Effects of normovolemic hemodilution combined with controlled hypotension on extravascular lung water and systematic oxygen metabolism for elderly patients

Objective: To investigate the effect of acute normovolemic hemodilution (ANH) combined with controlled hypotension (CH) on extravascular lung water and systematic oxygen metabolism for elderly patients, and to explore the clinical security of ANH + CH. Methods: 45 elderly patients undergoing elective spine and hip replacement surgery were selected and randomly divided into 3 groups (n=15 in each): control group (group A); acute normovolemic hemodilution group (group B); acute normovolemic hemodilution combined with controlled hypertension group (group C). Artery blood samples of patients were collected for blood-gas analysis at four time points: before induction of anesthesia (T1), after hemodilution (T2), 30 min after controlled hypotension (T3), after surgery (T4). We observed and recorded heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), cardiac index (CI), systemic vascular resistance (SVR), intrathoracic blood volume (ITBV), extravascular lung water (EVLW), and calculated the values of oxygen delivery (DO2) and oxygen consumption (VO2). The recorded values of each group were compared and analyzed. Results: The Hct and Hb of patients in group B and group C decreased obviously after ANH compared with that of pre-surgery. After controlled hypotension, the HR of patients in group C elevated while MAP dropped, but the CVP was maintained at the preoperative level. There were differences in CI, SVR, ITBV and EVLW between the three groups at the same time point but without statistical significance, and all patients recovered to preoperative levels after operation. The SVR in both group B and C decreased obviously after hemodilution and controlled hypotension by comparing with preoperative level; and the SVR in patients of group C dropped more sharply at T3, which had statistical significance by comparing with group A at the same time point. The ITBV in group C at T3 changed obviously compared with the value at T1; but the decline, compared with group A at the same time point, was not obvious. The DO2 value in both group B and C increased at T2 and was significantly different from the value at T1 and the value of group A at T2; the DO2 in group B was still at the high level after CH, while the DO2 in group C recovered to the basic levels. The VO2 values of three groups all declined after ANH and CH, but the decreases were not obvious, and all groups recovered to preoperative levels after operation. Conclusion: Preoperative ANH can obviously increase the reserve of circulating blood volume for elderly patients; combining with controlled hypotension, it can maintain a stable perioperative circulatory function, significantly reduce ITBV and keep EVLW at normal level to avoid increasing the occurrence of pulmonary edema. In addition, it also can increase the oxygen supply and maintain a stable body oxygen metabolism.