Perioperative hypothermia in paediatric non cardiac surgery: incidence, risk factors, consequences, management and prevention

SPECIAL ARTICLE

Perioperative hypothermia in paediatric non cardiac surgery: incidence, risk factors, consequences, management and prevention

Natalia Belîi^1*

¹Chair of anaesthesiology and reanimatology no. 1 „Valeriu Ghereg”, Nicolae Testemițanu State University of Medicine and Pharmacy, Chisinau, Republic of Moldova.

Correspondent author:

Natalia Belîi, PhD, assistant professor

Chair of anaesthesiology and reanimatology no. 1 „Valeriu Ghereg”

Nicolae Testemițanu State University of Medicine and Pharmacy

165, Stefan cel Mare si Sfant bd., Chisinau, Republic of Moldova, MD-2004

e-mail: natalia.belii.med@gmail.com;

Short title: Paediatric patient thermoregulation: hypo- and hyperthermia

What it is not known yet, about the topic

Interestingly, but there exist no guides, practical recommendations or norms of perioperative thermic management of paediatric patient.

Research hypothesis

Literature reviews on perioperative thermic management of the paediatric patient, especially on preventing intraoperative unplanned hypothermia, could be sufficient to summarise tendencies and synthesize certain clinical recommendations.

Article’s added novelty on this scientific topic

The article summarizes certain recommendations synthetized from recent textbooks and study reports on perioperative thermic management in paediatric practice.

ABSTRACT

Introduction. Perioperative inadvertent hypothermia (PIH) (central temperature <36.0°C) is a risk associated with surgery with an incidence between 4.2% and 60%. Prevention of this complication is the responsibility of the entire team that takes care of the patient during the perioperative period. Due to less efficient thermoregulation capacity, surgical patients with extreme ages (child and elderly patients) are especially vulnerable of this risk. PIH has multiple physio-pathological effects: induce coagulopathies and, by this, rises transfusion requirements, prolongs duration of drug’s metabolisation, multiplies the incidence of postsurgical infection, prolongs duration of spitasation etc. For now, it does not exist a guide or practical recommendation that could assist the specialist in practical approach of PIH prevention in paediatric patient.

Material and methods. It was performed a search in PubMed, including a search by hand, inclusive in references of the found articles. In the same time, it was performed a search on electronic pages of French, Canadian, American and Australian Societies of Anaesthesiology for perioperative hypothermia prevention in children guidelines and protocols. There were used the following key words: „perioperative hypothermia in children”, „preventing perioperative hypothermia in children guidelines”, „unplanned hypothermia in children”.

Results. It was detected 90 citations: 5 clinical trials, 16 literature reviews and 2 hypothermia prevention in adult patient guidelines. Regarding paediatric patient, there were not found clinical practice guidelines for perioperative hypothermia prevention, but searching browsers offered results of episodic studies reporting PIH in children incidence, some risk factors that make paediatric patients especially susceptible, methods of temperature monitoring, the importance of pre-warming, hypothermia consequences in children. All the results were analysed and synthetized in the present literature review.

Conclusions. At the moment there exists a stringent necessity to elaborate a guideline or practical recommendations regarding PIH, with clear consensual statements, evidence based.  Also, further evidence is needed to determine the impact of hypothermia prevention on early and tardive perioperative morbidity in pediatric non-cardiac surgery.

Key words: inadvertent intraanesthetic hypothermia, pre-warming, thermoregulation, paediatric surgical population.

INTRODUCTION

Usually, the operating room is not considered an extremal environment. Anyway, in some circumstances, it can gain such a characteristic. Surgical patients frequently complain of cold temperature in the operating room. Ambient temperature is the critical factor that influences heat loos and the temperature difference determines the magnitude of phenomena. Most operating room staff find the ambient temperatures required for maintaining normothermia as ”uncomfortably” warm. The most vulnerable are surgeons and surgical nurse because they must wear special equipment – sterile gloves and gowns – which are waterproof, exchanging air poorly and, in consequence, prevents dissipation of body heat [1, 2].

