Cardiac and vascular findings using ultrasound in hypovolemic children

Abstract

Background:

Ultrasound is a non-invasive tool that helps assess volume status.

Objectives:

To assess the dehydration and passive leg raising impact on ultrasound-derived cardiac and inferior vena cava parameters to improve early detection of hypovolemia in children.

Design:

Prospective observational study in a tertiary paediatric intensive care unit.

Methods:

We recruited 66 healthy children 8–14 years old who fasted in Ramadan. Inferior vena cava diameter, inferior vena cava collapsibility, velocity time integral and maximum velocity (Vmax) were measured at left ventricle outflow tract pre- and post-fasting, with and without passive leg raising. Aorta diameter in systole was also measured pre- and post-fasting.

Outcome Measures:

Inferior vena cava diameter and collapsibility, velocity time integral and Vmax with and without passive leg raising, pre and post fasting, and inferior vena cava/Ao ratio pre and post fasting were measured.

Results:

Median percentage of weight loss after fasting was 1.1% (range, 0%–3.9%). Inferior vena cava maximum diameter and inferior vena cava/aorta did not change significantly after fasting (p < 0.05). Inferior vena cava diameters increased and inferior vena cava collapsibility decreased after passive leg raising (p < 0.001) pre and post fasting. Velocity time integral increased with passive leg raising (p < 0.001) but was not affected by fasting (p = 0.17). Vmax increased with passive leg raising and decreased in fasting (p = 0.001).

Conclusion:

Passive leg raising affected ultrasound measurements. Left ventricle outflow tract Vmax was affected by fasting/mild dehydration, and further trials are needed to confirm its value in predicting hypovolemia in children.

Limitations:

There was no significant effect of dehydration on the measurements probably because of the small sample and mild dehydration. This cannot be generalised because it is a single-centre study and younger children were not included.

Keywords

Dehydration hypovolemia children ultrasound echocardiography inferior vena cava aorta collapsibility velocity time integral maximum velocity left ventricular outflow tract passive leg raising

Introduction

Dehydration in children is a common problem with potentially severe consequences; hence, accurate estimation of the degree of dehydration is necessary to guide fluid treatment and early resuscitative interventions. On the other hand, excessive fluid administration and a positive cumulative net fluid balance have been independently associated with worsening respiratory status, prolonged intensive care unit and hospital length of stay, and mortality.

The gold standard for assessing the degree of dehydration in paediatrics is the percent weight loss between the weight pre and post the acute illness.¹ Since those weight measurements are not always available upon patient presentation, other parameters must be examined to assess the degree of dehydration and predict fluid responsiveness. History, physical examination and laboratory tests have been used to reach the clinical decision, but they lack the sensitivity, specificity and the ability to detect significant degrees of dehydration.¹

Bedside ultrasound has emerged as a potentially helpful, readily available and non-invasive means for the quick assessment of volume status in both adults and children. Measurement of the inferior vena cava shows that its diameter changes in respiratory cycle according to the variation in intra-thoracic pressure and appears to change with overall intravascular volume.

These characteristics of the inferior vena cava (IVC) have enabled physicians to measure both the collapsibility index and the ratio of the IVC to aorta, which in contrast does not vary in size with the respiratory cycle or volume status. IVC measurements were studied in volume-depleted children presenting with vomiting and diarrhoea, though all have been relatively small studies.^1–4 Literature in paediatric age group addressing this concept is extremely limited.

Our study’s aim is to describe the different measurements of the heart and great vessels in dehydrated children, namely, IVC to abdominal aortic diameter ratio (IVC/Ao), IVC collapsibility index, velocity time integral (VTI) and maximum velocity at left ventricle out tract (LVOT) and the impact of passive leg raising (PLR) manoeuvre on the above indices.

Materials and methods

Prospective observational study was conducted in King Fahad Medical City (KFMC), a tertiary care hospital in Riyadh, KSA.

We recruited 66 healthy children between the ages of 8 and 14 years living inside KFMC campus who were able to perform voluntary continuous fasting from dawn until sunset for around 15 hours. Ramadan fasting was chosen as it provided a practical and controlled model of mild dehydration in a healthy paediatric cohort. While this is relevant to our region, we acknowledge that this may not be generalisable globally. Children were expected to develop variable degrees of dehydration by the time of breakfast. We excluded any child with any heart disease such as arrhythmias, hypertension, congenital heart diseases, children who had renal diseases, thyroid disease, any acute illness and those receiving any medications.

