Pulmonary artery catheter problems.
Explore the source record for details and available documents.
Arrhythmias, Cardiac↗
Biomedical subjects
M J Tobin
Publications and source records attributed to M J Tobin.
Respiratory monitoring during mechanical ventilation.
Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and for providing an opportunity for the timely institution of lifesaving measures. Pulmonary gas exchange can be assessed by indices derived from arterial blood gas measurements, but these are limited by their invasive and intermittent nature. Intra-arterial electrodes that provide a continuous recording of blood gases are under development and appear very promising. Specially designed pulmonary artery catheters permit continuous recording of mixed venous O2 saturation, whereas continuous, non-invasive recordings of arterial oxygenation can be obtained with pulse oximetry and transcutaneous electrodes. A satisfactory method of monitoring CO2 tension does not exist. Measurements of respiratory drive can be obtained at the bedside, but their clinical usefulness remains unknown. Assessment of respiratory muscle strength is helpful in determining the need for mechanical ventilation, but a practical method of diagnosing respiratory muscle fatigue remains elusive. Recordings of the airway pressure waveform, calculation of thoracic compliance, and detailed examination of the pattern of breathing are helpful in assessing pulmonary mechanics. Although respiratory monitoring provides much useful information, it does not substitute for careful bedside examination.
Blood Gas Analysis↗
Weaning from mechanical ventilation.
Although the majority of patients can be easily weaned from mechanical ventilation, a substantial minority pose considerable difficulty. These patients account for a disproportionate amount of health care costs, and they pose enormous clinical, economic, and ethical problems. The major determinants of weaning outcome include the adequacy of pulmonary gas exchange, respiratory muscle pump function, and psychological problems. Many of the physiologic indices that have been used to predict weaning outcome are frequently inaccurate. Several techniques of weaning can be used, and there are no data to suggest the superiority of one technique over another. Management of the problem patient should be directed at the underlying cause of ventilator dependency, and an organized plan should be followed.
Humans↗
PEEP, auto-PEEP, and waterfalls.
Explore the source record for details and available documents.
Humans↗
Variability of resting respiratory drive and timing in healthy subjects.
Studies of breathing pattern have focused primarily on changes in the mean values of the breathing pattern components, whereas there has been minimal investigation of breath-to-breath variability, which should provide information on the constancy with which respiration is controlled. In this study we examined the variability of breathing pattern both on a breath-to-breath and day-to-day basis by calculating the coefficient of variation (i.e., the standard deviation expressed as a percentage of the mean). By examining breath-to-breath data, we found that the coefficients of variation of tidal volume (VT) and fractional inspiratory time (TI/TT, an index of timing) obtained with an inductive plethysmograph and spirometer were within 1% of each other. Examination of breath-to-breath variability in breathing pattern over a 15-min period in 65 subjects revealed large coefficients of variation, indicating the need to base calculations on a relatively large number of breaths. Less breath-to-breath variability was observed in respiratory frequency [f, 20.8 +/- 11.5% (SD)] and TI/TT (17.9 +/- 6.5%) than in VT (33 +/- 14.9%) and mean inspiratory flow (VT/TI, an index of drive; 31.6 +/- 12.6%; P less than 0.0001). Older subjects (60-81 yr) displayed greater breath-to-breath variability than young subjects (21-50 yr). Use of a mouthpiece did not affect the degree of variability.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Dyspnea: mechanisms, evaluation and treatment.
Explore the source record for details and available documents.
Biomechanical Phenomena↗
Respiratory monitoring in the intensive care unit.
Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and providing an opportunity for the timely institution of lifesaving measures. Arterial oxygenation can be monitored noninvasively using oximetry or transcutaneous oxygen electrodes, while mixed venous oxygenation can be recorded continuously with modified pulmonary artery catheters. A satisfactory method of monitoring carbon dioxide tension does not exist. Measurements of respiratory drive can be obtained at the bedside, but their clinical usefulness remains unknown. Assessment of respiratory muscle strength is helpful in determining the need for mechanical ventilation, but a practical method of diagnosing respiratory muscle fatigue remains elusive. Measurement of thoracic compliance and detailed examination of the breathing pattern, i.e., tidal volume, respiratory frequency, and the pattern of rib cage-abdominal motion, are helpful in assessing abnormal pulmonary mechanics. The detailed information provided by respiratory monitoring can complement but not replace careful bedside examination.
Biomechanical Phenomena↗
Weaning from mechanical ventilation.
Explore the source record for details and available documents.
Fatigue↗
Respiratory muscles in disease.
The respiratory muscles play an important role in the clinical manifestations of different disease states. Respiratory muscle dysfunction plays a primary role in the development of ventilatory failure in patients with neuromuscular disorders. Although the respiratory muscles are placed at a mechanical disadvantage in patients with obstructive lung disease, there is little clinical evidence to suggest that respiratory muscle dysfunction plays a primary role in the development of ventilatory failure.
