Nasal ventilation in pregnancy: treatment of nocturnal hypoventilation in a patient with kyphoscoliosis

The management of a young woman with congenital kyphoscoliosis, who developed symptomatic nocturnal hypoventilation during the third trimester of pregnancy, is described. Nasal intermittent positive pressure ventilation (NIPPV) was safely and effectively used to correct nocturnal hypoxaemia and hypercapnia from the 30th-36th week of gestation, when a healthy boy was delivered by Caesarean section. Following delivery, the mother no longer required NIPPV and returned to her prepregnancy level of activity.

Haemodynamic and endocrinological effects of noninvasive mechanical ventilation in respiratory failure

The aim of this study was to investigate the haemodynamic and endocrinological effects of noninvasive positive pressure ventilation (NIPPV). Eleven patients with oedema and recent hypercapnic and hypoxaemic worsening of a chronic respiratory insufficiency were included. Echocardiography, cardiac radionuclide assessment, blood catecholamines, salt and water handling hormones were measured at admission and discharge (long study (LS)). To discriminate between the action of NIPPV and other treatments, measurements were performed on the fourth day, for 4 h without NIPPV and 4 h with NIPPV (short study (SS)). NIPPV entailed a correction of P(a,CO2) and an increase of P(a,O2) in LS and SS. Oedema disappeared. Body weight decreased (from 85+/-42 to 81+/-40 kg) during LS. Systolic and mean pulmonary arterial pressure decreased in LS and SS. Right ventricular ejection fraction increased in LS. Left ventricular ejection fraction did not change. Cardiac index was normal on admission and then decreased. Natriuretic peptides and catecholamines were increased on admission, whereas plasma renin activity, aldosterone and vasopressin were normal. We suggest that in these patients, oedema can occur independently of renin-angiotensin-aldosterone-vasopressin and with a normal cardiac output. Noninvasive positive pressure ventilation allowed a correction of blood gases, associated with the resolution of oedema, a decrease in pulmonary arterial pressures and an increase in right ventricular ejection fraction.

Efficacy of noninvasive positive pressure ventilation by facial and nasal mask in hypercapnic acute respiratory failure: experience in a respiratory ward under usual care

Noninvasive intermittent positive pressure ventilation (NIPPV) via a nasal or facial mask is an effective treatment of hypercapnic acute respiratory failure (ARF) caused by various diseases preventing endotracheal intubation (ETI) in 60-90% of patients. The technique can even be effective for routine care, using simplified ventilators, after adequate personnel training. In this study, the effectiveness, in a general respiratory ward under usual care, of NIPPV delivered by simplified ventilators via facial or nasal mask was evaluated in 40 patients with hypercapnic ARF (NIPPV group) and compared to 30 matched historical patients under conventional treatment (Conv group). Compared to conventional treatment, NIPPV was associated with a reduction in negative events such as ETI and mortality together (17% versus 60%, p = 0.0002), but not mortality alone (5% versus 13.5%, NS) or in the mean (+/- SD) length of the hospital stay (27.31 +/- 16.2 versus 27.5 +/- 20.5 days, NS). Patients treated with NIPPV, but not those treated conventionally, showed significant and rapid changes in arterial carbon dioxide tension (Pa,CO2) and pH between baseline and subsequent evaluation after 6 h, 1, 3 and 7 days and upon the discharge from hospital; in fact, in the NIPPV group after 6 h the arterial pH had risen from 7.30 +/- 0.062 to 7.35 +/- 0.066 and Pa,CO2 had decreased from 9.4 +/- 1.5 to 8.5 +/- 1.1 kPa. In the Conv group pH was stable at 7.29 and Pa,CO2 had risen from 9.39 +/- 1.8 to 9.43 +/- 1.6 kPa. In the NIPPV group no differences were found in the admission characteristics between patients successfully and unsuccessfully ventilated, although a significant improvement was observed after 1 h, for pH from 7.31 +/- 0.058 to 7.36 +/- 0.57 and Pa,CO2 from 9.2 +/- 1.3 to 8.3 +/- 1.3 kPa in successfully ventilated patients. In patients who failed to be ventilated with NIPPV pH worsened, from 7.26 +/- 0.069 to 7.24 +/- 0.078 and Pa,CO2 from 10.0 +/- 2.1 to 11.3 +/- 2.5 kPa. In conclusion, addition of noninvasive positive pressure ventilation delivered by nasal or face mask to conventional therapy, reducing the need for endotracheal intubation, may improve the management of patients with hypercapnic acute respiratory failure as compared to conventional therapy alone, even when instituted in a respiratory ward under usual care with simplified ventilators.

End-inspiratory airway occlusion: a method to assess the pressure developed by inspiratory muscles in patients with acute lung injury undergoing pressure support

We evaluated the end-inspiratory occlusion maneuver as a means to estimate the inspiratory effort during pressure support ventilation (PS). In nine nonobstructed acute lung injury (ALI) patients, we applied four levels of PS (0, 5, 10, 15 cm H2O) to modify the inspiratory effort. End inspiratory occlusions (2 to 3 s) were performed at the end of each experimental period by pushing the inspiratory hold button of the ventilator (Servo 900 C; Siemens, Berlin, Germany). We took the difference between the end-inspiratory occlusion plateau pressure and the airway pressure before the occlusion (PEEP + PS) as an estimate of the inspiratory effort and called it PMI (Pmusc,index). From the esophageal pressure tracing we obtained a reference measurement of the pressure developed by the inspiratory muscles at end inspiration (Pmusc,ei) and of the pressure-time product per breath (PTP/b) and per minute (PTP/min). In each patient, PMI was correlated with Pmusc,ei (p < 0.01) and PTP/b (p < 0.01). A PMI threshold of 6 cm H2O detected PTP/min < 125 cm H2O s/min with a sensitivity of 0.89 and a specificity of 0.89. We conclude that PMI is a good estimate of the pressure developed by the inspiratory muscles in ALI patients and may be used to titrate PS level. The major advantage of PMI is that it can be obtained from the ventilator display without any additional equipment.

