Post-operative pressure lability and cardiac baroreflex in normotensive patients as a function of age.

BACKGROUND: Pressure lability may be linked to the loss of the cardiac baroreflex. The reduction of the sensitivity of the cardiac baroreflex has not been delineated in the post-operative period according to age in normotensive patients. This study addresses pressure lability and slope of the cardiac baroreflex as a function of age. METHODS: Patients were allocated to the following three groups: young (20-39 years, n=7), middle aged (40-59 years, n=7) and elderly (60-79 years, n=6), and studied before minor intra-abdominal surgery under CO(2) peritoneal insufflation and nitrous oxide-isoflurane-sufentanil anesthesia, up to 24 h after extubation. An electrocardiogram and non-invasive beat-by-beat pressure monitoring (Finapres) allowed offline calculation of the sensitivity of the cardiac baroreflex ('sequence' technique) and standard deviation (SD) of heart rate (HR; HR variability) and systolic blood pressure (SBP; pressure lability). RESULTS: Before anesthesia, (a) an inverse relationship was observed between the slope of the cardiac baroreflex and age and (b) a trend (P<0.09) existed between the slope of the cardiac baroreflex and pressure lability, irrespective of age. During the early post-operative period, young patients returned to their baseline slope of the cardiac baroreflex; no inverse relationship between increased SD of SBP and decreased SD of RR interval was observed. Middle-aged and elderly patients displayed a depressed slope of the cardiac baroreflex both before and after anesthesia. CONCLUSION: At variance with the pre-operative period, no simple inverse relationship was observed between increased pressure lability and depressed HR variability in young patients during the early post-operative period.

Spontaneous cardiac baroreflex in humans. Comparison with drug-induced responses.

We compared two methods of assessment of baroreflex sensitivity in eight supine healthy volunteers during repeated baseline measurements and various conditions of cardiac autonomic blockade. The spontaneous baroreflex method involved computer scanning of recordings of continuous finger arterial pressure and electrocardiogram to locate sequences of three or more beats in which pressure spontaneously increased or decreased, with parallel changes in pulse intervals. The mean regression slope of all these sequences during each study condition was considered to represent the mean spontaneous baroreflex slope. In the drug-induced method, sigmoidal curves were constructed from data obtained by bolus injections of phenylephrine and nitroprusside; the tangents taken at the resting pressure of each of these curves were compared with the mean spontaneous baroreflex slopes. The two methods yielded slopes that were highly correlated (r = .96, P < .001), with significant but similar intraindividual baseline variability. Atropine virtually eliminated the baroreflex slope; subsequent addition of propranolol did not alter it further. Propranolol or clonidine alone increased average baroreflex slope to the extent that they increased resting pulse interval (r = .69 to .83). The spontaneous baroreflex method provides a reliable, noninvasive assessment of human vagal cardiac baroreflex sensitivity within its physiological operating range.

A kinetic study of plasma renin and aldosterone during changes of posture in man.

Cardiovascular parameters, hematocrit (Ht), plasma electrolytes, renin activity (PRA) and aldosterone concentration (PAC) were measured in 12 normal human subjects (6 males and 6 females) eating an ad lib diet. At 8 AM, volunteers assumed the following postural changes: 1 hour supine, then 2 hours upright and finally 1 hour supine. Orthostatism induced the following changes: heart rate, systolic and diastolic blood pressure increased immediately; Ht rose significantly at the 5th min in males but not in females; Plasma sodium showed no variations but potassium increased after 30 min; PRA rose significantly at the 5th min and, after 120 min of orthostatism, was found to be 3 times greater than its value after recumbency; and PAC increased significantly at the 15th min and exhibited a plateau 4.5 times its basal values after 90 min of upright posture. When subjects returned to the supine position all the parameters, except PAC decreased. During active orthostatism, a significant correlation was found between PAC and plasma potassium, but correlation was closer between PAC and PRA and between PAC and PRA + potassium. It can be concluded that the renin-angiotensin system is a more potent stimulus for aldosterone secretion than plasma potassium in normal man assuming postural changes. The results presented here can be applied to the development of a short posture test in non-hospitalized patients.

Recovery of [13C]bicarbonate as respiratory 13CO2 in mechanically ventilated patients.

