14.2 Geriatric Burn Care: Thin Dermis, Altered Fluid Tolerance, Pre-existing Comorbidities, and Mortality Prognostication (Baux Score)

14.2 Geriatric Burn Care: Thin Dermis, Altered Fluid Tolerance, Pre-existing Comorbidities, and Mortality Prognostication (Baux Score)

Core Knowledge: The geriatric population (>= 65 years) represents the fastest-growing demographic in modern burn centers and carries disproportionately high morbidity and mortality following thermal injury. Even modest burns (10% to 20% TBSA) in older adults carry mortality rates equivalent to massive burns (>50% TBSA) in younger cohorts. This heightened vulnerability stems from skin atrophy, reduced physiological organ reserve, baseline frailty, and pre-existing cardiopulmonary and renal comorbidities. Successful management requires conservative fluid titration, advanced hemodynamic monitoring, aggressive delirium prevention, and early multidisciplinary goals-of-care discussions.

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1. Pathophysiological Vulnerabilities of Aging Skin

Cutaneous aging (dermatoporosis) fundamentally alters the skin's structural integrity and regenerative capacity:

                 AGE-RELATED CUTANEOUS PATHOPHYSIOLOGY IN BURNS
  ┌────────────────────────────────────────────────────────────────────────┐
  │ 1. EPIDERMAL AND DERMAL ATROPHY                                        │
  │ • Marked thinning of the stratum spinosum and dermal collagen matrix.  │
  │ • Low thermal inertia: Heat conducts rapidly into deep dermal and      │
  │   subcutaneous vascular plexuses.                                      │
  │ • Superficial scalds/flames convert to FULL-THICKNESS BURNS in seconds.│
  ├────────────────────────────────────────────────────────────────────────┤
  │ 2. FLATTENING OF RETE RIDGES (Dermo-Epidermal Junction)                │
  │ • Interlocking dermal papillae and epidermal rete pegs become flattened│
  │ • Greatly reduced mechanical resistance to shearing forces.           │
  │ • Extensive blister formation and epidermal peeling under minimal tape │
  │   or shear stress.                                                     │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 3. LOSS OF DERMAL APPENDAGES AND STEM CELL POOLS                       │
  │ • Hair follicles, sebaceous glands, and eccrine sweat glands atrophy.  │
  │ • Loss of follicular epithelial stem cells that drive spontaneous      │
  │   re-epithelialization in partial-thickness burns.                     │
  │ • Spontaneous wound healing is severely prolonged or absent, requiring│
  │   earlier surgical excision and skin grafting.                         │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 4. REDUCED MICROVASCULAR DENSITY AND SENSORY INNERVATION               │
  │ • Diminished dermal capillary loops impair inflammatory hyperemia and  │
  │   tissue oxygen delivery.                                              │
  │ • Diabetic neuropathy and reduced cutaneous thermoreceptors delay      │
  │   escape reflexes during hot bath or heating pad contact.              │
  └────────────────────────────────────────────────────────────────────────┘

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2. Cardiopulmonary and Renal Senescence: The Narrow Resuscitation Window

Resuscitation in older adults is complicated by pre-existing organ senescence and a severely contracted physiological reserve. The margin between under-resuscitation and lethal fluid overload is extraordinarily narrow.

                   THE NARROW GERIATRIC RESUSCITATION WINDOW
  ┌────────────────────────────────────────┬────────────────────────────────────────┐
  │ RISK OF UNDER-RESUSCITATION            │ RISK OF OVER-RESUSCITATION             │
  ├────────────────────────────────────────┼────────────────────────────────────────┤
  │ • Decreased baseline GFR & nephron loss│ • Diastolic dysfunction & stiff LV     │
  │ • Rapid Acute Tubular Necrosis (ATN)   │ • Flash Cardiogenic Pulmonary Edema    │
  │ • Splanchnic vasoconstriction ->       │ • Exacerbation of Fluid Creep          │
  │   Non-occlusive Mesenteric Ischemia    │ • Abdominal Compartment Syndrome (ACS) │
  │ • Deepening metabolic acidosis         │ • Prolonged mechanical ventilation     │
  └────────────────────────────────────────┴────────────────────────────────────────┘

