Discussion
tricuspid valve movements, cardiac and renal disorders, congenital heart disease
This triple-blinded randomized trial investigated the minimally required amount of NS injection for confirming proper PIV placement via precordial Doppler ultrasound technology in children under general anesthesia. The identification rate of Doppler signal changes in both the S-test and V-test were decreased in the 0.1 mL/kg NS group. There were no significant differences in identification rates between the 0.3 mL/kg and 0.5 mL/kg dose groups, suggesting a ceiling effect for the NS dose. Despite the subjective nature of the judgments, the S-test results exhibited good inter-rater agreement, thus indicating high reliability. The V-test demonstrated a higher sensitivity than the S-test in all dose groups. The 0.3 mL/kg NS dose was considered as minimally required dose for both the S- and V-tests when confirming correct PIV placement in children.While previous studies have reported on the utility of the precordial Doppler machine for confirming correct PIV, a detailed method has not yet been established. Precordial Doppler technology has been demonstrated to be one of the most sensitive and non-invasive tests for the detection of intravenous air emboli during craniotomyThe optimal dose of NS must be investigated for several reasons. First, the amount of NS in each injection should be minimized to avoid unnecessary volume loading, as even a small amount of NS may affect a patient’s circulatory condition if multiple injections are administered, especially in patients with cardiac and renal disorders. Nevertheless, as correct PIV placement needs to be confirmed at regular intervals during surgery, multiple repeat NS injections are required during long surgical procedures. An insufficient NS dose may also increase the risk of false-negative results in both the S- and V-tests, which can result in unnecessary placement of an additional PIV access and interrupt surgical procedures.This study compared the rates of positive results between the S- and V-tests for different NS dose groups. The V-test yielded significantly higher detection rates than the S-test in all NS dose groups. Furthermore, given its objective nature, the V-test may represent an optimal approach for confirming correct PIV access in children, provided that an NS dose of at least 0.3 mL/kg is administered. Further multi-center investigations will be required to confirm this finding. In the meantime, the V-test requires data analysis using computer software and is therefore inconvenient for intraoperative use. Further developments in hardware and software are vital for addressing this issue.The mechanisms underlying changes in the precordial Doppler signal after NS injection are currently unclear. An earlier study presumed that the Doppler probe detects the signals created by tricuspid valve movements since Doppler sounds are often detected over the right parasternal area, just prior to and during the onset of systoleSeveral important limitations of the present study should be acknowledged. First, the gauge of the PIV catheter may have been a confounding variable. The smaller gauge of the PIV may have slowed the injection speed, resulting in fewer microbubbles. Nevertheless, the randomization procedure should have minimized any potential residual confounding effects. Second, multiple anesthesiologists carried out NS injections during the study period. Although the research investigators instructed them to inject the NS at the highest speed possible, there may have been some variations in the injection speed. Third, the timing of the injection may not have been exactly 10 s after the initiation of the recording in either the S-test or the V-test. This small time difference may have been a source of measurement bias in the V-test. To minimize such bias, our data collection procedure specified the elapsed time for each measurement. Fourth, there may have been selection bias, as we limited our inclusion criteria to children with a body weight ranging from 10 to 20 kg and the absence of any history of congenital heart disease or any major comorbidities. Thus, further prospective studies in different populations are required. Fifth, our results lack generalizability, as the study was conducted at a single center. Sixth, the S-test applies a subjective outcome that is based on the physician’s judgment, which can cause a measuring bias. However, we used an objective outcome in the V-test (the proportion of cases with a change in the mean blood flow velocity of ≥ 1 cm/s in the 5-s period before and after NS injection via PIV access). This threshold value was determined based on a previous studyIn conclusion, the current results indicate that the minimally required NS dose for detecting changes in precordial Doppler signals and confirming correct PIV placement in children is 0.3 mL/kg. However, further multi-center prospective investigations are needed to evaluate the applicability of this finding to other pediatric patient groups.