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Revista Brasileira de Anestesiologia

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

Rev. Bras. Anestesiol. vol.56 no.6 Campinas Nov./Dec. 2006 



Hypobaric 0.15% bupivacaine versus hyperbaric 0.5% bupivacaine for posterior (dorsal) spinal block in outpatient anorectal surgery*


Bupivacaína a 0,15% hipobárica para raquianestesia posterior (dorsal) versus bupivacaína a 0,5% hiperbara para procedimientos quirúrgicos anorrectales en régimen ambulatorial



Luiz Eduardo Imbelloni, TSAI; Eneida Maria Vieira, TSAI; M. A. Gouveia, TSAI; João Gomes NetinhoII; José Antonio CordeiroIII

IDiretor do Instituto de Anestesia Regional, Hospital de Base da FAMERP
IIChefe da Disciplina de Coloproctologia da Escola de Medicina da FAMERP
IIIProfessor da Escola de Medicina da FAMERP

Correspondence to




BACKGROUND AND OBJECTIVES: The aim of this study was to study low dose hypobaric 0.15% bupivacaine and hyperbaric 0.5% bupivacaine in outpatient anorectal surgical procedures.
METHODS: Two groups of 50 patients, physical status ASA I and II, undergoing anorectal surgical procedures in a jackknife position, received 6 mg of hypobaric 0.15% bupivacaine in the surgical position (Group 1) or 6 mg of hyperbaric 0.5% bupivacaine in the sitting position for 5 minutes, after which they were placed in a jackknife position (Group 2). Sensitive and motor blockade, time of first urination, ambulation, complications, and the need for analgesics were evaluated. Patients were followed until the third postoperative day and questioned whether they experienced post-puncture headache or temporary neurological symptoms, and until the 30th day and questioned about permanent neurological complications. The test t Student, Mood's median, and Fisher Exact test were used for statistical analysis, and a p < 0.05 was considered significant.
RESULTS: Every patient in Group 1 presented selective blockade of the posterior sacral nerve roots, while patients in Group 2 experienced blockade of the anterior and posterior nerve roots. Blockade was significantly higher in Group 1. Motor blockade was significantly less severe in Group 1. Forty-nine patients in Group 1 transferred to the stretcher unassisted while only 40 patients in Group 2 were able to do so. Recovery in Group 1 occurred in 105 ± 25 minutes and in 95 ± 15 minutes in Group 2, and this difference was not statistically significant. There were no hemodynamic changes, nausea or vomiting, urine retention, or post-puncture headache.
CONCLUSIONS: Anorectal surgical procedures under spinal block with low dose bupivacaine, hyperbaric or hypobaric, can be safely done.

Key Words: ANESTHETICS, Local: bupivacaine; ANESTHETIC TECHNIQUES, Regional: hypobaric spinal block; SURGERY: Proctologic.


JUSTIFICATIVA Y OBJETIVOS: Estudiar baja dosis de bupivacaína hipobárica a 0,15% e hiperbara a 0,5% en pacientes ambulatoriales para procedimientos quirúrgicos anorrectales.
MÉTODO: Dos grupos de 50 pacientes, estado físico ASA I y II, sometidos a intervenciones quirúrgicas anorrectales, en posición de cuchilla, recibieron 6 mg de bupivacaína a 0,15% hipobárica en la posición quirúrgica (Grupo 1) o 6 mg de bupivacaína a 0,5% hiperbara en la posición sentada por cinco minutos, y después colocados en posición de cuchilla (Grupo 2). Se evaluaron los bloqueos sensitivo y motor, primera micción, deambulación, complicaciones y necesidad de analgésico. Se monitorearon hasta el tercer día de postoperatorio y preguntados sobre cefalea pospunción o síntomas neurológicos temporales, y hasta 30 días sobre complicación neurológica permanente. Para análisis estadística fueron utilizadas las pruebas t de Student, mediana de Mood y Exacto de Fisher, siendo p < 0,05 significativo.
RESULTADOS: El bloqueo selectivo de las raíces sacrales posteriores se obtuvo en todos los pacientes del Grupo 1 y bloqueo de las raíces anteriores y posteriores se observó en los pacientes del Grupo 2. El bloqueo fue significativamente más alto en el Grupo 1. El bloqueo motor fue significativamente menos intenso en el Grupo 1. Cuarenta y nueve pacientes del Grupo 1 pasaron para la cama sin ayuda mientras que solamente 40 pacientes del Grupo 2 lograron hacerlo. La recuperación se dio en 105 ± 25 minutos en el Grupo 1 y de 95 ± 15 minutos en el Grupo 2, sin diferencia significativa. No se dio alteración hemodinámica, náusea o vómito, retención urinaria o cefalea pospunción.
CONCLUSIONES: La intervención quirúrgica anorrectal bajo raquianestesia con bajas dosis de bupivacaína, hiperbara o hipobárica, puede ser hecha con seguridad.




