Hipotermia perioperatoria / Perioperative hypothermia

Perioperative hypothermia is a common complication of general anesthesia, but it can also occur in patients undergoing regional anesthesia. It signifiicantly increases perioperative morbidity and mortality. Complications such as increased incidence of surgical site infection, delayed healing, coagulation abnormalities, increased surgical bleeding, perioperative cardiac events, decreased metabolism of drugs involved in anesthesia and a great discomfort in the immediate postoperative period (due to shivering), have been identified. The decrease in the patient's core temperature is due to a combination of physiological events related to the surgical anesthetic act. These include deterioration of the effector responses of the hypothalamus (tending to conserve heat), heat distribution between the central compartment and the periphery, and net heat loss to a generally colder environment, such as the surgical ward. Hypothermia is often an undetected complication of the anesthetic act due to the lack of regular temperature monitoring. It is not considered a basic standard of care, despite the fact that in recent years new guidelines and recommendations have emerged, which suggest its implementation in all patients in whom the duration of their surgery is expected to last longer than 1 hour. The measures aimed at keeping the patient normothermic can be classified as passive, within which the simplest is to cover the patient for as long as possible during their presence in the ward, and active, which are those that transfer heat to the body, within the which the most effective is the use of convective heat blankets. It has recently been suggested that prewarming the patient before inducing anesthesia is an efficient strategy to avoid hypothermia, decreasing temperature differences between core and peripheral tissues. However, the effectiveness of this measure remain to be evaluated with prospective, randomized trials. In the context of the emergency patient, although hypothermia shows the same characteristics as in the elective patient, it becomes more relevant in three clinical settings: patient with major burns, patient in hemorrhagic shock and the polytraumatized patient. In these scenarios, keeping the patient normothermic will prevent a series of serious complications, which can strongly affect mortality.

La hipotermia perioperatoria es una complicación frecuente de la anestesia general, pero que también se puede presentar en pacientes sometidos a anestesia regional. Se relaciona con un aumento significativo de la morbilidad y mortalidad perioperatorias, donde se han identificado complicaciones como aumento de la incidencia de infección del sitio quirúrgico, retardo de la cicatrización, alteraciones de la coagulación, aumento del sangrado quirúrgico, de los eventos cardiacos perioperatorios, disminución del metabolismo de drogas implicadas en la anestesia y sensación de gran incomodidad del paciente en el posoperatorio inmediato, por la presencia de calosfríos. La disminución de la temperatura central del paciente se debe a un combinación de eventos fisiológicos relacionados con el acto anestésico quirúrgico, con deterioro de las respuestas efectoras del hipotálamo tendientes a conservar calor, fenómenos distributivos de calor entre el compartimiento central y la periferia del propio paciente y pérdida de calor neta hacia un medio ambiente en general más frío, como lo es el pabellón quirúrgico. El hecho de que la hipotermia sea muchas veces considerada una complicación no detectada del acto anestésico, se debe a que aún la monitorización regular de la temperatura no se considera un estándar básico de cuidado, pese a que en los últimos años han surgido nuevas guías y recomendaciones, que sugieren que ésta sea implementada en todo paciente en que se proyecte una duración de la cirugía mayor a 1 hora. Las medidas tendientes a mantener al paciente normotérmico, pueden ser clasificadas en pasivas, dentro de las cuales la más simple es cubrir al paciente el mayor tiempo posible durante su presencia en pabellón y activas, que son aquellas que transfieren calor al cuerpo, dentro de las cuales la más efectiva es el uso de mantas de calor convectivo. Recientemente, se ha sugerido que una de las estrategias eficientes para evitar la HPO es el precalentamiento del paciente, que permite que sus tejidos periféricos estén a mayor temperatura al momento de inducir la anestesia, sin embargo, la efectividad de esta medida debe ser evaluada con estudios prospectivos y aleatorizados más concluyentes. La hipotermia en el contexto del paciente de urgencia, si bien presenta las mismas características que en el paciente electivo, cobra mayor relevancia en tres escenarios clínicos: el gran quemado, el paciente en hemorrágico y el paciente politraumatizado, escenarios en que mantener al paciente normotérmico, implicará evitar una serie de complicaciones graves, que pueden incidir fuertemente en la mortalidad.

