• Positive End-Expiratory Pressure (PEEP) [ Time Frame: 10 minutes after intubation ]
  Positive End-Expiratory Pressure (cmH2O) in supine position
• Positive End-Expiratory Pressure (PEEP) [ Time Frame: 10 minutes after positioning ]
  Positive End-Expiratory Pressure (cmH2O) in prone position
• Change in Positive End-Expiratory Pressure (PEEP) [ Time Frame: From determination of optimal PEEP until the first hour and then every hour, assessed up to the end of surgery (maximum 6 hours) ]
  Variation of Positive End-Expiratory Pressure (cmH2O) during surgery in prone position with respect to PEEP value at 10 minutes after positioning

• Static compliance [ Time Frame: 10 minutes after intubation ]
  Tidal volume / Plateau pressure ratio (mL/cmH2O) in supine position
• Static compliance [ Time Frame: 10 minutes after positioning ]
  Tidal volume / Plateau pressure ratio (mL/cmH2O) in prone position
• Change in static compliance [ Time Frame: Measured at the same time as Auto PEEP until the first hour and then every hour, assessed up to the end of surgery (maximum 6 hours) ]
  Variation of static compliance (Tidal volume / Plateau pressure ratio, in mL/cmH2O) during surgery in prone position
• Arterial oxygen pressure (PaO2) [ Time Frame: 10 minutes after intubation ]
  Partial pressure of oxygen (mmHg) in supine position
• Arterial oxygen pressure (PaO2) [ Time Frame: 10 minutes after positioning ]
  Partial pressure of oxygen (mmHg) in prone position
• Change in arterial oxygen pressure (PaO2) [ Time Frame: Measured at the same time as Auto PEEP until the first hour and then every hour, assessed up to the end of surgery (maximum 6 hours) ]
  Variation of partial pressure of oxygen (mmHg) during surgery in prone position
• Arterial carbon dioxide pressure (PaCO2) [ Time Frame: 10 minutes after intubation ]
  Partial pressure of carbon dioxide (mmHg) in supine position
• Arterial carbon dioxide pressure (PaCO2) [ Time Frame: 10 minutes after positioning ]
  Partial pressure of carbon dioxide (mmHg) in prone position
• Change in arterial carbon dioxide pressure (PaCO2) [ Time Frame: Measured at the same time as Auto PEEP until the first hour and then every hour, assessed up to the end of surgery (maximum 6 hours) ]
  Variation of partial pressure of carbon dioxide (mmHg) during surgery in prone position

Background:

There is a lack of studies regarding Optimal (best) positive end-expiratory pressure (PEEP) in prone position during surgery, and its relation with optimal PEEP in supine position.

Hypothesis:

In patients undergoing scheduled spinal surgery, optimal PEEP in the prone position is lower than optimal PEEP in the supine position.

Aims:

To assess the difference optimal PEEP in supine vs. prone positions in patients undergoing spine surgery.

To evaluate the changes in optimal PEEP in prone position throughout the surgical procedure.

Methods:

Observational study, one center. Main variable: optimal PEEP. Secondary variables: PaO2, pCO2 and dynamic compliance (Crd) in prone and supine position.

• Anesthesia
• Surgery

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Inclusion Criteria:

• Age ≥18 years.
• Spine prone surgery lasting ≥2 hours.
• Absence of known pulmonary pathology.

Exclusion Criteria:

• Pregnancy or lactation.
• Contraindication to alveolar recruitment maneuvers (risk of barotrauma, hemodynamic instability).
• Body mass index (BMI) >35.
• Heart failure defined as IC <2.5 L/min/m2 and/or inotropic support requirements prior to surgery.
• Diagnosis or suspicion of intracranial hypertension (intracranial pressure >15 mmHg).