Asthma↗
Accuracy of the respiratory inductive plethysmograph during loaded breathing.
Indirect methods of measuring ventilation, such as the respiratory inductive plethysmograph (RIP), operate on the assumption that the respiratory system possesses two degrees of freedom of motion: the rib cage and abdomen. Accurate measurements have been obtained in many patients with pulmonary disease who possess additional degrees of freedom. Since calibration and validation of the RIP was carried out during quiet breathing in these patients, the amount of asynchronous or paradoxic breathing was presumably similar during the calibration and validation runs. Conversely, accuracy might be lost if following the initial calibration procedure the magnitude of chest wall distortion increased during subsequent validation runs. We calibrated the RIP during quiet breathing and examined its accuracy while subsequently breathing against resistive loads that required the generation of 20-80% of the subject's maximum inspiratory mouth pressure (Pmmax). We compared the relative accuracy of three commonly employed calibration methods: isovolume technique, least-squares technique, and single position loop-area technique. Up to 60% of Pmmax, 89% of the RIP values with the least-squares technique were within +/- 10% of simultaneous spirometric (SP) measurements and 100% were within +/- 20% of SP, compared with 63 and 91%, respectively, for the loop-area technique and 19 and 54%, respectively, for the isovolume technique. At 70 and 80% of Pmmax accuracy deteriorated. Accuracy of respiratory timing was judged in terms of fractional inspiratory time (TI/TT).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Does rib cage-abdominal paradox signify respiratory muscle fatigue?
Studies suggesting that abnormal motion of the rib cage (RC) and abdomen (Ab) may indicate respiratory muscle fatigue have not separated the influence of respiratory load from that of fatigue in its pathogenesis. We hypothesized that abnormalities on RC-Ab motion are primarily related to increased load rather than fatigue. We tested this hypothesis in subjects breathing against resistive loads while maintaining 30 and 60% of maximum mouth pressure (Pmmax). RC-Ab asynchrony and paradox and the degree of variation in compartmental contribution to tidal volume were measured by inductive plethysmography and quantitated by the Konno-Mead method of analysis. Comparing measurements of base line and 30 and 60% of Pmmax indicated that the degree of asynchrony, paradox, and variation in compartmental contribution were significantly related to the level of the load; significant abnormalities were observed at even 30% of Pmmax, a target pressure that can be sustained indefinitely. In another group of subjects, fatigue was induced by sustaining 60% of Pmmax to the limits of tolerance. Indexes of abnormal RC-Ab motion increased from base line during the 1st min of loaded breathing but displayed no progression from the beginning to the end of the fatigue run. Immediately on discontinuation of the load, the indexes returned to levels similar to base line despite persistence of the fatigue state. These results in healthy subjects breathing against severe resistances indicate that RC-Ab asynchrony and paradox and variation in compartmental contribution to tidal volume are predominantly due to increases in respiratory load rather than muscle fatigue.
Abdomen↗
Konno-Mead analysis of ribcage-abdominal motion during successful and unsuccessful trials of weaning from mechanical ventilation.
Respiratory muscle fatigue is considered a common cause of weaning failure but its detection is hampered by the lack of a satisfactory diagnostic test. Abdominal paradox has been proposed as a valuable clinical index of fatigue and thus its presence may lead to curtailment of weaning trials. However, sensitivity and specificity of this sign as a predictor of weaning outcome is unknown. We hypothesize that abnormal ribcage-abdominal (RC-Ab) motion is a common finding in the early stages of weaning and its presence does not inevitably imply an unsuccessful weaning outcome. We tested this hypothesis in patients undergoing a weaning trial: one group had a successful weaning outcome and were extubated (n = 10) and the other group failed the trial (n = 7). Normal RC-Ab motion was separately characterized in 17 healthy subjects. Employing a calibrated respiratory inductive plethysmograph, quantitative assessment of asynchrony and paradox was obtained by computing several indices from series of breaths at fixed time periods using the Konno-Mead method of analysis. During the weaning trial, both groups of patients displayed significant increases in asynchrony and Ab paradox compared to normal values. As a group, patients who failed the trial displayed significantly greater asynchrony and paradox of the RC and Ab than patients with a successful outcome. However, there was considerable overlap between the individual patients in the 2 study groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Abdominal Muscles↗
Diagnosis of pneumonia: techniques and problems.
