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Can your blood/fluid warmer handle intermittent (bolus) flows?

If your warmer can’t manage high flow rates and is the “weak link” in your treatment, then it’s time to get a blood/fluid warmer that can


“Technology in EMS is ever evolving as we strive to better treat patients. Remember, you’re only as strong as your weakest link; the same goes for patient treatment.”

Photo/Cypress Creek EMS

Content provided by QinFlow

By Stephen Alexander

In a previous article, we discussed the top ten things you need to look for when choosing a blood/fluid warmer. One function that is absolutely necessary for your blood or fluid warmer to have that is often overlooked is the ability to warm and handle intermittent flows.

Most EMS service providers rely on gravity flow or pressure bags to try to infuse blood/fluids into a hypotensive patient. They might, if they’re lucky, get a couple hundred cc’s into the patient before they arrive at the hospital. From there, if the physician determines that the patient needs a rapid bolus, the trauma team could utilize their rapid infusers in hospital. So, why don’t we use the rapid infusers the trauma units have in EMS? They are simply too large (and not battery powered). The model of rapid infusers that I have seen used are as tall as an IV pole and very, very bulky, which is fine if you’re in a trauma bay where space is a given. But, in the back of an ambulance, space is a very limited resource. An answer to this problem was introduced by handheld, push-pull, syringe-style infusers that allow for rapid infusion of blood products or fluids in a matter of minutes, in an intermittent fashion.

What is intermittent flow? Intermittent flow is a term used to describe the flow of fluids generated by infusing devices such as the LifeFlow, hand pumps and other push-pull style methods that infuse blood/fluids at very high rates and volumes and under increased velocity to patients in need. Some of the intermittent flow methods have been around for many years. However, newer intermittent flow infusers have been introduced recently, particularly in EMS, as crews discover that transfusing blood fast to patients is often tricky due to the viscosity of the blood.

How do these devices operate? LifeFlow, for example, is using a 10cc syringe that can be reloaded fast to deliver a unit of whole blood (~500cc) in just two minutes. Some push-pull methods are using a 60cc syringe and a 3-way stopcock to achieve the same effect. Similarly, a recently introduced high-flow hand pump uses a 50cc squeeze chamber and wide trauma line to deliver the same results. The point here, however, is that irrespective of the method being used, all these handheld infusers are designed to deliver a large bolus of blood/fluids in a relatively short amount of time, and they are all capable of exceeding 200mL/min.

Further, unlike continuous flow, and as the name implies, intermittent flow starts and stops abruptly due to the nature of how fluids are being delivered. These rapid flows and intermittent patterns are extremely challenging for blood/fluid warmers. Therefore, if your agency is utilizing intermittent flow devices, or if you are considering using such methods in the future, then I highly suggest that you are using a blood/fluid warmer that is up to the job.

Patient care

Intermittent flow devices are used for the sickest patients. These are patients suffering from hypovolemic shock and need fluids/blood immediately. Think of the patient who has suffered from severe hemorrhage, or fluid displacement such as in septic shock, or a dehydrated hypovolemic pediatric patient. Patients that fall into these categories don’t have time for gravity flow, pressure bags, or even the highest flow rates that standard IV pumps can produce (most max out at 999mL/hr). These patients have utilized their compensating mechanisms by the time you arrive on scene to help them, and are often minutes from irreversible, decompensated shock. These patients are the sickest of the sick patients we are going to see and should be treated with rapid IV fluid/blood bolus before it’s too late.

However, this presents a problem. Is it a good idea to infuse a rapid bolus of cold blood products (stored at 4℃) into a hypovolemic trauma patient? Consider the trauma triad – a triangle with three conditions on each side that includes: hypothermia, acidosis and coagulopathy. When one side gets worse, it causes a chain reaction to make the other sides worse, thus creating a vicious circle that results in death if not corrected.

