Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside

Introduction

Due to complexities in its measurement, adequacy of ventilation is seldom used to categorize disease severity and guide ventilatory strategies. Ventilatory ratio (VR) is a novel index to monitor ventilatory adequacy at the bedside. VR=(V˙Emeasured×PaCO2measured)/(V˙Epredicted×PaCO2ideal). V˙Epredicted is 100 mL.Kg^-1.min^-1 and Pa_{CO2 ideal} is 5 kPa. Physiological analysis shows that VR is influenced by dead space (V_D/V_T) and CO2 production (V˙CO2). Two studies were conducted to explore the physiological properties of VR and assess its use in clinical practice.

Methods

Both studies were conducted in adult mechanically ventilated ICU patients. In Study 1, volumetric capnography was used to estimate daily V_D/V_T and measure V˙CO2 in 48 patients. Simultaneously, ventilatory ratio was calculated using arterial blood gas measurements alongside respiratory and ventilatory variables. This data was used to explore the physiological properties of VR. In Study 2, 224 ventilated patients had daily VR and other respiratory variables, baseline characteristics, and outcome recorded. The database was used to examine the prognostic value of VR.

Results

Study 1 showed that there was significant positive correlation between VR and VD/VT (modified r = 0.71) and V˙CO2 (r = 0.14). The correlation between VR and V_D/V_T was stronger in mandatory ventilation compared to spontaneous ventilation. Linear regression analysis showed that V_D/V_T had a greater influence on VR than V˙CO2 (standardized regression coefficient 1/1-V_D/V_T: 0.78, V˙CO2: 0.44). Study 2 showed that VR was significantly higher in non-survivors compared to survivors (1.55 vs. 1.32; P < 0.01). Univariate logistic regression showed that higher VR was associated with mortality (OR 2.3, P < 0.01), this remained the case after adjusting for confounding variables (OR 2.34, P = 0.04).

Conclusions

VR is an easy to calculate bedside index of ventilatory adequacy and appears to yield clinically useful information.     

Modes of ventilatory support and weaning parameters in children

Pediatric respiratory therapy management has become increasingly complex. Mechanical ventilation has become a mainstay in neonatal and pediatric intensive care units. Thorough knowledge of the modes of ventilatory support and criteria for weaning are essential for the critical care nurse to anticipate patient needs. Ventilatory support is initiated when a patient exhibits respiratory failure. For whatever reason, the respiratory system cannot meet the metabolic demands for oxygenation and carbon dioxide (CO2) elimination. Indications for mechanical ventilation in children include marked hypoxia, hypercapnea, peripheral airway obstruction, chest wall deformities, and central nervous system abnormalities. Nurses caring for these children must possess adequate knowledge of the underlying disease process as well as normal respiratory physiology and technical features of ventilators. Nursing strategies can then be directed toward weaning children from the mechanical ventilatory support.     

Measurement of functional residual capacity by nitrogen washout during partial ventilatory support

OBJECTIVE: Evaluation of an open circuit multiple breath nitrogen washout (MBNW) technique for measurement of functional residual capacity (FRC) during partial ventilatory support using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen. DESIGN: Measurements in a lung model with known reference volume simulating spontaneous breathing and duplicate measurements in patients breathing spontaneously with partial ventilatory support. SETTING. Experimental laboratory and intensive care units of a university hospital. PATIENTS: Eighteen patients with acute respiratory failure. INTERVENTIONS: Change of FiO(2) from baseline to 1.0. MEASUREMENTS AND MAIN RESULTS: FRC was measured by MBNW during spontaneous breathing with continuous positive airway pressure, pressure support ventilation, proportional assist ventilation, automatic tube compensation, and airway pressure release ventilation. In the lung model, repeated measurements at three volumes were done with all partial ventilatory support modalities, and baseline FiO(2 )was varied with one mode and FRC. The mean of differences between MBNW (FRC(MBNW)) and reference was 28 ml (1.6%), and the 2.SD-interval was 84 ml (4.9%) for all modes. Measurements up to a baseline FiO(2) of 0.8 showed differences of 5 ml (-0.3%) and the 2.SD-interval of 38 ml (2.2%) between reference and FRC(MBNW). In 18 patients, 66 duplicate measurements revealed a mean difference of 30 ml (0.9%) with a coefficient of repeatability of 358 ml (13%) independent of ventilatory mode and chronological order. CONCLUSION: This study suggests that, using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen, FRC can be determined with good repeatability in patients and good accuracy in a lung model during partial ventilatory support.     

Effects of a closed tracheal suction system on ventilatory and cardiovascular parameters.

