Effects of Ultrathin Silicone Coating of Porous Membrane on Gas Transfer and Hemolytic Performance

Abstract: To assess the effect of an ultrathin (0.2 μm) silicone-coated microporous membrane oxygenator on gas transfer and hemolytic performance, a silicone-coated capillary membrane oxygenator (Mera HP Excelung-prime, HPO-20H-C, Senko Medical Instrument Mfg. Co., Ltd. Tokyo, Japan) was compared with a noncoated polypropylene microporous membrane oxygenator of the same model and manufacturer using an in vitro test circuit. The 2 oxygenators showed little difference in the oxygen (O₂) transfer rate over a wide range of blood flow rates (1 L/min to 8 L/min). The carbon dioxide (CO₂) transfer rate was almost the same in both devices at low blood flow rates. but the silicone-coated oxygenator showed a decrease of more than 20% in the CO₂ transfer rate at higher blood flow rates. This loss in performance could be partly attenuated by increasing the gas/blood flow ratio from 0.5 or 1.0 to 2.0. In the hemolysis study, the silicone-coated membrane oxygenator showed a smaller increase in plasma free hemoglobin than the noncoated oxygenator. The pressure drop across both oxygenators was the same. These results suggest that the ultrathin silicone-coated porous membrane oxygenator may be a useful tool for long-term extracorporeal lung support while maintaining a sufficient gas transfer rate and causing less blood component damage.     

From the spinning disc to the membrane oxygenator for open-heart surgery

Gibbon's rotating cylinder could not be enlarged to oxygenate an animal larger than a cat. The spinning disc oxygenator, introduced in 1947, had the capacity to perfuse a dog and the potential to increase oxygenation capacity by addition of more discs. When centers began to do three to four open-heart operations per day, the disposable bubble oxygenator was more practical. Bubble size was optimized to decrease the flow of oxygen relative to the blood flow and reduce trauma to blood. The bubble oxygenator is the type most commonly used today. Use of deep hypothermia with whole blood at an esophageal temperature of 10 degrees C was initially complicated by brain damage due to aggregation of white blood corpuscles and platelets. The introduction of hemodilution permitted safe utilization of hypothermic perfusion. Perfusion of infants should not be carried out at hematocrit below 25 ml/100 m. Early membrane oxygenators used nonporous silicone, or modified silicone membranes. High priming volumes, high pressure drop and marginal gas transfer efficiency characterized these devices. Recent advances in membrane technology have spawned a new generation of membrane oxygenators utilizing microporous polypropylene. In these new oxygenators, with either microporous hollow fibers or sheet membrane, the gas transfer characteristics are far superior to those of types produced in the past. The hollow-fiber devices typically have larger surface areas and higher pressure drop than in the new state-of-the-art flat plate models. An evaluation of one of these new-generation membrane oxygenators gave optimal oxygen and carbon dioxide exchange at a gas flow of 1 l/min of 60% oxygen in air at 30 degrees C and 2 l/min of 80% oxygen in air at normal temperature and rewarming for an adult. Today, after almost 40 years of oxygenator development, these new membrane device can offer better platelet preservation and reduced blood trauma as compared with types developed in the past. The new membrane oxygenators are fast becoming the preferred choice for use in infants and in protracted perfusion.     

Maternal Insufflation during the Second Trimester Equivalent Produces Hypercapnia, Acidosis, and Prolonged Hypoxia in Fetal Sheep

Background: Anecdotal reports suggest that the second trimester is the safest time to conduct a laparoscopic procedure on a pregnant patient, but this supposition has not been tested empirically.

Methods: Previously instrumented preterm sheep (total n = 8) at gestational day 90 (term, 145 days) were anesthetized and then insufflated with carbon dioxide for 60 min at a pressure of 15 mmHg. Cardiovascular parameters were continuously recorded while blood gas status was determined before and at 15-min intervals during and up to 2 h after insufflation.

