Treatment of the adult respiratory distress syndrome with continuous positive airway pressure

Performance of helmet CPAP using different configurations: Turbine-driven ventilators vs Venturi devices

BACKGROUND

Traditionally, Venturi-based flow generators have been preferred over mechanical ventilators to provide continuous positive airway pressure (CPAP) through the helmet (h-CPAP). Recently, modern turbine-driven ventilators (TDVs) showed to be safe and effective in delivering h-CPAP. We aimed to compare the pressure stability during h-CPAP delivered by Venturi devices and TDVs and assess the impact of High Efficiency Particulate Air (HEPA) filters on their performance.

METHODS

We performed a bench study using an artificial lung simulator set in a restrictive respiratory condition, simulating two different levels of patient effort (high and low) with and without the interposition of the HEPA filter. We calculated the average of minimal (Pmin), maximal (Pmax) and mean (Pmean) airway pressure and the time product measured on the airway pressure curve (PTPinsp). We defined the pressure swing (Pswing) as Pmax - Pmin and pressure drop (Pdrop) as End Expiratory Pressure - Pmin.

RESULTS

Pswing across CPAP levels varied widely among all the tested devices. During "low effort", no difference in Pswing and Pdrop was found between Venturi devices and TDVs; during high effort, Pswing (p<0.001) and Pdrop (p<0.001) were significantly higher in TDVs compared to Venturi devices, but the PTPinsp was lower (1.50 SD 0.54 vs 1.67 SD 0.55, p<0.001). HEPA filter addition almost doubled Pswing and PTPinsp (p<0.001) but left unaltered the differences among Venturi and TDVs systems in favor of the latter (p<0.001).

CONCLUSIONS

TDVs performed better than Venturi systems in delivering a stable positive pressure level during h-CPAP in a bench setting.

Performance of EasyBreath Decathlon Snorkeling mask for delivering continuous positive airway pressure

During the COVID-19 pandemic, the need for noninvasive respiratory support devices has dramatically increased, sometimes exceeding hospital capacity. The full-face Decathlon snorkeling mask, EasyBreath (EB mask), has been adapted to deliver continuous positive airway pressure (CPAP) as an emergency respiratory interface. We aimed to assess the performance of this modified EB mask and to test its use during different gas mixture supplies. CPAP set at 5, 10, and 15 cmH₂O was delivered to 10 healthy volunteers with a high-flow system generator set at 40, 80, and 120 L min^-1 and with a turbine-driven ventilator during both spontaneous and loaded (resistor) breathing. Inspiratory CO₂ partial pressure (PiCO₂), pressure inside the mask, breathing pattern and electrical activity of the diaphragm (EAdi) were measured at all combinations of CPAP/flows delivered, with and without the resistor. Using the high-flow generator set at 40 L min^-1, the PiCO₂ significantly increased and the system was unable to maintain the target CPAP of 10 and 15 cmH₂O and a stable pressure within the respiratory cycle; conversely, the turbine-driven ventilator did. EAdi significantly increased with flow rates of 40 and 80 L min^-1 but not at 120 L min^-1 and with the turbine-driven ventilator. EB mask can be safely used to deliver CPAP only under strict constraints, using either a high-flow generator at a flow rate greater than 80 L min^-1, or a high-performance turbine-driven ventilator.

Assessing the performance of the Whisperflow continuous positive airway pressure generator: a bench study

BACKGROUND

There are few data describing the performance of the Whisperflow continuous positive airway pressure (CPAP) generator.

METHODS

(i) (a) A static test of 11 Whisperflow devices examining maximum flow generation with no load and with 2.5, 5, 7.5, 10, 15, and 20 cm H2O valve loading, at varying Fi(O2). (b) CPAP valves (Accu-peep(R), Vital Signs, Totowa, NJ, USA) were tested by measuring mean upstream pressure at varying flows in five valves (2.5, 5, 7.5, 10, 15, and 20 cm H2O). (ii) We measured the mean and minimum inspiratory mask pressure generated by a representative Whisperflow device in a model of spontaneous respiration. Measurements were made with combinations of Fi(O2), ventilatory frequency, tidal volume, and valve loading similar to those encountered in clinical practice.

