Noninvasive cardiac output monitoring.
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Cardiac Output↗
Biomedical subjects
R Dueck
Publications and source records attributed to R Dueck.
Assessment and monitoring of flow limitation and other parameters from flow/volume loops.
Flow/volume (F/V) spirometry is routinely used for assessing the type and severity of lung disease. Forced vital capacity (FVC) and timed vital capacity (FEV1) provide the best estimates of airflow obstruction in patients with asthma, chronic obstructive pulmonary disease (COPD) and emphysema. Computerized spirometers are now available for early home recognition of asthma exacerbation in high risk patients with severe persistent disease, and for recognition of either infection or rejection in lung transplant patients. Patients with severe COPD may exhibit expiratory flow limitation (EFL) on tidal volume (VT) expiratory F/V (VTF/V) curves, either with or without applying negative expiratory pressure (NEP). EFL results in dynamic hyperinflation and persistently raised alveolar pressure or intrinsic PEEP (PEEPi). Hyperinflation and raised PEEPi greatly enhance dyspnea with exertion through the added work of the threshold load needed to overcome raised pleural pressure. Esophageal (pleural) pressure monitoring may be added to VTF/V loops for assessing the severity of PEEPi: 1) to optimize assisted ventilation by mask or via endotracheal tube with high inspiratory flow rates to lower I:E ratio, and 2) to assess the efficacy of either pressure support ventilation (PSV) or low level extrinsic PEEP in reducing the threshold load of PEEPi. Intraoperative tidal volume F/V loops can also be used to document the efficacy of emphysema lung volume reduction surgery (LVRS) via disappearance of EFL. Finally, the mechanism of ventilatory constraint can be identified with the use of exercise tidal volume F/V loops referenced to maximum F/V loops and static lung volumes. Patients with severe COPD show inspiratory F/V loops approaching 95% of total lung capacity, and flow limitation over the entire expiratory F/V curve during light levels of exercise. Surprisingly, patients with a history of congestive heart failure may lower lung volume towards residual volume during exercise, thereby reducing airway diameter and inducing expiratory flow limitation.
Asthma↗
Resolving disagreements in the patient-physician relationship: tools for improving communication in managed care.
Managed care uses financial incentives and restrictions on tests and procedures to attempt to influence physician decision making and limit costs. Increasingly, the public is questioning whether physicians are truly making decisions based on the patient's best interest or are unduly influenced by economic incentives. These circumstances lead to the potential for disagreements and conflict in the patient-physician relationship. We convened a group of individuals in October 1998, including patient representatives, leaders from health care organizations, practicing physicians, communication experts, and medical ethicists, to articulate the types of disagreements emerging in the patient-physician relationship as a result of managed care. We addressed 3 specific scenarios physicians may encounter, including allocation, illustrated by a patient who is referred to a different ophthalmologist based on a new arrangement in the physician's group; access, illustrated by a patient who wishes to see his own physician for a same-day visit rather than a nurse specialist; and financial incentives, illustrated by a patient who expects to have a test performed and a physician who does not believe the test is necessary but is afraid the patient will think the physician is not ordering the test because of financial incentives. Using these scenarios, we suggest communication strategies that physicians can use to decrease the potential for disagreements. In addition, we propose strategies that health plans or physician groups can use to alleviate or resolve these disagreements.
Communication↗
A pilot study of expiratory flow limitation and lung volume reduction surgery.
