Patients in end-stage renal failure on long-term renal dialysis require anesthesia for the creation of arteriovenous fistulas (AVF). These patients may have anemia, diabetes mellitus, or cardiopulmonary disease. These medical problems may make general anesthesia undesirable (1). Brachial plexus block is often used to provide anesthesia for the creation of AVF (2). There are many potential advantages to a regional anesthetic with brachial plexus block in the creation of an AVF: decreased surgical stress (3), better vasodilation (2), avoidance of the stress of the induction of general anesthesia, and faster recovery and less hypotension because only a limited vascular bed is affected by the anesthetic. The brachial plexus may be blocked with four different techniques: interscalene, supraclavicular, infraclavicular, and axillary. The approach used depends on the site of operation. Although the supraclavicular and infraclavicular approaches are appropriate for AVF in the antecubital region, these techniques include the risk of pneumothorax and hemorrhagic injuries (4). In the axillary approach, vascular injury proximal to the AVF is a major concern for the vascular surgeon (1). Considering the above-mentioned problems, we used the interscalene approach for brachial plexus block to create an AVF in the antecubital region.
Brachial plexus blocks are performed on healthy patients with infrequent expected morbidity and mortality (5). Previous investigations reported that hemidiaphragmatic paralysis occurred in 100% of patients after interscalene brachial plexus block (IBP). The interscalene approach to brachial plexus anesthesia depresses pulmonary function as a consequence of ipsilateral hemidiaphragmatic paresis. Moreover, it has been reported that ipsilateral hemidiaphragmatic paralysis does not present clinically significant respiratory problems in healthy patients (6–8). Because these studies were performed on ASA status I–II patients, we designed our study in ASA status III patients with chronic renal failure (CRF). We performed brachial plexus block by using the interscalene approach for creation of the AVF and used bupivacaine and ropivacaine in concentrations to produce differential sensory/motor blocks (8). In this study, we evaluated the anesthetic characteristics of 30 mL of either 0.33% bupivacaine or 0.33% ropivacaine in equal doses (used in our clinical practice) and their effects on diaphragmatic motion. It was hypothesized that if 0.33% ropivacaine (having sensorimotor discrimination) may affect less diaphragmatic motion, then the decreases in pulmonary function variables might be attenuated.
Approval for the study was obtained from the medical ethics committee. Forty-two ASA class III patients aged 17 to 61 years gave written, informed consent to participate in this randomized, double-blind trial. All patients were scheduled to undergo IBP anesthesia for the creation of AVF in the antecubital region.
Sedatives were not administered in any case. After the placement of a 20-gauge IV cannula, all patients received an infusion of 0.9% NaCl solution at 1 mL · kg−1 · h−1. Standard monitoring was used throughout, including noninvasive arterial blood pressure (BP), heart rate, and arterial saturation by peripheral pulse oximetry (Spo2) (Millenia® Vital Signs Monitoring System).
Under sterile conditions, IBP block was performed according to the method of Winnie (9) with the aid of a nerve stimulator (Stimuplex HNS® 11; B. Braun, Melsungen, Germany) with a current <0.5 mA by the same investigator. A short-beveled stimulating needle (Stimuplex® Kanule A, 50 mm; B. Braun) was inserted at the level of the cricoid cartilage until electrical motor response was elicited in the shoulder, upper arm, or elbow. With use of sealed envelopes, patients were randomized to receive 30 mL of either 100 mg of bupivacaine 0.33% (n = 16; group B) or 100 mg of ropivacaine 0.33% (n = 18; group R). Bicarbonate 0.5 mL was added to local anesthetics to accelerate the onset of the block.
Before the IBP injection (baseline value) and at the end of surgery, the ipsilateral and contralateral hemidiaphragmatic excursions were measured with 3.5-MHz convex probes using M-mode ultrasonography (Sonoline® SI 400; Siemens Medical Solutions, Issaquah, WA) according to the method described by Urmey et al. (6). All measurements were taken with the patient in the supine position and were evaluated by the same blinded radiologist. Hemidiaphragmatic excursion was defined as the difference between the diaphragm position recorded at functional residual capacity and that measured at the end of a deep inspiration. Excursion distance was expressed in millimeters from the functional residual capacity position. Normal inspiratory caudad diaphragmatic excursion was designated as a positive motion (+), and paradoxical cephalad motion was designated as a negative motion (−) (4). Negative motion or immobility of the ipsilateral hemidiaphragm was defined as full paralysis. In addition, a decrease of >10 mm in positive motion compared with the baseline value was assumed as partial paralysis (10). Three consecutive measurements were recorded, and the average was taken.
