Abstract
Jugular venous oxygen saturation monitoring provides useful information regarding cerebral oxygenation supply and demand. Jugular oximetry can be facilitated by insertion of a catheter by an anesthesiologist or an intensivist. While monitoring neurocritically ill patients to diagnose cerebral hypoxia, jugular venous oximetry can also provide vital information to optimize the relationship between cerebral oxygen demand and supply with the goal to improve patient outcomes.
Keywords
Cerebral oxygenation, Jugular venous oxygen, Monitoring
Contents
Introduction 58
Basic Principles 58
Understanding the Equipment 59
Jugular Bulb Monitoring Equipment 59
Jugular Bulb Catheter Placement 60
Side of Jugular Bulb Monitoring 61
Indications and Contraindications 63
Neurointensive Care Use 63
Traumatic Brain Injury 63
Aneurysmal Subarachnoid Hemorrhage (SAH) 64
Intracranial Arteriovenous Malformation (AVM) 64
Intraoperative Use of Jugular Venous Monitoring 64
Contraindications and Complications of Jugular Bulb Catheter Monitoring 66
Readings and Interpretation 66
Effect of Anesthetics 68
Advantages and Disadvantages 70
Summary 70
Suggested Readings 70
References 71
Introduction
Jugular venous oxygen saturation monitoring (SjvO 2 ) is one of the multimodal neuromonitoring methods used to indirectly assess global cerebral oxygen balance and guide physiologic management decisions in both intraoperative and intensive care unit (ICU) settings. Normal SjvO 2 values range from 55% to 75%, and SjvO 2 less than 55% reflects cerebral desaturation and has been associated with poor outcomes. Jugular bulb monitoring has been integrated into multimodal monitoring together with other hemodynamic and intracranial pressure (ICP) monitoring techniques for the care of neurocritically ill patients. Jugular venous oximetry has been used in a variety of neurosurgical procedures to guide the management of ventilation and hemodynamic strategies.
Basic Principles
Anatomy of Venous Drainage of the Brain
The venous drainage of the brain flows into superficial (external or cortical) and deep (internal) cerebral veins. The superficial cerebral veins drain predominantly into the superior sagittal sinus and partially to the cavernous sinus or sphenoparietal sinus. The deep cerebral veins, on the other hand, drain into the straight sinus. Both the superior sagittal sinus and straight sinus then join to form the confluence of sinuses where the two lateral sinuses originate before continuing laterally to the right and left transverse (sigmoid) sinuses and right and left jugular bulbs. Although the dural sinuses join at the confluence of sinuses, mixing is incomplete. The blood from the superior sagittal sinus (venous drainage from cortical area) is more likely to drain into the right lateral sinus, whereas the blood from the straight sinus (venous drainage from subcortical area) flows into the left side. In the cavernous and circular sinuses, which are the two sinuses at the base of the brain, the venous blood drains freely and equally through the petrosal sinuses to both right and left jugular bulbs. Each side of the internal jugular veins comprises two dilated parts: the superior and inferior jugular bulbs. The superior bulb is a sampling site for jugular venous oxygen saturation (SjvO 2 ) because it is less contaminated by extracerebral venous return.
Jugular Venous Oxygen Saturation (SjvO 2 )
Jugular venous oxygen saturation directly reflects the global balance between cerebral oxygen supply and metabolic consumption per the Fick principle.
When CMRO 2 = cerebral metabolic rate for oxygen, CBF = cerebral blood flow, CaO 2 = arterial oxygen content, and CjO 2 = jugular venous oxygen content.
Cerebral oxygen supply (delivery):
Cerebral oxygen demand (consumption):
Oxygen content is directly proportional to oxygen saturation with minor contributions from dissolved oxygen (0.003 × PO 2 ) with hemoglobin being the constant. Therefore, the arterial-jugular oxygen content difference (AjvDO 2 ) is largely determined by the gradient between SaO 2 and SjvO 2 .
From the preceding equation:
If CMRO 2 remains constant, changes in AjvDO 2 are inversely proportional to CBF. If AjvDO 2 decreases, we assume that oxygen supply is excessive compared to demand (hyperemic state). In contrast, if AjDO 2 increases, the brain is extracting more oxygen when the supply is too low for the metabolic requirement (hypoperfusion state). If CMRO 2 increases without an appropriate increase in CBF, AjvDO 2 is widened; thus, if hemoglobin and SaO 2 remain constant, SjvO 2 is an indicator of cerebral oxygen demand. In the clinical setting, the reduction in SjvO 2 is an indicator of imbalance between cerebral oxygen demand and supply, which is either a relative increase in CMRO 2 or a reduction in CBF. Assuming constant CMRO 2 , low CBF may be due to hypotension or hypocarbia.
