Preemptive analgesia: its role and efficacy in anterior cruciate ligament reconstruction.

As more outpatient orthopaedic surgical procedures are performed, postoperative pain control has gained importance. The benefits of preemptive analgesia, the use of analgesics or anesthetics or both before painful stimuli to prevent or reduce pain, have been widely published in the anesthesia and general surgery literature, but not in orthopaedic literature. We prospectively compared the effects, on postoperative pain and narcotic use, of intraarticular preoperative injections of 1) placebo with epinephrine, 2) bupivacaine with epinephrine, and 3) bupivacaine and morphine with epinephrine. Thirty patients (10 in each group) underwent arthroscopic anterior cruciate ligament reconstruction using patellar tendon autograft under general anesthesia. Pain was assessed with a 10-point visual analog scale pre- and postoperatively, and postoperative narcotic pain medication use was recorded. Postoperative pain was significantly greater in group 1 (placebo) than in the preemptive-treatment groups (groups 2 and 3), and in group 2 than in group 3. The differences became less apparent with time, and after 1 hour, no significant differences in pain scores existed between the groups. However, intravenous narcotic pain medication was administered in the recovery room to patients with pain scores greater than 5, equalizing pain scores. Group 3 used significantly less postoperative narcotic medication than group 1. Preemptive analgesia using intraarticular bupivacaine and morphine with epinephrine resulted in lower pain scores during the 1st hour after an arthroscopic anterior cruciate ligament reconstruction than did preemptive treatment with bupivacaine and epinephrine or placebo and epinephrine.

Intraarticular morphine and bupivacaine reduces postoperative pain after rotator cuff repair.

BACKGROUND AND OBJECTIVES: To determine whether intraarticular injection of morphine, fentanyl, or sufentanil added to bupivacaine provided pain control after open rotator cuff repair. METHODS: These data were collected as a prospective, randomized, blinded observer study. All patients received a standard interscalene anesthetic with 1.4% mepivacaine with 1:200,000 epinephrine. At the conclusion of surgery, they received an intraarticular injection after the shoulder capsule was closed. Patients were randomized into 4 groups. All received 20 mL of 0.25% bupivacaine: group 1, plain; group 2, with 1 mg of morphine added; group 3, with 50 microg of fentanyl added; and group 4, with 10 microg of sufentanil added. Pain scores in the postanesthesia care unit were evaluated at 0, 30, 60, 90, 120, and 240 minutes and at 4-hour intervals postoperatively using a visual analogue scale. Breakthrough pain was managed with morphine, via patient controlled analgesia pump. RESULTS: Thirty-nine patients were entered into the study. Pain scores at 2 hours and beyond were lowest in group 2. Total morphine utilization was significantly lower for the first 24 hours in group 2. CONCLUSIONS: Intraarticular injection of the shoulder with 0.25% bupivacaine and 1 mg morphine at the conclusion of surgery provided pain control and diminished morphine used in the first 24 hours after open rotator cuff repair. Fentanyl and sufentanil did not improve the analgesia over that achieved with bupivacaine alone.

An unusual cause of acute chest pain during epidural anesthesia.

BACKGROUND AND OBJECTIVES: Selective sympathetic denervation during epidural anesthesia results in a small, active gut. These changes can also result in selective activity in one segment of the gut that is absent in other segments. CASE REPORT: A 61-year-old male was scheduled for bilateral total knee replacement during epidural anesthesia. Following onset of the epidural block, he experienced severe left-sided chest pain. Surgery was canceled. A portable chest radiograph revealed a widened mediastinum, and he underwent angiography to rule out a dissecting thoracic aortic aneurysm. The left subclavian artery could not be visualized, and an MRI was obtained, which was normal. After his return to the intensive care unit, he had a large bowel movement and his chest pain resolved. CONCLUSION: Selective activity of the gastrointestinal tract during the onset of epidural anesthesia created a visceral pain, which effectively simulated pain with a cardiovascular origin.

Preoperative intra-articular morphine and bupivacaine for pain control after outpatient arthroscopic anterior cruciate ligament reconstruction.

