Influence of Diaphragmatic Motion on Inferior Vena Cava Diameter Respiratory Variations in Healthy Volunteers

Inferior vena cava distensibility during pressure support ventilation: a prospective study evaluating interchangeability of subcostal and trans‑hepatic views, with both M‑mode and automatic border tracing

The Inferior Vena Cava (IVC) is commonly utilized to evaluate fluid status in the Intensive Care Unit (ICU),with more recent emphasis on the study of venous congestion. It is predominantly measured via subcostal approach (SC) or trans-hepatic (TH) views, and automated border tracking (ABT) software has been introduced to facilitate its assessment. Prospective observational study on patients ventilated in pressure support ventilation (PSV) with 2 × 2 factorial design. Primary outcome was to evaluate interchangeability of measurements of the IVC and the distensibility index (DI) obtained using both M-mode and ABT, across both SC and TH. Statistical analyses comprised Bland-Altman assessments for mean bias, limits of agreement (LoA), and the Spearman correlation coefficients. IVC visualization was 100% successful via SC, while TH view was unattainable in 17.4% of cases. As compared to the M-mode, the IVC-DI obtained through ABT approach showed divergences in both SC (mean bias 5.9%, LoA -18.4% to 30.2%, ICC = 0.52) and TH window (mean bias 6.2%, LoA -8.0% to 20.4%, ICC = 0.67). When comparing the IVC-DI measures obtained in the two anatomical sites, accuracy improved with a mean bias of 1.9% (M-mode) and 1.1% (ABT), but LoA remained wide (M-mode: -13.7% to 17.5%; AI: -19.6% to 21.9%). Correlation was generally suboptimal (r = 0.43 to 0.60). In PSV ventilated patients, we found that IVC-DI calculated with M-mode is not interchangeable with ABT measurements. Moreover, the IVC-DI gathered from SC or TH view produces not comparable results, mainly in terms of precision.

Preoperative echocardiography as a predictor of spinal anesthesia-induced hypotension in older patients with mild left ventricular diastolic dysfunction: a retrospective observational study

BACKGROUND

Spinal anesthesia-induced hypotension (SAH) frequently occurs in older patients, many of whom have mild left ventricular (LV) diastolic dysfunction, often asymptomatic at rest. This study investigated the association between preoperative echocardiographic measurements and SAH in older patients with mild LV diastolic dysfunction.

METHODS

We conducted a retrospective observational study using data from electronic medical records. The patients ≥ 65 years old who underwent spinal anesthesia for urologic surgery between January 2016 and December 2017 and whose preoperative echocardiography within 6 months before surgery revealed grade I LV diastolic dysfunction were recruited. SAH was investigated using the anesthesia records. Logistic regression and receiver operating characteristic (ROC) curve analyses were performed.

RESULTS

A total of 163 patients were analyzed. SAH and significant SAH developed in 55 (33.7%) patients. The mitral inflow E velocity was an independent risk factor for SAH (odds ratio [OR], 0.886; 95% confidence interval [CI], 0.845-0.929; P < 0.001). The area under the ROC curve for mitral inflow E velocity to predict SAH was 0.819 (95% CI, 0.752-0.875; P < 0.001). If mitral inflow E velocity was ≤ 60 cm/s, SAH was predicted with a sensitivity of 83.6% and specificity of 70.4%.

CONCLUSIONS

The preoperative mitral inflow E velocity demonstrated the greatest predictability of SAH in older patients with mild LV diastolic dysfunction. This may assist in identifying patients at high risk of SAH and guiding preventive strategies in the future.

Use of POCUS for the assessment of dehydration in pediatric patients-a narrative review

In pediatric practice, POCUS (point-of-care ultrasound) has been mostly implemented to recognize lung conditions and pleural and pericardial effusions, but less to evaluate fluid depletion. The main aim of this review is to analyze the current literature on the assessment of dehydration in pediatric patients by using POCUS. The size of the inferior vena cava (IVC) and its change in diameter in response to respiration have been investigated as a tool to screen for hypovolemia. A dilated IVC with decreased collapsibility (< 50%) is a sign of increased right atrial pressure. On the contrary, a collapsed IVC may be indicative of hypovolemia. The IVC collapsibility index (cIVC) reflects the decrease in the diameter upon inspiration. Altogether the IVC diameter and collapsibility index can be easily determined, but their role in children has not been fully demonstrated, and an estimation of volume status solely by assessing the IVC should thus be interpreted with caution. The inferior vena cava/abdominal aorta (IVC/AO) ratio may be a suitable parameter to assess the volume status in pediatric patients even though there is a need to define age-based thresholds. A combination of vascular, lung, and cardiac POCUS could be a valuable supplementary tool in the assessment of dehydration in several clinical scenarios, enabling rapid identification of life-threatening primary etiologies and helping physicians avoid inappropriate therapeutic interventions.   Conclusion: POCUS can provide important information in the assessment of intravascular fluid status in emergency scenarios, but measurements may be confounded by a number of other clinical variables. The inclusion of lung and cardiac views may assist in better understanding the patient's physiology and etiology regarding volume status. What is Known: • In pediatric practice, POCUS (point-of-care ultrasound) has been mostly implemented to recognize lung conditions (like pneumonia and bronchiolitis) and pleural and pericardial effusions, but less to evaluate fluid depletion. • The size of the IVC (inferior vena cava) and its change in diameter in response to respiration have been studied as a possible screening tool to assess the volume status, predict fluid responsiveness, and assess potential intolerance to fluid loading. What is New: • The IVC diameter and collapsibility index can be easily assessed, but their role in predicting dehydration in pediatric age has not been fully demonstrated, and an estimation of volume status only by assessing the IVC should be interpreted carefully. • The IVC /AO(inferior vena cava/abdominal aorta) ratio may be a suitable parameter to assess the volume status in pediatric patients even though there is a need to define age-based thresholds. A combination of vascular, lung, and cardiac POCUS can be a valuable supplementary tool in the assessment of intravascular volume in several clinical scenarios.

