Low Frequency Positive Pressure Ventilation Research Articles

Le traitement de l’insuffisance respiratoire aiguë par l’oxygénation extracorporelle au moyen d’un oxygénateur à membrane (ECMO) : les origines

Extracorporeal membrane oxygenation (ECMO) applied to acute respiratory distress syndrome was clinically used as soon as the early seventies. A large randomized trial sponsored by the US National Institute of Health failed to show superiority over conventional treatment, i.e. mechanical ventilation with positive end-expiratory pressure. Mortality was high (95%) in both arms. Venoarterial bypass was the most commonly used route for perfusion at that time. Overall complications were common, some of them deadly: hemolysis, bleeding, hypo- or hyper-coagulation, superinfections, lower limb ischemia, lack of oxygenation of coronary and bronchial arteries… Large utilization stopped after the ECMO trial results were published in JAMA, in 1979. During the eighties, L. Gattinoni and collaborators renewed the rationale of extracorporeal support and started to implement what was called “low frequency positive pressure ventilation with extracorporeal CO2 removal”, with much better results.

Extracorporeal membrane oxygenation in respiratory failure for pulmonary contusion and bronchial disruption after trauma

Extracorporeal membrane oxygenation (ECMO) may offer lifesaving treatment in severe pulmonary contusion or acute respiratory distress syndrome when conventional treatments have failed.1Peek G.J. Moore H.M. Moore N. Sosnowski A.W. Firmin R.K. Extracorporeal membrane oxygenation for adult respiratory failure.Chest. 1997; 112: 759-764Crossref PubMed Scopus (173) Google Scholar, 2Zwischenberger J.B. Conrad S.A. Alpard S.K. Grier L.R. Bidani A. Percutaneous extracorporeal arteriovenous CO2 removal for severe respiratory failure.Ann Thorac Surg. 1999; 68: 181-187Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar Although ECMO has become the standard treatment for neonatal severe respiratory failure, interest in adult ECMO weakened because of the high mortality until investigators3Gattinoni L. Pesenti A. Mascheroni D. Marcolin R. Fumagalli R. Rossi F. et al.A low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory failure.JAMA. 1986; 256: 881-886Crossref PubMed Scopus (507) Google Scholar began dictating that it should be used in children and in adult respiratory failure. Use in trauma is restricted4Willms D.C. Watchel T.L. Daleiden A.L. Dembitsky W.P. Schibanoff J.M. Gibbons J.A. Venovenous extracorporeal life support in traumatic bronchial disruption and adult respiratory distress syndrome using surface-heparinized equipment: case report.J Trauma. 1994; 2: 252-254Crossref Scopus (12) Google Scholar, 5Michaels A.J. Schriener R.J. Kolla S. Awad S.S. Rich P.B. Reickert C. et al.Extracorporeal life support in pulmonary failure after trauma.J Trauma. 1999; 4: 638-645Crossref Scopus (118) Google Scholar because of the risk of systemic anticoagulation in patients with multiple trauma. A 14-year-old boy experienced a serious blunt thoracic trauma during a go-cart race. On admission to the emergency department, he was awake and spontaneously breathing but dyspneic with hemoptysis and severe hypoxemia (Sao2 < 50%). As soon as endotracheal ventilation was started, the gas exchange rapidly worsened with subcutaneous emphysema and cardiac arrest, which necessitated resuscitation and urgent chest drainage for the onset of a hypertensive right pneumothorax. Oxygen saturation levels worsened, and continuous massive air leakage was present. A bronchoscopy was mandatory, but it failed to reveal injuries in the trachea and main stem bronchi. An endobronchial tube with left intubation was inserted (Robertshaw n.35), but the gas exchange did not improve dramatically. Emergency chest and abdomen computed tomography scans showed a suspicious lower right bronchial tear with bilateral pulmonary contusion, a large quantity of abdominal fluid, and a mild left pneumothorax. After another chest tube was inserted on the left, drainage on the left gas exchange remained stable with an Sao2 of 50%. A team of cardiothoracic surgeons and anesthesiologists recommended a venovenous ECMO, because they agreed that the boy would not survive. Regardless of the trauma, the patient was placed on an extracorporeal circuit (Bio-Medicus; Medtronic Inc, Minneapolis, Minn) with venous access achieved through the right jugular vein and right femoral vein using a percutaneous Seldinger technique. Anticoagulation with intravenous heparin was set to activated clotting times between 250 and 300 seconds. Heparinized blood was extracted from the internal jugular vein and through a centrifugal pump (Bio-Medicus; Medtronic Inc) reached a membrane oxygenator (Affinity, Avecor Cardiovascular, Plymouth, Minn) and heat exchanger (Biotherm; Medtronic Inc) and returned through the femoral vein. With a blood flow of 2.5 L/min and an Fio2 of 60%, the oxygenation saturation increased and the patient maintained good oxygen levels averaging 95%; thus, surgical intervention was possible. An exploratory laparotomy showed a large amount of ascites without intraperitoneal or retroperitoneal visceral injury, and a right posterolateral thoracotomy confirmed the large pulmonary contusion with multiple parenchymal tears and a transverse disruption in the intermediate bronchus. The location of the injury, size of the bronchial tree, and presence of irregular borders did not allow a conservative approach to bronchus without the risk of subtotal stenosis; therefore, a lower bilobectomy was performed. Three days later, after a short period of coagulopathy that was treated with fresh-frozen plasma, the patient was successfully weaned from ECMO. In the postoperative course, a tracheostomy was planned, and the patient was then successfully discharged from any kind of ventilatory support within 4 weeks and referred to a rehabilitation center. Two years after the accident, the boy is doing well. In trauma victims with possible intracranial and abdominal bleeding, and long bones and pelvic fractures, ECMO should be performed only as a last resort. The successful outcome of this case is most likely attributable to the young age of the patient, early institution of ECMO, and aggressive surgical intervention after cardiopulmonary stabilization. Ascites was probably associated with prolonged mesenteric hypoxemia.

