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 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.     

A pressure regulator for the cuff of a tracheal tube

A regulator is described for the maintenance of a constant pressure difference above airway pressure during positive pressure ventilation in a cuffed tracheal tube. It comprises a tubular threshold valve which is powered by the anaesthetic gas supply source to a breathing system. The valve is interposed between the anaesthetic gas supply machine and the breathing system creating a pressure differential. The upstream pressure is transmitted to the pilot tube supplying the cuff of a tracheal tube via an upstream connection. The valve is suitable only for breathing systems that require a constant gas supply. The regulator was evaluated during anaesthesia, using a modified Mallinkrodt Hi-Lo jet ventilation tube to obtain simultaneous pressure measurements within the cuff and the lumen of the tracheal tube. A greater pressure was demonstrated in the cuff than in the airway and the two traces were approximately parallel throughout the respiratory cycle. The device should prevent excessive cuff inflation pressure and solves the problem of forgetting to let the cuff down before extubation.     

Effect of reduced expiratory pressure on pharyngeal size during nasal positive airway pressure in patients with sleep apnoea: evaluation by continuous computed tomography.

BACKGROUND: This study aimed to determine whether reducing the expiratory pressure during nasal positive airway pressure for reasons of comfort causes a substantial decrease in the upper airway calibre. METHODS: Eight patients with obstructive sleep apnoea were studied. Continuous computed tomography (each run lasting 12 seconds) was used to measure minimum and maximum pharyngeal cross sectional areas at the velopharynx and the hypopharynx. Pharyngeal areas were measured while patients were awake and breathing without assistance, during the application of 12 cm H2O continuous positive airway pressure, and during bi-level positive airway pressure with an inspiratory pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O. RESULTS: Nasal continuous positive airway pressure significantly increased the mean minimum and maximum upper airway areas at both the velopharynx and the hypopharynx compared with normal unassisted breathing. Bi-level positive airway pressure did not show a statistically significant increase in the minimum upper airway area at either level compared with normal unassisted breathing. The minimum areas of the velopharynx and hypopharynx were smaller with bi-level than continuous positive airways pressure in six of eight and eight of eight patients respectively but these were still greater than during unassisted breathing in seven of eight and six of eight patients respectively. CONCLUSIONS: Continuous positive airway pressure at 12 cm H2O is more effective in splinting the pharynx open than bi-level positive airway pressure with an inspiratory positive airway pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O in patients with obstructive sleep apnoea during wakefulness, suggesting an important role for expiratory positive airway pressure. The clinical importance of this finding needs to be evaluated during sleep.     

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.(Hayakawa J, Usuda Y, Numata K: Evaluation of ejectors using the Venturi effect for a continuous positive airway pressure system without compressed air. J Anesth 3: 166–171, 1989)     

A new CPAP system

The "AMBU-CPAP system" is a new, simple and reliable circuit for administering positive airway pressure in spontaneous-breathing therapy. Some disadvantages of other CPAP devices are avoided, and the use of the system with low gas flow is possible. The change of airway pressure during respiration was measured and was found to be less than 5 millibars.     

Daytime sleepiness, cognitive performance and mood after continuous positive airway pressure for the sleep apnoea/hypopnoea syndrome.

BACKGROUND--Patients with the sleep apnoea/hypopnoea syndrome often receive continuous positive airway pressure to improve their symptoms and daytime performance, yet objective evidence of the effect of this treatment on cognitive performance is lacking. METHODS--A prospective parallel group study was performed comparing the change in objective daytime sleepiness as assessed by multiple sleep latency, cognitive function, and mood in 21 patients (mean (SE) number of apnoeas and hypopnoeas/hour 57 (6)) who received continuous positive airway pressure for three months and 16 patients (49(6) apnoeas and hypopnoeas/hour) who received conservative treatment for a similar period. RESULTS--Both groups showed significant within group changes in cognitive function between baseline and three months, but when comparisons were made between groups the only significant difference was a greater improvement in multiple sleep latency with continuous positive airway pressure. However, the improvement in sleep latency with continuous positive airway pressure was relatively small (3.5 (0.5) to 5.6 (0.7) min). The group treated with continuous positive airway pressure was divided into those who complied well with treatment (> 4.5 hours/night) and those who did not. Those who complied well (n = 14) showed significant improvement in mean sleep latency and also in depression score compared with the controls but no greater improvement in cognitive function. CONCLUSION--This study confirms significant improvements in objective sleepiness and mood with continuous positive airway pressure, but shows no evidence of major improvements in cognitive function.     

