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Hemodynamic Instability


The utmost objective of anesthetic management of neurosurgical patients is the maintenance of adequate cerebral perfusion pressure (CPP) that prevents any secondary injury to the brain and spinal cord. Hemodynamic instability is often encountered intraoperatively or postoperatively and encompasses both hypotension and hypertension along with changes in heart rate. Specifically related to the brain, hypotension may decrease cerebral blood flow (CBF) causing ischemia, while hypertension may raise CBF, thereby increasing intracranial pressure (ICP) and edema and may even cause hemorrhaging. An interplay of systemic, neurogenic, and cardiogenic factors make blood pressure (BP) labile.

Prevention

Careful intraoperative positioning, monitoring of vitals, maintenance of adequate central venous pressure, and hematocrit are mainstays for the prevention of intraoperative hemodynamic variability. Arterial BP monitoring with transducer zeroed at the level of external auditory meatus gives an accurate beat-to-beat measurement. Noninvasive cardiac output monitors can be used in patients with preexisting heart disease.

Hemodynamic Instability in Specific Situations

Craniotomy for Tumor Excision

Brain stem handling during tumor excision is common, and it manifests as hypertension or hypotension, bradycardia or tachycardia ( Table 2 ). Surgeons should be immediately informed so that surgical stimulus can be promptly withdrawn. It is not advisable to pharmacologically treat it because it may mask further brain stem handling. Massive blood loss may result in hypovolemic hypotension and require fluids, blood, and resuscitation. Trigeminocardiac reflex (TCR) may result in bradycardia and hypotension due to stimulation of any sensory branch of a trigeminal nerve along its intracranial or extracranial course. It usually resolves on its own if stimulation is stopped, but in severe cases, a vagolytic may have to be administered. However, it should also be remembered that TCR may also manifest as a pressor response. At the end of craniotomy closure, negative pressure applied via a vacuum device connected to a drain placed in the extradural space has been reported to cause a sudden decrease in ICP, resulting in bradycardia.

Table 1
Reasons for Hemodynamic Instability in Neurosurgical Patients
Hypertension Hypotension
Systemic

  • Essential hypertension

  • Laryngoscopy and intubation

  • Incision

  • Pin fixation

  • Light level of anesthesia

  • Pain

  • Hypercarbia

  • Bladder distension

  • Autonomic neuropathy (e.g. Guillain–Barré syndrome)

Neurosurgical

  • Raised ICP: Tumor, ICH, SAH, AIS, TBI

  • Brain stem handling

  • Emergence

  • Induced hypertension for vasospasm

  • Postcarotid endarterectomy

  • Autonomic dysreflexia (SCI above T6)

Systemic

  • Preexisting cardiomyopathy

  • Arrhythmias

  • Cardiac failure

  • MI

  • Hypovolemia due to decreased intake, diuretics, Diabetes insipidus, cerebral salt wasting syndrome, hemorrhage from systemic injuries, surgical blood loss

  • Anesthesia drugs

  • Anaphylaxis

  • Sepsis

  • Tension Pneumothorax

  • Cardiac tamponade

  • Adrenal insufficiency

  • Autonomic neuropathy

Neurosurgical

  • Neurogenic stunned myocardium

  • Spinal shock

  • Carotid body stimulation

  • TCR

  • Brain stem handling

  • Hypothalamic lesions

  • Pituitary failure

Bradycardia Tachycardia

  • As part of the Cushing reflex (bradycardia, hypotension, and respiratory disturbances)

  • Brain stem handling during surgery

  • As part of TCR

  • Vagal stimulation

  • Acute spinal shock

  • Autonomic dysreflexia

  • Cardiac conduction disturbances

  • Drugs (calcium channel blockers, β-blockers, digitalis, etc.)

  • Hypothyroidism

  • Hypothermia

  • Hypoxia

  • Hypovolemia

  • Sudden blood loss

  • Pain

  • Fever

  • Hypercarbia

  • Lighter plane of anesthesia

  • Brain stem handling

  • Cardiac causes

  • Drugs (anticholinergics, adrenaline, dopamine, etc.)

  • Hyperthyroidism

ICH, Intracranial Hemorrhage; SAH, Subarachnoid hemorrhage; AIS, Acute ischemic stroke; TBI, Traumatic brain injury; SCI, Spinal cord injury.

Table 2
Hemodynamic Response During Stimulation of Structures
Structures Response
Trigeminal nerve stimulation Hypotension and bradycardia or hypertension and tachycardia
Vagus nerve stimulation Hypotension and/or bradycardia
Brain stem handling Hypotension/hypertension, bradycardia/tachycardia

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