Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrients for those who cannot, or will not—due to reduced mental states or otherwise—consume food or water by mouth. It may also be used to administer medications or other medical therapy such as blood products or electrolytes to correct electrolyte imbalances. Attempts at providing intravenous therapy have been recorded as early as the 1400s, but the practice did not become widespread until the 1900s after the development of techniques for safe, effective use.
The intravenous route is the fastest way to deliver medications and fluid replacement throughout the body as they are introduced directly into the circulatory system and thus quickly distributed. For this reason, the intravenous route of administration is also used for the consumption of some recreational drugs. Many therapies are administered as a "bolus" or one-time dose, but they may also be administered as an extended infusion or drip. The act of administering a therapy intravenously, or placing an intravenous line ("IV line") for later use, is a procedure which should only be performed by a skilled professional. The most basic intravenous access consists of a needle piercing the skin and entering a vein which is connected to a syringe or to external tubing. This is used to administer the desired therapy. In cases where a patient is likely to receive many such interventions in a short period (with consequent risk of trauma to the vein), normal practice is to insert a cannula which leaves one end in the vein, and subsequent therapies can be administered easily through tubing at the other end. In some cases, multiple medications or therapies are administered through the same IV line.
IV lines are classified as "central lines" if they end in a large vein close to the heart, or as "peripheral lines" if their output is to a small vein in the periphery, such as the arm. An IV line can be threaded through a peripheral vein to end near the heart, which is termed a "peripherally inserted central catheter" or PICC line. If a person is likely to need long-term intravenous therapy, a medical port may be implanted to enable easier repeated access to the vein without having to pierce the vein repeatedly. A catheter can also be inserted into a central vein through the chest, which is known as a tunneled line. The specific type of catheter used and site of insertion are affected by the desired substance to be administered and the health of the veins in the desired site of insertion.
Placement of an IV line may cause pain, as it necessarily involves piercing the skin. Infections and inflammation (termed phlebitis) are also both common side effects of an IV line. Phlebitis may be more likely if the same vein is used repeatedly for intravenous access, and can eventually develop into a hard cord which is unsuitable for IV access. The unintentional administration of a therapy outside a vein, termed extravasation or infiltration, may cause other side effects.
Intravenous (IV) access is used to administer medications and fluid replacement which must be distributed throughout the body, especially when rapid distribution is desired. Another use of IV administration is the avoidance of first-pass metabolism in the liver. Substances that may be infused intravenously include volume expanders, blood-based products, blood substitutes, medications and nutrition.
Fluids may be administered as part of "volume expansion", or fluid replacement, through the intravenous route. Volume expansion consists of the administration of fluid-based solutions or suspensions designed to target specific areas of the body which need more water. There are two main types of volume expander: crystalloids and colloids. Crystalloids are aqueous solutions of mineral salts or other water-soluble molecules. Colloids contain larger insoluble molecules, such as gelatin. Blood itself is considered a colloid.[1]
The most commonly used crystalloid fluid is normal saline, a solution of sodium chloride at 0.9% concentration, which is isotonic with blood. Lactated Ringer's (also known as Ringer's lactate) and the closely related Ringer's acetate, are mildly hypotonic solutions often used in those who have significant burns. Colloids preserve a high colloid osmotic pressure in the blood, while, on the other hand, this parameter is decreased by crystalloids due to hemodilution.[2] Crystalloids generally are much cheaper than colloids.[2]
Buffer solutions which are used to correct acidosis or alkalosis are also administered through intravenous access. Lactated Ringer's solution used as a fluid expander or base solution to which medications are added also has some buffering effect. Another solution administered intravenously as a buffering solution is sodium bicarbonate.[3]
Medications may be mixed into the fluids mentioned above, commonly normal saline, or dextrose solutions.[4] Compared with other routes of administration, such as oral medications, the IV route is the fastest way to deliver fluids and medications throughout the body.[5] For this reason, the IV route is commonly preferred in emergency situations or when a fast onset of action is desirable. In extremely high blood pressure (termed a hypertensive emergency), IV antihypertensives may be given to quickly decrease the blood pressure in a controlled manner to prevent organ damage.[6] In atrial fibrillation, IV amiodarone may be administered to attempt to restore normal heart rhythm.[7] IV medications can also be used for chronic health conditions such as cancer, for which chemotherapy drugs are commonly administered intravenously. In some cases, such as with vancomycin, a loading or bolus dose of medicine is given before beginning a dosing regimen to more quickly increase the concentration of medication in the blood.[8]
