A pilot study of continuous transtracheal mixed venous oxygen saturation monitoring

In this study, we investigated the feasibility and the accuracy of transtracheal mixed venous oxygen saturation (Svo(2)) monitoring. Ten patients undergoing thoracic surgery were included in this study. A single-use pediatric pulse oximetry sensor was attached to the double-lumen tube between the tracheal and bronchial cuff. After anesthesia was induced, the double-lumen tube was inserted into the trachea and adjusted to the proper position. During surgery, the pulmonary arterial blood was sampled every 3 min for 15 min to measure the Svo(2). The measurements made by the transtracheal pulmonary pulse oximeter (Sto(2)) were recorded at the same time that blood was sampled from the pulmonary artery for Svo(2) measurements. The levels of measurement agreement between the Sto(2) and the Svo(2) were analyzed using the Bland and Altman method. The mean +/- sd (range) oxygen saturation values during the data collecting period were 82.0% +/- 4.9% (72%-91%) for the Sto(2) and 82.2% +/- 5.5% (71%-91%) for the Svo(2), respectively. The linear correlation coefficient of the regression analysis between the Sto(2) and the Svo(2) was 0.934 (P < 0.05). A 95% confidence interval for absolute difference between the Sto(2) and the Svo(2) was 1.58%-2.09%. The mean +/- 2 sd difference between the Sto(2) and the Svo(2) was 0.12% +/- 3.97% on the Bland and Altman graph. We conclude that it is feasible to monitor the pulmonary artery oxygen saturation continuously by a transtracheal pulse oximetry technique and that it can be done so accurately. IMPLICATIONS: Mixed venous oxygen saturation (Svo2) is a measure of the balance between oxygen supply and consumption throughout the whole body. Svo2 can be measured invasively by inserting a pulmonary artery catheter with the associated disadvantages of cost and potential for patient injury. In this study, we investigated the feasibility of noninvasive Svo2 measurement using a transtracheal pulse oximetry technique.     

Continuous dual oximetry in surgical critical care. Indications and limitations.

Continuous dual oximetry combines pulse and venous oximetry to provide real-time information about oxygen utilization and pulmonary function. The authors undertook this study to examine the accuracy, utility, and limitations of the technique in surgical critical care. Twelve critically ill patients underwent placement of a modified pulmonary artery catheter and a pulse oximeter, both connected to an on-line computer. Paired blood gas and oximeter measurements were recorded every 4 to 6 hours, with a minimum of six sets per patient. Blood-gas-derived shunt fraction correlated well with oximeter-derived ventilation-perfusion index (r = 0.78, p less than 0.01). Further, the continuous oxygen extraction ratio (O2EI) and mixed venous oxygen saturation (SpvO2) correlated with the oxygen utilization coefficient (O2EI:r = 0.6, p less than 0.01; SpvO2, r = 0.76, p less than 0.01). Computer modeling of ventilation-perfusion index found limitations in accuracy that occur at high arterial oxygen saturations and when pulse oximetry errors are present. The authors conclude that (1) Continuous dual oximetry offers a significant advantage over routine blood gas analysis for monitoring cardiopulmonary parameters in critically ill patients because of its real-time display; (2) Oximeter-derived determinations parallel traditional parameters; and (3) The most significant technical limitations occur primarily at high arterial saturations and with pulse oximetry errors.     

Central venous oxygen saturation monitoring: role in adult donor care?

Monitoring oxygen saturation of blood drawn from a catheter placed within the superior vena cava (Scvo2) has recently been promoted as a substitute for evaluating oxygen saturation of mixed venous blood drawn from the pulmonary artery (Svo2). The Svo2 reflects the balance between oxygen delivery and oxygen consumption throughout the body and, among critically ill patients, may be helpful for assessing resuscitation, cardiac function, or oxygen homeostasis end points. Use of Scvo2 instead has been promoted because of its easier access and recent use during resuscitation of patients with severe infections. Although data from healthy subjects and critically ill patients are available, no study has been done among organ donors to evaluate customary values for either Scvo2 or Svo2 or how well the values correspond. After loss of oxygen consumption in the brain following brain death, the customary values for these variables may be different from values in other groups of patients. Therefore, until donor-specific normative values for these important parameters are identified, we do not recommend that Scvo2 be used to evaluate the balance between donor oxygen consumption and delivery or as a variable to guide treatment.     

