Question 16#

Currently accepted uses of transcranial Doppler (TCD) include all of the following EXCEPT:

A. Diagnosing vasospasm after subarachnoid hemorrhage

Transcranial Doppler (TCD) measurements of middle and anterior cerebral artery blood flow velocity are useful for the diagnosis of cerebral vasospasm after subarachnoid hemorrhage. Qureshi et al demonstrated that an increase in the middle cerebral artery mean flow velocity as assessed by TCD is an independent predictor of symptomatic vasospasm in a prospective study of patients with aneurysmal subarachnoid hemorrhage. In addition, while some have proposed using TCD to estimate ICP, studies have shown that TCD is not a reliable method for estimating ICP and CPP, and currently cannot be endorsed for this purpose. TCD also is useful to confirm the clinical examination for determining brain death in patients with confounding factors such as the presence of CNS depressants or metabolic encephalopathy. 

Question 17#

Regarding jugular venous oximetry in patients with TBI:

A. It requires placement of a catheter in the jugular bulb

When the arterial oxygen content, hemoglobin concentration, and the oxyhemoglobin dissociation curve are constant, changes in jugular venous oxygen saturation (Sjo₂) reflect changes in the difference between cerebral oxygen delivery and demand. Generally, a decrease in Sjo₂ reflects cerebral hypoperfusion, whereas an increase in Sjo₂ indicates the presence of hyperemia. Sjo₂ monitoring cannot detect decreases in regional cerebral blood flow if overall perfusion is normal or above normal. This technique requires the placement of a catheter in the jugular bulb, usually via the internal jugular vein. Catheters that permit intermittent aspiration of jugular venous blood for analysis or continuous oximetry catheters are available. Low Sjo₂ is associated with poor outcomes after TBI. Nevertheless, the value of monitoring Sjo₂ remains unproven. If it is employed, it should not be the sole monitoring technique, but rather should be used in conjunction with ICP and CPP monitoring. By monitoring ICP, CPP, and Sjo₂, early intervention with volume, vasopressors, and hyperventilation has been shown to prevent ischemic events in patients with TBI.

Question 18#

Monitoring local brain tissue oxygen tension (PbtO₂) in patients with severe TBI:

A. Has shown that normal ICP and CPP generally precludes the presence of brain tissue ischemia

While the standard of care for patients with severe TBI includes ICP and CPP monitoring, this strategy does not always prevent secondary brain injury. Growing evidence suggests that monitoring local brain tissue oxygen tension (PbtO₂) may be a useful adjunct to ICP monitoring in these patients. Normal values for PbtO₂ are 20 to 40 mm Hg, and critical levels are 8 to 10 mm Hg. A recent clinical study sought to determine whether the addition of a PbtO₂ monitor to guide therapy in severe TBI was associated with improved patient outcomes. Mortality was significantly lower in the patients who had therapy guided by PbtO₂ monitoring in addition to ICP and CPP (25%; P < 0.05). The benefits of PbtO₂ monitoring may include the early detection of brain tissue ischemia despite normal ICP and CPP. In addition, PbtO₂-guided management may reduce potential adverse effects associated with therapies to maintain ICP and CPP.