Moderate hyperventilation during intravenous anesthesia increases net cerebral lactate efflux

BACKGROUND:: Hyperventilation is known to decrease cerebral blood flow (CBF) and to impair cerebral metabolism, but the threshold in patients undergoing intravenous anesthesia is unknown. The authors hypothesized that reduced CBF associated with moderate hyperventilation might impair cerebral aerobic metabolism in patients undergoing intravenous anesthesia. METHODS:: Thirty male patients scheduled for coronary surgery were included in a prospective, controlled crossover trial. Measurements were performed under fentanyl-midazolam anesthesia in a randomized sequence aiming at partial pressures of carbon dioxide of 30 and 50 mmHg. Endpoints were CBF, blood flow velocity in the middle cerebral artery, and cerebral metabolic rates for oxygen, glucose, and lactate. Global CBF was measured using a modified Kety-Schmidt technique with argon as inert gas tracer. CBF velocity of the middle cerebral artery was recorded by transcranial Doppler sonography. Data were presented as mean (SD). Two-sided paired t tests and one-way ANOVA for repeated measures were used for statistical analysis. RESULTS:: Moderate hyperventilation significantly decreased CBF by 60%, blood flow velocity by 41%, cerebral oxygen delivery by 58%, and partial pressure of oxygen of the jugular venous bulb by 45%. Cerebral metabolic rates for oxygen and glucose remained unchanged; however, net cerebral lactate efflux significantly increased from -0.38 (2.18) to -2.41(2.43) μmol min 100 g. CONCLUSIONS:: Moderate hyperventilation, when compared with moderate hypoventilation, in patients with cardiovascular disease undergoing intravenous anesthesia increased net cerebral lactate efflux and markedly reduced CBF and partial pressure of oxygen of the jugular venous bulb, suggesting partial impairment of cerebral aerobic metabolism at clinically relevant levels of hypocapnia. Copyrigh

Argon does not affect cerebral circulation or metabolism in male humans

Objective: Accumulating data have recently underlined argońs neuroprotective potential. However, to the best of our knowledge, no data are available on the cerebrovascular effects of argon (Ar) in humans. We hypothesized that argon inhalation does not affect mean blood flow velocity of the middle cerebral artery (Vmca), cerebral flow index (FI), zero flow pressure (ZFP), effective cerebral perfusion pressure (CPPe), resistance area product (RAP) and the arterio-jugular venous content differences of oxygen (AJVDO2), glucose (AJVDG), and lactate (AJVDL) in anesthetized patients. Materials and methods: In a secondary analysis of an earlier controlled cross-over trial we compared parameters of the cerebral circulation under 15 minutes exposure to 70%Ar/30%O2versus 70%N2/30%O2in 29 male patients under fentanyl-midazolam anaesthesia before coronary surgery. Vmca was measured by transcranial Doppler sonography. ZFP and RAP were estimated by linear regression analysis of pressure-flow velocity relationships of the middle cerebral artery. CPPe was calculated as the difference between mean arterial pressure and ZFP. AJVDO2, AJVDG and AJVDL were calculated as the differences in contents between arterial and jugular-venous blood of oxygen, glucose, and lactate. Statistical analysis was done by t-tests and ANOVA. Results: Mechanical ventilation with 70% Ar did not cause any significant changes in mean arterial pressure, Vmca, FI, ZFP, CPPe, RAP, AJVDO2, AJVDG, and AJVDL. Discussion: Short-term inhalation of 70% Ar does not affect global cerebral circulation or metabolism in male humans under general anaesthesia

Small intra-individual variability of the preejection period justifies the use of pulse transit time as approximation of the vascular transit

Background Vascular transit time (VTT) is the propagation time of a pulse wave through an artery; it is a measure for arterial stiffness. Because reliable non-invasive VTT measurements are difficult, as an alternative we measure pulse transit time (PTT). PTT is defined as the time between the R-wave on electrocardiogram and arrival of the resulting pulse wave in a distal location measured with photoplethysmography (PPG). The time between electrical activation of the ventricles and the resulting pulse wave after opening of the aortic valve is called the pre-ejection period (PEP), a component of PTT. The aim of this study was to estimate the variability of PEP at rest, to establish how accurate PTT is as approximation of VTT. Methods PTT was measured and PEP was assessed with echocardiography (gold standard) in three groups of 20 volunteers: 1) a control group without cardiovascular disease aged 50 years, and 3) a group with cardiovascular risk factors, defined as arterial hypertension, dyslipidemia, kidney failure and diabetes mellitus. Results Per group, the mean PEP was: 1) 58.5 ± 13.0 ms, 2) 52.4 ± 11.9 ms, and 3) 57.6 ± 11.6 ms. However, per individual the standard deviation was much smaller, i.e. 1) 2.0-5.9 ms, 2) 2.8-5.1 ms, and 3) 1.6-12.0 ms, respectively. There was no significant difference in the mean PEP of the 3 groups (p = 0.236). Conclusion In conclusion, the intra-individual variability of PEP is small. A change in PT