OBJECTIVE: To determine whether patients ventilated in the assist-control mode experienced a change in oxygenation, respiratory rate, inspiratory:expiratory ratio, heart rate, blood pressure or acid-base balance when suctioned with a closed tracheal suction system. DESIGN: A quasi-experimental, within-subject, repeated-measures design was used. SUBJECTS: 18 patients ventilated on a fraction of inspired oxygen of 0.47 +/- 0.17 and 2.3 +/- 5.0 cm H2O positive end-expiratory pressure. INTERVENTIONS: Two suction passes were performed, with measurements at baseline, immediately after the first suction pass, immediately before the second suction pass, immediately after the second suction pass, 2 minutes after the second suction pass and 5 minutes after the second suction pass. No hyperoxygenation was used. RESULTS: Significant differences were seen over time for arterial oxygen saturation, respiratory rate and inspiratory:expiratory ratio. Arterial oxygen saturation decreased to less than 90% in four subjects (range 88% to 89%), with a maximum fall of 9%. No significant differences were seen for heart rate, blood pressure, partial pressure of carbon dioxide, bicarbonate, time to nadir (lowest arterial oxygen saturation) or recovery time. CONCLUSIONS: Subjects ventilated in the assist-control mode and suctioned with a closed tracheal suction system did not experience significant changes in cardiovascular or acid-base parameters when suctioned without hyperoxygenation. Although most subjects did not become desaturated, four subjects experienced desaturation at one or more intervals. To prevent desaturation, hyperoxygenation should be used before and after suctioning with a closed tracheal suction system.     

成人股骨上端部分参数测定

背景：在髋部骨折治疗中,内植物的设计和匹配对实现力学的传导及获得长期稳定具有熏要意义。然而由于人种的遗传,生活、工作环境等的影响,从而造成人种股骨参数各异。目的：测定重庆地区成年人股骨上端部分参数。方法：利用游标卡尺实体测量160例重庆地区股骨标本（左右各80例）的股骨头直径、股骨头长径、头颈轴长等5项相关参数,用浩辰CAD软件在影像资料上测量重庆地区成人股骨（男女各80例）上端内、外侧弧度及头颈轴线与股骨外侧皮质夹角。结果与结论：实体测量重庆地区股骨标本得出人股骨头直径为（45．26±3．17）mm;股骨头长径为（39．02±2．58）mm;头颈轴长为（93．23±5．43）mm;股骨颈最小上下颈为（31．28±2．18）mm;股骨颈最小前后径为（26．23±2．10）mm;测量成人股骨影像学资料得出的男性股骨上端内侧弧度为（0．267±0．024）TT;男性股骨上端外侧弧度为（0．219±0．019）TT;男性头颈轴线与股骨外侧皮质夹角为（130．92±2．31）°;女性股骨上端内侧弧度为（0．278±0．019）TT;女性股骨E端外侧弧度为（0．219±0．019）TT;女性头颈轴线与股骨外侧皮质夹角为（130．68±2．02）°。实体测量的股骨头直径、股骨头长径、股骨头颈轴长、股骨颈最小前后径和股骨颈最小上下径呈正相关,相关系数为0．246—0．588。软件测量的影像学数据中股骨上端内、外侧弧度无相关性（P〉0．05）;头颈轴线与股骨外侧皮质夹角和股骨上端内侧弧度呈负相关（r日：一0．446,ra=一0．509,P〈0．05）,而与股骨,卜端外侧弧度呈正相关（r=0．259,ra=0．311,P〈0．05）。测得的重庆地区成人股骨上端的部分参数为设计及改良出符合当地髋部骨折的内固定物提供参考依据。     

移动DR后处理参数对床旁胸片影像质量的影响

目的 探讨移动数字化X摄影（DR）不同后处理参数对床旁胸片影像质量的影响。方法 对150幅床旁胸片图像进行多频拉普拉斯变换（MLT）、图像处理（IP）等后处理参数调整,分析总结后处理参数的优化方案。测量肺部相关区域光学密度值,以配对样本t检验比较出厂设置默认参数与后处理参数优化肺部相关区域光学密度值的差异和图像质量评分的差异。结果 亮度、对比度以及动态范围中的低密度参数对床旁胸片图像质量影响较大。调整并优化后处理参数后,胸部第2肋间区域密度值为1.68±0.04,肺门密度值为0.77±0.46,肺周边部密度（近胸壁1 cm处与单肋骨重叠处）值为0.62±0.06,心影密度值为0.44±0.04,膈下密度值为0.37±0.04,两肺野外带纹理清晰显示,脊柱和心影后区肺纹理可见,符合诊断学要求。第2肋间、肺门、肺周边部、心影部、膈下部均为调整前密度值小于调整后密度值,差异有统计学意义,且调整后的密度值均较调整前接近参考密度值;优化后处理参数后所得影像质量评分为（3.53±0.14）分,高于优化前（3.02±0.23）分,差异有统计学意义。结论 适合的后处理参数值是保证移动DR床旁胸片肺部各区域合理密度值的关键,优化后处理参数可提高移动DR床旁胸片的影像质量。     

