Physiologic Effects of 3 Different Neonatal Volume-Targeted Ventilation Modes in Surfactant-Deficient Juvenile Rabbits

Abstract

BACKGROUND: Different brands of volume-targeted modes may vary the location of tidal volume (V T ) monitoring and whether peak inspiratory pressure is adjusted based on inspiratory, expiratory , or leak-compensated V T . These variables may result in different levels of support provided to patients, especially when an endotracheal tube (ETT) leak is present. We hypothesized that there would be no differences in gas exchange, triggering, or work of breathing between volume-targeted modes of 3 different brands of equipment in a surfactant-deficient, spontaneously breathing animal model with and without an ETT leak. METHODS: Twelve rabbits (mean ؎ SD 1.61 ؎ 0.20 kg) were sedated, anesthetized, intubated, lavaged with 0.9% saline solution, and randomized in a crossover design so that each animal was supported by 3 different volume-targeted modes at identical settings with and without an ETT leak. After 30 min, arterial blood gas, V T , and esophageal and airway pressure were recorded for each condition, and pressure-rate product and percentage of successfully triggered breaths were calculated. RESULTS: Gas exchange and the pressure-rate product were not different between the ventilators in the absence of an ETT leak. When an ETT leak was introduced, volume-guarantee modes allowed a higher percentage of triggered breaths and peak inspiratory pressure, which resulted in higher minute ventilation, pH, and lower P aCO 2 than the pressure-regulated volume control mode (P < .05). CONCLUSIONS: When a moderate ETT leak was present, volume-targeted modes that used proximal V T monitoring and triggering with adaptive leak compensation capabilities appeared more effective in providing ventilation support than did a ventilator that used measurements obtained from the back at the ventilator and does not have leak compensation.

Physiologic Effects of Instilled and Aerosolized Surfactant Using a Breath-Synchronized Nebulizer on Surfactant-Deficient Rabbits

“…Sample size calculation for surfactant treatment (n = 5 per group) was based on power analysis using mean and standard deviation of partial pres-sure of oxygen in the arterial blood (PaO 2 ) from a previous rabbit study that compared nebulized to directly instilled surfactant in intubated mechanically ventilated rabbits [22]. We included descriptive control animals (n = 2) that did not receive surfactant, based on our previous work with a similar animal rabbit injury model where disease severity was consistent up to 4 h following lung lavage [23]. Final sample size was determined as five animals per treatment group and two descriptive controls.…”

“…The FiO 2 was increased to 1.0, and the lungs were depleted of surfactant and injured by repeated lavage with 25 mL/kg of warmed (39 • C) normal saline (0.9%), with 5 min recoveries between lavages until dynamic compliance was 50% of the non-lavaged value or SpO 2 90-92% on FiO 2 of 0.5 [23]. The FiO 2 was reduced to 0.5 and animals were deemed surfactant-deficient when PaO 2 < 75 mmHg was confirmed with two consecutive ABGs 30 min apart following lavage/injury.…”

“…Disease severity calculation was based on ventilator parameters and ABG values at baseline and 30 min intervals as Oxygenation Index (OI), ventilation efficiency index (VEI), alveolar-arterial oxygen gradient (A-aDO 2 ), and dynamic compliance (Cdyn) were calculated [26][27][28]. Indices of breathing effort were based on pressure rate product (PRP) which is the product of peak-to-trough change in esophageal pressure (∆Pes, cmH 2 O) × respiratory rate (breaths/minute) generated by animals while breathing during assisted ventilation [23]. EIT measurements were used to estimate changes in end-expiratory lung volume (EELV) loss and recovery related to surfactant administration, as described in more detail elsewhere [29].…”

2019 Year in Review: Neonatal Respiratory Support

“…Several barriers have hampered the diffusion of volume-targeted ventilation, including provider experience level, lack of established V T targets based upon disease state, large endotracheal tube leaks (eg, > 50%), and a ventilator's ability to deliver and accurately measure V T . [77][78][79] Wong and colleagues 80 prospectively studied very low birthweight and ELBW subjects who underwent volumetargeted ventilation with the aim of describing breath-tobreath variation in expired V T . The authors analyzed 6 h of continuous ventilator data and found no significant variations in expired V T between cohorts, despite the ELBW cohort having significantly lower set V T (4.6 vs 7.2 mL, P < .001).…”

“…This study evaluated volume-targeted ventilation delivery in a single ventilator type because previous bench and animal studies have suggested considerable variability in ventilator performance, with variations in V T becoming more pronounced with increased leak or lower V T targets. 79,81 Future studies should evaluate V T target ranges for specific disease conditions, such as evolving RDS, congenital diaphragmatic hernia, meconium aspiration syndrome, and BPD, and incorporate performance data respective to different ventilators.…”