Oxygen cost of breathing and weaning process in newborn infants

Abstract

Newborn infants may have a high oxygen cost of breathing (OCB) at the time of being weaned from mechanical ventilation. We hypothesized that this increase in oxygen consumption (V'O 2 ) could be reduced by using certain weaning ventilatory modes.We designed a study to assess V'O 2 during three weaning ventilatory modes: patient triggered ventilation, synchronous intermittent mandatory ventilation (SIMV) and continuous positive airway pressure in 16 newborn infants before being weaned from mechanical ventilation In seven infants whose OCB was high. V 'O 2 was not significantly different between CV and PTV (8.9±0.6 versus 9.5±0.8, respectively) whereas it tended to increase to 10.8±1.1 mL·min -1 ·kg -1 during SIMV and increased significantly to 11.9±0.8 mL·min -1 ·kg -1 . In the other nine infants whose OCB was normal, no significant variation of V 'O 2 was observed.Patient triggered ventilation was a weaning ventilatory mode that significantly reduced the increase in oxygen consumption observed in infants with a high oxygen cost of breathing, as compared to synchronous intermittent mandatory ventilation or continuous positive airway pressure. Further investigations in newborn infants with a high oxygen cost of breathing should be performed prior to routine use of patient triggered ventilation. Eur Respir J 1997; 10: 2583-2585 Weaning from artificial ventilation is a critical challenge, especially in newborn infants with chronic lung disease. We have previously shown that these newborn infants increase their oxygen consumption (V'O 2 ) at the time of being weaned from mechanical ventilation [1]. This increase is secondary to a high oxygen cost of breathing (OCB) probably related to increased work of breathing, similar to that shown in adult patients [2]. Inspiratory pressure support, used during the weaning process in adult intensive care, may be useful in reducing the work of breathing [2]. Recent data have shown that patient triggered ventilation (PTV) decreases the work of breathing in premature neonates [3], and that PTV can be used as a weaning ventilatory mode [4][5][6][7]. We hypothesized that the increase in V'O 2 observed at the time of weaning in some newborn infants could be reduced by using PTV. We designed a study to assess V'O 2 during PTV as compared to synchronous intermittent mandatory ventilation (SIMV) and continuous positive airway pressure (CPAP) in newborn infants, before being weaned from mechanical ventilation. MethodsThe population was selected to include patients with normal and high OCB. Thus, in this prospective study, we included 16 infants requiring assisted ventilation for either acute respiratory distress (eight infants) or chronic lung disease (eight infants), after informed consent was obtained from the parents. The clinical characteristics, which covered a wide range, were at the time of measurement: gestational age; 33.9±1.0 (range, 28±41) weeks; postnatal age; 18±4 (2-65) days; postconceptional age; 36. 5±1.3 (31.3-48.3) weeks; and weight; 2.3±0.2 (1.4-3.5) kg.

Work of Breathing and Different Levels of Volume-Targeted Ventilation

“…We demonstrated that the PTPdi was 50% higher at a VT level of 4 mL/kg, compared with 6 mL/kg. For infants with a high oxygen cost of breathing, oxygen consumption (which is an indicator of the WOB) was ϳ30% lower with ACV, compared with SIMV (14 breaths per minute), 14 and weaning duration was prolonged when slow-rate SIMV rather than ACV was used, 15 which suggests that even a 30% increase in oxygen consumption is adverse. In another study, a 30% difference in the WOB was noted for prematurely born infants for whom extubation failed or succeeded.…”

Recent Advances in Neonatal Mechanical Ventilation?

“…Two of the trials showed no significant differences between the two trigger modes, but in the third trial A/C was associated with a shorter duration of weaning [11]. The duration of weaning was significantly shorter on A/C than on SIMV when the supported breath rate was reduced below 20 breaths/min as, at such a low level of ventilator support, oxygen consumption and the work of breathing are increased [12].…”

How has research in the past 5 years changed my clinical practice

“…There have been no recent large randomised studies comparing A/C and SIMV with conventional ventilation or each other, hence the rationale for my use of these modes as above is based on earlier evidence 4 – 8. Meta-analysis of randomised trials has shown that patient triggered ventilation (A/C or SIMV) is associated with a marked reduction in the duration of ventilation if started in the recovery rather than the acute stage of the illness 4.…”

“…Meta-analysis of randomised trials has shown that patient triggered ventilation (A/C or SIMV) is associated with a marked reduction in the duration of ventilation if started in the recovery rather than the acute stage of the illness 4. In a small randomised trial, A/C was associated with a shorter duration of weaning than SIMV,7 possibly reflecting that A/C is associated with lower oxygen consumption, indicating reduced work of breathing 8. Newer triggered modes, pressure support ventilation and proportional assist ventilation, have shown advantages in physiological studies in the past 5 years; I await positive results of definitive randomised studies before introducing them in my routine clinical practice.…”