Recommendation
Pulmonary artery catheter measurements, mean arterial pressure, pulse pressure variation, point of care transthoracic echocardiography (TTE), and arterial pulse contour technology can all be used in volume assessment of patients with DC, with the understanding of their limitations in this patient population. Typical end points of resuscitation can be used in DC; however, mixed venous oxygen saturation (SvO2) and serum lactate should be interpreted cautiously.
Discussion
The assessment of volume status in patients with DC is complicated secondary to marked systemic inflammation and hemodynamic disturbances including increased cardiac output (CO) and peripheral vasodilation.2 Portal hypertension leads to compensatory splanchnic and systemic vasodilation mediated by nitric oxide and other vasoactive agents. Decreased arterial blood flow to the kidneys stimulates the renin-angiotensin-aldosterone system which leads to volume expansion with sodium and water retention. However, central blood volume remains low and the hyperdynamic state continues.3 4 These patients require thoughtful volume assessment as excess fluid may increase mortality.2 5
Central venous pressure is a poor assessment of volume status in DC due to the presence of ascites, left ventricular diastolic dysfunction, and hypoalbuminemia. Pulmonary artery catheter placement can ameliorate some of these challenges using measures of cardiac filling including mean pulmonary artery pressure, CO, and pulmonary capillary wedge pressure.6 However, non-invasive monitoring has gained popularity and includes evaluation of mean arterial pressure (MAP), pulse pressure variation (PPV), point-of-care TTE (POC TTE), and arterial pulse contour technology.6
MAP can be monitored using an intra-arterial catheter or non-invasive blood pressure monitoring to gauge appropriate tissue perfusion, with a MAP goal of ≥60–65 mm Hg.7 Intra-arterial catheters can also be used to quantify pulse pressure variation, with the caveat that ascites, intra-abdominal hypertension, and low systemic vascular resistance (SVR) may alter aortic compliance which affects PPV utilization.2 Passive leg raise can provide a surrogate for fluid bolus; if there is an increase in MAP, this implies that the patient is fluid responsive.
POC TTE is a bedside evaluation of cardiac and intravascular volume status using five echocardiography views. Qualitative parameters include gross appearance, wall motion, and estimation of ejection fraction (EF). Quantitative parameters are calculations including but not limited to CO, left ventricular end diastolic area, stroke volume variation, change in velocity time integral, and dynamic inferior vena cava diameter assessment.8–11 This monitoring strategy is limited by provider training, pulmonary hypertension, cardiomyopathy, large volume ascites, and, in the mechanically ventilated patient, ventilator dyssynchrony. While single measurements can be helpful to assess a patient at a particular moment, trends are likely more useful.
Arterial pulse contour technology can give quantitative parameters similar to more invasive monitoring; however, it is limited by the need for a functioning arterial line and the patient being in sinus rhythm under controlled mechanical ventilation with conservative tidal volume settings (6–8 mL/kg). This technology is highly dependent on vascular integrity, so the hyperdynamic and low SVR state of patients with DC may impact its accuracy.2 12
End points of resuscitation include surrogates of microcirculatory flow and tissue oxygenation, such as vital signs, urine output, serum lactate, and SvO2, but should be used with caution in patients with DC. Low SvO2 indicates that the tissues are extracting a higher percentage of oxygen and the cardiac output is not high enough to meet tissue needs.13 At the microvascular level, SvO2 may be elevated in cirrhotic patients even if the patient is volume depleted secondary to high flow and low oxygen extraction.2 Lactate measurements should be used cautiously in liver disease as elevated lactic acid may be secondary to impaired clearance, and so there is no specific target recommended in these patients although trending may be useful.2 14