In our study, we assessed the consistency and trending ability of CO, CI, SVRI, and SVI measurements using PiCCO compared to PAC during OLT. The Bland-Altman analysis revealed high percentage errors for PiCCO: 54.06% for CO, 52.70% for CI, 62.18% for SVRI, and 51.97% for SVI, indicating poor accuracy. While Passing-Bablok plots showed favorable agreement for SVRI overall and during various phases, the agreement for other parameters was less satisfactory. The ICC results confirmed good overall agreement between the two devices across most parameters, except for SVRI during the new liver phase, which showed poor agreement. Additionally, four-quadrant and polar plot analyses indicated that all agreement rate values fell below the clinically acceptable threshold of over 90%, and all angular deviation values exceeded ± 5°, demonstrating that neither device reliably followed clinically acceptable trends. Using the TIM, the interchangeability rates were found to be quite low: 20% for CO and CI, 16% for SVRI, and 13% for SVI. These findings underscore that PiCCO does not compare favorably with PAC during OLT.

The patients undergoing liver transplant are subject to intense intraoperative hemodynamic fluctuations due to their pathophysiology and the specificity of the surgical procedure. Accurate and continuous monitoring of parameters such as cardiac output (CO), cardiac index (CI), systemic vascular resistance index (SVRI), and stroke volume index (SVI) is essential for perioperative hemodynamic management, and thermodilution of CO by floating pulmonary artery catheterization (PAC) is the accepted clinical gold standard. Nowadays, PAC are mainly used in patients having cardiac surgery, liver transplantation, and in critically ill patients with circulatory shock, especially with right ventricular dysfunction [12]. However, PAC is more invasive and is associated with various complications, including arrhythmias, pulmonary infarction, intrapulmonary hemorrhage, etc [26, 27], and due to coagulation function of liver transplantation patients and other pathophysiologic abnormalities, complications such as bleeding are more likely to occur.

Due to the high risk of PAC, technological advances in minimally invasive or noninvasive related monitoring devices are necessary. Several such alternatives have been developed, including transthoracic impedance methods, transesophageal echocardiography, arterial wave contour analysis and transpulmonary thermodilution [11, 28]. The latest research now concludes that PAC is the undisputed gold standard for hemodynamic monitoring in liver transplantation patients; however, it is highly invasive, and its use should be individualized. Cardiac output devices based on pulse contour analysis are minimally invasive devices with the advantage of real-time beat to beat monitoring of cardiac output [29]. PiCCO has gained widespread utilization, employing a combination of transpulmonary thermodilution and pulse contour analysis. Previous studies suggest its comparability to the PAC’s thermodilution method [30, 31], as well as less invasive and rare complications (e.g., inflammation and catheter-related infections) [26]. It also offers the advantage of the capacity to measure unique parameters, encompassing extravascular lung water index (EVLW), global end-diastolic volume (volume within the heart at end-diastole), and intrathoracic blood volume (volume within the heart and pulmonary circulation), all crucial for assessing cardiac load [28]. One such parameter, EVLW index, serves as an indicator of volume, cardiopulmonary function, and prognosis. It can intuitively reflect the severity of acute pulmonary edema, which may result from increased permeability and elevated hydrostatic pressure in the lungs. Continuous monitoring of EVLW is crucial for clinicians to accurately assess alveolar fluid volume, interstitial fluid volume, and gas diffusion function [32,33,34]. In our study, an EVLW greater than 10 warranted a high suspicion of pulmonary edema. By monitoring EVLW, we could effectively guide our interventions, including cardiac tonicity adjustments, diuretic therapy, ventilator settings optimization, and infusion regimen modifications. Thus, the unique parameters provided by PiCCO, such as the EVLW index and the pulmonary vascular permeability index, offer a robust basis for tailoring treatment.

However, opinions regarding the agreement between PICCO and PAC are differ among studies. Although the previous study in liver transplantation has been statistically homogeneous, it lack comparisons regarding other hemodynamic parameters, such as SVRI [18]. A comprehensive assessment and uniform conclusions in liver transplantation, the typical surgery with severe intraoperative hemodynamics fluctuations, regarding the agreement and trending ability of PiCCO to follow up with PAC in terms of hemodynamic monitoring are still lacking.

