The use of intermittent and continuous recordings of jugular venous bulb oxygen saturation in the unconscious patient

A new marker identification of high risk stroke patients: Jugular saturation

OBJECTIVES

The aim of this prospective study; to investigate in emergency patients with stroke the relationship between jugular saturation and National Institutes of Health Stroke Scale (NIHSS), lesion volume and mortality score.

MATERIALS AND METHODS

In this prospective study, 82 patients who fulfilling the criteria for inclusion in diagnosed with were enrolled in the study. Patients' demographic data, comorbid conditions and stroke type were recorded. The arterial blood pressure, heart rate, and consciousness were recorded at the emergency department. Glasgow Coma Score (GCS) and National Health Institutions Stroke Scale (NIHSS) scores were calculated. Complete Blood Count (CBC) and biochemical values were obtained at the time of admission to the emergency department. Arterial blood gas and jugular venous blood gas were taken and pO2, SpO2 and lactate values were recorded. Patients were grouped according to jugular desaturation (<50%). After imaging, the lesion was located by a specialist radiologist and the lesion volume was calculated. Afterwards, it was followed up by means of the hospital registry system where the patients were followed up (service, intensive care), hospitalization time and whether in-hospital mortality occurred.

RESULTS

82 patients were included in the study. Of the 82 patients, 36 (43.9%) were male and 46 (56.1%) were female. The mean age was 69.8 ± 13.3. Patients were divided into two groups, jugular venous saturation <50% and ≥50%. 16 patients with J.SpO2 <50% were detected. There was no difference between the two groups in terms of age, sex, Glasgow Coma Scale (GCS), National Health Institutions Stroke Scale (NIHSS) score, laboratory data other than hemoglobin and lesion volume (p > 0,05). In-hospital mortality occurred in 9 (13.6%) of patients with J.SpO2 ≥% 50; In the group with J.SpO2 < % 50, 6 patients (37.5%) died within the hospital and this difference was statistically significant (p < 0,05).

CONCLUSION

SjVO2 measurement can be used to identify high-risk stroke patients and to direct critical interventions. However, no correlation was found between this value and lesion volume and NIHSS scale.

Interstitial brain adenosine and xanthine increase during jugular venous oxygen desaturations in humans after traumatic brain injury

OBJECTIVE

Adenosine decreases the cerebral metabolic rate for oxygen and increases cerebral blood flow, and it may play an important role in cerebrometabolic and cerebrovascular responses to hypoperfusion after traumatic brain injury. Jugular venous oxygen saturation is monitored after traumatic brain injury to assess brain oxygen extraction, and desaturations may reflect secondary brain insults. We hypothesized that brain interstitial adenosine and related purine metabolites would be increased during jugular venous oxygen saturation desaturations (<50%) and determined associations between the purines, lactate, and glucose to assess the role of adenosine during secondary insults in humans.

DESIGN

Study of critically ill adults with severe traumatic brain injury.

SETTING

Adult neurointensive care unit.

PATIENTS

We prospectively defined periods of normal saturation and desaturation in six patients after severe traumatic brain injury.

INTERVENTIONS

During these periods, cerebral microdialysis samples of brain interstitial fluid were collected, and adenosine and purine metabolites were measured by high-pressure liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

Adenosine increased 3.1-fold and xanthine increased 2.5-fold during desaturation periods (both p <.05 vs. normal saturation period, signed rank). Adenosine, xanthine, hypoxanthine, and cyclic-adenosine monophosphate correlated with lactate over both study periods (r(2) =.32,.14,.31,.07, and.26, respectively, all p <.05, Pearson product moment correlation).

CONCLUSION

The marked increases in interstitial brain adenosine that occur during jugular venous oxygen desaturations suggest that adenosine may play an important role during periods of secondary insults after traumatic brain injury. The correlation of these metabolites with lactate further suggests that adenosine is increased during periods of enhanced glycolytic metabolism.

