1. Correct Answer: D. Begin infusion of norepinephrine

Rationale: Intravascular volume resuscitation is a core competency among healthcare providers managing acutely ill patients. Unfortunately, there are few definitive answers to questions such as when to infuse fluids and how much to administer to a hypotensive patient. Furthermore, increasing evidence of harm from over-resuscitation suggests that a more judicious approach to volume resuscitation may be appropriate. There is no single monitor or metric that is invariably predictive—thus, integrating data from different sources is often the most useful approach. Ultrasound-guided fluid resuscitation, in the context of other commonly used indices of predicting fluid responsiveness, may help guide volume resuscitation. This patient presented with severe sepsis (life-threatening organ dysfunction caused by a dysregulated host response to infection). Volume resuscitation is recommended as the initial intervention to improve perfusion by the Surviving Sepsis Guidelines, specifically, at least 30 mL/kg of crystalloid within the first 3 hours of presentation. However, some key pieces of information should cause us to pause before further volume resuscitation—the fact that his BP has not changed after intravenous volume expansion, and that his oxygen saturation is decreasing (Option A is incorrect). In the absence of a detailed past medical history (history of heart failure or chronic kidney disease, for example) and without further examination, it is difficult to define whether his desaturation is from pulmonary edema (either cardiogenic or noncardiogenic) or from decreased alveolar ventilation in the setting of increasing drowsiness and respiratory fatigue. The presence of a bilateral anterior B-line profile on lung ultrasound suggests significant extravascular lung water (EVLW). A bilateral B-line profile has been suggested to correlate with a PCWP >18 mm Hg, but this is not invariably true. While it is possible to have a bilateral B-line profile in noncardiogenic pulmonary edema, given his decreasing oxygen saturation and clear evidence of worsening EVLW, starting the patient on norepinephrine (the initial vasoactive medication of choice in severe sepsis or septic shock) is reasonable while a more detailed assessment is carried out regarding further therapy. Dopamine is associated with worse outcomes for sepsis when compared to norepinephrine (Option C is incorrect). While supplemental oxygenation is not unreasonable, there is no indication for a non-rebreathing mask—the degree of hypoxemia (SpO₂ 89% on room air) does not warrant a non-rebreather (Option B is incorrect).

1. Bentzer P, Griesdale DE, Boyd J, MacLean K, Sirounis D, Ayas NT. Will this hemodynamically unstable patient respond to a bolus of intravenous fluid? JAMA 2016;316:1298-1309.

2. De Backer D, Aldecoa C, Njimi H, Vincent JL. Dopamine versus norepinephrine in the treatment of septic shock: a meta-analysis. Crit Care Med. 2012;40(3):725-730.

3. De Backer D, Biston P, Devriendt J, et al. Comparison of dopamine and norepinephrine in the treatment of shock. N Engl J Med. 2010;362(9):779-789.

4. Lichtenstein DA, Meziere GA, Lagoueyte J-F, Biderman P, Goldstein I, Gepner A. Lung ultrasound as a bedside tool for predicting pulmonary artery occlusion pressure in the critically ill. Chest. 2009;136:1014-1020.

5. Picano E, Pellikka PA. Ultrasound of extravascular lung water: a new standard for pulmonary congestion. Eur Heart J. 2016;37:2097-2104.

6. Price S, Platz E, Cullen L, et al. Echocardiography and lung ultrasonography for the assessment and management of acute heart failure. Nat Rev Cardiol. 2017;14:427-440.

7. Rhodes A, Evans LE, Alhazzani W, et al. Surviving sepsis campaign: international guidelines for the management of sepsis and septic shock: 2016. Crit Care Med. 2017;45:486-552.

8. Singer M, Deutschman CS, Seymour CW, et al. The third international consensus definitions for sepsis and septic shock (sepsis 3). JAMA. 2016;315(8):801-810.