Forced vital capacity (FVC), forced expiratory volume at 1 s (FEV1), and peak expiratory flow (PEF) were measured immediately before IBP block (baseline), 30 min after interscalene block injection, and at the end of surgery by using bedside spirometry equipment (Microloop®; Micro Medical Limited, UK) with the patient in the sitting position.
Sensory and motor function were evaluated immediately before the block; at 2, 5, 10, 15, 20, 25, and 30 min after the block; and every 2 h after surgery until complete recovery according to the following criteria. The sensory block was assessed between the C5 and T2 dermatomes by pinprick and graded as follows: 0, no loss of sensation; 1, analgesia (patient feels touch, but it is not sharp); or 2, anesthesia (patient does not feel touch). Motor function was tested according to the following criteria: C5 and C6, abduct the arm at the shoulder joint; C7, extend the forearm elbow joint and the hand at the wrist against resistance; C8, make a fist; and T1, cross the middle finger over the index finger (11). It was graded as follows: 0, no weakness; 1, paresis; 2, paralysis (12). The onset of surgical anesthesia was defined as the loss of pinprick sensation at the skin dermatomes involved in the surgical field. The duration of sensory and motor blocks was recorded. The adequacy of the block was judged according to the need for supplementary local anesthetic for infiltration. Patients with insufficient blocks were excluded from the study.
Peripheral venous blood samples were drawn for assay of ropivacaine and bupivacaine in the nonoperated arm before the induction of the block and 30 and 120 min after the injection of local anesthetic. Blood samples, which were collected in EDTA-containing glass tubes, were subsequently separated by centrifugation, and plasma was stored at −20°C until analysis. Gas chromatography and mass spectrometry were used to determine free bupivacaine and ropivacaine concentrations (13). Gas chromatography/mass spectrometry was performed with a Hewlett-Packard 6890 and 5973 gas chromatography/mass spectrometry system (Hewlett-Packard, Palo Alto, CA). The gas chromatograph was fitted with an HP 5 (30 m × 0.25 mm × 0.25 μm thick) film. Free ropivacaine concentrations were not measured in two patients because of kit constraints. Possible complications were recorded during the operation and thereafter. The patients were monitored for 24 h after surgery.
Data are expressed as mean ± sd. The data of only 34 patients underwent statistical evaluation because seven patients required supplemental local anesthetic and one developed spinal anesthesia. Parametric values were compared between groups with Student’s t-test. One-way analysis of variance was used for comparing pulmonary function and sensory and motor block gradings within groups with post hoc Bonferroni’s tests. Fisher’s exact test was used for the incidence of complications. P < 0.05 was considered significant.
The two groups were comparable regarding age, weight, sex, ASA classification, duration of operation, and the time of the ultrasonographic evaluation of diaphragmatic excursion at the end of surgery (P > 0.05) (Table 1).
Of the studied patients, 7 required supplemental local anesthetic (3 in Group B and 4 in Group R), and 1 developed total spinal anesthesia; these 8 patients were excluded from the study. The patients with total spinal anesthesia had an inability to phonate at the 15th minute and had motor block of the lower extremity and contralateral arm and respiratory arrest at the 30th minute. Full recovery, after 6 hours, was achieved by respiratory and hemodynamic support. The free plasma concentrations were 47, 27, 12, and 0 ng/mL at 30, 60, 120, and 240 min, respectively, and the free plasma concentration was 750 ng/mL in cerebrospinal fluid at the 120th minute of IBP in this patient.
The success rate of the IBP block was 80.9%. Data from the remaining 34 patients were statistically analyzed. The mean onset time of sensory anesthesia in C7 and C8 was 8.4 ± 5.9 min and 13.8 ± 8.3 min in Groups B and R, respectively (P < 0.05; (Table 2). The duration of sensory block also did not differ between groups (9.2 ± 1.8 h and 9.5 ± 2.2 h in Groups B and R, respectively) (P > 0.05).