RESULTS

(i) (a) The flow generated by the Whisperflow valves decreases with increasing valve load and increasing Fi(O2) (from 140 to 20 litre min(-1)). (b) The CPAP valves maintain the required pressure within acceptable limits against varying flow. (ii) At all permutations, the mean inspiratory mask pressure was significantly lower than that required. At high inspiratory flow rates, the minimum inspiratory pressure approached atmospheric pressure.

CONCLUSIONS

The Whisperflow may not perform as expected. Clinicians should be cautious when using this device, particularly with high Fi(O2) and CPAP valve load. The flow setting should be set at maximum. Failure of CPAP therapy may be due to failure of the generator. Further in vivo data are required.

Continuous positive airway pressure modulates effect of inhaled nitric oxide on the ventilation-perfusion distributions in canine lung injury

OBJECTIVES

The present study was designed to evaluate if continuous positive airway pressure (CPAP) augments the effect of nitric oxide (NO) inhalation on matching between ventilation and perfusion (VA/Q) during acute lung injury.

DESIGN

Prospective, randomized study.

SETTING

A research laboratory at a university medical center.

SUBJECTS

Ten anesthetized mongrel dogs with oleic acid-induced lung injury.

INTERVENTIONS

Zero or 40 parts per million of NO in the inspiratory gas, with and without 10 cm H2O CPAP in random order.

MEASUREMENTS AND MAIN RESULTS

Gas exchange was assessed by estimating the VA/Q distributions using the multiple inert gas elimination technique. Application of CPAP decreased blood flow to shunt units by 26 +/- 2 percent (mean +/- SD) and increased the fraction of cardiac output to normal VA/Q units (VA/Q ratio of 0.1 to 10) by 26 +/- 2 percent (p < 0.05). Inhalation of NO during CPAP accounted for a further 10 +/- 2 percent decrease in the blood flow to shunt units and an 8 +/- 2 percent increase in the fraction of the cardiac output to normal VA/Q units (p < 0.05). Inhalation of NO alone had no significant effect on the VA/Q distributions. Inhalation of NO decreased mean transmural pulmonary artery pressure (Ppatm) both without (Ppatm from 30 +/- 2 to 23 +/- 2 mm Hg; PVR from 323 +/- 44 to 228 +/- 43 dynes.s .cm-5; p < 0.05) and with CPAP (Ppatm from 25 +/- 2 to 20 +/- 2 mm Hg; PVR from 255 +/- 30 to 173 +/- 31 dynes.s.cm-5; p < 0.05).

CONCLUSIONS

Although pulmonary vascular resistance can be lowered with NO inhalation alone, recruitment of gas exchange units with CPAP is necessary to produce a beneficial effect of NO inhalation on VA/Q matching and oxygenation. When recruitment of gas exchange units with CPAP brings gaseous NO in contact with enough pulmonary blood vessels, NO-induced vasodilation will augment VA/Q matching by a steal mechanism.

Effect of weaning on oxygen consumption and cardiovascular function. A comparison of continuous flow and demand valve systems

This study compared the continuous positive airways pressure mode of the demand valve system of the Engstrom Erica ventilator with a custom-made continuous flow continuous positive airways pressure system in terms of the oxygen cost of breathing during weaning from mechanical ventilation. Ten consecutive patients in our intensive care unit, with thermodilution pulmonary artery flotation catheters in situ, were studied. Measurements were carried out under steady-state conditions, initially when breathing spontaneously with continuous positive airways pressure via the Erica and then when transition to the continuous flow system was achieved. There were no significant differences between the two methods of providing continuous positive airways pressure in terms of the measured and derived physiological variables studied, with the exception of oxygen consumption. Oxygen consumption with the continuous flow system was significantly less than with the Erica (142.8 (SEM 31.4) ml.min-1.m-2 compared with 165.8 (SEM 30.5) ml.min-1.m-2, p < 0.05). This difference reflects the reduced oxygen cost of breathing when the custom-made continuous flow system was used during weaning.

