7.2 Central Nervous System Infections & Increased Intracranial Pressure

Central Nervous System Infections & Increased Intracranial Pressure

Quick Clinical Summary: Acute central nervous system (CNS) infections and intracranial hypertension represent time-critical pediatric neurological emergencies. Bacterial meningitis triggers intense subarachnoid purulent inflammation, cerebral vasculitis, and cerebral edema that can lead to permanent neurosensory loss, brain herniation, or death within hours. Pediatric nurses must rapidly interpret age-specific clinical manifestations—recognizing subtle paradoxical irritability in infants versus classic meningeal signs in older children—differentiate cerebrospinal fluid (CSF) profiles, initiate empirical antimicrobials with adjunctive dexamethasone, and enforce droplet precautions. Concurrently, managing increased intracranial pressure (ICP) hinges on the Monro-Kellie hypothesis, vigilance for late pre-herniation warnings (Cushing's triad), and rigid execution of midline positioning, normothermia, and hyperosmolar therapy.

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1. Acute Bacterial Meningitis: Pathophysiology & Age-Specific Pathogens

Acute bacterial meningitis is a severe infectious inflammation of the meninges (arachnoid mater, pia mater, and intervening cerebrospinal fluid-filled subarachnoid space). Pathogens typically colonize the nasopharynx or respiratory epithelium, invade the bloodstream (bacteremia), breach the blood-brain barrier via receptor-mediated transcytosis, and multiply rapidly within the immunologically vulnerable subarachnoid space.

Bacterial lysis releases toxic cell wall fragments (endotoxin, lipopolysaccharides, peptidoglycans), triggering massive release of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6). This induces:

1. Vasogenic Edema: Disruption of tight junctions in the cerebral capillary endothelium, flooding the interstitium with albumin and plasma.
2. Cytotoxic Edema: Intracellular accumulation of water and sodium within astrocytes and neurons secondary to cellular energy failure and toxic mediators.
3. Interstitial Edema: Blockage of CSF resorption at the arachnoid villi by purulent, viscous exudate, leading to non-communicating or communicating hydrocephalus.
4. Cerebral Vasculitis & Thrombosis: Inflammation of cortical vessels resulting in focal cerebral ischemia, infarction, and irreversible encephalomalacia.

Age-Stratified Microbiological Etiologies

The causative microorganisms of pediatric bacterial meningitis are strictly age-dependent:

NEONATES (0 TO 28 DAYS):
  * Group B Streptococcus (Streptococcus agalactiae) [Most common: ~50%]
  * Escherichia coli (and other Gram-negative enteric bacilli, e.g., Klebsiella)
  * Listeria monocytogenes

INFANTS & CHILDREN (1 MONTH TO ADOLESCENCE):
  * Streptococcus pneumoniae (Pneumococcus) [Leading cause; high morbidity & hearing loss]
  * Neisseria meningitidis (Meningococcus) [Epidemic potential; petechial/purpuric rash]
  * Haemophilus influenzae type b (Hib) [Dramatically reduced in vaccinated populations]

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2. Clinical Manifestations: Infants vs. Older Children & Meningeal Signs

Clinical presentation differs fundamentally based on neurodevelopmental maturity and whether cranial fontanelles and sutures are open or closed.

Manifestations in Neonates & Young Infants (<1 Year)

In young infants, the classical signs of meningeal irritation are absent due to immature neuromotor reflexes and open fontanelles which accommodate expanding intracranial volume without acute nuchal rigidity. The presentation is notoriously subtle, non-specific, and insidious:

• Paradoxical Irritability (Characteristic Behavioral Sign):

• Fontanelle Changes: Full, bulging, tense, or non-pulsatile anterior fontanelle (best examined when the infant is upright and quiet/not crying).
• High-Pitched Piercing Cry: A shrill, inconsolable, sharp cry reflecting severe meningeal pain and intracranial irritation.
• Feeding Patterns & Lethargy: Poor suck, refusal to feed, projectile vomiting, and extreme somnolence or difficult arousal.
• Thermoregulatory Instability: While fever may occur, neonates frequently manifest hypothermia (temperature <36.0°C [96.8°F]), cold and clammy extremities, gray/mottled skin, and bradycardia or apnea.

Manifestations in Older Children & Adolescents

In children older than 1 to 2 years, presentation mirrors adult meningitis with the classic clinical triad:

1. Fever (acute, high-grade, often accompanied by rigors)
2. Severe, throbbing generalized headache (worsened by head motion, coughing, or light)
3. Altered mental status (confusion, irritability, delirium, lethargy progressing to stupor)

Clinical Examination of Meningeal Irritation

• Nuchal Rigidity: Severe stiffness and resistance when the examiner attempts to passively flex the child's neck toward the chest. The child resists motion to avoid stretching the inflamed posterior cervical meninges.
• Kernig's Sign: With the child lying supine, the examiner flexes the hip and knee to 90 degrees, and then attempts to extend the knee. A positive sign is elicited when passive knee extension is resisted or produces severe pain and hamstring spasm along the posterior thigh.
• Brudzinski's Sign: With the child lying supine, the examiner passively flexes the neck toward the chest. A positive sign occurs when the child involuntarily flexes both hips and knees in response, demonstrating an involuntary reflex to relieve meningeal tension.

