5.2 Burn Assessment & Fluid Resuscitation

5.2 Burn Assessment & Fluid Resuscitation

Core Clinical Rule: In severe burn trauma, time starts ticking from the moment of injury, not from the time of hospital arrival. The Parkland formula ($4\text{ mL} \times \text{body weight in kg} \times %\text{TBSA}$) dictates the total volume of Ringer's Lactate for the first 24 hours, with 50% administered in the first 8 hours calculated from the time of the burn. Superficial (first-degree) burns must be strictly excluded from TBSA calculations. Always maintain a high index of suspicion for inhalation injury and intubate early before laryngeal edema completely obstructs the glottic aperture.

Burn trauma represents a frequent and devastating surgical emergency in Kenya, commonly precipitated by domestic open-flame cooking (jikos, kerosene stoves), boiling water/oil scalds in pediatric populations, electrical flash injuries, and industrial chemical exposures. Extensive burns induce massive capillary permeability, systemic inflammatory cascade activation, and dramatic fluid extravasation into interstitial spaces—producing profound hypovolemic burn shock if not countered by precise, protocolized crystalloid resuscitation.

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1. Jackson's Burn Wound Zones & Depth Classification

Understanding local burn pathophysiology relies on Jackson's classic burn wound model, consisting of three concentric zones:

1. Zone of Coagulation: The central point of maximum heat damage. Tissue suffers irreversible protein coagulation and cellular necrosis. Requires surgical debridement.
2. Zone of Stasis: Surrounds the zone of coagulation. Characterized by microvascular hypoperfusion, cellular ischemia, and sluggish capillary flow. This zone is salvageable with timely, effective fluid resuscitation and wound infection prevention; conversely, hypoperfusion, edema, or sepsis converts it into irreversible necrosis.
3. Zone of Hyperemia: The outermost peripheral zone. Characterized by prominent vasodilation and increased perfusion driven by local inflammatory mediators. This tissue uniformly recovers unless severe sepsis supervenes.

                               [ Zone of Coagulation ]
                                (Irreversible Necrosis)
                                           |
                                           v
                                 [ Zone of Stasis ]
                        (Ischemic Tissue; Salvageable with
                            Adequate Fluid Resuscitation)
                                           |
                                           v
                               [ Zone of Hyperemia ]
                               (Reversible Hyperemia
                                  and Inflammation)

Clinical Burn Depth Classification

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2. Estimation of Total Body Surface Area (TBSA)

Accurate calculation of Total Body Surface Area (TBSA) burned is critical to avoid under-resuscitation (leading to hypovolemic shock and acute tubular necrosis) or over-resuscitation (causing pulmonary edema and abdominal compartment syndrome).

The Wallace Rule of Nines (Adults)

In adults, anatomical regions represent multiples of 9% of the total body surface area:

• Head and Neck: $9%$ total (anterior head and neck $4.5%$, posterior $4.5%$).
• Anterior Trunk (Chest and Abdomen): $18%$ total.
• Posterior Trunk (Upper back and Lower back/Buttocks): $18%$ total.
• Each Upper Extremity: $9%$ each (anterior $4.5%$, posterior $4.5%$) $\rightarrow$ Both arms = $18%$.
• Each Lower Extremity: $18%$ each (anterior $9%$, posterior $9%$) $\rightarrow$ Both legs = $36%$.
• Perineum and External Genitalia: $1%$.
• Total: $9 + 18 + 18 + 9 + 9 + 18 + 18 + 1 = 100%$.

The Palmar Surface Method

For small, scattered, or irregular patchy burns, the patient's palmar surface (the palm including the fingers) represents approximately $1%$ of their own total body surface area. The palm without fingers represents roughly $0.5%$ to $0.8%$.

Pediatric Considerations: Lund and Browder Chart

Children possess a disproportionately large head and shorter lower extremities compared to adults. In a newborn infant, the head represents $18%$ of TBSA while each leg represents only $14%$. For every year of life up to age 10, subtract $1%$ from the head and add $0.5%$ to each leg. Always utilize a pediatric-specific Lund and Browder chart when calculating pediatric burns to prevent massive dosing errors.

