Anesthesiology
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To determine whether prematurely born infants with a history of idiopathic apneic episodes are more prone than other infants to life-threatening apnea during recovery from anesthesia, the authors prospectively studied 214 infants (173 full term, 41 premature) who received anesthesia. Fifteen premature infants had a preanesthetic history of idiopathic apnea. Six of these required mechanical ventilation because of idiopathic apneic episodes during emergence from anesthesia. ⋯ Infants ventilated for apnea were younger (postnatal age 1.6 +/- 1.2 months, mean +/- SD; conceptual age 38.6 +/- 3.0 weeks) than those who recovered normally (postnatal age 5.6 +/- 2.7 months; conceptual age 55.1 +/- 11.3 weeks) (P less than 0.01). No other premature or full-term infant was ventilated because of postoperative apneic episodes. The authors conclude that anesthetics may unmask a defect in ventilatory control of prematurely born infants younger than 41-46 weeks conceptual age who have a preanesthetic history of idiopathic apnea.
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The authors studied the incidence of and factors related to recurrent perioperative myocardial infarction retrospectively during 1973-1976 (Group 1) and prospectively during 1977-1982 (Group 2). Reinfarction occurred in 28 of 364 (7.7%) patients in Group 1 and 14 of 733 (1.9%) in Group 2 (P less than 0.005). When the previous infarction was 0-3 and 4-6 months old, perioperative reinfarction occurred in 36% and 26% of Group 1 patients, respectively, and only 5.7% and 2.3% of Group 2 patients, respectively, (P less than 0.05). ⋯ Patients who had intraoperative hypertension and tachycardia or hypotension develop had a higher incidence of reinfarction in both groups. The results suggest that preoperative optimization of the patient's status, aggressive invasive monitoring of the hemodynamic status, and prompt treatment of any hemodynamic aberration may be associated with decreased perioperative morbidity and mortality in patients with previous myocardial infarction. Which of these factors, if any, contributed to the improved outcome was not determined in this study.
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We tested the hypothesis that different anesthetic techniques for elective cesarean section would be reflected in the pattern of breathing and its control after birth. The pattern of breathing, including tidal volume, total breath duration (TTOT), minute ventilation, inspiratory (TI) and expiratory times, TI/TTOT ratio, and mouth occlusion pressure, was measured in 27 infants delivered by elective cesarean section during maternal epidural (lidocaine-carbon dioxide-epinephrine, n = 19) or general anesthesia (66% oxygen in N2O and 0.5% halothane, n = 8) at 10, 60, and 90 min and 3-5 days of age. ⋯ In general, at any given age the values of the respiratory parameters measured and their variability were similar between the two groups of infants. These findings indicate that the pattern of breathing after birth is not different following epidural or general anesthesia, and on the basis of our measurements, both epidural or general anesthesia appeared equally suitable for elective cesarean section.
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Compression of gases (Boyle's law) and circuit compliance are major determinants of anesthesia circuit function. The materials of which circuits are constructed and the use of heated humidifiers may result in clinically important variations in delivered minute ventilation (VE) secondary to variations in compression volume. We examined eight anesthetic circuits both with and without a heated humidifier in an in vitro setting. ⋯ Pediatric circle systems were intermediate and adult circle systems had the largest compression volume and were the least efficient. Humidifiers uniformly increased compression volume. The following conclusions were drawn: 1) the anesthetic circuit, its material, and the pressure at which it operates are important determinants of circuit function; 2) humidifiers increase compression volume; 3) Mapleson D circuits had the lowest compression volume and therefore were the most efficient; 4) highly compliant adult circuits may result in compression volume losses that exceed the tidal volume of a pediatric ventilator; 5) humidifiers with low volume and rigid tubing should have the least effect on minute ventilation; and 6) highly compliant adult circuits when used in the care of infants and small children must be used with caution.
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Associations between airway closure, alveolar-arterial oxygen tension difference (A-aDO2), and positive end-expiratory pressure (PEEP) were investigated in anesthetized, paralyzed, artifically ventilated patients. The difference between closing capacity (CC) and functional residual capacity (FRC) was measured with a modified standard technique using a bolus of N2 to detect airway closure in denitrogenated patients. At FIO2 = 0.4 during anesthesia before application of PEEP, A-aDO2 was larger than expected in comparable conscious subjects and increased at about 1 mmHg/yr of age. ⋯ Patients in whom CC was initially below FRC failed to improve oxygenation with PEEP. At least half of the decrease in A-aDO2 associated with application of PEEP persisted for 20-30 min after the withdrawal of PEEP, although the withdrawal resulted in an immediate recurrence of airway closure above FRC. The authors conclude that closure of pulmonary units operates in some circumstances to contribute to pulmonary dysfunction in anesthetized patients but is neither the only nor necessarily the most important such mechanism.