A team of six paediatric intensivists who were trained in critical care ultrasonography were committed to obtaining and saving the images after an agreement on the standard way of doing the examination. The team was divided into three groups, each examination was done in the presence of two team members to agree on the image acquisition. At the end, all the images and measurements were reviewed by the most experienced consultant intensivist in the team before data entry. Children were assessed by the same study team pre and post fasting, asked to come in the same dress and weighed on the same scale for both assessment occasions.

The ultrasound examination was performed using ultrasound Sonosite M-Turbo machine utilising phase array and curvilinear array probe, vital signs were recorded using GE transport monitor, height and weight by Seca 707 electronic medical standing scale and were placed on Stryker adjustable stretcher.

The examination was performed two times, first, while the child is fasting for 12 hours, then was repeated after breakfast. The following data were recorded on both occasions: height, weight, heart rate, blood pressure, O₂ sat, IVC and aortic maximum diameter, and IVC diameter/aortic diameter ratio before and after fasting. The following measurements were recorded before and after fasting, with and without PLR: IVC collapsibility, maximum velocity and VTI at LVOT.

The subjects were placed in a supine position on an adjustable stretcher. We examined the subcostal transverse view at the level of aorta (Ao) and the IVC, recorded maximum inner to inner wall diameter in the IVC during the expiration and the maximum diameter of the aorta during systole (Figure 1).

Next, a sub-costal long-axis view of the IVC was obtained and IVC collapsibility was measured in m-mode. IVC collapsibility was calculated as: maximum – minimum diameter/maximum diameter multiplied by 100 (Figure 2).

Finally, measurements of VTI and maximum velocity were performed at the level of the left ventricle outflow tract (LVOT) on an apical 5-chamber view, and the average of three readings was recorded (Figure 3).

The whole procedure was repeated after the PLR manoeuvre. The above measurements were performed the night before fasting and compared to the examination on the next day between 4 and 6 p.m. (the end of fasting time) (Figure 4).

Primary outcome: Change in IVC/Ao, VTI and maximum velocity at LVOT between pre- and post-fasting states.

Secondary outcome: IVC minimum, maximum diameters, IVC collapsibility index, VTI and maximum velocity at LVOT after PLR in both pre- and post-fasting states.

Ethical considerations: The study protocol was approved by KFMC institutional review board (IRB), children’s assent and guardians’ consent were obtained.

Statistical analysis

All categorical variables, gender and age presented as numbers and percentages. Continuous variables such as heart rate, respiratory rate and systolic blood pressure expressed as mean ± SD. Paired-sample t-test was to determine the mean significant difference between pre and post analysis. p value of less than 0.05 was considered statistically significant. All data entered and analysed through statistical package SPSS 25 (SPSS Inc., Chicago, IL, USA).

Results

Over the month of Ramadan, we were able to recruit 66 children from 7 nationalities, 54 male and 12 female. The median age was 11.7 years (10.6, 13 interquartile range (IQR)) and median height was 146 cm (136.7, 153 IQR). The median percentage of weight loss was 1.1% (0, 3.9 minimum and maximum). There was slight decrease in heart rate, systolic blood pressure and O₂ saturation after fasting that was statistically significant (p < 0.05); however, we considered it clinically insignificant (Table 1). IVC and aortic maximum diameter and IVC/Ao ratio have not changed significantly after fasting (p > 0.05) (Table 2). There was a significant increase in IVC maximum and minimum diameter, decrease in IVC collapsibility index after PLR manoeuvre (p < 0.001) (Table 3) and a significant rise in VTI and maximum velocity with PLR (Table 4), but this change was not different between fasting and non-fasting status except in terms of maximum velocity at LVOT which showed significant difference pre and post fasting (Table 5).

Table 1.

Hemodynamic parameters before and after fasting.

Measurement	Before fasting(Mean ± SD)	After fasting(Mean ± SD)	P – value
HR	85.52 ± 14.61	79.46 ± 13.263	< 0.001
RR	21.58 ± 3.05	21.06 ± 3.15	0.185
SBP	112.62 ± 9.741	109.30 ± 9.569	0.002
DBP	64.55 ± 6.63	62.50 ± 7.13	0.058
O₂ sat	98.80 ± 1.02	98.25 ± 1.22	0.044

HR: heart rate; RR: respiratory rate; SBP: systolic blood pressure; DBP: diastolic blood pressure; O₂ sat: oxygen saturation.

