Biomechanical analysis of supra-acetabular insufficiency fracture using finite element analysis

Background

Supra-acetabular insufficiency fractures (SAIFs) occur in the upper acetabulum and are rare compared with insufficiency sacral, femoral head, or ischial fractures. However, SAIFs are known to occur in low grade trauma, and the underlying mechanism is still remained unclear.

Short uncemented stems allow greater femoral flexibility and may reduce peri-prosthetic fracture risk: a dry bone and cadaveric study

BackgroundShort femoral stems for uncemented total hip arthroplasty have been introduced as a safe alternative to traditional longer stem designs. However, there has been little biomechanical examination of the effects of stem length on complications of surgery. This study aims to examine the effect of femoral stem length on torsional resistance to peri-prosthetic fracture.ResultsSynthetic femora implanted with short stems fractured at a significantly higher torque (27.1 vs. 24.2 Nm, p = 0.03) and angle (30.3° vs. 22.3°, p = 0.002) than those implanted with long stems. Fracture patterns of the two groups were different, but showed remarkable consistency within each group. These characteristic fracture patterns were closely replicated in the pair of cadaveric femora.ConclusionsThis new short-stemmed press-fit femoral component allows more femoral flexibility and confers a higher resistance to peri-prosthetic fracture from torsional forces than long stems.     

神经肌肉阻滞剂在急性呼吸窘迫综合征中的应用

目前神经肌肉阻滞剂在ICU应用较广,其中25％ ～ 55％的急性呼吸窘迫综合征（acuterespiratory distress syndrome,ARDS）机械通气患者接受该药作为辅助治疗,但至今神经肌肉阻滞剂在ARDS机械通气患者的应用仍存在不少争议.本文对神经肌肉阻滞剂在ARDS中的应用进行系统阐述.     

Hemodynamic effects of partial liquid ventilation with perfluorocarbon in acute lung injury

Objective To assess the effect of partial liquid ventilation with perfluorocarbons on hemodynamics and gas exchange in large pigs with induced acute lung injury (ALI).Design Randomized, prospective, double-control, experimental study.Setting Experimental intensive care unit of a university.Materials Eighteen large pigs (50±5 kg body weight) with an average anterior posterior thoracic diameter of 24 cm and induced acute lung injury.Interventions All animals were surfactant depleted by lung lavage to aP _aO₂ below 100 mmHg and randomized to receive either perflubron (n=6) or saline (n=6) in five intratracheal doses of 5 ml/kg at 20-min intervals, or no instillation (n=6).Measurements and results In all animals heart rate, arterial pressures, pulmonary pressures, cardiac output and blood gases were recorded at 20-min intervals. There was no deleterious effect on any hemodynamic parameter in the perflubron group, whereas systolic and mean pulmonary arterial pressure values showed a persistent decrease after the first 5 ml/kg of perflubron, from 48.7±14.1 to 40.8±11.7 mmHg and from 39.7±13.2 to 35.2±12.0 mmHg, respectively. Perflubron resulted in a significant (ANOVAP<0.01), dose-dependent increase inP _aO₂ values from 86.3±22.4 to a maximum of 342.4±59.4 mmHg at a dose of 25 ml/kg; the other groups showed no significant increase inP _aO₂.Conclusions Tracheal instillation of perflubron in induced ALI results in a dose-dependent increase inP _aO₂ and has no deleterious effect on hemodynamic parameters.     

A Dual Closed-Loop Control System for Mechanical Ventilation

OBJECTIVE: Closed-loop mechanical ventilation has the potential to provide more effective ventilatory support to patients with less complexity than conventional ventilation. The purpose of this study was to investigate the effectiveness of an automatic technique for mechanical ventilation. METHODS: Two closed-loop control systems for mechanical ventilation are combined in this study. In one of the control systems several physiological data are used to automatically adjust the frequency and tidal volume of breaths of a patient. This method, which is patented under US Patent number 4986268, uses the criterion of minimal respiratory work rate to provide the patient with a natural pattern of breathing. The inputs to the system include data representing CO2 and O2 levels of the patient as well as respiratory compliance and airway resistance. The I:E ratio is adjusted on the basis of the respiratory time constant to allow for effective emptying of the lungs in expiration and to avoid intrinsic positive end expiratory pressure (PEEP). This system is combined with another closed-loop control system for automatic adjustment of the inspired fraction of oxygen of the patient. This controller uses the feedback of arterial oxygen saturation of the patient and combines a rapid stepwise control procedure with a proportional-integral-derivative (PID) control algorithm to automatically adjust the oxygen concentration in the patient's inspired gas. The dual closed-loop control system has been examined by using mechanical lung studies, computer simulations and animal experiments. RESULTS: In the mechanical lung studies, the ventilation controller adjusted the breathing frequency and tidal volume in a clinically appropriate manner in response to changes in respiratory mechanics. The results of computer simulations and animal studies under induced disturbances showed that blood gases were returned to the normal physiologic range in less than 25 s by the control system. In the animal experiments understeady-state conditions, the maximum standard deviations of arterial oxygen saturation and the end-tidal partial pressure of CO2 were +/- 1.76% and +/- 1.78 mmHg, respectively. CONCLUSION: The controller maintained the arterial blood gases within normal limits under steady-state conditions and the transient response of the system was robust under various disturbances. The results of the study have showed that the proposed dual closed-loop technique has effectively controlled mechanical ventilation under different test conditions.     