KERNIG'S SIGN: Hip flexed 90 deg -> Attempt knee extension -> Resistance / Pain in hamstrings
BRUDZINSKI'S SIGN: Passive neck flexion -> Involuntary reflexive flexion of hips and knees

Petechial & Purpuric Rashes (Meningococcemia)

The development of a non-blanching petechial or purpuric rash in a febrile child is a catastrophic medical emergency indicating invasive meningococcal disease (Neisseria meningitidis):

• Lesions begin as small, discrete, erythematous maculopapules that rapidly transform within hours into non-blanching petechiae and coalescent, ecchymotic purpura (purpura fulminans).
• Indicates widespread vascular endothelial necrosis, microvascular thrombosis, disseminated intravascular coagulation (DIC), severe septic shock, and bilateral adrenal hemorrhage (Waterhouse-Friderichsen syndrome).

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3. Cerebrospinal Fluid (CSF) Analysis & Diagnostic Matrix

Definitive diagnosis requires a lumbar puncture (LP), typically performed at the L3–L4 or L4–L5 vertebral interspace. Lumbar puncture must be immediately performed unless contraindicated by signs of impending brain herniation (focal neurological deficits, papilledema, Cushing's triad, pupillary asymmetry) or severe cardiopulmonary instability, in which case blood cultures must be drawn and empirical IV antibiotics administered immediately without waiting for imaging or LP.

Diagnostic Lumbar Puncture Profiles

Why does CSF glucose drop in bacterial meningitis? Bacteria consume glucose for metabolic survival, but more importantly, inflammatory cytokines and damaged blood-brain barrier transport systems severely impair active, facilitated glucose transport across cerebral capillary endothelium into the CSF space.

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4. Infection Control, Empirical Antimicrobial Protocols & Chemoprophylaxis

Infection Control & Isolation Mandates

• Droplet Precautions: All patients with suspected or confirmed bacterial meningitis must be immediately placed in a private room under Droplet Precautions (surgical mask worn within 3–6 feet of patient, eye protection if splashing anticipated).
• Duration of Precautions: Droplet precautions must be maintained until the patient has completed at least 24 continuous hours of effective intravenous antimicrobial therapy that clears nasopharyngeal colonization (specifically applicable to Neisseria meningitidis and Haemophilus influenzae type b).

Empirical Intravenous Antibiotic Therapy

Antibiotics must never be delayed for imaging, diagnostic procedures, or bed placement:

• Neonates (<28 Days):
  • IV Ampicillin (to cover Listeria monocytogenes and Group B Streptococcus) PLUS IV Gentamicin (aminoglycoside) OR IV Cefotaxime.

• Infants & Children (>1 Month to Adolescents):
  • IV Vancomycin (15 mg/kg IV q6h; to provide definitive coverage against penicillin- and cephalosporin-resistant Streptococcus pneumoniae) PLUS IV Ceftriaxone (50 mg/kg IV q12h or 100 mg/kg q24h) OR IV Cefotaxime (third-generation cephalosporins providing high CSF bactericidal penetration against N. meningitidis, H. influenzae, and susceptible S. pneumoniae).

Adjunctive Dexamethasone Protocol

• Indication & Timing: Intravenous dexamethasone (0.15 mg/kg IV every 6 hours for 2 to 4 days) is recommended in infants and children ≥6 weeks of age with suspected or confirmed H. influenzae type b, and strongly considered in S. pneumoniae meningitis.
• Critical Administration Rule: Dexamethasone must be administered prior to or concurrently with the very first dose of intravenous antibiotics. Administering dexamethasone blunts the massive inflammatory surge of TNF-alpha and IL-1 triggered when bactericidal antibiotics lyse bacterial cell walls. In clinical trials, early dexamethasone dramatically reduces the incidence of sensorineural hearing loss and long-term neurological sequelae. If antibiotics have already been running for hours, post-antibiotic steroids provide no documented neuroprotective benefit.

Close Contact Post-Exposure Chemoprophylaxis

Chemoprophylaxis eradicates nasopharyngeal carriage of Neisseria meningitidis in close contacts to prevent secondary transmission:

• Definition of Close Contacts: Household members, daycare center contacts, roommates, anyone directly exposed to the index patient's oral secretions within 7 days prior to onset (e.g., mouth-to-mouth resuscitation, endotracheal intubation, or suctioning without wearing a surgical mask).
• First-Line Chemoprophylaxis Regimens for Meningococcal Disease:
  1. Oral Rifampin:
     • Children ≥1 month: 10 mg/kg PO every 12 hours for 4 doses (2 days) (max 600 mg/dose).
     • Neonates <1 month: 5 mg/kg PO every 12 hours for 4 doses.
     • Family Counseling: Warn patients and families that rifampin causes harmless, reversible red-orange discoloration of urine, saliva, sweat, tears, and will permanently stain soft contact lenses. It also induces cytochrome P450 enzymes, reducing the efficacy of oral contraceptive pills.
  2. Intramuscular Ceftriaxone: Single IM dose (125 mg for children <15 years; 250 mg for adults/teens ≥15 years). Regimen of choice for pregnant close contacts and infants <1 month.
  3. Oral Ciprofloxacin: Single oral dose (500 mg) for adults and older adolescents.

