Daniel M. Thys

Combination of intraneural injection and high injection pressure leads to fascicular injury and neurologic deficits in dogs.

Background Unintentional intraneural injection of local anesthetics may cause mechanical injury and pressure ischemia of the nerve fascicles. One study in small animals showed that intraneural injection may be associated with higher injection pressures. However, the pressure heralding an intraneural injection and the clinical consequences of such injections remain controversial. Our hypothesis is that an intraneural injection is associated with higher pressures and an increase in the risk of neurologic injury as compared with perineural injection. Methods Seven dogs of mixed breed (15-18 kg) were studied. After general endotracheal anesthesia, the sciatic nerves were exposed bilaterally. Under direct microscopic guidance, a 25-gauge needle was placed either perineurally (into the epineurium) or intraneurally (within the perineurium), and 4 mL of lidocaine 2% (1:250,000 epinephrine) was injected by using an automated infusion pump (4 mL/min). Injection pressure data were acquired by using an in-line manometer coupled to a computer via an analog digital conversion board. After injection, the animals were awakened and subjected to serial neurologic examinations. On the 7th day, the dogs were killed, the sciatic nerves were excised, and histologic examination was performed by pathologists blinded to the purpose of the study. Results Whereas all perineural injections resulted in pressures ≤4 psi, the majority of intraneural injections were associated with high pressures (25-45 psi) at the beginning of the injection. Normal motor function returned 3 hours after all injections associated with low injection pressures (≤11 psi), whereas persistent motor deficits were observed in all 4 animals having high injection pressures (≥25 psi). Histologic examination showed destruction of neural architecture and degeneration of axons in all 4 sciatic nerves receiving high-pressure injections. Conclusions High injection pressures at the onset of injection may indicate an intraneural needle placement and lead to severe fascicular injury and persistent neurologic deficits. If these results are applicable to clinical practice, avoiding excessive injection pressure during nerve block administration may help to reduce the risk of neurologic injury.

Injection pressures by anesthesiologists during simulated peripheral nerve block

Background and Objectives: Anesthesiologists typically rely on a subjective evaluation (“syringe feel”) of possible abnormal resistance to injection while performing a peripheral nerve block (PNB). A greater force required to perform the injection is believed to be associated with intraneural injection. The hypothesis of this study is that anesthesiologists vary in their perception of “normal” injection force, that the syringe feel method is inconsistent in estimating resistance, and that needle design may affect the injection force. Methods: Thirty anesthesiologists were asked to inject a local anesthetic, as they would in their everyday practice, through a commonly used syringe and needle assembly. Injection force was measured using an in-line manometer coupled to a computer via an analog-to-digital conversion board. In addition, injection force at clinically relevant injection speeds was determined using 3 differently sized needles from 4 different manufacturers. Results: During a steady injection rate, all anesthesiologists perceived an increase in the force required to inject, even with minor pressures changes (0.6 ± 0.3 psi). However, the 30 anesthesiologists, 21 (70%) initiated injection using a force that resulted in pressures greater than 20 psi; 15 (50%) used a force greater than 25 psi, and 3 (10%) exerted pressures greater than 30 psi. Pressures varied as much as 20-fold among needles of the same gauge/length from different manufacturers (P < .01). Conclusions: Anesthesiologists vary widely in their perception of appropriate force and rate of injection during PNB. The syringe-feel method of assessing injection force is inconsistent and may be further affected by variability in needle design.

Use of Atraumatic Spinal Needles Among Neurologists in the United States

Objective.—To evaluate atraumatic spinal needle use among US neurologists.

Combined popliteal and posterior cutaneous nerve of the thigh blocks for short saphenous vein stripping in outpatients: An alternative to spinal anesthesia

STUDY OBJECTIVEnTo compare a combination of peripheral nerve blocks with spinal anesthesia in ambulatory patients undergoing short saphenous vein stripping.nnnDESIGNnProspective, randomized study.nnnSETTINGnUniversity hospital.nnnPATIENTSn28 ASA physical status l and II ambulatory surgery patients undergoing short saphenous vein stripping.nnnINTERVENTIONSn14 patients received a popliteal block (sciatic nerve block at the popliteal fossa) using 30 ml of alkalinized 3% chloroprocaine and a posterior cutaneous nerve of the thigh block with 10 ml of 1% lidocaine. The 14 patients who were randomized to the spinal anesthesia group received 65 mg of 5% hyperbaric lidocaine.nnnMEASUREMENTS AND MAIN RESULTSnThere were no significant differences in age and gender between the two groups (mean age 53 +/- 13 years, 8 men and 20 women). Patients in the peripheral nerve block group recovered significantly faster in phase 1 of the postanesthesia care unit (PACU) (67 +/- 10 min vs. 122 +/- 50 min, p < 0.01) and were discharged home sooner (222 +/- 53 min vs. 294 +/- 69 min, p < 0.01) than the patients in the spinal anesthesia group.nnnCONCLUSIONSnThe combination of popliteal and posterior cutaneous nerve of the thigh blocks provided adequate anesthesia and a faster recovery profile with a similar subjective acceptance of both anesthetic techniques in ambulatory patients undergoing short saphenous vein stripping in the prone position.