Ventilatory support during exercise in patients with pulmonary tuberculosis sequelae

STUDY OBJECTIVE

The aim of this study was to determine whether intermittent positive pressure ventilation through a nasal mask (NIPPV) applied during exercise in patients with pulmonary tuberculosis sequelae (PTS) could improve arterial blood gas measurements, ameliorate breathlessness, and increase exercise endurance.

PATIENTS

Seven PTS patients with a severe restrictive ventilatory defect (mean [SD] vital capacity, 1.02 [0.25] I) enrolled in this study had experienced NIPPV previously, and were familiar with the procedure.

DESIGN

The patients underwent four constant-load cycle ergometer tests in the supine position to tolerance. The tests were performed with and without NIPPV, while breathing normoxic air (Air) or supplemental oxygen (O2; 35%). NIPPV was delivered during exercise in a controlled, volume-cycled mechanical ventilation mode, and the ventilator settings were modulated manually to meet patients' respiratory demands as estimated from the airway pressure waveform and the patient's breathlessness.

RESULTS

All patients matched their breathing to the ventilator cycle during most of the exercise while receiving NIPPV. NIPPV significantly prolonged their exercise endurance time, from a mean (SD) of 180 (58) s to 310 (96) s in Air, and from 227 (64) s to 465 (201) s in O2. During exercise, NIPPV effectively decreased their breathlessness and significantly improved arterial blood gas measurements.

CONCLUSIONS

NIPPV applied during exercise can effectively support ventilation, significantly ameliorate breathlessness, and consequently improve exercise endurance in patients with PTS.

Sequential use of noninvasive pressure support ventilation for acute exacerbations of COPD

OBJECTIVES

To compare the efficacy of noninvasive pressure support ventilation (NIPSV) in acute decompensation in chronic obstructive pulmonary disease (COPD) by means of a bi-level positive airway pressure support system (BiPAP) in a sequential mode with medical therapy alone; to assess the short-term physiologic effects of the device on gas exchange; and to compare patients successfully ventilated with NIPSV with those in whom NIPSV failed.

DESIGN

A prospective case series with historically matched control study.

SETTING

A general intensive care unit (ICU) of a university hospital.

PATIENTS

We evaluated the efficacy of administration of NIPSV in 42 COPD patients and compared this with standard treatment in 42 matched historical control COPD patients.

INTERVENTIONS

NIPSV was performed in a sequential mode, i.e., BiPAP in the spontaneous mode was used for at least 30 min every 3 h. Between periods of ventilation, patients could be systematically returned to BiPAP when the arterial oxygen saturation was < 0.85 or when the respiratory rate was > 30 breaths/min.

MEASUREMENTS AND RESULTS

Success rate, mortality, duration of ventilatory assistance, and length of ICU stay were recorded. Eleven of the 42 patients (26%) in the NIPSV group needed tracheal intubation compared with 30 of the 42 control patients (71%). The 31 patients in whom NIPSV was successful were ventilated for a mean of 6 +/- 3 days. In-hospital mortality was not significantly different in the treated versus the control group, but the duration of ventilatory assistance (7 +/- 4 days vs 15 +/- 10 days, p < 0.01) and the length of ICU stay (9 +/- 4 days vs 21 +/- 12, p < 0.01) were both shortened by NIPSV. BiPAP was effective in correcting gas exchange abnormalities. The pH values, measured after 45 min of BiPAP with optimal settings, in the success (7.38 +/- 0.04) and failure (7.28 +/- 0.04) patients were significantly different (p < 0.05).

CONCLUSIONS

NIPSV, performed with a sequential mode, may be used in the management of patients with acute exacerbations of COPD.

Noninvasive positive pressure ventilation and not oxygen may prevent overt ventilatory failure in patients with chest wall diseases

Some patients with chest wall diseases (CWD) without respiratory failure manifest important alterations in nocturnal gas exchange, as a previous stage to the future development of daytime respiratory failure. The purpose of this study was to evaluate the efficacy of nasal intermittent positive pressure ventilation (NIPPV) during sleep in a group of obese patients and in another group with restrictive thoracic diseases (RTD), comparing the results with those obtained from conventional nocturnal oxygen therapy. From a total of 42 patients with CWD free of daytime respiratory failure, 27 (64%) were considered nocturnal oxygen desaturators without sleep apnea and were included in the study. The study protocol was completed by 21 of these patients. After 2 weeks of treatment, symptoms of dyspnea, morning headaches, and morning obnubilation improved significantly (p<0.05) in both groups of patients after NIPPV but not with oxygen. Baseline daytime PaO2 was 68+/-7 mm Hg in the obese group of patients and 73+/-11 mm Hg in the RTD group. It improved significantly with NIPPV to 73+/-5 mm Hg in obese patients (p<0.05) and to 77+/-12 mm Hg in the RTD group (p<0.05) but did not change with oxygen (68+/-8 mm Hg in the obese group and 73+/-12 mm Hg in the RTD group). Both treatments improved oxygen saturation during sleep, but oxygenation tends to be higher with oxygen than with NIPPV. Only NIPPV was able to normalize the baseline nocturnal alveolar hypoventilation. From the 21 patients treated, 19 decided to continue with long-term NIPPV, one with oxygen, and one refused treatment. We conclude that in patients with CWD who manifest nighttime oxygen desaturation and hypoventilation, early initiation of NIPPV is preferable to supplemental oxygen. Our results also suggest that NIPPV initiated before overt ventilatory failure could prevent its onset.

[Initial experiments with controlled assisted ventilation by nasal mask in exacerbated chronic respiratory failure in chronic obstructive bronchopneumopathies]

The authors are presenting the first cases in Romania in which volumetric ventilators Monnal D type were used for external ventilatory assistance on nasal mask of the chronic obstructive pulmonary diseases in exacerbation. The paper reviews the problems issued during the use of ventilators in 5 chronic patients, with numerous previous admittances in our clinic, as well as the latest news in the field of modern therapy of COPD.

