Research participants

The present study specifically focused on septic shock patients undergoing mechanical ventilation who required PiCCO monitoring due to their condition. Eligible patients were individuals who were hospitalized in the intensive care unit (ICU) of Henan Provincial People’s Hospital between January 1, 2021, and December 31, 2021. All experiments were conducted with the approval of the Henan Provincial People’s Hospital Medical Ethics Committee [(2020) Ethics No. (176)], and all experiments were performed in accordance with relevant guidelines and regulations. Informed consent was obtained from all participants and/or their legal guardians, and all procedures were performed in accordance with the Helsinki Declaration.

Inclusion and exclusion criteria

Patients who (1) were male or female, at least 18 years old, and were diagnosed with septic shock according to SEPSIS 3.0⁶, (2) required PiCCO monitoring and mechanical ventilation, and (3) themselves or their authorized representatives were able to understand and comply with the study requirements, voluntarily participated in the study and provided written informed consent.

Patients were excluded if (1) they exhibited contraindications for PiCCO monitoring or catheterization; (2) they were suffering from end-stage diseases, tumour cachexia, or other severe diseases or were likely to die in the immediate future; (3) they required emergency interventions not compatible with PiCCO monitoring, including cardiopulmonary resuscitation for cardiac and respiratory arrest or extracorporeal membrane oxygenation (ECMO); or (4) they were pregnant.

Sample size calculations

The sample size was calculated using PASS 21.0 software on the basis of correlation coefficients between LUS and EVLW as the primary index for study evaluation. According to a previous study exploring the clinical value of lung ultrasound as a means of assessing EVLW and prognostic outcomes in acute respiratory distress syndrome patients published by Yu K et al.³, an estimated correlation coefficient of 0.745 is necessary to define the relationship between the LUS and EVLW, with α being set to 0.05 and a test efficiency (1-β) of 90%. When a two-sided test was performed, a total of 14 patients was needed, but the goal was to recruit 20 participants to account for the possibility of missing data.

Research approach

Following enrolment, the researchers obtained general clinical and demographic data for the study participants, including age, sex, height, weight, Acute Physiology and Chronic Health Evaluation II (APACHE II) scores, major disease status upon intensive care unit (ICU) admission, and vital signs. At 0, 2, 6, 12, 24, and 48 h after enrolment (The completion time of the PiCCO catheter insertion is defined as the 0-hour time point), bedside ultrasound and PiCCO were used to collect relevant data, as detailed below:

PiCCO analyses: The same specialist analysed data from all patients included in this study. A total of 2–3 luminal internal carotid or subclavian central venous catheters were placed in all the patients, while a PiCCO catheter was placed in the femoral artery using the Seldinger method. The measurement approach was as follows: (1) 15 mL of cold (< 5 °C) saline was added; (2) the cardiac output (CO) calculation page of the monitor monitoring system was opened, and basic patient information [height, weight, central venous pressure (CVP), etc.] was collected; (3) following baseline stabilization, 15 mL of cold saline was injected as quickly as possible (< 5 s); and (4) these thermal-dilution measurements were repeated three times, after which the PiCCO measurements were calculated and recorded.

Bedside ultrasound analyses^7,8,9: Patients were placed in the supine position under deep sedation and analgesia without spontaneous breathing, and the target examination site was fully exposed. Following the connection of the conventional ultrasound equipment, a lung ultrasound examination was conducted with an abdominal convex array probe. LUS were computed for 12 areas on the basis of measured ultrasonic signs (2020, The Lung, Paradigm of point-of-care ultrasound). The axillary front and midline were each used to separate the chest wall into three regions (before, during, and after), with the nipple level serving as the upper lung boundary. These boundaries and the lower lung boundary were used to separate the lung into 12 zones. Using ultrasonographic signs, areas with A lines or < 2 separate B lines were scored as 0 points, areas with moderately reduced ventilation (≥ 3 B lines) were scored as 1 point, areas with severely reduced ventilation (diffuse coalescent B lines) were scored as 2 points, and sections exhibiting lung consolidation without air bronchograms were scored as 3 points. The most severe score for each of the 12 regions was recorded, and these 12 scores were summed together for a total value ranging from 0 to 36.

Instruments and equipment

The equipment used in this study was as follows: a PC4000 core output measurement instrument (PiCCO) monitoring module for monitoring the PiCCO Pulsion (Germany); a PiCCO femoral artery indwelling catheter (Shanghai McCorvair Medical Equipment Co., Ltd.); central venous catheters placed in the internal jugular vein (Guangdong Baihe Medical Technology Co., Ltd.); and an M9 portable colour Doppler ultrasound system (Shenzhen Mindray Biomedical Electronics Co., Ltd.).

Statistical methods

The data were analysed using SPSS 25.0 and MEDCALC 15.0. Normally distributed continuous data are reported as the means ± standard deviations, whereas nonnormally distributed data are reported as medians and interquartile ranges (P25-P75). Differences in indices over time were analysed via repeated-measures ANOVAs with Bonferroni correction. Correlation analyses for nonnormally distributed data were performed via Spearman’s correlation coefficient (R_S). Analysis of Bland–Altman limits of agreement and interclass correlation coefficients was performed to evaluate consistency. Regression analysis was used to compute the weight of the LUS on the EVLW. A P value < 0.05 indicated statistical significance.