9.1 Pediatric Assessment Triangle and Pathophysiology

Pediatric Assessment Triangle and Pathophysiology

The Pediatric Assessment Triangle (PAT)

In critical care transport, the flight paramedic must rapidly differentiate between stable and unstable pediatric patients. The Pediatric Assessment Triangle (PAT) is a structured, rapid-assessment tool designed to establish a "general impression" within the first 15 to 30 seconds of patient contact. It is a strictly visual and auditory assessment that does not involve touching the patient, minimizing agitation which can artificially alter clinical findings.

The PAT consists of three components:

1. Appearance: This is the most important component when assessing overall central nervous system (CNS) function, oxygenation, and brain perfusion. It is structured using the TICLS mnemonic:

   • Tone (T): Is the child active, moving, and muscle-toned, or limp, flaccid, and hypo/hypertonic?
   • Interactability (I): Is the child alert, engaging with the environment or caregivers, and playing, or disinterested, lethargic, and unresponsive to stimulation?
   • Consolability (C): Can the child be consoled or comforted by the caregiver, or is there persistent, inconsolable crying?
   • Look/Gaze (L): Does the child make eye contact and track objects, or is there a vacant, glassy, or "nobody home" stare?
   • Speech/Cry (S): Is the speech or cry strong, age-appropriate, and vigorous, or is it weak, high-pitched, muffled, or absent?

2. Work of Breathing: This reflects the adequacy of airway patency, ventilation, and oxygenation. It represents the patient's physical effort to move air. Key visual and auditory indicators include:

   • Nasal Flaring: Dilation of the nares during inspiration, reducing airway resistance.
   • Retractions: Inward pulling of the soft tissues (intercostal, subcostal, suprasternal, clavicular) indicating accessory muscle use to overcome high resistance or low compliance.
   • Grunting: An expiratory sound produced by closing the glottis against expired air. This creates a physiological PEEP effect to prevent alveolar collapse and recruit lung volume.
   • Head Bobbing: Expiratory extension and inspiratory flexion of the neck, utilizing accessory neck muscles to assist respiration; an indicator of severe fatigue and impending respiratory failure.
   • Abnormal Sounds: Stridor (upper airway obstruction), wheezing (lower airway bronchoconstriction), or stertor (snoring, upper airway occlusion).

3. Circulation to Skin: This evaluates the adequacy of cardiac output and core tissue perfusion. In states of shock, the pediatric patient compensates by shunt-induced peripheral vasoconstriction. Assess for:

   • Pallor: Pale or white skin/mucous membranes, an early sign of peripheral vasoconstriction and compensated shock.
   • Mottling: Patchy, reticulated, blue-gray discoloration of the skin. It indicates advanced perfusion failure and systemic vasoconstriction.
   • Cyanosis: Blue or purple discoloration of the skin and mucous membranes. Central cyanosis (lips, tongue, trunk) indicates severe hypoxemia, whereas peripheral cyanosis (acrocyanosis) can be a normal finding in newborns or indicate localized vasoconstriction.
   • Petechiae/Purpura: Small or large non-blanching hemorrhagic spots, indicating capillary leak and potential septicemia (e.g., meningococcemia).

Physiological States Derived from the PAT

By combining the findings of the three arms of the Pediatric Assessment Triangle, the flight paramedic can categorize the patient's physiological state:

• Respiratory Distress: The child compensates for gas exchange impairment by increasing respiratory effort. Perfusion to the brain and vital organs is maintained, so appearance remains normal.
• Respiratory Failure: The compensatory mechanisms of respiratory distress fail. Hypoxia and hypercapnia impair cerebral function, leading to abnormal appearance (lethargy, obtundation, or agitation). Immediate airway and ventilatory support are required.
• Compensated Shock: Perfusion to vital organs is maintained by systemic vasoconstriction, resulting in abnormal skin circulation (pallor, cool extremities) while brain perfusion (appearance) and breathing remain normal.
• Decompensated Shock: Vasoconstrictive mechanisms fail to maintain cerebral perfusion. The child presents with abnormal appearance (altered mental status) and abnormal circulation. Hypotension is a late, catastrophic sign.
• Cardiopulmonary Failure: Extreme hypoxia and acidosis lead to myocardial depression. The patient presents with gasping, agonal respirations, bradycardia, and profound shock. Cardiopulmonary arrest is imminent.

Pediatric Pathophysiology

Pediatric patients are not simply "small adults." Their anatomy and physiology present distinct clinical challenges:

Cardiovascular Physiology

• Stroke Volume and Cardiac Output: The pediatric myocardium has fewer contractile elements and is non-compliant. Consequently, the ventricle cannot significantly increase stroke volume (SV) in response to a fluid bolus or increased preload. Since $\text{Cardiac Output (CO)} = \text{Heart Rate (HR)} \times \text{Stroke Volume}$, pediatric cardiac output is highly heart rate-dependent.
• Response to Hypoxemia: While adults respond to hypoxemia with tachycardia, infants and young children often respond with vagal-mediated bradycardia. A heart rate $< 60$ beats per minute in an infant or child with signs of poor perfusion despite effective ventilation and oxygenation is an indication to initiate chest compressions under Pediatric Advanced Life Support (PALS) guidelines.
• Hypotension as a Late Sign: Pediatric patients can maintain a normal blood pressure despite losing up to 30-40% of their circulating volume through intense systemic vasoconstriction. Once hypotension develops, the patient is in decompensated shock, and rapid arrest can occur. Hypotension is defined as:
  • Neonates (0-28 days): SBP $< 60\text{ mmHg}$
  • Infants (1-12 months): SBP $< 70\text{ mmHg}$
  • Children (1-10 years): SBP $< 70 + (2 \times \text{age in years})\text{ mmHg}$
  • Children (> 10 years): SBP $< 90\text{ mmHg}$

Respiratory Physiology

• Airway Resistance: According to Poiseuille's Law, airway resistance ($R$) is inversely proportional to the fourth power of the airway radius ($r$): $R \propto 1/r^4$ for laminar flow. In an infant, the baseline airway diameter is small. Just 1 mm of mucosal edema reduces the cross-sectional area of an infant's airway by 75% and increases airway resistance by 16-fold (compared to only a 3-fold increase in adults).
• Oxygen Demand and Storage: Children have a metabolic rate and oxygen consumption rate that is double that of adults (6-8 mL/kg/min vs. 3-4 mL/kg/min). Conversely, they have a smaller Functional Residual Capacity (FRC) relative to body size, meaning they have very little oxygen reserve. During apnea, pediatric patients desaturate rapidly, leaving a very narrow window for airway management.

Thermoregulation

Pediatric patients, particularly neonates, are highly susceptible to hypothermia due to a high body surface area-to-mass ratio, thin skin, and lack of subcutaneous fat. Children cannot shiver to generate heat; instead, they rely on non-shivering thermogenesis by metabolizing brown adipose tissue. This process consumes large amounts of oxygen and glucose, leading to hypoxia, lactic acidosis, and hypoglycemia. Hypothermia also directly impairs surfactant production and the coagulation cascade.

Fluid Distribution

Total body water (TBW) represents approximately 75-80% of body weight in neonates compared to 60% in adults. A higher proportion of this water is located in the extracellular fluid (ECF) compartment (up to 40% in infants vs. 20% in adults). Because ECF is lost more rapidly than intracellular fluid, pediatric patients can dehydrate extremely quickly during illnesses causing vomiting, diarrhea, or poor oral intake.