A guide to noninvasive intermittent ventilatory support

Patients who use home-based medical technologies, such as noninvasive intermittent ventilatory support, may require hospitalization on units where the staff is unfamiliar with this type of equipment. Consequently, acute care clinicians need resources so they can provide safe care to these patients. This article provides background information about noninvasive intermittent ventilatory support, presents a case study to illustrate key aspects of each type of support, and provides quick reference tables to assist acute care clinicians in managing this technology.

[Pressure versus volume constant ventilation in chronic ventilatory insufficiency]

BACKGROUND

Volume controlled intermittent ventilation (IPPV) via face mask is a treatment of proven efficacy for chronic respiratory failure (CRF). Pressure support ventilation has recently been introduced in the treatment of CRF. In this study we investigated whether pressure constant ventilation (PCV) via face mask could be an adequate long term alternative to IPPV.

PATIENTS AND METHODS

We studied 30 (24 male, age: 52.2 +/- 15.9 years) patients with CRF. We measured the following parameters at baseline, after 1, 2 and 6 months, respectively: blood gas analysis, oxygen saturation, vital capacity, forced exspiratory volume, breathing frequency, tidal volume, inspiratory mouth occlusion pressure, maximal inspiratory pressure, subjective symptom scores and ventilator acceptance scores. In all patients, we attempted to treat with IPPV over 1 month, followed by 1 month's trial of PCV. If PCV, compared to IPPV, was adequate, PCV was continued for a follow-up period of 4 months' duration. If patients deteriorated after PCV they were treated the following 4 months with IPPV.

RESULTS

In 28 out of 30 patients CRF improved concerning subjective and objective parameters. After IPPV 18 out of 28 patients changed to PCV, with an equal quality of treatment (PCV-responder). Ten patients were PCV-nonresponders since compared to IPPV the subjective scores deteriorated and the PaCO2 increased again. In all patients of either therapy group, subjective and objective parameters remained constant for another 4 months period. At baseline the PCV-nonresponders had significantly higher degree of hypercapnia and oxygen desaturation; no other parameters were found to be of predictive value concerning the efficacy of PCV.

CONCLUSIONS

PCV proved to be an alternative to IPPV in the treatment of chronic respiratory insufficiency in approximately 60% of the patients with CRF. However there is a subgroup with more severe CRF at baseline in whom PCV is inadequate.

Long-term domiciliary treatment with nasal intermittent positive-pressure ventilation plus supplemental oxygen in COPD with severe hypercapnia

An effective treatment of advanced states of chronic obstructive pulmonary disease (COPD) has yet to be established. We report the case of a COPD patient with severe hypoxemia (pO2 = 32.0 mm Hg) and hypercapnia (pCO2 = 90.0 mm Hg) who was successfully treated for 8 months with nasal intermittent positive-pressure ventilation (NIPPV) plus supplemental O2 in a domiciliary treatment. The reduction of hypoxemia parallel to the alleviation of hypercapnia reversed the patient's continuously declining condition.

Long-term management of acute respiratory failure in metabolic myopathy

OBJECTIVE

To describe how patients cope with the proposal of treatment with intermittent artificial ventilation after acute respiratory failure due to progressive respiratory muscle weakness.

DESIGN

Case series, follow-up study.

SETTING

Neurological intensive care unit (ICU).

PATIENTS

7 consecutive patients with metabolic myopathy treated for acute respiratory failure between 1983 and 1992.

INTERVENTIONS

Intermittent positive pressure ventilation (IPPV) via tracheostomy.

MEASUREMENTS AND RESULTS

Symptoms of chronic hypoventilation preceded acute respiratory failure for months. With one exception, patients were mainly disabled from respiratory muscle weakness and sleep-related breathing disorders. IPPV was recommended to prevent recurrent respiratory failure. Two of three patients who accepted home IPPV returned to full-time jobs. One patient, who decided against IPPV, died from CO2 narcosis several months after discharge. All patients adhered to the respiratory regimen once instituted.

CONCLUSIONS

Acute respiratory failure in chronic myopathy is heralded by daytime drowsiness. IPPV, or at least regular monitoring of waking and sleeping partial pressure of carbon dioxide, is highly recommended even if weaning is successful. IPPV improved quality of life. The treatment strategy at discharge from the ICU should be optimal, as patients are reluctant to modify regimens.

Glottic aperture and effective minute ventilation during nasal two-level positive pressure ventilation in spontaneous mode

Our goal was to verify glottic behavior and its effects on effective minute ventilation during intermittent positive pressure ventilation applied at increasing inspiratory pressure levels through a nasal mask (nIPPV) using a two-level positive pressure ventilator (two-level IPPV) in spontaneous mode. Ten subjects were studied while awake. The spontaneous mode was used at three levels of inspiratory positive airway pressure (IPAP): 10, 15, and 20 cm H2O. The expiratory pressure was kept at 4 cm H2O. Records of spontaneous breathing without nIPPV were also performed. The glottis was continuously monitored through a fiberoptic bronchoscope. We measured, breath by breath, the widest inspiratory angle formed by the vocal cords at the anterior commissure, the corresponding tidal volume (with respiratory inductive plethysmography), the respiratory frequency and other indices. Our data during wakefulness show that inspiratory pressures of 10 and 15 cm H2O did not result in increases in effective minute ventilation with respect to spontaneous breathing. Only at 20 cm H2O of IPAP did effective minute ventilation increase. This was due essentially to a decrease in respiratory frequency with increasing pressures, offsetting increases in tidal volume at 10 and 15, but not at 20 cm H2O of inspiratory pressure. Changes in end-tidal CO2 suggest that alveolar ventilation increased due to the change in breathing pattern. Contrary to what we observed previously with either two-level IPPV used in the controlled mode, or nIPPV performed with volumetric ventilators, the glottis did not play any noticeable role in the control of effective minute ventilation.

Long-term effects of nasal intermittent positive-pressure ventilation on pulmonary function and sleep architecture in patients with neuromuscular diseases

STUDY OBJECTIVE

This article evaluates the long-term clinical and physiologic effects of nocturnal nasal intermittent positive-pressure ventilation (NIPPV) in patients with neuromuscular disease.

