Detecting the need for fluid resuscitation remains a challenge for the intensive care physician in managing patients on mechanical ventilation. Different methods exist with variable sensitivity and specificity. The End-Expiratory Occlusion Test, or EEO Test, is a simple tool that can reliably help the clinician in determining the fluid resuscitation goal. This brief procedure should increase cardiac preload and can serve as a test to assess preload responsiveness and hence predicts the response to a subsequent fluid infusion. In this blog, we will try to answer the following questions based on the most recent evidence:
What is the EEO test and how can it be used to assess fluid responsiveness in ICU patients?
How reliable is the EEO test to detect fluid responsiveness?
How to perform the test and how its effects are detected?
What are the limitations of the EEO test
What is the EEO test and how can it be used to assess fluid responsiveness in ICU patients?
The EEO is a way of assessing changes in cardiac output (CO) levels during positive pressure ventilation. The test consists of interrupting the ventilator at end-expiration for 15 to 30 seconds and then observing the resulting changes in CO levels. This suppresses the cyclic decrease in cardiac preload, which normally occurs at each mechanical insufflation. During positive pressure ventilation, insufflation increases intrathoracic pressure, which is transmitted to the right atrial pressure. This, in turn, decreases the backward pressure of venous return. When ventilation is stopped in expiration, at the level of positive end-expiratory pressure (PEEP), the cyclic impediment in venous return is interrupted and the right cardiac preload reaches its maximum. If EEO is performed for a long enough duration, the increase in right cardiac preload is transmitted to the left side. An increase in stroke volume and CO in response may indicate preload responsiveness of both ventricles. Hence the idea that, if the respiratory cycling was interrupted at the end of Expiration, then this will act as a fluid challenge without subjecting the patient to the danger of excess fluid if he is not fluid responsive.
Do you use EEO test in the assessment of fluid responsiveness in MV Patients?
- Yes
- No
- Never heard of it!
How reliable is the EEO test to detect fluid responsiveness?
Multiple studies have examined the reliability of the EEO in determining fluid responsiveness. In a study published in critical care medicine in 2009, the investigators found that an increase in the cardiac index of 5% or more during a 15-second EEO reliably predicted the response to a 500-mL saline infusion in critically ill ventilated patients with sensitivity and specificity of 91% and 100% respectively [1]. At least 10 out of 12 other studies have confirmed this high reliability with areas under the receiver operating characteristic curve (AUROC) ranging from 0.90 to 1.00 The test was more reliable if performed with a tidal volume at 8 mL/kg but can be done with 6 mL/kg. or higher [2].
In a systematic review and meta-analysis, Gavelli et al. included thirteen studies with a total of 530 patients and revealed a pooled sensitivity and the specificity for the EEO test-induced changes in CO were 0.85 [0.77-0.91] and 0.88 [0.83-0.91], respectively. The AUSROC curve was 0.91 [0.86-0.94]. The accuracy of the test was not different when changes in CO were monitored through pulse contour analysis compared to other methods (AUSROC: 0.93 vs. 0.87, p = 0.62). Also, it was not different in studies in which the tidal volume was ≤ 7 mL/kg compared to the remaining ones (AUSROC: 0.96 vs. 0.89, p = 0.44) [3].
How to perform the test and how its effects are detected?
The test can be performed with an expiratory hold similar to the maneuver that you use to detect auto-PEEP. Ideally, tidal volume (VT) should be 8ml/kg, but the test can be performed with 6ml/kg of TV. The duration of the expiratory hold should be at 15 seconds but can be increased up to 30 seconds (most studies 15-20s). The test can be done with an extrinsic PEEP of as high as 14 cm H2O (as in one study without affecting the reliability of the test). The test is still reliable even if the patient had occasional spontaneous breaths provided that they do not interrupt the EEO.
Hemodynamic changes in cardiac output are mainly observed in the last seconds of a 15s test. A 5% change in cardiac output is considered an indicator of fluid responsiveness. Surrogate of cardiac output such as arterial pulse pressure has been used but results need to be confirmed [1]. Pulse contour analysis methods can estimate beat-to-beat variation in stroke volume and cardiac output and provide real-time and precise measurement using different devices (e.g. PiCCO, EV 1000, FloTrac). Other methods that are sensitive to detecting a 5% change in cardiac output can be used [2].
What are the limitations of the EEO test
The EEO should not be used as the sole indicator of fluid responsiveness and should be combined with other clinical signs and hemodynamic parameters such as pulse pressure variation and IVC IVC indices. There are some situations where the test is not reliable such as arrhythmias, low cardiac output states, or when there is a significant shunt. The EEO can only be used on patients who are mechanically ventilated and it is not possible to use this test on spontaneously breathing patients.
Some patients with intense spontaneous breathing activity may not be able to sustain a 15-s expiratory hold. As mentioned above, the test can be performed with a PEEP level as high as 14 cm H2O. Higher levels of PEEP may affect the reliability of the test. Two studies reported that the test was not reliable with a tidal volume of 6 mL/kg, this needs further investigation. Finally, the test should perform similarly in the prone position, however, one study found poor reliability and requires further investigations.
Conclusion
The End-Expiratory Occlusion Test is a reliable tool used by clinicians to assess fluid responsiveness in ICU patients. The test can be used to measure the patient's cardiac output in response to preload during an end-expiratory hold in patients on mechanical ventilation. The EEO Test is easy to perform and clinicians should use the results of the test to determine if a patient is responsive to increased fluids. However, there are some limitations to using the EEO test and the clinician should be aware of such limitations. The test should not be used as the sole indicator of fluid responsiveness.
REFERENCES
Monnet X, Osman D, Ridel C, Lamia B, Richard C, Teboul J-L. Predicting volume responsiveness by using the end-expiratory occlusion in mechanically ventilated intensive care unit patients. Crit Care Med. 2009;37:951–6.
Gavelli, F., Teboul, JL. & Monnet, X. The end-expiratory occlusion test: please, let me hold your breath!. Crit Care 23, 274 (2019). https://doi.org/10.1186/s13054-019-2554-y.
Gavelli F, Shi R, Teboul JL, Azzolina D, Monnet X. The end-expiratory occlusion test for detecting preload responsiveness: a systematic review and meta-analysis. Ann Intensive Care. 2020 May 24;10(1):65. doi: 10.1186/s13613-020-00682-8. PMID: 32449104; PMCID: PMC7246264.