Induction of Anesthesia With Sevoflurane Preserving Spontaneous Breathing: Cardiorespiratory Effects.

Airway management is of outmost importance in the perioperative period. One of the main questions while making a plan for airway management is whether spontaneous ventilation should be maintained or not. Induction of anesthesia with Sevoflurane is a conventional technique that preserves spontaneous ventilation. It is used especially in non-collaborating patients or when other pharmaceutical agents or sophisticated airway management equipment is out of reach.

Inhalational induction of anesthesia with Sevoflurane is well studied. However, there are few studies investigating the effects of Sevoflurane on induction and intubating conditions, on cardiopulmonary physiology, on emergence conditions, when it is used as one and only agent to achieve induction of anesthesia, intubation and maintenance of anesthesia in adult patients. There is also no consensus on the appropriate duration of the inhalational induction or other criteria to guarantee successful intubation conditions, since most studies investigate Sevoflurane administration until induction of anesthesia and not until intubation.

From all the above, it appears that there are a few gaps in the management of patients who are to be intubated with Sevoflurane only, without the use of any other anesthetic agents.

Preoperatively, the study protocol-mandated baseline data will be recorded: gender, age, body weight, body mass index, body surface area, ASA-PS, type of surgery. The airway assessment will include Mallampati score, thyromental distance, cervical spine mobility, upper lip bite test, mouth opening, micrognathia, protruding incisors, beard, denture, snoring.

Patients will be randomly allocated into one of two groups: the S group was to be intubated after inhalational anesthesia with Sevoflurane only and maintenance of anesthesia with Sevoflurane 1MAC. The P group will receive standard anesthesia induction with propofol 1,5mg/Kg, fentanyl 2mcg/Kg, rocuronium 0,5mg/Kg, while anesthesia will be maintained by sevoflurane.

Before induction of anesthesia, we will record baseline data including BIS, SpO2, heart rate, invasive blood pressure, cardiac output, stroke volume, stroke volume variation, respiratory rate, and arterial blood gas sample recordings.

During induction of anesthesia, the following data will be recorded: BIS, SpO2, heart rate, invasive blood pressure, cardiac output, stroke volume, stroke volume variation, respiratory rate, recordings from arterial blood gas sample, induction to anesthesia conditions (limb movement, cough, salivation, laryngospasm, and apnea), respiratory rate, tidal volume, minute volume, end-tidal CO2, the concentration of sevoflurane (inhaled, exhaled), peak inspiratory pressure, mean inspiratory pressure, dynamic respiratory compliance. In the S group, these data will be recorded again five minutes after the induction to anesthesia commencement.

During intubation, we will record BIS, SpO2, heart rate, blood pressure, cardiac output, stroke volume, stroke volume variation, intubating conditions (jaw relaxation, vocal cord position, vocal cord movement, limb movement, bucking), Cormack-Lehane grade, duration of intubation.

After intubation we will register: BIS, SpO2, heart rate, invasive blood pressure, cardiac output, stroke volume, stroke volume variation, respiratory rate, recordings from arterial blood gas sample, respiratory rate, tidal volume, minute volume, end-tidal CO2, the concentration of sevoflurane (inhaled, exhaled), peak inspiratory pressure, mean inspiratory pressure, dynamic respiratory compliance, were recorded. Patients having abolished spontaneous breathing will be set on the IMV mode of ventilation receiving tidal volume 8ml/Kg, 10 breaths/min, PEEP=5cmH2O, I: E=1:2, Plateau time 30%.

Upon the end of the surgical stimuli the following parameters will be registered: BIS, blood pressure, heart rate, SpO2, stroke volume, stroke volume variation, cardiac output, etCO2, respiratory rate, sevoflurane concentration (exhaled, inhaled), peak inspiratory pressure, mean inspiratory pressure, dynamic compliance, time of establishing spontaneous breathing, time of extubation.

BIS, blood pressure, heart rate, SpO2, stroke volume, stroke volume variation, cardiac output, etCO2, the respiratory rate will be recorded 5 and 10 minutes respectively post-extubation.

Eligibility Criteria:
Inclusion Criteria:

* Age \>18 and \< 71 years
* ASA-PS 1-3 (American Society of Anesthesiologists Physical Status classification)
* General anesthesia for abdominal surgery
* Elective cases
* Signed informed consent

Exclusion Criteria:

* Urgent/emergency surgeries
* BMI\<18.5 or BMI\>34.9
* Intraabdominal hypertension
* Gastroesophageal reflex
* Pregnancy
* Liver or renal failure
* intracranial hypertension