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The competition between intergranular (IG) and transgranular (TG) fracture in fcc polycrystalline aggregates with physically representative GB misorientation distributions comprised of random low-angle, random high-angle, and coincident site lattice (CSL) GBs has been investigated. Physically-based critical conditions for IG fracture, due to the formation of dislocation pileups, and TG fracture, due to the propagation of cracks on cleavage planes, were coupled to a dislocation-density-based crystal plasticity formulation and a computational fracture scheme for crack branching to investigate how dislocation–GB interactions influence dislocation transmission, pileup formation, and local failure modes. The predictions indicate that aggregates with a large fraction of random and CSL high-angle GBs are dominated by IG fracture, as low GB transmission leads to extensive dislocation-density pileup formation and localized stress accumulations that induce IG fracture. Aggregates with a majority of low-angle GBs are dominated by TG failure, which is consistent with experimental observations. This investigation provides a fundamental understanding of the physical mechanisms governing IG and TG fracture in polycrystalline aggregates.

Intergranular (IG) fracture behavior near triple junctions (TJs) in f.c.c. tricrystals with a variety of grain boundary (GB) misorientations has been investigated. Based on a dislocation-density GB interaction scheme, critical fracture conditions were coupled to evolving dislocation-density pileups and local stresses by using a dislocation-density-based crystalline plasticity formulation within a nonlinear finite-element framework to elucidate the effects of local GB structure, dislocation–GB interactions, and misorientations on IG crack propagation in f.c.c. crystalline materials. Tricrystals with low-angle GBs had higher fracture toughness than tricrystals with high-angle GBs. In TJs with a combination of random low- and high-angle GBs, the formation of dislocation-density pileups in the high-angle GB led to IG crack propagation along the high-angle GB rather than along the low-angle GB. These predictions, which are consistent with experimental observations, indicate that fracture behavior near TJs is controlled by highly local, evolving, and interrelated events, such as dislocation-density pileups and GB misorientations.

Evolving dislocation-density pile-ups at grain-boundaries (GBs) spanning a wide range of coincident site lattice (CSL) and random GB misorientations in face-centered cubic (fcc) bicrystals and polycrystalline aggregates has been investigated. A dislocation-density GB interaction scheme coupled to a dislocation-density-based crystalline plasticity formulation was used in a nonlinear finite element (FE) framework to understand how different GB orientations and GB-dislocation-density interactions affect local and overall behavior. An effective Burger's vector of residual dislocations was obtained for fcc bicrystals and compared with molecular dynamics (MDs) predictions of static GB energy, as well as dislocation-density transmission at GB interfaces. Dislocation-density pile-ups and accumulations of residual dislocations at GBs and triple junctions (TJs) were analyzed for a polycrystalline copper aggregate with Σ1, Σ3, Σ7, Σ13, and Σ21 CSLs and random high-angle GBs to understand and predict the effects of GB misorientation on pile-up formation and evolution. The predictions indicate that dislocation-density pile-ups occur at GBs with significantly misoriented slip systems and large residual Burger's vectors, such as Σ7, Σ13, and Σ21 CSLs and random high-angle GBs, and this resulted in heterogeneous inelastic deformations across the GB and local stress accumulations. GBs with low misorientations of slip systems had high transmission, no dislocation-density pile-ups, and lower stresses than the high-angle GBs. This investigation provides a fundamental understanding of how different representative GB orientations affect GB behavior, slip transmission, and dislocation-density pile-ups at a relevant microstructural scale.

Acrylic bone cement has been used successfully as a slow-release depot for antibiotics after orthopaedic surgery. The feasibility of administering local anesthetics in this way was examined in this preliminary in vitro study. Discs weighing approximately 4 g were prepared from five brands of acrylic cement (40 g) containing as much as 2 g of anesthetic base. Elution of the anesthetics into saline was measured during 72 hours. Prilocaine eluted the fastest and bupivacaine the slowest, with lidocaine between them. The elution rates were greatest in the first hour, declining thereafter. Rates also depended on the brand of cement with the quickest elution from CMW3 and the slowest from Surgical Simplex P. Using cement as a depot, therapeutic levels of a drug should be achievable in vivo at a negligible risk of toxicity. Before in vivo trials it is necessary to optimize elution of drugs in relation to the cement (brand, microstructure, method of preparation) and the concentration of a drug in the cement above which the cements' mechanical and adhesive properties are compromised.

To survey the provision of pre-anesthetic assessment clinics in hospitals in Ontario during the summer of 1997.Mail survey questionnaire of all 300 hospitals in Ontario.Replies were received from 260 hospitals (86.7%) of which 131 provide anesthesia. Of these, 86% are community and 14% teaching hospitals. Regular clinics are held in 63% of these hospitals, most commonly daily. As to location, 73% are held in the outpatient department. Written guidelines detailing which patients should be referred are issued by 77% of departments. The attending surgeon is the most common source of referral (64%). Referred patients are most commonly seen by a nurse (52%) who decides on onward referral to an anesthesiologist. Services generating the most referrals are general surgery (83%), orthopedics (64%) and obstetrics/gynecology (49%). In 47% of hospitals 10-50 patients are seen per month and they travel most commonly up to 100 km. The average "no show" rate is 6.2%. Only 36% of departments assess patients the same day as seen by the surgeon. On attending the clinic, 51% can see an internist the same day in contrast to 30% being able to see a cardiologist. Pre-admission testing is available to 97% on the same day. Direct funding is available for the nurse (87%), physician (1%) and secretarial help (43%). Remuneration of the anesthesiologist is fee for service (99%) and sessional (1%).Pre-anesthetic assessment clinics are common in Ontario. More development is required to enable patients to receive all aspects of their preoperative assessment during one visit.

