Robert M. Smith

EFFECT OF AIRWAY HYPOCAPNIA ON MECHANICS OF BREATHING DURING CARDIOPULMONARY BYPASS

Total cardiopulmonary bypass separates the lungs from the pulmonary arterial circulation. Continued ventilation with non CO2-containing mixtures during bypass will result in airway hypocapnia. Airway hypocapnia results in decreased compliance, increased work of breathing, and increased resistance to air flow. Reversal of airway hypocapnia increased compliance one-third, decreased work of breathing 20%, and decreased air flow resistance approximately 40% when compared to the values obtained during the period of low airway CO2. These changes in airway mechanics must be considered for pulmonary management during cardiac bypass.

BLOOD LOSS DURING PEDIATRIC OPERATIONS

The gravimetric method of measuring blood loss was used during all types of pediatric operations at The Montreal Childrens Hospital. Results of 1787 such measurements indicated that the method is of value in the management of transfusion. Grading blood loss as minor, moderate or severe, in terms of its relation to total blood volume or body weight is a procedure of practical value. Operations were grouped into those that usually led to a loss of less than 10% of the blood volume (7.5 ml./kg.), those with a loss usually between 10% and 14% and those with blood loss usually over 14% (10.5 ml./kg.), in order that appropriate plans for transfusion could be made to reduce the incidence of serious hypovolemia without fear of cardiovascular overloading. Blood loss at operation (adenotonsillectomy) was noted to vary considerably among surgeons but was fairly constant for each surgeon and seemed to be independent of the surgeons experience. Two alleged hemostatic agents, adrenochrome carbazone (Statimo) and estrogenic substances (Premarin), were not effective in reducing the amount of blood lost during adenotonsillectomy. The importance of calculation of approximate equivalent amounts of blood at various ages of childhood is emphasized.

DIFFERENCES OF SOMATIC AND RESPIRATORY RESPONSE TO HYPOXIA IN NEWLY BORN AND OLDER INFANTS

The somatic and respiratory responses to hypoxia of two groups of infants were studied. Infants 16 to 82 days of age manifested both increased somatic and respiratory activity, whereas infants under 24 hours of age remained inert and demonstrated respiratory depression. The responses in the younger group of infants occurred despite a pronounced decline in oxygen saturation of the blood. The findings suggested the presence of a somatic reflex in the older infants which, like the peripheral chemoreceptors, is stimulated by a fall in arterial oxygen tension. Neither this reflex nor evidence of chemoreflex function were observed in the very young infants, suggesting a lingering of fetal behavior.