Usefulness of respiratory variation of inferior vena cava diameter for estimation of elevated central venous pressure in children with cardiovascular disease

Hepatic vein Doppler ultrasound to estimate central venous pressure in mechanically ventilated children

Monitoring central venous pressure (CVP) is crucial for managing critically ill patients yet poses challenges in pediatric cases. This study aimed to correlate CVP with hepatic vein Doppler and IVC ultrasound variables in children. Mechanically ventilated children underwent simultaneous ultrasound and CVP measurements. Hepatic vein Doppler assessed peak velocities (A, S, V, D) and systolic filling fraction. IVC ultrasound included respiratory variability indices, IVC/aorta ratio, and IVC/body surface area ratio. Fifty-three children were included (median age of 8.3 months and weight of 6.3 kg). Significant correlations were found between CVP values and all hepatic vein Doppler-based variables. The strongest correlation was found between CVP and the sum of the absolute values of the A- and D-wave peak velocities (AD velocity), with a ρ = 0.61 (95% confidence interval [CI] of 0.40 to 0.75; p < 0.001). The AD velocity > 38.55 cm/s was able to discriminate patients with CPV > 12 mmHg with a sensitivity of 100%, specificity of 95.3%, positive predictive value of 83.3%, and negative predictive value of 100%. No correlations were observed between CVP and variables derived from IVC respiratory variability indices or the IVC/aorta ratio. Conclusion: Hepatic vein Doppler ultrasound provides variables that significantly correlate with CVP and may be useful for estimating cardiac preload in mechanically ventilated children. Indices derived from IVC ultrasound were not reliable for estimating CVP. What is known? • Increased central venous pressure (CVP) can cause interstitial edema and reduce vital organ perfusion, leading to organic dysfunctions, with encapsulated organs such as the kidneys and liver being at higher risk. • However, measuring CVP in children poses challenges due to the difficulties and risks of central venous catheterization, frequent partial or total luminal obstructions in venous catheters, and potential technical errors in measurements. What is new? • Variables obtained through hepatic vein Doppler ultrasonography outperformed those obtained by inferior vena cava ultrasound for estimating CVP in this population. • Hepatic vein Doppler ultrasonography holds potential as an accurate, safe, and non-invasive method for discriminating patients with increased cardiac preload.

Assessment of fluid removal using ultrasound, bioimpedance and anthropometry in pediatric dialysis: a pilot study

BACKGROUND

Fluid overload is associated with morbidity and mortality in children receiving dialysis. Accurate clinical assessment is difficult, and using deuterium oxide (D₂O) to measure total body water (TBW) is impractical. We investigated the use of ultrasound (US), bioimpedance spectroscopy (BIS), and anthropometry to assess fluid removal in children receiving maintenance hemodialysis (HD).

METHODS

Participants completed US, BIS, and anthropometry immediately before and 1-2 h after HD for up to five sessions. US measured inferior vena cava (IVC) diameter, lung B-lines, muscle elastography, and dermal thickness. BIS measured the volume of extracellular (ECF) and intracellular (ICF) fluid. Anthropometry included mid-upper arm, calf and ankle circumferences, and triceps skinfold thickness. D₂O was performed once pre-HD. We assessed the change in study measures pre- versus post-HD, and the correlation of change in study measures with percent change in body weight (%∆BW). We also assessed the agreement between TBW measured by BIS and D₂O.

RESULTS

Eight participants aged 3.4-18.5 years were enrolled. Comparison of pre- and post-HD measures showed significant decrease in IVC diameters, lung B-lines, dermal thickness, BIS %ECF, mid-upper arm circumference, ankle, and calf circumference. Repeated measures correlation showed significant relationships between %∆BW and changes in BIS ECF (r_rm =0.51, 95% CI 0.04, 0.80) and calf circumference (r_rm=0.80, 95% CI 0.51, 0.92). BIS TBW correlated with D₂O TBW but overestimated TBW by 2.2 L (95% LOA, -4.75 to 0.42).

