Effect of Interscalene Brachial Plexus Block on the Pulmonary Function of Obese Patients: A Prospective, Observational Cohort Study.

BACKGROUND: The effect of interscalene block (ISB) on pulmonary function of obese participants has not been investigated. The goal of this study is to assess the association of obesity (body mass index [BMI] >29 kg/m vs BMI <25 kg/m) and change in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) after ISB in participants undergoing outpatient shoulder surgery. METHODS: This prospective, observational cohort study compared obese (BMI >29 kg/m) and normal-weight (BMI <25 kg/m) groups undergoing ISB for ambulatory shoulder surgery, on preblock and postblock FVC and FEV1, at 30 minutes postblock and in the postanesthesia care unit (PACU). The primary outcome in this study was FVC% change (percentage change from preblock to postblock values of FVC) at 30 minutes postblock in the supine position. Secondary outcomes included FVC% change at PACU and in the sitting position, FEV1% change (percentage change from preblock to postblock values of FEV1), FVC, FEV1, incidence of diaphragmatic paresis, modified Borg scale for perceived dyspnea, Richmond Agitation-Sedation Scale scores for sedation, and intraoperative airway events. RESULTS: Fourteen participants were recruited to each group. The mean (standard deviation) BMI in the normal-weight and obese groups was 23 (1.7) and 33 (3.1) kg/m, respectively. ISB success rate was 100%. All participants demonstrated hemidiaphragmatic paresis after ISB. Compared to the normal-weight group, in the sitting position, the obese group had a significant decrease in FVC% change at 30 minutes (-30 [10.5] vs -23 [7.2], P = .046) and an FEV1% change in the PACU (-40 [12.6] vs -27 [13.9], P = .02). No difference was found for measurements taken in the supine position. A repeated-measures analysis demonstrated that, adjusted for position, there is no significant group effect on FVC% change or FEV1% change from 30 minutes to PACU. The 2 groups were not different in terms of breathlessness and sedation at 30 minutes (P = .67, P = .48, respectively) and in the PACU (P = .69, P > .99, respectively) nor in the occurrence of intraoperative airway events (P > .99). CONCLUSIONS: ISB is associated with greater FVC and FEV1 reductions in obese participants undergoing shoulder surgery compared to normal-weight participants. Neither time (30 minutes versus PACU) nor position (sitting versus supine) affected this relationship. Despite these changes, obesity was not associated with increased clinical respiratory symptoms or events.

Changes in Brain Resting-state Functional Connectivity Associated with Peripheral Nerve Block: A Pilot Study.

BACKGROUND: Limited information exists on the effects of temporary functional deafferentation (TFD) on brain activity after peripheral nerve block (PNB) in healthy humans. Increasingly, resting-state functional connectivity (RSFC) is being used to study brain activity and organization. The purpose of this study was to test the hypothesis that TFD through PNB will influence changes in RSFC plasticity in central sensorimotor functional brain networks in healthy human participants. METHODS: The authors achieved TFD using a supraclavicular PNB model with 10 healthy human participants undergoing functional connectivity magnetic resonance imaging before PNB, during active PNB, and during PNB recovery. RSFC differences among study conditions were determined by multiple-comparison-corrected (false discovery rate-corrected P value less than 0.05) random-effects, between-condition, and seed-to-voxel analyses using the left and right manual motor regions. RESULTS: The results of this pilot study demonstrated disruption of interhemispheric left-to-right manual motor region RSFC (e.g., mean Fisher-transformed z [effect size] at pre-PNB 1.05 vs. 0.55 during PNB) but preservation of intrahemispheric RSFC of these regions during PNB. Additionally, there was increased RSFC between the left motor region of interest (PNB-affected area) and bilateral higher order visual cortex regions after clinical PNB resolution (e.g., Fisher z between left motor region of interest and right and left lingual gyrus regions during PNB, -0.1 and -0.6 vs. 0.22 and 0.18 after PNB resolution, respectively). CONCLUSIONS: This pilot study provides evidence that PNB has features consistent with other models of deafferentation, making it a potentially useful approach to investigate brain plasticity. The findings provide insight into RSFC of sensorimotor functional brain networks during PNB and PNB recovery and support modulation of the sensory-motor integration feedback loop as a mechanism for explaining the behavioral correlates of peripherally induced TFD through PNB.

