Jeffrey D. Swenson

Outpatient management of continuous peripheral nerve catheters placed using ultrasound guidance: an experience in 620 patients.

BACKGROUND:Continuous peripheral nerve block (CPNB) is an optimal choice for analgesia after orthopedic procedures, but is not commonly used in outpatients because of concern regarding the possibility of catheter-related complications. In addition, it may be difficult to provide adequate patient access to physicians in this setting. We present 620 outpatients who were treated with CPNB using an established protocol. METHODS:All catheters were placed using direct ultrasound visualization. These patients received extensive oral and written preoperative instruction and were provided continuous telephone access to the anesthesiologist during the postoperative period. All patients were also contacted at home by telephone on the first postoperative day. In addition, each patient was seen and examined by the surgeon within 2 wk of hospital discharge. RESULTS:Of the 620 patients, there were 190 interscalene (brachial plexus), 206 fascia iliaca (femoral nerve), and 224 popliteal fossa (sciatic nerve) catheters. Two patients (0.3%) had complications related to the nerve block. In both of these patients, the symptoms resolved within 6 wk of surgery. Twenty-six patients (4.2%) required postoperative interventions by the anesthesiologist. One patient returned to the hospital for catheter removal. CONCLUSIONS:In this large series of outpatients treated with CPNB, there were surprisingly few interventions requiring an anesthesiologist. Likewise, patients were able to manage and remove their catheters at home without additional follow-up. This suggests that with adequate instruction and telephone access to health care providers, patients are comfortable with managing and removing CPNB catheters at home.

Transesophageal Echocardiography: An Objective Tool in Defining Maximum Ventricular Response to Intravenous Fluid Therapy

Ventricular preload is an important determinant of cardiac function, which is indirectly measured in the clinical setting by the pulmonary capillary wedge pressure (PCWP).Transesophageal echocardiography (TEE) is rapidly gaining acceptance as a monitor of cardiac function. Although it provides high-resolution images of cardiac structures, clinical assessment of ventricular preload using TEE has been subjective, since quantitative measurements have been difficult to perform in a timely fashion. Automated border detection (ABD) is a new technology used in conjunction with TEE that allows quantitative real-time, two-dimensional measurement of cavity areas. To determine whether end-diastolic area (EDA) measured by ABD can be used to determine an appropriate end point for intravenous fluid administration, nine mongrel dogs were studied. Anesthetized animals were hemorrhaged to achieve a central venous pressure of 0-5 mm Hg. Each animal was then given intravenous fluid (autologous blood followed by hetastarch) until a peak in thermodilution cardiac output (CO) was achieved. Measures of PCWP, EDA, CO, and left ventricular stroke work (LVSW) were obtained after each fluid bolus. Bivariate plots displaying administered volume versus CO, LVSW, and EDA revealed parallel curves for each of these variables with peaks evident at cumulative volumes of 50-55 mL/kg. Multiple regression with mixed model analysis of covariance was performed to determine the significance of EDA in relation to changes in CO and LVSW. Analysis was likewise performed comparing the relationship between PCWP and changes in CO or LVSW. A significant relationship was demonstrated when comparing EDA to changes in CO and LVSW (P = 0.03 and P < 0.0001, respectively). Similar analysis comparing PCWP to changes in CO and LVSW failed to demonstrate a significant relationship (P = 0.54 and P = 0.36, respectively). These data suggest that changes in EDA measured using TEE with ABD are related to trends in cardiac function and can suggest an appropriate end point for intravenous fluid administration as defined by maximum CO and LVSW. PCWP did not demonstrate a significant relationship to changes in CO and LVSW. (Anesth Analg 1996;83:1149-53)

A novel approach for assessing catheter position after ultrasound-guided placement of continuous interscalene block.

The increasing use of ultrasound has allowed anesthesiologists to perform nerve blocks with a high success rate and without nerve stimulation or eliciting a paresthesia. The ability to visualize peripheral nerve catheters using ultrasound is limited. We present a novel method to confirm the position of an interscalene catheter tip using injection of agitated contrast. The described technique is simple and allows timely assessment of catheter tip position.

The effect of prior dural puncture on cisternal cerebrospinal fluid morphine concentrations in sheep after administration of lumbar epidural morphine

Combined spinal epidural anesthesia has become increasingly popular as a method of providing rapid onset of analgesia or surgical block with access for further administration of analgesics or anesthetics.No in vivo studies have evaluated the relationship between dural puncture and drug transfer from the epidural space to the cerebrospinal fluid (CSF). To determine whether morphine administered in the epidural space adjacent to a dural puncture results in increased CSF concentrations at the cisterna magna (CM), 12 adult ewes were studied. Each animal was assigned to one of three groups. Animals in Group 1 served as a control and received no dural puncture. Animals in Group 2 received a dural puncture with a 25-gauge (G) Whitacre needle, while Group 3 animals received a dural puncture with an 18-G Tuohy needle. One hour after dural puncture, each animal was given epidural morphine, 0.2 mg/kg. Six hours after the administration of epidural morphine, CSF from the CM was sampled and analyzed by gas chromatographymass spectrometry for morphine concentration. The mean morphine concentration at the CM for Group 1 (control) was 22 +/- 12 ng/mL, whereas animals with 25-G and 18-G dural punctures had concentrations of 154 +/- 32 ng/mL and 405 +/- 53 ng/mL, respectively (P = 0.0005). These data demonstrate that a significant increase in CSF morphine concentration at the brainstem will occur when lumbar epidural morphine is administered adjacent to a dural puncture. Furthermore, the increase in CSF morphine concentration is positively correlated with the size of the needle producing the dural puncture. These findings highlight the potential for delayed respiratory depression when epidural opiate administration follows a dural puncture. (Anesth Analg 1996;83:523-5)

