Different ventilatory approaches to keep the lung open.
OBJECTIVE
To study the ability of different ventilatory approaches to keep the lung open.


METHODS
Different ventilatory patterns were applied in surfactant deficient lungs with PEEP set to achieve pre-lavage PaO2.


METHODS
Experimental laboratory of a University Department of Anaesthesiology and Intensive Care.


METHODS
15 anaesthetised piglets.


METHODS
One volume-controlled mode (L-IPPV201:1.5) and two pressure-controlled modes at 20 breaths per minute (bpm) and I:E ratios of 2:1 and 1.5:1 (L-PRVC202:1 and L-PRVC201.5:1), and two pressure-controlled modes at 60 bpm and I:E of 1:1 and 1:1.5 (L-PRVC601:1 and L-PRVC601:1.5) were investigated. The pressure-controlled modes were applied using "Pressure-Regulated Volume-Controlled Ventilation" (PRVC).


RESULTS
Gas exchange, airway pressures, hemodynamics, FRC and intrathoracic fluid volumes were measured. Gas exchange was the same for all modes. FRC was 30% higher with all post-lavage settings. By reducing inspiratory time MPAW decreased from 25 cmH2O by 3 cmH2O with L-PRVC201.5:1 and L-PRVC601:1.5. End-inspiratory airway pressure was 29 cmH2O with L-PRVC201.5:1 and 40 cmH2O with L-IPPV201:1.5, while the other modes displayed intermediate values. End-inspiratory lung volume was 65 ml/kg with L-IPPV201:1.5, but it was reduced to 50 and 49 ml/kg with L-PRVC601:1 and L-PRVC601:1.5. Compliance was 16 and 18 ml/cmH2O with L-PRVC202:1 and L-PRVC201.5:1, while it was lower with L-IPPV201:1.5, L-PRVC601:1 and L-PRVC601:1.5. Oxygen delivery was maintained at pre-lavage level with L-PRVC201.5:1 (657 ml/min.m2), the other modes displayed reduced oxygen delivery compared with pre-lavage.


CONCLUSIONS
Neither the rapid frequency modes nor the low frequency volume-controlled mode kept the surfactant deficient lungs open. Pressure-controlled inverse ratio ventilation (20 bpm) kept the lungs open at reduced end-inspiratory airway pressures and hence reduced risk of barotrauma. Reducing I:E ratio in this latter modality from 2:1 to 1.5:1 further improved oxygen delivery.
Sjöstrand
U H
UH
Department of Anesthesiology and Intensive Care, University Hospital, Uppsala, Sweden.
Lichtwarck-Aschoff
M
M
Nielsen
J B
JB
Markström
A
A
Larsson
A
A
Svensson
B A
BA
Wegenius
G A
GA
Nordgren
K A
KA
D000704:Analysis of Variance; D000818:Animals; D005652:Functional Residual Capacity; D006612:High-Frequency Ventilation; D008855:Microscopy, Electron, Scanning; D011175:Positive-Pressure Respiration / Q000379:methods*; D011650:Pulmonary Alveoli / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000648:ultrastructure; D011663:Pulmonary Surfactants / Q000172:deficiency; D011859:Radiography; D012129:Respiratory Function Tests; D012131:Respiratory Insufficiency / Q000628:therapy*; D013552:Swine
D011663:Pulmonary Surfactants