Effect of continuous positive airway pressure applied by face mask on right ventricular function after cardiac surgery

The effect of respiratory therapy with continuous positive airway pressure (CPAP) on right ventricular function 24 hours after elective cardiac surgery was evaluated in patients with or without severe coronary artery disease. The first group included 10 patients following coronary artery bypass graft (CABG) surgery, and the second group included 10 patients following aortic valve replacement (AVR) without preexisting coronary artery disease. Patients of both groups had preoperative left ventricular ejection fractions above 40%. CPAP was applied by face mask at a flow rate of 20 L/min with 40% oxygen in nitrogen and with a positive end-expiratory pressure of 12 cmH2O. Right ventricular function was estimated at end-expiration by a fast-response thermodilution cardiac output catheter. The results demonstrate that in both groups of patients, CPAP did not significantly modify right ventricular indices, ejection fraction, end-systolic and end-diastolic volume indices, and stroke volume index, indicating that CPAP can safely be applied after elective cardiac surgery in patients with or without severe coronary artery disease and preoperative left ventricular ejection fractions above 40%. Furthermore, the concomitant postoperative intravenous infusion of nitroglycerin (to all 10 patients of the CABG group and to 4 patients of the AVR group) counteracted the expected beneficial effect of CPAP therapy on arterial oxygenation.

Skin necrosis following continuous positive airway pressure with a face mask

A 60-year-old woman with respiratory failure required ventilatory support using a continuous positive airway pressure face mask. She developed extensive necrosis of the skin of the bridge of the nose. A number of precipitating factors are discussed and suggestions made to minimise the risk of this complication.

Improvement in gas exchange with nasal continuous positive airway pressure in pulmonary alveolar microlithiasis

A 37-yr-old man with pulmonary alveolar microlithiasis (PAM) presented with respiratory failure and cor pulmonale. The FEV1/FVC was 1.4/1.8 L with total lung capacity of 3.2 L using the helium dilution method (54% predicted) and 6.1 L using body plethysmography (102% predicted), indicating large noncommunicating regions. The KCO (transfer factor per liter lung volume) was 3.05 ml/min/mm Hg/L (47% predicted). Despite home oxygen (3 L/min) and diuretic therapy, the patient remained hypoxic (PaO2, 55 mm Hg) and incapacitated with dyspnea. Nasal continuous positive airway pressure (nCPAP) at 12 cm H2O and oxygen at 1 L/min improved his oxygenation (PaO2, 93 mm Hg), and introduction of this regimen at night resulted in subjective improvement in daytime function. A Grandjean right heart catheter was introduced at the bedside, and the multiple inert gas elimination technique (MIGET) was used to measure ventilation and blood flow distributions at ambient pressure and with the addition of 10 cm H2O nCPAP. The patient had severe pulmonary hypertension (mean Ppa, 57 mm Hg) and severe hypoxemia (PaO2 37 mm Hg), which was mainly due to shunt (16% of cardiac output) and a broadening of the main mode of the ventilation-perfusion (VA/Q) distribution (log SD Q, 0.94). There was a significant reduction in shunt during nCPAP to 6% of cardiac output without increasing Ppa, and this effect appeared to extend past the period of application. We conclude that nCPAP reduces intrapulmonary shunt in this rare condition and allows for correction of hypoxemia with a smaller oxygen flow rate.

Inspiratory work imposed by continuous positive airway pressure (CPAP) machines: the effect of CPAP level and endotracheal tube size

Inspiratory work imposed by Continuous Positive Airway Pressure (CPAP) machines has been a matter of concern. The imposed inspiratory work of CPAP machine circuits (Wcir) and the effect of the total breathing apparatus with endotracheal tube (ETT) and connector included in the circuit (Wapp), were measured in three continuous flow (CF) and various configurations of three demand flow (DF) CPAP machines. The performance was assessed at 0, 5, 10 and 15 cmH2O CPAP using a Michigan Instruments Test Lung Model 1600, internal compliance set at 50 ml/cmH2O, driven at square wave inspiratory flows (VI) of 20, 40 and 60 l/min at a tidal volume of 500 ml. Work, expressed in mJ/l, was calculated from the area of pressure-volume loops. Inspiratory work, Wcir and Wapp, was dependent upon the particular CPAP machine, VI and ETT size, but not upon CPAP level, being maximum at VI 601/min and with ETT 7.0 mm i.d. Work values (Wcir) varied from 50 to 325 mJ/l with both CF and DF machines and up to 1100 mJ/l with ETT and connector (Wapp). No consistent advantage of CF over DF machines was demonstrated. There was little advantage of high gas flows (greater than 5 l/min) in various DF circuits. Within an individual machine maximum negative pressures generated during inspiration correlated with both Wcir and Wapp.