Results: Insufflation produced minimal maternal blood gas or cardiovascular changes except for a significant reduction in uterine blood flow. The decrease in perfusion increased fetal arterial blood partial pressure of carbon dioxide and decreased fetal pH, oxygen saturation, and oxygen content; there was also progressive fetal hypotension and bradycardia. After manually deflating the ewe, uterine blood flow returned to normal, and the fetal partial pressure of carbon dioxide and pH changes resolved within 1 h. However, fetal oxygen saturation and content remained depressed, and fetal cardiovascular status continued to decline during the 2-h postinsufflation monitoring period.     

Gas flow in relation to blood flow in oxygenators. An evaluation of the new Shiley bubble oxygenator.

A new bubble oxygenator, designed by the Shiley Laboratories, which utilizes a low gas flow for oxygenation, was first tested in dogs and then in 100 clinical cases. For perfusion in adult patients, a gas flow as low as 0.6 litre oxygen per 1 litre blood has given adequate oxygenation and removal of carbon dioxide with no untoward effect on the blood, as compared with other oxygenators, including the membrane type.     

Maternal insufflation during the second trimester equivalent produces hypercapnia, acidosis, and prolonged hypoxia in fetal sheep

BACKGROUND: Anecdotal reports suggest that the second trimester is the safest time to conduct a laparoscopic procedure on a pregnant patient, but this supposition has not been tested empirically. METHODS: Previously instrumented preterm sheep (total n = 8) at gestational day 90 (term, 145 days) were anesthetized and then insufflated with carbon dioxide for 60 min at a pressure of 15 mmHg. Cardiovascular parameters were continuously recorded while blood gas status was determined before and at 15-min intervals during and up to 2 h after insufflation. RESULTS: Insufflation produced minimal maternal blood gas or cardiovascular changes except for a significant reduction in uterine blood flow. The decrease in perfusion increased fetal arterial blood partial pressure of carbon dioxide and decreased fetal pH, oxygen saturation, and oxygen content; there was also progressive fetal hypotension and bradycardia. After manually deflating the ewe, uterine blood flow returned to normal, and the fetal partial pressure of carbon dioxide and pH changes resolved within 1 h. However, fetal oxygen saturation and content remained depressed, and fetal cardiovascular status continued to decline during the 2-h postinsufflation monitoring period. CONCLUSION: Previous studies with near-term sheep determined that carbon dioxide pneumoperitoneum produces respiratory acidosis but does not decrease fetal oxygenation. In contrast, the current findings indicate that in the preterm fetus, insufflation-induced hypercapnia and acidosis are accompanied by prolonged fetal hypoxia and cardiovascular depression. This result suggests that additional work should be conducted to confirm the presumed safety of conducting minimally invasive procedures during the second trimester.     

The Pressure-Flow Relations of the Canine Brain in Acute Mechanically Induced Arterial Hypertension at Different Levels of Cerebral Blood Flow

Cerebral pressure-flow relations were studied in anaesthetized dogs during acute arterial hypertension, induced by compression of the thoracic aorta. In one group of animals steady state measurements were made with the radioactive gas elimination method. In another group the immediate changes of blood flow at a blood pressure change, as indicated by variations in the cerebral venous oxygen saturation, were studied with continuous oximetric analyses of the superior sagittal sinus blood. The initial blood flow was varied by variations of the arterial carbon dioxide tension of injections of papaverine. At low or normal blood flows autoregulation was efficient up to pressures around 180-200 mmHg, while at higher flows the upper autoregulatory pressure limit was found at lower blood pressures. Above the autoregulatory limit-irrespective of the control flow level-there was a rise in blood flow and a decrease in cerebrovascular resistance.     