Internal jugular vein collapsibility does not predict fluid responsiveness in spontaneously breathing patients after cardiac surgery

PURPOSE

The objective of our study was to evaluate the diagnostic accuracy of internal jugular vein (IJV) collapsibility as a predictor of fluid responsiveness in spontaneously breathing patients after cardiac surgery.

METHODS

In this prospective observational study, spontaneously breathing patients were enrolled on the first postoperative day after coronary artery bypass grafting. Hemodynamic data coupled with simultaneous ultrasound assessment of the IJV were collected at baseline and after passive leg raising test (PLR). Continuous cardiac index (CI), stroke volume (SV), and stroke volume variation (SVV) were assessed with FloTracTM/EV1000™. Fluid responsiveness was defined as an increase in CI ≥ 10% after PLR. We compared the differences in measured variables between fluid responders and non-responders and tested the ability of ultrasonographic IJV indices to predict fluid responsiveness.

RESULTS

Fifty-four patients were included in the study. Seventeen (31.5%) were fluid responders. The responders demonstrated significantly lower inspiratory and expiratory diameters of the IJV at baseline, but IJV collapsibility was comparable (P = 0.7). Using the cut-off point of 20%, IJV collapsibility predicted fluid responsiveness with a sensitivity of 76.5% and specificity of 38.9%, ROC AUC 0.55.

CONCLUSION

In spontaneously breathing patients after surgical coronary revascularisation, collapsibility of the internal jugular vein did not predict fluid responsiveness.

Short- and long-term reproducibility of peripheral superficial vein depth and diameter measurements using ultrasound imaging

Background

Ultrasound imaging is used for diagnosis, treatment, and blood vessel visualization during venous catheter placement. However, various physiological factors (e.g., body temperature and exercise) influence vein diameters, which are expected to exhibit daily or diurnal fluctuations. Therefore, this study aimed to determine the intraday (short-term) and interday (long-term) reproducibility of repeated measurements of the depth and diameter of peripheral superficial veins.

Methods

Twenty-three healthy young women (mean age, 21.7 ± 0.8 years) participated in the study to examine the short- and long-term reproducibility of the depth and diameter of the cutaneous vein in the left elbow fossa acquired by ultrasound imaging. Short-term measurement intervals were 10 s, and the probe was released from the skin for each acquisition, which was repeated five consecutive times. Long-term measurements were performed at the same time on the next day following the same procedure. The acquired images were analyzed for vein depth and diameter using ImageJ software. The intraclass correlation coefficient (ICC) was calculated to determine the short- and long-term reproducibility of the measurements. The relationship between the venous depth and venous diameter intra-individual variation was analyzed, as well as the influence of body composition (body fat and muscle mass) on the venous diameter and depth.

Results

For vein depth measurements, the short- and long-term ICCs were 0.94–0.96 and 0.88, respectively. For the vein diameter, the short- and long-term ICCs were 0.94–0.97 and 0.67, respectively. The short-term ICCs for both vein depth and diameter exceeded 0.9, indicating that the ultrasound vascular measurement was sufficiently reliable. However, long-term reproducibility was slightly lower, especially for the vein diameter. No correlation was found between the intra-individual variation of the vein diameter and vein depth. Although the vein diameter and body fat mass uncorrelated, the vein depth and body fat mass significantly correlated (r = 0.675, 95% confidence interval = 0.281–0.830).

Conclusions

The long-term reproducibility of vein diameters was somewhat lower than that of the short-term reproducibility. This could be attributed to fluctuations in the physiological state of the participant rather than to the instability of the measurement. Therefore, ultrasound measurement of the peripheral superficial vein is sufficiently reliable.

The Cardiac Caval Index: Improving Noninvasive Assessment of Cardiac Preload

OBJECTIVES

Inferior vena cava (IVC) pulsatility quantified by the Caval Index (CI) is characterized by poor reliability, also due to the irregular magnitude of spontaneous respiratory activity generating the major pulsatile component. The aim of this study was to test whether the IVC cardiac oscillatory component could provide a more stable index (Cardiac CI-CCI) compared to CI or respiratory CI (RCI).

METHODS

Nine healthy volunteers underwent long-term monitoring in supine position of IVC, followed by 3 minutes passive leg raising (PLR). CI, RCI, and CCI were extracted from video recordings by automated edge-tracking and CCI was averaged over each respiratory cycle (aCCI). Cardiac output (CO), mean arterial pressure (MAP) and heart rate (HR) were also recorded during baseline (1 minutes prior to PLR) and PLR (first minute).

RESULTS

In response to PLR, all IVC indices decreased (P < .01), CO increased by 4 ± 4% (P = .055) while HR and MAP did not vary. The Coefficient of Variation (CoV) of aCCI (13 ± 5%) was lower than that of CI (17 ± 5%, P < .01), RCI (26 ± 7%, P < .001) and CCI (25 ± 7%, P < .001). The mutual correlations in time of the indices were 0.81 (CI-RCI), 0.49 (CI-aCCI) and 0.2 (RCI-aCCI).

