Reliability of measured tidal volume in mechanically ventilated young pigs with normal lungs

Objective This study examined whether volumes can be accurately measured at the expiratory valve of a conventional ventilator using pressure support ventilation and positive end expiratory pressure with software compensation for circuit compliance available in the Servo ventilator.Design and setting Comparison of two methods for measuring tidal volume in an animal laboratory.Subjects Twenty healthy, intubated, sedated, spontaneously breathing pigs.Interventions Volume was measured in ten neonatal-sized and ten pediatric-sized pigs ventilated with the Servo ventilator using pressure support ventilation and positive end expiratory pressure with and without circuit compliance compensation. We compared volume measured at the airway opening by pneumotachography to volume measured at the expiratory valve of a conventional ventilator.Measurements and results The use of circuit compliance compensation significantly improved the agreement between the two volume methods in neonatal-sized piglets (concordance correlation coefficient: with circuit compliance compensation, 0.97; without, 0.87, p=0.002). In pediatric-sized pigs there was improvement in agreement between the two measurement methods due to circuit compliance compensation (concordance correlation coefficient with circuit compliance compensation, 0.97; without, 0.88, p=0.027). With circuit compliance compensation off there was positive bias: mean difference (bias) 2.97±0.12 in neonatal-sized and 3.75±0.38 in pediatric-sized pigs.Conclusions Our results show that volume can be accurately measured at the expiratory valve of a conventional ventilator in neonatal- and pediatric-sized animals.This research was supported by an unrestricted grant from Maquet, Inc.     

Exhaled tidal volume overestimation in mechanically ventilated patients with large cardiogenic oscillation

OBJECTIVES: In postcardiac surgery patients, we often noticed that monitored tidal volumes exceeded the ventilator settings. We investigated whether cardiogenic oscillation causes overestimation of tidal volume. DESIGN: Prospective, observational, clinical study. SETTING: Surgical intensive care unit in a national heart institute. PATIENTS: Eight postcardiac surgery patients (age 13-70). INTERVENTIONS: Patients were paralyzed and received flow-triggered volume-controlled ventilation with a tidal volume of 10 mL/kg. In random order, two types of ventilator (Bird 8400 STi and Servo-300) and two respiratory rates (5 and 10 breaths/min) were applied to each patient via a disposal ventilatory circuit and heat-and-moisture exchanger. For each ventilator, we adjusted the flow-triggering sensitivity to prevent autotriggering due to cardiogenic oscillation: 10 L/min for the Bird 8400 STi and green zone for the Servo-300. MEASUREMENTS AND MAIN RESULTS: The magnitude of cardiogenic oscillation during mechanical ventilation was defined as peak expiratory flow fluctuation at end-expiration. We recorded tidal volume using the monitoring devices on the ventilators and calculated the discrepancy from the set tidal volume.Cardiogenic oscillation was significantly greater with the Bird 8400STi (4.0 +/- 1.8 L/min) than with the Servo-300 (1.7 +/- 0.8 L/min). With the Bird 8400 STi, the discrepancy between monitored tidal volume and set tidal volume ranged from 15 to 260 mL when the respiratory rate was 5 breaths/min and from -9 to 75 mL at 10 breaths/min; there was a linear correlation between the overestimation of tidal volume and the magnitude of cardiogenic oscillation. In contrast, with the Servo-300, the discrepancy was relatively small (-36 to 14 mL). CONCLUSIONS: In mechanically ventilated patients with large cardiogenic oscillation, exhaled tidal volume is overestimated on at least one model of ventilator.     

The effects of vasoactive drugs on pulse pressure and stroke volume variation in postoperative ventilated patients

Introduction

Although pulse pressure variation (PPV) and stroke volume variation (SVV) during mechanical ventilation have been shown to predict preload responsiveness, the effect of vasoactive therapy on PPV and SVV is unknown.

Methods

Pulse pressure variation and SVV were measured continuously in 15 cardiac surgery patients for the first 4 postoperative hours. Pulse pressure variation was directly measured from the arterial pressure waveform, and both PPV and SVV were also calculated by LiDCO Plus (LiDCO Ltd, Cambridge, United Kingdom) before and after volume challenges or changes in vasoactive drug infusions done to sustain cardiovascular stability.