9. Volpicelli G, Skurzak S, Boero E, et al. Lung ultrasound predicts well extravascular lung water but is of limited usefulness in the prediction of wedge pressure. Anesthesiology. 2014;121:320-327.

2. Correct Answer: C. No change in the velocity-time integral (VTI) obtained at the left ventricular (LV) outflow tract (LVOT) following a passive leg raise maneuver

Rationale: Frequent assessment of the patient’s clinical status should drive fluid administration, particularly as over-resuscitation has been shown to be associated with adverse consequences. A CVP of 8 cm H₂O does not discriminate effectively between patients that will or will not benefit from additional intravascular volume expansion. The value of respiratory variation in IVC diameter in spontaneously breathing patients to determine fluid responsiveness is unclear. The EF by itself is not particularly useful in identifying patients who will increase their cardiac output following a fluid bolus. The change in the VTI at the LVOT in response to a passive leg raise maneuver can be used to predict volume responsiveness, by “autotransfusing” intravascular volume from the lower extremities into the central circulation and evaluating the change in stroke volume. Since the LVOT diameter remains constant in a given patient, stroke volume is directly proportional to the LVOT VTI. Given the information available, the absence of an increase in the VTI in response to passive leg raise predicts a lack of volume responsiveness (Figure 49.6). In this context, additional intravascular volume is unlikely to provide a hemodynamic benefit and more likely to exacerbate deleterious effects.

1. Airapetian N, Maizel J, Alyamani O, et al. Does inferior vena cava respiratory variability predict fluid responsiveness in spontaneously breathing patients? Crit Care. 2015;19:400.

2. Marik PE, Cavallazzi R. Does the central venous pressure predict fluid responsiveness? An updated meta-analysis and a plea for some common sense. Crit Care Med. 2013;41:1774-1781.

3. Vignon P, Repessé X, Bégot E, et al. Comparison of echocardiographic indices used to predict fluid responsiveness in ventilated patients. Am J Respir Crit Care Med. 2017;195:1022-1032.

3. Correct Answer: C. An S′ velocity at the tricuspid annulus of 6 cm/s and diastolic flattening of the interventricular septum in the parasternal short-axis mid-papillary view.

Rationale: The findings in Option A are consistent with significant intravascular hypovolemia, which could present as pulse pressure variation and would likely respond to volume resuscitation. Echocardiographic features described in Option B are consistent with pericardial tamponade. Rapid volume expansion is a key supportive measure while definitive management (drainage or evacuation of the effusion) is being arranged, particularly in hypotensive patients (systolic BP <100 mm Hg). The findings described in Option C are consistent with RV dysfunction and volume overload of the right ventricle. RV dysfunction can also present with pulse pressure variation due to ventricular interdependence. One well-validated echocardiographic marker of RV systolic function is tissue Doppler interrogation (TDI) of the tricuspid annulus velocity (S′). An S′ velocity <10 cm/s is consistent with RV dysfunction (Figure 49.7). In the setting of RV dysfunction, further fluid administration should be undertaken with caution, if at all. A focused point-of-care echocardiography examination can rapidly differentiate between these three key causes of pulse pressure variation and, if available, should be considered in the evaluation of all hemodynamically unstable patients.

1. Magder S. Further cautions for the use of ventilatory-induced changes in arterial pressures to predict volume responsiveness. Crit Care. 2010;14(5):197.

2. Mahjoub Y, Pila C, Friggeri A, et al. Assessing fluid responsiveness in critically ill patients: false-positive pulse pressure variation is detected by Doppler echocardiographic evaluation of the right ventricle. Crit Care Med. 2009;37:2570-2575.

3. Rudski LG, Lai WW, Afilalo J, et al. Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. J Am Soc Echocardiogr. 2010;23(7):685-713.

4. Sagrista-Sauleda J, Angel J, Sambola A, Permanyer-Miralda G. Hemodynamic effects of volume expansion in patients with cardiac tamponade. Circulation. 2008;117:1545-1549.

