Effect of Continuous Negative Extrathoracic Pressure on Respiratory Mechanics and Timing in Infants Recovering from Neonatal Respiratory Distress Syndrome

Abstract

Stoke-on-Trent, United Kitlgdom (D. P.S. IChanges in respiratory mechanics and timing produced by continuous negative extrathoracic pressure (CNEP) of -0.6 kPa were assessed in 18 infants recovering from neonatal respiratory distress syndrome. The mcdian gcstational age was 28 wk (range 2 4 3 6 wk). All infants were recruited before discharge from neonatal intensive care and were measured at a median postnatal age of 58 d (range 10-127 d) and a mcdian wcight of 2.67 kg (range 1.99-3.77 kg). All had been treated for respiratory distress syndrome; 11 were diagnosed as having chronic lung disease. At the time of the study, all infants were stable breathing room air. There was a significant decrease of the respiratory rate in all but one infant from 63.6 2 10.0 to 49.3 ? 9.1 breaths per min (mean * SD) during CNEP. This was predominantly due to a marked prolongation of the expiratory timc. Passive respiratory mechanics were assessed using airway occlusion techniques. Whereas respiratory system compliance (C,,) did not change in the infants with a normal baseline measurement, there was a significant improvement of C,, in the 11 infants with low C,, values in atmosphere: In the latter, all of whom were very-low-birthweight infants, C,, assessed by the multiple occlusion technique (mean ? SD) corrected for body wcight increased from 7.9 ? 1.5 to 9.4 ? 1.9 mL-kPa-'.kg-' in CNEP (p = 0.012). There was no consistent change in respiratory system resistance in this population of 18 infants. These preliminary results suggest that the beneficial effects of CNEP observed in clinical studies may be partially explained by its effects on respiratory mechanics and timing. (Pediatr Res 36: 364-372, 1994) Abbreviations CNEP, continuous negative extrathoracic pressure RDS, respiratory distress syndrome C,, respiratory system compliance (mL.kPa I ) IPPV, intermittent positive pressure ventilation C,,.,,,, dynamic lung compliance (mL-kPa-I) VLBW, very-low-birth-weight infants ( < 1500 g) CLD, chronic lung disease MOT, multiple occlusion technique SBT, single breath technique R,,, respiratory system resistance (kPa.L-'.s) Pa,, pressure at the airway opening (kPa) t,,,,, expiratory time during end-inspiratory occlusion (s) t,, expiratory time (s) V.,., tidal volume (mL) t,, inspiratory time (s) FRC, functional residual capacity (mL) EEL, end-expiratory level PNT, pneumotachograph CI, confidence interval The use of negative extrathoracic pressure as a means described in 1889. Intermittent negative extrathoracic of respiratory support has a long history dating back to pressure ventilation was subsequently used widely for the first half of the last century (1). The first apparatus treatment of respiratory failure in children with poliomydesigned for use in the resuscitation of neonates was elitis and, during the 1960s and 1970s, both intermittent negative extrathoracic pressure and CNEP ventilation

Influence of volume dependency and timing of airway occlusions on the Hering-Breuer reflex in infants

“…The HBIR may therefore play a vital role in determining the optimal breathing strategy in infants to prevent alveolar collapse until the chest wall stiffens with maturity (21,22). In contrast to phasic input, the tonic component of the HBIR can be assessed by measuring the response to a sustained change in FRC, induced by either continuous positive airway pressure or continuous negative extrathoracic pressure (14,23,34). Under these circumstances, a small increase in FRC will cause significant reductions in respiratory rate, primarily because of marked prolongation of TE, with virtually no impact on TI, tidal volume, or the measured strength of the phasic component of the HBIR (14).…”

“…Small increases in lung volume (less than one-half a tidal volume) are also associated with less marked modulation (braking) of expiratory flow, and hence less dynamic elevation of lung volume, demonstrating that infants modulate both expiratory flow and timing to control their end-expiratory level (14). By contrast, any decrease in FRC is frequently associated with a decreased TE, increased respiratory rate, and increased modulation of expiratory flow, resulting in compensatory dynamic elevation of end-expiratory level (35,36).…”

Continuous negative extrathoracic pressure respiratory support for neonates after congenital diaphragmatic hernia repair

“…However, it has been suggested that this only occurs when negative pressure is produced with a cuirass applied only to the thorax and abdomen (9). Secondly, there may be an increase in functional residual capacity (10, 11) and possibly even respiratory system compliance in some neonates (12) when using CNEP. Furthermore, there may be support of a compliant chest wall and possible stabilization of the diaphragm, with a reduction in paradoxical motion, which encroaches on tidal volume, and a possible reduction in diaphragmatic fatigue.…”

“…Vitamin B 12 is essential for DNA synthesis and hematopoesis and deficiency of vitamin B 12 is not uncommon in man, especially in the elderly. Nutritional vitamin B 12 deficiency has also been reported in infants, most often with vegetarian mothers (5)(6)(7)(8), causing megaloblastic anemia, cerebral atrophy with symptoms of lethargy, or cerebral involvement with hyperirrit-…”

The role of negative pressure ventilation

“…Changes in respiratory mechanics and timing produced by continuous negative extrathoracic pressure have been assessed in infants recovering from respiratory distress syndrome 19. The introduction of continuous negative expiratory pressure produced a significant decrease in the respiratory rate due to prolongation of expiratory time.…”