CONCLUSIONS

Long-term IVC monitoring by automated edge-tracking allowed us to evidence that 1) respiratory and averaged cardiac pulsatility components are uncorrelated and thus carry different information and 2) the new index aCCI, exhibiting the lowest CoV while maintaining good sensitivity to blood volume changes, may overcome the poor reliability of CI and RCI.

Ultrasonographic assessment of the caudal vena cava diameter in cats during blood donation

OBJECTIVES

Ultrasonography of the caudal vena cava (CVC) has been previously established to assess fluid status in dogs but not in cats. The aim of this study was to determine CVC diameter changes during feline blood donation.

METHODS

Inter- and intra-observer variability were assessed in 11 client-owned cats. Minimal and maximal CVC diameters were assessed longitudinally in the subxiphoid view (SV) and right paralumbar view (PV), and transversely in the right hepatic intercostal view (HV). Eighteen client-owned, healthy, anaesthetised cats were evaluated during 21 blood donation procedures of 10 ml/kg in the same anatomical locations before (T0) and after (T1) blood donation, and after volume resuscitation with 30 ml/kg lactated Ringer's solution (T2). The CVC index was calculated.

RESULTS

Intra-observer variability was acceptable for all probe positions, except for the HV, whereas inter-observer variability was considered unacceptable for all probe positions. Complete measurements were obtained during 21 blood donations at T0, T1 and T2 at the SV, during 18/21 blood donations at the HV and during 16/21 blood donations at the PV. At the SV, the minimal CVC diameter between T1 and T2 (P <0.001), and the maximal CVC diameter between T0 and T1 and between T1 and T2 (P <0.001) were significantly different. At the HV, the minimal vertical diameter, maximal vertical diameter and minimal horizontal diameter were different between all timepoints (P <0.001). The maximal horizontal diameter was different between T1 and T2 (P = 0.002). At the PV, both diameters were different between all timepoints (P <0.001). The CVC index was not different between timepoints.

CONCLUSION AND RELEVANCE

Significant probe position dependent CVC diameter changes with marked overlap were observed before and after blood donation, and after fluid bolus. No absolute CVC diameter could be used to indicate hypovolaemia. Ultrasonographic assessment of the feline CVC is highly operator-dependent. The CVC index is not useful in cats.

Focused ultrasound of the caudal vena cava in dogs with cavitary effusions or congestive heart failure: A prospective, observational study

INTRODUCTION

Ultrasonographic indices of the inferior vena cava are useful for predicting right heart filling pressures in people.

OBJECTIVES

To determine whether ultrasonographic indices of caudal vena cava (CVC) differ between dogs with right-sided CHF (R-CHF), left-sided CHF (L-CHF), and noncardiac causes of cavitary effusion (NC).

MATERIALS AND METHODS

113 dogs diagnosed with R-CHF (n = 51), L-CHF (30), or NC effusion (32) were enrolled. Seventeen of the R-CHF dogs had pericardial effusion and tamponade. Focused ultrasound was performed prospectively to obtain 2-dimensional and M-mode subxiphoid measures of CVC maximal and minimal size (CVCmax and CVCmin), CVCmax indexed to aortic dimension (CVC:Ao), and CVC collapsibility index (CVC-CI). Variables were compared between study groups using Kruskal-Wallis and Dunn's-Bonferroni testing, and receiver operating characteristics curves were used to assess sensitivity and specificity.

RESULTS

All sonographic CVC indices were significantly different between R-CHF and NC dogs (P < 0.001). Variables demonstrating the highest diagnostic accuracy for discriminating R-CHF versus NC were CVC-CI <33% in 2D (91% sensitive and 96% specific) and presence of hepatic venous distension (84% sensitive and 90% specific). L-CHF dogs had higher CVC:Ao and lower CVC-CI compared to NC dogs (P = 0.016 and P = 0.043 in 2D, respectively) but increased CVC-CI compared to the R-CHF group (P < 0.001).

CONCLUSIONS

Ultrasonographic indices of CVC size and collapsibility differed between dogs with R-CHF compared to NC causes of cavitary effusions. Dogs with L-CHF have CVC measurements intermediate between R-CHF and NC dogs.

Inferior Vena Cava Collapsibility Index: Clinical Validation and Application for Assessment of Relative Intravascular Volume

Accurate assessment of relative intravascular volume is critical to guide volume management of patients with acute or chronic kidney disorders, particularly those with complex comorbidities requiring hospitalization or intensive care. Inferior vena cava (IVC) diameter variability with respiration measured by ultrasound provides a dynamic noninvasive point-of-care estimate of relative intravascular volume. We present details of image acquisition, interpretation, and clinical scenarios to which IVC ultrasound can be applied. The variation in IVC diameter over the respiratory or ventilatory cycle is greater in patients who are volume responsive than those who are not volume responsive. When 2 recent prospective studies of spontaneously breathing patients (n = 214) are added to a prior meta-analysis of 181 patients, for a total of 7 studies of 395 spontaneously breathing patients, IVC collapsibility index (CI) had a pooled sensitivity of 71% and specificity of 81% for predicting volume responsiveness, which is similar to a pooled sensitivity of 75% and specificity of 82% for 9 studies of 284 mechanically ventilated patients. IVC maximum diameter <2.1 cm, that collapses >50% with or without a sniff is inconsistent with intravascular volume overload and suggests normal right atrial pressure (0-5 mmHg). Inferior vena cava collapsibility (IVC CI) < 20% with no sniff suggests increased right atrial pressure and is inconsistent with overt hypovolemia in spontaneously breathing or ventilated patients. These IVC CI cutoffs do not appear to vary greatly depending on whether patients are breathing spontaneously or are mechanically ventilated. Patients with lower IVC CI are more likely to tolerate ultrafiltration with hemodialysis or improve cardiac output with ultrafiltration. Our goal for IVC CI generally ranges from 20% to 50%, respecting potential biases to interpretation and overriding clinical considerations. IVC ultrasound may be limited by factors that affect IVC diameter or collapsibility, clinical interpretation, or optimal visualization, and must be interpreted in the context of the entire clinical situation.