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3. Acute Fluid Resuscitation: The Parkland Formula

Fluid resuscitation is indicated for all adult burns involving $\ge 20%$ TBSA (or $\ge 10%$ TBSA in children and elderly patients), as burns of this magnitude trigger generalized capillary leak throughout unburned tissues.

The Parkland (Baxter) Formula

$\text{Total 24-Hour Fluid Volume (mL)} = 4\text{ mL} \times \text{Patient Body Weight (kg)} \times \%\text{TBSA Burn (2nd and 3rd degree only)}$

• Fluid of Choice: Ringer's Lactate (Hartmann's Solution). It represents the most physiological balanced crystalloid, containing sodium ($130\text{ mEq/L}$), potassium ($4\text{ mEq/L}$), chloride ($109\text{ mEq/L}$), and lactate ($28\text{ mEq/L}$), which metabolizes in the liver to bicarbonate, counteracting metabolic acidosis. Avoid unbuffered $0.9%$ Normal Saline, which precipitates hyperchloremic acidosis and worsens renal arteriolar vasoconstriction.
• Administration Schedule:
  • First 8 Hours Post-Injury: Administer $50%$ of the calculated 24-hour volume over the first 8 hours, calculated from the time the burn occurred, NOT the time of hospital presentation.
  • Subsequent 16 Hours: Administer the remaining $50%$ of the calculated volume over the subsequent 16 hours.

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|                WORKED CLINICAL EXAMPLE: PARKLAND CALCULATION                      |
+-----------------------------------------------------------------------------------+
| CASE: A 70 kg male sustains full-thickness burns to his entire anterior trunk     |
| (18%) and circumferential deep partial-thickness burns to his entire left leg      |
| (18%) in a house fire at 08:00 AM. He arrives in the emergency department at       |
| 10:00 AM (2 hours post-injury).                                                   |
|                                                                                   |
| 1. Calculate % TBSA Burned:                                                       |
|    % TBSA = Anterior Trunk (18%) + Left Leg (18%) = 36% TBSA                      |
|                                                                                   |
| 2. Calculate Total 24-Hour Volume:                                                |
|    Volume = 4 mL x 70 kg x 36 = 10,080 mL of Ringer's Lactate                     |
|                                                                                   |
| 3. First 8-Hour Volume (08:00 AM to 04:00 PM):                                    |
|    50% of 10,080 mL = 5,040 mL                                                    |
|    *Crucial Step:* 2 hours have already elapsed! The 5,040 mL must be infused     |
|    over the REMAINING 6 hours.                                                    |
|    Hourly rate = 5,040 mL / 6 hours = 840 mL/hr.                                  |
|                                                                                   |
| 4. Next 16-Hour Volume (04:00 PM to 08:00 AM next day):                           |
|    Remaining 50% = 5,040 mL over 16 hours = 315 mL/hr.                            |
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Clinical Monitoring & Resuscitation Endpoints

The Parkland formula provides only a starting estimate. Fluids must be continually titrated based on objective physiological response:

• Indwelling Foley Catheter: Insert a urinary catheter immediately in all patients requiring fluid resuscitation to measure strict hourly urine output.
• Adult Target Urine Output: 0.5 to 1.0 mL/kg/hr (approximately 30 to 50 mL/hr in a 70 kg adult).
• Pediatric Target Urine Output: 1.0 to 1.5 mL/kg/hr in children weighing $< 30\text{ kg}$.
• Electrical Injury with Myoglobinuria / Pigmenturia: Dark, reddish-brown urine signals massive rhabdomyolysis and release of nephrotoxic myoglobin, threatening acute tubular necrosis. Increase fluid administration to target an hourly urine output of 1.5 to 2.0 mL/kg/hr (or 75 to 100 mL/hr in adults) until the urine clears grossly. Add sodium bicarbonate to IV fluids to alkalinize the urine ($pH > 6.5$), preventing intratubular myoglobin cast precipitation.
• Titration Rule: If hourly urine output drops below target, increase the IV fluid rate by $20%$ to $30%$. If urine output exceeds target, decrease the infusion rate by $20%$ to $30%$. Avoid "fluid creep"—excessive fluid administration leading to pulmonary edema, orbital compartment syndrome, and fatal abdominal compartment syndrome (intra-abdominal pressure $> 20\text{ mmHg}$ with new organ failure).

