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ORIGINAL ARTICLE
Year : 2020 | Volume
: 22
| Issue : 2 | Page : 151-155
Inferior vena cava collapsibility index for the assessment of fluid responsiveness among spontaneously breathing preoperative fasting patients - An observational study
Kiran Kalshetty1, Nikahat Jahan1, Rangraj Setlur1, Alok Jaiswal1, Deepak Dwivedi2
1 Department of Anesthesiology and Critical Care, Armed Forces Medical College, Pune, Maharashtra, India
2 Department of Anesthesiology and Critical Care, Command Hospital (SC), Pune, Maharashtra, India
Correspondence Address:
Col (Dr) Nikahat Jahan
Department of Anesthesiology and Critical Care, Armed Forces Medical College, Pune, Maharashtra
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/jmms.jmms_64_20
Background: It is challenging to assess intravascular volume status for clinicians caring for patients in the perioperative period. Previous studies have recommended the inferior vena cava collapsibility index (IVCCI) to assess the volume status of a patient. However, these studies have been carried out in mechanically ventilated patients with consistent tidal volumes. The evidence for this technique in spontaneously breathing patients is far weaker. This study was performed to assess if IVCCI was increased in spontaneously breathing fasting preoperative patients and if this measure decreased with a fluid bolus. Materials and Methods: After ethical approval and registration, we conducted a prospective study to assess the ability of IVCCI in fasting preoperative patients and the change in IVCCI after a fluid bolus. Fifty adult patients scheduled for surgery, who had been fasting for >6 h, had their IVCCI assessed by scanning of the IVC before and after a 500 ml normal saline intravenous fluid bolus. Results: Prior to the fluid bolus, 46 patients (92%) had an IVCCI of >12%, while 41 patients (82%) had a IVCCI of >12% after a fluid bolus. The mean IVCCI before the fluid bolus was 32.2% (standard deviation [SD] 13.4) and it reduced to a mean IVCCI of 26.3% (SD 20) after administration of a 500 ml fluid bolus, indicating fluid responsiveness. The value of P was < 0.001. Conclusion: In this study, IVCCI in spontaneously breathing patients was both a sensitive indicator of fluid depletion and had a high positive predictive value to identify fluid responsiveness.
Keywords: Collapsibility index, fluid responsiveness, inferior vena cava, ultrasound
Patients listed for elective surgery are often kept fasting overnight. This leads to dehydration-related hypovolemia and manifests as hypotension on the induction of general anesthesia or after administration of subarachnoid block. It has been shown that perioperative hypotension is associated with adverse postoperative outcomes, especially myocardial injury, acute kidney injury, and death.[1]
It is challenging to assess intravascular volume status for clinicians caring for patients in the perioperative period. Traditional methods of assessing fluid status, such as blood pressure and heart rate (HR), do not accurately and reliably identify fluid responders. Pulmonary artery catheter and central venous pressure for fluid status estimation are static indicators of preload with poor predictive value.[2],[3]
Previous studies have suggested that bedside ultrasound measurement of the inferior vena cava (IVC) diameter and its variability with respiration is a noninvasive and reliable method of estimating volume status of a patient.[4],[5],[6],[7]
The IVC is a large collapsible vein whose diameter varies with respiration, blood volume, and right heart function and reflects the volume status of the patient.[8],[9]
Hence, hypovolemia can be assessed by the collapsibility of IVC with respiration using bedside ultrasonography (USG). The collapsibility of the IVC has been extensively studied in critically ill patients as a marker of fluid responsiveness. An IVC collapsibility index (IVCCI) of more than 12% is considered significant and a marker of fluid responsiveness.[4] However, these studies have been carried out in paralyzed and mechanically ventilated patients with consistent tidal volumes,[8],[9] and the evidence of reliability of this technique in spontaneously breathing patients is far weaker.[10]
We carried out this study to examine whether IVC collapsibility in spontaneously breathing fasting preoperative patients was present and whether this IVC collapsibility could be reduced by administration of a fluid bolus. We hypothesized that this would provide evidence both of IVCCI to detect relative hypovolemia and its ability to detect fluid responsiveness.
Materials and MethodsAfter obtaining approval of the Institutional Ethics Committee and obtaining a Clinical Trials Registry – India registration, a prospective study was conducted to assess the prevalence of IVC collapsibility in fasting preoperative patients and if the change in IVCCI after a fluid bolus predicted fluid responsiveness.
