Susan B. McDonald

Current Issues in Spinal Anesthesia

ConclusionSpinal anesthesia is an old, simple, and popular anesthetic technique, yet much remains unknown regarding pertinent anatomy, physiology, and pharmacology. Investigations into physiologic effects of spinal anesthesia reveal complex actions on multiple organ systems. New local anesthetics, analgesic additives, and techniques are being investigated for different applications as the practice of medicine focuses on outpatient care. Safety of spinal agents and complications from spinal anesthesia continue to be examined and re-examined to improve safety. Further study will be needed to fully resolve these issues and to further understand and improve the clinical use of spinal anesthesia.

Hyperbaric Spinal Ropivacaine A Comparison to Bupivacaine in Volunteers

Background: Ropivacaine is a newly introduced local anesthetic that may be a useful alternative to low-dose bupivacaine for outpatient spinal anesthesia. However, its relative potency to bupivacaine and its dose-response characteristics are unknown. This double-blind, randomized, crossover study was designed to determine relative potencies of low-dose hyperbaric spinal ropivacaine and bupivacaine and to assess the suitability of spinal ropivacaine for outpatient anesthesia. Methods: Eighteen healthy volunteers were randomized into three equal groups to receive one spinal administration with bupivacaine and a second with ropivacaine, of equal-milligram doses (4, 8, or 12 mg) of 0.25% drug with 5% dextrose. The duration of blockade was assessed with (1) pinprick, (2) transcutaneous electrical stimulation, (3) tolerance to high tourniquet, (4) electromyography and isometric force dynamometry, and (5) achievement of discharge criteria. Differences between ropivacaine and bupivacaine were assessed with linear and multiple regression. P < 0.05 was considered significant. Results: Ropivacaine and bupivacaine provided dose-dependent prolongation of sensory and motor block and time until achievement of discharge criteria (R 2 ranges from 0.33-0.99; P values from < 0.001 through 0.01). Spinal anesthesia with ropivacaine was significantly different from bupivacaine and was approximately half as potent for all criteria studied. A high incidence of back pain (28%; P = 0.098) was noted after intrathecal ropivacaine was given. Conclusion: Ropivacaine is half as potent and in equipotent doses has a similar profile to bupivacaine with a higher incidence of side effects. Low-dose hyperbaric spinal ropivacaine does not appear to offer an advantage over bupivacaine for use in outpatient anesthesia.

Hyperbaric spinal levobupivacaine: A comparison to racemic bupivacaine in volunteers

Levobupivacaine is the isolated S-enantiomer of bupivacaine and may be a favorable alternative to spinal bupivacaine. However, its clinical efficacy relative to bupivacaine and its dose-response characteristics, in spinal anesthesia, must first be known. This double-blinded, randomized, cross-over study was designed to compare the clinical efficacy of hyperbaric levobupivacaine and bupivacaine for spinal anesthesia. Eighteen healthy volunteers were randomized into three equal groups to receive two spinal anesthetics, one with bupivacaine and the other with levobupivacaine, of equal-milligram doses (4, 8, or 12 mg). We assessed blockade quality and duration with pinprick, transcutaneous electrical stimulation, thigh tourniquet, abdominal and quadriceps muscle strength, modified Bromage scale, and time until achievement of discharge criteria. Sensory and motor block were similar between the same doses of levobupivacaine and bupivacaine (P > 0.56 to 0.86). For example, in the 12-mg groups of levobupivacaine versus bupivacaine, mean duration of tolerance to transcutaneous electrical stimulation at T12 was 100 min for both. The duration of motor block at the quadriceps was 71 versus 73 min, and time until achievement of discharge criteria was 164 min for both. Hyperbaric spinal levobupivacaine has equivalent clinical efficacy to racemic bupivacaine for spinal anesthesia in doses from 4 to 12 mg.

Parasternal block and local anesthetic infiltration with levobupivacaine after cardiac surgery with desflurane: the effect on postoperative pain, pulmonary function, and tracheal extubation times.