METHODS

Before and after 18 +/- 2 months of NIPPV, we measured during the daytime arterial blood gases, lung mechanics, and respiratory muscle strength in 8 patients (51 +/- 5 years; mean +/- SEM). Sleep parameters were also evaluated at 10 +/- 2 months.

RESULTS

All patients tolerated NIPPV and none required hospitalization during follow-up. After NIPPV, daytime arterial PO2 increased (71 +/- 4 to 81 +/- 2 mm Hg; p < 0.05) and arterial PCO2 decreased (46 +/- 3 to 41 +/- 1 mm Hg; p < 0.05). The change of PaO2 after NIPPV was related to its baseline value (r2 = 0.78, p < 0.05). Vital capacity (50 +/- 6% predicted), total lung capacity (63 +/- 4% predicted), alveolar-arterial oxygen gradient (20 +/- 3 mm Hg), and maximal inspiratory (39 +/- 9% predicted) or expiratory (32 +/- 5% predicted) pressures did not change after NIPPV. The apnea-hypopnea index fell from 22 +/- 6 to 1 +/- 1 (p < 0.05), and both sleep architecture and sleep efficiency (from 59 +/- 8% to 83 +/- 5%; p < 0.05) were enhanced. The time spent with an arterial oxygen saturation (SaO2) value below 90% decreased from 160 +/- 53 min to 8 +/- 4 min (p < 0.05). Mean (88 +/- 3 to 95 +/- 1%; p < 0.05) and minimal nocturnal SaO2 (67 +/- 5 to 89 +/- 1%; p < 0.001) improved after NIPPV.

CONCLUSIONS

In patients with neuromuscular disease, long-term NIPPV is well tolerated and easy to implement clinically. In these patients, long-term NIPPV improves daytime arterial blood gas values and sleep-disordered breathing. However, it does not modify lung mechanics or respiratory muscle strength.

Noninvasive positive-pressure ventilation for acute respiratory failure in a medical intensive care unit in Singapore

The main advantage of noninvasive ventilation over conventional mechanical ventilation is in the avoidance of endotracheal intubation and its related complications. Currently, the role of noninvasive ventilation in the management of patients with acute respiratory failure is still not firmly established. We conducted a prospective study to evaluate the efficacy of nasal positive pressure ventilation in patients with acute respiratory failure. Thirty-three consecutive patients with acute failure in whom intubation and mechanical ventilation were strongly considered were included in the study. They received ventilatory support by means of BiPAP ventilatory support system and nasal mask. Physical findings and laboratory measurements were documented before and at specific intervals after initiation of support. Eighty per cent (24/30) of patients were successfully supported. Successfully supported patients tolerated the device with improved gas exchange, hence avoiding endotracheal intubation. The mean duration of support was 19.2 hours. There were major associated complications, e.g. gastric distention or aspiration.

Improved arterial oxygenation after oleic acid lung injury in the pig using a computer-controlled mechanical ventilator

We compared computer-controlled mechanical ventilation programmed for biologic variability of respiratory rate (RR) and tidal volume (VT) with conventional intermittent positive-pressure ventilation (IPPV) in an oleic acid (OA) lung injury model. Seventeen pigs were ventilated with an Ohio 7000 anesthesia ventilator. Minute ventilation (VE) was adjusted to maintain PaCO2 at 30 to 35 mm Hg at baseline and was not altered further. OA was infused at 0.2 ml/kg/h until PaO2 decreased to < 125 mm Hg (F(I)O2 = 0.5). Animals were randomly assigned to continue with conventional IPPV (control group; n = 8) or had IPPV computer-controlled (computer group; n = 9). Hemodynamic, respiratory gas, airway pressure, and volume data were obtained at baseline (before OA infusion), at Time 30 (after infusion), and at 30-min intervals for 240 min after OA. At experiment completion, the lungs were removed to determine the wet:dry weight ratios. The control group had RR fixed at 20 breaths/min. The computer group had a RR of 20 +/- 2.3 breaths/min (range, 15 to 27 breaths/min), comprising 369 different RR values with reciprocal changes in VT over 1,089 s before the program looped to repeat itself. There was no difference between groups in the volume of OA infused. By 120 min after lung injury, animals in the computer group had significantly greater PaO2, associated with a lower Qs/QT. Mean airway pressures and mean peak airway pressures were not different in the two groups. By 180 min, respiratory system compliance (Crs) was significantly lower in the control group. The wet:dry lung weight ratios were greater in the control group. Thus, in a porcine model of OA lung injury, computer-controlled mechanical ventilation, which is programmed for biologic variability, resulted in improved blood oxygenation without increasing mean airway pressures when compared with conventional IPPV.

Treatment of severe exacerbation of chronic obstructive pulmonary disease with mask-applied continuous positive airway pressure

The efficacy of mask-applied continuous positive airway pressure (CPAP) in the treatment of patients with acute severe exacerbations of chronic obstructive pulmonary disease (COPD) was examined. Ten patients with severe exacerbation of COPD who had deteriorated during conventional therapy were treated with face-mask delivered CPAP (+5 cmH2O; Downs Vital signs Inc., New Jersey, USA) instead of tracheal intubation and mechanical ventilation. The patients that were selected required mental alertness, intact upper airway reflexes, the clinical signs of dynamic hyperinflation and a positive end-expiratory pressure auto-(PEEP) manifested as expiratory wheeze and grunting. Nine out of 10 patients responded promptly to mask-CPAP with less distress, better oxygenation, lower respiratory and pulse rates. There was no significant change in arterial carbon dioxide tension with mask-CPAP treatment. One patient deteriorated on mask-CPAP and required intubation and mechanical ventilation. Three patients died (none of these patients died during the acute period of exacerbation). It was concluded that Mask-CPAP may be an alternative to mechanical ventilation in the treatment of selected patients with severe hypercapnic exacerbations of COPD.