Hysterectomy and spinal surgery inpatient trials suggest favorable interactions between cyclooxgenase-2 inhibitors and gabapentin/pregabalin on postoperative days 1-2. We present the first trial of meloxicam-gabapentin combination after outpatient laparoscopic cholecystectomy.This was a randomized, double-blind trial comparing daily oral administration of 1) meloxicam 15 mg, 2) gabapentin 1200-1600 mg, and 3) a combination of the two starting 1 h before until 2 days after surgery. Primary outcomes included day of surgery spontaneous and movement-evoked pain. Secondary outcomes included pain on Days 1, 2, and 30, adverse effects, opioid consumption, spirometry, pain-related interference, hospital discharge time, return to work time, and patient satisfaction.On the day of surgery, 60-min rest pain (0-10 numerical rating scale +/- sd) was significantly lower (P0.05) with gabapentin alone (2.0 +/- 1.6) versus meloxicam alone (3.6 +/- 2.1). Observed pain differences between the combination (2.9 +/- 2.1) and gabapentin alone were fairly small in favor of gabapentin alone (P0.05). Secondary analyses indicated that nausea was significantly less frequent with the combination (24%) versus the single-drug meloxicam (57%) only.Although nausea was reduced with combination therapy, this trial provides little or no support for the combined use of meloxicam and gabapentin for pain relief on the day of surgery. This suggests that perioperative analgesic polypharmacy may not always be necessary or appropriate.

OBJECTIVES To test whether the pulmonary risk of repeated volume recruitment is greater or less than the risk associated with unreversed atelectasis during 6 hrs of high-frequency oscillatory ventilation in the atelectasis-prone rabbit lung. DESIGN Prospective, controlled, randomized comparison over 6 hrs of ventilator management. SETTING Laboratory. SUBJECTS Twenty-eight adult New Zealand white male rabbits (weight 2.3 to 2.8 kg). BACKGROUND Controversy exists over whether high-frequency oscillatory ventilation should be used with volume recruitment maneuvers in the atelectasis-prone lung, or be used at low mean and peak pressures without volume recruitment to avoid the risks of even transient pulmonary overdistention. Potential risks and benefits accompany both alternatives. INTERVENTIONS We evaluated the pulmonary effects of three high-frequency oscillatory ventilation protocols in anesthetized rabbits made surfactant deficient by saline lavage, using animals ventilated with conventional positive-pressure ventilation with positive end-expiratory pressure as a reference group; n = 5 in each group. The three high-frequency oscillatory ventilation groups were ventilated for 6 hrs at 15 Hz (900 breaths/min), FIO2 = 1.0. The repeated stretch group received 15-sec sustained inflations at 30 cm H2O mean airway pressure every 20 mins, with maintenance mean airway pressure sufficient to keep PaO2 > 350 torr (46.7 kPa). The repeated deflation group was maintained at levels that produced PaO2 70 to 120 torr (9.3 to 16 kPa), with the endotracheal tube opened to atmospheric pressure for 15 secs every 20 mins. Animals in the repeated stretch after deflations group were managed as in the repeated stretch protocol but each sustained inflation was preceded by a 15-sec deflation to functional residual capacity. The conventional positive-pressure ventilation group was ventilated at rates of 30 to 100 breaths/min, keeping PaO2 70 to 120 torr (9.3 to 16 kPa). End-points included terminal functional residual capacity and a compliance index computed from respiratory system pressure-volume curves. MEASUREMENTS AND MAIN RESULTS After 6 hrs of ventilation, respiratory system compliance in the repeated stretch group had returned to control values (1.35 +/- 0.18 [SD] mL/kg/cm H2O). Respiratory system compliance was significantly less than this number in both the repeated deflation (0.89 +/- 0.08) and repeated stretch after deflations (1.24 +/- 0.22) groups (p < .05). Respiratory system compliance after 3 hrs of conventional positive-pressure ventilation decreased to 0.34 +/- 0.10 mL/kg/cm H2O. Functional residual capacity changes paralleled these changes of respiratory system compliance. CONCLUSIONS These data demonstrate that the potential pulmonary risk of repeated lung stretch during volume recruitment is significantly less than the damage arising from the avoidance of such maneuvers in lungs in which alveolar recruitment is possible. We conclude that sustained inflations during high-frequency oscillatory ventilation produce the benefits of increased oxygenation for a given mean airway pressure plus decreased progression of lung injury.

On rapporte le cas ďune femme de 69 ans se presentant pour une dissection de ľaorle ascendante et qui a developpe une tamponnade lors de ľinduction de eanesthesie. La tamponnade elait diagnostiquee par le profit hemodynamique qui a demontre une egalisation de la pression veineuse centrale, pression de ľartere pulmonaire bloquee el de la pression diastolique de ľartere pulmonaire. Elle fat traitee par une intervention chirurgicale rapide et un drainage de ľhemopericarde. La tamponnade cardiaque et la dissection de ľanevrysme de ľaorte ascendante sont des conditions qui presentent des considerations anesthesiques opposees. Celles-ci ainsi que les problemes encourus sont discutes.

Major vascular, nonthromboembolic complications of total hip arthroplasty are rare: only 23 have been reported over the last 20 years. This is a report of two additional cases. In an 84-year-old woman, the external iliac artery was lacerated following removal of the acetabular component. Two such injuries have been reported previously, but this is the first case that resulted from a posterolateral approach to the hip. In a 69-year-old woman, a heretofore unrecorded complication consisted of external iliac vein compression occurring 20 months after total hip arthroplasty and culminating in iliac artery thrombosis and an ischemic foot. A below-knee amputation was performed after removal of the total hip components.