OPENING LEARNING ZONE KEYWORDS Hypothermia / Inadvertent hypothermia / Normothermia / Patient warming Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication June 2013.
Strategies for the management and avoidance of hypothermia in the perioperative environment by A Singh Correspondence address: c/o AfPP, Daisy Ayris House, Harrogate, HG3 1DH. Email: [email protected]
This Open Learning Zone article outlines the necessity of monitoring temperature for patients undergoing surgical procedures with either general or local anaesthesia. An overview of the physiology of heat production and loss in the human body, and temperature as thermal measurement is given. Introduction Normothermia refers to the normal human body temperature and depends where on the body it is measured. The core body temperature is the measurement made deep inside body tissues or cavities. Body activity and external factors such as the time of day and climatic conditions all affect body temperature. The body temperature largely depends on metabolic activity of the tissues and organs as these activities generate heat. Heat is a form of energy that can create a thermal state in a substance which it occupies; this state is temperature. The digestion of organic food ingredients and the metabolism of glucose, protein and fat produce energy inside the body. The end products of metabolism are carbon dioxide and water. The produced energy is stored intracellularly in a molecule called adenosine triphosphate (ATP) and the process is accompanied by heat. The energy lost during electron transport and oxidative phosphorylation is, to a great extent, converted into heat and this helps in maintaining the body temperature at 37°C. The combustion of glucose and protein produces 4.1kcal/kg, while fat combustion yields 9.3kcal/kg (Mrozek et al 2012 p1). Therefore, energy metabolism leads to production of heat (Alberts et al 2002 p112).
homogeneous. The peripheral component includes tissues in which temperature is variable and inhomogeneous (lower limbs, hands, and skin). The temperature in the peripheral component is generally 2-4°C lower than in the central component and is highly dependent on vascular tonus. Located in the hypothalamus, an integrative centre is responsible for core temperature regulation (Saper et al 2005). The response mechanisms of this centre are still not completely known, however, they are likely to involve neurotransmitters such as norepinephrine, dopamine, acetylcholine, neuropeptides, and prostaglandins such as dinoprostone (PGE2). Core temperature undergoes circadian variation that is controlled by the release of melatonin from the suprachiasmatic nucleus. The temperature of the central component is regulated by the hypothalamus in response to information
In humans, two thermal components have been described: a central and a peripheral one (Sessler 2000). The central component consists of the trunk, head and brain and these tissues are highly perfused. Heat exchanges are rapid in this part, and temperature is relatively
April 2014 / Volume 24 / Issue 4 / ISSN 1750-4589
Discussion
‘Energy is produced and lost inside the body.’ Consider this statement and discuss ways of heat production and expenditure.
Notional Learning Hours 1 hour Knowledge and skills dimension ✔ Communication ✔ Personal and people development
from thermoreceptors and this is described as the monosynaptic pathway; feeding, locomotor activity or secretion of corticosteroids regulate temperature by a plurisynaptic pathway (Mrozek et al 2012 p3). Heat generation within the body in the form of biochemical reactions may take place as a response to cellular respiration, muscular activity and the ingestion of food. Heat loss from the body is by radiation from the skin, cutaneous vasodilatation, sweat evaporation from the skin and breathing. Homeostasis is defined as the mechanism that keeps the body at optimum temperature. Thermoregulation is a set of physiologic reactions that work to maintain the human body temperature within normal range without harmful fluctuations.