Suivi clinique et fonctionnel respiratoire de 39 nourrissons traités par assistance respiratoire extracorporelle néonatale

The aim of this prospective study was to evaluate the consequences of neonatal treatment with a venovenous extracorporeal respiratory assistance. Thirty nine neonates (28 boys) with acute respiratory failure were included. Extracorporeal respiratory assistance consisted of an apnoeic oxygenation with low frequency positive pressure ventilation and extracorporeal membrane CO2 removal through a venous single canula perfusion circuit. The causes of respiratory distress were: 15 meconium aspiration syndrome, 12 respiratory distress syndrome, six hyaline membrane disease, three sepsis, two diaphragmatic hernia, and one post-surgery Mendelson syndrome. The mean duration of mechanical ventilation was 18 days, including 5 days of extracorporeal respiratory assistance. The prospective follow-up included physical examination, chest radiographs, scintigraphy and pulmonary function tests. These tests studied the following parameters: functional residual capacity by helium dilution technique, lung resistance and dynamic lung compliance by the esophageal balloon technique and blood gases with arterialized blood samples. The mean duration of the follow-up was 21.3 months (6 months to 5 years). Results showed in the first year 33% of children with chronic obstructive pulmonary disease and chest (X-ray abnormalities, such as bronchopulmonary dysplasia in 23% of children. Data of pulmonary function test at the end of the first year: lung resistance and functional residual capacity were within limits of predicted values for height, and dynamic lung compliance was slightly decreased; according to the analysis of the functional profile: 31% without abnormality, 41% of obstructive syndrome and 26% with restrictive pattern. Blood gases were normal in 37 children. At the end of the second year, we noticed normal functional residual capacity, an increase of lung resistance while lung compliance was normalized; functional profile was quite different: with a decrease of the number of patients without abnormality (22%) and increase of those with obstructive syndrome (56%). The percentage of abnormalities is high but these are moderate in most cases, especially if we compare with the initial seriousness of the pulmonary pathology. We suggest a regular follow-up to study the respective incidence of pulmonary disease and/or extracorporeal respiratory assistance over these abnormalities.

The spatial distribution of pulmonary lesions in severe ARDS An autopsy study of 35 cases: An autopsy study of 35 cases

