The preoperative warming of patients at high risk of hypothermia, such as those having arthroscopic surgery, is recommended in evidence-based guidelines 114. Warming the peripheral tissues preoperatively reduces the impact of core to periphery thermal redistribution caused by anaesthetic-induced peripheral vasodilatation 15. Consequently, patients experience less post-induction temperature loss and recover from any loss at a faster rate intraoperatively 16171819. A forced air warming device has been shown to be the most effective method for preoperative warming, consistently demonstrating higher core temperatures in preoperative normothermic patients compared to other warming techniques 171920212223.

It is well documented that the use of room temperature irrigation solution increases the risk of inadvertent perioperative hypothermia during arthroscopic surgery. A systematic review of 13 randomised controlled trials including 686 patients showed that room-temperature irrigation fluid caused a greater drop in core body temperature and more episodes of hypothermia in patients, than warmed irrigation fluid 4. There is a significant correlation between the volume of room temperature irrigation solution used and a patients’ mean postoperative temperature 624. The use of warmed solution for intraoperative irrigation during arthroscopic surgery has been recommended as a method for preventing perioperative hypothermia 1414.

There is clear evidence that these two interventions assist in the maintenance of perioperative normothermia but there is now a call for robust well designed research to demonstrate improved clinical outcomes associated with their use 1. This trial will study the effects of these warming interventions on outcomes of particular interest to perioperative nurses, namely, post-operative temperature, thermal comfort, and total recovery time.

To investigate the effect of preoperative forced air warming and warmed intraoperative irrigation solution, alone and in combination, on postoperative temperature, thermal comfort, and total recovery time in adult patients undergoing elective arthroscopic shoulder surgery.

The trial will employ a randomised 2 x 2 factorial design. An equal ratio of participants will be allocated to each group. This design will enable the study of each intervention on the outcome variable, as well as the effects of interactions between interventions on the outcome variable.

The trial will be conducted in the day surgery unit of a private hospital in Sydney, Australia.

Participants will be deemed eligible for the trial if they are over the age of 18 years and are scheduled for elective arthroscopic shoulder surgery. They must be classified as American Society of Anaesthesiologists grade I-III (see Table 1) and have a body mass index between 18.5 and 40. Patients will be excluded if they have a preoperative temperature above 37.5°C or if they are unable to speak or understand English.

Participants will be allocated to one of four groups (see Table 2): Group one will receive preoperative warming with a forced air warming device; group two will receive warmed intraoperative irrigation solutions; group three will receive both preoperative warming and warmed intraoperative irrigation solutions; and group four will comprise the control group receiving neither intervention.

The primary outcome measure in this trial is postoperative temperature. The secondary outcomes of interest are thermal comfort and total recovery time. Baseline data on patient temperature and thermal comfort will be collected on arrival into the department (T₀). Follow-up measures will be collected at four time points; immediately prior to induction (T₁), on arrival into the recovery unit (T₂), 20 minutes after arrival into the recovery unit (T₃) and immediately prior to discharge from the recovery unit (T₄) (see Figure 1).

The trial has been powered to detect a 0.05°C (SD 0.5) difference in temperature between the four study groups. This was deemed a clinically significant difference based on the researchers experience and previous published studies 1224. Based on this number, and given the trial’s design, a total sample size of 120 participants is required to power the trial at 80% with a significance level of 5%.

An interim analysis of efficacy will be performed when 75% of participants have been enrolled in the trial. The level of significance will maintain an overall P value of 0.05 and be calculated according to the O’Brien-Fleming stopping boundaries 29.

A statistician, with no clinical involvement in the trial, will computer-generate a stratified (by anaesthetist) block randomised sequence. This list will remain concealed from the trial coordinator at all times. When the trial coordinator has assessed and enrolled a participant, she will telephone an independent person to obtain the treatment allocation. She will then inform the appropriate nursing and medical staff who will deliver the intervention(s). The trial coordinator will not collect outcome data, deliver the intervention(s), or provide patient care.

Outcome measures will be collected by recovery unit nursing staff who are blinded to the participants’ treatment allocation. The two interventions will be delivered by separate groups of perioperative staff (preoperative and intraoperative staff) and each group will be blinded to the treatment delivered by the other. The trial will adhere to procedures to maintain separation between the recovery unit nursing staff who will record the outcome data and the preoperative and intraoperative nursing and medical staff who will deliver the intervention(s). Due to the difficulty in blinding participants to the preoperative warming intervention, they will be blinded to the trial hypothesis and design 30.

Intention-to-treat analysis will be applied. Data will be analysed according to the 2x2 randomised factorial study design. The two-way analysis of covariance (two-way ANCOVA) will be used for the primary and secondary outcome measures of temperature, thermal comfort and total recovery time. The two-way ANCOVA model will also include operating room ambient temperature, volume of irrigation solution, length of surgery, blood loss and other covariates identified in the bivariate analyses. The analysis will be adjusted for baseline temperature and thermal comfort. Pair-wise comparison between groups will be conducted based on the results obtained from the two-way ANCOVA.

The project has been approved by the hospital’s human research ethics committee. Informed consent will be obtained from all participants.