Comparison of the Effect of Etomidate and Desflurane on Brain Tissue Gases and pH during Prolonged Middle Cerebral Artery Occlusion

Background: The authors compared the effects of etomidate and desflurane on brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH in patients who had middle cerebral artery occlusion for > 15 min.

Methods: After a craniotomy, a probe that measures PO2, P (CO)2, and pH was inserted into cortical tissue at risk for ischemia during middle cerebral artery occlusion. A burst suppression pattern of the electroencephalogram was induced with etomidate (n = 6) or 9% end-tidal desflurane (n = 6) started before middle cerebral artery occlusion. Mean blood pressure was supported with phenylephrine to 90-95 mmHg.

Results: During baseline conditions, tissue PO2, PCO (2), and pH were similar between the two groups (PO2 = 15 mmHg, PCO2 = 60 mmHg, pH = 7.1). During administration of etomidate before middle cerebral artery occlusion, tissue PO2 decreased in five of six patients without a change in PCO2 or pH. During administration of 9% desflurane, tissue PO2 and pH increased before middle cerebral artery clipping. Middle cerebral artery occlusion for an average of 33 min with etomidate and 37 min with desflurane produced a decrease in pH with etomidate (7.09 to 6.63, P <0.05) but not with desflurane (7.12 to 7.15).     

Brain tissue PO(2), PCO(2), and pH during cerebral vasospasm

BACKGROUND: The purpose of the present study was to assess brain tissue monitoring for detection of ischemia due to vasospasm in aneurysmal subarachnoid hemorrhage (SAH) patients. METHODS: After obtaining informed consent, a burr hole was made in 10 patients and a Neurotrend 7 probe was inserted ipsilateral to the region of SAH. In eight patients the probe was inserted during surgery for clipping the aneurysm and in two patients the probe was inserted in the neurosurgery ICU. Brain tissue gases and pH were collected over 6-hour periods for 7 to 10 days until the termination of monitoring. The onset of vasospasm was confirmed by angiography and xenon computed tomography (Xe/CT) cerebral blood flow studies. RESULTS: Seven patients did not develop vasospasm during monitoring and were considered as controls. In this group, brain tissue oxygen pressure (PO(2)) remained above 20 mmHg, carbon dioxide pressure (PCO(2)) stabilized at 40 mmHg and pH remained between 7.1 and 7.2. In three patients who developed vasospasm during monitoring, PO(2) was not different from the control group. However, PCO(2) increased to 60 mmHg and pH decreased to 6.7 (p < 0.001). CONCLUSION: In this study, patients with SAH who developed vasospasm had significantly lower brain tissue pH and higher PCO(2) compared to controls. However, there was no significant change in PO(2) levels associated with vasospasm. Brain tissue monitoring can provide an indication of ischemia during vasospasm.     

Electrothrombosis of saccular aneurysms via endovascular approach. Part 1: Electrochemical basis, technique, and experimental results

Eleven experimental saccular aneurysms were created on the common carotid artery of swine. Between 3 and 15 days after creation of these aneurysms, they were thrombosed via an endovascular approach, using a very soft detachable platinum coil delivered through a microcatheter positioned within the aneurysm. This detachable platinum coil was soldered to a stainless steel delivery guidewire. Intra-aneurysmal thrombosis was then initiated by applying a low positive direct electric current to the delivery guidewire. Thrombosis occurred because of the attraction of negatively charged white blood cells, red blood cells, platelets, and fibrinogen to the positively charged platinum coil positioned within the aneurysm. The passage of electric current detached the platinum coil within the clotted aneurysm in 4 to 12 minutes. This detachment was elicited by electrolysis of the stainless steel wire nearest to the thrombus-covered platinum coil. Control angiograms obtained 2 to 6 months postembolization confirmed permanent aneurysm occlusion as well as patency of the parent artery in all cases. No angiographic manifestation of untoward distal embolization was noted. Due to the encouraging results of this research, this technique has been applied in selected clinical cases which are described in Part 2 of this study.     

