bluuebunny/crossref_metadata_2025 huggingface dataset:
From oxygen content to pulse oximetry: Completing the picture in the newborn
Authors: WHYTE R. K. , JANGAARD K. A. , DOOLEY K. C.
Published: January 2009

In recent years clinicians caring for sick preterm infants have come to depend on pulse oximetry to avoid hyperoxia, which means assuming saturation values for critical levels of oxygen tension. This prediction is made difficult by the shape of the haemoglobin‐oxygen dissociation curve at critical values for arterial pO2 and by the effects of changes in acid‐base balance on p50. Combined blood gas and co‐oximetry measurements can be used to determine critical limits for pulse oximetry. Fetal haemoglobin has slightly different light absorption characteristics from adult haemoglobin. To adjust for this, adult and fetal matrices are available in the OSM™ HEMOXIMETER™ (Radiometer Medical A/S, Denmark) but the measurement requires an extra preliminary step to estimate fetal haemoglobin concentration. We sought to determine the importance of this extra procedure for measuring the saturation of newborn blood, and to determine whether the adult or fetal mode should be used for determining saturation for comparison with pulse oximeters. We measured the effect of the correction for fetal haemoglobin by obtaining absorbances from the co‐oximeter and multiplying them by the adult and fetal matrices. We demonstrated that, at 90% saturation, failure to use the fetal correction in the presence of high levels of fetal haemoglobin result in a 4% overestimate of saturation, with resultant underestimation of the safe range for pulse oximetry. Published values for extinction coefficients for fetal and adult blood at wavelengths used by pulse oximeters are inconsistent, but it appears that fetal haemoglobin does not bias pulse oximetry readings. Determining saturation limits by co‐oximetry for use with pulse oximeters in preterm infants requires the description of the haemoglobin‐oxygen dissociation curve with the correction for fetal haemoglobin.
A comparative study of two near infrared spectrophotometers for the assessment of cerebral haemodynamics
Authors: COLIER W. N. J. M. , VAN HAAREN N. J. C. W. , OESEBURG B.
Published: January 2009

Conventional near infrared spectroscopy (NIRS), introduced by Jobsis in 1977, can be considered as a reliable trend monitor for cerebral oxygenation. Quantisation, however, is complex and cumbersome. Recently a relatively simple system for cerebral oximetry (INVOS 3100, Somanetics Corporation, USA) was developed, measuring the regional oxygen saturation (rSo2) in the capillary bed of the cerebrum, presented as a numerical figure for easy interpretation. In this study a comparison was made between a conventional NIRS instrument and the new INVOS instrument, in order to obtain information about sensitivity and usefulness of the INVOS system. Changes in cerebral haemodynamics were induced by a moderate decrease of the arterial oxygen saturation (Sao2) and by varying the arterial carbon dioxide level (PaCO2). This will result in a higher (hypercapnia) or lower (hypocapnia) cerebral blood flow and subsequent change of both NIRS signals and INVOS signal. Healthy volunteers were used for this study. It was found that the steady state value for rSo2 was 70 ± 6% (mean ± SD). During the lowering of arterial saturation a poor correlation was found between rSo2 and Sa02 (r=0. 47). Increased cerebral blood flow induced by hypercapnia was detected by both conventional NIRS and the INVOS. Decreased cerebral blood flow induced by hypocapnia could only be detected by conventional NIRS. It was concluded that due to the variation in displayed rSo2 and the high amount of averaging in the algorithm the INVOS instrument does not yet provide more information than conventional NIRS.
Modelling of acid‐base equilibria
Authors: JABOR A. , KAZDA A.
Published: January 2009

A quantitative evaluation of metabolic acid‐base component is described. The model is based on Stewart's analysis of acid‐base chemistry. The metabolic component of acid‐base disturbances is divided into four partial metabolic disorders; they can result from abnormal concentrations of chloride, albumin and phosphate disturbances, or from appearance of abnormal unidentified strong anions. The efficiency of the model is sufficient, quantitative partial results are given in the same units as base excess. In complex acid‐base disturbances, such as are seen in critically ill patients, a detailed analysis of the specific components of the metabolic acid‐base status allows one to plan specific therapeutic interventions.
Base excess or buffer base (strong ion difference) as measure of a non‐respiratory acid‐base disturbance
Authors: SIGGAARD‐ANDERSEN O. , FOGH‐ANDERSEN N.
Published: January 2009

Stewart in 1983 (Can J Physiol Pharmacol 1983: 61: 1444) reintroduced plasma buffer base under the name “strong ion difference” (SIDl. Buffer base was originally introduced by Singer and Hastings in 1948 (Medicine (Baltimore) 1948: 27: 223). Plasma buffer base, which is practically equal to the sum of bicarbonate and albuminate anions, may be increased due to an excess of base or due to an increased albumin concentration. Singer and Hastings did not consider changes in albumin as acid‐base disorders and therefore used the base excess, i. e., the actual buffer base minus the buffer base at normal pH and pCO2, as measure of a non‐respiratory acid‐base disturbance. Stewart and followers, however, consider changes in albumin concentration to be acid‐base disturbances: a patient with normal pH, pCO2, and base excess but with increased plasma buffer base due to increased plasma albumin concentration get the diagnoses metabolic (strong ion) alkalosis (because plasma buffer base is increased) combined with metabolic hyperalbuminaemic acidosis. Extrapolating to whole blood, anaemia and polycytaemia should represent types of metabolic alkalosis and acidosis, respectively. This reveals that the Stewart approach is absurd and anachronistic in the sense that an increase or decrease in any anion is interpreted as indicating an excess or deficit of a specific acid. In other words, a return to the archaic definitions of acids and bases as being the same as anions and cations.