BACKGROUND AND OBJECTIVES: The purpose of this study was to determine whether intra-articular injection of bupivacaine, morphine, or a combination prior to surgery provided pain control after arthroscopic anterior cruciate ligament (ACL) reconstruction. METHODS: These data were collected as a two-stage prospective, randomized, blinded observer study. All patients received a standard general anesthetic, which included an intra-articular injection 20 minutes prior to incision. In phase I, three solutions were assigned randomly in a 60-mL volume. Group 1 was saline, group 2 was 0.25% bupivacaine, and group 3 was 0.25% bupivacaine with 1 mg morphine sulfate (MS). Phase II was identical to phase I in technique and had four groups. Group 1 was 0.25% bupivacaine, group 2 was 1 mg MS in saline, group 3 was 0.25% bupivacaine with 1 mg MS, and group 4 was 0.25% bupivacaine with 3 mg MS. All groups in phases I and II contained 1:200,000 epinephrine, freshly added. Pain scores were evaluated at 0, 30, 60, 90, 120, and 240 minutes postoperative using a visual analog scale. For pain scores of 5 or greater, 50 microg fentanyl was administered at 5-minute intervals until pain was controlled. After transition from phase I to phase II of the postanesthesia care unit (PACU), hydrocodone/acetaminophen tablets were used. RESULTS: Thirty patients were entered into phase I of the study. Both treatment groups (2 and 3) had significant (P < .05) pain reduction on arrival to the PACU. Group 3 had significantly (P < .05) reduced need for fentanyl during the PACU stay. Forty-nine patients entered phase II of the study. In phase II, group 3 had the lowest pain scores on arrival to the PACU. At 120 and 240 minutes, pain scores were lower in groups 3 and 4. Fentanyl and hydrocodone uses were significantly lower during the PACU stay in groups 3 and 4. CONCLUSIONS: Presurgical injection of a solution of 0.25 % bupivacaine, morphine, and epinephrine provided pain control and decreased opioid use in the PACU. Increasing the morphine dose did not improve the clinical result.

An introduction to the World Wide Web.

BACKGROUND AND OBJECTIVES: Anesthesiologists are increasingly utilizing the Internet for personal and professional purposes. Without guidance, the task of searching the Internet for information may be time-consuming and frustrating. This article includes a basic introduction to the Internet with suggestions and guidelines for accessing information resources. Future articles will address locating articles about human anatomy, regional anesthesia and pain medicine. EDITORS NOTE: This is the first in an informal series of articles demonstrating and describing information technology. The articles will include nontechnical information and will detail the experiences and wisdom obtained from experienced anesthesiologists. The series is geared toward the computer novice with interest in regional anesthesia and pain medicine. These articles are also available in full text on the American Society of Regional Anesthesia website (www.asra.com) with links to the websites in the article.

Asymptomatic profound oxyhemoglobin desaturation following interscalene block in a geriatric patient.

BACKGROUND AND OBJECTIVES: Interscalene block can be chosen for complete anesthesia for shoulder surgery. Phrenic nerve block occurs with almost all interscalene blocks, but is well tolerated in most patients. This may not be the case in selected geriatric patients. METHODS: The patient is a 90-year-old female with osteoarthritis of the left shoulder scheduled for total shoulder anthroplasty. Past medical history revealed hypertension, mild mitral valve insufficiency, and a remote episode of congestive heart failure. She underwent interscalene block with 40 mL of 1.4% mepivacaine, 1:200,000 epinephrine freshly added, alkalinized with sodium bicarbonate. RESULTS: The onset of the block was rapid and complete. The patient had minimal intravenous sedation (0.5 mg midazolam) and was resting comfortably with a respiratory rate of 12-14 breaths/min. Approximately 5 minutes after the injection of local anesthetic, the patient was noted to be alert, cyanotic, denying dyspnea, with an oxygen saturation of 75-85%. A chest radiograph revealed elevation of the ipsilateral hemidiaphragm and no pneumothorax or other pathology. Despite supplemental oxygen by face mask, desaturation persisted and general anesthesia was induced. On emergence from anesthesia, the patient had a complete interscalene block. Repeat chest radiograph after resolution of the block revealed return of hemidiaphragm position and no other pathology. The patient was extubated in the recovery room without difficulty. Following extubation the patient demonstrated stable respirations and normal oxyhemoglobin saturation. CONCLUSIONS: Ipsilateral phrenic nerve paralysis caused significant respiratory compromise in an elderly patient without known significant pulmonary disease.

Influence of lumbar spine pathology on the incidence of paresthesia during spinal anesthesia.