Medullary osteogenesis with platinum cathodes

Studies of electrical stimulation of osteogenesis with stainless steel electrodes have previously established a dose-response relationship between current and bone growth. Examination of the effect of differing geometric current densities resulted in the conclusion that very little electrode surface area was involved in stimulation and led to the design of a multiport "distributive" cathode. A series of experiments were performed to extend these results to wire and multiport platinum electrodes. As before, a current-bone growth dose-response relationship was found. Peak bone growth was greater than for stainless steel. However, peak bone growth occurred at 2.0 microA (versus 20 microA for stainless steel). Correlation studies suggest that small changes in cathodic potential affect bone growth more than similar size changes in current. Finally, the generally benign local host response to platinum suggests that platinum may be a suitable material for chronic indwelling anodes for stimulation of osteogenesis.     

Continuous Measurement of Arterial Po2, Pco2 and pH During Autotransplantation of Canine Hearts

Arterial PO2, PCO2 and pH were measured continuously with electrodes placed in a flow cuvette. Comparison between continuous readings and results of single sample analyses showed practically no discrepancy, and the drifts of the electrodes during time of measurements were negligible. During hypothermic perfusion with a Rygg-Kyvsg?rd bubble oxygenator, autotransplantation of canine hearts was performed. PO2, PCO2 and pH were measured continuously to check the performance of the heart-lung machine, and to evaluate the therapeutic and diagnostic significance of these blood gas values during cardiac surgery. At the start of perfusion, a steep fall in all three parameters was observed. The average fall in PO2 was 313 mmHg; PCO2 fell by 15 mmHg and pH BY 0.15. PCO2 rapidly returned to normal values, while pH and PO2 increased slowly during the perfusion period. PO2 reached its highest value at the lowest temperature and fell during rewarming. PCO was regulated by the carbon dioxide concentration in the heart-lung machine. pH did not return to normal levels within the time of perfusion. In the transistional period from perfusion, PCO2 increased and pH fell. Alterations in the distribution and direction of blood flow and a low systemic blood pressure are possible explanations of the initial fall in PO2 and the post-perfusion changes in PCO2 and pH. The variations in pH and PCO2 at the start of perfusion were caused by an acid priming fluid with low CO2 content. The post-perfusion changes indicated an unstable circulation, but imminent myocardial failure could not alone be diagnosed by continuous measurement.     

Cathodic oxygen consumption and electrically induced osteogenesis.

Small amounts of electric current stimulate bone formation in the region of a cathode. The purpose of this experiment is to compare changes in oxygen and hydroxyl ion concentration that occur at the cathode at current levels known to be capable of inducing osteogenesis (10-20 muamps) with those changes that occur at current levels known to be toxic to bone (100 muamps). An oxygen consumption chamber containing an oxygen electrode is fitted with two stainless steel electrodes which are connected to a constant current source. At the cathode, with a current of 100 muamps, oxygen is consumed at nearly stoichiometric rates. At higher current (100 muamps) levels, cathodic oxygen consumption gives way to hydrogen evolution. Cathodic hydroxyl ion production is directly proportional to current. It is concluded from these in vitro experiments that at 10-20 muamps the oxygen tension in the vicinity of the cathode is lowered and the pH is moderately increased. At 100 muamps the oxygen tension is not lowered, but the pH is increased dramatically. If these same changes occur in the vicinity of a cathode in vivo, then lowering the local tissue oxygen tension and raising the local pH may be mechanisms operative in electrically induced bone formation.     

Bone formation near direct current electrodes with and without motion.

The osteogenesis induced in the medullary canal of rabbits by the implantation of moving and stationary wire electrodes was studied with and without the simultaneous application of 20-microA constant direct cathodic current. After 3 weeks, the formation of new trabecular bone in the canal was studied and measured microscopically. Electrically stimulated osteogenesis was not observed at stationary electrodes. As in previous studies with this model, a movable electrode alone stimulated new bone formation whose area was 7-10% of the canal area. The amount of this bone was not statistically increased by the addition of cathode current. Movable, electrically active cathodes were associated, however, with fluid-filled spaces incorporated within the new trabecular bone. When mechanical stimuli were controlled, we were not able to demonstrate that the direct current stainless steel cathode acts either as an inducer or a substantial enhancer of medullary osteogenesis.     

