EFFECTS OF HYPOTHERMIA WITH AND WITHOUT BUFFERING IN HYPERCAPNIA AND HYPERCAPNIC HYPOXEMIA

Anesthetized, paralyzed and mechanically ventilated pigs were hypoventilated to extreme hypercapnia (Paco(2) approximate to 20 kPa) at Fio(2) 0.5, and allotted to receive hypothermia (approximate to 31.5 degrees C) and buffer infusion, (HB-group, n = 6) or to a hypothermic control group (H-group, n = 6). The HB-group had higher arterial pH (7.34 vs 7.09, P < 0.01) and plasma bicarbonate (58.8 vs 35.4 mmol.l(-1), P < 0.01) than the controls, but lower mean pulmonary arterial pressure (MPAP), (16 vs 23 mmHg (2.1 vs 3.1 kPa), P < 0.01) and pulmonary vascular resistance (PVR), (512 vs 699 dyn.s.cm(-5) (5120 vs 6990 mu N.s.cm(-5)), P < 0.05). Mixed venous Po-2 (Pvo(2)) was lower in the HB-group (5.1 vs 6.8 kPa, P < 0.01), as well as serum potassium (2.8 vs 3.7 mmol.l(-1), P < 0.01) and ionized calcium (1.01 vs 1.29 mmol.l(-1), P < 0.01). Subsequently, the inspired oxygen fraction (Fio(2)) was decreased stepwise (0.3, 0.25, 0.21, 0.15, 0.10) at 30 min intervals. At Fio(2) 0.3, the HB-group had lower Pvo(2) (6.6 vs 7.8 kPa, P < 0.01), O-2 half saturation tension (3.6 vs 4.2 kPa, P < 0.01), MPAP (17 vs 25 mmHg (2.3 vs 3.3 kPa, P < 0.01) and WR (598 vs 793 dyn.s.cm(-5) (5980 vs 7930 mu N.s.cm, P < 0.05) compared with the controls, but higher arterial O-2 saturation (95.3 vs. 88.6%, P < 0.01) and O-2 content (17.7 vs 15.7 ml.100 ml(-1), P < 0.05). The groups did not differ in O-2 delivery, in spite of their difference in arterial O-2 content, because of a lower cardiac output in the HB-group (1.6 vs 2.21.min(-1), P < 0.05). Mixed venous O-2 content, O-2 consumption and O-2 extraction did not differ between groups. Combined use of hypothermia and buffering did not improve survival in hypercapnic hypoxemia as compared to a hypothermic regimen without buffer.