肺内分流量对部分CO2重复吸入法测定心输出量的影响

目的探讨部分CO2重复吸入法测定危重病患者心输出量的准确性及肺内分流量对其影响.方法26例机械通气患者接无创心输出量监测仪(NICO监测仪),利用部分CO2重复吸入法测定心脏指数(CINICO),同时置入肺动脉漂浮导管,以热稀释法测定心脏指数(CITD).公式法与NICO监测仪同时计算肺内分流量并进行比较.公式法计算的肺内分流量≤15%的患者为低分流组,＞15%为高分流组.结果低分流组(n=16)NICO监测仪计算的肺内分流量与公式法测定的肺内分流量无显著差异;CINICO与CITD相关性良好(r=0.91,P＜0.01),CINICO为(2.24±0.42)L/(min·m2),CITD为(2.25±0.40)L/(min·m2),两者差异无显著性.高分流组(n=10)NICO监测仪计算的肺内分流量明显低于公式法计算的肺内分流量(P＜0.01);CINICO与CITD亦显著相关(r=0.81,P＜0.01),但CINICO明显低于CITD(P＜0.01),两者分别为(2.56±0.64)L/(min·m2)和(2.87±0.64)L/(min·m2).结论CINICO与CITD相关性良好,肺内分流量是影响CINICO准确性的重要因素.     

Non-invasive measurements of cardiac output in atrial fibrillation: Inert gas rebreathing and impedance cardiography

Abstract

Background. Atrial fibrillation (AF) is associated with significant morbidity and mortality. To test the effect of interventions, knowledge of cardiac output (CO) is important. However, the irregular heart rate might cause some methods for determination of CO to have inherent weaknesses. Objective. To assess the validity of these methods in AF, a new inert gas rebreathing device and impedance cardiography was tested with echocardiography as reference. Methods. Using a cross-sectional design, 127 patients with AF and 24 in SR were consecutively recruited. Resting CO was measured using inert gas rebreathing (n = 62) or impedance measurement of intrathoracic blood flow (n = 89) in separate studies with echocardiographic measurement as reference. Results. CO determined with impedance cardiography was mean 4.77 L/min ± 2.24(SD) compared to 4.93 L/min ± 1.17 by echocardiography (n = 89, n.s.) in patients with AF. CO by inert gas rebreathing was 4.98 L/min ± 2.49(SD) compared to 5.70 L/min ± 2.49 by echocardiography (n = 62, n.s.) in patients with AF and SR (AF 5.42 ± 2.9 vs. 6.27, n.s. and SR 4.09 ± 1.08 vs. 4.35 ± 0.86, n.s.). Mean bias between impedance cardiography and echocardiography was 0.14 ± 0.95 L/min and ?0.13 ± 0.98 L/min between inert gas rebreathing and echocardiography. Inert gas rebreathing showed larger intra-patient variation than impedance cardiography (0.11 vs. 0.054). Correlation between inert gas rebreathing and echocardiography was r = ?0.060 and between impedance cardiography and echocardiography was r = 0.128. Impedance cardiography and inert gas rebreathing both underestimated CO compared to echocardiography. Conclusion. Variation between the inert gas rebreathing and the reference method for AF patients was less than desired. Impedance cardiography was superior to inert gas rebreathing and showed acceptable agreement with echocardiography and variability similar to echocardiography.     

Non-invasive stroke volume measurement by cardiac magnetic resonance imaging and inert gas rebreathing in pulmonary hypertension