Non-destructive evaluation of membrane lung gas exchange performance

This paper describes a method of evaluating the gas exchange effectiveness of hollow fiber oxygenators utilizing gas on both sides of the membrane. The goal of the study was to develop an evaluation technique which was accurate, reliable, and did not harm or contaminate a new, sterile oxygenator. Three pediatric oxygenators were tested and compared: the Medtronic Minimax Plus, the Terumo Capiox 320, and the Sorin Masterflo 34 (all with rated blood flows of 2-2.5 L/min). Gas entering the "blood" side was a mixture of CO2, O2, and N2 in a mixture matching typical venous blood partial pressures. The "blood" flows used were 0.5, 1, 1.5, or 2 L/min. Gas entering the gas port had an FiO2 of 0.4 flowing at 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 L/min. Fractional contents of CO2 and O2 at all inlets and outlets were determined using a gas analyzer and converted to partial pressures. Efficacy indices and gas transfer rates were calculated and compared. Of the devices studied, the Masterflo 34 had the highest gas transport rates and effectiveness followed by the Minimax-Plus and the Capiox 320. Reversing the direction of the flow through the "blood" phase of the Minimax-Plus greatly changed its gas exchange effectiveness. The techniques described in this study should allow for a more uniform and consistent evaluation of gas exchange by membrane lungs which can be made inexpensively and relatively quickly. In addition, these methods should allow manufactures to evaluate gas exchange effectiveness and transfer rates of individual units during production as well as reduce the complexity involved when evaluating newly developed oxygenators.     

EFFECT OF INCREASED CONCENTRATIONS OF CARBON DIOXIDE DURING HALOTHANE ANAESTHESIA ON LIVER BLOOD FLOW AND HEPATIC OXYGEN CONSUMPTION

The effects of hypercapnia (during halothane anaesthesia) onthe hepatic circulation and hepatic oxygen consumption wereinvestigated in anaesthetized greyhounds. The administrationof 1% halothane alone caused significant decreases in both hepaticarterial and portal venous blood flows. Hepatic oxygen consumptiondid not change significantly. When carbon dioxide was addedto the inspired gas mixture during the continued administrationof halothane, hepatic arterial blood flow showed a further decrease(P< 0.01), while portal venous flow increased markedly. Thisresulted in an overall increase in total liver blood flow. Hepaticoxygen supply increased also. However, hepatic oxygen consumptionincreased during the periods of hypercapnia. Thus, althoughthe hypercapnia increased the oxygen supply to the liver, therewas no improvement in the supply: demand ratio. ^*Present address: Department of Anaesthesia, Stobhill Hospital,Glasgow     

The history of extracorporeal oxygenators

Extracorporeal oxygenators are artificial devices that substitute for anatomical lungs by delivering oxygen to, and extracting carbon dioxide from, blood. They were first conceptualised by the English scientist Robert Hooke (1635-1703) and developed into practical extracorporeal oxygenators by French and German experimental physiologists in the 19th century. Indeed, most of the extracorporeal oxygenators used until the late 1970s were derived from von Schroder's 1882 bubble oxygenator and Frey and Gruber's 1885 film oxygenator. As there is no intervening barrier between blood and oxygen, these are called 'direct contact' oxygenators; they contributed significantly to the development and practice of cardiac surgery till the 1980s. Membrane extracorporeal oxygenators introduce a gas-permeable interface between blood and oxygen. This greatly decreased the blood trauma of direct-contact extracorporeal oxygenators, and enabled extracorporeal oxygenators to be used in longer-term applications such as the intensive therapy of respiratory distress syndrome; this was demonstrably beneficial for neonates but less so for older patients. Much work since the 1960s focused on overcoming the gas exchange handicap of the membrane barrier, leading to the development of high-performance microporous hollow-fibre oxygenators that eventually replaced direct-contact oxygenators in cardiac theatres.     

Impact of hollow-fiber membrane surface area on oxygenator performance: Dideco D903 Avant versus a prototype with larger surface area

This study compares the gas transfer capacity, the blood trauma, and the blood path resistance of the hollow-fiber membrane oxygenator Dideco D 903 with a surface area of 1.7 m2 (oxygenator 1.7) versus a prototype built on the same principles but with a surface area of 2 m2 (oxygenator 2). Six calves (mean body weight: 68.2 +/- 3.2 kg) were connected to cardiopulmonary bypass (CPB) by jugular venous and carotid arterial cannulation, with a mean flow rate of 4 l/min for 6 h. They were randomly assigned to oxygenator 1.7 (N = 3) or 2 (N = 3). After 7 days, the animals were sacrificed. A standard battery of blood samples was taken before the bypass, throughout the bypass, and 24 h, 48 h, and 7 days after the bypass. The oxygenator 2 group showed significantly better total oxygen and carbon dioxide transfer values throughout the perfusion (p < .001 for both comparison). Hemolytic parameters (lactate dehydrogenase and free plasma hemoglobin) exhibited a slight but significant increase after 5 h of bypass in the oxygenator 1.7 group. The pressure drop through the oxygenator was low in both groups (range, 43-74 mmHg). With this type of hollow-fiber membrane oxygenator, an increased surface of gas exchange from 1.7 m2 to 2 m2 improves gas transfer, with a limited impact on blood trauma and no increase of blood path resistance.     