Every patient beneficiating from surgical treatment is exposed to risk of hypothermia [3]. Paediatric surgical population, especially neonates and infants under 1-year-old are in the group of special risk of intraanesthetic hypothermia [4]. Accidental intraanesthetic hypothermia rates are variable: in adults – from 20% [5, 7] to 52% [6], in children – from 4.2 to 60% [8].

Hypothermia (<36.0°C) can threefold increase in the frequency of surgical site infections and alter coagulation cascade, reduce tissue perfusion, inhibits thrombocyte’s function and causes immunosuppression (via Natural Killer cells reduced activity). Also, hypothermia reduces twice metabolism of drugs for every 10°C reduced body temperature [2, 9]. In spite of all known consequences of perioperative incidental hypothermia (PIH), for the moment, there exist no guides or practical recommendations on thermic management or PIH prevention in paediatric patient. Respectively, the goal of the present article was to search and systematize the information regarding PIH prevention in paediatric patient.

MATERIAL AND METHODS

It was performed a search in PubMed and on electronic pages of French, Canadian, American and Australian Societies of Anaesthesiology for PIH prevention in children guidelines and protocols. There were selected scientific publications in English over the last 10 years. There were used the following keywords: „perioperative hypothermia in children”, „preventing perioperative hypothermia in children guidelines”, „unplanned hypothermia in children”. Also, it was studied, including a search by hand, the list of references of the selected articles, in an effort to extend the search area of the needed information.

From the literature identified by searching browsers, it was made a further selection, based on title and abstract correspondence to the searched items, full-text availability and clear statement, in the content, of clinical recommendations regarding PIH prevention in paediatric patient. The searched parameters were: risk factors for the occurrence of PIH, clinical judgment in choosing monitoring and patient normothermia maintenance methods, according to clinical situation, the values range in maintaining temperature, special concerns, and recommendations.

RESULTS

It was detected 90 citations, of which: 5 clinical trials, 16 literature reviews and 2 PIH prevention in adult patient guidelines [10, 11]. Unfortunately, regarding paediatric patient, there were not found clinical practice guidelines for PIH prevention. Searching browsers offered results of episodic studies reporting PIH incidence in children, some risk factors that make paediatric patients especially susceptible, methods of temperature monitoring, the importance of pre-warming, hypothermia consequences in children, reduced PIH incidence after implementation of local institutional protocols for hypothermia prevention. Also, there were found separated protocols for malignant hyperthermia. All the results were analyzed and synthesized. The final bibliography is based on 40 citations.

Biophysical milestones

The heat transfers from the patient to the ambiance occur through 4 basic mechanisms [2, 3, 9]:

• conduction (3%) – heat loss between objects that are in direct contact. The amount of heat loss depends on temperature gradient and surface of contact areas.
• evaporation (24%) – heat loss by slow evaporation of water or some any other liquid evaporating on the body surface – sweating on the skin, evaporation on the surgical wound, from mucosal surfaces. Regarding mucosal surfaces, heat loss can reach more than 30% in a child ventilated with dry air. Evaporation becomes the main mechanism when the ambient temperature exceeds 37o C. From this point, the radiation mechanism becomes insufficient.
• convection (34%) – heat loss from a body to moving molecules (air, liquid), via air currents, the extent of heat loss is proportional to the air temperature and speed of movement.
• radiation (39%) – heat loss between the objects that are not in direct contact, e.g., between the child and cool wall (or any other object from operating room), opened window, colder wall of incubator.

Physiology of paediatric patient’s thermoregulation

Thermoregulation is a real challenge for human beings, especially for paediatric patient. There exist differences between thermoregulation of a child under 1-year-old, toddler and teenager – all of them being potential patients of paediatric anaesthesia or intensive care unit.

Thermic vulnerability of neonates lies in anatomical and physiological differences with the adult [2]: (1) a proportional bigger head, frequently with a circumference exceeding that of chest; (2) a high skin surface area to body mass rate: ≈1 in neonate, in comparison with 0,4 in adult, and, with this, the most part of heat loss by radiation; (3) reduced heat loss by evaporation in comparison with adults, due to reduced keratin layer in derma; (4) more heat loss via conduction due to thinner layer of subcutaneous insulating tissue [2].

