Journal of Gerontological Nursing

Inadvertent Hypothermia

Nancy L Burkle, BSN, RN, CNOR

Abstract

Inadvertent hypothermia can be a common, yet underestimated, hazard of the elderly surgical patient.

Abstract

Inadvertent hypothermia can be a common, yet underestimated, hazard of the elderly surgical patient.

The demographic trend in this country is toward a growth in the number of elderly people. ' As the number of older people increases, they will utilize more health-care services. Consequently, there will be an expansion in the field of geriatric surgery. It is projected that major operative procedures will be performed on this aged patient population, with a commitment to decreasing the surgical risks and mortality.

Man is homeothermic; the temperature of the body normally stays within very narrow limits, 360C to 37.50C (96.80F to 99.50F). One very serious complication of undergoing anesthesia and surgery is the development of inadvertent intraoperative hypothermia. Hypothermia can be defined as a core body temperature below 360C (96.80F).2 Hypothermia can have extremely complex and potentially very dangerous effects if it is not recognized, understood, and deterred by those caring for geriatric patients during the perioperative period.

A normal oral temperature for a person over the age of 90 may be 36.050C (96.90F).1 This is lower than the normal temperature of a younger adult. There is evidence that the elderly have a more difficult time adjusting to both a hot and a cold environmental temperature change than do the young.4 Likewise, certain drugs such as phenothiazines and barbiturates can cause hypothermia.5

TTie elderly lack some of the mechanisms for producing body heat. Muscle bulk and strength are decreased.6 Immobility itself may play a part in producing hypothermia, because heat is generated in the body from muscular activity. Furthermore, the basal metabolic rate, which plays a part in temperature regulation, decreases in the elderly due to a decreased amount of metabolizing tissue.7 Consequently, elderly persons are at high risk for intraoperative hypothermia because they have less heat to lose before reaching the hypothermie state.

The fact that surgery and anesthesia decrease body temperature has been widely reported. Similarly, many studies have indicated that older patients become hypothermie more frequently during surgical procedures than do younger patients.8*" In addition, elderly people are particularly at risk because they sometimes have defects in thermorégulation caused by the agerelated decline in the autonomie nervous system.12

The elderly person who is a surgery candidate needs to be thoroughly assessed preoperatively for any underlying pathological states that could impact on the individual's temperatureregulating ability. Burns, paraplegia, chronic arthritis, hypothyroidísm, and hypoadrenalism are examples of conditions that may need special attention and management during the perioperative period. Also, the repercussions of inadvertent hypothermia on patients having major vascular surgery, vascular anastomoses, or digit reimplantation need to be considered by those caring for the aged.

The Hazards of Hypothermia

Preventing hypothermia during the operative procedure is important because it can be devastating for the elderly person in the immediate postoperative period. During the rewarming period that follows anesthesia and surgery, shivering often occurs. Shivering can lead to an increased oxygen demand, which the already over stressed or debilitated elderly patient may not be able to meet.

Roe, Goldberg, Blair, and Kinney9 found that patients had an average increase in oxygen consumption of 92% above resting preoperative values, when there was a fall in body temperature of 0.3 to 1.20C (32.54 to 34.160F). The postoperative hypothermie aged patient, with limited cardiovascular and respiratory reserves, may then be at risk for developing heart failure, cardiac arrhythmias, or even myocardial infarction.13

The elderly may also experience circulatory complications as a result of intraoperative hypothermia. Pflug, Foster, Martin, and Winter14 concluded that adult patients who were hypothermie at the end of surgery had decreased limb blood flow when compared with patients who were not hypothermie at the end of surgery. Prolonged anesthesia and a cool surgical environment are thought to cause peripheral vasoconstriction, which reduces blood flow to the limbs.14

In addition, reduced limb blood flow during or after surgery has been associated with increased peripheral venous thrombosis, particularly in the elderly who have a high incidence of arteriosclerosis.14 Furthermore, according to Lunn,15 hypothermia may mask hypovolemia in the postoperative period. When rewarming occurs, the patient's blood pressure can drop as the peripheral vessels vasodilate and more blood leaves the core compartments of the body.

