Nexfin co trek

Blood pressure (BP) was continuously measured using a non-invasive volume clamp method (Nexfin, Edwards Lifesciences BMEYE, Amsterdam, the Netherlands). Left ventricular SV was estimated by a pulse contour method (Nexfin CO-trek, Edwards Lifesciences BMEYE, Amsterdam, the Netherlands) [24 (link), 25 (link)] and CO was SV times heart rate (HR). SV index (SVI) was the ratio of SV and body surface area [26 ]. SPV and PPV were calculated from the BP signal:
$100\times \frac{{\text{A}}_{\text{max}}-{\text{A}}_{\text{min}}}{({\text{A}}_{\text{max}}+{\text{A}}_{\text{min}})/2}$
with A_max/min equal to, respectively, systolic arterial pressure (SAP) and pulse pressure (PP; SAP minus diastolic arterial pressure (DAP)). PPV and SPV were calculated for each breath and averaged over 5 consecutive breaths.
Airway flow and pressure were measured using an Alveotest flowmeter (Jaeger, Würzburg, Germany), tidal volume (TV) was the integral of airway flow (expressed in mL per kg predicted body weight) and end-tidal CO₂ (PetCO₂) was measured by capnography (Tonocap, Datex-Ohmeda, Madison, USA). Signals were visually inspected for artefacts and 60-second intervals were used for offline analysis (Matlab R2007b, Mathworks Inc. MA, USA).

Continuous blood pressure (BP) was measured noninvasively by finger plethysmography with the cuff placed around the middle phalanx of the nondominant hand placed at heart level (Nexfin, Edwards Lifesciences BMEYE, the Netherlands). Left ventricular stroke volume (SV) was estimated beat by beat by pulse contour (Nexfin CO‐trek, Edwards Lifesciences BMEYE, Amsterdam, the Netherlands) and by inert gas rebreathing (Innocor, Innovision A/S, Odense, Denmark) (Gabrielsen et al. 2002; Bartels et al. 2011). CO was stroke volume (SV) times heart rate (HR). Total peripheral resistance (TPR) was the ratio of mean arterial pressure (BP_mean) and CO. End‐tidal CO₂ partial pressure (PetCO₂) was monitored through a nasal cannula connected to a sampling capnograph (Datex Normocap 200, Helsinki, Finland).
Changes in MCAV were followed in the proximal segment of the middle cerebral artery (MCA) by transcranial Doppler ultrasonography (TCD; DWL Multidop X4, Sipplingen, Germany). The left MCA was insonated through the temporal window just above the zygomatic arch at a depth of 40–60 mm with a pulsed 2 MHz probe. Once the optimal signal‐to‐noise ratio was obtained, the probe was immobilized by a head band.