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of SjvO2 values obtained by catheter and with direct measurement of O2 saturation by a co-oximeter on venous blood withdrawn through the catheter was excellent after in vivo calibration when there was adequate light intensity at the catheter tip (176 measurements: r = 0.87, p less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.     

Study on therapeutic mechanism and clinical effect of mild hypothermia in patients with severe head injury

BACKGROUND: The therapeutic mechanism and clinical effect of mild hypothermia in patients with severe head injury were studied. METHODS: All 396 patients with severe head injury [Glasgow Coma Scale score (GCS) equal to or less than 8 on admission] were randomly divided into the hypothermic group (198 cases) and the control group (198 cases). Hypothermia was induced within 24 hours of injury. Rewarming began 1 to 7 days (average 62.4 +/- 27.6 h) after the rectal temperature (RT) reached 32.0 to 35.0 degrees C. Meanwhile, the vital signs, intracranial pressure (ICP), blood gas values, blood electrolytes, brain tissue oxygen pressure (P(bt)O2), brain tissue temperature (BT), cerebral blood flow (CBF), and jugular venous oxygen saturation (S(jv)O2) were measured. The rectal temperature of control patients was induced to 36.5 to 37.0 degrees C. According to GOS, the prognosis of the patients was evaluated. RESULTS: In comparison with control group, during mild hypothermia the high level of ICP, hyperglycemia and blood lactic acid significantly decreased (p < 0.05) and cerebral flow improved dominantly. The vital signs, blood gas values, and blood electrolytes did not change significantly. Decreased mortality and good recovery were also found in hypothermia group. CONCLUSIONS: Mild hypothermia is safe and effective for preventing brain damage on patients with severe head injury, as well as reducing mortality and improving the prognosis. It is important to monitor P(bt)O2, BT, CBF, and S(jv)O2 in hypothermic therapy.     

Accuracy of a Cerebral Oximeter in Healthy Volunteers under Conditions of Isocapnic Hypoxia

Background: A cerebral oximeter measures oxygen saturation of brain tissue noninvasively by near infrared spectroscopy. The accuracy of a commercially available oximeter was tested in healthy volunteers by precisely controlling end-tidal oxygen (PET O2) and carbon dioxide (PET CO2) tensions to alter global cerebral oxygen saturation.

Methods: In 30 healthy volunteers, dynamic end-tidal forcing was used to produce step changes in PET O2 resulting in arterial saturation ranging from [approximately] 70% to 100% under conditions of controlled normocapnia (each person's resting PET CO2) or hypercapnia (resting plus 7-10 mmHg). Blood arterial (SaO2) and jugular bulb venous (Sjv with bar O2) saturations during each PET O2 interval were determined by co-oximetry. The cerebral oximeter reading (rSO2) and an estimated jugular venous saturation (Sjv with bar O2), derived from a combination of SaO2 and rSO2, were compared with the measured Sjv with bar O2.

Results: The Sjv with bar O2 was significantly higher with hypercapnia than with normocapnia for the same SaO2. The rSO sub 2 and Sjv with bar O2 were both highly correlated with S sub jv with bar O2 for individual volunteers (mean r2 = 0.91 for each relation); however, the slopes and intercepts varied widely among volunteers. In three of them, the cerebral oximeter substantially underestimated the measured Sjv O2.     

Experimental study of acute brain swelling under acute intracranial hypertension (author's transl)]

