Tag Archives: bolus

Does Your Warmer Handle Intermittent (Bolus) Flows?

In a previous article I discussed the top ten things you need to look for when choosing a blood/fluid warmer. In this article I want to talk about one function that, in my opinion, is absolutely necessary for your warmer to have and unfortunately completely overlooked. That is the ability to warm and handle intermittent flows.

Let’s start with a short background: 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 were lucky, get a couple hundred CC’s into the patient before they arrived at the hospital. From there, if the physician determined that the patient needed 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? Well they are simply too large (let alone that they are not battery powered). The model of rapid infusers that I have seen used are as tall as an IV pole and very, very bulky. This is fine when you’re in a trauma bay where space is a given. But in the back of an ambulance, space is a very limited resource. So an answer to this problem was introduced by handheld, push-pull, and syringe style infusers that allow for rapid infusion of blood products or fluids, in a matter of minutes, in an intermittent fashion.

So what exactly 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, especially in the EMS world. This has to do, to some extent, with the continuous expansion of blood programs across the nation: EMS teams 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 2 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 your blood/fluid warmer. 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. The QinFlow’s Warrior is one great example of a warmer that has been designed to meet this challenge, and I will address it in greater detail later in the article. For now, I would like to share with you some of the clinical aspects of intermittent flows.

So now that we know what intermittent flow is and how they are generated, let’s address the question of which patient population we as providers are going to utilize it on? Intermittent flow devices are used for the sickest patients. These patients are suffering from hypovolemic shock and need fluids/blood now! 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 already utilized all of their compensating mechanisms and by the time you arrive on scene to help them, they can be just minutes from irreversible, decompensated shock. These patients are the sickest of the sick patients we are going to see. So these patients are going to be treated with rapid IV fluid/blood bolus before it’s too late.

This presents a problem however. Do you think it’s a good idea to infuse a rapid bolus of cold blood products (stored at 4℃) into a hypovolemic trauma patient? Some of you may know the answer, but I’m going to explain why for those of us who might not know exactly why this isn’t a good idea. Let’s look at the trauma triad. It’s a triangle with three conditions on each side. They are; hypothermia, acidosis, and coagulopathy. When one side gets worse, it causes a chain reaction to make the other side 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. In this scenario, I highly doubt that a provider would do this on purpose, however if you are using an inadequate blood warmer that can’t efficiently warm intermittent flows, you might do this unintentionally. How does this affect acidosis and coagulopathy? For every 1℃ in core body temperature, coagulation function decreases by 10-15%. Which means less ability to form clots and more blood loss. More blood loss 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 by the way 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 because we didn’t prevent the hypothermia side of the lethal triad.

However, when we warm the patient (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 we are giving the patient blood products so more life saving red blood cells and clotting factors will be circulating in your patient!

So we can see that giving warm blood is absolutely essential in preventing the trauma triad! Better still when we can infuse 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 (i.e. this typically happens when the intermittent flow device reloads) so as to avoid overheating. And this process should go on and on until the transfusion is done. This is an extremely complex task for any warmer out there and not all blood/fluid warmers can deal with intermittent flows. In order to successfully handle rapid intermittent flows, a blood/fluid warmer has to meet four criteria. They are: 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 highly efficient heat exchange process allows it to respond as necessary to warm the fluids to the proper temperature before being delivered into 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, your warmer also has to 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 has to 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.

I hope this article has shed some light on not only the importance of warming blood/fluids, but also how necessary it is that your blood warmer be able to handle intermittent flows. Fortunately, 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. The Warrior is one of their finest answers to solving the problem of blood/fluid warming in general and intermittent flow handling in particular across the entire continuum of emergency care. Irrespective of the infusion method used, from pressure bag to rapid intermittent flow methods, you can trust the Warrior to warm near freezing blood/fluids (4°C) to body temp within seconds! You can check out the Warrior and other solutions from QinFlow Here.


QinFlow is proud to announce that the Warrior line is now validated to effectively warm rapid intermittent (aka “bolus”) flows generated via various intermittent transfusion techniques to accelerate the delivery of blood and fluid products to critically-ill patients.


