Transient Apnea During Flexible Ureteroscopic Lithotripsy (TA-fURS)

Transient Apnea to Stabilize Renal Motion During Flexible Ureteroscopic Lithotripsy: A Randomized Controlled Trial of Efficiency and Physiological Safety

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.

Study Overview

• Status: Completed
• Conditions: Renal Calculi; Kidney Stones
• Intervention / Treatment: Other: Regular mechanical ventilation during flexible ureteroscopic lithotripsy; Other: Small tidal-volume ventilation during flexible ureteroscopic lithotripsy; Other: Transient apnea during flexible ureteroscopic lithotripsy

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Actual): 150
• Phase: Not Applicable

Contacts and Locations

Study Locations

• China
  • Shanghai Municipality
    • Shanghai, Shanghai Municipality, China, 200433
      • Changhai Hospital, Naval Medical University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 80 years (Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

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.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Regular Mechanical Ventilation; Participants received regular mechanical ventilation during flexible ureteroscopic laser lithotripsy under general anesthesia.	Other: Regular mechanical ventilation during flexible ureteroscopic lithotripsy; Standard controlled mechanical ventilation was maintained during the active lithotripsy phase according to routine anesthetic practice.
Active Comparator: Small Tidal-Volume Ventilation; Participants received small tidal-volume controlled ventilation during active flexible ureteroscopic laser lithotripsy to reduce respiration-related renal motion while maintaining clinically acceptable oxygenation and ventilation.	Other: Small tidal-volume ventilation during flexible ureteroscopic lithotripsy; Controlled ventilation with a reduced tidal-volume strategy was applied during active lithotripsy under continuous anesthetic monitoring.
Experimental: Transient Apnea; Participants underwent transient apnea during active flexible ureteroscopic laser lithotripsy after adequate preoxygenation and confirmation of physiologic stability by the anesthesiologist.	Other: Transient apnea during flexible ureteroscopic lithotripsy; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	Intraoperative

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Active lithotripsy time	Active lithotripsy time was defined as the duration of active laser fragmentation or dusting during flexible ureteroscopic lithotripsy.	Intraoperative
Total operative time	Total operative time was defined as the time from endoscope insertion to completion of the procedure.	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.	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.	Baseline to 3 minutes after resumption of ventilation
Arterial carbon dioxide tension	Arterial PaCO₂ was measured at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.	Baseline to 3 minutes after resumption of ventilation
Arterial oxygen tension	Arterial PaO₂ was measured at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.	Baseline to 3 minutes after resumption of ventilation
Arterial lactate	Arterial lactate was measured at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.	Baseline to 3 minutes after resumption of ventilation
Base excess	Base excess was measured at baseline, 3 minutes, 6 minutes, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation.	Baseline to 3 minutes after resumption of ventilation
Protocol-defined interruption of transient apnea	Protocol-defined interruption was recorded when transient apnea was discontinued because of SpO₂ <90%, systolic blood pressure >160 mmHg or <80 mmHg, heart rate <50 beats/min, obvious arrhythmia, hemodynamic instability, or anesthesiologist concern.	Intraoperative
Postoperative complications	Postoperative complications were recorded and graded according to the Clavien-Dindo classification.	Up to 3 months after surgery

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
duration of the operation	We record the duration of the operation	from the start of the surgery to the end of the surgery
recovery time	We record how long it will take for the patients to act accoreding to our order after ceasing anesthesia.	from the end of anesthesia to return of consciousness
intraoperative awareness	We will record if patinets have any memory during the operative, namely intraoperatiove awareness.	from the initiation of anesthesia to the end of the surgery

Collaborators and Investigators

• Sponsor: Chinese Medical Association

Study record dates

Study Major Dates

• Study Start (Actual): June 15, 2020
• Primary Completion (Actual): December 27, 2024
• Study Completion (Actual): April 16, 2025

Study Registration Dates

• First Submitted: April 2, 2013
• First Submitted That Met QC Criteria: April 11, 2013
• First Posted (Estimated): April 19, 2013

Study Record Updates

• Last Update Posted (Actual): June 15, 2026
• Last Update Submitted That Met QC Criteria: June 11, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Flexible ureteroscopy; Arterial blood gas; Mechanical ventilation; Laser lithotripsy; Renal stone; Transient apnea; Renal motion; Lithotripsy efficiency; Small tidal-volume ventilation
• Additional Relevant MeSH Terms: Urogenital Diseases; Male Urogenital Diseases; Calculi; Pathological Conditions, Anatomical; Kidney Diseases; Urologic Diseases; Female Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Urolithiasis; Urinary Calculi; Pathological Conditions, Signs and Symptoms; Kidney Calculi; Nephrolithiasis
• Other Study ID Numbers: SMV-312

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be publicly shared because the dataset contains patient-level perioperative, imaging, and physiologic monitoring data, and public sharing was not included in the original informed consent. Deidentified data underlying the published results may be made available from the corresponding investigator upon reasonable request and after institutional ethics approval.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No