All diagnostic strategies in patients suspected of having pneumonia have considerable limitations. While the diagnostic strategy varies from patient to patient, an overview of one possible approach is summarized in Figures 2 and 3. The diagnosis and management of pneumonia usually poses little difficulty in the community setting, but the value of various diagnostic approaches in patients with hospital-acquired pneumonia is a subject of considerable controversy. Clinical criteria of pneumonia, including fever, purulent tracheobronchial secretions, leukocytosis, and a new infiltrate on chest radiograph are hampered by the high frequency with which these findings are observed in patients without pneumonia. Since tracheobronchial secretions are commonly contaminated by microorganisms colonizing the upper airways, routine culture of expectorated sputum, with the inevitable recovery of a potpourri of potential pathogens, can hardly be regarded as a meaningful exercise for the physician. Such cultures with subsequent extensive susceptibility testing form one of the largest workloads and expenses in microbiology laboratories. Clinical decisions based on such information may result in serious patient mismanagement with antibiotics, with the potential of superinfection and drug complication, which further add to hospital expenditures. Blood cultures are valuable when positive, but negative results are more common even in severe pneumonia. Transtracheal aspiration of tracheobronchial secretions is satisfactory in the diagnosis of community-acquired pneumonia in patients without pre-existing lung disease, but its value in the diagnosis of hospital-acquired pneumonia needs further evaluation. Transthoracic aspiration, especially with the newer finer needles, holds considerable promise but the significant risk of barotrauma deters most physicians from employing this procedure in patients requiring mechanical ventilation. Immunologic techniques of detecting microbial antigens, like countercurrentimmunoelectrophoresis and ELISA, are promising but presently inadequate to screen for a wide variety of organisms. Although it also has its limitations, fiberoptic bronchoscopy appears to be the most satisfactory technique if an invasive approach is being considered in a patient suspected of pneumonia. Samples taken with the plugged telescoping catheter technique, when properly performed, combined with quantitative cultures (and possibly antibody coating of bacteria) probably provide the least misleading information when a bacterial pathogen is being considered.(ABSTRACT TRUNCATED AT 400 WORDS)
Biopsy, Needle↗
Update on strategies in mechanical ventilation.
Explore the source record for details and available documents.
Barotrauma↗
Breathing pattern and metabolic behavior during anticipation of exercise.
The mechanisms responsible for the marked increase in ventilation at the onset of exercise are incompletely defined. A conditioned response to exercise anticipation has been suggested as an influencing factor, but systematic measurements have not been made during the transition from rest to the time when exercise is anticipated but has not yet commenced. We tested the hypothesis that cortical activity associated with the anticipation of exercise causes hyperpnea, which is at least partly responsible for the increased ventilation at the onset of exercise. To assess the influence of continuous cortical activity in the absence of exercise anticipation the subjects performed mental arithmetic tasks. Fifteen subjects performed the two experiments in a random order. Ventilation was measured noninvasively using a calibrated respiratory inductive plethysmograph and end-tidal CO2 concentration (FETCO2) was monitored at the nasal vestibule. Both exercise anticipation and mental arithmetic caused an increase in minute ventilation (VI) (P less than 0.01) and mean inspiratory flow (VT/TI, P less than 0.01), which reflects respiratory center drive, although the derivation differed in that the former was volume based, whereas the latter was due to alteration in timing. Despite the increase in VI, FETCO2 remained constant in both instances. In a complementary study the constant FETCO2 in the face of increased VI was shown to be due to increased CO2 output. The results show that the mere anticipation of exercise causes an increase in ventilation. The mechanism responsible for this hyperpnea cannot be due solely to respiratory center activation because of the constancy of FETCO2 and the associated alterations in cardiac and metabolic behavior.
Adult↗
The pattern of breathing during successful and unsuccessful trials of weaning from mechanical ventilation.
We prospectively examined the pattern of breathing in patients being weaned from mechanical ventilation: one group (n = 10) underwent a successful weaning trial and were extubated, whereas another group (n = 7) developed respiratory failure and required the reinstitution of mechanical ventilation. During the period of ventilator support, minute ventilation (VI), tidal volume (VT), and respiratory frequency (f) were similar in the 2 groups. After discontinuation of the ventilator, VI remained similar in the 2 groups, but VT was lower and f was higher in the patients who failed the trial compared with those who were successful, 194 +/- 23 and 398 +/- 56 ml (p less than 0.001), respectively, and 32.3 +/- 2.3 and 20.9 +/- 2.8 breaths/min (p less than 0.001), respectively. The failure group displayed a significant increase in PaCO2 (p less than 0.005) during spontaneous breathing, without a concomitant increase in the alveolar-arterial PO2 difference. Eighty-one percent of the variance in PaCO2 was accounted for by the pattern of rapid, shallow breathing. During weaning, resting respiratory drive (reflected by mean inspiratory flow, VT/TI) and fractional inspiratory time (TI/Ttot) were similar in the 2 groups. The patients in the failure group showed significant increases in VT/TI, 265 +/- 27 to 328 +/- 32 ml/s (p less than 0.01), and VI, 5.82 +/- 0.53 to 7.32 +/- 0.52 L/min (p less than 0.01), from the beginning to the end of the weaning trial; VT and f showed no further change.(ABSTRACT TRUNCATED AT 250 WORDS)
Acidosis, Respiratory↗