Objective: Right ventricular function determines the prognosis of pulmonary hypertension (PAH). Measurement of stroke volume (SV) non‐invasively could be a promising method to monitor disease progression. Cardiac magnetic resonance (CMR) imaging is recognized as an accurate and reproducible method to measure SV. Inert gas rebreathing (IGR) using acetylene is a validated but cumbersome method for pulmonary blood flow (PBF) measurement in PAH. A more convenient rebreathing technique using rapid photoacoustic analysis of nitrous oxide has been introduced and validated in left heart failure. We investigated the accuracy of CMR imaging and IGR using photoacoustic analysis to measure SV in patients under investigation for PAH. Methods: Thirty‐three patients (16♀:17♂) with suspected PAH following echocardiography had SV measured by CMR imaging (using pulmonary arterial{CMR PA} and aortic {CMR Ao} flow methods) and IGR. The results were compared with our reference standard: thermodilution (TD) measured during right heart catheterization (RHC). Results: All methods showed similar correlation for SV. Bland–Altman analysis con‐firmed acceptable levels of agreement between the four techniques. TD versus CMR Ao flow had bias (limits of agreement) of ?5·41 ml (?22·37 to 11·56 ml), TD versus CMR PA flow 0·12 ml (?20·13 to 20·37 ml) and TD versus IGR 6·25ml (?16·01 to 28·51 ml). Conclusion: Cardiac magnetic resonance imaging and IGR using photoacoustic analysis in patients with suspected PAH provided non‐invasive measurements of SV that agreed closely with those obtained from TD measured during RHC.     

Noninvasive cardiac output determined with a new method based on gas exchange measurements and carbon dioxide rebreathing: A study in animals/pigs

A system has been designed to determine cardiac output noninvasively. The system's main component is a closed breathing circuit and it measures oxygen uptake (Vo ₂), carbon dioxide elimination (Vco ₂), and end-tidal CO₂ partial pressure (Pet). As an integral part of the system, periods of CO₂ rebreathing can be automatically implemented. The CO₂ partial pressure of oxygenated mixed venous blood (Pv) is obtained from the measured exponential rise of thePet value during such a CO₂ rebreathing maneuver. A new method is described for estimating the pulmonary blood flow, alveolar ventilation, cardiac output (CO), and mixed venous oxygen saturation (Svo ₂) fromPv,Pet,Vo ₂,Vco ₂, tidal volume, and arterial oxygen saturation. The method was evaluated in 6 anesthetized and mechanically ventilated pigs. A wide range of cardiac output, shunt fractions, and dead space to tidal volume ratios were induced by combinations of bronchoalveolar lavage, hypervolemia, hypovolemia, and variable levels of positive end-expiratory pressure (PEEP). The bias between the CO obtained with the noninvasive technique (CO L/min) and the thermodilution CO (Qt L/min) was 0.13 L/min (SD=0.78 L/min) and the correlation was N=64; R=0.92; CO=0.95*Qt+0.38. The bias obtained for double determinations with the noninvasive CO technique was 0.3 L/min (SD=0.5 L/min). The bias between the noninvasive estimates ofSvo ₂ and the directly measured values was 1.1% (SD=9.3%). For double determination with the noninvasive technique the bias was -0.9% (SD=4.7%). It is concluded that in mechanically ventilated pigs the proposed method produces good estimates of CO andSvo ₂ also in the presence of significant ventilation/perfusion mismatch.     

Noninvasive cardiac output determined with a new method based on gas exchange measurements and carbon dioxide rebreathing: A study in animals/pigs

A system has been designed to determine cardiac output noninvasively. The system's main component is a closed breathing circuit and it measures oxygen uptake (Vo ₂), carbon dioxide elimination (Vco ₂), and end-tidal CO₂ partial pressure (Pet). As an integral part of the system, periods of CO₂ rebreathing can be automatically implemented. The CO₂ partial pressure of oxygenated mixed venous blood (Pv) is obtained from the measured exponential rise of thePet value during such a CO₂ rebreathing maneuver. A new method is described for estimating the pulmonary blood flow, alveolar ventilation, cardiac output (CO), and mixed venous oxygen saturation (Svo ₂) fromPv,Pet,Vo ₂,Vco ₂, tidal volume, and arterial oxygen saturation. The method was evaluated in 6 anesthetized and mechanically ventilated pigs. A wide range of cardiac output, shunt fractions, and dead space to tidal volume ratios were induced by combinations of bronchoalveolar lavage, hypervolemia, hypovolemia, and variable levels of positive end-expiratory pressure (PEEP). The bias between the CO obtained with the noninvasive technique (CO L/min) and the thermodilution CO (Qt L/min) was 0.13 L/min (SD=0.78 L/min) and the correlation was N=64; R=0.92; CO=0.95*Qt+0.38. The bias obtained for double determinations with the noninvasive CO technique was 0.3 L/min (SD=0.5 L/min). The bias between the noninvasive estimates ofSvo ₂ and the directly measured values was 1.1% (SD=9.3%). For double determination with the noninvasive technique the bias was -0.9% (SD=4.7%). It is concluded that in mechanically ventilated pigs the proposed method produces good estimates of CO andSvo ₂ also in the presence of significant ventilation/perfusion mismatch.     

