Sex-specific issues of central and peripheral arginine-vasopressin concentrations in neurocritical care patients

BACKGROUND

Arginine-Vasopressin (AVP) is a nonapeptide that exerts multiple functions within the central nervous system and in the blood circulation that might contribute to outcome in critically ill patients. Sex differences have been found for mental and physical effects of AVP. For example, stress response and response due to hemorrhage differ between males and females, at least in animal studies. Data on humans -especially on AVP within the central nervous system (CNS)-are scarce, as cerebrospinal fluid (CSF) which is said to represent central AVP activity, has to be collected by means of invasive procedures. Here we present data on 30 neurocritical care patients where we simultaneously collected blood, CSF and saliva to analyze concentrations in the central and peripheral compartments.

PATIENTS AND METHODS

30 neurocritical care patients were included (13 male, 13 postmenopausal female, 4 premenopausal female) with a median age of 60 years. CSF, plasma and saliva were obtained simultaneously once in each patient and analyzed for AVP concentrations. Correlations between the central compartment represented by CSF, and the peripheral compartment represented by plasma and saliva, were identified. Relations between AVP concentrations and serum sodium and hematocrit were also determined.

RESULTS

In the whole patient collective, only very weak to weak correlations could be detected between AVP plasma/CSF, plasma/saliva and CSF/saliva as well as between AVP concentrations in each of the compartments and serum sodium/hematocrit. Regarding the subgroup of postmenopausal females, a significant moderate correlation could be detected for AVP in plasma and CSF and AVP CSF and serum sodium.

CONCLUSION

Absolute concentrations of AVP in central and peripheral compartments did not show sex differences. However, correlations between AVP plasma and CSF and AVP CSF and serum sodium in postmenopausal females indicate differences in AVP secretion and AVP response to triggers that deserve further examination.

Effects of hyperoxic ventilation on hemodilution-induced changes in anesthetized dogs

BACKGROUND

In subjects who have undergone acute preoperative normovolemic hemodilution (ANH), intraoperative hemorrhage is generally treated by immediate return of autologous blood collected during ANH. Simply increasing blood oxygen content by hyperoxic ventilation (HV, inspiratory fraction [FIO2] 1.0) might compensate for the acute anemia, allow further ANH, and delay onset of autologous blood return.

STUDY DESIGN AND METHODS

This study 1) evaluated the effects of HV (FIO2 1.0) upon ANH to a hemoglobin (Hb) concentration of 7 g per dL in anesthetized dogs ventilated with room air and 2) compared the effects of subsequent profound ANH (Hb, 3 g/dL) with and without an intravenous perfluorocarbon emulsion (perflubron 60% wt/vol) versus those of autologous red cell transfusion. The results of the entire study are presented in two parts. Organ tissue oxygenation was assessed in skeletal muscle and liver, and systemic oxygenation status was evaluated. Myocardial contractility was deduced from left ventricular pressure-volume relationship. Seven of 22 dogs underwent further hemodilution while breathing 100-percent O2, for a determination of the Hb concentration at which HV-induced effects were abolished.

RESULTS

HV completely reversed the ANH-induced increase in cardiac index (4.6 +/- 0.7 vs. 3.8 +/- 0.9 L/min/m2 before and during HV; p < 0.05) and partially reversed the decrease in systemic vascular resistance (1784 +/- 329 vs. 2087 +/- 524 dyn x cm-5 x sec x m-2; p < 0.05). Despite unchanged global O2 delivery, organ tissue oxygenation improved during HV (mixed venous partial pressure of O2: 40 +/- 3 vs. 59 +/- 7 torr; coronary venous pressure of O2: 30 +/- 4 vs. 43 +/- 6 torr; p < 0.05; liver surface: 31 +/- 11 vs. 39 +/- 13 torr; skeletal muscle surface: 30 +/- 14 vs. 41 +/- 22 torr; p < 0.05). This improvement was due to an increased contribution of physically dissolved O2 in plasma to O2 delivery (3.2 +/- 0.2% before HV vs. 14.6 +/- 1% during HV; p < 0.05) and O2 consumption (whole body: 6 +/- 1% vs. 47 +/- 8%, p < 0.05; myocardium: 4.3 +/- 0.9% vs. 31 +/- 6%, p < 0.05). The beneficial effects of HV were lost after an additional volume-compensated exchange of 19 percent of blood volume (Hb, 5.6 g/dL).

