液体复苏对严重脓毒症及脓毒性休克患者的治疗作用研究

目的评价液体复苏手段对严重脓毒症或脓毒性休克的治疗作用。方法通过液体复苏使20例严重脓毒症或脓毒性休克患者达到如下治疗目标：中心静脉压8—12mmHg（机械通气者12—15mmHg）、平均动脉压65～90mmHg、混合静脉血氧饱和度〉70％。测定达标前后血流动力学、组织灌注、血管内皮细胞功能的变化。结果液体复苏达标后,肺动脉楔压明显升高（P〈0．01）,心指数及体循环阻力指数增加（P〈0．01）,肺循环阻力指数下降（P〈0．01）,左心室做功指数上升（P〈0．01）;组织灌注指标中动脉血乳酸（ABL）在复苏后下降（P〈0．01）,胃黏膜二氧化碳分压与动脉血二氧化碳分压差（Pg—aCO2）在复苏后明显下降（P〈0．01）,血管内皮细胞功能中内皮素及血管性假血友病因子在液体复苏后下降（P〈0．05）。结论液体复苏早期达标可改善严重脓毒症或脓毒性休克患者血流动力学和组织灌注并可减轻血管内皮细胞的损伤,是一种有效的治疗方式。     

Objective assessment of cardiac output in infants after cardiac surgery

An accurate measurement of cardiac performance in infants after cardiopulmonary bypass has long been considered to be an important part of postoperative management. To be useful in clinical decision making, such measurements should ideally be reproducible, non invasive and accurately reflect tissue perfusion and oxygen delivery. Historically, we have relied on intermittent measurements of cardiac output using indicator dilution methods; and more recently, technologies that use pulse contour analysis, bio-impedance, or Doppler methodology. These all have the same shortcoming, that they provide a number that the information as to whether it provides adequate tissue perfusion. There is increasing emphasis being placed on the measurement of oxygen delivery either by mixed venous oxygen saturation and serum lactate, which are important markers of the adequacy of organ perfusion; and relating this to outcome, the development of organ dysfunction and length of ICU stay.     

重度蒸汽吸入性损伤后组织氧合的变化

采用蒸汽吸入造成实验犬急性肺损伤，探讨伤后心输出量（ＣＯ）、氧供量（ＤＯ_２）、氧耗量（ＶＯ_２）、氧摄取率（ＥＲＯ_２）、动脉和混合静脉血氧分压（ＰａＯ_２和ＰｖＯ_２）、动脉和混合静脉血氧饱和度（ＳａＯ_２和ＳｖＯ_２）、肺泡氧分压（Ｐ_ＡＯ_２）以及肺泡－动脉氧分压差（Ｐ_（Ａ－ａ）Ｏ_２）等变化。结果表明，蒸汽吸入４ｈ内，ＣＯ、Ｄ０_２、ＰａＯ_２、ＰｖＯ_２、ＳａＯ_２、ＳｖＯ_２、ＰＡＯ_２和ｐＨ值均显著下降（Ｐ＜０．０１）、Ｐ_（Ａ－ａ）Ｏ_２、ＥＲＯ_２和ＰａＣＯ_２均显著升高（Ｐ＜０．０１和０．０５），ＶＯ_２则无显著变化。提示，蒸汽吸入性损伤后２～４ｈ即可出现组织缺氧，其直接原因是组织灌注和供氧不足。     

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.     

The Haldane effect--an alternative explanation for increasing gastric mucosal PCO2 gradients?

When venous oxygen saturation increases as a result of increased blood flow, changes in venous blood PCO2 and carbon dioxide content may differ because of the Haldane effect. The Haldane effect may also explain increases in gastric mucosal-arterial PCO2 gradient despite major increases in splanchnic blood flow. We re-analysed data from 22 patients after cardiac surgery who were randomized to receive either dobutamine or placebo, and a separate group of patients who received dobutamine for low cardiac output (n = 6). Three different values of gastric mucosal oxygen extraction at baseline were assumed (0.3, 0.5 and 0.7). In nine of 14 patients with both increasing splanchnic blood flow and mucosal-arterial PCO2 gradient, an equal increase in mucosal and total splanchnic blood flow, oxygen consumption and carbon dioxide production together with the Haldane effect would have caused an increase in mucosal-arterial PCO2 gradients from a mean value of 0.53 (SD 0.88) kPa at baseline to 0.68-0.82 (0.89-0.90) kPa (P < 0.01). In the remaining patients, disproportionate changes in flow and metabolism must have been involved in addition to the Haldane effect. We conclude that whenever major changes in mucosal tissue oxygen extraction are likely to occur, an increase in the mucosal-arterial PCO2 gradient may be explained in part or completely by the Haldane effect, and may therefore not reflect worsening perfusion.      