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.

Fluctuating CPAP (F-CPAP) versus conventional CPAP (C-CPAP) in dogs with blood aspiration

Fluctuating CPAP(F-CPAP) is a combination of spontaneous ventilation and fluctuating PEEP, in which end-expiratory pressure (EEP) is periodically changed within a certain range. In a dog model with localized lung injury induced by the aspiration of non-heparinized blood (2 ml.kg(-1) body weight), we carried out a comparative study of the effects of F-CPAP in which the EEP was cyclically changed from 4 to 12 cmH(2)O with periods of 10 min and those of conventional CPAP with a fixed EEP of 8 cmH(2)O (C-CPAP), on hemodynamics and pulmonary oxygenation. The blood aspiration produced significant increases in the intrapulmonary shunt (Qsp/Qt), the alveolar-arterial difference of partial pressure of oxygen (A-aD o(2)), and the respiratory rate (RR). Although both F-CPAP and C-CPAP reduced Qsp/Qt and A-aD o(2) and RR, 7 dogs treated with F-CPAP showed a significantly greater recovery of Qsp/Qt and A-aD o(2) than 7 dogs treated with C-CPAP. There were no significant differences in hemodynamic variables between the two groups. These results suggest that F-CPAP is more useful in the treatment of some kinds of hypoxic respiratory failure due to uneven distribution of lung injury.

Hemodynamic and gas exchange alterations during Intralipid infusion in patients with adult respiratory distress syndrome

Hemodynamic and pulmonary gas exchange consequences of 20 percent intravenous fat emulsion infusion (3.0 +/- .3 mg/kg/min) were evaluated in 19 patients who demonstrated ARDS. Lipid infusion precipitated a significant reduction in PaO2/FIO2 from 241 +/- 50 to 184 +/- 41 (mean +/- SD) and increased MPAP from 26.0 +/- 5.1 to 31.8 +/- 4.8 mm Hg, pulmonary vascular resistance from 149 +/- 78 to 179 +/- 61 dyne.s/cm5 and pulmonary venous admixture (Qva/Qt) from 20.7 +/- 15.2 to 30.6 +/- 8.6 percent. Further analysis revealed that the magnitude of increased Qva/Qt was greater in patients who manifested septicemia (N = 10) compared to those who did not (N = 9): 12.3 vs 7.3 percent, respectively. We conclude that intravenous lipid administration was associated with increased MPAP and Qva/Qt in patients with ARDS, particularly when accompanied by septicemia. Although these alterations resolved after the lipid infusion was terminated, we suggest that prudent measures should be taken to guarantee adequate oxygenation during intravenous fat emulsion therapy in patients suffering from ARDS.

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.

A high flow turbine CPAP system

A continuous high flow CPAP system incorporating a turbine blower is described. The system achieves inspiratory flow rates of 150 l/min or more by means of reticulated gas flow and inspired oxygen fractions of 0.21-0.95. Positive airway pressure is provided by weighted disc valves and a modified aviation-type CPAP face mask provides electronic communication with the patient. The mobility of the system also enables its use as an intermittent physiotherapy aid. Work of breathing of the system, as assessed by total pressure fluctuations is at a minimum.

Comparison between fluctuating PEEP and conventional PEEP in dogs with lung injury induced by blood aspiration

It has been documented that in some patients with acute hypoxic respiratory failure the application of positive end-expiratory pressure (PEEP) may produce no improvement or even a deterioration of pulmonary oxygenation due to an increase in ventilation-perfusion mismatching. Fluctuating PEEP (F-PEEP) is a newly developed PEEP in which end-expiratory pressure (EEP) is periodically changed within a certain range. In a dog model with localized lung injury induced by the aspiration of non-heparinized blood (2 ml.kg body weight-1), F-PEEP in which the EEP was periodically changed from 0.5 to 1.5 kPa at frequencies of 10 min, and conventional PEEP with 3 different fixed EEPs, 0.5, 1.0 and 1.5 kPa (C-PEEP0.5, C-PEEP1.0 and C-PEEP1.5) were each applied for 60 min. F-PEEP produced a periodical change in PaO2 and hemodynamic variables including cardiac output, and in comparison with C-PEEP0.5, C-PEEP1.0 and C-PEEP1.5, a significantly greater improvement of A-aDO2 and dynamic compliance with relatively large cardiac output in the low EEP phase. These results suggest that F-PEEP is a useful mode of artificial ventilation for treating some kinds of acute hypoxic respiratory failure due to increased ventilation-perfusion mismatching.

