Effects of halothane on respiratory mechanics and lung histopathology in normal rats.

It is generally accepted that halothane reduces airway and tissue resistance in lungs with preexisting airway tone. However, under conditions of resting airway tone, pulmonary resistance remains unaltered. In this study, we have determined the effects of halothane on respiratory system, pulmonary and chest wall resistive, elastic and viscoelastic mechanical properties, and related the results to findings from lung histology in intact normal rats. Sixteen adult male Wistar rats were allocated randomly to one of two groups (n = 8 in each group): control or halothane group. In the control group, animals were sedated with diazepam 5 mg i.p. and anaesthetized with pentobarbital 20 mg kg-1 i.p. In the halothane group, the anaesthetic was administered at an end-tidal concentration of I MAC throughout the study. Rats were paralysed and underwent mechanical ventilation. Halothane decreased airway resistance but increased the tissue component of resistance (caused by viscoelastic elements and lung inhomogeneity). Static and dynamic elastance also increased with halothane anaesthesia. Pulmonary resistance remained unchanged. Lung histopathology demonstrated airway dilatation and a greater degree of lung collapse and hyperinflation in the halothane group. We conclude that halothane anaesthesia acts both on airway and lung tissue. In airway tissue, dilatation occurs but the lung periphery stiffens. Consequently, these opposing effects result in no overall apparent change in mechanical properties, although changes are observed during halothane anaesthesia in normal animal and subjects.

Glucose homeostasis. Comparison between hypothermic and normothermic cardiopulmonary bypass.

STUDY OBJECTIVE: Disturbance in blood glucose homeostasis during cardiac surgery may cause visceral and metabolic alterations. Hypothermic CPB induces glucose and hormonal changes. As normothermic CPB is used at some institutions, a comparison of blood glucose and plasma hormones between hypothermic and normothermic CPB was performed. DESIGN: Prospective nonrandomized study. SETTING: University cardiac center. PATIENTS: Twenty-two nondiabetic adults undergoing elective coronary bypass and/or valvular surgery. INTERVENTIONS: Group 1 (n = 12) underwent hypothermic CPB (25 degrees C) and group 2 (n = 10) normothermic CPB (37 degrees C). In both groups nonpulsatile CPB was achieved with a membrane oxygenator and dextrose-free crystalloid priming. Dextrose was not administered during surgery but was infused postoperatively (125 mg/kg/h). MEASUREMENTS AND RESULTS: Eight blood samples were drawn during the period of arrival in the operating room (control) to the third postoperative hour. During hypothermic CPB in group 1, blood glucose level increased to 154 +/- 20 mg/dl (mean +/- SD) associated with a decrease in plasma insulin and an increase in epinephrine, despite a decrease in cortisol and growth hormone. During rewarming, the blood glucose value continued to increase (to 197 +/- 35 mg/dl) associated with an increase in glucagon, growth hormone and catecholamines, despite a 374 percent increase in insulin. During CPB in group 2, insulin, glucagon, cortisol and catecholamines were significantly higher than during hypothermic CPB so that the blood glucose level was not significantly different between the two groups during CPB. Blood glucose value was higher in group 1 than in group 2 at closure of the chest (208 +/- 30 vs 175 +/- 19 mg/dl, respectively, p less than 0.02) and at the third postoperative hour (271 +/- 30 vs 221 +/- 51 mg/dl, p less than 0.01). In both groups, however, the postoperative increase in blood glucose was accompanied by a similar increase in insulin, cortisol and catecholamines but glucagon was lower after hypothermic CPB. CONCLUSIONS: Hyperglycemia occurred perioperatively in cardiac surgery with dextrose-free priming both during hypothermic and normothermic CPB but normothermic CPB resulted in a slow and steady increase in both glucose and insulin concentrations without the major perturbations that occurred with hypothermic CPB. Postoperatively, higher blood glucose was observed in the hypothermic CPB group.

Hemodynamic and hormonal responses to hypothermic and normothermic cardiopulmonary bypass.

Normothermic cardiopulmonary bypass (CPB) is used in cardiac surgery at some institutions. To compare hemodynamic and hormonal responses to hypothermic (29 degrees C) and normothermic nonpulsatile CPB, 20 adults undergoing coronary artery bypass graft and/or aortic valve replacement were studied. Hemodynamic measurements and plasma hormone concentrations were obtained from preinduction to the third postoperative hour. The two groups were given similar amounts of anesthetics and vasodilators. Systemic vascular resistance increased only during hypothermic CPB, and heart rate was higher at the end of hypothermic CPB. Postoperative central venous pressure and pulmonary capillary wedge pressure were lower after hypothermic CPB. Oxygen consumption decreased by 45% during hypothermic CPB, did not change during normothermic CPB, but increased similarly in the two groups after surgery; mixed venous oxygen saturation (SvO2) was significantly lower during normothermic CPB. Urine output and composition were similar in the two groups. In both groups, plasma epinephrine, norepinephrine, renin activity, and arginine vasopressin concentrations increased during and after CPB. However, epinephrine, norepinephrine, and dopamine were 200%, 202%, and 165% higher during normothermic CPB than during hypothermic CPB, respectively. Dopamine and prolactin increased significantly during normothermic but not hypothermic CPB. Atrial natriuretic peptide increased at the end of CPB and total thyroxine decreased during and after CPB, with no difference between groups. This study suggests that higher systemic vascular resistance during hypothermic CPB is not caused by hormonal changes, but might be caused by other factors such as greater blood viscosity. A higher perfusion index during normothermic CPB might have allowed higher SvO2.