We conclude that the acid‐base status (the hydrogen ion status) of blood and extracellular fluid is described in terms of the arterial pH, the arterial pCO2, and the extracellular base excess. It is measured with a modern pH‐blood gas analyser. The electrolyte status of the plasma is a description of the most important electrolytes, usually measured in venous blood with a dedicated electrolyte analyser, i. e., Na+ Cl‐, HCO3“, and K+. Albumin anions contribute significantly to the anions, but calculation requires measurement of pH in addition to albumin and is usually irrelevant. The bicarbonate concentration may be used as a screening parameter of a nonrespiratory acid‐base disturbance when respiratory disturbances are taken into account. A disturbance in the hydrogen ion status automatically involves a disturbance in the electrolyte status, whereas the opposite need not be the case.
The oxygen status of fetal blood
Authors: SIGGAARD‐ANDERSEN O. , HUCH R.
Published: January 2009

Objective: To estimate the acid‐base and oxygen status of fetal blood and compare with maternal placental venous blood.

Data sources and calculations: We selected pH and blood gas data from the literature pertaining to umbilical vein and artery blood obtained by cordocentesis and estimated values for the 30th and 40th gestational week.

Average values for maternal venous blood leaving the placenta were estimated on the assumption of equal maternal arterio‐venous and umbilical veno‐arterial total oxygen concentration differences.

Results: pH and pCO2 of maternal blood leaving the placenta and umbilical vein blood are almost identical at week 30. A small pCO2 and pH difference may exist at week 40. The pO2 of the maternal placental venous blood and umbilical vein blood are almost identical at week 30, but at week 40 a pO2 difference indicates an umbilical arterio‐venous shunting of as much as 30%. The fetal mixed venous pO2 falls from 2. 6 kPa to 2. 2 kPa from the 30th to the 40th gestational week.

Conclusion: More accurate measurements are needed to confirm our results. Future measurements should be performed with a combined pH‐blood gas analyser and haemoximeter to allow determination of the complete oxygen status of the blood.
Simulation of maximum respiratory venous PCO2in vitro
Authors: SCHLICHTIG R.
Published: January 2009

PvCO2 that would result from full O2Hb desaturation at a given O2‐CO2 exchange ratio, in the absence of metabolic acid, may be termed maximum respiratory venous PCO2 (PvmrCO2). This theoretical condition of 100% O, extraction, in the absence of metabolic acid, should simulate maximum aerobic PCO2 in tissue, provided that PCO2 of tissues and large veins is similar. Hence, the value of PvmrCO2 is of interest in identifying critical tissue PCO2. Analysis of the Dill nomogram indicates that PvmrCO2 is 77 torr at RQ = 1. 0, PaCO2 = 40 torr in vitro, and that the PvCO2, versus SO2 relation is linear. Since the Dill nomogram is confined to the condition, [Hb] = 15 g · dL‐1, [BE] = 0, the goal of the present analysis was to determine variability of PvmrCO2 with [Hb], arterial [base excess] ([BE]), and PaCO2. Venous CO2 titrations for multiple arterial conditions were simulated using published in vitro [BE] and whole blood [total CO2 formulae. In the RQ range of 0. 7 to 1. 0, the simulation yielded PvCO2 values that were essentially identical to those obtainable from the Dill nomogram. The simulation predicted that PvmrCO2 should decrease in direct proportion to [Hb], and increase non‐linearly with decreasing arterial [BE]. The simulation further predicted that venoarterial PCO2 difference should increase linearly with increasing PaCO2. Simulated PvmrCO2 ‐ PaCO2 difference varied from 5 torr at arterial [BE] = +10 mmol/L, [Hb]= 6 g · dL‐1, PaCO2 = 25 torr, RQ = 0. 7 to 67 torr at [BE] = ‐20 mmol/L, [Hb] = 15 g‐ dL‐1, PaCO2 = 65 torr, RQ = 1. 0. It is concluded that the PvCO2 versus SO2 relation is not linear when arterial [Hb] and/or [BE] vary. An equation that predicts in vitro PvmrCO2 as a function of arterial [BE], [Hb], RQ, and PaC02 is provided. It's accuracy in vivo should be testable.
Determination of oxygen consumption in muscle during exercise using near infrared spectroscopy
Authors: COLIER W. N. J. M. , MEEUWSEN I. B. A. E. , DEGENS H. , OESEBURG B.
Published: January 2009

The aim of this study was to determine oxygen consumption (VO2) during isometric exercise in human muscles using near infrared spectroscopy (NIRS). The technique was used to study the relationship between VO2 in the soleus muscle and the level of isometric exercise expressed as percentages of the maximum voluntary contraction (MVC). For the study 11 healthy male volunteers were recruited. Reproducibility was studied in 6 subjects. The subjects were seated in a chair with the knee joint at an angle of 90°. The optodes of the NIRS instrument were attached to the lateral aspect of the soleus muscle. A horizontal bar above the knee was connected to a dynamometer. Subjects applied isometric force to the bar by producing a torque at the ankle joint. Firstly the MVC was determined. Secondly the VO2 at rest and at 5 levels of isometric exercise, ranging from 5% to 25% of MVC and increasing by 5% each stage, was measured. In all cases the VO2 at rest or during isometric contraction was determined from the decrease of the oxyhaemoglobin (O2Hb) signal immediately after arterial occlusion of the thigh. Repeated measurements showed no significant difference between trials, indicating that the measurements were reproducible. At rest a VO2 of 6.7 ± 1.1 μMO2Hb min‐1 (mean ± S.E.M.) was found, a result comparable with other studies. In all subjects a linear relationship was found between the VO2 and the level of exercise. The average slope of the regression lines of all individuals was 0.85 ± 0.22 μuMO, Hb min‐1 MVC‐1 (mean ± S.E.M.). Inter‐individual variation of the slopes was high and ranged from 0.28 to 2.29 μuMO2 Hb‐ min‐1 %MVC‐1, which can be explained by differences in fat percentage and in the measuring volume of the NIRS instrument. NIRS appeared to be a reproducible and reliable method for the non‐invasive measurement of VO2 in human muscles. The method could be used to investigate regional differences as well as changes in time between muscle groups as a function of training.
The influence of arterial carbon dioxide on cerebral oxygenation and haemodynamics during ECMO in normoxaemic and hypoxaemic piglets
Authors: LIEM K. D. , KOLLÉE L. A. A. , HOPMAN J. C. W. , DE HAAN A. F. J. , OESEBURG B.
Published: January 2009