There are many problems about the cause, pathophysiology and treatment of acute brain swelling under intracranial hypertension frequently encountered in the neurosurgical clinics. Generally, rapid increase of the cerebral vasoparesis caused by unknown etiology is thought to be the main cause of acute brain swelling under intracranial hypertension. Moreover, disturbance of the cerebral venous circulatory system is discussed recently by many authors. But, research from the point of systemic respiration and hemodynamics is necessary for resolving these problems. This experiment was designed to study the effects of respiration and hemodynamics on the cerebral vasoparesis. Method: Using 22 adult dogs, acute intracranial hypertension was produced by epidural balloon inflation sustained at the level of 300 - 400 mmH2O. Simultaneously with measurement of intracranial pressure at the epidural space, superior sagittal sinus pressure, respirogram, systemic blood pressure (femoral artery), central venous pressure, common carotid blood flow, EKG and bipolar lead EEG were monitored continuously. The experimental group was divided by the respiratory loading into 5 groups as follows: control (6 cases), 10% CO2 hypercapnia (4 cases), 10% O2 hypoxia (4 cases), stenosis of airway (5 cases), 100% O2-controled respiration (3 cases). Results and conclusions: 1) Cerebral vasoparesis under acute intracranial hypertension took place earlier and showed more rapid progression in groups of stenosis of airway, hypercapnia and hypoxia than control group of spontaneous respiration in room air. No occurrence of cerebral vasoparesis was found out in a group of 100% O2 controlled respiration. It is proved that increased airway resistance or asphyxia, hypercapnia and hypoxia have strictly reference to the occurrence and progression of cerebral vasoparesis and for the prevention of cerebral vasoparesis, correct 100% O2 cont rolled respiration is effective. 2) From the hemodynamic change, the progression of rapid increase of cerebral blood volume with increase of blood volume in the superior sagitta sinus during cerebral vasoparesis under intracranial hypertension is presumed. It is suggested from the superior sagittal sinus pressure in various experimental groups that the site, reactivity and disturbed degree of the cerebral venous system are changed by the difference of respiratory or ventrilatory state and the cerebral venous circulatory disturbance has also reference to the occurrence of acute brain swelling. 3) During cerebral vasopareris under acute intracranial hypertension, remarkable supression of respiration, increased central venous pressure and increased common carotid blood flow were observed. It is concluded that the reaction of systemic hemodynamics following respiratory change effects on cerebral circulation markedly and they are being important factors to occurrence of acute brain swelling.     

Effects of PEEP on the intracranial system of patients with head injury and subarachnoid hemorrhage: the role of respiratory system compliance

BACKGROUND: Positive end-expiratory pressure (PEEP) can be effective in improving oxygenation, but it may worsen or induce intracranial hypertension. The authors hypothesized that the intracranial effects of PEEP could be related to the changes in respiratory system compliance (Crs). METHODS: A prospective study investigated 21 comatose patients with severe head injury or subarachnoid hemorrhage receiving intracranial pressure (ICP) monitoring who required mechanical ventilation and PEEP. The 13 patients with normal Crs were analyzed as group A and the 8 patients with low Crs as group B. During the study, 0, 5, 8, and 12 cm H2O of PEEP were applied in a random sequence. Jugular pressure, central venous pressure (CVP), cerebral perfusion pressure (CPP), intracranial pressure (ICP), cerebral compliance, mean velocity of the middle cerebral arteries, and jugular oxygen saturation were evaluated simultaneously. RESULTS: In the group A patients, the PEEP increase from 0 to 12 cm H2O significantly increased CVP (from 10.6 +/- 3.3 to 13.8 +/- 3.3 mm Hg; p < 0.001) and jugular pressure (from 16.6 +/- 3.1 to 18.8 +/- 3.2 mm Hg; p < 0.001), but reduced mean arterial pressure (from 96.3 +/- 6.7 to 91.3 +/- 6.5 mm Hg; p < 0.01), CPP (from 82.2 +/- 6.9 to 77.0 +/- 6.2 mm Hg; p < 0.01), and mean velocity of the middle cerebral arteries (from 73.1 +/- 27.9 to 67.4 +/- 27.1 cm/sec; F = 7.15; p < 0.001). No significant variation in these parameters was observed in group B patients. After the PEEP increase, ICP and cerebral compliance did not change in either group. Although jugular oxygen saturation decreased slightly, it in no case dropped below 50%. CONCLUSIONS: In patients with low Crs, PEEP has no significant effect on cerebral and systemic hemodynamics. Monitoring of Crs may be useful for avoiding deleterious effects of PEEP on the intracranial system of patients with normal Crs.     