Organ-Specific Resuscitation Challenges:

1. Cardiovascular Impairment: Older hearts frequently feature concentric left ventricular hypertrophy, impaired myocardial relaxation (diastolic dysfunction / HFpEF), and blunted beta-adrenergic responsiveness. When subjected to standard high-volume crystalloid resuscitation ($>4\text{ mL/kg/%TBSA}$), the non-compliant left ventricle cannot accommodate the sudden volume expansion, resulting in elevated left atrial pressures and acute flash pulmonary edema.
2. Renal Senescence: Normal aging produces progressive glomerulosclerosis and tubular atrophy, reducing baseline glomerular filtration rate by approximately $1\text{ mL/min/year}$ after age 40. Furthermore, the aging kidney loses tubular concentrating ability and free water excretion. In the face of hypovolemia, older patients develop oliguric acute kidney injury (AKI) rapidly; however, aggressively forcing urine output with crystalloid boluses induces severe fluid overload.
3. Pulmonary Vulnerability: Decreased chest wall compliance (calcified costal cartilages, kyphosis), loss of alveolar elastic recoil, and underlying chronic obstructive pulmonary disease (COPD) impair gas exchange. Fluid overload rapidly precipitates respiratory failure and ventilator dependence.

Clinical Management Strategy:

• Conservative Crystalloid Resuscitation: Initiate fluid resuscitation at 2.0 to 3.0 mL/kg/%TBSA of Lactated Ringer's rather than supranormal rates.
• Target Urine Output: Maintain adult urine output at 0.3 to 0.5 mL/kg/hr (or $30\text{--}50\text{ mL/hr}$). Avoid chasing high urine outputs with excessive crystalloids.
• Advanced Dynamic Monitoring: Early placement of arterial lines for continuous blood pressure and arterial blood gas analysis (tracking lactate clearance and base deficit). Utilize bedside echocardiography (evaluating inferior vena cava collapsibility and cardiac contractility) and pulse contour cardiac output monitoring (SVV/PPV) rather than static central venous pressure (CVP).
• Early Albumin / Colloid Rescue: If resuscitation fluid requirements exceed predicted volumes or fluid creep ensues, initiate early $5%$ albumin infusion ($0.5\text{--}1.0\text{ mL/kg/%TBSA}$) at 8 to 12 hours post-injury to restore intravascular oncotic pressure and minimize edema.

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3. Mortality Prognostication: The Baux and Revised Baux (rBaux) Scores

Objective mortality prediction is vital in geriatric burn care to guide clinical decision-making, set realistic expectations, and inform timely palliative discussions.

                       BAUX & REVISED BAUX SCORING SYSTEMS
  ┌────────────────────────────────────────────────────────────────────────┐
  │ CLASSIC BAUX SCORE:                                                    │
  │               $$\text{Baux Score} = \text{Age (years)} + \%\text{TBSA}$$│
  │ • Historical standard; score ≥ 100 historically predicted ~50% mortality│
  ├────────────────────────────────────────────────────────────────────────┤
  │ REVISED BAUX SCORE (rBaux) [Modern Standard]:                          │
  │   $$\text{rBaux} = \text{Age (years)} + \%\text{TBSA} + [17 \times (\text{Inhalation Injury})]$$│
  │ • Inhalation Injury: 1 if present (bronchoscopy confirmed), 0 if absent│
  │ • Inhalation adds a heavy mortality penalty (+17 points)               │
  └────────────────────────────────────────────────────────────────────────┘