Objective. To investigate the cerebrovascular response to changes in arterial CO2 tension during extracorporeal membrane oxygenation (ECMO) in normoxaemic and hypoxaemic piglets.

Methods. Four groups of six anaesthetized, paralysed and mechanically ventilated piglets: group 1 ‐ normoxaemia without ECMO, group 2 ‐ ECMO after normoxaemia, group 3 ‐ hypoxaemia without ECMO, and group 4 ‐ECMO after hypoxaemia, were exposed successively to hypercapnia and hypocapnia. Changes in cerebral concentrations of oxyhaemoglob in (cO2Hb), deoxyhaemoglobin (cHHb), (oxidized ‐ reduced) cytochrome aa3 (cCyt. aa3) and blood volume (CBV) were continuously measured using near infrared spectrophotometry. Heart rate, arterial O2 saturation, arterial blood pressure, central venous pressure, intracranial pressure (ICP) and left common carotid artery blood flow (LCaBF) were measured simultaneously.

Results. Hypercapnia resulted in increased CBV, cO2Hb and ICP in all groups, while cHHb was decreased. No changes in LCaBF were found. Hypocapnia resulted in decreased cO2Hb and increased cHHb except in group 3. LCaBF decreased in all groups except group 2. CBV decreased only in groups 2 and 4. No effect on ICP was observed in any of the groups. The other variables showed no important changes either during hypercapnia or hypocapnia. ECMO after hypoxaemia resulted in a greater response of cO2Hb and cHHb during hypocapnia. The effect of hypercapnia on CBV while on ECMO was greater than without ECMO.

Conclusion. Since cerebrovascular reactivity to CO2 remains intact during ECMO in piglets, it is important to keep arterial CO2 tension stable and in normal range during clinical ECMO.
Effect of hypoxaemia on water and sodium homeostatic hormones and renal function
Authors: OLSEN N. V.
Published: January 2009

Changes in body fluid homeostasis during acute hypoxaemia suggest a crucial role of renal function in acclimatization processes. Hypoxaemia stimulates sympathetic nervous activity, and also the cardiovascular system is affected with increases in heart rate and cardiac output. In most subjects, a hypoxic ventilatory response produces hypocapnia and respiratory alkalosis. Acute hypoxaemia depresses aldosterone secretion secondary to a direct effect on adrenal cells. Also plasma renin is decreased in resting hypoxaemic conditions, but the mechanism remains unknown. These hormonal changes may have the advantage of opposing excessive sodium and water retention, which characterizes acute mountain sickness. Short‐term isocapnic or hypocapnic hypoxaemia in spontaneously breathing humans causes moderate if any increases in renal blood flow and only minor changes in GFR. In contrast, renal blood flow and GFR decreases during hypercapnic hypoxaemia. Renal clearance studies in humans after 24–48 hours in altitude hypoxia (4 350 m) demonstrate that glomerular and tubular function is only slightly changed in spite of marked depression of the renin‐aldosterone system and increased plasma levels of norepinephrine. However, renal vascular tone may increase most probably secondary to the increased adrenosympathetic activity. In the first hours, acute hypoxaemia may induce an increased excretion of sodium and water. Previous studies suggest that the natriuretic response is caused by decreased reabsorption of sodium and bicarbonate in the proximal tubules secondary to the associated hyperventilation and hypocapnia. After 6 hours, sodium and water excretion is normalized or even depressed, dependent on the severity of acute mountain sickness. In view of the prompt increase in sodium and water excretion found during short‐term hypoxaemia, the absence of such a response to more prolonged hypoxaemia suggests an adaptive time‐dependent course of renal functional changes in hypoxaemia. Taken together, previous studies suggest that effects of acute hypoxaemia on renal haemodynamics are minor compared with effects on cerebral and coronary circulation. This might be the result of an appropriate resetting of autoregulatory mechanisms that would maintain the role of the kidney as a major sense organ to hypoxaemia and, subsequently, as a mediator of plasma volume regulation and erythropoietin synthesis.
Oxygen availability in critical illness ‐ An investigation using the oxygen status algorithm
Authors: MORGAN J. , KANOWSKI D.
Published: January 2009

Using the oxygen status algorithm of Siggaard‐Andersen to derive 2, 3‐diphosphoglycerate concentrations and parameters of oxygen extractivity, 143 arterial blood specimens from 73 ICU patients were compared with 119 venous blood specimens from 119 healthy outpatients. The venous extractivity parameters were calculated by arbitrarily assigning an oxygen tension of 90 mmHg to each specimen.

