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Revista Brasileira de Anestesiologia

Print version ISSN 0034-7094On-line version ISSN 1806-907X

Rev. Bras. Anestesiol. vol.58 no.3 Campinas May/June 2008 



The intraoperative use of warming blankets in patients undergoing radical prostatectomy is related with a reduction in post-anesthetic recovery time


El uso de manta térmica en el intraoperatorio de pacientes sometidos a la prostatectomía radical está relacionado con la disminución del tiempo de recuperación pos anestésica



Cláudia PanossianI; Cláudia Marquez Simões, TSAII; Wilson Roberto Oliveira MilaniIII; Marília Bonifácio BaranauskasI; Clarita Bandeira Margarido, TSAIV

IME3 do São Paulo – Serviços Médicos de Anestesia (SMA/HSL)
IIAnestesiologista do Instituto Central do Hospital das Clínicas FMUSP; Membro do Comitê de Hipertermia Maligna/SBA
IIIAnestesiologista do São Paulo – SMA/HSL
IVDoutora em Medicina pela FMUSP; Responsável pela Pesquisa do São Paulo – SMA/HSL

Correspondence to




BACKGROUND AND OBJECTIVES: Anesthesia and the surgeries cause substantial thermal changes, and hypothermia can lead to cardiovascular complications, clotting disorders, immunologic changes, and disruption of water and electrolyte balances, besides decreasing drug metabolism and, therefore, increasing post-anesthetic recovery time (PART). Circulation of warm air (forced-air warming blanket) is the most effective non-invasive warming method currently available. The objective of the present study was to compare the time spent in the recovery room of patients undergoing radical prostatectomy with and without the intraoperative use of a forced-air warming blanket.
METHODS: Male patients between 45 and 75 years, ASA PS I, II, and III undergoing radical prostatectomy under general anesthesia during 2004 were studied. Data gathered included: age, weight, physical status, anesthetic technique, use of warming blanket, and time spent in the recovery room. The data was recorded on an Excel chart and analyzed by the Mann-Whitney test.
RESULTS: Patients in whom the warming blanket was used intraoperatively remained a mean of 139.66 ± 58.6 minutes in the recovery room, while patients without the warming blanket spent a mean of 208.28 ± 65.8 minutes in the recovery room (p < 0.0001).
CONCLUSIONS: We concluded that the intraoperative use of the warming blanket in patients undergoing radical prostatectomy was associated with a significant reduction in the time patients spent in the recovery room.

Key Words: COMPLICATIONS: hypothermia; PHYSIOLOGY: temperature; POST-ANESTHETIC RECOVERY TIME: recovery room.


JUSTIFICATIVA Y OBJETIVOS: La anestesia y el procedimiento quirúrgico causan alteraciones térmicas ostensivas, y la hipotermia puede causar complicaciones cardiovasculares, disturbios de la coagulación, alteraciones inmunológicas, hidro electrolíticas, además de reducir el metabolismo de fármacos aumentando el período de recuperación pos anestésica (RPA). La circulación de aire caliente (manta térmica), es el método de calentamiento no invasivo más efectivo que está a disposición actualmente. El objetivo del presente estudio fue comparar el tiempo de permanencia en el RPA de pacientes sometidos a la prostatectomía radical con y sin el uso de manta térmica en el período intraoperatorio.
MÉTODO: Fueron estudiados pacientes, ASA PS I, II, III, entre 45 y 75 años, sometidos a prostatectomía radical con anestesia general en el año 2004. Los datos recolectados incluyeron: edad, peso, estado físico, técnica anestésica, uso de manta térmica y tiempo de permanencia en la RPA, esos fueron puestos en una planilla Excel y analizados por la prueba de Mann-Whitney.
RESULTADOS: Los pacientes en que la manta térmica fue utilizada en el período intraoperatorio permanecieron en promedio 139,66 ± 58,6 minutos en la RPA, ya en los pacientes en que la manta térmica no fue utilizada el general de permanencia fue como promedio de 208,28 ± 65,8 minutos en la RPA (p < 0,0001).
CONCLUSIONES: En las condiciones del presente estudio se concluyó que el uso de manta térmica en el intraoperatorio de pacientes sometidos a la prostatectomía radical estuvo asociado a la disminución significativa del tiempo general de permanencia en la RPA.




Core body temperature is one of the most rigorously controlled physiologic parameter. The human thermoregulatory system allows variations of 0.2 to 0.4°C around 37°C to maintain the normal metabolic functions of the body 1.

Anesthesia and surgeries cause substantial thermal changes; hypothermia is a typical change that results from the combination of anesthetic induction, low temperature in the operating room, and factors related with the extension of the surgical wound that lead to heat loss 2.

Perioperative hypothermia causes several undesirable effects that begin intraoperatively and extend throughout the postoperative period. Induction of general anesthesia is responsible for a 20% reduction in metabolic heat production and it also abolishes physiologic thermoregulatory responses normally triggered by hypothermia 3. Redistribution of heat from the central compartment to the periphery by circulatory convection and conduction, leading to a reduction in core temperature and increase in peripheral temperature, but without changes in mean body temperature and heat content of the body, is the main mechanism responsible for the development of hypothermia 4. The development of hypothermia can be divided in three phases: initially, a rapid reduction in core temperature by redistribution after anesthetic induction can be observed, which is followed by the second phase, characterized by the linear reduction in temperature (0.5 to 1°C per hour) as long the difference between the metabolic production rate and heat loss to the environment continues. After this phase, vasoconstriction is triggered, restricting the flow of heat between compartments, with a reduction in the internal redistribution of heat and heat loss to the environment. Maintenance of metabolic heat production, despite the continuous loss, generates a plateau in the temperature that is capable of reestablishing the normal gradient between compartments. The last phase is characterized by a new thermal balance, but at a lower temperature 5.

