In my opinion: carbon monoxide: what should we do?
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Anesthesiology↗
Biomedical subjects
R A Epstein
Publications and source records attributed to R A Epstein.
Assessment of suitability for low-fee control psychoanalysis: some theoretical and technical considerations.
In the assessment of suitability for low-fee control analysis, various factors may interfere with successful referral, evaluation, and disposition. Variables within the referring analyst, patient, candidate, and supervisor are examined in their interaction with the circumstances of the assessment enterprise. Issues of competence, self-esteem, and oedipal rivalry, as well as guilt feelings, concerns about rejection, and other conflicts may be mobilized and may prevent a successful outcome. Clinical data from three assessments are presented and discussed. The concept of an assessment process, analogous to the psychoanalytic process, is proposed. In this process, manifestations of the patient's intrapsychic life and indicators of potential transferences emerge in the context of the analysis of the patient's reactions to the assessment. Potential sources of interference with the assessment process are identified, and measures to avoid them are suggested.
Adult↗
Frequency dependence of dead space during high-frequency ventilation in rhesus monkeys.
A rotary valve ventilator, designed to allow the direct measurement of expired gas volume and composition, was used to maintain gas exchange in anesthetized, paralyzed, rhesus monkey at ventilatory frequencies up to 20 Hz. A total of five studies were carried out on three animals. Determinations of the minute ventilation required to maintain a normal steady-state PCO2, together with the FECO2 and arterial PO2, PCO2, and pH, were made at a number of frequencies. The results so obtained were used to calculate the Bohr (physiological) dead space. Dead space remained approximately constant at close to the value determined during spontaneous ventilation for each individual animal in the range of ventilatory frequencies from below 1 to around 5 Hz, but decreased somewhat with increasing frequency above 5 Hz. The calculated physiological dead space at 15 Hz was about 70% of the value at normal respiratory frequencies. These findings in primates, obtained using a ventilator system which allows very accurate determinations of expired gas volume and content, when compared with those from our previous studies in rabbits and dogs, provide further evidence that the relationship between efficiency of gas exchange and ventilatory frequency during HFV is highly species-specific.
Animals↗
Effective dead space of differently shaped airways during high-frequency ventilation of a CO2-producing lung model.
A simple lung model is described which simulates the mechanical properties and CO2 production of the lungs of a small animal, and which can be used with high-frequency ventilators. The model was ventilated by a rotary-valve ventilator and the system was used to determine the increment in 'physiological' (Bohr) dead space produced at various ventilatory frequencies between 0.5 and 15 Hz by the insertion of various additional volumes and configurations of 'anatomical' dead space in its 'upper airway'. It was found that the insertion of a straight tube with an internal diameter similar to that of the ventilator outlet tube produced an increment in 'physiological' dead space that remained commensurate with the volume of the added tube at all combinations of the tube volume and ventilatory frequency. The insertion of similar volumes of dead space in the form of tubes with smoothly expanded central portions produced increments in 'physiological' dead space which were commensurate with the volume of the added tube only at the lowest frequencies, and actually became negative at higher frequencies and volumes. These findings provide further evidence that the volume and configuration of the external portion of a high-frequency ventilator system may be of at least as much importance in determining its efficiency as is the lung structure of the animal or patient being ventilated.
Animals↗
End-expiratory carbon dioxide measurement as an estimate of alveolar carbon dioxide tension.
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Carbon Dioxide↗
Frequency dependence of dead space during high-frequency ventilation in dogs.
A rotary valve ventilator, designed to allow the direct measurement of expired gas volume and composition, was used to maintain gas exchange in anesthetized, paralyzed, mongrel dogs at ventilatory frequencies up to 20 Hz. A total of eleven studies were carried out on four animals. Determinations of the minute ventilation required to maintain a normal steady-state PCO2, together with the FECO2 and arterial PO2, PCO2, and pH, were made at a number of frequencies. The results so obtained were used to calculate the Bohr (physiological) dead space. Dead space remained approximately constant at close to the value measured during spontaneous ventilation for each individual dog in the range of ventilatory frequencies from below 1 to around 5 Hz, but decreased with increasing frequency above 5 Hz. The calculated physiological dead space at 15 Hz was about half of the value at normal respiratory frequencies. These findings in dogs, obtained using a ventilator system which allows very accurate determinations of expired gas volume and content, are consistent with published results for this species from other laboratories. They contrast with our earlier findings in rabbits that dead space remains constant with increasing frequency, suggesting that the effects of high-frequency ventilation on CO2 transport are species-dependent.