Our study assessed the agreement and tracking ability by using PiCCO compared to PAC. Our results indicated that, when assessing each parameter in conjunction with specific statistical methods, PiCCO can not be considered comparable to PAC during OLT. These results are specified through two aspects: (1) The Bland-Altman analysis showed that percentage errors for each parameter were outside the acceptable range, indicating poor agreement. Evaluation via ICC and PBR analyses reveals a degree of alignment between the two methods. These analyses consider both systematic and random errors. Additionally, judgments are formed by combining polar plots, four-quadrant plots, and the TIM with professional significance. (2) The acceptability of agreement rates of polar plots, four-quadrant plots and TIM is limited. PiCCO displays a greater negative polarity deviation for each parameter than the recommended ± 5°, and the agreement rate was lower than the recommended 90% [22]. Thus, PiCCO demonstrates a tendency to underestimate the continuous fluctuations during liver transplantation compared to PAC. In terms of tracking consistency trends, inadequate agreement is evident across all parameters.

In addition, our study cohort includes 52 liver transplantation patients from our database, encompassing 18 classical procedure cases, 8 piggyback procedure and 26 ischemia-free procedure cases. The “ischemia-free” technique significantly reduces the incidence of reperfusion syndrome(Post-reperfusion syndrome occurred in three recipients (9%) randomized to ischemia-free liver transplantation (IFLT) and in 21 (64%) randomized toconventional liver transplantation (CLT)(p < .001) [35]. IFLT stabilizes the intraoperative hemodynamic, and the patient’s perioperative survival rate is increased by nearly 10%, and the incidence of early liver insufficiency is reduced from 25% to less than 5% [36]. Considering the possible impact of different surgical techniques on our research results, we further compared the"ischemia-free” technique with the conventional liver transplantation technique and founded that there were still significant differences in agreement or trending ability between PiCCO and PAC (Supplementary Material).

PiCCO obtains hemodynamic parameters of patients based on two principles. One is by actual transpulmonary thermodilution, and the other is by arterial pulse wave analysis. The transpulmonary thermodilution method is a non-continuous measurement that can only be obtained at the time of thermodilution for a specific data. In our study, the transpulmonary thermodilution method was mainly used for PiCCO calibration, whereas the continuously obtained CO, CI, SVI and SVRI were all based on the arterial pulse contour analysis. We focused on the arterial pulse wave analysis (pulse contour) by using PiCCO during OLT in our study. PiCCO has good reproducibility, due to the longer transport time of the thermal bolus (20 s), which reduces respiratory-generated artifacts compared with PAC (3–4 s) [37]. In our study, the data from PAC and PICCO at the same time point were compared, but did not consider the influence of respiratory cycles, which maybe one of the reasons for the inconsistency between PiCCO and PAC.

Recalibrated frequency maybe the another reasons for the inconsistency between PiCCO and PAC. The current PAC can automatic calibration continually during surgery. However, continuous measurements of PiCCO are based on the arterial pulse wave analysis, which still requires intermittent transpulmonary thermodilution for calibration; however, transpulmonary thermodilution of PiCCO requires recalibration after significant hemodynamic changes [38, 39]. We routinely recalibrate at the beginning of prehepatic, hepatic-free, and neohepatic phases respectively, or the time after dramatic hemodynamic fluctuations during the operation, but the dramatic hemodynamic fluctuations is not be defined. At the same time, it is difficult to achieve recalibration of PiCCO frequently during the operation. We agree that agreement between the pulse wave assessment by PiCCO and the PAC thermodilution can vary. This latter variation most likely results from “drift” of the arterial-based system, requiring re-calibration. In addition, the choice of correction frequency is important in hemodynamically unstable patients, such as the liver-free and neohepatic phases in our study. We therefore recommend shortening the intraoperative calibration frequency of the PiCCO thermodilution method in liver transplant patients.

The main limitation of our study is that when taking the data from retrospective database, although we try to minimize errors using statistical methods, there are still a lot of confounding factors that influence the measurements and can reflect on results, including technical mistakes, delay between the measurements, etc.

In summary, our study assessed the agreement and tracking ability by using PiCCO compared to PAC during OLT. Our results indicated that, when assessing each parameter in conjunction with specific statistical methods, PiCCO cannot currently be considered comparable to PAC. Actually, PiCCO has been widely used in procedures with severe intraoperative hemodynamics fluctuations such as liver transplantation because of the advantages of being minimally invasive, safe, and having unique measurement parameters. We suggest that the selection of hemodynamic monitoring techniques in liver transplantation should take into account the patient’s physiological condition, surgical technique, and anesthesiologist’s level of expertise. In addition, the clinical use of PiCCO in liver transplantation should consider the advantages of its minimally invasiveness and multiple parameters with the disadvantages of its lack of accuracy. And it may be necessary to shorten the interval of calibration time and recalibrate more frequently during the operation with severe hemodynamics.