Basic life support with four different compression/ventilation ratios in a pig model: the need for ventilation.
BACKGROUND
During cardiac arrest the paramount goal of basic life support (BLS) is the oxygenation of vital organs. Current recommendations are to combine chest compressions with ventilation in a fixed ratio of 30:2; however the optimum compression/ventilation ratio is still debatable. In our study we compared four different compression/ventilation ratios and documented their effects on the return of spontaneous circulation (ROSC), gas exchange, cerebral tissue oxygenation and haemodynamics in a pig model.


METHODS
Study was performed on 32 pigs under general anaesthesia with endotracheal intubation. Arterial and central venous lines were inserted. For continuous cerebral tissue oxygenation a Licox PtiO(2) probe was implanted. After 3 min of cardiac arrest (ventricular fibrillation) animals were randomized to a compression/ventilation-ratio 30:2, 100:5, 100:2 or compressions-only. Subsequently 10 min BLS, Advanced Life Support (ALS) was performed (100%O(2), 3 defibrillations, 1mg adrenaline i.v.). Data were analyzed with 2-factorial ANOVA.


RESULTS
ROSC was achieved in 4/8 (30:2), 5/8 (100:5), 2/8 (100:2) and 0/8 (compr-only) pigs. During BLS, PaCO(2) increased to 55 mm Hg (30:2), 68 mm Hg (100:5; p=0.0001), 66 mm Hg (100:2; p=0.002) and 72 mm Hg (compr-only; p<0.0001). PaO(2) decreased to 58 mmg (30:2), 40 mm Hg (100:5; p=0.15), 43 mm Hg (100:2; p=0.04) and 26 mm Hg (compr-only; p<0.0001). PtiO(2) baseline values were 12.7, 12.0, 11.1 and 10.0 mm Hg and decreased to 8.1 mm Hg (30:2), 4.1 mm Hg (100:5; p=0.08), 4.3 mm Hg (100:2; p=0.04), and 4.5 mm Hg (compr-only; p=0.69).


CONCLUSIONS
During BLS, a compression/ventilation-ratio of 100:5 seems to be equivalent to 30:2, while ratios of 100:2 or compressions-only detoriate peripheral arterial oxygenation and reduce the chance for ROSC.
Kill
Clemens
C
Department of Anaesthesiology and Critical Care, Philipps-University, D-35033 Marburg, Germany.
Torossian
Alexander
A
Freisburger
Christian
C
Dworok
Sebastian
S
Massmann
Martin
M
Nohl
Thorsten
T
Henning
Ronald
R
Wallot
Pascal
P
Gockel
Andreas
A
Steinfeldt
Thorsten
T
Graf
Jürgen
J
Eberhart
Leopold
L
Wulf
Hinnerk
H
D000818:Animals; D004195:Disease Models, Animal; D004867:Equipment Design; D006323:Heart Arrest / Q000503:physiopathology / Q000628:therapy*; D008021:Life Support Systems / Q000592:standards*; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012119:Respiration; D012121:Respiration, Artificial / Q000295:instrumentation*; D013552:Swine