Influence of cardiac output level on oxygen exchange in chronic obstructive pulmonary disease patients

STUDY OBJECTIVES: In the course of chronic obstructive pulmonary disease (COPD), pulmonary gas exchange deteriorates as a result of ventilation/perfusion inequalities and hypoxaemia. The aim of the present study was to evaluate the influence of cardiac output (CO) level observed at rest in COPD patients on interaction between central and peripheral O(2) exchange. METHODS: One hundred and nine patients with advanced but stable COPD were analysed in a retrospective study by the multiple inert gas elimination technique. As a function of CO, simulations were conducted to evaluate the respective part of PvO(2) and VA/Q inequalities on the degree of hypoxaemia. MEASUREMENTS AND RESULTS: PaO(2) was linked (i) to cardiac index (CI), (ii) to mean VA/Q ratio of blood flow distribution and (iii) to PvO(2), but PvO(2) was not correlated with CO. By comparing two groups with CI above and below the mean value of the series respectively, a significant difference was identified in PaO(2) (57 +/- 9 mmHg in the high CI group versus 63 +/- 10 mmHg in the low CI group, P<0.05) because of higher VA/Q inequalities in the high CI group. Comparing two other groups with values of PvO(2) above and below the mean value of the series respectively, a significant difference was identified in PaO(2): (mean +/- SD was 65 +/- 8 in high PvO(2) group versus 56 +/- 9 mmHg, P<0.001) but with no difference in either CI or perfusion distribution. Analysis of the cumulated effects of PvO(2) and CI values, indicated that high CI and low PvO(2) gave rise to the lowest PaO(2) (53 +/- 8 mmHg), with the highest PaO(2) (68 +/- 8 mmHg) being found in the low CI and normal PvO(2) group. CONCLUSIONS: We concluded that in COPD patients, PaO(2) appeared to be maintained better when peripheral gas exchange coped with tissue demand without an increase in CO. Conversely, when the physiological increase in CO could not maintain adequate tissue gas exchange, PaO(2) continued to fall due to the cumulative effects of increasing CO on VA/Q inequalities and low PvO(2).     

A comparative evaluation of thermodilution and partial CO<Subscript>2</Subscript> rebreathing techniques for cardiac output assessment in critically ill patients during assisted ventilation

Objective To evaluate the reliability and clinical value of partial noninvasive CO₂ (NICO₂) rebreathing technique for measuring cardiac output compared with standard thermodilution in a group of intensive care nonpostoperative patients.Design and setting Clinical investigation in a university hospital ICU.Patients Twelve mechanically ventilated patients with high ( n =6) and low ( n =6) pulmonary shunt fractions.Measurements and results Thirty-six paired measurements of cardiac output were carried out with NICO₂ and thermodilution in patients ventilated in pressure-support mode and sedated with a sufentanil continuous infusion to obtain a Ramsay score value of 2. The mean cardiac output was: thermodilution 7.27±2.42 l/min; NICO₂ 6.10±1.66 l/min; r ² was 0.62 and bias –1.2 l/min±1.5. Mean values of cardiac output were similar in the low shunt group ( ), with r ²=0.90 and a bias of 0.01 l/min±0.4; conversely, in the high pulmonary shunt group ( ) the mean was 9.32±1.23 l/min with thermodilution and a mean NICO₂CO value was 6.97±1.53 l/min, with r ² of 0.38 and a bias of –2.3 l±1.2 min.Conclusions The partial CO₂ rebreathing technique is reliable in measuring cardiac output in nonpostoperative critically ill patients affected by diseases causing low levels of pulmonary shunt, but underestimates it in patients with shunt higher than 35%.     