Effect of PEEP on the arterial minus end-tidal carbon dioxide gradient

The effect of PEEP on the arterial minus end-tidal carbon dioxide gradient (PaCO2-PetCO2) was evaluated in 13 adult patients with acute respiratory failure. The morphologic study of the pressure-volume (P-V) curves allowed separation of the patients into two groups: group 1 (n = 7) with initial inflection point in the (P-V) curve, and group 2 without inflection point. We hypothesized that the profile of the PaCO2-PetCO2 gradient would indicate an appropriate PEEP level only in patients with recruitable air spaces. We ventilated group 1 patients with zero end expiratory pressure (ZEEP), PEEP corresponding to inflection point pressure (PEEPPi) and PEEP5 cm H2O above PEEPPi, and group 2 patients with ZEEP, 6 cm H2O PEEP and 12 cm H2O PEEP. The PaCO2-PetCO2 gradient changed significantly in group 1 (ZEEP: 13.59 mm Hg; PEEPPi: 8.33 mm Hg; PEEPPi + 5 cm H2O: 10.54 mm Hg), but not in group 2 (ZEEP: 14.15 mm Hg; PEEP 6 cm H2O: 14.20 mm Hg; PEEP 12 cm H2O: 16.53 mm Hg). Our results show that the PaCO2-PetCO2 gradient may be useful in selecting a PEEP level which produces alveolar recruitment, but only in those patients with initial inflection point in the P-V curve.

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.

Added inspiratory work of breathing during CPAP ventilation: comparison of two demand-valve devices with a continuous flow-system

Measurements of added inspiratory work (AIW) of breathing imposed by three different CPAP systems were performed in 10 patients. One system was a continuous flow system while the two others were demand flow systems separated from respirators (Ohmeda VD 101 and Draeger CPAP 800 devices). AIW was calculated from pressure and flow signals recorded at the mouthpiece level. The AIW calculated with the two demand-flow systems was found to be the same as the AIW calculated with the continuous flow system although the results obtained by the Draeger device were less constant. The results obtained with the Ohmeda device in our patients conflicted with data previously published using a lung model.

The adult respiratory distress syndrome

The adult respiratory distress syndrome (ARDS) is a common form of acute respiratory failure that has been increasingly reported as associated with a wide variety of medical conditions. Unlike other identifiable pathological events causing severe lung injury, it is now recognized that ARDS is not a single disease, but a complex interaction of pathophysiological events that result in diffuse injury to lung parenchyma. Only through a thorough understanding of ARDS pathophysiology, pathogenesis, and clinical course can medical intervention be instituted in a judicious and timely manner. This review article is intended to provide an overview of the suspected precipitating causes, discrete pathophysiologic changes, and monitorable clinical events associated with ARDS. With mortality from ARDS high, significant attention is being given to improving therapeutic intervention with such conventional measures as mechanical ventilation, positive end-expiratory pressure, and fluid management, along with corticosteroids and several new experimental pharmacologic approaches.

High-frequency jet ventilation vs continuous positive airway pressure for postoperative respiratory support

In ten patients after recovery from general anesthesia for major vascular surgery, we compared continuous positive airway pressure (CPAP) and high-frequency jet ventilation (HFJV) at the same fractional concentration of oxygen in the inspired gas, both being superimposed on spontaneous breathing. The HFJV was delivered by a ventilator ( Acutronic VS-600) through the lateral lumen of a three-lumen endotracheal tube. Mean airway pressure was increased (3, 8, and 11 mm Hg) by adjusting the driving pressure during HFJV and by the setting of the expiratory valve during CPAP. During HFJV, the frequency (10 Hz) and inspiratory-expiratory ratio (0.25) were kept constant. Control values were measured when patients breathed spontaneously without positive end-expiratory pressure. Cardiac output and transmural filling pressures remained unchanged throughout the study. Neither the arterial oxygen pressure (PaO2) nor intrapulmonary shunt (Qs/Qt) changed significantly during CPAP. The 20- to 30-percent increase in PaO2 and the 5- to 10-percent decrease in Qs/Qt during HFJV when compared to control reflected a slightly but significantly (p less than 0.05) better oxygenation. The increase in arterial carbon dioxide tension was significantly greater during CPAP than during HFJV.