There were no significant differences in 2, 3‐diphosphoglycerate, but the mean concentration of extractable oxygen corrected for low haemoglobin values (cxlcHb) was significantly greater in the ICU patients (males: 0. 017 ± 0. 004 mmol/g, females: 0. 016 ± 0. 004 mmol/g) than in the healthy outpatients (males and females: 0. 014 ± 0. 001 mmol/g, p < 0. 05). This reduction in haemoglobin‐oxygen affinity was attributed to the high incidence of acidaemia in the ICU specimens (mean pH 7. 36 ± 0. 08), despite a reduced mean 2, 3‐diphosphoglycerate concentration in the ICU acidaemic specimens (when pH < 7. 35, mean 2, 3‐diphosphoglycerate concentration was 4. 9 ± 1. 6 mmol/L; when 7. 35 < pH < 7. 45: mean 2, 3‐diphosphoglycerate concentration was 5. 7 ± 1. 6 mmol/L, p < 0. 05). Hypophosphataemia had no demonstrable effect on 2, 3‐diphosphoglycerate concentrations or extractivity parameters in the ICU patients. We conclude that oxygen release from haemoglobin to the tissues in critical illness is enhanced because of a tendency to acidaemia.
Clinical assessment of oxygen delivery and consumption during hypotensive anaesthesia ‐ A clinical application of The Deep Picture™
Authors: UEDA N. , MUTEKI T. , YAMADA S. , MASUDA Y.
Published: January 2009

Usual evaluation of the relationship between oxygen delivery (DO2) and oxygen uptake (VO2) is based on the arterial oxygen tension (pO2), oxygen saturation (sO2), haemoglobin concentration (ctHb), the same indicators in mixed venous blood and cardiac output, sometimes supplemented by the expiratory carbon dioxide concentration. And, so far, the relationship among DO2, VO2 and the new parameters for an evaluation of oxygen status (oxygen extraction tension: pK, concentration of extractable oxygen: cx, oxygen compensation factor: Qx) (1) has not been discussed enough.

Therefore, this study was designed to evaluate whether the new parameters give the clinically significant information to analyse the relationship between DO2 and VO2 during the acute haemodynamic change with intentionally induced hypotension in anaesthetized adult patients.
Oxygen status during haemodialysis
Authors: NIELSEN A. L. , JENSEN H. Æ. , HEGBRANT J. , BRINKENFELDT H. , THUNEDBORG P. ,   THE CORD‐GROUP
Published: January 2009

Hypoxia during haemodialysis, mainly acetate, has been reported several times. In our study we have monitored oxygen status during 258 bicarbonate haemodialyses. A significant drop below 80 mmHg in mean oxygen tension occurred. Mean oxygen saturation reflected this drop but did not reach levels below 90%. The mean oxygen concentration was on the whole critical low, though slightly increasing during each haemodialysis session due to ultrafiltration.

It is concluded that both hypoxia and hypoxaemia do occur during bicarbonate haemodialysis. To a group of patients generally having limited cardiac reserves, a poor oxygen status is a potentially serious complication to haemodialysis. Monitoring oxygen status is thus advisable.
Permissive hypercapnia in ARDS and its effect on tissue oxygenation
Authors: HICKLING K. G. , JOYCE C.
Published: January 2009

Many experimental studies have shown that mechanical ventilation with high tidal volumes (V1) or with a low end‐expiratory volume allowing repeated end‐expiratory collapse, can result in acute parenchymal lung injury and probably an inflammatory response. Low volume ventilation with permissive hypercapnia has been used in an attempt to avoid such injury in ARDS.

Such management can affect oxygenation in many complex ways. The right‐shift of the haemoglobin‐oxygen dissociation curve during acute respiratory acidosis may increase venous oxygen tension (PvO2) which could allow increased O2 uptake in ischaemic tissues. Acidosis may reduce intrapulmonary shunt (Qs/Qt) by potentiating hypoxic pulmonary vasoconstriction, and there may also be direct and autonomically mediated effects of hypercapnia both on the lung vasculature and on the airways. Cardiac output usually increases as a consequence of hypercapnia and perhaps as a result of reduced intrathoracic pressure, further increasing Pv02 and CvO2, but the increase in cardiac output (CO) may tend to increase Qs/Qt as flow increases preferentially in unventilated lung. The reduction of mean airway pressure may directly increase Qs/Qt. Hypercapnia may affect the distribution of systemic blood flow both within organs and between organs.

Limited clinical studies suggest that tissue oxygenation is usually unchanged or improved during permissive hypercapnia with increased CO2 reduced arterio‐venous O2 content difference and reduced blood lactate concentration. However, acute hypercapnia per se can reduce lactate production. Further studies are required of this complex issue.
Pentoxifylline and oxygen consumption in severe sepsis ‐ A preliminary report
Authors: CASTAÑON‐GONZALEZ J. A. , EID‐LIDT G. , WACHER N. , GALLEGOS‐PEREZ H. , MIRANDA‐RUIZ R.
Published: January 2009

Objective: To demonstrate that pentoxifylline (PTX) and not placebo improves oxygen consumption (VO2) in critically ill patients with severe sepsis.

Setting: Multidisciplinary intensive care unit in a university affiliated hospital.

Design: A randomized, double blinded clinical trial comparing 300 mg of PTX administered in a 120 min iv infusion with an identically looking placebo.

Patients: 13 patients (9 men and 4 women) average age 39 (24–62) years old received PTX, and 12 patients (5 men and 7 women) average age 38 (21–83) years old received placebo. All satisfied ACCP/SCCM criteria for severe sepsis.

Measurements and interventions: Patients fulfilling criteria for severe sepsis were identified on admission, cardiac output, DO2 and VO2 were measured by thermodilution and standard oximetric technics after adequate volume replacement at baseline, 60 and 120 during infusion. F‐test of analysis of variance was used to test hypothesis about differences of DO2 and VO2 by group, by time and for the interaction terms, a “p” value <0. 05 was considered significant.