The bioavailability of an IV medication is by definition 100%, unlike oral administration where medication may not be fully absorbed, or may be metabolized prior to entering the bloodstream.[4] For some medications, there is virtually zero oral bioavailability. For this reason certain types of medications can only be given intravenously, as there is insufficient uptake by other routes of administration,[9] such is the case of severe dehydration where the patient is required to be treated via IV therapy for a quick recovery.[10] The unpredictability of oral bioavailability in different people is also a reason for a medication to be administered IV, as with furosemide.[11] Oral medications also may be less desirable if a person is nauseous or vomiting, or has severe diarrhea, as these may prevent the medicine from being fully absorbed from the gastrointestinal tract. In these cases, a medication may be given IV only until the patient can tolerate an oral form of the medication. The switch from IV to oral administration is usually performed as soon as viable, as there is generally cost and time savings over IV administration. Whether a medication can be potentially switched to an oral form is sometimes considered when choosing appropriate antibiotic therapy for use in a hospital setting, as a person is unlikely to be discharged if they still require IV therapy.[12]
Some medications, such as aprepitant, are chemically modified to be better suited for IV administration, forming a prodrug such as fosaprepitant. This can be for pharmacokinetic reasons or to delay the effect of the drug until it can be metabolized into the active form.[13]
A blood product (or blood-based product) is any component of blood which is collected from a donor for use in a blood transfusion.[14] Blood transfusions can be used in massive blood loss due to trauma, or can be used to replace blood lost during surgery. Blood transfusions may also be used to treat a severe anaemia or thrombocytopenia caused by a blood disease. Early blood transfusions consisted of whole blood, but modern medical practice commonly uses only components of the blood, such as packed red blood cells, fresh frozen plasma or cryoprecipitate.[15]
Parenteral nutrition is the act of providing required nutrients to a person through an intravenous line. This is used in people who are unable to get nutrients normally, by eating and digesting food. A person receiving parenteral nutrition will be given an intravenous solution which may contain salts, dextrose, amino acids, lipids and vitamins. The exact formulation of a parenteral nutrition used will depend on the specific nutritional needs of the person it is being given to. If a person is only receiving nutrition intravenously, it is called total parenteral nutrition (TPN), whereas if a person is only receiving some of their nutrition intravenously it is called partial parenteral nutrition (or supplemental parenteral nutrition).[16]
Medical imaging relies on being able to clearly distinguish internal parts of the body from each other. One way this is accomplished is through the administration of a contrast agent into a vein.[17] The specific imaging technique being employed will determine the characteristics of an appropriate contrast agent to increase visibility of blood vessels or other features. Common contrast agents are administered into a peripheral vein from which they are distributed throughout the circulation to the imaging site.[18]
IV rehydration was formerly a common technique for athletes.[19] The World Anti-Doping Agency prohibits intravenous injection of more than 100 mL per 12 hours, except under a medical exemption.[19] The United States Anti-Doping Agency notes that, as well as the dangers inherent in IV therapy, "IVs can be used to change blood test results (such as hematocrit where EPO or blood doping is being used), mask urine test results (by dilution) or by administering prohibited substances in a way that will more quickly be cleared from the body in order to beat an anti-doping test".[19] Players suspended after attending "boutique IV clinics" which offer this sort of treatment include footballer Samir Nasri in 2017[20] and swimmer Ryan Lochte in 2018.[21]
In the 1960s, John Myers developed the "Myers' cocktail", a non-prescription IV solution of vitamins and minerals marketed as a hangover cure and general wellness remedy.[22] The first "boutique IV" clinic, offering similar treatments, opened in Tokyo in 2008.[22] These clinics, whose target market was described by Elle as "health nuts who moonlight as heavy drinkers", have been publicized in the 2010s by glamorous celebrity customers.[22] Intravenous therapy is also used in people with acute ethanol toxicity to correct electrolyte and vitamin deficiencies which arise from alcohol consumption.[23]
In some countries, non-prescription intravenous glucose is used to improve a person's energy, but is not a part of routine medical care in countries such as the United States where glucose solutions are prescription drugs.[24] Improperly administered intravenous glucose (called "ringer" [citation needed]), such as that which is administered clandestinely in store-front clinics, poses increased risks due to improper technique and oversight.[24] Intravenous access is also sometimes used outside of a medical setting for the self-administration of recreational drugs, such as heroin and fentanyl, cocaine, methamphetamine, DMT, and others.[25]
Intravenous therapy is also used for veterinary patient management.[26]
Some medications can be administered as a bolus dose, which is called an "IV push". A syringe containing the medication is connected to an access port in the primary tubing and the medication is administered through the port.[27] A bolus may be administered rapidly (with a fast depression of the syringe plunger) or may be administered slowly, over the course of a few minutes.[27] The exact administration technique depends on the medication and other factors.[27] In some cases, a bolus of plain IV solution (i.e. without medication added) is administered immediately after the bolus to further force the medicine into the bloodstream. This procedure is termed an "IV flush". Certain medications, such as potassium, are not able to be administered by IV push due to the extremely rapid onset of action and high level of effects.[27]
