The influence of uncemented femoral stem length and design on its primary stability: a finite element analysis.

One of the crucial factors for short- and long-term clinical success of total hip arthroplasty cementless implants is primary stability. Indeed, motion at the bone-implant interface above 40 µm leads to partial bone ingrowth, while motion exceeding 150 µm completely inhibits bone ingrowth. The aim of this study was to investigate the effect of two cementless femoral stem designs with different lengths on the primary stability. A finite element model of a composite Sawbones(®) fourth generation, implanted with five lengths of the straight prosthesis design and four lengths of the curved prosthesis design, was loaded with hip joint and abductor forces representing two physiological activities: fast walking and stair climbing. We found that reducing the straight stem length from 146 to 54 mm increased the average micromotion from 17 to 52 µm during fast walking, while the peak value increased from 42 to 104 µm. With the curved stem, reducing length from 105 to 54 mm increased the average micromotion from 10 to 29 µm, while the peak value increased from 37 to 101 µm. Similar findings are obtained for stair climbing for both stems. Although the present study showed that femoral stem length as well as stem design directly influences its primary stability, for the two femoral stems tested, length could be reduced substantially without compromising the primary stability. With the aim of minimising surgical invasiveness, newer femoral stem design and currently well performing stems might be used with a reduced length without compromising primary stability and hence, long-term survivorship.

Nitinol versus stainless steel stents: acute thrombogenicity study in an ex vivo porcine model.

Acute and subacute stents thrombosis along with thrombus mediating neointimal proliferation within the stent struts remain major concerns in coronary stenting. Up to date, there is an obvious lack of data on the thrombogenicity of stent materials in physiological conditions. This study was performed to compare the relative thrombogenicity of nitinol versus stainless steel stents. Nitinol stents were laser cut to reproduce the exact geometry of the stainless steel Palmaz stents and tested in an ex vivo AV shunt porcine model under controlled conditions. Nitinol stents presented only small amounts of white and/or red thrombus principally located at the strut intersections while Palmaz stents clearly exhibited more thrombus. As a result, 125I-fibrin(ogen) adsorption and (111)I-platelets adhesion were significantly lower on nitinol than on stainless steel devices (36%, p = 0.03 for fibrin(ogen) and 63%, p = 0.01 for platelet). These results were confirmed by scanning electron observations showing different thrombus morphologies for nitinol and stainless steel. Along with the unique mechanical properties of nitinol, its promising haemocompatibility demonstrated in our study may promote their increasing use for both peripheral and coronary revascularization procedures.

Anesthesia breathing circuits protected by the DAR Barrierbac S breathing filter have a low bacterial contamination rate.

PURPOSE: In order to reuse the same anesthesia breathing circuit for more than one patient, it has been proposed to add a breathing filter between the Y-piece and the artificial airway. The purpose of this study was to evaluate the in vivo bacterial filtration efficacy of an anesthesia filter in a usual clinical anesthesia setting. METHODS: A sterile DAR Barrierbac S breathing filter was inserted at the Y-piece of a sterile single-use anesthesia breathing circuit before induction of general anesthesia. At the end of anesthesia, the breathing circuit connector of the filter and of the endotracheal tube connector were cultured separately on growth media (chocolate and blood agar). These were incubated for 48 hr and bacterial identification was conducted using standard methods. RESULTS: Bacterial cultures were negative on both sides of the filter membrane of 1842 of the 2001 filters studied. Cultures were positive on the patient side of 104 filters. In two of those, the same bacteria were found on both the circuit side and the patient side of the filter. Therefore these data indicate a clinical effectiveness of 99.9% (confidence interval, CI 95%, 99.6-99.998%), and an in vivo filtration efficacy of 98.08% (CI 95%, 92.54-99.67%). CONCLUSION: Using the upper limit of the CI, it can be assumed that the practice of using a sterile DAR Barrierbac S breathing filter for every patient while reusing the anesthesia breathing circuit would result in a cross contamination rate of the breathing circuit lower than once every 250 cases.

Another feature of TURP syndrome: hyperglycaemia and lactic acidosis caused by massive absorption of sorbitol.

Endoscopic transurethral resection of the prostate (TURP) can be complicated by absorption of a large volume of irrigation fluid. The clinical features of this complication are referred as the TURP syndrome. We report a case where hyperglycaemia and lactic acidosis complicated the TURP syndrome caused by the massive absorption (approximately 15 litres) of a sorbitol- mannitol irrigation solution. The proposed mechanism is a type B lactic acidosis related to the metabolism of sorbitol.

Effect of surface treatment and sterilization processes on the corrosion behavior of NiTi shape memory alloy.