Continuous intra-arterial oximetry, pulse oximetry, and co-oximetry during cardiac surgery.

This study evaluated arterial catheter oximetry versus pulse oximetry in eight patients (ASA III-IV) who underwent cardiac surgery. Co-oximeter saturation values served as the standard. Arterial oxygen saturation was determined simultaneously with these three methods at 162 prospectively defined points of measurement before, during, and after cardiopulmonary bypass (CPB). At the same times before and after CPB, arterial, pulmonary arterial, and central venous pressures, and cardiac output determinations were recorded. Saturation readings were obtained in more than 99% of measurements with catheter oximetry and in only 59% to 84% of measurements with pulse oximetry. Failure of pulse oximetry correlated with low mean arterial pressures and low cardiac outputs, but not with high systemic vascular resistance. The mean saturation values determined by catheter oximetry as well as by pulse oximetry differed from the mean values obtained by co-oximetry by less than 1% (= bias). The standard deviations of the individual differences between readings of catheter or pulse oximetry and readings of co-oximetry (= precision) were +/- 0.5% to +/- 1.0% for catheter oximetry and +/- 1.0% to +/- 1.2% for pulse oximetry. In summary, catheter oximetry was superior to pulse oximetry with regard to obtaining readings and to reliability of the obtained readings. Invasiveness and high costs influence the decision as to whether to use catheter oximetry, but if reliable and precise measurements of saturation are important at any time during surgery, pulse oximetry is an insufficient method and co-oximetry is a time-consuming method of analysis, whereas catheter oximetry is quick, reliable, and precise.     

Trends but not individual values of central venous oxygen saturation agree with mixed venous oxygen saturation during varying hemodynamic conditions

BACKGROUND: Previous studies found contradictory results regarding the question whether mixed venous oxygen saturation (Svo2) and central venous oxygen saturation (Scvo2) are equivalent. The inconsistency of study results may result from different study designs and different, partly questionable, statistical approaches. METHODS: The authors performed a prospective clinical trial comparing individual oxygen saturation values as well as the trend of values in blood from the superior vena cava (Scvo2), the right atrium (Srao2), and the pulmonary artery (Svo2) during varying hemodynamic situations. The subjects were 70 patients scheduled to undergo elective neurosurgical operations in the sitting position. Oxygen saturation was measured photospectrometrically in blood samples simultaneously taken at four different time points during supine and sitting positions. Statistical analysis was performed following the recommendations of Bland and Altman. RESULTS: Five hundred two comparative sets of measurements were obtained. Ninety-five percent limits of agreement ranging from +/-6.83 to +/-9.30% for single values were interpreted as clinically unacceptable. In contrast, correlations between changes of Svo2 and Scvo2 as well as of Svo2 and Srao2 were interpreted as clinically acceptable (R > or = 0.755, Pearson correlation coefficient; P < or = 0.0001). CONCLUSIONS: In this sample of patients, exact numerical values of Scvo2 and Srao2 are not equivalent to those of Svo2 in varying hemodynamic conditions. However, for clinical purposes, the trend of Scvo2 may be substituted for the trend of Svo2. In addition, previous studies investigating the agreement between Svo2 and Scvo2 were found to be lacking in their chosen statistical approaches.     

Trends but Not Individual Values of Central Venous Oxygen Saturation Agree with Mixed Venous Oxygen Saturation during Varying Hemodynamic Conditions

Background: Previous studies found contradictory results regarding the question whether mixed venous oxygen saturation (Svo2) and central venous oxygen saturation (Scvo2) are equivalent. The inconsistency of study results may result from different study designs and different, partly questionable, statistical approaches.

