Aggressive fluid administration is a hallmark of septic shock management and has been espoused by the Surviving Sepsis Campaign and is a part of the CMS SEP-1 sepsis bundle. The sepsis bundle includes administration of 30 ml/kg crystalloid bolus (LR or NS) within the first 3 hours of the diagnosis of severe sepsis or septic shock. Compliance with the SEP-1 sepsis bundle (which includes the early administration of broad-spectrum antibiotics, serial lactate measurements, blood cultures prior to antibiotics and administration of vasopressors if hypotension persists despite a fluid challenge) has been found to decrease the 30-day mortality from severe sepsis/septic shock by 5.6%.[i] One problem that has been identified is that many emergency department, hospitalist or critical care physicians continue to administer large amounts of crystalloid for patients who remain in shock. Sometimes this is appropriate and sometimes it is not. When it is inappropriate, the septic patients are fluid non-responders and develop fluid overload when given more IV fluids. The inappropriate administration of fluids to a fluid non-responder will worsen their clinical condition. One way to mitigate the risk of fluid overload is to insert an arterial line and attach this to a continuous cardiac output monitor for continuous assessment of stroke volume, cardiac output and stroke volume variability.
Therefore, the fundamental question when faced with a patient in vasodilatory shock is whether the patient is fluid responsive or not. Fluid responsiveness is simply a state where further fluid administration will improve the patient’s shock state. There are several methods to assess if a patient with vasodilatory shock is fluid responsive. Static measurements of cardiac preload such as the measurement of the central venous pressure (CVP) are poor predictors of fluid responsiveness. [ii] Conversely, dynamic measurements are much better predictors of fluid responsiveness in vasodilatory shock and should be used. [iii] The Holy Grail of shock management in critically ill patients is to optimize the patient’s cardiac output (CO)/cardiac index (CI). The most common way to assess a patient’s CO/CI is to place an arterial line that is connected to a continuous cardiac output monitor (e.g., PiCCO, EV1000 or LiDCO systems). These monitors allow continuous assessments of a patients stroke volume (SV), CO/CI and stroke volume variability (SVV). The dynamic measurements that can be assessed to determine fluid responsiveness include a mini-fluid challenge (250 mL crystalloid challenge over 10-15 minutes), passive leg raise (PLR), SVV, pulse pressure variation (PPV) and an end-expiratory occlusion test (EEOT). A mini-fluid challenge suggests fluid responsiveness if there is an increase of the CO/CI/SV by at least 10% or an increase in the SBP by 10 mmHg.
The SVV and PPV can be good assessments of intravascular volume status if the patient is in normal sinus rhythm, controlled mechanical ventilation, and PEEP (positive end-expiratory pressure) £10. SVV can still be helpful in spontaneously breathing patients but at a reduced sensitivity. In addition, the accuracy of SVV is improved with a tidal volume (Vt) ³ 8 mL/kg. Decreased intravascular volume will cause an increase in both SVV or PPV. An SVV of 13% or higher and a PPV of 11% or higher suggest intravascular volume depletion.
A PLR and EEOT are also good tests to assess fluid responsiveness. The PLR should be conducted with the patient in supine position and the legs are raised to at least 45 degrees for several minutes which provides an internal increase in preload by about 300 mL. An increase of the CO/CI/SV by at least 10% or an increase in the SBP by 10 mmHg all suggest fluid responsiveness. The EEOT is another technique that does not provide fluid administration. The ventilator should be paused at end-expiration for at least 12 seconds causing an increased venous return. An increase in SV by at least 5% suggests fluid responsiveness. These findings with their associated sensitivities and specificities are summarized in the table below[iv]:
| Stroke Volume Changes from Provocative Maneuvers | |||
| Maneuver | Threshold | Sensitivity | Specificity |
| Mini-fluid challenge | 5% | 0.82 | 0.83 |
| PLR | 10% | 0.85 | 0.91 |
| EEOT | 5% | 0.86 | 0.91 |
| Changes of Dynamic Variables from Heart-Lung Interactions | |||
| Test | Threshold | Sensitivity | Specificity |
| SVV | 12% | 0.83 | 0.85 |
| PPV | 10% | 0.74 | 0.77 |
In Summary, patients who have persistent vasodilatory shock after the initial fluid challenge should have serial assessments of fluid responsiveness using dynamic measurements to avoid fluid overload. The dynamic tests to assess include a mini-fluid challenge, a PLR, an EEOT, SVV or PPV. All patients with persistent vasodilatory shock on vasopressors should have a continuous cardiac output arterial line placed to follow continuous measurements of CO, CI, SV and SVV to optimize the patient’s intravascular volume status and avoid fluid overload states.
REFERENCES:
[i] Townsend, S et al. Effects of Compliance With the Early Management Bundle (SEP-1) on Mortality Changes Among Medicare Beneficiaries With Sepsis A Propensity Score Matched Cohort Study. Chest. 2022 Feb;161(2):392-406
[ii] Kalantari K, Chang JN, Ronco C, Rosner MH. Assessment of intra-vascular volume status and volume responsiveness in critically ill patients. Kidney Int 2013; 83: 1017-1028. doi: 10.1038/ki.2012.424.
[iii] Douglas IS, Alapat PM, Corl KA, et al. Fluid response evaluation in sepsis hypotension and shock: a randomized clinical trial. Chest 2020; 158: 1431-1445. doi: 10.1016/j.chest.2020.04.025.
[iv] Wojciech W et al. Methods of assessing fluid responsiveness in septic shock patients: a narrative review. Anaesthesiol Intensive Ther. 2022 Apr 13;46844.