BACKGROUND AND OBJECTIVES: Paresthesia occasionally occurs during dural puncture or injection of local anesthetic for spinal anesthesia. Although the incidence of neurologic complications after spinal anesthesia is extremely low, the significance of paresthesia is unknown. The influence of known lumbar spine pathology on the incidence of paresthesia during spinal anesthesia is studied. METHODS: Incidence of paresthesia with dural puncture (PP) or injection (PI) was studied in two groups of patients. Group 1 included patients for elective total joint replacement without known spine pathology or complaints. Group 2 included patients for elective lumbar spine surgery who received spinal anesthesia. RESULTS: Significantly more PP (20% vs 9%) and PI (16% vs 6%) occurred in the spine surgery group. There were no neurologic sequelae of spinal anesthesia. CONCLUSIONS: This information suggests that the incidence of paresthesia during the conduct of spinal anesthesia is higher in patients with lumbar spine pathology. Although there were no neurologic complications, the sample size is too small to exclude an increase in the neurologic risk of spinal anesthesia in patients with known intraspinal pathology.

A survey of exposure to regional anesthesia techniques in American anesthesia residency training programs.

BACKGROUND AND OBJECTIVES: The American Board of Anesthesiologists and the Residency Review Committee for Anesthesiology do not keep records regarding the individual resident's cumulative exposure to specific peripheral nerve block techniques. Further, little is known about individual trainee confidence in performing regional anesthetic blocks. To improve training and anesthesia practice, such information is necessary. In this nationwide survey, we assessed residents' perceived cumulative regional anesthesia experience and their confidence level. METHODS: A survey was distributed to 42 U.S. residency programs in 22 states. Information collected included the resident's clinical anesthesia (CA) training level, estimated number of regional anesthetics performed, and the resident's confidence level in performing these techniques. Confidence was graded on a 3-point scale, as being very confident (1.0), somewhat confident (2.0), or not confident (3.0). We analyzed the estimated cumulative number and type of blocks performed in relation to training level and confidence level; differences were considered significant when P< .001. RESULTS: The response rate was 67.2% (736/1,096); 32% (n = 232) of responders were CA-3 residents. At all training levels, the number of blocks performed varied widely according to type of block, with spinal and epidural blocks being performed most often at all training levels and sciatic, retrobulbar, and femoral blocks being performed least (median = 0 each for CA-1, CA-2, and CA-3 residents). Confidence was high with frequently performed blocks (spinal and lumbar epidural) and low for those performed less than 10 times per resident. The CA-3 residents reported a cumulative experience with a median (interquartile range) of 100 (50-100) spinal anesthetics and 150 (100-200) lumbar epidural blocks with all residents being very confident. The CA-3 residents completed a median of 20 (10-30) axillary blocks but a median of less than 10 for each of these techniques: intravenous regional anesthesia, ankle, interscalene, femoral, sciatic, and retrobulbar. For interscalene block, 51% of CA-3 residents were not confident; for femoral, 62%; for sciatic, 75%; and for retrobulbar block, 91%, were not confident. CONCLUSIONS: Most CA-3 residents are confident in performing lumbar epidural and spinal anesthesia. However, many are not confident in performing the blocks with which they have the least exposure. Changes need to be made in the training processes so that residents can graduate with enough confidence to continue selecting less familiar blocks in postgraduate practice.

Severe perioperative lactic acidosis: how clinically significant is it?

BACKGROUND: Lactic acidosis, generally defined as a plasma lactate concentration in excess of 5 mmol/L with a concomitant blood pH less than 7.25, is reported to have a direct association with mortality. OBJECTIVE: To report a case of unexplained perioperative lactic acidosis and to discuss the etiology, recognition, treatment, and importance of a transient rise in plasma lactate concentration. SUMMARY: Severe lactic acidosis developed in a 40-year-old man with Crohn's disease during major abdominal surgery. The plasma lactate concentration reached 16.9 mmol/L (normal range 1.5 to 2.2 mmol/L). This condition resolved within 14 hours without harm to the patient. CONCLUSIONS: When lactate accumulates in the perioperative period, the responsible condition is most often self-limiting. Reversible, subacute, marked lactic acidosis should not be assumed to predict mortality as it does in patients whose plasma lactate concentrations remain chronically elevated during severe systemic diseases such as sepsis.

Alkalinization of mepivacaine does not alter onset of caudal anesthesia.