The present study was undertaken in order to describe the local distribution and temporal course of pulmonary lesions in severe ARDS. We investigated a total of 35 patients (22 females), ranging in age from 2 to 51 years, who suffered from ARDS III and IV and were treated by extracorporeal CO2 removal and low frequency positive pressure ventilation (ECCO2-R). The extent of acute and chronic diffuse alveolar damage was assessed on histologic gross sections in the ventral, central and dorsal zone of the upper and lower lobes. The lesions showed a characteristic uniform distribution. Areas with chronic DAD were predominantly situated in the ventral portions of the upper lobes. Acute DAD predominated in the dorsal and basal areas of the lung. The extent of acute and chronic DAD was virtually independent of the duration of disease. Hemorrhage occurred at the interface zone between chronic and acute DAD and made up a significant volume portion of the lung tissue, ranging between 8% (lower lobes) and 42% (upper lobes). We conclude that the progression of acute DAD to chronic DAD is mainly determined by local factors (hydrodynamic and hydrostatic forces, intraalveolar pressure) that differ within the lung, whereas the duration of disease plays a minor role. Parenchymal hemorrhage occurs at the interface between areas of acute and chronic DAD and may therefore primarily be due to an increased susceptibility of the pulmonary parenchyma to mechanical stress.

Respiratory and haemodynamic effects of conventional volume controlled PEEP ventilation, pressure regulated volume controlled ventilation and low frequency positive pressure ventilation with extracorporeal carbon dioxide removal in pigs with acute ARDS.

The purpose of this study was to evaluate whether any benefit of low frequency positive pressure ventilation with extracorporeal carbon dioxide removal (LFPPV-ECCO2R) existed over either volume controlled ventilation (VCV) with measured best-PEEP or pressure regulated volume controlled ventilation (PRVCV) with an inspiration/expiration (I/E) ratio of 4:1, with respect to arterial oxygenation, lung mechanics and haemodynamics, in acute respiratory failure. Fifteen adult pigs were used for the study. Respiratory failure was induced by surfactant depletion by repeated lung lavage. The different therapeutic approaches were applied randomly to each pig for 1 h. Measurements of gas exchange, airway pressures and haemodynamics were performed during ventilatory and haemodynamic steady state. Paco2 was kept constant in all modes. At almost similar total-PEEP, Pao2 values were significantly higher with LFPPV-ECCO2R compared to VCV with best-PEEP. Peak inspiratory pressure (PIP) and intrapulmonary pressure amplitude defined as the difference between PIP and total-PEEP were significantly lower with PRVCV and LFPPV-ECCO2R compared to VCV with best-PEEP. There was no significant difference between the modes concerning cardiocirculatory parameters. PRVCV with I/E ratio of 4:1 and LFPPV-ECCO2R proved to be better modes to achieve better gas exchange and lower PIP at lower intrapulmonary pressure amplitudes. It is concluded that PRVCV is an adequate form of treatment under these experimental conditions imitating acute respiratory failure, without necessitating other invasive measures.

Extracorporeal carbon dioxide removal technique improves oxygenation without causing overinflation.

Extracorporeal CO2 removal combined with low frequency positive pressure ventilation (ECCO2R-LFPPV) improves gas exchange and decreases peak pressures, respiratory rates, and tidal volumes in animals and in humans. Recent evidence suggests that pulmonary barotrauma results from lung overinflation rather than from high pressures. This study was to test the hypothesis whether ECCO2R-LFPPV could improve gas exchange without causing lung overinflation, despite the use of higher levels of PEEP, when compared with conventional mechanical ventilation. Eleven patients with severe adult respiratory distress syndrome (ARDS) who failed to respond to different modes of mechanical ventilation were treated with ECCO2R-LFPPV. Risk of pulmonary barotrauma was evaluated by static pressure-volume (P-V) curves and dynamic changes in volumes monitored by respiratory inductive plethysmography (Respitrace). ECCO2R-LFPPV PaO2/FIO2 increased from 79 +/- 21 to 207 +/- 108 (p = 0.003). Risk of barotrauma, as shown by the shape of the P-V curve, was present in all patients receiving mechanical ventilation even though most of them were treated with permissive hypoventilation. By contrast, no evidence of persistent lung overinflation could be detected by either static P-V curves or dynamic measurements in nine of 11 patients who were treated by ECCO2R-LFPPV. The two remaining patients had severe airway obstruction because of bleeding, and they remained ventilated with persistent risk of barotrauma. We conclude that ECCO2R-LFPPV improves gas exchange without causing lung overinflation in a majority of patients with ARDS.

