How controversial are anesthetic controversies?

STUDY OBJECTIVES: To determine how controversial the management of a number of clinical scenarios that are labeled as controversial (eg, how to induce anesthesia in the "open eye-full stomach" patient) are among those practicing anesthesia. DESIGN: Written survey. SETTING: A national anesthesiology review course. SUBJECTS: 575 anesthesiologists attending the review course. INTERVENTIONS: Anesthesiologists were presented 11 scenarios regarding some specific controversies in anesthetic management; each scenario also described a suggested course of management. Two questions were asked for each scenario: "Is this acceptable practice?" and "Would you do this in your own practice?" The scenarios included using succinylcholine for an "open eye-full stomach" patient, not evaluating preoperatively the cardiac status of a patient after receiving adriamycin therapy, using triggering drugs after a negative muscle biopsy for malignant hyperthermia, ordering a pregnancy test preoperatively for all females of child-bearing age, and seven others. MEASUREMENTS AND MAIN RESULTS: For each scenario, comparisons between the number of respondents who felt a particular management was acceptable practice and the number who would do this in their own practice were made using chi-square analysis; p < or = 0.05 was considered significant. 160 (27.8%) surveys were returned. In ten scenarios, there was 70% or less agreement about whether a technique was acceptable. In six scenarios, there was a significant difference between the number of respondents who felt a suggested management was acceptable practice and the number who would use it in their own practice. CONCLUSIONS: This survey of anesthesiologists regarding these controversial clinical scenarios showed that (a) most scenarios were in fact controversial amongst those in practice, and (b) there were disparities between whether a technique is believed to be acceptable practice and whether it would be used in one's own practice.

Dexmedetomidine and halothane produce similar alterations in electroencephalographic and electromyographic activity in cats.

Dexmedetomidine, an alpha2-adrenergic agonist, produces sedation and reduces volatile anesthetic requirements. This investigation compared the actions of dexmedetomidine and halothane on the processed EEG and on the electromyogram (EMG) which has not been previously described. Chronically instrumented cats were prepared with arterial and venous cannulae, quadriceps EMG electrodes and EEG electrodes in the lateral geniculate nucleus and over the frontal and occipital cortices. Hemodynamics, EEG and EMG were recorded in the conscious state and after randomly administered halothane or intravenous dexmedetomidine (on separate days). Blink and tail-clamp responses also assessed level of consciousness. Halothane resulted in unconsciousness and a lack of response to tail clamping, while dexmedetomidine produced profound sedation, with preservation of tail-clamp responses. Both agents similarly decreased (P < 0.05) the median power frequency from 9.5 +/- 0.9 to 5.7 +/- 0.4 Hz (2% halothane) and from 9.6 +/- 0.7 to 5.9 +/- 0.8 Hz (20 microg/kg dexmedetomidine), and 95% power frequency from 23.0 +/- 0.2 to 18.2 +/- 0.6 Hz (2% halothane) and from 23.0 +/- 0.2 to 19.1 +/- 0.8 Hz (20 microg/kg dexmedetomidine). Both agents increased the total spectral power and delta band power of the EEG and reduced integrated EMG activity. Halothane and dexmedetomidine produced differing effects on level of consciousness as assessed by response to tail clamping. The results suggest that conventional processing of EEG and EMG parameters are inadequate to assess anesthetic depth in the presence of alpha2-adrenergic agonists.

Somatosensory evoked potentials are not a sensitive indicator of potential positioning injury in the prone patient.

OBJECTIVE: This study monitored somatosensory evoked potentials (SSEP) at the median and ulnar nerves in awake volunteers placed in a simulated position for prone surgery. Neurologic symptoms were used as a surrogate endpoint for position related peripheral nerve injury; the occurrence of these symptoms was correlated with the presence or absence of SSEP changes in median and ulnar nerves. METHODS: Median and ulnar nerve SSEP data was obtained from awake volunteers in the supine and prone positions. With the head midline in the prone position, SSEPs were measured as the arms were advanced in four cephalad increments. Symptoms, defined as tingling, numbness, or aching in the hand, forearm, or upper arm, were recorded at each position. SSEP changes were considered significant when amplitude decreased 60% and/or latency increased 10% compared with baseline prone measurements. Symptoms were correlated with SSEP changes using chi-squared analysis (p < 0.05), and Fisher's exact analysis (p < 0.07). RESULTS: Data were collected on 14 patients, mean age 34 +/- 3 years. Seven (50%) subjects reported symptoms with changes in position, while four (29%) subjects displayed SSEP changes. There was no statistically significant association between symptoms and SSEP changes. There were no false positives (no symptoms in the presence of significant SSEP changes), but there were 3 (21%) false negatives (positive symptoms without SSEP changes). CONCLUSIONS: While all SSEP changes were associated with symptoms, the development of symptoms in 3 of 7 patients without SSEP changes suggests that SSEPs may be an imperfect monitor for the detection of positioning injury. The limited sensitivity of SSEPs in this study may be due to the duration of the monitoring, sample size, or the validity of symptoms as a surrogate for nerve injury.