Nickel-titanium (NiTi) alloy derives its biocompatibility and good corrosion resistance from a homogeneous oxide layer mainly composed of TiO(2), with a very low concentration of nickel. In this article, we described the corrosion behavior of NiTi alloys after mechanical polishing, electropolishing, and sterilization processes using cyclic polarization and atomic absorption. As a preparative surface treatment, electropolishing decreased the amount of nickel on the surface and remarkably improved the corrosion behavior of the alloy by increasing the mean breakdown potential value and the reproducibility of the results (0.99 +/- 0.05 V/SCE vs. 0.53 +/- 0. 42). Ethylene oxide and Sterrad(R) sterilization techniques did not modify the corrosion resistance of electropolished NiTi, whereas a steam autoclave and, to a lesser extent, peracetic acid sterilization produced scattered breakdown potential. In comparing the corrosion resistance of common biomaterials, NiTi ranked between 316L stainless steel and Ti6A14V even after sterilization. Electropolished NiTi and 316L stainless-steel alloys released similar amounts of nickel after a few days of immersion in Hank's solution. Measurements by atomic absorption have shown that the amount of released nickel from passive dissolution was below the expected toxic level in the human body. Auger electron spectroscopy analyses indicated surface contamination by Ca and P on NiTi during immersion, but no significant modification in oxide thickness was observed.

Submental endotracheal intubation: an alternative to tracheotomy in patients with midfacial and panfacial fractures.

BACKGROUND: The submental route for endotracheal intubation has been proposed as an alternative to tracheotomy in the surgical management of patients with maxillofacial trauma. The purpose of this study was to review our experience with this procedure. METHODS: Medical records of 25 patients who had surgical reduction of midfacial or panfacial fractures while securing their airway with submental intubation were reviewed. After standard orotracheal intubation, a passage was created by blunt dissection with a hemostat clamp through the floor of the mouth in the submental area. The proximal end of the orotracheal tube was pulled through the submental incision. Surgery was completed with minimal interference from the endotracheal tube. At the end of surgery, the tube was pulled back to the usual oral route. RESULTS: Mean duration of surgery was 7.9 hours (range, 2-16 hours). Mean duration of postoperative mechanical ventilation was 5.2 days (range, 1-24 days). Fourteen of these patients required prolonged (>24 hours) postoperative mechanical ventilation because of associated injuries. Two patients later required a tracheotomy because of prolonged respiratory failure. One patient died of multiple organ failure. One complication of the submental intubation was observed: a superficial infection of the submental wound. CONCLUSION: Submental intubation is a simple technique associated with a low morbidity. It is an attractive alternative to tracheotomy in the surgical management of selected cases of maxillofacial trauma.

Alfentanil causes less postoperative nausea and vomiting than equipotent doses of fentanyl or sufentanil in outpatients.

BACKGROUND: The relative potencies of alfentanil, fentanyl, and sufentanil as a risk factor for postoperative nausea and vomiting have not been determined. They were compared in a randomized study designed to obtain equipotent plasma concentrations of these three opioids at the beginning of the recovery period. METHODS: The study included 274 patients treated on an outpatient basis. The steady state opioid plasma concentration providing a predicted 50% reduction of the minimum alveolar concentration of isoflurane was used to determine the relative potency of the opioids. The opioids were prepared in equal volumes at concentrations of alfentanil 150 microg/ml, fentanyl 50 microg/ml, and sufentanil 5 microg/ml and were administered in vol/kg. Anesthesia was induced in a blinded fashion with a bolus of the study opioid (0.05 ml/kg) and 4-6 mg/kg thiopental and was maintained with isoflurane (0.6-1%) in a nitrous oxide-oxygen mixture with a continuous infusion of the study opioid (0.06 ml x kg(-1) x h(-1)). If necessary, up to five additional boluses of opioid (0.02 ml/kg) could be given. This opioid administration protocol was tested by pharmacokinetic simulations. RESULTS: The incidence of postoperative nausea and vomiting was not different in the postanesthesia care unit, but in the ambulatory surgery unit it was significantly lower for alfentanil compared with fentanyl and sufentanil (12, 34, and 35%, respectively P < 0.005). Pharmacokinetic modeling showed that the end-anesthesia opioid plasma concentrations were approximately equipotent in the three groups. However, modeling does not support that the difference between groups in the postoperative period can be explained by a more rapid disappearance of alfentanil from the plasma. CONCLUSIONS: Alfentanil, compared with approximately equipotent doses of fentanyl and sufentanil, is associated with a lower incidence of postoperative nausea and vomiting in outpatients.

Preliminary investigation of the effects of surface treatments on biological response to shape memory NiTi stents.