Another consequence of inadvertent hypothermia in the elderly is delayed drug clearance and the potentiation of muscle relaxants.16 Drugs that were supposed to have been metabolized by the patient or antagonized in the OR may not have been because of delayed hepatic drug clearance or slower renal excretion. Then their effects can appear later in the postoperative period, as the patient's temperature increases. Medications given earlier during surgery, such as narcotics, barbiturates, and muscle relaxants, can often have a detrimental effect on the elderly patient's postoperative respiratory effort. Therefore, keeping the aged patient warm during the surgical intervention is a major goal of the nursing, medical, and anesthesia personnel in the OR.

Factors Influencing Perioperative Heat Loss

There are many factors during the perioperative period that promote heat loss from patients. Three major factors are: the ambient temperature of the operating room, the type of anesthesia administered, and the positioning and cleansing of the operative site.

The modern operating room is airconditioned and cool with a temperature usually between 2O0C and 240C (680F and 750F). The humidity is kept at a 50% minimum. The cool temperature and low humidity are thought to decrease bacterial growth, suppress static electricity, and to keep the gowned and gloved members of the surgical team comfortable.

In addition, many new ORs are built with at least 25 room air exchanges per hour and many rooms are equipped with laminar air flow devices. Thus, the environment in the surgical suite is a chilly one and cool air is constantly circulating around the elderly patient.

The kind of anesthetic drugs administered and the type of anesthesia delivered are known to decrease body temperature. Halothane and other common inhalational anesthetic agents promote surface blood flow and are thought to depress central thermoregulatory structures. 16 Similarly, skeletal muscle relaxants, often used with general anesthesia, abolish shivering and eliminate motor activity. Thus, the patient is unable to move around to create body heat.

Furthermore, patients receiving epidural or spinal anesthesia will lose body heat distal to the level of the block. Vasoconstriction and shivering are blocked and a decrease in body temperature results. In fact, Vaughan, Vaughan, and Cork10 found that the rate at which body temperature returns toward normal was shorter for patients receiving a general anesthetic than that observed for patients receiving regional anesthesia.

After the patient is anesthetized, surgical positioning and skin preparation begin. Heat is lost when the patient's body is uncovered and exposed to the cool environment. This can sometimes be a long period of time, when the surgical position is a difficult one to achieve. Then, as the operative site is washed with volatile fluids and antiseptics, heat can be lost through evaporation, especially when the area to be prepared is an extensive one.

There are several other factors that can lead to hypothermia during surgery. As the surgery progresses, more heat is lost when the peritoneum, pleura, or other large area of the body is entered. Heat loss might be expected to occur by evaporation from the most serous surfaces of the bowel. Similarly, radiative heat may be lost from the warm surface of the bowel to the cooler operating room air.

Administration of unhumidified anesthetic gases, the infusion of unwarmed intravenous fluids and blood, and the lack of a wanning mattress on the OR table can lead to increased heat loss. The person, while undergoing surgery, is further at risk for having his temperature lowered if large amounts of cool saline are used to irrigate his wound. Likewise, heat is lost from the surgical suite when the doors to the room are left open after the healthcare personnel enter and exit the room.

Intraoperative Care

It is ironic that there sometimes exists a double standard in the way the pediatrie patient is cared for in surgery and the way the geriatric patient is cared for during surgery. Frequently, all efforts are taken to keep the pediatrie patients warm in surgery. Unfortunately, sometimes the same measures are not used for those elderly patients at the opposite end of the age continuum. For example, prior to the start of a pediatrie case, the ambient temperature of the OR is often increased. However, it is only in the extraordinarily long and major surgeries, such as a thoracoabdominal aortic aneurysm resection, that the ambient temperature of the OR is warmed up for an elderly patient.

In the same way, a portable radiant heating lamp is often placed a safe distance from a baby or small child in the OR to keep the infant warm, but rarely is one placed near the elderly patient in surgery to provide additional heat. Certainly, it is essential that patients of all ages be viewed as important and given the appropriate specialized care.

