Echocardiography as a guide for fluid management

Abstract

Background: In critically ill patients at risk for organ failure, the administration of intravenous fluids has equal chances of resulting in benefit or harm. While the intent of intravenous fluid is to increase cardiac output and oxygen delivery, unwelcome results in those patients who do not increase their cardiac output are tissue edema, hypoxemia, and excess mortality. Here we briefly review bedside methods to assess fluid responsiveness, focusing upon the strengths and pitfalls of echocardiography in spontaneously breathing mechanically ventilated patients as a means to guide fluid management. We also provide new data to help clinicians anticipate bedside echocardiography findings in vasopressor-dependent, volume-resuscitated patients.

Objective: To review bedside ultrasound as a method to judge whether additional intravenous fluid will increase cardiac output. Special emphasis is placed on the respiratory effort of the patient.

Conclusions: Point-of-care echocardiography has the unique ability to screen for unexpected structural findings while providing a quantifiable probability of a patient's cardiovascular response to fluids. Measuring changes in stroke volume in response to either passive leg raising or changes in thoracic pressure during controlled mechanical ventilation offer good performance characteristics but may be limited by operator skill, arrhythmia, and open lung ventilation strategies. Measuring changes in vena caval diameter induced by controlled mechanical ventilation demands less training of the operator and performs well during arrythmia. In modern delivery of critical care, however, most patients are nursed awake, even during mechanical ventilation. In patients making respiratory efforts we suggest that ventilator settings must be standardized before assessing this promising technology as a guide for fluid management.

Keywords: Echocardiography; Point-of-care ultrasound; Resuscitation; Shock.

Fig. 1

A 57-year-old male patient admitted with septic shock 18 hours before imaging required 0.2 μg/kg/minute of norepinephrine to maintain a mean arterial blood pressure of 70 mmHg. Central venous pressure via the right internal jugular catheter was 13 mmHg and he was in atrial fibrillation, rate of 100 beats/minute. Sedation had been discontinued and the patient was awake and spontaneously breathing on a mechanical ventilator. Using a subcostal approach the IVC was imaged using M-mode at 1.5 cm from the IVC–right atrial junction. The patient then began a spontaneous breathing trial, with some translational movement of the IVC noted, and imaging continued. In this case the IVC diameter during inspiration did not change according to the level of pressure support, whereas the end-expiratory IVC diameters were markedly greater with positive pressure applied. Thus the delta IVC during usual mechanical ventilation was 29 %, while during his spontaneous breathing trial the delta IVC was only 11 %. A CardioQ™ esophageal Doppler probe was in place and an optimal descending aortic blood flow was calculated. In this patient the stroke volume increased from 49 to 65 ml (33 % increase) with a 500 ml bolus of plasmalyte™, and thus was truly volume responsive. IVC inferior vena cava, PEEP positive end-expiratory pressure