Understanding the Equipment
Jugular Bulb Monitoring Equipment
Jugular venous oximetry can be monitored by either intermittent sampling (using standard intravascular catheters) or continuous monitoring (using fiberoptic catheters). The fiberoptic technology used in a spectrophotometric catheter allows continuous displays of SjvO 2 values based on the differential absorption of light at the different wavelengths between oxyhemoglobin and deoxyhemoglobin. The available catheters are the Baxter–Edwards system (Edslab Sat II, Baxter Edwards Critical Care Division, Irvine, California, USA) and the Abbott system (Opticath Oximetrix, Abbott Critical Care System, Abbott Park, Illinois, USA). Both catheters have two lumens, one for blood sampling and the other one has two optical fibers transmitting lights to and from the venous blood. Although the basic principle is similar, the Abbott system uses three wavelengths of light for reflectance spectrophotometry instead of two wavelengths allowing the automatic measurement of both hemoglobin concentration and oxygen saturation and minimizing artifact interference. This feature is important in patients with rapid changes in hemoglobin concentration, e.g., during cardiopulmonary bypass.
Jugular Bulb Catheter Placement
Unlike central line placement, the operator stands in the axillary space facing the cephalad position to facilitate retrograde placement of the jugular venous catheter. The anatomical relationship between the jugular vein and carotid artery is visualized, and the jugular vein is punctured under ultrasound-guided technique at the apex of the triangle formed by the sternal head, the clavicular head of the sternocleidomastoid muscle, and the clavicle. However, in contrast to that of the central line placement, the needle, the guidewire, and the catheter are pointed in the cephalad direction. The final position of the catheter needs to be as proximal to the jugular bulb as possible to facilitate blood sampling but minimize extracranial blood contamination. Patients may be placed in the Trendelenburg position to improve the visualization of the internal jugular vein if they do not have poor intracranial compliance.
We routinely use a 16G, 5.25-inch-long venous cannula for this procedure in the operating room. Alternatively, a fiberoptic catheter can also be placed using the Seldinger technique. Here a J-shaped guidewire is passed into the jugular bulb and advanced no further than 2–3 cm beyond the needle insertion site if needed. In adults, an introducer sheath (5–6 French size) is then inserted before an oximetry catheter (4.5–5 French) is advanced until resistance is met at the jugular bulb (approximately 15–20 cm in adults). Resistance felt is due to a slight bend in the vessel lumen distal to the jugular foramen just below the skull exit. In the awake patient, a sensation in the ipsilateral jaw or ear may be noted when the catheter reaches this point. The catheter is then pulled back about 0.5–1 cm distally to avoid continuously abutting the roof of the jugular bulb. Alternatively, the catheter tip can be inserted at a distance measured from the insertion point to the level of mastoid process (approximately the level of the jugular bulb) until resistance is met.
The desired final position of the catheter is as close to the roof of the jugular bulb as possible to minimize extracranial venous blood contamination. As little as a 2-cm difference can result in as high as 10% contamination. Radiographic assessment can be used to confirm position of the catheter tip and to detect any kinking, and it is commonly practiced in the ICU. On a lateral X-ray of the skull, the catheter tip should be just above the lower border of C1, medial to the mastoid process. An anteroposterior (AP) neck radiographic view can also be used as an alternative. On AP view, the tip should be more cephalad to a line extending from the atlantooccipital joint and caudal to the inferior margin of orbit. The catheter tip should be cephalad to an imaginary line connected between the tips of mastoid processes. We do not routinely use X-ray to confirm jugular venous catheter placement.
Side of Jugular Bulb Monitoring
Approximately 70% of the blood from one side of the internal carotid artery drains to the ipsilateral jugular bulb, and 30% is drained contralaterally. Although each side of the jugular bulbs receives venous drainage from both cerebral hemispheres, generally most patients have a dominant side (usually the right). We recommended that SjvO 2 should be obtained from the patient’s dominant side, especially in patients with bilateral brain injury, unless it interferes with surgical procedure. The cerebral venous dominant side can be determined by several imaging techniques, including examining the venous caliber size on the venous phase of a cerebral angiogram, size of internal jugular vein by ultrasonography, or computed tomography assessment of the jugular foramen size. Moreover, the dominant side can be determined by the effect on ICP after compression of the internal jugular veins. A greater increase in ICP is an indicator for a more prominent venous drainage.