4. Correct Answer: D. Given a VTI variation of 25%, his cardiac output is likely to increase with a fluid bolus.

Rationale: Although the patient is oliguric and has lactic acidosis, there is not enough information to determine whether renal replacement therapies should be initiated immediately (Option A). If, for instance, his cardiac output improves with a fluid bolus, his lactic acidosis may decrease and urine output increase. A PCWP of 16mm Hg does not reliably discriminate between volume responders and nonresponders (Option B). It is important to remember that the static indices of volume status (e.g., PCWP, CVP, or EF) are of very limited value in defining patients who are volume responsive. Dynamic indices of fluid responsiveness, on the other hand, look at the effect of a physiologic perturbation of venous return and its influence on cardiac output. This may involve respirophasic variation or assessing response to small fluid boluses or passive leg raising, among others. Variation in LVOT VTI >20% with controlled respiration predicts volume responsiveness, although the sensitivity of this finding may be reduced in patients being ventilated with low tidal volumes (<8 mL/kg); however, lower tidal volumes are likely to underestimate volume responsiveness. It is unclear whether epinephrine is better than a combination of norepinephrine and dobutamine (Option C). The CATS trial addressed this question in patients with septic shock and found that the two approaches were largely equivalent, with the exception of a higher incidence of lactic acidosis with epinephrine.

1. Annane D, Vignon P, Renault A, et al. Norepinephrine plus dobutamine versus epinephrine alone for management of septic shock: a randomised trial. Lancet. 2007;370:676-684.

2. Bentzer P, Griesdale DE, Boyd J, MacLean K, Sirounis D, Ayas NT. Will this hemodynamically unstable patient respond to a bolus of intravenous fluid? JAMA 2016;316:1298-1309.

3. De Backer D, Fagnoul D. Intensive care ultrasound: VI. Fluid responsiveness and shock assessment. Ann Am Thorac Soc. 2014 11:129-136.

4. Marik PE, Monnet X, Teboul JL. Hemodynamic parameters to guide fluid therapy. Ann Intensive Care. 2011;1:1.

5. Correct Answer: A. A crystalloid bolus of 500 mL over 15 minutes is likely to increase her cardiac output.

Rationale: Although many critical care physicians use the CVP to make decisions regarding fluid administration, the CVP is a poor tool for this purpose (Option C). Like measuring changes in VTIs with respiration, changes in maximal aortic velocity >12% can predict fluid responsiveness, that is, an increase in cardiac output by 10-15% in response to a crystalloid bolus. An additional advantage of this technique is that it is quicker to measure the maximal velocity compared to tracing the VTI envelope. Although initiating diuresis (Option B) in patients on vasopressors who are grossly volume overloaded is not unreasonable, in the absence of those indications diuresis is often initiated after patients are no longer vasopressor dependent, as in the Fluid and Catheter Treatment Trial (FACTT). While the CVP is not particularly helpful in identifying patients who are fluid responsive, it can be very helpful in many contexts, including as a measure of RV dysfunction.

1. Cannesson M, Pestel G, Ricks C, Hoeft A, Perel A. Hemodynamic monitoring and management in patients undergoing high risk surgery: a survey among North American and European anesthesiologists. Crit Care. 2011;15:R197.

2. Feissel M, Michard F, Mangin I, Ruyer O, Faller JP, Teboul JL. Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock. Chest. 2001;119:867-873.

3. National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network, Wiedemann HP, Wheeler AP, Bernard GR, et al. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med. 2006;354:2564-2575.

6. Correct Answer: B. An increase of 15% in her pulse pressure on performing a passive leg raising test.

Rationale: Many of the dynamic indices of fluid responsiveness require stable ventilation with large tidal volumes (>8 mL/kg) to induce a sufficient perturbation in venous return that can reliably modify cardiac output. Similarly, most tests require the patient to be in a sinus rhythm. An important exception is the passive leg raising test, which has been shown to accurately predict fluid responsiveness in a broad range of patient conditions, including assisted or spontaneous ventilation, reduced lung compliance, and arrhythmias.