Pressure support ventilation with the ProSeal laryngeal mask airway. A comparison of sevoflurane, isoflurane and propofol

BACKGROUND AND OBJECTIVE: There are no data about the influence of anaesthetics on cardiovascular variables during pressure support ventilation of the lungs through the laryngeal mask airway. We compared propofol, sevoflurane and isoflurane for maintenance of anaesthesia with the ProSeal laryngeal mask airway during pressure support ventilation. METHODS: Sixty healthy adults undergoing peripheral musculo-skeletal surgery were randomized for maintenance with sevoflurane end-tidal 2%, isoflurane end-tidal 1.1% or propofol 6 mg kg(-1) h(-1) in oxygen 33% and air. Pressure support ventilation comprised positive end-expiratory pressure set at 5 cmH2O, and pressure support set 5 cmH2O above positive end-expiratory pressure. Pressure support was initiated when inspiration produced a 2 cmH2O reduction in airway pressure. A blinded observer recorded cardiorespiratory variables (heart rate, mean blood pressure, oxygen saturation, airway occlusion pressure, respiratory rate, expired tidal volume, expired minute volume and end-tidal CO2), adverse events and emergence times. RESULTS: Respiratory rate and minute volume were 10-21% lower, and end-tidal CO2 6-11% higher with the propofol group compared with the sevoflurane or isoflurane groups, but otherwise cardiorespiratory variables were similar among groups. No adverse events occurred in any group. Emergence times were longer with the propofol group compared with the sevoflurane or isoflurane groups (10 vs. 7 vs. 7 min). CONCLUSION: Lung ventilation is less effective and emergence times are longer with propofol than sevoflurane or isoflurane for maintenance of anaesthesia during pressure support ventilation with the ProSeal laryngeal mask airway. However, these differences are small and of doubtful clinical importance.     

Beneficial effects of bilevel positive airway pressure after surgery under cardiopulmonary bypass

To support injured lungs, we have been applying bilevel positive airway pressure for adult patients undergoing surgery with cardiopulmonary bypass. Among 120 consecutive patients, 31 patients whose PaO2/FiO2 decreased to less than 180 after extubation assigned to the intermittent 15 min bilevel positive airway pressure (7.3+/-3.6 times per patient). Bilevel positive airway pressure improved oxygenation (PaO2/FiO2: 128+/-43 vs. 198+/-62, P=0.004) and allowed the patients with poor oxygenation after extubation to maintain PaO2/FiO2 levels similar to those of the patients without bilevel positive airway pressure. In conclusion, the bilevel positive airway pressure therapy after extubation was effective to improve lung oxygenation non-invasively in adult patients undergoing more invasive surgery with prolonged cardiopulmonary bypass.     

Positive pressure versus pressure support ventilation at different levels of PEEP using the ProSeal laryngeal mask airway

We compared positive pressure ventilation with pressure support ventilation at different levels of positive end expiratory pressure (PEEP) using the ProSeal laryngeal mask airway (PLMA). Forty-two anaesthetized adults (ASA 1-2, aged 19 to 63 years) underwent positive pressure ventilation and then pressure support ventilation each with PEEP set at 0, 5 and 10 cmH2O in random order. Pressure support ventilation was with the inspired tidal volume (VTInsp) set at 7 ml/kg and the respiratory rate adjusted to maintain the end-tidal CO2 (ETCO2) at 40 mmHg. Pressure support ventilation was with pressure support set at 5 cmH2O above PEEP and initiated when inspiration produced a 2 cmH2O reduction in airway pressure. Tidal volumes were similar during positive pressure and pressure support ventilation with PEEP, but were higher for the former without PEEP Respiratory rate and peak inspiratory flow rate were higher during pressure support than positive pressure ventilation (all P < 0.001). Peak airway pressure (Ppaw), mean airway pressure (Mpaw), peak expiratory flow rate, and expired airway resistance were lower during pressure support than positive pressure ventilation (all P < 0.001). With PEEP set at 10 cmH2O, ETCO2 was lower for pressure support than positive pressure ventilation. During positive pressure ventilation, there was an increase in Ppaw, Mpaw and dynamic compliance (Cdyn) with increasing levels of PEEP (all P < 0.01). During pressure support ventilation, there was an increase in inspired and expired tidal volume, Ppaw, peak inspiratory and expiratory flow rates and Cdyn, and a reduction in ETCO2, work of breathing, and expired airway resistance with increasing levels of PEEP (all P < 0.01). There were no differences in SpO2, non-invasive mean arterial pressure, heart rate or leak fraction. We conclude that pressure support ventilation provides equally effective gas exchange as positive pressure ventilation during PLMA anaesthesia with or without PEEP at the tested settings. During pressure support, PEEP increases ventilation and reduces work on breathing without increasing leak fraction.     