Jugular bulb oximetry during cardiac surgery

Imbalance between cerebral oxygen supply and demand is thought to play an important role in the development of cerebral injury during cardiac surgery. This article presents an overview of cerebral oxygenation monitored by jugular bulb oximetry during cardiac surgery with cardiopulmonary bypass. The general principles of jugular bulb oximetry including physiology, intermittent and continuous monitoring, technical considerations, limitations and potential complications are discussed. Different applications of jugular bulb oximetry during bypass surgery and the possible therapeutic approaches to impaired cerebral oxygenation are described.

Comparison of jugular venous oxygen saturation and brain tissue Po2 as monitors of cerebral ischemia after head injury

OBJECTIVE

To compare the characteristics of jugular venous oxygen saturation (Sjvo2) and brain tissue Po2 (Pbto2) as monitors for cerebral ischemia after severe head injury. Sjvo2 has been useful as a monitor for cerebral ischemia, but it is limited by its inability to identify regional cerebral ischemia. Pbto2 may be superior to Sjvo2 for this purpose, because oxygenation in localized areas of the brain can be monitored.

DESIGN

Sjvo2 and Pbto2 were successfully monitored in 58 patients with severe head injury. The changes in Sjvo2 and Pbto2 were compared during ischemic episodes.

SETTING

Neurosurgical intensive care unit of a level I trauma center.

MEASUREMENTS AND MAIN RESULTS

During the monitoring period, which averaged 90 hrs/patient, there were 54 episodes during which Sjvo2 decreased to <50% and/or Pbto2 decreased to <8 torr. Two of these episodes were caused by an infarction in the area of the Po2 probe, leaving 52 episodes of global hypoxia/ischemia that were identified by one of the two monitors. The sensitivities of the two monitors for detecting ischemia, using the thresholds of 50% and 8 torr for Sjvo2 and Pbto2, respectively, were similar. The Sjvo2 catheter detected 69.7% of the episodes and the Pbto2 catheter detected 63.5% of the episodes. In most of the remaining episodes, both probes reflected a decrease in oxygenation, but not to levels below the defined thresholds. The major differences in the two measures of oxygenation included the following: a) Sjvo2 more consistently reflected a reduction in oxygenation during hyperventilation; b) Pbto2 was affected more by changes in arterial Po2; and c) during severe global ischemia, Pbto2 decreased to 0 and remained at 0, whereas Sjvo2 initially decreased but then increased again as cerebral blood flow ceased, and the only blood in the jugular bulb was of extracerebral origin.

CONCLUSIONS

The two monitors provide complimentary information, and neither monitor alone identifies all episodes of ischemia. The best strategy for using these monitors is to take advantage of the unique features of each monitor. Sjvo2 should be used as a monitor of global oxygenation; but Pbto2 should be used as a monitor of local oxygenation, ideally with the catheter placed in an area of the brain that is vulnerable to ischemia but that may be salvageable with appropriate treatment.

Assessment of spatially resolved spectroscopy during cardiopulmonary bypass

Controversy remains about which tissue is primarily responsible for light attenuation of near infrared spectroscopy (NIRS) in the adult, the spatial resolution provided and the preferred algorithm for quantification. Until recently, changes in NIRS have not been fully quantified and have been difficult to interpret without sophisticated computation. A new development by Hamamatsu Photonics, the spatially resolved spectrometer (SRS), may be able to give a quantitative measure of oxygen saturation. We have incorporated the SRS into a multimodality monitoring system for the purpose of direct validation against jugular bulb oxygen saturation (SjO2) in patients undergoing routine cardiopulmonary bypass (CPB). The importance of this investigation is in the development of the SRS machine which shows potential as a useful clinical tool. The results demonstrated good correlation between SRS and SjO2 in 12 out of the 24 patients studied. Although these results are encouraging, this study suggests that the SRS, in its present form, is not a reliable clinical monitor of cerebral oxygen saturation during CPB. © 1999 Society of Photo-Optical Instrumentation Engineers.

