Our findings demonstrate the value of the internal jugular vein distensibility index and the inferior vena cava collapsibility index in predicting fluid responsiveness in spontaneously breathing septic patients.
The main issue facing septic patients is circulatory failure which is often the result of hypovolemia, profound vasodilatation, or both. Therefore, volume expansion may be beneficial in improving tissue perfusion and prognosis or hazardous in causing volume overload and worsening previous cardiac condition or gas exchange. The use of vasopressors may limit vigorous vasodilatation and improve tissue perfusion or cause tissue hypoxia and worsen the condition (Wiedemann et al., 2006).
Static hemodynamic parameters have been found to be of little clinical value by many studies if compared to dynamic parameters in predicting fluid responsiveness (Preisman et al., 2005; Osman et al., 2007). Dynamic predictors for fluid responsiveness are more precise, but some of them are invasive procedures (Theerawit et al., 2016; Guerin et al., 2013).
Ultrasound has become one of the cornerstones of modern ICU. It can be used in daily ICU practice to measure the different dynamic predictors of fluid responsiveness (Theerawit et al., 2016; Orso et al., 2016), such as inferior vena cava collapsibility index (variation of IVC diameter with respiration) (Barbier et al., 2004; Feissel et al., 2004) and internal jugular vein distensibility index to differentiate between fluid responders and nonresponders (Guarracino et al., 2014).
Any pressure or volume change in the intrathoracic systemic venous system is reflected in the extrathoracic system, such as the inferior vena cava and the internal jugular vein (Chiaco et al., 2013).
This observational cross-sectional study has been conducted for 1 year in the ICU. Collected data from 40 patients were analyzed for reaching the final results. We studied IVC-CI and IJV-DI in terms of their reliability and effectiveness as simple bedside noninvasive dynamic tools to define fluid responsiveness in spontaneously breathing septic patients.
Our study demonstrated that changes in the internal jugular vein and the inferior vena cava accompanied with respiration are well-correlated with fluid responsiveness.
Patients in our study were defined as responders when their CI increased by 15% or more after 30 min of fluid resuscitation with 7 ml/kg crystalloid (Ringer Acetate). The responders represented 60% of the cases.
Our study found that the inferior vena cava collapsibility index (IVC-CI) > 35% was a good tool to predict fluid responsiveness with AUC 0.97, revealing sensitivity of 95.8% and specificity of 93.7% with positive predictive value of 95.8 and negative predictive value of 93.7 (p value < 0.001) and 95% confidence interval from 0.861 to 0.999.
Furthermore, our study revealed that the internal jugular vein distensibility index (IJV-DI) > 17.65% was a good predictor for fluid responsiveness with AUC 0.969, revealing sensitivity of 95.83% and specificity of 87.5% with positive predictive value of 92 and negative predictive value of 93.3 (p value < 0.001) and 95% confidence interval from 0.859 to 0.999.
Regarding the inferior vena cava collapsibility index, in line with our study, Caplan et al. (Caplan et al., 2020) (who studied the effect of the site of measurement of IVC readings), confirmed the predictive power of IVC variability of fluid responsiveness in spontaneously breathing septic patients. They collected data from 81 patients. Patients were considered responders with increased SVI (systolic volume index) > 10% after intravenous administration of 500 ml of 4% Gelatin. They found that 4 cm from the right atrium–ivc junction is the best site to measure IVC with AUC 0.85, cutoff value of 33%, sensitivity of 66%, and specificity of 92% (Caplan et al., 2020).
In the same context, Pereira et al. (Pereira et al., 2020) compared pulse pressure variation (ppv) and IVC variation as predictors for fluid responsiveness in surgical patients. They conducted their study on 22 patients and stated that patients with ppv > 13% were considered fluid responsive. They also discovered that IVC variation had strong predictive value with cutoff value > 40%, AUC 0.98, sensitivity of 100%, and specificity of 93.3% for the IVC collapsibility index (Pereira et al., 2020).
Furthermore, Sanchez et al. (Sánchez et al., 2021) collected data from 33 studies conducted on 1352 patients to assess predictors for fluid responsiveness in mechanically ventilated patients at tidal volume ≤ 8 ml/kg. They found that IVC variation strongly predicts fluid responsiveness with AUC 0.86, sensitivity of 77%, and specificity of 87% at cutoff value of 16%. Their low cutoff value could be explained because it was conducted on mechanically ventilated patients, and different calculation equations were used (IVCmax − IVCmin/IVCmin) (Sánchez et al., 2021).