Non-invasive ventilation

Nasal intermittent positive pressure ventilation is an effective treatment for nocturnal hypoventilation secondary to chest wall deformity or respiratory muscle weakness. Physicians should be aware that, in these groups of patients, disabling breathlessness can be alleviated and established cor pulmonale reversed by the technique.

Effects of long-term nocturnal nasal ventilation on spontaneous breathing during sleep in neuromuscular and chest wall disorders

Nocturnal nasal intermittent positive pressure ventilation (NIPPV) is an effective means of normalizing awake blood gases in patients with respiratory insufficiency due to neuromuscular or chest wall dysfunction. However, little attention has been paid to the effects of long-term ventilation on spontaneous breathing during sleep in such patients. The purpose of this study was to determine whether spontaneous breathing during sleep improved after long-term nasal ventilation. Fourteen patients with documented nocturnal respiratory failure, who had been treated with nocturnal NIPPV for at least 6 months, were reviewed with an all night polysomnograph on a night without ventilatory support. The severity of nocturnal desaturation both in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep without nocturnal ventilation was compared to desaturation measured during the initial diagnostic study. Spontaneous daytime blood gas values (mean +/- SD) were significantly improved at follow-up compared to values obtained prior to nasal ventilation: arterial oxygen tension (Pa,O2): 7.5 +/- 1.2 to 10.2 +/- 1.3 kPa (p < 0.005); arterial carbon dioxide tension (Pa,CO2) 8.2 +/- 1.6 to 6.4 +/- 0.7 kPa (p < 0.001). Significant improvements in inspiratory muscle strength were also observed with maximal inspiratory pressure (Pl, max) increasing from a baseline value of 41 +/- 18 to 65 +/- 26% predicted measured prior to the night of ventilation withdrawal (p < 0.003). Spontaneous breathing during sleep after long-term treatment was markedly improved although still abnormal. During NREM sleep without ventilatory support, oxygen desaturation was significantly less severe compared to the initial study (arterial oxygen saturation (Sa,O2) 88 +/- 4 vs 78 +/- 8%; p < 0.001). Minimum Sa,O2 during REM sleep similarly improved from a mean value of 49 +/- 14% during the diagnostic night to 73 +/- 10% at review follow-up (p < 0.001). In 12 patients, transcutaneous carbon dioxide was measured continuously during sleep on both occasions and demonstrated significantly less CO2 retention during follow-up compared to control studies both in NREM (p < 0.003) and REM sleep states (p < 0.004). Long-term nocturnal ventilation produces improved respiratory drive both asleep and awake and improved arousal responses to abnormal blood gases.

Chronic noninvasive ventilation in obstructive airways disease

Early experience with noninvasive ventilation in patients with chronic obstructive pulmonary disease was largely unsuccessful, with no benefit over long-term oxygen therapy. Nasal positive pressure ventilation, however, produces improvements in arterial blood gases, nocturnal-hypoventilation, and quality of life. Experience with nasal ventilation in other obstructive airways diseases, such as bronchiectasis and cystic fibrosis, is limited and less favorable.

The use of noninvasive respiratory muscle aids in the management of patients with progressive neuromuscular diseases

Most patients with primarily ventilation impairment can use noninvasive alternatives to tracheostomy for long-term ventilatory support and airway secretion management. The most important and versatile method of noninvasive ventilatory support is mouthpiece intermittent positive pressure ventilation. Mouthpiece intermittent positive pressure ventilation also can be used via a Lipseal for nocturnal support. The intermittent abdominal pressure ventilator is an option for daytime aid, and nasal intermittent positive pressure ventilation is usually preferred for nocturnal support. Manually assisted coughing and mechanical insufflation-exsufflation can be critical for airway secretion elimination.

Respiratory management, survival, and quality of life for high-level traumatic tetraplegics

Although spinal cord injury is devastating and can compromise the respiratory system, particularly when the cervical cord is injured, aggressive use of noninvasive respiratory muscle aids can reduce the otherwise commonly seen complications of pneumonia, bronchial mucous plugging, atelectasis, and respiratory failure. Accessory muscle function can also usually be improved and the muscles then recruited to help maintain adequate alveolar ventilation during the acute spinal cord injury recovery period. Noninvasive assisted ventilation can be successful for patients with compromised lung function during the acute rehabilitation period as well as on a long-term basis. Removal of an indwelling tracheostomy tube results in improved quality of life from many points of view, a decreased number of local tracheostomy complications, a decreased number of serious respiratory infections, an improved ability to communicate, and an increased ability to use the mouth for functions such as operating computers and wheelchairs.

Long-term nasal intermittent positive pressure ventilation (NIPPV) in sixteen consecutive patients with bronchiectasis: a retrospective study

Life expectancy and quality of life are poor in patients with chronic respiratory failure due to bronchiectasis. The indication for nocturnal nasal intermittent positive pressure ventilation (NIPPV) remains controversial in chronic obstructive lung disease. The purpose of the present study was to determine whether some of the objectives of home mechanical ventilation, i.e. improvement in blood gas values and reduced length of hospitalization, were fulfilled by NIPPV and oxygen plus medical treatment in patients with chronic respiratory failure due to bronchiectasis. Sixteen consecutive patients (12 females and four males; mean age 57 +/- 11 yrs) with chronic respiratory failure due to bronchiectasis, treated at home with nocturnal NIPPV in addition to oxygen therapy, were retrospectively studied in terms of blood gas values and duration of hospitalization before and after NIPPV. Details of the therapy received by each patient were recorded. Nine patients agreed to complete a questionnaire to determine their perception of the benefits of the treatment. NIPPV was performed using a volumetric respirator and was applied with a customized nasal mask modelled with silicone paste. NIPPV was used for a mean of 26 months (range 0.5-60 months). Eleven patients were alive 12 months after use of NIPPV. No significant improvement in blood gas values was noted on room air during NIPPV, but arterial carbon dioxide tension (Pa,CO2) stabilized after the period of worsening observed before initiation of NIPPV. Duration of hospitalization, the year before and the year after NIPPV, was 19 (3-40) and 16 (8-37) days, respectively (NS). For the 11 patients who were alive 2 yrs after the start of NIPPV, duration of hospitalization the year before NIPPV and between 12 and 24 months after NIPPV were 17 (4-40) and 7 (2-27) days, respectively (p < 0.05). Nine patients who had received NIPPV for at least 12 months at the time of the study reported an improvement in their quality of life. The results suggest that home ventilatory support by nasal intermittent positive pressure ventilation offers an acceptable alternative to tracheotomy, with less discomfort, in the management of severe respiratory failure due to bronchiectasis, in order to allow the patient to return home. These results should be confirmed by controlled studies.