Methods: The authors performed a prospective clinical trial comparing individual oxygen saturation values as well as the trend of values in blood from the superior vena cava (Scvo2), the right atrium (Srao2), and the pulmonary artery (Svo2) during varying hemodynamic situations. The subjects were 70 patients scheduled to undergo elective neurosurgical operations in the sitting position. Oxygen saturation was measured photospectrometrically in blood samples simultaneously taken at four different time points during supine and sitting positions. Statistical analysis was performed following the recommendations of Bland and Altman.

Results: Five hundred two comparative sets of measurements were obtained. Ninety-five percent limits of agreement ranging from +/-6.83 to +/-9.30% for single values were interpreted as clinically unacceptable. In contrast, correlations between changes of Svo2 and Scvo2 as well as of Svo2 and Srao2 were interpreted as clinically acceptable (R >= 0.755, Pearson correlation coefficient; P <= 0.0001).     

Perioperative evaluation of a new mixed venous oxygen saturation catheter in cardiac surgical patients.

Fiberoptic pulmonary artery flotation catheters have gained clinical acceptance for continuous monitoring of mixed venous oxygen saturation (SvO2), especially in the management of hemodynamically unstable patients. Therefore, the performance of the oximetry system used is extremely important. The accuracy and stability of a new two-wavelength oximetry pulmonary artery catheter and SAT-2 oximeter were assessed in adult patients during and following cardiac surgery. After in vitro calibration of the system, the catheter was inserted through the right internal jugular vein and positioned in the pulmonary artery prior to induction of anesthesia. During the study period, the system was updated for hemoglobin changes of 1.8 g/dL or more. In vivo SvO2 values obtained by the oximetry catheter were compared with those determined with a reference oximeter from simultaneously drawn mixed venous blood specimens at different intervals. A total of 604 paired data points from 52 patients were analyzed, 572 (94.7%) of which were within the 95% confidence interval. Overall bias was -1.7% +/- 3.5% (SD). The results suggest that over the time course of the study, in vivo SvO2 values obtained with the two-wavelength catheter and the SAT-2 oximeter closely approximated SvO2 measured with a reference oximeter from mixed venous blood samples (r = 0.917; SEE 3.5%) in cardiac surgical patients in whom marked physiological changes occur.     

Early goal-directed therapy (EDGT) using continuous central venous oxygen saturation monitoring in a patient with septic shock

Septic shock is an adverse clinical condition resulting in multiple organ failure from global tissue hypoxia. The importance of initial treatment is widely recognized. Thus, guidelines for septic shock recommend early goal-directed therapy (EGDT) during the first six hours of treatment. Central venous oxygen saturation monitoring is useful to maintain adequate tissue oxygen delivery. A newly developed central venous oximetry catheter (PreSep Oximetery Catheter, Edwards Lifesciences) allows continuous and easy monitoring of central venous oxygen saturation. This report shows the usefulness of this catheter in a patient who developed septic shock during an emergency operation for perforated bowel. By using EGDT perioperatively with continuous central venous oximetry, multiple organ failure might be successfully avoided.     

Marked mixed venous desaturation during early mobilization after aortic valve surgery

We investigated the physiological reaction to mobilization the first and second day after aortic valve replacement in an open, prospective study. Hemodynamic and oxygenation variables were recorded in 15 patients using a pulmonary artery oximetry catheter and bench oximetry. Serious intraoperative events occurred in 3 patients, but all patients began mobilization on the first postoperative day and mobilization was accomplished without clinical problems. Mixed venous oxygen saturation (SvO(2)) at rest was 58.0 +/- 7.7% (mean +/- SD) on the first postoperative day and 58.0 +/- 6.2% on the second day (NS). During mobilization, oxygen consumption increased by 64 +/- 41% and 58 +/- 33% on the first and second days (P < 0.01; NS between days). No compensatory increase in cardiac index and oxygen delivery was seen. Oxygen extraction increased, resulting in SvO(2) values during exercise of 35.7 +/- 6.8% on the first day and 36.7 +/- 7.7% on the second day (P < 0.01; NS between days), whereas mixed venous oxygen partial pressure was 3.0 +/- 0.4 kPa on both days. The lowest recorded value for SvO(2) was 10%. The marked and consistent mixed venous desaturation during early mobilization has not been described before and the clinical consequences and underlying mechanism require further investigation. IMPLICATIONS: During early mobilization after aortic valve replacement, a marked and consistent reduction in mixed venous oxygen saturation to 35% and mixed venous oxygen partial pressure to 3 kPa was observed.     