Efeito da suplementação com óleo de avocado (Persea americana Mill) na temperatura superficial corpórea de equinos antes e após exercício em esteira / [Effect of supplementation with avocado oil (Persea americana Mill) on body surface temperature of horses before and after exercise on treadmill]

Oito equinos foram distribuídos em delineamento randomizado cruzado, sendo um grupo sem suplementação (GC) e outro grupo suplementado com óleo de avocado (GOAv) por um período de sete semanas. Ao fim da sexta semana, os animais foram submetidos a teste padrão de exercício progressivo (TPEP) e, após sete dias, a teste de baixa intensidade e longa duração (BILD). Após o primeiro ciclo, houve período de descanso "washout" de 30 dias para troca de grupos para o segundo ciclo, que seguiu o protocolo do primeiro. A termorregulação foi avaliada com base na temperatura retal e na temperatura superficial corpórea, obtidas por termografia, de 15 regiões de interesse. A temperatura retal e as imagens termográficas foram obtidas antes, um minuto e 15 minutos após o exercício. Não houve diferença entre os grupos GC e GOAv em nenhum momento. Os resultados obtidos neste estudo revelaram que a suplementação de 5% da matéria seca (MS) com óleo de avocado por seis e sete semanas não influenciou na termorregulação com base na temperatura superficial corpórea dos equinos submetidos ao teste padrão de exercício progressivo (TPEP) e ao exercício de baixa intensidade e longa duração (BILD), respectivamente.(AU)

Eight equines were distributed in a randomized crossover design, one control group (CG) without supplementation and another group supplemented (SG) with avocado oil for a period of six weeks. At the end of the sixth week, the animals were submitted to standard exercise test (SET) and after seven days to the low intensity test (LIT). After the first cycle, there was a 30-day washout rest period to exchange groups for the second cycle, which followed the protocol of the first one. Thermoregulation was evaluated based on rectal temperature and body surface temperature of 15 regions of interest obtained by thermography. Rectal temperature and thermographic images were obtained before, one minute and 15 minutes after exercise. There was no difference between the CG and SG at any time. The results obtained in this study revealed that the supplementation of 5% of dry matter with avocado oil for six and seven weeks did not influence the thermoregulation based on the body surface temperature of the horses submitted to SET and LIT, respectively.(AU)

Antipyretic potential of herbal coded formulation [Pyrexol]

The antipyretic effect of the aqueous extract of herbal coded formulation containing equal amount of Salix alba, Emblica officinalis, Glycyrrhiza glabra, Adhatoda vasica, Viola odorata, Thea sinensis, Veleriana officinalis, Foeniculum vulgare, Sisymbrium irrio and Achillea millefolium was investigated using the yeast induced pyrexia model in rabbits. Paracetamol was used as a control group. Rectal temperatures of all rabbits were recorded immediately before the administration of the extract or paracetamol and again at 1 hour, after this, temperature was noted at 1 hrs interval for 5 hrs using digital thermometer. At 240 mg/kg dose the extract showed significant reduction in yeast-induced elevated temperature as compared with that of standard drug paracetamol [150 mg/kg]. It is concluded that herbal coded medicine at a dose of 240 mg/kg has marked antipyretic activity in animal models and this strongly supports the ethno pharmacological uses of medicinal plants of this formulation

Lipid-Emulsion Propofol Less Attenuates the Regulation of Body Temperature than Micro-Emulsion Propofol or Sevoflurane in the Elderly

PURPOSE: Anesthesia and surgery commonly cause hypothermia, and this caused by a combination of anesthetic-induced impairment of thermoregulatory control, a cold operation room environment and other factors that promote heat loss. All the general anesthetics markedly impair normal autonomic thermoregulatory control. The aim of this study is to evaluate the effect of two different types of propofol versus inhalation anesthetic on the body temperature. MATERIALS AND METHODS: In this randomized controlled study, 36 patients scheduled for elective laparoscopic gastrectomy were allocated into three groups; group S (sevoflurane, n=12), group L (lipid-emulsion propofol, n=12) and group M (micro-emulsion propofol, n=12). Anesthesia was maintained with typical doses of the study drugs and all the groups received continuous remifentanil infusion. The body temperature was continuously monitored after the induction of general anesthesia until the end of surgery. RESULTS: The body temperature was decreased in all the groups. The temperature gradient of each group (group S, group L and group M) at 180 minutes from induction of anesthesia was 2.5+/-0.6degrees C, 1.6+/-0.5degrees C and 2.3+/-0.6degrees C, respectively. The body temperature of group L was significantly higher than that of group S and group M at 30 minutes and 75 minute after induction of anesthesia, respectively. There were no temperature differences between group S and group M. CONCLUSION: The body temperature is maintained at a higher level in elderly patients anesthetized with lipid-emulsion propofol.

