Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.54 no.4 Campinas July/Aug. 2004
High thoracic epidural anesthesia associated or not to low thoracic epidural anesthesia in outpatient procedures: clinical implications*
Peridural torácica alta asociada o no a la peridural torácica baja en pacientes ambulatoriales: implicaciones clínicas
Djalma Sperhacke, M.D.I; Karl Otto Geier, M.D.II; João Carlos Correia Eschiletti, M.D. III
Clínica Rio Branco
IIAnestesiologista do Hospital Municipal de Pronto Socorro de Porto Alegre/RS; Anestesiologista Colaborador da Clindor do Hospital São Lucas da PUC/RS; Mestre em Cirurgia pela UFRGS
IIICirurgião Plástico da Clínica Rio Branco
BACKGROUND AND OBJECTIVES:
Hemodynamic changes are easily controlled under low or median thoracic epidural
block. Since high thoracic epidural block (T2-T3) often
affects brachial plexus roots (C4) C5-T1(T2),
some of them responsible for phrenic nerve formation (C3-C4-C5),
potential motor repercussions on this nerve are to be expected. Our study performed
during cosmetic surgeries under isolated segmental epidural block in T2-T3
or associated to segmental epidural block in T11-T12,
has evaluated motor repercussions on respiratory dynamics, upper and lower limbs.
METHODS: Participated in this study 32 patients physical status ASA I and II, without active bronchospastic pulmonary disease and body weight equal to or above 50 kg, 21 of whom were submitted to isolated thoracic epidural blocks in T2-T3 and the remaining patients (11) were submitted to a combined thoracic epidural blocks in T11-T12 with 7.5% ropivacaine (45 to 90 mg) associated to sufentanil (10 to 20 µg). Hemodynamic, respiratory and upper and lower limbs motor repercussions were evaluated by noninvasive monitoring, spirometry hand grasping strength and Bromage score, respectively.
RESULTS: Mean mammary surgeries duration was 105 minutes with upper limbs motor depression (p < 0.001), with motor recovery at 117.2 ± 51.3 min and first pain complaint at 485 ± 221.2 min. Combined surgeries with mean duration of 165 min, with lower limbs motor depression level 1 in 40% and level 2 in 60% of patients according to Bromage score, with recovery at 223.9 ± 57.1 min and first pain complaint at rest at 555 ± 197.9 min. Pulmonary functions VEF1 (L/sec); PFE (L.min-1); FVC (liters) were changed in 15.20% (p < 0.009); 13.36% (p < 0.029) and 18.09% (p < 0.007), respectively, with 8.75% VEF1/FVC increase (p < 0.162). There has been hypotension (< 30% above baseline values) and bradycardia (< 55 pbm) in 5 patients and shivering during blockade in 13 patients.
CONCLUSIONS: Under high thoracic or cervico-thoracic blockades with decreased anesthetic solution doses and volumes, there have been upper limbs and pulmonary functions motor repercussions. However, according to preliminary observations and this study, spirometric changes were statistically significant, but without clinical expression in respiratory dynamics, being essentially more a consequence of intercostal nerves than of phrenic nerve paralysis.
Key Words: ANESTHESIA, Ambulatorial; ANESTHETIC TECHNIQUES, Regional: thoracic epidural
JUSTIFICATIVA Y OBJETIVOS:
Sobre bloqueo peridural torácico bajo o medio, las alteraciones hemodinâmicas
son fácilmente controladas. Como el bloqueo peridural torácico alto
(T2-T3) acomete, frecuentemente, las raíces del plexo
braquial (C4)C5-T1(T2), algunas
de estas responsables por la formación del nervio frénico (C3-C4-C5)
es de suponer, posibles repercusiones motoras de este último. El presente
estudio realizado en cirugías estéticas, sobre bloqueo peridural segmentar
aislado en T2-T3 o asociado al bloqueo peridural segmentar
en T11-T12, evaluó las repercusiones motoras en la
dinámica respiratoria así como en los miembros superiores e inferiores.