Ideally, the passive leg raise maneuver should be coupled with a measure of cardiac output or its surrogate (such as the VTI or aortic maximum velocity). If the expertise to measure VTI is unavailable, the pulse pressure variation (>12%) is an acceptable alternative. It is important to keep in mind that while changes in pulse pressure induced by passive leg raising are relatively specific, they are not very sensitive, which is why a metric of cardiac output is preferable.

Both IVC diameter variation (Option A) and pulse pressure changes with respiration (Option C) are not well-validated in spontaneously breathing patients and AF, although at least one study suggests that IVC diameter variation may remain valid in patients with dysrhythmias. While IVC collapse of >40-50% in spontaneously breathing patients is a specific predictor of fluid responsiveness, IVC collapsibility has poor sensitivity in this population, limiting its overall value. In any case, the IVC variation in this example is only 25%. As discussed earlier, CVP is not very useful in predicting volume responsiveness. It is also worth emphasizing that, while the respiratory variation in pulse pressure is not accurate in spontaneously breathing patients or in patients with arrhythmias, pulse pressure variation in response to passive leg raise may be. Note that, since this patient has AF, the change in pulse pressure should be averaged over a few heartbeats to improve accuracy.

1. Bortolotti P, Colling D, Colas V, et al. Respiratory changes of the inferior vena cava diameter predict fluid responsiveness in spontaneously breathing patients with cardiac arrhythmias. Ann Intensive Care. 2018;8(1):79.

2. Monnet X, Bleibtreu A, Ferré A, et al. Passive leg raising and end-expiratory occlusion tests perform better than pulse pressure variation in patients with low respiratory system compliance. Crit Care Med. 2012;40:152-157.

3. Monnet X, Marik P, Teboul JL. Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis. Intensive Care Med. 2016;42:1935-1947.

4. Monnet X, Rienzo M, Osman D, et al. Passive leg raising predicts fluid responsiveness in the critically ill. Crit Care Med. 2006;34:1402-1407.

7. Correct Answer: C. The IVC collapsibility index has not been validated in patients being ventilated with the tidal volumes being used in this case.

Rationale: The IVC collapsibility index is defined as: [(Maximum IVC diameter – Minimum IVC diameter)/Minimum IVC diameter] or [(Maximum IVC diameter – Minimum IVC diameter)/Mean IVC diameter]. Depending on which method is used, the cutoff values for predicting volume responsiveness are 18% or 12%, respectively. Importantly, both studies were among mechanically ventilated patients with tidal volumes >8 to 10 mL/kg ideal body weight. In patients being ventilated by small tidal volumes, as in this case, the sensitivity of the index is much lower. Therefore, the IVC collapsibility index cannot be used to reliably evaluate volume responsiveness in this patient and is likely to underestimate volume responsiveness. Early studies of IVC diameter variation were conducted in spontaneously breathing patients with the purpose of estimating CVP and are the source of the American Society of Echocardiography’s guidelines for estimating CVP. However, in sedated ventilated patients with large tidal volumes and a lack of spontaneous breathing, the IVC index is a reasonable predictor of fluid responsiveness. There is no convincing evidence that colloid-based resuscitation is superior to crystalloid-based resuscitation in ARDS.

1. Barbier C, Loubières Y, Schmit C, et al. Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated patients. Intensive Care Med. 2004;30:1740-1746.

2. Feissel M, Michard F, Faller JP, Teboul JL. The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30(9):1834-1837.

8. Correct Answer: B. She is likely to be volume responsive, but should not get rapid volume resuscitation.

Rationale: This patient has a mechanism for intra-abdominal hemorrhage. The fluid in the lienorenal (or splenorenal) space, together with her mechanism of injury, raises the suspicion of splenic injury. Given this predisposition to hypovolemia, an IVC maximal diameter of 1.5 cm is consistent with hypovolemia, and she would likely be volume responsive. However, the principles of damage control resuscitation advise against volume resuscitation, as long as perfusion to critical organs is maintained.