Non-shivering thermogenesis is a metabolic process that occurs in brown fat which constitutes 2-6% of term neonate body mass, maintaining up to about 5 months [2], according to other sources – up to 2 years old [9]. The fat tissue is called ”brown” due to chromatic characteristic gained after coloring of numerous mitochondria in the cell’s cytoplasma. They have propriety to uncouple oxidative phosphorylation and generate heat over ATP production. Moreover, they recruit additional local blood flow (up to 25% of cardiac output), being preferentially vascularized – every single adipocyte receives a capillary – thus directly transferring heat to the circulation. Anatomically, the so-called ”brown” fat tissue is concentrated in the area between the scapulae, the axillae, the mediastinum, and the perinephric retroperitoneum. So, in usual conditions, children under 1 year old can double their basal metabolic rate, capacity that is significantly reduced under anaesthesia [2], with no difference either inhalational or intravenous anaesthesia is practiced [9].

Because of the musculoskeletal system immaturity and its relatively small mass, shivering thermogenesis does not contribute significantly to preservation of body heat in the neonate [2] or child under 1 year old [9]. Toddlers are shivering between 35.0oC and 35.3oC; but the effect is neglectable for central temperature maintenance [9]. Anyway, shivering thermogenesis is shut down under anaesthesia.

Effects of anaesthesia on the thermoregulation

In comparison with adults, in children heat loss takes place, preponderantly through conduction and radiation mechanisms, due to reduced isolating subcutaneous fat tissue and a high skin surface to body mass rate. Heat production due to basal metabolic rate is reduced 20-30% under anaesthesia, for all patient’s ages. The intubated neonates lose their capacity to generate heat via respiratory effort. Also, central thermoregulation is inhibited, with a delayed vasoconstriction response to central temperature lowering, with significantly depressed mechanisms of thermogenesis: with and without shivering.

For a neonate, hypothermia represents a major stress with noradrenaline release, raised oxygen and nutritive substrate consumption. Activated by this pathway sympathetic nervous system leads to increase of pulmonary vascular resistance, increasing right to left shunts, reduced peripheral perfusion and oxygen delivery, acidosis. Pharmacokinetics and pharmacodynamics of the administered drugs are affected, especially neuromuscular blocking agents and inhalational volatile anaesthetics. The final common pathway of hypothermia and increased oxygen consumption is metabolic acidosis and organ dysfunction.

General anaesthesia affects thermogenesis due to redistribution to the periphery of the ”central heat” via vasodilatation [2, 9], reducing with 30% heat production due to basal metabolic rate, central thermoregulation inhibition. Long surgical interventions imply prolonged exposing of the body to colder ambient temperatures. Also, intravenous infusion solutions, fresh gas flow used for intraanesthetic ventilation and surgical instruments used by surgeons are much colder than the child’s body temperature [2]. The only thermoregulatory responses that are functional under anaesthesia are vasoconstriction and non-shivering thermogenesis. Vasoconstriction capacity is similar in the awake and anaesthetised patient, but the threshold for vasoconstriction is reduced [9].

Although under loco-regional anaesthesia central thermoregulation is preserved, areas that are anaesthetised cannot sense temperature (cold, warm) and that’s why have an inappropriate redistribution of blood flow via vasodilatation [9].

Consequences of hypothermia

Central temperature between 36-38°C is considered, by convention, as normothermia. In condition of ambient normality, adult’s core temperature variates between 36.5-37.5°C, neonate’s – between 36.5-37.7°C. Hypothermia is defined as core temperature below 36.0°C and can be mild (33.9-36.0°C), moderate (33.8-32.2°C) or severe (32.2°C). Such signs and symptoms like shivering, piloerection, and peripheral vasoconstriction can be found in the presence of a normal body temperature.

Normothermia maintenance in paediatric patients for non-cardiac surgery is a real challenge. Study in adult patients reports that even moderate intraanesthetic hypothermia associates with postoperative adverse outcomes. Many landmark studies [12, 13, 14] have demonstrated an association between hypothermia in patients undergoing both – clean, ”uncontaminated” surgery (hernia repair) [12] and contaminated surgery (colorectal surgery) [13] an increased incidence of surgical site infection. Other consequences: prolonged drug metabolising periods [3], postoperative adverse cardiac events [7, 15], thermic discomfort [3], hypoglycaemia [7], acidosis [7], coagulopathies and increased transfusion requirements [7, 16-18], increased length of hospital stay in general [13, 15, 19] and in intensive care unit in particular [19]. By this, we conclude that PIH is a multidisciplinary problem.

