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To determine the effect of warming arthroscopic irrigation solution on core body temperature during hip arthroscopic surgery in patients with femoroacetabular impingement.
An analytical, prospective, observational study was performed in a cohort of 166 consecutive patients. All patients underwent hip arthroscopy for treatment of femoroacetabular impingement. Two groups were studied: patients operated on with arthroscopic irrigation solution warmed up to 32°C ± 2°C (89.6°F ± 3.6°F) and a control group comprising patients operated on with irrigation solution used at room temperature. Relevant information was collected regarding the patients (age, sex, body mass index, and blood pressure) and the procedure (volume and temperature of saline solution, pressure of fluid pump, surgery time, and room temperature). Corresponding statistical analysis was performed with STATA 11.0 (StataCorp, College Station, TX), by use of descriptive statistics, parametric and nonparametric tests, and a generalized estimating equation model for repeated measurements.
Both groups were comparable in terms of age, sex, systolic and diastolic blood pressure, body mass index, volume of irrigation solution used, and room temperature. The mean age of the cohort was 33 years (range, 14 to 60 years); mean body mass index, 23.7 kg/m2 (range, 17.2 to 34 kg/m2); mean volume of irrigation solution, 26 L (range, 12 to 39 L); mean systolic blood pressure, 97 mm Hg; mean diastolic blood pressure, 51 mm Hg; and mean surgical time, 110 minutes. A decrease in core body temperature by 0.5°C (0.9°F) or greater occurred during the course of surgery in 66% of patients in the control group versus 28% in the warmed-solution group (P < .001). At least 1 core body temperature measurement of less than 36°C (96.8°F) was recorded in 48% of patients in the control group versus 14% in the warmed-solution group (P < .001). The trend toward a decrease in core body temperature was 4 times greater in the control group than in the warmed-solution group (P < .001).
Use of arthroscopic irrigation solution warmed up to 32°C (89.6°F) reduces the risk of a decrease in core body temperature during hip arthroscopy in patients with femoroacetabular impingement.
Level of Evidence
Level II, analytical, prospective, comparative study in a cohort of consecutive patients.
Variations in core body temperature during a surgical procedure can lead to physiological changes at the systemic and tissular level. Intraoperative hypothermia (<35°C [<95°F])
and altering tissue regeneration ability. It promotes bleeding by affecting platelet activity and the coagulation cascade. Furthermore, it can also raise the risk of cardiovascular events by increasing the adrenergic response.
The purpose of our study is to determine the effect of warming arthroscopic irrigation solution on core body temperature during hip arthroscopic surgery in patients with FAI. Our hypothesis is that the use of warmed arthroscopic irrigation solution in comparison to room-temperature irrigation solution reduces the decline in core body temperature during hip arthroscopy.
An analytical, prospective, observational study was performed in a cohort of 166 consecutive patients undergoing hip arthroscopy for the FAI treatment. The cohort was divided into 2 consecutive groups; in the first group, arthroscopic irrigation solution was warmed up to 32°C ± 2°C (89.6°F ± 3.6°F) in an oven specially designed for this reason (AMSCO Warming Cabinet, dual-compartment model; Steris, Mentor, OH). The second group (control group) included all patients operated on with irrigation solution at room temperature without warming, as recorded by a laser thermometer (TMINI12 Temp-Seeker; CPS Products, Hialeah, FL).
Inclusion criteria were as follows: patients with FAI who underwent hip arthroscopy and were operated on at the same medical institution by the same surgeon; general intravenous anesthesia by the same anesthesiologist; use of a warming blanket at a temperature up to 43.3°C (109.94°F) from the umbilical region up to the neck region (Warm Air, Cincinnati Sub-Zero, Cincinnati, OH)
; and use of a joint irrigation solution infusion pump between 45 and 65 mm Hg (DYONICS 25 Solution Management System; Smith & Nephew, Andover, MA). Exclusion criteria were heart failure, kidney failure, and use of β-blockers, all assessed during the preanesthetic assessment.
Seven patients who met the initial inclusion criteria were excluded because of technical difficulties in the measurement of core body temperature.
The calculation of sample size was determined before initiation of the study to identify statistically significant differences between groups with regard to the core body temperature. A power of 80% and an α error of 5% was considered, resulting in 73 patients per group (STATA 11.0); an error margin over 10% was estimated for this value in case of losses.
Continuous temperature variables (room, arthroscopic irrigation solution, and core body temperature) were measured at systematic intervals of 15 minutes during the entire surgical procedure from time 0 (outset of arthroscopy, before starting solution irrigation). Core body temperature was measured with an esophageal thermometer (Reusable Temperature Probe 400 series; General Electric, Helsinki, Finland) that was correlated to body temperature at the intra-articular level at time 0 to certify the correct measurement of the esophageal thermometer.
The arthroscopic irrigation solution temperature was measured with a laser thermometer (TMINI12 Temp-Seeker). Other generic variables were also measured: sex, age, body mass index (BMI), surgical time, systolic blood pressure, diastolic blood pressure, and volume of arthroscopic irrigation solution.