New medications and techniques in ambulatory anesthesia.

Novel anesthetic and analgesic agents are currently under development or investigation to improve anesthetic delivery and patient care. The pharmacokinetic and analgesic profiles of these agents are especially tailored to meet the challenges of rapid recovery and opioid minimization associated with ambulatory anesthesia practice.

Long-acting serotonin antagonist (Palonosetron) and the NK-1 receptor antagonists: does extended duration of action improve efficacy?

In a growing outpatient surgical population, postdischarge nausea and vomiting (PDNV) is unfortunately a common and costly anesthetic complication. Identification of risk factors for both postoperative nausea and vomiting and PDNV is the hallmark of prevention and management. New pharmacologic interventions with extended duration of action, including palonosetron and aprepritant, may prove to be more efficacious.

Peripheral nerve stimulation in regional anesthesia.

Peripheral nerve stimulation has a long history in regional anesthesia. Despite the advent of ultrasound-guided peripheral nerve blockade, nerve stimulation remains a popular technique used alone or, now, in combination with ultrasound-guided techniques. In light of this evolving utility of nerve stimulation, this is an appropriate time to review the basic concepts and knowledge base of this historically important tool. Electrical nerve stimulation facilitates nerve localization, using threshold current as a surrogate for needle-to-nerve distance. Preferential activation of motor nerves is possible because motor nerve fibers are more readily activated with a shorter duration of current compared with sensory nerves. The association between current and needle-to-nerve distance predicts that less current is needed to evoke a motor response as the needle moves closer to the nerve. Thus, an elicited motor response at or below 0.5 mA is considered a common end point for successful neural blockade. However, current magnitude is neither 100% sensitive nor specific. Independent of technical ability, both the biological environment and the equipment used impact the current-distance relationship. Thus, successful electrical nerve stimulation is dependent on an anesthesiologist with a solid foundation in anatomy and a thorough understanding of electrophysiology.

Management of postdischarge nausea and vomiting after ambulatory surgery.

PURPOSE OF REVIEW: Although there are extensive studies of postoperative and postdischarge nausea and vomiting (PONV/PDNV) up to 24  h, few investigate 'delayed PDNV'. With an increasing outpatient surgical population, specific 'delayed PDNV' risk identification and management is necessary for improving outcomes and helping patients after discharge. This review will discuss possible PDNV specific risk factors, successful prevention and management of PDNV following ambulatory anesthesia and the principles and pharmacology of these interventions. RECENT FINDINGS: Current research has demonstrated beneficial PDNV management up to 72  h with the long-acting 5-hydroxytryptamine-3 receptor antagonist palonosetron. Neurokinin-1 antagonists have demonstrated superior antiemesis, but not antinausea compared with more traditional and less expensive options. Dexamethasone provides improvements in quality of recovery associated with improved PDNV outcomes. SUMMARY: Further PDNV specific research is needed, including PDNV predictive models in directing antiemetic interventions. Long-acting antiemetics and postdischarge oral antiemetics are effective in PDNV pharmacologic management. Neurokinin-1 receptor antagonists are effective in reducing the incidence of vomiting, but not nausea. The addition of nonpharmacologic interventions such as acustimulation may reduce PDNV. Multimodal analgesia including nonopioid analgesics and ambulatory continuous peripheral nerve blocks are encouraged to achieve adequate postoperative analgesia and reduce opioid induced PDNV.

Contralateral local anesthetic spread from an outpatient interscalene catheter.

