Minimizing Lung Injury During Laparoscopy in Steep Trendelenburg Position
Condition: Atelectasis
MeSH terms: Lung Injury; Pulmonary Atelectasis
Study type: Interventional

Summary: 
      The investigators hypothesize that the level of PEEP is often suboptimally applied in certain
      operative conditions, such as in laparoscopy with head down (Trendelenburg) positioning. This
      can result in excessive levels of lung stress and postoperative pulmonary complications.

      In patients with steep Trendelenburg and a pneumoperitoneum, the investigators aim to

        1. measure apical versus basal atelectasis using the lung ultrasound score

        2. compare lung ultrasound scores at different PEEP levels

        3. compare respiratory mechanics at the different PEEP levels

        4. contrast the optimal PEEP level to standard practice

        5. provide guidance to optimal PEEP titration in this setting for the clinician
    

Detailed description: 
      The investigators hypothesize that the level of positive end-expiratory pressure (PEEP) is
      often incorrectly applied in certain operative conditions, such as in laparoscopy with head
      down (Trendelenburg) positioning. This can result in excessive levels of lung stress and
      postoperative pulmonary complications.

      Incorrect intra-operative ventilator management can be harmful for the patient, potentially
      leading to postoperative pulmonary complications and ventilator-induced lung injury. During
      routine anesthesia procedures, most anesthetists will set the ventilator by rule of thumb
      with a PEEP of 4-6 cmH2O, a tidal volume of 6-8 ml/kg of ideal body weight and a frequency of
      10-15 breaths per minute in order to provide lung protective ventilation. However, due to
      recent advances in surgical practice, patients are more frequently placed in non-
      physiological states, such as Trendelenburg position up to 30° with concurrent
      pneumoperitoneum and intra-abdominal pressures of 15mmHg or higher, as in for example
      robot-assisted radical prostatectomy or gynecological procedures. This extreme positioning
      and increased intra-abdominal pressure can have a significant effect on respiratory mechanics
      and can potentially result in excessive lung stress. The changes in applied positive pressure
      ventilation will result in changes of regional ventilation: both an increased amount of
      atelectasis and an increased amount of regional hyperinflation are observed in this setting.
      The ideal PEEP level balances the recruitment of atelectasis versus excessive hyperinflation.
      These changes in regional ventilation can be assessed by lung ultrasound. The lung ultrasound
      score can distinguish atelectasis from normal aeration in the different lung regions of
      interest.

      This project is designed as a single center cohort study. Non-obese (BMI < 30kg/m2),
      lung-healthy non-pregnant, non-smoking individuals without right sided heart failure,
      scheduled for elective laparoscopy of the lower abdomen, will be recruited. Standardized
      induction and maintenance with propofol TCI (3-6μg/l plasma concentration as calculated by
      the Marsh model), sufentanil (0.2μg/kg) and rocuronium (0.6mg/kg) will be provided.
      Neuromuscular blockade will be monitored using a train-of-four (TOF) monitor and kept with a
      TOF count < 1 throughout the study using additional doses if indicated. A radial arterial
      line will be placed. Mechanical ventilation will be provided in volume control mode with a
      tidal volume of 4-6 ml/kg of ideal body weight (IBW) aiming for a driving pressure ≤ 15cmH2O,
      a starting PEEP of 5cmH2O, a frequency of 12-18 breaths per minute titrated to the end-tidal
      CO2 measurement and an initial FiO2 of 0.4. An esophageal balloon catheter with pressure
      sensor will be used to calculate transpulmonary pressures. The balloon and pressure sensor
      will be calibrated as per manufacturers guideline. Respiratory parameters will be recorded
      and saved for later evaluation using the FluxMed GrT monitor and software (MBMED, Argentina).
      After inflation of the pneumoperitoneum, lung ultrasound will be performed bilaterally at the
      midclavicular line between the second and third ribs, at the posterior axillary line above
      the level of T4 and at the posterior axillary line closely superior to the diaphragm, thus
      retaining 6 ultrasound loops which will be saved for post-hoc lung ultrasound scoring. The
      lung ultrasound measurements will be repeated at different decremental levels of PEEP: 15,
      10, 5 and 0 cmH2O respectively. Arterial blood gas analysis will be performed before
      insufflation of the pneumoperitoneum and repeated at each level of PEEP. A minimum of 4
      minutes equilibration time will be provided after changing PEEP.
    

Intervention name(s): Decremental PEEP; Lung ultrasound score; Blood gas analysis; Registration of respiratory mechanics; Evaluation of dead space
Intervention type(s): Procedure; Diagnostic Test; Diagnostic Test; Diagnostic Test; Diagnostic Test
Intervention description(s): High PEEP to low PEEP.; lung ultrasound to determine the extend of atelectasis. Uses validated lung ultrasound score.; Blood gas analysis to determine arterial oxygen tension; Pressures and volumes will be registered by the Fluxmed respiratory monitor (MBMED, Argentina); Dead space will be measured non-invasively using volumetric capnography on the FluxMed respiratory monitor (MBMED, Argentina)
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: Positive-Pressure Respiration; Respiratory Mechanics; positive end-expiratory pressure