STUDY OBJECTIVES: To examine the relationships between changes in expiratory flow limitation (FL) during anesthesia and postoperative responses to lung volume reduction surgery (LVRS). DESIGN: Prospective consecutive case comparison. SETTING: University medical center. PATIENTS: Eight patients with severe emphysema. INTERVENTIONS: General anesthesia with muscle paralysis and thoracic epidural analgesia were provided for LVRS via median sternotomy. MEASUREMENTS: FEV(1), functional residual capacity (FRC), and total lung capacity (TLC) were measured preoperatively and 3 months postoperatively. Tidal volume (VT) flow/volume (F/V) curves were obtained with a Pitot-type spirometer. VT, expiratory flow rate at 0. 25 x VT (V'VT,25% ), and peak expiratory flow rate (V'VT,MAX) were obtained from VT F/V curves to derive V'VT,25%/V'VT,MAX ratio as a measure of FL. RESULTS: Closed chest VT F/V curves during anesthesia pre-LVRS showed four patients with FL (group A) whose V'VT,25%/V'VT, MAX ratio was 0.38 +/- 0.06 (mean +/- SD) and four patients without FL (group B) whose V'VT,25%/V'VT,MAX ratio was 0.82 +/- 0.06 (p = 0. 0001). Closed chest post-LVRS V'VT,25%/V'VT,MAX ratio during anesthesia increased by 0.48 +/- 0.08 in group A, compared with a 0. 19 +/- 0.16 reduction in group B (p = 0.0001). Preoperative FEV(1) was 0.57 +/- 0.10 L for group A vs 0.82 +/- 0.13 L for group B (p = 0.02). Postoperative FEV(1) increased by 67 +/- 40% for group A (p = 0.03) vs 29 +/- 21% for group B (not significant). FRC decreased by 33 +/- 3% for group A vs 17 +/- 5% for group B (p = 0.0007), and FRC/TLC decreased by 0.14 +/- 0.05 for group A vs 0.01 +/- 0.07 for group B (p = 0.026). Post-LVRS V'VT,25%/V'VT,MAX ratio change during anesthesia correlated with postoperative reduction in FRC (r(2) = 0. 89, p = 0.0004) and FRC/TLC (r(2) = 0.52, p = 0.045). CONCLUSION: Post-LVRS change in V'VT,25%/V'VT,MAX ratio during anesthesia showed a linear relationship with 3-month postoperative improvement in dynamic hyperinflation. Thus, V'VT,25%/V'VT,MAX ratio may help provide valuable insights into the interactions between chest wall recoil, dynamic hyperinflation, and VT flow rates in patients with severe COPD and LVRS.
Aged↗
Effects of endotracheal intubation on airway neuropeptide content, arterial oxygenation and lung volumes in anaesthetized rats.
BACKGROUND: General anaesthesia affects lung volume and pulmonary gas exchange. What role is played by mechanical stimulation by the endotracheal tube? METHODS: We investigated the effects of intubation on arterial oxygenation and lung volume in rats. RESULTS: Endotracheal intubation caused an increase in PA-aO2 and volume of trapped gas in the lung. This was accompanied by a reduction in neuropeptides and calcitonin gene-related peptide (CGRP) in trachea, bronchi and lung, and in vasoactive intestinal peptide (VIP) in the trachea. The increase in PA-aO2 and volume of trapped gas due to intubation was not altered in the animals given capsaicin, in which neuropeptide levels were reduced. CONCLUSIONS: These data suggest that the decrease in CGRP and VIP content in the airway tissues may be one of the consequences, but not the cause, of impaired gas exchange by endotracheal intubation. The increase in volume of trapped gas in the lung is apparently not mediated by activation of capsaicin-sensitive sensory nerves.
Anesthesia, General↗
Pulmonary mechanics changes associated with cardiac surgery.
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Aged↗
The experience of a breast mass CQI team.
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Breast Neoplasms↗
Effect of parainfluenza infection on gas exchange and FRC response to anesthesia in sheep.