PURPOSE: Ambulatory continuous infusions have been associated with improved analgesia and few serious complications. This report describes an unusual case of a patient with a continuous interscalene nerve block who developed a contralateral upper extremity sensory block. The complication did not occur until postoperative day two while the patient was at home. CLINICAL FEATURES: A 56-yr-old woman had a continuous interscalene catheter placed for arthroscopic lysis of adhesions of her shoulder. The insertion needle was initially injected with 0.5% ropivacaine 25 mL (1:400,000 epinephrine), producing a unilateral interscalene block. Postoperatively, the patient was started on a continuous interscalene infusion of 0.2% ropivacaine at 8 mL·hr(-1) via a disposable infusion pump. The next day, the patient had a unilateral brachial plexus block and an associated Horner's syndrome and was discharged home with the infusion. On the morning of the second postoperative day, the patient developed ipsilateral and contralateral Horner's syndrome with associated numbness in both shoulders. The catheter was removed and symptoms resolved four hours later. CONCLUSIONS: Ambulatory continuous infusions are typically associated with few serious complications and a favourable safety profile. This case demonstrates that unexpected complications can still occur even after days of normal operation. Based on our previous experience, we believe this to be a rare but potentially serious event that requires awareness by those discharging patients with continuous infusions of local anesthetics.

Processed electroencephalogram during donation after cardiac death.

We present a case series of increased bispectral index values during donation after cardiac death (DCD). During the DCD process, a patient was monitored with processed electroencephalogram (EEG), which showed considerable changes traditionally associated with lighter planes of anesthesia immediately after withdrawal of care. Subsequently, to validate the findings of this case, processed EEG was recorded during 2 other cases in which care was withdrawn without the use of hypnotic or anesthetic drugs. We found that changes in processed EEG immediately after withdrawal of care were not only reproducible, but can happen in the absence of changes in major electromyographic or electrocardiographic artifact. It is well documented that processed EEG is prone to artifacts. However, in the setting of DCD, these changes in processed EEG deserve some consideration. If these changes are not due to artifact, dosing of hypnotic or anesthetic drugs might be warranted. Use of these drugs during DCD based primarily on processed EEG values has never been addressed.

Double-blind comparison of granisetron, promethazine, or a combination of both for the prevention of postoperative nausea and vomiting in females undergoing outpatient laparoscopies.

PURPOSE: Postoperative nausea and vomiting (PONV) and postdischarge nausea and vomiting (PDNV) are common problems after surgery. Prophylactic combination antiemetic therapy is recommended for patients at high risk for developing PONV and PDNV. Granisetron, a serotonin antagonist, is an effective antiemetic that is devoid of sedative side effect. Although promethazine is effective, commonly used doses are associated with sedation. This study investigates the combination of low doses of granisetron and promethazine for the prevention of PONV. METHODS: Women undergoing ambulatory gynecological laparoscopy were enrolled. A standard general anesthetic regimen was prescribed. Fifteen minutes before the expected end of surgery, the patients were randomly assigned to receive granisetron 0.1 mg iv, promethazine 6.25 mg iv, or a combination of the two drugs. Prophylaxis with oral promethazine 12.5 mg, granisetron 1 mg, or both was started in the respective groups 12 hr after the end of surgery and continued every 12 hr until postoperative day 3 (a total of five oral doses). The following outcomes were recorded: total response rate (defined as no vomiting, no more than mild nausea, and no use of rescue antiemetic); incidence of nausea, vomiting, and use of rescue antiemetics; severity of nausea; patient activity level; and patient satisfaction with PONV management. RESULTS: Patients in the combination group had a higher total response rate at 6, 24, 48, and 72 hr after surgery compared with those who received promethazine alone (at 24 hr, Combination 69.6%, Promethazine 36.2%, Granisetron 53.3%; P = 0.0079). The maximum nausea scores were also lower in the combination group at 6, 24, 48, and 72 hr (Combination 1.7 +/- 2.2, Promethazine 4.0 +/- 3.6, Granisetron 3.1 +/- 3.2 at 24 hr; P < 0.05). There was no difference in the sedation scores, incidence of drowsiness, patient activity level, and satisfaction with PONV management. CONCLUSIONS: Low-dose granisetron and promethazine combination was more effective in reducing PONV and PDNV than promethazine monotherapy. The combination also reduced the severity of nausea.

Computer-based finite element modeling of insulated Tuohy needles used in regional anesthesia.