Cerebral circulation and metabolism in the acute stage of subarachnoid hemorrhage

OBJECT: The mechanism of reduction of cerebral circulation and metabolism in patients in the acute stage of aneurysmal subarachnoid hemorrhage (SAH) has not yet been fully clarified. The goal of this study was to elucidate this mechanism further. METHODS: The authors estimated cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), O2 extraction fraction (OEF), and cerebral blood volume (CBV) preoperatively in eight patients with aneurysmal SAH (one man and seven women, mean age 63.5 years) within 40 hours of onset by using positron emission tomography (PET). The patients' CBF, CMRO2, and CBF/CBV were significantly lower than those in normal control volunteers. However, OEF and CBV did not differ significantly from those in control volunteers. The significant decrease in CBF/CBV, which indicates reduced cerebral perfusion pressure, was believed to be caused by impaired cerebral circulation due to elevated intracranial pressure (ICP) after rupture of the aneurysm. In two of the eight patients, uncoupling between CBF and CMRO2 was shown, strongly suggesting the presence of cerebral ischemia. CONCLUSIONS: The initial reduction in CBF due to elevated ICP, followed by reduction in CMRO, at the time of aneurysm rupture may play a role in the disturbance of CBF and cerebral metabolism in the acute stage of aneurysmal SAH.     

Comparison of alpha-stat and pH-stat cardiopulmonary bypass in relation to jugular venous oxygen saturation and cerebral glucose-oxygen utilization

Jugular venous oxygen saturation (SJVO(2)) reflects the balance between cerebral blood flow and metabolism. This study was designed to compare the effects of two different acid-base strategies on jugular venous desaturation (SJVO(2) <50%) and cerebral arteriovenous oxygen-glucose use. We performed a prospective, randomized study in 52 patients undergoing cardiopulmonary bypass (CPB) at 27 degrees C with either alpha-stat (n = 26) or pH-stat (n = 26) management. A retrograde internal jugular vein catheter was inserted, and blood samples were obtained at intervals during CPB. There were no differences in preoperative variables between the groups. SJVO(2) was significantly higher in the pH-stat group (at 30 min CPB: 86.2% +/- 6.1% versus 70.6% +/- 9.3%; P < 0.001). The differences in arteriovenous oxygen and glucose were smaller in the pH-stat group (at 30 min CPB: 1.9 +/- 0.82 mL/dL versus 3.98 +/- 1.12 mL/dL; P < 0.001; and 3.67 +/- 2.8 mL/dL versus 10.1 +/- 5.2 mL/dL; P < 0.001, respectively). All episodes of desaturation occurred during rewarming, and the difference in the incidence of desaturation between the two groups was not significant. All patients left the hospital in good condition. Compared with alpha-stat, the pH-stat strategy promotes an increase in SJVO(2) and a decrease in arteriovenous oxygen and arteriovenous glucose differences. These findings indicate an increased cerebral supply with pH-stat; however, this strategy does not eliminate jugular venous desaturation during CPB. IMPLICATIONS: A prospective, randomized study in 52 patients during cardiopulmonary bypass revealed that pH-stat increased jugular venous oxygen saturation and decreased arteriovenous oxygen-glucose differences. There was no difference in the incidence of jugular venous desaturation. These findings suggest an increased cerebral blood flow with no protection against jugular venous desaturation during pH-stat.     

Acute left ventricular dysfunction and subarachnoid hemorrhage.

OBJECTIVE: Severe left ventricular (LV) dysfunction associated with acute subarachnoid hemorrhage (SAH) due to cerebral aneurysm rupture. SETTING: An adult 12-bed surgical intensive care unit of a university hospital. PATIENT: A female patient presenting with SAH (Hunt & Hess grade III) and severe left ventricular dysfunction. INTERVENTIONS: Central venous pressure, arterial blood pressure, extravascular lung water catheter, transesophageal echocardiography, blood gas analysis, electrocardiograms, and chest x-ray for clinical management. MEASUREMENTS AND MAIN RESULTS: On admission to the district hospital, an electrocardiogram (ECG) revealed a sinus rhythm with transient ST elevations. A transesophageal echocardiography showed a left ventricular ejection fraction (LV-EF) of approximately 10%. Severe LV dysfunction required inotropic and vasopressor support to maintain mean arterial pressure above 60 mmHg, while the first measurement of an extravascular lung water catheter revealed a cardiac index of 2.0 L/min/m2 and moderate hypovolemia. Despite stepwise volume loading that increased intrathoracic blood volume--an indicator of cardiac preload--from 719 mL/m2 to 927 mL/m2, cardiac index remained poor. Enoximone lead to a marked increase of cardiac index up to 3.9 L/min/m2 and LV-EF to about 30%, but had to be stopped due to thrombopenia. Surgical clipping of an intracranial aneurysm was postponed because of the impaired cardiac function and was performed on day 18 after admission. Interestingly, neurologic outcome was not as poor as might be expected from the literature. CONCLUSION: Severe left ventricular dysfunction may occur in acute SAH and may necessitate delay of aneurysm surgery.     