Measurement of the nutrient oxidation rate with 13C as a tracer requires knowledge of the value of its coefficient of fractional recovery in the expired gas (FR). We measured FR in nine intensive care patients who were mechanically ventilated and received total parenteral nutrition. NaH13CO3 was administered at a priming dose (3.75 mumol.kg-1.min-1) followed by a continuous infusion (0.05 mumol.kg-1.min-1). Metabolic rate and pulmonary carbon dioxide elimination (VCO2) were measured by using a mass-spectrometer system. The 13C-12C ratio was measured in the expired gas with an isotopic-ratio mass spectrometer and FR was calculated by using standard equations. The average value of FR was 0.899 +/- 0.026 (means +/- SE) and remained stable for each patient on 2 consecutive days. Between patients, the coefficient of variation of FR was 8.6%. Metabolic rate was the only physiological factor found to affect the FR value.

Oxygen cost of breathing in postoperative patients. Pressure support ventilation vs continuous positive airway pressure.

In seven postoperative patients with normal preoperative pulmonary function tests, we evaluated the oxygen cost of breathing (VO2resp) during continuous positive pressure ventilation (CPAP) and during a 15 cm H2O inspiratory pressure support ventilation (IPSV). For both periods, VO2 resp was estimated as the difference between total oxygen uptake of the period (VO2tot), measured by a mass-spectrometer system, and that during controlled ventilation. During CPAP ventilation, VO2resp was found to be 11.2 +/- 1.4 percent of VO2tot. During IPSV, VO2resp was found insignificant. It is concluded that a 15 cm H2O IPSV takes over the major part of the work of breathing in postoperative patients without preexisting pulmonary disease.

Lack of oxygen supply dependency in patients with severe sepsis. A study of oxygen delivery increased by military antishock trouser and dobutamine.

BACKGROUND: During severe sepsis, the existence of a pathologic oxygen supply dependency remains controversial. STUDY OBJECTIVE: To evaluate the relationship between oxygen delivery (DO2) and oxygen consumption (VO2) during severe sepsis and to compare, in this respect, survivors and nonsurvivors and patients with normal or increased concentration of plasma lactate. STUDY DESIGN: Cohort analytic study. SETTING: Three European ICUs in university hospitals. PATIENTS: Seventeen mechanically ventilated patients with severe sepsis (six with high blood lactate levels) studied within the first day of diagnosis. INTERVENTIONS AND MEASUREMENTS: Pulmonary elimination of carbon dioxide, or carbon dioxide production (VCO2) and VO2 were measured by indirect calorimetry before and after two interventions designed to increase DO2 (calculated from the Fick equation): inflation of a military antishock trouser (MAST) and infusion of dobutamine. RESULTS: During MAST inflation, DO2 increased by 19% in patients with a normal concentration of plasma lactate (p < 0.01), but remained unchanged in patients with high lactate levels. During dobutamine infusion, DO2 increased in both groups by 16% (p < 0.01) and 20% (p < 0.05), respectively. In both groups, we found that the VO2 and VCO2 were not affected by either the MAST or the dobutamine-induced increase in DO2. There was no difference between survivors and nonsurvivors. CONCLUSION: There was no evidence of a pathologic oxygen supply dependency in patients with severe sepsis, even in those who had an elevated concentration of plasma lactate and in those who ultimately died. These results do not favor the conclusion that maximizing DO2 is a primary therapeutic objective in such patients.

Oxygen cost of breathing and diaphragmatic pressure-time index. Measurement in patients with COPD during weaning with pressure support ventilation.

The oxygen cost of breathing and the time integral of the transdiaphragmatic pressure were measured at the onset of the weaning period in eight patients with chronic obstructive pulmonary disease requiring mechanical ventilation. Measurements were achieved during continuous positive airway pressure ventilation and during 15 cmH2O pressure support ventilation. For both periods, the O2COB was estimated as the difference between oxygen uptake of the period and that during controlled ventilation. During CPAP ventilation, the O2COB was 16.9 +/- 1.5 percent. During PSV, it was only 6.3 +/- 1.3 percent, and PTdi decreased by 73 percent compared to the CPAP period. Both effects illustrate the ability of PSV to facilitate spontaneous breathing during weaning from mechanical ventilation. However, we found these measurements to be of no help in predicting the duration of the weaning process.

