PCV-VG Versus VCV Through the I-gel in Young Children

Background and Rationale:

Controlled positive-pressure ventilation (PPV) via second-generation supraglottic airway devices (SADs) such as the i-gel is widely practiced in pediatric anesthesia. However, because SADs do not provide an absolute tracheal seal, peak inspiratory pressure (PIP) exceeding the individual oropharyngeal leak pressure (OLP) risks gas bypassing the cuff into the esophagus. Gastric insufflation increases intra-abdominal pressure, restricts diaphragmatic excursion, and elevates the risk of aspiration. Pressure-controlled ventilation with volume guarantee (PCV-VG) combines a decelerating flow profile with breath-by-breath feedback to deliver target tidal volume at the lowest feasible PIP. While studied in laparoscopic settings, prospective evidence evaluating PCV-VG versus VCV using serial radiologist-performed gastric antrum ultrasonography in non-laparoscopic pediatric surgery remains lacking.

Objectives:

To compare PCV-VG against VCV in children aged 2 to 7 years undergoing elective non-laparoscopic surgery with the i-gel across two co-primary domains:

Ventilatory efficacy: mean expired tidal volume (VTe) delivery relative to ideal body weight target.

Gastric safety: incidence of ultrasonographically confirmed gastric insufflation (antral cross-sectional area \[CSA\] increase ≥ 20% from baseline).

Trial Design \& Interventions:

A prospective, single-center, parallel-group, double-blind, randomized superiority trial conducted at Beni-Suef University Hospital. Ninety children (2-7 years, weight 10-25 kg, ASA I-II) scheduled for elective non-laparoscopic procedures under general anesthesia with i-gel placement will be randomized 1:1 to:

Group PCV-VG (n = 45): Target VT 6-7 mL/kg IBW, PEEP 4 cmH2O, I:E 1:2, respiratory rate adjusted to EtCO2 35-45 mmHg, with closed-loop pressure adjustment capped at baseline OLP minus 3 cmH2O (absolute maximum 20 cmH2O).

Group VCV (n = 45): Target VT 6-7 mL/kg IBW with constant square inspiratory flow, identical PEEP, I:E, and RR targets, without active leak compensation.

Ultrasonic Evaluation Protocol:

A blinded consultant radiologist will perform serial sagittal gastric antrum ultrasonography at three defined timepoints:

T0: Immediately post-i-gel placement (baseline) T1: 20 minutes post-initiation of mechanical ventilation T2: End of surgery (pre-emergence) Antral cross-sectional area (CSA) will be calculated via the ellipse formula (π × D1 × D2 / 4). A positive gastric insufflation event is defined as a post-baseline CSA increase ≥ 20% confirmed on at least 2 of 3 measurements.

Patients in this group will receive mechanical ventilation using Pressure-Controlled Ventilation with Volume Guarantee (PCV-VG; Draeger AutoFlow or platform equivalent) through an i-gel supraglottic airway device following standard intravenous induction and muscle relaxation with atracurium.

Ventilation parameters: Target tidal volume (VT) set at 6-7 mL/kg ideal body weight (IBW), PEEP 4 cmH2O, I:E ratio 1:2, and age-stratified respiratory rate adjusted to maintain EtCO2 at 35-45 mmHg. The closed-loop algorithm dynamically auto-titrates inspiratory pressure (Pinsp) breath-by-breath based on the previous breath's expired tidal volume (VTe) to achieve target VT, with Pinsp safety ceiling capped at the individual baseline oropharyngeal leak pressure (OLP) minus 3 cmH2O (absolute maximum 20 cmH2O).

Procedure: Pressure-Controlled Ventilation with Volume Guarantee (PCV-VG)

Patients in this group will receive standard mechanical ventilation using Volume-Controlled Ventilation (VCV) through an i-gel supraglottic airway device following standard intravenous induction and muscle relaxation with atracurium.

Ventilation parameters: Set tidal volume (VT) programmed at 6-7 mL/kg ideal body weight (IBW) with a constant square inspiratory flow waveform, PEEP 4 cmH2O, I:E ratio 1:2, and age-stratified respiratory rate adjusted to maintain EtCO2 at 35-45 mmHg. No active closed-loop leak-compensation or pressure-guarantee algorithm is engaged. Peak inspiratory pressure safety limit is set at baseline OLP minus 3 cmH2O (absolute maximum 20 cmH2O). If VTe falls \> 20% below set VT for ≥ 3 consecutive breaths, VT may be up-titrated in 0.5 mL/kg IBW increments up to maximum 9 mL/kg IBW provided peak pressure remains below OLP.

Procedure: Volume-Controlled Ventilation (VCV)

Administration of closed-loop pressure-controlled ventilation with volume guarantee via the i-gel supraglottic airway, maintaining target VT 6-7 mL/kg IBW with breath-by-breath inspiratory pressure auto-titration.

Administration of traditional volume-controlled ventilation with constant inspiratory flow via the i-gel supraglottic airway, maintaining set VT 6-7 mL/kg IBW without automated pressure adaptation.

Time frame: Measured at 20 minutes post-initiation of mechanical ventilation (T1) and at end of surgery / pre-emergence (T2, up to 120 minutes)

Measured in milliliters per kilogram of ideal body weight (mL/kg IBW) using the anesthesia workstation flow sensor. Evaluates delivery accuracy relative to the prescribed target (6.0-7.0 mL/kg IBW).

