Continuous SvO2 monitoring. A research review.

Nurses have access to continuous SvO2 monitoring as one parameter for evaluating the hemodynamic status in critically ill patients. The research studies on SvO2 monitoring have demonstrated inconsistent results regarding the utility of SvO2 as an assessment tool. Hence, it is necessary to carefully review these research findings for their impact on nursing practice. Nurses must be aware of the possibility of overreliance on continuous SvO2 monitoring and of the limitations of the SvO2 measurement itself.     

Utilisation de la SvO2

Monitoring of O₂ venous saturation (SvO₂) is easily performed with fiberoptic pulmonary artery catheters and is used in circulatory shock to assess global balance between tissue O₂ supply and O₂ demand (VO₂). Simultaneous measurement of SvO₂ and continuous Cardiac Output (CO), as recently allowed by modified artery catheters, improve SvO₂ interpretation. Indeed, a decrease in SvO₂ may result from a decrease in arterial O₂ saturation, a decrease in hemoglobin or CO or from an increase in VO₂. SvO₂ is a surrogate marker of tissue O₂ extraction (EO₂) with SvO₂ = 1 – EO₂. When EO₂ is altered, as observed in septic shock, SvO₂ does not anymore guarantee correct interpretation of tissue oxygenation. Central venous O₂ saturation (ScvO₂) can be monitored with more easiness and a lower risk than mixed venous O₂ saturation with a good correlation between SvO₂ and ScvO₂. ScvO₂ has been recently used for early goal-directed therapy in patients with severe sepsis in order to improve hemodynamics at the emergency room; this was associated with a 16% reduction (p = 0.009) in in-hospital mortality.     

Continuous monitoring of mixed venous saturation (SvO2): an adjunct to nursing assessment?

Technological advances in oximetry have enabled the development of a pulmonary artery catheter which allows the continuous monitoring of a patient's mixed venous oxygen saturation (SvO2), which is recognised as a valuable indication of cardiac output and the balance between oxygen supply and demand (delivery and consumption). This paper briefly explains the rationale for monitoring SvO2 and highlights possible areas where the data it provides could influence the assessment and implementation of nursing interventions undertaken within intensive care units, and enable those decisions to be made more safely.     

连续血流动力学监测技术在机械通气患者中的应用研究

目的 通过对机械通气患者进行Swan-Ganz肺动脉热稀释法、脉搏轮廓动脉压波形分析法（PiCCO）及部分CO2重复呼吸法（无创心排血量监测，NICO）连续血流动力学监测。阐述3种监测技术的相关性。方法 13例各种原因导致呼吸衰竭行机械通气的患者，每例患者均同时行Swan-Ganz、PiCCO、NICO监测，在治疗手段及呼吸机设置条件相同的情况下，于同一时间点采集3种监测方法的血流动力学数据，比较3种监测技术的相关性。结果 相关分析显示。在各种方法所测心排血指数（CI）间PiCCO与Swan-Ganz相关系数为0．883。NICO与Swan-Ganz相关系数为0．853，PiCCO与NICO相关系数为0．857，PiCCO、NICO均与Swan-Ganz有较好的相关性。结论 PiCCO及NICO连续血流动力学监测可作为重症监护室（ICU）机械通气患者床旁监测的可靠手段，从而进一步指导制订有效的治疗策略。     

The potential of accurate SvO2 monitoring during venovenous extracorporeal membrane oxygenation: an in vitro model using ultrasound dilution