CONCLUSION

BIS and calf circumference may be helpful to assess changes in fluid status in children receiving maintenance HD. IVC diameter, lung B-lines and dermal thickness are potential candidates for future studies.

Diagnostic Utility of Point-of-Care Ultrasound in the Pediatric Cardiac Intensive Care Unit

Purpose of Review

Recent Findings

Summary

Supplementary Information

Correlation Between Ultrasound-Measured Diameter and Blood Flow Velocity of the Internal Jugular Veins with the Preoperative Blood Volume in Elderly Patients

The study aimed to explore the correlation of the diameter and blood flow velocity of the internal jugular vein with the preoperative blood volume in elderly patients and to providence for rapid evaluation of preoperative blood volume with ultrasound in elderly patients. Thirty patients over 65 years old were recruited in the study. Patient’s central venous pressure (CVP) was recorded before anesthesia. The maximum diameter (Dmax) and the minimum diameter (Dmin) of the left internal jugular vein were measured by M type ultrasound and the respiratory variation index (RVI), defined as (Dmax − Dmin) / Dmax × 100%, was calculated. The maximum blood flow velocity (BVmax) and the minimum blood flow velocity (BVmin) were measured by Doppler ultrasound, and the blood flow variation index (BVI), defined as (BVmax − BVmin) / BVmax × 100%, was calculated. Then, each of the patients was given with 5 ml/kg crystalloid solution, and the relevant data were measured again and compared to that before infusion. The correlation between each measurement index and CVP, and their efficiency in predicting CVP > 6 mmHg were statistically evaluated. No matter before or after infusion, Dmax, Dmin, BVmax, and BVmin were positively correlated with CVP (Correlation is significant at the 0.01 level (2-tailed)); and RVI was negatively correlated with CVP (Correlation is significant at the 0.01 level (2-tailed)); however, BVI is negatively correlated with the CVP with no statistically significant difference. Through the analysis of ROC curve, Dmax, Dmin, RVI, BVmax, and BVmin could be used to predict the CVP > 6 mmHg in these patients, and the best index was BVmax; BVI diagnosis was not effective. Ultrasonic measurements of internal jugular vein diameter, respiratory variability, and blood flow velocity were correlated with preoperative CVP in elderly patients, indicating that these indexes could potentially be used to evaluate the preoperative blood volume in elderly patients.

Pericardial Constriction and Myocardial Restriction in Pediatric Mulibrey Nanism: A Complex Disease With Diastolic Dysfunction

Background

Mulibrey nanism (MUL) is a rare condition with profound growth delay. Congestive heart failure is a major determinant of prognosis. The aim was to delineate pericardial constriction and myocardial functional abnormalities in a pediatric MUL sample.

Methods

A total of 23 MUL patients and 23 individually sex- and age-matched healthy control subjects were prospectively assessed in a cross-sectional study with echocardiography.

Results

Clinical signs of heart failure were present in 7 MUL patients, with severe congestive heart failure in 2. Significant diastolic dysfunction, mainly related to constriction, was found in MUL patients without pericardiectomy (N = 18)—septal bounce, pronounced hepatic vein atrial reversal and right heart inflow–outflow variations, and decreased inferior vena cava collapse during respiration. The appearance of the pericardium was not different from that of control subjects. Longitudinal diastolic myocardial velocities were similar to those in control subjects, suggesting an absence of significant myocardial restriction. Right ventricular free wall longitudinal systolic strain and bilateral longitudinal myocardial systolic velocities were decreased in MUL patients, indicating mild biventricular systolic dysfunction. Myocardial motion abnormalities and persistent congestive heart failure were common (in 3 of 6) in MUL patients with a history of pericardiectomy. Cardiac dimensions were similar between MUL patients and control subjects when adjusting for body size, except for smaller biventricular volumes.