Anatomical variation of cerebral venous drainage: the theoretical effect on jugular bulb blood samples

Recent studies have demonstrated significant variation in bilateral jugular venous oxygen saturation measurements which may be of clinical significance. We have therefore measured variations in normal dural sinus venous drainage to assess the possible effects of normal anatomical variations on measured jugular venous oxygen saturation. Normal volunteers (n = 25) were imaged using magnetic resonance venography to demonstrate variations in venous anatomy. Flow was measured in the superior sagittal sinus and bilaterally in the transverse sinus, sigmoid sinus proximal to the jugular bulb and proximal jugular vein using phase difference magnetic resonance imaging. Examination of magnetic resonance venogram images showed considerable variability in the symmetry of transverse sinus flow. Complete absence of one transverse sinus was seen in four cases and significant asymmetry in the size of the transverse sinuses was present in 13. Quantitative flow studies demonstrated that the ratio of superior sagittal sinus to combined jugular bulb flow showed remarkably little variation (0.46 +/- 0.06). Measurements of transverse sinus flow showed significant asymmetry (< 40% of superior sagittal sinus flow in one transverse sinus) in 21 of 25 volunteers. The effect of the observed asymmetry on jugular venous oxygen saturation was modelled based on the assumption of either a supratentorial or infratentorial lesion. This model predicted significant asymmetry in jugular venous oxygen saturation measurements (> 10%) in 65% of cases with a supratentorial lesion which is in close agreement with clinical observations. This study suggests that normal variations in venous drainage may account for observed asymmetry in jugular venous oxygen saturation measurements.

Accuracy of continuous jugular bulb oximetry in the intensive care unit

OBJECTIVE

To address the accuracy of a bedside jugular bulb oxygen saturation (SjO2) catheter monitor (Baxter-Edwards, Santa Ana, CA) versus in vitro co-oximetry measurements in the intensive care unit (ICU).

METHODS

By prospective protocol, we compared blood gas measurements with simultaneously recorded continuous bedside oximetric monitor values for 31 ICU patients with traumatic brain injury undergoing jugular bulb catheter monitoring. For suboptimal fiberoptic light signal quality indices, the catheter was repositioned, flushed, or both before drawing the sample for in vitro measurement. Laboratory and bedside monitor data were examined for association using the chi2 and paired t tests and a linear regression model.

RESULTS

We assessed 195 samples (median, 5 per patient; range, 1-14) who were monitored an average of 3.4 (range, 1-6) days. The in vivo monitor (range, 32-94%) and in vitro co-oximetry (range, 38-93%) values had acceptable correlation (y = 0.94x + 4.4, r2 = 0.80). For bedside monitor detection of jugular bulb desaturation (SjO2 < 50% for 10 min), the kappa statistic was 0.35, the sensitivity was 45 to 50%, and the specificity was 98 to 100%.

CONCLUSION

Continuous ICU SjO2 monitoring correlates significantly with in vitro values, but less so than previously described during intracranial surgery. Although sensitivity of the bedside monitor to detect confirmed desaturations remains an issue, the high specificity indicates that it is less of a concern that patients may be misdiagnosed as having desaturations resulting in unnecessary interventions. Nonetheless, suspected jugular bulb desaturation should be verified before taking therapeutic actions.

[Measurement of arteriovenous oxygen difference in the monitoring of patients with subarachnoid hemorrhage due to cerebral aneurysm]

The arterious venous oxygen difference (AVDO2) due to the close relationship with cerebral metabolic rate of oxygen and cerebral blood flow shows metabolic alterations that occur in some pathological situations in the brain including subarachnoid haemorrhage. The AVDO2 was calculated by the Fick equation and the results evaluated by the Glasgow outcome scale. Measurements of arteriojugular oxygen difference were carried out in 30 patients with subarachnoid haemorrhage due to rupture of intracranial aneurysms, as an attempt to monitor the relationship between changes in AVDO2, clinical picture, and evolution of the patients. The subarachnoid haemorrhage was diagnosed by CT scan in 17 patients and by lumbar punction in 13 and the diagnosis of arterial vasospasm was carried out by clinical evaluation and confirmed by four vessels angiogram in only eight patients. Eighteen patients were admitted with Hunt & Hess (H&H) I/II, seven with H&H III and five with H&H IV/V. Nineteen patients had AVDO2 normal and this group had three deaths; five patients had AVDO2 continuously low with three deaths; and six patients had AVDO2 continuously high with two deaths. The patients with normal AVDO2 had better prognosis and clinical evolution than the patients with abnormal values of AVDO2. In conclusion, AVDO2 measurements could not be correlated with the diagnosis of vasospasm, but was useful in the early identification of metabolic changes that occur after subarachnoid haemorrhage and could be used as an supplementary monitoring in the clinical evaluation of patients with this pathology.

