that the patient cannot easily reach. Relative to intravenous therapy, hypodermoclysis is generally associated with lesser use of restraints and is less restrictive to patients' mobility. Furthermore, subcutaneous fluids can be administered in long-term care settings, thus potentially preventing the necessity for patient transfers to hospitals, which may lead to substantial cost savings.

The limitations of subcutaneous fluid therapy must also be recognized. It is not appropriate in the management of severe dehydration because the volume and rate of rehydration is limited. Complications are similar to those associated with intravenous therapy but occur less often. Sterile precautions are required to avoid infections at infusion sites. Catheters should be replaced at least every 72 hours or sooner if signs of infection develop. The catheter should be covered with a transparent adhesive film to keep it in place and allow monitoring of the site for localized reactions.

A recent prospective, observational study⁸ has confirmed many of the benefits of subcutaneous fluid infusion. This study of 55 patients shows that hypodermoclysis is safe and effective in providing maintenance fluids and rehydration therapy in frail elderly subjects with mild to moderate dehydration. Overall, hypodermoclysis is associated with significantly fewer adverse effects compared with intravenous therapy.⁸

Hypodermoclysis is underused as a technique for treating dehydration in terminally ill patients and institutionalized older adults. Subcutaneous fluid infusion is easily administered and has several important advantages over hospitalization for intravenous therapy in these patient populations. After a century of changing fortunes, interest in hypodermoclysis is again mounting.^1,2,9