Conclusions

MUL disease presents with significant constriction-related diastolic dysfunction and mild bilateral systolic dysfunction. Constriction–restriction assessments during follow-up could be of benefit in decision-making regarding pericardiectomy in MUL disease. Myocardial abnormalities were prevalent among MUL patients who had undergone pericardiectomy and are consistent with progression of myocardial disease in a significant proportion of patients.

Point-of-care ultrasound to assess volume status and pulmonary oedema in malaria patients

PURPOSE

Fluid management is challenging in malaria patients given the risks associated with intravascular fluid depletion and iatrogenic fluid overload leading to pulmonary oedema. Given the limitations of the physical examination in guiding fluid therapy, we evaluated point-of-care ultrasound (POCUS) of the inferior vena cava (IVC) and lungs as a novel tool to assess volume status and detect early oedema in malaria patients.

METHODS

To assess the correlation between IVC and lung ultrasound (LUS) indices and clinical signs of hypovolaemia and pulmonary oedema, respectively, concurrent clinical and sonographic examinations were performed in an observational study of 48 malaria patients and 62 healthy participants across age groups in Gabon.

RESULTS

IVC collapsibility index (CI) ≥ 50% on enrolment reflecting intravascular fluid depletion was associated with an increased number of clinical signs of hypovolaemia in severe and uncomplicated malaria. With exception of dry mucous membranes, IVC-CI correlated with most clinical signs of hypovolaemia, most notably sunken eyes (r = 0.35, p = 0.0001) and prolonged capillary refill (r = 0.35, p = 0.001). IVC-to-aorta ratio ≤ 0.8 was not associated with any clinical signs of hypovolaemia on enrolment. Among malaria patients, a B-pattern on enrolment reflecting interstitial fluid was associated with dyspnoea (p = 0.0003), crepitations and SpO₂ ≤ 94% (both p < 0.0001), but not tachypnoea (p = 0.069). Severe malaria patients had increased IVC-CI (p < 0.0001) and more B-patterns (p = 0.004) on enrolment relative to uncomplicated malaria and controls.

CONCLUSION

In malaria patients, POCUS of the IVC and lungs may improve the assessment of volume status and detect early oedema, which could help to manage fluids in these patients.

Inferior Vena Cava Collapsibility Index to Assess Central Venous Pressure in Perioperative Period Following Cardiac Surgery in Children

The inferior vena cava collapsibility index (IVCCI) is an ultrasound method used to assess central venous pressure (CVP). Our objective was to evaluate the correlation between IVCCI and CVP in children during the early period following surgery for congenital heart disease (CHD). Prospective study performed in a single tertiary care center. Patients  ≤ 18 years old, who underwent cardiopulmonary bypass surgery for CHD, were enrolled. Ultrasound images of the inferior vena cava (IVC) were obtained at two time points; the first was within 2 h of arrival to the CICU and the second was 12-18 h from the first measurement. CVP measured by catheter placed during surgery was recorded within minutes of performing ultrasound. Maximum and minimum IVC diameters were measured by 2D images and M mode method. Seventy patients (47.1% males), with median age 7 months (IQR 4-47 months) and weight 6.9 kg (IQR 4.8-13.5 kg), were evaluated. The 2D IVCCI had inverse correlation with CVP in patients breathing spontaneously; r =  - 0.76 (p < 0.01) and r =  - 0.73 (p < 0.01), during the first and second measurements, respectively. The 2D IVCCI ≤ 0.24 had sensitivity, specificity, and negative predictive value of 94%, 79%, and 88.9% , respectively, to detect CVP ≥ 10 mmHg. No correlation was found between IVCCI and CVP during positive pressure ventilation. There is a significant inverse correlation between 2D IVCCI and CVP in spontaneously breathing children after surgery for CHD. Use of 2D IVCCI for monitoring CVP could reduce the frequency and duration of CVP catheters and their inherent complications.

New directions in point-of-care ultrasound at the crossroads of paediatric emergency and critical care

PURPOSE OF REVIEW

The diagnostic capability, efficiency and versatility of point-of-care ultrasound (POCUS) have enabled its use in paediatric emergency medicine (PEM) and paediatric critical care (PICU). This review highlights the current applications of POCUS for the critically ill child across PEM and PICU to identify areas of progress and standardized practice and to elucidate areas for future research.