The inclusion criteria were healthy adults, aged 18 years or more in American Society of Anesthesiologists Physical status (ASA PS) I or ASA PS II, fasted for 8 h or more, and patients listed for elective surgery.
Exclusion criteria were patients in ASA PS III, IV, and V pregnant women, patients with abdominal mass or ascites, fasting duration of <8 h, and patients listed for emergency surgery.
The study was conducted in the preoperative waiting area of the operation theater. Informed consent was obtained.
Using a USG machine and a 3 Mhz echocardiography probe, IVC diameter was measured during inspiration and expiration using the M-Mode in the subxiphoid view. IVC diameter collapsibility was measured. Following this, a 500 ml bolus of 0.9% normal saline was administered over 20 min and then IVC diameter collapsibility measurement was repeated. The two sets of readings that is the IVC diameter collapsibility before and after fluid bolus were compared to assess fluid responsiveness.
The study was carried out by a junior resident who had completed the focus-assessed transthoracic echocardiography course. A senior anesthesia faculty who supervised the study validated all measurements and images.
Sample size
Prior to this study, a pilot study was carried out to determine the mean and standard deviations before and after fluid bolus. Based on the pilot study, to detect a difference of >12% IVC collapsibility for an alpha of 0.01 and a beta of 0.9, a sample size of 23 in each group was calculated. As a measure of abundant caution, we recruited 50 patients in each arm and each patient was his/her own control arm.
Duration of the study
The study was carried out over a 12-month period from March 2019 to March 2020.
Technique of inferior vena cava diameter measurement
Following informed consent, patients who fulfilled the inclusion criteria were assessed in the preoperative room. Height, weight, body mass index (BMI), and baseline non invasive blood pressure (NIBP) and HR were recorded. The patient was positioned supine on a couch. Using a portable Sonosite (Model S-ICU S-N003) ultrasound machine and an echocardiographic probe (1–5 MHz), a subxiphoid view of the heart was obtained.[11] Once the right atrium (RA) was well visualized, the echocardiographic probe was turned counterclockwise to visualize the IVC entering the RA. Pulse wave Doppler was used to differentiate the aorta from the IVC. Variations in IVC diameter with respiration were assessed using a full-screen trace of M-mode imaging at the point of entry of hepatic vein into the IVC. Once a good trace of the IVC on M-Mode was obtained, the image was frozen, and the maximum (dIVCmax) and minimum IVC diameter (dIVCmin) was measured using the calipers' feature and IVCCI was calculated [Figure 1]. Following this, a 500 ml of 0.9% normal saline fluid bolus was administered through an 18G intravenous (IV) cannula over 20 min. Immediately after this, a second set of measurements of the maximum and minimum IVC diameter were recorded. IVCCI was calculated. The IVC diameter CI was calculated by the following formula:
IVCCI = ([dIVCmax − dIVCmin]/dIVCmax) ×100
The difference between the before and after measurements was noted. Although the location of the hepatic vein is variable from patient to patient, it provides a fixed point which can be used for measurement in a before and after study in the same patient.
Statistical analysis
The null hypothesis was that there was no statistically significant difference in CI before and after bolus of fluid.
The alternate hypothesis was that there is a difference in CI before and after fluid bolus, indicating that IVCCI is a reliable indicator of fluid responsiveness in spontaneously breathing preoperative patients who are likely to be dehydrated due to prolonged fasting.
A Chi-square test was used to analyze categorical variables and continuous variables were analyzed using a paired two-tailed t-test.
ResultsWe recruited 53 patients in our study. Three patients were excluded due to poor sonoanatomy leading to nonvisualization of the IVC. Data from the remaining 50 patients were analyzed. Thirty-nine patients were male and 11 were female. Their mean age was 39.86 years and ranged from 18 years to 68 years, and the mean BMI was 25.2 kg/m2. The average duration of fasting was 10.98 h [Table 1].
Prior to the fluid bolus, 46 patients (92%) had an IVCCI of >12%, while 41 patients (82%) had an IVCCI of >12% after a fluid bolus. Paradoxically, in five patients (10%), the IVCCI increased after administration of the fluid bolus.