CONCLUSION

In anesthetized dogs ventilated with room air and hemodiluted to a Hb of 7 g per dL, simple oxygen therapy by HV (FIO2 1.0) rapidly improves tissue oxygenation and permits extended hemodilution to Hb of 5.8 g per dL until the HV-induced effects are lost.

Hemodilution and intravenous perflubron emulsion as an alternative to blood transfusion: effects on tissue oxygenation during profound hemodilution in anesthetized dogs

BACKGROUND

Intravenously administered perfluorocarbon (PFC) emulsions increase oxygen solubility in plasma. PFC might therefore temporarily replace red cells (RBCs) lost during intraoperative hemorrhage. In patients who have undergone hemodilution, the return of autologous blood may be delayed by the administration of PFC, and autologous RBCs may be saved for transfusion after surgical bleeding is stopped and PFC is cleared by the reticuloendothelial system.

STUDY DESIGN AND METHODS

In 22 anesthetized, hemodiluted dogs (hemoglobin [Hb] 7 g/dL) breathing 100-percent O2, an intraoperative volume-compensated blood loss was simulated. The efficacy of three therapeutic regimens in maintaining tissue oxygenation was compared: 1) RBC group (n = 7): maintenance of a Hb > 7 g per dL by transfusion of autologous RBCs; 2) PFC group (n = 7): bolus application of a second-generation PFC emulsion (60% wt/vol perflubron) and further acute normovolemic hemodilution (ANH) to a Hb of 3 g per dL; and 3) control group (n = 7): further ANH alone to a Hb of 3 g per dL. Systemic and myocardial oxygenation status and tissue oxygenation were assessed.

RESULTS

Autologous RBCs transfused to maintain a Hb of 7 g per dL preserved hemodynamics and tissue oxygenation during blood loss. In the PFC and control groups, heart rate and cardiac index increased significantly in response to further ANH. Tissue oxygenation was not different in the PFC and the RBC groups. Direct comparison of the PFC and control groups revealed better tissue oxygenation in the PFC group, as reflected by significantly higher mixed venous, coronary venous, and local tissue pO2 on liver and skeletal muscle.

CONCLUSION

Bolus intravenous administration of 60-percent (wt/vol) perflubron emulsion and further hemodilution from a Hb of 7 g per dL to one of 3 g per dL were as effective as autologous RBC transfusion in maintaining tissue oxygenation during volume-compensated blood loss designed to mimic surgical bleeding.

The effect of acute normovolemic hemodilution (ANH) on myocardial contractility in anesthetized dogs

The influence of severe acute normovolemic hemodilution (ANH) on myocardial contractility (MC) was investigated in 14 splenectomized, anesthetized dogs. MC was assessed by the maximum rate of left ventricular pressure increase (LVdp/dt(max)), end-systolic elastance (Ees), and preload recruitable stroke work (PRSW) (conductance catheter, left ventricular pressure-volume relationship). Measurements of myocardial perfusion and oxygenation (radioactive microsphere technique) assured comparability of the model to previously performed studies. Global and regional myocardial blood flow increased significantly upon hemodilution with preference to midmyocardium and subendocardium. This resulted in preservation of both myocardial oxygen delivery and consumption after ANH. Myocardial oxygen extraction as well as coronary venous Po2 were unaffected by ANH, while coronary venous lactate concentration decreased, indicating that myocardial oxygen need was met. LVdp/dt(max) decreased significantly after hemodilution (2278 +/- 577 vs 1884 +/- 381 mm Hg/s, P < 0.01), whereas Ees and PRSW increased significantly (1.76 +/- 0.54 vs 2.15 +/- 0.75 mm Hg/mL, P < 0.05, for Ees and 33 +/- 14 vs 45 +/- 14 mm Hg.mL, P < 0.05, for PRSW). While the decrease of LVdp/dt(max) most likely reflects ANH-induced changes of ventricular pre- and afterload, the increase of Ees and PRSW indicates a true increase of myocardial contractility during ANH in anesthetized dogs.