Evaluation of Optimal Esophageal Catheter Balloon Inflation Volume in Mechanically Ventilated Children.

BACKGROUND: Accuracy of esophageal pressure measured by an air-filled esophageal balloon catheter is dependent on balloon filling volume. However, this has been understudied in mechanically ventilated children. We sought to study the optimal filling volume in children receiving ventilation by using previously reported calibration methods. Secondary objectives included to examine the difference in pressure measurements at individualized optimal filling volume versus a standardized inflation volume and to study if a static hold during calibration is required to identify the optimal filling volume. METHODS: An incremental inflation calibration procedure was performed in children receiving ventilation, <18 y, instrumented with commercially available catheters (6 or 8 French) who were not breathing spontaneously. The balloon was manually inflated by 0.2 to 1.6 mL (6 French) or 2.6 mL (8 French). Esophageal pressure (Pes) and airway pressure tracings were recorded during the procedure. Data were analyzed offline by using 2 methods: visual determination of filling range with the calculation of the highest difference between expiratory and inspiratory Pes and determination of a correctly filled balloon by calculating the esophageal elastance. RESULTS: We enrolled 40 subjects with median (interquartile range [IQR]) age 6.8 (2-25) months. The optimal filling volume ranged from 0.2 to 1.2 mL (median [IQR] 0.6 [0.2-1.0] mL) in the subjects with a 6 French catheter and 0.2-2.0 mL (median [IQR] 0.7 [0.5-1.2] mL) for 8 French catheters. Inflating the balloon with 0.6 mL (median computed from the whole cohort) gave an absolute difference in transpulmonary pressure that ranged from -4 to 7 cm H2O compared with the personalized volume. Pes calculated over 5 consecutives breaths differed with a maximum of 1 cm H2O compared to Pes calculated during a single inspiratory hold. The esophageal elastance was correlated with weight, age, and sex. CONCLUSIONS: The optimal balloon inflation volume was highly variable, which indicated the need for an individual calibration procedure. Pes was not overestimated when an inspiratory hold was not applied.

Ultrasound assessment is useful for evaluating balloon volume of resuscitative endovascular balloon occlusion of the aorta.

BACKGROUND: Endovascular balloon occlusion of the aorta (EBOA) increases proximal arterial pressure but may also induce life-threatening ischemic complications. Although partial REBOA (P-REBOA) mitigates distal ischemia, it requires invasive monitoring of femoral artery pressure for titration. In this study, we aimed to titrate P-REBOA to prevent high-degree P-REBOA using ultrasound assessment of femoral arterial flow. METHODS: Proximal (carotid) and distal (femoral) arterial pressures were recorded, and perfusion velocity of distal arterial pressures was measured by pulse wave Doppler. Systolic and diastolic peak velocities were measured among all ten pigs. Total REBOA was defined as a cessation of distal pulse pressure, and maximum balloon volume was documented. The balloon volume (BV) was titrated at 20% increments of maximum capacity to adjust the degree of P-REBOA. The distal/proximal arterial pressure gradient and the perfusion velocity of distal arterial pressures were recorded. RESULTS: Proximal blood pressure increased with increasing BV. Distal pressure decreased with increasing BV, and distal pressure sharply decreased by > 80% of BV. Both systolic and diastolic velocities of the distal arterial pressure decreased with increasing BV. Diastolic velocity could not be recorded when the BV of REBOA was > 80%. CONCLUSION: The diastolic peak velocity in the femoral artery disappeared when %BV was > 80%. Evaluation of the femoral artery pressure by pulse wave Doppler may predict the degree of P-REBOA without invasive arterial monitoring.

Delivery balloon volume positively correlates with the diameter and effective orifice area of implanted SAPIEN 3.