INTRODUCTION: Some degree of recirculation occurs during venovenous extracorporeal membrane oxygenation (VV ECMO) which, (1) reduces oxygen (O2) delivery, and (2) renders venous line oxygen saturation monitoring unreliable as an index of perfusion adequacy. Ultrasound dilution allows clinicians to rapidly monitor and quantify the percent of recirculation that is occurring during VV ECMO. The purpose of this paper is to test whether accurate patient mixed venous oxygen saturation (SvO2) can be calculated once recirculation is determined. It is hypothesized that it is possible to derive patient mixed venous saturations by integrating recirculation data with the ECMO circuit arterial and venous line oxygen saturation data. METHODS: A test system containing sheep blood adjusted to three venous saturations (low-30%, med-60%, high-80%) was interfaced via a mixing chamber with a standard VV ECMO circuit. Recirculation, arterial line and venous line oxygen saturations were measured and entered into a derived equation to calculate the mixed venous saturation. The resulting value was compared to the actual mixed venous saturation. RESULTS: Recirculation was held constant at 30.5 +/- 2.0% for all tests. A linear regression comparison of "actual" versus "calculated" mixed venous saturations produced a correlation coefficient of R2 = 0.88. Direct comparison of actual versus calculated saturations for all three test groups respectively are as follows; Low: 31.8 +/- 3.95% vs. 37.0 +/- 6.7% (NS), Med: 61.7 +/- 1.5% vs. 72.3 +/- 1.8% (p < 0.05), High: 84.4 +/- 0.9% vs. 91.2 +/- 1.1% (p < 0.05). DISCUSSION: There was a strong correlation between actual and calculated mixed venous saturations; however, significant differences between actual and calculated values where observed at the Med and High groups. While this data suggests that using quantified recirculation data to calculate SvO2 is promising, it appears that a straightforward derivative of the oxygen saturation-based equation may not be sufficient to produce clinically accurate calculations of actual mixed venous saturations.     

Noninvasive continuous hemodynamic monitoring

Monitoring of continuous blood pressure and cardiac output is important to prevent hypoperfusion and to guide fluid administration, but only few patients receive such monitoring due to the invasive nature of most of the methods presently available. Noninvasive blood pressure can be determined continuously using finger cuff technology and cardiac output is easily obtained using a pulse contour method. In this way completely noninvasive continuous blood pressure and cardiac output are available for clinical use in all patients that would otherwise not be monitored. Developments and state of art in hemodynamic monitoring are reviewed here, with a focus on noninvasive continuous hemodynamic monitoring form the finger.     

实时动态血糖监测联合胰岛素泵与回顾性动态血糖监测联合胰岛素泵在2型糖尿病患者治疗中的优势探讨

目的评价对比实时动态血糖监测系统(CGMS)、持续皮下胰岛素输注(CSII)、Carelink管理软件分析系统联合应用(三C治疗)与CGMS联合CSII(双C治疗,为对照组)对初诊2型糖尿病患者血糖控制效果。方法入选新诊断2型糖尿病、未采用过任何治疗、糖化血红蛋白大于9.0%患者,随机分为两组,其中三C治疗组30例(男18例,女12例)应用三C治疗9 d,对照组30例(男14例,女16例)应用双C治疗9 d,三C组根据每日实时查看血糖数值调整胰岛素泵输注方案,对照组根据每日三餐前、三餐后2 h、睡前血糖、3 d读取动态血糖监测数值图谱,调整胰岛素泵剂量,10 d后对比两组患者血糖下降及血清胰岛素、血清C肽水平升高幅度、发生低血糖事件情况,计算胰岛素抵抗指数(HOMA-IRI)。结果与对照组相比,治疗后三C治疗组空腹血糖下降幅度更大[分别为(6.29±1.91)mmol/L,(4.26±1.23)mmol/L],血清胰岛素、血清C肽水平升高幅度更显著[分别为(7.48±1.41)μU/ml,(2.14±0.62)ng/dl],三C治疗组HOMA-IRI下降幅度为3.29±0.91,对照组1.96±0.82,低血糖为24例次,对照组发生低血糖为39例次。结论三C治疗组较对照组降糖效果更快更好,低血糖事件更少,可以更好地改善胰岛素抵抗,增加胰岛素敏感性,保护胰岛β细胞功能。     