In the past, patients undergoing surgerys remained in the hospital for several days after the surgery. Economical and social pressures forced surgeons and anesthesiologists to change this practice. Nowadays, about 60% to 70% of all elective surgical procedures in the United States and in some European countries are done in an outpatient basis 1. Outpatient surgical procedures are also done in patients with more severe conditions 2,3.

Nowadays, spinal block for outpatient surgical procedures is being challenged by the new general anesthetics that allow the patient to be discharged after a short recovery period 4-7.

Pavlin et al. 5, demonstrated that patients who received conventional doses of anesthetics for spinal blocks had longer recovery time and hospital stay than those who received general anesthesia. However, spinal anesthesia has fewer side effects than general anesthesia, better cost/efficacy relationship, and is very well accepted by patients.

Conventional doses used in spinal block may be inadequate for outpatient usage; therefore, anesthesiologists need to familiarize themselves with techniques that present a rapid recovery profile. Most of them know the technique of spinal block with conventional doses for saddle block for perineal and anorectal surgeries. Nevertheless, this technique is not widely used and is not suitable to be used in an outpatient basis. The dose is more important than the concentration or volume of the local anesthetic regarding the distribution of the spinal block, especially when the solution has the same density of the cerebrospinal fluid. Recently, it was reported the successful use of selective spinal block 8. Lidocaine (25 mg) with fentanyl (25 µg) or ropivacaine (4 mg) with fentanyl (25 µg) were used for low spinal block maintaining the patient in a sitting position for 10 minutes. This study demonstrated that low dose ropivacaine (4 mg) is similar to lidocaine (25 mg) in promoting adequate anesthesia for outpatient anorectal surgeries.

A previous study used 7.5 mg of hypobaric 0.15% bupivacaine after removing 3 to 5 mL of cerebrospinal fluid (CSF), obtaining unilateral block in 71% f the patients 9. Another study using 5 mg of 0.15% hypobaric bupivacaine demonstrated that it was not necessary to remove CSF, since the success rate was virtually the same, with 75% of unilateral spinal block 10.

Three approaches to lumbar somatic nerve block were described. The patient may be in the sitting position, in lateral decubitus, or ventral decubitus. Currently, surgical procedures are still performed in hospitalized patients. The potential benefits of performing this type of procedure in an outpatient basis include a fast return home, reduction in the risk of nosocomial infections, and lower costs.

The aim of this prospective study was to compare low dose hypobaric 0.15% bupivacaine with low dose hyperbaric 0.5% bupivacaine in outpatient anorectal surgical procedures.



After approval by the Ethics Committee and signing of the informed consent, 100 patients, physical status ASA I and II, 20 to 60 years, old were selected to undergo elective anorectal surgery in ventral decubitus. Exclusion criteria included hypovolemia, coagulation disorders, and patient's refusal of the method. Monitoring included non-invasive blood pressure, ECG, heart rate, and pulse oxymeter. Patients did not receive premedication. They were all fasting for 6 hours. Before the subarachnoid block, each patient received IV fentanyl, 1 µ Anesthesia failure was defined as absence of perineal analgesia. Hydration was done with IV Ringer's lactate, up to a maximum of 500 mL during the entire procedure.

Spinal block was the main anesthetic technique. A table with numbers, in a proportion of 1:1, was randomly generated by a computer. The patient's number was placed in an envelope and given to the anesthesiologist before the procedure. Patients were placed in one of the following groups: Group 1: hypobaric bupivacaine (n = 50), spinal block with 6 mg of hypobaric bupivacaine (prepared from 7.5 mg of the 0.5% isobaric solution diluted in 3.5 mL of bidestilled water) and Group 2: hyperbaric bupivacaine (n = 50), spinal block with 6 mg of the commercially available hyperbaric bupivacaine (with 8% dextrose in water) (Table I).



After cleansing the skin with alcoholic chlorhexedine and removing the excess solution, subarachnoid puncture was done with the patient in ventral decubitus with a 25 cm pad placed under the abdomen (Group 1) or with the patient in a sitting position (Group 2), in the L3-L4 space, through the median approach, using a 27G Quincke needle (B. Braun Melsungen) without introducer. After drainage of cerebrospinal fluid to confirm needle placement, 6 mg of hypobaric 0.15% bupivacaine or 6 mg of hyperbaric 0.5% bupivacaine at 1 mL.15s-1 were administered. Patients in Group 1 were in ventral decubitus until the end of the surgical procedure. Patients in Group 2 were in a sitting position for five minutes, after which they were placed in ventral decubitus, in a jackknife position.

