Perioperative Hemodynamic Optimization using ΔPP and Stroke Volume

We placed all patients on standard non-invasive monitors. Anesthesia was induced according to the standard operating procedures [SOP] of our hospital using 1.5–2.5 mg/kg body weight (BW) Propofol, 0.2–0.5 µg/kg BW Sufentanil and 0.5–0.6 mg/kg ideal body weight (IBW) Atracurium or 0.6 mg/kg IBW Rocuronium at the discretion of the attending anesthesiologist. Maintenance of anesthesia was accomplished using Sevoflurane adjusted to age-corrected mean alveolar concentration. Analgesia was adapted to meet patient individual demands using additional Sufentanil boluses of 5–10 µg. A non-opioid analgetic was administered 30 min before the end of the procedure for early post-operative analgesia.
An arterial cannula was placed in the radial artery for continuous, invasive blood pressure monitoring (Philips IntelliVue MX700, Philips Medizin Systeme GmbH, Boeblingen, Germany). Invasive blood pressure monitoring was calibrated by placing the pressure transducer at the level of the right atrium and venting the transducer to atmospheric pressure for reference. ∆PP was calculated as $$\mathrm{\Delta }\mathrm{PP}[\%](({\mathrm{PP}}_{\max }-{\mathrm{PP}}_{\min })/([{\mathrm{PP}}_{\max }+{\mathrm{PP}}_{\min }]/2))\times 100$$
where PP_max and PP_min are the maximum and minimum pulse pressure during one respiratory cycle. ΔPP measurements were calculated from beat-to-beat arterial pressure values and reported as the average value of the last 32 s.
Stroke volume was measured by esophageal doppler monitoring (CardioQ-ODM®, Deltex Medical Ltd, Chichester, UK). The tip of the doppler probe was placed in the pars thoracica of esophagus at the level of the descending aorta. Stroke volume was calculated by the product of stroke distance (area of the doppler derived velocity–time waveform) and aortic cross-sectional area [12 (link)].
Patients were mechanically ventilated with a tidal volume ≥ 8 ml/kg IBW using pressure-controlled ventilation. Positive end-exspiratory pressure was kept between 5–8 mbar, respiratory rate was set to 12–16 min⁻¹ and fraction of inspired oxygen (F_iO₂) was set to keep oxygen saturation above 95% according to departmental standard operating procedures. All settings and target values were continuously adapted to patient characteristics and clinical situation using repetitive blood gas analyses.
In case of possible hypovolemia a fluid bolus of 7 ml/kg IBW was administered at the discretion of the attending anesthesiologist.
Trigger for fluid bolusing were:

Difference in pulse pressure [∆PP] ≥ 9% [13 (link), 14 (link)] and/or

corrected flow time [FTc] ≤ 350 ms [15 (link)]

An increase in stroke volume ≥ 10% following the fluid bolus was considered ‘fluid responsive’.