Human polymorphonuclear leukocyte metabolism and lipoperoxidation during adult respiratory distress syndrome treated by extracorporeal carbon dioxide removal

Circulating polymorphonuclear leukocyte (PMNs) oxidative metabolism and lipoperoxidation were evaluated in patients with the adult respiratory distress syndrome (ARDS) treated with low-frequency positive-pressure ventilation and extracorporeal carbon dioxide removal. Chemiluminescence (CL) of resting PMNs from ARDS patients was significantly enhanced relative to controls ( P < 0.001). A significant decrease in CL of resting PMNs from ARDS patients was observed after cell incubation with serum from ARDS patients and healthy controls ( P < 0.05). CL of normal opsonized zymosan (OZ)-stimulated PMNs was significantly enhanced ( P < 0.01) after preincubation with ARDS serum. A significant decrease ( P < 0.05) in control PMN O 2− production was observed after pre-incubation with normal and ARDS serum. Plasma malondialdehyde (MDA) and α 1 proteinase inhibitor-elastase levels were significantly increased in ARDS patients plasma ( P < 0.05), whereas erythocyte glutathione peroxidase was significantly higher in patients who survived ARDS episodes than in those who died ( P < 0.01). CL of resting ARDS PMNs correlated with elastase levels ( r = 0.824; P < 0.001), and MDA levels correlated with the ‘injury severity score’ ( r = 0.46; P = 0.056). Our results show that oxygen metabolism and plasma elastase levels in circulating PMNs from ARDS patients are significantly enhanced. Furthermore, ARDS PMN functions are not enhanced by exogenous stimuli. No correlation between PMN functions and peroxidation was found in ARDS sera. These findings confirm that PMNs are primed during ARDS, but free radical production seems to be only one of the events responsible for the increased lipoperoxidation.

Extracorporeal Carbon Dioxide Removal and Low-Frequency Positive-Pressure Ventilation: Improvement in Arterial Oxygenation With Reduction of Risk of Pulmonary Barotrauma in Patients With Adult Respiratory Distress Syndrome

Mortality of the adult respiratory distress syndrome (ARDS) remains high and could be increased by pulmonary barotrauma induced by positive-pressure mechanical ventilation. Extracorporeal CO2 removal combined with low-frequency positive-pressure ventilation (ECCO2R-LFPPV) has been proposed to reduce lung injury while supporting respiratory failure. Use of this technique in 23 patients resulted in the following: a dramatic and highly significant increase of PaO2 obtained rapidly with ECCO2R-LFPPV, allowing subsequent reduction in inspired oxygen fraction; a reduction of the risk of barotrauma evidenced by a significant decrease in pressures and insufflated volumes; a survival rate of 50 percent. Bleeding was the only complication related to the technique and was the cause of death in four patients. This method allowed improvement in gas exchange along with reduction of the risk of barotrauma caused by the ventilator.

Progress in Veno-Venous Long-Term Bypass Techniques for the Treatment of Ards

Extracorporeal CO2 removal combined with low-frequency positive pressure ventilation (ECCO2-R LFPPV) is a new therapeutic approach in treatment of ARDS. The main problem during long-term extracorporeal support is anticoagulation and related bleeding problems. We conducted a prospective, randomized and controlled clinical trial in 18 patients to compare the effect of the non-heparin-coated (Scimed = group 1) with the heparin-coated (Carmeda = group 2) extracorporeal circuit on clinical course and complication rate. In group 2 the daily blood loss, the amount of substituted red cells and the i.v. heparin dose were significantly lower than in group 1. Bleeding complications were less and more patients survived in group 2. The disadvantage of the hollow fiber oxygenators in the heparin-coated system was plasma leakage, which was more frequent in patients with pancreatitis and hyperbilirubinemia.

Multicentre randomised controlled trial of high against low frequency positive pressure ventilation. Oxford Region Controlled Trial of Artificial Ventilation OCTAVE Study Group.

