Increased end-expiratory pressures improve lung function in near-term newborn rabbits with elevated airway liquid volume at birth

Abstract

Approximately 53% of near-term newborns admitted into intensive care, experience respiratory distress. These newborns are commonly delivered by caesarean section and have elevated airway liquid volumes at birth, which can cause respiratory morbidity. We investigated the effect of providing respiratory support with a positive end expiratory pressure (PEEP) of 8cmH2O on lung function in newborn rabbit kittens with elevated airway liquid volumes at birth.Near-term rabbits (30d; term=32d) with airway liquid volumes that corresponded to vaginal delivery (~7mL/kg, Control, n=11) or caesarean section (~37mL/kg; Elevated Liquid (EL), n=11) were mechanically ventilated (tidal volume=8mL/kg). The PEEP was changed after lung aeration from 0 to 8 to 0 cmH2O (Control, n=6; EL, n=6) and in a separate group of kittens, PEEP was changed after lung aeration from 8 to 0 to 8 cmH2O (Control, n=5; EL, n=5). Lung function (ventilator parameters, compliance, lung gas volumes and distribution of gas within the lung) was evaluated using plethysmography and synchrotron-based phase contrast X-ray imaging. EL kittens initially receiving 0 cmH2O PEEP had reduced functional residual capacities and lung compliance, requiring higher inflation pressures to aerate the lung compared to Control kittens. Commencing ventilation with 8 cmH2O PEEP mitigated the adverse effects of EL, increasing lung compliance, functional residual capacity and the uniformity and distribution of lung aeration, but did not normalize aeration of the distal airways. Respiratory support with PEEP supports lung function in near-term newborn rabbits with elevated airway liquid volumes at birth who are at greater risk of suffering respiratory distress.

Evaluating Clinical Outcomes and Physiological Perspectives in Studies Investigating Respiratory Support for Babies Born at Term With or at Risk of Transient Tachypnea: A Narrative Review

“…However, the timing of onset markedly varied from 20 min after birth, at NICU admission or at 6 h after birth. As airway liquid clearance after birth increases lung interstitial tissue pressures ( 29 ), recent scientific evidence indicates that these elevated pressures play a key role in respiratory distress symptoms displayed by term or near-term newborns ( 9 , 12 ). As a result, it is difficult to compare outcomes between studies when the lung is at different stages of transition, with respect to clearing this liquid from the airways and tissue ( 10 ).…”

“…Blue, lung liquid; beige, lung tissue. Included are synchrotron phase contrast X-ray images of newborn rabbits (equivalent to 38 weeks gestational age in terms of humans lung development) with elevated airway liquid volume at birth receiving respiratory support with no end-expiratory pressure (A: 0 cmH 2 O) or a positive end-expiratory pressure of 8 cmH 2 O (B) via mechanical ventilation to show the effect on lung aeration [white speckle pattern; reproduced with permission ( 12 )]. FRC, functional residual capacity.…”

“…Reduced end-expiratory lung volumes between breaths (functional residual capacity, FRC) ( 9 , 11 ). As the reduction in FRC can be localized to lung regions with elevated liquid, this clearly demonstrates that the local clearance of liquid into lung tissue is the primary cause for the reduction in FRC ( 12 ).…”

“…Recent scientific studies indicate that greater airway liquid volumes at birth underpin the respiratory symptoms suffered by newborns with TTN, including tachypnea and expiratory grunting with rapid and labored breathing (9,11). They have also shown that an end-expiratory pressure of 8 cmH 2 O (vs. 5 cmH 2 O) improves FRC and lung mechanics in mechanically ventilated newborn rabbits with airway liquid volumes similar to that expected following elective CS birth (∼37 ml/kg) (12). The higher end-expiratory pressures prevented liquid from reflooding the airways between inflations, resulting in higher FRCs (Figure 3) and improved gas exchange (10) by increasing the lung's surface area available for gas exchange throughout the respiratory cycle.…”

Efficacy and Safety of Standardized Protocol of CPAP Therapy for Full-Term Newborns in Delivery Room at Transient Tachypnea: Clinical Trial with Historical Control

“…Согласно РКИ, в котором изучали эффективность и безопасность применения СРАР в родовом зале при ТТН, значения среднего давления в дыхательных путях (Mean Airway Pressure; МАР) варьировали в пределах от 5 до 10 см Н 2 О; при этом давлении не было отмечено ни одного случая развития пневмоторакса [19,20]. В исследовании на модели новорожденных животных сравнивали результаты использования давления в дыхательных путях в диапазоне от 0 до 8 см Н 2 О. Анализ показал, что большее давление в дыхательных путях в конце вдоха -8 см Н 2 О -приводит к лучшему удалению фетальной жидкости из легких [21]. Исследований эффективности различной продолжительности СРАР в родовом зале при ТТН, а также эффективности различных интерфейсов для проведения СРАР в родовом зале при ТТН до настоящего времени не проводили.…”