Intraoperative jugular desaturation during surgery for traumatic intracranial hematomas

Traumatic intracranial hematomas which are present on hospital admission or which develop during the hospital course are associated with a worse neurological outcome than diffuse injuries. The purpose of this study was to monitor jugular venous oxygen saturation (Sjvo2) during surgery for evacuation of traumatic intracranial mass lesions, to determine the incidence and the causes of jugular venous desaturation, and to assess the usefulness of Sjvo2 monitoring in this setting. Twenty-five severely head injured patients were monitored during 27 surgical procedures. At the start of the surgical procedure, the median Sjvo2 was 47% (range 25%-89%). Seventeen (63%) of the patients had a Sjvo2 less than 50%. Five patients had extremely low Sjvo2 values (< or = 30%). Upon evacuation of the intracranial hematoma, there was a significant (P < 0.001) increase in the median Sjvo2 to 65% (range 50%-88%). Intracranial hypertension was the primary cause of the low Sjvo2, as confirmed by the response to surgical evacuation. Hypotension (mean arterial pressure < 80 mm Hg) was a contributing factor in seven of the cases of jugular desaturation. The definitive treatment of a traumatic intracranial hematoma is surgical evacuation. However, during the period prior to evacuation of the hematoma, jugular venous desaturation was common, suggesting that monitoring Sjvo2 might provide useful information about the adequacy of cerebral perfusion.

Diagnosis of traumatic carotid-cavernous sinus fistula by monitoring venous oxygen saturation in the jugular bulb: report of two cases

OBJECTIVE AND IMPORTANCE

A traumatic carotid-cavernous sinus fistula (CCF) is rarely diagnosed early and may sometimes be missed until clinical signs and symptoms appear. The continuous monitoring of cerebral venous oxygen saturation may reveal the presence of a CCF by means of a fiberoptic catheter that records very high oxygen saturation values when positioned in the jugular bulb.

CLINICAL PRESENTATION

We report two cases of early diagnosis of CCFs unexpectedly revealed by monitoring the jugular bulb for venous oxygen saturation values that approximated arterial saturation values. One case was diagnosed on Day 3 after admission, and the other was diagnosed shortly after cannulation of the ipsilateral jugular bulb.

INTERVENTION

Confirmation of the diagnosis of CCF was obtained by angiography. Intravascular treatment was performed in one case.

CONCLUSION

These cases add another diagnostic role to cerebral venous oxygen saturation monitoring. When high cerebral venous oxygen saturation values rapidly or abruptly reach arterial oxygen saturation, the presence of a CCF must be considered and confirmed by arterial angiography.

Intraoperative data acquisition for the study of cerebral dysfunction following cardiopulmonary bypass

As a first step in our study to document postoperative cerebral dysfunction, and to determine whether global cerebral blood flow can be implicated in the etiology of this postoperative change, we have assembled a flexible data acquisition system to acquire and record data from four independent sources, three in digital form and one analog. Each of the monitors that we use has a different requirement: One has eight channels of analog output; the other three have RS-232 digital outputs, each with a data stream with different characteristics. The central element of our data collection is a personal computer running the data acquisition and analysis program, LabVIEW for Windows (National Instruments, Austin, TX). All data are processed through separate LabVIEW global variables; the data strings are concatenated and stored on the hard disk in a spreadsheet format for further analysis. We illustrate an intraoperative recording made during cardiopulmonary bypass (CPB) by showing a graph of the mean arterial pressure (MAP), mixed venous oxyhemoglobin saturation recorded from the jugular bulb (JVO2Sat), and temperature measured from the nasopharynx. A decrease in the MAP after unclamping the aorta is accompanied by a decrease in JVO2Sat.