The dermatomal evaluation of motor block revealed no significant differences between the two groups (P > 0.05; Table 3). The duration of motor block was 7.7 ± 2.3 h in Group B and 7.3 ± 1.1 h in Group R (P > 0.05). No significant changes in BP, heart rate, Spo2, or duration of postoperative analgesia were observed in either group.
Before the IBP, ultrasonographic evaluation of diaphragmatic excursions showed positive motion in all patients. The mean baseline ipsilateral hemidiaphragmatic excursion was 36.8 ± 7.32 mm and 46.2 ± 8.14 mm in Groups B and R, respectively. There was no difference between groups (P > 0.05). At the end of surgery, there was a significant reduction in ipsilateral hemidiaphragmatic excursion in both groups compared with baseline values within the groups (15.8 ± 11.2 mm in Group B and 28.9 ± 17.2 mm in Group R) (P < 0.01).
Paradoxical motion or no motion of the ipsilateral hemidiaphragm were observed in 4 and 2 patients in Group B, respectively, whereas 4 had partial paralysis. Three patients in Group R showed paradoxical motion (1 patient) and no motion at all (2 patients), while 5 patients had partial paralysis. There was no difference between groups (P > 0.05). The overall incidence of paresis was 52.9% in all patients.
Pulmonary function variables (FVC, FEV1, and PEF) decreased approximately 30% in patients of Group B at 30 min after IBP block and at the end of surgery compared with baseline values (P < 0.001). Patients in Group R also showed significant decreases in FVC and FEV1 (17%; P < 0.001)—but not PEF—compared with baseline values. The decreases in all pulmonary function variables were statistically significant in Group B compared with Group R (P < 0.05). Figure 1a,b,c shows the reductions in FVC, FEV1, and PEF as a percentage of baseline values in both groups.
Free bupivacaine concentrations were less than those of ropivacaine at 30 and 120 min after the injection of local anesthetic (48.56 ± 10.46 ng/mL and 26.18 ± 6.53 ng/mL; and 70.13 ± 16.97 ng/mL and 53.86 ± 11.40 ng/mL, respectively) (P < 0.05). The largest individual free plasma concentrations of ropivacaine and bupivacaine at 30 min were 101 and 75 ng/mL, respectively.
The number of the patients who developed complications is shown in Table 4. No significant difference was found between groups with regard to these complications (P > 0.05). Respiratory distress, defined as a hemoglobin saturation of <85% while breathing room air, was treated with supplemental oxygen via a nasal mask throughout the surgery, with no further therapy needed. The Spo2 was always >95% during the operation in the remaining patients.
We compared the anesthetic characteristics of 30 mL of 0.33% bupivacaine and 0.33% ropivacaine in equal doses, as well as their influences on diaphragmatic motion and pulmonary function. In our study, complete sensorimotor block (C5 to T1) was achieved in 34 of 42 patients. The overall success rate for IBP in our study was 80.9%. Schroeder et al. 14) reported a 75% success rate with the interscalene approach for brachial plexus block. In the same study, success with the axillary approach compared with the interscalene approach was more frequent in patients undergoing elbow surgery, although interscalene block is not advocated for surgery to the distal humerus, elbow, or proximal forearm because of the insufficient block at this level (14). The requirement for supplemental local anesthetic in seven patients may have been due to insufficient block of the intercostobrachial nerves (15). Moreover, one patient developed total spinal anesthesia 30 minutes after IBP. The mechanisms of total spinal anesthesia due to IBP may be explained by the direct injection into the epidural subdural space as a result of incorrect needle placement, perineural or intraneural injection of local anesthetic, or prevertebral spread or absorption of drug from an unusually long dural root sleeve (16). The actual reason could not be determined in our case, but intrathecal injection of the drug might not have been the etiology because of the rather late occurrence.
The onset and duration of the motor block were similar to the results of previous studies (12,17). The duration of analgesia for both groups was shorter (13 and 14 hours) than that found by Klein et al. (17). This may be attributed to the smaller local anesthetic concentration and the CRF of the patients in our study groups. Bromage and Gertel (18) reported that the hyperdynamic cardiovascular system and acidosis secondary to chronic anemia increase the elimination rate of local anesthetics—with or without epinephrine—and in turn cause a 40% reduction in the duration of analgesia.
