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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.54 no.2 Campinas Mar./Apr. 2004
Shivering during epidural anesthesia with and without fentanyl: comparative study*
Incidencia de tremor en anestesia peridural con y sin fentanil: estudio comparativo
Múcio Paranhos de Abreu, TSA, M.D.I; João Lopes Vieira, TSA, M.D.II; Marcelo Negrão Lutti, TSA, M.D.I; Emily Santos Montarroyos, M.D.III; Randal de Tarso Rossi, M.D.III; Rodrigo Moraes, M.D.III
IInstrutor do CET/SBA
IICo-Responsável pelo CET/SBA do Instituto Penido Burnier
IIIME2 do CET/SBA (2002)
BACKGROUND AND OBJECTIVES:
Most studies in the literature correlating epidural opioids to postoperative
shivering were carried out with obstetric patients whose thermoregulation center
response might be different from non-pregnant patients. Our study aimed at comparing
intra and postoperative shivering and other complications of epidural block
with and without fentanyl in patients submitted to varicose vein surgery under
epidural anesthesia with 0.5% bupivacaine and 1:200,000 epinephrine.
METHODS: Participated in this study 34 patients, physical status ASA I and II, submitted to lower limbs varicose vein surgery, who were randomly distributed in 2 groups (n = 17) and received intravenous midazolam (0.05 mg.kg-1) followed by lumbar epidural anesthesia. Group S received 20 mL of 0.5% bupivacaine (with epinephrine) associated to 2 mL of 0.9% saline solution, and Group F received 20 mL of 0.5% bupivacaine (with epinephrine) associated to fentanyl (100 µg). Shivering, temperature, meperidine need, nausea and vomiting were evaluated in the following moments: M1 - admission to the operating room; M2 - immediately before anesthesia; M3 - 30 minutes after local anesthetic injection; M4 - 60 minutes after local anesthetic injection; M5 - 90 minutes after local anesthetic injection; M6 - end of anesthesia; M7 - immediately before PACU discharge.
RESULTS: There have been no statistically significant differences between groups in demographics, physical status, mean anesthesia and surgery duration, patients and operating room temperature, and the incidence of nausea and vomiting. There have been statistically significant differences in shivering occurrence at 60 (M4) and 90 minutes (M5) after epidural block, with higher incidence of shivering in Group S as compared to Group F. A greater demand for meperidine was observed in patients submitted to epidural block without fentanyl.
CONCLUSIONS: In the conditions of our study, 100 µg fentanyl associated to epidural local anesthetics did not abolish shivering but is able to decrease its incidence without increasing the incidence of nausea and vomiting.
Key Words: ANALGESICS: Opioids, fentanyl; ANESTHETIC TECHNIQUES: Regional, epidural; COMPLICATIONS: hypothermia, shivering
JUSTIFICATIVA Y OBJETIVOS:
La mayoría de los trabajos encontrados en la literatura, relacionando la
influencia de los opioides administrados por vía peridural con el tremor
per y pos-operatorio, fueron realizados con grupos de pacientes obstétricas,
en las cuales la respuesta del centro termorregulador puede ser diferente de
las pacientes no embarazadas. El objetivo de este trabajo fue comparar el bloqueo
peridural con y sin fentanil, cuanto a la incidencia de tremores y otras complicaciones
en el intra y pos-operatorio en pacientes sometidos a cirugía de várices
bajo anestesia peridural con bupivacaína a 0,5% con adrenalina a 1:200.000.
MÉTODO: Treinta y cuatro pacientes, estado físico ASA I y II, sometidos a cirugía para tratamiento de várices de miembros inferiores, fueron divididos aleatoriamente en 2 grupos (n = 17), y recibieron: midazolam (0,05 mg.kg-1), por vía venosa seguido de anestesia peridural lumbar, utilizandose: en el grupo S, 20 ml bupivacaína a 0,5% (con vasoconstrictor) asociado a 2 ml de solución fisiológica a 0,9% y en el grupo F, 20 ml de bupivacaína a 0,5% (con vasoconstrictor) asociada al fentanil (100 µg). Fueron estudiados: incidencia de tremor, temperatura de los pacientes, necesidad del uso de meperidina, y la incidencia de náuseas y vómitos en los siguientes momentos: M1 - admisión del paciente en la sala de operación; M2 - inmediatamente antes de la anestesia; M3 - 30 minutos después del término de la inyección del anestésico local (AL); M4 - 60 minutos después del término de la inyección de AL; M5 - 90 minutos después del término de la inyección de AL; M6 - final de la anestesia; M7 - antecediendo al alta de la sala de recuperación pos-anestésica.