RECENT FINDINGS

POCUS technology continues to evolve and advance bedside clinical care for critically ill children, with ongoing research extending its use for an array of clinical scenarios, including respiratory distress, trauma and dehydration. Rapidly evolving and upcoming applications include diagnosis of pneumonia and acute chest syndrome, identification of intra-abdominal injury via contrast-enhancement, guidance of resuscitation, monitoring of increased intracranial pressure and procedural guidance.

SUMMARY

POCUS is an effective and burgeoning method for both rapid diagnostics and guidance for interventions and procedures. It has clinical application for a variety of conditions that span PEM and PICU settings. Formal POCUS training is needed to standardize and expand use of this valuable technology by PICU and PEM providers alike.

Fluid status evaluation by inferior vena cava diameter and bioimpedance spectroscopy in pediatric chronic hemodialysis

Background

Evaluation of patient’s dry weight remains challenging in chronic hemodialysis (HD) especially in children. Inferior Vena Cava (IVC) measurement was reported useful to assess fluid overload both in adults and children.

Methods

We performed a monocentric prospective study to evaluate the relation between predialytic IVC diameter measurements and hydration status evaluated by physicians and bioimpedance spectroscopy (BIS) and between IVC measurements and persistent hypertension.

Results

Forty-eight HD sessions in 16 patients were analyzed. According to physicians, patients were overhydrated in 84.5% of dialysis sessions, 20.8% according to BIS, and 0%, 4.1% and 20.8% according to IVC inspiratory, expiratory and collapsibility index reference curves respectively. There was no correlation between relative overhydration evaluated by BIS and IVC measurements z-scores (p = 0.20). Patients whose blood pressure normalized after HD had a more dilated maximal IVC diameter before dialysis session than patients with persistent hypertension (median − 0.07SD [−0.8; 0.88] versus −1.61SD [−2.18; −0.74] (p = 0.03)) with an optimal cut-off of −0.5 SD.

Conclusions

In our study, IVC measurement is not reliable to assess fluid overload in children on HD and was not correlated with extracellular fluid volume assessed by BIS measurements. However, IVC measurements might be of interest in differentiating volume-dependant hypertension from volume-independant hypertension.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0793-1) contains supplementary material, which is available to authorized users.

Dynamic Limb Bioimpedance and Inferior Vena Cava Ultrasound in Patients Undergoing Hemodialysis

Assessment of volume status in critically ill patients poses a challenge to clinicians. Measuring changes in the inferior vena cava (IVC) diameter using ultrasound is becoming a standard tool to assess volume status. Ultrasound requires physicians with significant training and specialized expensive equipment. It would be of significant value to be able to obtain this measurement continuously without physician presence. We hypothesize that dynamic changes in limb's bioimpedance in response to respiration could be used to predict changes in IVC. Forty-six subjects were tested a hemodialysis session. Impedance was measured via electrodes placed on the arm. Simultaneously, the IVC diameter was assessed by ultrasound. Subjects were asked to breathe spontaneously and perform respiratory maneuvers using a respiratory training device. Impedance (dz) was determined and compared with change in IVC diameter (dIVC; r = 0.76, p < 0.0001). There was significant relationship between dz and dIVC (p< 0.0001). Receiver-operator curves for dz at thresholds of dIVC (20% to70%) demonstrated high predictive power with areas under the curves (0.87-0.99, p < 0.0001). This evaluation suggests that real-time dynamic changes in limb impedance are capable of tracking a wide range of dynamic dIVC. This technique might be a suitable surrogate for monitoring real-time changes in dIVC to assess intravascular volume status.