1. Cap AP, Pidcoke HF, Spinella P, et al. Damage control resuscitation. Mil Med. 2018;183(suppl_2):36-43.

2. Schmidt GA, Koenig S, Mayo PH. Shock: ultrasound to guide diagnosis and therapy. Chest. 2012;142(4):1042-1048.

9. Correct Answer: A. Transesophageal echocardiography (TEE) is required to assess the SVC.

Rationale: Like the IVC, variations in SVC diameter can also be used to predict volume responsiveness. Although the SVC can be visualized by transthoracic echocardiography (TTE), it is inconsistently visible, and TTE-based SVC evaluation has not been well studied. SVC variation using transesophageal echo (Option A) has been well-validated in mechanically ventilated patients. It is more sensitive and specific than either IVC diameter variation or pulse pressure variation (Option B). Like the IVC collapsibility index, it is not well-validated in patients on assisted breathing modes (Option C).

1. Vignon P, Repessé X, Bégot E, et al. Comparison of echocardiographic indices used to predict fluid responsiveness in ventilated patients. Am J Respir Crit Care Med. 2017;195(8):1022-1032.

10. Correct Answer: C. Severely reduced LV systolic function does not, contraindicate fluid resuscitation, but the volume of fluid used should be carefully determined by repeated assessment of volume responsiveness to minimize the risk of complications.

Rationale: This patient presents with signs and symptoms consistent with the current definition of sepsis, but also has a documented history of heart failure with a reduced EF. POCUS examination shows severely decreased LVEF in apical three-chamber and apical two-chamber views ( Videos 49.5 and 49.6).

However, poor LV systolic function or high filling pressures (central venous or pulmonary capillary wedge) do not preclude fluid administration (Option A). Nonetheless, the tolerance of patients with poor LV function for large volumes of fluid may be limited. The best response would be to administer relatively small fluid boluses (250-500 mL) and reassess for evidence of fluid responsiveness (Option C). The videos show severely reduced LV systolic function, so Option B is incorrect. There is not enough data to determine whether this patient will need an inotrope such as dobutamine, certainly not as the next step in management (Option D).

1. Singer M, Deutschman CS, Seymour CW, et al. The third international consensus definitions for sepsis and septic shock (sepsis 3). JAMA. 2016;315(8):801-810.

2. Vincent JL, Weil MH. Fluid challenge revisited. Crit Care Med. 2006;34(5):1333-1337.

11. Correct Answer: D. Combining EEOT with an end-inspiratory occlusion test (EIOT) can improve the sensitivity of the technique when using echocardiography.

Rationale: The EEOT is based on the principle that a sustained (>15 seconds) interruption in positive pressure ventilation can increase venous return and consequently increase cardiac output in volume-responsive patients. Conversely, in volume-replete patients, there is a minimal difference in venous return with interruption of ventilation, and therefore no change in cardiac output. In practice, EEOT can be performed with a prolonged expiratory hold in sedated and paralyzed patients. The EEOT has been shown to be useful in patients with poor lung compliance, unlike pulse pressure variation (Option A). It is not a static maneuver, as it relies on altering venous return in response to intrathoracic pressure changes (Option B). Combining EEOT with EIOT allows the incorporation of the decrease in VTI with a sustained inspiratory hold. EIOT is maintained for 15 seconds (as with EEOT), with 1 minute between measurements. If the total change in VTI (increase with EEOT + decrease with EIOT) is >13%, the patient is likely to be fluid responsive (see Figure 49.8). While the test can be carried out in patients who have some spontaneous respiratory activity, the patient should be able to tolerate a 15-second breath-hold without taking a spontaneous breath. In practice, this limits its use in spontaneously breathing patients.

1. Jozwiak M, Depret F, Teboul JL, et al. Predicting fluid responsiveness in critically ill patients by using combined end-expiratory and end-inspiratory occlusions with echocardiography. Crit Care Med. 2017;45:e1131-e1138.

