Dysrhythmia management plays only a small role in the resuscitation of children. Since rhythm disturbances are usually secondary to hypoxia and not primary cardiac events, careful attention must be given to the correction of hypoxia, acidosis, and fluid balance. Ventilation and oxygenation must be accomplished first. Pulse oximetry, or arterial blood-gas analysis, should be performed to assess oxygen and blood-gas status. An IV of 0.9% NaCl or lactated Ringer solution should be established and the child placed on a cardiac monitor.

A patient with an abnormal cardiac rhythm or rate, coupled with evidence of poor end-organ perfusion (cyanosis, mottled skin, lethargy, etc.), has an unstable cardiac rhythm and requires immediate intervention. The parameters of clinical assessment and expression of instability vary with a child's age. In neonates, blood pressure measurement is difficult, and a heart rate of 80 bpm or less, coupled with evidence of poor end-organ perfusion, requires immediate intervention. In infants and children, variations in heart rate may be well tolerated clinically, and a blood pressure of 70 mmHg or less, coupled with evidence of poor end-organ perfusion, is used to define instability. Figure10-4 and Figure 10-5. summarize electrical and drug therapy of unstable cardiac rhythms in children.

FIG. 10-4. Asystole and pulseless arrest decision tree. IV, intravenous/IO, intraosseous; ET, endotracheal.

The most common rhythms seen in pediatric arrest are the bradycardias, which lead to asystole if untreated. Treatment consists of maximizing oxygenation and ventilation. Chest compression should be started in children with a heart rate of less than 60 bpm and signs of poor perfusion.

Paroxysmal atrial tachycardia (supraventricular tachycardia, or SVT) is most commonly seen in infants and most often presents as a narrow complex tachycardia with rates usually between 250 and 350 bpm. Treatment of unstable patients consists of rapid synchronized cardioversion. Treatment of stable patients varies. Adenosine, vagal maneuvers, or cardioversion are used to treat stable SVT. Adenosine (0.1 mg/kg) is the current recommended drug for SVT in children. This dose can be doubled if the first dose is unsuccessful.

Differentiating a rapid secondary sinus tachycardia from a rapid primary cardiac tachycardia can be difficult. Although heart rates of 150 to 200 bpm in adults are usually cardiac in origin, young children not uncommonly have compensatory sinus tachycardias as fast as 200 to 220 bpm, especially small infants. Children can tolerate rapid primary cardiac heart rates for long periods before congestive heart failure or lethal dysrhythmias develop. Differentiating primary from secondary tachycardia is critical to patient management. However, an ECG may not be very helpful because, at very fast rates, in either sinus tachycardia or SVT, identifiable P waves may not be readily apparent. Historical features pointing to volume loss likely suggest sinus tachycardia. Evidence of congestive heart failure is more likely associated with a pathologic rhythm.

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