Regarding pediatric patient, studies are episodic, inclusively due to bioethical implications of creating trials ”with hypothermia” and ”warmed”. In their observational study, Pearce B. et al. (2010) followed outcome in children whose intra operative temperature stayed more than 36°C, and in those with hypothermia [6]. They reported an incidence of PIH of 52%, with increased blood loss and blood product requirement in this group.

In children under 1-year-old moderate hypothermia can cause apnea [2], slower metabolism of the administered drugs [20], induce coagulopathies [21]. Also, we are expecting results of o prospective observational cohort study ”Perioperative hypothermia in children”, coordinated by Shu Ying Lee (KK Women's and Children's Hospital, Singapore), which will finish in 2020, with 4400 patients enrolled. Expected outcomes: PIH incidence and duration, adverse events linked with active heating methods (eventually, hyperpyrexia, burns), immediate (e.g., blood loss, arrhythmia, post-anesthesia shivering, discomfort from cold, prolonged intensive care unit stay) and tardive (e.g., surgical site infection and hospitalization stay) complications [22].

In some clinical situations hypothermia is induced deliberately [2]. So, hypothermia is a necessity for cardiopulmonary by-pass [23, 24]. There continue to be studied the potential benefits of moderate hypothermia in an effort to minimise neurological consequences in neonates with asphyxia [25, 26]. However, the protective effects of hypothermia have not been confirmed in the case of brain trauma and cardiac arrest in children [27, 28].

Continuous temperature monitoring in paediatric patient

There are many methods of estimating both core and peripheral temperature in paediatric patients. (Table 1).

Core temperature can be monitored in several modalities: nasopharynx, oesophagus, rectum, temporal artery, bladder, tympanic membrane and blood measurement [29].

Peripheral (non-core) temperature measurement can be realised using axillary thermometry, with condition that the accuracy depends on the device being in continuous close proximity to the axillary artery [29]. A study reported that temperature monitoring with the probe placed over de carotid artery skin equates to the nasopharynx in paediatric population [30].

However, the core temperature is the decisive control element of human thermoregulation, being the trigger of the hypothalamic central response. Therefore, under anaesthesia, the core temperature is much more relevant than the peripheral.

The type of monitoring decision will depend on patient and surgical factors. Unfortunately, does not exist an ideal and universal method of temperature monitoring [29].

Usually, in adults, monitored skin temperature is lower with 2 degrees in comparison with core temperature [34]. Given this fact, may be hypothermia values should be specified depending on the monitoring methodology. Many studies have reported difficulties in finding clinical hypothermia due to the variability of monitoring methods [34-36]. Drake-Brockman T. et al. (2014) compared different temperature methods in paediatric patient. Thus, temperatures varied depending on the location of the monitoring [36]. The average difference between nasopharyngeal and tympanic temperatures, measured at the temporal, axillary and cutaneous (thoracic) artery was +0.24; 0.35; -0.38 and -1.7°C, respectively. Also, tympanic and temporal temperatures showed net superior efficiency in detecting moderate hypothermia compared to axillary monitoring. Understanding these variations is important for interpreting the monitored temperatures.

Thermoneutrality

Thermoneutrality is defined as the ambient temperature at which oxygen demand and metabolic heat production are minimal. At the same time, the cutaneous arteriovenous shunts are open and skin blood flow is maximum. The approximately temperature’s values are: 28°C for an unclothed adult, 32°C – for neonate, and 34°C – for the preterm infant, with the remark that there is no defined room temperature that assures thermoneutrality in all clinical scenarios that one can imagine. The most clinically relevant is the temperature gradient from skin to environment, rather than that from core to environment. It was experimentally established that a skin-to-environment gradient of 2-4°C minimize oxygen consumption. Healthy infants respond to cold stress by increasing both cardiac output and brown fat metabolism (non-shivering thermogenesis). In some comorbidities, the rising reserve of cardiac output can be restricted and non-shivering thermogenesis is severely attenuated by volatile anaesthetics [2].