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5. Increased Intracranial Pressure (ICP) & The Monro-Kellie Hypothesis

The Monro-Kellie Doctrine

The cranial vault is a rigid, non-distensible bony structure with a fixed internal volume. Under normal physiological conditions, intracranial contents consist of three dynamic compartments:

1. Brain Tissue Parenchyma: ~80% of total intracranial volume.
2. Cerebrospinal Fluid (CSF): ~10% of total volume.
3. Intravascular Blood (Arterial and Venous): ~10% of total volume.

Total Intracranial Volume = V(Brain) + V(CSF) + V(Blood) = CONSTANT

The Monro-Kellie hypothesis dictates that because the total volume is fixed, an increase in the volume of one compartment must be compensated by an equal, reciprocal reduction in the volume of another compartment to maintain normal intracranial pressure (ICP):

• Compensatory Phase: When a mass lesion, cerebral edema, or ventricular fluid expands, the body compensates by displacing CSF downward into the distensible spinal subarachnoid space, accelerating CSF absorption at arachnoid granulations, and compressing low-pressure cerebral venous sinuses to shoo venous blood into the internal jugular veins.
• Decompensation Phase: Once compensatory spatial displacement is exhausted, the compliance curve turns sharply vertical. Tiny subsequent increases in intracranial volume produce catastrophic, exponential spikes in ICP, collapsing cerebral perfusion pressure and driving brain tissue through internal cranial apertures (cerebral herniation).

Normal Pediatric ICP: Infants: 1.5–6 mmHg | Children: 3–7 mmHg | Adolescents: 10–15 mmHg
Pathological Threshold: Sustained ICP > 20 mmHg requires aggressive therapeutic intervention

Clinical Manifestations of Increased ICP Across Ages

Why CN VI Palsy? The sixth cranial nerve (abducens) has the longest intracranial pathway along the base of the skull, making it exceptionally vulnerable to compression and traction when brain tissue shifts downward under high ICP.

Cushing's Triad: The Pre-Terminal Herniation Warning

Cushing's triad is a late, ominous physiological response to severe, life-threatening intracranial hypertension and brainstem compression (typically signifying transtentorial or tonsillar herniation). It is caused by severe ischemia of the medullary vasomotor center:

CUSHING'S TRIAD (Pre-Herniation Signs):
1. BRADYCARDIA (Marked drop in heart rate; baroreceptor-mediated vagal response)
2. IRREGULAR, DEPRESSED RESPIRATIONS (Cheyne-Stokes breathing, central neurogenic hyperventilation, or apnea)
3. WIDENED PULSE PRESSURE WITH SYSTOLIC HYPERTENSION (Progressive increase in systolic BP with stable/falling diastolic BP)

The Hemodynamic Mechanism: When ICP exceeds mean arterial pressure, cerebral blood flow halts, causing profound ischemia of medullary neurons. The sympathetic nervous system mounts a massive adrenergic surge to force blood through cerebral capillaries, causing severe systolic hypertension. Carotid sinus and aortic arch baroreceptors detect this extreme hypertension and trigger intense parasympathetic (vagal) output to the heart, generating profound bradycardia. Concurrently, downward compression of the pontine and medullary respiratory control centers disrupts automated breathing rhythms.

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6. Multimodal Nursing Management of Increased Intracranial Pressure

Managing increased ICP centers on optimizing Cerebral Perfusion Pressure (CPP), defined mathematically as:

CPP = MAP (Mean Arterial Pressure) - ICP
Pediatric Target CPP: Infants: 40–50 mmHg | Young Children: 50–60 mmHg | Older Adolescents: >60–70 mmHg

Evidence-Based Nursing Interventions Matrix for Increased ICP

Hyperosmolar Pharmacotherapy Monitoring

• Hypertonic Saline (3% NaCl): Target serum sodium is typically 145 to 155 mEq/L; target serum osmolality <360 mOsm/L. Serum sodium must be drawn every 4 to 6 hours. Central venous access is preferred to prevent peripheral vein phlebitis.
• Mannitol (20%): Target serum osmolality is <320 mOsm/L (serum osmolality >320 mOsm/L induces acute renal tubular necrosis). An indwelling Foley catheter is mandatory to measure rapid osmotic diuresis and prevent bladder distension. Always inspect the vial for crystallization prior to administration; always use an in-line intravenous filter.