Effects of hypothermia in hypercapnia and hypercapnic hypoxemia.
Anesthetized, paralyzed and mechanically ventilated pigs were hypoventilated to extreme hypercapnia (PaCO2 approximately 20 kPa) at FiO2 0.5, and allotted to a hypothermic group (31.5 +/- 0.1 degrees C, n = 6) or a control group (39.6 +/- 0.2 degrees C, n = 6). Compared with the controls, the hypothermic animals had higher PaO2 (19.2 vs 15.6 kPa, P < 0.05), SaO2 (97.2 vs 89.3%), SvO2 (78.7 vs 68.2%), end-tidal O2 (34.5 vs 24.8 kPa) and arterial pH (7.01 vs 6.91), (P < 0.01), but lower PvO2 (7.0 vs 10.2 kPa) and PaCO2 (13.2 vs 23.5 kPa), (P < 0.01). Hypothermia reduced O2 delivery (DO2), O2 consumption (VO2) and CO2 production by 40-45% (P < 0.05), but O2 extraction ratio, i.e. VO2.DO(2)-1 x 100(%), did not differ between groups. Hypothermic animals had lower heart rate (127 vs 223 beats.min-1, P < 0.05) and cardiac output (2.5 vs 3.9 l.min-1, P < 0.01). Subsequently, the inspired oxygen fraction (FiO2) was decreased stepwise (0.3, 0.25, 0.21, 0.15, 0.10) at 30-min intervals. At FiO2 0.3, the hypothermic group had higher PaO2 (10.0 vs 5.7 kPa), SaO2 (91.3 vs 28.5%), PvO2 (5.8 vs 3.4 kPa), SvO2 (70.7 vs 10.3%), end-tidal O2 (16.7 vs 8.5 kPa), O2 delivery (344 vs 155 ml.min-1), arterial pH (7.02 vs 6.94) and systemic vascular resistance (3850 vs 1652 dyn.s.cm-5 (38,500 vs 16,520 microN.s.cm-5)) compared with the controls (P < 0.01), while PaCO2 was lower (12.4 vs 22.7 kPa), as well as O2 extraction ratio (23 vs 63%) and O2 half saturation tension (4.3 vs 8.0 kPa) (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Anesthesiology and Intensive Care, University of Lund, Sweden.
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Wetterberg
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Sjöberg
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Steen
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D002496:Central Venous Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology*; D007036:Hypothermia, Induced; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D011175:Positive-Pressure Respiration; D011188:Potassium / Q000097:blood; D011651:Pulmonary Artery; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D015996:Survival Rate; D013552:Swine; D013990:Tidal Volume; D014655:Vascular Resistance / Q000502:physiology
D002245:Carbon Dioxide; D011188:Potassium; D010100:Oxygen