Safety of percutaneous dilational tracheostomy in hematopoietic stem cell transplantation recipients requiring long-term mechanical ventilation

Purpose

Recent reports have shown that the outcome of mechanically ventilated patients after hematopoietic stem cell transplantation (HSCT) has improved. This study was conducted to clarify if percutaneous dilational tracheostomy is safe in this group of patients and to report the outcome of HSCT recipients requiring long-term mechanical ventilation.

Methods

A retrospective review of our 8-year experience with patients with acute respiratory insufficiency after HSCT, requiring long-term mechanical ventilation and percutaneous dilational tracheostomy and an analysis of patient outcomes were made.

Results

Percutaneous dilational tracheostomy was safely performed in all 51 patients. Although 1 patient (2%) developed a pneumothorax that required drainage, stoma infections or severe bleeding complications were not observed. Of the 51 patients in the study, 14 (27%) survived the intensive care unit stay, and 10 of them were ventilated for more than 20 days. The intensive care unit survival rate for the period from 1998 to 2001 was 11% compared with 38% for the period from 2002 to 2005 (P = .053).

Conclusions

Percutaneous dilational tracheostomy can be safely performed on patients with acute respiratory failure after HSCT. This procedure did not result in postoperative wound infections or significant bleeding complications. Furthermore, the results of our study indicate that today even patients with prolonged mechanical ventilation (>20 days) have a chance of long-term survival.     

The effect of induced hypothermia on respiratory parameters in mechanically ventilated patients

Aim

Mild hypothermia is increasingly applied in the intensive care unit. Knowledge on the effects of hypothermia on respiratory parameters during mechanical ventilation is limited. In this retrospective study, we describe the effect of hypothermia on gas exchange in patients cooled for 24 h after a cardiac arrest.

Methods

Respiratory parameters were derived from electronic patient files from 65 patients at the start and end of the hypothermic phase and at every centigrade increase in body temperature until normo-temperature, including tidal volume, positive end expiratory pressure (PEEP), plateau pressure, respiratory rate, exhaled CO₂ concentrations (etCO₂) and FIO₂. Static compliance was calculated as V_T/P_plateau − PEEP. Dead space ventilation was calculated as (PaCO₂ − etCO₂)/PaCO₂.

Results

During hypothermia, PaCO₂ decreased, at unchanged PaCO₂-etCO₂ gap and minute ventilation. During rewarming, PaCO₂ did not change, while etCO₂ increased at unchanged minute ventilation. Dead space ventilation did not change during hypothermia, but lowered during rewarming. During hypothermia, PaO₂/FIO₂ ratio increased at unchanged PEEP levels. Respiratory static compliance did not change during hypothermia, nor during rewarming.

Conclusion

Hypothermia possibly improves oxygenation and ventilation in mechanically ventilated patients. Results may accord with the hypothesis that reducing metabolism with applied hypothermia may be beneficial in patients with acute lung injury, in whom low minute ventilation results in severe hypercapnia.     

Volume-targeted modes of modern neonatal ventilators: how stable is the delivered tidal volume?

Objective Volume-targeted modes are designed to deliver a constant tidal volume (V_t) at lowest possible pressure independently of changes in compliance, resistance, and leak of the respiratory system. We examined whether these volume-targeted modes respond rapidly enough to sudden changes in respiratory mechanics (e.g., selective intubation, surfactant administration, endotracheal tube kinking, de-kinking, obstruction), resulting in insufficient or excessive V_t delivery. Design and setting Bench study of six neonatal ventilators in the volume-targeted mode simulating preterm and full-term infant settings on a test lung. Measurements and results Breath-to-breath expiratory V_t were measured after rapid compliance, resistance, and leak changes. Under our test settings all ventilators showed important volume overshooting following rapid increase in compliance or decrease in resistance. Between one and 16 inflations were required to return to the set V_t. Some ventilators delivered inaccurate V_t under steady state condition while others showed considerable breath-to-breath V_t variability. Conclusions We observed inaccurate V_t delivery under specific conditions as well as immediate and sometimes prolonged volume overshooting after a rapid respiratory system compliance increase or resistance decrease in volume-targeted modes of modern neonatal ventilators. Similar discrepancies between the set V_t and the delivered inflations can be harmful in clinical situations, especially in newborns. Their clinical relevance needs to be clarified with safety studies in the neonatal population and we encourage manufacturers to further improve the ventilators algorithms. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.