Avoiding hyperoxemia at the start of cardiopulmonary bypass while optimizing gas flow and temperature

There seems to be a wide range of practice in relation to the optimum oxygen setting before, and at the start of, cardiopulmonary bypass. Even manufacturers of blood oxygenators vary in their suggestions for this phase of extracorporeal circulation. Most of these suggestions are based on peak performance, Association for the Advancement of Medical Instrumentation (AAMI) standards, experience, and legal considerations. Therefore, suggested gas:blood flow ratios will vary from no gas flow at the start of bypass, to a ratio setting of 1:1. On the other hand, suggested inspired oxygen concentrations will generally vary between 0.80 to 1.0 at the start of cardiopulmonary bypass. In regard to perfusate temperatures before going on bypass, there are no clearly defined standards other than those of clinical preference. The manufacturer of the oxygenator used in this study clearly states in the operating instructions that gas flow should be proportional to blood flow at the start of bypass, and gas flow should be turned off when there is no fluid flow through the oxygenator. The presence of hyperoxic perfusates and wide patient/perfusate temperature gradients at the start of bypass has been suspected in the appearance of gaseous microemboli during this critical period. Hyperoxemia during the bypass period is also implicated in the introduction of oxygen free radicals and nitric oxide into the hypoxic myocardium during cardioplegia delivery. Presented here are the results of a randomized clinical study involving 39 adult patients undergoing cardiopulmonary bypass for the surgical treatment of coronary artery disease. All patients were randomly selected into five groupings. The first group had 1 L of gas flow through the perfusate before bypass, and bypass was then started with an FIO2 of 0.80. The second two groups had no gas flow through the perfusate prior to bypass and a starting FIO2 of 0.21. Groups 4 and 5 had 1 L of gas flowing through the perfusate and a starting FIO2 of 0.21. Results indicate that gas flow through Normosol R/Albumin perfusates will prevent the acidosis that is found in this solution when the system is previously flushed with carbon dioxide. Also, suggested high FIO2 settings will produce hyperoxic perfusates at the start of cardiopulmonary bypass. However, the use of an FIO2 of 0.21 at the start of bypass will produce normoxemic conditions that are both safe and reliable for the conduct of initiating cardiopulmonary bypass.     

Cerebrovascular and cerebral metabolic effects of alterations in perfusion flow rate during hypothermic cardiopulmonary bypass in man.

Recent experimental and clinical investigations provide conflicting evidence regarding the effects of changes in the systemic flow rate from the pump oxygenator on cerebral blood flow and the cerebral metabolic rate of oxygen consumption. However, the results of existing clinical studies are difficult to interpret because of the confounding effects of differences in management of arterial carbon dioxide tension and use of anesthetic and vasoactive agents during cardiopulmonary bypass. To clarify the relationship among perfusion flow rate, cerebral blood flow, and cerebral metabolic rate of oxygen consumption in man during hypothermic cardiopulmonary bypass, we varied perfusion flow rate in random order to either 1.75 or 2.25 L.min-1.m-2 and studied cerebral blood flow (measured by clearance of xenon 133) and cerebral metabolic rate of oxygen consumption (estimated as the product of cerebral blood flow and the cerebral arteriovenous oxygen content difference) in patients managed with both the alpha-stat (group 1) and the pH-stat (group 2) methods of pH and arterial carbon dioxide tension adjustment. We measured the cerebral arteriovenous oxygen content difference using radial arterial and jugular venous bulb blood samples. In each patient other variables known to exert effects on cerebral blood flow and cerebral metabolic rate of oxygen consumption, including temperature, arterial carbon dioxide tension, arterial oxygen tension, mean arterial pressure, and hematocrit, were maintained constant between measurements. In both groups, mean arterial pressure at both pump flow rates was similar because of spontaneous reciprocal alterations in systemic vascular resistance, that is, as perfusion flow rate declined, systemic vascular resistance increased; as perfusion flow rate increased, systemic vascular resistance declined. Under these tightly controlled conditions, pump flow variation per se exerted no effect on cerebral blood flow or cerebral metabolic rate of oxygen consumption in either group.     