It is controversial in patients with unilateral brain lesion as to which side the jugular venous catheter should be placed if the affected side is not the dominant side. In a study comparing between SjvO 2 from the jugular veins of the 32 patients with traumatic brain injury (TBI), the authors reported only 8 (25%) patients with the difference of SjvO 2 < 5% between right and left sides, while 15 (47%) had a maximal right-to-left difference of >15%. Another study by Beards et al. also reported that asymmetry between right and left SjvO 2 > 10% occurred in 65% of monitored time. Therefore, it is reasonable to choose the dominant side as it has greater venous flow for jugular venous catheter insertion.
Continuous Monitoring of SjvO 2 Versus Intermittent Sampling
As described earlier, catheters can be of the intravenous catheter or fiberoptic type. Regardless of which placement technique is used, arterial blood sampling should occur at the same time jugular bulb samples are obtained to interpret SjvO 2 in relation to PaCO 2 . When arterial sampling is obtained at the same time, the arterial-jugular oxygen content difference (AjvDO 2 ) can be calculated. The advantage of continuous monitoring is that it can detect intermittent hypoperfusion events, reduce frequency of sampling, and avoid error from too rapid sampling. One intraoperative study of 12 neurosurgical patients demonstrated good correlation between SjvO 2 from fiberoptic catheter (Baxter–Edwards, Santa Ana, CA) and intermittent blood samples (111 readings). In the ICU, Coplin et al. compared 195 blood gas measurements with continuous bedside oximetric values of 31 patients with TBI and reported acceptable correlation between the in vivo monitor (Baxter–Edwards, Santa Ana, CA) and intermittent in vitro co-oximetry. The sensitivity for desaturation detection was low (45%–50%) but the specificity was high (98%–100%), which implies that misdiagnosis is less of a concern. However, a prospective ICU study of 25 patients with severe TBI reported poor correlation for the first in vivo calibration before a close correlation was met later during episodes of desaturation. Therefore, these investigators proposed that the desaturation detected from in vivo monitor should be verified before therapeutic interventions to avoid unnecessary procedures. The Edslab catheter (Baxter Healthcare Corporation, Irvine, CA, USA) was also found to have good correlation in SjvO 2 values up to 24 h after calibration. Thus, it is recommended to have at least daily blood samples to calibrate the fiberoptic catheter SjvO 2 with laboratory oximetry.
The correlation between continuous SjvO 2 monitored and intermittent sampling during cardiac surgery is debatable. While some of the studies showed accurate and reliable SjvO 2 measured using the Baxter–Edwards and the Abbott systems, one study demonstrated poor agreement. Inadequate light reflection was observed in the study by Nakajima et al. during the low flow stage of CPB, which the catheter tips migrated extracranially below the jugular foramen. Low amplitude signals were also observed when the catheter touched the vessel walls. A study by Millar et al. showed limited agreement between two methods during cardiac surgery but good correlation 18 h after surgery. Wall artifacts and changes in patient position on the operating table may be the cause of these discrepancies.
Sampling Rate
Facial and retromandibular venous blood return to the heart via the internal jugular veins below the jugular bulbs. Faster rates of sampling can cause contamination from venous blood below the jugular bulb and can lead to falsely high SjvO 2 values. A study by Matta and Lam reported a significantly elevated SjvO 2 when the sampling rate was faster than 2 mL/min in mechanically ventilated patients undergoing neurosurgical procedures. Thus, it is recommended that the sampling blood should be drawn slower than 2 mL/min, especially in patients who may have reduced CBF such as hyperventilated patients or during barbiturate therapy.
Indications and Contraindications
Neurointensive Care Use
A primary role of SjvO 2 monitoring is for cerebral ischemia detection, cerebral perfusion pressure (CPP) optimization, and therapeutic hyperventilation guidance. However, there are no studies that support direct benefit of treatment guided by SjvO 2 values and outcomes in neurocritically ill patients.
Traumatic Brain Injury
Patients with TBI are susceptible to secondary ischemic insults when glucose and oxygen delivery to the brain does not meet the metabolic requirement. The most common causes of ischemic injury in patients with TBI are high ICP, hypocapnia from hyperventilation, and systemic hypotension. Currently, the Brain Trauma Foundation Guidelines for the Management of Severe Traumatic Brain Injury recommended the use of jugular venous monitoring in addition to traditional ICP and hemodynamic monitoring (level III recommendation). It is also recommended to avoid SjvO 2 < 50% to decrease mortality and improve outcomes. Patients with severe TBI who experienced at least one episode of cerebral desaturation (SjvO 2 < 50%) had an increased risk of mortality compared to those without. Cerebral desaturation commonly occurs in the first 48 h after injury, so monitoring of SjvO 2 may help with early diagnosis, treatment, and follow-up of early ischemia from intracranial or systemic causes. Moreover, high SjvO 2 (> 75%) may also be associated with poor outcomes following severe TBI. Jugular venous monitoring is helpful in optimizing therapeutic hyperventilation without causing cerebral hypoperfusion from hypocapnia. Moreover, information obtained from jugular venous monitoring can also guide fluid management and oxygenation and CPP. However, studies are needed to show direct patient outcomes benefits of jugular venous monitoring in TBI.