RESULTADOS: Cuanto a los datos antropométricos, estado físico, tiempo medio de duración de la anestesia y cirugía, temperatura de los pacientes y de la sala de operación e incidencia de náuseas y vómitos no hubo diferente estadística entre los grupos. Hubo diferencia estadística a los 60 minutos (momento 4) y 90 minutos (momento 5) después del bloqueo peridural, con mayor incidencia de tremor en el Grupo-S que en el Grupo-F. Hubo mayor necesidad de utilización de meperidina en los pacientes sometidos al bloqueo peridural no asociado al fentanil.
CONCLUSIONES: En las condiciones de este estudio, la adición de 100 µg de fentanil al anestésico local, por vía peridural, mostró que el opioide no tiene la propiedad de suprimir el tremor, más de reducir su incidencia y la intensidad, sin aumentar la incidencia de náuseas y vómitos.
Systemic epidural anesthesia complications are predictable and mostly avoidable. There is a high incidence of intra and postoperative shivering, which is sometimes difficult to control, the etiology of which has not been totally explained by the literature 1,2.
Decreased body temperature induced by the sympathetic block-induced vasodilation may lead to hypothermia and, consequently, to shivering.
Some authors have suggested that shivering during epidural anesthesia does not result from hypothermia alone and that the association of epidural opioids, such as fentanyl, seems to have consistent results in decreasing shivering 3-5. On the other hand, interpreting those studies is cumbersome for several reasons: 1) most studies were carried out with pregnant patients whose thermoregulation center response might be different from non-pregnant patients 6; 2) some studies have included obstetric patients submitted to labor analgesia together with patients submitted to C-section under epidural anesthesia 5; 3) other studies were carried out just with patients submitted to C-section 5.
A study has shown the efficacy of 6.25 to 50 mg intravenous meperidine to prevent and control shivering in patients submitted to epidural anesthesia 7.
Fentanyl is a liposoluble opioid which, associated to local anesthetics in epidural anesthesia, is able to increase hypothalamic thermoregulation center threshold for triggering shivering 2,8.
This study aimed at evaluating the effects of epidural fentanyl associated to local anesthetics in preventing intra and immediate postoperative shivering in patients submitted to lower limb varicose vein surgery under epidural anesthesia with 0.5% bupivacaine plus epinephrine 1:200,000.
After the Centro Médico de Campinas Ethics Committee approval and their formal consent, participated in this study 34 patients aged 21 to 62 years, physical status ASA I and II, submitted to lower limb varicose vein surgery under epidural anesthesia with 0.5% bupivacaine and 1:200,000 epinephrine. Patients were randomly distributed in two groups: Group F, with epidural fentanyl (100 µg) and Group S, without fentanyl.
Venoclysis was performed with 20G catheter in the operating room in an upper limb followed by 500 ml previously warmed to 37 ºC lactated Ringer's solution infusion before blockade. The same warmed solution was used for intraoperative hydration and was infused with conventional device. Monitoring parameters were: noninvasive blood pressure, heart rate, oxygen hemoglobin saturation with pulse oximetry (SpO2) and ECG at DII lead. Body temperature was measured through tympanic temperature with digital infrared ear thermometer of intermittent use and graduated in degrees Celsius (ºC). Operating room temperature was continuously monitores with an environmental digital thermometer.
All patients received intravenous midazolam (0.05 mg.kg-1) immediately before epidural anesthesia. Epidural puncture was performed with patients in the sitting position, with 17G Weiss needle and identification of lumbar epidural space (L2-L3 or L3-L4), through the loss of resistance to air technique. After aspiration and test dose with 3 ml of 2% lidocaine with 1:200,000 epinephrine, Group S received 20 mL of 0.5% bupivacaine (with epinephrine) associated to 2 mL of 0.9% saline solution, and Group F received 20 mL of 0.5% bupivacaine (with vasoconstrictor) associated to 2 mL fentanyl (100 µg). All patients received routinely oxygen (2 L.min-1) through a nasal catheter. Hemodynamic data, patients and operating room temperature and the presence of shivering were recorded in seven moments:
M1 - at operating room
M2 - immediately before epidural anesthesia;
M3 - 30 minutes after local anesthetic injection (LA);
M4 - 60 minutes after LA injection;
M5 - 90 minutes after LA injection;
M6 - end of anesthesia;
M7 - immediately before PACU discharge.
The incidence of shivering was evaluated by the anesthesiologist and was classified as 0 = no shivering; 1 = masseter muscle fasciculation; 2 = face, neck and upper extremities muscles fasciculation and 3 = muscle shakes. Intravenous 5 to 50 mg meperidine was used in patients with shivering class 2 or 3. Initial dose was standardized in 5 mg and 5 mg increments would be added until shivering disappearance, however not beyond 50 mg. Adverse effects, such as nausea and vomiting were recorded and data were compared between groups.
Student's t test was used to compare age, weight and height. Chi-square test was used to compare gender and physical status. Non-parametric Mann-Whitney test for two independent samples was used to compare onset and incidence of shivering as well as meperidine consumption for both groups, considering significant p < 0.05.