The massively bleeding patient.

The resuscitation of the massively bleeding patient may seem superficially to be successful once the patient's vital signs have stabilized. The restoration of stable vital signs, however, does not confirm two critical elements of a thorough physiologic resuscitation: that there is truly adequate delivery of oxygen to all tissue beds and that physiologic disturbances that may have occurred because of massive transfusion during the resuscitation process have resolved. With respect to the adequacy of oxygen delivery, the current clinical endpoints, including mixed venous oxygen saturation, cardiac output, and serum lactate, reflect global perfusion and not regional oxygenation. Of these global measures, serum lactate is currently the best indicator as to whether some circulatory beds remain inadequately perfused. Serum lactate should be followed, and, in the event that elevated levels persist, measures to augment oxygen delivery (e.g., increasing cardiac output, hemoglobin concentration, oxygen saturation) should be undertaken. Gastric tonometry provides a method for specific examination of the splanchnic circulation. The current measurement techniques, however, require steady-state conditions and make it impractical in many physiologically dynamic situations. The physiologic disturbances associated with massive resuscitation (e.g., hyperkalemia, hypocalcemia, hypomagnesemia, hypothermia) should be anticipated. Coagulation disturbances occur, especially when massive transfusion is accompanied by hypotension, hypothermia, or acidosis. Coagulation parameters should be measured with the loss of each one half of blood volume or after each 30-minute interval, whichever occurs first. Evaluation at blood volume intervals is relevant to the development of a strictly dilutional coagulopathy. The development of DIC, occurring because of tissue factor exposure or acidosis, however, is related more to the time lapsed than to the absolute volume lost or replaced.     

The Influence of Arterial Carbon Dioxide Tension on the Cerebrovascular Response to Arterial Hypoxia and to Haemodilution

Cerebral blood flow (CBF) measurements and blood gas analyses were performed on anaesthetized and artifically ventilated dogs during arterial hypoxia or haemodilution in different ranges of arterial carbon dioxide tension. Arterial hypoxia as well as haemodilution produced a flow increase in all ranges of ventilation. However, this flow increase was elicited at a cerebrovenous oxygen tension which rose with the arterial carbon dioxide tension, but which tended to be maintained by the flow increase during continued decrease of the arterial oxygen content. On the assumption that the cerebrovenous oxygen tension reflects the oxygen tension of the brain tissue, it is suggested that the arterial carbon dioxide tension influences the ability of the brain tissue to maintain the aerobic metabolism during reduced tissue oxygen tension. This means that tissue hypoxia, in the sense of utilisation of anaerobic metabolism, occurs at a tissue oxygen tension which is lower the lower the arterial carbon dioxide tension is.     

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.     

Effect of graded hemorrhage on renal cortical perfusion in dogs

Renal cortical tissue gas tensions, systemic oxygen supply and some features of energy metabolism and central hemodynamics were recorded in splenectomized dogs during graded hemorrhage and subsequent reinfusion of shed blood. Renal cortical partial pressure of oxygen and carbon dioxide responded rapidly to changes in blood volume and cardiac output. Lowest cortical partial pressure of oxygen values and highest cortical partial pressure of carbon dioxide levels were achieved at a maximal 50 percent blood loss. The decrease in arterial pressure, blood hemoglobin and hematocrit as well as the increase in blood lactate concentration lagged behind blood loss. Renal cortical partial pressure of oxygen, arterial pressure and cardiac output responded rapidly to reinfusions of withdrawn blood, while the cortical partial pressure of carbon dioxide, heart rate, arterial pH and blood lactate concentration returned to initial levels more slowly. Arterial blood gases remained normal throughout the observation period and did not provide an adequate index of tissue oxygenation. In contrast, the partial pressure of oxygen of the renal cortex proved an excellent and sensitive indicator of renal perfusion during hemorrhagic shock and its management.     