STUDY OBJECTIVE: To determine the effect of alkalinization of mepivacaine on onset of caudal anesthesia. DESIGN: Randomized, blind study. SETTING: Colon-Rectal Surgery Service of the Tertiary Center at Cleveland Clinic Foundation. PATIENTS: Young, healthy adults undergoing anal surgery. INTERVENTIONS: Addition of bicarbonate (study group) or saline (control group) to mepivacaine. MEASUREMENTS AND MAIN RESULTS: At the onset of sacral anesthesia, demographics were measured. A slightly faster onset was found in the study group (4.28 vs. 6.08 minutes), but this was not statistically significant. CONCLUSIONS: Alkalinization of mepivacaine does not significantly accelerate the onset of caudal anesthesia.

Use of key words as an adjunctive learning tool improves learning during a perioperative medicine rotation for anesthesiology residents.

Designing a successful block rotation for anesthesiology residents requires not only an appropriate curriculum but also a set of teaching tools, which promote learning. Traditional clinical rotations in Anesthesiology residencies emphasize clinical teaching, supported by interaction with staff. Since Perioperative Medicine is a nontraditional subject for anesthesia residents, we introduced a syllabus and didactic curriculum to support clinical teaching. We hypothesized that the use of key words would enhance learning. Alternating groups of residents were assigned to receive key words, while control residents were expected to learn without key words. The key words were delivered in writing on the first day of the rotation and the syllabus was highlighted to identify the key words in the text. Pretests and posttests were administered to residents participating in the perioperative rotation. Learning was assessed by calculating the change in test scores. There was significantly more learning in the group given the key words. We conclude that key word designation improved learning in a rotation designed to teach perioperative medicine.

Interscalene brachial plexus anesthesia for shoulder surgery: report of a complicated intraoperative course.

We present a case of abrupt hemodynamic and mental status changes that occurred during shoulder surgery. During interscalene anesthesia for rotator cuff repair, there was abrupt onset of altered mental status and hemodynamic changes, which had a variety of possible contributing causes. Complete recovery occurred during care in the post-anesthesia care unit. A variety of physiologic changes can occurred during interscalene anaesthesia for shoulder surgery, which require prompt identification and management.

Total airway obstruction with neck extension: airway management of a patient with pharyngeal tumor.

Airway obstruction with the induction of anesthesia in children is common. Normally, neck extension with jaw thrust improves the airway. Flexion typically completes the obstruction. With the presence of a pharyngeal tumor, these relationships may not be the same. We present a case of complete airway obstruction with neck extension in the presence of a nasopharyngeal tumor. Flexion rather than extension of the neck relieved this airway obstruction. We highly recommend radiologic studies with neck extension and flexion in such cases.

Continuing medical education and the anesthesiologist.

There are a large variety of scheduled activities and courses available to meet the continuing medical education (CME) needs of anesthesiologists. The presentation of CME material varies in format and delivery style. The reasons for attending CME activities include licensure requirements, participation in state and national societies, keeping current with technology, review of old subject material, participation as a lecturer, and other personal reasons. Funding occurs via personal funds, employer support, commercial support, or by research grants. External bodies, such as the American Council of Continuing Medical Education and the American Medical Association, have imposed guidelines in these areas. Methods to evaluate CME activities include retrospective needs analysis based on exit interviews, prospective needs assessment, focus groups, and complex systems such as the CRISIS criteria. Self-directed CME can be evaluated by data collection that identifies how quickly information is received and by the effect of this data on measurable outcome. In the future, CME will increasingly utilize simulators and multimedia computers. Multimedia can bring CME to the physician as opposed to the physician traveling to a CME site. Virtual reality and artificial intelligence are on the horizon and may interface well with the field of anesthesiology due to the technical nature of the discipline and the increasing use of computers and electronic data collection already occurring in clinical practice.

Tourniquet-induced hypertension correlates with autonomic nervous system changes detected by power spectral heart rate analysis.

STUDY OBJECTIVE: To determine the autonomic changes associated with pneumatic tourniquet-induced hypertension as measured by power spectral heart rate analysis (PSHR). DESIGN: Prospective study. SETTING: Tertiary teaching hospital. PATIENTS: 21 healthy-patients scheduled for lower extremity surgery, during which pneumatic tourniquet inflation was expected to exceed 90 minutes. INTERVENTIONS: Hemodynamic and PSHR data collected at 5 minute intervals during inflation of the pneumatic tourniquet. Tourniquet-induced hypertension (T-HTN) defined at 30% increase above baseline. MEASUREMENTS AND MAIN RESULTS: Blood pressure, heart rate, maximum changes in low frequency variability (LFa), high frequency variability (HFa), and their ratio (LFa/HFa) were measured. Of the 21 patients, 11 had T-HTN. A significantly greater increase in LFa and LFa/HFa ratio was seen in the T-HTN group, where patients were greater in age. LFa, HFa, and ratio were not significantly different with T-HTN until 60 minutes or greater. Best correlation with T-HTN occurred with maximum increase in LFa/HFa ratio compared with increase in LFa or decrease in HFa. CONCLUSION: Tourniquet hypertension correlated with activation of the sympathetic nervous systems, as measured by PSHR variables.