2. Monnet X, Osman D, Ridel C, Lamia B, Richard C, Teboul JL. Predicting volume responsiveness by using the end-expiratory occlusion in mechanically ventilated intensive care unit patients. Crit Care Med. 2009;37:951-956.

12. Correct Answer: C. The VTI at the LVOT increases by 20% with a passive leg raise.

Rationale: The passive leg raise test has proven to be useful in identifying fluid responsiveness in patients under a diverse set of conditions. To be most effective, the passive leg raise should be coupled with measurement of cardiac output. One of the ways to do this is to acquire an LVOT VTI by echocardiography before and after the maneuver. It should be noted that although this is a well-validated method, it requires advanced echocardiographic skills. While the IVC distensibility index is approximately 33% for this patient, the IVC index has not been validated in patients on assisted (but not passive) ventilation. Similarly, changes in LVOT maximal velocity have not been shown to be predictive in patients on assisted ventilation. The EF can appear normal in patients with severe diastolic dysfunction and low stroke volume, as well as with severe valvular regurgitant lesions, and adds little value in predicting fluid responsiveness.

1. Brun C, Zieleskiewicz L, Textoris J, et al. Prediction of fluid responsiveness in severe preeclamptic patients with oliguria. Intensive Care Med. 2013;39(4):593-600.

13. Correct Answer: B. The LSC in the VTI that can be reliably measured by a single operator is about 11%.

Rationale: For most dynamic measures of fluid responsiveness, measuring cardiac output or its surrogates (such as VTI) is more reliable than measuring the pulse pressure variation. Since the echocardiographic assessments of VTI are commonly used to assess fluid responsiveness, it is important to assess the accuracy, precision, and the LSC that can be reliably detected. There is a paucity of studies that address this question; however, recent work by Jozwiak, et al. has provided some guidance. The authors found that sequential measurements of VTI were able to detect a smaller change in the VTI when the examinations were performed by the same operator than when different operators performed the examinations (Option A is incorrect). The median LSC that can be detected by a single examiner was found to be 11% (Option B is correct). Interestingly, the LSC was similar for both spontaneously breathing and mechanically ventilated patients (Option C is incorrect). Finally, given that the LSC in sequential VTI measurements is around 11%, smaller changes are unlikely to be reliably detected by echocardiography (Option D is incorrect).

1. Jozwiak M, Mercado P, Teboul JL, et al. What is the lowest change in cardiac output that transthoracic echocardiography can detect? Crit Care. 2019;23(1):116.

2. Monnet X, Marik P, Teboul JL. Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis. Intensive Care Med. 2016;42(12):1935-1947.

14. Correct Answer: D. The portal vein is typically nonpulsatile—a PVPI >50% is a useful indicator of systemic congestion and RV dysfunction.

Rationale: Systemic congestion can have detrimental effects on organ function, inducing acute kidney injury and congestive hepatopathy. In ventilated patients, the value of IVC measurements in inferring CVP measurements can be poor (Option A is incorrect). Assessing portal venous pulsatility can be a valuable technique for detecting systemic venous congestion and RV dysfunction. The portal vein can be imaged with a 2.5 to 5 MHz transducer (cardiac or abdominal) at the posterior axillary line, allowing the IVC, the hepatic vein, and the portal vein to be visualized (Option B is incorrect). The walls of the portal vein are relatively more hyperechoic than the walls of the hepatic vein. Blood flow in the portal vein is normally nonpulsatile, and significant pulsatility (a PVPI >50%) indicates RV dysfunction or systemic congestion (Option D). While other causes of portal hypertension (cirrhosis, portal venous thrombosis) can also cause a high PVPI, cardiac dysfunction (e.g., tricuspid regurgitation) can also be a cause (Option C is incorrect). (See Figure 49.9.)

