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Resuscitating very premature lambs with a Laerdal bag without PEEP or set tidal volumes with PEEP: the effect on carbon dioxide and oxygenation

Presented at the Neonatal Society 2004 Summer Meeting (programme).

Morley CJ, Probyn M, Hooper S, Dargaville P, McCallion N, Harding R

Department of Physiology, Monash University, Melbourne, Australia, the Royal Children's Hospital, Melbourne, Australia and the Royal Women's Hospital, Melbourne, Australia

Background: Hypocarbia during neonatal ventilation has been associated with neonatal chronic lung disease and adverse neurodevelopmental outcomes. It has been suggested hypocarbia may occur during resuscitation. Very immature surfactant deficient lungs collapse easily after expansion. PEEP is used during neonatal ventilation to reduce expiratory lung collapse but it is not recommended during resuscitation.

Aim: To investigate the effect on carbon dioxide and oxygenation of resuscitating very premature lambs with different tidal volumes and end expiratory pressures.

Methods: Anaesthetised lambs delivered at 126 days gestation were randomised to 15 min resuscitation with three regimes: 1) Laerdal resuscitation bag (BR) with 100% oxygen and no PEEP, 2) tidal volume (VT) of 5 mL/kg (VG5), or 3) VT of 10 mL/kg (VG10) delivered with a Babylog 8000 ventilator in volume guarantee mode. Groups (2) and (3) received 8 cm H2O PEEP and variable FiO2. Blood gases were measured every five min and VT, mean airway pressure, minute volume, ventilation rate, respiratory system compliance and alveolar/arterial oxygen difference (AaDO2) were recorded or calculated.

Results: Twenty intubated lambs were studied during resuscitation. BR (1) was associated with more variable VT and peak inspiratory pressures compared to volume guarantee ventilation (groups 2 and 3). The lambs ventilated from birth with a tidal volume of 10 mL/kg were hypocarbic; and those ventilated at 5 mL/kg were hypercarbic. Lambs resuscitated with the Laerdal bag had a mean VT of 7.5 mL/kg and were normocarbic. The two set tidal volumes had little effect on oxygenation. The set tidal volume groups had PEEP and their improved oxygenation compared with the Laerdal bag without PEEP. The coefficient of variation of the VT was greatest with bagging (31.4 2.7%) compared to the 5 mL/kg group (6.5 0.3%) and 10 mL/kg group (5.5 0.5%) (p<0.001). The Table shows the values at 15 minutes expressed as mean and SEM.

* P<0.05 for VG10 vs BR and VG5. P<0.05 VG5 vs BR. ** P<0.05 for BR vs the others

Conclusion: Very premature lambs can be effectively resuscitated from birth using a set tidal volume and volume guarantee ventilation. Within minutes of birth different tidal volumes had a large effect on PaCO2. The use of PEEP halved the oxygen requirement in 15 min. Studies are needed to determine the tidal volume and PEEP for resuscitating very premature infants to obtain acceptable levels of PaCO2 and oxygenation.

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