Effects of Temperature on Cerebral Tissue Oxygen Tension, Carbon Dioxide Tension, and pH during Transient Global Ischemia in Rabbits

Background: A decrease in brain temperature (Tbrain) causes a decrease in the cerebral metabolic rate for oxygen (CMRO2) and provides potent neuroprotection against ischemic damage. In the present study, the effects of mild to moderate hypothermia on cerebral tissue oxygen tension (PO2 brain), carbon dioxide tension (PCO2 brain), and pH (pHbrain) were monitored during short episodes of global cerebral ischemia.

Methods: After approval by the Animal Care and Use Committee, 10 New Zealand white rabbits were anesthetized (1% halothane in air) and mechanical ventilation was adjusted to maintain the arterial carbon dioxide tension at 35 mmHg (alpha-stat). A sensor to measure PO2 brain, PCO2 brain, pHbrain, and Tbrain was inserted into the brain through a burr hole in the skull. Tbrain was adjusted to 38 [degree sign] Celsius, 34.4 [degree sign] Celsius, and 29.4 [degree sign] Celsius in a random sequence in each animal. PO2 brain, PCO sub 2 brain, and pHbrain (all variables are reported at the actual Tbrain) were recorded every 10 s during a 5-min baseline, 3 min of cerebral ischemia induced by inflation of a neck tourniquet, and 10 min of reperfusion at each level of Tbrain. Analysis of variance and Dunnett's test were used for statistical analysis. Data are presented as means +/- SD.

Results: During ischemia, PO2 brain decreased from 56 +/- 3 to 33 +/- 2 mmHg at 38 [degree sign] Celsius, from 58 +/- 3 to 32 +/- 3 mmHg at 34.4 [degree sign] Celsius, and from 51 +/- 2 to 32 +/- 2 mmHg at 29.4 [degree sign] C (p = NS). PCO2 brain increased by 6.7 +/- 2 mmHg at 38 [degree sign] Celsius, by 5.1 +/- 1.4 mmHg at 34.4 [degree sign] Celsius, and by 2.3 +/- 0.8 mmHg at 29.4 [degree sign] Celsius. pH sub brain inversely followed the trend of PCO2 brain.     

Accuracy and performance of a modified continuous intravascular blood gas monitoring device during thoracoscopic surgery

OBJECTIVE: The only commercially available continuous intravascular blood gas monitoring system for adults, the Paratrend (Diametrics Medical Inc, High Wycombe, UK), was modified by the manufacturer to the Paratrend 7+ (PT7+) in 1999. The aim of this study was to evaluate the modified probe over a wide range of blood gas and pH values during thoracoscopic surgery in a similar setup as done with the previous model. DESIGN: Prospective methods comparison study. SETTING: University hospital. PARTICIPANTS: Twenty-three patients. INTERVENTIONS: Elective thoracoscopic surgery. MEASUREMENTS AND MAIN RESULTS: One hundred thirteen PT7+ readings and their corresponding arterial blood gas and pH measurements (ABGA) were evaluated. The ranges for ABGA values were 50 to 474 mmHg for PO(2), 29 to 58 mmHg for PCO(2), and 7.28 to 7.49 for pH. Bland and Altman analysis revealed a bias +/- 2 standard deviation of -20 +/- 86 mmHg for PO(2), 3 +/- 9 mmHg for PCO(2), and -0.01 +/- 0.06 for pH. No specific complications attributable to the probe were observed. CONCLUSION: In patients undergoing thoracoscopic surgery with rapidly changing blood gas parameters, the PT7+ device is a valuable trend indicator and hence may be helpful for clinical decision making. However, the underestimation of PO(2) values by 20 mmHg on average and the wide limits of agreement documented in this study must be regarded as limiting factors.     