MÉTODO: Treinta y dos pacientes, estado físico ASA I y II, sin molestia pulmonar broncoespástica, en actividad y peso corporal igual o superior a 50 kg, fueron sometidos a 21 bloqueos peridurales torácicos aislados en T2-T3 y las 11 restantes, a bloqueos peridurales torácicos en T11-T12, con ropivacaína a 7,5% (45 a 90 mg) asociada al sufentanil (10 a 20 µg). Repercusiones hemodinámicas, respiratorias y motoras en los miembros superiores e inferiores fueron evaluadas respectivamente, sobre monitorización no invasiva, espirometria, fuerza de preensión de la mano y escala de Bromage.
RESULTADOS: La media de duración de las cirugías mamarias fue de 105 min con depresión motora de los miembros superiores (p < 0,001), con recuperación motora aconteciendo a los 117,2 ± 51,3 min y la primera manifestación de dolor a los 485 ± 221,2 min. Las cirugías combinadas, que tuvieron una duración media de 165 min, con depresión motora de los miembros inferiores grado 1, en 40% y grado 2, en 60% de los pacientes por la escala de Bromage, cuya recuperación ocurrió 223,9 ± 57,1 min y la primera manifestación de dolor en reposo, a los 555 ± 197,9 min. Las funciones pulmonares, VEF1 (l/seg); PFE (l.min-1); CVF (litros) se presentaron alteradas respectivamente, en 15,20% (p < 0,009); 13,36% (p < 0,029) y 18,09% (p < 0,007), con elevación de 8,75% del VEF1/CVF (p < 0,162). Hipotensión arterial (< 30 % de los valores iniciales) y bradicardia (< 55 bpm) ocurrieron en cinco pacientes y tremores durante los bloqueos, en trece pacientes.
CONCLUSIONES: Sobre bloqueo torácico alto o cérvico-torácico con dosis y volúmenes reducidos de soluciones anestésicas, ocurren repercusiones motoras en los miembros superiores y en las funciones pulmonares. Entre tanto, a juzgar por observaciones preliminares y del presente estudio, las alteraciones espirométricas fueron estadísticamente significativas, pero, sin expresión clínica en la dinámica respiratoria, siendo esencialmente decurrentes de la parálisis de los nervios intercostales, más que del nervio frénico.
Mastectomies and thoracoplasties under thoracic epidural block were firstly performed more than 50 years ago1. Since then, few studies on the subject have been published. In addition to Figueiredo1, other Brazilian studies have outlined segmental epidural anesthesia with low anesthetic volumes for cervico-brachial procedures2 and thoraco-abdominal plastic surgeries3. However, when segmental epidural anesthesia is not the objective, large anesthetic volumes are needed, especially for associated surgeries4. All authors1-4 emphasize hemodynamic changes and have shown that these can be controlled. Thoraco-abdominal motor involvement affecting pulmonary functions, however, has only been evaluated in a small series of patients submitted to high abdominal wall surgeries with epidural blockade of the lower thoracic third (T8-T9)5. Since high thoracic epidural block often affects brachial plexus roots (C4-C5-T1-T2), some of them responsible for phrenic nerve formation (C3-C4-C5), potential motor repercussions in this nerve are to be expected. Spirometric evaluations of respiratory dynamics, however, have indicated unchanged or mildly decreased pulmonary tests6. This study, performed with female patients submitted to cosmetic surgeries under segmental epidural block in T2-T3 and in T11-T12 with low volume of 7.5% ropivacaine plus sufentanil has objectively evaluated motor repercussions on upper (UL) and lower (LL) limbs7 and, indirectly, on respiratory muscles by pulmonary functions spirometric test.
