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Ventilation and thoracoabdominal asynchrony during halothane anesthesia in infants
M Benameur1, M D Goldman, C Ecoffey
1Laboratory of Physiology, Hopital Antoine Beclere, Clamart, France.
Insights
Infants show greater ventilation depression with halothane anesthesia due to their reliance on inspiratory intercostal muscles for chest wall stability. This leads to increased thoracic paradox and reduced tidal volume in younger children.
Area of Science:
- Anesthesiology
- Pediatric Pulmonology
- Thoracic Mechanics
Background:
- Infants possess a highly compliant chest wall compared to older children.
- Anesthetic agents like halothane can depress respiratory drive and muscle function.
Purpose of the Study:
- To investigate the ventilatory effects of halothane in infants with high chest wall compliance.
- To compare the respiratory responses between infants and older children under halothane anesthesia.
Main Methods:
- Assessed ventilation, rib cage, and abdominal movements in infants (<=12 months) and children (>12 months).
- Administered halothane at 0.75, 1.0, and 1.5 minimum alveolar concentration (MAC).
- Measured minute ventilation, tidal volume, duty cycle (TI/TT), and thoracic paradox.
Main Results:
- Minute ventilation decreased significantly in infants (20.6%) but not in children.
- Tidal volume reduction was greater in infants (32.7%) than in children (22.6%).
- Thoracic paradox increased with halothane in infants, indicating greater instability.
Conclusions:
- Infants rely more on inspiratory intercostal muscles for thoracic stability during anesthesia.
- Halothane-induced depression of these muscles leads to greater ventilatory impairment in infants.
- High chest wall compliance in infants exacerbates anesthetic-related respiratory depression.
Abstract:
To evaluate the ventilatory consequences of high chest wall compliance during anesthesia in infants, we assessed the effects of halothane at different fractions of minimal alveolar concentration (0.75, 1.0, and 1.5 MAC) on ventilation and movements of the rib cage and abdomen in infants < or = 12 mo of age (group I) and children (group II) > or = 12 mo of age. Minute ventilation decreased in group I, (20.6%, 0.75 to 1.5 MAC), but the change in group II did not reach the level of statistical significance. Tidal volume decreased with halothane level between 0.75 and 1.5 MAC, and its fall was greater in group I (32.7 +/- 11.2 vs. 22.6 +/- 9.3% in group II, P < 0.05). Duty cycle, or ratio of inspiratory to total time (TI/TT), increased in group II with halothane level but did not change in group I, resulting in a decreased TI in group I at higher halothane levels. Thoracic paradox increased with halothane level in group I but not group II. The increase in thoracic paradox in association with the fall in tidal volume between 0.75 and 1.5 MAC was greater in group I than group II (P < 0.05). We conclude that smaller infants depend more on inspiratory intercostal muscle activity to stabilize the thorax, leading to a greater degree of depression of ventilation during halothane depression of inspiratory intercostal activity.