Nasal two-level positive-pressure ventilation in normal subjects. Effects of the glottis and ventilation

The purpose of this study was to examine the behavior of the glottis during intermittent positive-pressure ventilation (nIPPV) using a two-level positive-pressure ventilator and to compare the glottic adaptation to this ventilatory mode with the one observed using volumetric ventilators, recently reported by us. Six healthy subjects were studied during both wakefulness and sleep. Their glottis was continuously monitored through a fiberoptic bronchoscope. We measured breath by breath the widest inspiratory angle formed by the vocal cords at the anterior commissure, the corresponding tidal volume, and other indices. We used the controlled ventilatory mode. The expiratory pressure was kept at 4 cm H2O, and the inspiratory pressure was increased by steps from 10 to 15 to 20 cm H2O. Increases in inspiratory pressure did not always lead to increases in effective ventilation reaching the lungs. This was due to a significant narrowing of the glottis by adduction of the vocal cords in all subjects. Periodic breathing with or without apneas were common during wakefulness, but especially during sleep, representing 10.5 +/- 11% (SD) of total sleep time. We conclude that effective ventilation during nIPPV using a two-level positive-pressure ventilator in the controlled mode is less predictable and less stable than during nIPPV using volumetric ventilators.

Supplemental oxygen and nasal intermittent positive pressure ventilation

When supplementary oxygen is necessary with nasal intermittent positive pressure ventilation (NIPPV), the optimal route by which it should be added to the ventilator circuit is unknown. We investigated the oxygen concentration received when oxygen was supplied at flow rates between 0 and 6 L.min-1 into the proximal ventilator tubing or the nasal mask whilst patients were ventilated with air. Eleven patients with stable chronic hypercapnic respiratory failure were studied. A calibration curve was produced for each by supplying different known oxygen concentrations through a Monnal D or DCC ventilator and measuring the arterial oxygen saturations achieved. Oxygen was then supplied into the ventilator tubing or nasal mask and arterial saturation again measured. The oxygen concentration received was estimated using the calibration curve. Tracheal oxygen concentration throughout the respiratory cycle was studied in one patient when oxygen was supplied by both routes. Peak inspired oxygen concentration occurred at end-inspiration when oxygen was supplied into the ventilator tubing, but at mid-inspiration when supplied into the nasal mask. However, there was no significant difference between the two routes in the inspired oxygen concentration achieved at all flow rates: 1 L.min-1 supplied approximately 31% oxygen; 2 L.min-1 37%; 3 L.min-1 40%; and 4 L.min-1 44%. Flow rates above 4 L.min-1 had little additional effect. In conclusion, oxygen supplementation during nasal intermittent positive pressure ventilation can be provided into the ventilator tubing or the nasal mask with equal efficiency.

Noninvasive mechanical ventilation improves the immediate and long-term outcome of COPD patients with acute respiratory failure

Noninvasive positive pressure ventilation (NPPV) has been proposed in COPD patients with acute on chronic respiratory failure (ACRF) in order to avoid endotracheal intubation and to improve immediate outcome, but long-term outcome of this therapeutic approach is still undefined. We evaluated short- and long-term (1 year) outcome of early administration of NPPV in 24 patients with ACRF due to exacerbated COPD (Group A) in comparison with 24 matched historical-control patients treated conventionally (Group B). Patients of Group A were initially treated with NPPV via nasal mask in the presence of pH < or = 7.32, and/or Pa,O2 < 7.98 kPa, and/or Pa,CO2 > 7.18 kPa, plus signs of respiratory distress. In-hospital survival rate was not significantly different in Group A vs Group B, but the patients treated with NPPV showed an earlier improvement in blood gases and a better pH and respiratory rate at discharge. Only 2 patients of Group A needed endotracheal intubation as compared with 9 of Group B. Hospital stay was significantly reduced in survivors of Group A vs Group B. Further severe relapses of ACRF in Group A were treated using NPPV. The number and length of further hospitalizations for pulmonary exacerbations were significantly higher in Group B compared with Group A. The survival rate at 12 months was significantly lower in Group B than in Group A (50% vs 71%). In conclusion, NPPV administration in patients with ACRF due to exacerbated COPD improves not only immediate but also long-term outcome.

[Invasive ventilation. Classification, technique and clinical experiences with BiPAP/APRV (Biphasic Positive Airway Pressure/Airway Pressure Release Ventilation)]

BiPAP (bilevel or biphasic positive airway pressure) and APRV (airway pressure release ventilation) are new, and from a technical viewpoint closely related techniques recently introduced to the field of invasive ventilatory support. BiPAP/APRV can be described as a pressure controlled continuous high flow positive airway pressure system with a time-cycled change between a high inspiratory pressure level and a lower expiratory pressure level. Due to highly sensitive valves placed in the inspiratory and expiratory part of the system, unrestricted spontaneous breathing is possible at any moment of the mechanically supported ventilatory cycle. During invasive ventilation BiPAP offers potential advantages by allowing unrestricted spontaneous breathing thus reducing the need for sedation and facilitating weaning. APRV has primarily been investigated in conditions of moderate to severe acute lung injury and it seems that APRV is associated with less detrimental effects on the cardiopulmonary system compared to conventional ventilatory strategies. Apart from a review of the literature the article gives a classification and a technical description of the systems and focuses on the practical approach to BiPAP/APRV, e.g. the initiation and adjustment of respiratory support and the weaning from ventilatory support when applying these techniques.

