Sevoflurane and Isoflurane Reduce Oxygen Saturation in Infants: DISCUSSION

In: Anesthesia

24 Jan 2010

Respiratory system

Our results demonstrate that sevoflurane and isoflurane but not enflurane decrease Spo2 in infants receiving 67% nitrous oxide and oxygen. A preliminary study indicated that this phenomenon was not commonly observed with low concentrations of sevoflurane or isoflurane or in patients over 3 years of age.

All subjects in this investigation were free of any upper or lower airway obstruction, and they were ventilated artificially to maintain the same Petco2 throughout the study. Therefore, the changes in Sp02 should not have arisen from any alteration in breathing rate or volume or airway obstruction. Because these changes were reversible, it is apparent that they did not come from injury to the lung or pulmonary microvasculature. A remaining possibility is that these changes in Spo2 might be caused by anesthetic-induced alterations in the oxygen gas exchange system there were no differences in Petco2 or airway pressure during the three stages of this study, making it difficult to postulate that sevoflurane or isoflurane might lower Spo2 by altering the conductive zone of the airway during general anesthesia.

Neither enflurane nor nitrous oxide influences the ox Volatile anesthetics generally exert some inhibitory effects on the pulmonary and systemic circulations. As for the pulmonary system, no significant change occurs either in pulmonary arterial pressure or pulmonary vascular resistance. Systemically, sevoflurane depresses peripheral vascular resistance similarly to enflurane at 2 MAC. Our experiments demonstrated no difference in heart rate among the 3 treatment groups in stage 1, when many subjects in the sevoflurane and isoflurane groups experienced reduced Spo2 compared with stage 2. However, in stage 3, when Spo2 values were equivalent to stage 1, heart rate was lower in the enflurane group than in the sevoflurane and isoflurane groups. Meanwhile, blood pressure did not vary significantly by group or stage. These findings suggest that enflurane may have inhibited the sinus node in comparison with sevoflurane or isoflurane but not the contractile state of the heart. The changes in Spo2 do not seem to be consistent with these disturbances in cardiovascular function; thus, they may be independent of anesthetic-induced effects on the pulmonary and/or systemic circulations. erectalis 20

Volatile anesthetics exert several influences on respiration. Sevoflurane, eg, relaxes tracheal smooth muscle. Isoflurane irritates the respiratory tract and sometimes induces coughing, laryngospasm, or broncho-spasm during induction and recovery but not during maintenance of general anesthesia. Nevertheless, there were no differences in Petco2 or airway pressure during the three stages of this study, making it difficult to postulate that sevoflurane or isoflurane might lower Spo2 by altering the conductive zone of the airway during general anesthesia.

Neither enflurane nor nitrous oxide influences the ox­ygen dissociation curve, suggesting that these anesthetics do not modify the affinity of hemoglobin for oxygen. The effects of sevoflurane and isoflurane on hemoglobin remain unknown. In infants, the oxyhemoglobin dissociation curve is shifted to the left. Since there were no group differences in age and since no altered distributions of Sa02/Pa02 ratios were evident in subjects who had a lower Spo2 in stage 1 versus subjects who did not, it seems unlikely that the hemoglobin affinity for oxygen in infants was affected by sevoflurane, isoflurane, or enflurane.

The alveolar capacity is relatively small in infants, and artificial ventilation during general anesthesia induces a significant fall in functional residual capacity. Despite the maintenance of the same airway pressure in this study, it is conceivable that alveolar oxygen exchange could be perturbed by effects of anesthetics on the terminal respiratory or conducting passages. Then the lower Spo2 in the sevoflurane and isoflurane groups might result from an increase of right-to-left shunting in the pulmonary circulation of affected infants.

In conclusion, artificial ventilation with 2 MAC sevoflurane and 2 MAC isoflurane but not 2 MAC enflurane in 67% nitrous oxide and oxygen induced lower Spo2 readings in infants. These findings suggest that there might be some volatile anesthetic-specific effect on oxygen gas exchange in the respiratory system of infants. Further experiments will need to examine the effects of volatile anesthetic on developmental changes in the respiratory system. canadian antibiotics


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