Emergency teams often apply pressure bag to accelerate the flow of blood and fluid products to critically-ill patients or use electro-mechanical pump to control the flow rate or the total volume delivered. Both methods deliver a fairly constant flow. However, in many instances, and especially for the sickest patients, emergency teams may apply various types of flow-inducing methods to accelerate the flow of blood/fluids to patients, control the volume (e.g. as typical for pediatric patients), or both. These methods typically generate intermittent (or bolus) flow pattern. Popular methods include the “push-pull” method, and a hand pump. A new device called the LifeFlow® PLUS introduces an intuitive and novel method of rapid delivery. Irrespective of the flow-inducing method used, it is important to note that all these methods generate rapid flows that are delivered intermittently; that is, a fast pulse of high flow followed by short period of no-flow (in which the device is reloaded with blood/fluid), and so on, until the transfusion ends.


The potentially aggressive nature of the intermittent flows generated by the techniques listed above poses great challenges on prevailing blood and IV fluid warming devices, which were predominantly designed to handle constant flows generated by gravity, pressure bag, or mechanical pump. In order for the warmers to sufficiently perform, the warmers typically require the following 4 characteristics:

  1. Real-Time Sensing: continuous, real-time sensing is required in order to promptly identify changes in the flow so that the warmer will be able to react to these changes in a fast manner;
  2. High Delivery Rate / High Efficiency: high delivery rate of 180ml/min or higher for 4°C fluid/blood is required in order to properly warm the intermittent flows before they reach the patient. High efficiency is required so as to effect immediate changes in the warming profile;
  3. Sufficient Priming Volume: sufficient priming volume is required in order to warm the rapid flows and yet ensure safe (i.e. incremental and relaxed) heat transfer process to the fluids/blood; and
  4. Robust Mechanical Structure: robust mechanical structure is required in order to address the elevated pressure that these techniques often generate.

To the best of our knowledge, the Warrior line is the only technology in the market nowadays that can effectively address these aggressive intermittent flows:

  1. Real-Time Sensing: a sensor array embedded on the Warrior’s disposable unit measures fluids/blood temperature hundreds of times per second and the system adjusts the heating distribution accordingly so as to ensure 38°C ±2°C output;
  2. High Delivery Rate / High Efficiency: with its high battery capacity and nearly 100% warming efficiency (patented technology), the Warrior line is capable of delivering up to 180 (Warrior lite with Extra Power battery) and 200 (Warrior and Warrior EXTREME) ml/min for 4°C fluids/blood. With AC power source, the Warrior can deliver up to 290 ml/min for 4°C fluids/blood (Warrior AC);
  3. Sufficient Priming Volume: comfortable 19ml priming volume facilitate the warming of the rapid flows while ensuring safe heat exchange process; and
  4. Robust Mechanical Structure: the Warrior consumable was validated to withstand the elevated pressure generated through rapid intermittent flows without leaking or breaking.

To sum up: prevailing warmers cannot warm fluids/blood delivered intermittently, in rapid flows. In some cases, the cassette may even break due to the elevated pressure. As a result, your sickest patients may receive cold blood/fluids! This abnormality is now fixed by the Warrior line!


As of August, 2021 –
All Warrior Base Units (i.e Warrior lite, Warrior, and Warrior EXTREME base units) delivered from our factory include tightened performance specifications, designed to effectively warm rapid intermittent flows. The performance of the systems with constant flows remains top notch.
The warming performance of the Warrior line when intermittent flows are applied is second to none even prior to introducing the tightened performance specifications; however, wider tolerances may be observed.
Recent and successful validation studies were performed with the methods listed above, and predominantly with the LifeFlow® and LifeFlow PLUS® infusers.


As indicatively shown in the figure below, set temperature of 38°C ±2°C will be maintained also when rapid intermittent flows rates are applied. The figure provides an indicative performance of the Warrior device with the LifeFlow® PLUS device, when cold fluids (4°C input) are delivered intermittently in rapid flows (approximately 200ml delivered in one minute). The Warrior’s fast adjustments to the rapid flow fluctuations is reflected by the minor tolerances (±2°C) around the device’s target temperature (38°C). The warming is maintained within spec (38±2°C).
Please note that restrictions apply; therefore, contact us for more details.



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Thank you,
Team QinFlow