Measurement of irradiation doses secondary to bedside radiographs in a medical intensive care unit

The authors prospectively studied the radiation doses to radio-sensitive organs secondary to bedside radiographs in intensive care patients and in a control phantom. Dosimeters were taped on different organs during each bedside X-ray. The mean radiation doses, expressed in 10^-5 Gy (m-rad), for an average patient who was hospitalized 9 days and had 6 chest X-rays were respectively: 292 to the sternal bone marrow; 239 to the thyroid gland; 3 to the testes; 1 to the ovaries; 605 to the eye for 2 maxillary sinus X-rays. No diffused irradiation was measured during a 2-month period in the intensive care unit nor on dosimeters worn by four nurses.     

ICU标准化护理床旁交接班的实施及效果

护士交接班是临床护理工作中的一个重要环节,对保证临床护理工作质量起着举足轻重的作用[1].但在实际工作中,由于部分护理人员不规范交接班,对工作造成影响,因此完善护理交接班内容,提高交接班质量,从而节约护士时间,把护士真正还给病人,是护理工作中至关重要的一环.2009年7月开始,我科护士对ICU床旁交接班的模式进行了改进,效果良好,现报告如下.     

Non-conventional techniques of ventilatory support

The non-conventional techniques for ventilatory support represent a new approach to the management of patients with respiratory failure. A large number of studies indicate that these techniques can maintain adequate gas exchange under conditions in which the traditional concepts of gas transport no longer hold. We have reviewed the group of techniques, collectively called high frequency ventilation (HFV), in which the tidal volumes are much less (1 to 5 ml per kg) than those observed during conventional mechanical ventilation. Although HFV has theoretical advantages in some clinical settings, it has been shown to be superior to conventional mechanical ventilation in but a few. HFV appears to provide adequate ventilation while still allowing access to tracheal and laryngeal surgical fields. It has been successful during pneumonectomy, and in the treatment of bronchopleural fistulae. The relevance of tracheal insufflation (TRIO) of oxygen and constant flow ventilation (CFV) to the human clinical setting is uncertain. TRIO may be useful to oxygenate patients who are difficult to intubate, or TRIO could be applied for ventilation of patients involved in mass casualties. Although CFV does not maintain normal levels of PaCO2 in humans, it can provide adequate oxygenation. It might be clinically applicable during thoracic surgery, in which movement of the abdominal and thoracic contents associated with conventional mechanical ventilation is undesirable. During CFV, the lung is kept motionless with sufficient airway pressures to maintain patency of airways and alveoli. CFV is useful as a tool for studying phenomena affected by breathing. The rationale for the use of an artificial lung during extracorporeal membrane oxygenation (ECMO) or extracorporeal carbon dioxide removal with low positive pressure ventilation (ECCO2R-LFPPV) in the treatment of acute respiratory failure is to provide temporary respiratory function while the pulmonary lesion is being treated or is resolving. The factors that most limit the usefulness of ECMO are not technical but relate to the ability of the lung to recover structurally and functionally after a severe insult. Poor survival figures in the published series of ECMO in adults reflect the gravity of illness prior to treatment. However, results in neonates have been quite encouraging. ECCO2R allows less exposure of blood to the extracorporeal circuit and avoids the reduction in pulmonary blood flow associated with ECMO. Although the reported survival of adults with severe acute respiratory failure treated with ECCO2R is extremely promising, it is important to point out that none of the published reports are controlled, randomized studies.(ABSTRACT TRUNCATED AT 400 WORDS)     

Patients' perceptions of bedside handover

Gone are the days when a nurse would discuss a patient's progress in a matter of fact way behind their back when handing over their care to a colleague. Handover has now moved from the office to the bedside to maximise patient involvement and continuity of care. Catherine Greaves reveals how patients perceive this practice.     

母婴床旁护理的实施

目前医院产科大部分婴儿的沐浴、抚触等护理操作,都是由护士将婴儿带到新生儿沐浴间进行集中护理,这个过程不免让许多家长担忧:离开父母视线,宝宝能否得到精心护理,会不会在集中护理中将宝宝抱错,会不会发生交叉感染.针对集中护理存在的诸多问题,2010年1月我院产科母婴同室温馨病区推出母婴床旁护理,受到了产妇及家属的普遍欢迎.这种护理模式,满足了产妇及家属的需求,解决了许多家长的困惑,实现了产科安全优质护理服务.