Diagnosis and management of transient neurologic symptoms following subarachnoid block with single-shot isobaric 2% lidocaine.

Hyperbaric 5% lidocaine has been used extensively for spinal anesthesia for the last 50 yr. The implication of lidocaine as specifically etiologic for transient neurologic symptoms (TNS) has led to increasing focus on lidocaine spinal anesthesia and reports of TNS with single-shot, hyperbaric lidocaine. We report the details of a case of TNS associated with single-shot, isobaric 2% lidocaine in a 69-year-old female, scheduled for outpatient hysteroscopy, dilatation and curettage, and endometrial biopsy while placed in the lithotomy position.

Redefining the preoperative evaluation process and the role of the anesthesiologist.

STUDY OBJECTIVE: To assess the effects of implementing an ambulatory and same-day surgery preoperative evaluation patient triage system over a 3-year period. DESIGN: Retrospective analysis of 63,941 ambulatory surgical patients presenting for elective surgery. SETTING: Tertiary care, academic medical institution. INTERVENTIONS: The following preoperative evaluation model components were implemented over a 3-year period: HealthQuest, which is an outpatient preoperative assessment computer program developed by the Department of General Anesthesiology; a general internal medicine clinic designated specifically for preoperative evaluation and medical optimization; disease specific algorithms for both preoperative patient assessment and management; and a preoperative anesthesia clinic that no longer performs preoperative medical optimization. MEASUREMENTS AND MAIN RESULTS: During the 3-year study period ambulatory and same-day surgical case volume increased 34.7%. A total of 50,967 patients used HealthQuest as part of their preoperative evaluation. Of these patients 22,744 (35.6%) did not need to see an anesthesiologist until the day of surgery as guided by both a computer-assigned HealthQuest score and surgical classification scheme. Also, 41,197 patients were evaluated in our anesthesia preoperative clinic with a cost per evaluation of $24.86, which increased only 0.9% per year. In addition, both patient interview time and patient dissatisfaction with the preoperative process decreased over the 3-year period. There were 20, 088 patient encounters in the general internal medicine clinic for patient medical evaluation and optimization. The average monthly preoperative surgical delay rate decreased 49% during the study period. Finally, significant monetary saving resulted due to decreased unnecessary laboratory testing. CONCLUSIONS: Efficient, cost-effective patient care can be provided by using this preoperative evaluation model. Some institutions may find portions of this preoperative model applicable to their current situation.

Effectiveness of bupivacaine administered via femoral nerve catheter for pain control after anterior cruciate ligament repair.

STUDY OBJECTIVE: To evaluate the quality of pain control achieved with continuous local anesthetic infusion via a femoral nerve catheter, and to determine the optimum concentration of bupivacaine necessary to maintain pain control after full surgical anesthesia is established with 0.5% bupivacaine. DESIGN: Randomized, prospective study. SETTING: Tertiary care teaching center. PATIENTS: 25 ASA physical status I and II patients scheduled to undergo arthroscopically-aided anterior cruciate ligament (ACL) reconstruction by one surgeon, and who were willing to accept a femoral nerve catheter for postoperative pain control. INTERVENTIONS: All patients received general anesthesia with propofol/alfentanil (10 ml/1 ml) mixture and nitrous oxide/oxygen (60%/40%) mixture via endotracheal tube. After induction of general anesthesia, a femoral nerve catheter was inserted with the aid of a nerve stimulator, and 20 ml of 0.5% bupivacaine was administered. The surgery was completed in a standard manner and the patients were randomized into three groups for the concentration of local anesthetic to continue the pain relief into the recovery phase. On awakening, all patients were determined to have a functioning femoral nerve catheter. Group 1 received 0.0625% (n = 8) bupivacaine, Group 2 0.125% (n = 9) bupivacaine, and Group 3 0.25% (n = 8) bupivacaine; all doses were initiated in a blinded manner at 0.12 ml/kg/hr. Patients also received intravenous patient-controlled analgesia with morphine via demand mode only, with a 1.0 mg dose and a 6 minute lock-out interval. MEASUREMENTS AND MAIN RESULTS: Pain was determined at defined intervals by visual analog scale (VAS). Data collected included demographics, VAS scores, and total morphine administered. All patients were pain-free on emergence from general anesthesia. No patient required parenteral opioid for pain control while in the postanesthesia care unit. There were no significant differences in pain scores among groups, and average pain scores (2.5 to 4.0) indicate good pain control throughout the entire hospitalization. There were no complications. CONCLUSIONS: Low concentrations of bupivacaine delivered via femoral nerve catheter after an established femoral nerve block can provide excellent postoperative pain control after ACL reconstruction.