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.     

Constant positive airway pressure. A review.

Constant positive airway pressure (CPAP) represents a major advance in the treatment of hypoxaemia. By increasing the functional residual capacity (FRC), airway closure and airway resistance are minimized. Ventilation and perfusion are more evenly matched so that gas exchange is made more efficient. In addition, the lung remains on a favourable portion of the compliance curve so that the work of breathing is reduced. The increased oxygenation is achieved at the lowest possible inspired oxygen concentration (FiO2) to minimize oxygen toxocity. A unified approach to the terms used, as well as their abbreviations, is presented.     

Continuous positive airway pressure breathing increases the spread of sensory blockade after low-thoracic epidural injection of lidocaine

Factors affecting the distribution of sensory blockade after epidural injection of local anesthetics remain incompletely clarified. To evaluate if increasing intrathoracic pressure affects the spread of thoracic epidural anesthesia, we randomized 20 patients who received an epidural catheter at the T7-8 or T8-9 intervertebral space into 2 groups. The control group (n = 10) received an epidural test dose of 4 mL lidocaine 2% during spontaneous breathing at ambient pressure. The continuous positive airway pressure (n = 10) group received the same epidural test dose but during spontaneous respiration with 7.5 cm H2O continuous positive airway pressure. The groups were comparable with respect to demographic variables. Fifteen minutes after the conclusion of the epidural injection, the sensory block ranged from from T4 [median, interquartile range 2.75 segments] to T11 (interquartile range 3.5 segments) in the control group and from T5 (interquartile range 2.25 segments) to L2 (IQR 2.25 segments) in the continuous positive airway pressure group (P = 0.005 for the caudal border). The total number of segments blocked was 7 (median, interquartile range 2.25) in the control group and 11 (interquartile range 3.5) in the continuous positive airway pressure group (P = 0.004). The number of segments blocked caudad to the injection site was 3 (median, interquartile range 3.5) in the control group and 6 (interquartile range 2.25) in the continuous positive airway pressure group (P = 0.005). We conclude that continuous positive airway pressure increases the spread of sensory blockade in thoracic epidural anesthesia, primarily by a more caudad extension of sensory blockade.     

Evaluation of a humidified nasal high-flow oxygen system, using oxygraphy, capnography and measurement of upper airway pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow, Fisher and Paykel Healthcare) by measuring delivered FiO, and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order FiO2, F(E)O2, F(E)CO2 and airway pressures were measured. Calculation of FiO2 from F(E)O2 and F(E)CO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cm H20. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.     

Ventilatory support by continuous positive airway pressure breathing improves gas exchange as compared with partial ventilatory support with airway pressure release ventilation

In acute lung injury, airway pressure release ventilation (APRV) with superimposed spontaneous breathing improves gas exchange compared with controlled mechanical ventilation. However, the release of airway pressure below the continuous positive airway pressure (CPAP) level may provoke lung collapse. Therefore, we compared gas exchange and hemodynamics using a crossover design in nine pigs with oleic acid-induced lung injury during CPAP breathing and APRV with a release pressure level of 0 and 5 cm H(2)O. At an identical minute ventilation (V(E) 8 L/min) spontaneous breathing averaged 55%, 67%, and 100% of V(E) during the two APRV modes and CPAP, respectively. Because of the concept of APRV, mean airway pressure was highest during CPAP and lowest during APRV with a release pressure of 0 cm H(2)O. Shunt was reduced to almost half during CPAP (6.6% of Q(t)) compared with both APRV-modes (13.0% of Q(t)). Cardiac output and oxygen consumption, in contrast, were similar during all three ventilatory settings. Thus, in our lung injury model, CPAP was superior to partial ventilatory support using APRV with and without positive end-expiratory pressure. This may be attributable to beneficial effects of spontaneous breathing on gas exchange as well as to rapid lung collapse during the phases of airway pressure release below the CPAP level. These findings may suggest that the amount of mechanical ventilatory support using the APRV mode should be kept at the necessary minimum. IMPLICATIONS: Oxygenation is better with continuous positive airway pressure breathing than with partial mechanical ventilatory support using airway pressure release ventilation. Therefore, mechanical ventilatory support achieved by a cyclic release of airway pressure during APRV should be kept at the minimum level that enables enough ventilatory support for patients to avoid respiratory muscle fatigue.     