The anatomic relationship of the sciatic nerve to the lesser trochanter: implications for anterior sciatic nerve block.

Classic descriptions of the anterior sciatic nerve block suggest needle placement at the level of the lesser trochanter of the femur. Recently, investigators have reported that the sciatic nerve is not accessible at this level. To define more accurately the anatomic relationship of the sciatic nerve to the lesser trochanter, we analyzed magnetic resonance scans performed on 20 patients in the supine position. After IRB approval, magnetic resonance scans of the hip and proximal femur were reviewed in 20 supine patients in the neutral position. Images from five axial levels were studied, specifically, at the level of the lesser trochanter and at 1-cm intervals inferior to the lesser trochanter for 4 cm. In each axial image, the medial or lateral distance was measured from the sciatic nerve to a sagittal plane at the medial border of the femur. If the sciatic nerve was lateral to this sagittal plane (inaccessible), the distance was assigned a negative value, and if the sciatic nerve was medial to the sagittal plane (accessible), the distance was assigned a positive value. The distance between the coronal plane at the anterior border of the femur and the coronal plane through the sciatic nerve was also recorded for each level. At the level of the lesser trochanter, the sciatic nerve was lateral to the femoral border (inaccessible) in 13 of 20 patients with a mean distance of −4.0 ± 7.7 mm. At 4 cm below the lesser trochanter, the sciatic nerve was medial to the femoral border (accessible) in 19 of 20 patients with a mean distance 7.8 ± 5.8 mm. The distance from the anterior border of the femur to the sciatic nerve was 42.9 ± 5.8 mm at the level of the lesser trochanter and 45.7 ± 9.5 mm at 4 cm below the lesser trochanter. The classic description of the anterior approach to the sciatic nerve suggests that the needle be walked off medially at the level of the lesser trochanter. Our data are consistent with recent reports suggesting that in the majority of subjects, the position of the sciatic nerve relative to lesser trochanter made it inaccessible from an anterior approach at this level. In contrast, at 4 cm below the lesser trochanter, the sciatic nerve was medial to the femur in 19 of 20 subjects. We conclude that needle insertion medial to the proximal femur, 4 cm below the lesser trochanter, is a more direct anatomical approach to the anterior sciatic nerve block.

The effect of distance from injection site to the brainstem using spinal sufentanil.

Background and Objectives Intrathecal (IT) sufentanil is commonly used in parturients to provide rapid onset of labor analgesia without motor block. This practice, although widely used, has been associated with severe respiratory depression in some patients. The mechanism of this respiratory depression is unclear, however, rapid cephalad movement and interaction with parenteral opioids are 2 frequently cited explanations for this complication. Because this complication has occurred only in women with heights between 150 and 157 cm, we elected to study the effect of the distance from injection site to the cisterna magna (CM) on peak brainstem cerebrospinal fluid (CSF) concentrations. Methods Ten adult ewes were injected with IT sufentanil (0.3 μg/kg) at a mean distance of either 71 cm (65 to 78 cm) from the brainstem (pelvic group) or 37 cm (34 to 42 cm) from the brainstem (thoracic group). CSF was then sampled at 5-minute intervals from the CM. Results Measurable CM concentrations of sufentanil were noted in the brainstem at 20 and 25 minutes, respectively, for the thoracic and the pelvic groups. Peak sufentanil concentrations from the thoracic group were nearly 10-fold higher (0.553 ± 0.43 ng/mL) compared with the pelvic group (0.064 ± 0.002 ng/mL) when measured in the CM (P = .023). Conclusions Our results suggest that sufentanil migrates relatively large distances in the IT space. Injection site (distance from the brainstem) appears to be a prominent factor in determining brainstem concentrations and subsequent respiratory depression after spinal administration.