Cardio-haemodynamic assessment and venous lactate in severe dengue: Relationship with recurrent shock and respiratory distress

Background

Dengue can cause plasma leakage that may lead to dengue shock syndrome (DSS). In approximately 30% of DSS cases, recurrent episodes of shock occur. These patients have a higher risk of fluid overload, respiratory distress and poor outcomes. We investigated the association of echocardiographically-derived cardiac function and intravascular volume parameters plus lactate levels, with the outcomes of recurrent shock and respiratory distress in severe dengue.

Methods/Principle findings

We performed a prospective observational study in Paediatric and adult ICU, at the Hospital for Tropical Diseases (HTD), Ho Chi Minh City, Vietnam. Patients with dengue were enrolled within 12 hours of admission to paediatric or adult ICU. A haemodynamic assessment and portable echocardiograms were carried out daily for 5 days from enrolment and all interventions recorded.

102 patients were enrolled; 22 patients did not develop DSS, 48 had a single episode of shock and 32 had recurrent shock. Patients with recurrent shock had a higher enrolment pulse than those with 1 episode or no shock (median: 114 vs. 100 vs. 100 b/min, P = 0.002), significantly lower Stroke Volume Index (SVI), (median: 21.6 vs. 22.8 vs. 26.8mls/m², P<0.001) and higher lactate levels (4.2 vs. 2.9 vs. 2.2 mmol/l, P = 0.001). Higher SVI and worse left ventricular function (higher Left Myocardial Performance Index) on study days 3–5 was associated with the secondary endpoint of respiratory distress. There was an association between the total IV fluid administered during the ICU admission and respiratory distress (OR: 1.03, 95% CI 1.01–1.06, P = 0.001). Admission lactate levels predicted patients who subsequently developed recurrent shock (P = 0.004), and correlated positively with the total IV fluid volume received (rho: 0.323, P = 0.001) and also with admission ALT (rho: 0.764, P<0.001) and AST (rho: 0.773, P<0.001).

Conclusions/Significance

Echo-derived intravascular volume assessment and venous lactate levels can help identify dengue patients at high risk of recurrent shock and respiratory distress in ICU. These findings may serve to, not only assist in the management of DSS patients, but also these haemodynamic endpoints could be used in future dengue fluid intervention trials.

Dengue is a viral illness that can lead to severe and potentially fatal complications. The most common complication is fluid leakage from blood vessels, which can cause low blood pressure or dengue shock syndrome (DSS). The majority of patients recover with simple intravenous fluid replacement, however in approximately 30% of DSS cases, recurrent episodes of shock occur, and these patients have a higher risk of fluid overload, respiratory distress and death. We investigated whether using portable echocardiograms (Echo) in the intensive care unit (ICU) to assess cardiac function and intravascular volume parameters as well as blood lactate levels, can help identify these patients. We found patients who developed recurrent shock had higher heart rates and lower Stroke Volume Index (SVI), and higher lactate levels at enrolment than those with 1 episode or no shock. Higher SVI and worse cardiac function after 3 days in ICU was associated with respiratory distress. Admission lactate levels predicted patients who subsequently developed recurrent shock and correlated positively with the total IV fluid volume received. These results demonstrate that Echo-derived intravascular volume assessment and venous lactate levels can help identify dengue patients at high risk of poor outcomes in the ICU, and could assist in the management of severe dengue.

Noninvasive Assessment of Pulmonary Artery Pressure in Patients with Extracardiac Conduit Total Cavopulmonary Connection