After the Institution's approval and their consent, participated in this study 32 adult female patients, physical status ASA I and II, without active bronchospastic pulmonary disease, weighing 50 kg or above in whom the behavior of epidural blocks was randomly and continuously observed in outpatient setting. Blockades were distributed in 21 isolated blockades in T2-T3 and the 11 remaining blockades were combined with blockades in T11-T12. Peripheral venous access with 18G catheter was obtained and continuous 15 to 20 mL.kg-1 saline solution with glucose and lactated Ringer's were infused for the first 45 minutes, followed by maintenance rate to control hemodynamic stability. Noninvasive monitoring consisted of cardiac electric activity (continuous ECG with 5 electrodes placed on patients' dorsum), heart rate (bpm), systolic blood pressure (SBP), mean blood pressure (MBP), diastolic blood pressure (DBP) and hemoglobin oxygen saturation (SpO2), and was recorded at zero, 5, 15, 30, 60, 90, 120, 150 and 180 minutes. Before anesthetic block and in the sitting position, patients were informed about spirometric and upper limb motor tests. In both cases, values obtained for the last 19 patients before (control/reference values) and 20 minutes after blockade (study values) were compared. As from a deep breathe, the following were observed for epidural blocks in T2-T3: a) levels of high thoracic expansion amplitude as compared to low thoracic amplitude (level 0 = deep breathe without distortions between high and low thoracic expansion; level 1 = deep breathe with mild high thoracic distortion and normal low thoracic expansion; level 2 = deep breathe with moderate high thoracic distortion and normal low thoracic expansion; level 3 = deep breathe with marked high thoracic distortion or without high thoracic expansion and mild low thoracic distortion; level 4 = apnea); b) pulmonary function with portable Enhance VMI® spirometer (Clement Clarke International, Edinburgh); and c) upper limbs motor involvement by hand grasping an Erka®, Germany mercury column pressure cuff previously inflated to 40 mmHg (level 0 = normal grasping; level 1 = 33% grasping decrease as compared to baseline; level 2 = 33% to 66% grasping decrease as compared to baseline; level 3 = 66% to 100% grasping decrease as compared to baseline but still with digital movements). When combined with epidural block in T11-T12, motor block repercussions on lower limbs, hip and inguinal region were evaluated by modified Bromage's score7.
All patients were submitted to segmental epidural blocks aiming at decreasing local anesthetic dose and volume, in the sitting position with lower limbs pending outside the table, feet placed on a support, head bent with chin touching the externum, forearms over thighs and shoulders supported by a nurse positioned in front of them, under level 2 sedation according to Mackenzie's sedation score8 with intravenous titrated midazolam (1 to 3 mg). Three non-cooperative patients were excluded due to sedation level 3. After previously blocking punctures pathway (T2-T3 and T11-T12) with 2% lidocaine, an 18G Tuohy needle was introduced by median puncture until the epidural space, identified by loss of resistance to air. While isolated blockades in T2-T3 aimed at mammaplasties with or without tumescent axillary and arm posterior and medial faces (T1-T2) liposuctions (1 epinephrine ampoule in 400 mL saline), T11-T12 blockades aimed at combined surgical procedures, with high abdominal liposuctions and abdominplasty or low abdominal liposuctions of trochanter (L1-L2) and medial thigh region (L1-L3). In those cases, epidural access T11-T12 with 18G catheter positioned in the epidural space up to 4 cm, respectively in the cephalad direction for surgeries involving higher metamers and caudally for lower metamers was prioritized. Catheter patency was tested with 1 to 2 mL anesthetic solution and before fixing it on the skin until the suprascapular region, T2-T3 blockade was induced. In the sequence, after dorsal placement of electrodes, patients were placed in the supine position and slightly head up < 10º while lower limbs were wrapped and raised in the "open knife" position to prevent blood retention in lower extremities and to maintain Frank-Starling reflex. Twenty minutes after and with the blockade installed, a mild 45º head up position would allow for new pulmonary test measurement. In mammary surgeries, with or without arm or axillary liposuction, single dose anesthetic solution was 7.5% ropivacaine (6 mL = 45 mg) plus sufentanil (2 mL = 10 µg), in a total volume of 8 mL and slowly administered. For associated abdominal surgeries, the volume of the same mixture has varied 12 mL to 14 mL (75 to 90 mg of 7.5% ropivacaine and 10 µg sufentanil) as a function of weight, and was administered via catheter approximately 15 minutes after surgery completion. When needed, booster doses equivalent to 50% of the initial dose were administered for longer surgeries going beyond 200 minutes. Dermatomes level and sensitivity were evaluated by the anesthesiologist through 27G needle prick during mammaplasties, every 3 minutes until final blockade installation, approximately at 20 minutes, or by the surgeon with surgical clamp on metamers involved in combined interventions. All surgeries were performed under 2 L.min-1 oxygen flow via nasal catheter. Blockade adverse events were recorded.
Patients' demographics data (n = 32) and types of surgery are shown in table I.
Mean duration of isolated mammary surgeries or combined with arm liposuctions was 105 and 165 minutes, respectively, while mean total motor recovery was 117.2 ± 51.3 minutes (105 to 130 minutes). First pain complaint was at 485 ± 22.1 minutes (400 to 820 minutes). In combined surgeries, total lumbosacral motor recovery by Bromage's scale was 223.9 ± 57.1 minutes (198 to 327 minutes) and first pain complaint at rest at 555 ± 197.9 minutes (203 to 645 minutes). Three patients received booster dose.
