This observational, single-center, retrospective study was carried out at the University-Hospital of Udine (Italy)—a level-3 maternity center performing approximately 300 cesarean sections per year. Ethical approval was provided by the Regional Ethics Committee of Friuli-Venezia-Giulia on 5th February 2019, ID #2637, for principal investigators Dr. V.L. and Dr. T.D.
Before performing the statistical analysis, the trial was registered at clinicaltrials.gov with NCT number 03851679 on 20th February 2019. Given the retrospective design of the present study, patient consent was waived, but the European Privacy Regulation 2016/679 on General Data Protection Regulation (GDPR) was respected. Only pregnant women aged 18 years or over undergoing elective cesarean section in the absence of hypertensive disorders at gestational age no less than 37 weeks were included in the study; all women presented a physical status of 2 according to the American Society of Anesthesiologists classification system. Exclusion criteria were: emergent cesarean section, a history of pre-existing respiratory or cardiac disease, twin pregnancy; refusal to participate in the study.
In the operating theater, non-invasive standard monitoring with heart rate, non-invasive arterial pressure, and peripheral oxygen saturation were used (Philips, IntelliVue MX 700, Milano, Italy). For subarachnoid anesthesia, the patient was placed on their left side and a 25 G Sprotte needle (Pajunk Sprotte 25G × 90 mm, Geisingen, Germany) inserted by the resident physician or the consultant anesthesiologist following a failed first attempt. Following cephalorachidian fluid spread, 2 mL hyperbaric bupivacaine 0.5% (10 mg in total) (Bupivacaine Fresenius Kabi 5 mg/mL, Verona, Italy) plus 0.1 mg morphine (Morfina Cloridrato 10 mg/1 mL Monico, Venezia, Italy), as long-term analgesia, were injected. Immediately afterward, the patient was returned to the supine position, and the uterus pushed to the left. Arterial hypotension was controlled using a 3 mL/kg fluid challenge of crystalloids (RA Baxter Viaflo 1000 mL, Monselice-Padua, Italy) or an ephedrine bolus (ephedrine 3 mg/mL, 10 mL Aguettant, Venezia, Italy). A bladder catheter was placed in the ward before coming into the theater. The surgeon then performed a Pfannenstiel skin incision with the layered opening of the abdomen and celiotomy. The bladder–uterine fold was opened and the bladder detached at the bottom. A transverse incision was made on the lower uterine segment and the uterine breach opened by digital divulsion followed by fetal extraction .
Patient venous access was obtained before entering the operating theater, and a blood sample taken for the first BNP dosage (T0). Postoperative BNP was measured at 6 (T1) and 24 h (T2) after surgery. Blood was collected in EDTA and lithium heparin vacutainer tubes, and sent immediately for analysis to the laboratory (through a specialized internal transport service) where BNP concentrations were assayed using a Bayer ADVIA Centaur-TM. Test values were not known in real-time, and the physician and patients were blind to their results.
Thoracic ultrasound was performed in a semi-recumbent position using a SonoSite machine (S-Fast, Ltd.-Alexander House, Wilbury Way, Hitchin, Herts, SG4 OAP, UK) with a convex or linear probe and the “eight-region technique” as defined by the “International Consensus Conference on Lung Ultrasound” . The probe was placed perpendicular to the ribs to visualize the “bat sign”, then translated into the oblique position along the intercostal spaces. A healthy lung was described as “A-Line with sliding”; an abnormal lung was described as “A-Line without sliding” (A’); a “B-Line” lung was one with three or more B-Lines per region; a coalescent B-Line was considered a “white lung”; and a “C-profile,” i.e., consolidated parenchyma and anechoic space, indicated pleural effusion . The exam was performed at T0 (before cesarean section, immediately after obtaining the first BNP sample), at T1 (6 h after cesarean section), and T2 (24 h after surgery).
The perioperative data collected also included details regarding the duration of surgery; the spinal thermal level at discharge from the operating room, blood loss (mL); intraoperative diuresis (mL); and administered crystalloids (mL). Follow-up was planned until discharge.
The quantitative variables are presented as means and standard or median deviations plus the range according to their distribution. Qualitative variables are expressed as absolute and relative frequencies. The relative frequency and 95% confidence interval of patients with an altered TUS pattern is also shown. The quantitative variables of the positive TUS and negative TUS group are compared using the Mann–Whitney non-parametric test for independent samples, taking into account the distribution of the variables. The Chi-square test is used to estimate the association between qualitative variables. We also assessed the distribution of the relative increase in BNP ([logBNP2 − logBNP1]/BNP1) at the different time points (T0, T1, and T2) and applied ANOVA to assess for any statistically significant differences between the three groups. We used Hommel’s method to correct for multiplicity .
All statistical analyses were carried out using SPSS Statistical Package version 22 (Armonk, NY: IBM Corp) and R-Cran ver. 3.4.2 language and environment for statistical computing (R Core Team; R Foundation for Statistical Computing, Vienna, Austria, http://www.R-project.org).
Our study was an observational retrospective study that intends to estimate the relative frequency of pregnant women with an elective cesarean section presenting sub-clinical changes in the TUS pattern in the peripartum period. Data of a total of approximately 80 patients were available. Having no previous information on the prevalence of pregnant women with elective cesarean section presenting sub-clinical changes in the TUS picture in the peripartum period and assuming that this prevalence settled at around 50% (cases with maximum variability), 80 patients would allow us to obtain an estimate of this prevalence with an accuracy of 10%, which for this study was considered acceptable from the clinical point of view.