Effects of PEEP on residual vascularization in oesophageal substitution gastroplasty by surface oximetry-capnometry and photoplethysmography: an experimental study

OBJECTIVE: To evaluate the effects of positive end-expiratory pressure (PEEP) on residual vascularization in gastric tubes for oesophageal replacement. DESIGN: Experimental open study. MATERIALS: Eleven mongrel dogs. METHODS: Intestinal parietal blood flow was evaluated by photoplethysmography (PPG) and measurement of surface oxygen (PsO(2)) and carbon dioxide (PsCO(2)) tensions under basal conditions. After Akiyama's tubular gastroplasty, three levels of PEEP were administered. At each level, fluids were infused to counter the drop in cardiac output. PPG, surface gas tensions, arterial pressure, cardiac output and arterial blood gas tensions were monitored. Control sections of the bowel were also monitored by PPG. RESULTS: Cardiac output dropped for each level of PEEP and returned to basal levels on volume restabilization and on removal of PEEP. Central venous pressure and pulmonary arterial and capillary pressures increased for each level of PEEP and only returned to basal levels on removal of PEEP. PsO(2) values dropped for each level of PEEP and returned to basal levels on volume restabilization and on removal of PEEP. PsCO(2) levels rose, and PPG wave amplitude dropped, for each level of PEEP; these two variables only returned to basal levels on removal of PEEP. PPG values for the control sections reflected those of the anastomotic area. CONCLUSIONS: PEEP affects surface oxygen values at the level of the gastroplasty by means of its effect on cardiac output. PEEP also creates a venous return compromise and PPG wave amplitude and surface carbon dioxide values are related to this compromise. All three variables could be significant in anastomotic wound healing.     

Experimental study of peritoneal blood flow and insufflation pressure during laparoscopy

BACKGROUND: Port-site metastases after laparoscopic surgery may occur with greater frequency than would be expected following open resection of intra-abdominal malignancies, but the causal mechanism for this is incompletely understood. The possibility that insufflation may increase peritoneal blood flow producing a wound environment conducive to the formation of metastases was investigated.METHODS: The effects of insufflation gas type and pressure were studied in 30-kg female pigs. Pigs were divided into five groups, which were subjected to insufflation at 12 mmHg pressure with helium, insufflation at 12, 8 or 4 mmHg pressure with carbon dioxide, or laparotomy. A microsphere technique utilizing two distinct radiotracers, 99mTc-labelled macroaggregated albumin (MAA) and 51Cr-labelled MAA, was used to study blood flow to the peritoneum, liver and kidneys.RESULTS: Insufflation with carbon dioxide or helium gases had no effect on renal (P < 0.09) or hepatic blood flow (P = 0.54). However, insufflation significantly increased peritoneal blood flow when carbon dioxide (P < 0.05), but not when helium (P = 0.99), was used as the insufflating gas.CONCLUSION: These data suggest that blood flow within the peritoneum is influenced by insufflation with carbon dioxide. It is conceivable that such hyperaemia could increase the propensity for implanted tumour cells to metastasize in these sites following laparoscopy.     