Response time of the Opti-Q continuous cardiac output pulmonary artery catheter in the urgent mode to a step change in cardiac output

Objectives.This study was conducted to determine the response timeof the Opti-Q continuous cardiac output (CCO) device to a step change incardiac. Design.Prospective study. Setting.University hospitalanimal lab. Model.Female sheep. Interventions.In ten animals,cardiac output was altered suddenly by opening and closing a peripheralarteriovenous shunt to test the response time of the CCO system.Measurements and main results.Cardiac output was measured continuouslyby thermodilution and ultrasonic techniques while an arteriovenous shunt wasopened and closed. A total of 53 dynamic observations were made (5–6 peranimal). The mean response time of the continuous cardiac output device was86 seconds and was unaffected by the magnitude or direction of the change incardiac output. It was also unaffected by the animal's weight. CCOvalues were not statistically different from standard thermodilutionmeasurement (p= 0.895). Shunt flow ranged from 430 to 1730 ml/minand averaged 812 ml/min. The mean CCO with the shunt closed was 4.62 L/min.There was 1.5 to 2 minutes under or overshoot in cardiac output in 11% of themeasurements. Conclusions.Continuous cardiac output measurement wasas accurate as those made by standard bolus thermodilution. The averageresponse time to acute changes in cardiac output was approximately 1.5 minutesor ten times faster than previously reported systems. Response time isindependent of animal mass, shunt volume and the direction of cardiac outputperturbations.     

Accuracy of continuous thermodilution cardiac output monitoring by pulmonary artery catheter during therapeutic hypothermia in post-cardiac arrest patients

Purpose

Thermodilution continuous cardiac output measurements (TDCCO) by pulmonary artery catheter (PAC) have not been validated during therapeutic hypothermia in post-cardiac arrest patients. The calculated cardiac output based on the indirect Fick principle (FCO) using pulmonary artery blood gas mixed venous oxygen saturation (FCO-BG-SvO2) is considered as the gold standard. Continuous SvO2 by PAC (PAC-SvO2) has also not been validated previously during hypothermia. The aims of this study were (1) to compare FCO-BG-SvO2 with TDCCO, (2) to compare PAC-SvO2 with BG-SvO2 and finally (3) to compare FCO with SvO2 obtained via PAC or blood gas.

Methods

We analyzed 102 paired TDCCO/FCO-BG-SvO2 and 88 paired BG-SvO2/PAC-SvO2 measurements in 32 post-cardiac arrest patients during therapeutic hypothermia.

Results

TDCCO was significantly although poorly correlated with FCO-BG-SvO2 (R² 0.21, p < 0.01) without systematic bias (−0.15 ± 1.76 l/min). Analysis according to Bland and Altman however showed broad limits of agreement ([−3.61; 3.45] l/min) and an unacceptable high percentage error (105%). None of the criteria for clinical interchangeability were met. Concordance analysis showed that TDCCO had limited trending ability (R² 0.03). FCO based on PAC-SvO2 was highly correlated with FCO-BG-SvO2 (R² 0.72) with a small bias (−0.08 ± 0.72 l/min) and slightly too high percentage error (44%).

Conclusion

Our results show an extreme inaccuracy of TDCCO by PAC in post-cardiac arrest patients during therapeutic hypothermia. We found a reasonable correlation between BG-SvO2 and PAC-SvO2 and subsequently between FCO calculated with SvO2 obtained either via blood gas or PAC. The decision to start or titrate inotropics should therefore not be guided by TDCCO in this setting.     

Evaluation of pulmonary blood flow in bilateral bidirectional Glenn shunts: value of 4‐D flow cardiac magnetic resonance in the evaluation of pulmonary artery confluence stenosis

Bilateral bidirectional Glenn shunts are associated with the risk of developing pulmonary artery bifurcation stenosis, resulting in variable pulmonary blood flow to either lung. This could negatively impact the subsequent stages of the single ventricle palliation pathway. This report highlights the value of 4D flow sequence from the cardiac magnetic resonance imaging in demonstrating the pulmonary blood flow characteristics following a bilateral bidirectional Glenn procedure. Mapping the blood flow pattern and its quantification to each lung provide objective insights into the possible predisposing factors for the development of pulmonary bifurcation stenosis.     