1. Beaubien-Souligny W, Bouchard J, Desjardins G, et al. Extracardiac signs of fluid overload in the critically ill cardiac patient: a focused evaluation using bedside ultrasound. Can J Cardiol. 2017;33(1):88-100.

2. Denault AY, Azzam MA, Beaubien-Souligny W. Imaging portal venous flow to aid assessment of right ventricular dysfunction. Can J Anaesth. 2018;65(11):1260-1261.

3. Jue J, Chung W, Schiller NB. Does inferior vena cava size predict right atrial pressures in patients receiving mechanical ventilation? J Am Soc Echocardiogr. 1992;5(6):613-619.

4. Styczynski G, Milewska A, Marczewska M, et al. Echocardiographic correlates of abnormal liver tests in patients with exacerbation of chronic heart failure. J Am Soc Echocardiogr. 2016;29(2):132-139.

15. Correct Answer: C. The combination of low tidal volumes and poor lung compliance in this patient makes VTI variation with respiration relatively unpredictable.

Rationale: This patient has severe ARDS with low lung compliance, reflected in the need to reduce his tidal volumes to 5 mL/kg to keep plateau pressure and driving pressure within recommended limits. In such patients, airway pressure changes may not be reliably transmitted from the lung parenchyma to the extrapulmonary intrathoracic space, and therefore have unpredictable effects on preload. Because of this, the effects of changes in cardiac output, VTI, or pulse pressure variation with respiration can be unpredictable (Option C is correct). Therefore, the lack of significant VTI variation with respiration is not sufficient to define this patient as being fluid unresponsive (Option A is incorrect). It is important to recognize that the test retains its specificity—a large VTI variation would imply volume responsiveness in the setting of poorly compliant lungs/small tidal volumes. A number of dynamic indices of fluid responsiveness lose sensitivity in the setting of low-tidal-volume ventilation/poor lung compliance. Those which do not rely on changes in intrathoracic pressure, such as passive leg raise, do not. Measuring the change in VTI in response to a passive leg raise maneuver is a good technique to assess fluid responsiveness in this situation (Option B is incorrect).

1. Charron C, Fessenmeyer C, Cosson C, et al. The influence of tidal volume on the dynamic variables of fluid responsiveness in critically ill patients. Anesth Analg. 2006;102(5):1511-1517.

2. De Backer D, Fagnoul D. Intensive care ultrasound: VI. Fluid responsiveness and shock assessment. Ann Am Thorac Soc. 2014 11:129-136.

3. Monnet X, Marik PE, Teboul JL. Prediction of fluid responsiveness: an update. Ann Intensive Care. 2016;6(1):111.

4. Vignon P, Repessé X, Bégot E, et al. Comparison of echocardiographic indices used to predict fluid responsiveness in ventilated patients. Am J Respir Crit Care Med. 2017;195(8):1022-1032.

16. Correct Answer: C. The esophageal Doppler signal detects flow in the ascending aorta and therefore reflects the total LV stroke volume.

Rationale: The esophageal Doppler probe is placed transorally into the esophagus to a depth of about 35 to 40 cm, capturing the flow signal from the descending thoracic aorta (Option C is false, and therefore the correct answer). Therefore, only a part of the LV stroke volume is accessible, and manufacturers use algorithms to extrapolate that value into the cardiac output. The use of these probes in goal-directed resuscitation during major surgery has been found to reduce the incidence of postoperative complications in some studies (Option A). The stroke distance on the Doppler signal is directly proportional to the stroke volume (Option B), and changes in the morphology of the Doppler signal can be used to detect aortic regurgitation and cardiac tamponade (Option D).

1. Singer M. Oesophageal Doppler. Curr Opin Crit Care. 2009;15(3):244-248.

2. Wakeling HG, McFall MR, Jenkins CS, et al. Intraoperative oesophageal Doppler guided fluid management shortens postoperative hospital stay after major bowel surgery. Br J Anaesth. 2005;95:634-642.

17. Correct Answer: B. The number and severity of B-lines will decrease as fluid is removed.