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. 2014 Feb 15:14:43.
doi: 10.1186/1471-2431-14-43.

Pressure- versus volume-limited sustained inflations at resuscitation of premature newborn lambs

Graeme R Polglase, David G Tingay, Risha Bhatia, Clare A Berry, Robert J Kopotic, Clinton P Kopotic, Yong Song, Edgardo Szyld, Alan H Jobe, Jane J Pillow  1
Affiliations

Pressure- versus volume-limited sustained inflations at resuscitation of premature newborn lambs

Graeme R Polglase et al. BMC Pediatr. .

Abstract

Background: Sustained inflations (SI) are advocated for the rapid establishment of FRC after birth in preterm and term infants requiring resuscitation. However, the most appropriate way to deliver a SI is poorly understood. We investigated whether a volume-limited SI improved the establishment of FRC and ventilation homogeneity and reduced lung inflammation/injury compared to a pressure-limited SI.

Methods: 131 d gestation lambs were resuscitated with either: i) pressure-limited SI (PressSI: 0-40 cmH2O over 5 s, maintained until 20 s); or ii) volume-limited SI (VolSI: 0-15 mL/kg over 5 s, maintained until 20 s). Following the SI, all lambs were ventilated using volume-controlled ventilation (7 mL/kg tidal volume) for 15 min. Lung mechanics, regional ventilation distribution (electrical impedance tomography), cerebral tissue oxygenation index (near infrared spectroscopy), arterial pressures and blood gas values were recorded regularly. Pressure-volume curves were performed in-situ post-mortem and early markers of lung injury were assessed.

Results: Compared to a pressure-limited SI, a volume-limited SI had increased pressure variability but reduced volume variability. Each SI strategy achieved similar end-inflation lung volumes and regional ventilation homogeneity. Volume-limited SI increased heart-rate and arterial pressure faster than pressure-limited SI lambs, but no differences were observed after 30 s. Volume-limited SI had increased arterial-alveolar oxygen difference due to higher FiO2 at 15 min (p = 0.01 and p = 0.02 respectively). No other inter-group differences in arterial or cerebral oxygenation, blood pressures or early markers of lung injury were evident.

Conclusion: With the exception of inferior oxygenation, a sustained inflation targeting delivery to preterm lambs of 15 mL/kg volume by 5 s did not influence physiological variables or early markers of lung inflammation and injury at 15 min compared to a standard pressure-limited sustained inflation.

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Figures

Figure 1
Figure 1
Volume and pressure measurements at completion of the 20 s sustained inflation (SI). A) Delivered volume (SI Volume at 20 s) and B) peak inspiratory pressure (PIP) during pressure-limited (PressSI; black circles) and volume-limited (VolSI; open squares) sustained inflations. * indicates significant difference (p<0.05).
Figure 2
Figure 2
Temporal measures of gas exchange over 15 minutes following pressure or volume limited SI: A) Partial pressure of arterial (Pa) oxygen (PaO2), B) carbon dioxide (PaCO2), C) percentage of inspired oxygen (FiO2) and D) alveolar-arterial difference in oxygen (AaDO2) in pressure-limited (PressSI; black circles) and volume-limited (VolSI; open squares) sustained inflations. * p<0.05.
Figure 3
Figure 3
Temporal changes in cardiovascular responses to Pressure and Volume limited SI: A) Heart rate and B) arterial blood pressure during the sustained inflation (shaded region) and upon subsequent ventilation in pressure-limited (PressSI; black circles) and volume-limited (VolSI; open squares) sustained inflations. * indicates significant difference between Press SI and Vol SI groups (p<0.05). ^ indicates significant difference from fetal (F) value within each group. BPM – beat/min.
Figure 4
Figure 4
Effect of pressure- and volume-limited SI on regional lung impedance determined by electrical impedance tomography: A) Global change in end-expiratory lung volume (∆EEV) expressed as percentage change from the total lung volume determined at autopsy, in pressure-limited (PressSI; black circles) and volume-limited (VolSI; open squares) sustained inflations. Regional end-expiratory lung volume in dependent (closed shapes) and non-dependent (open shapes) in PressSI (B), and VolSI (C). # indicates significant difference between 20 s and 1 minute.
Figure 5
Figure 5
Temporal changes in lung mechanics associated with pressure- and volume-limited SI: (A) Newtonian (airway) resistance (Raw); (B) tissue damping (G); and (C) tissue elastance (H) in pressure-limited (PressSI; black circles) and volume-limited (VolSI; open squares) sustained inflations. * significantly different to 5 min for PressSI; # significantly different to 5 min for Vol SI. There were no intergroup differences in mechanics.
Figure 6
Figure 6
Instantaneous changes in pressure and volume during the sustained inflation: Pressure (panels A and B) and volume (panels C and D) during pressure limited (left panel) and volume-limited (right panel) sustained inflations. Solid line represents mean, dashed line indicates SD of mean, varying with time.
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References

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