A novel approach to assess hemorrhagic shock severity using the arterially determined left ventricular isovolumic contraction period.

Recently, the ventilatory variation in pre-ejection period (ΔPEP) was found to be useful in the prediction of fluid-responsiveness of patients in shock. In the present study we investigated the behavior of the ventilation-induced variations in the systolic timing intervals in response to a graded hemorrhage protocol. The timing intervals studied included the ventilatory variation in ventricular electromechanical delay (ΔEMD), isovolumic contraction period (determined from the arterial pressure waveform, ΔAIC), pulse travel time (ΔPTT), and ΔPEP. ΔAIC and ΔPEP were evaluated in the aorta and carotid artery (annotated by subscripts Ao and CA) and were compared with the responses of pulse pressure variation (ΔPPAo) and stroke volume variation (ΔSV). The graded hemorrhage protocol, followed by resuscitation using norepinephrine and autologous blood transfusion, was performed in eight anesthetized Yorkshire X Landrace swine. ΔAICAo, ΔAICCA, ΔPEPAo, ΔPEPCA, ΔPPAo, ΔPPCA, and ΔSV showed significant increases during the graded hemorrhage and significant decreases during the subsequent resuscitation. ΔAICAo, ΔAICCA, ΔPEPAo, and ΔPEPCA all correlated well with ΔPPAo and ΔSV (all r ≥ 0.8, all P < 0.001). ΔEMD and ΔPTT did not significantly change throughout the protocol. In contrast with ΔPEPAo, which was significantly higher than ΔPEPCA (P < 0.01), ΔAICAo was not different from ΔAICCA. In conclusion, ventilation-induced preload variation principally affects the arterially determined isovolumic contraction period (AIC). Moreover, ΔAIC can be determined solely from the arterial pressure waveform, whereas ΔPEP also requires ECG measurement. Importantly, ΔAIC determined from either the carotid or aortic pressure waveform are interchangeable, suggesting that, in contrast with ΔPEP, ΔAIC may be site independent.

Effects of simultaneous aortocaval occlusion on oxygen consumption in patients.

The effects of simultaneous occlusion of the thoracic aorta and inferior vena cava on oxygen consumption (V O 2) have not yet been reported in humans. Ten patients (all ASA II) needed such simultaneous occlusion to allow hypoxic abdominal perfusion in the treatment of pancreatic cancer. With the development of the PhysioFlex anaesthesia machine for closed-circuit anaesthesia, intra-operative real-time curves of V O 2 became available. Thus, we can continuously measure F I O 2, V E, V O 2, and air consumption. By placing a pulmonary artery catheter, we could also intermittently calculate D O 2 during the several phases of the perfusion procedure. Immediately after the simultaneous aortocaval occlusion started, V O 2 decreased by 35% (68 ml min-1 m-2) and D O 2 decreased below the critical value of 330 ml min-1 m-2. At reperfusion, repayment of the oxygen debt was by a two-stage pattern: a fast repayment stage with an increase of about 65% was followed by a slow repayment stage of 14% increase (values compared to steady state). Oxygen consumption in women was found to be significantly lower than in men (P = 0.02), with significant variation between the sexes during different stages of the procedure. The oxygen debt was not completely repaid by the end of the procedure. We conclude that the significant variation found in oxygen consumption will have consequences while performing low-flow anaesthesia, that additional oxygen supply during the recovery period because of the initially incomplete repayment of oxygen debt may be useful and that studies on oxygen consumption must present gender-specific data because of the gender-dependent variation found in oxygen consumption.