Transient Apnea During Flexible Ureteroscopic Lithotripsy

Chinese Medical Association150 enrolled

Overview

Respiration-related renal motion may reduce targeting stability during flexible ureteroscopic laser lithotripsy and thereby decrease lithotripsy efficiency. This single-center, three-arm randomized controlled trial evaluated whether transient apnea during active lithotripsy could improve lithotripsy efficiency while maintaining short-term physiologic safety. A total of 150 patients undergoing flexible ureteroscopic lithotripsy for renal stones were randomized in a 1:1:1 ratio to regular mechanical ventilation, small tidal-volume ventilation, or transient apnea. The primary outcome was active lithotripsy efficiency, defined as CT-based stone volume divided by active lithotripsy time. Physiologic safety was assessed using serial arterial blood gas measurements at baseline, 3, 6, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation, together with continuous intraoperative cardiopulmonary monitoring.

Respiration-related renal motion is a common technical challenge during flexible ureteroscopic laser lithotripsy. Movement of the kidney and collecting system may reduce laser targeting stability, interrupt continuous lithotripsy, and decrease active lithotripsy efficiency. Ventilation strategies that reduce respiratory motion may therefore improve operative stability, but they must be evaluated together with physiologic safety. This study was designed as a single-center, prospective, three-arm, parallel-group randomized controlled trial. Adult patients scheduled for elective flexible ureteroscopic laser lithotripsy for renal stones under general anesthesia were screened for eligibility. After informed consent and eligibility confirmation, participants were randomized in a 1:1:1 ratio to one of three intraoperative ventilation strategies: regular mechanical ventilation, small tidal-volume ventilation, or transient apnea during active laser lithotripsy. In the regular mechanical ventilation group, standard controlled ventilation was maintained during lithotripsy. In the small tidal-volume ventilation group, a reduced tidal-volume strategy was used during the lithotripsy phase to decrease respiration-related renal motion while maintaining clinically acceptable oxygenation and ventilation. In the transient apnea group, apnea was initiated during active laser lithotripsy after adequate preoxygenation and confirmation of hemodynamic stability by the anesthesiologist. Apnea was discontinued if any prespecified safety criterion occurred, including SpO₂ \<90%, systolic blood pressure \>160 mmHg or \<80 mmHg, heart rate \<50 beats/min, obvious arrhythmia, hemodynamic instability, or any safety concern from the attending anesthesiologist. The primary efficacy outcome was active lithotripsy efficiency, defined as CT-based stone volume divided by active lithotripsy time. Secondary outcomes included active lithotripsy time, total operative time, postoperative stone-free status, residual stone burden, physiologic changes on arterial blood gas analysis, protocol-defined apnea interruption, and postoperative complications. Stone-free status was assessed by CT, and non-stone-free status was defined as any residual fragment \>2 mm. Arterial blood gas measurements were obtained at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.

Interventions

Regular mechanical ventilation during flexible ureteroscopic lithotripsyOTHER

Standard controlled mechanical ventilation was maintained during the active lithotripsy phase according to routine anesthetic practice.

Small tidal-volume ventilation during flexible ureteroscopic lithotripsyOTHER

Controlled ventilation with a reduced tidal-volume strategy was applied during active lithotripsy under continuous anesthetic monitoring.

Transient apnea during flexible ureteroscopic lithotripsyOTHER

Transient apnea was applied during active laser lithotripsy to reduce respiration-related renal motion. Apnea was initiated after adequate preoxygenation and confirmation of physiologic stability. Apnea was terminated if SpO₂ was \<90%, systolic blood pressure was \>160 mmHg or \<80 mmHg, heart rate was \<50 beats/min, obvious arrhythmia occurred, hemodynamic instability developed, or the attending anesthesiologist had any safety concern.

Eligibility

Sex: ALLMin age: 18 YearsMax age: 80 Years

Medical Language ↔ Plain English

Inclusion Criteria: 1. Age 18 to 80 years. 2. Scheduled for elective flexible ureteroscopic laser lithotripsy for renal stones under general anesthesia. 3. Preoperative CT confirming renal stones suitable for flexible ureteroscopic lithotripsy. 4. Stone size ≥10 mm and \<20 mm. 5. American Society of Anesthesiologists physical status I to III. 6. Ability to provide written informed consent. Exclusion Criteria: 1. American Society of Anesthesiologists physical status IV or V. 2. Stone size \<10 mm or ≥20 mm. 3. Multiple renal stones requiring a combined or alternative surgical strategy. 4. Radiolucent stone or inadequate radiographic assessment. 5. Uncontrolled urinary tract infection. 6. Reduced pulmonary function, including FEV1/FVC \<70%, or other clinically relevant pulmonary dysfunction judged unsuitable for transient apnea. 7. Significant cardiopulmonary instability or anesthetic contraindication to transient apnea. 8. Pregnancy or planned pregnancy during the study period. 9. Planned combined procedure or alternative surgical strategy. 10. Incomplete preoperative assessment. 11. Declined participation after counselling. 12. Withdrawal of consent before randomization.

Outcomes

Primary Outcomes

Active lithotripsy efficiency

Active lithotripsy efficiency was defined as CT-based stone volume divided by active lithotripsy time. Stone volume was calculated from stone length, width, and depth using the ellipsoid formula. Active lithotripsy time was defined as the duration of active laser fragmentation or dusting and excluded ureteral access, endoscopic inspection, stent placement, and other non-lithotripsy procedural time.

Time frame: Intraoperative

Secondary Outcomes

Active lithotripsy time

Active lithotripsy time was defined as the duration of active laser fragmentation or dusting during flexible ureteroscopic lithotripsy.

Time frame: Intraoperative

Total operative time

Total operative time was defined as the time from endoscope insertion to completion of the procedure.

Time frame: Intraoperative

Stone-free status on postoperative day 1 CT

Stone-free status was assessed using CT on postoperative day 1. Non-stone-free status was defined as any residual fragment \>2 mm.

Time frame: Postoperative day 1

Arterial pH

Arterial pH was measured at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.