Dexmedetomidine for the prevention of shivering during spinal anesthesia

PURPOSE: The aim of this study was to evaluate the effect of dexmedetomidine on shivering during spinal anesthesia. METHODS: Sixty patients (American Society of Anesthesiologists physical status I or II, aged 18-50 years), scheduled for elective minor surgical operations under spinal anesthesia with hyperbaric bupivacaine, were enrolled. They were administered saline (group C, n = 30) or dexmedetomidine (group D, n = 30). Motor block was assessed using a Modified Bromage Scale. The presence of shivering was assessed by a blinded observer after the completion of subarachnoid drug injection. RESULTS: Hypothermia was observed in 21 patients (70 percent) in group D and in 20 patients (66.7 percent) in group C (p = 0.781). Three patients (10 percent) in group D and 17 patients (56.7 percent) in group C experienced shivering (p = 0.001). The intensity of shivering was lower in group D than in group C (p = 0.001). Time from baseline to onset of shivering was 10 (5-15) min in group D and 15 (5-45) min in group C (p = 0.207). CONCLUSION: Dexmedetomidine infusion in the perioperative period significantly reduced shivering associated with spinal anesthesia during minor surgical procedures without any major adverse effect during the perioperative period. Therefore, we conclude that dexmedetomidine infusion is an effective drug for preventing shivering and providing sedation in patients during spinal anesthesia.

Tepid sponging plus dipyrone versus dipyrone alone for reducing body temperature in febrile children / Banho tépido e dipirona versus dipirona isolada no tratamento de crianças com febre

CONTEXT AND OBJECTIVE: The role of tepid sponging to promote fever control in children is controversial. We did not find any studies reporting on the effectiveness of tepid sponging in addition to dipyrone. The aim of this study was to compare the effects of tepid sponging plus dipyrone with dipyrone alone for reducing fever. DESIGN AND SETTING: A randomized clinical trial was undertaken at Instituto Materno-Infantil Professor Fernando Figueira, Recife, Pernambuco. METHODS: Children from six months to five years old with axillary temperature greater than 38 ºC in the emergency ward between January and July 2006 were eligible. One hundred and twenty children were randomly assigned to receive oral dipyrone (20 mg/kg) or oral dipyrone and tepid sponging for 15 minutes. The primary outcome was mean temperature reduction after 15, 30, 60, 90 and 120 minutes. Secondary outcomes were crying and irritability. RESULTS: 106 children finished the study. After the first 15 minutes, the fall in axillary temperature was significantly greater in the sponged group than in the control group (p < 0.001). From 30 to 120 minutes, better fever control was observed in the control group. Crying and irritability were observed respectively in 52 percent and 36 percent of the sponged children and in none and only two of the controls. CONCLUSIONS: Tepid sponging plus dipyrone cooled faster during the first 15 minutes, but dipyrone alone presented better fever control over the two-hour period. Tepid sponging caused mild discomfort, crying and irritability for most of the children.