A History of Fluid Management-From "One Size Fits All" to an Individualized Fluid Therapy in Burn Resuscitation

Fluid management is a cornerstone in the treatment of burns and, thus, many different formulas were tested for their ability to match the fluid requirements for an adequate resuscitation. Thereof, the Parkland-Baxter formula, first introduced in 1968, is still widely used since then. Though using nearly the same formula to start off, the definition of normovolemia and how to determine the volume status of burn patients has changed dramatically over years. In first instance, the invention of the transpulmonary thermodilution (TTD) enabled an early goal directed fluid therapy with acceptable invasiveness. Furthermore, the introduction of point of care ultrasound (POCUS) has triggered more individualized schemes of fluid therapy. This article explores the historical developments in the field of burn resuscitation, presenting different options to determine the fluid requirements without missing the red flags for hyper- or hypovolemia. Furthermore, the increasing rate of co-morbidities in burn patients calls for a more sophisticated fluid management adjusting the fluid therapy to the actual necessities very closely. Therefore, formulas might be used as a starting point, but further fluid therapy should be adjusted to the actual need of every single patient. Taking the developments in the field of individualized therapies in intensive care in general into account, fluid management in burn resuscitation will also be individualized in the near future.

Measurement site of inferior vena cava diameter affects the accuracy with which fluid responsiveness can be predicted in spontaneously breathing patients: a post hoc analysis of two prospective cohorts

Background

The collapsibility index of the inferior vena cava (cIVC) has potential for predicting fluid responsiveness in spontaneously breathing patients, but a standardized approach for measuring the inferior vena cava diameter has yet to be established.

The aim was to test the accuracy of different measurement sites of inferior vena cava diameter to predict fluid responsiveness in spontaneously breathing patients with sepsis-related circulatory failure and examine the influence of a standardized breathing manoeuvre.

Results

Among the 81 patients included in the study, the median Simplified Acute Physiologic Score II was 34 (24; 42). Sepsis was of pulmonary origin in 49 patients (60%). Median volume expansion during the 24 h prior to study inclusion was 1000 mL (0; 2000). Patients were not severely ill: none were intubated, only 20% were on vasopressors, and all were apparently able to perform a standardized breathing exercise. Forty-one (51%) patients were responders to volume expansion (i.e. a ≥ 10% stroke volume index increase). The cIVC was calculated during non-standardized (cIVC-ns) and standardized breathing (cIVC-st) conditions. The accuracy with which both cIVC-ns and cIVC-st predicted fluid responsiveness differed significantly by measurement site (interaction p < 0.001 and < 0.0001, respectively). Measuring inferior vena cava diameters 4 cm caudal to the right atrium predicted fluid responsiveness with the best accuracy. At this site, a standardized breathing manoeuvre also significantly improved predictive power: areas under ROC curves [mean and (95% CI)] for cIVC-ns = 0.85 [0.78–0.94] versus cIVC-st = 0.98 [0.97–1.0], p < 0.001. When cIVC-ns is superior or equal to 33%, fluid responsiveness is predicted with a sensitivity of 66% and a specificity of 92%. When cIVC-st is superior or equal to 44%, fluid responsiveness is predicted with a sensitivity of 93% and a specificity of 98%.

Conclusion

The accuracy with which cIVC measurements predict fluid responsiveness in spontaneously breathing patients depends on both the measurement site of inferior vena cava diameters and the breathing regime. Measuring inferior vena cava diameters during a standardized inhalation manoeuvre at 4 cm caudal to the right atrium seems to be the method by which to obtain cIVC measurements best-able to predict patients’ response to volume expansion.

Dynamic assessment of the central vein throughout the cardiac cycle in adults with no right heart disease by cardiac CT

PURPOSE

The aim of this study was to investigate the effect of the cardiac cycle on the vena cava and determine the phase of measuring maximum diameters.

METHODS

A total of 152 patients who underwent cardiac computed tomography (CT) were included. Patients' basic information was collected. The major axis, minor axis, and cross-sectional area (CSA) of the vena cava in 10 phases reconstructed at 10% step from 5% to 95% R-R interval were measured in four planes (SVC1 layer: the bifurcation of the pulmonary artery; SVC2 layer: the superior vena cava (SVC) into the right atrium; IVC1 layer: the intersection of the inferior vena cava (IVC) and the right atrium; IVC2 layer: the IVC into the anterior hepatic plane). The difference in vena cava diameters between cardiac cycles was determined using the linear mixed model.