IBP block depresses pulmonary function as a result of unilateral hemidiaphragmatic paresis (6). It has been shown that IBP block causes diaphragmatic paralysis in up to 100% of cases and causes a considerable reduction (41% in FVC and 30% in FEV1) in pulmonary function. Such reductions are unlikely to cause further clinical symptoms in healthy patients (6–8). The patients could compensate by increasing their respiratory rate and respiratory muscular activity (intercostal and accessory muscles of respiration) (6,7). Inspiratory muscle functions are worsened for patients with unilateral hemidiaphragmatic paresis when cardiopulmonary disease is present (19).
In our study, we found the incidence of paresis to be <100%. This could be explained by the patient population we selected. An increased elimination rate of local anesthetics is present in patients with CRF because of the hyperdynamic cardiovascular system and acidosis (18). In addition, we used less local anesthetic. Al-Kaisy et al. (20) reported that diaphragmatic excursion was affected less with 10 mL of 0.25% bupivacaine for IBP and caused a limited adverse respiratory effect compared with the same volume of 0.5% bupivacaine, whereas both solutions gave a similar degree of sensory and motor anesthesia. In this study, the incidence of diaphragmatic paresis was comparable in the two groups. However, the decreases in the pulmonary function variables were larger in the bupivacaine group. The 30% decrease in spirometric volumes confirms similarities with previously published results in healthy patients (7). These results were similar to those encountered after full unilateral phrenic nerve section and pathologic hemidiaphragm paralysis as reported by Fackler et al. (21). Our results in Group R show that the pulmonary function was affected less by IBP block. This may be attributed to ropivacaine’s having a more marked differential effect in sensory/motor blockade (8). The differential sensory/motor nerve block of ropivacaine could theoretically minimize the motor block of the ipsilateral hemidiaphragm and increase as the concentration of ropivacaine is reduced. In addition, the local anesthetic doses used in this study were equal doses—not equipotent, as used in our anesthesia practice. Therefore, it is suggested that ropivacaine 0.33% may produce less motor block than bupivacaine 0.33%.
Mild respiratory distress was observed in 4 patients (3 in Group B and 1 in Group R), similar to healthy patients. Spontaneous ventilation was supported by oxygen via nasal mask throughout the surgery.
Horner’s syndrome is common after IBP. The incidence of Horner’s syndrome is approximately 40% to 70% (22). The association of a recurrent laryngeal block with Horner’s syndrome may occur. Hoarseness associated with IBP may occur in 1.3% of patients (23). In our study, Horner’s syndrome and hoarseness were observed in a percentage of patients similar to that found by Hickey et al. (23).
The free plasma concentration of ropivacaine was larger than that of bupivacaine at 30 and 120 minutes after injection with the same dose as reported by Ala-Kokko et al. (24) in children. The smaller free plasma concentrations of bupivacaine, despite use of the same dose, are attributed to more rapid initial distribution in tissues caused by the higher lipid solubility compared with ropivacaine and, thus, the larger volume of distribution of bupivacaine. There was no clinical evidence of toxicity in any of our patients. In our study, the free concentration of ropivacaine and bupivacaine at 30 and 120 minutes after injection was well below the toxic threshold (0.6 μg/mL) (25).
In conclusion, our study showed that equal doses of ropivacaine 0.33% and bupivacaine 0.33% provided a similar degree of sensory/motor anesthesia for IBP block in patients with CRF. Bupivacaine 0.33% caused larger decreases in spirometric volumes than ropivacaine 0.33% in equal doses, whereas the incidence of hemidiaphragmatic paresis was similar in both groups. Therefore, these results suggest that ropivacaine 0.33% is a better local anesthetic than bupivacaine 0.33% for use in an interscalene approach for brachial plexus block in high-risk patients with CRF. However, because of concerns about the success rate and the risk of serious complications, the interscalene approach may not be optimal for this patient population, particularly when combined with the associated reduction in pulmonary function.
The authors thank Anthony P. Adams, MD, for his critical review of this manuscript.
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