Subcutaneous tissue oxygen and carbon dioxide tensions during hyperbaric oxygenation: an experimental study in rats.

OBJECTIVE: To investigate the response of subcutaneous tissue oxygen (O2) and carbon dioxide (CO2) tensions to hyperbaric oxygenation. DESIGN: Experimental study. SETTING: University hospital, Finland. SUBJECTS: 10 Wistar rats. INTERVENTION: Subcutaneous tissue PO2 and PCO2 were directly measured with an implanted Silastic tube tonometer and capillary sampling technique while breathing air and exposed to hyperbaric oxygen (HBO) at 2.5 or 2.8 ATA pressure. Hyperbaric exposures were carried out in a large multiplace chamber pressurised with air. MAIN OUTCOME MEASURES: Subcutaneous tissue PO2 and PCO2. RESULTS: The mean subcutaneous PO2 rose from the baseline of 8 kPa (60 mmHg) to 16 kPa (112 mmHg) when rats breathed room air during pressurisation to 2.8 atm. When the rats breathed oxygen at 2.5 ATA the maximal mean tissue PO2 was four times higher than the mean starting value. During the HBO treatment at 2.8 ATA the tissue PO2 rose to a value about five times above baseline. The tissue PCO2 values almost doubled during the exposure to HBO at 2.5 ATA, probably because elimination of carbon dioxide was impaired. CONCLUSION: Measurements of tissue PO2 and PCO2 with an implanted Silastic tonometer and a capillary sampling technique can successfully be adapted to hyperbaric conditions. The method yielded reproducible results and is applicable to clinical use in hyperbaric medicine.     

Intramyocardial gas tensions in the canine heart

Intramyocardial gas tensions were determined in the left ventricular wall of the canine heart by means of chronically implanted silastic tonometers. In the central zone of the myocardial wall the mean baseline PO2 was 22 mmHg and the mean baseline PCO2 28 mmHg. Breathing of pure oxygen elevated the myocardial PO2 to a level of 60 to 90 mmHg. Hypovolaemic shock induced by shedding 30% of the blood volume resulted in a sharp decrease of the myocardial PO2 and a marked increase of the myocardial PCO2. During hypovolaemia, ventilation with pure oxygen elevated the oxygen tension to the control level and, after re-infusion of the shed blood, the response of the myocardial PO2 to oxygen breathing became higher than normal. Correction of hypovolaemic with a plasma expander Haemaccel restored the myocardial oxygen tension to the baseline level. Ligation of the left anteior descending coronary artery produced a rapid fall of PO2 and a profound increase of PCO2 in the corresponding myocardial area. After coronary ligation, developing tissue ischaemia usually resulted in ventricular fibrillation within a few minutes. Cardiac massage was started immediately, but produced no correction of tissue gas tensions, although the arterial blood gases remained normal. Ligation of the right coronary artery or the left circumflex coronary artery for short periods increased the myocardial PO2 in the vicinity of the left anterior descending branch, probably due to reactive hyperaemia around the ischaemic tissue.     

The influence on foetal outcome of maternal carbon dioxide tension at caesarean section under general anaesthesia

The influence on foetal outcome of maternal PCO2 at caesarean section under general anaesthesia was assessed in 27 "clinically acceptable ideal patients" as defined by Crawford. A standard anaesthetic technique was employed which utilised left lateral tilt and an F1O2 of 0.5. A highly significant relationship (p less than 0.001) was found between umbilical vein PO2 and maternal end-tidal PCO2 in the range 20-40 mmHg, such that hypocarbia was associated with a lowering of umbilical vein PO2. In spite of this relationship, only three values of PO2 were less than normal (28 mmHg). No relationship was found between clinically measured parameters of foetal outcome and maternal end-tidal PCO2. The relevant literature is reviewed.     