Let’s say we make the hypothermia side worse by bolusing cold fluids into a patient. If you are using an inadequate blood warmer that can’t efficiently warm intermittent flows, this might happen unintentionally. How does this affect acidosis and coagulopathy? For every 1℃ loss in core body temperature, coagulation function decreases by 10-15%, which means less ability to form clots and more blood loss, which means less oxygen delivery to tissues. Tissues deprived of oxygen revert to anaerobic respiration for energy production, a byproduct of which is lactic acid. This worsens the acidosis, which also hurts coagulation and oxygen-carrying capacity of red blood cells. Metabolic acidosis also decreases cardiac performance meaning less blood circulating in the body, triggering further hypothermia. Thus the downward cycle of death continues, all due to hypothermia from the trauma triad.

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However, when the patient is warmed (via warm, rapid blood bolus), clotting factor activity increases, thus decreasing blood loss. Less blood loss means more red blood cells to carry oxygen to tissues. More oxygen to tissues means more efficient, aerobic respiration, and decreased lactic acid production, reducing acidosis. Correct the metabolic acidosis and your patient’s cardiac function will improve. Plus, the patient is receiving blood products, so more life saving red blood cells and clotting factors will be circulating in your patient.

It’s obvious that giving warm blood is essential in preventing the trauma triad and is assisted by infusing those blood products via rapid (most likely intermittent) flow. But if we’re going to be rapidly infusing blood using intermittent flow, we need a warmer that is “smart” enough to recognize the intermittent flow pattern quickly, capable enough to warm those rapid flows, and responsive enough to stop the warming immediately when the infusion stops (this typically happens when the intermittent flow device reloads), to avoid overheating. This process should continue until the transfusion is done. This is an extremely complex task for any warmer out there and not all blood/fluid warmers can handle intermittent flows. In order to successfully handle rapid intermittent flows, a blood/fluid warmer has to meet four criteria: real time temperature sensing, robust mechanical structure, high delivery rates/high efficiency, and optimal priming volume.

An example of a warmer that was validated to effectively warm intermittent flows is the QinFlow’s Warrior. The Warrior senses fluid temperatures hundreds of times per second. When a bolus flow is identified by the sensors, the Warrior’s heat exchange process allows it to respond as necessary to warm the fluids to the proper temperature before being delivered to the patient. The heating will cease as soon as the sensors identify that the flow has stopped, avoiding overheating.

As discussed earlier, when using intermittent flow, warmers should be able to handle the high flow rates that are pushed out by these methods. Intermittent flow mechanisms are capable of delivering more than 200mL over one minute, at high velocity. Having a warmer that can physically handle this elevated pressure is essential. If your warmer can’t withstand the high flow rates, it’s time to get a warmer that can. The last thing your patient needs is to have a warmer break in the middle of a blood transfusion.

Apart from physically withstanding the high flow rates and pressures of intermittent flows, your blood/fluid warmer has to be able to warm those fluids to body temperature just as fast. Whole blood is stored at 4℃ and needs to be warmed to 38℃ before entering the patient. At a flow rate of 200mL/min (or more), your blood warmer must be able to perform this function. A critical part of warming fluids efficiently and adequately is to have sufficient priming volume. Sufficient priming volume allows the transfer of heat from the warmer to the fluids in a relaxed and incremental manner to ensure safe, yet rapid heating to match the high flow rates produced. The Warrior has a comfortable 19 mL priming volume which best fits the challenge of safely and effectively warming rapid intermittent flows.

Technology in EMS is ever evolving as we strive to better treat patients. Remember, you’re only as strong as your weakest link; the same goes for patient treatment. If your warmer can’t manage high flow rates and is the “weak link” in your treatment, then it’s time to get a blood/fluid warmer that can.

It should not come as a surprise that the QinFlow Warrior can cope with the intermittent flow challenge. The engineers at QinFlow have roots in Israeli Special Operations and Search and Rescue. For decades these individuals have been coming up with solutions to save patients. Whether on the battlefield, natural disasters, or in civilian EMS, QinFlow’s experts have developed solutions with real world experience and application. Learn more about the Warrior and other solutions from QinFlow.

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