Results: Evaluation of baseline measurements of both groups revealed no significant difference in any haemo‐dynamic function or oxygen transport variables. The average V02 difference (0–120 min) between groups was 21 mL/min · m2 and it was higher in the experimental group, however, this difference was non significant.

Conclusion: We think that the trend in VO2 followed by the experimental group is clinically important. If this difference is sustained we will probably be able to demonstrate our hypothesis.
Optimal values for oxygen transport during hypothermia in sepsis and ARDS
Authors: PERNERSTORFER T. , KRAFFT P. , FITZGERALD R. , FRIDRICH P. , KOC D. , HAMMERLE A. F. , STELTZER H.
Published: January 2009

Mild hypothermia (33 °C to 35. 5 °C) is reported to improve oxygenation and survival in patients with lung failure (1). Although hypermetabolism may account for about 50% of the ventilatory demand in ARDS patients, the concept of reducing oxygen consumption (VO2) by lowering metabolic rate, has only recently gained attention (2). Our study was aimed to test whether mild hypothermia established by continuous veno‐venous haemofiltration (CVVHF), could optimize values for oxygen kinetics in ARDS patients.

Overall, we recruited 27 patients with ARDS and sepsis. Prior initiation of CVVHF patients had to meet the following criteria: a) Murray score >2. 5, and hypoxaemia with PaO2/FIO2 <200, b) hyperthermia of >38 °C, c) cardiovascular instability requiring inotropic support. Evaluation of cardio‐respiratory data was performed within four different phases (1= before, II + III during and IV= after CVVHF) every 6 hours. Core temperature as derived from the thermistor of pulmonary artery catheter was aimed to be between 35. 0 °C anil 36. 5 °C.

Optimal values for oxygen delivery (DO2) (>550 mL/min/m2) and VO2 (>160 mL/min/m2) were defined according to Shoemaker and achieved by fluid loading, transfusion and inotropic support (3).

Septic shock occurred in 10 of 14 nonsurvivors (nons) and 2 of 13 survivors (surv). Mean values for DO2 and VO2 were calculated at different body temperature ranges. While at 37 °C DO2 was identical between surv and nons, (663±128 versus 666±127 mean±SD) moderate hypothermia led to a small decrease of DO2 in surv and a significant decrease in nons (632±134 versus 605±128 mL/min/m2) at 35 °C. Concerning VO2 during hypothermia, there was a significant drop in nonsurvivors while in survivors the decrease was less pronounced.

We could demonstrate a decrease in DO2 and VO2 during mild hypothermia during CVVHF. However, decreases in nonsurvivors were more pronounced than in survivors. These results suggest that the inability to achieve optimal values for DO2 and VO2 during mild hypothermia induced by CVVHF could serve as a prognostic sign for fatal outcome. Although oxygen consumption is decreased during hypothermia, hypoxaemia may result due to alterations of the oxygen transport on a cellular basis. The relationship between oxygen transport and temperature during CVVHF therefore deserves further studies.
Oxygen uptake/oxygen supply dependency: Fact or fiction?
Authors: VINCENT J.‐L. , DE BACKER D.
Published: January 2009

More than a decade ago, observations of co‐variance between VO2 and DO2 led to the identification of a condition known as pathological O2 supply dependency. This condition was subsequently observed in critically ill patients with sepsis and acute circulatory failure. More recently, other authors have challenged the existence of this condition, often citing methodological problems or mathematical coupling to account for spurious observations in the earlier studies. Here, we review the evidence for and against pathological O2 supply dependency. We find that many of the arguments have some validity but only in specific circumstances. We conclude, therefore, that pathological O2 supply dependency is a hallmark of acute circulatory failure and that an effective therapeutic approach should be based on an evaluation of organ system function in each individual case. Parameters such as blood lactate, pHi and veno‐arterial Pco2 may be useful in this respect.
Effects of catecholamines on regional perfusion and oxygenation in critically ill patients
Authors: MEIER‐HELLMANN A. , REINHART K.
Published: January 2009

Multiple organ failure is the major cause of death in patients with sepsis. Bacterial translocation from the gut is considered to induce and maintain sepsis. Therefore, the splanchnic region plays an important role in the pathogenesis and treatment of sepsis. There is evidence for a very high risk of imbalance between oxygen delivery and oxygen consumption especially in the splanchnic region. Consequently, there is a crucial interest whether it is possible to influence the splanchnic perfusion by specific catecholamines. Unfortunately, only a few, conflicting studies have looked at the effects of the various catecholamines on regional blood flow. Therefore, a clear recommendation for a specific catecholamine regimen in septic shock is impossible. Furthermore, it is unknown whether the choice of a specific catecholamine in the treatment of septic shock affects the patient's outcome. In most patients, the use of vasopressors is indispensable because adequate haemodynamic perfusion pressure is not achieved with fluid therapy alone. The negative effects of vasopressors on splanchnic perfusion are known from studies carried out under non septic conditions. Norepinephrine and dopamine in doses of 10 μg/kg/min in septic animals are without negative effects on splanchnic perfusion. Preliminary results show a decrease in splanchnic oxygenation in patients with septic shock treated with epinephrine.

Catecholamines with beta mimetic effects are often used to increase DO2. The question as to whether dobuta‐mine or dopamine should be used first in treatment of septic shock cannot be answered yet.