Consequences of inadvertent intraoperative hypothermia include: cardiovascular complications (myocardial ischemia, hypertension, tachycardia, deep venous thrombosis), clotting disorders (platelet activation, coagulopathies), immunologic changes (increased incidence surgical wound infection), water and electrolyte imbalances (hypocalemia, hypomagnesemia, hypophosphatemia), and endocrine-metabolic changes (decreased levels of corticosteroids and insulin, increased peripheral resistance to insulin, increased levels of thyroid-stimulating hormone), among others 1.

Hypothermia also changes the anesthetic procedure by changing the pharmacokinetics and pharmacodynamics of drugs, increasing the duration of action of neuromuscular blockers and the plasma levels of propofol, potentiating the cardiotoxicity of bupivacaine, and decreasing the minimal alveolar concentration (MAC) by 5% for every degree of reduction in the temperature. It also interferes with pulse oximetry and, consequently, the length of stay in the recovery room is increased 1.

Prevention of hypothermia is very important, especially in patients undergoing medium and major surgeries. Several methods have been described in an attempt to maintain intraoperative normothermia. Intraoperative passive warming consists of covering all cutaneous surfaces possible, with sheets or blankets, which reduce heat loss by 30% 6. Active warming includes thermal mattresses with circulating water that only are beneficial if placed over the patient 6; infusion of warm solutions, which is useful when one needs to infuse more than 2 liters over one hour 7 (one liter of crystalloid solution at room temperature decreases core temperature by 0.25°C) 8; warming and humidification of the gases administered to the patient has very little impact in body temperature 9. The most effective method of maintaining normothermia is to prevent it by warming the body prior to the surgery; warming of cutaneous surfaces with forced warm air (at 43°C) during one hour before the surgery transfers enough heat to decrease the effects of redistribution, the most common intraoperative heat loss process. Forced warm air (thermal blanket) is the most effective non-invasive warming method currently available to treat hypothermia, increasing the temperature a mean of 0.75°C per hour 10.



This study was conducted at the Hospital Sírio e Libanês after approval by the Ethics Commission.

Data from records of patients who underwent radical prostatectomy in 2004, which were obtained with the Medical Files Services of the Hospital Sírio e Libanês (SAME, from the Portuguese Serviços de Arquivos Médicos), were analyzed.

Characteristics evaluated included: ages between 47 and 75 years, ASA PS I, II, or III, and patients undergoing radical prostatectomy under general anesthesia.

Exclusion criteria included: ASA PS IV or V, surgical complications, and the need for blood transfusion.

Data gathered included: age, weight, physical status, anesthetic technique, time in the recovery room, and the intraoperative use of thermal blanket. Patients were divided in two groups: with thermal blanket and without. The data were plotted on an Excel chart and analyzed by the Mann-Whitney test.



During the period of this study, 224 records of patients who underwent radical prostatectomy and stayed in the recovery room were identified. One-hundred and sixty-three patients used the thermal blanket intraoperatively and 61 did not.

Table I shows physical status, age, and weight of the patients, and anesthesia performed (intravenous and balanced). Statistically significant differences between both groups were not observed.



Table II shows the mean time (minutes) in the recovery room of both groups. The time in the recovery room was greater in patients that did not use the thermal blanket, and this difference was statistically significant.



Figure 1 shows the distribution of patients in three time-periods: < 120 minutes, between 121 and 180 minutes, and > 180 minutes. We observed that 47.85% (78) of patients who used the thermal blanket spent less than 120 minutes in the recovery room, while 67.21% (41) of the patients who did not use the thermal blanket spent more than 180 minutes in the recovery room.



This retrospective study evaluated the association between the intraoperative use of thermal blanket in patients undergoing radical prostatectomy and the length of time spent in the recovery room.

A significant reduction in the time spent in the recovery room of patients who used the thermal blanket was the main finding of this study (Table II), which is compatible with the data found in the literature 11.Previous studies have shown a greater predisposition for hypothermia of elderly patients and those with co-morbidities 1. However, in this study, statistically significant differences in physical status, weight and age between both groups were not observed (Table II). Therefore, the indication of the thermal blanket was not guided by those criteria, it was a random indication. After this study, the intraoperative use of the thermal blanket was standardized in those patients by the Anesthesiology department.

During the study period, the thermal blanket at the Hospital Sírio Libanês cost R$126,40 (one-hundred and twenty-six reais) and the hour in the recovery room cost R$340,00 (three-hundred and forty reais). This study has been quoted in reports of the surgical team to justify the use of the thermal blanket for health insurance providers.

In this study, body temperature was not analyzed, since most records did not have this datum because it was not checked or was not recorded. Although temperature monitoring is a relevant parameter for perioperative care, it is still widely overlooked. Other factors that increase the time of stay in the recovery room, such as pain, nausea, vomiting, and drowsiness, were not analyzed, which is another limitation of this study. Therefore, a prospective study, with adequate intra- and postoperative monitoring, as well as monitoring of factors that could be associated with increased time of stay in the recovery room, is necessary to obtain more conclusive results.

One can conclude that, under the conditions of the present study, the use of the thermal blanket is associated with a significant reduction in the time of stay in the recovery room.



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Correspondence to:
Dra. Cláudia Panossian
Rua dos Franceses, 498/73 – Morro dos Ingleses
01329-010 São Paulo, SP

Submitted em 13 de abril de 2007
Accepted para publicação em 19 de fevereiro de 2008



* Received from Hospital Sírio Libanês (HSL), São Paulo, SP

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