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Why Warming Matters
Patient normothermia is a key concern for successful anesthesia outcomes.
Gary Lawson
Publish Date: June 18, 2014   |  Tags:   Anesthesia
cooling core temperature HEAD OF THE TABLE Anesthesia's gases, oxygen and IV fluids play significant roles in cooling a patient's core temperature.

Perioperative patient warming is typically viewed through the lens of surgical quality measures, infection prevention efforts or even patient satisfaction scores. Less frequently discussed is the role that patients' core temperatures play in anesthesia effects and PACU stays. Let's review the reasons why maintaining normothermia is critical to successful ambulatory anesthesia.

Where the risks lie
Hypothermia carries many risks through the potentially hazardous physiological changes it triggers, including the following conditions:

  • Increased oxygen demand. Shivering increases the body's demand for oxygen by 300%. A patient who is shivering after a case may experience blood oxygen desaturation that causes hypoxia, which may exacerbate coronary artery disease, leading to myocardial ischemia and arrhythmias.
  • Impaired consciousness, which can prolong a patient's awakening and discharge. After the use of paralytic agents during general surgery, anesthesia providers perform a test called the "Train of Four," an electrical stimulation of the peripheral nerves that measures the level of neuromuscular blockade remaining in the patient's system, to determine whether they're able to breathe on their own again. A hypothermic core temperature may trigger a false positive response and an overestimation of the patient's paralysis. If unneeded reversal agents are administered, there is a risk of post-op nausea and vomiting.
  • Vasoconstriction, which can hinder peripheral perfusion and deliver false desaturation readings on the pulse oximeter.
  • Decreased renal and liver blood flow, which slows the body's metabolism of anesthetics. A hypothermic body does not metabolize drugs as effectively as one in the normal core temperature range does. This results in a buildup of drugs, prolonged drug effects and, ultimately, a patient who is slower to wake and become oriented once the procedure has concluded.
  • Breathing complexities. An increase in pulmonary "dead space" — the inhaled air that isn't part of the oxygen-for-carbon-dioxide exchange — plus increased anesthetic gas solubility equals a longer recovery time from general anesthetic agents.
  • Decreased platelet function. Hypothermia raises the risk of surgical site bleeding.
  • Weakened endocrine system. An impaired metabolism of medications can decrease the amount of insulin and increase the amount of glucose in the blood, which can put diabetic or borderline patients at risk. Since glucose is also food for bacteria, the risk of surgical site infections is higher. Also, metabolic acidosis can result in an increase in the blood's potassium levels, which can be harmful to the heart.

Are Warming Efforts Effective?

maintenance of patient normothermia GET CONNECTED Effective anesthesia and efficient recovery can be complicated by hypothermia.

There may be a gap between compliance with quality performance measures that demand warming and competent maintenance of patient normothermia, according to Victoria M. Steelman, PhD, RN, CNOR, FAAN, an assistant professor of nursing at the University of Iowa in Iowa City.

For a study published online in the Journal for Healthcare Quality in January, Dr. Steelman and her colleagues reviewed the cases of patients undergoing surgery at a community hospital, with general and regional anesthesia, over the course of 48 months. They found that 5.8% of the patients for whom the Joint Commission and CMS quality performance measure for active warming was met were actually hypothermic when admitted to PACU. Broken down by specialty, urology (8.5% of patients) and orthopedics (7.7%) had the highest percentage of warmed patients who were hypothermic in PACU.

"Patients who receive care compliant with the quality performance measure by receiving active warming are still at risk for hypothermia," writes Dr. Steelman. This highlights the need for routine monitoring of patients' core temperatures in recovery, regardless of how diligently you work to maintain normothermia throughout their care.

— David Bernard

Warming solutions
A core temperature that is below the normal range — 36.7 to 37 degrees Celsius — can adversely affect how anesthesia works on a patient and how he recovers from it. It's important to note, though, that the process of administering anesthesia itself involves physiological effects that inevitably cool the patient. But hypothermia is not unavoidable. Anesthesia providers can minimize the risks they create.

  • Limit inhalational agents. From an inhalation standpoint, anything you give patients to breathe will affect their core temperature, because anesthetic gases and oxygen are inherently cold. Heat is lost from the airway by way of evaporation. What's more, a neuromuscular blockade has been administered, which disables the body's ability to warm itself through shivering.

In the past, heating devices have been employed between the anesthesia machine and the patient for lengthy procedures such as organ surgeries, but there's a simpler, more cost-effective solution for outpatient cases. Many anesthesia machines are now equipped with low-flow gas delivery settings. Decreasing the amount of gas administered to less than 2 liters per minute can minimize the shivers patients will suffer after emergence.

  • Heat fluids. Intravenously administered fluids — not to mention arthroscopy irrigation and skin prepping solutions — can also bring on a chill. They may not be any colder than room temperature, but keep in mind that surgical rooms tend to be on the cool side.

For cases that will require a large volume of fluid, fluid warming is an effective way to help maintain normothermia from the inside out. There are no rules prohibiting the warming of IV fluids in a cabinet until they are needed, as long as it's done safely: The fluid's temperature should be no greater than 100 degrees Fahrenheit. Warming cabinets specifically designed for fluids will likely include safeguards, but those built for warming cloth blankets have higher temperature settings and should be used and monitored with caution.

Pay attention to the fluid product's directions as well. The manufacturers of packaged fluid provide details on how many days a bag can be warmed and to what temperature. The limiting factor here is the packaging: After a certain point, the bag's material may leach into the solution it contains, so be sure to label each cabinet-warmed bag with the date it was put in the warmer and the highest temperature allowed. Specialized in-line fluid warming systems that attach to the IV tubing and warm the fluid on the spot are also available.

maintaining perioperative normothermia OUNCE OF PREVENTION Maintaining perioperative normothermia can prevent the need for post-op interventions
  • Employ active warming. Lastly, don't neglect the potential effects of the surgical environment on a patient's core temperature. Body heat is lost through the skin's contact with a cold OR table and cold drapes, and through wind chill to the air in the room.

The OR should be set at 26 degrees Celsius (28 to 30 degrees Celsius for pediatric patients), and active perioperative patient warming is a must, whether through cabinet-warmed cotton blankets, convective forced-air warming garments or a radiant warming device.

Rewarding results
Patients who arrive normothermic in PACU rewarm effectively from the cooling effects of surgery and anesthesia. If they're not shivering, which increases their oxygen needs, you won't see desaturation during their recoveries and can avoid intervening. In outpatient surgery, where time- and cost-efficiencies are in demand, the value of faster awakenings and faster discharges is clear.