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 relationship between the arterial to end-tidal PCO2 difference and hemoglobin saturation in patients with congenital heart disease

In right-to-left (RL) intracardiac shunting, the venous blood that is added to the oxygenated blood in the left heart is both poor in oxygen and rich in carbon dioxide. Thus, any given degree of arterial desaturation is associated with an obligatory arterial to end-tidal carbon dioxide tension difference (PaCO2--PETCO2). This paper presents a theoretical analysis of the relationship between PaCO2-PETCO2 and arterial hemoglobin saturation (SaO2) in cyanotic heart disease. Using the shunt equation as a starting point, a curvilinear, negative correlation between PaCO2-PETCO2 and SaO2 can be demonstrated. The slope of the regression of PaCO2--PETCO2 against SaO2 is shown to be positively correlated to Hb concentration, PaCO2, and the respiratory quotient R. The slope of the regression is also slightly increased at relatively high SaO2s and at high inspired oxygen fractions, although these latter factors are of lesser significance. However, in addition to the above primary effects of RL shunting, secondary effects may occur if pulmonary perfusion is reduced sufficiently to cause "alveolar hypoperfusion," which also creates an alveolar dead space. Primary and secondary effects are additive. This theoretical analysis is illustrated with a study of 27 children with congenital heart disease. Their lungs were ventilated with a Servoventilator 900 C, and carbon dioxide single-breath tests were obtained on-line with the use of a computerized system based on the Siemens-Elema carbon dioxide analyzer 930. Blood was sampled for PaCO2 measurement and arterial Hb saturation was measured by pulse oximetry (SpO2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation between cerebral oxygen saturation measured by near-infrared spectroscopy and jugular oxygen saturation in patients with severe closed head injury.

Near-infrared spectroscopy has been used to monitor cerebral oxygen saturation during cerebral circulatory arrest and carotid clamping. However, its utility has not been demonstrated in more complex situations, such as in patients with head injuries. The authors tested this method during conditions that may alter the arteriovenous partition of cerebral blood in different ways. METHODS: The authors compared changes in measured cerebral oxygen saturation and other hemodynamic parameters, including jugular venous oxygen saturation, in nine patients with severe closed head injury during manipulation of arterial carbon dioxide partial pressure and after mean arterial pressure was altered by vasopressors. RESULTS: The Bland and Altman representation of cerebral oxygen saturation versus jugular oxygen saturation showed a uniform scatter. Values for changing arterial carbon dioxide partial pressure were: bias = 1.1%, 2 SD = +/-21%, absolute value; and those for alterations in mean arterial pressure: bias = 3.7%, 2 SD = +/-24%, absolute value. However, a Bland and Altman plot of changes in cerebral oxygen saturation versus changes in jugular oxygen saturation had a negative slope (alteration in arterial carbon dioxide partial pressure: bias = 2.4%, 2 SD = +/-17%, absolute value; alteration in mean arterial pressure: bias = -4.9%, 2 SD = +/-31%, absolute value). Regression analysis showed that changes in cerebral oxygen saturation were positively correlated with changes in jugular venous oxygen saturation during the carbon dioxide challenge, whereas correlation was negative during the arterial pressure challenge. CONCLUSIONS: Cerebral oxygen saturation assessed by near-infrared spectroscopy does not adequately reflect changes in jugular venous oxygen saturation in patients with severe head injury. Changes in arteriovenous partitioning, infrared-spectroscopy contamination by extracerebral signal, algorithm errors, and dissimilar tissue sampling may explain these findings.     