Results

Seventy-one paired events were studied (38 vasodilator, 10 vasoconstrictor, 14 inotropes, and 9 volume challenges). The difference between the measured and LiDCO-calculated PPV was 1% ± 7% (1.96 SD, 95% confidence interval, r² = 0.8). Volume challenge decreased both PPV and SVV (15% to 10%, P < .05 and 13% to 9%, P = .09, respectively). Vasodilator therapy increased PPV and SVV (13% to 17% and 9% to 15%, respectively, P < .001), whereas increasing inotropes or vasoconstrictors did not alter PPV or SVV. The PPV/SVV ratio was unaffected by treatments.

Conclusion

Volume loading decreased PPV and SVV; and vasodilators increased both, consistent with their known cardiovascular effects. Thus, SVV and PPV can be used to drive fluid resuscitation algorithms in the setting of changing vasoactive drug therapy.     

Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of tidal volume

Objective: The delivery of bronchodilator drugs with metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become a widespread practice. However, the various ventilator settings that influence the efficacy of MDI are not well established. The tidal volume (V_T) during drug delivery has been suggested as one of the factors that might increase the effectiveness of this therapy. To test this, the effect of two different V_T on the bronchodilation induced by β ₂-agonists administered with MDI and a spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined.¶Methods: Nine patients with COPD, mechanically ventilated on volume-controlled mode, were prospectively randomised to receive six puffs of salbutamol (S, 100 μg/puff) either with a V_T of 8 ml/kg (normal V_T, 582 ± 85) or with a V_T of 12 ml/kg (high V_T, 912 ± 137). With both modes inspiratory flow was identical. S was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud enhancer spacer. After a ¶6-h washout, patients were crossed-over to receive S by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance, the difference between Rrs and Rint (ΔR), static end-inspiratory respiratory system compliance (Cst,rs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR) were measured before and at 15, 30 and 60 min after S.¶Results: S caused a significant decrease in dynamic and static airway pressures, PEEPi, Rint and Rrs. These changes were not influenced by V_T and were evident at 15, 30 and 60 min after S. With normal and high V_T, Cst,rs, ΔR and HR did not change after S.¶Conclusions: We conclude that S delivered with an MDI and a spacer device induces significant bronchodilation in mechanically ventilated patients with COPD, the magnitude of which is not affected by at least a 50 % increase in V_T. These results do not support the V_T manipulations when bronchodilators are administered in adequate doses during controlled mechanical ventilation.     

Influence of tidal volume on the compliance of the respiratory system in mechanically ventilated newborn infants

We measured the compliance of the respiratory system (Crs) at 4 different tidal volumes (VT = 2.5, 5.0, 7.5, 10.0 ml/kg) in 29 mechanically ventilated newborn infants and determined the VT associated with the highest Crs ("optimal" VT) and with the lowest Crs ("worst" VT). Crs depended on the VT in all newborn infants investigated. The "optimal" VT most frequently observed was 2.5 and 5.0 ml/kg and the "worst" VT most frequently observed was 2.5 and 10.0 ml/kg. Mean Crs at the "optimal" VT was 62.3% higher than at the "worst" VT. The "optimal" VT was lower (2.5 ml/kg) in newborn infants with controlled ventilation than in newborn infants with intermittent mandatory ventilation (5.0 ml/kg). We conclude that it may be useful to determine the VT associated with the highest Crs in order to avoid unnecessarily high inflation pressures for the mechanical ventilation of newborn infants. Further studies are needed to assess long-term effects of such a Crs guided respirator therapy.     

Prediction of fluid responsiveness using respiratory variations in left ventricular stroke area by transoesophageal echocardiographic automated border detection in mechanically ventilated patients

Background  

Left ventricular stroke area by transoesophageal echocardiographic automated border detection has been shown to be strongly correlated to left ventricular stroke volume. Respiratory variations in left ventricular stroke volume or its surrogates are good predictors of fluid responsiveness in mechanically ventilated patients. We hypothesised that respiratory variations in left ventricular stroke area (ΔSA) can predict fluid responsiveness.     

