End-Tidal CO₂ as a Function of Tidal Volume in Mechanically Ventilated Infants

ABSTRACT

Objective: To test the hypothesis that end-tidal CO₂ (PETCO₂) varies with tidal volume (Vt) in preterm infants. Design: Intervention study, nonrandomized trial. Setting: Neonatal ICU, regional referral center. Subjects: 29 preterm infants 790 to 2135 g in weight requiring mechanical ventilation studied on 73 occasions. Intervention: Measurement of PETCO₂ during variations of Vt. Measurement: Statistical correlation of PETCO₂ to Vt. Result: PETCO₂ is minimal when Vt is either too low or too high. Conclusion: Vt, through its effect on dead space/Vt (Vd/Vt) ratios and arterial-alveolar CO₂ differences, has a significant effect on PETCO₂. Observation of PETCO₂ across a range of Vt can be used to select an appropriate Vt for preterm infants requiring mechanical ventilation.

KEYWORDS

Mechanical ventilation - preterm infants - end-tidal CO₂

REFERENCES

• 1 West J B. Regional differences in blood flow and ventilation in the lung. In: Caro CG, ed. Advances in Respiratory Physiology Baltimore: Williams & Wilkins 1966: 198-254
• 2 Farhi L E. Ventilation-perfusion relationship and its role in alveolar gas exchange. In: Caro CG, ed. Advances in Respiratory Physiology Baltimore: Williams & Wilkins 1966: 138-197
• 3 Thibeault D W, Poblete E, Auld P AM. Alveolar-arterial O₂ and CO₂ differences and their relation to lung volume in the newborn.  Pediatrics . 1968;  41 574-587
• 4 Krauss A N, Auld P AM. Ventilation-perfusion abnormalities in the premature infant: triple gradient.  Pediatr Res . 1969;  3 255-264
• 5 Tori C A, Krauss A N, Auld P AM. Serial studies of lung volume and VA/Q in hyaline membrane disease.  Pediatr Res . 1973;  7 82-88
• 6 Epstein M F, Cohen A R, Feldman H A, Raemer D B. Estimation of PaCO₂ by two non-invasive methods in the critically ill newborn infant.  J Pediatr . 1985;  106 282-286
• 7 Badgwell J M, McLeod M E, Lerman J, Creighton R E. End-tidal PCO₂ measurements sampled at the distal and proximal ends of the endotracheal tube in infants and children.  Anesth Analg . 1987;  66 959-964
• 8 McEvedy B AB, McLeod M E, Mulera M, Kirpalani H, Lerman J. End-tidal, transcutaneous, and arterial PCO₂ measurements in critically ill neonates: a comparative study.  Anesthesiology . 1988;  69 112-116
• 9 Hand I L, Shepard E K, Krauss A N, Auld P AM. Discrepancies between transcutaneous and end-tidal carbon dioxide monitoring in the critically ill neonate with respiratory distress syndrome.  Crit Care Med . 1989;  17 556-559
• 10 Tsuno K, Prato P, Kolobow T. Acute lung injury from mechanical ventilation at moderately high airway pressures.  J Appl Physiol . 1990;  69 956-961
• 11 West J. Ventilation/Blood Flow and Gas Exchange.  5th ed. Oxford: Blackwell Scientific Publications 1990: 80-82
• 12 Croxton F E. Elementary Statistics with Applications in Medicine and the Biological Sciences.  New York: Dover Publications; 1953
• 13 Minitab. Release 8. State College, PA 1991
• 14 Axum Technical Graphics and Data Analysis. Release 4.0 Seattle, WA; 1994
• 15 Russell G B, Graybeal J M. Reliability of the arterial to end-tidal carbon dioxide gradient in mechanically ventilated patients with multisystem trauma.  J Trauma . 1994;  36 317-322