Optimal Perfusion Pressure For Experimental Retrograde Cerebral Perfusion

We evaluated cerebral metabolism during retrograde cerebral perfusion (RCP) and circulatory arrest during profound hypothermia, and also investigated the effects of perfusion pressure on RCP. Twenty-four adult mongrel dogs were placed on cardiopulmonary bypass and cooled to a nasopharyngeal temperature of 20°C. At this temperature, hypothermic circulatory arrest (HCA; n = 6), and RCP with a perfusion pressure of 10 mmHg (RCP10; n = 6), 20 mmHg (RCPPO; n = 6), and 30 mmHg (RCPBO; n = 6) were carried out for 60 minutes. RCP was performed with oxygenated blood via the bilateral maxillary veins, and the retrograde flow rate was regulated to maintain a mean perfusion pressure of 10, 20, or 30 mmHg in the external jugular vein. At 60 minutes of RCP, we measured nasopharyngeal temperature; regional cerebral blood flow (rCBF); cerebral oxygen consumption, carbon dioxide excretion, and excess lactate; cerebral tissue adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and energy charge; and cerebral tissue water content. In the RCP10 group, there was excess cerebral lactate, and ATP and energy charge were low. In the RCP30 group, the water content of cerebral tissue was significantly higher than in other groups. In the RCP20 group, temperature was maintained in a narrow range, oxygen consumption and carbon dioxide excretion could be observed, there was no excess lactate, and ATP and energy charge were significantly higher than In the HCA group. In conclusion, RCP can provide adequate metabolic support for the brain during circulatory arrest, and a perfusion pressure of 20 mmHg is most appropriate for RCP. (J Card Surg 1994;9:548–559)     

Measurement of intracerebral oxygen pressure: practicalities and pitfalls

Two probes, using different technologies, are currently available to measure tissue oxygen pressure. One of these also measures oxygen pressure, carbon dioxide pressure, pH and temperature. Research has delineated normal brain tissue oxygen pressure as 25-45 mmHg and ischemic thresholds of less than 10 mmHg that are related to ischemic injury. Oxygen pressure measures are correlated with other indicators of brain oxygenation such as jugular bulb oxygen saturation and near infrared spectroscopy, but are more reliable for detecting regional ischemic events. Oxygen pressure is correlated with local blood flow in the brain, and treatments that enhance tissue perfusion improve oxygenation.     

Simultaneous Automatic Control of Oxygen and Carbon Dioxide Blood Gases During Cardiopulmonary Bypass

In this work an automatic control strategy is presented for the simultaneous control of oxygen and carbon dioxide blood gas partial pressures to be used during cardiopulmonary bypass surgery with heart–lung machine support. As the exchange of blood gases in the artificial extracorporeal lung is a highly nonlinear process comprising varying time delays, uncertainties, and time‐varying parameters, it is currently being controlled manually by specially trained perfusionist staff. The new control strategy includes a feedback linearization routine with augmented time‐delay compensation and two external linear gain‐scheduled controllers, for partial oxygen and carbon dioxide pressures. The controllers were robustly tuned and tested in simulations with a detailed artificial lung (oxygenator) model in cardiopulmonary bypass conditions. Furthermore, the controllers were implemented in an ex vivo experiment using fresh porcine blood as a substitute fluid and a special deoxygenation technique to simulate a patient undergoing cardiopulmonary bypass. Both controllers showed robust stability during the experiments and a good disturbance rejection to extracorporeal blood flow changes. This automatic control strategy is proposed to improve patient's safety by fast control reference tracking and good disturbance rejection under varying conditions.     

A clinical evaluation of the Terumo Capiox SX18R hollow fiber oxygenator

The Terumo Capiox SX18R is a commercially available, low prime, reverse phase, hollow fiber membrane oxygenator. The oxygenator consists of a 1.8 m2 microporous polypropylene hollow fiber bundle, a 2200 cm2 tubular stainless steel heat exchanger, and an open hard shell venous reservoir with integral cardiotomy filter. The Terumo Capiox SX18R oxygenator was evaluated to determine its clinical oxygenating performance. Blood samples were drawn from 25 patients yielding 114 data points. The following parameters were recorded: blood flow, cardiac index, gas flow, gas to blood flow ratio, and oxygen fraction. Samples were assayed for hematocrit, hemoglobin, arterial and venous blood gas values, and venous oxygen saturation. The data and assay results were used to calculate arterial, venous, and membrane gas oxygen content, oxygen transfer, shunt fraction, and oxygen diffusion capacity. The Terumo Capiox SX18R oxygenator performed adequately with sufficient oxygen transfer reserve and carbon dioxide clearance under a variety of clinical conditions for the tested population.     

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.     

