Assure that patients with severe asthma and status asthmaticus receive adequate intravascularvolume expansion

Assure that patients with severe asthma and status asthmaticus receive adequate intravascularvolume expansion: Excerpt from Avoiding Common Pediatric Errors

Author: David Stockwell, MD

What to Do - Take Action

Asthma is one of the most common illnesses in pediatrics, with considerable variation in presentation. Patients can have an asthma attack with mild respiratory difficulties and not require more than an intermittent inhaled β-agonist. Alternatively, a severe asthmatic patient may require mechanical ventilation or even extracorporeal life support. Although an asthma attack that requires endotracheal intubation is rare, it is important to identify the risk factors for intubation. These include low socioeconomic status, active tobacco smoking or second-hand smoke exposure, parenteral history of allergy or asthma, prior intubation, intercurrent respiratory infection, prior asthma emergency room visit in past year, prior asthma hospitalization in past year, and steroid dependence.

Children require mechanical ventilation for asthma when they have profound hypoxemia, life-threatening respiratory muscle fatigue, or altered mental status. However, high airway pressures, barotrauma, and patient- ventilator dyssynchrony complicate mechanical ventilation in patients with asthma. Although potentially lifesaving, use of mechanical ventilation during an asthma exacerbation is associated with an increased risk of death from asthma. Therefore, the decision to intubate an asthmatic should not be made lightly. These patients are at high risk for cardiac dysfunction. A particularly difficult combination of factors merges to impact the asthmatic patient's cardiac preload. Namely, dehydration, increased pulmonary vascular resistance due to bronchospasm, and the addition of positive pressure to the thoracic cavity will also decrease venous return to the heart and increase resistance to pulmonary blood flow. All of these factors combine to dramatically lower preload for the left ventricle.

Typically people withsevere enough asthmato consider intubation have dehydration owing to the extreme work of breathing and lack of fluid intake. These patients have often been sick for a number of hours and have extreme respiratory difficulty. Their insensible losses due to their respiratory distress are high.

Bronchospasm severe enough to cause the typical hyperexpanded lung findings on chest x-ray limits left ventricular preload. While the chest is hyperexpanded, the resistance to pulmonary blood flow increases due to the over filled alveoli increasing pulmonary vascular resistance. In addition, hyperexpanded chests can decrease systemic venous return to the heart by increasing the resistance in the vena cava.

Finally,byaddingpositivepressureventilationtoahyperexpandedchest there is typically an exacerbated reduction in cardiac preload. Similar to the mechanism of action for the hyperexpanded chest, the systemic venous return is limited due to increased resistance in both vena cava. Additionally, positive pressure ventilation will increase intrathoracic pressures because there is a chance from negative pressure ventilation to positive pressure ventilation. The combination of all of these factors can lead to severe cardiac depression and hypotension. It is important to understand that the increased positive pressure from bag-mask ventilation is the initial period that cardiacdysfunction isobserved. If unrecognizedas decreased preload, it will progress as a patient is placed on a ventilator. Providing the patient with isotonic intravenous solution as a bolus prior to intubation is sound practice. This will augment venous return to the heart and decrease the likelihood of cardiac depression.

Suggested Readings

LeSon S, Gershwin ME. Risk factors for asthmatic patients requiring intubation. I. Observa tions in children. J Asthma. 1995;32(4):285–294.
RobertsJS,BrattonSL,Brogan TV.Acute severeasthma:differencesintherapiesandoutcomes among pediatric intensive care units. Crit Care Med. 2002;30:581–585.

Book Source Details

• Book Title: Avoiding Common Pediatric Errors
• Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
• Year of Publication: 2008
• Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: Avoiding Common Pediatric Errors Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7489-6

 » Next page: Asthma (The 5-Minute Pediatric Consult)

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