Spirometric evaluations of respiratory dynamics under high thoracic epidural anesthesia are shwon below (table II).
Epidural block in T2-T3 of 29 patients (from 32 patients, 3 were excluded for non cooperation during tests) has recorded asymmetric sensory distribution as from C8 (Figure 1). Loss of cranial sensitivity was unequal in two patients in metamers C7 and C6 with predominance in one side, and in 3 patients in metamers C5 and C4. Caudal sensory block was uniformly located in T6-T7.
In parallel, upper limbs motor block has revealed pre-blockade (125.5 ± 21.9 mmHg)/post-blockade (79.9 = 26.7 mmHg) to the right, and pre-blockade (121.34 ± 23.44 mmHg)/post-blockade (85.4 ± 26.9 mmHg) to the left, which were clinically and statistically significant (p < 0.001). Motor intensity levels by grasping score were: right hand, level 1 = 15.8% (3 patients); level 2 = 36.8% (7 patients); level 3 = 47.4% (9 patients); left hand, level 1 = 31.6% (6 patients); level 2 = 47.4% (9 patients); level 3 = 21% (4 patients) (Figures 2, 3 and Table III).
As a function of catheter orientation in the epidural space, cranial sensory spread of T11-T12 has reached or overlapped lower T2-T3 blockade limits and caudal spread has reached the sacral region. Epidural motor block in T11-T12 was evaluated by modified Bromage's scale, recording level 1 or partial in 4 patients (40%) and level 2 or semi-complete in 6 patients (60%) (Figure 3).
Demographics data are shown in mean, standard deviation and amplitude. Bromage scale data, epidural blocks para-effects and spirometric pulmonary functions test were expressed in relative frequencies using paired Student's t test for variables EFP, VEF1, FVC and VEF1/FVC aiming at evaluating ventilatory parameters changes.
Paired Student's t test was used for Hand Grasping scores before and after T2-T3 blockade, and ANOVA parametric test (Analysis of Variance) for repeated measures followed by significant minimum differences test were used to compare hemodynamic means (SBP, MBP, DBP and HR). Significance level was p < 0.05.
In Brazil, epidural block has become popular for outpatient cosmetic mammaplasties with or without sedation. Continuous propofol4 or midazolam9 with or without fentanyl are titrated to obtain sedation levels in regional anesthesia. Because the level of sleepiness is a marker to determine sedation regardless of its pharmacological etiology, Mackenzie's Sedation Score8 was used for midazolam. The level of ideal sedation in regional anesthetic techniques is "conscious sedation"10 or level 28, especially when patient's cooperation is needed for some research tests.
Notwithstanding chest dermatomes for mammaplasties be located between T1-T5, there is the need to include cervical dermatome C5, whose root also participates in the formation of the phrenic nerve. As a function of nervous fibers thickness, regional anesthesia with local anesthetics on the neuraxis is dissociative, being more cranial for b fibers (sympathetic), and more caudal for Aa fibers (motor) and, in the intermediate position, sensory fibers. Three reasons are considered for such phenomenon: 1) higher motor fibers resistance as compared to sensory fibers; 2) insufficient anesthetic solution spread to reach at least three consecutive Ranvier nodules11 of motor roots located within the dural "sleeve" at intervertebral foramens level12; and 3) physiological susceptibility of nervous fibers to local anesthetics, as a consequence of sodium and potassium channels density and metabolic activity of ion pumps12.
Something similar must have happened with hand motor evaluation involving radial [C5-(T1)], median [(C5-T1] and ulnar [C7-(T1)] nerves, and with forearm bending through the cutaneous muscle (C5-C7). The act of closing the hand, squeezing or not objects, as well as the ability to bend and extend the elbow, recruit the referred nerves. Grasp exerted on a pressure cuff previously inflated to 40 mmHg of a mercury column, checked before and 20 minutes after blockade installation gives quantitative information about changes in hand motor activity. In general, anesthetized dermatomes do not overlap corresponding miotomes. This is what happens with upper limbs due to peripheral brachial plexus distribution and ropivacaine's pharmacokinetics in the epidural space.