Assessment of the sensitive blockade was done every minute. After determining the latency time, the assessment was done every 5 minutes until the 20th minute. The latency time was defined as the length of time until there was a loss of sensibility in the region corresponding to the puncture level. In Group 1 the assessment was done with the touch of the needle and in Group 2 the assessment was done by the patient informing whether he had any feelings in the perineal region. Assessment of the motor blockade of the lower limbs was done using the modified Bromage scale (0 to 3) 11: 0 = free movement of the lower limbs; 1 = unable to raise extended limb; 2 = unable to bend the knee; 3 = unable to move the ankle. Motor and sensitive blockades were evaluated in both lower limbs at 10, 20, 30, 40, and 60 minutes, as well as at the end of the surgical procedure. The duration of the analgesia was determined by the length of time it took the patient to regain perineal sensibility. The duration of the motor blockade was defined as the length of time it took until the patient fully recovered muscular activity in the lower limbs. Hemodynamic parameters were evaluated every three minutes in the first 15 minutes, and every five minutes until the end of the surgical procedure.

Hypotension, defined as a reduction in systolic blood pressure greater than 30% of baseline values, would be treated initially with volemic expansion. If it did not improve, successive doses of etilephrine, 2 mg, would be administered. Bradycardia was defined as a reduction in heart rate below 50 bmp and would be treated with atropine, 0.75 mg. Every patient received O2 (1 to 2 L.min-1) through a Hudson mask. Sedation during the procedure was maintained with small doses of midazolam. Fentanyl (50 µg) would be administered if the patient complained of discomfort.

Before being discharged from the clinic, an anesthesiology resident (AR) recorded the patient's satisfaction with the technique that was classified as good, satisfactory, or bad. Patient's were released four hours after the surgery if the vital signs were stable for more than one hour and they were oriented, did not complaint of nausea or pain, and had no signs of bleeding, were able to swallow liquids, urinate, get dressed, and walk on a straight line. Every patient was followed over the phone until the third postoperative day and questioned whether they experienced post-puncture headache or any transitory neurological symptom, and up to the 30th day regarding any permanent neurological complication.

The data regarding the length of time between the injection and the resolution of the motor and sensitive blockades, until the first spontaneous urination, until ambulation, and until the patient was able to be discharged according to the study's discharge criteria, as well any complications in the posthanestetic recovery unit, the need for urinary catheter, and pain treatment were recorded by an observer. Analgesia was done with Tramadol, 50 mg PO every 8 hours at the day of the surgery. The test t Student was used to compare two samples of the demographic data; Mood's median was used for the motor and sensitive blockades; and Fisher's Exact test was used to compare the percentage of the blockade characteristics. Values of p refer to paired tests, and a p < 0.05 was considered statistically significant.



There were no significant differences between the groups regarding weight and BMI, but the patients in Group 1 were older and taller than the patients in Group 2 (Table II). Adequate analgesia was achieved in both groups.

Sensitive blockade was significantly higher in Group 1 in every evaluation. At 20 minutes the blockade varied from S2 to T10, with T12 as the mode in Group 1, and from S2 to T11, with L2 as the mode in Group 2 (Figure 1). Latency time was significantly higher in Group 1 (Table III), but the duration of the blockade showed no significant difference (Table II). The mean time for recovery from the blockade was 105 ± 25 minutes in Group 1, and 95 ± 15 in Group 2 and this difference was not statistically significant (Table III).



Table III shows the motor blockade in the lower limbs, which was significantly less severe in Group 1 (Table IV). Motor blockade degrees 1 and 2 were observed in 4 patients (8%) in Group 1 and 41 patients (82%) in Group 2 at 20 minutes. At 60 minutes, 42 patients (84%) in Group 1 did not present motor blockade while only 5 patients (10%) in Group 2 did not. At the end of the surgery, 49 patients in Group 1 transferred to the stretcher on their own, while only 40 patients in Group 2 did so.







The spinal block was adequate for the surgery in both groups. There were no changes in blood pressure and heart rate, and there were no episodes of nausea or vomiting. There were no cases of urinary retention or post-puncture headache. There were no complaints of lumbar pain, or pain in the buttocks or legs that could be classified as transitory neurological symptoms (TNS), and no neurological complications were recorded. Both groups of patients considered the anesthesia good.



