Emergency ventilatory management in hemorrhagic states: Elemental or Detrimental?

Methods:Eight swine (ventilated with 12 mL/kg tidal volume, 0.28 FIO_SB; 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/SaO₂ > 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 PaO₂ and PaCO₂ (< 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).