To assess quantitative measurement of mean pulmonary artery pressure (PAP) in extracardiac total cavopulmonary connection (TCPC) patients by noninvasive echocardiographic inferior vena cava collapsibility index (IVC-CI) and also correlation between the peripheral vein pressure and mean PAP. In 19 TCPC patients with at least 1-year follow-up after completion of TCPC, complete echocardiography including IVC-CI was recorded. All patients underwent cardiac catheterization for mean PAP pressure, peripheral vein pressure (PVP) and contrast study. Different cutoff points of mean PAP were analyzed, and based on the highest cutoff point, patients were categorized into two groups: mean PAP < 17 mmHg (acceptable) and > = 17 mmHg (high) for comparison analysis. Between 2006 and 2015, from 43 patients who had undergone TCPC, nineteen patients with a mean age 12.9 ± 6.6 years and mean follow-up time of 3.4 ± 1.9 years were included in this study. Mean PAP was 14.6 ± 3.97 (range 8-22 mmHg). Thirteen (68 %) patients had PAP < 17 mmHg. No significant statistical difference was detected with respect to age, sex, type of congenital heart disease and fenestration between these two groups. But, right ventricular dominancy was more prevalent in the high PAP group (50 % vs. 7.7 % P value 0.03). IVC-CI had a correlation with mean PAP (r 0.67, P < 0.001). IVC-CI < 21.8 % can predict PAP > = 17 mmHg with 83 % sensitivity and 100 % specificity. Regression analysis proposed an equation for PAP measurement: PAP (mmHg) = 20.2097-0.1796 × (IVC-CI), (r2 = 0.56). Peripheral vein pressure measurement also showed a good correlation with mean PAP and may be used to estimate PAP with the following equation: PAP (mmHg) = 0. 8675 × PVP, (r 0.90, P < 0.0001). In conclusion, IVC-CI as noninvasive and peripheral vein pressure measurement as a minimal invasive method may be useful for quantitative estimation of PAP in patients with extracardiac TCPC.

Prospective evaluation of intravascular volume status in critically ill patients: does inferior vena cava collapsibility correlate with central venous pressure?

BACKGROUND

In search of a standardized noninvasive assessment of intravascular volume status, we prospectively compared the sonographic inferior vena cava collapsibility index (IVC-CI) and central venous pressures (CVPs). Our goals included the determination of CVP behavior across clinically relevant IVC-CI ranges, examination of unitary behavior of IVC-CI with changes in CVP, and estimation of the effect of positive end-expiratory pressure (PEEP) on the IVC-CI/CVP relationship.

METHODS

Prospective, observational study was performed in surgical/medical intensive care unit patients between October 2009 and July 2013. Patients underwent repeated sonographic evaluations of IVC-CI. Demographics, illness severity, ventilatory support, CVP, and patient positioning were recorded. Correlations were made between CVP groupings (<7, 7-12, 12-18, 19+) and IVC-CI ranges (<25, 25-49, 50-74, 75+). Comparison of CVP (2-unit quanta) and IVC-CI (5-unit quanta) was performed, followed by assessment of per-unit ΔIVC-CI/ΔCVP behavior as well as examination of the effect of PEEP on the IVC-CI/CVP relationship.

RESULTS

We analyzed 320 IVC-CI/CVP measurement pairs from 79 patients (mean [SD] age, 55.8 [16.8] years; 64.6% male; mean [SD] Acute Physiology and Chronic Health Evaluation II, 11.7 [6.21]). Continuous data for IVC-CI/CVP correlated poorly (R = 0.177, p < 0.01) and were inversely proportional, with CVP less than 7 noted in approximately 10% of the patients for IVC-CIs less than 25% and CVP less than 7 observed in approximately 85% of patients for IVC-CIs greater than or equal to 75%. Median ΔIVC-CI per unit CVP was 3.25%. Most measurements (361 of 320) were collected in mechanically ventilated patients (mean [SD] PEEP, 7.76 [4.11] cm H2O). PEEP-related CVP increase was approximately 2 mm Hg to 2.5 mm Hg for IVC-CIs greater than 60% and approximately 3 mm Hg to 3.5 mm Hg for IVC-CIs less than 30%. PEEP also resulted in lower IVC-CIs at low CVPs, which reversed with increasing CVPs. When IVC-CI was examined across increasing PEEP ranges, we noted an inverse relationship between the two variables, but this failed to reach statistical significance.

