ZOLL Thermogard XP IVTM Physician Manual - Manual (Page 23)

ZOLL IVTM™ System Physicians' Manual
600248-001 Rev 3 22
cooperative, be hemodynamically stable and warm, is not bleeding, and has
adequate respiratory function” [22]. The maintenance of normothermia is one of
many homeostatic functions that must return. In focused trials it has been shown
that, with attention to temperature management post-operatively, the recovery team
can eliminate postoperative shivering which resulted in the lowering of oxygen
uptake, carbon dioxide production, and required ventilatory volumes[18][21].
Variation in external conditions such as room temperature and humidity, patient size,
and concurrent pharmacologic treatments affect both the core temperature and the
speed at which it changes.
In effect, the thermal challenge after CPB is to restore the patient to normothermia
quickly, but without allowing an overshoot of the target temperature. Measures used
historically for temperature control are effective in different applications, and each
has its disadvantages.
Rewarming Post-Cardiac Surgery
The most commonly used warming techniques are external and “passive”; that is,
they rely primarily on the body’s own heat-producing mechanisms to restore normal
temperature. Applying heated or reflective blankets, using radiant heat sources from
overhead or near the bed, and raising the room temperature are uncomplicated,
inexpensive and readily available. However, they are labor-intensive and can be
uncomfortable for nursing staff and visitors.
“Active” rewarming methods such as heated mattresses and forced-air tents seem to
be more effective and faster at raising the core temperature; but they too require
substantial management by hospital staff, and still leave the temperature fluctuating
around a desired target. Villamaria et al [24] reported, in a randomized controlled
trial, that both forced air warming devices and more conventional warm blankets and
overhead heating lamps showed similar performance. They reported rewarming
rates of 0.25ºC per hour. In a randomized controlled trial, the use of warming
blankets in a typical recovery area resulted in a 0.5ºC/h increase in core temperature
[16]. The rate for the Bair Hugger system was 0.75ºC/h.
Neurosurgery
Operative Hypothermia
Hypothermia is desired in some forms of neurosurgical procedures and has been
used for over a decade [33]. Outside of the use of cardiac bypass pumps, the limit to
this hypothermia is typically set to 32°C to avoid the temperatures at which cardiac
ventricular arrhythmia are likely[28][29]. The theoretical basis for the use of
hypothermia comes from studies that show reduced intra-operative stress responses
[34] and ischemic insult, and better neural repair in the context of cooling[35][36].
Typical conventional methods of cooling involve the use of cooling blankets and/or
convection via cold air. Iwata et al [37] showed cooling rates using conventional
convection and water blanket methods of 2.5°C in 1.5 hours (i.e. 1.6ºC/h). Their
study was a randomized controlled trial that examined the difference in cooling rates
between two anesthetic agents; Profofol and Sevoflurance. Their well controlled data
provides an insight into the rate of cooling that is expected in such patients. It also
illustrates that the use of more than one method of cooling is acceptable within this
clinical setting.
The limits of surface cooling are set by vasoconstriction [38]. As skin temperature
drops skin vasoconstriction increases so that heat exchange between the external
environment and the internal milieu is reduced. The skin acts as an insulator. As a