Who uses transesophageal echocardiography in the operating room?

A survey was made of 155 anesthesiology residency programs in the United States to determine the patterns of use, responsibility for interpretation, and training of those responsible for intraoperative transesophageal echocardiography (TEE). Survey questions included numbers and types of cases for which TEE is used, who interprets TEE data and how they are trained, the extent of resident training in TEE, and beliefs about the utility of TEE. One hundred eight completed surveys were returned (70% response). Of those responding, 98 (91%) use intraoperative TEE. In 53 of those 98 institutions (54%), an anesthesiologist was primarily responsible for the interpretation of TEE data, whereas a cardiologist was responsible in the remainder. Approximately 35% of anesthesiologists using TEE had training in its use during residency or fellowship; the remainder were trained after finishing residency or fellowship. Forty-two percent of anesthesiologists who use TEE leave a formal interpretation on the chart apart from the anesthesia record, and 43% bill specifically for performing TEE. Although 69% of those responding thought that formal credentials should be required for anesthesiologists to use intraoperative TEE, only 32% reported that their institutions actually mandated this. 38% of those responding stated that they offer a dedicated TEE rotation to their residents, and 13% thought that their graduating residents were trained well enough to use TEE on their own. Among academic institutions responding, the use of intraoperative TEE is nearly universal, responsibility for its interpretation is split almost evenly between cardiologists and anesthesiologists, and there is a disparity between opinions and reality with regard to TEE credentialing for anesthesiologists.

Effects of neurolytic concentrations of alcohol and phenol on Dacron and Gore-Tex vascular prosthetic grafts.

BACKGROUND AND OBJECTIVES: Neurolytic nerve block, using either alcohol (A) or phenol (P), is frequently used to treat intractable pain. However, these agents may disrupt the integrity of prosthetic vascular grafts. To investigate this possibility, the tensile strength of Dacron (Meadox Medicals, Oakland, NJ) and Gore-Tex (W.L. Gore Associates, Flagstaff, AZ) vascular grafts was determined after in vitro exposure to various clinically used concentrations of A or P. METHODS: Segments of Dacron and Gore-Tex graft were placed in the following solutions: saline (S), 6% and 9% P, and 25%, 50%, 75%, and 100% A, and stored at 23 degrees +/- 1 degree C for 72 hours. Axial maximum load (in kilonewtons, KN) and strain (in mm/mm) were determined with an Instron universal testing machine (Instron Corporation, Camden, MA). Samples from the S, 9% P, and the 100% A groups were evaluated using a scanning electron microscope. RESULTS: Dacron tensile strength decreased a maximum of 23% after exposure to 50%, 75%, and 100% A. Dacron strain capacity decreased after exposure to A (50%, 75%, 100%) and P (6%, 9%). Scanning electron microscope of both P and A showed significant degradation. No changes were found in the Gore-Tex group after exposure to P or A, however, scanning electron microscope of the 100% A sample showed moderate fiber degradation. CONCLUSIONS: The study shows that Dacron woven grafts are degraded by concentrations of A of at least 50%, and to a lesser extent, concentrations of at least 6%, while Gore-Tex had only minimal changes. While neurolytic block offers distinct advantages in patients with terminal cancer pain, the findings suggest that the use of more conservative modalities, such as oral medication regimens, be considered for the treatment of intractable pain in patients with vascular prosthetic grafts that are proximate to the proposed site of neurolysis.

The effects of halothane, isoflurane, and enflurane on thermoregulatory responses in the neuraxis of cats.

