Monitoring Of Intracranial Pressure In Ischemic Stroke Patients

Patients with massive cerebral infarction may require ICP monitoring, as this may help to guide therapy and predict outcome. Schwab et al.102 evaluated 48 patients with massive hemispheric infarctions and clinical signs of elevated ICP. They found that ICP measurements correlated well with the patient's clinical status, CT findings and outcome, although they did not find a significant effect of their therapies for elevated ICP on patient outcomes. Multiple methods of monitoring ICP are avail able for stroke patients at risk for herniation, each with advantages and disadvantages. Unfortunately, noninvasive techniques have not proven to be sufficiently reliable for detecting elevations in ICP, and thus clinicians are left with a host of invasive techniques.

The clinical examination is a valuable tool for monitoring the patient's status and should be performed frequently during the time of concern for swelling. Clinical signs to follow include the patient's mental status and level of alertness, cranial nerve function (particularly the pupillary reaction in patients at risk for uncal herniation), motor strength, and signs of increased ICP, such as worsening headache and nausea/vomiting. Patients developing hydrocephalus often lose their upgaze (assuming that adequate upgaze was present at baseline, which is not always the case with older patients) and develop more sluggish pupillary responses. Neuroima-ging, such as CT and MRI, can be performed to assess for progression of cerebral edema, but it is not feasible or safe to perform repeat imaging more frequently than twice a day, at most. Neurosonology with TCD examination may provide clues to the development of increasing ICP, as compression of the basal arteries causes a narrowing of the vessel lumen, thereby increasing the flow velocity and the pulsi-tility index.103

For more invasive ICP monitoring, the gold standard is an external ventricular drain (EVD), which is a hollow catheter inserted directly into the ventricle, providing a direct measurement of the ICP as transmitted through the CSF.104 It also allows for CSF drainage, thereby alleviating pressure within the cranial vault. However, it is also the most invasive monitor, having to transverse not only the epidural and subdural spaces but also the brain parenchyma en route to the ventricle, and thus it poses a risk of intracerebral hemorrhage in approximately 2-6% of patients.105 It is also associated with an increased risk of infection, especially if left in place for >5 days,106 although this risk can be minimized with the use of a tunneling technique beneath the scalp.107 The prophylactic use of antibiotics remains unproven, but is considered standard of care in most Neurointensive Care Units.108

Other methods for ICP monitoring include Camino ICP monitors, which are positioned into the brain parenchyma, but do not transverse the hemisphere nearly to the degree that EVDs do, and are associated with a lower risk of intracerebral hemorrhage. The ICP is measured by a fiberoptic transducer at the tip of the cathe-ter.109 ICP monitors, however, are subject to inaccuracy over time, so-called "drift," and thus may become less reliable after the first few days post-insertion. Epidural and subarachnoid bolts/catheters are the least invasive, placed external to or just within the dura, thereby carrying a much lower risk of hemorrhage and infection, but with unfortunately compromised accuracy.110

Newer techniques include monitors capable of performing microdialysis, or measuring brain oxygenation and lactate, which may be useful in monitoring penumbral tissue adjacent to a large area of infarction.111 No randomized studies have been performed to clearly document their impact on patient outcomes to date.

EEG monitoring may be useful in acute stroke patients. Seizures are not uncommon following stroke, occurring in 6-9% of patients in the acute setting.112 The possibility of seizures in the patient with a massive stroke with cerebral edema is concerning, given that it could contribute to ICP elevations and worsen herniation effects. In one study of two groups of stroke patients, with (n = 110) and without (n = 275) seizures, the patients with seizures were significantly more likely to exhibit periodic lateralized epileptiform discharges (PLEDs) and frontal intermittent rhythmic delta activity (FIRDA).113 Some endorse the use of continuous EEG monitoring in patients with acute ischemic stroke, perhaps adding value to outcome prediction, clinical management, and seizure detection,114 but its use has not become routinely incorporated. Although it is reasonable to institute antiepileptic drug (AED) therapy in patients with ischemic stroke who have had a clinical or electro-graphic seizure, the prophylactic administration of AED therapy in patients who have not had a seizure has not been rigorously studied and cannot be routinely recommended.

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