Whether treatment with low dose dopamine or dopexamine actually improves renal function and splanchnic oxygenation is the purpose of ongoing studies.
Lactate, pH, and blood gas analysis in critically ill patients
Authors: WALDAU T. , LARSEN V. H. , BONDE J. , FOGH‐ANDERSEN N.
Published: January 2009

To obtain information about the relationship between different types of circulatory insufficiency, a series of oxygen parameters and plasma lactate, we have performed a pilot study comprising five patients with circulatory insufficiency.

Plasma lactate was measured on a Stat Profile 7 (NOVA Biomedical, USA) and pH/blood gases on an ABL™ 520 (Radiometer Medical A/S, Denmark).

Plasma lactate seems to be inversely related to base excess (BE), whereas no relationship to venous oxygen tension pO2(v) of the vein draining the inadequately perfused region seemed to exist. In one patient we made simultaneous measurements from v. cava inferior., v. cava superior., a. pulmonalis and a. radialis. Simultaneously sampled plasma lactate from different sites differed up to 0. 6 mmol/L with the highest value obtained from v. cava inferior.

This pilot study indicates that the increase of plasma lactate may vary with the type of circulatory disturbance and the sampling site.
Pharmacology of flumazenil
Authors: WHITWAM J. G. , AMREIN R.
Published: January 2009

Flumazenil, an imidazobenzodiazpine, is the first benzodiazepine antagonist available for clinical use. It is a specific competitive antagonist at benzodiazepine receptors, which are associated with receptors for gammaaminobutyric acid, the most important inhibitory neurotransmitter in the central nervous system. Administered orally, it has a low bioavailability and the preferred route is intravenous. Its usual clinical role is to reverse the effects of benzodiazepine sedation; however, administered before, or with, other benzodiazepines, it modifies their effects, the extent of such modification depending on the dose, duration of effect and relative receptor affinity of the agonist. Flumazenil also reverses adverse physiological effects of benzodiazepines. Its indications include reversal of benzodiazepine‐induced sedation, termination of benzodiazepine‐induced anaesthesia, return of spontaneous respiration and consciousness in intensive care patients and the treatment of paradoxical reactions to benzodiazepines. Other potential indications include its use in hepatic encephalopathy, alcohol intoxication and coma; however, these claims still require substantiation. Following sedation reversed with flumazenil, minimal residual effects of the agonist can sometimes be detected using psychomotor tests and are due to the relatively short half‐life of flumazenil, but are of no clinical consequence. There is concern that flumazenil could precipitate an acute withdrawal syndrome following long‐term benzodiazepine administration; however, the available evidence suggests otherwise and that it could be useful in the treatment of benzodiazepine tolerance. The existence of flumazenil is important, with implications for future research and the development of minimally invasive therapy and day‐case surgery. With increasing pressures on non‐anaesthetically trained practitioners to perform sedation, flumazenil has important implications for safety.
Reversal of conscious sedation by flumazenil: current status and future prospects
Authors: McGloy R. F.
Published: January 2009

Flumazenil is safe and highly effective at reversing both benzodiazepine‐induced sedation and amnesia. Bolus intravenous injection is the most appropriate technique when the goal is to fully reverse conscious sedation. Currently, the proven effective dose of flumazenil is 0.5 mg. For practical purposes, in this clinical setting, true resedation does not occur, and if the appropriate type and dose of agonist have been used, residual sedation is not a clinical problem. Concerns over acute anxiety reactions and precipitation of acute withdrawal syndrome in chronic benzodiazepine users remain theoretical and unsubstantiated by human data. Further clinical studies are required to determine whether the clinical practice of using flumazenil could include this group of patients. Depression of ventilatory responsiveness induced by benzodiazepines can be reversed effectively and promptly by flumazenil. Flumazenil must be immediately available as an emergency drug in any area where benzodiazepines are used. The clinical and economic benefits of elective and routine use of flumazenil have been demonstrated, but have yet to gain widespread acceptance.
Improvement of arterial oxygenation by selective infusion of prostaglandin E1 to ventilated lung during one‐lung ventilation
Authors: Chen T.‐L. , Ueng T.‐H. , Huang C.‐H. , Chen C.‐L. , Haung F.‐Y. , Lin C.‐J.
Published: January 2009

Background:One‐lung anesthesia provides a better surgical field for thoracic procedures but also impairs the arterial oxygenation and venous admixture. During one‐lung ventilation, pulmonary vasoconstriction is assumed to be present within both ventilated and collapsed lungs. We propose that arterial oxygenation could be optimized by offsetting the vasoconstriction within the microcirculation of ventilated lung.

Method:In an anesthetized dog model, incremental doses of prostaglandin E1 (PGE1) were selectively infused into the main trunk of the pulmonary artery of the ventilated lung after one‐lung ventilation for 60 min (PGE1 group, n=9). Arterial oxygenation and calculated venous admixture (Qs/Qt) was also assessed in a time‐course control group (Control group, n =5). During two‐lung ventilation (FIO2: 0.66), arterial PO2 and venous admixture was 44.22 ± 3.5 kPa and 10.7±2.3%, respectively. One‐lung ventilation (FIO2: 0.66) with left lung collapsed reduced arterial PO2 to 11.6±1.7 kPa and increased venous admixture to 40.7±5.8% (P<0.001). Venous O2 tension also decreased from 6.3±0.7 kPa to 5.0±0.6 kPa with a slight increase in mean pulmonary artery pressure and pulmonary vascular resistance (P <0.05).

