Francine D'Ercole

Thromboelastography as a perioperative measure of anticoagulation resulting from low molecular weight heparin : a comparison with anti-Xa concentrations

Low molecular weight heparin (LMWH) is commonly used to prevent postoperative thromboembolism. Currently, there is no convenient test to measure the degree of anticoagulation from LMWH. This prospective study examines the relationship of thromboelastography and serum anti-Xa concentration in patients treated with enoxaparin. Twenty-four adult patients scheduled for orthopedic surgery using epidural anesthesia were enrolled. Epidural catheters were removed the morning after surgery before the commencement of subcutaneous enoxaparin 30 mg twice daily. Venous blood samples were obtained at 1) the induction of anesthesia (baseline), 2) immediately before the third dose of enoxaparin postoperatively (Day 2-trough), 3) 4 h after the third dose postoperatively (Day 2-peak), and 4) immediately before the fifth dose postoperatively (Day 3-trough). Whole blood samples were obtained for thromboelastography, activated clotting time, and anti-Xa level analyses at each of the four time intervals. At the four sample intervals, the r time (mean ± sem). (20 ± 1, 25 ± 2, 51 ± 6, 31 ± 3 mm) and the k time (9 ± 0.7, 12 ± 1, 27 ± 5, 14 ± 2 mm) of the thromboelastograph were significantly correlated with the expected peak and trough levels of LMWH and serum anti-Xa levels (P < 0.05). At the Day 3-trough, thromboelastograph r times exceeded the normal range in 6 of 25 patients (25%). Prolongation of r time and k time on postoperative Day 3 may indicate an exaggerated response to LMWH. Thromboelastography is a test that could potentially correlate with the degree of anticoagulation produced by low molecular weight heparin. Implications Thromboelastography is a test that could potentially correlate with the degree of anticoagulation produced by low molecular weight heparin. The r time from the thromboelastogram correlates with serum anti-Xa concentration.

Central nervous system toxicity following the administration of levobupivacaine for lumbar plexus block: A report of two cases.

Background and Objectives Central nervous system and cardiac toxicity following the administration of local anesthetics is a recognized complication of regional anesthesia. Levobupivacaine, the pure S(-) enantiomer of bupivacaine, was developed to improve the cardiac safety profile of bupivacaine. We describe 2 cases of grand mal seizures following accidental intravascular injection of levobupivacaine. Case Report Two patients presenting for elective orthopedic surgery of the lower limb underwent blockade of the lumbar plexus via the posterior approach. Immediately after the administration of levobupivacaine 0.5% with epinephrine 2.5 μg/mL, the patients developed grand mal seizures, despite negative aspiration for blood and no clinical signs of intravenous epinephrine administration. The seizures were successfully treated with sodium thiopental in addition to succinylcholine in 1 patient. Neither patient developed signs of cardiovascular toxicity. Both patients were treated preoperatively with β-adrenergic antagonist medications, which may have masked the cardiovascular signs of the unintentional intravascular administration of levobupivacaine with epinephrine. Conclusions Although levobupivacaine may have a safer cardiac toxicity profile than racemic bupivacaine, if adequate amounts of levobupivacaine reach the circulation, it will result in convulsions. Plasma concentrations sufficient to result in central nervous system toxicity did not produce manifestations of cardiac toxicity in these 2 patients.

A New Teaching Model for Resident Training in Regional Anesthesia

The adequacy of resident education in regional anesthesia is of national concern. A teaching model to improve resident training in regional anesthesia was instituted in the Anesthesiology Residency in 1996 at Duke University Health System. The key feature of the model was the use of a CA-3 resident in the preoperative area to perform regional anesthesia techniques. We assessed the success of the new model by comparing the data supplied by the Anesthesiology Residency to the Residency Review Committee for Anesthesiology for the training period July 1992–June 1995 (pre-model) and the training period July 1998–June 2001 (post-model). During the 3-yr training period, the pre-model CA-3 residents (n = 12) performed a cumulative total of 80 (58–105) peripheral nerve blocks (PNBs), 66 (59–74) spinal anesthetics, and 133 (127–142) epidural anesthetics. The CA-3 post-model residents (n = 10) performed 350 (237–408) PNBs, 107 (92–123) spinal anesthetics, and 233 (221–241) epidural anesthetics (P < 0.0001). All results are reported as median (interquartile range). We conclude that our new teaching model using our CA-3 residents as block residents in the preoperative area has increased their clinical exposure to PNBs.

Spinal cord neural anatomy in rats examined by In Vivo magnetic resonance microscopy

Background and Objectives. Magnetic resonance microscopy (MRM) is a technique that is worthwhile for anesthesiologists because it allows spinal cord and plexus anatomy to be visualized three dimensionally and followed over time in the same animal. For example, the long‐term effect of indwelling intrathecal or plexus catheters can be studied in situ, and convective and diffusive forces within intrathecal, epidural, or nerve sheath spaces can be investigated. Further, diffusion‐weighted MRM, which measures an “apparent diffusion coefficient” (ADC), can be used to track the presence of ischemia, hypoperfusion, or cytotoxic edema. This study investigates problems associated with the use of in vivo MRM for spinal cord and peripheral nerve studies in the rat. Methods. Twenty‐one anesthetized female Fisher CDF rats were used. Group 1 (n = 7) was used for anatomic three‐dimensional studies. Groups 2 (n = 4), 3 (n = 4), and 4 (n = 6) were used for measurements of the ADC. Group 2 served as controls, group 3 received lumbar intrathecal catheters, and group 4 received cervical intrathecal catheters. Results. Cervical spine, lumbar spine, and spinal nerves and ganglia were accurately visualized with MRM. As a rule, spinal cord gray and white matter were better demonstrated using diffusion‐weighted proton stains. By contrast, T2‐weighted proton staining superiorly demonstrated structures surrounding the spinal cord. In groups 3 and 4, indwelling intrathecal catheters did not affect the spinal cord ADC, indicating normal blood flow and no cytotoxic edema. Contrast studies revealed nonhomogeneous distribution of contrast predominately in the lateral and ventral intrathecal space. Conclusions. Threedimensional diffusion‐weighted MRM displays cervical and lumbar spine anatomy accurately in vivo. Apparent diffusion coefficients measurements are feasible in rat cervical spinal cord with intrathecal catheters. Spinal cord ADCs are unaffected by intrathecal catheters, indicating normal spinal cord perfusion.

Variability in determination of point of needle insertion in peripheral nerve blocks: A comparison of experienced and inexperienced anaesthetists

Accurate identification of surface landmarks is essential for the successful performance of peripheral nerve blocks. The variability between experienced and inexperienced practitioners in identifying anatomical landmarks has not been studied previously. Anaesthetists were asked to identify the point of needle insertion for posterior lumbar plexus and sciatic nerve blocks on a volunteer using a standard textbook description. The chosen point for needle insertion was described in terms of X and Y co‐ordinates, measured in millimetres, from a zero reference point marked on a volunteers back. Fifteen experienced and 22 inexperienced anaesthetists took part in the study. The lumbar plexus block mean [range] values for the X, Y co‐ordinates were 80 [62–108], 66 [46–86] and 92 [49–150], 62 [0–131] in the experienced and inexperienced groups, respectively. The sciatic nerve block X, Y co‐ordinates were 77 [62–99], 70 [49–89] and 68 [29–116], 62 [26–93] in the experienced and inexperienced groups, respectively. The variance for the point of needle insertion was significantly greater in the inexperienced group (p < 0.01) for both the lumbar plexus and sciatic nerve blocks. We conclude that with increasing experience, there is decreased variability in determining the point of needle insertion using anatomical landmarks.