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4. Emergency Airway in Inhalation Injury

Inhalation injury increases burn-related mortality by more than $20%$. It encompasses upper airway thermal injury, lower tracheobronchial chemical irritant injury, and systemic chemical asphyxiation (carbon monoxide and cyanide).

Clinical Red Flags for Inhalation Injury

• History of fire or explosion in an enclosed or confined space.
• Deep facial, perioral, or anterior cervical burns.
• Singed nasal vibrissae (hairs) and eyebrows.
• Soot or carbonaceous deposits in the mouth, posterior pharynx, or nares.
• Carbonaceous sputum (black, sooty secretions coughed from the lower airway).
• Acute voice change, brassy cough, hoarseness, or audible inspiratory stridor.
• Carboxyhemoglobin ($COHb$) level $> 10%$ on arterial blood gas.

Airway Management Algorithm

1. Immediate High-Flow Oxygen: Place the patient on $100%$ humidified oxygen via a non-rebreather reservoir mask immediately. This accelerates carbon monoxide elimination, reducing carboxyhemoglobin half-life from 320 minutes on room air to approximately 60–90 minutes on $100%$ oxygen.
2. Early Prophylactic Endotracheal Intubation: Do not wait for arterial blood gas deterioration, declining oxygen saturation, or severe respiratory distress. Upper airway mucosal edema progresses rapidly over the first 12 to 24 hours as fluid resuscitation expands interstitial spaces. A patient with minor hoarseness at hour 2 may exhibit complete supraglottic obliteration by hour 6, turning an easy direct laryngoscopy into an impossible airway requiring emergency surgical cricothyroidotomy. Secure the airway early using an endotracheal tube with an internal diameter of at least 7.5 to 8.0 mm to facilitate subsequent bronchoscopy and pulmonary toilet.

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5. Circumferential Burns & Emergency Escharotomy

Full-thickness burns produce tough, inelastic, leathery eschar. As fluid resuscitation progresses, massive dermal and subcutaneous edema accumulates beneath this rigid ring of coagulated tissue, elevating tissue interstitial pressure and precipitating compartment syndrome.

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|                    INDICATIONS AND TECHNIQUE FOR ESCHAROTOMY                      |
+-----------------------------------------------------------------------------------+
| 1. CIRCUMFERENTIAL TORSO BURNS:                                                   |
|    - Complications: Severe restriction of chest wall excursion, high peak airway  |
|      pressures (> 40 cm H2O on ventilator), hypoventilation, hypercapnia, and     |
|      decreased venous return leading to profound hypotension.                     |
|    - Incision Technique: Bilateral longitudinal incisions along the anterior      |
|      axillary lines extending from the 2nd rib down to the 12th rib, connected     |
|      by a transverse horizontal incision across the epigastrium / subcostal margin|
|      (resembling an inverted 'U' or rectangular chest flap).                      |
|                                                                                   |
| 2. CIRCUMFERENTIAL EXTREMITY BURNS:                                               |
|    - Complications: Severe ischemia, loss of distal pulses, cyanosis, delayed     |
|      capillary refill (> 3 seconds), paresthesias, deep ischemic muscle pain.     |
|    - Incision Technique: Incise along the mid-medial and mid-lateral anatomical   |
|      lines of the limb through the entire depth of the leathery eschar until the   |
|      subcutaneous fat bulges outward and tension is fully relieved.                |
|    - Distinction: Escharotomy cuts only the burned skin/eschar (bloodless and     |
|      painless because full-thickness burns destroy nerve endings). Fasciotomy     |
|      divides deep investing muscle fascia and is reserved for electrical burns or |
|      true subfascial compartment syndromes.                                       |
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