                     rBAUX MORTALITY PROBABILITY MATRIX
  ┌───────────────────────┬────────────────────────────────────────────────┐
  │ rBaux Score Range     │ Estimated In-Hospital Mortality Risk           │
  ├───────────────────────┼────────────────────────────────────────────────┤
  │ < 75                  │ Low Mortality (< 5%–10%)                       │
  │ 75 – 100              │ Moderate Mortality (15%–35%)                   │
  │ 101 – 120             │ High Mortality (40%–65%)                       │
  │ 121 – 139             │ Severe / Critical Mortality (70%–90%)          │
  │ ≥ 140                 │ Extreme Mortality (> 95%–100%) [Near-Futile]   │
  └───────────────────────┴────────────────────────────────────────────────┘

Clinical Application Example:

• Patient: 78-year-old male with a 45% TBSA flame burn and bronchoscopy-confirmed inhalation injury. $\text{rBaux Score} = 78 + 45 + [17 \times 1] = 140$
• Interpretation: An rBaux score of 140 predicts a $>95%\text{ to }100%$ probability of in-hospital death. This score provides objective data for the burn team to conduct early, transparent goals-of-care conferences with family surrogates.

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4. Geriatric-Specific ICU Complications

A. Delirium Screening and Non-Pharmacological Bundles

Geriatric burn patients have the highest incidence of ICU delirium ($>60%\text{ to }75%$), characterized by fluctuating disturbances in attention and cognition. Delirium is independently associated with prolonged mechanical ventilation, self-extubation, autograft disruption, and increased mortality.

• Screening: Perform the Confusion Assessment Method for the ICU (CAM-ICU) or Intensive Care Delirium Screening Checklist (ICDSC) every shift.
• Subtypes: Hypoactive delirium (quiet, withdrawn, lethargic) is far more common in older adults than hyperactive delirium (agitated, combative) and is frequently missed without routine CAM-ICU screening.
• ABCDEF Prevention Bundle: Assess and treat pain first; spontaneous awakening and breathing trials; judicious sedation (avoiding benzodiazepines and high-dose anticholinergics); early physical therapy and mobilization; sleep hygiene protocols (dimming lights, minimizing nighttime alarms); and providing sensory aids (hearing aids, eyeglasses, familiar family presence).

B. Polypharmacy and Medication Interactions

C. Pre-Injury Frailty and Malnutrition

Pre-burn functional reserve is assessed using the Clinical Frailty Scale (CFS) (Score 1 = Very Fit to Score 9 = Terminally Ill). A pre-injury CFS >= 5 (mildly frail or worse) is a stronger independent predictor of mortality, prolonged length of stay, and discharge to long-term skilled nursing than age alone. Sarcopenia (loss of skeletal muscle mass) limits pulmonary mechanics and weaning from mechanical ventilation. Early enteral nutrition with high-protein formulations ($1.5\text{--}2.0\text{ g protein/kg/day}$) must be initiated within 12 hours of admission.

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5. Goals of Care, Advance Directives, and Palliative Integration

Integrating palliative care into burn management does not mean abandoning curative or restorative treatment; rather, it provides concurrent symptom relief, emotional support, and values-aligned decision-making.

                  PROACTIVE PALLIATIVE INTEGRATION TIMELINE
  ┌────────────────────────────────────────────────────────────────────────┐
  │ WITHIN 24 TO 72 HOURS OF ADMISSION:                                    │
  │ • Identify legal healthcare surrogate / durable power of attorney (DPOA)│
  │ • Review existing Advance Directives, Living Wills, and POLST/MOLST.   │
  │ • Hold multidisciplinary family conference (Burn Surgeon, Nurse,       │
  │   Palliative Specialist, Social Work, Chaplaincy).                     │
  │ • Present transparent, objective prognostic data (rBaux, CFS, organ reserve).│
  │ • Define patient-centered goals: Aggressive surgical restoration vs.   │
  │   time-limited clinical trials of therapy vs. comfort-focused care.    │
  └────────────────────────────────────────────────────────────────────────┘