Risk factors for intraanaesthetic hypothermia in children

The most important risk factors that can contribute to perioperative hypothermia in paediatric patient are: small age (neonate, child under 1 year old), major surgery (invasive > non-invasive), duration of surgery [6, 4, 11], malnutrition [11], operating/recovery room temperature, special pre-existent conditions (open wounds, burns, endocrine pathologies, peripheral vascular pathology) [11, 16], emergent cases (by-pass the pre-warming step) [10], high ASA risk [10], intravenous infusion more than 30ml/kg or transfusion necessity [29].

Prevention of perioperative hypothermia in paediatric patient

Prevention of heat loss via conduction mechanism is realized by covering the head (which for a child under 1 year old equates with 20% of total body surface area) with a hat, warming the infused solutions, warming blankets (more efficient for neonates), drapes or blankets.

Prevention of heat loss through evaporation mechanism can be ensured by heating and humidifying the inspired gases. Also, for premature child (<28-30 weeks) exist plastic bags for wrapping the preterm.

Prevention of heat loss via radiation mechanism can be realized by using a radiant warmer, forced air warmers, pre-warming of the operating room or the incubator at the transport between operating room and neonatal intensive care unit.

Prevention of heat loss via convection is possible by continuous maintaining of the thermoneutral environment (operating room, incubator), warming blankets [9].

In addition to active patient’s warming methods, there are simple measures which can be taken to reduce heat – in cases when they are transferred long distances through the hospital to theatre – efforts should be made to keep children warm, for example using hats, sheets, blankets and socks. When situation allows, older children should be encouraged to walk to operating theatre [29]. Patient’s temperature should be monitored in the morning of the surgery, 30 minutes before surgery and immediate before induction in anesthesia [11]. Engorn B. et al. (2017) reported reduced hypothermia prevalence (from 23% to 6%) in neonates on neonatal intensive care admission from the operating room after implementation of the heating measures during intrahospital transportation [37]. It is mandatory to maintain operating room temperature between 20-23°C [29]. Higher temperature values are favourable for hypothermia prevention (>25°C), especially in neonates (optimal operating temperature 26.6°C), but it can cause discomfort for the surgical team [2]. The study of Duryea E. et al. (2016) on maternal and neonatal hypothermia reports reducing of neonate’s hypothermia incidence in case of pre-warming the delivery room up to 23°C (5%), in comparison with other group of patients where environment temperature was 20°C (19%) [38].

Guidelines for adult patients recommend maintenance of the ambient temperature at 21°C while exposing patient and after initiating of active warming measures, the temperature can be reduced up to the thermic comfort of the surgeons [10, 11]. It will be avoided exposing of big and wet skin surface areas expecting the moment when surgical intervention will finally start. Fresh flow gases used for patient’s ventilation should be warm and humidified by using heat and moisture exchange filters (HME filters) [29]. In correct circumstances, when interposed between endotracheal tube and ventilator circuit, HME filter maintain the temperature and humidity of inspired anaesthetic gases, but cannot contribute directly to rise the patient’s temperature. We should note that that even the smallest HME filter expand the death space and resistance in the respiratory circuit, blunting the capnogram until it is almost uninterpretable [2]. In spite of this, HME filters are efficient for preventing the contamination of devices attached to the airway. Heated humidifiers or heated breathing circuits are placed within one limb of the breathing circuit are more efficient in normothermia maintenance in comparison with HME filters, but are prone overheating, condensation, changes in the volume of the circuit, leaks in the tubing, in case if are not connected correctly [2].

National Institute of Clinical Excellence (NICE) of the United Kingdom and Northern Ireland guideline for adult patient, suggests that for preventing inadvertent intraanesthetic hypothermia, adults undergoing surgery with anaesthesia lasting more than 30 minutes should be warmed from the very beginning, from induction, using a forced air warming device. For patients who are at higher risk of hypothermia (for example: combined regional and general anaesthesia) or those at risk of cardiovascular complications, forced air warmers are indicated for even shorter procedures less than 30 minute. Also, is contraindicated to start induction of elective anaesthesia in case if hypothermia is installed. It will be maintained a central temperature of at least 36.5°C [10].