Importance Of The Effective Cerebral Perfusion Pressure

The aim of this thesis was to investigate important determinants of the effective cerebral perfusion pressure regulation and subsequently to provide recommendations on how to keep adequate cerebral perfusion in the perioperative setting.__Scope and relevance of the thesis__ This thesis focuses on the importance of cerebral perfusion pressure. The results are relevant to all patients in the perioperative setting, as all heath providers will receive practical tools that enable them to better guide patients in cases of deregulated cerebral perfusion. __Problem statement__ Maintaining adequate cerebral perfusion in the perioperative setting is an important task for the anesthesiologist. However, this is sometimes difficult to achieve because the cerebral perfusion of the patient is influenced by different factors such as age, cerebrovascular diseases, positioning during surgery, anesthetic and vasoactive drugs, and artificial ventilation. Furthermore, cerebrovascular physiology and pathophysiology are still not fully understood as stated above. __Aim of the thesis__ The aim of this thesis is to investigate important determinants of CPPe regulation and subsequently to provide recommendations on how to maintain adequate cerebral perfusion in the perioperative setting

Carbon dioxide induced changes in cerebral blood flow and flow velocity: Role of cerebrovascular resistance and effective cerebral perfusion pressure

In addition to cerebrovascular resistance (CVR) zero flow pressure (ZFP), effective cerebral perfusion pressure (CPPe) and the resistance area product (RAP) are supplemental determinants of cerebral blood flow (CBF). Until now, the interrelationship of PaCO2 -induced changes in CBF, CVR, CPPe, ZFP, and RAP is not fully understood. In a controlled crossover trial, we investigated 10 anesthetized patients aiming at PaCO2 levels of 30, 37, 43, and 50 mm Hg. Cerebral blood flow was measured with a modified Kety-Schmidt-technique. Zero flow pressure and RAP was estimated by linear regression analysis of pressure-flow velocity relationships of the middle cerebral artery. Effective cerebral perfusion pressure was calculated as the difference between mean arterial pressure and ZFP, CVR as the ratio CPPe/CBF. Statistical analysis was performed by one-way RM-ANOVA. When comparing hypocapnia with hypercapnia, CBF showed a significant exponential reduction by 55% and mean V MCA by 41%. Effective cerebral perfusion pressure linearly decreased by 17% while ZFP increased from 14 to 29 mm Hg. Cerebrovascular resistance increased by 96% and RAP by 39%; despite these concordant changes in mean CVR and Doppler-derived RAP correlation between these variables was weak (r=0.43). In conclusion, under general anesthesia hypocapnia-induced reduction in CBF is caused by both an increase in CVR and a decrease in CPPe, as a consequence of an increase in ZFP

Influence of isoflurane on the diastolic pressure-flow relationship and critical occlusion pressure during arterial CABG surgery: A randomized controlled trial

The effects of isoflurane on the determinants of blood flow during Coronary Artery Bypass Graft (CABG) surgery are not completely understood. This study characterized the influence of isoflurane on the diastolic Pressure-Flow (P-F) relationship and Critical Occlusion Pressure (COP) during CABG surgery. Twenty patients undergoing CABG surgery were studied. Patients were assigned to an isoflurane or control group. Hemodynamic and flow measurements during CABG surgery were performed twice (15 minutes after the discontinuation of extracorporeal circulation (T15) and again 15 minutes later (T30)). The zero flow pressure intercept (a measure of COP) was extrapolated from a linear regression analysis of the instantaneous diastolic P-F relationship. In the isoflurane group, the application of isoflurane significantly increased the slope of the diastolic P-F relationship by 215% indicating a mean reduction of Coronary Vascular Resistance (CVR) by 46%. Simultaneously, the Mean Diastolic Aortic Pressure (MDAP) decreased by 19% mainly due to a decrease in the systemic vascular resistance index by 21%. The COP, cardiac index, heart rate, Left Ventricular End-Diastolic Pressure (LVEDP) and Coronary Sinus Pressure (CSP) did not change significantly. In the control group, the parameters remained unchanged. In both groups, COP significantly exceeded the CSP and LVEDP at both time points. We conclude that short-term application of isoflurane at a sedative concentration markedly increases the slope of the instantaneous diastolic P-F relationship during CABG surgery implying a distinct decrease with CVR in patients undergoing CABG surgery

Organ donation after circulatory death

Approximately 17 million inhabitants live in the Netherlands. The number of potential organ donors in 1999 was the lowest in Europe with only 10 donors per million inhabitants. Medical associations, public health services, health insurance companies and the government had to find common solutions in order to improve organ allocation, logistics of donations and to increase the number of transplantations. After a prolonged debate on medical ethical issues of organ transplantation, all participants were able to agree on socio-medico-legal regulations for organ donation and transplantation. In addition to improving the procedure for organ donation after brain death (DBD) the most important step was the introduction of organ donation after circulatory death (DCD). Measures such as the introduction of a national organ donor database, improved information to the public, further education on intensive care units (ICU), guidelines for end of life care on the ICU, establishment of transplanta

Surgery for a large tracheoesophageal fistula using extracorporeal membrane oxygenation

We report a patient with a giant tracheoesophageal fistula (TEF) planned for reconstructive surgery. Because mechanical ventilation in any form was technically impossible, we successfully used venovenous extracorporeal membrane oxygenation (VV-ECMO) without the need for mechanical ventilation