The effects of preprimed oxygenators on gas transfer efficiency

Cancellation of on-pump coronary artery bypass grafting after the circuit is primed may result in the discarding of unused circuits. In some off-pump cases, a surgeon may request that the circuit be primed, but complete the surgical procedure without utilizing the circuit. The major concerns about the unused circuit are its sterility and the performance of the oxygenator after it has been primed for a long period of time. The goal of this study is to determine whether prepriming of the circuit with and without albumin has an effect on the gas transfer efficiency of oxygenators during simulated cardiopulmonary bypass. Monolyth integrated membrane lungs (Sorin Biomedical, Arvada, CO) were used to deoxygenate and oxygenate the bovine blood. Oxygenators were preprimed for 72 (N = 6) and 24 (N = 6) hours before testing. In control group (N = 6), oxygenators were tested immediately (0 h) after they were primed. Three different priming solutions were used: physiological saline solution (Group A); 1.25% of human albumin (Group B); and 5% human albumin (Group C). The blood was modified to the American Association of Medical Instrumentation Standards before testing. The blood flow through the oxygenators was set at 2 Lpm and 4 Lpm, with gas (FiO2 at 1.0) to blood flow ratio at 1:1. Cultures were also obtained from preprimed oxygenators to test circuit sterility. Oxygen transfer in oxygenators primed for 0 h at blood flow of 4 Lpm were 203 mL/min +/- 9.7 (Group A), 263.1 mL/min +/- 52.9 (Group B), and 270.5 mL/min +/- 13.1(Group C, p < .01 vs. Group A). In oxygenators preprimed for 72 h, the CO2 transfers were 135.0 mL/min +/- 21.8 (Group A), 104.9 mL/min +/- 2.4 (Group B), and 148.9 +/- 26.6 (Group C, p < .006 vs. Group B). In addition, the pressure drops were 56.5 mmHg +/- 5.5 (Group A), 82.6 mmHg +/- 13.4 (Group B), and 67.6 mmHg +/- 15.3 (Group C, p < .05 vs. Group B). In group A, O2 transfer were 203.5 mL/min +/- 9.7 (0 h), 272.4 mL/min +/- 66.6 (24 h), and 260.8 mL/min +/- 31.1 (72 h, p < .01 vs. 0 h). In group B, O2 transfer were 263.1 mL/min +/- 52.0 (0 h), 302.7 mL/min +/- 77.4 (24 h), and 235.2 mL/min +/- 16.5 (72 hr, p < .02 vs. 24 hr). Cultures obtained from 12 preprimed oxygenators presented no organism growth for up to 5 days. In conclusion, oxygen transfer increases in oxygenators preprimed with albumin immediately after they were primed. However, gas transfer decreased after they were primed with albumin for 72 h. Oxygenators preprimed for 24 h and 72 h with 0.9% saline had better O2 transfer than those primed for 0 h.     

Expired gas backflow in oxygen delivery tubing

Using capnography, we investigated the backflow of expired gas into oxygen delivery tubing in 18 sedated patients receiving supplementary oxygen via a disposable facemask during spinal anaesthesia. At 5 cm from the mask, with an oxygen flow of 2 l.min(-1), carbon dioxide was detected in the oxygen delivery tubing of three patients (18%) on coughing. With the patient wearing the facemask but the oxygen tubing disconnected from the oxygen source, carbon dioxide was detectable 1 m from the facemask (i.e. at the fresh gas outlet) in 14 patients. In a second group of 20 similar patients, no carbon dioxide was detected sampling at the fresh gas outlet with flows of 2 and 4 l.min(-1). Assuming that detection of carbon dioxide indicates at least the possibility of contamination, oxygen tubing should be strictly single-use in this setting. Our findings suggest that filters are not required to protect gas supply outlets, provided that the patient's facemask is removed when the fresh gas outlet is disconnected.     

Cerebral oxygen extraction and autoregulation during extracorporeal whole body hyperthermia in humans

