Hypothermia is a well-known complication of general and neuraxial anaesthesia. After a caesarean section under spinal anaesthesia, 30 to 40% of the mothers have a core temperature \<36°C. Perioperative hypothermia induces maternal thermal discomfort and shivering, but also increases the amount of blood loss and the risks of postoperative wound infections and cardiac complications. In addition, maternal hypothermia may also have an impact on neonatal outcomes. Prevention of maternal hypothermia in women scheduled for caesarean delivery is consequently necessary, and is an important part of enhanced recovery after surgery. Active warming is efficient in preventing postoperative hypothermia. Forced-air warming is the most commonly used modality of active warming. However forced-air warming should be applied for at least 60 minutes to be efficient. As surgical duration for a caesarean is lower than one hour, this technic does not appear really appropriate in this context. In addition, upper body forced-air warming is uncomfortable for women and can interfere with bonding. Consequently forced-air warming is not generally used during caesarean delivery. Warmed IV fluid is another option to prevent perioperative hypothermia, but with contrasting results, depending mainly on the device and on the amount of perioperative fluids infusion. Co-loading IV fluid is recommended to prevent maternal hypotension induced by spinal anaesthesia in the context of caesarean delivery. Small released fluid warmings routinely used in scheduled surgery, are able to warm IV fluid administered with high flows, such as in co-loading IV fluid. But the efficiency of these devices to prevent maternal hypothermia has never been explored in the context of caesarean section under spinal anaesthesia with co-loading.

The investigators hypothesized that warmed IV fluid administered in co-loading with enFlow® or Fluido®Compact decreases the incidence of postoperative maternal hypothermia after caesarean section under spinal anaesthesia.

The investigators will perform a double blinded randomized controlled trial comparing active IV warming with enFlow® or Fluido®Compact versus placebo.

Indeed at the beginning of the study, the performance of the enFlow device were tested. But in February 2019, a study published in Anaesthesia showed that uncoated aluminium plates in fluid warming systems, such as those used in the enFlow system, yielded potentially harmful concentrations of aluminium when using balanced electrolyte solutions (ref Perl Anaesthesia 2019). Consequently this device was quarantined unless there are no alternative fluid warmers available Of note no adverse event has been reported associated with the use of enFlow® device. Consequently, we choose to continue our study with the Fluido®Compact, which is a very similar small fluid warmer but with coated aluminium plate.

After obtaining written informed consent from the patients, 70 pregnant women ASA status 1 or 2 and scheduled for caesarean delivery will be enrolled and randomized into two groups: active IV fluid warming vs no active warming. Written informed consent will be obtained before randomisation using an Internet based randomisation system. Participants will be randomized just after their arrival in the operative room. The clinicians in charge of the patients, the researcher and the woman will be blinded. In the operative room, a venous cannula will be inserted into the forearm, and an infusion of Ringer's lactate solution fluids will be initiated. An enFlow® or Fluido®Compact device will be placed on the IV for all the patients, but turned on only in the group active warming. The device will be hidden in all the patients. Every patient will have a spinal anaesthesia in sitting position with hyperbaric bupivacaine 10mg, sufentanil 3µg and morphine 100µg. An IV co loading with Ringer-Lactate 1000 ml will be started at the beginning of the spinal administration. All the women will be monitored using heart rate, continuous SpO2, non-invasive arterial blood pressure every 1-minute until the baby is born, and then every 5 minutes. Maternal arterial hypotension will be corrected with ephedrine or phenylephrine as appropriate. All the women will receive carbetocin 100µg just after baby extraction. While in the operative room, all the data will be collected on a standardized data collection sheet. In case of maternal temperature \<35°C during surgery, an active warming blanket will be used. The enFlow® or Fluido®Compact device will be taken off at the end of the surgery just before leaving the operative room.

In addition, postoperative data will be collected during the admission to the post-anaesthesia care unit (PACU). In case of maternal temperature \<36°C in the PACU, a warming blanket will be used.

The sample size calculation revealed that 62 participants were required to ensure that a 30% decrease in the incidence of postoperative maternal hypothermia will be detected (power = 0.9 ; α= 0,05). The investigators decided to enroll 70 women because of the risks of secondary exclusions and of lost of follow up.