RESULTS

The variations in diameter and CSA of the SVC in cardiac cycles were statistically significant (p < 0.05), while those of the suprahepatic IVC were not. In the SVC1 layer, the maximum value of the SVC major and minor axes was observed in 85% and 45% phases, respectively, while that in the SVC2 layer was observed in 45% phases. The maximum SVC diameters in the SVC1 and SVC2 layers were 19.48 ± 2.57 mm and 17.43 ± 3.09 mm, respectively. The SVC and IVC diameters and CSA were positively correlated with the body surface area in the linear mixed model.

CONCLUSION

The maximum SVC diameter and CSA were mostly observed in 45% phase, which provides a reference for selecting the best phase to measure the abnormality of vena cava diameter in the future.

Using Dynamic Variables to Guide Perioperative Fluid Management

Dynamic variables that quantify the variations in the arterial pressure and plethysmographic waveforms during mechanical ventilation reflect fluid responsiveness. These variables may be helpful in identifying occult hypovolemia and in preventing unnecessary fluid administration.

Performance of a 25% Inferior Vena Cava Collapsibility in Detecting Fluid Responsiveness When Assessed by Novice Versus Expert Physician Sonologists

OBJECTIVES

Inferior vena cava collapsibility (cIVC) measured by point-of-care ultrasound (POCUS) has been proposed as a noninvasive means of assessing fluid responsiveness. We aimed to prospectively evaluate the performance of a 25% cIVC cutoff value to detect fluid responsiveness among spontaneously breathing intensive care unit (ICU) patients when assessed with POCUS by novice versus expert physician sonologists.

METHODS

Prospective observational study of spontaneously breathing ICU patients. Fluid responsiveness was defined as a >10% increase in cardiac index following a 500 mL fluid bolus, measured by bioreactance. Novice sonologist measured cIVC with POCUS. Their measurements were later compared to an expert physician sonologist who independently reviewed the POCUS images and assessed cIVCs.

RESULTS

Of the 85 participants, 44 (52%) were fluid responders. A 25% cIVC cutoff value performed better when assessed by expert sonologists than novice physician sonologists (receiver-operator characteristic curve, ROC = 0.82 [0.74-0.88] vs ROC = 0.69 [0.60-0.77]).

CONCLUSIONS

A 25% cIVC cutoff value measured by POCUS detects fluid responsiveness. However, the experience of the physician sonologist affects test performance and should be considered when interpreting and clinically using cIVC to direct intravenous fluid resuscitation.

Diagnostic accuracy of inferior vena caval respiratory variation in detecting fluid unresponsiveness: A systematic review and meta-analysis

BACKGROUND

The accuracy of respiratory variation of the inferior vena cava (rvIVC) in predicting fluid responsiveness, particularly in spontaneously breathing patients is unclear.

OBJECTIVES

To consider the evidence to support the accuracy of rvIVC in identifying patients who are unlikely to benefit from fluid administration.

DESIGN

Systematic review and meta-analysis.

DATA SOURCE

We searched MEDLINE, EMBASE, Cochrane Library, KoreaMed, LILCAS and WHO Clinical Trial Registry from inception to June 2017.

ELIGIBILITY CRITERIA

Case-control or cohort studies that evaluated the accuracy of rvIVC in living adult humans were included. A study was included in the meta-analysis if data enabling construction of 2 × 2 tables were reported, calculated or could be obtained from authors and met the above cited criteria.

RESULT

A total of 23 studies including 1574 patients were included in qualitative analysis. The meta-analysis involved 20 studies and 761 patients. Pooled sensitivity and specificity of rvIVC in 330 spontaneously breathing patients were 0.80 [95% confidence interval (CI) 0.68 to 0.89] and 0.79 (95% CI 0.60 to 0.90). Pooled sensitivity and specificity of rvIVC in 431 mechanically ventilated patients were 0.79 (95% CI 0.67 to 0.86) and 0.70 (95% CI 0.63 to 0.76).

CONCLUSION

Decreased inferior vena caval respiratory variation is moderately accurate in predicting fluid unresponsiveness both in spontaneous and mechanically ventilated patients. The findings of this review should be used in the appropriate clinical context and in conjunction with other clinical assessments of fluid status.

IDENTIFIER

CRD 42017068028.

Respiratory changes of the inferior vena cava diameter predict fluid responsiveness in spontaneously breathing patients with cardiac arrhythmias

Background

Whether the respiratory changes of the inferior vena cava diameter during a deep standardized inspiration can reliably predict fluid responsiveness in spontaneously breathing patients with cardiac arrhythmia is unknown.

Methods

This prospective two-center study included nonventilated arrhythmic patients with infection-induced acute circulatory failure. Hemodynamic status was assessed at baseline and after a volume expansion of 500 mL 4% gelatin. The inferior vena cava diameters were measured with transthoracic echocardiography using the bi-dimensional mode on a subcostal long-axis view. Standardized respiratory cycles consisted of a deep inspiration with concomitant control of buccal pressures and passive exhalation. The collapsibility index of the inferior vena cava was calculated as [(expiratory–inspiratory)/expiratory] diameters.

Results

Among the 55 patients included in the study, 29 (53%) were responders to volume expansion. The areas under the ROC curve for the collapsibility index and inspiratory diameter of the inferior vena cava were both of 0.93 [95% CI 0.86; 1]. A collapsibility index ≥ 39% predicted fluid responsiveness with a sensitivity of 93% and a specificity of 88%. An inspiratory diameter < 11 mm predicted fluid responsiveness with a sensitivity of 83% and a specificity of 88%. A correlation between the inspiratory effort and the inferior vena cava collapsibility was found in responders but was absent in nonresponder patients.