Prior to the fluid bolus, the mean maximum diameter of the IVC (dIVCmax) was 1.69 cm (standard deviation [SD]: 0.33) and the mean minimum diameter (dIVCmin) was 1.16 cm (SD: 0.38), leading to a mean IVCCI before fluid bolus of 32.2% (SD: 13.4). This degree of collapsibility indicates that most of the patients were dehydrated, preoperatively due to fasting.
After administration of a 500-ml fluid bolus, the mean maximum IVC diameter (dIVCmax) was 1.84 cm (SD 0.30) and the mean minimum IVC diameter (dIVCmin) was 1.41 cm (SD: 0.35). The IVCCI after administration of the fluid bolus was 23.7% (SD: 10.3). The mean percentage change in IVCCI before and after the fluid bolus was 26.3% (SD: 20). The reduction in IVCCI from 32.2% to 26.3% after administration of a fluid bolus indicates that these patients were fluid responsive. However, even with a fluid bolus of 500 ml, the mean IVCCI was 26.3% (SD: 20), indicating that the patients remained hypovolemic and the fluid deficit was larger than 500 ml.
In majority of cases, IVCCI decreased after administration of the fluid bolus; however paradoxically, in six patients, the IVC diameter collapsibility increased after giving the fluid bolus. The increase in IVCCI in those six cases after administration of fluid bolus varied from 1.6% to 15.1%.
However, in all other cases, the IVCCI decreased after giving fluid bolus and the average decrease in IVCCI was 23.7% (SD 10.3). The data were analyzed using a two-tailed t-test and P < 0.001.
In spite of modern fasting guidelines, patients undergoing elective surgery frequently do not drink water for periods longer than 6 h. This prolonged duration of fasting lead in our study to dehydration and hypovolemia, as indicated by a mean baseline IVCCI of 32.2% (SD 13.4). The IVCCI reduced to 26.3% (SD 20) after administration of a 500 ml fluid bolus, indicating fluid responsiveness. This indicates that in our study subjects, IVCCI is both a sensitive indicator of fluid depletion and it has a high positive predictive value to identify fluid responsiveness [Table 2].
Table 2: Measured inferior vena cava diameters and inferior vena cava collapsibility index Discussion A majority of patients presenting for surgery and anesthesia have a functional intravascular volume deficit before surgery. This is due to prolonged fasting in the preoperative period which in spite of the modern guidelines is much longer than required or recommended.[12],[13],[14] This deficit is generally minor, but a fraction of patients present with a deficit that may be of clinical relevance, emphasizing the importance of an individual approach of goal-directed fluid therapy.[15]
We evaluated IVCCI as a possible bedside test for identifying patients who are significantly hypovolemic preoperatively. IVC diameter collapsibility has been the subject of many studies as well as systemic reviews and meta-analysis in critically ill patients as a noninvasive method of assessment of volume status and fluid responsiveness.[9],[16],[17]
The IVCCI as a predictor of fluid responsiveness was initially validated in paralyzed mechanically ventilated patients.[9] There are few studies on IVCCI in spontaneously breathing patients. Airapetian et al. studied spontaneously breathing patients in the intensive care unit who had suspected hypovolemia and found that IVC diameter was not predictive of fluid responsiveness, but respiratory variations of IVC >42% had a high specificity to predict an increase of cardiac output after fluid infusion.[18]
Szabó et al. conducted an observational study on 83 patients to assess the role of IVCCI to predict hypotension associated with general anesthesia. They concluded that in spontaneously breathing preoperative noncardiac surgical patients, preoperatively detected IVCCI ≥50% can predict postinduction hypotension with high specificity, but it has a low sensitivity. They suggested that despite moderate performance, IVCCI is an easy, noninvasive, and attractive option to identify patients at risk.[18]
Ceruti et al. conducted a study on patients scheduled to undergo surgery under spinal anesthesia (SA). They randomized 160 patients into two groups. In one group, the IVCCI was used to identify patients who were fluid responders, that is patients with an IVCCI >36%. These patients were given fluid boluses of 500 ml till they became fluid nonresponder based on IVCCI <36%. The other group received usual treatment and their IVCCI was not measured. The IVCCI group received more preoperative fluids and had less hypotension and less requirement of vasopressors as compared to the control group. Overall, fluid requirement was not different between both the groups. They concluded that IVC ultrasound is an effective method to prevent post-SA hypotension by IVC ultrasound-guided fluid administration before SA.[19]
On the other hand, Mačiulienė et al. conducted a study on patients undergoing elective knee replacement surgery to evaluate the change of IVCCI in spontaneously breathing patients during SA to predict manifestation of intraoperative hypotension and bradycardia. There were no significant changes in IVCin (inspiration), IVCex (Expiration), and IVCCI compared to baseline and other time point measurements in hypotensive versus nonhypotensive and bradycardic versus nonbradycardic patients (P > 0.05). The study authors concluded that reduction in IVC diameters and increase in IVCCI did not predict hypotension and bradycardia in spontaneously breathing patients under SA for elective knee joint replacement surgery.[20]