Comparison of the effects of positive end-expiratory pressure and jugular venous compression on canine cerebral venous pressure

The confluent sinus pressure was measured in eight mongrel dogs in the head-up position to compare the effectiveness of positive end-expiratory pressure (PEEP) and jugular venous compression in increasing cerebral venous pressure. When the head was elevated 30 cm above the heart, confluent sinus pressure decreased from 9.6 +/- 1.8 (mean +/- SEM) to -5.3 +/- 0.5 mmHg. At constant arterial carbon dioxide tension (PaCO2 = 28 +/- 2 mmHg), PEEP (20 cmH2O) did not increase cerebral venous pressure. However, when the jugular veins were compressed with a neck tourniquet with pressures of 20-140 mmHg, cerebral venous pressure increased rapidly. When neck tourniquet pressure was maintained at 40 mmHg, confluent sinus pressure in all dogs was increased and sustained at 2.4 +/- 0.8 mmHg. Carotid artery pressure measured distal to the tourniquet was not altered. The efficacy of extrathoracic venous pressure elevation (neck tourniquet) is greater than intrathoracic (PEEP), and this may relate to the Starling resistor effects of neck veins and the presence of jugular venous valves. We conclude that prophylactic use of PEEP in the prevention of air embolism during the sitting position may not be as effective as jugular venous compression.     

Continuous jugular venous oximetry in the neurointensive care unit — a brief review

PURPOSE: To describe the technique of continuous jugular venous oxygen saturation (SjVO(2)) monitoring and review its applications in the neurointensive care unit (NICU), with special reference to the management of raised intracranial pressure (ICP) following severe acute brain injury. SOURCE: This narrative review is based on a selection of current literature on SjVO(2) monitoring in conjunction with local experience using this technique. Principal findings: Despite limitations, the use of SjVO(2) monitoring has the potential to impact on patient care in the NICU. The placement of the catheter is relatively simple. Studies have confirmed that abnormalities in cerebral venous oxygen saturation are associated with adverse outcome following traumatic brain injury. There is evidence that SjVO(2) may be a useful adjunct to ICP monitoring of patients with intracranial hypertension. Furthermore, managing cerebral extraction of oxygen in conjunction with cerebral perfusion pressure may result in an improved outcome. Further research in this area is needed. Other indications for SjVO(2) monitoring include subarachnoid hemorrhage, cardiopulmonary bypass and following ischemic stroke. CONCLUSION: In the past, the management of severe acute brain injury was targeted at ICP and perfusion pressure with little consideration for the metabolic requirements of the injured brain. SjVO(2) monitoring is another tool the intensivist can use to obtain information about the global oxygen requirements of the injured brain on a continuous basis. Whether this will impact on care in the long term remains to be seen.     

Monitoring of intracranial pressure and cerebral hemodynamics by transjugular dural sinus catheterization

Cerebral venous sampling may be useful in the evaluation of cerebral damage. A catheter was successfully inserted 18 cm deep from the right internal jugular vein into the transverse sinus in a 38 year old man with B-mode ultrasound guidance to measure pressure and sample blood. Transverse sinus venous oxygen saturation (StvO₂) was lower than normal ranges (55% - 75%) for jugular venous oxygen saturation (SjvO₂). At the time spontaneous cardiac rhythm was restored, transverse sinus pressure increased briefly to 26 mmHg [more than 15 mmHg higher than normal intracranial pressure (ICP)]. This case suggests that catheterization of the dural sinus may be accomplished with B-mode ultrasound guidance and that the catheter can be used to monitor ICP and cerebral hemodynamics.     