Table 2.

IVC and aortic diameters and ratio before and after fasting.

Measurement	Before fasting(Mean ± SD)	After fasting(Mean ± SD)	p value
IVC peak diameter–transverse view	1.53 ± 0.30	1.54 ± 0.29	0.784
Aortic maximum diameter–transverse view	1.26 ± 0.19	1.30 ± 0.21	0.09
IVC diameter/aortic diameter ratio	1.22 ± 0.23	1.19 ± 0.22	0.28

IVC: inferior vena cava.

Table 3.

IVC measurements before and after fasting, with and without PLR.

Measurement	Before PLR(Mean ± SD)	After PLR(Mean ± SD)	p value
IVC maximum measurement pre-fasting	1.58 ± 0.27	1.71 ± 0.25	<0.001
IVC minimum measurement pre-fasting	1.09 ± 0.24	1.28 ± 0.26	<0.001
IVC maximum measurement post fasting	1.56 ± 0.26	1.71 ± 0.27	<0.001
IVC minimum measurement post fasting	1.08 ± 0.29	1.24 ± 0.31	<0.001
IVC collapsibility index pre-fasting	31.08 ± 10.65	24.42 ± 10.47	<0.001
IVC collapsibility index post fasting	31.58 ± 13.21	27.70 ± 12.42	0.007

IVC: inferior vena cava; PLR: passive leg raising.

Table 4.

VTI and V-max before and after fasting, with and without PLR.

Measurement	Before PLR(Mean ± SD)	After PLR(Mean ± SD)	p value
VTI pre-fasting	18.00 ± 0.38	19.03 ± 0.36	<0.001
VTI post fasting	17.5621 ± 0.30	18.6379 ± 0.31	<0.001
V-max pre-fasting	92.32 ± 1.89	95.26 ± 1.73	0.001
V-max post fasting	86.18 ± 1.40	90.05 ± 1.46	<0.001

VTI: velocity time integral; V-max: maximum velocity; PLR: passive leg raising.

Table 5.

IVC collapsibility index, VTI, and V-max in supine before and after fasting.

Measurement	Before fasting(Mean ± SD)	After fasting(Mean ± SD)	p value
IVC collapsibility index	31.08 ± 10.65	31.58 ± 13.21	0.74
VTI	18.01 ± 0.37	17.56 ± 0.30	0.172
V-max	92.32 ± 1.89	86.18 ± 1.40	0.001

VTI: velocity time integral; V-max: maximum velocity.

Discussion

Traditional assessment of hydration status in children such as clinical signs and symptoms, stool and urine output, weight and laboratory tests can be imprecise or sometimes difficult to obtain. Ultrasound is a non-invasive tool that showed good efficacy in adults and paediatric literature in volume status evaluation. Our study sought to determine which ultrasound parameter could be used to detect hypovolemia or dehydration in otherwise healthy children.

In our cohort of children with prolonged fasting, our results demonstrated a strong association between mild dehydration (fasting) and maximum velocity at LVOT, but was not significantly associated with vital signs, VTI at LVOT, static measurements of aorta and IVC diameters, or IVC collapsibility index. Our study also showed a significant effect of PLR on IVC collapsibility, maximum velocity and VTI at LVOT regardless of fluid deprivation state.

PLR was studied as a substitute for a fluid bolus, and it was found that improvement of cardiac index following PLR could predict fluid responsiveness.^5,6 Our study supports the concept by showing an improvement in IVC collapsibility, maximum velocity and VTI at LVOT.

Significant inspiratory IVC collapsibility has been shown to help in the assessment of volume status in adults,^1,7 but same findings were not seen in children with either spontaneously breathing,^1,8 or mechanically ventilated ones.⁹ Similarly, our study did not show any correlation between IVC collapsibility and mild dehydration. This can probably be explained by the different vascular elasticity in children compared with adults.

Our study did not replicate the results of previous ones that had shown a correlation between the ratio of IVC/Ao and the degree of volume depletion in children presenting with vomiting and diarrhoea.