BACKGROUND: In transcatheter aortic valve replacement (TAVR) using SAPIEN 3 (S3) (Edwards Lifesciences, Irvine, CA, USA), some clinicians decrease or increase the delivery balloon volume (VOL) when deploying S3 or conducting post-dilatation. However, the effects of controlling VOL on transcatheter heart valve diameter (THVD) and valve function remain unclear. We assessed associations among VOL, THVD, and effective orifice area (EOA) of S3. METHODS: We enrolled patients undergoing TAVR using 23- and 26-mm S3 in Sendai Kousei Hospital between 2017 and 2019. VOL was controlled based on preprocedural computed tomography and intraprocedural transesophageal echocardiography (TEE). THVD were defined as the diameters of transcatheter heart valve at mid-level measured by TEE. RESULTS: In enrolled 332 patients (23-mm, n = 188; 26-mm, n = 144), one (0.3%) and two (0.6%) developed annulus rupture and moderate/severe paravalvular leak, respectively. VOL at deployment was positively correlated with THVD on deployment (23-mm, r = 0.44, p < 0.001; 26-mm, r = 0.57, p < 0.001) and EOA (23-mm, r = 0.23, p = 0.0019; 26-mm, r = 0.22, p = 0.0094). In multiple regression analyses, VOL and post-dilatation were significant determinants of THVD, although aortic annulus area, calcium volume, and pre-dilatation were not. The areas under the receiver operating characteristic curve that were used to evaluate the accuracy of the index obtained by dividing THVD by body surface area (indexed THVD) to predict patient-prosthesis mismatch (PPM) were 0.744 and 0.811 in the 23- and 26-mm cohorts, respectively. A cut-off indexed THVD of ≤11.5 and 12.1 mm/m2 well predicted PPM (23-mm, odds ratio, 5.20; 95% confidence interval, 1.33-20.3; 26-mm, odds ratio 14.1, 95% confidence interval 2.40-81.0). CONCLUSION: VOL was positively correlated with THVD and EOA. Smaller indexed THVD was associated with a higher incidence of PPM. Controlling VOL under on-site THVD evaluation may be useful in reducing the PPM incidence.

Distal pressure monitoring and titration with percent balloon volume: feasible management of partial resuscitative endovascular balloon occlusion of the aorta (P-REBOA).

INTRODUCTION: Resuscitative endovascular balloon occlusion of the aorta (REBOA) increases proximal arterial pressure, but may also induce life-threatening distal ischemia. Partial REBOA (P-REBOA) is thought to mitigate distal ischemia during aortic occlusion. However, feasible indicators of the degree of P-REBOA remain inconsistent. We hypothesised percent balloon volume could be a substitute for pressure measurements of gradients during P- REBOA. This study aimed to compare balloon volume and arterial pressure gradient, and analysed with intra-balloon pressure and balloon shape. METHODS: Proximal (carotid) and distal (femoral) arterial pressures were recorded and a 7-Fr REBOA catheter was placed in four swine. Total REBOA was defined as a cessation of distal pulse pressure and maximum balloon volume was documented. The balloon volume was titrated by 20% increments of maximum capacity to adjust the degree of P-REBOA. The distal/proximal arterial pressure gradient and the intra-balloon pressures were also recorded. The changes in shape and the cross-sectional area of the balloon were evaluated with computed tomography (CT) images. RESULTS: The proximal mean arterial pressure (MAP) plateaued after 60% balloon volume; meanwhile, distal pulse pressure was still left. The balloon pressure was traced with proximal MAP before contact with aortic wall. The balloon shape changed unevenly from "cone" to "spindle" shape, although the balloon cross-sectional area of the mid-segment linearly increased. CONCLUSION: Monitoring distal pressure and titrating percent balloon volume is feasible to manage P-REBOA. In this experiment, 60% balloon volume was enough inflation to elevate central pressure allowing distal perfusion. The intra-balloon pressure was not reliable due to the strong influence of proximal MAP and uneven change of the balloon shape.

Optimal esophageal balloon volume for accurate estimation of pleural pressure at end-expiration and end-inspiration: an in vitro bench experiment.

