Central hyperventilation, Neuro herniation, cushing triad, breathing patterns

also see Increased ICP, acute management

• Central hyperventilation = sustained, rapid, and fairly deep hyperpnea,
• vs rapid, shallow respirations of simple tachypnea.

Signs of subacute increase in ICP

• patients who have elevated intracranial pressure from a mass lesion or hydrocephalus initially exhibit
  • lethargy, irritability, somnolence, and headache
  • may vomit and complain of horizontal diplopia (double vision side-to-side) from an abducens palsy that is triggered by compression of the nerve toward the edge of the tentorium cerebri.
• Physical examination may reveal:
  • head tilt from strabismus or pressure on the cervical spine nerve roots
  • bilateral small-to-midposition, poorly reactive pupils.
  • Papilledema may be absent in children in whom increased intracranial pressure is evolving rapidly or among infants who have open fontanelles.
• Infants may display additional findings, including
  • shrill, inconsolable cry
  • bulging anterior fontanelle and split cranial sutures
  • increased head circumference
  • "sunsetting" eyes (Parinaud syndrome) or persistent downward deviation of gaze that is due to pressure upon the dorsal midbrain.
    
     

Signs of acutely increased ICP

• earliest signs are decreased level of consciousness and alterations in the respiratory pattern
• Patients who have central hyperventilation may have hypertension and bradycardia (Cushing triad).

If increased intracranial pressure from a supratentorial mass lesion proceeds unrecognized, stupor progresses to coma. Signs advance rostrocaudally from compression of the contralateral hemisphere or thalamus. During herniation, specific signs  develop as injury progresses inferiorly along the brainstem

1. Low diencephalic stage (thalamic level)
   • dilated pupil ipsilateral to the supratentorial lesion and an ipsilateral hemiparesis (a false localizing sign, due to pressure on the contralateral pyramidal long tract fibers against the tentorium) - those fibers are crossing from the contralateral to ipsilateral side
   • comatose
   • Cheyne-Stokes respirations (crescendo-decrescendo hyperventilation to apnea)
   • small and sluggishly reactive pupils
   • doll's eyes (oculocephalic) - (cortical control gone, brainstem intact)
   • caloric (oculovestibular) reflexes
   • decorticate response to pain (flexion of the upper extremities and extension/internal rotation of the lower extremities)
2. Later, at the midbrain stage
   • respiratory pattern changes to sustained central hyperventilation
   • pupils become midposition and fixed (midbrain = midposition)
   • a stereotyped decerebrate (extensor/internal rotation of all extremities) posturing to noxious stimuli.
3. At the pontine stage
   • hyperventilation gives way to apneustic breathing (deep respirations with prolonged pauses)
   • pupils are small-to-pinpoint and nonreactive (pontine = pinpoint)
   • caloric and doll's eyes reflexes may be absent.
   • finally, the extremities become flaccid with absent motor response, breathing becomes irreversible ataxic, and death ensues.

To rephrase:

• respirations: Cheyne-stokes -- central hyperventilatio -- apneustic breathing -- ataxic
• eyes: small, reactive, intact dolls eyes and calorics -- midposition, fixed -- pinpoint, nonreactive, absent reflexes
• motor: decorticate -- decerebrate -- flaccid

Loss of pupillary response is typical for a midbrain or pontine brainstem process and, combined with loss of consciousness, should alert the clinician to the possibility of impending uncal herniation.

Other causes for bilateral loss of pupillary reflex should be considered only after the possibility of increased intracranial pressure has been excluded.

• pilocarpine drops
• atropine drops
• opiates
• cocaine
• jimson weed

Decreased oxygen saturation and diminished mental status are nonspecific findings that can characterize many processes other than central hyperventilation, such as hypoxia secondary to pulmonary disease. A decreased arterial carbon dioxide pressure can be seen in hyperventilation attacks or psychogenic hyperventilation as well as central hyperventilation. Sternal retractions are typical of hypoxia in patients who have lower airway disease and are not a feature of central hyperventilation.

Workup

• Head computed tomography (CT) is the diagnostic procedure of choice  for assessing acutely increased intracranialpressure because it is readily available; study time is short; and airway, breathing, and circulation can be maintained and monitored easily.
• Magnetic resonance imaging (MRI) is more cumbersome in the critically ill child, with a longer scanning time and greater difficulty in managing mechanical ventilation because of limited access to the patient.
• Ultrasonography is a useful screening tool for hydrocephalus, intraventricular hemorrhage, and periventricular leukomalacia in infants whose open anterior fontanelles provide an acoustic window for images of the brain, but it is not as useful in an older child.
• Lumbar puncture is contraindicated in any patient in whom increased intracranial pressure is suspected, even in the absence of papilledema, until CT or MRI has ruled out any possible risk of brain herniation.
• Electroencephalography is useful in the evaluation of seizures and to augment the neurologic examination in coma, but it has no role in the acute evaluation of elevated intracranial pressure.
• A toxicology screen could be useful in the evaluation of a child who has unreactive, small pupils that suggest ingestion of opiates,  phenothiazines, or organophosphates, but it is not indicated when signs of increased intracranial pressure are present.

Increased ICP, acute management

References:
Bergman I. Increased intracranial pressure. Pediatr Rev. 1994;15:241-244
Rubenstein JS. Initial management of coma and altered consciousness in
the pediatric patient. Pediatr Rev. 1994;15:204-207
Stokes DC. Respiratory failure. Pediatr Rev. 1997;18:361-366
Haslam RH. Neurologic evaluation: special diagnostic procedures. In:
Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of
Pediatrics. 16th ed. Philadelphia, Pa: WB Saunders Co; 2000:1800-1803
Larsen GY, Goldstein B. Consultation with the specialist. Increased
intracranial pressure. Pediatr Rev. 1999;20:234-239
Morriss MC, Hyder DJ, Zimmerman RA. Neurodiagnostic techniques.
Pediatr Rev. 1997;18:192-203