The SvO2 study: General design and results of the feasibility phase of a multicenter,randomized trial of three different hemodynamic approaches and two monitoring techniques in the treatment of critically ill patients

Although the attainment of normal hemodynamic values has always been assumed to be the therapeutic target for critically ill patients, recent studies reported increased values in oxygen transport variables in survivors of high-risk surgery. It has been supposed that the higher values observed in survivors might indicate a physiological compensation for the increased metabolic requirements due to disease. We designed a randomized, multicentric trial to evaluate the effect of high values of cardiac index (CI) and oxygen delivery (DO₂) in critically ill patients. Patients enrolled in the study are randomized to three different hemodynamic targets: normal values of CI (2.5 ≤ CI ≤ 3.5 L min⁻¹ m⁻²), supranormal values of CI (CI ≥ 4.5 L min⁻ m⁻²), and mixed venous oxygen saturation (SvO₂) ≥ 70% or (Sat a—Sat v) ≤ 20%. Two different monitoring systems are used to maintain the target: conventional Swan-Ganz catheter with scheduled samples of mixed venous O₂ saturation, and optical catheter with continuous SvO₂ evaluation. The aim of the study is to answer three questions regarding the hypothesis reported above: (1) Are results in postoperative patients applicable to other pathological groups? (2) Does continuous monitoring of SvO₂ provide advantages over conventional hemodynamic monitoring? (3) Is a normal SvO₂ rather than a supranormal CI a good and predictable therapeutic goal? We report herein the protocol of the study and the results of the pilot phase, which was conducted in 98 critically ill patients enrolled by 56 participating centers to evaluate the safety and feasibility of the proposed trial.     

Normal values of SvO2 as therapeutic goal in patients with multiple injuries

Objective: To determine whether maintaining normal levels of mixed venous oxygen saturation (SvO₂) in patients with multiple injuries is more relevant to survival than maintaining above-normal levels of oxygen transport. Design: Non-randomised, retrospective control study over a 38-month period. Setting: Multidisciplinary intensive care unit in a university hospital. Patients: 40 patients with multiple injuries divided in to group A (23 patients) and group B (17 patients). Interventions: In group A patients, we maintained normal SvO₂ by manipulation of oxygen transport variables; oxygen delivery (DO₂) was increased only if SvO₂ decreased or the dobutamine test was positive. In group B patients, DO₂ was routinely maintained at above-normal levels by aggressive use of fluids and dobutamine. Measurements and results: In group A we measured SvO₂ continuously and performed the dobutamine test. Oxygen transport-related variables were recorded every 12 h in the first 5 days after injury in both groups, as well as lactate concentrations. Survival was significantly greater in group A than in group B (p<0.01). Multiple organ failure was less frequent in group A than in group B (p<0.01). The average DO₂ in group A was significantly lower than in group B from day 2 onwards (p<0.05–0.01). Average values of DO₂ of 605–688 ml/min per m² were required to maintain normal SvO₂ and aerobic metabolism in group A; 10 patients required dobutamine 2.5–5 μg/kg per min. The average DO₂ in group B was 622 ml/min per m² on day 1 and then it increased to 835 ml/min per m² on day 5 after trauma. Conclusions: Our results indicate that for patients with multiple injuries maintaining normal SvO₂ values and increasing DO₂ only if required are more relevant for survival than routine maintenance of above-normal oxygen transport values. Received: 4 March 1996 Accepted: 28 September 1996     