BACKGROUND: Esophageal pressure, used as a surrogate for pleural pressure, is commonly measured by air-filled balloon, and the accuracy of measurement depends on the proper balloon volume. It has been found that larger filling volume is required at higher surrounding pressure. In the present study, we determined the balloon pressure-volume relationship in a bench model simulating the pleural cavity during controlled ventilation. The aim was to confirm whether an optimal balloon volume range existed that could provide accurate measurement at both end-expiration and end-inspiration. METHODS: We investigated three esophageal balloons with different dimensions and materials: Cooper, SmartCath-G, and Microtek catheters. The balloon was introduced into a glass chamber simulating the pleural cavity and volume-controlled ventilation was initiated. The ventilator was set to obtain respective chamber pressures of 5 and 20 cmH2O during end-expiratory and end-inspiratory occlusion. Balloon was progressively inflated, and balloon pressure and chamber pressure were measured. Balloon transmural pressure was defined as the difference between balloon and chamber pressure. The balloon pressure-volume curve was fitted by sigmoid regression, and the minimal and maximal balloon volume accurately reflecting the surrounding pressure was estimated using the lower and upper inflection point of the fitted sigmoid curve. Balloon volumes at end-expiratory and end-inspiratory occlusion were explored, and the balloon volume range that provided accurate measurement at both phases was defined as the optimal filling volume. RESULTS: Sigmoid regression of the balloon pressure-volume curve was justified by the dimensionless variable fitting and residual distribution analysis. All balloon transmural pressures were within ±1.0 cmH2O at the minimal and maximal balloon volumes. The minimal and maximal balloon volumes during end-inspiratory occlusion were significantly larger than those during end-expiratory occlusion, except for the minimal volume in Cooper catheter. Mean (±standard deviation) of optimal filling volume both suitable for end-expiratory and end-inspiratory measurement ranged 0.7 ± 0.0 to 1.7 ± 0.2 ml in Cooper, 1.9 ± 0.2 to 3.6 ± 0.3 ml in SmartCath-G, and 2.2 ± 0.2 to 4.6 ± 0.1 ml in Microtek catheter. CONCLUSIONS: In each of the tested balloon, an optimal filling volume range was found that provided accurate measurement during both end-expiratory and end-inspiratory occlusion.

Novel method for dynamic control of intracranial pressure.

OBJECT Intracranial pressure (ICP) pulsations are generally considered a passive result of the pulsatility of blood flow. Active experimental modification of ICP pulsations would allow investigation of potential active effects on blood and CSF flow and potentially create a new platform for the treatment of acute and chronic low blood flow states as well as a method of CSF substance clearance and delivery. This study presents a novel method and device for altering the ICP waveform via cardiac-gated volume changes. METHODS The novel device used in this experiment (named Cadence) consists of a small air-filled inelastic balloon (approximately 1.0 ml) implanted into the intracranial space and connected to an external programmable pump, triggered by an R-wave detector. Balloons were implanted into the epidural space above 1 of the hemispheres of 19 canines for up to 10 hours. When activated, the balloons were programed to cyclically inflate with the cardiac cycle with variable delay, phase, and volume. The ICP response was measured in both hemispheres. Additionally, cerebral blood flow (heat diffusion and laser Doppler) was studied in 16 canines. RESULTS This system, depending on the inflation pattern of the balloon, allowed a flattening of the ICP waveform, increase in the ICP waveform amplitude, or phase shift of the wave. This occurred with small mean ICP changes, typically around ± 2 mm Hg (15%). Bilateral ICP effects were observed with activation of the device: balloon inflation at each systole increased the systolic ICP pulse (up to 16 mm Hg, 1200%) and deflation at systole decreased or even inverted the systolic ICP pulse (-0.5 to -19 mm Hg, -5% to -1600%) in a dose-(balloon volume) dependent fashion. No aphysiological or deleterious effects on systemic pressure (≤ ±10 mm Hg; 13% change in mean pressure) or cardiac rate (≤ ± 17 beats per minute; 16% change) were observed during up to 4 hours of balloon activity. CONCLUSIONS The results of these initial studies using an intracranially implanted, cardiac-gated, volume-oscillating balloon suggest the Cadence device can be used to modify ICP pulsations, without physiologically deleterious effects on mean ICP, systemic vascular effects, or brain injury. This device and technique may be used to study the role of ICP pulsatility in intracranial hemo- and hydrodynamic processes and introduces the creation of a potential platform of a cardiac-gated system for treatment of acute and chronic low blood flow states, and diseases requiring augmentation of CSF substance clearance or delivery.