CONTEXTO E OBJETIVO: O papel do banho tépido no controle da febre em crianças é controverso. Não encontramos estudos verificando a eficácia do banho tépido associado à dipirona. O objetivo deste estudo foi comparar a eficácia da dipirona associado com banho tépido, com a dipirona isolada no tratamento da febre. TIPO DE ESTUDO E LOCAL: Foi realizado um ensaio clínico randomizado no hospital de ensino Instituto Materno-Infantil Professor Fernando Figueira, Pernambuco. METODOS: Foram elegíveis crianças com idade entre 6 a 60 meses, atendidas no setor de emergência com temperatura axilar acima de 38 ºC, entre janeiro a julho de 2006. Cento e vinte crianças receberam de forma randomizada, dipirona (20 mg/kg), associada ou não com banho tépido durante 15 minutos. O desfecho primário foi a redução da temperatura axilar, mensurada após 15, 30, 60, 90 e 120 minutos da intervenção; desfechos secundários foram choro e irritabilidade. RESULTADOS: 106 crianças finalizaram o estudo. Nos primeiros 15 minutos, a temperatura diminuiu de forma mais significativa no grupo do banho tépido (p < 0.001). No período de 30 a 120 minutos foi observada maior redução da temperatura no grupo controle. Choro e irritabilidade foram mais observados no grupo estudo, respectivamente, 52 por cento e 36 por cento versus nenhuma e duas no grupo controle. CONCLUSÕES: Banho tépido associado com dipirona baixou de forma mais rápida a temperatura nos primeiros 15 minutos. Ao final dos 120 minutos, observou-se um melhor controle da temperatura com a dipirona isoladamente. Banho tépido provocou moderado desconforto, choro e irritabilidade na maioria das crianças.

Effect of amino acids infusion on thermoregulatory response and blood loss during spinal anesthesia

Intravenous amino acids infusion during general anesthesia prevents decreases in core temperature resulting from increased energy expenditure and heat accumulation. Mild hypothermia may increase surgical bleeding. We studied the effect of amino acids infusion on changes in core temperature and blood loss during spinal anesthesia in patients undergoing hip surgery. Fifty patients were divided into two equal groups. Group 1 patients received an amino acids infusion at a rate of 2 ml /kg/ hr., corresponding to 4kjkg-1h-1, started 1 hr before spinal anesthesia and two hours during surgery. Group 2 patients received normal saline for the same period. Mean blood pressure, heart rate, tympanic membrane core temperature, forearm-fingertip temperature gradient and mean skin temperature, coagulations profile were monitored during the study period and blood loss was measured. Changes in mean arterial pressure and heart rate did not differ significantly between the two groups during the study period. Mean final core temperature 120 min. after induction of spinal anesthesia was 34.37 [SD 0.37] °C in the saline group and 36.02 [SD 0.21]°C in the amino acid group [p < 0.05] The thermal vasoconstriction threshold was increased in the amino acid group [36.1 +/- 0.1 °C] compared with the saline group [34.0 +/- 0.1 °C]. Blood loss during surgery was significantly larger in the saline group [704.88 +/- 175.9 ml] than in the amino acids group [553.2 +/- 107.14] [p < 0.05]. Platelet counts decreased significantly in both groups immediately and first day after surgery [p < 0.05]. However, there were no differences in coagulation values between the two groups. The amino acids infusion before and during spinal anesthesia was able to prevent the occurrence of intraoperative hypothermia and reduces blood loss without significant effect on coagulation profile

The terrestrial Gastropoda Megalobulimus abbreviatus as a useful model for nociceptive experiments: effects of morphine and naloxone on thermal avoidance behavior

We describe the behavior of the snail Megalobulimus abbreviatus upon receiving thermal stimuli and the effects of pretreatment with morphine and naloxone on behavior after a thermal stimulus, in order to establish a useful model for nociceptive experiments. Snails submitted to non-functional (22°C) and non-thermal hot-plate stress (30°C) only displayed exploratory behavior. However, the animals submitted to a thermal stimulus (50°C) displayed biphasic avoidance behavior. Latency was measured from the time the animal was placed on the hot plate to the time when the animal lifted the head-foot complex 1 cm from the substrate, indicating aversive thermal behavior. Other animals were pretreated with morphine (5, 10, 20 mg/kg) or naloxone (2.5, 5.0, 7.5 mg/kg) 15 min prior to receiving a thermal stimulus (50°C; N = 9 in each group). The results (means ± SD) showed an extremely significant difference in response latency between the group treated with 20 mg/kg morphine (63.18 ± 14.47 s) and the other experimental groups (P < 0.001). With 2.5 mg/kg (16.26 ± 3.19 s), 5.0 mg/kg (11.53 ± 1.64 s) and 7.5 mg/kg naloxone (7.38 ± 1.6 s), there was a significant, not dose-dependent decrease in latency compared to the control (33.44 ± 8.53 s) and saline groups (29.1 ± 9.91 s). No statistically significant difference was found between the naloxone-treated groups. With naloxone plus morphine, there was a significant decrease in latency when compared to all other groups (minimum 64 percent in the saline group and maximum 83.2 percent decrease in the morphine group). These results provide evidence of the involvement of endogenous opioid peptides in the control of thermal withdrawal behavior in this snail, and reveal a stereotyped and reproducible avoidance behavior for this snail species, which could be studied in other pharmacological and neurophysiological studies.