Results: During selective infusion of PGE1 at a dose of 0.04 to 0.2 μg kg‐1 min‐1, there was a dose‐dependent improvement in arterial PO2 with a parallel reduction of venous admixture during one‐lung ventilation. Arterial PO2 increased to a maximum of 23.0±4.3 kPa, and the venous admixture decreased significantly to a minimum of 27.4±4.2% by PGE1 at a dose of 0.04‐0.4 μg kg‐1 min‐1 (P<0.01). PGE1 resulted in a small increase in cardiac output and decreases of pulmonary pressure and pulmonary vascular resistance at a relatively high dose of 0.4 μg kg‐1 min‐1 during selective infusion (P<0.05).

Conclusion: These results suggest that a selective pulmonary artery infusion of PGE1 to the ventilated lung within the dose range of 0.04‐0.4 μg kg‐1 min‐1 is practical and effective to improve arterial oxygenation and reduce venous admixture during one‐lung ventilation.
An audit of perioperative aspiration pneumonitis in gynaecological and obstetric patients
Authors: Soreide E. , Bjørnestad E. , Steen P. A.
Published: January 2009

Obstetric patients are considered to be at increased risk of anaesthesia‐related Aspiration Pneumonitis. Less is known about the incidence and morbidity of this complication in younger women undergoing gynaecological surgery. We performed a 4‐year audit of perioperative Aspiration Pneumonitis, defined as bronchospasm, hypoxia, cough and dyspnea, together with radiographic or auscultatory abnormalities, following a witnessed episode of gastric content entering the trachea or an intraoperative episode making pulmonary aspiration likely, in two larger Norwegian hospitals. Eleven cases were identified; 4 in Caesarean Section (C‐section) patients, 5 in gynaecological (GYN) outpatients and 2 in GYN inpatients, with incidences of 0.11%, 0.04% and 0.01% respectively (P=0.03). Risk factors were present in all patients. No patient died, but the short‐time morbidity in the form of prolonged ICU stay and hospitalisation was significant. At discharge all patients noted symptoms of dyspnea, cough, and tightness of the chest; symptoms explainable by bronchial hyperreactivity. Five patients felt these symptoms did not disappear within 3 months and were followed up for a median of 2 years (range 4 months to 4 years). All were smokers and had multiple confounding causes, which made it hard to link their prolonged complaints directly to the pulmonary aspiration incident. All experienced improvement of symptoms during the follow‐up period. Compared to gynaecological patients of similar age, C‐section patients still have an increased risk of suffering Aspiration Pneumonitis. Prevention can be further improved in both groups. A cause‐relationship between the incidence and respiratory complaints lasting longer than 3 months could not be established, and a structured follow‐up may be helpful to avoid later medicolegal claims.
Does epidural sufentanil provide effective analgesia per‐and postoperatively for abdominal aortic surgery?
Authors: Broekema A. A. , Kuizenga K. , Hennis P. J.
Published: January 2009

To assess the efficacy of epidural sufentanil in providing per‐and postoperative analgesia, 40 patients undergoing elective abdominal aortic surgery received either 50 μg sufentanil in 10 ml normal saline solution (n=20, ES group) or 10 ml normal saline (n=20, control group) via a thoracic epidural catheter. The study solution was given (double‐blind and at random) after the patients had been anaesthetized with i.v. midazolam, sufentanil and vecuronium. Anaesthesia was maintained with 60% nitrous oxide in oxygen and halothane at a 1% inspiratory concentration. When patients showed signs of inadequate analgesia, supplementary doses of 25 μg sufentanil were given i.v. The number of patients requiring additional i.v. sufentanil differed significantly between the two groups: 5 out of 20 patients in the ES group vs 13 out of 20 patients in the control group required additional sufentanil (P<0.05). The mean dose administered i.v. did not differ significantly between the two groups: 105±109.5 μg vs 138.5±126.9 μg (mean±SD) in 5 and 13 patients, respectively. No cardiovascular changes were observed after the epidural bolus dose.

Postoperative analgesia, consisting of a continuous epidural infusion of 50 μg sufentanil in 50 ml bupivacaine 0.125% at a rate of 6–10 ml/h after a bolus dose of 10 ml of this solution, was adequate in the majority of patients, as determined by VAS‐scores assessed during the epidural treatment (4.3±1.5 days).
Haemodynamic effects of high‐dose vecuronium compared with pancuronium in beta‐blocked patients with coronary artery disease during fentanyl‐diazepam‐nitrous oxide anaesthesia
Authors: Husby P. , Gramstad L. , Rosland J. H. , Vamnes J. S. , Segadal L.
Published: January 2009

Background. Different combinations of neuromuscular blockers and opioids have been used in patients with angina pectoris to provide cardiovascular stability and reduce risk of myocardial ischaemia during anaesthesia.

Methods. We have compared the haemodynamic effects of high‐dose vecuronium (0.3 mg kg‐1) with those of a standard dose of pancuronium (0.1 mg kg‐1) in patients scheduled for coronary artery bypass grafting during fentanyl‐diazepam‐nitrous oxide anaesthesia. All patients were receiving beta‐adrenergic blocking agents. The given doses of vecuronium and pancuronium are equieffective with respect to duration of neuromuscular blockade.

Results. During a 25‐min experimental period following the administration of the randomly selected drug, no significant changes in the haemodynamic parameters were observed in the vecuronium group. The administration of pancuronium, however, resulted in a significant mean increase in heart rate (20%), rate‐pressure product (23%) and cardiac index (21%). Following endotracheal intubation in the pancuronium group, we observed an additional significant increase in mean arterial pressure and rate‐pressure product.