Nickel-titanium (NiTi) offers many advantages for the fabrication of coronary stents: shape memory, superelasticity, and radiopacity. However, many authors highlighted the selective dissolution of Ni from the alloy during the corrosion process that could lead to potential toxicity. The improvement of the NiTi stent's corrosion resistance by different surface treatments (electropolishing, heat treatment, and nitric acid passivation) was reported in a previous article. In the present study a comparative biocompatibility evaluation of such stents was performed through in vitro and in vivo assays. A cell proliferation test was completed to evaluate the cytotoxicity of surface treated NiTi using human fibroblasts. Then a stent implantation was performed in rabbit paramuscular muscle to study the inflammatory response generated by the same implants. Cell proliferation tests generally indicated an in vitro biocompatibility of our samples similar to the control group. An in vivo implantation study demonstrated the gradual overall reduction with time of the fibrocellular capsule thickness surrounding the implants. After a 12-week implantation period, the fibrous capsules surrounding the different implants tended toward the same value of 0.07 mm, which suggested that all surface treatments produced a similar biological response. This low value of the fibrocellular capsule indicated that our NiTi surface treated implants were relatively inert.

Esophageal and tracheal distortion by the Esophageal-Tracheal Combitube: a cadaver study.

PURPOSE: To understand the anatomical relationships of the Esophageal-Tracheal Combitube (ETC) with the larynx, pharynx, esophagus and trachea. METHODS: An extensive dissection of the neck and thorax of a 70-yr-old caucasian male cadaver was done to expose the larynx, pharynx, trachea and esophagus. The ETC was inserted following the manufacturer's recommendations. Effects of the ETC on the surrounding structures were observed with the ETC first inserted in the esophagus and then, in the trachea. RESULTS: When inserted in the esophagus, the ETC produced marked bulging of the anterior wall of the esophagus and anterior displacement (4.5 cm) of the trachea. Inflation of the distal cuff of the ETC produced distension of the esophagus. When inserted in the trachea, the ETC also caused anterior protrusion. CONCLUSION: Protrusion of the anterior wall of the esophagus and distension resulting from inflation of the distal cuff could lead to esophageal injuries. These observations may explain the previously reported complications associated with the use of the ETC.

Effect of modification of oxide layer on NiTi stent corrosion resistance.

Because of its good radiopacity, superelasticity, and shape memory properties, nickel-titanium (NiTi) is a potential material for fabrication of stents because these properties can facilitate their implantation and precise positioning. However, in vitro studies of NiTi alloys report the dependence of alloy biocompatibility and corrosion behavior on surface conditions. Surface oxidation seems to be very promising for improving the corrosion resistance and biocompatibility of NiTi. In this work, we studied the effect on corrosion resistance and surface characteristics of electropolishing, heat treatment, and nitric acid passivation of NiTi stents. Characterization techniques such as potentiodynamic polarization tests, scanning electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy were used to relate corrosion behavior to surface characteristics and surface treatments. Results show that all of these surface treatments improve the corrosion resistance of the alloy. This improvement is attributed to the plastically deformed native oxide layer removal and replacement by a newly grown, more uniform one. The uniformity of the oxide layer, rather than its thickness and composition, seems to be the predominant factor to explain the corrosion resistance improvement.

Complications associated with the use of the Esophageal-Tracheal Combitube.

PURPOSE: To report four cases of subcutaneous emphysema, pneumomediastinum and pneumoperitoneum associated with the use of the Esophageal-Tracheal Combitube (ETC) during prehospital management of cardiac arrest. CLINICAL FEATURES: Between September 1994 and April 1996, 1139 patients were resuscitated with the ETC and the semiautomated external defibrillator as part of the CPR protocol for prehospital management of cardiac arrest by basic emergency medical technicians. Eight of these patients presented with subcutaneous emphysema. Four of them, declared dead after arrival in the emergency room (ER), had autopsy studies. In two, autopsy revealed large (6 and 6.5 cm respectively) longitudinal transparietal lacerations of the anterior wall of the oesophagus. Multiple superficial lacerations of the oesophagus were also present in another patient, while no lesion of the airway or the oesophagus was found in the last patient. CONCLUSION: These cases suggest that subcutaneous emphysema, pneumomediastinum and pneumoperitoneum might be complications associated with the use of the ETC. At least in two cases, oesophageal laceration appears to be the mechanism by which these complications occurred.

Neostigmine requirements for reversal of neuromuscular blockade following an infusion of mivacurium.

