Autonomic Nervous System Modulation During Laparoscopic Prostatectomy
Condition: Intervention Affecting Autonomic Nervous System
Study type: Observational

Summary: 
      The purpose of this study is to measure the variations of autonomic nervous system (ANS)
      modulation directed to the heart and vessels induced by pneumoperitoneum and steep
      trendelenburg position.
    

Detailed description: 
      The association of pneumoperitoneum and steep trendelenburg position, commonly used during
      laparoscopic radical prostatectomy, leads to significant changes in hemodynamics. Many
      studies found modifications of cardiac output, stroke work index, arterial pressure, central
      vein pressure and wedge pressure. Moreover, there are reports of severe bradycardia and
      cardiac arrest following pneumoperitoneum in association with steep trendelenburg. A vagal
      hypertone (induced by the combination of these two factors) or sympathetic hypractivity
      (elicited by pneumoperitoneum) had been alternatively postulated to cause these hemodynamic
      changes. To date there are not sufficient physiologic evidences of modification of ANS
      activity during steep trendelenburg position in association with pneumoperitoneum.

      ANS modulation is studied non invasively by means of heart rate variability and baroreflex
      sensitivity. Beat-to-beat intervals are computed detecting the QRS complex on the ECG and
      locating the R-apex using parabolic interpolation. The maximum arterial pressure within each
      R-to-R interval is taken as systolic arterial pressure (SAP). Sequences of 300 values are
      randomly selected inside each experimental condition. The power spectrum is estimated
      according to a univariate parametric approach fitting the series to an autoregressive model.
      Autoregressive spectral density is factorized into components each of them characterized by a
      central frequency. A spectral component is labeled as LF if its central frequency is between
      0.04 and 0.15 Hz, while it is classified as HF if its central frequency is between 0.15 and
      0.4 Hz. The HF power of R-to-R series is utilized as a marker of vagal modulation directed to
      the heart , while the LF power of SAP series is utilized as a marker of sympathetic
      modulation directed to vessels. The ratio of the LF power to the HF power assessed from
      R-to-R series is taken as an indicator simpatho-vagal balance directed to the heart.
      Baroreflex control in the low frequencies is computed as the square root of the ratio of
      LF(RR) to LF(SAP). Similarly baroreflex control in the high frequencies is defined as the
      square root of the ratio of HF(RR) to HF(SAP).

      The optic nerve sheet's diameter is assessed echographically after induction of general
      anesthesia and at the end of the surgery.

      Management of general anesthesia is standardized:

        -  induction with propofol 1.5-2 mg/kg, Remifentanil Target Controlled Infusion (TCI) Ce 4
           ng/ml , neuromuscolar blockade with cisatracurium 0.2 mg/kg.

        -  Maintenance: Sevoflurane 0.6-1.5 MAC (State Entropy target: 40-60); Remifentanil TCI
           (range Ce 3-15 ng/ml) (Surgical Pleth Index target: 20-50).

        -  mechanical ventilation at respiratory rate ≥14 breats/min, with tidal volume adjusted to
           maintain end-tidal carbon dioxide at 32-38 mmHg, and Pplateu <32 cmH2O.

      Sample size:

      to detect a difference in LF/HF ratio of 0.8 with a SD of 1.7, a power of 0.80 and type I
      error of 0.05, 37 patients are needed.
    

Intervention name(s): steep trendelenburg position with pneumoperitoneum
Intervention type(s): Other
Intervention description(s): ANS activity and baroreflex modulation is assessed at (i) baseline; (ii) after induction of general anesthesia; (iii) after steep trendelenburg position (head down at 25 degrees); (iv) after induction of pneumoperitoneum and (v) after removal of trendelenburg and pneumoperitoneum
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Human males undergoing elective laparoscopic prostatectomy
      
Keywords: autonomic nervous system modulation; heart rate variability; prostatectomy; steep trendelenburg; pneumoperitoneum