A total of 346 infants aged less than 72 hours were randomly allocated to be treated either by high frequency positive pressure ventilation (HFPPV; rate fixed at 60/minute throughout treatment and initial inspiratory:expiratory (I:E) ratio 1:2, increased to 1:1 if necessary) or by low frequency positive pressure ventilation (LFPPV; rate less than or equal to 40/minute and initial I:E ratio usually 1:1, both decreasing during weaning). The main hypotheses were that HFPPV reduces pneumothorax, chronic lung disease and death before discharge in all infants, as well as those with hyaline membrane disease, and that it reduces the incidence of later neurodevelopmental complications in infants of less than 33 weeks' gestation. Among all the infants the rate of pneumothorax was 19% in the HFPPV group and 26% in the LFPPV group (p = 0.13; odds ratio 0.7, 95% confidence intervals (CI) 0.4 to 1.1); there was no difference in mortality or the incidence of chronic lung disease. In infants of less than 33 weeks' gestation there were no differences in adverse neurodevelopmental outcomes. Among the subgroup of 237 infants with hyaline membrane disease, median fractional inspired oxygen at the time of entry to the trial was 0.6 in the HFPPV group and 0.7 in the LFPPV group, indicating that many had moderately severe disease. In patients with hyaline membrane disease HFPPV was associated with a lower rate of pneumothorax (18% in the HFPPV group compared with 33% in the LFPPV group, p = 0.013, odds ratio 0.5, 95% CI 0.3 to 0.8, with no differences in mortality, or in duration of intubation or supplementary oxygen in survivors. As used in this study, HFPPV was the preferred ventilator regimen for infants with hyaline membrane disease.

Extracorporeal CO2 Removal in a Lung Lavage Induced Respiratory Distress Syndrome

Ten pigs with experimental respiratory distress syndrome were treated by extracorporeal CO2 removal (ECCO2-R) combined with low frequency positive pressure ventilation (LPPV). After lung damage had been induced by repeated lung lavages a PEEP trial was conducted in order to find the appropriate PEEP for the damaged lungs. This PEEP was then applied during the ECCO2-R/LPPV period. Blood gas values improved significantly on extracorporeal bypass within a short time (pre-bypass paO2: 54.2 +/- 3.7 vs 168.5 +/- 31.6 mmHg after 15 min on bypass, p less than 0.001) and were kept constant during the next 4 hours. Minute ventilation (MV) was reduced from 4.01 +/- 0.31 to 0.74 +/- 0.07 l/min (p less than 0.0001), FiO2 of the ventilator from 1.0 to 0.46 +/- 0.08 (p less than 0.0001) whereas FiO2 of the membrane lung (ML) was not changed significantly (FIO2ML 0.59 +/- 0.07 vs 0.53 +/- 0.06). During controlled mechanical ventilation (CMV), comparable adequate gas exchange was only achieved at a significantly higher mean airway pressure (Paw 14.1 +/- 0.08 vs 21.2 +/- 0.47 cmH20, p less than 0.0001). Hemodynamic variables did not change significantly during bypass time. ECCO2-R/LPPV driven by a simple renal perfusion system allows adequate gas exchange in experimental respiratory failure.

Preliminary report: Extracorporeal lung support for neonatal acute respiratory failure

A technique for ventilatory support of life-threatening neonatal acute respiratory failure by use of apnoeic oxygenation and low-frequency positive-pressure ventilation, with extracorporeal membrane CO 2 removal through a single-cannula perfusion circuit, is described. 20 severely ill babies with respiratory failure were treated with this technique, 17 of whom survived with no clinical evidence of pulmonary handicap or neurological deficit at discharge from hospital. All 10 patients followed up at 6 months showed normal growth and development.

Low-frequency positive-pressure ventilation with extracorporeal carbon dioxide removal

Successful use of a new technique, low-frequency positive-pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCR) is presented. The association of fulminant respiratory failure with CNS hemangioblastoma, described in the present patient, has been reported only once before, in 1928.

Venovenous Long Term Extracorporeal CO2 Removal With Biopump and Hollow Fiber Membrane Oxygenator For the Failing Lung

A 14-year-old male patient developed a severe respiratory insufficiency after a cart racing accident complicated by a bilateral pneumothorax, lung contusion and a rupture of a segmental lobe bronchus, for which two subsequential surgical interventions were needed. Due to a decreased lung compliance, alveolar ventilation was decreased to a minimum, resulting in the development of hypercapnia. The patient was placed on partial venovenous bypass utilizing the Biomedicus centrifugal pump and two Sarns hollow fiber membrane oxygenators, in combination with low frequency positive pressure ventilation, for extracorporeal CO2 removal with limited anticoagulation. This case report illustrates the safe use and continuous effective performance of the hollow fiber membrane oxygenator and centrifugal pump for more than 60 hours. Despite all efforts to create an environment for the lungs to heal, the patient succumbed due to irreversible traumatic cerebral damage and the bypass procedure was terminated after 60 hours.