Rapid onset of ulnar nerve dysfunction during transient occlusion of the brachial artery

Perioperative ulnar neuropathy is a complication that occurs even in patients who seem to be appropriately padded and positioned.The disproportionately high incidence of postoperative ulnar nerve injury compared with the median and radial nerves has largely been attributed to its vulnerability to compression or stretch at the cubital tunnel. Some clinical and laboratory evidence suggests that compromise of perfusion to the upper extremity may also play a role in this complication. To determine whether the ulnar nerve is more sensitive to ischemia of the upper extremity, we studied 10 men during general anesthesia. Somatosensory evoked potentials of the radial, median, and ulnar nerves were simultaneously recorded during general anesthesia with the brachial artery occluded proximal to the cubital fossa. All three nerves showed rapid changes in signal amplitude in response to occlusion of the brachial artery, but the amplitude of the ulnar nerve was affected earlier and to a greater degree. Compared with the median nerve, the change in ulnar nerve signal amplitude during ischemia was significantly greater after 4 min (P = 0.002). This trend persisted at 6 and 8 min (P = 0.008). At 4, 6, and 8 min of ischemia, the ulnar nerve likewise showed a greater decrease in amplitude compared with the radial nerve, with corresponding P values of 0.015, 0.008, and 0.008. We conclude that the ulnar nerve is more sensitive to ischemia of the upper extremity compared with the radial and median nerves. In addition to its increased vulnerability at the elbow, compromise of arterial flow may contribute to some cases of postoperative ulnar neuropathy. Implications: Postoperative ulnar neuropathy is thought to result from compression or stretch of the ulnar nerve at the elbow. However, patients may sustain this complication despite careful padding and positioning. This study suggests that the ulnar nerve may also be unusually sensitive to decreases in blood supply to the arm. Care should not only to properly position and pad the elbows, but also to ensure adequate perfusion of the upper extremities. (Anesth Analg 1998;87:677-80)

Psychological Distress in Hip Arthroscopy Patients Affects Postoperative Pain Control

PURPOSE To determine whether patients with higher levels of preoperative psychological distress more frequently use a postoperative fascia iliaca nerve block for pain control after hip arthroscopy, and to determine whether a fascia iliaca nerve block is an effective adjunct to multimodal oral and intravenous analgesia after hip arthroscopy. METHODS One hundred seven patients undergoing hip arthroscopy were prospectively enrolled. Before surgery, patients were administered the Distress Risk Assessment Method questionnaire to quantify their level of preoperative psychological distress. Postoperatively, patients with pain inadequately controlled by multimodal oral and intravenous analgesics could request and receive a fascia iliaca nerve block. Pain scores, opioid consumption, time in the post-anesthesia care unit (PACU), and postoperative complications were recorded for all patients. RESULTS Patients with normal Distress Risk Assessment Method scores requested fascia iliaca nerve blocks approximately half as frequently (18 of 50 [36%]) as patients in the at-risk category (28 of 47 [60%]) or distressed category (7 of 10 [70%]) (P = .02). Patients with high levels of distress also received 40% more intraoperative opioid than patients with normal scores (P = .04). In the study population as a whole, patients who received a fascia iliaca nerve block (n = 53) had a higher initial visual analog scale (VAS) pain score in the PACU (7.2 ± 0.3 v 5.5 ± 0.4, P = .001) and showed greater improvement in the VAS pain score by PACU discharge (-4.3 ± 0.2 v -2.1 ± 0.3, P ≤ .0001) compared with patients who did not receive a block (n = 54). CONCLUSIONS Patients with higher levels of preoperative psychological distress more frequently requested a postoperative nerve block to achieve adequate pain control after hip arthroscopy. Patients receiving a block had greater improvement in VAS pain scores compared with patients managed with oral and intravenous analgesics alone. LEVEL OF EVIDENCE Level IV, case series.

Congenital tracheal bronchus: the inability to isolate the right lung with a univent bronchial blocker tube.

Tracheal bronchus is a congenital anomaly in which the right upper lobe bronchus originates from the lateral tracheal wall. This anatomic variant is reported in approximately 1 of 250 patients at bronchoscopy. Although it is usually of little clinical significance, this atypical origin of the right upper lobe bronchus may complicate one-lung ventilation during thoracic surgery.

Preoperative "fentanyl challenge" as a tool to estimate postoperative opioid dosing in chronic opioid-consuming patients.

When opioids are used for postoperative pain control, it is useful to define the dose-response relationship for analgesia and respiratory depression. We studied 20 chronically opioid-consuming patients having elective multilevel spine fusion. Preoperatively, each patient received a fentanyl infusion of 2 &mgr;g · kg−1 · min−1 until the respiratory rate was <5 breaths/min. Pharmacokinetic simulations were used to estimate the effect site concentration at the time of respiratory depression and to predict the patient-controlled analgesia settings that would provide an effect-site fentanyl concentration that was 30% of the concentration associated with respiratory depression. Postoperatively, patient-controlled analgesia settings were adjusted to achieve 2–3 demand doses per hour. At steady-state patient-controlled analgesia settings, arterial blood gases and plasma fentanyl levels were measured. Sixteen patients required no adjustment or one patient-controlled analgesia adjustment. The median arterial Pco2 level was 41 mm Hg and the interquartile range was 39–46 mm Hg. Plasma fentanyl levels demonstrated a significant correlation to the estimated effect-site concentration associated with respiratory depression determined during the preoperative fentanyl challenge. A preoperative fentanyl challenge used with pharmacokinetic simulations may be a useful tool to individualize the administration of analgesics to chronically opioid-consuming patients.