Emergency ventilatory management in hemorrhagic states: elemental or detrimental?
BACKGROUND
A study was performed to demonstrate that slower respiratory rates (RRs) of positive-pressure ventilation can preserve adequate oxygenation and acid-base status in hemorrhagic states, whereas "normal" or higher RRs worsen hemodynamics.


METHODS
Eight swine (ventilated with 12 mL/kg tidal volume, 0.28 Fio(2); RR of 12 breaths/min) were hemorrhaged to < 65 mm Hg systolic arterial blood pressure (SABP). RRs were then sequentially changed every 10 minutes to 6, 20, 30, and 6 breaths/min.


RESULTS
With RRs at 6 breaths/min, the animals maintained pH > 7.25/Sao(2) > 99%, but increased mean SABP (from 65 to 84 mm Hg; p < 0.05), time-averaged coronary perfusion pressure (CPP) (from 50 +/- 2 to 60 +/- 4 mm Hg; p < 0.05), and cardiac output (Qt) (from 2.4 to 2.8 L/min; p < 0.05). With RRs of 20 and 30 breaths/min, SABP (73 and 66 mm Hg), CPP (47 +/- 3 and 42 +/- 4 mm Hg), and Qt (2.5 and 2.4 L/min) decreased, as did Pao(2) and Paco(2) (< 30 mm Hg), with p < 0.05 for each comparison, respectively. When RR returned to 6 breaths/min, SABP (95 mm Hg), CPP (71 +/- 6 mm Hg), and Qt (3.0 L/min) improved significantly (p < 0.05).


CONCLUSIONS
After even moderate levels of hemorrhage in animals, positive-pressure ventilation with "normal" or higher RRs can impair hemodynamics. Hemodynamics can be improved with lower RRs while still maintaining adequate oxygenation and ventilation.
Pepe
Paul E
PE
Department of Surgery, University of Texas Southwestern Medical Center at Dallas, 75390-8579 USA. paul.pepe@utsouthwestern.edu
Raedler
Claus
C
Lurie
Keith G
KG
Wigginton
Jane G
JG
D000136:Acid-Base Equilibrium / Q000502:physiology; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D004630:Emergencies; D005260:Female; D006439:Hemodynamics; D006470:Hemorrhage / Q000503:physiopathology* / Q000628:therapy*; D007385:Intermittent Positive-Pressure Ventilation / Q000009:adverse effects; D023421:Models, Animal; D015656:Respiratory Mechanics / Q000502:physiology; D013552:Swine