Low dose hypobaric 0.15% bupivacaine (6 mg), at 1 mL.15s-1 through a 27G Quincke needle (Group 1), blocked only the posterior nerve roots (sensitive) in 84% of the patients. The same dose of hyperbaric 0.5% bupivacaine blocked the posterior and the anterior nerve roots (sensitive and motor) in every patient. The highest sensitive blockade obtained with the hypobaric solution is probably due to the larger volume (4 mL) administered, to achieve the same dose (6 mg), compared to 1.1 mL of the hyperbaric solution. In most hospitals, spinal block is the technique used most often for anorectal surgeries. This form of regional anesthesia is not adequate to be used in patients scheduled to return home after a few hours. The spinal block performed with the patient in ventral decubitus provided for surgical quality analgesia with excellent relaxation of the sphincter, and lasting long enough in every patient. Most importantly, it allowed the patient to remain in a jackknife position, providing for greater surgical exposure. But the relaxation of the puborectalis muscle was not adequate. Consequently, deeper rectal lesions (p. ex., high fistulas, rectal polyps) cannot be removed 12. Besides, very anxious patients who might be submitted to more prolonged surgical procedures, are not good candidates for this anesthetic technique.

The solution of 0.15% bupivacaine was chosen because it guarantees that the necessary hypobaric solution is achieved 9,10. By definition, the baricity of a solution is determined by the relationship between its density and the density of the CSF. The mean density of the CSF is 1.00059 ± 0.00020 g.mL-1 13. The baricity of local anesthetics can be reduced by diluting them in distilled water. 0.5% bupivacaine with 8% dextrose in water is hyperbaric for every patient. The baricity of 0.15% bupivacaine is 0.9954 g.mL-1 at 37°C and, therefore, hypobaric for every patient. This was confirmed when 42 patients presented pure sensitive blockade (blockade of the posterior roots only) when the puncture was done with the patients in ventral decubitus, and only eight demonstrated some degree of motor blockade.

In 1961, Tanasichuck et al. 14 described a particular technique of spinal block in patients who underwent orthopedic procedures of a lower limb. They called it spinal hemianalgesia. A unilateral spinal block can only produce a unilateral motor blockade and a sensitive blockade affecting the same side. There are three membranes protecting the spinal cord inside the vertebral canal: pia mater, arachnoid, and dura mater. Between the pia mater and the arachnoid we find the subarachnoid space, used for the administration of spinal anesthesia. This space contains cerebrospinal fluid (CSF), spinal nerves, a trabecular network between the membranes, blood vessels that supply the spinal cord, and lateral extensions of the pia mater, the denticulate ligaments. The denticulate ligaments provide lateral support to the spinal cord, inserting in the dura mater. In theory, they may be important when a unilateral or mapped spinal block results from what appeared to be a technically adequate blockade15. The targets of the anesthetics are the spinal nerves and the spinal cord. The same way as the volume of the CSF, individual variations in the anatomy of the spinal nerves may explain the variability in spinal blocks 16,17. Recent autopsies and microscopic studies demonstrated a great variability, among individuals, in the size of the human dorsal nerve roots. Other interesting anatomic results include the greater relative size of the dorsal nerve roots when compared to the ventral nerve roots, which can be easily separated in smaller bundles 17. Although a large dorsal nerve root might seem to be more impenetrable to the local anesthetic, the separation in bundles creates a wider surface for the penetration of the anesthetic than the apparently smaller ventral nerve root. This anatomic characteristic might help explain the relative ease of the sensitive blockade compared to the motor blockade.

In this study, the positioning of the patients and the doses of the anesthetics were projected to obtain preferentially a sacral blockade while at the same time attempting to avoid the motor blockade in the lower limbs. Performing the spinal block with the patient in ventral decubitus using low dose of a hypobaric solution produced sensitive blockade in 42 patients, while in the hyperbaric bupivacaine Group, who remained in the sitting position during the administration of the anesthetic, only five patients presented pure sensitive blockade. Higher doses of the local anesthetic or dorsal decubitus were associated with a more prolonged motor blockade, demanding help to position the patients. One of the advantages when the motor blockade was minimal or absent was the patients' ability to position themselves on the table without help after the block. This was confirmed by 49 patients who transferred themselves from the stretcher to the table without assistance, compared to 40 patients that received the hyperbaric solution.