BACKGROUND: Differences in needle design may impact nerve localization. This study evaluates the electrical properties of two insulated Tuohy needles using computational finite element modeling. METHODS: Three-dimensional geometric computer-based models were created representing two 18-gauge, insulated Tuohy needles: (1) with an exposed metal tip and (2) with an insulated tip. The models were projected in simulated human tissue. Using finite element methodology, distributions of current-density were calculated. Voltages in the modeled medium were calculated, and activation patterns of a model nerve fiber around the tip of each needle were estimated using the activating function. RESULTS: Maximum current density on the exposed-tip needle occurred along the edge of the distal tip; the distal edge was 1.7 times larger than the side edges and 3.5 times larger than the proximal edge. Conversely, maximum current density occurred along the proximal edge of the insulated-tip Tuohy opening; the proximal edge was 1.9 times larger than the side edges of the opening and 3.5 times larger than the distal edge of the opening. Voltages generated by the exposed-tip needle were larger and had a wider spatial distribution than that of the insulated-tip needle, which restricted to the area immediately adjacent to the opening. Different changes in threshold were predicted to excite a nerve fiber as the needles were rotated or advanced toward the modeled nerve. CONCLUSIONS: The needles displayed different asymmetric distributions of current density and positional effects on threshold. If this analysis is validated clinically, it may prove useful in testing stimulating needles before clinical application.

Piezoelectric vibrating needle and catheter for enhancing ultrasound-guided peripheral nerve blocks.

Ultrasound imaging has been used for performing single-injection peripheral nerve blocks and continuous catheters. One limitation with current technology is the inability to confirm the location of the needle or catheter tip. We describe a new needle and catheter design that permits distal tip visualization using color flow Doppler. An 18-gauge 100-mm insulated Tuohy needle and a 20-gauge 50-mm polyamide catheter (open tip) with a Teflon-coated steel stylet (B. Braun, Bethlehem, PA) were customized by adhering in place two piezoelectric actuators. These created 1-8 kHz vibrations when coupled to a function generator (FG502, Tektronix, Richardson, TX) and a 100 W audio amplifier (R3000, KLH, Sun Valley, CA). Mimicking a lateral popliteal fossa block, the needle and catheter were inserted into the leg of an unembalmed cadaver. When activated, the tip of each was highlighted in color when scanned in the short axis using the color Doppler mode of a two-dimensional ultrasound and a 12 MHz L38 probe (MicroMaxx, Sonosite, Bothell, WA). Vibration technology may be a useful adjunct while performing ultrasound-guided regional anesthesia. Further study evaluating its usefulness and safety in live tissue is warranted.

Pudendal nerve stimulation evokes reflex bladder contractions in persons with chronic spinal cord injury.

AIMS: Although electrical stimulation of the pudendal nerve has been shown to evoke reflex micturition-like bladder contractions in both intact and spinalized cats, there is little evidence to suggest that an analogous excitatory reflex exists in humans, particularly those with spinal cord injury (SCI). We present two cases where electrical activation of pudendal nerve afferents was used to evoke excitatory bladder responses. SUBJECTS AND METHODS: A percutaneously placed catheter electrode was used to electrically stimulate the pudendal nerve trunk in two males with SCI. The response was quantified with recorded changes in detrusor pressure and EMG activity of the external anal sphincter. RESULTS: In both individuals, frequency specific (f = 20-50 Hz) activation of the pudendal nerve trunk evoked excitatory bladder contractions that also depended on the stimulus amplitude and bladder volume. CONCLUSION: The results suggest that selective activation of the perineal branches of the pudendal nerve may further augment the excitatory reflex evoked by electrical stimulation.

A computer model of electrical stimulation of peripheral nerves in regional anesthesia.