We examined the interaction of viral pneumonitis with the respiratory effects of halothane/N2O anesthesia in six tracheostomized sheep. Ventilation-perfusion (VA/Q) distribution, pulmonary artery pressure (PAP), metabolic rate (VO2), and functional residual capacity (FRC) measurements were compared in awake and anesthetized animals before and 1 week after inoculation by tracheal instillation of ovine parainfluenza type-3 (PI-3) virus. Awake shunt (VA/Q less than 0.005) was 0.6 +/- 0.4% (+/- standard deviation [SD]) before, versus 3.9 +/- 2.0% after PI-3 infection (P less than 0.05). Awake arterial O2 tension (PaO2) was 139.9 +/- 14.0 mmHg before and 114.5 +/- 8.7 mmHg after infection (P less than 0.05). Mean PAP increased from 6.0 +/- 1.9 mmHg before to 11.5 +/- 1.6 mmHg after infection (P less than 0.05). Anesthesia shunt increased to 5.7 +/- 2.3% before and 11.2 +/- 3.4% after PI-3 (P less than 0.05 for the change from awake, and P less than 0.05 for a PI-3 anesthesia shunt difference). PAP was not significantly different from awake, either before or after infection. Anesthesia also produced an average 14.8 +/- 3.8% FRC reduction before and 17.4 +/- 6.4% reduction after infection (P less than 0.05 for FRC reduction with anesthesia, not significantly different for PI-3). Three of the six sheep developed shunt at higher FRCs after infection, both awake and during anesthesia; however, the average slope of the shunt/FRC response to anesthesia was unchanged, suggesting that this was not a neurogenic form of auto-PEEP. We therefore conclude that viral infection significantly enhanced the pulmonary effects of anesthesia.
Anesthesia, Inhalation↗
The lung volume at which shunting occurs with inhalation anesthesia.
The relationship between functional residual capacity (FRC) and shunt development with halothane anesthesia in 18 nonobese surgical patients (age, 21-34 yr) was studied. FRC was measured by helium dilution, and intrapulmonary shunt was distinguished from ventilation-perfusion inequality by multiple tracer inert gas elimination analysis. Awake supine FRC was 34.6 +/- 6.6% (mean +/- SD) of total lung capacity (TLC), and closing capacity (CC) was 29.8 +/- 5.3% of TLC. Anesthesia, muscle paralysis, tracheal intubation, and mechanical ventilation produced an average 14.6 +/- 13.3% FRC reduction to an average anesthesia FRC 29.8% of TLC (P = 0.002). Shunt increased from 1.2% +/- 1.5% awake to 8.6 +/- 8.3% during anesthesia (P = 0.005). A nonlinear relationship was found between shunt and FRC/TLC so that anesthetized subjects with an FRC less than awake CC had an average 11.4 +/- 8.3% shunt, whereas subjects with an FRC greater than CC had a 2.4 +/- 2.8% shunt (P = 0.025). Nonsmokers developed shunt only if FRC was less than CC. Smokers showed a significantly higher shunt for a given (FRC-CC)/TLC compared to nonsmokers (P less than 0.001). The slope of the regression of shunt on BMI (body mass index = weight/height2) showed a significant increase during anesthesia (P = 0.005), and smokers had a significantly higher slope compared to nonsmokers (P = 0.001). These findings suggest a gravity-dependent mechanism for intrapulmonary shunting during anesthesia. Therefore, shunting was due to dependent regional lung volume reduction associated with an FRC decrease to less than closing capacity. The enhanced intrapulmonary shunting in smokers may have been related to the increased dependent regional residual volume associated with smoking.
Adult↗
Effects of barbiturate anesthesia on functional residual capacity and ribcage/diaphragm contributions to ventilation.