Regarding paediatric patient, at the moment, does not exist yet an official guideline which stipulates risk factors for intra-operative hypothermia, or what kind of warming devices should be used to avoid this risk. It is suggested that starting ”warming” of the paediatric patient in the pre-anaesthesia unit or operating room is beneficial, especially for long duration surgery or when type of surgery necessitates big surface areas of skin exposure. Study of Gorges M. and colleagues (2013) find a high correlation between forced air warmers and reduced rates of intra-operative hypothermia in spinal paediatric surgery [39]. Beedle S. and colleagues (2019) report reduction of intra-anaesthetic paediatric hypothermia rate to 1.84%, comparative with 16.3%; after implementation of patient’s worming methods and temperature monitoring on skin over temporal artery, according to the guideline elaborated by a group of nurses from Midwestern Children’s Hospital [8].

Forced air warmers reduce radiant heat loss by providing a barrier between skin and ambient air [40]. By placing them underneath the child, we allow warm air to circulate around the child and reduce both, radiation and conductive heat loss. Regarding under body blankets a high level vigilance should be taken that the whole child is on the blanket, as limbs extending beyond the edge may obstruct uniform air flow, and, by this, become exposed to the risk of burns. Also, medical staff must pay attention at the cleaning fluids and ensure that this does not pool around patient, because this will then evaporate, causing cooling effect [29].

Also, in an effort to prevent PIH in adults, NICE guideline indicates to use a fluid warmer in patients receiving ≥500 ml of intravenous fluids (up to 37°C), or any blood products should have used. Also, it is recommended to pre-warm intraoperative irrigation solutions up to 38-40°C [10].

There is no such guidance to date for paediatric practice. In the tutorial article from 2014, Haberman E. suggests that for infusion volumes greater than 30 ml/kg fluid, a fluid warmer should be considered [29]. Extrapolating clinical experience from adult patient anaesthetic practice, in case of children, solutions should be warmed when there are planned big volume infusions (e.g., open abdominal surgery) and when blood products are likely to be required. According to the same NICE guideline [10], in immediate postoperative period, it is suggested to evaluate and document the temperature at least once in 15 minutes, one of the criteria of discharge from recovery room being normothermia. Further, in surgical ward, temperature will be routinely monitored once in 4 hours. In case of hypothermia, there will be initiated warming measures and body temperature will be monitored once in 30 minutes [10].

On the other side, paediatric patient beneficiating of active warming procedures for normothermia maintenance is susceptible to risk of over-heating and hyperthermia. Therefore, in case when we use medical warming devices continuous temperature monitoring is mandatory. Medical devices with non-uniform warming of patient can cause induced hyperthermia and burns. The effects of hyperthermia are increased localised blood flow (skin and muscles), increased vascular permeability, with oedema, cell death, and organ dysfunction. The intraanaesthetic installed hypothermia necessitates close monitoring and differential diagnostic with the following states: iatrogenic hyperpyrexia, malignant hyperthermia, viral or bacterial infection, arthrogryposis, osteogenesis imperfecta, immune dysfunction Riley-Day, thyrotoxic crisis, pheochromocytoma, neuroleptic malign syndrome, administration of meperidine with monoamine oxidase inhibitors [2].

CONCLUSION

Paediatric patient is more susceptible for risk of perioperative hypothermia. Long lasting surgery, major surgery, neonate and child under 1-year-old, malnutrition, emergent cases, ASA III-V risk and total intravenous infusion of more than 30 ml/kg are factors that can significantly contribute to PIH installation.

At the moment there exists a stringent necessity to elaborate a guideline that explores physiologic particularities of PIH in paediatric patients, with very clear recommendations, evidence-based, but, at the same time, a practical approach, at „the patient’s bed”. Also, further evidence is needed to determine the impact of PIH prevention on perioperative outcomes in paediatric surgery. Until then, the type of temperature monitoring and normothermia maintenance chosen are, for now, up to the anaesthesiologist.

Declaration of conflicting interests

The author has no financial or nonfinancial disclosures to declare.

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