BACKGROUND: Normal thermoregulatory function is believed to be modulated by thermosensitive neurons in the preoptic region of the anterior hypothalamus and other sites within the central nervous system including the spinal cord. Previous evidence has demonstrated modulation of segmental spinal cord thermoregulatory mechanisms from more rostral central nervous system sites. The ability of the volatile anesthetics to disrupt normal thermoregulatory function and produce shivering-like activity during emergence is well documented. The purpose of the current investigation was to examine the action purpose of the current investigation was to examine the action of the volatile anesthetics halothane, isoflurane, and enflurane on thermoregulatory responses produced at the preoptic region and spinal cord. METHODS: Cats were chronically instrumented with bilateral cannulas allowing selective heating and cooling of the preoptic region. Electrodes were implanted in hindlimb and forelimb muscles for electromyographic (EMG) analysis. Animals underwent selective heating and cooling of the preoptic region in the awake state, during volatile agent anesthesia and during emergence. In a separate series of animals, pontine-transected cats with epidural thermodes and a thermocouple underwent alternate heating and cooling of the spinal cord. Heating and alternate heating and cooling of the spinal cord. Heating and cooling was performed in the nonanesthetized state, at graded concentrations of halothane, and during emergence. In all animals deep core peritoneal temperature, epidural spinal cord temperature, forelimb and hindlimb EMG activity were continuously recorded and digitally processed. EMG responses in both experiments were quantitated and analyzed for power spectral density. RESULTS: In the chronically prepared animals, heating and cooling of the preoptic region in the conscious state resulted in appropriate thermoregulatory responses, including shivering-like activity and increased EMG power with preoptic region cooling. Halothane, isoflurane, and enflurane each abolished these thermoregulatory responses. During emergence from anesthesia, however, the typical spontaneous increases in EMG power observed at normothermia were significantly attenuated by heating of the preoptic region and augmented by cooling of the preoptic region. In the acutely prepared animals, cooling of the spinal cord produced graded increases in EMG activity. Increased concentrations of halothane dose-dependently diminished this response to cooling of the spinal cord. During emergence, cooling of the spinal cord resulted in a shivering response similar to those observed during control conditions. CONCLUSIONS: The ability of preoptic region heating and cooling to modulate postanesthetic shivering implies that while thermoregulatory pathways remain intact, volatile anesthetics produce an imprecision in the control of thermoregulatory responses at the level of the anterior hypothalamus. Attenuation of shivering-like responses generated at spinal cord levels in pontine-transected cats implies a significant blunting action of thermoregulatory response mechanisms at the level of the spinal cord or lower brain stem.

The effect of halothane on thermosensitive neurons in the preoptic region of the anterior hypothalamus in acutely instrumented cats.

Normal thermoregulatory processes are significantly impaired by halothane anesthesia. However, the direct effects of halothane on thermosensitive neurons in the preoptic region of the anterior hypothalamus, a major thermoregulatory site, have not been previously investigated. Thirty-eight cats were anesthetized with alpha-chloralose (60 mg/kg) and urethane (600 mg/kg) and placed in stereotactic restraint. Stainless steel thermodes for highly selective local heating and cooling were stereotactically placed into the preoptic region with thermocouples used to monitor regional temperature. Using tungsten microelectrodes, 148 single neurons in the preoptic region were identified and subjected to local heating (to 42 degrees C) and cooling (to 30 degrees C). Eighteen percent (n = 27) in 15 different cats were classified as thermosensitive by accepted criteria (change in firing rate per degree centigrade of greater than 0.8 spikes.s-1.degrees C-1 or less than -0.6 spikes.s-1.degrees C-1). Thermosensitve units were then subjected to graded concentrations of halothane (0.25-1.0% end-tidal), and local heating and cooling were repeated. The spontaneous firing rate (spikes per second) at 37 degrees C of 21 warm-sensitive neurons was significantly (P less than 0.05) reduced, to 65.5 +/- 8.3, 42.6 +/- 10.7, 28.0 +/- 9.5, and 18.1 +/- 6.0% of control at 0.25, 0.50, 0.75, and 1% halothane, respectively. Spontaneous firing rate returned to 99.5 +/- 19.8% of control within 30 min after discontinuation of halothane. Thermosensitivity (change, per degree centigrade, in spikes per second) was also significantly reduced, to 33.3 +/- 5.6, 28.5 +/- 14.6, and 13.9 +/- 6.6% of control at 0.50, 0.75 and 1.0% halothane (all P less than 0.05 compared to control).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of isoflurane, midazolam, and etomidate on cardiovascular responses to stimulation of central nervous system pressor sites in chronically instrumented cats.