Effects of intravenous nitroglycerin combined with dopamine on intracranial pressure and cerebral arteriovenous oxygen difference in patients with acute subarachnoid haemorrhage

The effects of intravenous nitroglycerin (NTG) combined with dopamine on intracranial pressure (ICP) and cerebral arteriovenous oxygen difference (AVDO2) were studied in 11 patients with acute subarachnoid haemorrhage (SAH). The study was performed on Days 1 to 3 of SAH after aneurysmal clipping. Treatment consisted of an intravenous drip infusion of NTG in increasing incremental doses of 0.5, 1.0, 1.5, 2.0, and 2.5 micrograms/kg/min at one-hour intervals. Dopamine (5 to 10 micrograms/kg/min) was also given concurrently to maintain systemic blood pressure. ICP values before NTG administration ranged from 7 to 24 mmHg (mean. 11.91 +/- 5.30 mmHg). ICP began to increase immediately after the administration of NTG 0.5 microgram/kg/min and peaked at 14.64 +/- 5.93 mmHg 10 minutes after onset of infusion. Thereafter, ICP gradually returned to pretreatment levels. Increasing the dose of NTG failed to induce further significant rises in ICP. Mean AVDO2 before NTG administration was 4.69 +/- 0.62 ml/dl. This parameter showed no significant change during NTG infusion, although cerebral perfusion pressure decreased to between 75% to 94% of the control value after NTG administration. These results indicate that continuous NTG infusion combined with dopamine does not have adverse effects on ICP (the ICP increase is minimal and transient) and may even have beneficial effects on CBF in patients with acute SAH.

Early jugular bulb oxygenation monitoring in comatose patients after an out-of-hospital cardiac arrest

OBJECTIVE

To determine the role of early jugular bulb oxygenation monitoring in comatose patients after cardiac arrest.

DESIGN

Prospective sequential study.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

Thirteen patients comatose after out-of-hospital cardiac arrest.

INTERVENTIONS

A standard hemodynamic protocol.

MEASUREMENTS AND RESULTS

Jugular bulb oxygen saturation levels and oxygen extraction ratios could not discriminate between patients with good (6) and poor (7) cerebral outcome. This was also true for the jugular bulb-arterial lactate difference. Survivors had significantly higher overall oxygen transport values than non-survivors.

CONCLUSIONS

Jugular bulb oxygenation monitoring during the first few hours after cardiac arrest cannot reliably discriminate between comatose patients with a good and poor cerebral outcome. Further studies with an extended monitoring period are thus required.

Detection of cerebral hypoperfusion during cardiopulmonary bypass. Continuous measurement of cerebral venous oxyhaemoglobin saturation during myocardial revascularisation

We measured continuously cerebral venous oxyhaemoglobin saturation (SjvO2) using a 4F fibreoptic catheter in 11 patients scheduled for elective myocardial revascularisation. The aims of this study were to assess the Oximetrix 3 computer and Opticath 40 cm catheter during moderate hypothermic cardiopulmonary bypass, and identify epochs of cerebral hypoperfusion (SjvO2 < 54%). Radial artery pressure, brain electrical activity, arterial and cerebral venous oximetry (dual oximetry), end-tidal CO2 and nasopharyngeal temperature were recorded continuously in each patient. Following in vivo calibration of 11 continuous SjvO2 catheters and monitor, 57 simultaneous, paired recordings were additionally taken. The mean difference between the catheter SjvO2 and the in vitro laboratory derived value was 0.34%, with a 95% confidence interval -3.2% to 2.4%. In 10 patients SjvO2 decreased below normal at rewarming and myocardial reperfusion: mean lowest value 37%, range 19%-55%. Reduced SjvO2 were associated with a decrease in perfusion pressure (r = 0.292, 80 DF, p = 7.7* 10(-3)), and with an increase in nasopharyngeal temperature (r = -0.46, 115 DF, p = 2.7* 10(-7)) after moderate hypothermia. The Oximetrix 3 computer and Opticath 40 cm catheter provided reliable and accurate continuous monitoring of SjvO2 during nonpulsatile cardiopulmonary bypass involving hypothermia with haemodilution and identified rewarming as the period of greatest risk of global cerebral hypoperfusion.