If the operative procedure is estimated to be a lengthy one, then the ambient temperature of the operating room should be increased prior to the arrival of the patient in the room. Morris17 found that adult patients maintained a body temperature in the normal 360C to 37.50C (96.80F to 99.50F) range, regardless of the site of the surgical procedure, if the operating room temperature was above 21 .00C (69.80F). Once the elderly patient arrives in surgery, several warm bath blankets can be used to cover the patient. If the patient refuses a blanket, then another one can be offered soon afterwards, because it may take several minutes for the patient to feel the cool environment of surgery. When feasible, a warming mattress can be placed on the operating room table and activated before the patient is transferred over on to the table.

Keeping the patient well covered until the last possible minute before positioning is important. Likewise, as the patient is being positioned and the operative site is being cleansed (prepped) prior to the skin incision, as much of the patient's body as is possible needs to be kept covered. This will prevent unnecessary exposure of large body surface areas to the cool air of the surgical suite environment. Then, after the operative site is prepped, it is good to cover patients with several thicknesses of paper or cloth drapes to help keep them warm during the surgical procedure.

In the same way, it is best to warm the prep set by placing it in a warming cabinet before it is used to cleanse the operative site. In her study, Ozuna18 found that a large percentage of the recorded falls in body temperature occurred from the time of the patients' arrival in surgery to the time of the skin incision. Thus, it is imperative that the nurse be cognizant of the need to keep the unconscious or sedated elderly patient warm even before the surgical incision is made.

The inhalation of dry anesthetic gases is another cause of heal loss for the surgical patient.19 Therefore, by using a commercially available heated humidifier system, the anesthesia personnel can heat and humidify the inspired agents and this will help to prevent hypothermia.20 Blood and fluid warmers and warming mattresses are also employed by the anesthesia personnel to keep the patient warm during surgery. It was determined by ToIlofsrud, Gundersen, and Andersen20 that the use of a warming blanket, along with heating and humidifying anesthetic gases, was more effective in reducing intraoperative hypothermia than either of the methods used alone.

Keeping the patient's head covered as much as is possible during surgery is another way to conserve body heat.21 Irrigating the wound with only warmed solutions is preferable to solutions that have been cooled to room temperature. Last of all, reflective blankets can be placed over the elderly patient and radiant heating lamps can be used near the patient to provide additional warmth when it is needed.

Postoperative Care

Clear communication following surgery is necessary between the operating room personnel, the postanesthesia recovery room staff, and the floor nurses. Precise details regarding the surgical procedure and any complications experienced by the elderly patient facilitate care during this critical postoperative period. Important information such as the type of anesthetic used, the patient's response to the anesthesia, the intraoperative fluid loss, the record of blood, fluids, and drugs administered, and any drop in the patient's temperature needs to be accurately conveyed.

Nurses caring for the hypothermie elderly postoperative Iy will have to continue to implement measures that provide warmth for the patient. Again, warm or reflective blankets can be used to cover the patient. In the same way, a warming mattress or a radiant heating lamp can be placed over the patient. Underlying wet sheets need to be changed to assure warmth and comfort for the patient.

Administration of warmed infused fluids and warm, moist oxygen will help decrease heat loss. Finally, placing warm containers of saline near the groin or axilla can provide additional heat for the elderly patient. However, caution is advised to assure that these containers do not burn the thin, fragile skin of the aged.

Assessment of pain, observation of the wound drainage, measurement of fluid intake, and monitoring urine output are other fundamental nursing measures that are necessary. Certainly, temperature monitoring is a high priority. Moreover, it is important to keep in mind that complications in geriatric patients occur quickly and can rapidly advance to life-threatening situations. It is the conscientious nurse who is aware of the special care and considerations the geriatric patient needs during this crucial postoperative period.

Conclusion

A real problem health-care professionals face when caring for the elderly during the perioperative period is that of helping them to maintain adequate body temperature. Inadvertent hypothermia can be a common, yet underestimated, hazard of the elderly surgical patient. The aged, unlike younger persons, do not have as wide a margin of physiological reserve. Therefore, inadvertent hypothermia and its detrimental consequences need to be prevented during all surgical interventions.

References

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10.3928/0098-9134-19880601-09

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