23.04.2016 | What's New in Intensive Care
Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view
Erschienen in: Intensive Care Medicine | Ausgabe 7/2016
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Assessment of 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 severe hypovolaemia [1], predict fluid responsiveness (FR) [2, 3] and assess potential intolerance to fluid loading. IVC size, collapsibility (IVCc) [2] and distensibility (IVCd) [3] have gained acceptance by emergency and intensive care unit (ICU) clinicians as FR predictors in patients with shock [4]. The ease of acquisition, reproducibility of measurements and increasing availability of ultrasound devices have supported the expansion of its use. Conflicting results have also been published [5, 6]. Injudicious application in clinical contexts where these indices have not been specifically tested may, however, mislead. On the basis of physiological principles and available, although limited, scientific evidence, it can be hypothesized that in a number of clinical conditions IVC size and/or respiratory variability may not depend on volume status and may not predict FR accurately. Although not specifically investigated yet, these conditions can be described and grouped on the basis of their main physiological determinant, as follows (Table 1) (pictorial samples are also presented as electronic supplementary material, ESM):
Physiological determinant
|
Condition affecting IVC ultrasound reliability for FR
|
Cause of inaccuracy for FR
|
Type of inaccuracy for FR
|
---|---|---|---|
Ventilator settings
|
1. Mechanical ventilation with high PEEP and/or low tidal volumes
|
Larger IVC size, potentially with systemic venous congestion and low respiratory variations, but coexisting with FR
|
FN
|
Patient’s inspiratory efforts
|
2. Assisted ventilation modalities, NIV, CPAP
|
Spontaneous breathing activity makes IVC variation unpredictable
|
FP and FN
|
3. Varying respiratory pattern in spontaneous breathing
|
Significant inspiratory effort, producing markedly negative intrathoracic pressures may induce IVCc in absence of FR
|
FP
|
|
Shallow breathing, with small intrathoracic pressure changes, may induce absence of IVCc in presence of FR
|
FN
|
||
Lung hyperinflation
|
4. Asthma/COPD exacerbation
|
Lung hyperinflation and auto-PEEP simultaneously reduce venous return and induce IVC distension: this may mimic absence of FR
|
FN
|
Forced expiration (“abdominal breathing” causing expiratory collapse) may mimic IVCc
|
FP
|
||
Cardiac conditions impeding venous return
|
5. Chronic RV dysfunction, severe TR
|
Chronic enlargement of IVC and reduced IVCc may erroneously rule out FR
|
FN
|
6. RV myocardial infarction
|
RV dilatation and systemic venous congestion (large IVC) may be associated with FR
|
FN
|
|
7. Cardiac tamponade
|
Marked venous return hindrance: fluid challenge may be a beneficial haemodynamic intervention despite IVC plethora
|
FN
|
|
Increased abdominal pressure
|
8. Intra-abdominal hypertension
|
Smaller IVC size, IVCd or IVCc abolition (depending on type respiration/ventilation mode)
|
FP and FN
|
Other factors
|
9. Local mechanical factors
|
Venous return hindrance, IVC dilatation (stenosis, thrombosis)
|
FN
|
IVC compression (masses)
|
FP
|
||
Hindrance to IVC size change (ECMO cannulae, cava filters)
|
FN
|
||
10. Patients with pronounced IVC inspiratory lateral displacement
|
Migration of IVC imaging plane, false inspiratory size reduction
|
FP
|