The Blood flow surveillance includes invasive monitoring, minimally invasive monitoring, noninvasive monitoring. In detail, the invasive hemodynamic monitoring refers to measure central venous pressure (CVP) by means of Swan-Ganz catheter, in order to assess cardiac function indicators. Nevertheless, these indicators are not only associated with cardiac volume, but also can be influenced by myocardial compliance, chest pressure and other potential factors [20,21,22,23]. Therefore, the invasive hemodynamic monitoring can not reflect the cardiac volume in the filling period. Besides, the external Swan-Ganz catheter can probably lead to various serious complications, such as cardiac mechanical damage, ventricular rhythm Abnormal, pulmonary embolism, pulmonary artery rupture, etc. . Meanwhile, the non-invasive monitoring can not result in serious tissue damages, and the operation method appears more convenient. But, the detection accuracy remains relatively poor. On the contrary, the parameters which are provided by PICCO monitor, such as cardiac index (CI), global ejection fraction (GEF), global end diastolic volume index (GEDI), can not be influenced by these factors mentioned above. Therefore, PICCO monitor is able to monitor hemodynamic parameters in real time manners, and can better reflect the changes of cardiac functions [25,26,27].
As far as we are concerned, PICCO is a minimally invasive hemodynamic monitoring technology, with the advantages of repeatable, sensitive, simple, etc. Hence, this Monitoring technique can provide comprehensive hemodynamic monitoring parameters, and can reflect cardiac contractile function more accurately. When compared with conventional monitor method, PICCO also possess much more advantages, including simple operation, longer time of indwelling catheter, convenient observation and nursing. Before the formal monitor, the PICCO calibrating standard solution should be diluted for at least three times, and the final temperature of calibrating standard solution is 0 °C . Currently, it has not been proved about the drip speed of calibrating standard solution. For instance, Jiang et al.  suggested that the solution should be injected within 4 s, Cao  suggested that the standard solution should be injected within 7 s, and Li  suggested it within 10 s. After comprehensive data analysis, it can be illustrated that the majority of searchers did consider that the calibrating standard solution should be injected within 4 s, and a fraction of them did not mention the specific injection speed. Meanwhile, it has been acknowledged that the different drip speed of calibrating standard solution can cause the unavoidable errors. And, on the basis of results in this research, we conclude that PICCO monitor can provide the corresponding parameters when the calibrating standard solution is titrated at the speed of 4–10 s. In this study, we attempt to compare three different injection rates of calibrating standard solution. Firstly, a total of 108 critically ill patients in the stroke intensive care unit (SICU) were included in this research. Secondly, all these identified patients received PICCO monitor. In detail, the ice salt solution at 0 °C was injected into superior vena cava, at the drip speed of 2–4, 5–7 and 8–10 s, respectively. After data analysis and comprehensive comparison among them, as shown in Fig. 1 and Table 1, these various parameters obtained from PICCO monitor were assessed on the basis of paired-samples t-test, and the statistical differences among 2–4, 5–7 and 8–10 s were significant (P < 0.05). Besides, as shown in Table 2, the data obtained from 2 to 4 s was highly consistent with the results provided by ultrasonography. But, the data obtained from 5–7 to 8–10 s was not highly consistent with that acquired from ultrasonography, the consistency between them was not good. In addition, the PICCO parameters gained at the drip speed of 2–4 s were positively correlated with the results provided by transesophageal cardiac color Doppler ultrasound, and the correlation coefficient appeared much higher when compared with the data obtained at the injection speed of 5–7 and 8–10 s.
The calculation method of PICCO PLUS system (Manufacturer: PULSION company) refers to the combination of average transmission time of thermal dilution curve and exponential descent time. When the measurement based on the principle of thermodilution was carried out, the quantitative cooling solution should be injected into vein as soon as possible, and its temperature should below the blood temperature at least 10 °C. In addition, the occurrence time of PICCO monitoring curve shifted to an earlier time point, when the ice salt solution at 0 °C was injected at the drip speed of 2–4 s, and the crest appeared higher. On the contrary, when the ice salt solution was injected at the speed of 5–7 s and 8–10 s, the occurrence time of PICCO monitoring curve shifted to a later time, and the crest appeared lower. Therefore, the PICCO parameters obtained at the injection rate of 2–4 s were more close to the indicators provided by transesophageal cardiac color Doppler ultrasound (as shown in Table 2). Namely, when the 0 °C calibrating standard solution was injected at the speed of 2–4 s, the PICCO parameters appeared more valuable.