Animals↗
Soda lime adsorption of isoflurane and enflurane.
The authors demonstrated that soda lime will adsorb enflurane or isoflurane as a function of the water content of the soda lime. Various volumes of liquid enflurane or isoflurane were placed in an equilibration flask containing fresh (15% water by weight) or dried soda lime and the vapor phase anesthetic concentrations plotted. When dry soda lime was used, the plot of concentration as a function of volume of liquid added was biphasic: initially flat and then rising linearly. This is qualitatively similar to data reported previously for halothane. The authors hypothesize that drying soda lime produces a molecular sieve-like structure, as adsorption is greatest for molecules with small carbon chain lengths and kinetic diameters, or with structural characteristics such as cis/trans isomerism, which effectively reduce molecular size.
Adsorption↗
A new ventilator for physiologic studies during high-frequency ventilation.
Research in the field of high frequency ventilation (HFV) has been hampered by the difficulty of collecting and analyzing expired gas, uncontaminated by gas of inspiratory composition, at ventilatory frequencies in the relevant range. A new mechanical ventilator is described, which has been designed to facilitate studies on the respiratory physiology of small animals during HFV. Ventilation is controlled by a single rotary valve, which alternately switches the airway to an approximately constant-flow gas source during inspiration, and to gas measurement and analysis apparatus during expiration, which takes place passively. Theoretical and experimental studies, using the techniques of mechanical and mathematical modelling, are used to measure the performance of the ventilator and to demonstrate that it allows the quantitative collection of expired gas during ventilation at rates up to at least 20 Hz. The advantages and limitations of this approach are discussed.
Animals↗
Constancy of physiological dead space during high-frequency ventilation.
A ventilator, specially designed to allow the direct measurement of expired gas volume and composition, was used to maintain gas exchange in anesthetized, paralyzed, New Zealand White rabbits at ventilatory frequencies up to 22 Hz. A total of eleven studies were carried out on seven animals. Determinations of the minute ventilation required to maintain a normal steady-state PCO2, together with the FECO2 and arterial PO2, PCO2, and pH, were made at a number of frequencies. The results so obtained were used to calculate the physiological dead space. It was found that this value remained remarkably constant for each individual rabbit over a range of ventilatory frequencies from 1 to 22 Hz. Our findings in rabbits are in contrast to those of other workers (in dogs) that adequate gas exchange can be maintained at high ventilatory frequencies with the use of tidal volumes much smaller than the volume of anatomical dead space.
Animals↗
Halothane adsorption complicating the use of soda-lime to humidify anaesthetic gases.
If the anaesthetic circle system is arranged to increase the humidity of fresh anaesthetic gases by placing the carbon dioxide absorbent canister between the fresh gas inlet and the patient, drying of the soda-lime can occur. Very dry soda-lime adsorbs significant quantities of halothane. Using fresh soda-lime, effluent halothane concentration reached 50% of the input concentration in 35s, but this time increased to 500 s when dry soda-lime was used. The use of dry soda-lime can result in a slow inhalation induction or in the release of absorbed halothane during a subsequent anaesthetic.
Adsorption↗
Mechanisms of halothane adsorption by dry soda-lime.
Using fresh soda-lime (15% water by weight) the soda lime/air partition coefficient of halothane was found to decrease as a function of vapour phase halothane concentration from 2.40 at 0.3% halothane by volume to 1.15 at 2.6%, but adsorption generally followed Henry's law. However, soda-lime dried to a constant weight and subsequently exposed to various concentrations of halothane adsorbed approximately 320 microlitre of vaporized liquid halothane per 100 g before a measurable concentration of halothane was detected in the vapour phase. Adding additional halothane then caused a linear increase in vapour concentration. We conclude that dry soda-lime can absorb large quantities of halothane by a mechanism which is similar to that of a molecular sieve. After these "high affinity" sites are satisfied, additional halothane is absorbed by a mechanism following Henry's law.