每搏量变异对老年严重脓毒症患者液体反应的预测

目的 评价每搏量变异(SVV)预测机械通气老年严重脓毒症患者的液体反应性.方法 采用前瞻性临床研究方法,在液体复苏过程中共对17例机械通气的老年严重脓毒症患者进行31次液体负荷试验.采用脉搏波指示剂连续心排血量(PiCCO)技术监测SVV.将液体负荷后心脏指数(CI)增加值(ΔCI)≥10%定义为液体反应阳性.观察液体负荷试验前后血流动力学及肺水指标的变化,评价SVV、中心静脉压(CVP)与ΔCI的相关性.结果 液体负荷后SVV显著降低[(6.6±2.1)%比(12.1±3.7)%,P<0.01],CVP显著增高[(12.5±3.6) mm Hg比(8.9±4.1) mm Hg,1 mm Hg=0.133 kPa,P＜0.01].直线相关分析显示,液体负荷前SVV与ΔCI显著相关(r=0.447,P=0.012),CVP与ΔCI无直线相关关系(r=0.082,P=0.674).受试者工作特征曲线(ROC曲线)分析示,液体负荷前SVV、CVP与CI的曲线下面积(AUC)分别为0.672[95%可信区间(95%CI)0.463～0.885]和0.336(95%CI 0.133～0.539).SVV为11.5%时对液体反应的敏感性为71%,特异性为67%.结论 SVV能反映机械通气状态下老年脓毒症患者液体复苏时的液体反应性,可作为指导老年严重脓毒症患者液体治疗的指标.     

Penetration of ertapenem into muscle measured by in vivo microdialysis in mechanically ventilated patients

Ertapenem at 1 g once daily has been suggested to be underdosed in intensive care unit (ICU) patients to attain optimal concentrations in target tissues. Therefore, our study aimed to assess the kinetics of ertapenem in plasma and skeletal muscle in ICU patients using microdialysis. Average muscle free-ertapenem concentrations were above the MIC values of targeted pathogens. In a few patients, the concentrations were below the MIC values. The clinical efficiency of ertapenem at 1 g once daily should be evaluated in a large population of ICU patients.     

No change in the regional distribution of tidal volume during lateral posture in mechanically ventilated patients assessed by electrical impedance tomography

We assessed the distribution of regional lung ventilation during moderate and steep lateral posture using electrical impedance tomography (EIT) in mechanically ventilated patients. Seven patients were placed on a kinetic treatment table. An elastic belt containing 16 electrodes was placed around the chest and was connected to the EIT device. Patients were moved to left and right lateral positions in a stepwise (10°) mode up to 60°. EIT images [arbitrary units (AU)] were generated and scanned for assessment of relative ventilation distribution changes [tidal volume (V_T)]. A calibration procedure of arbitrary units (AUs) versus ventilator‐derived V_T performed in all patients during three predefined positions (supine, 60°‐left dependent and 60°‐right‐dependent) showed a significant correlation between V_T in supine, left and right lateral positions with the corresponding AUs (r² = 0·356, P<0·05). Changes in V_T were calculated and compared to supine position, and specific regions of interest (ROIs) were analysed. In our study, in contrast to recent findings, a change in lateral positions did not induce a significant change in regional tidal volume distribution. In right lateral positions, a broader variation of V_T with a trend towards an increase in the dependently positioned lung was observed in comparison with supine. Lateral positioning promotes the redistribution of ventilation to the ventral regions of the lung. The use of EIT technology might become a helpful tool for understanding and guiding posture therapy in mechanically ventilated patients.     