Although epidural blocks in T2-T3 in our study have also recorded loss of sensitivity in C4, cranial anesthetic solution spread in the epidural space has not been uniform as from C8 with different sensory (Figure 1) and motor (Figure 2) block levels. Cranially, as from C7, medullary cervical widening caused by higher neural density aimed at upper limbs, results in epidural space decrease and may influence anesthetic solution spread. In addition to epidural space narrowing, there are other causes14 although there are divergences as to the role of "plica mediana dorsalis"15, which is the conjunctive band between dura and ligamentum flavum in the epidural space dividing it in one ventral and two postero-lateral compartments16. Since ropivacaine has high anesthetic dissociation as compared to bupivacaine, and especially in relation to lidocaine when added to sufentanil of intense segmental lipophylic property, it may asymmetrically impregnate the narrow cervical epidural space. Both were chosen due to these pharmacological properties to obtain good metameric anesthesia with low risk for respiratory depression as compared to hydrophilic morphine.
In addition to diaphragm, sternocleidomastoid (C2-C3)17, medium (C3-C4)17, anterior and posterior (C5-C8)18 scalene muscles participate in deep breathe. On the other hand, lower intercostal nerves participate on diaphragm innervation17. As a function of these uniquenesses, it is supposed that motor medullary integrity of the cervical contingent, including the phrenic nerve, in the presence of motor paralysis of all intercostal muscles, will assure respiratory continuity and vice-versa19,20. However, cervical epidural blockade, according to some investigators6,21, determines a certain involvement of the phrenic nerve with 25% decrease in VEF1 and 9% in PaO2, although without clinical expression. Conversely, Wittich et al.22, inducing epidural block in C7-T1 with 18 mL of 0.5% bupivacaine or 1% mepivacaine, during head and neck surgeries, some of them extending to the chest for oncologic mastectomies, have observed and increase in VEF1 in patients with chronic obstructive pulmonary disease. Similarly, with tracheostomy metamers level C3 and C4 under epidural block in C7-T1, with loss of sensitivity in C2, with 6 mL of 1.5% lidocaine, there has been no spontaneous ventilation decrease22. In this patient, "handshaking" test was normal.
Motor depression of intercostal muscles may be evaluated by coughing24, by clinical observation of chest expansion during deep breathe, by magnetometry of forced chest expansion25, by electromyography, by arterial blood gas analysis or spirometric test. Total pulmonary capacity is obtained with maximum inspiration and expiration as fast and intense as possible in a portable spirometer to obtain Forced Vital Capacity (FVC). Other pulmonary functions may be evaluated during this expiratory maneuver, such as Forced Expiratory Volume in the first second (FEV1) and Expiratory Flow Peak (EFP). FEV1 is more easily reproduced for being effort-dependent, but EFP is also a good indicator in the initial stage of breathing where internal intercostal muscles (T1-T11) and abdominal muscles (T6-L1) have active participation. According to arterial blood gas analysis and spirometric tests, high thoracic epidural block should not be the reason for respiratory distress. Although the sensation of dispnea may5,21 or not26,27 be a consequence of mild hypercapnia, respiratory distress referred by few patients may be a consequence of the excitation of "J" receptors of alveolar walls, as result of blood accumulation or vasodilation by thoracic sympathetic block, especially in dependent regions28, or by partial blockade of respiratory muscles motor fibers with decreased respiratory dynamics, phenomenon especially observed in anxious patients.
Most of the times, hemoglobin desaturation depends on respiratory depression promoted by preanesthetic opioids or associated to epidural or spinal anesthetic solutions, changes in chest compliance29, tachypnea with low tidal air volume resulting in low effective alveolar ventilation and inhaled O2 concentration. Since patients in our study have received oxygen via nasal catheter during the procedures, values obtained were stable or slightly higher that baseline values (Figure 4). It is worth highlighting that anxiety and sedation may influence oximetry. In fact, this has been observed in some anxious and worried patients who presented tachypnea and initial oximetry values lower than intraoperative values during "conscious" sedation with midazolam.
Under lumbar epidural block, the persistence of abdominal and lower limbs motor activity is relevant during labor and hospital discharge in outpatient procedures, respectively. In our study, we have given priority to motor function in territories reached by epidural block in lower limbs by Bromage score7, for being more practical and doable than Van Zundert et al. Score30, because according to the latter, as from the supine position, not all patients are able to bend the trunk toward lower limbs.
