Chapter 70: Hypotension and Shock

I. PROBLEM

The nurse reports that an infant is hypotensive and may be showing signs of shock. Hypotension is defined as a decreased blood pressure. There is no consensus on the exact definition of a normal blood pressure range or a clear accepted definition of hypotension in the term or preterm neonate. Hypotension can occur in a neonate with normal tissue perfusion or poor perfusion and overwhelming shock. Hypotension is very common in premature infants; however, the blood pressure that indicates end-organ damage in the very low birthweight (VLBW) infant is unknown.

1. Hypotension. Data are conflicting on the exact blood pressure that requires treatment based on gestational age, postnatal age, and infant weight. There are many definitions of hypotension:

   1. Mean blood pressure <5th to 10th percentile of normative blood pressure values from a reference population for the infant’s gestational age, birth weight, or postnatal age (term).

   2. Mean blood pressure that is less than the gestational age of the infant in weeks (preterm infants during the first 3–5 days of life). For example, in a 28-week-old neonate, hypotension would be a mean blood pressure <28 mm Hg.

   3. Mean blood pressure <30 mm Hg.

   4. For a rapid reference of premature and term infant blood pressure ranges, see Table 70–1 and Figure 70–1, and for more detailed blood pressure values, see Appendix C.

2. Shock is a clinical syndrome of inadequate tissue perfusion that frequently accompanies hypotension. The types of shock are: hypovolemic, cardiogenic, obstructive, distributive, and dissociative. Some clinical scenarios may constitute many types of shock such as sepsis (distributive, hypovolemic, and cardiogenic), necrotizing enterocolitis (NEC) (hypovolemic and distributive), or pulmonary hypertension (obstructive and cardiogenic).

II. IMMEDIATE QUESTIONS

1. What is the method of measurement? Blood pressure can be measured by invasive and noninvasive techniques. The invasive technique is considered the gold standard and is performed by transducing an indwelling arterial or umbilical artery catheter. A dampened waveform suggests air in the system or inappropriate position of the transducer and may result in inaccurate measurements. Because small bubbles in the system can affect the systolic and diastolic values, the mean blood pressure is considered the most accurate measurement of systemic perfusion pressure. The noninvasive technique most commonly performed is the oscillometric method using a blood pressure cuff on an extremity. Ensure that the cuff size is appropriate and that the cuff is applied properly to the extremity. Other noninvasive techniques include auscultation, Doppler ultrasound, and palpation, all of which are less accurate in infants.

2. Are signs of shock present? Signs of shock include lethargy, poor tone, respiratory distress, tachypnea, apnea and bradycardia, tachycardia, narrow pulse pressure, weak pulses, prolonged capillary refill time (>3–4 seconds), pallor, and cold extremities (with a normal core temperature). Hypothermia is typically seen in infants with shock since they have an impaired autonomic nervous system. Systolic hypotension is a marker for decreased cardiac output secondary to impaired preload, ...