The systemic hemodynamic actions of isoflurane (a volatile anesthetic) and etomidate and midazolam (intravenous anesthetics) have been well documented. However, few studies have investigated the actions of these agents on central cardiovascular control sites. The present investigation examined the actions of these agents on the responses of systolic arterial pressure (SAP), heart rate, infrarenal aortic blood flow, and lower body vascular resistance to central nervous system pressor site stimulation in chronically instrumented cats. Male and female cats (n = 23) were chronically instrumented with bipolar stimulating electrodes in the regions of the ventrolateral hypothalamus (anterior, 10.0 mm; lateral, 2.5 mm; depth, -4.0 mm) and mesencephalic reticular formation (anterior, 2.0 mm; lateral, 2.0 mm; depth, -1.0 mm). Control experiments consisted of stimulation sequences at 1x, 2x, and 4x threshold current levels to elicit pressor responses. Stimulation of the hypothalamic site produced current-dependent increases in SAP (6-85 mm Hg), in heart rate (3-56 beats/min), and in infrarenal aortic blood flow (0-85 mL/min). Reticular formation site stimulation produced graded increases in SAP (6-129 mm Hg) only. Isoflurane (1.5%, 2.5%, and 3.0%), etomidate (3.0-mg/kg bolus and 0.4-mg.kg-1. h-1 infusion), and midazolam (7.5-mg/kg bolus and 0.2-mg.kg-1.h-1 infusion) were then administered in separate experimental groups. After a steady hemodynamic state was established with each agent, stimulation sequences were repeated. Isoflurane produced an attenuation of the responses of SAP (from 85.1 +/- 8.2 to 17.8 +/- 6.1 mm Hg at 1.5%, to 7.2 +/- 2.0 mm Hg at 2.5%, and to 4.7 +/- 2.0 mm Hg at 3%, all P less than 0.05), heart rate (from 41.1 +/- 13.0 to 12.5 +/- 2.7 beats/min at 2.5% and to 6.2 +/- 1.7 beats/min at 3%, all P less than 0.05), and of the infrarenal aortic blood flow (from 72.6 +/- 14.3 to 11.8 +/- 4.2 mL/min at 1.5%, to 10.2 +/- 5.6 mL/min at 2.5%, and to 3.2 +/- 1.5 mL/min at 3%, all P less than 0.05) to the highest level of hypothalamic site stimulation. Isoflurane similarly produced an attenuation of the SAP response (from 128.7 +/- 10.3 to 15.4 +/- 8.1 mm Hg at 1.5%, to 0.2 +/- 1.1 mm Hg at 2.5%, and to 0.3 +/- 0.5 mm Hg at 3.0%, all P less than 0.05) to the highest level of reticular formation site stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Central venous air embolism without a catheter.

Venous air embolism is a well-recognized complication of central venous catheterization. Although previous reports have documented venous air embolism occurring in a number of ways, including during initial catheterization, when catheters crack or are disconnected, and after catheter removal, no reports mention the possibility of air embolism occurring when a guide wire without a catheter was in place. A patient is presented who displayed signs and symptoms of venous air embolism (tachypnoea, chest pain, and arterial hypoxaemia) during central venous catheter manipulation while a guide wire alone was in place. Pulse oximetry was used to detect hypoxaemia and suggest an aetiology for the patient's clinical symptoms. It is postulated that a previously described gasp reflex or some sort of sustained negative pressure manoeuvre caused venous air embolism around the guide wire and accounted for the patient's signs and symptoms. During central venous catheter placement, a high index of suspicion for venous air embolism should be maintained, pulse oximetry should be used, the skin entrance site should be kept covered by an occlusive dressing, and the patient should be positioned head-down.

Defects of the broad ligament of the uterus.

A case of intestinal obstruction resulting from passage of the entire small bowel and cecum and its mesentery through a fenestration in the broad ligament of the uterus is presented. A review of the literature reveals that broad ligament defects may occur in multiple locations, which may be responsible for intestinal obstruction. A simple classification of broad ligament defects is proposed. Type 1 defects occur caudal to the round ligament of the uterus. Type 2 defects occur above the round ligament. Type 3 defects occur between the round ligament and the remainder of the broad ligament, through the meso-ligamentum teres.