On-line monitoring of global cerebral hypoxia in acute brain injury. Relationship to intracranial hypertension

Global cerebral oxygenation, perfusion pressure, and expired CO2 tension were continuously monitored in 69 adults with acute severe closed brain trauma. Cerebral oxygenation was assessed by continuous fiberoptic monitoring of jugular bulb oxyhemoglobin saturation, in conjunction with continuous monitoring of arterial oxyhemoglobin saturation. Jugular desaturation associated with arterial desaturation (hypoxemic cerebral hypoxia) was evaluated and managed. A total of 121 episodes of combined arterial and jugular desaturation were documented, 76 in the presence of gross abnormalities identified on chest roentgenograms. Prolonged episodes that did not respond promptly to treatment occurred 32 times in 12 patients, usually after the initial 72 hours posttrauma. The remaining 89 episodes promptly responded to treatment and occurred predominantly within the initial 72 hours. Profound but brief desaturation was not associated with neurological deterioration, while profound and prolonged desaturation was accompanied by significant decreases in Glasgow Coma Scale scores, even though intracranial pressure levels were not significantly different in these two groups. Global cerebral hypoxia that does not respond promptly to treatment appears to be independently deleterious to neurological function in severely head-injured patients.

Percutaneous catheterization of the jugular bulb with a Doppler probe: technical note

On-line measurement of jugular venous bulb oxygen saturation may be of clinical value in patients with head injuries. Cannulation of the jugular bulb may be technically difficult in this group of patients. Trendelenberg positioning and head rotation may be associated with increased morbidity or mortality. A technique is described whereby catheterization can be performed with the head of the bed elevated and the neck in a neutral position. A needle with a Doppler probe is used to distinguish between the carotid artery and the internal jugular vein. The needle and the probe are then directed to the audible signal representative of the jugular vein. Once the vein is penetrated, placement of a fiberoptic oxygen saturation catheter is performed in the usual fashion. This technique allows auditory feedback to guide the course of the needle and decreases the morbidity that may be associated with the "blind" technique.

[Cerebral hemometabolism: from isolated measurements to monitoring and therapy]

An overview is presented on historical and multivariate aspects of cerebral hemometabolism. This involves a full multivariate approach, from blood pressure to cerebral metabolism. From isolated measurements, to monitoring and management, a comprehensive overview of cerebral hemometabolism is addressed, from its inception to current days, up to a new concept, the cerebral hemodynamic reserve. A multivariate functional diagram is proposed, to summarize the multivariate interrelationships of cerebral hemometabolism. A generic proposition is made for studies of truly normal cerebral hemometabolism in children, for subsequent clinical applications. Another proposition is made for multivariate cerebral hemometabolic monitoring, in a broad variety of circumstances of predominantly global changes in intracranial dynamics, both in animal and clinical research.

Desaturation episodes after severe head injury: influence on outcome

The relationship of jugular venous desaturation and neurological outcome was examined in 116 patients with severe head injury. Seventy-six episodes of jugular venous desaturation were prospectively identified in 46 (40%) of the patients. The etiology of the desaturations varied, including both systemic and cerebral causes. A poor neurological outcome was strongly associated with the occurrence of jugular venous desaturation.

