Allergic reaction is a complication associated with any medication administration. However, because it happens more rapidly when intravenous medication is administered, it is often considered more of an issue in this context.

An allergic reaction is a response to a medication or solution to which the patient is sensitive and may be immediate or delayed (Lamb and Dougherty [162], Perucca [283]). Clinical features may start with chills and fever, with or without urticaria, erythema and itching. The patient may then go on to experience shortness of breath with or without wheezing, then angioneurotic oedema and in severe cases anaphylactic shock (Lamb and Dougherty [162]). Prevention is achieved by assessing and recording patient allergies (drug, food and products) and applying allergy identification wristbands (NPSA [270], Perucca [283]). In the event of an allergic reaction, the infusion should be stopped immediately, the tubing and container changed, and the vein kept patent. The doctor should be notified and any required interventions undertaken (Lamb and Dougherty [162]).

A critical and common complication of intravenous therapy is circulatory overload, or ‘isotonic fluid expansion’. It is caused by infusion of fluids of the same tonicity as plasma into the vascular circulation, for example 0.9% sodium chloride. As isotonic solutions do not affect osmolarity, water does not flow from the extracellular to the intracellular compartment. The result is that the extracellular compartment expands in proportion to the fluid infused (Weinstein and Hagle [363]). Because of the electrolyte concentration, no extra water is available to enable the kidneys to selectively excrete and restore the balance. Circulatory overload can also occur due to:

Prevention includes thorough assessment of the patient before commencing intravenous therapy, close monitoring of the patient, maintaining infusion rates as prescribed and the use of infusion devices where required (Lamb and Dougherty [162]). If circulatory overload is detected early, the patient should be sat upright (Macklin and Chernecky [181]). Treatment consists of withholding all fluids until excess water and electrolytes have been eliminated by the body and/or administration of diuretics to promote rapid diuresis (Weinstein and Hagle [363]). However, careful monitoring should be continued to prevent the occurrence of isotonic contraction (where there is loss of fluid and electrolytes isotonic to the extracellular fluid, such as blood and large volumes of fluid from diarrhoea and vomiting) (Weinstein and Hagle [363]). If fluid administration is allowed to continue unchecked, it can result in left‐sided heart failure, circulatory collapse and cardiac arrest (Dougherty [75]).

Dehydration may be categorized as either hypertonic or hypotonic contraction and may be caused by underinfusion. Hypertonic contraction occurs when water is lost without corresponding loss of salts (Weinstein and Hagle [363]) and occurs in patients unable to take sufficient fluids (the elderly, unconscious patients and incontinent patients) or who have excessive insensible water loss via skin and lungs or as a result of certain drugs in excess. Hypotonic contraction occurs when fluids containing more salt than water are lost; this results in a decrease in osmolarity of the extracellular compartment (Weinstein and Hagle [363]).

It is important that nurses recognize the symptoms of overinfusion or underinfusion; certain factors should be considered when monitoring patients (Weinstein and Hagle [363]) (Table 15.20).

Speed shock is a systemic reaction that occurs when a substance foreign to the body is rapidly introduced into the circulation (Perucca [283], Weinstein and Hagle [363]). This complication can manifest following administration of intravenous bolus injections or when large volumes of fluid are given too rapidly (Perucca [283]). It should not be confused with pulmonary oedema, which relates to the volume of fluid infused into the patient. Rapid, uncontrolled administration of drugs will result in toxic concentrations reaching vital organs (Lamb and Dougherty [162]). Toxicity may be manifested via an exaggeration of the usual pharmacological actions of the drug or via signs and symptoms specific to that drug or class of drugs. The most extreme toxic response that can occur if a drug is given at a dose or rate exceeding that recommended is termed the ‘lethal response’.

Signs of speed shock include:

Prevention of speed shock involves the nurse having knowledge of the drug and the recommended rate of administration. When commencing an infusion using gravity flow, check that the solution is flowing freely before adjusting the rate and monitoring regularly (Perucca [283]). Movement of the patient or the device within the vessel can cause the infusion to flow more or less freely after a few minutes of setting the rate (Weinstein and Hagle [363]). For high‐risk medications, an electronic flow‐control device is recommended (RCN [295]). Although most pumps have an anti‐free‐flow mechanism, always close the roller clamp prior to removing the set from the pump (MHRA [202], Pickstone [284]).

If speed shock occurs, the infusion must be slowed down or discontinued. Medical staff should be notified immediately and the patient's condition treated as clinically indicated (Perucca [283]).