Lung extravascular volume during venovenous bypass with extracorporeal CO2-removal in dogs

Extracorporeal circulation can cause lung damage, which would be especially counterproductive during extracorporeal gas exchange for the treatment of acute respiratory failure. To test the hypothesis that partial venovenous bypass with extracorporeal CO2-removal combined with low-frequency positive pressure ventilation (ECCO2R-LFPPV) can adversely affect lung fluid balance, extravascular thermal lung volume (ETV) and hemodynamics were assessed before, during and after ECCO2R-LFPPV in normal closed chest dogs. In series I dogs (n = 6) subjected to 10 h of ECCO2R-LFPPV, ETV did not change significantly from control (7.1 ml/kg +/- 0.99 SE) during or after bypass. Gravimetric extravascular lung water and lung histology after bypass were found to be normal. In series II dogs (n = 5), subjected to shorter periods of ECCO2R-LFPPV, ETV also remained unchanged. In contrast to previous reports using sheep, pulmonary arterial hypertension during bypass was not observed. Thus, ECCO2R-LFPPV was not associated with increased lung water, pulmonary hypertension or morphological lung changes under the conditions studied and does not seem to cause lung damage in normal lungs.

Determinants of ventilation during high-frequency jet ventilation

To better define the variables unrelated to ventilator frequency that affect gas transport during high-frequency jet ventilation (HFJV), we performed experiments in anesthetized paralyzed dogs (n = 8). The independent effects of changing driving pressure (300, 200, 150 kPa), catheter used for HFJV delivery (14-gauge and jet port of endotracheal tube), inspiratory time (30%, 50%, and 70%), and injector cannula diameter (12-gauge, 14-gauge, and 16-gauge) on minute volume (VE ), gas exchange, and cardiac output were studied at a ventilatory frequency of 100 min −1. V E increased with increasing driving pressure and inspiratory time. Entrainment decreased with increasing inspiratory time or when HFJV was delivered either via the jet port of the endotracheal tube, or via a jet cannula with distal side holes. Arterial PCO 2 varied inversely with V E. Arterial oxygenation increased with hypocarbia, whereas venous admixture and cardiac output were unchanged. Several factors affect the ventilator-delivered and entrained volumes during HFJV, which in turn affect gas exchange. The determinants of gas exchange during HFJV appear to be similar to those described for conventional low-frequency positive-pressure ventilation.

Low-Frequency Positive-Pressure Ventilation with Extracorporeal CO2 Removal in Severe Acute Respiratory Failure

GATTINONI, L.; PRESENTI, A.; MASCHERONI, D.; MARCOLIN, R.; FUMAGALLI, R.; ROSSI, F.; IAPICHINO, G.; ROMAGNOLI, G.; UZIEL, L.; AGOSTONI, A.; KOLOBOW, T.; DAMIA, G. Author Information

Low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory failure

Low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory failure

Alternative modes of ventilation. Part II. High and low frequency positive pressure ventilation PEEP, CPAP inversed ratio ventilation.

Alternative modes of ventilation. Part II. High and low frequency positive pressure ventilation PEEP, CPAP inversed ratio ventilation.

Alternative modes of ventilation. Part I. Disadvantages of controlled mechanical ventilation: intermittent mandatory ventilation.

Controlled mechanical ventilation is an accepted therapy for acute respiratory failure but by virtue of the increase in intrathoracic pressure has a large number of disadvantages. It is to overcome these disadvantages that alternative modes of ventilation have been introduced. These aim to reduce the effects of abnormally high airway pressure on the lung whilst recruiting solid alveoli and at the same time maintaining effective blood volume. Intermittent mandatory ventilation is a mode of ventilation first introduced to aid weaning which may reduce the need for sedation, permit better tolerance of high levels of PEEP and maintain urine osmolar output. High frequency ventilation utilising low airway pressures can maintain pulmonary gas exchange whilst reducing the effects of stretch on the lung. Its major role would seem to be in cases of bronchopleural fistula and necrotising pneumonia where a low mean airway pressure is essential. Low frequency positive pressure ventilation with extra corporeal CO2 removal, whilst a very labour intensive technique, has produced a favourable outcome in patients with terminal respiratory failure. Use of PEEP is associated with further deleterious haemodynamic effects which are largely overcome with use of continuous positive airway pressure during spontaneous respiration. PEEP is widely used. Its effect on pulmonary compliance, dead space and oxygen delivery are unpredictable making haemodynamic monitoring mandatory. Inversed ratio ventilation requires further evaluation whereas differential lung ventilation is logical, complicated but very valuable where the time constants for each lung are significantly different.