Effects of a neuronal nitric oxide synthase inhibitor on lipopolysaccharide-induced fever

It has been demonstrated that nitric oxide (NO) has a thermoregulatory action, but very little is known about the mechanisms involved. In the present study we determined the effect of neuronal nitric oxide synthase (nNOS) inhibition on thermoregulation. We used 7-nitroindazole (7-NI, 1, 10 and 30 mg/kg body weight), a selective nNOS inhibitor, injected intraperitoneally into normothermic Wistar rats (200-250 g) and rats with fever induced by lipopolysaccharide (LPS) (100 µg/kg body weight) administration. It has been demonstrated that the effects of 30 mg/kg of 7-NI given intraperitoneally may inhibit 60 per cent of nNOS activity in rats. In all experiments the colonic temperature of awake unrestrained rats was measured over a period of 5 h at 15-min intervals after intraperitoneal injection of 7-NI. We observed that the injection of 30 mg/kg of 7-NI induced a 1.5oC drop in body temperature, which was statistically significant 1 h after injection (P<0.02). The coinjection of LPS and 7-NI was followed by a significant (P<0.02) hypothermia about 0.5oC below baseline. These findings show that an nNOS isoform is required for thermoregulation and participates in the production of fever in rats.

Effect of carbachol injection in the medial preoptic area on sleep-wakefulness and body temperature in free moving rats.

The aim of the present study was to find out the changes in sleep-wakefulness and body temperature brought about by application of cholinergic agonist, carbachol, in the medial preoptic area (mPOA). Carbachol, when injected bilaterally into the mPOA of male rats, through chronically implanted cannulae, produced a fall in rectal temperature and long lasting arousal. There was temporal dissociation in the duration of changes produced in the two parameters. It is suggested that the cholinergic system at the medial preoptic area brings about arousal response and fall in body temperature through different circuits.

Characterization of dopamine receptors involved in central thermoregulation in rabbits.

Intracerebroventricularly administered dopamine produced dose dependent hyperthermia in rabbits. Haloperidol, a D1 receptor blocker produced consistent hypothermia, whereas D2 receptor blocker metoclopramide produced hyperthermia, pretreatment with haloperidol competitively blocked the hyperthermic response of dopamine. Pretreatment with metoclopramide augmented the onset and peak response of dopamine. It is suggested that D1 receptors are involved in producing hyperthermia and D2 receptors in hypothermia.

Hypothalamic adrenoceptors concerned with control of temperature, elicited by chemical stimulation.

Norepinephrine (NE) and its blockers (alpha-1, alpha-2, beta-1 and beta-2) were micro-injected into the anterior hypothalamus of male albino rats and the effects of these injections on rectal temperature were recorded. The results indicated that the thermoregulatory effects of NE were dependent on ambient temperature. The present study further demonstrated the specific involvement of beta-2 receptors present in the anterior hypothalamus concerned with thermoregulation.

Characterization of alpha-adrenoceptors involved in central thermoregulation in rabbits.

Intracerebroventricular (icv) injection of methyldopa induced body temperature changes in the rabbits. The dose of 100 micrograms/kg did not produce any significant change on body temperature whereas 250 micrograms/kg of the drug induced hyperthermia. Higher dose of 500 micrograms/kg produced initial hypothermia which was followed by hyperthermia. On further increase of the dose to 1 mg/kg, consistent hypothermia was evident. Prazosin, a specific post-synaptic alpha 1 adrenoceptor blocker, induced hypothermia whereas piperoxan (presynaptic alpha 2 antagonist) produced hyperthermia. The pretreatment with prazosin, blocked the hyperthermic response of methyldopa. The initial hypothermia by 500 micrograms/kg of methyldopa was also potentiated. The pretreatment with piperoxan completely blocked the hypothermia but had no effect on hyperthermic response of methyldopa. Pretreatment of rabbits with both prazosin and piperoxan completely blocked the hypothermia as well as hyperthermic response of methyldopa. Thus it appeared that both presynaptic alpha 2 and postsynaptic alpha 1 adrenoceptors are involved in central thermoregulation in rabbits.