Continuous measurement of cardiac output based on the Fick principle in cardiac anesthesia

With the development of fiberoptic and pulse oximetry, as well as the development of the more modern methods of oxygen consumption measurements, the online monitoring of Fick cardiac (FCO) output has become possible in the clinical treatment routine. The aim of this study was to compare fiberoptically measured mixed venous oxygen saturation with values from blood samples and continuously determined Fick cardiac output with intermittent thermodilution cardiac output (TCO). Ten patients undergoing coronary artery bypass grafting were measured during the perioperative period. Total body oxygen consumption was determined with a metabolic monitor (Deltatrac Datex) from respiratory gases. Arterial oxygen saturation was assessed by pulse oximetry (Nellcor). Mixed venous oxygen saturation was measured by a balloon tipped pulmonary artery fiberoptic catheter (Opticath) attached to an electronic device based on three wavelengths (Oximetrix cardiac output monitor). Hemoglobin, Methemoglobin and CO-hemoglobin were determined from intermittent blood samples by in vitro analysis. FCO was calculated from corresponding differences in arterial mixed venous oxygen and total body oxygen consumption. TDCO values were calculated from microcomputer recordings of the thermodilution data by monoexponential curve-fitting with respect to baseline drift. A significant systematic difference between FCO and TCO was observed. FCO exceeded TCO on average by 0.42 +/- 0.12 l/min. The limits of confidence (95%) were 0.18 to 0.66 l/min. There was no systematic difference between mixed venous saturation measurements with the fiberoptic system and from blood samples. The cardiac output values derived from fiberoptic and pulse oximetry can be considered sufficiently reliable for clinical purposes.(ABSTRACT TRUNCATED AT 250 WORDS)     

The marked reduction in mixed venous oxygen saturation during early mobilization after cardiac surgery: the effect of posture or exercise?

Early mobilization after cardiac surgery induces a marked reduction in mixed venous oxygen saturation (Svo2). Using pulmonary artery catheters and indirect calorimetry, we investigated the effects of exercise and postural change on cardiac index (CI) and Svo2 before and on the first morning after coronary artery bypass surgery. Sixteen patients with an ejection fraction >0.50 were studied at rest, during supine bicycle exercise, and during passive standing. Supine cycling at 30 W increased CI by 1.5 +/- 0.8 L x min(-1) x m(-2) before and 0.9 +/- 0.7 L x min(-1) x m(-2) after surgery (P < 0.05), whereas Svo2 was reduced from 80% +/- 4% at rest to 63 +/- 6% preoperatively (P < 0.05) and from 71% +/- 5% to 46% +/- 11% postoperatively (P < 0.05). Passive standing reduced CI by 0.8 +/- 0.5 L x min(-1) x m(-2) before and 0.3 +/- 0.4 L x min(-1) x m(-2) after surgery (P < 0.05). Svo2 was reduced from 79% +/- 5% to 64% +/- 7% preoperatively (P < 0.05) and from 72% +/- 6% to 60% +/- 6% postoperatively (P < 0.05). The exercise challenge revealed an altered cardiovascular response after surgery, causing a larger reduction in Svo2 for the same workload. Passive standing significantly reduced Svo2 both days, but this effect was less pronounced after surgery. The response to postural change and exercise was altered after surgery and may both contribute to the reduction in Svo2 during postoperative mobilization.     

Does hypothermia prevent cerebral ischaemia during cardiopulmonary bypass?

