### Introduction

### Materials and Methods

_{out}, 76 cm) were achieved using a 55-cm fluid extension line, three-way connectors, and 18-gauge intravenous catheters connected to the outlet of the fluid warmers in series (Fig. 1). These extended lines were exposed to ambient room temperature. Two PT 100 temperature probes (KRGA-50, Kimo Instruments, Edenbridge, UK) were connected to a Kistock Datalogger (KTH350, Kimo Instruments, Edenbridge, UK). The probes were inserted at the inlet point (P

_{in}) and at P

_{out}. An artificial lung was ventilated with 500 ml of tidal volume, at 10 breaths/min, and 6 L/min of oxygen and medical air using Mega Acer Kit® without humidification in all groups. Normal saline was then delivered at flow rates of 440 ml/h, which was sum of the one third (300 ml/h) of maintenance fluid, simply calculated with “4-2-1” formula for a 70 kg patient with 8 h NPO, and the required deficit replacement [140 ml/h (2 ml/kg/h)] due to losses by losses third spacing and evaporation during surgery with anticipated minimal to moderate tissue trauma [14,15].

_{in}and TP

_{out}) were recorded automatically using the Kistock Datalogger at 5-min intervals for 60 min. After downloading each result at the aforementioned time points to our computer using a software (Kilog; Kimo Instruments, Edenbridge, UK), we calculated the mean values of TP

_{in}and TP

_{out}recorded at 5-min intervals for 60 min after infusion in each group for the expected decrease in mean body temperature (ΔMBT). Each test was repeated ten times.

_{in}in groups M, R, and T for each test, and we defined it as a group UWF. For calculating ΔMBT, the mean TP

_{out}of each group (group M, group R, and group T) and the mean fluid temperature of group UWF were used. This was done using Horowitz's formula, as given below [16]: where ΔMBT is the expected decrease in mean body temperature; TF, the temperature of the infused fluid; TPt, the patient's baseline core temperature (37℃); SF, the specific heat of the infused fluid (1.0 1 kcal/L/℃ for saline); Vol, the volume of the infused fluid (L); SPt, the specific heat of human tissue (0.83 kcal/L/℃); and Wt, the weight of the patient (kg).

### Statistical analysis

### Results

_{out}60 min after infusion was highest in group M (36.01 [35.73–36.29]℃), followed by groups T (29.81 [29.38–30.24]℃, P < 0.001) and R (29.12 [28.52–29.72]℃, P < 0.001), respectively (Table 1, Fig. 2). The TP

_{out}at 5-min intervals for 60 min was significantly higher in group M than in groups R and T at all time points (Fig. 2, P < 0.001). However, it was not significantly higher in group T than group R except at some time points (Fig. 2).

_{out}was significantly highest in group M (36.07 [35.84–36.30]℃), compared to groups T (29.93 [29.59–30.27]℃, P < 0.001) and R (29.17 [28.56–29.78]℃, P < 0.001) (Table 1). It was significantly higher in group T than in group R (Table 1, P = 0.028). The mean TP

_{in}showed no significant differences among the three groups. None of the investigated fluid warmers provided a constant normothermic temperature (above 36.5℃) (Fig. 2).

_{in}in all groups (group UWF), the ΔMBT at 5 h after infusion was significantly higher [−0.59 (−0.59 to −0.58)℃] (Table 1, Fig. 3, P < 0.001). ΔMBT at 1 h intervals for 5 h after fluid infusion using each warmer was significantly lower in group M than in groups T, R, and UWF for a 70 kg patient (Fig. 3, P < 0.001).