Continuous Positive Airway Pressure System Research Articles

Use of the Inspiron nebuliser during continuous positive airway pressure ventilation

The Inspiron Nebuliser 002305 with air entrainment was assessed as a gas delivery device in a continuous positive airway pressure system. Inspired oxygen concentrations, total gas flows and pressures within the system were measured over a range of settings, with and without positive and expiratory pressure. Inspired oxygen concentrations and total flows were completely disrupted when a positive and expiratory pressure valve was applied, and the system failed to generate continuous positive airway pressure. We would not therefore recommend the Inspiron nebuliser as a gas delivery system for continuous positive airway pressure.

A New Continuous Positive Airway Pressure (CPAP) Device

While continuous positive airway pressure (CPAP) is being increasingly employed for many forms of acute respiratory failure and postoperative hypoxaemia, most CPAP systems are either 'home made' or incorporated in sophisticated ventilators used in intensive care units. This paper describes the development of a continuous low flow CPAP system using a large latex reservoir bag and venturi generated positive end expiratory pressure (PEEP). The system has been successfully used for over twelve months in the general wards, the intensive care unit, accident and emergency department, the recovery ward and the coronary care unit.

Pressure-Time Product during Continuous Positive Airway Pressure, Pressure Support Ventilation, and T-Piece during Weaning from Mechanical Ventilation

The objective of this study was to compare the effects of continuous positive airway pressure (CPAP), pressure support ventilation (PS), and T-piece on the pressure-time product (PTP) during weaning from mechanical ventilation. The PTP is an estimate of the metabolic work or oxygen consumption of the respiratory muscles. We studied 10 intubated patients recovering from acute respiratory failure of various etiologies. A modified continuous flow (flow-by) CPAP of 0 and 5 cm H2O (CPAP-0 and CPAP-5, respectively), PS of 5 cm H2O (PS-5), and T-piece were applied in random order for 30 min each. In the last 5 min of the 30-min periods, we measured the esophageal pressure and transdiaphragmatic pressure-time products--PTP(es) and PTP(di), cm H2O.s/min, respectively-multiplied by respiratory frequency. Breathing pattern, total lung resistance (RL), quasi-static lung compliance (CL), intrinsic positive end-expiratory pressure (PEEPi), end-expiratory transpulmonary pressure (Ptpexp), arterial blood gases, blood pressure, and heart rate were also measured. In comparison to T-piece, CPAP-5 decreased PTP(es) 40% (p less than 0.01) and PTP(di) 43% (p less than 0.02), whereas PS-5 decreased PTP(es) 34% (p less than 0.01) and PTP(di) 38% (p less than 0.05). The decrease in PTP(es) with CPAP-5 was associated with a significant reduction in RL, and to a less extent in PEEPi relative to airway pressure. The contribution of the decrease in PEEPi to the reduction in PTP(es) amounted to 36%. With PS-5, respiratory system mechanics and PEEPi were not significantly different compared with T-piece. With CPAP-0, PTP tended to be lower than with T-piece.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-regulated continuous positive airway pressure to minimize imposed work of breathing

We have developed a new continuous positive airway pressure (CPAP) system, which consists of an electropneumatic regulator, a microcomputer, and a pneumotachograph placed between the endotracheal tube and the breathing circuit of the CPAP apparatus. This flow-regulated CPAP (FR-CPAP) system delivers a basal flow and also regulates this flow every 20 msec to match the patient's flow demand. To evaluate the performance of this FR-CPAP system, we compared the imposed work of breathing of the FR-CPAP and continuous flow CPAP (CF-CPAP) systems. A model lung was used to simulate spontaneous breathing. The imposed work of breathing of the FR-CPAP system was less than that of the CF-CPAP system. These results indicate that the FR-CPAP system could minimize the imposed work of breathing of a patient receiving CPAP.

Treatment of an infant with tracheobronchomalacia at home with a lightweight, high-humidity, continuous positive airway pressure system

From the Section of Pediatric Intensive Care, Children's Hospital at Albany Medical Center, Albany, NY.

Evaluation of conventional weaning criteria in patients with acute respiratory failure.

We evaluated the reliability of conventional weaning criteria from a ventilator during 33 weaning trials on 25 patients with acute respiratory failure (ARF). Of 13 criteria, a ratio of maximal voluntary ventilation to minute ventilation (MV) >2, a vital capacity >12 ml.kg(-1), a spontaneous respiratory rate <25 breaths.min(-1), and a MV <10 l.min(-1) appeared to be useful for predicting successful weaning outcome. However, even using those criteria, there were many falsely-negative cases. The alveolar-arterial P(O)(2) gradient <350 mmHg at an F i(O)(2) 1.0 was not useful as a predictor of weaning outcome. The present study demonstrates that conventional criteria are frequently inaccurate for predicting weaning outcomes and suggests that the use of some of these criteria may unnecessarily prolong the length of ventilator support. Since ventilation of most patients with poor oxygenation can be successfully discontinued by placing them on a continuous positive airway pressure system, these results suggest that the improvement of oxygenation is not an indispensable prerequisite for weaning from mechanical ventilators.