An infusion of medication may be used when it is desirable to have a constant blood concentration of a medication over time, such as with some antibiotics including beta-lactams.[28] Continuous infusions, where the next infusion is begun immediately following the completion of the prior, may also be used to limit variation in drug concentration in the blood (i.e. between the peak drug levels and the trough drug levels).[28] They may also be used instead of intermittent bolus injections for the same reason, such as with furosemide.[29] Infusions can also be intermittent, in which case the medication is administered over a period of time, then stopped, and this is later repeated. Intermittent infusion may be used when there are concerns about the stability of medicine in solution for long periods of time (as is common with continuous infusions), or to enable the administration of medicines which would be incompatible if administered at the same time in the same IV line, for example vancomycin.[30]
Failure to properly calculate and administer an infusion can result in adverse effects, termed infusion reactions. For this reason, many medications have a maximum recommended infusion rate, such as vancomycin[30] and many monoclonal antibodies.[31] These infusion reactions can be severe, such as in the case of vancomycin, where the reaction is termed "red man syndrome".[30]
Any additional medication to be administered intravenously at the same time as an infusion may be connected to the primary tubing; this is termed a secondary IV, or IV piggyback.[27] This prevents the need for multiple IV access lines on the same person. When administering a secondary IV medication, the primary bag is held lower than the secondary bag so that the secondary medication can flow into the primary tubing, rather than fluid from the primary bag flowing into the secondary tubing. The fluid from the primary bag is needed to help flush any remaining medication from the secondary IV from the tubing.[27] If a bolus or secondary infusion is intended for administration in the same line as a primary infusion, the molecular compatibility of the solutions must be considered.[27] Secondary compatibility is generally referred to as "y-site compatibility", named after the shape of the tubing which has a port for bolus administration.[27] Incompatibility of two fluids or medications can arise due to issues of molecular stability, changes in solubility, or degradation of one of the medications.[27]
The simplest form of intravenous access is by passing a hollow needle through the skin directly into a vein. A syringe can be connected directly to this needle, which allows for a "bolus" dose to be administered. Alternatively, the needle may be placed and then connected to a length of tubing, allowing for an infusion to be administered.[32]: 344–348 The type and location of venous access (i.e. a central line versus peripheral line, and in which vein the line is placed) can be affected by the potential for some medications to cause peripheral vasoconstriction, which limits circulation to peripheral veins.[33]
A peripheral cannula is the most common intravenous access method utilized in hospitals, pre-hospital care, and outpatient medicine. This may be placed in the arm, commonly either the wrist or the median cubital vein at the elbow. A tourniquet may be used to restrict the venous drainage of the limb and make the vein bulge, making it easier to locate and place a line in a vein. When used, a tourniquet should be removed before injecting medication to prevent extravasation. The part of the catheter that remains outside the skin is called the connecting hub; it can be connected to a syringe or an intravenous infusion line, or capped with a heplock or saline lock, a needleless connection filled with a small amount of heparin or saline solution to prevent clotting, between uses of the catheter. Ported cannulae have an injection port on the top that is often used to administer medicine.[32]: 349–354
The thickness and size of needles and catheters can be given in Birmingham gauge or French gauge. A Birmingham gauge of 14 is a very large cannula (used in resuscitation settings) and 24-26 is the smallest. The most common sizes are 16-gauge (midsize line used for blood donation and transfusion), 18- and 20-gauge (all-purpose line for infusions and blood draws), and 22-gauge (all-purpose pediatric line). 12- and 14-gauge peripheral lines are capable of delivering large volumes of fluid very fast, accounting for their popularity in emergency medicine. These lines are frequently called "large bores" or "trauma lines".[32]: 188–191, 349
A peripheral intravenous line is inserted in peripheral veins, such as the veins in the arms, hands, legs and feet. Medication administered in this way travels through the veins to the heart, from where it is distributed to the rest of the body through the circulatory system. The size of the peripheral vein limits the amount and rate of medication which can be administered safely.[35] A peripheral line consists of a short catheter inserted through the skin into a peripheral vein. This is usually in the form of a cannula-over-needle device, in which a flexible plastic cannula comes mounted over a metal trocar. Once the tip of the needle and cannula are placed, the cannula is advanced inside the vein over the trocar to the appropriate position and secured. The trocar is then withdrawn and discarded. Blood samples may also be drawn from the line directly after the initial IV cannula insertion.[32]: 344–348