Thermal changes produced by norepinephrine application in the preoptic area of monkeys.

The effect of injection of norepinephrine in the anterior regions of hypothalamus on rectal temperature, skin temperature, heart rate and respiratory rate in rhesus monkeys was studied. The injection of 2 micrograms of norepinephrine in the preoptic area produced a fall in body temperature without any accompanying change in skin temperature, heart rate and respiratory rate. The findings suggest that the suppression of heat production may be responsible for the norepinephrine induced hypothermia in monkeys.

Involvement of histamine receptors in mediation of histamine induced thermoregulatory response in rats.

At there ambient air temperature range, the rectal temperature changes following infusion of histamine either into lateral ventricle (L.V.) or IVth ventricle (IVth V) were studied. At an ambient temperature range of 19-22 degrees C, hypothermia occurred following histamine infusion either into L.V. or IVth V. Hypothermia elicited from infusion of histamine into L.V. was prevented with pretreatment of H1-receptor blocker (mepyramine), but in case of IVth V, it was prevented with H2-receptor blocker(cimetidine). These H1 and H2-receptor antagonists were ineffective in preventing hypothermia following histamine infusion into either L.V. or IVth V, when the ambient air temperature was maintained low (11-13 degrees C).

Thermoregulatory response in rats following administration of histamine in different CSF compartments.

Recently histamine is being considered as an important neurotransmitter/neuromodulator in the central nervous system. This has been supported from the present observations with regard to thermoregulatory responses elicited following histamine administration into different CSF compartments. Administration of histamine into the right lateral cerebral ventricle of rats showed a dose dependent fall in rectal temperature. This hypothermic response was evident only at moderately low or at thermoneutral ambient temperature. Administration of histamine into fourth ventricle produced hypothermic response at low ambient temperature and hyperthermia at thermoneutral ambient temperature, which was no longer observed when the ambient temperature remained above the thermoneutral zone. Infusion of histamine into spinal subarachnoid space produced hyperthermia which developed very slowly. However, the infusion of histamine into the subarachnoid space around the brain stem did not exhibit any change in rectal temperature. The significance of these observations has been discussed.

Effects of succinylcholine and related substances administered into the medial preoptic area on the local EEG, body temperature, heart rate, galvanic skin resistance and biogenic amines.

Succinylcholine (Sch) which is a cholinergic neuromuscular blocker has been known to occasionally lead to episodes of malignant hyperthermia in swine and humans. In order to find whether it produces any hyperthermic effects through action on medial preoptic area, experiments were carried on by administering intracerebrally the chemical into the medial preoptic area through an in-dwelling cannula-cum-electrode in the free moving rat. The changes in body temperature and the local EEG were studied. For comparison purpose, the effects of carbachol, atropine and phenylephrine were also studied. Further, in the curarized state of no muscular activity, the effect of SCh on the preoptic area was again tested and also the changes in the other autonomic parameters of heart rate and galvanic skin resistance (GSR) were studied. It was observed that SCh given into preoptic area caused a clear hyperthermic effect. The effect was countered by prior administration of atropine into the site. After SCh the local EEG changed into a high amplitude slow wave format. The heart rate was not altered but the GSR increased by two-fold. Carbachol caused a rise in body temperature, heart rate and also GSR. SCh also caused a reduction in noradrenaline content of the hypothalamus by 23% while no change in dopamine and serotonin occurred. Serotonin increased by 28% in the brainstem with no change in the other amines. Septum showed an increase of noradrenaline and dopamine contents by 40% and 25% respectively. Keeping in view the monoaminergic connections and thermoregulatory role of the preoptic area, one may postulate that SCh could inhibit the warm sensors and the controls of the dual sympathetic mechanism which normally leads to an increase of sudomotor activity and a decrease of vasomotor activity, the inhibition resulting in rise of body temperature.