The effect of tidal volume and intravascular volume state on systolic pressure variation in ventilated dogs

Both tidal volume and effective blood volume may affect the variation in the arterial pressure waveform during mechanical ventilation. The systolic pressure variation (SPV), which is the difference between the maximal and minimal systolic pressure values following one positive pressure breath was analyzed in 10 anesthetized and ventilated dogs, during ventilation with tidal volumes of 15 and 25 ml/kg. The dogs were studied during normovolemia, hypovolemia (after bleeding of 30% of estimated blood volume) and hypervolemia (after retransfusion of shed blood with additional 50 ml/kg of plasma expander). The SPV reflected hemodynamic changes and was maximal during hypovolemia and minimal during hypervolemia. Unlike all other hemodynamic parameters it was also affected by the tidal volume and significantly increased at higher tidal volumes during each volume state. We conclude that the SPV and its components are useful parameters in evaluating the intravascular volume state. They also reflect the magnitude of the tidal volume employed.Supported by the Ministry of Industry — Hadassah Foundation for Applied Research, and partly by the MJF foundation     

Usefulness of left ventricular stroke volume variation to assess fluid responsiveness in patients with reduced cardiac function

OBJECTIVE: Stroke volume variation as measured by the analysis of the arterial pressure waveform enables prediction of volume responsiveness in ventilated patients with normal cardiac function. The aim of this study was to investigate the ability of monitoring stroke volume variation to predict volume responsiveness and to assess changes in preload in patients with reduced left ventricular function after cardiac surgery. DESIGN: Prospective study. SETTING: University hospital. PATIENTS: Fifteen mechanically ventilated patients with a left ventricular ejection fraction <0.35 (study group) and 15 patients with an ejection fraction >0.50 (control group) after coronary artery bypass grafting following admission to the intensive care unit. INTERVENTIONS: Volume loading with 10 mL of hetastarch 6% times body mass index. If stroke volume index increased >5%, successive volume loading was performed until no further increase in stroke volume index was reached. MEASUREMENTS AND MAIN RESULTS: Stroke volume variation, central venous pressure, pulmonary artery occlusion pressure (PAOP), and left ventricular end-diastolic area index (LVEDAI) were measured at baseline and immediately after each volume loading step. In both groups, stroke volume variation at baseline correlated significantly with changes in stroke volume index caused by volume loading (p <.01). Further, changes in stroke volume variation as a result of volume loading correlated significantly with the concomitant changes in stroke volume index in both groups (p <.01). Using receiver operating characteristic analysis, in the study group areas under the curve for stroke volume variation, PAOP, central venous pressure, and LVEDAI did not differ significantly. In the control group, the area under the curve for stroke volume variation was statistically larger than for PAOP, central venous pressure, and LVEDAI. CONCLUSIONS: Continuous and real-time monitoring of stroke volume variation by pulse contour analysis can predict volume responsiveness and allows real-time assessment of the hemodynamic effect of volume expansion in patients with reduced left ventricular function after cardiac surgery.     

Ultrasound estimation of volume of pleural fluid in mechanically ventilated patients

Objective The aim was to develop a practical method for estimation of the volume of pleural effusion using ultrasonography in mechanically ventilated patients. Design Prospective observational study. Setting 20-bed general intensive care unit in the university hospital. Patients and participants 81 patients were included after initial suspicion of pleural fluid on chest supine X-ray and pre-puncture ultrasound confirming effusion. Patients with thoracic deformities, post-lung surgery, with diaphragm pathology, haemothorax, empyema and with incomplete aspiration of pleural fluid on post-puncture ultrasound were excluded. Interventions Patients were supine with mild trunk elevation at 15°. Probe was moved upwards in posterior axillary line, and transverse section perpendicular to the body axis was obtained with pleural separation visible at lung base. The maximal distance between parietal and visceral pleura (Sep) in end-expiration was recorded. Thoracentesis was performed at previous probe position and volume of pleural fluid (V) recorded. Measurements and results 92 effusions were evaluated and drained; 11 (12%) were excluded for incomplete aspiration. Success rate of obtaining fluid under ultrasound guidance was 100%; the incidence of pneumothorax or bleeding was zero. Mean Sep was 35 ± 13 mm. Mean V was 658 ± 320 ml. Significant positive correlation between both Sep and V was found: r = 0.72; r ² = 0.52; p < 0.001. The amount of pleural fluid volume can be estimated with the simplified formula: V (ml) = 20 × Sep (mm). Mean prediction error of V using Sep was 158.4 ± 160.6 ml. Conclusions Easy quantification of pleural fluid may help to decide about performing thoracentesis in high-risk patients, although thoracentesis under ultrasound guidance appears to be a safe procedure.     

