Philip Drinker

Tidal Volume and Frequency Dependence of Carbon Dioxide Elimination by High-Frequency Ventilation

Six patients with chronic respiratory failure received mechanical ventilation with tidal volumes less than or equal to the dead-space volume, at frequencies of 30 to 900 breaths per minute. The rate of elimination of carbon dioxide from the ventilator system during a brief trial of high-frequency ventilation accurately predicted the long-term effectiveness of a given combination of frequency and tidal volume. Below frequencies of about 200 breaths per minute, the volume of carbon dioxide eliminated from these patients was most strongly related to the product of frequency and tidal volume; at higher frequencies, carbon dioxide elimination was determined by the tidal volume and was independent of frequency. These results suggest that although the effectiveness of high-frequency ventilation is primarily a function of the product of tidal volume and frequency, above a critical frequency the mechanical characteristics of the lung reduce gas transport by limiting the volume transmitted to the periphery of the lung.

Effect of bias flow rate on gas transport during high-frequency oscillatory ventilation.

Ventilatory support with low tidal volume, high-frequency oscillatory ventilation (HFOV) usually uses a bias flow system to provide fresh gas. Although the bias flow rates (Vbf) used previously have varied widely among experimental configurations, the precise role of the bias flow in HFOV-mediated gas transport has not been defined. We assessed the effect of bias flow rate on gas transport during HFOV by measuring CO2 removal rate (MCO2) in anesthetized, paralyzed dogs, using a wide range of bias flow rates (0.7-28.9 L X min-1). When a fixed tidal volume of 40 ml was applied at HFOV frequencies of 2-12 Hz, MCO2 was proportional to the time-averaged alveolar-bias flow CO2 concentration difference. Thus, when Vbf was reduced below a value which resulted in a substantial increase in bias flow CO2 concentration, MCO2 was reduced. These findings are consistent with a simple framework in which the relative magnitudes of the resistances to gas transport of the airways and of the bias flow (1/Vbf) determine the contribution of the bias flow rate to overall gas transport during HFOV. This relationship may be employed to assess the intra-airway contribution to HFOV-mediated gas transport at any bias flow rate, and may therefore allow comparison of results from experiments utilizing various bias flow rates.

Upper and lower bounds on oxygen transfer rates

Approximate methods for evaluating oxygen transfer in extracorporeal devices are considered. It is shown that the constant slope approach and the advancing front concept can be used to bracket the exact solution. Generalization of the constant slope approach allows the use of available correlations for heat or mass transfer. In the case of complicated geometries for which no correlations exist, the method shows how one can experiment with different fluids and gases and estimate performance of the device as a blood oxygenator.Analytical expressions for some typical geometries using the advancing front approach are presented. These expressions show good agreement with experimental data and with an available computer solution which includes nonlinearities of the dissociation curve.

The prolonged administration of artificial respiration

Abstract A review and brief history, with bibliography and illustrations of the development of the apparatus described.

Extracorporeal Membrane Oxygenation in Severe Acute Respiratory Failure. A Randomized Prospective Study

Nine medical centers collaborated in a prospective randomized study to evaluate prolonged extracorporeal membrane oxygenation (ECMO) as a therapy for severe acute respiratory failure (ARF). Ninety adult patients were selected by common criteria of arterial hypoxemia and treated with either conventional mechanical ventilation (48 patients) or mechanical ventilation supplemented with partial venoarterial bypass (42 patients). Four patients in each group survived. The majority of patients suffered acute bacterial or viral pneumonia (57%). All nine patients with pulmonary embolism and six patients with posttraumatic acute respiratory failure died. The majority of patients died of progressive reduction of transpulmonary gas exchange and decreased compliance due to diffuse pulmonary inflammation, necrosis, and fibrosis. We conclude that ECMO can support respiratory gas exchange but did not increase the probability of long-term survival in patients with severe ARF.

MASS TRANSFER IN A TWO-PHASE (LIQUID-LIQUID) CROSSFLOW BLOOD OXYGENATOR

Publisher Summary Many investigators have designed and tested oxygenators employing gravity-driven films of fluorocarbon as the oxygen carrier. While most of the devices achieved high oxygen transfer rates, biocompatibility problems associated with the formation of a blood-fluorocarbon emulsion have prevented their further development to the clinical stage. This chapter describes the development of a simple analytical model for predicting mass transfer in a two-phase contacting device. Combined analytical and experimental results indicate that the parameters that govern the mass transfer are also of importance in considering the emulsion problem. Experimental carbon dioxide transfer to distilled water or oxygen transfer to cow blood in vitro occurred from annular films of dense fluorocarbon to either liquid in cross-flow across a falling interface. For liquids with constant solubility and no chemical reaction, such as fluorocarbon and water, the concentration profile in a small fluid element on one side of the interface is determined by the complementary error function. The chapter describes eight series of experiments that were performed transferring carbon dioxide to distilled water over a range of the two dimensionless groups. An experimental mass transfer coefficient was based on a log-mean partial pressure difference analogous to the representation of heat exchange performance.

Industrial Hygiene and Air Pollution

In the first edition of her Industrial Toxicology, Dr. Alice Hamilton had the following to say: &dquo; ... A great deal of money has been wasted by well-meaning employers who sought to protect lead furnace men or oxide roasters or white lead grinders against poisoning, by providing baths and lunchrooms and clean overalls and mouth washes and such, instead of preventing the escape of lead into the air the men were obliged to breathe, and unfortunately this has sometimes been done under a physician’s advice. It must never be forgotten that the great majority of industrial poisons enter the body with the inspired air and that while a workman eats only three times a day he breathes sixteen times a minute during the eight or ten hours of his working day.&dquo; These are maxims and guides which we will always apply in practice of industrial hygiene and in air pollution control.

HUMIDITY CONTROL IN RESIDENCES.

IN A LARGE portion of this country the severity of the winter makes cen,tral heating units an economic necessity. The average householder must give some attention to temperature control in his residence, but he pavs little heed to the control of moisture in the air. He may be aware that cold, moderately dry, outdoor air means excessively dry air within the house; of this latter condition he may complain, but he usually does nothing to correct it. This paper draws attention to the difficulties encountered in humidity control in the average residence, and suggests methods by which unduly dry air conditions can be remedied.