March 1997

Propofol or halothane for children with asthma: effects on respiratory mechanics.

Habre W, Matsumoto I, Sly PD.

British Journal of Anaesthesia 1996;77:739-743.

[ see abstract below ]

This study examined respiratory mechanics in 60 children ages 2-12 years. Half the children had a history of reactive airway disease and half were considered normal. Anesthesia was induced with propofol (3mg/kg), fentanyl (1 ug/kg), and the trachea intubated following neuromuscular blockade with atracurium (0.5 mg/kg). The early phase of anesthesia was maintained with a propofol infusion and 50% nitrous oxide in oxygen. Respiratory mechanics were measured in triplicate using 20 second epochs after 5 minutes of stabilization during propofol anesthesia. The children were then anesthetized with halothane to achieve an expiratory concentration of 0.7%. After 5 minutes the measurements were repeated.

The two groups were comparable regarding age, weight, and sex distribution. Seventeen of the patients had received bronchodilator therapy the morning before admission; there was no significant difference between those who had received bronchodilator therapy and those who had not. Ventilatory variables were comparable between groups. During administration of halothane there was a statistically significant but clinically unimportant increase in tidal volume and reduction in resistance. Overall however, there was no difference between anesthetic techniques.

This is an interesting study attempting to obtain further information on anesthetic techniques which can be safely applied to children with reactive airway disease. This study would appear to demonstrate that propofol infusions are safe. It is of interest that nearly half of the patients were on treatment for their asthma. Would the results have been different had the patients not been well controlled? This is perhaps the most important message. If the child is well controlled - don't stop the medications and likely no matter what technique is chosen all will be well. If the child is not well controlled and the surgery is elective, things will likely be much safer if the surgery is postponed and the reactive airway disease adequately treated.

Perhaps as important as the anesthetic technique , although poorly investigated, is the long held opinion that a tracheal foreign body - the endotracheal tube - is the major cause of bronchospasm in patients with reactive airway disease. Unfortunately it would be difficult to randomize such patients to be managed with or without an endotracheal tube.

Another area which should be investigated is the common practice to administer a nebulizer treatment just prior to anesthetic induction. Again although unproved, many practitioners feel that such "prophylaxis" will reduce the propensity toward bronchospasm. I suppose this practice does not injure anyone but it can be costly if a respiratory therapist is required. Thiopental is often avoided in asthmatic patients for the same concerns these investigators had regarding propofol; to this point in life I have used thiopental in many asthmatic patients yet I have not observed bronchospasm as a result of thiopental administration.

One further precaution is to have a beta agonist which can be administered intratracheally in the operating room and ready to administer should a problem arise. This whole patient population has been poorly characterized regarding anesthetic risk and my own personal experience has been that the worst bronchospasm I have ever witnessed was in a patient who had a latex reaction but no history of reactive airway disease.

The bottom line is to make sure asthmatic patients are well controlled, keep their medication schedule uninterrupted, and be prepared to intervene with a bronchodilator if necessary.

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ABSTRACT