The effect of iv methohexital infusion anesthesia on functional residual capacity (FRC) (helium dilution) in 14 surgical patients (age 23 to 59 years) was determined. Eight subjects were studied wearing an inflatable mask, sealed with surgical lubricant. They showed a mean +/- SD 3.5 +/- 6.4% FRC decrease (no significance). Six subjects studied via mouthpiece awake and via endotracheal tube during anesthesia showed a mean 22 +/- 19% reduction in FRC, significantly greater than face mask studies (P less than 0.05). The greatest FRC decrease occurred in subjects with repetitive or protracted coughing after intubation. The serum methohexital level was 6.6 +/- 3.6 micrograms/ml for intubated patients, and 6.0 +/- 1.1 micrograms/ml in those with face mask (no significance). The depth of anesthesia was sufficient to produce a 50% reduction in ventilatory response to CO2 rebreathing, from 15.8 to 8.7 l/min/% CO2. Respitrace plethysmography indicated a 38 +/- 12% ribcage contribution to tidal volume during quiet breathing, which increased to 47 +/- 14% with CO2 breathing (end-tidal FCO2 9-10%). There was no dimunition of ribcage contribution during anesthesia in either group, irrespective of CO2 concentration. The authors interpret their findings to indicate that iv methohexital anesthesia does not produce FRC reduction, in contrast to an inhaled anesthetic such as halothane. It is proposed that this difference may be related to maintenance of coordinated ribcage/diaphragm muscle activity, because ribcage activity is markedly suppressed by halothane. In addition, it is proposed that FRC reduction in intubated subjects was the result of a confounding variable, namely coughing in response to the endotracheal tube.
Adult↗
Intermittent tracheostomy in sheep.
A modified tracheostomy was designed for respiratory function studies in sheep. Our primary objective was to prevent development of severe tracheal stenosis, which was observed with procedures designed for canine tracheostomy. Surgery consisted of an intercartilaginous tracheal slit, with apposition of tracheal mucosa to skin. This procedure produced no significant stenosis at postmortem evaluation in 19 sheep. In contrast, 5 of 20 sheep with excision of the ventral 1/3 of the third and fourth tracheal rings, had severe tracheal stenosis.
Animals↗
Mechanisms of abnormal gas exchange during anesthesia.
A review of the literature and of our recent data (obtained by computer-based analysis of multiple inert gas elimination) re-emphasizes the significant gas exchange disturbances found to occur during general anesthesia which develop for probably several reasons. In this report we suggest firstly that the reduction in functional residual capacity (FRC) may well be an effect of anesthesia just as is abnormal gas exchange. In other words, the reduction in FRC is not per se the cause of gas exchange disturbances, but rather occurs alongside them. Secondly, the causes of abnormal gas exchange may have more to do with local ventilatory reserve in lung regions, be that reserve via the existence of collateral ventilation as in dogs or via acute or chronic airway pathology in disease. Thus, species without adequate collateral ventilation or with some degree of airway disease would seem to be at greatest risk of developing highly significant gas exchange disturbances during general anesthesia. We speculate that this vulnerability is probably due to multiple factors that change as a result of the particular anesthetic agents used. Such factors include altered hypoxic vasoconstriction, a change in airway secretions and clearance of those secretions, changes in bronchomotor tone, changes in surfactant activity, and alveolar volume loss due to rapid uptake of soluble anesthetic gases like nitrous oxide. To qualitatively and quantitatively distinguish amongst these various potential factors will require experimental protocols and techniques of a highly controlled and accurate nature. That in 1983 we still do not understand the basic mechanisms behind abnormal gas exchange during anesthesia attests to the difficulty of mounting such an experiment.
Adult↗
Thiopental: false-positive RAST in patients with elevated serum IgE.
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Adult↗
Lung volume and VA/Q distribution response to intravenous versus inhalation anesthesia in sheep.