BACKGROUND: Nerve stimulation for regional anesthesia can be modeled mathematically. The authors present a mathematical framework to model the underlying electrophysiology, the development of software to implement that framework, and examples of simulation results. METHODS: The mathematical framework includes descriptions of the needle, the resulting potential field, and the active nerve fiber. The latter requires a model of the individual membrane ionic currents. The model geometry is defined by a three-dimensional coordinate system that allows the needle to be manipulated as it is clinically and tracked in relation to the nerve fiber. The skin plane is included as an electrical boundary to current flow. The mathematical framework was implemented in the Matlab (The MathWorks, Natick, MA) computing environment and organized around a graphical user interface. Simulations were performed using an insulated needle or an uninsulated needle inserted perpendicular to the skin with the nerve fiber at a depth of 2 cm. For each needle design, data were obtained with the needle as cathode or anode. Data are presented as current-distance maps that highlight combinations of current amplitude and tip-to-nerve distance that evoked a propagated response. RESULTS: With the needle tip positioned 2 mm proximal to the depth of the nerve, an insulated needle required a current greater than 0.457 mA for impulse propagation when attached to the cathode; when attached to the anode, the minimal current was 2.354 mA. In the same position, an uninsulated needle attached to the cathode required a current greater than 2.395 mA to generate a response. However, when an uninsulated needle was attached to the anode, currents up to 7 mA were inadequate to produce a propagated response. Of particular interest were combinations of current amplitude and needle position that activated the fiber but blocked impulse propagation for cathodal stimulation. CONCLUSIONS: Mathematical modeling of nerve stimulation for regional anesthesia is possible and could be used to investigate new equipment or needle designs, test nerve localization protocols, enhance clinical and experimental data, and ultimately generate new hypotheses.

Interscalene brachial plexus block for outpatient shoulder arthroplasty: Postoperative analgesia, patient satisfaction and complications.

BACKGROUND: Shoulder arthroplasty procedures are seldom performed on an ambulatory basis. Our objective was to examine postoperative analgesia, nausea and vomiting, patient satisfaction and complications of ambulatory shoulder arthroplasty performed using interscalene brachial plexus block (ISB). MATERIALS AND METHODS: We prospectively examined 82 consecutive patients undergoing total and hemi-shoulder arthroplasty under ISB. Eighty-nine per cent (n=73) of patients received a continuous ISB; 11% (n=9) received a single-injection ISB. The blocks were performed using a nerve stimulator technique. Thirty to 40 mL of 0.5% ropivacaine with 1:400,000 epinephrine was injected perineurally after appropriate muscle twitches were elicited at a current of less than 0.5% mA. Data were collected in the preoperative holding area, intraoperatively and postoperatively including the postanesthesia care unit (PACU), at 24h and at seven days. RESULTS: Mean postoperative pain scores at rest were 0.8 ± 2.3 in PACU (with movement, 0.9 ± 2.5), 2.5 ± 3.1 at 24h and 2.8 ± 2.1 at seven days. Mean postoperative nausea and vomiting (PONV) scores were 0.2 ± 1.2 in the PACU and 0.4 ± 1.4 at 24h. Satisfaction scores were 4.8 ± 0.6 and 4.8 ± 0.7, respectively, at 24h and seven days. Minimal complications were noted postoperatively at 30 days. CONCLUSIONS: Regional anesthesia offers sufficient analgesia during the hospital stay for shoulder arthroplasty procedures while adhering to high patient comfort and satisfaction, with low complications.

Combined lumbar-plexus and sciatic-nerve blocks: an analysis of plasma ropivacaine concentrations.

BACKGROUND AND OBJECTIVES: Lumbar-plexus and sciatic-nerve blocks are commonly combined for lower-extremity anesthesia using large doses of ropivacaine. Limited information is available about the pharmacokinetics of this practice. We analyzed plasma ropivacaine concentrations after single-injection lumbar-plexus blocks with and without sciatic-nerve blocks. METHODS: Twenty patients having lower-extremity surgery using a lumbar-plexus block with 0.5% ropivacaine with 1:400,000 epinephrine (35 mL, n = 10) or the same lumbar-plexus block with the addition of a sciatic-nerve block (25 mL, n = 10, 60 mL total) using the same solution were enrolled. Venous blood samples were collected at 5, 15, 30, 45, 60, 120, and 240 minutes after block placement and analyzed for total ropivacaine concentration by use of gas chromatography. Individual timepoints, maximum concentrations (C(max)), and time to C(max) (T(max)) were compared. Values are mean +/- SD. RESULTS: Both groups demonstrated a rapid increase in plasma concentration over the first 30 to 45 minutes. Concentrations were greater for those who received both blocks (P = .0005) at all timepoints. The lumbar-plexus block C(max) was less (986 +/- 221 ng/mL) than for the combined blocks (1,560 +/- 351 ng/mL, P = .0004). The T(max) was greater for the lumbar plexus (80 +/- 49 min) than for the combined blocks (38 +/- 22 min, P = .03). There was no relationship between the C(max) and patient age, weight, or body mass index. CONCLUSIONS: The results of this study demonstrate that the plasma ropivacaine concentrations increase quicker when a sciatic-nerve block is added to a lumbar-plexus block, but C(max) remains below the toxicity threshold.