Complications of acute respiratory failure

Acute respiratory failure is frequently fatal. Attempts to decrease mortality must include attention to pulmonary and extrapulmonary complications. Pulmonary complications include pulmonary emboli, barotrauma, fibrosis, and pneumonia. Swan-Ganz catheters, tracheal intubation, and mechanical ventilation can also result in pulmonary complications. Extra-pulmonary complications such as gastrointestinal hemorrhage, renal failure, infection, and thrombocytopenia may increase mortality. Early diagnosis, aggressive treatment, and prophylaxis of complications should increase survival.

Effectiveness of CPAP by mask for pulmonary edema associated with hypercarbia

We describe continuous positive airway pressure (CPAP) by mask to reduce hypercarbia in two patients who had pulmonary edema due to congestive heart failure. In such patients, beside reducing venous return and filling pressures, CPAP improves compliance and decreases the work of breathing, thereby improving effective ventilation. Hence, CPAP may be useful to combat not only hypoxemia but also hypercarbia that is associated with pulmonary edema.

Efficacy of continuous positive airway pressure administered by face mask

The efficacy of administering continuous positive airway pressure (CPAP) by face mask was evaluated in 40 consecutive patients treated with 10 cm of water pressure or greater. Thirty-five patients were treated for progressive hypoxemia with all patients improving their PaO2/FIO2 ratio within the first hour of therapy. Oxygen delivery, when measured, also improved in each patient, although five patients ultimately required endotracheal intubation and higher CPAP levels to further improve their arterial hypoxemia. Five other patients were treated for atelectasis unresponsive to the usual therapeutic measures, with three patients demonstrating roentgenographic improvement. Face mask CPAP proved to be a safe and effective method for treating hypoxemia associated with early progressive respiratory distress in alert, spontaneously breathing patients.

Treatment of acute pulmonary failure by CPAP via face mask: when can intubation be avoided?

Continuous positive airway pressure (CPAP) is used frequently to improve gas exchange in acute pulmonary failure. We investigated clinical and respiratory variables in 98 patients presenting with two or more of the classical criteria for endotracheal intubation and mechanical ventilation. CPAP applied by a face mask was efficient in 60 cases. Posttraumatic and postoperative pulmonary problems responded better to this therapy than lung dysfunction secondary to left heart failure, sepsis or pneumonia. Abundant expectorations, discoordination of respiratory movements and an increase in arterial carbon dioxide were frequently associated with failure of CPAP by mask and the necessity of endotracheal intubation and mechanical ventilation.

Central haemodynamics and oxygen transport during CPAP with and without mandatory ventilations

Ten patients, subjected 16 h earlier to open-heart surgery (aortocoronary bypass and/or aortic valve replacement), were studied during the weaning period after postoperative mechanical ventilation. Central haemodynamics and oxygen transport were assessed along with total oxygen consumption during continuous positive airway pressure with four mandatory ventilations per minute (mode CPAP + IMV) and, subsequently, during CPAP alone. During the two modes of ventilation, airway pressure was adjusted to be equal during the spontaneous inspiratory phases. All parameters of haemodynamics, oxygenation and oxygen consumption were found to be essentially satisfactory and unchanged during both modes of ventilation. Our observations suggest that, as the parameters studied were unaltered with the change from CPAP + IMV to CPAP, the use of ventilatory support for these patients during the weaning period (in the form of four mandatory ventilations per minute) appears, in terms of central haemodynamics and oxygen transport, to be well tolerated in cases where adequate spontaneous ventilation is in doubt.

Reversal of obstructive sleep apnoea by continuous positive airway pressure applied through the nares

Five patients with severe obstructive sleep apnoea were treated with continuous positive airway pressure (CPAP) applied via a comfortable nose mask through the nares. Low levels of pressure (range 4.5-10 cm H2O) completely prevented upper airway occlusion during sleep in each patient and allowed an entire night of uninterrupted sleep. Continuous positive airway pressure applied in this manner provides a pneumatic splint for the nasopharyngeal airway and is a safe, simple treatment for the obstructive sleep apnoea syndrome.