No statistically significant differences were observed between groups in demographics, physical status, mean anesthesia and surgery duration, patients and operating room temperature, and the incidence of nausea and vomiting (Table I, II, III and IV). A significant difference on shivering occurrence at 60 (M4) and 90 minutes (M5) after epidural block was observed, with a higher incidence of shivering in Group S as compared to Group F (Table V). Shivering intensity was also higher in Group S as compared to Group F in moments M4 and M5 (Table VI).
Patients submitted to epidural block without fentanyl (Group S) needed more meperidine. Mean meperidine dose for Group S was 26.67 ± 11.69. Meperidine was only needed for one Group F patient (Table VII).
Epidural anesthesia shivering is considered a response of hypothalamic thermoregulation center and, although not being clear in the literature, seems to be due to hypothermia caused by local epidural anesthetic injection and partially resulting from the redistribution of body warmth from the central to the peripheral region 3,9-15, among other causes. Mild or moderate hypothermia (35.9 to 34 ºC) during general or regional anesthesia triggers the activation of thermoregulatory mechanisms responsible for decreasing temperature loss and increasing heat generation: muscle shivering, sympathetic centers hyperactivity promoting vasoconstriction in the area above sympathetic block, increase in enzyme reactions by catecholamines and elimination of sweating, among others.
Other factors contributing to body temperature decrease involve low operating room temperature (below 21 ºC) with insufficient protection against heat loss; skin cleaning with cold alcoholic solutions; volume replacement with room temperature solutions; administration of anesthetic drugs depressing metabolic heat-producing activity, leading to skin vasodilation and consequent increase in heat loss.
Intra and post-anesthetic shivering etiology may too be related to the inhibition of medullary reflexes, regional sympathetic activity block leading to peripheral vasodilation and heat loss and pyrogenic substances release, among other causes 13.
Shivering consequences are a function of its intensity and may increase oxygen consumption in 200% to 800% above baseline values 13. In patients with decreased cardiac reserves, this oxygen consumption increase may peak with the decrease in tissue oxygen supply, contributing for increased incidence of postoperative ventricular arrhythmias 16,17.
Among epidural anesthesia-related side-effects, such as nausea, vomiting and headache among others, shivering has been mentioned as a disagreeable and very uncomfortable experience 18,19.
Shivering prevention during epidural anesthesia includes some measures such as:
- Warming infused fluids to 37 ºC 1,21;
- Maintaining operating room temperature between 21 and 24 ºC 18;
- Using thermal mattresses and blankets;
- Irradiating heat emission to increase central blood temperature in up to 17.7 kcal.h-1 23.
Depending on surgery type and duration, visceral exposure, etc., these measures alone may not prevent hypothermia and shivering.
It has been described that shivering may be abolished by intravenous opioids, leading to increased tolerance to hypothermia due to decrease in central temperature needed to trigger shivering 2,3,22,23.
Epidural opioids may also abolish shivering although their mechanism of action on shivering threshold is still not well defined 2,6.
It is known that epidural fentanyl has its non-ionized fraction rapidly transferred through the dura to CSF and from it to spinal cord. It reaches spinal cord through the absorption by radicular arteries. There is also a fast systemic absorption originating significant plasma fentanyl concentrations resulting in systemic and medullary analgesic action 2,25,26. How epidural fentanyl reaches thermoregulatory center and influences shivering threshold is still not totally known. Due to its liposolubility, low fentanyl concentrations reach the brain through CSF; so, the mechanism by which fentanyl reaches hypothalamus in concentrations enough to interfere with shivering threshold is still not known 2,25. It is believed that such concentrations are reached through systemic epidural fentanyl absorption 26.
In our study, the incidence of shivering was significantly higher at 60 and 90 minutes after epidural injection in the group not receiving fentanyl, as compared to the group receiving fentanyl, although fentanyl has not abolished shivering. Shivering intensity was also higher in the group without fentanyl and resulting in a greater number of patients (6) needing intravenous meperidine. Only one patient needed meperidine in the group receiving fentanyl. With fractioned meperidine doses, no patient has reached 50 mg (Group S = 26.67 ± 11.89 and Group F = 30 mg).
Disadvantages of epidural opioids are their side-effects: pruritus, nausea and vomiting, urinary retention, sedation and respiratory depression which, although important, are not frequent when opioids are used in low doses.
No significant differences in the incidence of nausea and vomiting were observed in our study.
One may conclude that, in the conditions of our study, the association of 100 µg fentanyl to epidural local anesthetics is unable to abolish shivering but is able to decrease its incidence and intensity without increasing the incidence of nausea and vomiting.
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Apresentado (Submitted) em 13 de
Aceito (Accepted) para publicação em 23 de junho 2003
* Recebido da (Received from) CET/SBA do Instituto Penido Burnier e Centro Médico de Campinas, SP