Jaremko et al. also studied the role of IVCCI in predicting hypotension after SA in patients undergoing elective knee replacement surgery. They found that the baseline preoperative IVCCI was not predictive of hypotension on administration of SA.[21]
Muller et al. conducted a study on 40 patients in acute circulatory failure and looked at IVCCI and echocardiographic measurements and found that IVCCI of >40% indicated fluid responsiveness; however, IVCCI <40% did not exclude fluid responsiveness. They concluded that despite being simple to use, IVC collapsibility should be interpreted cautiously in spontaneously breathing patients with acute circulatory failure. Their study suggests that IVCCI has a good positive predictive value but a low negative predictive value.[10]
In a commentary on the Muller study, Bodson and Barron state that it is hazardous to manage intraoperative IV fluids in a spontaneously breathing patient using IVC diameter variations only until further data are published. Alternative methods such as passive leg raising and a mini-fluid challenge could be used.[22]
In a review, Mandeville and Colebourn conclude that transthoracic echocardiography is a powerful noninvasive tool for assessment of critically ill patients, and transaortic stroke volume variation with the respiratory cycle and IVC diameter changes with respiration provide good prediction of the likelihood of a response to a fluid bolus. The techniques can be used individually to address the needs of different patients.[23]
To summarize the literature available on the subject, there is a huge variation in the way the studies were conducted, which makes it difficult to compare them. The patient characteristics are diverse, as also the cutoff values for what is considered a significant CI. Moreover, some studies have looked at the IVCCI and the others have looked at the IVC distensibility index (IVCDI). The difference between the two is that the IVCCI has dIVCmax as its denominator, while IVCDI has dIVCmin as its denominator and the cutoff values for fluid responsiveness are 12% and 18%, respectively.[24]
Moreover, some studies done on spontaneously breathing patients have taken an IVCCI of >40% as indicative of fluid responsiveness.[10]
In our study, we looked at 50 patients and we assessed the IVCCI in fasting preoperative patients before and after a fluid bolus of 500 ml normal saline. We observed that all patients had increased IVC collapsibility prior to surgery. This could be due to both the facts that patients are fasting longer than recommended and that India being a tropical country with mostly nonair-conditioned hospital wards leads to higher insensible fluid loss. This finding might not be seen in centers where air-conditioning is present in the wards.
Limitations of the study
This is a single-center observational study done on healthy ASA I and II patients and these findings may not be valid in patients in ASA III and IV who may have comorbid conditions that interfere with IVC diameter measurements. These findings are also not applicable to patients with lung and abdominal pathologies.
This study was not conducted with the aim of determining any IVCCI threshold for fluid responsiveness in spontaneously breathing patients. The study did not assess whether the patients with increased IVCCI actually developed hypotension under anesthesia-general or subarachnoid block. Randomizing patients into two groups where one group was given fluids preoperatively based on the IVCCI and the other group that was not given fluids and then assessing the incidence of hypotension in both the groups on the induction of anesthesia would have strengthened the clinical value of the IVCCI as a predictor of fluid responsiveness.
ConclusionOur findings suggest that healthy patients listed for elective surgery are fasting longer than the recommended 6 h preoperatively, and as a result, they are dehydrated and hypovolemic. Measurement of the IVCCI in spontaneously breathing healthy patients awaiting elective surgery is a reliable method to assess both their volume status and fluid responsiveness. Assessing fluid status in the preoperative period and giving fluids preoperatively, wherever indicated, could lead to reduced incidence of hypotension on induction of general anesthesia or administration of subarachnoid block.
Based on our study, we conclude that IVCCI has both the ability to predict fluid depletion and identify fluid responders. As the literature in the field has shown varying results, it may be advisable to wait for larger studies or for a systemic review or meta-analysis before making a firm conclusion. For effective meta-analysis, it is important that a consistent means of reporting of IVCCI is agreed upon.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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