Biomedical subjects
G C Carlon
Publications and source records attributed to G C Carlon.
An automated mechanism for protection of mass spectrometry sampling tubing.
The usefulness of medical mass spectrometers in intensive care units can be limited by too frequent obstruction of the tubing that transports gases from the patients to the analyzing unit. To overcome this problem, we developed an automated system consisting of an infrared light sensor and a three-way valve. One port of the three-way valve connects to 2.4-m disposable tubing that collects gases from the patient's airway. The second port is connected to a mass spectrometer analyzing unit through 30-m permanently installed tubing. The third port is connected to a pressurized oxygen source. An infrared light sensor is placed on the shorter tubing, between the patient and the three-way valve. When increased optical density is detected, due to entrainment of respiratory secretions, the three-way valve is activated. Gas flow is closed between the patient and the mass spectrometer and opened between the pressurized oxygen source and patient tubing to flush its contents. During the six years that the protection system has been in use, the frequency with which the disposable gas collection tubing is changed has been halved. Furthermore, periodic tests of delay and response times, performed at each bedside station, indicate that permanent connection tubing only needed cleaning at 2- to 3-year intervals. The system has decreased the cost of operating our mass spectrometers while also reducing periods of unavailability due to equipment failure.
Capnography in mechanically ventilated patients.
Capnography, the science of CO2 waveforms analysis, can play a role in the management of mechanically ventilated patients. Mass spectrometers are the devices most commonly used to collect sequentially and examine CO2 waveforms from multiple patients in the ICU or operating rooms. We present here a review of some clinical and technical problems, which may be resolved efficiently and expeditiously through the use of mass spectrometry and capnography. Mechanical failures, especially those that lead to rebreathing of exhaled gases, can be readily detected. The patient's progress during weaning and the consequences of changes in mechanical assistance can be virtually and noninvasively determined. An expanded role of capnography in mechanically ventilated patients can increase the use of mass spectrometers in the ICU.
Admitting cancer patients to the intensive care unit.
The allocation of critical care resources must follow criteria of distributive justice. Because most societies cannot indefinitely expand medical care costs, difficult decisions on the quality and quantity of care that can be rendered to each patient are inevitable. Data on which objective decisions can be based are currently being gathered at many levels. It is reasonable to anticipate that over the next few years regulations will be formulated to decide which patients can be admitted to the ICU. Critical care physicians have the right and obligation to be involved in all aspects of these decision-making processes.
High-frequency jet ventilation during thoracic surgical procedures.
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Reinventing the triangular wheel.
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Case of embolization by a sheared pulmonary artery catheter tip.
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Evaluation of a closed-tracheal suction system.
A new tracheo-bronchial closed-suction system has been recently introduced. The Trach Care catheter can be connected to the endotracheal tube of a patient on mechanical ventilation and be left in place as long as 24 h. Thus, suctioning does not require disconnection from the mechanical ventilator. We evaluated the benefits of this new system in 20 patients receiving mechanical ventilation; ten patients required PEEP of 10 cm H2O and under, while the other ten patients needed PEEP over 10 cm H2O to maintain acceptable oxygenation. PaCO2, arterial oxygen saturation, and alveolar-arterial oxygen tension difference were measured before and after suctioning, using a conventional catheter and the Trach Care closed-suction method. Oxygenation only deteriorated when the open technique was used in patients receiving over 10 cm H2O of PEEP. The changes were statistically, but not clinically, significant. The Trach Care system is approximately 25 times as expensive as conventional suctions catheter, so its use cannot be justified economically. A potential advantage of the technique is preventing the dissemination of contaminated secretions, which are dispersed when the patient is disconnected from the ventilator and inspiratory gas flow persists. While no universal advantage of the closed-suction system was found, potential benefits may be considered on a case-by-case basis.
Pulmonary embolus-induced disseminated intravascular coagulation.
Pulmonary embolus as a cause of disseminated intravascular coagulation has only recently been recognized. The hemorrhagic disorder reported in the past was associated with little or no bleeding. We report a case of pulmonary embolus associated with life-threatening disseminated intravascular coagulation.
'APACHES,' chiefs, and Indians.
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Airway humidification with high-frequency jet ventilation.