Mesure du pH et des gaz du sang sur des micro-echantillons: effets de la conservation à 4°C pendant une heure. Etude chez le rat

The effects of one hour storage at 4 degrees C on micro blood gas samples (150 microliters) were studied for a wide range of values (pH: 7.11-7.58; PCO2: 26-97 mmHg; PO2: 31-503 mmHg) in 20 rats with indwelling carotid artery catheters. Blood gas values were modified by varying the composition of inspired gases: normoxia, hypocapnic hypoxia, hyperoxia, hypercapnia (in this case eight animals were anaesthetized with halothane 1.1%). One hundred and eight double micro-samples were taken. For each double sample, one was analysed immediately (H0) and compared with the second sample after one hr storage at 4 degrees C (H1). The Bland and Altman method was used for the statistical analysis of results. After one hr storage at 4 degrees C, the PCO2 was slightly higher than at H0 (mean difference +/- SD: +1.08 +/- 1.7 mmHg) and arterial pH was slightly lower (mean difference +/- SD: -0.016 upH +/- 0.011 upH). These results show that for these two variables, in the range studied, one hour storage at 4 degrees C had little effect. In contrast, for arterial PO2 the mean difference between all measurements between H1 and H0 was -17 +/- 25 mmHg. If results lower than 200 mmHg (56 double samples) are considered separately, the mean difference between values at H1 and H0 was only -0.98 +/- 5.3 mmHg. For PaO2 greater than 200 mmHg (52 double samples), the mean difference was -34 +/- 26.3 mmHg; this may be due to low reproducibility of measurements of elevated PO2 levels and to the effects of cellular metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Monitoring the conjunctiva for carbon dioxide and oxygen tensions and pH during cardiopulmonary bypass

The purpose of this study was to measure, for the first time, multiple physiologic parameters of perfusion (pH, PCO2, PO2, and temperature) from the conjunctiva of adult patients during cardiopulmonary bypass while undergoing cardiothoracic surgery. Ten patients who underwent either intracardiac valve repair, atrial septal defect repair, or coronary artery bypass graft surgery had placement of a sensor which directly measured pH, PCO2, PO2, and temperature from the conjunctiva. Data were stratified into seven phases (0-5 minutes prior to bypass; 0-5, 6-10, and 11-15 minutes after initiation of bypass; 0-5 minutes prior to conclusion of bypass; and 0-5 and 6-10 minutes after bypass) and analyzed using a mixed model analysis.The change in conjunctival pH over the course of measurement was not statistically significant (p = .56). The PCO2 level followed a quadratic pattern, decreasing from a mean pre-bypass level of 37.7 mmHg at baseline prior to the initiation of cardiopulmonary bypass to a nadir of 33.2 mmHg, then increasing to a high of 39.4 mmHg at 6-10 minutes post bypass (p < .01). The PO2 declined from a mean pre-bypass level of 79.5 mmHg to 31.3 mmHg by 6-10 minutes post bypass and even post-bypass, it never returned to baseline values (p < .01). Temperature followed a pattern similar to PCO2 by returning to baseline levels as the patient was re-warmed following bypass (p < .01). There was no evidence of any eye injury or inflammation following the removal of the sensor. In the subjects studied, the conjunctival sensor yielded reproducible measurements during the various phases of cardiopulmonary bypass without ocular injury. Further study is necessary to determine the role of conjunctival measurements in critical settings.     

Assessment of graded intestinal hypoperfusion and reperfusion using continuous saline tonometry in a porcine model.