Added inspiratory work of breathing during CPAP ventilation: comparison of two demand-valve devices with a continuous flow-system.

Measurements of added inspiratory work (AIW) of breathing imposed by three different CPAP systems were performed in 10 patients. One system was a continuous flow system while the two others were demand flow systems separated from respirators (Ohmeda VD 101 and Draeger CPAP 800 devices). AIW was calculated from pressure and flow signals recorded at the mouthpiece level. The AIW calculated with the two demand-flow systems was found to be the same as the AIW calculated with the continuous flow system although the results obtained by the Draeger device were less constant. The results obtained with the Ohmeda device in our patients conflicted with data previously published using a lung model.

Clinical validation of the Deltatrac monitoring system in mechanically ventilated patients.

OBJECTIVE: To evaluate a monitor of pulmonary gas exchange (Deltatrac, Datex) in a clinical setting. DESIGN: After in vitro evaluation, comparison over 2 min between VO2 and VCO2 values measured by the Deltatrac and the Douglas bag technique. Comparisons were also achieved over 8 h periods between the Deltatrac and a system using a mass-spectrometer. SETTING: Polyvalent intensive care unit (ICU 15 beds) in a 1200 bed general hospital. PATIENTS: Comparison with the Douglas bag technique in 10 patients undergoing controlled ventilation. Comparison with the mass-spectrometer system in 25 other patients undergoing controlled or pressure support ventilation. MEASUREMENTS AND RESULTS: Compared to the results obtained by the Douglas bag technique, the bias (+/- 2 SD) for VO2 and VCO2 was -3.5 +/- 26.6 and 6.1 +/- 12.7 ml.min-1, respectively. By comparison with the mass-spectrometer system, the bias for VO2 and RQ was -5.8 +/- 16.0 ml.min-1 and 0.018 +/- 0.048, respectively. No drift between the two systems was observed over time. CONCLUSIONS: The Deltatrac appears suitable for VO2 and VCO2 measurements in ventilated patients and equivalent to a mass-spectrometer system for long term measurements.

Energy expenditure in the acute renal failure patient mechanically ventilated.

Twenty mechanically ventilated patients with acute renal failure were studied on 31 occasions to determine their energy expenditure (EE) during a 2 h period before a hemodialysis. Oxygen consumption and CO2 elimination were measured continuously with a mass spectrometer system. EE (1660 +/- 48 kcal day-1) was close to the total caloric intake (1682 +/- 83 kcal day-1) and represented 1.19 +/- 0.03 times the predicted resting energy expenditure (PREE) with large inter-individual variations (0.7-1.7 PREE). EE/PREE was higher when sepsis was present (1.31 +/- 0.03 versus 1.14 +/- 0.02; p less than 0.05). Glucose oxidation rate (4.35 mg kg-1 min-1) exceeded glucose intake (2.6 mg kg-1 min-1). Respiratory quotient was 1.02 +/- 0.01. Nitrogen loss was 17.3 +/- 1.7 g day-1 and nitrogen balance -11.9 +/- 1.9 g day-1. In conclusion, EE values were scattered but never exceeded 1.7 times the PREE. Sepsis increased EE. With a nutritional support covering EE, nitrogen balance remained markedly negative and a preferential utilisation of glucose and lipogenesis occurred.

Increased lactate/pyruvate ratio with normal beta-hydroxybutyrate/acetoacetate ratio and lack of oxygen supply dependency in a patient with fatal septic shock.

We report a case of fatal septic shock, with hyperlactatemia and blood cultures positive for Streptococcus pneumoniae, in a 70-year-old patient. On two occasions (5 days, and 2 days before the patient's death), the relationship between oxygen delivery (DO2) and consumption (VO2) was examined in conjunction with two presumed markers of tissue oxygenation: the lactate/pyruvate ratio (L/P), and the beta-hydroxybutyrate acetoacetate ratio (beta OHB/AcAc). Increasing DO2 by about 30% ("oxygen flux test") failed to increase VO2. The beta OHB/AcAc ratio remained within normal limits, thus suggesting uncompromised tissue oxygenation at the hepatic level. The L/P ratio remained persistently above normal limits, thus suggesting actual organ or regional hypoxia. This case shows that during an overwhelming septic shock, the "oxygen flux test" can be negative, despite the presence of hyperlactatemia and of an increased L/P ratio suggestive of impaired tissue oxygenation.