Continuous monitoring of jugular bulb oxygen saturation in comatose patients — Therapeutic implications

Summary Comatose patients run a high risk of developing cerebral ischaemia which may considerably influence final outcome. It would therefore be extremely useful if one could monitor cerebral blood flow in these patients. Since there is a close correlation between the arteriovenous difference of oxygen and cerebral blood flow, it was a logical step to place a fiberoptic catheter in the jugular bulb for continuous measurement of cerebrovenous oxygen saturation.We have monitored cerebral oxygenation in 54 patients, comatose because of severe head injury, intracerebral haemorrhage or subarachnoid haemorrhage.Normal jugular venous oxygen saturation (SJVO₂) ranges between 60 and 90%. A decline to below 50% is considered indicative of cerebral ischaemia. Spontaneous episodes of desaturation (SJVO₂<50% for at least 15 min) were frequent during the acute phase of these insults. Many of these desaturation episodes could be attributed to hyperventilation, even though considered moderate. Likewise, insufficient cerebral perfusion pressure and severe vasospasm were found to be important causes of desaturation episodes. In many instances, tailoring of ventilation or induced hypervolaemia and hypertension were capable of reversing these low flow states.The new method of continuous cerebrovenous oximetry is expected to contribute to a better outcome by enabling timely detection and treatment of insufficient cerebral perfusion.     

Changes in superior sagittal sinus pressure in children with head elevation, jugular venous compression, and PEEP

Air embolism is a potential hazard during craniotomy whenever intracranial venous pressure is subatmospheric. In order to better understand both the risk of air embolism and its treatment in neurosurgical patients, the authors have investigated the relationship of superior sagittal sinus pressure (SSP) to head position in 15 children and examined the effects of both jugular venous compression and positive end-expiratory airway pressure (PEEP) on SSP. Progressive head elevation significantly decreased mean SSP and, in five patients, SSP was less than 0 mm Hg at 90 degrees torso elevation. A PEEP of 10 cm H2O was ineffective in significantly increasing SSP at any degree of head elevation, whereas bilateral internal jugular compression always caused a significant increase in SSP. The authors conclude that children are at risk for venous air embolism when undergoing suboccipital craniectomy in the sitting position because intracranial venous pressure is often subatmospheric when the head is elevated. Furthermore, maintaining PEEP does not appear to be a reliable treatment for increasing SSP, whereas bilateral internal jugular compression is effective.     

Acute subdural haematoma due to ruptured intracranial aneurysms

Acute spontaneous subdural haematoma (SDH) is rarely associated with rupture of intracranial saccular aneurysm. We report our experience with four cases of non-traumatic SDHs secondary to rupture of an intracranial aneurysm and discuss the diagnosis and management of this condition. We retrospectively reviewed of four cases of acute SDH due to cerebral aneurysm rupture confirmed by cerebral angiography and surgery. Patients were evaluated using the Glasgow Coma Scale (GCS) and subarachnoid grade of the World Federation of Neurosurgical Societies (WFNS) and outcome with the Glasgow Outcome Scale (GOS). Of the 232 patients with non-traumatic subarachnoid haemorrhage (SAH) treated between 1993 and 2002, only four patients (1.72%) presented SDH due to aneurysmal rupture. The SAH grade on admission was grade IV in one patient and V in the other three. In all cases the aneurysm was located in the posterior communicating artery. Spontaneous acute SDH secondary to aneurysm rupture has been rarely reported. We suggested that timely SDH removal and aneurysmal clipping surgery should be performed in such patients, including those in poor neurological condition.     

Intracerebral monitoring of a patient with vasopasm

Delayed neurological deficit occurs among 30% of patients after aneurysmal subarachnoid haemorrhage, mainly related to cerebral vasospasm. The early detection of cerebral ischemia remains problematic. Conventional cerebral monitoring (as intracranial pressure and cerebral perfusion pressure) appears to be insufficient, because cerebral ischemia may occur without elevated intracranial pressure. Global cerebral monitoring as venous jugular oxygen saturation are useful for regional monitoring. Local monitoring as oxygen tissue partial pressure (PtiO2) and microdialysis are sensible for brain ischemia detection, but may also ignore episodes occurring in non-monitored brain area. For the detection of most episodes of brain ischemia, several monitoring system should be use performing a multimodal intracerebral monitoring. Brain microdialysis and oxygen tissue partial pressure are promising monitoring system.     

