Prolonged Neural Expiratory Time Induced by Mechanical Ventilation in Infants

Abstract

Mechanical ventilation may interfere with the spontaneous breathing pattern in infants because they have strong reflexes that play a large role in the control of breathing. This study aimed to answer the following questions: does a ventilator-assisted breath 1) reduce neural inspiratory time, 2) reduce the amplitude of the diaphragm electrical activity, and 3) prolong neural expiration, within the delivered breath? In 14 infants recovering from acute respiratory failure (mean age and weight were 2.3 Ϯ 1.3 mo and 3.95 Ϯ 0.82 kg, respectively), we measured 1) the electrical activity of the diaphragm with a multiple-array esophageal electrode, and 2) airway opening pressure, while patients breathed on synchronized intermittent mandatory ventilation (mean rate, 11.2 Ϯ 6.5 breaths/min). We compared neural inspiratory and expiratory times for the mandatory breaths and for the spontaneous breaths immediately preceding and following the mandatory breath. Although neural inspiratory time was not different between mandatory and spontaneous breaths, neural expiratory time was significantly increased (p Ͻ 0.001) for the mandatory breaths (953 Ϯ 449 ms) compared with the premandatory and postmandatory spontaneous breaths (607 Ϯ 268 ms and 560 Ϯ 227 ms, respectively). Delivery of the mandatory breath resulted in a reduction in neural respiratory frequency by 28.6 Ϯ 6.4% from the spontaneous premandatory frequency. The magnitude of inspiratory electrical activity of the diaphragm was similar for all three breath conditions. For the mandatory breaths, ventilatory assist persisted for 507 Ϯ 169 ms after the end of neural inspiratory time. Infant-ventilator asynchrony (both inspiratory and expiratory asynchrony) was present in every mandatory breath and constituted 53.4 Ϯ 26.2% of the total breath duration. Newborn infants have strong reflexes that play a large role in the control of breathing (1). The work of Hering and Breuer in 1868 demonstrated in newborn animals that expansion of the lung reflexly inhibits inspiration-the HB inspiratoryinhibiting reflex-and promotes expiration-the HB expiratory-promoting reflex (2). With respect to mechanical ventilation in infants, it is reasonable to expect that delivery of ventilatory assistance should reflexly reduce neural Ti and neural inspiratory activity within the breath delivered. With respect to the HB expiratory-promoting reflex, one would expect an increase in neural Te during the assisted breath, compared with a spontaneous unassisted breath. The expiratory-promoting reflex has been clinically observed in mechanically ventilated infants, but was described with indirect estimates of neural timing (such as airway or esophageal pressure or flow) to gauge its effects (3-5). In addition to the fact that no quantitative evaluation of the reflex was made, the recent work of Parthasarathy et al. (6) has demonstrated that indirect estimates of respiratory timing are in poor agreement with more direct measurements of neural activity.Much of the available literature on reflex control of ...

Feasibility Study on Neurally Adjusted Ventilatory Assist in Noninvasive Ventilation After Cardiac Surgery in Infants

“…This delay is explained by the neuro-ventilatory coupling of the patient who corresponds to the time between the start of the activation of the diaphragm and the start of the appearance of the pressure. 16 It corresponds to the time required to reach the neurological trigger of 0.5 V and varies from cycle to cycle with an approximate value of 65 ms. When the delay exceeded the normal neuro-ventilatory delay (that we arbitrarily set at 100 ms), the ventilator was defined as out of sync with the patient.…”

“…When comparing all CPAP periods with all NIV-NAVA periods, the only significant differences were a greater EA di(max) in the beginning of the CPAP periods compared with the beginning of the NIV-NAVA periods (respectively, 16.97 Ϯ 7.68 V and 10.55 Ϯ 5.60 V, P Ͻ .001) and a greater breathing frequency at the end of the NIV-NAVA periods compared with the end of the CPAP periods (respectively, 51.64 Ϯ 12.02 breaths/min and 40.35 Ϯ 11.39 breaths/min, P Ͻ .001) ( Table 3).…”

Neurally adjusted ventilatory assist improves patient–ventilator interaction in infants as compared with conventional ventilation

“…During PSV, even if the critical volume has been reached and Edi begins to decline, the assist may continue until the cycling-off criteria have been reached. The elevated and prolonged volume-via this reflex-promotes a prolongation in expiratory time (3). This in turn results in a reduced respiratory rate (3).…”

“…Note that the Edi is the same measurement as EAdi used in previous publications (3,(7)(8)(9)12,16). Edi, as well as Pvent were acquired from the ventilator on a laptop (NAVA tracker, Maquet; software version 2.0) and stored for later analysis.…”

“…c onventional modes of mechanical ventilation are clearly limited in their ability to provide synchrony between the patient and the assist delivered, as demonstrated repeatedly in adults (1,2) and more recently in children (3). Patientventilator asynchrony has been associated with poor clinical outcome (1,2,4).…”