PURPOSE: To study the efficacy of neostigmine compared with placebo for the antagonism of neuromuscular blockade at the end of a mivacurium infusion, and to determine its optimal dose. METHODS: One hundred adult patients undergoing an elective surgical procedure received a standardized anaesthetic with 20-30 micrograms.kg-1 alfentanil, a propofol infusion and nitrous oxide. Muscle relaxation was maintained at 90-95% T1 depression with 0.2 mg.kg-1 mivacurium followed by an infusion. Neuromuscular blockade was measured with an integrated evoked electromyogram in response to train-of-four (TOF) stimuli at the ulnar nerve every 20 sec. Patients were randomized into four groups. At the end of surgery, the mivacurium infusion was stopped and patients received, immediately, in a double-blind manner, neostigmine (10, 20, or 40 micrograms.kg-1) or placebo according to a random number table. The T1 and TOF ratio were recorded until adequate recovery of neuromuscular function (TOF ratio > 0.70). During the reversal period, non-invasive blood pressure and heart rate were recorded every minute. The incidence of postoperative nausea and vomiting (PONV) was recorded in the recovery room. RESULTS: Data from 94 patients who completed the protocol were analysed. Compared with placebo, neostigmine 10 micrograms.kg-1 did not reduce the time to TOF > 0.70 (17.0 +/- 5.1 vs 14.6 +/- 4.2 min respectively). However the time was decreased with neostigmine 20 micrograms.kg-1 and 40 micrograms.kg-1 (P < 0.001), but with no difference between these last two groups (11.4 +/- 3.0 and 11.4 +/- 3.5 min respectively). Changes in systolic blood pressure and heart rate were not different between the four groups. Very few PONV events were observed in all groups (global incidence 7.4%). CONCLUSION: Recovery of neuromuscular blockade following a mivacurium infusion is accelerated by neostigmine. A dose of neostigmine 20 micrograms.kg-1 appears optimal with no further reduction in recovery time obtained from a larger dose.

Treatment of postoperative nausea and vomiting: comparison of propofol, droperidol and metoclopramide.

PURPOSE: To compare the efficacy of propofol in a subhypnotic dose (10 mg iv), droperidol (1.25 mg iv), or metoclopramide (10 mg iv) in the treatment of PONV in the post anaesthesia care unit (PACU). METHODS: In a prospective, randomized, double-blind protocol, over four months, all eligible inpatients and outpatients were asked to give their consent to be included in the study should they suffer PONV in the PACU. They received a standardized general anaesthetic without any prophylactic antiemetic drug. In the recovery room, patients complaining of persistent nausea (lasting more than ten minutes) and/or experiencing at least two episodes of retching or vomiting were given one of the three study drugs. Recurrence of retching or vomiting was recorded for 60 min after administration of the study drug and nausea severity was assessed on a visual analog scale. Patients still complaining of PONV 30 min after administration of the study drug received a rescue medication (dimenhydrinate). RESULTS: Seventy-eight patients received one of the study drugs. The recurrence of retching or vomiting was higher with propofol (58%) than with droperidol (4%) or metoclopramide (24%) (P < 0.001). More patients who received propofol needed the rescue medication (54%) than those who received droperidol (15%) or metoclopramide (28%) (P < 0.02). No difference was observed in nausea severity. CONCLUSION: A subhypnotic dose of propofol (10 mg iv) is less effective than the conventional antiemetic drugs droperidol and metoclopramide for the treatment of PONV in the PACU.

Perioperative gastric aspiration increases postoperative nausea and vomiting in outpatients.

The efficacy of aspiration of gastric contents to reduce postoperative nausea and vomiting was investigated in a controlled randomized, double-blind study of 265 outpatients. Patients in the treated group had their stomachs aspirated with an orogastric tube. In the control group no tube was inserted. Data on the incidence of nausea and vomiting were collected in the recovery room, the day surgery unit and the day after surgery. The overall incidence of postoperative nausea and vomiting was comparable in the two groups. It was also comparable in the recovery room and the day surgery unit. However, treated patients had a higher incidence of both nausea (26.5% vs 12.0%, P < 0.005) and vomiting (16.7% vs 6.8%, P < 0.02) after their discharge from the day surgery unit. We conclude that aspiration of gastric contents with an orogastric tube does not decrease postoperative nausea and vomiting in outpatients and may increase it after discharge of the patient.

Renal function and hemodynamics during prolonged isoflurane-induced hypotension in humans.

The effect of isoflurane-induced hypotension on glomerular function and renal blood flow was investigated in 20 human subjects. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured by inulin and para-aminohippurate (PAH) clearance, respectively. Anesthesia was maintained with fentanyl, nitrous oxide, oxygen, and isoflurane. Hypotension was induced for 236.9 +/- 15.1 min by increasing the isoflurane inspired concentration to maintain a mean arterial pressure of 59.8 +/- 0.4 mmHg. GFR and ERPF decreased with the induction of anesthesia but not significantly more during hypotension. Postoperatively, ERPF returned to preoperative values, whereas GFR was higher than preoperative values. Renal vascular resistance increased during anesthesia but decreased when hypotension was induced, allowing the maintenance of renal blood flow. We conclude that renal compensatory mechanisms are preserved during isoflurane-induced hypotension and that renal function and hemodynamics quickly return to normal when normotension is resumed.