The statistical analysis was performed with STATA 11.0 software. A descriptive statistical analysis was performed with the χ2 test, Mann-Whitney U test, Student t test, and a generalized estimating equation model for repeated measurements using a multivariate analysis to determine the impact of warming irrigation solution on core body temperature.
The mean age of the 166 patients who underwent hip arthroscopy for the treatment of FAI was 33 years (range, 14 to 60 years). All patients met the inclusion criteria, without the exclusion of patients according to the pre-established criteria. The first 83 patients comprised the control group, and the following 83 patients comprised the warmed-solution group. Room temperature was, on average, 20.57°C (69.026°F) ± 3 SDs (SD, 1.275°C); it was 20.46°C (68.82°F) in the control group and 20.71°C (69.27°F) in the warmed-solution group. Both groups were comparable in terms of number of patients, sex (P = .875), age (P = .113), BMI (P = .835), systolic blood pressure (P = .648), diastolic blood pressure (P = .339), volume of irrigation solution (P = .542), and room temperature (P = .153). The irrigation solution temperature was different from the core body temperature within the groups (P < .001, Mann-Whitney test in both cases).
A description of variables (demographic data and groups) is shown in Table 1. We determined the median values (with 50th percentiles) of the sample to examine the dispersal between the groups. The difference in body temperature was statistically significant based on a t test (P < .001). A decrease in core body temperature by 0.5°C (0.9°F) or greater during the course of surgery occurred in 66% of patients in the control group versus 28% in the warmed-solution group (P < .001) (Fig 1). At least 1 core body temperature measurement of less than 36°C (96.8°F) during surgery was recorded for 48% of patients in the control group versus 14% in the warmed-solution group (P < .001) (Fig 2).
The multivariate analysis with the generalized estimating equation model for repeated measurements allowed us to define all the variables that influence core body temperature both at the total level and at the group level (Table 2). In this multivariate analysis, core body temperature tended to decrease at a rate of 0.18°C/h (0.323°F/h) during surgery in the control group versus 0.04°C/h (0.072°F/h) in the warmed-solution group (P < .001) (Figs 3 and 4). In the control group, there was an increase in core body temperature with a higher irrigation solution temperature, which stabilized when the irrigation solution temperature exceeded 27°C (80.6°F) (P < .001). In the warmed-solution group, we found no increases in body temperature despite increasing the irrigation solution temperature (Fig 5).
Table 2Variables That Decrease Core Body Temperature
A decrease in core body temperature is a condition that can occur during FAI arthroscopic treatment, resulting in physiological changes in the patient. In general, these changes have not been described sufficiently in the literature.
In hip arthroscopy surgery, patients are exposed to factors that influence the decrease in body temperature. Our investigation group previously showed that the incidence of hypothermia, with a temperature below 35°C (95°F), in patients who underwent hip arthroscopy for the treatment of FAI was 2.7%.
The factors that contributed to the development of hypothermia during hip arthroscopy surgery were prolonged surgery time, low BMI, low blood pressure during the procedure, and low temperature of the arthroscopic irrigation fluid, with the last 2 factors being the main factors.
We monitored the irrigation solution temperature, heating it up to 32°C (89.6°F) on average, and found that this prevented a body temperature decrease during irrigation and decreased the tendency to lower the body temperature from 0.18°C/h (0.323°F/h) in the control group to 0.04°C/h (0.072°F/h) in the warmed-solution group. In this latter group, only 28% of patients had a decrease in core body temperature of 0.5°C (0.9°F/h) or more compared with 66% in the control group. This drop in body temperature, though lower for the warmed–irrigation solution group, can be explained by the length of surgery and liters of solution used. Other variables analyzed such as BMI and room temperature also influence the body temperature decrease, with an equal effect in both groups.
By controlling the irrigation solution temperature variable, we noted that the variable of volume of irrigation solution exerted the same influence in both groups. The differences in room temperature between the groups showed no statistically significant difference; however, these findings were considered a result of random variation. The differences in saline solution temperature in each group were due to possible variations from heating in a furnace compared with storage at ambient room temperature.
In the warmed-solution group there were no patients with a core body temperature lower than 35°C (95°F) versus 2.4% in the control group; in addition, there were no cases of chills versus 6% in the control group. No other complications were registered.
Our results conclusively show that heating the irrigation solution significantly prevents a decrease in body temperature (P < .001). Therefore our recommendation is to heat arthroscopic irrigation solution to 32°C (89.6°F) to prevent a decrease in the core body temperature in patients undergoing hip arthroscopy for the treatment of FAI.
The main limitation of this study is that the surgical time has decreased in relation to the surgeon's experience curve. Independently of this, there is a tendency toward a decrease in core body temperature in both groups that is not affected by a longer or shorter surgical time, except in the group of patients with a variation of 0.5°C (0.9°F/h) or more. Another limitation of this work is selection bias because of the lack of randomization. Further randomized studies are need to eliminate this bias.
Use of arthroscopic irrigation solution warmed up to 32°C (89.6°F) reduces the risk of a decrease in core body temperature during hip arthroscopy in patients with FAI.
Electrocardiographic manifestations of hypothermia.