The effects of intravenous pentobarbital versus nitrous oxide/halothane inhalation anesthesia on blood gases, distribution of ventilation-perfusion ratios (VA/Q), and lung volume (FRC) were compared in 8 tracheostomized sheep in the lateral decubitus position. Pentobarbital anesthesia produced no significant changes (from awake control) in arterial blood PO2 or PCO2, ventilation-perfusion inequality, intrapulmonary shunt, or FRC during either spontaneous breathing or mechanical ventilation with muscle paralysis. With inhalation anesthesia, PaO2 decreased from 132 +/- 13 mmHg awake to 106 +/- 11 mmHg and 104 +/- 6 mmHg (FIO2 all 0.3) during spontaneous and mechanical ventilation. Shunt increased from 1.4 +/- 1.0% awake to 10.6 +/- 4.5 and 13.9 +/- 5.3%, respectively. Mean VA/Q decreased from 0.39 +/- 0.07 awake, to 0.21 +/- 0.06 and 0.29 +/- 0.07. Log standard deviation of VA/Q increased from 0.66 +/- 0.12 awake to 0.83 +/- 0.28 and 0.89 +/- 0.15. FRC decreased from 1.66 +/- 0.65 1 to 1.46 +/- 0.62 and 1.22 +/- 0.63 1, respectively. Differences in response to intravenous versus inhalation anesthesia for the above variables all were statistically significant at P less than 0.05. FRC and shunt changes with anesthesia showed significant correlation for both spontaneous (r = -0.80) and mechanical ventilation (r = 0.77), P less than 0.005 for both. We therefore propose that the differences between lung volume and gas exchange effects of intravenous versus inhalation anesthesia in sheep may have been related causally.
Anesthesia, Inhalation↗
The neurologic effects of thiopental therapy following experimental cardiac arrest in cats.
To define the utility of high-dose barbiturate therapy following an episode of complete global cerebral ischemia, we investigate the effects of 60 mg/kg of thiopental given to cats five minutes after resuscitation from 12, 14, or 16 min of electrically induced ventricular fibrillation (VF). All aspects of the arrest, resuscitation, with post-arrest care were carefully controlled, with the EEG becoming isoelectric 20-25 s after the onset mean resuscitation time of 2.5 +/- 0.2 (SEM) min. For any given duration of VF, there were no differences (control vs thiopental) in any pre- or post-arrest parameters (blood pressure, blood gases, electrolytes, etc.) A total of 68 resuscitated cats were entered into various treatment and control groups, and all but one group received 20-24 h of post-resuscitation paralysis, mechanical ventilation, and ICU support before being extubated. Cats received an additional six days of aggressive nursing care, and daily examinations were performed with the assignment of a neurologic deficit score (NDS) between 0 (normal) and (brain dead). Autopsies were performed to determine the cause of death in animals which died before the end of the seven-day observation period. The early post-arrest period was marked by the occurrence of repetitive, rhythmic bursts of high-frequency electroencephalographic (EEG) activity (? seizures) in 38 per cent of control animals (16/42, all arrest times combined). Ten of these animals died as a result of severe neurologic injuries. By contrast, only 12 per cent of treated cats (3/26) developed similar EEG patterns (P less than 0.05) and there were no neurologic deaths in the thiopental groups. The differences in the incidence of neurologic deaths (control vs. thiopental) was significant (P less than 0.02). The change in overall mortality did not quite reach significance (36 per cent vs. 21 per cent), and treatment had no effect on the incidence of deaths due to cardiovascular causes (e.g., myocardial infarctions). In spite of the effects on mortality, treatment had no effect on the neurologic function of survivors (assessed by NDS). These findings suggest that thiopental improved survival rates by suppressing an unusual post-arrest EEG pattern (? anticonvulsant effect), but had no additional cerebral protective effects.
Animals↗
Carotid artery exteriorization for percutaneous catheterization in sheep and dogs.
Summary and reliable physiologic or pharmacologic investigation in animal models often requires arterial catheterization in awake animal subjects. This can be facilitated by surgical exteriorization of the carotid artery for subsequent percutaneous catheterization. A simplified surgical procedure is described that has been demonstrated to have limited morbidity and excellent applicability for multiple use, as well as to ensure high blood flow rates when needed. The surgical technique involves transfer of the carotid artery from a deep paratracheal position to a ventrolateral neck subcutaneous position, protected from the underlying mattress sutures by the sternomastoid muscle.
Animals↗
Canine VA/Q distribution responses to inhalation anesthesia and mechanical ventilation.
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Anesthesia, Inhalation↗