BACKGROUND: The effects of hyperthermia on the human brain are incompletely understood. This study assessed the effects of whole body hyperthermia on cerebral oxygen extraction and autoregulation in humans. METHODS: Nineteen patients with chronic hepatitis C virus infection, not responding to interferon treatment, were subjected to experimental therapy with extracorporeal whole body hyperthermia at 41.8 degrees C for 120 min under propofol anesthesia (23 sessions total). During treatment series A (13 sessions), end-tidal carbon dioxide was allowed to increase during heating. During series B (10 sessions), end-tidal carbon dioxide was maintained approximately constant. Cerebral oxygen extraction (arterial to jugular venous difference of oxygen content) and middle cerebral artery blood flow velocity were continuously measured. Cerebral pressure-flow autoregulation was assessed by static tests using phenylephrine infusion and by assessing the transient hyperemic response to carotid compression and release. RESULTS: For treatment series A, cerebral oxygen extraction decreased 2.2-fold and cerebral blood flow velocity increased 2.0-fold during heating. For series B, oxygen extraction decreased 1.6-fold and flow velocity increased 1.5-fold. Jugular venous oxygen saturation and lactate measurements did not indicate cerebral ischemia at any temperature. Static autoregulation test results indicated loss of cerebrovascular reactivity during hyperthermia for both series A and series B. The transient hyperemic response ratio did not decrease until the temperature reached approximately 40 degrees C. Per degree Celsius temperature increase, the transient hyperemic response ratio decreased 0.07 (95% confidence interval, 0.05-0.09; P = 0.000). This association remained after adjustment for variations in arterial partial pressure of carbon dioxide, mean arterial pressure, and propofol blood concentration. CONCLUSION: Profound hyperthermia during propofol anesthesia is associated with decreased cerebral oxygen extraction, increased cerebral blood flow velocity, and impaired pressure-flow autoregulation, indicating transient partial vasoparalysis.     

Spontaneous gas bubbling in microporous oxygenators

During operation of the microporous membrane oxygenators at some conditions, gas microbubbles penetrate into the blood. This effect, so-called spontaneous bubbling, takes place even when the blood pressure is higher than the gas pressure. This phenomenon was confirmed experimentally both in a model cell with hydrophobic microporous hollow fibers being used in the oxygenators and in in vitro tests on the actual microporous hollow fiber oxygenator. We proposed a mechanism of spontaneous gas bubbling into liquid that contains dissolved gases. Because of a partial pressure gradient, the dissolved gases and water vapors are transported from blood into the gas pore. This causes Stefans gas flow directed from the liquid-gas interface. Because of the high hydraulic resistance of the micropores, gas pressure at the meniscus increases up to gas bubbling. A mishandled priming of the oxygenator as well as the blood pressure pulsation caused by the roller pump operation contribute to spontaneous gas bubbling in the microporous oxygenators. The flow and pressure in the hydrophobic pores were calculated for various gases.     

The effect of intracapsular pressure and extension of the hip on oxygenation of the juvenile femoral epiphysis. A study in the goat

We have investigated the effect of joint tamponade and of traction in extension on the oxygen and carbon dioxide tensions in the femoral head of the immature goat, using mass spectrometry. Tamponade of 75 mmHg caused the oxygen tension in the femoral head to drop from 48 +/- 4 mmHg to 29 +/- 3 mmHg. Traction in extension further decreased the oxygen tension. Both these changes were highly significant. The partial pressure of carbon dioxide increased, but to a lesser extent and only effusion together with traction gave a statistically significant effect. Our study showed that joint effusion can produce hypoxia in the bone as a result of impaired blood flow to the femoral head. The application of traction increases this haemodynamic effect.     

Development of an Intravenous Membrane Oxygenator: Enhanced Intravenous Gas Exchange Through Convective Mixing of Blood around Hollow Fiber Membranes

Abstract: In vitro testing of a new prototype intravenous membrane oxygenator (IMO) is reported. The new IMO design consists of matted hollow fiber membranes arranged around a centrally positioned tripartite balloon. Short gas flow paths and consistent, reproducible fiber geometry after insertion of the device result in an augmented oxygen flux of up to 800% with balloon activation compared with the static mode (balloon off). Operation of the new IMO device with the balloon on versus the balloon off results in a 400% increase in carbon dioxide flux. Gas flow rates of up to 9. 5 L/min through the 14–cm–long hollow fibers have been achieved with vacuum pressures of 250 mm Hg. Gas exchange efficiency for intravenous membrane oxygenators can be increased by emphasizing the following design features: short gas flow paths, consistent and reproducible fiber geometry, and most importantly, an active means of enhancing convective mixing of blood around the hollow fiber membranes