Techniques for temperature measurement Temperature can be measured by electrical and non-electrical techniques. Electrical techniques include the resistance thermometer, thermistor and thermocouple. Non-electrical techniques are based on liquid expansion, as in mercury and alcohol thermometers or dial thermometers such as the bimetallic strip and Bourdon gauge thermometers. All techniques have a wide application in clinical settings, with preference depending on the advantages and disadvantages of each type. In patients undergoing surgical operations under general or local anaesthesia, there is a great risk of hypothermia. Hence, it is of vital importance to monitor temperature at regular intervals during anaesthesia. A core body temperature less than 36°C is 75
OPENING LEARNING ZONE
Strategies for the management and avoidance of hypothermia in the perioperative environment Continued
defined as hypothermia (NICE 2008, Hart et al 2011). The Association of Anaesthetists of Great Britain and Ireland (AAGBI) states that, during induction and maintenance of anaesthesia a means of measuring the patient’s temperature must be available. Whereas in recovery from anaesthesia a means of measuring temperature must be immediately available (AAGBI 2007). Some patients, especially the elderly, maybe unable to increase their metabolic rate to offset heat loss and so an imbalance of oxygen demand over respiratory capacity may lead to shivering. Measuring and maintaining the patient’s body temperature will aid their recovery (AAGBI 2001).
Effect of anaesthesia on core body temperature After induction of anaesthesia, hypothermia takes place in three stages:
evaporation, respiration, cold cleaning and intravenous fluids.
Plateau stage A plateau in core temperature occurs when heat production equals heat loss. This is brought about by an increase of vasoconstriction which limits heat loss from the core temperature.
National guidelines have been published by the National Institute for Health and Care Excellence regarding management of inadvertent hypothermia (NICE 2008). The guidance is subdivided into care during perioperative, preoperative and postoperative phases:
Importance of temperature measurement
n Advice should be given to patients about staying warm before surgery.
Linear stage
Preoperative phase
The linear stage begins at the start of a surgical procedure as the patient is exposed to factors which cause heat loss to exceed heat production. These factors include: convection, radiation, conduction,
n The risk of inadvertent perioperative hypothermia should be assessed preoperatively.
Study
Notional Learning Hours 1 hour Knowledge and skills dimension ✔ Communication ✔ Personal and people development
76
n The patient’s temperature should be measured and documented before induction of anaesthesia.
n Anaesthesia should not be induced unless the patient’s temperature is 36.0°C or higher.
Heat redistribution is responsible for the large drop of core temperature which occurs as vasodilatation causes transfer of heat from the core to periphery. A patient’s initial heat content affects redistribution and patients with a cooler periphery will experience a greater degree of hypothermia. Obese patients have a warmer periphery.
Select a non-electrical technique for temperature measurement which you are familiar with. Apply it to measure the temperature of your colleagues. Outline its advantages and disadvantages.
Intraoperative phase
n The patient’s temperature should be monitored every 30 minutes until the end of surgery.
Maintenance of body temperature during the surgical process
Perioperative phase
Redistribution
on the ward or in the emergency department and should be continued throughout the intraoperative stage.
n Patients should bring extra warm clothes such as slippers, vest and dressing gown. n Patients should inform a healthcare professional if they become cold.
Hypothermia affects the perianaesthesia and perioperative patient by exposing them to postoperative infections, blood coagulation and cardiac problems. Therefore, temperature measurement during anaesthesia is of vital importance for such patients (Mahoney & Odom 1999). The human body tends to adapt to environmental temperature, therefore artificial cooling devices in surgical theatres are likely to induce hypothermia in patients. Surgical exposure, infusion of intravenous fluids at room temperature, certain drugs, and low ambient temperature also contribute to the risk of hypothermia. In addition, general anaesthesia hinders
• There is a higher risk of perioperative hypothermia if two or more of the following apply: • The patient’s physical state prior to anaesthesia or surgery is of a higher grade, as assessed by the American Society of Anesthesiologists (ASA) grading system (II to V).