Humidification of inspired gases is indispensible to prevent serious injury to the tracheal mucosa of patients on mechanical ventilation. High-frequency jet ventilation (HFJV), recently introduced for the management of some forms of respiratory failure, presents unusual technical problems of humidification. The present investigation evaluated a technique to humidify jet gases by delivering small droplets of normal saline in front of the injector cannula, and utilizing the jet flow to nebulize the fluids administered. One millicurie of technetium-99m sulfur colloid (Tc-99m) was diluted in 10 ml of saline and infused in the airway of nine patients supported on HFJV. Six patients were orotracheally intubated and three were tracheostomized. A portable gamma camera was used to determine the distribution of radioactive contrast in the airway every 200 sec. When the injector catheter was directed upward, as was the case in tracheostomized patients, contrast material accumulated in the ventilator lines, and visualization of the airway was limited to the trachea. In orotracheally intubated patients, the injector catheter was generally directed downward, and radioactive contrast material extended beyond the major bronchi. The radioactive tracer reached the most distal airway location in patients with the lowest PaCO2 values. Thus, when humidification systems rely on jet-stream nebulization of fluids, the position of the injector cannula should facilitate saline flow by gravity. In the presence of poor alveolar ventilation, the concomitant risk of inadequate humidification should be considered.
Development of high-frequency ventilation techniques.
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High-frequency jet ventilation: technical implications.
A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.
Experimental evaluation of high-frequency jet ventilation.
The consensus of available studies indicates that high-frequency jet ventilation (HFJV) can adequately ventilate animals in respiratory failure, although a clear superiority to volume-cycled ventilation (VCV) cannot be established. HFJV is probably useful in the presence of airway disruption and in tracheal or pulmonary surgery. Clinical trials and additional bench and animal studies must be performed, to reach a full understanding of the potential benefits of this technique.
Hemodynamic effects of continuous positive-pressure ventilation and high-frequency jet ventilation with positive end-expiratory pressure in normal dogs.
The hemodynamic effects of high-frequency jet ventilation (HFJV) at 60, 120, 240, and 480 breath/min, and conventional ventilation at 15 breath/min were compared in 6 anesthetized, paralyzed dogs, at 0, 10, and 20 cm H2O of positive end-expiratory pressure (PEEP). On HFJV at the same inspired oxygen, PaCO2, and PEEP levels, hemodynamic function improved significantly. Cardiac output was higher, whereas transmural CVP and pulmonary vascular resistances were lower. The improvement was primarily related to a decrease in mean airway pressure, particularly at higher PEEP levels. When PEEP was applied, hemodynamic function improved even when mean airway pressure was maintained constant. The findings suggest that lung volume was smaller during HFJV, and/or that lung volume changes during each respiratory cycle contributed to differences in venous return and ventricular function.
Critical care nurse and high-frequency ventilation.
As the treatment of respiratory failure becomes more sophisticated and technical, the critical care nurse is faced with many challenges. High-frequency ventilation is a modality of respiratory support employing principles different from those of conventional ventilation. For these reasons, the nurse must be familiar with the indications for its use and the practical management of the ventilated patient. This paper addresses those aspects of respiratory support which have the greatest impact on nursing care.
Early prediction of outcome of respiratory failure. Comparison of high-frequency jet ventilation and volume-cycled ventilation.
Data from a prospective randomized investigation comparing volume-cycled ventilation and high-frequency jet ventilation were reexamined to determine whether improvement of respiratory and hemodynamic function, as well as ultimate outcome (death or survival), could be predicted early in the course of the disease. End points were selected for the ratio of the arterial oxygen pressure over the fractional concentration of oxygen in the inspired gas (PaO2/FIO2), the arterial oxygen saturation (SaO2), the arterial carbon dioxide tension (PaCO2), and the cardiac index. Patients were assigned to "success" or "failure" groups, according to the values recorded for those end points 24 hours after institution of mechanical ventilation. Values obtained from initiation of mechanical ventilation to 16 hours later were divided into four time groups. Differences between patients who "succeeded" and "failed" were compared at each time interval. Ultimate outcome was also compared. The PaCO2 and cardiac index were poor predictors of survival. Early values did not foretell the progression of these variables. The PaO2/FIO2 and SaO2 effectively discriminated, at all time intervals, between patients who succeeded and failed on volume-cycled ventilation. On high-frequency jet ventilation, significant differences were evident only after eight hours of support. With both types of ventilator, patients who reached the end point of oxygenation at 24 hours survived in far greater numbers than those who did not. On the basis of this investigation, it appears justified to attempt high-frequency jet ventilation in patients who do not rapidly improve on volume-cycled ventilation. Institution of high-frequency jet ventilation as the initial support method may not be advisable, since failure does not become apparent for many hours.