Early tracheal extubation has become common after cardiac surgery. Anesthetic techniques designed to achieve this goal can make immediate postoperative analgesia challenging. We conducted this randomized, placebo-controlled, double-blind study to investigate the effect of a parasternal block on postoperative analgesia, respiratory function, and extubation times. We enrolled 20 patients having cardiac surgery via median sternotomy; 17 patients completed the study. A de-sflurane-based, small-dose opioid anesthetic was used. Before sternal wire placement, the surgeons performed the parasternal block and local anesthetic infiltration of sternotomy and tube sites with either 54 mL of saline placebo or 54 mL of 0.25% levobupivacaine with 1:400,000 epinephrine. Effects on pain and respiratory function were studied over 24 h. Patients in the levobupivacaine group used significantly less morphine in the first 4 h after surgery (20.8 ± 6.2 mg versus 33.2 ± 10.9 mg in the placebo group; P = 0.013); they also had better oxygenation at the time of extubation. Four of nine in the placebo group needed rescue pain medication, versus none of eight in the levobupivacaine group (P = 0.08). Peak serum levobupivacaine concentrations were below potentially toxic levels in all patients (0.64 ± 0.43 &mgr;g/mL; range, 0.24–1.64 &mgr;g/mL). Parasternal block and local anesthetic infiltration of the sternotomy wound and mediastinal tube sites with levobupivacaine can be a useful analgesic adjunct for patients who are expected to undergo early tracheal extubation after cardiac surgery.

Spinal 2-chloroprocaine: A Dose-ranging Study and the Effect of Added Epinephrine

With the availability of preservative- and antioxidant-free 2-chloroprocaine (2-CP), there may be an acceptable short-acting alternative to lidocaine for spinal anesthesia. We examined the safety, dose-response characteristics, and effects of epinephrine with spinal 2-CP. Six volunteers per group were randomized to receive 30, 45, or 60 mg of spinal 2-CP with and without epinephrine. Intensity and duration of sensory and motor blockade were assessed. When 11 of the 18 volunteers complained of vague, nonspecific flu-like symptoms, breaking of the blind revealed that all spinal anesthetics associated with the flu-like symptoms contained epinephrine. There were no complaints of flu-like symptoms in the volunteers who received 2-CP without epinephrine. No further spinal anesthetics containing epinephrine were administered, resulting in 29 anesthetics (11 with epinephrine, 18 without epinephrine.) Plain 2-CP demonstrated a dose-dependent increase in peak block height and duration of effect at all variables except time to 2-segment regression and time to regression to T10. Time to complete sensory regression with plain 2-CP was 98 ± 20, 116 ± 15, and 132 ± 23 min, respectively. 2-CP with epinephrine produced times to complete sensory regression of 153 ± 25, 162 ± 33, and 148 ± 29 min, respectively. Preservative and antioxidant free 2-CP can be used effectively for spinal anesthesia in doses of 30–60 mg. Epinephrine is not recommended as an adjunct because of the frequent incidence of side effects.

Regional anesthesia for outpatient surgery

In summary, regional techniques offer significant advantages in the outpatient setting. They can avoid the side effects of nausea, vomiting, and pain that frequently delay discharge or cause admission. They can also provide prolonged analgesia as well as offer, with the use of continuous catheters, the promise of a pain-free perioperative period. The choice of drugs must be carefully adjusted, especially with neuraxial techniques. Despite frequently requiring some additional time at the outset, regional techniques have consistently been shown to provide competitive discharge times and costs when compared with general anesthesia. They deserve a prominent place in outpatient surgery.

Lidocaine pretreatment with tourniquet versus lidocaine-propofol admixture for attenuating propofol injection pain: a randomized controlled trial.

Objective: Findings from studies investigating optimal techniques for attenuating propofol-related injection pain are inconsistent. In previous studies, lidocaine pretreatment using a tourniquet has been reported to be superior, inferior, or equivalent to a lidocaine-propofol admixture for reducing pain. This discordance could represent either no meaningful difference in the treatments or underlying methodological differences in the previous studies. We hypothesized that tourniquet-controlled pretreatment with lidocaine would be superior to lidocaine-propofol admixture for reducing propofol injection pain. Methods: This randomized controlled trial compared 3 groups-a control group (saline pretreatment/saline admixture; n = 50), a pretreatment group (lidocaine pretreatment/saline admixture; n = 51), and an admixture group (saline pretreatment/lidocaine admixture; n = 50). The primary outcome was verbal pain score after injection. The incidence of pain on injection was explored as a secondary outcome. Results: The median (interquartile range) verbal pain score after study solution injection were as follows-control group: 3 (0-6), pretreatment group: 0 (0-0), and admixture group: 0 (0-2). The pretreatment group had significantly lower pain scores when compared with the admixture group (P = 0.016), and both groups were superior to the control group. The pretreatment group had fewer subjects experiencing any injection pain than did the admixture group (20% vs. 44%, respectively; P = 0.024). Conclusions: Tourniquet-controlled pretreatment with lidocaine is statistically superior to admixing lidocaine with propofol for reducing propofol injection pain intensity, but the clinical importance of this small effect is questionable. However, pretreatment more effectively eliminates injection pain.