Evaluation of ejectors using the venturi effect for a continuous positive airway pressure system without compressed air.

The purpose of this study is to perform a test in the application of the existing ejectors with the continuous positive airway pressure (CPAP) system without compressed air. Four types of ejector (jet mixer, the former and new puritan nebulizer and the deluxe nebulizer) for blending oxygen and room air by the Venturi effect were tested. A decrease of mixed gas flow and an increase of oxygen concentration were observed according to the increase of positive pressure in all systems. The former puritan nebulizer and deluxe nebulizer were found to be unavailable for the CPAP system for high oxygen concentration and low mixed gas flow for the increase of positive pressure. In the system, however, with the new puritan nebulizer and jet mixer, a sufficient mixed gas flow and an appropriate oxygen concentration could be supplied at an adequate positive pressure. The CPAP system using only oxygen was judged as possibly giving availability.

Jet Flow-Regulated Expiratory Resistance to Maintain Constant CPAP During the Entire Respiratory Phase

We have developed a new continuous positive airway pressure (CPAP) device that consists of a microcomputer, a pressure transducer, and a pair of electronic interface valves. One of these valves creates the inspiratory demand flow, and the other creates the opposing jet flow by acting as an expiratory valve to maintain a constant CPAP. By controlling the two electronic interface valves, the airway pressure can be kept constant during the entire respiratory cycle. We compared our device with CPAP systems supplied with commercially available ventilators: the Puritan-Bennett 7200a, the Bear 5, the Servo 900C, and the CV 2000. A two-chambered spring loaded model lung was used to simulate inspiration and a piston pump model lung to simulate active exhalation. We compared both the inspiratory triggering work (WWIt) and expiratory flow-resistive work (WE) of each ventilator while in CPAP mode by calculating the corresponding areas of the pressure-volume loops using electrical integration. The WWIt of our apparatus and demand-flow ventilators was much smaller than that of the CV 2000. In our device, WE was also much smaller than those of the others. These results indicate that our device can be used for CPAP without causing airway pressure fluctuation, and therefore, without imposing an extra workload on the patient.

EVALUATION OF THE AMBU CPAP SYSTEM

We have assessed a Venturi driven device for delivering continuous positive airway pressure (CPAP) using a reservoir bag and expiratory valve under conditions of continuous flow and simulated spontaneous breathing. The system performed well and was economical, consuming only 3.5 litre min-1 of fresh gas. One Venturi was partially blocked and performed inadequately, but the function of a second one was close to the manufacturer's specification (inspired oxygen 33%, flow 20 litre min-1 against end-expiratory pressures of 0-1.8 kPa). Compliance curves for two reservoir bags (new and old) were defined; these showed that compliance increased as the pressure in the circuit increased. The characteristics of the expiratory valve approached those of a threshold resistor. Small fluctuations in airway pressure occurred at all settings of CPAP and decreased with the increasing compliance of the circuit at higher values of CPAP. The method provided to monitor the airway pressure was inaccurate and overestimated the true pressure by 20% at pressures greater than 1 kPa.

Flow Resistance of Expiratory Positive-Pressure Systems

We measured the flow-resistance of five commercially available 10 cm H2O expiratory positive-pressure (EPP) valves (n = five per valve type) at bias flows of between 0 and 2,000 ml/s. We found that individual valves of each type and manufacturer functioned similarly. Different valve types, however, functioned differently: with one type, system pressure was higher than rated (p less than 0.05), and with another type, system pressure was significantly flow-dependent (p less than 0.01). The remaining types of valves had no flow-resistive properties and maintained a system pressure of 10 cmH2O. We conclude that system pressure is not similar in all continuous positive airway pressure (CPAP) systems using bias flow and EPP valves. The work of breathing imposed by CPAP circuits will be increased in systems whose EPP valves have flow-dependent properties.

Airway pressure release ventilation.