OBJECTIVE: To evaluate effects of graded intestinal hypoperfusion and reperfusion on intestinal metabolic parameters as assessed by a modified continuous saline tonometry technique. MATERIALS: Twelve barbiturate-anaesthetized female pigs. METHODS: Measurements were performed prior to and during three predefined levels of superior mesenteric mean arterial blood pressure (P(SMA) 70, 50 and 30 mmHg, respectively, each 80 min long), obtained by an adjustable clamp around the origin of the superior mesenteric artery, and during reperfusion. We continuously measured jejunal mucosal perfusion (laser Doppler flowmetry), jejunal tissue oxygen tension (PO(2TISSUE); microoximetry) and intramucosal PCO(2) (continuous saline tonometry) and calculated net intestinal lactate production, mesenteric oxygenation, PCO(2) gap (jejunal mucosal PCO(2)-arterial PCO(2)) and pHi. RESULTS: At P(SMA) 70 and 50 mmHg mesenteric oxygen uptake and net lactate production remained unaltered, in spite of decreased oxygen delivery. At these P(SMA) levels PCO(2) gap increased, while pHi and PO(2TISSUE) decreased. At P(SMA) 30 mmHg pronounced increases in PCO(2) gap and mesenteric net lactate production as well as marked decreases in PO(2TISSUE) and pHi were demonstrated. Data indicate absence of anaerobic conditions at an intestinal perfusion pressure (IPP)> or =41 mmHg, a pHi> or =7.22 or PCO(2) gap< or =15.8 mmHg. CONCLUSIONS: Continuous saline tonometry detected intestinal ischemia as induced by graded reductions in IPP. A threshold could be defined above which intestinal ischemia does not occur.     

Multiparameter fiber optic sensor for the assessment of intramyocardial perfusion

OBJECTIVES: The objective of this study was to characterize a multiparameter fiber optic sensor for detection of changes in intramyocardial perfusion and to demonstrate a method of determining critical values for pH, PCO2, and PO2 to indicate onset of anaerobic metabolism. METHODS: Six swine underwent a 20-minute occlusion of the left anterior descending coronary artery (LAD). Myocardial pH, PCO2, and PO2 were measured continuously in the LAD and left circumflex coronary artery (CFX) territories. Critical values for each parameter were calculated from these data. RESULTS: During occlusion LAD myocardial pH declined from 7.36 +/- 0.04 to 6.85 +/- 0.04; PCO2 rose from 57.0 +/- 2.9 to 154.0 +/- 18.0 torr, PO2 fell from 78 +/- 20 to 6 +/- 5 torr. No myocardial pH or PCO2 changes were observed in the CFX region, however, CFX PO2 was affected in some animals during LAD occlusion and release. Methods for determining the ischemic threshold from these sensor data are presented. CONCLUSIONS: Multiparameter fiber optic sensors reliably respond to coronary occlusion and thus have the potential to help guide myocardial protection strategies for both on- and off-pump cardiac surgery.     

Monitoring brain PO2, PCO2, and pH during graded levels of hypoxemia in rabbits.

Brain ischemia and hypoxia are of concern when they occur following traumatic brain injury because they frequently result in potentially preventable secondary brain damage. In this study, we examined the ability of an implantable catheter (Paratrend 7; Diametrics Medical, St. Paul, MN) to continuously measure brain tissue pH, PCO2, and PO2 during graded levels of hypoxia. Values obtained from this catheter were compared with simultaneous measurements of arterial and sagittal sinus blood. As expected, there was a good correlation between the changes in pH, PCO2, and PO2 in brain tissue and sagittal sinus blood. Brain tissue PO2 was numerically lower than sagittal sinus blood at all inspired levels of oxygen. These data suggest that the Paratrend 7 may be useful in monitoring brain tissue oxygen tension in patients at risk for regional cerebral ischemia and hypoxia.     

Local tissue oxygenation following radial artery cannulation

The effect of radial artery cannulation on local tissue oxygenation and acid-base balance was studied in 20 patients. Using capillary samples drawn from each thumb, a significant difference was observed between capillary PO2 on each side (p less than 0.001), with the higher PO2 on the cannulated side. There were no significant differences between sides in terms of [H+] or PCO2. It is considered that the differences in capillary PO2 were due to local tissue vasodilatation. The presence of chlorbutol in the sodium heparin flushing solution is implicated as the causative factor. Further study of 20 patients using preservative-free heparin demonstrated no significant differences between cannulated and non-cannulated sides in terms of capillary PO2, PCO2 or [H+]. Sodium heparin with chlorbutol appears to improve local tissue oxygenation and is recommended for use in flushing solutions for invasive arterial monitoring.     

