Ischemic stroke
After subarachnoid hemorrhage delayed onset vasospasm can result in devastating ischemic stroke.
Ischemia results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute.
Epidemiology
Classification
Perinatal arterial ischemic stroke.
Pathogenesis
Cerebral Ischemia Pathogenesis
There are four categories of cerebral hypoxia; they are, in order of severity:
Diffuse cerebral hypoxia (DCH),
Focal cerebral ischemia, cerebral infarction, and global cerebral ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis, resulting in a hypoxic brain injury.
Etiology
pneumothorax,MI,CHF…
The cranial cavity is a closed compartment and any breach to this confined space secondary to neurosurgery or trauma causes an imbalance between atmospheric pressure and intracranial pressure. As the altitude increases, the atmospheric pressure decreases, and hypoxia with hypercarbia is a well-known fact. In children, there is an argument to suggest that hypoxia can contribute to a mild increase in intracranial pressure during commercial flights 1).
Many competitive breath-hold divers use dry apnoea routines to improve their tolerance to hypoxia and hypercapnia, varying the amount of prior hyperventilation and lung volume. When hyperventilating and exhaling to residual volume prior to starting a breath-hold, hypoxia is reached quickly and without too much discomfort from the respiratory drive. Cerebral hypoxia with loss of consciousness (LOC) can easily result.
Valdivia-Valdivia et al. from the Neurosurgery Department, St. Joseph's Hospital, Tampa report on a case where an unsupervised diver used a nose clip that is thought to have interfered with his resumption of breathing after LOC. Consequently, he suffered an extended period of severe hypoxia, with poor ventilation and recovery. He also held his breath on empty lungs; thus, trying to inhale created an intrathoracic sub-atmospheric pressure. Upon imaging at the hospital, severe intralobular pulmonary edema was noted, with similarities to images presented in divers suffering from pulmonary barotrauma of descent (squeeze, immersion pulmonary edema). Describing the physiological phenomena observed in this case highlights the risks associated with unsupervised exhalatory breath-holding after hyperventilation as a training practice in competitive freediving 2).
Risk factors
Pathophysiology
In brain tissue, a biochemical cascade known as the ischemic cascade is triggered when the tissue becomes ischemic, potentially resulting in damage to and death of brain cells.
Clinical features
Delirium, agitation or combativeness.
Pupils: Dilate widely with hypoxia.
Diagnosis
see Acute Ischemic stroke diagnosis
Treatment
see Ischemic stroke treatment.
Prevention
Choice of oral anticoagulant: compared to vitamin K antagonists (VKAs) (e.g. warfarin), the novel oral anticoagulants (NOACs) dabigatran, rivaroxaban & edoxaban are at least as effective in preventing ischemic stroke and systemic embolization in patient with atrial fibrillation.
Complications
see Ischemic stroke complications.
Outcome
Ischemic stroke is a major cause of death and long-term disability worldwide.
Books
Ischemic Stroke (Emergency Management in Neurology) By Giuseppe D'Aliberti, Marco Longoni, Valentina Oppo, Valentina Perini, Luca Valvassori, Simone Vidale, Cristina Motto