The effects of norepinephrine infusion on oxygen consumption in a patient with septic shock.

A 65-year-old man developed postsurgical septic shock, unresponsive to plasma volume expansion and administration of dopamine and dobutamine. A continuous norepinephrine infusion was then started and the dose increased to 0.62 micrograms.kg-1.min-1 until the mean arterial pressure was 70 mmHg. Prior to and during the norepinephrine infusion, oxygen consumption was continuously measured with a mass spectrometer system. There was a parallel increase in mean arterial pressure and oxygen consumption (+ 35%). There was also an increase in cardiac index and oxygen delivery. Systemic vascular resistance was only transiently increased. In this case with septic shock, norepinephrine infusion improved hemodynamic variables with an associated increase in oxygen consumption.

Maternal and fetal plasma renin and dopamine-beta-hydroxylase activities in toxemic pregnancy.

Toxemic and normotensive pregnant women were compared for plasma renin activity (PRA), aldosterone (PA), and dopamine-beta-hydroxylase (DBH). At term, hypertensive patients exhibited higher levels of PRA and PA, but similar levels of DBH, progesterone, and estradiol. Their elevated blood pressure was significantly correlated to their levels of PRA. During the delivery levels of PRA increased significantly in toxemic patients in spontaneous labor. Venous and arterial cord PRA levels were higher in babies born to hypertensive mothers than in babies born to normotensive mothers. Three days postpartum, maternal PRA level was lower than at term. Seven days postpartum, PRA levels remained higher in toxemic than in normal women. Maternal DBH levels did not change during and after delivery. Levels of DBH were undetectable in cord blood. We conclude that the renin-angiotensin system is involved in the pathogenesis of toxemia.

Effect of position, nitric oxide, and almitrine on lung perfusion in a porcine model of acute lung injury.

In a porcine model of oleic acid-induced lung injury, the effects of inhaled nitric oxide (iNO) and intravenous almitrine bismesylate (ivALM), which enhances the hypoxic pulmonary vasoconstriction on the distribution of regional pulmonary blood flow (PBF), were assessed. After injection of 0.12 ml/kg oleic acid, 20 anesthetized and mechanically ventilated piglets [weight of 25 +/- 2.6 (SD) kg] were randomly divided into four groups: supine position, prone position, and 10 ppm iNO for 40 min followed by 4 microg x kg(-1) x min(-1) ivALM for 40 min in supine position and in prone position. PBF was measured with positron emission tomography and H(2)15O. The redistribution of PBF was studied on a pixel-by-pixel basis. Positron emission tomography scans were performed before and then 120, 160, and 200 min after injury. With prone position alone, although PBF remained prevalent in the dorsal regions it was significantly redistributed toward the ventral regions (P < 0.001). A ventral redistribution of PBF was also obtained with iNO regardless of the position (P = 0.043). Adjunction of ivALM had no further effect on PBF redistribution. PP and iNO have an additive effect on ventral redistribution of PBF.

Epinephrine, norepinephrine, and dopamine during a 4-day head-down bed rest.

Head-down bed rest at an angle of 6 degrees was used as an experimental model to simulate the hemodynamic effects of microgravity, i.e., the shift of fluids from the lower to the upper part of the body. The sympathoadrenal activity during acute (from 0.5 to 10 h) and prolonged (4 days) head-down bed rest was assessed in eight healthy men (24 +/- 1 yr) by measuring epinephrine (E), norepinephrine (NE), dopamine (DA), and methoxylated metabolite levels in their plasma and urine. Catecholamine (CA) and methoxyamine levels were essentially unaltered at any time of bed rest. Maximal changes in plasma were on the second day (D2): NE, 547 +/- 84 vs. 384 +/- 55 pg/ml; DA, 192 +/- 32 vs. 141 +/- 16 pg/ml; NS. After 24 h of bed rest, heart rate decreased from 71 +/- 1 to 63 +/- 3/min (P less than 0.01). Daily dynamic leg exercise [50% maximum O2 uptake (VO2 max)] used as a countermeasure did not alter the pattern of plasma CA during bed rest but resulted in a higher urinary NE excretion during postexercise recovery (+45% on D2; P less than 0.05). The data indicate no evident relationship between sympathoadrenal function and stimulation of cardiopulmonary receptors or neuroendocrine changes induced by central hypervolemia during head-down bed rest.

