Shock and Hypotension in the Newborn Workup

Updated: Dec 18, 2020
  • Author: Samir Gupta, MD, DM, MRCP, FRCPCH, FRCPI; Chief Editor: Ted Rosenkrantz, MD  more...
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Workup

Approach Considerations

At this stage, attempt to determine the type of shock (eg, hypovolemic, cardiogenic, maldistributive) because each requires a different therapeutic approach. In neonates who are hypotensively compromised, the authors encourage the early use of a bladder catheter. Hourly urine output is one of the few objective methods of evaluating hypoperfusion that leads to specific organ failure, and its accurate objective measurement can augment clinical decision making.

Obtain the patient’s hematocrit level, electrolyte levels, blood culture, blood gases (for acid/base status), and glucose level as soon as vascular access is obtained. Among laboratory investigations, data supporting the diagnosis of shock include metabolic acidosis on an arterial blood specimen in the face of reasonable oxygenation.

Elevated plasma lactate with a normal pyruvate suggests anaerobic metabolism triggered by tissue hypoxia-ischemia.

Specific studies must be performed to determine the causes (eg, sepsis, cardiac lesions, anemia) and sequelae (eg, renal, hepatic, endocrine) of shock.

Other pertinent tests include the following:

  • Automated Doppler: Automated Doppler provides blood pressure readings through a noninvasive method

  • Manual oscillometric techniques: Manual oscillometric techniques are used for noninvasive blood pressure testing

  • Infant blood pressure testing: Invasive methods for infant blood pressure testing include direct manometry using an arterial catheter and the use of an in-line pressure transducer and continuous monitor

A study by Wahab and Saeed indicated that serum levels of mannose-binding lectin (MBL) can be used to predict the development of sepsis and septic shock, as well as their prognosis, in neonates. In a comparison of 62 newborns with sepsis with 35 controls, the investigators found that MBL levels were lower in the infants with sepsis and were lowest in those with septic shock, this being particularly the case in infants with septic shock who died. [10]

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Blood Gases

Mixed venous blood gases may be more helpful than arterial measurements, because mixed venous blood gases reflect oxygen extraction and waste products at the tissue level. Conversely, arterial blood reflects lung function and the gas composition of blood before it is delivered to the tissues.

Comparison of simultaneous arterial and mixed venous blood gas determinations may be more useful in assessing cardiac output, tissue oxygenation, and acid-base balance.

The value of capillary blood gas determinations is severely limited because they may only reflect diminished perfusion to the periphery and not reflect central perfusion.

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Echocardiography and Doppler Flow Velocimetry

Echocardiography and Doppler flow velocimetry may provide semiquantitative and semiqualitative noninvasive analysis of myocardial function.

Assessment of left ventricular output

Echocardiography is increasingly used as an imaging tool to objectively assess and manage hypotension. The left ventricular output (LVO) can be quantified to guide the management of hypotension.

If the LVO is normal or high and patent ductus arteriosus (PDA) is not evident, a vasopressor (eg, dopamine) can initially be instituted. If a hemodynamically significant PDA is diagnosed, additional treatment should be directed toward the PDA.

If the LVO is low and the left ventricle (LV) is underfilled, volume expansion is the first-line management. If the LVO is normal and the contractility of the LV is impaired, dobutamine should be the initial choice. Additionally, a low LVO with paradoxical movement of the interventricular septum would benefit from dobutamine.

There are noninvasive methods to assess cardiac output now available, which use either Doppler principle or impedance methods to calculate LVO. Echocardiography remains the criterion standard to evaluate cardiac function.

Newer modalities such as functional MRI are being evaluated to assess cardiac function. This technology is promising but is limited to the research findings and is subject to availability of an MRI scanner. It also has the limitation of the inability to perform repeated longitudinal measurements at point of care, such as bedside echocardiography.

Assessment of superior vena cava flow

Superior vena cava (SVC) flow in newborn infants has been reported to be a novel marker of systemic blood flow. [11] Low SVC flow (< 41 mL/kg/min) has been used to diagnose hypotension and to predict long-term outcome. [12]

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