Discussion
Access a copy of the national guidelines (NICE 2008) on keeping patients warm before, during and after an operation and discuss how these guidelines can be identified in your daily practice. Notional Learning Hours
• The patient has a preoperative temperature below 36.0°C. • The surgery will be carried out with a combination of general and regional anaesthesia. • The patient is undergoing intermediate or major surgery. • The patient is at risk of cardiovascular complications. n If the patient is hypothermic (temperature is
Strategies for the management and avoidance of hypothermia in the perioperative environment by A Singh Correspondence address: c/o AfPP, Daisy Ayris House, Harrogate, HG3 1DH. Email: [email protected]
This Open Learning Zone article outlines the necessity of monitoring temperature for patients undergoing surgical procedures with either general or local anaesthesia. An overview of the physiology of heat production and loss in the human body, and temperature as thermal measurement is given. Introduction Normothermia refers to the normal human body temperature and depends where on the body it is measured. The core body temperature is the measurement made deep inside body tissues or cavities. Body activity and external factors such as the time of day and climatic conditions all affect body temperature. The body temperature largely depends on metabolic activity of the tissues and organs as these activities generate heat. Heat is a form of energy that can create a thermal state in a substance which it occupies; this state is temperature. The digestion of organic food ingredients and the metabolism of glucose, protein and fat produce energy inside the body. The end products of metabolism are carbon dioxide and water. The produced energy is stored intracellularly in a molecule called adenosine triphosphate (ATP) and the process is accompanied by heat. The energy lost during electron transport and oxidative phosphorylation is, to a great extent, converted into heat and this helps in maintaining the body temperature at 37°C. The combustion of glucose and protein produces 4.1kcal/kg, while fat combustion yields 9.3kcal/kg (Mrozek et al 2012 p1). Therefore, energy metabolism leads to production of heat (Alberts et al 2002 p112).
homogeneous. The peripheral component includes tissues in which temperature is variable and inhomogeneous (lower limbs, hands, and skin). The temperature in the peripheral component is generally 2-4°C lower than in the central component and is highly dependent on vascular tonus. Located in the hypothalamus, an integrative centre is responsible for core temperature regulation (Saper et al 2005). The response mechanisms of this centre are still not completely known, however, they are likely to involve neurotransmitters such as norepinephrine, dopamine, acetylcholine, neuropeptides, and prostaglandins such as dinoprostone (PGE2). Core temperature undergoes circadian variation that is controlled by the release of melatonin from the suprachiasmatic nucleus. The temperature of the central component is regulated by the hypothalamus in response to information
In humans, two thermal components have been described: a central and a peripheral one (Sessler 2000). The central component consists of the trunk, head and brain and these tissues are highly perfused. Heat exchanges are rapid in this part, and temperature is relatively
April 2014 / Volume 24 / Issue 4 / ISSN 1750-4589
Discussion
‘Energy is produced and lost inside the body.’ Consider this statement and discuss ways of heat production and expenditure.
Notional Learning Hours 1 hour Knowledge and skills dimension ✔ Communication ✔ Personal and people development
from thermoreceptors and this is described as the monosynaptic pathway; feeding, locomotor activity or secretion of corticosteroids regulate temperature by a plurisynaptic pathway (Mrozek et al 2012 p3). Heat generation within the body in the form of biochemical reactions may take place as a response to cellular respiration, muscular activity and the ingestion of food. Heat loss from the body is by radiation from the skin, cutaneous vasodilatation, sweat evaporation from the skin and breathing. Homeostasis is defined as the mechanism that keeps the body at optimum temperature. Thermoregulation is a set of physiologic reactions that work to maintain the human body temperature within normal range without harmful fluctuations.
