Thermal Compression Device for Maintenance of Perioperative Normothermia
Condition: Hypothermia
MeSH terms: Hypothermia
Study type: Interventional

Summary: 
      Getting cold (not maintaining normothermia) around surgery (perioperative period) leads to
      many negative outcomes for patients including increased wound complications, abnormal heart
      rhythms and increased blood loss. These all lead to increased length of hospital stay and
      higher requirements for post operative monitoring. These add to around $3500 of extra costs
      per patient. The investigators aim to study the effects of a warming device, placed around
      the patient's legs and/or feet, to determine it's safety, efficacy and eventually compare to
      the current gold standard of a forced air warming blanket. Forced air warming has been
      associated with the spread of germs over the surgical field. Hence the need for warming
      equipment that won't do that.
    

Detailed description: 
      Cases of inadvertent perioperative hypothermia (IPH) within a hospital setting are often
      overlooked and should be where the incidence of hypothermia can be eliminated. Heat loss
      occurs predominantly via convective heat transfer, particularly through glabrous surfaces
      such as the palms and soles. A decrease in core body temperature can be categorized into mild
      (32 deg C-36 deg C), moderate (28 deg C-32 deg C), or severe (<28 deg C) hypothermia (2).
      During preoperative care, patients are dressed solely in a gown and are often exposed to cold
      waiting areas with little insulation. They are exposed to cold liquids during the wash of the
      surgical site during sterilization preparation.

      Once in the operating room (OR), the patients are naked and exposed to a room temperature
      well below 36 deg C. To compensate for hypothermia, the hypothalamus attempts to stimulate
      heat production through sympathetically mediated vasoconstriction, shivering and increased
      adrenal activity, and through the erection of hair follicles to trap air and retain heat. At
      the onset of surgery, delivered anesthetics immediately impair the normal autonomic
      thermoregulatory controls. Colder blood is transferred from the peripheries of the body to
      the core through a phenomenon known as redistributive hypothermia. Vasodilatation and
      reduction in muscle tone creates a significant drop in core temperature within the first
      half-hour of surgery.

      IPH is not a rare occurrence. Several sources, including the NICE guidelines, estimate that
      as many as 70% of patients undergoing normal surgery may be admitted to the Post Anesthesia
      Care Unit (PACU) hypothermic if the risk is not managed. More conservative estimates put the
      incidence at 20%. An estimated 48 million inpatient surgical visits were made in the US in
      2009, translating to between 10 to 34 million cases of IPH per year in the US alone. All
      patients are at risk of developing IPH, although certain factors increase the risk of IPH.
      American Society for Anesthesiology (ASA) grade, lower preoperative temperatures, combined
      regional and general anesthesia, and intermediate or major surgery are all associated with
      increased risk of IPH. Under these risk factors, over 17 million patients are at high-risk
      for becoming hypothermic.

      Clinical Impact The development of IPH is strongly correlated with a multitude of
      physiological organ system changes, impacting the cardiovascular, respiratory, neurologic,
      immunologic, hematologic, drug metabolic, and wound healing mechanisms. The incidence of
      several post-surgical complications is increased due to even mild hypothermia (Table 1).
      Intraoperatively, hypothermia can cause a decrease in cardiac output and heart rate, which
      can lead to ventricular dysrhythmias. Platelet functions become impaired and there is a
      decrease in coagulation factors, which lead to greater intraoperative bleeding and blood
      loss. Hypothermia is associated with a four-fold increase in surgical would infection and
      twice as many morbid cardiac events.

      Overall, compared to non-hypothermic patients, those who suffer IPH experience greater rates
      of surgical site infections, bleeding, cardiac complications which may require additional
      monitoring, PACU length of stay, total length of stay, and subjective discomfort.
      Interestingly, the likelihood of developing hypothermia in an open versus laparoscopic
      surgery is similar across various types of procedures, most likely attributable to the fact
      that most laparoscopic procedures are significantly longer when compared to their open
      surgery counterpart.

      Prevention of the effects of redistribution hypothermia is best done before their peripheries
      become cold, which often occurs before they arrive in the OR. Our audit of Stanford
      Hospital's Ambulatory Care Centre OR times, from January to March 2013, showed this time was
      at least 2 hours for all elective patients. Placing responsibility of the device placement on
      preoperative staff rather than OR staff is also better for compliance, as OR staff are
      burdened with many other priorities prior to the incision and are more rushed for time.

      The critical period to intervene and prevent perioperative hypothermia is in the preoperative
      phase. This is when peripheral warming can be in place so that when redistribution occurs due
      to general anesthesia, warm blood flows back from the core rather than cold blood if no
      peripheral warming is in place. Without preoperative warming, patients will become
      hypothermic at the beginning of surgery. Intraoperative warming minimizes the extent but does
      not prevent it.

      In one study, 2 cohorts were compared to show the effect on core temperature of preoperative
      warming to those with no preoperative warming. Both cohorts received intraoperative forced
      air warming. Without preoperative warming in this cohort, forced air warming methods take 2-5
      hours to return the patient to normothermia. Patients cannot leave the PACU hypothermic.

      Using a crude works-like prototype the investigators conducted bench testing and collection
      of preliminary data. In the first hour, no heating was applied followed by two hours with the
      device turned on. During this time temperature was recorded (oral, arm and leg surface),
      thermal and general comfort was measured using a visual analogue scale and the presence of
      shivering or sweating was noted. The device was set up to maintain a maximum at skin
      temperature of 43°C. This was shown previously to be the higher limit and optimal
      preoperative warming temperature. This was shown previously to be the higher limit and
      optimal preoperative warming temperature. The experiment showed that core temperature was
      maintained in three of the four subjects with one patient becoming hypothermic in the pre
      device on period. Arm temperature was constant and hypothermic during the experiment. Leg
      temperature increased with the device on. Thermal comfort and general comfort levels showed
      the prototype was well tolerated.

      The investigators hope to learn from the study:

      Prototype development What are the best configurations to apply the device to the patient?

      Safety Will the device maintain a consistent temperature at the skin? Will there be no burns
      occuring? Will the patient not get hyperthermic?

      Efficacy Will the device keep the patient from getting cold? If so, what are the relative
      effects of warming at the soles of the feet and / or with waring at the popliteal fossa? If
      efficacy is established, is it better than / equivalent to the gold standard of the forced
      air warming blanket?

      Usability Does the device fit into the operative workflow What are the opinions of the users
      (patients, nurses, doctors) about the usability of the device? Will the device causes patient
      discomfort while they are awake? Does it improve their thermal comfort?
    

Intervention name(s): Bair Hugger; Prototype / Experimental device
Intervention type(s): Device; Device
Intervention description(s): Forced Air Warming Blanket placed over the body of the patient during surgery; Contact heating device provides heat to the sole of the foot and popliteal fossa while providing intermittent compression to the lower leg.
Other intervention name(s): Forced Air Warming Blanket
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: perioperative hypothermia; thermal compression; forced air warming