间接测热法测定并比较不同疾病机械通气患者的静息能量消耗

目的:传统的公式计算不能客观、正确地评定疾病状况下的能量消耗,所以利用间接测热法测定并分析机械通气的慢性阻塞性肺疾病患者与其他机械通气患者的静息能量消耗特点,并进行相关因素探讨。方法:于2007-02/07,用美国Med Graphic公司CCM/D能量代谢测试系统测定华西医院ICU病房的21例慢性阻塞性肺疾病和24例非慢性阻塞性肺疾病的机械通气患者静息能量消耗,并比较其差异,观察血浆白蛋白、动脉血氧分压、动脉血二氧化碳分压和全天能量供给与静息能量消耗和呼吸商的相关性。结果:45例患者进入结果分析。①慢性阻塞性肺疾病患者静息能量消耗高于非慢性阻塞性肺疾病患者(P<0.05),而两组患者的呼吸商比较差异无显著性意义(P>0.05)。②静息能量消耗和呼吸商与白蛋白、动脉血氧分压、动脉血二氧化碳分压均无明显相关性(P>0.05),呼吸商与全天能量供给存在显著的相关性(P<0.05),但静息能量消耗与全天能量供给无明显相关性。结论:机械通气患者中,慢性阻塞性肺疾病患者的静息能量消耗比其他机械通气患者高,全天能量供给对呼吸商有影响,但不能用呼吸商指导营养支持。     

Influences of different vasopressors on stroke volume variation and pulse pressure variation

Pulse pressure variation (PPV) and stroke volume variation (SVV) during mechanical ventilation have been shown to be effective parameters to predict preload responsiveness. Although induced hypertension decreases PPV and SVV, the influences of different vasopressors on PPV and SVV are unknown. 94 patients undergoing elective otologic surgery were randomly divided into three groups: Group P (patients were given phenylephrine), Group D (patients were given dopamine), Group E (patients were given ephedrine). When surgery was ongoing and the circulation state was stable, patients were given the vasopressor to increase the systolic arterial pressure (SAP) to the pre-calculated levels: low level, 10 % < ΔSAP ≤ 20 %; medium level, 20 % < ΔSAP ≤ 30 %; high level, 30 % < ΔSAP ≤ 40 %. When invasive arterial pressure reached the target value, PPV, SVV and other parameters were recorded. Dopamine decreased the PPV and SVV more significantly than ephedrine, but less significantly than phenylephrine. The influences of phenylephrine, dopamine and ephedrine on SVV and PPV are different due to their different pharmacological mechanisms.     

Assessment of left ventricular function by pulse wave analysis in critically ill patients

Purpose

Left ventricular (LV) performance is often quantified by echocardiography in critically ill patients. Pulse wave analysis (PWA) systems can also monitor cardiac function but in a continuous fashion. We compared echocardiographic and PWA-derived indices of LV function.

Methods

We enrolled 70 critically ill patients equipped with invasive arterial pressure monitoring who required echocardiography. We simultaneously assessed LV ejection fraction (LVEF), the rate of LV pressure rise during systole (dP/dt _MAX) obtained with echocardiography (EC-dP/dt _MAX), the ratio of effective arterial elastance to LV end-systolic elastance (E _a/E _es) determined by echocardiography, the dP/dt _MAX estimated from the arterial pressure waveform (AP-dP/dt _MAX) and the cardiac cycle efficiency (CCE) using PWA.

