Running wide open: Advances in IV therapy
Here are some ways the design and materials used to obtain vascular access have evolved into what we use today
Intravenous therapy has been a mainstay practice of EMS providers since the beginning of the prehospital profession. Intravenous access allows the delivery of multiple medications without having to puncture the patient’s veins multiple times, and permits volume replacement in dehydrated patients.
Within the hospital environment, health care practitioners can utilize a variety of monitoring equipment and perform certain procedures such as percutaneous transluminal coronary angioplasty (PTCA) through intravenous access.
In the early days of IV therapy, practitioners inserted hollow needles in patients’ veins, and administered glass bottles of sterile fluid through slim rubber tubing. Over time, the design and materials used to obtain and maintain vascular access have evolved into what we use today.
The majority of devices used today to obtain IV access are of the “catheter over needle” or angiocatheter construction. A Teflon or plastic tube surrounds a hollow metal needle that is sharpened on one end. The needle is inserted through the skin and punctures a suitable vein. Blood passes through the needle and into a visible receptacle, known as a flashback. The catheter is advanced off the needle and into the vein. The needle is then removed, leaving the catheter behind. A universal-sized hub, located at the end of the exposed catheter, allows the user to attach an intravenous fluid administration set, a saline or heparin lock, or a phlebotomy vacuum collection needle for drawing blood.
Catheters come in a variety of lengths and diameters. In general, a longer catheter flows fluid more slowly, due to the resistance in the catheter. A smaller diameter, or gauge, will also slow the flow. In EMS, most practitioners will use an 18 or 20 gauge catheter for the majority of medical patients; if a large amount of fluid replacement is needed, a 16 or 14 gauge catheter may be used.
Needle stick safety
Nearly all catheter-over-needle designs incorporate a safety mechanism that prevents accidental needle sticks, either by advancing a cap over the sharp end of the needle while it is being withdrawn, or having the entire needle retract into a safety device. Nevertheless, there is a brief moment where the EMS provider is potentially exposed to the patient’s blood; that’s when the needle has been removed, but the administration set or other device has not yet been inserted. An experienced provider can minimize blood splash from the catheter end, but that is challenging in the mobile environment of EMS.
IV administration sets
Intravenous administration sets are constructed of polypropylene or nylon, which is soft and flexible, to have some strength to resist tearing. One end is designed to access an intravenous fluid bag, and contains a drip chamber that allows the provider to observe the flow of fluid. The distal end has a universal luer shape that fits snugly within the IV angiocatheter hub. Between the two ends, there are a variety of flow control devices and medication ports that providers use to inject or infuse medications. Most common injection ports today are either pre-pierced or luer activated, which accommodates a variety of needleless devices to be used to administer medications.
Administration sets come in a variety of lengths and drip rates. The drip rate tells the user how many drops of fluid would make up one milliliter (mL). An inverse relationship exists: The greater the number of drops, the smaller the drops are, and the slower it flows through the administration set. For most medical patients, a 60 drop administration set is sufficient; in volume replacement, a 10, 15 or 20 drop set can be used.
Multidrip administration sets
Historically EMS systems would purchase a variety of drip sets to accommodate patient type. This practice can prove costly and results in the storage of numerous administration sets in medical kits and in the back of the ambulance.
There are administration sets that allow the provider to select a variety of drip rates. The drip chamber consists of multiple ports that, when rotated into place, control the rate of fluid flow.
Instead of stocking several different types of administration tubing, EMS agencies can simply buy one multidrip set, saving space and money as a result.
The manual flow control devices found on intravenous administration sets generally work well. However, in certain situations, EMS providers need to be very precise in the delivery of the amount of fluid or infusion of medication over time. In these situations, intravenous pumps are needed.
An IV pump can precisely regulate the flow of fluid or medication to as little as 0.01 mL/hour. An electric motor governs the diameter of the administration tubing as it passes through a channel. Today’s pumps use an electronic interface to set the drip rate and amount. IV pumps have two sets of power, AC electricity and DC current batteries.
Emerging “smart” technology allows pumps to be programmed to specific uses. For example, an IV pump can be programmed to prevent the user from setting an infusion rate that could over- or underdose the patient. A hospital can set profiles within a pump specific to the needs of a unit such as ICU or Surgery.
IV pumps in EMS have becoming increasingly smaller, lighter and specifically designed for transport use. They can detect problems in fluid flow, such as a blocked administration set or an infiltrated IV site. Some units have automated IV fluid bolus administration features. Others will have accurate flow rates regardless of position in the ambulance.
IV warmers and coolers[SBP2] With all of the focus on therapeutic hypothermia for post cardiac arrest patients, it can be easy to forget that cool IV fluids may not be helpful for other types of situations. It’s estimated that one liter of room-temperature crystalloid solution such as normal saline can lower core body temperature by a quarter degree (Celcius). While that does not sound significant, patients who are critically ill or injured will need to divert precious energy reserves to create body heat, rather than preserving basic life functions.
While the concept of intravenous access is not new, ongoing advances in IV therapy make it safer for patients and providers alike. Given the unstable nature of the EMS operating environment, these developments will help in refining prehospital practice.