It is believed that moderate hypothermia (25-32 degrees C) during cardiopulmonary bypass provides cerebral protection by reducing the cerebral metabolic rate (CMRO2). Nevertheless episodes of ischaemia do occur and thus it has been suggested that cerebral oxygenation should be monitored by jugular venous oximetry. However, this technique is cumbersome and invasive. Near infrared spectroscopy (NIRS) provides a non-invasive assessment of cerebral oxygenation and this was used together with continuousjugular venous oximetry in 21 patients undergoing hypothermic cardiopulmonary bypass. During the hypothermic period, jugular venous oximetry indicated reduced oxygen extraction consistent with a reduction in CMRO2 (increase from 61 +/- 2.5% to 74 +/- 2.5%). In contrast, near infrared spectroscopy demonstrated increased oxygen extraction (HbO2 - 11.5 +/- 1 microM, HHb + 3.2 +/- 0.3 microM) and a fall in the cerebral concentration of oxidized cytochrome oxidase ( - 1.7 +/- 0.3 microM) indicating ischaemia. These results suggest that cerebral ischaemia occurs during hypothermic cardiopulmonary bypass with a spurious rise in jugular venous oxygen saturation, which represents arterio-venous shunting. Thus if hypothermia does facilitate cerebral protection it does not appear to be a direct result of a reduction in CMRO2 and oxygen requirement.     

Intra-arterial catheter oximetry and pulse oximetry in comparison with CO-oximetry in heart surgery]

This study evaluates the measurement of oxygen saturation by arterial catheter oximetry and pulse oximetry. The values are compared to values obtained by CO-oximetry. METHODS. In eight patients undergoing cardiac surgery, we determined the oxygen saturation of arterial and mixed-venous blood by CO-oximetry (IL 282, Instrumentation Lab) at prospectively defined points of measurement before, during, and after extracorporeal circulation. At the same points of measurement, saturation readings obtained by arterial catheter oximetry (U425C, Abbott) and pulse oximetry (Siemens/Nellcor) were recorded. RESULTS. The mean saturation values determined by both catheter oximetry and pulse oximetry differed from the mean values obtained by CO-oximetry by less than 1% (= bias). The standard deviations of the readings in relation to readings of CO-oximetry (= precision) were +/- 0.5% to +/- 1.0% for catheter oximetry and +/- 1.0% to +/- 1.3% for pulse oximetry. Furthermore, it was possible to obtain saturation readings in 99%-100% of measurements by catheter oximetry; in contrast, this was possible by pulse oximetry in only 59%-84% of measurements. Low mixed-venous saturation values were not indicated by any of the arterial methods of measurement. CONCLUSIONS. Catheter oximetry was superior to pulse oximetry with regard to both precision of saturation values and reliability to obtain values. Invasiveness and high costs are disadvantages of catheter oximetry, but if reliable and exact measurements are important at any time during surgery or intensive therapy, intra-arterial catheter oximetry is preferable to pulse oximetry.     

Continuous monitoring of mixed venous oxygen saturation during aortofemoral bypass grafting

Measurement of mixed venous oxygen saturation (SvO2) may be helpful in the care of critically ill patients. Serial determinations of SvO2 give an index of the relationship between oxygen delivery and tissue oxygen consumption. Continuous monitoring of SvO2 is now readily available with the Shaw Oximetrix pulmonary artery catheter (Oximetrix Inc., Mountain View, CA). This system has provided useful information in the high risk cardiac surgery patient. Continuous monitoring of mixed venous saturation may be helpful in high risk or critically ill general and peripheral vascular surgery patients both in the intensive care unit and in the operating room. The following clinical report is presented to illustrate the usefulness of continuous SvO2 monitoring in a high risk vascular surgery patient.     

Simple method for measurement of cardiac output by thermodilution after cardiac operation.

Cardiac output by the thermodilution technique was measured by a new No. 2 Fr. transthoracic (2F-TT) thermistor catheter placed at cardiac operation into the pulmonary artery directly through the right ventricular outflow tract. Cold (0 degree C) 5% dextrose in water (D5W) was used as indicator and injected through a percutaneously placed central venous pressure (CVP) catheter in the jugular vein. Comparison to the No. 7 Fr. Swan-Ganz (7F-SG) catheter demonstrated a close correlation (r = 0.87) and almost identical mean thermodilution cardiac output values during 530 determinations in 10 patients. No difficulty was experienced in insertion or removal of the 2F-TT catheter and no bleeding complications were noted. Experiments in six dogs showed that variation in position of the tip of the CVP catheter within the superior vena caval venous system and right atrium was not a critical factor in measurement of thermodilution cardiac output. The thermodilution cardiac output technique in general and the ease of insertion, as well as the small size of the 2F-TT catheter, should make this method especially advantageous in infants and small children.     