Conclusions

In spontaneously breathing patients with cardiac arrhythmias, the collapsibility index and inspiratory diameter of the inferior vena cava assessed during a deep inspiration may be noninvasive bedside tools to predict fluid responsiveness in acute circulatory failure related to infection. These results, obtained in a small and selected population, need to be confirmed in a larger-scale study before considering any clinical application.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0427-1) contains supplementary material, which is available to authorized users.

Echocardiographic Applications of M-Mode Ultrasonography in Anesthesiology and Critical Care

Proficiency in echocardiography and lung ultrasound has become essential for anesthesiologists and critical care physicians. Nonetheless, comprehensive echocardiography measurements often are time-consuming and technically challenging, and conventional 2-dimensional images do not permit evaluation of specific conditions (eg, systolic anterior motion of the mitral valve, pneumothorax), which have important clinical implications in the perioperative setting. M-mode (motion-based) ultrasonographic imaging, however, provides the most reliable temporal resolution in ultrasonography. Hence, M-mode can provide clinically relevant information in echocardiography and lung ultrasound-driven approaches for diagnosis, monitoring, and interventional procedures performed by anesthesiologists and intensivists. Although M-mode is feasible, this imaging modality progressively has been abandoned in echocardiography and is often underutilized in lung ultrasound. This article aims to comprehensively illustrate contemporary applications of M-mode ultrasonography in the anesthesia and critical care medicine practice. Information presented for each clinical application will include image acquisition and interpretation, evidence-based clinical implications in the critically ill and surgical patient, and limitations. The present article focuses on echocardiography and reviews left ventricular function (mitral annular plane systolic excursion, E-point septal separation, fractional shortening, and transmitral propagation velocity); right ventricular function (tricuspid annular plane systolic excursion, subcostal echocardiographic assessment of tricuspid annulus kick, outflow tract fractional shortening, ventricular septal motion, wall thickness, and outflow tract obstruction); volume status and responsiveness (inferior vena cava and superior vena cava diameter and respiratory variability [collapsibility and distensibility indexes]); cardiac tamponade; systolic anterior motion of the mitral valve; and aortic dissection.

The value of dynamic preload variables during spontaneous ventilation

PURPOSE OF REVIEW

To discuss the physiological significance and clinical value of dynamic preload variables in spontaneously breathing patients.

RECENT FINDINGS

Dynamic preload variables reflect the response of the cardiac output to a modification of preload and can therefore be used to assess fluid responsiveness. Continuous dynamic parameters that are calculated from the variations in the arterial and plethysmographic waveforms following a mechanical breath have been shown to predict fluid responsiveness much better than static preload parameters. These parameters are displayed on many patient monitors though their use is limited to mechanically ventilated patients. However, spontaneous breathing may also induce significant hemodynamic changes because of the repetitive negative swings in the pleural pressure. By better understanding the physiological basis of these changes, the same 'dynamic parameters' can be used to gain unique physiological insights during spontaneous breathing. These include the ability to identify and/or monitor respiratory rate, respiratory effort (e.g., patient-ventilator asynchrony), fluid responsiveness (to some degree), pulsus paradoxus (e.g. asthma, cardiac tamponade), and, importantly, upper airway obstruction.

SUMMARY

Although originally intended to be used only during mechanical ventilation, 'dynamic parameters' may offer valuable clinical information in spontaneously breathing patients.

Assessment of adequacy of volume resuscitation

PURPOSE OF REVIEW

It has recently become evident that administration of intravenous fluids following initial resuscitation has a greater probability of producing tissue edema and hypoxemia than of increasing oxygen delivery. Therefore, it is essential to have a rational approach to assess the adequacy of volume resuscitation. Here we review passive leg raising (PLR) and respiratory variation in hemodynamics to assess fluid responsiveness.

RECENT FINDINGS

The use of ultrasound enhances the clinician's ability to detect and predict fluid responsiveness, whereas enthusiasm for this modality must be tempered by recent evidence that it is only reliable in apneic patients.

SUMMARY

The best predictor of fluid response for hypotensive patients not on vasopressors is a properly conducted passive leg raise maneuver. For more severely ill patients who are apneic, mechanically ventilated and on vasopressors, point of care echocardiography is the best choice. Increases in vena caval diameter induced by controlled positive pressure breaths are insensitive to arrhythmias and can be performed with relatively brief training. Most challenging are patients who are awake and on vasopressors; we suggest that the best method to discriminate fluid responders is PLR measuring changes in cardiac output.

Relationship Between the Subcostal and Right Lateral Ultrasound Views of Inferior Vena Cava Collapse: Implications for Clinical Use of Ultrasonography

BACKGROUND

The collapsibility index of the inferior vena cava is traditionally visualized from the subcostal region in the sagittal plane, referred to here as cIVC_SS. Alternatively, the collapsibility index of the inferior vena cava can be visualized from the right midaxillary line in the coronal plane, referred to here as cIVC_RC. It is unclear whether values of cIVC_RC are comparable with values of cIVC_SS because the inferior vena cava collapses asymmetrically into an elliptical form, quantified as the flat ratio of the inferior vena cava (F-IVC). This study aimed (1) to establish if cIVC_RC is concordant or discordant to cIVC_SS, and (2) to describe how this concordance or discordance is related to F-IVC.

METHODS

This single-center cross-sectional study enrolled 110 spontaneously breathing patients. Values of cIVC_RC were compared with cIVC_SS. Performance of cIVC_RC ≥ 42% in predicting fluid responsiveness, defined as cIVC_SS ≥ 42%, was assessed. F-IVC was also correlated to the difference between cIVC_SS and cIVC_RC.