The effect of carbon dioxide tension on cerebral circulation during hypothermic selective cerebral perfusion

BACKGROUND: Some reports have observed the response of cerebral blood flow to PaCO2 during hypothermic cardiopulmonary bypass. We studied the effect of PaCO2 on the cerebral circulation during hypothermic selective cerebral perfusion. METHODS: Between June 1992 and January 1998, 35 patients underwent aortic arch grafting using hypothermic selective cerebral perfusion (20 degrees C). In the earlier four patient (Group 1), carbon dioxide gas was not added. In the latter 31 patient (Group 2), carbon dioxide gas was added to the cerebral perfusion. The hemodynamics and rates of change in cerebral oxygen saturation were evaluated. RESULTS: In Group 1, the index of cerebral arterial resistance was 9.2+/-2.2 at the start of selective cerebral perfusion and increased to 15.7+/-0.1 at the re-warming stage (p<0.05), and there was a significant decrease in cerebral oxygen saturation at the re-warming stage (p<0.001). In Group 2, the index of cerebral arterial resistance was 4.7+/-1.7 at the start of selective cerebral perfusion and 4.3+/-1.5 at the re-warming stage, a non-significant change. The change in cerebral oxygen saturation was also nonsignificant between the start of selective cerebral perfusion and the re-warming stage. Among the neurological outcomes, there was only one small cerebral infarction in Group 2; however, no delayed conscious recovery was observed. CONCLUSIONS: The addition of CO2 to cerebral perfusion was a factor in inhibiting the increase in the cerebral vascular resistance at the re-warming stage.     

Oxygen parameters of arterial and mixed venous blood, - new and old

A complete pH and blood gas analysis of arterial and mixed venous blood may comprise more than forty different quantities. We have selected sixteen, including patient temperature. The arterial oxygen tension group includes the oxygen tension, fraction of oxygen in inspired air, and fraction of mixed venous blood in the arterial (total physiological veno-arterial shunting). The haemoglobin oxygen capacity group includes effective haemoglobin concentration and fractions of carboxy- and methaemoglobin. The haemoglobin oxygen affinity group includes half-saturation tension and estimated 2,3-diphosphoglycerate concentration of erythrocytes. In a neonatal care unit fraction of fetal haemoglobin need to be included. The arterial oxygen extractivity is measured as the oxygen extraction tension, which indicates the degree of compensation among the oxygen tension, capacity, and affinity. The mixed venous group includes mixed venous oxygen tension, and, when measured, cardiac output, and oxygen consumption rate. The acid-base status includes blood pH, arterial carbon dioxide tension, and extracellular base excess. Other quantities such as haemoglobin oxygen saturation, respiratory index, total oxygen concentration (oxygen content), oxygen extraction fraction, oxygen delivery, and several others, seem to be redundant.     

Effect of alpha-stat versus pH-stat strategy on oxyhemoglobin dissociation and whole-body oxygen consumption during hypothermic cardiopulmonary bypass.

To determine whether alpha-stat or pH-stat strategy should be used, 20 patients undergoing coronary artery bypass grafting during moderate hypothermic hemodilutional cardiopulmonary bypass were studied. The carbon dioxide management during bypass was randomly done according to alpha-stat strategy in 10 patients (i.e., temperature-uncorrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4) and according to pH-stat strategy in the other 10 patients (i.e., temperature-corrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4). In both groups, when the central venous temperature was stable at 26.5 +/- 2.5 degrees C, the perfusion flow was altered sequentially from 2.4 to 1.8 and 1.2 L.min-1.m-2. The mixed venous oxyhemoglobin saturation at the different perfusion flows was monitored by the Oxy-Stat meter and was correlated with the corresponding mixed venous oxygen tension to construct an oxyhemoglobin dissociation curve. Also, the whole-body oxygen consumption at the different perfusion flows was computed. The whole-body oxygen consumption and the oxyhemoglobin dissociation were not significantly different between the alpha-stat and the pH-stat groups. In both groups, the dissociation curve is shifted to the left, but the oxygen consumption per unit time does not significantly change despite decreasing the perfusion flow from 2.4 to 1.2 L.min-1.m-2. The results suggest that oxygen delivery is not impaired during moderate hypothermic cardiopulmonary bypass independent of whether alpha-stat or pH-stat strategy is used.