Techniques for temperature measurement Temperature can be measured by electrical and non-electrical techniques. Electrical techniques include the resistance thermometer, thermistor and thermocouple. Non-electrical techniques are based on liquid expansion, as in mercury and alcohol thermometers or dial thermometers such as the bimetallic strip and Bourdon gauge thermometers. All techniques have a wide application in clinical settings, with preference depending on the advantages and disadvantages of each type. In patients undergoing surgical operations under general or local anaesthesia, there is a great risk of hypothermia. Hence, it is of vital importance to monitor temperature at regular intervals during anaesthesia. A core body temperature less than 36°C is 75
OPENING LEARNING ZONE
Strategies for the management and avoidance of hypothermia in the perioperative environment Continued
defined as hypothermia (NICE 2008, Hart et al 2011). The Association of Anaesthetists of Great Britain and Ireland (AAGBI) states that, during induction and maintenance of anaesthesia a means of measuring the patient’s temperature must be available. Whereas in recovery from anaesthesia a means of measuring temperature must be immediately available (AAGBI 2007). Some patients, especially the elderly, maybe unable to increase their metabolic rate to offset heat loss and so an imbalance of oxygen demand over respiratory capacity may lead to shivering. Measuring and maintaining the patient’s body temperature will aid their recovery (AAGBI 2001).
Effect of anaesthesia on core body temperature After induction of anaesthesia, hypothermia takes place in three stages:
evaporation, respiration, cold cleaning and intravenous fluids.
Plateau stage A plateau in core temperature occurs when heat production equals heat loss. This is brought about by an increase of vasoconstriction which limits heat loss from the core temperature.
National guidelines have been published by the National Institute for Health and Care Excellence regarding management of inadvertent hypothermia (NICE 2008). The guidance is subdivided into care during perioperative, preoperative and postoperative phases:
Importance of temperature measurement
n Advice should be given to patients about staying warm before surgery.
Linear stage
Preoperative phase
The linear stage begins at the start of a surgical procedure as the patient is exposed to factors which cause heat loss to exceed heat production. These factors include: convection, radiation, conduction,
n The risk of inadvertent perioperative hypothermia should be assessed preoperatively.
Study
Notional Learning Hours 1 hour Knowledge and skills dimension ✔ Communication ✔ Personal and people development
76
n The patient’s temperature should be measured and documented before induction of anaesthesia.
n Anaesthesia should not be induced unless the patient’s temperature is 36.0°C or higher.
Heat redistribution is responsible for the large drop of core temperature which occurs as vasodilatation causes transfer of heat from the core to periphery. A patient’s initial heat content affects redistribution and patients with a cooler periphery will experience a greater degree of hypothermia. Obese patients have a warmer periphery.
Select a non-electrical technique for temperature measurement which you are familiar with. Apply it to measure the temperature of your colleagues. Outline its advantages and disadvantages.
Intraoperative phase
n The patient’s temperature should be monitored every 30 minutes until the end of surgery.
Maintenance of body temperature during the surgical process
Perioperative phase
Redistribution
on the ward or in the emergency department and should be continued throughout the intraoperative stage.
n Patients should bring extra warm clothes such as slippers, vest and dressing gown. n Patients should inform a healthcare professional if they become cold.
Hypothermia affects the perianaesthesia and perioperative patient by exposing them to postoperative infections, blood coagulation and cardiac problems. Therefore, temperature measurement during anaesthesia is of vital importance for such patients (Mahoney & Odom 1999). The human body tends to adapt to environmental temperature, therefore artificial cooling devices in surgical theatres are likely to induce hypothermia in patients. Surgical exposure, infusion of intravenous fluids at room temperature, certain drugs, and low ambient temperature also contribute to the risk of hypothermia. In addition, general anaesthesia hinders
• There is a higher risk of perioperative hypothermia if two or more of the following apply: • The patient’s physical state prior to anaesthesia or surgery is of a higher grade, as assessed by the American Society of Anesthesiologists (ASA) grading system (II to V).
Discussion
Access a copy of the national guidelines (NICE 2008) on keeping patients warm before, during and after an operation and discuss how these guidelines can be identified in your daily practice. Notional Learning Hours
• The patient has a preoperative temperature below 36.0°C. • The surgery will be carried out with a combination of general and regional anaesthesia. • The patient is undergoing intermediate or major surgery. • The patient is at risk of cardiovascular complications. n If the patient is hypothermic (temperature is
