Between 25 and 90% of all patients who undergo elective surgery experience hypothermia, defined as a body temperature below 36°C.1 Anesthesia (regional and general) can interfere with the body’s thermoregulatory processes.2 The anesthetic drugs themselves can create challenges for temperature control either centrally or peripherally. The risk of hypothermia is influenced by the temperature of the operating room suite, the temperature of stock fluids and blood products, and the rate of administration of intravenous infusates.3
Hypothermia is associated with an increased risk of complications, some of which can be severe.4 Several authors have reported an association with poor wound healing, cardiac dysrhythmias, and increased bleeding.4–6 Even mild hypothermia of only 1-3°C is associated with increased complications such as delayed wound healing, ventricular tachycardia, poor anesthetic drug clearance, coagulopathy, and susceptibility to infection.7 In contrast, maintenance of normothermia reduces hospital costs and death rates.8
Numerous methods have been devised to prevent inadvertent hypothermia.9 Surgical personnel typically use warming blankets10, warm the surgical suite, warm the inspired air in the ventilator, utilize cabinet storage warmers for infusates11, and reduce the rate of infusion of fluids and blood products. These and numerous other techniques have been described as the prevention of hypothermia has gained increased attention.9,12−14
Current guidelines recommend incorporating a method of warming infused fluids during surgery.3,9,13,15 The heating performance of several fluid warmers has been evaluated in the past.
Kim et al. studied the effect of higher flow rates of fluid on output temperature over time.16 In their study set-up, they tested pressurized isotonic saline at 5°C and 20°C, flowing at 30, 50 and 100 ml/min for 6 minutes. They found that the ThermoSens® (Sewoon Medical Company, Seoul, Korea) and buddy light™ (Belmont Instrument Corporation, Billerica, MA, USA) underperformed at higher flow rates compared to the uncoated enFlow™ (Vyaire Medical, Mettawa, IL, USA). Zoremba17 and colleagues found similar performance results using ice-cold saline comparing the Fluido Compact® (The 37° Company, Amersfoort, Netherlands) and the Thermosens® (Barkey, Leopoldshöhe, Germany) fluid warmers to the uncoated enFlow. Room temperature (24.4°C) fluid and chilled (6°C) fluid were run through the warmers at 25, 50, 75, and 100 ml/min. At a flow rate of 25 ml/min and 50 ml/min, the outlet temperature from enFlow was significantly higher (p < 0.01) than the output temperatures of Fluido Compact and Thermosens warmers. Another study by Xu et al. used isotonic saline at infusion drip rates of 3, 4, 5, 6, 7, 8, 10, and 17.5 ml/min adjusted to room temperatures of 20°C, 22°C, and 24°C. They measured temperatures at the outlet of both the 3M Ranger™ (3M) dry heat transfer heater and the FT2800™ (Keewell Medical Technology, China) coaxial coil heater. Output temperatures were significantly affected by room temperature and flow rates.18 Even at only 17.5 ml/min, neither unit tested was able to reach its target temperature as flow rates increased.
Intravenous fluid warmers based on aluminum heating blocks have been troubled with aluminum leaching into the fluid, leading to concerns about aluminum toxicity.19− 21 The Food and Drug Administration recently issued a letter to health care providers in this regard, mentioning that multiple fluid warmers have been restricted or recalled.22 In response to this issue, the enFlow® intravenous fluid warmer (Vyaire Medical, Mettawa, IL) was recently redesigned to include a parylene coating over the heating block.21 As previous studies only evaluated the heating performance of the uncoated enFlow system, currently no published data are available on the performance of the new parylene-coated enFlow cartridge. Therefore, we compared the uncoated and coated models of the enFlow fluid warmer at varying fluid rates at different fluid temperatures to evaluate if the parylene coating is an acceptable option to overcome the described issues with aluminium leaching, without impacting the heating performance of enFlow cartridge.