On the other hand, Pinar et al. (Pınar et al., 2020) measured the effectiveness of end-tidal carbon dioxide and inferior vena cava variation to assess fluid responsiveness in 31 spontaneously breathing patients. Patients were considered fluid responsive (15 patients) if cardiac output increased by > 15% after passive leg raising. They discovered that end-tidal carbon dioxide would be a good predictive, while IVC variation did not show a significant difference between responders and nonresponders with AUC 0.50 and 95% CI 0.32–0.69. The decision of the patients who required IV fluid treatment was at the discretion of the treating physicians, thus explaining the discordant results between the studies. Different treatment strategies of the treating physicians can affect the homogeneity of the study population (Pınar et al., 2020).
Moreover, Yao et al. (Yao et al., 2019) in a study on 67 mechanically ventilated patients compared IVC variation and IVC diameter ratio as predictors for fluid responsiveness. They concluded that IVC variation had weak correlation with fluid responsiveness, with AUC 0.68 and 95% CI 0.56–0.81, but they claimed that the reason for their results is the usage of assisted ventilation modalities. In the assisted ventilation modality, there is a variable contribution to inspiration because the unpredictable interplay of ventilator-generated positive pressure and patient-generated negative pressure confusingly influence the IVC. Additionally, because of the lung-protective ventilation strategy, their tidal volume is lower than 8 ml/kg. If the tidal volume is less than 8 ml/kg, it may cause smaller variations in intrathoracic blood volume and pressure, and IVC variation will be smaller. Therefore, these two factors can influence the IVC accuracy in predicting fluid responsiveness (Yao et al., 2019).
Regarding the internal jugular vein distensibility index, our results were confirmed by Haliloğlu et al. (Haliloglu et al., 2017) who collected hemodynamic data from 44 spontaneously breathing septic patients. They found that the IJV collapsibility index was a good predictor for fluid responsiveness with 78% sensitivity and 85% specificity at the cutoff value of 36%. Patients were considered responders with cardiac index increase > 15% after passive leg raising (Haliloglu et al., 2017). Their results are different from ours because of different calculation equations.
Our results are in accordance with the work of Lizuka et al. (Iizuka et al., 2020) who found that IJV variation is a useful predictor for fluid responsiveness when they carried out the study on 27 mechanically ventilated patients with acute circulatory failure. The study found AUC 0.88 and 95% CI 0.75–0.99 with sensitivity of 84% and specificity of 93% at the cutoff value of 11.4%. Patients were considered responsive with 8% increase in stroke volume measured by arterial pulse contour after passive leg raising (Iizuka et al., 2020). Their cutoff value differs from our results because of the usage of mechanical ventilation and different calculation equations.
In the same context, Ma et al. (Ma et al., 2018) confirmed our results stating that IJV is a strong predictor for fluid responsiveness with AUC 0.88, 95% CI 0.78–0.94, sensitivity of 91.2%, and specificity of 82.8% at cutoff value > 12.99%. They collected hemodynamic data from 70 mechanically ventilated post-cardiac surgery patients. Patients were classified as responders when stroke volume increased by > 15% after passive leg raise and intravenous infusion of 500 ml of Gelofusine (Ma et al., 2018). Their cutoff value differs from ours presumably because of mechanical ventilation usage and different calculation equations.
On the other hand, Unluer and Kara (Unluer & Kara, 2013) found that the IJV collapse index was not a useful parameter for the evaluation of hypovolemia in a study performed on 80 volunteers to assess hypovolemia after blood donation. The medians of IJV collapse indices before and after blood donation were 32.74 (95% CI 32.73–39.50) and 38.88 (95% CI 35.54–42.95), respectively. They argued that carotid artery as a pulsatile structure will cause a bias for measurement of IJV diameter, especially in the real traumatized hemorrhagic patient due to tachycardic state. In addition, even a little pressure will cause a great change in the cross-sectional image and diameter of the jugular vein during scanning. In patients with shock, venous scanning becomes more difficult. They also suggested that the longitudinal measure of the internal jugular vein is more accurate and of stronger prediction. Finally, their study was performed on healthy volunteers hemodynamically stable after blood donation who did not normally need fluid resuscitation, while our study was performed on hemodynamically unstable septic patients (Unluer & Kara, 2013).
Limitation
Our observational study has many limitations. The first one is the accuracy of measuring COP (cardiac output) by VTI (velocity time integral). Using TTE (transthoracic echo) necessitates good echogenicity of the patients, so we excluded patients who did not fulfill these criteria. Additionally, using TTE requires skilled personnel, and it was documented that learning this technique is not difficult among critical care doctors (Jozwiak et al., 2014).
The second limitation was the intra-abdominal pressure measure because we did not measure it in our patients. However, we excluded all patients with any expected cause of increased intra-abdominal pressure, like ascites, pregnancy, abdominal malignancy, distension, and acute abdomen.
The third limitation is that the carotid artery as a pulsatile structure will cause a bias for the measurement of IJV diameter. Even a little pressure will cause a great change in the cross-sectional image and diameter of the jugular vein during scanning, especially with tachycardia. The final limitation is that we did not study the prediction of our indices in ventilated patients.
