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A Pilot Study to Assess Effects of Self-Adjusted Nitrous Oxide (SANO) on Urodynamic Study (UDS) Parameters
Abigail J. Escobar, BS1, Ranveer Vasdev, MS2, Mary Gallo, NP1, Kenneth Softness, MD1, Hsin-Hsiao S. Wang, MD, MPH, MBAn3, Heidi J. Rayala, MD, PhD1.
1Beth Israel Deaconess Medical Center, Boston, MA, USA, 2University of Minnesota School of Medicine, Minneapolis, MN, USA, 3Boston Children's Hospital, Boston, MA, USA.

Introduction: A urodynamic study (UDS) is a challenging invasive examination associated with significant patient distress. Sedatives such as ketamine and midazolam have been shown to compromise a patient's ability to give verbal feedback during UDS. Thus, there exists a need for an agent that alleviates pain and anxiety, yet preserves patient communication and reliability of UDS outcomes. Nitrous oxide (NO) is routinely used in the ambulatory setting to relieve peri-procedural pain and anxiety. When administered at concentrations <50%, NO is classified as minimal sedation, eliminating the need for anesthesia personnel, NPO status and a patient escort. NO's rapid onset and offset also allows for near-immediate analgesia. Our study seeks to determine whether SANO alters UDS outcomes and also assess effects of SANO on patient-reported pain.
Materials & Methods: This is a single-center prospective randomized controlled trial comparing UDS with or without SANO. Each patient received SANO during catheter placement to determine patient-preferred NO level. Subsequently, the patient underwent two UDS fills, randomized to one run with oxygen and one run with SANO. Both the patient and operator performing the UDS were blinded to which gas was being delivered. UDS were interpreted by two blinded urologists.
Primary outcomes were standard UDS parameters (compliance, capacity, detrusor overactivity and contractility, flow rate, and post-void residuals (PVR)). Secondary outcomes included patient-reported pain measured immediately before maximum capacity during both fills using the Visual Analog Scale for Pain (VAS-P). Maintenance of positioning, patient responsiveness, and tolerance of the procedure were rated by the blinded operator performing the UDS. Wilcox Rank Sum and Chi-Squared Tests, adjusted for paired observations, were used. Sensitivity analysis was performed to compare outcomes with SANO as the 1st or 2nd round.
Results: 19 participants, each with 2 runs (n=38 UDS) were included for analysis. Between SANO and oxygen runs, there was no significant difference in bladder capacity, maximum flow rate, pressure at max flow rate, detrusor overactivity, void quality, or bladder compliance. Sensitivity analysis adjusting for SANO as the 1st or 2nd round demonstrated no significant difference in outcomes. Two patients were unable to void during the oxygen run, but were able to volitionally void during the SANO run. Patients reported significantly less pain during the SANO run compared to the oxygen run (0.7 1.5 vs. 2.0 3; p=0.047). The UDS operator rated patient responsiveness and tolerance of procedure to be significantly better than expected during runs with SANO when compared to runs with oxygen (p=0.001, p <0.001, respectively). There were no complications in the 19 participants. Post-procedure survey of the patients revealed that 78.9% (n=15) would prefer to receive SANO during a future UDS if provided the option.
Conclusions: Patients receiving SANO during UDS have comparable UDS tracings while reporting lower pain and future preference to receive SANO. SANO is a feasible and safe alternative with high satisfaction for patients undergoing UDS.

UDS CharacteristicControl, N = 191SANO, N = 191Difference2p-value3
Capacity (mL)441 (301)458 (285)-18 (-211, 175)0.23
Detrusor Overactivity4 (21%)6 (32%)-11% (-44%, 23%)0.61
Post Void Residual (mL)145 (184)132 (184)13 (-108, 134)0.66
Qmax (mL/sec)11 (8)12 (8)-1.8 (-7.2, 3.7)0.78
Pdet at Qmax (cmH2O)48 (27)50 (25)-1.7 (-19, 16)0.73
Bladder Outflow Obstruction Index (BOOI)31 (36)30 (38)0.48 (-24, 25)0.46
Bladder Contractility index (BCI)100 (45)112 (39)-12 (-39, 16)0.92
Poor Compliance2 (11%)3 (16%)-5.3% (-32%, 21%)>0.99
Flat, Short, or Weak Void14 (74%)12 (63%)11% (-24%, 45%)0.48
Patient Pain & Anxietyp-value3
Intra-procedural VAS-P2.3 (2.3)1.5 (2.5)0.8 (-0.8, 2.4)0.047
Intra-procedural VAS-A1.9 (2.0)1.5 (1.4)0.5 (-0.7, 1.7)0.26
Patient Responsiveness0.001
Worse than expected0 (0)1 (5.3)NA
As expected19 (100)5 (26.3)NA
Better than expected0 (0)13 (68.4)NA
Procedure Tolerance <0.001
Worse than expected0 (0)0 (0)NA
As expected18 (94.7)3 (15.8)NA
Better than expected1 (5.3)16 (84.2)NA
SANO, self-adjusted nitrous oxide; VAS-P, Visual Analog Scale-Pain; VAS-A, Visual Analog Scale-Anxiety; NA, Not Applicable 1Mean (SD); n (%) 2Mean Difference (95% Confidence Interval) 3Wilcoxon signed rank test with continuity correction; McNemar's Chi-squared test with continuity correction


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