Monitoring of jugular venous oxygen saturation in comatose patients with subarachnoid haemorrhage and intracerebral haematomas

To prevent secondary cerebral ischemia in comatose patients it would be of great importance to assess cerebral blood flow. Recently monitoring of the jugular venous oxygen saturation (SJVO2) has been shown to continuously evaluate cerebral oxygenation and to estimate cerebral blood flow. While most of these studies have dealt with severely head injured patients, we investigated cerebral oxygenation in 50 comatose patients due to an intracerebral haematoma (n = 14), subarachnoid haemorrhage (n = 12) and severe head injury (n = 24). In these groups of patients, the reaction of SJVO2 to hyperventilation and to lowering of blood pressure was studied. Moderate hyperventilation from 35 to 28 mmHg resulted in a significant decrease of SJVO2 in all groups. A critical SJVO2 between 50 and 55% was found in one half of the patients studied, a pathological SJVO2 below 50% was seen in 23% of the cases. Lowering of arterial blood pressure within the limits of autoregulation resulted in decreases of SJVO2 in patients with intracerebral haematomas only. 55% of these patients showed signs of insufficient cerebral oxygenation. Furthermore the frequency of spontaneous desaturation episodes was studied retrospectively and comparison made between the different groups. These episodes were found more frequently in patients with intracerebral haematomas compared to patients with severe head injury. In conclusion, monitoring of jugular venous oxygen saturation is a valuable tool for detecting and treating insufficient cerebral oxygenation in comatose patients following intracerebral haemorrhage, subarachnoid haemorrhage and severe head injury.

Continuous monitoring of jugular venous oxygen saturation in head-injured patients

The continuous measurement of jugular venous oxygen saturation (SjvO2) with a fiberoptic catheter is evaluated as a method of detecting cerebral ischemia after head injury. Forty-five patients admitted to the hospital in coma after severe head injury had continuous and simultaneous monitoring of SjvO2, intracranial pressure, arterial oxygen saturation, and end-tidal CO2. Cerebral blood flow, cerebral metabolic rates of oxygen and lactate, arterial and jugular venous blood gas levels, and hemoglobin concentration were measured every 8 hours for 1 to 11 days. Whenever SjvO2 dropped to less than 50%, a standardized protocol was followed to confirm the validity of the desaturation and to establish its cause. Correlation of SjvO2 values obtained by catheter and with direct measurement of O2 saturation by a co-oximeter on venous blood withdrawn through the catheter was excellent after in vivo calibration when there was adequate light intensity at the catheter tip (176 measurements: r = 0.87, p less than 0.01). A total of 60 episodes of jugular venous oxygen desaturation occurred in 45 patients. In 20 patients the desaturation value was confirmed by the co-oximeter. There were 33 episodes of desaturation in these 20 patients, due to the following causes: intracranial hypertension in 12 episodes, hypocarbia in 10, arterial hypoxia in six, combinations of the above in three, systemic hypotension in one, and cerebral vasospasm in one. The incidence of jugular venous oxygen desaturations found in this study suggests that continuous monitoring of SjvO2 may be of clinical value in patients with head injury.

Per- and postoperative changes in the arterio-venous oxygen content difference (AVDO2) in patients subjected to craniotomy for cerebral tumours

Sixteen patients with supratentorial cerebral tumours were subjected to craniotomy under thiopentone, fentanyl, nitrous oxide, halothane anaesthesia during moderate hypocapnia (PaCO2 level 4.0 kPa). The arterio-venous oxygen content difference (AVDO2) was measured peroperatively, and repeatedly during the first three hours after extubation. Peroperatively the level of AVDO2 averaged 8.0 vol% during opening of the dura, and decreased to 7.0 vol% during closure of the dura (P less than 0.05). Immediately after extubation the AVDO2 decreased to 4.3 vol% (P less than 0.05), and during the next 3 hours a gradual increase to 5.8 vol% (P less than 0.05) was disclosed. In individual cases the postoperative changes in AVDO2 correlated fairly well with changes in mean arterial blood pressure (MABP), but other factors including duration of the operation, age of the patients, size of the tumour, level of PaCO2 and adaptation to prolonged hyperventilation during operation are supposed to be responsible for the low levels of AVDO2 observed in the postoperative period.