Cardiac output measurement by the thermodilution method: An in vitro test of accuracy of three commercially available automatic cardiac output computers

Objective To describe the accuracy and the reproducibility of the thermodilution flow measurements obtained using 3 commercially available cardiac output computers commonly used in intensive care units.Design An experimental in vitro study. Twelve different values of control flow (Qctr) were measured (Qmsr) using 3 different cardiac output computers (Abbott Critical Care System, Oximetrix 3 SvO₂/CO Computer, Baxter Oximeter/Cardiac Output Computer SAT-1^TM; American Edwards Laboratories, 9520 A Cardiac Output Computer). Standard equipment and techniques were employed, taking account of the specific weight and heat of warm water relative to blood. In addition, separate sets of measurements were performed in order to investigate the effect on Qmsr of some variables which may influence the indicator loss (time for injection, depth of immersion of the catheter, temperature of the injected fluid).Setting Our laboratory, inside the intensive care unit.Measurements and results The analysis of the linear regression of Qmsr versus Qctr (r values between 0.992 and 0.984; residual standard deviation values comprised between 0.24 and 0.49 l/min; intercepts and slopes not significantly different from identity line), the values of the percentage errors (PE=[Qctr–Qmsr]·100/Qctr; PE mean values 7.9, 5.0 and 13.1), and those of the coefficients of variability (CV=standard deviation mean value, %; CV mean values 5.4, 5.8 and 4.6), show a good level of accuracy and reproducibility of the measurements. Our data confirm previously reported results. Furthermore, the cumulative effect of variables capable of influencing the indicator loss, even if corrected according to the calculation constant the manufacturers provide, was found to result in statistically significant changes of Qmsr.Conclusion The accuracy and reproducibility of the automatic cardiac computers tested is sufficient for practical clinical purpose. It may also depend on the modality of injection of the cooling bolus, which may significantly influence the effective indicator losses.     

The effect of lung injury and excessive lung fluid, on impedance cardiac output measurements, in the critically ill

Objectives: To investigate the relationship between the attenuation of impedance cardiac output (IC_co) measurements and lung fluid content in critically ill patients.¶Design: Observational study.¶Setting: Intensive Care Unit of a major teaching hospital in Hong Kong.¶Patients: Twenty-four critically ill patients who required a pulmonary artery catheter.¶Measurements and main results: Triplicate thermodilution cardiac output (TD_co) and BoMed NCCOM3 (IC_co) measurements were made simultaneously on a single occasion in each patient. Lung fluid accumulation was assessed by: (a) thoracic impedance (Zo), (b) radiological assessment of chest X-rays using an alveolar consolidation score (0–4) and (c) scoring the degree of hypoxia and use of positive end-expiratory pressure (PEEP). Offsets (TD_co–IC_co)/TD_co, expressed as percentage, were compared with these indices of excess lung fluid. Patients were divided into those with sepsis (n = 13), fluid balance problems (n = 5) and cardiothoracic problems (n = 6). Mean cardiac output values were: 6.7 l/min TD_co (range 3.6–12.9) and 5.2 l/min IC_co (range 2.7–9.0). Overall the TD_co and IC_co values showed great variance, with a bias and limits of agreement of 1.49 ± 4.16 l/min, or ± 69 %. In septic patients, increasing offset was correlated with decreases in Zo (r = 0.73, P = 0.005) and increases in alveolar consolidation score (r = 0.72, P = 0.005).¶Conclusions: The BoMed under-estimates cardiac output in critically ill patients. In septic patients the degree of attenuation of IC_co can be related to the extent of lung injury and fluid accumulation within the thorax.     

