Posted to the PICU list 4/15/96 by Dr. Gideon Paret, Tel Aviv, Israel
Modified with permission

Heliox in Bronchiolitis: Report of a Case and Discussion

A four-month-old boy was admitted to the PICU with severe respiratory
distress three days after developing an upper respiratory tract infection
manifested by nasal discharge, coughing, and low-grade fever. The patient
looked extremely dyspneic, utilising accessory muscles and with perioral
cyanosis. His vital signs were: Temperature 37.8”C, heart rate 140
beats/min, respiratory rate 70 breaths/min, blood pressure 90/70 mm Hg. On
chest auscultation, coarse crackles and diffuse wheezes were noted. The
remainder of the physical examination was normal. An enzyme-linked
immunoabsorbment assay of nasal secretion was positive for RSV.

Arterial blood gas measurements with the patient breathing 60% oxygen
revealed pH 7.41, PCO2 43 mm Hg, and PO2 110 mm Hg. Chest x-ray showed
hyperinflation.

Treatment with nebulised solbutamol and ipratropium bromide was initiated
immediately. However, over the following hours the patient experienced
increasing respiratory distress associated with nasal flaring, marked use of
accessory muscles, and increasing respiratory rate. Supplemental oxygen and
nebulised bronchodilators were given continuously, with the patientās heart
rate rising up to 170 beats/min.

The patient's respiratory status continued to deteriorate, suggesting
imminent respiratory failure Arterial blood gas measurement showed
progressive worsening: pH 7.29, PCO2 58 mm Hg, and partial pressure of
oxygen 62 mm Hg.

Prior to restoring to intubation and mechanical ventilation, the patient was
switched to treatment with heliox containing 80% helium and 20% oxygen.
Additional oxygen was given to maintain 92% oxygen saturation as measured by
pulse oximetry. The patient's nasal flaring and use of accessory muscles
markedly decreased, respiratory rate fell within minutes, and hypercapnia
improved. Removal of heliox after six hours worsened hypercapnia , and
treatment with heliox was restarted. Over the next 48 hours the patient was
cautiously weaned from the heliox, and continued to do well, with
intermittent administration of nebulised solbutamol. Intubation and
mechanical ventilation was not required during the subsequent hospital stay.

DISCUSSION

Helium is a biologically inert gas of low molecular weight, first introduced
to the medical community by Barach in the management of obstructive lesions
of the lower trachea and major bronchi (1). Subsequently, mixtures of
helium and oxygen (He/O2) have been reported to be a successful measure in
treating post-extubation upper airway obstruction (2), acute airway swelling
associated with radiation therapy (3), and in patients with COPD (4).
Recent literature suggests the use of heliox as an inhaled medium to relieve
the effect of airflow obstruction secondary to asthma (5).

Grahm's law states that the flow of gas through an orifice is inversely
proportional to the square root of its density (6) due to this physical
property. Helium, a low-density gas, is useful in overcoming airway
resistance and obstruction. Furthermore, helium-oxygen mixtures reduce
turbulent flow, and allow laminar conditions to persist at higher flow rates
than nitrogen-oxygen, leading to a reduction the flow resistive work (5, 6).
A substitution of helium for nitrogen would cause an overall increase in the
value of bulk gas flow, and a concomitant decrease in the associated work of
breathing (7).

Gluck et al reported that heliox reduces the differences in the time
constants among various lung areas, thus increasing the dynamic compliance
for a given ventilatory pattern (5). In this survey of adult asthmatic
patients, the helium-oxygen mixture was also shown to improve gas exchange
and decrease peak airway pressure. This effect was achieved by normalising
uneven ventilation and perfusion caused by bronchoconstricted airways. In
addition, in patients with significant airflow obstruction there is evidence
that the pleural pressure time constants may be different from normal
patients. Breathing heliox facilitates removal of alveolar gas by reducing
the difference between airway and pleural time constants (5).

It should be emphasised that one should use heliox cautiously. Helium has a
high thermal conductivity, and there is a risk of hypothermia when the
temperature of the heliox mixture is lower than 36”C (6). Furthermore,
heliox is expensive, thus increasing cost of care. However, heliox may
reduce the number of patients requiring mechanical ventilation, which has
the potential for gas trapping, dynamic hyperinflation, and subsequent
pulmonary barotrauma.

Taking into account all considerations, we opted to use the helium-oxygen
mixture in trying to avert the need for mechanical ventilation. Indeed, the
reduction in respiratory rate and PCO2, and the increase in PO2 were
manifested shortly after use of the He/O2, and averted the need for
mechanical ventilation.

We conclude that heliox may represent a beneficial additive to the
conventional therapeutic armamentarium in critically ill children with RSV
bronchiolitis. It should be considered as an adjunctive therapy for these
patients, and may avert the need for mechanical ventilation, thus reducing
further morbidity.

REFERENCES

1. Barach AL. The therapeutic use of helium. JAMA 1936;107:1273.

2. KJ Kemper, MS Benson, MJ Bishop. Predictors of postextubation stridor in
pediatric trauma patients. Crit Care Med. 1991;19:352-355.

3. S Mizrahi, Y Yaari, C Lugasy, S Cohen. Major airway obstruction relieved
by helium/oxygen breathing. Crit Care Med. 1986;14(11):986-987.

4. DM Swidwa, HD Montenegro, B Goldman, KR Lutchen, GM Saidel. Helium
oxygen breathing in severe chronic obstructive pulmonary disease. Chest.
1985;87:790-795.

5. EH Gluck, DJ Onorato, R Castriotta. Helium oxygen mixtures in intubated
patients with status asthmaticus and respiratory acidosis. Chest.
1990;98:693-698.

6. JF Nunn. Diffusion and alveolar/capillary permeability. In: Applied
Respiratory Physiology. J. F. Nunn, London: Butterworths, 1987; pp 184-206.

7. AB Dubois. Resistance to breathing. In: Handbook of Physiology,
section B, Vol 1, Washington, DC: American Physiology Society, 1964; pp
451-462.


GIDEON PARET ,M.D.
PICU ,THE CHAIM SHEBA MEDICAL CENTER
TEL-AVIV; ISRAEL
gparet@post.tau.ac.il
TELEFAX:972-3-5302885

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