Morphometric differences in pulmonary lesions in primary and secondary ARDS. A preliminary study in autopsies

The present study was undertaken in order to describe the morphological differences between pulmonary lesions in acute respiratory distress syndrome originating from direct pulmonary injury (ARDSp) and those originating from extrapulmonary injury (ARDSexp). We investigated a total of 38 ARDS-patients (27 males) ranging in age from 19 to 75 years, classified according to underlying disease in pulmonary (ARDSp) and extrapulmonary disease (ARDSexp). The extent of acute diffuse alveolar damage was assessed morphometrically on histologic gross sections in the upper and lower lobes of one lung. The lesions showed quantitative differences in extent and distribution according to underlying disease (primary pulmonary or secondary involvement). In pulmonary ARDS, a predominance of alveolar collapse (16.6%+/-12.3% versus 10.3%+/-11.9%, p = 0,03), fibrinous exudate (1.7%+/-3.2% versus 0.4%+/-1.1%, p = 0.01) and alveolar wall edema (11.2%+/-7.4% versus 6.6%+/-4.4%, p = 0,05) were found compared to extrapulmonary ARDS. We conclude that the morphology of acute diffuse alveolar damage (DAD) is mainly determined by underlying disease (pulmonary ARDS or extrapulmonary ARDS) differing in quantitative terms within the lung. Physiological, radiographic and respiratory system mechanics differences described in ARDSp and ARDSexp may therefore be due to morphometric differences in pulmonary lesions.

Hypomagnesemia in critically ill cancer patients: a prospective study of predictive factors

Hypomagnesemia is the most common electrolyte disturbance seen upon admission to the intensive care unit (ICU). Reliable predictors of its occurrence are not described. The objective of this prospective study was to determine factors predictive of hypomagnesemia upon admission to the ICU. In a single tertiary cancer center, 226 patients with different diagnoses upon entering were studied. Hypomagnesemia was defined by serum levels <1.5 mg/dl. Demographic data, type of cancer, cause of admission, previous history of arrhythmia, cardiovascular disease, renal failure, drug administration (particularly diuretics, antiarrhythmics, chemotherapy and platinum compounds), previous nutrition intake and presence of hypovolemia were recorded for each patient. Blood was collected for determination of serum magnesium, potassium, sodium, calcium, phosphorus, blood urea nitrogen and creatinine levels. Upon admission, 103 (45.6%) patients had hypomagnesemia and 123 (54.4%) had normomagnesemia. A normal dietary habit prior to ICU admission was associated with normal Mg levels (P = 0.007) and higher average levels of serum Mg (P = 0.002). Postoperative patients (N = 182) had lower levels of serum Mg (0.60 +/- 0.14 mmol/l compared with 0.66 +/- 0.17 mmol/l, P = 0.006). A stepwise multiple linear regression disclosed that only normal dietary habits (OR = 0.45; CI = 0.26-0.79) and the fact of being a postoperative patient (OR = 2.42; CI = 1. 17-4.98) were significantly correlated with serum Mg levels (overall model probability = 0.001). These findings should be used to identify patients at risk for such disturbance, even in other critically ill populations.

Respiratory system mechanics in patients treated with isotonic or hypertonic NaCl solutions

Twenty-one patients who underwent elective surgery for coronary artery bypass were studied right after chest wall closure. They were anesthetized, paralyzed, and artificially ventilated with a constant-flow ventilator. Airflow, changes in lung volume, and tracheal pressure were measured. Respiratory system resistance (Rrs,max) was partitioned into its homogeneous (Rrs,min) and uneven (Rrs,u) components. Respiratory system elastance (Ers) was also measured. The subjects were randomly divided into two groups injected with test solutions just after chest wall closure: eleven patients received isotonic saline (0.9% NaCl solution), whereas the remaining ten were injected with hypertonic saline (7.5% NaCl solution). In all patients, mechanical parameters were measured at six different times: just before infusion, at 5 and 10 min (end of infusion); and at 15, 20, and 25 min after beginning of injection. No statistically significant differences were observed in respiratory system mechanical parameters between groups or between different times within each group. Our data suggest that hypertonic saline infusion does not result in significant changes in respiratory system mechanics in patients submitted to coronary artery bypass.

Flow and volume dependence of respiratory system mechanics during constant flow ventilation in normal subjects and in adult respiratory distress syndrome

Seven control subjects and seven patients with adult respiratory distress syndrome (ARDS) were artificially ventilated and flow, volume, and tracheal pressure were monitored. Respiratory system resistance (Rrs,max) was partitioned into its homogeneous (Rrs,min) and uneven (Rrs,u) components. Respiratory system elastance (Ers) was also measured. In both groups Ers did not vary with different inspiratory flows and volumes, but was significantly higher in ARDS. With increasing volume (isoflow maneuvers), Rrs,max and Rrs,u increased but Rrs,min remained unaltered in ARDS. In control patients, however, resistances did not vary but Rrs,max and Rrs,u were smaller and Rrs,min equaled their corresponding values in ARDS. Hence, stress relaxation seems to be increased in ARDS. During isovolume maneuvers Rrs,max and Rrs,u decreased with increasing flows (both groups), although they were significantly higher in ARDS. Rrs,min was not modified by different flows and was similar in both groups. Thus, pendelluft is also increased in ARDS. In conclusion, the mechanical profile of ARDS is characterized by increased Ers and Rrs,max, the latter being secondary to augmented mechanical unevenness within the system.

Respiratory system mechanics in guinea pigs after acute hemorrhage: role of adrenergic stimulation

We evaluated the effects of acute blood loss on the respiratory mechanics of guinea pigs. We measured respiratory system elastance (Ers) and resistance (Rrsmax) using the end-inflation occlusion method. Rrsmax was partitioned into its homogeneous component (Rrsmin) and that due to the unevenness within the respiratory system (Rrsu). Respiratory mechanics were studied both before and immediately after bleeding in eight animals. Another eight guinea pigs had received propranolol previously and were also submitted to hemorrhage. Propranolol-treated animals showed higher control values of Rrsmax (p less than .02) and Rrsmin (p less than .0001). Animals not treated with propranolol exhibited a decrease (p less than 0.001) in Rrsmax after hemorrhagic hypovolemia (from 0.375 +/- 0.051 to 0.323 +/- 0.042 cm H2O/ml.sec), due to a decrease (p less than 0.005) in Rrsmin (from 0.140 +/- 0.031 to 0.094 +/- 0.032 cm H2O/ml.sec), whereas Ers and Rrsu did not change. Propranolol-treated animals showed an increase (p less than .001) in Rrsmax (from 0.512 +/- 0.133 to 0.664 +/- 0.144 cm H2O/ml.sec), Rrsu (p less than 0.01) from 0.252 +/- 0.09 to 0.345 +/- 0.139 cm H2O/ml.sec, and Ers (p less than 0.001) (from 4.565 +/- 0.933 to 5.402 +/- 1.24 cm H2O/ml) after bleeding. The results indicate that the immediate effects of acute bleeding on respiratory mechanics are significantly influenced by catecholamines.