A study of 113 children in one of United States paediatric referral centre found an area under the curve (AUC) for the IVC/aorta ratio of 0.72 (95% confidence interval (CI): 0.5, 0.9) for the prediction of significant dehydration, and the sensitivity and specificity of IVC-to-aorta ratio at the cut-point of 0.8 were 67% and 71%, respectively.² In a similar study of 112 children in another United States paediatric referral hospital, the IVC/aorta ratio predicted significant (>5%) dehydration, with an AUC of 0.73 (95% CI: 0.6, 0.8) and sensitivity of 86% and specificity of 51% at the same cut point of 0.8.⁴

In these studies, the prediction was found in children with higher degrees of dehydration than the one observed in our cohort. This could probably mean that IVC/AO may not detect milder degree of dehydration.

Finally, a study of 51 children in a paediatric intensive care unit in the United States showed that IVC/aorta ratio did not correlate with the central venous pressure. In this study, the majority of patients were on positive pressure ventilation that can reverse normal inspiratory and expiratory pressure gradients between chest and abdomen, a factor that can have an important effect on IVC diameter.¹

Paediatric studies have shown that respiratory variation in LVOT Vmax (∆Vmax) predicts the responders to fluid loading in mechanically ventilated children,^10–16 but spontaneously breathing children were not studied. Two paediatric systematic reviews demonstrated that respiratory variation in aortic blood flow maximum velocity was shown to predict fluid responsiveness in children.^10,12 Even though the study samples in these systematic reviews were taken mainly from mechanically ventilated children with different underlying diseases, this could still mean that aortic maximum velocity as a direct measurement of aortic blood flow may detect small changes in preload due to alteration in venous return during respiratory cycle.

While there is no available evidence in the literature to our knowledge about effectiveness of LVOT Vmax in spontaneously breathing children in intravascular volume assessment and fluid responsiveness, our study showed that LVOT Max was different before and after fasting as well as after PLR in our mildly dehydrated spontaneously breathing children. This may make it a promising effective parameter in assessing mild hypovolemia in spontaneously breathing children, but further studies are needed.

Adult literature has shown an association between LVOT Vmax and hypovolemia and fluid responsiveness in septic shock patients,^17,18 and that higher LVOT Vmax measurement may predict both 28th-day and in-hospital mortality.¹⁹ In a systematic review examining fluid responsiveness in spontaneously breathing adults,²⁰ it was found that only one study tested aortic velocity variation and found that it was not predictive for fluid responsiveness, but this study was limited by small sample size.²¹

Clinical implications

Our study explored how ultrasound-derived cardiac and vascular parameters could potentially be used in early detection and management of dehydration in paediatric patients, particularly in emergency and critical care settings.

Limitations

First, the degree of dehydration from fasting in our cohort was mild; for this reason, probably the change in ratio between IVC and aorta diameters (IVC/Ao) was not significant. Second, the small sample size may be a reason for our inability to show a significant effect of dehydration on the measurements. Third, it is a single-centre study and did not include children from the younger age group, so the results cannot be generalised.

Specifically, we acknowledge that the study cohort consisted of healthy children fasting during Ramadan, and the results may be extrapolated to other paediatric populations with caution. Further studies are needed to assess the broader applicability in diverse clinical settings and age groups. We recognise that the small sample size and the mild dehydration observed may influence the findings and emphasise the need for future studies with larger, more various cohorts.

Despite all limitations, it is worth considering this technique along with the traditional methods of dehydration assessment. It is non-invasive, readily available and can be repeated several times during treatment with no side effects.

Future research directions

Based on our study’s findings, we propose several future research avenues, including investigations into different paediatric populations exploring younger age groups, pathological dehydration states and multicenter studies to validate the findings.

Conclusion

PLR manoeuvre as alternative to fluid bolus has shown a significant effect on all volume status measurement in our mildly dehydrated cohort, while the effect of mild dehydration (fasting) was significant only on maximum velocity at LVOT.

Further controlled trials are needed to confirm the value of this dynamic measurement as one of early predictors of hypovolemia.

Footnotes

Acknowledgements

This study was approved by King Fahad Medical City Research Center.

Contributors

All the authors fulfil the criteria for authorship.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

Ethics approval

This study was approved by King Fahad Medical City Research Centre IRB.

Guarantor

Rehab Gabr

ORCID iD

Rehab Gabr

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