Balloon pump-induced pulsatile perfusion during cardiopulmonary bypass does not improve brain oxygenation.

BACKGROUND: Whether pulsatile flow offers substantial advantages for brain protection during cardiopulmonary bypass is controversial. The purpose of this study is to determine whether differences exist between pulsatile and nonpulsatile bypass concerning the effects on internal jugular venous saturation and on the state of regional cerebral oxygenation during normothermia. METHODS: Twenty-two patients undergoing elective coronary artery bypass grafting were randomly divided into 2 groups: group 1 (n = 11) received nonpulsatile perfusion during cardiopulmonary bypass and group 2 (n = 11) received pulsatile perfusion during bypass. We used an intra-aortic balloon pump to generate pulsatility. A spectrophotometric probe (INVOS 3100R, Somanetics, Troy, Mich) was used to assess the state of regional cerebral oxygenation. A 4F fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to monitor jugular venous oxygen saturation. Hemodynamic variables, arterial and jugular venous blood gases, and regional cerebral oxygenation were measured at 7 times points. RESULTS: In both groups, jugular venous oxygen saturation decreased at the early stage of the cardiopulmonary bypass (P =.03). Five patients in group 1 and 6 in group 2 had a jugular venous oxygen saturation of less than 50%. In both groups, the regional cerebral oxygenation value decreased during cardiopulmonary bypass (P =.04). CONCLUSIONS: The present results showed that pulsatility generated through the use of intra-aortic balloon pumping did not produce any beneficial effects on jugular venous oxygen saturation and regional cerebral oxygenation at normothermia.     

The feasibility of transesophageal echocardiograph-guided right and left ventricular oximetry in hemodynamically stable patients undergoing coronary artery bypass grafting

There are no techniques available for continuous noninvasive measurement of the oxygen saturation of blood flowing through the heart. We assessed the feasibility and accuracy of transesophageal echocardiograph (TEE)-guided left ventricular (SpO2 LV) and right ventricular (SpO2 RV) oximetry. Twenty hemodynamically stable, well-oxygenated anesthetized patients (ASA physical status III, aged 51-75 yr) undergoing coronary artery bypass grafting were studied. A TEE probe was modified by attaching a single-use pediatric reflectance pulse oximeter just proximal to the ultrasound transducer. The TEE probe was directed toward the LV by using the transgastric mid-short axis view or toward the RV by using the transgastric RV inflow view, in random order. Readings were taken every 30 s for 10 min during a hemodynamically stable period of anesthesia. Simultaneous blood samples were taken from the radial artery and pulmonary artery to determine arterial oxygen saturation (SaO2) and mixed venous oxygen saturation (SvO2), respectively. During SpO2 LV readings, simultaneous finger pulse oximetry (SpO2 finger) was also recorded. SpO2 LV was feasible in 20 of 20 patients, and SpO2 RV was feasible in 19 of 20 patients. The mean +/- SD (range) oxygen saturation for each method was the following: SpO2 LV, 98.7% +/- 0.6% (97%-100%); SaO2, 98.7% +/- 0.6% (96.6%-99.4%); SpO2 finger, 98.1% +/- 1.2% (97%-100%); SpO2 RV, 73.9% +/- 4.7% (64%-85%); and SvO2, 74.5% +/- 4.4% (66.8%-82.6%). SpO2 LV agreed closely with SaO2 (mean difference, 0.072%). SpO2 RV agreed closely with SvO2 (mean difference, 0.65%). SpO2 LV agreed more closely with SaO2 than finger oximetry (mean difference, -0.072 vs -0.692). TEE-guided SpO2 LV and SpO2 RV are feasible in hemodynamically stable anesthetized patients and provide similar readings to arterial and mixed venous blood samples. The technique merits further investigation. IMPLICATIONS: Transesophageal echocardiograph-guided left and right ventricular oximetry is feasible in hemodynamically stable anesthetized patients and provides similar readings to arterial and mixed venous blood samples.     