Effects of profound anemia on brain tissue oxygen tension, carbon dioxide tension, and pH in rabbits

This study sought to determine the maximum tolerable limit of anemia for the brain during halothane anesthesia. Using a multiparameter sensor, we continuously monitored brain tissue oxygen tension (PO2), carbon dioxide tension (PCO2), and pH during profound hemodilution and subsequent transfusion. Twelve New Zealand White rabbits were anesthetized, intubated, and mechanically ventilated at a fraction of inspired oxygen (FiO2) of 21% to produce an arterial carbon dioxide tension (PaCO2) of 35 to 40 mm Hg. The femoral artery was cannulated to continuously monitor arterial blood pressure and to intermittently measure arterial blood gases. The electroencephalogram (EEG) was recorded throughout the course of the study. A fiberoptic sensor was inserted into the brain for the continuous measurement of brain PO2, PCO2, pH, and temperature. Cerebral blood flow (CBF) was measured by the hydrogen clearance method. Severe anemia was induced by repeatedly withdrawing 50-mL aliquots of blood and infusing an equal volume of 6% hetastarch. This procedure was performed four times for each rabbit. After the forth blood draw and fluid infusion, a total of 60 mL of packed red blood cells were transfused. Upon completion of the hemodilution, the hemoglobin concentration was 2.4 +/- 0.3 g/dL (mean +/- SEM). Brain tissue PO2 decreased from 27 +/- 3 mm Hg to a minimum of 12 +/- 2 mm Hg. Brain tissue pH also decreased from 7.22 +/- 0.03 to 7.12 +/- 0.05 and returned to the baseline value with transfusion. Brain PCO2 did not change significantly during the experiment. Cerebral blood flow increased from 37 +/- 3 to 66 +/- 15 mL x 100 g(-1) x min(-1) during hemodilution and returned to baseline after infusion of red blood cells. There was some loss of EEG amplitude and the calculated cerebral metabolic rate (CMRO2) decreased from 4.3 +/- 0.6 to 1.9 +/- 0.3 mL x 100 g(-1) x min(-1) at the most profound level of anemia. This is the first report of which the authors are aware of continuous monitoring of brain tissue pH, PCO2, and PO2 during profound hemodilution and transfusion. Hemodilution results in a decrease in brain tissue PO2. Increases in CBF and oxygen extraction can only partially compensate for the decreased oxygen carrying capacity of the blood. Decreases in brain tissue PO2, pH, CMRO2, and a loss of EEG amplitude suggest that the maximum tolerable limit of hemodilution was achieved in this study.     

Clinical evaluation of myocardial protection by oxygenated crystalloid cardioplegic solutions with DBcAMP]

Possible enhancement of myocardial protection by adding DBcAMP and oxygenation of a crystalloid cardioplegic solution (CCS) was evaluated in a three group study. The patients having coronary bypass operation or valvular operation were divided into three groups, each consisting of 15 patients, and differing only in the type of CCS employed. Group I was protected by nonoxygenated CCS (PO2 190 mmHg, PCO2, 32 mmHg, pH 7.78, K 30 mmEq/L), Group II by adding DBcAMP to nonoxygenated CCS and Group III by adding DBcAMP to oxygenated CCS (PO2 790 mmHg, PCO2 26 mmHg, pH 7.87). Group III had significantly improved CI and double product (p less than 0.05) compared with Group II. However, CPK, CPK-MB, and myoglobin in the serum were similar in each group. Lactate and pyruvate ratio (L/P) in the coronary sinus bloods were improved to lower value after the pump than before the pump only in Group III. Base excess in the coronary sinus held on alkalosis after aortic declamp only in Group III. The refunction time was significantly shortest with Group III than with other groups (p less than 0.01, 0.05) and Group II was significantly shorter than Group I (p less than 0.05). It is concluded that oxygenation and adding DBcAMP to CCS are effectual for the myocardial metabolism and protect the myocardial damage during cardiac arrest.