CONCLUSION

IVC-CI and CVP correlate inversely, with each 1 mm Hg of CVP corresponding to 3.3% median ΔIVC-CI. Low IVC-CI (<25%) is consistent with euvolemia/hypervolemia, while IVC-CI greater than 75% suggests intravascular volume depletion. The presence of PEEP results in 2 mm Hg to 3.5 mm Hg of CVP increase across the IVC-CI spectrum and lower collapsibility at low CVPs. Although IVC-CI decreased with increasing degrees of PEEP, this failed to reach statistical significance. While this study represents a step forward in the area of intravascular volume estimation using IVC-CI, our findings must be applied with caution owing to some methodologic limitations.

LEVEL OF EVIDENCE

Diagnostic study, level III. Prognostic study, level III.

Estimation of right atrial pressure on inferior vena cava ultrasound in Asian patients

BACKGROUND

 Right atrial pressure (RAP) is commonly estimated using inferior vena cava (IVC) diameter and its respirophasic variations. Although a guideline has been provided for estimation of RAP due to variation in IVC dimensions based on studies in Western subjects, echocardiographic values in Asian subjects are unknown.

METHODS AND RESULTS

 We studied 369 patients who underwent IVC ultrasound within 24h of right heart catheterization (RHC). The maximum and minimum IVC diameter during a respiratory cycle and the percent collapse after a sniff test were measured. These IVC parameters were compared with mean RAP measured on RHC. Receiver operating characteristic curves were generated for each IVC parameter to determine the optimal cut-off to detect RAP >10mmHg. The IVC maximum diameter cut-off for detecting RAP >10mmHg was 19mm (sensitivity, 75%; specificity, 78%) and the percent collapse cut-off was 30% (sensitivity, 75%; specificity, 83%). Both cut-offs were smaller than those previously reported in patients from Western countries. When the cut-off values from the existing guideline were applied to the present cohort, the sensitivity and specificity for normal RAP (0-5mmHg) were 38.6% and 74.2%, respectively, and 60.0% and 92.0% for elevated RAP (>10mmHg).

CONCLUSIONS

 The optimal IVC maximum diameter and percent collapse cut-offs to detect elevated RAP were smaller in Asian subjects than in a previously reported Western cohort. 

Inferior vena cava displacement during respirophasic ultrasound imaging

Background

Ultrasound measurement of dynamic changes in inferior vena cava (IVC) diameter can be used to assess intravascular volume status in critically ill patients, but published studies vary in accuracy as well as recommended diagnostic cutoffs. Part of this variability may be related to movements of the vessel relative to the transducer during the respiratory cycle which results in unintended comparison of different points of the IVC at end expiration and inspiration, possibly introducing error related to variations in normal anatomy. The objective of this study was to quantify both craniocaudal and mediolateral movements of the IVC as well as the vessel's axis of collapse during respirophasic ultrasound imaging.

Methods

Patients were enrolled from a single urban academic emergency department with ultrasound examinations performed by sonographers experienced in IVC ultrasound. The IVC was imaged from the level of the diaphragm along its entire course to its bifurcation with diameter measurements and respiratory collapse measured at a single point inferior to the confluence of the hepatic veins. While imaging the vessel in its long axis, movement in a craniocaudal direction during respiration was measured by tracking the movement of a fixed point across the field of view. Likewise, imaging the short axis of the IVC allowed for measurement of mediolateral displacement as well as the vessel's angle of collapse relative to vertical.

Results

Seventy patients were enrolled over a 6-month period. The average diameter of the IVC was 13.8 mm (95% CI 8.41 to 19.2 mm), with a mean respiratory collapse of 34.8% (95% CI 19.5% to 50.2%). Movement of the vessel relative to the transducer occurred in both mediolateral and craniocaudal directions. Movement was greater in the craniocaudal direction at 21.7 mm compared to the mediolateral movement at 3.9 mm (p < 0.001). Angle of collapse assessed in the transverse plane averaged 115° (95% CI 112° to 118°).

Conclusions

Movement of the IVC occurs in both mediolateral and craniocaudal directions during respirophasic ultrasound imaging. Further, collapse of the vessel occurs not at true vertical (90°) but 25° off this axis. Technical approach to IVC assessment needs to be tailored to account for these factors.