Muscle shivering during blockade might not have been a sign of bupivacaine toxicity, due to the low dose used, but rather a thermoregulating reflex in an attempt to maintain body temperature as opposed to heat dissipation by peripheral vasodilation of sympathetic block.
Circulatory changes promoted by high thoracic epidural anesthesia are related to sympathetic block which decreases heart rate (negative chronotropism) and contractility (negative inotropism). In relaxed volunteers, plasma catecholamine levels during different epidural blockade levels (T8, T4, C8) have not recorded significant norepinephrine decrease, suggesting that chemical sympathectomy is only partial31 and that compensatory vasoconstriction of other territories not affected by nervous block attenuates blood pressure decrease.
Outpatient setting discharge after epidural block implies motor block recovery of affected limbs without residual instability on upper limbs. Hand motor function evaluation is also a criterium for hospital discharge. However, since there is no quantitative test for upper limbs involvement, subjective "handshaking" test was replaced by an adaptation of Bouaziz et al.'s technique32 to determine hand muscle strength. Motor control of lower limbs, responsible for orthostatic posture stability without dizziness, should allow normal ambulation without help. In parallel, the presence of spontaneous micturition, hemodynamic stability, tolerance to food intake, lack of nausea and vomiting, and postoperative analgesia complete discharge criteria33.
Two thirds of phrenic roots partially participate on upper limbs plexus formation, especially it if is pre-fixed. Although most authors have not observed possible motor repercussions on upper limbs under high thoracic or cervico-thoracic blockades with decreased anesthetic doses and volumes, these in fact occur, as it has been quantitatively shown in this study by the pressure cuff with mercury column. However, according to preliminary observations and to this study, mild spirometric changes without clinical repercussions are observed under thoracic epidural block, being more a consequence of intercostal nerves paralysis than of phrenic nerve paralysis, resulting in respiratory dynamics preservation.
The author acknowledges the epidemiologist Tânia Hirakata and Martin Geier for their help in this study.
01. Figueiredo RR - Nossa experiência com 1201 casos de anestesia extradural. Rev Bras Cirurgia, 1948;133-152. [ Links ]
02. Gouveia MA, Ribeiro RC - Anestesia peridural cérvico-torácica. Rev Bras Anestesiol, 1974;24:238-248. [ Links ]
03. Leão DG - Peridural torácica: estudo retrospectivo de 1240 casos. Rev Bras Anestesiol, 1997;47:138-147. [ Links ]
04. Nociti JR, Serzedo PSM, Zuccolotto EB et al - Ropivacaína em bloqueio peridural torácico para cirurgia plástica. Rev Bras Anestesiol, 2002;52:156-165. [ Links ]
05. Imbelloni LE - Avaliação da função motora abdominal e parâmetros ventilatórios após peridural torácica. Rev Bras Anestesiol, 1988;38:233-236. [ Links ]
06. Stevens RA, Frey K, Sheikh T et al - Time course of the effects of cervical epidural anesthesia on pulmonary function. Reg Anesth Pain Med, 1998;23:20-24. [ Links ]
07. Bromage PR - A comparison of the hydrochloride and carbon dioxide salts dioxide salts of lidocaine and prilocaine in epidural analgesia. Acta Anaesthesiol Scand, 1965;16:(Suppl):55-69. [ Links ]
08. Mackenzie N, Grant IS - Propofol for intravenous sedation. Anaesthesia, 1987;42:3-6. [ Links ]
09. Geier KO, Rocha VHB - Bloqueio contínuo do plexo lombar via compartimento ilíaco, combinado com bloqueio contínuo do nervo femoral em trauma grave de membro inferior. Relato de caso. Rev Bras Anestesiol, 2001;51:53-58. [ Links ]