The effect of age on sciatic nerve block duration.

The physiologic changes that occur with advancing age and their effect on the duration of peripheral nerve blocks have yet to be defined. We prospectively studied the duration of sciatic nerve block using mepivacaine in younger and older patients. Eighty ASA physical status I-III patients, aged 18-35 (n = 40) or 55-80 (n = 40) yr, having outpatient knee arthroscopy with a femoral block and a standardized sciatic nerve block were enrolled; 37 in each group completed the study. All patients received a Labat sciatic nerve block using 20 mL of 1.0% mepivacaine with 0.1 mEq/mL sodium bicarbonate and 1:400,000 (2.5 microg/mL) epinephrine and a femoral nerve block. The duration of sensory block (sensation of pinprick, temperature, and vibration), motor block (plantar and dorsi flexion), and complete sensory and motor block in the sciatic nerve distribution of the operative extremity were measured. The time for complete return of both sensory and motor function was longer in the older group, 329 +/- 47 min compared with 306 +/- 46 min (mean +/- sd) in the younger group (P = 0.04). The difference was small under the conditions of this study and would not be perceived clinically. Age also increased the time to return of vibratory sensation (younger = 292 +/- 58 min, older = 257 +/- 50 min; P = 0.007). The other measurements did not differ between groups. We conclude that age may affect peripheral nerve blocks and that more investigation is needed to determine the pharmacologic, physiologic, and chronologic factors behind these findings.

Peripheral nerve block techniques for ambulatory surgery.

Peripheral nerve blocks (PNBs) have an increasingly important role in ambulatory anesthesia and have many characteristics of the ideal outpatient anesthetic: surgical anesthesia, prolonged postoperative analgesia, and facilitated discharge. Critically evaluating the potential benefits and supporting evidence is essential to appropriate technique selection. When PNBs are used for upper extremity procedures, there is consistent opioid sparing and fewer treatment-related side effects when compared with general anesthesia. This has been demonstrated in the immediate perioperative period but has not been extensively investigated after discharge. Lower extremity PNBs are particularly useful for procedures resulting in greater tissue trauma when the benefits of dense analgesia appear to be magnified, as evidenced by less hospital readmission. The majority of current studies do not support the concept that a patient will have difficulty coping with pain when their block resolves at home. Initial investigations of outpatient continuous peripheral nerve blocks demonstrate analgesic potential beyond that obtained with single-injection blocks and offer promise for extending the duration of postoperative analgesia. The encouraging results of these studies will have to be balanced with the resources needed to safely manage catheters at home. Despite supportive data for ambulatory PNBs, most studies have been either case series or relatively small prospective trials, with a narrow focus on analgesia, opioids, and immediate side effects. Ultimately, having larger prospective data with a broader focus on outcome benefits would be more persuasive for anesthesiologists to perform procedures that are still viewed by many as technically challenging.

Continuous peripheral nerve block for battlefield anesthesia and evacuation.

Peripheral nerve and continuous peripheral nerve block (CPNB) have the potential to be valuable techniques in combat anesthesia. We describe the first successful application of CPNB in the pain management and surgical management of a combat casualty as he was evacuated from the Iraqi battlefield to the United States.

Peripheral nerve blocks and continuous catheter techniques.

Peripheral nerve blocks provide intense, site-specific analgesia and are associated with a lower incidence of side effects when compared with many other modalities of postoperative analgesia. Continuous catheter techniques further prolong these benefits. These advantages can facilitate a prompt recovery and discharge and achieve significant perioperative cost savings. This is of tremendous value in a modern health care system that stresses cost-effective use of resources and a continued shift toward shorter hospital stay as well as outpatient surgery.