Table 2.
Relationship of Subclavian Vein to Inferior Vena Cava Data for Our Study, and Comparison to Data Derived from Previous Studies
| Author/Year | Kaptein (Current study) | gMunir (2007)16 | gMunir (2007)16 | gKent (2013)13 | |||||
|---|---|---|---|---|---|---|---|---|---|
| Patient population | Medical with acute and/or chronic kidney disease | Medical requiring echocardiography | Surgical ICU | ||||||
| Respiratory status | Spontaneous breathing | Mechanical ventilation | Spontaneous breathing | Spontaneous breathing | Mixed Spontaneous breathing and Mechanical ventilation | ||||
| Patient position for SCV & IVC US | 30 to 45 degrees (Subclavicular) | 30 to 45 degrees (Subclavicular) | IVC flat/SCV 45 degrees (Supraclavicular) | IVC flat/SCV flat (Supraclavicular) | Not specified (Subclavicular) | ||||
| Correlation of SCV CI to IVC CI | 0.67 (n=95)a | 0.75 (n=65)a,c | 0.69 (n=39)a | 0.34 (n=39)b | 0.78 (n=94)a | ||||
| SCV CI cut-offs (%) and (95% confidence limits) at maximal Sensitivity and Specificity | |||||||||
| IVC CI hypervolemia cut-off (%) (IVC CI<20%) | 22 (21 to 23)e | 22 (21 to 23)e | 32d (30 to 34)e | N/A | 23 (23 to 24)e | ||||
| IVC CI hypovolemia cut-off (IVC CI>50%) | 39 (37 to 41)e | 39 (38 to 40)e | 39 (37 to 40)e | N/A | 40 (40 to 41)e | ||||
| SN/SP (%) | 74 (72 to 75)e | 70 (69 to 73)e | 88 (86 to 89)e | 91 (89 to 93)e | 81 (77 to 85)e | 82 (80 to 85)e | N/A | 81 (80 to 82)e | 85 (84 to 89)e |
| AUC (area±SD) | 0.828±0.043f | 0.739±0.058f | 0.917±0.037f | 0.925±0.032f | 0.826±0.078f | 0.871±0.058f | N/A | 0.878±0.035f | 0.924±0.035f |
| Concordance of IVC CI assessment to SCV CI assessment | Hypervolemia/not hypervolemia | Hypovolemia/not hypovolemia | Hypervolemia/not hypervolemia | Hypovolemia/not hypovolemia | Hypervolemia/not hypervolemia | Hypovolemia/not hypovolemia | N/A | Hypervolemia/not hypervolemia | Hypovolemia/not hypovolemia |
| Concordance (%) | 72 | 71 | 85 | 89 | 77 | 82 | N/A | 77 | 84 |
| PPV (%) | 53 | 39 | 86 | 67 | 68 | 72 | N/A | 74 | 30 |
| NPV (%) | 84 | 90 | 83 | 98 | 85 | 91 | N/A | 80 | 99 |
| + LR | 2.5 | 2.4 | 5.0 | 8.0 | 3.1 | 4.2 | N/A | 3.1 | 5.1 |
| - LR | 0.43 | 0.42 | 0.17 | 0.09 | 0.25 | 0.17 | N/A | 0.27 | 0.17 |
Notes: aP<0.001and bP<0.05indicates the significance of the correlation (R). cP=0.32 comparing correlation (R) values for spontaneous breathing encounters with mechanically ventilated encounters for our data. dCut-off may vary from that of the other two studies due to widely scattered and small data set (Figure 2E). The right SCV was imaged from the supraclavicular approach with the probe positioned above the medial end of the clavicle in the fossa between the sternal and the clavicular heads of the sternocleidomastoid muscle.16 e95% confidence interval. fP <0.001 testing whether AUC is =0.5. gData were extracted and transformed from published figures. For the data from Munir et al,16 collapsibility index ((max-min)/max) was derived from (1-the ratio of min/max) for both SCV CI and IVC CI. +LR is likelihood of a positive result for a positive patient/likelihood of a positive result for negative patient eg for a +LR >5.0, a positive result is 5 times more likely to be a true positive rather than a false positive. -LR is similar, eg for a –LLR <0.2, a negative result is 5 times more likely to be a true negative rather than a false negative. (is 0.2 times as likely to be a positive patient than a negative patient). +LR and –LR are independent of prevalence (ie distribution of the data) whereas PPV and NPV (positive predictive value and negative predictive value; fraction of positive/negative predictions that are correct) are affected by prevalence. DI and CI are mathematical transformations of each other as follows: DI =CI/(100%-CI) * 100%; CI=DI/(100%+DI) * 100%. Thus, an IVC CI cut-off of <20% for hypervolemia with spontaneous breathing and mechanical ventilation corresponds to an IVC DI cut-off of <25% and an IVC CI cut-off of >50% for hypovolemia in both spontaneous breathing and mechanical ventilation encounters corresponds to an IVC DI cut-off of >100%. An SCV CI cut-off of <22% corresponds to an SCV DI cut-off of <28% for predicting hypervolemia and SCV CI cut-off of >39% corresponds to a SCV DI cut-off of >64% for predicting hypovolemia.
Abbreviations: AUC, area under the curve expressed as a fraction of the total area; CI, collapsibility index; ICU, intensive care unit; IVC, inferior vena cava; LR, likelihood ratio; NPV, negative predictive value; PPV, positive predictive value; SCV, subclavian vein; SN, sensitivities; SP, specificities; US, ultrasound.