10. Gwirtz KH - Single-Dose Intrathecal Opioid in the Management of Acute Postoperative Pain, em, Sinatra RS, Hord AH, Ginsgerg B et al - Acute Pain. St Louis. Mosby Year Book, 1992;253-268. [ Links ]
11. Carpenter RL, Mackey DC - Local Anesthetics, em, Barash PG, Cullen BF, Stoelting RK - Clinical Anesthesia. Philadelphia. JB Lippincott, 1989;371-403. [ Links ]
12. Fink BR - Mechanism of differential epidural block. Anesth Analg, 1986;65:325-329. [ Links ]
13. Raymond SA, Strichartz GR - The long and short of differential block. Anesthesiology, 1989;70:725-728. [ Links ]
14. Sala-Blanch X, Izquierdo E, Fita G et al - Maintained unilateral analgesia. Acta Anaesthesiol Scand, 1995;39:132-135. [ Links ]
15. Asato F, Hirakawa N, Oda M et al - A medium epidural septum is not a common cause of unilateral epidural blockade. Anesth Analg, 1990;71:427-429. [ Links ]
16. Peduto VA, Tani R, Marinelli L et al - Bilateral analgesia and unilateral paresis after lumbar epidural blockade. Anesth Analg, 1992;74:294-296. [ Links ]
17. Gray H - Anatomia. 29ª Ed, Rio de Janeiro. Guanabara Koogan, 1977;782-788. [ Links ]
18. Netter FH - Atlas of Human Anatomy. Novartis. New Jersey. Ninth Printing, 1997;405. [ Links ]
19. Kainuma M, Shimada Y, Matsuura M - Cervical epidural anaesthesia in carotid artery surgery. Anaesthesia, 1986;41: 1020-1023. [ Links ]
20. Bonnet F, Derosier JP, Pluskwa F et al - Cervical epidural anaesthesia for carotid artery surgery. Can J Anaesth, 1990;37: 353-358. [ Links ]
21. Takasaki M, Takahashi T - Respiratory function during cervical and thoracic extradural analgesia in patents with normal lungs. Br J Anaesth, 1980;52:1271-1276. [ Links ]
22. Wittich DJ, Berny JJ, Davis RK - Cervical epidural anesthesia for head and neck surgery. Laryngoscope, 1984;94:615-619. [ Links ]
23. Ullman DA, Schmitt L - Tracheostomy performed under cervical epidural blockade. Anesthesiology, 1989;71:161-162. [ Links ]
24. Mineo R, Sharrock NE, Castellano P et al - Effects of adding epinephrine to epidural bupivacaine assessed by thoraco-abdominal muscle strength. Reg Anesth, 1990;15:A1. [ Links ]
25. Urmey WF - Marked distortion of rib cage expansion during epidural anesthesia as measured by magnetometry. Reg Anesth, 1990;15:(Suppl):70. [ Links ]
26. Egbert LD, Tamersoy K, Deas TC - Pulmonary function during spinal anesthesia: the mechanism of cough depression. Anesthesiology, 1961;22:882-885. [ Links ]
27. Askrog VF, Smith TC, Eckenhoff JE - Changes in pulmonary ventilation during spinal anesthesia. Surg Gynecol Obstet, 1964;119:563-567 [ Links ]
28. Guyton AC - Tratado de Fisiologia Médica. Rio de Janeiro. Guanabara Koogan, 1988;446-456 [ Links ]
29. Novaes MVM, Francisco CRL, Pimenta KB - Estudo comparativo entre bupivacaína a 0,25% e ropivacaína a 0,2% em anestesia peridural para cirurgia torácica. Rev Bras Anestesiol, 2001;51:493-502. [ Links ]
30. Van Zundert A, Vaes L, Van der AaP et al - Motor block during epidural anesthesia. Anesth Analg, 1986;65:333-336. [ Links ]
31. Stevens RA, Artuso JD, Kao TC et al - Changes in human plasma catecholamine concentrations during epidural anesthesia depend on the level of block. Anesthesiology, 1991;74: 1029-1034. [ Links ]
32. Bouaziz H, Vial F, Jochum D et al - An evaluation of the cutaneous distribution after obturator nerve block. Anesth Analg, 2002;94:445-449. [ Links ]
33. Bello CN - Recuperação pós-anestésica - escalas de avaliação, princípios gerais. CEDAR - Centro de Estudos de Anestesiologia e Reanimação da Disciplina de Anestesiologia da FMUSP, 2000;Ano IV:4-9. [ Links ]
Dr. Karl Otto Geier
Address: Rua Cel. Camisão, 172
ZIP: 90540-030 City: Porto Alegre, Brazil
Submitted for publication July 21,
Accepted for publication November 06, 2003
* Received from Clínica Rio Branco de Porto Alegre, RS