Comparative effects of propofol versus fentanyl on cerebral oxygenation state during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction

BACKGROUND: The purpose of this study was to examine the comparative effects of propofol and fentanyl on cerebral oxygenation during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction. METHODS: One hundred eighty patients scheduled for elective coronary artery bypass grafting were randomly divided into two groups: propofol group (n = 90) and fentanyl group (n = 90). After induction of anesthesia, a fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to monitor jugular venous oxygen hemoglobin saturation continuously. Hemodynamic measurements and arterial and jugular venous blood gases were measured at seven time points. All patients underwent a battery of neurologic and neuropsychological tests on the day before the operation and at 6 months after the operation. RESULTS: Cerebral desaturation (defined as a jugular venous oxygen hemoglobin saturation value less than 50%) during cardiopulmonary bypass was more frequent in the fentanyl group than in the propofol group. Cerebral desaturation time (duration when jugular venous oxygen hemoglobin saturation was less than 50%) and the ratio of cerebral desaturation time to total cardiopulmonary bypass time in the fentanyl group differed significantly from those in the propofol group (fentanyl group: 27 +/- 14 minutes, 20% +/- 9%; propofol group: 18 +/- 11 minutes, 14% +/- 7%, respectively, p < 0.05). There was no significant difference in postoperative cognitive dysfunction at 6 months after operation between the two groups (propofol group: 5 of 77, 6%; fentanyl group: 5 of 75, 7%). CONCLUSIONS: Propofol preserved cerebral oxygenation state estimated by jugular venous oxygenation during cardiopulmonary bypass compared with the fentanyl group. However, propofol did not affect postoperative cognitive dysfunction.     

The effect of cerebrospinal fluid drainage on cerebral perfusion in traumatic brain injured adults

Cerebrospinal fluid drainage is a first line treatment used to manage severely elevated intracranial pressure (> or = 20 mm Hg) and improve outcomes in patients with acute head injury. There is no consensus regarding the optimal method of cerebrospinal fluid removal. The purpose of this investigation was to determine whether cerebrospinal fluid drainage decreases intracranial pressure and improves cerebral perfusion and to identify factors that impact treatment effectiveness. This study involved 31 severely head injured patients. Intracranial pressure and other indices of cerebral perfusion (cerebral perfusion pressure, cerebral blood flow velocity, and regional cerebral oximetry) were measured before, during, and after cerebrospinal fluid drainage. Arterial and jugular venous oxygen content was measured before and after cerebrospinal fluid drainage. Patients underwent three randomly ordered cerebrospinal fluid drainage protocols that varied in the volume of cerebrospinal fluid removed (1 mL, 2 mL, and 3 mL) for a total of 6 mL of cerebrospinal fluid removed. There was a significant change in the intracranial pressure from a mean at baseline of 26.1 mm Hg (SD = 4.4) to 22.1 mm Hg immediately after drainage. One third of patients experienced a decrease in the intracranial pressure below 20 mm Hg; in two patients the intracranial pressure dropped less than 1 mm Hg. The following factors predicted 61.5% of the variance in the responsiveness of intracranial pressure to drainage: vecuronium hypothermia, baseline cerebral perfusion pressure and acuity of illness. Cerebrospinal fluid drainage provides a transient decrease in intracranial pressure without a measurable improvement in other indices of cerebral perfusion.     