脉搏指示连续心排血量监测技术在神经源性肺水肿 诊治中的应用价值:附4例报道并文献复习

目的 探讨脉搏指示连续心排血量(PiCCO)监测技术在神经源性肺水肿(NPE)患者诊治中的应用价值.方法 回顾性分析皖南医学院附属黄山市人民医院重症医学科2011年至2013年4例重症神经系统疾病并发NPE患者的PiCCO血流动力学特点及诊治经过,并结合文献进行分析讨论.结果 4例NPE患者PiCCO显示血管外肺水指数(EVLWI)明显升高(入科即刻为12~42 mL/kg,治疗24 h为10~22 mL/kg),均表现为高通透性肺水肿类型,第1个24 h的容量平衡均为正平衡(例1~例4分别为+1 130、+1 200、+1 750、+1 120 mL);治疗中加强胶体的补充,应用多巴胺、多巴酚丁胺、米力农等血管活性药物,循环氧合改善、EVLWI下降.最终3例改善,1例死亡.结论 NPE在临床中诊治复杂,治疗过程中出现矛盾多,PiCCO监测技术在早期诊断、鉴别肺水肿类型、指导补液和血管活性药物应用及评估病情、预测预后方面有着较好的作用.     

急性超容量血液稀释对高龄患者心排量及凝血功能的影响

目的探讨急性超容量血液稀释对高龄患者心排量及凝血功能的影响。方法选取大关节手术患者60例,随机分成实验组30例和对照组30例。实验组给予6%羟乙基淀粉和乳酸林格氏液15 m L/kg行AHH;对照组不行AHH,予常规补液。比较2组患者心排量及凝血功能。结果实验组患者行AHH后,心排量(CO)有所增加,凝血功能有所降低。2组各时点的CO、红细胞压积(HCT)、凝血酶原时间(PT)、部分活化凝血酶原时间(APTT)以及血浆纤维蛋白原(Fib)比较,差异均无统计学意义(P0.05)。结论急性超容量血液稀释对高龄患者心排量及凝血功能的影响较小。     

Divergent cardiac response to exercise in essential hypertension vs. normotension and the effect of enalapril

The aims of this study were to examine (1) the cardiac response to exercise in essential hypertension and (2) the effect of long-term enalapril treatment on cardiac reserve. Ten normotensive control subjects and 15 patients with moderate, essential hypertension underwent radionuclide ventriculography during graded, supine exercise (0 W–50 W–100 W). The hypertensive patients were studied during monotherapy using hydrochlorothiazide and 3 and 12 months after supplementation with enalapril 10–40 mg o.d. During exercise, the control subjects demonstrated a 17% increase in left ventricular ejection fraction (LVEF) mediated by a 30% decrease in end-systolic volume, a small increase in stroke volume and a minor biphasic (increase–decrease) change in end-diastolic volume. In the hypertensive patients, both the end-diastolic and the end-systolic volume increased substantially with no increase in LVEF, although stroke volume increased by 33%. Long-term therapy with enalapril induced only a minor change towards a more normal pattern of cardiac response to exercise. The hypertensive patients increased their stroke volume during exercise by recruiting preload reserve instead of increasing contractility. Long-term treatment with enalapril had little, if any, effect on this abnormal cardiac response.     

Discriminating between the effect of shunt and reduced VA/Q on arterial oxygen saturation is particularly useful in clinical practice

There is an extensive literature on methods for discriminating between an increased shunt and a reduced ratio of ventilation to perfusion. In this review we prefer the terms “VA/Q” and “reduced or low VA/Q” rather than “V/Q inequality” to refer to the effects on arterial oxygenation of reducing V/Q below 0.8 to about 0.1. Almost without exception the conventional methods for measuring shunt and reduced VA/Q are invasive as well as technically complex. For most clinicians who are dealing with a hypoxemic patient the relevance of these entities is not so obvious as to justify the time and difficulty in either understanding or measuring them. However this review shows that, while an increased shunt and a decreased VA/Q both reduce arterial oxygen saturation (SaO₂) at a particular inspired oxygen concentration (PIO₂), the effect of shunt and reduced VA/Q have important clinical differences on the relationship between PIO₂ and SaO₂. The review also outlines a simple non-invasive method for measuring shunt and reduced VA/Q which illustrates the value of discriminating between them in clinical practice. This revised version was published online in July 2006 with corrections to the Cover Date.