Airway pressure release ventilation (APRV) delivers continuous positive airway pressure (CPAP) and may support ventilation simultaneously. This investigation tested whether, after acute lung injury (ALI), APRV promotes alveolar ventilation and arterial oxygenation without increasing airway pressure (Paw) above the CPAP level and without depressing cardiac function. Ten anesthetized dogs randomly received either intermittent positive-pressure ventilation (IPPV) or APRV. APRV was delivered with a continuous-flow CPAP system. Expiration occurred when a switch in the expiratory limb opened and Paw decreased to near-ambient, which decreased lung volume. After baseline data collection, ALI was induced by infusing oleic acid iv. Two hours later, IPPV and APRV were administered randomly, and data were collected. With normal lungs, APRV and IPPV achieved similar gas exchange and hemodynamic function. During ALI, arterial oxygenation was improved, and peak Paw which did not exceed the CPAP level, was lower during APRV. Similar minute ventilations were delivered by both modes but resulted in lower PaCO2 with APRV. Thus, APRV decreased physiologic deadspace ventilation. Hemodynamic status was similar during both modes. Therefore, APRV is an improved method of oxygenation and ventilatory support for patients with ALI that will allow unrestricted spontaneous ventilation and may decrease the incidence of barotrauma.

Pressure characteristics of the Ambu CPAP system and the Servo Ventilator 900C in CPAP mode

Spontaneous breathing was stimulated in the Ambu continuous positive airway pressure (CPAP) system and the Servo Ventilator 900C by means of a lung model programmed to mimic the respiratory flow patterns of a healthy volunteer and a patient in severe respiratory distress. Changes in airway pressure, flow and volume were recorded during "breathing" with CPAP at 0.5, 1.0 and 1.5 kPa. In the Ambu system, the airway pressure decreased during inspiration and increased during expiration, while the mean airway pressure was close to the pre-set CPAP value. The pressure changes were minimal when the fresh gas flow was increased from 15 to 25 1 X min-1. The higher fresh gas flow is recommendable during deep or rapid breathing. In the Servo ventilator 900C, there was a short initial inspiratory pressure drop, succeeded by a pressure rise above the CPAP value. The expiratory airway pressure was somewhat higher than CPAP. Both systems were found to be recommendable for clinical use.

Effects of Periodic Positive Airway Pressure by Mask on Postoperative Pulmonary Function

Postoperative pulmonary complications, alveolar-arteriolar oxygen difference ([A-a]O2-diff), peak expiratory flow (PEF) and forced vital capacity (FVC) were compared in patients using continuous positive airway pressure (CPAP) and positive expiratory pressure (PEP) administered by face mask against those of a control group using a deep-breathing device (Triflo). Forty-three consecutive, randomized patients undergoing elective upper abdominal surgery were included. CPAP, PEP and Triflo were administered for 30 consecutive breaths in every waking hour for three days postoperatively. The (A-a)O2-difference increased equally and significantly in the three groups after surgery, reaching a maximum on the first postoperative day. After this day, however, (A-a)O2-diff decreased in the CPAP and PEP groups, being significantly lower in the PEP group compared to the control group, two days postoperatively (p less than 0.05) and significantly lower in both the PEP and CPAP groups three days postoperatively (p less than 0.001 and p less than 0.05, respectively.) PEF did not differ significantly between the groups before or after surgery, while FVC was significantly higher in the PEP and CPAP groups, compared to control, on the third postoperative day (p less than 0.05). Atelectatic consolidation was observed in six of 15 patients in the control group three days postoperatively, the incidence being significantly lower in both the PEP group (0 of 15, p less than 0.001) and the CPAP group (one of 13, p less than 0.05). We concluded that periodic face mask administration of CPAP and PEP are superior to deep breathing exercises with respect to gas exchange, preservation of lung volumes and development of atelectasis after upper abdominal surgery. We also conclude that the simple and commercially available PEP mask is as effective as the more complicated CPAP system.

Continuous positive airway pressure: a breathing system to minimize respiratory work.

During continuous positive airway pressure (CPAP) the work of breathing is least when there is no change of airway pressure measured at the mouth (delta Paw) during respiration. In this study we consider the physical properties of CPAP circuits which determine the magnitude of delta Paw, and apply this information to the design of a simple, reliable CPAP system that minimizes delta Paw and incorporates the additional advantages of low-flow rates and the use of commonly available proven components. Using a weighted reservoir bag and threshold CPAP valve to maintain pressure, we found that delta Paw may be reduced to less than 1.0 cm H2O during quiet breathing, at a tidal volume of 700 ml and maximum inspiratory flow of 1.35 L/sec. delta Paw was dependent on both the resistance and the reactance of the circuit components; it was increased when resistance or flow rates were high, and when delivery pressure depended on the elastic tension in the wall of the reservoir bag or on compression of the bag with springs or elastic bands.