Impact of hypoxemia on the performance of cerebral oximeter in volunteer subjects

Adverse neurological events during hypoxic episodes in high-risk patients or in patients not thought to be at risk while undergoing procedures increase morbidity and mortality. The ability to reliably monitor cerebral oxygenation could serve as an indicator for the need of therapeutic intervention and it's overall effect. This study was designed to verify the reliability of the only commercially available continuous noninvasive monitor, the INVOS 3100 (Somanetics Corp., Troy, MI), in subjects with varying levels of hypoxemia. Six adult volunteer subjects were enrolled. After placement of electrocardiogram (EKG), noninvasive blood pressure (NIBP), pulse oximeter (SpO2), cerebral oximeter (rSO2), a 20 g radial artery catheter, and a 4 F oximetric jugular bulb catheter, the subjects were given hypoxic mixtures to breathe to varying levels of desaturation. Arterial and mixed venous blood was drawn for blood-gas analysis at each level of O2 saturation. The cerebral hemoglobin saturation value from the cerebral oximeter was compared to the combined brain saturation using the formula: estimated field saturation between the light source and the detector (fSO2) = 0.25 x the arterial oxygen saturation (SaO2) + 0.75 x the jugular bulb venous oxygen saturation (SjvO2), (fSO2 = 0.25 SaO2 + 0.75 SjvO2). Statistical analysis demonstrated a correlation of 0.67 between rSO2 and fSO2 and a bias of -3.1% with a precision of 12.1%. Minimal bias of 0.38% and precision of 6.22% were calculated for transitional error. We concluded from the study that rSO2 may serve as a reliable indicator of changes in brain oxygenation induced by hypoxemia.     

Comparison of two sites of inflow pressure measurement during retrograde cerebral perfusion

OBJECTIVE: To determine whether internal jugular venous valves influence inflow pressure during retrograde cerebral perfusion. DESIGN: Prospective study. SETTING: Community hospital, university setting, single institution. PARTICIPANTS: Ten patients undergoing reconstructive aortic arch surgery with profound hypothermic circulatory arrest. INTERVENTIONS: During retrograde cerebral perfusion, inflow pressure was continuously measured at 2 separate sites relative to the left internal jugular venous valve (ie, superior vena cava inflow catheter [infravalvular pressure] and rostral left internal jugular vein [supravalvular pressure]). MEASUREMENTS AND MAIN RESULTS: Infravalvular pressure of 29.8 +/- 3.5 mmHg and supravalvular pressure of 22.7 +/- 0.8 mmHg were significantly different (mean difference, 7.1 +/- 3.6 mmHg; p = 0.041). In 8 patients, the pressure difference was <6 mmHg; whereas in 2 patients, the pressure difference was >20 mmHg. Bland and Altman analysis revealed 95% limits of agreement on mean bias of -12.9 to 27.8 mmHg. CONCLUSION: Internal jugular venous valves can obstruct retrograde cerebral perfusion inflow, manifest by an inflow pressure difference between the superior vena cava and internal jugular vein. In the presence of competent internal jugular venous valves, measurement of inflow pressure in the superior vena cava may be an inaccurate estimate of actual cerebral perfusion pressure. Internal jugular vein pressure should be monitored to avoid inadvertent cerebral hypoperfusion.     

Differential perfusion: a new technique for isolated brain cooling during cardiopulmonary bypass

BACKGROUND: The purpose of this study was to determine the feasibility of differential perfusion of the aortic arch and descending aorta during cardiopulmonary bypass using a cannula designed for aortic segmentation. METHODS: Pigs weighing 57 kg (n = 8), underwent cardiopulmonary bypass using the dual lumen aortic cannula. An inflatable balloon separated proximal (aortic arch) and distal (descending aorta) ports. During differential perfusion, the aorta was segmented and the arch and descending aorta perfused differentially using parallel heat exchangers. Ability to independently control brain and body temperature, cardiopulmonary bypass flow rate and mean arterial blood pressure was determined. RESULTS: During differential perfusion cerebral hypothermia (27 degrees C) with systemic normothermia (38 degrees C) was established in 23 minutes. Independent control of arch and descending aortic flow and mean arterial blood pressure was possible. Analysis of internal jugular venous O2 saturation data indicated an increase in the ratio of cerebral O2 supply to demand during differential perfusion. CONCLUSIONS: A cannulation system segmenting the aorta allows independent control of cerebral and systemic perfusion. This device could provide significant cerebral protection while maintaining the advantages of warm systemic cardiopulmonary bypass temperatures.