Conclusion. High‐dose administration of vecuronium has minimal haemodynamic effects and may thus offer a better alternative than pancuronium for long‐lasting neuromuscular blockade in patients with coronary artery disease during fentanyl‐diazepam‐nitrous oxide anaesthesia.
Haemodynamic interaction of high‐dose fentanyl and increasing doses of vecuronium in patients undergoing myocardial revascularization
Authors: Couture P. , Boudreault D. , Girard D. , Plante F. , McKenty S. , St‐Pierre J. , Poirier N. L.
Published: January 2009

Background. Bradyarrhythmia has been reported with vecuronium when given with high dose narcotics. We hypothesized that if the bradycardic response is dependent on a vagal reaction mediated by narcotics, it should be independent of the vecuronium dose. A dose‐related response of vecuronium on heart rate (HR) would be in favour of a chronotropic action of this agent.

Methods. We examined three induction techniques using high doses of fentanyl in which vecuronium was given in increasing doses. In addition, a reference group received a low dose of atracurium. Forty patients scheduled for elective CABG surgery were anaesthetized with fentanyl (50 μg) given over 5 min, and were randomly assigned to receive either 0.056, 0.14, 0.28 mg/kg of vecuronium or 0.28 mg/kg of atracurium. Haemodynamic measurements were obtained at the following intervals: before induction (time 0), after the administration of fentanyl (at 5 min), and 1, 2 and 5 min after tracheal intubation (at 10, 11 and 15 min).

Results. In vecuronium‐treated groups, there were significant decreases in HR, mean arterial pressure, and cardiac output (P<0.05). There were no differences between the three vecuronium groups. Although the atracurium‐treated group displayed no significant haemodynamic changes, 2 patients of this group developed HR < 40 bpm.

Conclusions. Over the range of vecuronium doses studied, we observed a reduction in HR during induction for CABG surgery with high doses of fentanyl and vecuronium. This effect was not dose dependent and is likely related to a direct effect of a high‐dose narcotic technique and/or due to a vagal stimulation regarding the airway procedure.
Effects of subarachnoid lidocaine, meperidine and fentanyl on somatosensory and motor evoked responses in awake humans
Authors: Fernández‐Galinski S. M. , Monells J. , Espadaler J. M. , Pol O. , Puig M. M.
Published: January 2009

Although the effects of local anaesthetics (LA) on motor and sensory transmission in the spinal cord have been described, the effects of opioids are controversial. Our aim was to evaluate the action of clinically relevant doses of subarachnoid (SA) meperidine (MP) and fentanyl (FN), on somatosensory (SSEP) and cortical motor evoked responses (CMER) in awake subjects. Thirty ASA I‐II patients scheduled for infra umbilical surgery received SA (N = 10/group): 1 mg/kg lidocaine (LD), 1 mg/kg MP or 25 μg FN. SSEP elicited by stimulation of the posterior tibial nerve at the ankle, and cortical motor evoked response at rest (r‐CMER) and during facilitation (f‐CMER) were obtained prior and 30 min after treatment. Conduction at the proximal segment of the motor nerve (F‐wave) was evaluated by stimulation ot the posterior tibial nerve at the popliteal fossa. Motor/sensory block and side effects were clinically assessed.

LD completely abolished SSEP and CMER. At the same dose, MP abolished SSEP in 40% of the patients, while r‐CMER and f‐CMER were absent in 70% and 30%, respectively; in addition, the F‐wave was absent in 50% of the patients. Fentanyl induced small changes in the latencies of SSEP and F‐wave; however, a 28% decrease in the amplitude of the f‐CMER (P<0.05) was observed. Pruritus was present in 60% of patients in the FN group (P<0.006).

Our results show that while LD and MP block sensory and motor conduction at the spinal roots, FN seems to decrease the excitability of the spinal interneurons in the corticospinal tract.
Intravenous sedation for retrobulbar injection and eye surgery: Diazepam and/or propofol?
Authors: Hampl K. F. , Marsch S. C. U. , Erb T. , Drewe J. , Schneider M. C.
Published: January 2009

Principle goals of sedation for eye surgery are to provide patient comfort and to allow the patient to stay calm during both retrobulbar injection and surgery. Insufficient sedation may not prevent the patient from moving during retrobulbar injection, whereas very deep sedation may result in respiratory complications during surgery. The aim of the present study was to evaluates the effectiveness and suitability of a combination of diazepam and propofol for sedation for both application of retrobulbar block and subsequent elective eye surgery.

One‐hundred and fifty patients were randomly allocated to receive either diazepam, propofol or a combination of both drugs before retrobulbar injection. Tolerance of retrobulbar injection and comfort during the surgical procedure were assessed by comfort scores using a nominal analogue scale between 1 (worst possible condition) and 6 (best conceivable condition). Side effects related to sedation were recorded.

The combination of diazepam and propofol resulted in the highest comfort scores for both retrobulbar block (5.3±0.3) and the surgical procedure (5.4±0.4). Diazepam alone did not produce adequate sedation for retrobulbar block (3.1±0.3), whereas comfort scores during surgery were significantly higher (5.3±0.3) compared to propofol alone (3.6±0.4). No severe side effects induced by sedation were noted in any of the study groups.

The combination of diazepam and propofol proved able to provide a reliable degree of sedation with minimal side effects for both retrobulbar block and surgery. The combination was clearly superior to the sedation induced by propofol or diazepam alone.
Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents
Authors: Viby‐Mogensen J. , Engbæk J. , Eriksson L. I. , Gramstad L. , Jensen E. , Jensen F. S. , Koscielniak‐Nielsen Z. , Skovgaard L. T. , ØStergaard D.
Published: January 2009

Based on an international consensus conference held in Copenhagen in the autumn of 1994, a set of guidelines for Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents are presented. The guidelines are intended to be a help for people working in this research field, and it is hoped that the guidelines will assist researchers, editors, and drug companies to enhance the quality of their pharmacodynamic studies of neuromuscular blocking agents.