Energy expenditure during severe acute pancreatitis.

Energy expenditure (EE) was measured, during 3 consecutive days, in six patients suffering from acute pancreatitis. Measurements were achieved postoperatively, under mechanical ventilation, using a mass spectrometer system. EE represented 1.49 times (range: 1.08-1.78) the predicted resting energy expenditure (PREE) according to the reevaluated Harris-Benedict equation. There was a weak positive correlation between EE and core temperature and a negative correlation between EE and nitrogen balance. EE/PREE was not different between septic and nonseptic patients (1.58 +/- 0.06 vs. 1.39 +/- 0.07). The calculations of nutrient oxidation rate indicated a high protein catabolic rate, a neoglucogenesis, and a lipolysis.

[The renin-angiotensin system and the sympathetic nervous system in essential hypertension]. / Système rénine-angiotensine et système nerveux sympathique dans l'hypertension artérielle essentielle.

In 112 patients with essential hypertension (HTA), free of any therapeutic and receiving the standard ward, a significant inverse relationship was found between age and plasma renin activity (PRA) and plasma aldosterone (PA), measured in the supine and upright position. Urinary epinephrine and norepinephrine were not related with age. When dividing the patients in 4 different age groups, it appeared that those younger than 30 years exhibited a significantly higher PRA and PA values and a higher frequency of borderline hypertension (45 p. 100) than the older ones (12 p. 100). So as to determine the characteristics associated with borderline HTA, it was necessary to eliminate the influence of age. This was achieved by comparing two groups of carefully age-matched patients, one with borderline HTA and the other with stable HTA. The only significant difference found was a significantly more marked increase in PRA in response to orthostatism, in patients with borderline HTA. Since renin responses to an orthostatic stress are largely mediated by renal nerves, this result suggest that borderline HTA could be associated with an increased reactivity of the sympathetic nervous system.

[Peranesthetic monitoring of ventilation in children: value of capnometry]. / Surveillance peranesthésique de la ventilation chez l'enfant: intérêt de la capnométrie.

Continuous measurement of the end-expiratory partial pressure of carbon dioxide (PETCO2) during anaesthesia has been proposed for non-invasive monitoring of arterial PCO2 (PaCO2). The values and the stability of the difference (PaCO2-PETCO2) during anaesthesia were studied for two ventilatory settings in eight children with healthy lungs and normal cardiac function undergoing minor surgery. PaCO2 values were all within a physiological range (30.2-43.6 mmHg). PaCO2-PETCO2 values ranged from 0.2 to 9.9 mmHg. With either mode of ventilation, there was no significant variation in PaCO2-PETCO2. It is concluded that estimation of PaCO2 was reliable during anaesthesia when haemodynamic and ventilatory states were stable, but a first determination of the PaCO2-PETCO2 gradient remained necessary for each child.

[Continuous measurement of gas exchange during artificial ventilation]. / Mesure en continu des échanges gazeux au cours de la ventilation artificielle.

A system for on-line measurement of respiratory gas exchange in patients undergoing artificial ventilation is described. Fractional concentrations were measured by a mass spectrometer and expired flow by a pneumotachometer; signals processing was carried out by a microcomputer. The accuracy of the measurement of the burning methanol RQ was within 1.6% at FIO2 lower or equal to 0.4. When compared to a reference method (the Douglas bag method), correlation was found to be excellent. The major problem in measuring gas exchange in a ventilated patient is that physiological signals are contaminated by artefacts which may lead to erroneous computations. An algorithm was developed in order to identify and disregard artefacted periods or ventilatory unsteady state in the patients. The technique used for data processing gave reliable continuous measurements of respiratory gas exchange for periods up to 24 h, without interfering with the nursing of the ventilated patients.