Shivering is a physiologic response to early hypothermia in mammals. The definition of shivering is an involuntary, oscillatory muscular activity that augments metabolic heat production.

Routinely in post anesthetic care unit (PACU), the core temperature via tympanic membrane is always measured in all patients. Sometimes patients who have low temperature have no shivering symptom in other hand patients who have normal temperature have shivering symptom. This indicates that, only core temperature is not enough for predicting or detecting patients who will have shivering symptom in PACU.

In this study, investigators hypothesise that the core-peripheral temperature difference in postoperative period indicates patients who will have shivering symptom.

Thus, the aims of this study are to evaluate the relationship between core-peripheral temperature difference and shivering symptom in patients in PACU.

Humans are warm-blooded animal or homeotherms. They are able to regulate their body temperature which in physiologic range themselves. The body temperature is controlled by balancing heat production and heat loss. The normal body temperature refers to either core temperature (eg. tympanic membrane, esophagus, and intra-urinary bladder) or peripheral temperature (eg. skin, forehead, and axillar). Core temperature is the temperature of the deep tissues of the body. The normal range of core temperature is between 36.5-37.5 degree celsius. The peripheral temperature, in contrast to the core temperature, can be changed by many factors such as the temperature of the surroundings environment.

The term of hypothermia is the core temperature less than or equal to 36.4 degree celsius. When the body exposes to cold temperature, heat loss is decreased and heat production is increased as defense mechanism for keeping balance in several means: stop sweating, piloerection, cutaneous arterioles constriction, shivering, which increases heat production in skeletal muscles, conversion from fat to energy by mitochondria.Hypothermia is one of factors, which relates to postoperative complications.

Shivering is an oscillatory muscular activity that augments metabolic heat production. Vigorous shivering increases metabolic heat production up to 600% above basal level. Shivering is a common postoperative period complication. The pathophysiology of postoperative shivering remains unclear otherwise various mechanisms have been proposed. Shivering may happen as a thermoregulatory response to hypothermia or muscle hyperactivity with clonic or tonic patterns. Although cold-induced shivering is an obvious source of postanesthetic tremor. Some of the patients who suffer from shivering are believed to be nonthermoregulatory because their core temperatures remain normal. The incidence of postoperative shivering is 65% of patients after general anesthesia and 33% of patients after regional anesthesia.

This is the prospective observation clinical study. Investigators will observe shivering symptom and measure the patients' temperature at tympanic membrane, forehead, and dorsal of hand at many time points.

Inclusion criteria

• Postoperative patient at PACU (Post Anesthesia Care Unit)
• Duration of operation from 1 to 4 hours
• The patients American Society of Anesthesiologist classification from I to III
• The patients' age from 18 years old

Exclusion criteria:

• The patients who reject or unwilling to participate
• The patient who was induced hypothermia in intra-operative period
• The patient who still has neuromuscular blocking agent drugs effect in PACU
• The patient with shock or receiving continuous vasopressor drugs

Withdrawal or termination criteria:

• The patient who has intra-operative or immediate post-operative cardiac arrest and/or death

All patients who are in the Siriraj PACU at 5th floor Siammintr building. The patients are one of the patients from head-neck-breast surgery, general surgery, or urology surgery.

When the other researcher required data, please direct contact to principle investigator.