A study of the human aortic valve orifice by transesophageal echocardiography

The transverse short-axis plane of the aortic valve was imaged by transesophageal echocardiography at a relatively high frame rate in 25 anesthetized patients undergoing heart surgery. The effective, time-averaged aortic valve area (a-AVA) was compared with areas obtained with triangular and circular valve orifice models (t-AVA and c-AVA, respectively). The aortic valve orifice was circular during 33.6% +/- 17.5% of systole. The relations between the triangular or circular aortic valve areas and a-AVA were as follows: t-AVA = 1.04 x a-AVA - 0.14 (r = 0.90; standard error of the estimate = 0.24 cm2) and c-AVA = 1.37 x a-AVA + 0.00 (r = 0.90; SEE = 0.30 cm2). Bias analysis showed no significant difference between a-AVA and t-AVA (bias = -0.04 +/- 0.23 cm2; difference not significant) but a significant overestimation of the average valve area by c-AVA (bias = +0.88 +/- 0.30 cm2; p < 0.001). Thus the aortic valve orifice was not circular for the entire duration of systole and valve area calculations based on a triangular model approximated a-AVA more closely than did those based on a circular model. These findings suggest that, for echocardiographic measurements that incorporate the aortic valve orifice area (e.g., stroke volume determinations), the use of a triangular valve area model, rather than a circular model, may produce more accurate results in anesthetized patients with heart disease.

Esmolol and intraoperative myocardial ischemia: a double-blind study.

Forty patients scheduled to undergo elective myocardial revascularization were included in a randomized, double-blind, placebo-controlled study to evaluate any influence of esmolol on the incidence of myocardial ischemia. Calibrated recordings of ECG leads II and V5 were continuously monitored with the QMED Monitor One TC (Qmed Inc, Clark, NJ) from the time of arrival in the operating room holding area through the induction of anesthesia, using a high-dose opioid technique, and until the initiation of cardiopulmonary bypass. One group received a bolus of esmolol, 1.0 mg/kg, followed by a continuous infusion of 100 micrograms/kg/min. The other group received a bolus and infusion of saline placebo of equal volume. The incidence of myocardial ischemia was not significantly different between the groups on arrival in the holding area, or at any study point. Heart rate, mean arterial pressure, and the number of patients developing myocardial ischemia during the course of the study also did not differ significantly between the groups. There were significant decreases in heart rate and mean arterial pressure compared with the awake baseline values in both groups during multiple study points. It is concluded that esmolol was ineffective at treating preexisting or new-onset myocardial ischemia at this dosage in this clinical setting.

Does metoclopramide supplement postoperative analgesia using patient-controlled analgesia with morphine in patients undergoing elective cesarean delivery?

Background and Objectives Recent studies have shown that metoclopramide may decrease postoperative narcotic requirements in patients undergoing secondtrimester induced abortions or prosthetic hip surgery. It is often used to decrease the incidence of nausea and vomiting in the patient undergoing cesarean delivery under regional anesthesia. If metoclopramide were found to be an analgesic adjunct in these patients, it would offer an additional impetus for its routine use. Methods. After elective cesarean delivery under spinal anesthesia, 32 patients were monitored for initial and 24-hour postoperative morphine requirements via intravenous patient-controlled analgesia. These patients were divided into two groups. Prior to spinal block, group 1 (n=17) received 10 mg intravenous metoclopramide, and group 2 (n=15) received an intravenous saline placebo. Results. No differences were found between groups in the time from spinal placement to the time of pain onset, the amount of morphine necessary to initially achieve comfort, or 24-hour postoperative morphine requirements. (P>.05). Conclusions. This study demonstrates that metoclopramide decreases intraoperative nausea but does not supplement analgesia in patients undergoing elective cesarean delivery.

Training Requirements for Peripheral Nerve Blocks

PURPOSE OF REVIEWnTo review the current recommendations and literature on training in regional anesthesia and suggest an improved model to prepare graduating residents better in the practice of regional anesthesia.nnnRECENT FINDINGSnPatient satisfaction, a growing demand for cost-effective anesthesia, and a favorable postoperative recovery profile have all resulted in the growing demand for regional anesthesia. However, it has been well established that the current teaching of regional anesthesia is suboptimal.nnnSUMMARYnA structured regional anesthesia rotation, a dedicated team of mentors with training in regional anesthesia, and adequate clinical volume are a pre-requisite for adequate training, but they may not be available in many anesthesia residency training programs. As the demand for regional anesthesia continues to increase in the years to come, it is imperative to ensure adequate education of graduating residents to meet this demand. In order to achieve this goal, the present recommendations should be re-evaluated, and perhaps a proficiency in a core group of widely applicable and relatively simple nerve blocks should be mastered by all graduates.

A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block

Sciatic nerve block in the popliteal fossa is associated with a highly variable success rate.Frequently, anesthesia is profound in the distribution of both the tibial (TN) and common peroneal nerves (CPN), although the response to nerve stimulation or paresthesia is obtained in the distribution of one division of the nerve. However, anesthesia in the distribution of only one division of the nerve is also a common occurrence under apparently identical clinical circumstances. Looking for a possible role of a common epineural sheath in these phenomena, we injected dye into the epineural sheath of the tibial nerve in 10 cadaver legs and observed its spread within the sheath. Injections of 15 mL and 30 mL of the dye resulted in a proximal spread of 147 +/- 34 mm and 172 +/- 50 mm, respectively, from the injection point 10 cm below the popliteal fossa crease. In a majority of the legs, the dye reached the division of the sciatic nerve in the popliteal fossa, bathing both the TN and CPN. Gross inspection and histologic examination of the sciatic nerve specimens revealed a common epineural sheath enveloping the TN and CPN. The presence of the common epineural sheath and its characteristics may have important clinical implications for sciatic nerve blockade in the popliteal fossa. (Anesth Analg 1997;84:387-90)