Organization of a comprehensive anesthesiology oral practice examination program: planning, structure, startup, administration, growth, and evaluation.

STUDY OBJECTIVE: To describe the planning, structure, startup, administration, growth, and evaluation of a comprehensive oral practice examination (OPE) program. SETTING: Midwest U.S. anesthesiology residency training program. MEASUREMENTS AND MAIN RESULTS: Committee planning involved consideration of formal and frequency of administration, timing for best resident and faculty availability, communication, forms design, clerical support, record keeping, and quality monitoring. OPE format was deliberately constructed to resemble that used by the American Board of Anesthesiology (ABA) to enhance resident familiarity with ABA style oral examination. Quality improvement tools consisted of regular examiner and examinee inservice sessions, liaison with ABA associate examiners, and review of examinee exit questionnaires. A set of OPE databases was constructed to facilitate quality monitoring and educational research efforts. A semiannual administration schedule on three to four consecutive Mondays optimally accommodated resident rotations and faculty work schedules. Continued administration of the OPE program required ongoing construction of a pool of guided case-oriented questions, selection of appropriate questions based on examinee training exposure, examination calendar publication, and scheduling of recurring examiner and examinee activities. Important issues that required action by the governing committee were examination timing, conflict with clinical demands, use of OPE results, and procurement of training resources. The OPE program grew from 56 examinations in the first year to 120 exams by year 3. It was perceived positively by the majority of residents. There were 90.2% of exit questionnaires that acknowledged specific learning about oral examination technique, while only 0.3% indicated lack of meaningful information exchange. Fewer than 10% of responses indicated misleading questions or badgering by examiners. Resident preparedness increased with repeat OPE exposure. CONCLUSIONS: A comprehensive mock oral examination program was successfully planned, initiated, and developed. It is well accepted by residents and faculty. Its inception was associated with an increase in resident preparedness. Now in its tenth year of existence it continues to be an asset and essential component of our training program.

Heart rate variability and the prone position under general versus spinal anesthesia.

STUDY OBJECTIVE: To evaluate heart rate (HR) variability in the prone position with power spectral heart rate (PSHR) analysis during spinal and general anesthesia. DESIGN: Prospective, clinical evaluation of HR variability in the prone position. SETTING: Tertiary care teaching hospital. PATIENTS: 20 healthy, ASA physical status I and II patients scheduled for elective lumbar spine surgery in the prone position. INTERVENTIONS: Anesthetic technique was either a standard general anesthetic or spinal anesthetic, based on the preference of the patient. Power spectral heart rate, HR, and blood pressure (BP) readings were determined prior to anesthetic intervention and as soon as a stable PSHR reading was available in the prone position. MEASUREMENTS AND MAIN RESULTS: Heart rate and BP were recorded at baseline prior to anesthesia and at the time of stable PSHR data in the prone position. Power spectral heart rate data included low-frequency activity (LFa), high-frequency activity (HFa), and the ratio (LFa/HFa). Spinal anesthesia level was recorded by thoracic dermatome at complete onset. Data were collected from 20 patients; 12 patients chose spinal anesthesia and 8 chose general anesthesia. The prone position resulted in significant increase in HR in the spinal group and significant decrease in BP in the general anesthesia group. Low-frequency activity and LFa/HFa ratio were unchanged in the spinal anesthesia group and were significantly decreased in the general anesthesia group. Spinal level was T8.7. CONCLUSIONS: The association of less change in LFa activity and preservation of BP on assumption of the prone position in patients during low spinal anesthesia suggests better preservation of autonomic nervous system compensatory mechanisms during low spinal anesthesia than with general anesthesia.