Aneurysmal Subarachnoid Hemorrhage (SAH)
Jugular venous monitoring is not commonly used in SAH patients, but it may also be helpful in diagnosis of cerebral ischemia and guiding appropriate treatment. A case series of 26 patients with SAH with 354 observations reported 10% of desaturation episodes, and the low SjvO 2 was associated with higher ICP and lower CPP. An observational study in 14 patients with SAH reported a significant increase in AVDO 2 can also help predict vasospasm in subsequent hours to days in patients with SAH before the onset of neurological deficits, and after treatments, symptoms also improved along with the resolution of AVDO 2 . However, there are limited data on the utilization of jugular venous monitoring in the clinical management of SAH.
Intracranial Arteriovenous Malformation (AVM)
Jugular venous oxygen monitoring can be useful in evaluating the adequacy of preoperative embolization of a large supratentorial AVM. SjvO 2 values are also correlated with the volume of AVM. After a successful embolization, SjvO 2 decreases, indicating a reduction in shunting of blood from the AVM, which reduces risk of hyperemic complications after resection. SjvO 2 monitoring has also been described in aiding antihypertensive therapy to prevent breakthrough bleeding after AVM resection.
Intraoperative Use of Jugular Venous Monitoring
Neurosurgery
The potential uses of SjvO 2 monitoring in patients undergoing craniotomy have been previously reported by Matta et al., in 1994, where authors reported the feasibility and ability to detect desaturation episodes during neurosurgery. This is important because patients undergoing neurosurgical procedures are susceptible to intraoperative cerebral ischemia from impaired autoregulation. Therefore, monitoring of hemodynamic alone may not be enough to ensure adequate cerebral oxygenation. Jugular venous oximetry can, therefore, be used to guide intraoperative hemodynamic management and determine the optimal limits of blood pressure and arterial carbon dioxide tension without interrupting operative fields in both adults and pediatrics during procedures, such as cerebral aneurysm clipping, tumor, AVM, and hematoma resections. A modest reduction in blood pressure can lead to impaired SjvO 2 , which can be addressed by raising blood pressure to the optimal goal in a personalized manner. During cerebral aneurysm surgery, SjvO 2 monitoring can be used to guide the minimum blood pressure limit without causing cerebral hypoperfusion. Moreover, SjvO 2 monitoring is also helpful when hyperventilation strategies are applied to provide brain relaxation during surgery at surgeon request.
Cardiac Surgery
During cardiopulmonary bypass (CPB), several factors contribute to inadequate cerebral oxygen delivery to meet cerebral metabolic demand, including low cerebral hypoperfusion and microembolism. Patients undergoing CPB are susceptible to neurological injury due to impaired cerebral autoregulation, and maintaining adequate CBF alone during CPB without balancing with cerebral metabolic demand may not prevent neurologic complications. SjvO 2 monitoring is useful in detecting the imbalance between CBF and CMRO 2 , which results in cerebral desaturation, particularly during a high-risk period such as rewarming. During hypothermic phases when patients are on CPB, the level of SjvO 2 increases (70%–80%) and decreases to slightly subnormal as body temperature rises during rewarming. The reported rates of cerebral desaturation during rewarming and weaning from CPB were 5%–10%, and patients with episodes of cerebral desaturation during rewarming had a higher incidence of impaired cognitive function post-CPB. Moreover, jugular venous bulb monitoring may be useful during cerebral cooling. Since direct measurement of cerebral temperature is not feasible, the jugular bulb temperature can reflect mixed cerebral venous temperature. During rewarming from deep hypothermia (< 27°c), jugular temperature is higher than nasopharyngeal temperature, indicating that jugular temperature can detect periods of brain hyperthermia that is undetected by conventional methods. Ineffective brain cooling can also result in increase in cerebral oxygen demand and low SjvO 2 .
Contraindications and Complications of Jugular Bulb Catheter Monitoring
Absolute contraindications to the jugular bulb catheter placement include unstable cervical spine injuries, presence of local neck trauma, and local infection and venous thrombosis. Relative contraindications are presence of a tracheostomy, severe coagulopathy or bleeding tendency, and impaired cerebral venous drainage.
Known complications from jugular bulb catheter placement are rare but include injuries to the surrounding structures from the catheter insertion such as hematoma, carotid artery puncture, and injuries to the stellate ganglion, cervical ganglion, and phrenic nerve. Retained catheter has also been reported
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