Adsorption↗
Breath-to-breath variations in rate and depth of ventilation in sleeping infants.
Ventilatory measurements were made noninvasively over 2- to 3-h periods during sleep in each of nine normal infants at 1 mo of age. To assess the changes that occur in ventilation on a breath-to-breath basis, we 1) examined the variations of each of tidal volume (VT), respiratory cycle time (Ttot), expiratory time (TE), and inspiratory time (TI) and 2) studied their interrelationships. We found that the variations of VT, Ttot, and TE but not of TI were significantly greater in rapid-eye-movement (REM) than in quiet sleep. In addition, on a breath-to-breath basis, VT had a positive linear relationship and strong correlation with TI; however, the correlation between VT and TE was weak in both sleep states. VT/Ttot was found to be moderately and negatively correlated with Ttot in both REM and quiet sleep. VT was weakly correlated with Ttot in REM sleep and was, on the average, more correlated with Ttot in quiet sleep. We suggest that in infants 1) on a breath-to-breath basis, VT/Ttot is likely to drop if respiratory frequency is decreased and 2) VT is nonlinearly related to Ttot during sleep; this lack of linearity depends on the lack of constancy of VT/Ttot, which is in turn closely related to the variability of the "on-switching" of inspiratory activity.
Humans↗
Flow to lung compartments with different time constants: effect of choice of model.
The thesis that an accelerating flow generator provides more even ventilation than a constant flow generator originated from studies using mechanical lung models. We simulated such studies by use of mathematical models. We found that the conclusions of these previous studies were dependent on the particular characteristics of their mechanical models. Studies employing more commonly used models indicate that constant flow generators, in fact, tend to provide more uniform ventilation, especially with long inspiratory times.
Humans↗
Automatic rezeroing of drifting physiologic signals.
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Electronics↗
Determinants of distortions in CO2 catheter sampling systems: a mathematical model.
A mathematical model was developed to predict the distortions in the measured expiratory CO2 concentration time profile caused by catheter sampling systems. Parameters considered included the expiratory flow and concentration profiles, the sample flow rate, the sample tube dimensions and the sample cell volume. Unless care is taken in choosing the parameters of a catheter sampling system, particularly in the presence of low expiratory flow rates and short expiratory times, the CO2 concentration profile may be severely distorted. In worst case situations end tidal CO2 plateaux may not be recognized or alternately artifactual plateaux may be produced. Sample flow rate and sample cell volume are the most important parameters while distortion within the sample tube itself is relatively less important.
Carbon Dioxide↗
Heart rate and heart rate variability during sleep in aborted sudden infant death syndrome.
Heart rate and heart rate variability were studied during sleep at monthly intervals in 18 normal infants and 12 infants with aborted sudden infant death syndrome during the first four months of life. At each age studied and in both REM and quiet sleep, the aborted SIDS infants had a 5 to 10% faster heart rate. Moreover, the aborted SIDS infants had a 10 to 45% smaller beat-to-beat and overall heart rate variability. Although the differences in overall variability persisted after normalization by the absolute heart rate, the differences in the beat-to-beat variability narrowed. These findings, when taken in conjunction with our previous observation that aborted SIDS infants have a smaller QT index than normal infants, suggest that infants with aborted SIDS have an increase in sympathetic activity or in circulating levels of catecholamines.
Female↗
Ventilatory requirements of critically ill neonates.
Ventrilatory requirement was assessed in 15 critically ill neonates on a total of 31 occasions. All were either currently receiving mechanical ventilation or had had mechanical ventilation in the recent past. Minute ventilation, respiratory frequency, carbon dioxide production (VCO2) and arterial blood PaCO2 were measured. Dead space-to-tidal volume ratios (VD/VT) were calculated. The ventilatory requirements of the infants ranged from 1.16 to 4.30 times normal. Derived parameters related the increased ventilatory requirement to pulmonary (VD/VT) and metabolic (VCO2) factors. The increased requirement was not significantly related more often to either of these two factors, although one or the other was frequently predominant in individual cases. Data presented allow specification of the minute volume range needed for ventilators designed for neonates, and the maximal compressible volume that can be tolerated when expired volume monitoring is desired.
Body Weight↗