Laparoscopy is increasingly used for major abdominal and pelvic surgery. As this approach is also recommended in elderly patients with serious comorbidities, optimal fluid therapy guidance during this procedure is important.

Many studies have reported that less invasive dynamic indices such as pulse pressure variation (PPV) and stroke volume variation (SVV), which are derived from the arterial pressure waveform, are superior to static indices to predict fluid responsiveness. PPV and SVV are based on the heart-lung interaction and reflect cyclic changes in stroke volume induced by mechanical ventilation in the closed-chest condition. Therefore, their ability to predict fluid responsiveness can be affected by factors that influence the arterial tone or the compliance of the respiratory system.

Laparoscopic surgery for the abdominal visceral organs requires pneumoperitoneum and the Trendelenburg position to optimize surgical conditions, and can reduce cardiac output and respiratory compliance. Accordingly, the usefulness of PPV and SVV in predicting fluid responsiveness during laparoscopic surgery under these conditions may be questioned.

It has been clearly shown that the values of dynamic parameters are significantly correlated with the magnitude of VT. Min et al. reported that augmentation of PPV and SVV via a temporary increase in VT from 8 to 12 ml/kg improved their predictive power in the inconclusive zone with respect to fluid responsiveness (PPV values of 9% and 13%, respectively). Another recent study reported that on increasing VT from 6 to 8 ml/kg, augmented PPV and SVV, as well as their absolute changes, predicted fluid responsiveness with high sensitivity and specificity, even in critically ill patients receiving low VT.

Therefore, the aim of the current study was to investigate whether increasing VT from 6 to 8 ml/kg would improve the predictive power of PPV and SVV in patients undergoing robot-assisted laparoscopic surgery in the Trendelenburg position under lung-protective ventilation. We also assessed the ability of absolute changes in PPV and SVV values induced by a temporary increase in VT from 6 to 8 ml/kg to predict fluid responsiveness.

Inclusion Criteria:

• Adult patients who performed robot assisted laparoscopic surgery under Trendelenburg position

Exclusion Criteria:

• preoperative arrhythmia
• Severe bradycardia
• Moderate to severe valvular disease
• left ventricular ejection fraction < 50%
• Poorly controlled hypertension (systolic BP > 160 mmHg)
• Patients with renal insufficiency (creatinine > 1.5 mg/dL)
• Moderate to severe liver disease
• BMI >.30 or < 15 kg/ m2
• preexisting pulmonary disease
• FEV1 < 60% of predicted value
• contraindications to oesophageal Doppler (OED) monitoring probe insertion (i.e. oesophageal stent, carcinoma of the oesophagus or pharynx, previous oesophageal surgery, oesophageal stricture, oesophageal varices, pharyngeal pouch, and severe coagulopathy)

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