The continuous monitoring of CO2 ductances in pulmonary intensive care

A cardiorespiratory monitoring system allows the measurement of FAECO2 and FECO2 in the expired air of the patient at the mouth (endtidal CO2) and in a mixing box. From these parameters, combined with the measured PACO2, the alveolo-expired (DuA = PECO2/PAECO2) and alveolar-arterial (Dua = PAECO2/PACO2) ductances which assimilate the respiratory system to a two-stage exchanger have brought about a lot of valuable information 1. DuA improves by 20% in 20 patients after removal of bronchial obstruction (p < 0.001) and by 9% in 7 intubated patients after tracheotomy (p < 0.02). DuA falls by 15% (p < 0.001) in 10 patients with hypocapnia (PaCO2 = 28 mmHg) after a dead space adjunction with the aim of normalizing PaCO2 (paCO2 = 35 mmHg). 2. Dua falls by 33% in six patients after pulmonary embolism, proved by angiography (p 0.001) by 9% in 34 patients after 30 min of pure oxygen breathing (p 0.001). On the other hand, inthe absence of clinical or radiological pulmonary edema, in increases by 19% in 38 patients with hypervolemia after diuresis (furosemide) (p < 0.001). Thus since DuACO2 varies with anatomical dead space and the air distribution disorder, DuaCO2 evolves according to the disorders of the blood distribution and arterial-alveolar diffusion. The determination of these coefficients, in the absence of significant changes in the arterial blood gases, helps the diagnosis, guides the early treatment and allows for the monitoring of its efficiency.     

Alternative sites for continuous arterial monitoring

During a 13-month period, we studied 148 patients who had percutaneous arterial cannulation for continuous intraoperative, postoperative, and intensive care monitoring. In all patients, alternative arteries were cannulated, which included the brachial (43%), axillary (19%), femoral (28%), dorsalis pedis (8%), and superficial temporal artery (1%). No patient sustained any functionally significant or serious complication requiring surgical intervention. Eighteen patients (12%) had minor, clinically insignificant complications. We conclude that in the absence of an available radial artery, there are at least five other reliable arterial sites that may be cannulated and safely used when direct arterial monitoring is required.     

SvO2 to monitor resuscitation of septic patients: let's just understand the basic physiology

Real-time monitoring of mixed venous oxygen blood saturation (SvO₂) or of central venous oxygen blood saturation is often used during resuscitation of septic shock. However, the meaning of these parameters is far from straightforward. In the present commentary, we emphasize that SvO₂ - a global marker of tissue oxygen balance - can never be simplistically used as a marker of preload responsiveness, which is an intrinsic marker of cardiac performance. In some septic shock patients, because of profound hypovolemia or myocardial dysfunction, SvO₂ can be low but obviously cannot alone indicate whether a fluid challenge would increase cardiac output. In other patients, because of a profound impairment of oxygen extraction capacities, SvO₂ can be abnormally high even in patients who are still able to respond positively to fluid infusion. In any case, other reliable dynamic parameters can help to address the important question of fluid responsiveness/unresponsiveness. However, whether fluid administration in fluid responders and high SvO₂ would be efficacious to reduce tissue dysoxia in the most injured tissues is still uncertain.     

2例幼儿糖尿病患者动态血糖监测的护理

报告2例1型糖尿病患儿进行动态血糖监测期间的护理.入院后为患儿进行全面的心理护理、饮食指导及胰岛素治疗的护理外,积极、主动与患儿及家属沟通,介绍动态血糖监测系统(CGMS)的基本工作原理和优点,使患儿和家属能配合医护人员做好CGMS的维护.并根据患儿的特点将CGMS安装部位由常规的下腹部改为臀部外上方,最终顺利完成动态血糖监测,为调整治疗方案提供了依据.     

Chromatographic techniques for therapeutic drug monitoring

Although GLC is still used with some frequency, HPLC is currently the most widely practiced chromatographic technique for the measurement of therapeutic drugs. Efficiency and selectivity can be manipulated to meet the requirements of clinical samples, especially when drug metabolites are present and their concentrations are of importance. The ability to simultaneously quantitate several drugs has led to the development of many methods for antiepileptic, antiarrhythmic, and antidepressant drugs. Selective detectors offer more sensitive analysis in many separations and are increasingly popular. The development of automated methods for sample preparation suggests that more cost-effective strategies for the chromatographic analysis of new drugs will be possible in the near future.