Comparison of Work of Breathing on High Gas Flow and Demand Valve Continuous Positive Airway Pressure Systems

Using on-line computer analysis, the work of breathing (WOB) was measured in ten normal subjects breathing through four continuous positive airway pressure (CPAP) circuits. Two systems (Emerson ventilator) and MGH elastic loaded reservoir bag (ELRB) were high continuous flow systems and two (Puritan-Bennett MA-2 and Bourns Bear Ventilators) were demand valve circuits. Mean values for the WOB were similar with either of the two continuous high flow systems (Emerson 0.41 +/- .21 kg . m . L-1; ERLB 0.49 +/- .29 kg . m . min-1) and significantly lower than with the two demand valve systems (MA-2 0.89 +/- .40 kg . m . min-1; Bourns .71 +/- .30 kg . m . min-1).

Effects of expiratory positive airway pressure vs continuous positive airway pressure in conscious, spontaneously breathing dogs.

The purpose of this study was to compare the cardiopulmonary effects of expiratory positive airway pressure (EPAP) and continuous positive airway pressure (CPAP) in conscious, spontaneously breathing dogs. Nine conscious dogs with elec- tromagnetic flow probes on their pulmonary arteries, catheters in their left atria and pulmo- nary arteries, and chronic tracheostomies, stood partially supported by slings, and breathed 100% oxygen through endotracheal tubes, pneumotachographs, and nonrebreathing valves which were part of either an EPAP or CPAP system. The effects of EPAP only were studied on four dogs while five were exposed to both EPAP and CPAP. After a 20-min control period, they breathed through either the EPAP or CPAP system for 10 min each under 5-, lo-, 15, and 20-cm H,O airway pressure. The mean pulmonary artery pressure, mean left atrial pressure, pulmonary vascular resistance, and minute ventilation were found to be significantly higher in the CPAP-treated group. Stroke volume and cardiac output were significantly higher in the EPAP-treated group. Both groups showed a significant carbon dioxide retention. Positive end-expiratory pressure, in conjunction with mechanical ventilation, is often used in the treatment of patients with pulmonary edema and adult respiratory distress syndrome. One potential disad- vantage of this therapy is a decrease in car- diac output (1 - 3).

A proximal system for positive end-expiratory pressure (peep) and continuous positive airway pressure (cpap)

A proximal positive end-expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) system was constructed by the simple addition of a venturi T-piece proximal to the exhalation limb of a breathing circuit. The level of PEEP or CPAP was determined by the amount of flow powering the venturi. This system can provide positive pressure in excess of 40 cm H2O without the need for check valves, dump valves or additional nebuliers and flowmeters.

Treatment of Respiratory Insufficiency in Infants Using Nasal CPAP and a Gas Jet

A light-weight system for continuous positive airway pressure (CPAP) based on a nasal vestibular cannula and a miniature gas jet has been tried out in 29 newborns with severe idiopathic respiratory distress syndrome (IRDS) and nine infants suffering from respiratory insufficiency caused by lower respiratory tract infections. In infants with IRDS, a permanent effect was achieved in 20% when the birth weight was below 1501 g, and in 74% when the birth weight was higher. The infants with lower respiratory tract infections all recovered without further ventilatory support. Significant complications occurred in only two infants, both of whom developed pneumothorax. The system forms a simple and safe alternative to existing nasal CPAP systems suitable for use in newborns as well as older infants with lung diseases resulting in alveolar collapse.

Sepsis in a CPAP system.

Bacterial contamination of a continuous positive airway pressure system has been investigated and found to be virtually confined to the adjustable valve 'at the mouth'. Organisms isolated from this site are probably derived from those in the sputum. The practical implications of these findings are outlined.

The use of nasal CPAP in newborns with respiratory distress syndrome.

The efficiency of applying continuous positive airway pressure (CPAP) by the nasal route was retrospectively nalyzed in 32 newborns with RDS (23 uncomplicated HMD with additional cardiac or pulmonary complications and 7 RDS of non-hyaline membrane etiology) who underwent nasal CPAP treatment at the Kinderspital Zurich from 1972--1974. 16 of the 23 infants with uncomplicated HMD were successfully treated with CPAP. They showed a significant rise in PaO2 as well as a significant drop in respiratory frequency during nasal CPAP application, the PaCO2 did not change significantly. The remaining 7 infants in this group (7/23) had to be intubated and mechanically ventilated owing to a persistent high FIO2 (4 infants), technical difficulties (1) or nasal hypersecretion (2). Two of these 23 infants died, one of meningitis, one of cerebral hemorrhage. The two infants with HMD and additional cardiac or pulmonary complications and 3 of 7 infants with RDS of non-hyaline membrane etiology had to be intubated and mechanically ventilated after failure of nasal CPAP. All 9 infants in these two groups survived. The nasal CPAP system as described is a simple, inexpensive and effective method of applying CPTPP in newborns with uncomplicated HMD, except radiological stage IV. In HMD with additional cardiac or pulmonary complications and in RDS of non-hyaline membrane etiology the results of nasal CPAP treatment were not convincing.