Values within the target prescribed range (6.0-7.0 mL/kg IBW) indicate a good result (effective alveolar ventilation). Values significantly below target (\< 5.0 mL/kg IBW) indicate a bad result (hypoventilation due to circuit leak), while values above target (\> 8.0 mL/kg IBW) indicate a bad result (risk of volutrauma).

Time frame: Intraoperative period (assessed at 20 minutes post-ventilation [T1] and end of surgery [T2], up to 120 minutes total)

Defined as an increase in serial radiologist-measured gastric antrum cross-sectional area (CSA) ≥ 20% from baseline (T0), confirmed on ≥ 2 of 3 measurements at either T1 or T2, calculated using the ellipse formula: CSA=(π × D1 × D2)/4 A lower percentage indicates a good result (enhanced gastric safety and effective airway seal). A higher percentage indicates a bad result (increased risk of gastric distension, elevated intra-abdominal pressure, and pulmonary aspiration).

Time frame: Measured at 20 minutes post-initiation of mechanical ventilation (T1) and at end of surgery / pre-emergence (T2, up to 120 minutes)

Peak airway pressure measured in centimeters of water (cmH2O) directly from the anesthesia workstation pressure transducer.

A lower value indicates a good result (reduced risk of barotrauma and lower potential to exceed oropharyngeal leak pressure). A higher value indicates a bad result (increased pulmonary barotrauma risk and higher likelihood of driving gas into the esophagus).

Time frame: Measured at 20 minutes post-initiation of mechanical ventilation (T1) and at end of surgery / pre-emergence (T2, up to 120 minutes)

Calculated using the formula: Cdyn= (VTe) ÷(Ppeak-PEEP), expressed in mL/cmH2O. A higher value indicates a good result (superior lung/thoracic compliance and lower resistance to inflation). A lower value indicates a bad result (stiffer lungs, higher airway resistance, or increased impedance).

Time frame: Measured immediately post-i-gel placement (T0) and at 20 minutes post-initiation of mechanical ventilation (T1)

Airway pressure in cmH2O at which an anterior cervical leak is detected on precordial auscultation during circuit occlusion.

A higher value indicates a good result (a tighter perilaryngeal device seal capable of sustaining higher positive pressure without leaking). A lower value indicates a bad result (poor device seal and higher risk of leak).

Time frame: Measured at T0 (post-i-gel placement), T1 (20 minutes post-ventilation start), T2 (end of surgery), and at emergence / i-gel removal (up to 120 minutes)

Measured in millimeters of mercury (mmHg) using continuous side-stream capnography on the anesthesia workstation to assess systemic ventilation status and carbon dioxide elimination.

Directional Interpretation: Values within the physiological target range (35-45 mmHg) indicate a good result (optimal normocapnic ventilation). Values significantly above target (\> 45 mmHg) indicate a bad result (hypercapnia/hypoventilation due to circuit leak or dead-space rebreathing), while values below target (\< 30 mmHg) indicate a bad result (hypocapnia due to hyperventilation).

Time frame: Total duration of mechanical ventilation (up to 120 minutes)

Percentage calculated as: 100 × \[(Duration of mechanical ventilation with EtCO2 \> 50 mmHg)÷(Total Mechanical Ventilation Time)\].

A lower percentage (ideally 0%) indicates a good result (effective carbon dioxide clearance throughout the surgical procedure). A higher percentage indicates a bad result (sustained alveolar hypoventilation or persistent leak leading to carbon dioxide retention).

Time frame: Entire duration of mechanical ventilation (up to 120 minutes)

Percentage calculated as: 100 × \[(Breaths where Ppeak)\> (Baseline OLP)÷ (Total Mechanical Breaths)\].

A lower value (ideally 0%) indicates a good result (effective pressure containment within safe seal thresholds). A higher value indicates a bad result (frequent pressure spikes above the seal threshold, driving air into the stomach).

Time frame: From i-gel insertion until PACU transfer (up to 180 minutes)

Composite incidence of laryngospasm, bronchospasm, oxygen desaturation (SpO2 \< 93%), i-gel displacement, or endotracheal intubation conversion.

A lower percentage indicates a good result (superior airway safety and stability). A higher percentage indicates a bad result (increased perioperative respiratory complications).

Time frame: At time of airway placement (induction period, approximately 1-3 minutes)

Time in seconds from first device handling until capnographic confirmation of airway placement.

A lower value indicates a good result (faster, smoother airway securing). A higher value indicates a bad result (prolonged or difficult device placement).

Time frame: Postoperative recovery period (up to 120 minutes)

PACU entry to achieving a modified Aldrete Score ≥ 9/10. A lower value indicates a good result (faster recovery and readiness for ward transfer). A higher value indicates a bad result (delayed recovery or lingering anesthetic effects).

Time frame: 24 hours postoperatively

Composite incidence of sore throat, hoarseness, or dysphagia assessed at 24 hours via telephone.

A lower percentage indicates a good result (minimal airway mucosal trauma). A higher percentage indicates a bad result (higher postoperative airway morbidity).

PCV-VG Versus VCV for Ventilatory Efficacy and Gastric Safety Through the I-gel Supraglottic Airway in Young Children: A Randomized Controlled Trial