Results

Mean LVEF was 53 ± 18 % and CCE 0.16 ± 0.26. CCE was correlated linearly with LVEF (r = 0.88, 95 % CI 0.81 to 0.92, P < 0.001), and the dP/dt _MAX values from the two techniques were linearly correlated (r = 0.93, 95 % CI 0.87 to 0.96, P < 0.001). There was minimal bias between the techniques for measurement of dP/dt _MAX (23.7 mmHg/ms; 95 % CI ?23.6 to 71.0). E _a/E _es and CCE were inversely correlated (r = ?0.81, 95 % CI ?0.88 to ?0.71, P < 0.001). A CCE value of <0.07 predicted LVEF <40 % with a sensitivity of 0.93 and a specificity of 0.96 (AUC 0.98, 95 % CI 0.90 to 1.0, P < 0.001). A CCE value of >0.12 predicted LVEF ≥50 % with a sensitivity of 0.96 and a specificity of 0.82 (AUC 0.94, 95 % CI 0.87 to 1.0, P < 0.001). A CCE value <0.12 predicted E _a/E _es ≥1.3 with a sensitivity of 0.93 and a specificity of 0.89 (AUC 0.94, 95 % CI 0.83 to 1.0, P < 0.001).

Conclusions

PWA-derived variables provide relevant information on cardiac contractility and performance in critically ill patients. PWA provides an easy method for online hemodynamic evaluation in critically ill patients.     

Usefulness of mitral annular plane systolic excursion in assessment of left ventricular systolic function in mechanically ventilated obese patients

BackgroundThe management of mechanically ventilated patients depends on a combination of clinical skills and measurement of physiological parameters.ObjectivesWe evaluated the role of mitral annular plane systolic excursion (MAPSE) in the determination of left ventricular systolic function (LVSF) in mechanically ventilated obese patients.MethodsA convenient sample of 60 of 68 obese, mechanically ventilated patients in the intensive care unit were included in the study. Transthoracic echocardiogram MAPSE measurement (averaged from 3 consecutive cycles) on 2 separate days, vs the eyeball ejection fraction (classic clinical method) on 2 separate days, and vs the biplane Simpson (classic research and consultative echocardiogram method) on 2 separate days was obtained. In patients with non sinus rhythm, measurements were collected over 5 to 10 heartbeats.ResultsThere was a significant positive correlation between MAPSE and LVSF assessment using the eyeball method and Simpson method (r= 0.89 and 0.87, respectively; P< .001). Mitral annular plane systolic excursion was significantly shorter in duration (P< .001).ConclusionsMitral annular plane systolic excursion is useful, an easier technique, and shorter in duration compared with the eyeball method in the determination of LVSF in mechanically ventilated obese patients.     

Diagnostic accuracy of stroke volume variation measured with uncalibrated arterial waveform analysis for the prediction of fluid responsiveness in patients with impaired left ventricular function: a prospective,observational study

Uncalibrated arterial waveform analysis enables dynamic preload assessment in a minimally invasive fashion. Evidence about the validity of the technique in patients with impaired left ventricular function is scarce, while adequate cardiac preload assessment would be of great value in these patients. The aim of this study was to investigate the diagnostic accuracy of stroke volume variation (SVV) measured with the FloTrac/Vigileo? system in patients with impaired left ventricular function. In this prospective, observational study, 22 patients with a left ventricular ejection fraction of 40 % or less undergoing elective coronary artery bypass grafting were included. Patients were considered fluid responsive if cardiac output increased with 15 % or more after volume loading (7 ml kg^?1 ideal body weight). The following variables were calculated: area under the receiver operating characteristics (ROC) curve, ideal cut-off value for SVV, sensitivity, specificity, positive and negative predictive values, and overall accuracy. In addition, SVV cut-off points to obtain 90 % true positive and 90 % true negative predictions were determined. ROC analysis revealed an area under the curve of 0.70 [0.47; 0.92]. The ideal SVV cut-off value was 10 %, with a corresponding sensitivity and specificity of 56 and 69 % respectively. Overall accuracy was 64 %, positive and negative predictive values were 69 and 56 % respectively. SVV values to obtain more than 90 % true positive and negative predictions were 16 and 6 % respectively. The ability of uncalibrated arterial waveform analysis SVV to predict fluid responsiveness in patients with impaired LVF was low.