The spinal block confined to the perineum, buttocks, and medial aspect of the thighs is called saddle block. The drugs recommended for anorectal surgeries are hyperbaric 0.5% bupivacaine, hyperbaric 5% lidocaine, and 5% pethidine. Patients must remain in the sitting position for 5 minutes. The saddle block was compared to 5% pethidine, 0.5, and 1 mL 5% lidocaine (50 mg) 18. The latency time and motor blockade with lidocaine were smaller than with pethidine. However, the sensitive and motor blockades lasted longer with pethidine. In another study, the authors compared the three different methods of regional anesthesia in patients who underwent transurethral resection of the prostate 19. Saddle block presents some advantages because it produces adequate analgesia, maintains the hemodynamic balance, and has a smaller degree of motor blockade when compared with the spinal block and epidural anesthesia. Saddle block with low dose hyperbaric 0.5% bupivacaine produced complete motor blockade in only two patients. Similar to the low dose of the hypobaric solution, low dose hyperbaric bupivacaine did not produce cardiovascular changes.

Control of postoperative pain is another concern. The postoperative pain after anorectal surgery is severe, requiring the use of IV opioids, which are commonly used in hospitals. There are reports on the success of morphine infusion with a pump for home administration, but it is a nuisance and increases the costs of the treatment 20. Tramadol has been used, being very useful, since it provides for equivalent analgesia without the side effects of nausea, psychomotor changes, respiratory depression, changes in the gastrointestinal rhythm, and the possibility of urinary retention. Since tramadol is available for parenteral and oral administration, analgesia can be continued with the oral form after an initial IV dose while still in the hospital, immediately after the procedure.

Urinary retention is a common complication of anorectal surgeries, especially hemorrhoidectomy 21-23. The mean prevalence reported for this complication is 15%, between 1% and 52% of the patients 22. It is believed that the anal pain and the manipulation cause an inhibitory reflex of the detrusor muscle via the pudendal nerves 24. In this study, none of the patients needed a vesical catheter.

When the patient is in a jackknife position, one should place a pad or pillow under his abdomen to reduce the lordosis and increase the intervertebral space at the time of the puncture of the subarachnoid space 25. In this study, patients' positioning and the doses of the anesthetics were calculated in order to achieve a blockade of the sensitive nerve roots while at the same time preventing weakness of the lower limbs.

The dose of 7.5 mg of hypobaric 0.15% bupivacaine associated with fentanyl has a recuperation period of 2.94 hours 9, similar to the 2.96 hours obtained with 6.1 mg of 0.18% bupivacaine 26. Reducing the dose of hypobaric 0.15% bupivacaine to 5 mg reduces the recovery time to 2.32 hours, representing a 10% reduction in the recuperation time 10. In this study, the hyperbaric solution presented a shorter recuperation time, but there was no statistically significant difference when compared to the other group.

Several authors have demonstrated the benefits of local anesthesia for anorectal surgery under sedation 27,28. This technique eliminates the risk of post-puncture headache, postural hypotension, urinary retention associated with the spinal block, without increasing the risk of perineal infection. The incidence of post-puncture headache should not be a limiting factor for the choice of spinal blocks if smaller caliber needles are used. The 27 G needle seems to be a consensus. Although local anesthesia with sedation is a viable alternative for spinal block in anorectal surgeries, many anesthesiologists and surgeons prefer a technique that does not imply manipulation in the surgical field. This study demonstrated that anorectal surgery could be safely and effectively done on an outpatient basis. The main advantages of this method of spinal block for this procedure include hemodynamic stability, patient satisfaction with the absence of motor blockade in the lower limbs, and fast recovery. Besides, there must be an added benefit resulting from the reduction in the rate of urinary retention.

Neither Group presented TNS, demonstrating a difference when compared to higher doses (which present a 33% incidence of TNS) and lower doses (3.5%) of hypobaric lidocaine for knee surgery, confirming the importance of the low dose in this study. Another factor that might have contributed to the absence of TNS in this study was the use of a jackknife position. Other authors have suggested that the position might contribute for the development of TNS, especially when the lithotomy position is used and in the case of knee surgeries 29,10.

This prospective study demonstrated the safety and efficacy of the spinal block with low doses of hyperbaric or hypobaric bupivacaine for anorectal surgeries in a jackknife position on an outpatient basis. This technique was suitable for every procedure and patient.



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Correspondence to:
Dr. Luiz Eduardo Imbelloni
Av. Epitácio Pessoa, 2356/203 Lagoa
22411-072 Rio de Janeiro, RJ

Submitted for publication 13 de fevereiro de 2006
Accepted for publication 24 de julho de 2006



* Received from Instituto de Anestesia Regional, Hospital de Base da Faculdade de Medicina de São José do Rio Preto (FAMERP), São José do Rio Preto, SP

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