“See one, do one, teach one, have one”: A novel variation on regional anesthesia training

Introduction Is it possible to determine the number of nerve blocks needed for residents to become competent in regional anesthesia? Several studies have focused on this question, and the Residency Review Committee (RRC) for Anesthesiology has now defined a “minimum clinical experience” for some aspects of regional anesthesia training. In our experience, personally being a regional block recipient can also serve to enhance training. Methods Many residents at Virginia Mason Medical Center have received regional anesthetics as volunteers in research projects. We designed questionnaires to define their perceptions in both performing and receiving regional anesthesia. Results Twenty-one residents were recipients of a total of 72 regional anesthetic procedures. Many residents’ comments focused on the discomfort of local anesthesia infiltration, the value of sedation, a better appreciation of the patients’ perspectives, and improved preoperative consultation. Residents experiencing paresthesias were more likely to consider paresthesias as bad (P = .0098). Conclusion The lessons learned from personally receiving a regional anesthetic are invaluable and can improve the quality of training, as well as the relationship between anesthesiologist and patient.

Monitoring Hirudin Anticoagulation in Two Patients Undergoing Cardiac Surgery with a Plasma-modified Act Method

HEPARIN-INDUCED thrombocytopenia (HIT) is an immunologically-mediated reaction to unfractionated heparin that can result in life-threatening thrombotic complications. When patients with a history of HIT present for cardiac surgery, anticoagulation for cardiopulmonary bypass (CPB) can be challenging. Recombinant hirudin (r-hirudin) has been reported as a feasible alternative for anticoagulation. 1-8 R-hirudin is a potent direct thrombin inhibitor that works independently of antithrombin-III, offers a rapid onset of anticoagulation, and has a relatively short half-life (60-90 min) in patients with normal renal function. 9 The ability to rapidly and reliably monitor intraoperative levels of r-hirudin anticoagulation, however, has been problematic. The levels of r-hirudin recommended for anticoagulation during CPB (3.5-4.5 μg/ml) 10 exceed those that can be effectively monitored with either the partial thromboplastin time or activated clotting time. 11 The authors described a plasma-modified kaolin-activated clotting time (PM-ACT) assay as a new point-of-care monitoring tool for r-hirudin anticoagulation has been previously described. 12 This assay, accomplished by mixing patient whole blood samples with an equal volume of citrated commercial normal plasma, extends the ACT monitoring range by correcting for hemodilution of coagulation factors and diluting r-hirudin plasma concentrations. The authors present two cases where the PM-ACT was used to monitor r-hirudin anticoagulation during cardiac surgery, and describe the potential for significant perioperative bleeding complications.

Hyperbaric spinal ropivacaine: a comparison to bupivacaine in volunteers

BACKGROUND Ropivacaine is a newly introduced local anesthetic that may be a useful alternative to low-dose bupivacaine for outpatient spinal anesthesia. However, its relative potency to bupivacaine and its dose-response characteristics are unknown. This double-blind, randomized, crossover study was designed to determine relative potencies of low-dose hyperbaric spinal ropivacaine and bupivacaine and to assess the suitability of spinal ropivacaine for outpatient anesthesia. METHODS Eighteen healthy volunteers were randomized into three equal groups to receive one spinal administration with bupivacaine and a second with ropivacaine, of equal-milligram doses (4, 8, or 12 mg) of 0.25% drug with 5% dextrose. The duration of blockade was assessed with (1) pinprick, (2) transcutaneous electrical stimulation, (3) tolerance to high tourniquet, (4) electromyography and isometric force dynamometry, and (5) achievement of discharge criteria. Differences between ropivacaine and bupivacaine were assessed with linear and multiple regression. P < 0.05 was considered significant. RESULTS Ropivacaine and bupivacaine provided dose-dependent prolongation of sensory and motor block and time until achievement of discharge criteria (R2 ranges from 0.33-0.99; P values from < 0.001 through 0.01). Spinal anesthesia with ropivacaine was significantly different from bupivacaine and was approximately half as potent for all criteria studied. A high incidence of back pain (28%; P = 0.098) was noted after intrathecal ropivacaine was given. CONCLUSION Ropivacaine is half as potent and in equipotent doses has a similar profile to bupivacaine with a higher incidence of side effects. Low-dose hyperbaric spinal ropivacaine does not appear to offer an advantage over bupivacaine for use in outpatient anesthesia.