Long-term nocturnal mechanical ventilation in patients with kyphoscoliosis

THE AIMS OF OUR STUDY WERE

1) to evaluate the long-term efficacy of nocturnal IPPV either via tracheostomy (tIPPV) or a nasal mask (nIPPV) as a means to improve alveolar ventilation in patients with chronic severe hypercapnia caused by kyphoscoliosis; and 2) to assess the effect of MV on hospitalizations and life-style. Twenty six patients with kyphoscoliosis in chronic respiratory failure were enrolled in the study. Patients were divided into two groups. The first group comprised 13 subjects who had been clinically stable for at least 1 month (arterial carbon dioxide tension (Pa,CO2) 81 +/- 1.5 kPa (60.8 +/- 10.9 mmHg), arterial oxygen tension (Pa,O2) 7.3 +/- 0.8 kPa (54.6 +/- 6.1 mmHg)). The second group comprised 13 patients who were either suffering or recovering from an episode of acute respiratory insufficiency (Pa,CO2 9.0 +/- 1.8 kPa (67.8 +/- 13.3 mmHg), Pa,O2 6.8 +/- 1.1 kPa (51.2 +/- 8.2 mmHg), breathing supplemental oxygen in seven cases). Patients in the first group were treated with nocturnal IPPV via a nasal mask, whilst those in the second received nocturnal IPPV via tracheostomy. Similar improvements in arterial blood gases (ABGs) were achieved with both methods. Despite the differences in the degree of severity at baseline, after 1 month, ABG values were: Pa,CO2 6.2 +/- 0.6 kPa (46.6 +/- 4.4 mmHg), Pa,O2 9.0 +/- 1.3 kPa (67.5 +/- 9.6 mmHg) (nIPPV patients); Pa,CO2 6.1 +/- 0.9 kPa (46.1 +/- 6.8 mmHg), Pa,O2 9.8 +/- 1.3 kPa (73.6 +/- 9.8 mmHg) (tIPPV patients). After 1 yr, this improvement was still evident. Days of hospitalization were significantly reduced in both groups during the first year of MV. We conclude that both tIPPV and nIPPV are effective in the long-term treatment of respiratory failure in patients with kyphoscoliosis. It would appear from our data that if nIPPV is initiated early in the evolution of chronic respiratory failure in patients with kyphoscoliosis it will delay the necessity to use an invasive technique; however, long-term follow-up studies and larger case series are needed to demonstrate this.

[Noninvasive ventilator support in patients with chronic obstructive pulmonary disease. A comparison of 2 methods]

The external high frequency oscillation around a negative baseline (EHFO-NB) is a new mode of non-invasive ventilatory support which could replace or complement nasal intermittent positive pressure ventilation (NIPPV) for treatment of patients with chronic obstructive pulmonary disease, both in the decompensation phases and as preventive measure in intercrisis periods. This was a prospective study in which tolerance and short term effects on acid-base balance and gas interchange of both NIPPV and EHFO-NB in twenty patients with severe chronic obstructive pulmonary disease were compared. With both methods similar decrease in PaCO2 and increases in pH were observed, with decrease and increase in respiratory frequency when using NIPPV and EHFO-NB, respectively; the latter in association with the high oscillation frequencies used. While an improvement of SaO2 and no changes in PaO2 and intrapulmonary shunt were observed on NIPPV, a decrease was observed in the SaO2 and an increase in the shunt on EHFO-NB. Comfort of patients, improvement of perceived sensation of dyspnea, and the absence of complications were similar with both methods. While on NIPPV, 75 per cent of patients required a short period of training and continuous supervision.

Amyotrophic lateral sclerosis: predictors for prolongation of life by noninvasive respiratory aids

The purpose of this study was to determine which pulmonary function variables best predicted the potential for prolonging survival of individuals with amyotrophic lateral sclerosis (ALS) by the use of physical medicine respiratory muscle aid alternatives to tracheostomy for ventilatory support and airway suctioning. The records of 27 such ALS ventilator users with less than 15 minutes of ventilator-free breathing time for a mean +/- standard deviation of 23.7 +/- 20.3 months (range, 1 to 65) were reviewed. All patients underwent measurements of vital capacity (VC), maximum insufflation capacity (MIC), MIC VC difference, forced expiratory volumes, and peak cough expiratory flows (PCEF) every 1 to 6 months, depending on rate of disease progression, until requiring 24-hour ventilatory support. The ability to generate assisted PCEF in excess of 3L/sec and the ability to hold an insufflation deeper than the VC were associated with the capacity to prolong survival by methods other than tracheostomy, whereas the extent of decrease in VC and autonomous breathing ability were not. Because the PCEF and MIC VC difference correlate with bulbar muscle function, it can be concluded that the ability to use 24-hour ventilatory support by noninvasive means is a function of residual bulbar muscle strength and is independent of VC or the extent of need for ventilatory support. Properly equipped and trained, some ALS patients can use noninvasive respiratory muscle aids to delay or eliminate the need for tracheostomy.

Effects of different intermittent mandatory ventilation rates on oxygen consumption in premature infants recovering from respiratory distress syndrome

Oxygen consumption at intermittent mandatory ventilation (IMV) rates of 10 and 20 breaths per minute was evaluated to determine whether a higher IMV rate in mechanically ventilated premature infants with apnea and respiratory insufficiency would reduce metabolic expenditure. Ten studies were performed in seven infants, with three infants studied twice after a trial of failed elective extubation. The mean birth weight was 952 +/- 183 kg (SD), and the mean postnatal age was 12 +/- 8 days (SD). Mean oxygen consumption per kilogram of body weight was not significantly related to pulmonary resistance, dynamic lung compliance, or resistive work of breathing. Mean oxygen consumption was not altered at the different IMV rates. The oxygen consumption difference at the two IMV rates was not significantly related to dynamic lung compliance, resistance, or work of breathing. These results demonstrate that mechanically dependent premature infants without bronchopulmonary dysplasia do not have significant alteration in oxygen consumption with changes in IMV. This finding suggests that there is no potential metabolic energy balance benefit in use of moderately higher IMV rates to achieve improved growth rates in this population of infants.