气道加压对全麻患者右颈内静脉穿刺置管术的影响

目的 探讨气道加压对全麻患者右颈内静脉穿刺置管术的影响.方法 需要进行右颈内静脉穿刺置管的全麻患者125例,随机分为对照组(C组,n=60)和气道加压组(P组,n=65).超声引导下于环状软骨平面,C组在暂停机械通气时、P组手控呼吸维持气道压力20 cm H2O时进行右颈内静脉穿刺置管.暂停机械通气时测定两组右颈内静脉横截面积和穿刺成功后CVP,P组患者气道压力20 cm H2O时测定颈内静脉横截面积和CVP,记录穿刺次数、颈内静脉管壁至皮肤的最短距离、进针深度、进针和退出过程中回抽血液通畅情况,气道加压前测定HR和MAP,并记录气道加压过程中的最低值,观察两组患者的穿刺置管情况.结果 P组气道压力20 cm H2O时颈内静脉横截面积和CVP较气道加压前增加(P＜0.01);与C组比较,P组进针深度降低,1次穿刺成功率、30 s内穿刺成功率、进针过程中回抽血液通畅率升高(P＜0.01),心动过缓、低血压发生率升高(P＜0.05).结论 气道加压有助于超声引导下右颈内静脉穿刺置管术的成功.     

Myocardial systolic function increases during positive pressure lung inflation

Lung inflation with positive airway pressure may have rapid and dynamic effects on myocardial contractile function. We designed this study to assess the magnitude and time to onset of myocardial function changes during the initiation of single positive pressure lung inflation at clinically relevant inflation pressures. In 8 anesthetized 40-kg pigs, left ventricular pressures and volumes were measured directly (conductance volumetry). A 15 cm H2O airway pressure plateau with lung inflation (PPLI-15) was performed, and 2 single beats from that sequence, one from resting apnea at zero airway pressure and the second from the point when the lungs were first maximally inflated, were selected for analysis. Systolic function variables for zero airway pressure and PPLI-15 were analyzed. Systolic elastance, derived from bilinear time-varying elastance curves, increased approximately 15% during PPLI-15 from zero airway pressure. This agreed with other systolic function variables that identified an increase in left ventricular contractile function for the lung inflation beat. Serial measurements of myocardial function should be conducted with constant airway pressure and lung inflation conditions.     

Assessment of the Caradyne WhisperFlow for administration of continuous positive airway pressure in a 3 Tesla magnetic resonance scanner

Demand for magnetic resonance investigations in critically ill patients is increasing. While these patients frequently need ventilatory support, not all of them require controlled ventilation and many may be treated with continuous positive airway pressure. Controlled ventilation, with the concurrent need for sedation, may be inappropriate when airway physiology is being studied and may retard weaning. No commercially available ventilator designed for the magnetic resonance environment can deliver high flow continuous positive airway pressure. We tested the Caradyne Whisperflow flow generator and five Whisperflow valves (2.5-15 cmH2O airway pressure) within a 3 Tesla environment for safety and possible dysfunction. All components had minimal ferromagnetic properties and tests showed no clinically relevant change in flow delivery or oxygen concentration in the magnetic field. In addition, the airway pressure generated by the valves was not affected by the magnetic field. We conclude that the tested system can be safely used in a 3 Tesla magnetic resonance environment.     

A new double lumen tube adaptor

The report describes a new double lumen tube adaptor which provides selective one lung ventilation without external clamping. It also facilitates, without disconnexion and remantling, both correct bronchial cuff inflation and continuous positive airway pressure administration using an underwater seal chest bottle. Oxygenation can be kept optimal during one lung anaesthesia by applying 1.0 kPa continuous positive airway pressure to the nonventilated lung using an oxygen flow of 1-2 litres/minute.     

Pneumencéphalie après ventilation non invasive en postopératoire de neurochirurgie par voie trans-sphénoïdale : à propos de deux cas

The early use of continuous positive airway pressure ventilation has been shown to be effective and is recommended for patients with obstructive sleep apnea. The complications of continuous positive airway pressure ventilation are not well described. We report two cases of pneumocephalus following the use of continuous positive airway pressure ventilation after transsphenoidal surgery. One patient had an obstructive sleep apnea and the other suffered acute respiratory failure. In both cases, pneumocephalus caused major morbidity and required specific treatment and prolonged considerably hospital stay. Based on these observations we believe new precautions in the use of noninvasive continuous positive airway pressure ventilation should be recommended.