Oro-naso-pharyngeal suction at birth: effects on respiratory adaptation of normal term vaginally born infants.

The effect of oro-naso-pharyngeal suction at birth on pulmonary mechanics is described in a random assigned controlled study of 40 normal term vaginally born infants. Twenty cases had their oro-naso-pharynx suctioned immediately after birth (S Group), whereas 20 were not suctioned in the neonatal period (NS Group). A computerized pneumotachographic system (MECVENT) was used for the assessment of respiratory mechanics (Dynamic Compliance (C. Dyn.) and Total Pulmonary Resistance (R) in inspiration and expiration at 10, 30 and 120 minutes after birth. In both groups the C. Dyn increased during the study period whereas the R decreased, mainly in the initial 30 minutes. No significant differences were observed between S and NS groups for any of the parameters of respiratory mechanics. The results obtained in this study provide no physiological basis to recommend routine airway suction at birth in normal, term, vaginally born infants.

[Whole body and thoracic impedance changes induced by cardiopulmonary bypass]. / Modifications de l'impédance corporelle totale et thoracique induites par la circulation extracorporelle.

Impedance is defined as resistance to alternating electrical current. It is inversely proportional to the volume of tissues traversed by the current. Cardiopulmonary bypass, as used in cardiac surgery, results in extravascular fluid overload manifested by a decrease in whole body and thoracic impedance. This non-invasive method has been used in 18 adult patients before, and in the days immediately following cardiopulmonary bypass for non-mitral cardiac surgery. Right and left thoracic impedances were reduced by 32 and 37 percent respectively during the first postoperative hour and returned to preoperative values after the second postoperative day. Whole body impedance was reduced by 14 percent in the first post-operative day, and this was accompanied by 17 percent and 16 percent decreases in the PaO2/PAO2 and PaO2/FIO2 ratios respectively. There was no correlation between impedance and these ratios which reflect pulmonary gases exchanges. Impedance appears to be a simple method to evaluate whole body and thoracic water contents, thereby providing guidance in post-cardiac surgery management.

Oxygen transport in newborns at different gestational ages.

Oxygen (O2) transport was assessed through the affinity between O2 and hemoglobin (Hb) in 123 newborns of 28 to 40 week gestational ge, with a minimum of 9 newborns for each gestational age group (see table). In order to assess the O2-Hb affinity, we studied the correlation between the pO2 and the Hb saturation for each gestational age, obtaining estimates of the oxy-hemoglobin dissociation curves corresponding to each gestational age (see fig. 3). The pO2 levels corresponding to the 50% saturation (P50) for each gestational age were estimated from there. All newborns were from single vaginal deliveries with no fetal distress before birth and with an adequate weight for gestational age. The latter was calculated according to the date of the last menstrual period (78% of the cases), echography (10.6% of the cases) or neonatal physical exam (11.4% of the cases). A P50 vs. gestational age linear regression showed a high determination rate (r2 = 0.957, p less than 0.00001) (see fig. 2) which supports the hypothesis of the P50 linear growth; decrease in the Hb-O2 affinity with increasive gestational age (Hb-O2 affinity is different in newborns of different gestational ages). With these results one may conclude that the Hb-O2 uptake varies according to gestational age (P50 changes linearly as gestational age increases) and that a single measurement of pO2 in a newborns, blood does not accurately evaluate the amount of O2 that is transported to the tissues, because the transport capacity depends, among other factors, upon gestational age. The Hb saturation better represents the amount of O2 that can get to the cell level.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of pulmonary dynamics in normal newborns: a pneumotachographic method.

A pneumotachographic method for assessment of pulmonary dynamics in critically ill newborns in an intensive care setting was developed in our laboratory. Before the results obtained with this method could be applied, the normal range of values were determined in 48 normal term and preterm newborns. Their body weight ranged between 1200 and 4100 g, and postnatal ages between 24 hours and 21 days. In three infants, two determinations were performed after an interval of 7 days. The studies were performed with a pneumotachograph applied to the upper airway by means of an inflatable face mask or latex nasal prongs. The air flow signal was electronically integrated to time to produce a volume signal. Airway pressure was determined proximal to the pneumotachograph. Esophageal pressure was determined with a water filled catheter placed in the lower third of the esophague. Tidal volume (VT), minute ventilation (V), Dynamic compliance (Cdyn), total pulmonary resistance (R), total pulmonary work (Wt), Elastic work (We), and flow resistive work (Wv), were determined. A significant linear correlation was found between Cdyn and body weight (r = 0.50, p less than 0.01) whereas no significative correlation was found between body weight and VT, V or R. Values for VT, V and Cdyn were corrected for body weight and means (X), standard deviation (SD) so as 10th and 90th percentiles are shown in table III. X, SD and percentiles for R were shown in table III. Wt, We and Wv were corrected for V, and X, SD and percentiles shown in table III. Values of VT/Kg, Cdyn/Kg and R are similar to those found by other authors with pneumotachography and plethysmography. The V/Kg values obtained by us were higher than those reported by other authors, which together with the lack of correlation of VT and V with body weight, question the reliability of V values in our study. This could be explained by: 1) excessive increase in dead space in cases in which a face mask was used; 2) nocioceptive stimulus produced by face mask or nasal prongs; 3) inadequate selection of the moment at which the record was obtained. Whichever the explanation, our values of V cannot be considered as basal, and should be interpreted with caution. The results obtained allow us to continue with our program and apply this method to the study of newborn infants with RDS.