RESULTS

cIVC_RC ≥ 42% was 61.5% sensitive (95% CI, 31.58%-86.14%) and 67.1% specific (95% CI, 55.81%-77.06%) for predicting cIVC_SS ≥ 42%. cIVC_RC underestimated cIVC_SS. The degree of discordance between cIVC_RC and cIVC_SS was proportional to the value of F-IVC.

CONCLUSIONS

cIVC_RC and cIVC_SS measures are discordant, where cIVC_RC underestimates cIVC_SS. The degree of discordance is directly proportional to the value of F-IVC. Therefore, we recommend that cIVC_RC ≥ 42% be used to rule in, but not to rule out, fluid responsivity. Wherever possible, F-IVC should be assessed to understand the clinical relevance of cIVC_RC.

Vena Cava Responsiveness to Controlled Isovolumetric Respiratory Efforts

OBJECTIVES

Respirophasic variation of inferior vena cava (IVC) size is affected by large variability with spontaneous breathing. This study aims at characterizing the dependence of IVC size on controlled changes in intrathoracic pressure.

METHODS

Ten healthy subjects, in supine position, performed controlled isovolumetric respiratory efforts at functional residual capacity, attaining positive (5, 10, and 15 mmHg) and negative (-5, -10, and -15 mmHg) alveolar pressure levels. The isovolumetric constraint implies that equivalent changes are exhibited by alveolar and intrathoracic pressures during respiratory tasks.

RESULTS

The IVC cross-sectional area equal to 2.88 ± 0.43 cm² at baseline (alveolar pressure = 0 mmHg) was progressively decreased by both expiratory and inspiratory efforts of increasing strength, with diaphragmatic efforts producing larger effects than thoracic ones: -55 ± 15% decrease, at +15 mmHg of alveolar pressure (P < .01), -80 ± 33 ± 12% at -15 mmHg diaphragmatic (P < .01), -33 ± 12% at -15 mmHg thoracic. Significant IVC changes in size (P < .01) and pulsatility (P < .05), along with non significant reduction in the response to respiratory efforts, were also observed during the first 30 minutes of supine rest, detecting an increase in vascular filling, and taking place after switching from the standing to the supine position.

CONCLUSIONS

This study quantified the dependence of the IVC cross-sectional area on controlled intrathoracic pressure changes and evidenced the stronger influence of diaphragmatic over thoracic activity. Individual variability in thoracic/diaphragmatic respiratory pattern should be considered in the interpretation of the respirophasic modulations of IVC size.

Influence of the Respiratory Cycle on Caudal Vena Cava Diameter Measured by Sonography in Healthy Foals: A Pilot Study

Background

Intravascular volume assessment in foals is challenging. In humans, intravascular volume status is estimated by the caudal vena cava (CVC) collapsibility index (CVC‐CI) defined as (CVC diameter at maximum expiration [CVC_max] – CVC diameter at minimal inspiration [CVC_min])/CVC_max × 100%.

Hypothesis/Objectives

To determine whether the CVC could be sonographically measured in healthy foals, determine differences in CVC_max and CVC_min, and calculate inter‐ and intrarater variability between 2 examiners. We hypothesized that the CVC could be measured sonographically at the subxiphoid view and that there would be a difference between CVC_max and CVC_min values.

Animals

Sixty privately owned foals <1‐month‐old.

Methods

Prospective study. A longitudinal subxiphoid sonographic window in standing foals was used. The CVC_max and CVC_min were analyzed by a linear mixed effect model. Inter‐rater agreement and intrarater variability were expressed by Bland‐Altman and intraclass correlation coefficients, respectively.

Results

Measurements were attained from 58 of 60 foals with mean age of 15 ± 7.9 days and mean weight of 75.7 ± 17.7 kg. The CVC_max was significantly different from CVC_min (D = 0.515, SE = 0.031, P < 0.001). Inter‐rater agreement of the CVC‐CI differed by an average of −0.9% (95% limits of agreement, −12.5 to +10.7%). Intrarater variability of CVC_max was 0.540 and 0.545, of CVC_min was 0.550 and 0.594, and of CVC‐CI was 0.894 and 0.853 for observers 1 and 2, respectively.

Conclusions and Clinical Importance

These results indicate it is possible to reliably measure the CVC sonographically in healthy foals, and the CVC‐CI may prove useful in assessing the intravascular volume status in hypovolemic foals.

Respiratory Variation in Femoral Vein Diameter Has Moderate Accuracy as a Marker of Fluid Responsivity in Mechanically Ventilated Septic Shock Patients

Ultrasound (US) is considered the first step in evaluation of patients with shock; respiratory variation of the inferior vena cava (inferior vena cava collapsibility [IVCc]) is an important measurement in this scenario that can be impaired by patient condition or technical skills. The main objective of this study was to evaluate if respiratory variation of the femoral vein (femoral vein collapsibility [FVc]), which is easier to visualize, can adequately predict fluid responsiveness in septic shock patients. Forty-five mechanically ventilated septic shock patients in a mixed clinical-surgical, 30-bed intensive care unit were enrolled in this study. All patients underwent assessments of FVc, IVCc and cardiac output using a portable US device. The passive leg raising test was used to evaluate fluid responsiveness. FVc presented an area under the receiver operating characteristic curve of 0.678 (95% confidence interval: 0.519-0.837, p = 0.044) with a cutoff point of 17%, yielding a sensitivity of 62% and specificity of 65% in predicting fluid responsiveness. IVCc had greater diagnostic accuracy compared with FVc, with an area under the receiver operating characteristic curve of 0.733 (95% confidence interval: 0.563-0.903, p = 0.024) and a cutoff point of 29%, yielding a sensitivity of 47% and specificity of 86%. In conclusion, FVc has moderate accuracy when employed as an indicator of fluid responsiveness in spontaneously mechanically ventilated septic shock patients.

Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients

PURPOSE

Measurement of inferior vena cava collapsibility (cIVC) by point-of-care ultrasound (POCUS) has been proposed as a viable, non-invasive means of assessing fluid responsiveness. We aimed to determine the ability of cIVC to identify patients who will respond to additional intravenous fluid (IVF) administration among spontaneously breathing critically-ill patients.

METHODS

Prospective observational trial of spontaneously breathing critically-ill patients. cIVC was obtained 3cm caudal from the right atrium and IVC junction using POCUS. Fluid responsiveness was defined as a≥10% increase in cardiac index following a 500ml IVF bolus; measured using bioreactance (NICOM™, Cheetah Medical). cIVC was compared with fluid responsiveness and a cIVC optimal value was identified.

RESULTS

Of the 124 participants, 49% were fluid responders. cIVC was able to detect fluid responsiveness: AUC=0.84 [0.76, 0.91]. The optimum cutoff point for cIVC was identified as 25% (LR+ 4.56 [2.72, 7.66], LR- 0.16 [0.08, 0.31]). A cIVC of 25% produced a lower misclassification rate (16.1%) for determining fluid responsiveness than the previous suggested cutoff values of 40% (34.7%).

CONCLUSION

IVC collapsibility, as measured by POCUS, performs well in distinguishing fluid responders from non-responders, and may be used to guide IVF resuscitation among spontaneously breathing critically-ill patients.

Focused Real-Time Ultrasonography for Nephrologists

We propose that renal consults are enhanced by incorporating a nephrology-focused ultrasound protocol including ultrasound evaluation of cardiac contractility, the presence or absence of pericardial effusion, inferior vena cava size and collapsibility to guide volume management, bladder volume to assess for obstruction or retention, and kidney size and structure to potentially gauge chronicity of renal disease or identify other structural abnormalities. The benefits of immediate and ongoing assessment of cardiac function and intravascular volume status (prerenal), possible urinary obstruction or retention (postrenal), and potential etiologies of acute kidney injury or chronic kidney disease far outweigh the limitations of bedside ultrasonography performed by nephrologists. The alternative is reliance on formal ultrasonography, which creates a disconnect between those who order, perform, and interpret studies, creates delays between when clinical questions are asked and answered, and may increase expense. Ultrasound-enhanced physical examination provides immediate information about our patients, which frequently alters our assessments and management plans.

Distensibility index of the inferior vena cava in experimental acute respiratory distress syndrome

We determined the accuracy of distensibility index of inferior vena cava (dIVC) for evaluation of fluid responsiveness in rats with acute respiratory distress syndrome (ARDS) and validated this index for use in rat models. In protocol 1, E. coli lipopolysaccharide was administered in Wistar rats (n=7). After 24h, animals were mechanically ventilated, and stroke volume (SV) and dIVC quantified after blood drainage and subsequent volume expansion (albumin 20%). A receiver operating characteristic (ROC) curve was plotted to determine the optimal dIVC cutoff. In protocol 2, rats (n=10) were divided into fluid-responders (SV increase >5%) and nonresponders (SV increase <5%). The dIVC cutoff obtained from protocol 1 was 25%. Fluid responders had a 2.5 relative risk of low dIVC (<25%). The sensitivity, specificity, positive predictive, and negative predictive values for dIVC were 74%, 62%, 59%, and 76%, respectively. In conclusion, a dIVC threshold <25% was associated with positive response after volume expansion and could be used to titrate fluids in endotoxin-induced ARDS.

Echocardiography as a guide for fluid management

Background

In critically ill patients at risk for organ failure, the administration of intravenous fluids has equal chances of resulting in benefit or harm. While the intent of intravenous fluid is to increase cardiac output and oxygen delivery, unwelcome results in those patients who do not increase their cardiac output are tissue edema, hypoxemia, and excess mortality. Here we briefly review bedside methods to assess fluid responsiveness, focusing upon the strengths and pitfalls of echocardiography in spontaneously breathing mechanically ventilated patients as a means to guide fluid management. We also provide new data to help clinicians anticipate bedside echocardiography findings in vasopressor-dependent, volume-resuscitated patients.

Objective

To review bedside ultrasound as a method to judge whether additional intravenous fluid will increase cardiac output. Special emphasis is placed on the respiratory effort of the patient.

Conclusions

Point-of-care echocardiography has the unique ability to screen for unexpected structural findings while providing a quantifiable probability of a patient’s cardiovascular response to fluids. Measuring changes in stroke volume in response to either passive leg raising or changes in thoracic pressure during controlled mechanical ventilation offer good performance characteristics but may be limited by operator skill, arrhythmia, and open lung ventilation strategies. Measuring changes in vena caval diameter induced by controlled mechanical ventilation demands less training of the operator and performs well during arrythmia. In modern delivery of critical care, however, most patients are nursed awake, even during mechanical ventilation. In patients making respiratory efforts we suggest that ventilator settings must be standardized before assessing this promising technology as a guide for fluid management.