Oxygenation during local anaesthesia for cataract surgery

The oxygenation of 48 elderly patients scheduled for cataract surgery under local anaesthesia was studied using pulse oximetry and nasopharyngeal oxygen measurement. After a control period the patients breathed supplemental oxygen 2 l/min and later 4 l/min, via either a face mask or a nasal catheter. The effects of the two oxygen flow levels and oxygen delivery methods on oxygenation were assessed. The lowest oxygen saturation values were seen after retrobulbar block before the patients were transferred to the operating room. The surgical draping did not cause hypoxaemia and the 2 l/min oxygen flow was sufficient to cause hyperoxaemia in all patients. The face mask and nasal catheter appeared to be equally good in oxygenating the patients.     

In vivo comparison of two mixed venous saturation catheters

The accuracy and stability of mixed venous saturation pulmonary arterial catheters under adverse physiologic conditions has not been assessed. Either a Shaw Opticath catheter (three-wavelength) or a Swan-Ganz oximetry TD catheter (two-wavelength) was calibrated in vitro and positioned in the pulmonary artery in each of ten mongrel dogs. The in vivo saturations were compared to measured saturations from anaerobically collected mixed venous blood analyzed with a reference cooximeter at each step in the protocol. Oxygen delivery was varied to obtain a broad range of mixed venous saturations (Sv-O2) by altering inspired oxygen concentration, isovolemic hemodilution, reducing cardiac output, and increasing afterload. Calculated oxygen consumption varied from 128 to 311 ml/min. Pre-insertion calibration for both catheter types compared favorably with the cooximeter prior to physiologic manipulations, although the three-wavelength catheter more closely approximated the cooximeter. The three-wavelength catheter tracked measured Sv-O2 accurately under adverse conditions for up to 10 h (R = .994; SEE = 2.2%). The two-wavelength catheter tended to drift under the same conditions (R = .808; SEE = 10.6%). At the conclusion of the experiment, the two-wavelength system was uniformly higher then the cooximeter by 5-31% with a mean of 21% (P less than or equal to .003 as compared with the initial difference by paired Student's t test). Pending further analysis of the tendency of the two-wavelength system to drift it would seem prudent to limit its clinical application.     

Measuring brain tissue oxygenation compared with jugular venous oxygen saturation for monitoring cerebral oxygenation after traumatic brain injury

Jugular bulb oximetry is the most widely used method of monitoring cerebral oxygenation. More recently, measurement of brain tissue oxygenation has been reported in head-injured patients. We compared the changes in brain tissue oxygen partial pressure (PbO2) with changes in jugular venous oxygen saturation (SjVO2) in response to hyperventilation in areas of brain with and without focal pathology. Thirteen patients with severe head injuries were studied. A multiparameter sensor was inserted into areas of brain with focal pathology in five patients and outside areas of focal pathology in eight patients. A fiberoptic catheter was inserted into the right jugular bulb. Patients were hyperventilated in a stepwise manner from a PaCO2 of approximately 35 mm Hg to a PaCO2 of 22 mm Hg. There was no significant change in cerebral perfusion pressure or arterial partial pressure of oxygen with hyperventilation. In areas without focal pathology, there was a good correlation between changes in SjVO2 and PbO2 (deltaSjVO2 and deltaPbO2; r2 = 0.69, P < 0.0001). In areas with focal pathology, there was no correlation between deltaSjVO, and APbO2 (r2 =0.07, P = 0.23). In this study, we demonstrated that measurement of local tissue oxygenation can highlight focal differences in regional cerebral oxygenation that are disguised when measuring SjVO2. Thus, monitoring of PbO2 is a useful addition to multimodal monitoring of patients with traumatic head injury. IMPLICATIONS: Brain oxygenation is currently monitored by using jugular bulb oximetry, which attracts a number of potential artifacts and may not reflect regional changes in oxygenation. We compared this method with measurement of brain tissue oxygenation using a multiparameter sensor inserted into brain tissue. The brain tissue monitor seemed to reflect regional brain oxygenation better than jugular bulb oximetry.