Restricted, optimized or liberal fluid strategy in thoracic surgery: A narrative review.

Perioperative fluid balance has a major impact on clinical and functional outcome, regardless of the type of interventions. In thoracic surgery, patients are more vulnerable to intravenous fluid overload and to develop acute respiratory distress syndrome and other complications. New insight has been gained on the mechanisms causing pulmonary complications and the role of the endothelial glycocalix layer to control fluid transfer from the intravascular to the interstitial spaces and to promote tissue blood flow. With the implementation of standardized processes of care, the preoperative fasting period has become shorter, surgical approaches are less invasive and patients are allowed to resume oral intake shortly after surgery. Intraoperatively, body fluid homeostasis and adequate tissue oxygen delivery can be achieved using a normovolemic therapy targeting a "near-zero fluid balance" or a goal-directed hemodynamic therapy to maximize stroke volume and oxygen delivery according to the Franck-Starling relationship. In both fluid strategies, the use of cardiovascular drugs is advocated to counteract the anesthetic-induced vasorelaxation and maintain arterial pressure whereas fluid intake is limited to avoid cumulative fluid balance exceeding 1 liter and body weight gain (~1-1.5 kg). Modern hemodynamic monitors provide valuable physiological parameters to assess patient volume responsiveness and circulatory flow while guiding fluid administration and cardiovascular drug therapy. Given the lack of randomized clinical trials, controversial debate still surrounds the issues of the optimal fluid strategy and the type of fluids (crystalloids versus colloids). To avoid the risk of lung hydrostatic or inflammatory edema and to enhance the postoperative recovery process, fluid administration should be prescribed as any drug, adapted to the patient's requirement and the context of thoracic intervention.