Indications for tracheostomy and decannulation of tracheostomized ventilator users

Ventilator users whose airway secretions can be effectively cleared do not require intubation or tracheostomy for ventilatory support, despite possibly having no measurable vital capacity and no significant ventilator-free breathing time (VFBT). Likewise, ventilator users receiving intermittent positive pressure ventilation (IPPV) via an indwelling tracheostomy can be safely decannulated and converted to the use of noninvasive ventilatory support methods provided that a minimum of 3 L.s-1 of peak cough expiratory flow (PCEF) can be achieved by unassisted coughing or by the use of manually- or mechanically-assisted coughing techniques. The use of up to 24 h.day-1 noninvasive ventilatory support is preferred by patients and caregivers over tracheostomy IPPV, and is less costly, and appears to be associated with fewer long-term complications.

Does continuous positive airway pressure (CPAP) during weaning from intermittent mandatory ventilation in very low birth weight infants have risks or benefits? A controlled trial

OBJECTIVE

The purpose of this study was to evaluate three ventilator weaning strategies and to evaluate whether the use of continuous positive airway pressure (CPAP) via a nasopharyngeal or endotracheal tube would increase the likelihood of extubation failure in very low birth weight (VLBW) infants.

STUDY DESIGN

We studied prospectively 87 preterm infants (mean +/- SD; birth weight: 1078 +/- 188 g; gestational age: 28.8 +/- 2.2 weeks) who were in the process of being weaned from intermittent mandatory ventilation (IMV). Infants were assigned by systematic sampling to one of the following three treatment groups: (1) direct extubation from IMV (D.EXT) (n = 30); (2) preextubation endotracheal CPAP (ET-CPAP) for 12-24 hr (n = 28); or (3) postextubation nasopharyngeal CPAP (NP-CPAP) for 12-24 hr (n = 29). Failure was defined as the need for resumption of mechanical ventilation within 72 hr of extubation due to frequent or severe apnea and/or respiratory failure (pH < 7.25, PaCO2 > 60 mm Hg, and/or requirement for oxygen FiO2 > 60%).

RESULTS

There were no significant differences in failure rates among the three procedures. Failures were 2/30 (7%) in D.EXT; 4/28 (14%) in ET-CPAP; and 7/29 (24%) in the NP-CPAP. There were also no differences in FiO2, PaO2, and respiratory rates before and after discontinuation of IMV among the three groups. PaCO2 values were slightly higher in the NP-CPAP group 12-24 hr after weaning from IMV.

CONCLUSION

We were unable to demonstrate a clear difference in extubation outcome by use of CPAP administered via an endotracheal or nasopharyngeal tube when compared to direct extubation from low-rate IMV in VLBW infants.

Treatment of respiratory insufficiency in Duchenne's muscular dystrophy: nasal ventilation in the initial stages

Fourteen patients with Duchenne's muscular dystrophy (DMD) received nasal ventilation at the beginning of the declining phase of their vital capacity (VC). At that point, the mean value (SD) of their vital capacity was 1,756 (363) mL notably inferior to the predicted values. Nasal ventilation was performed according to a precise protocol, with an average nocturnal duration of 8 h. The annual decline of vital capacity was about 70 ml, showing a significant reduction compared with the value of 200 mL.yr-1 of untreated patients. Follow-up of treated patients (3.8 yrs; SD 1.9 yrs) has enabled us to distinguish different groups of results with useful practical consequences. In 29% of cases, the initial progression of decline of vital capacity was poorly modified by the treatment. In 71% of patients, the decline of VC was significantly decreased. In 35% of cases tracheal ventilation followed nasal ventilation. The normal mortality rate of DMD has greatly changed as a result of this method.

Nocturnal assisted ventilation using bilevel positive airway pressure: the effect of expiratory positive airway pressure

Increasing expiratory positive airway pressure (EPAP) has theoretical advantages during overnight nasal ventilation. We wanted to evaluate the effect of the addition of EPAP upon the control of nocturnal hypoventilation. Seven patients with neuromuscular/skeletal (NMS) disorder (mean +/- SD forced vital capacity (FVC) 1.06 +/- 0.28 l, arterial oxygen tension (PaO2) 9.1 +/- 0.6 kPa, and arterial carbon dioxide tension (PaCO2) 6.9 +/- 0.9 kPa), and seven patients with chronic obstructive pulmonary disease (COPD) (FEV1 0.46 +/- 0.14 l, PaO2 6.2 +/- 0.6 kPa, and PaCO2 8.4 +/- 1.1 kPa) all underwent full polysomnography on two nights during bilevel positive airway pressure (BiPAP) ventilation, with and without the addition of expiratory positive airway pressure, which was matched to the level of dynamic positive end-expiratory pressure (PEEP) or set at a minimum value of 5 cmH2O. In the group with neuromuscular/skeletal disorders the maximum transcutaneous carbon dioxide tension (PtcCO2) overnight was lower (inspiratory positive airway pressure (IPAP) 8.1 +/- 1.4 kPa, IPAP/EPAP 7.3 +/- 0.9 kPa) and the minimum level of arterial oxygen saturation (SaO2 min) increased (IPAP 77.1 +/- 6.7%, IPAP/EPAP 83.6 +/- 4.2%) when expiratory positive airway pressure was added. There were no differences in mean PtcCO2 or mean oxygen saturation, but sleep quality was worse (non-rapid eye movement (non-REM) sleep IPAP 266 +/- 44 min, IPAP/EPAP 226 +/- 32 min). In the patients with COPD, expiratory positive airway pressure conferred no advantage.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved oxygenation during synchronized intermittent mandatory ventilation in neonates with respiratory distress syndrome: a randomized, crossover study

In a randomized, crossover study, we compared arterial partial pressure of oxygen and of carbon dioxide between consecutive periods of conventional and synchronized intermittent mandatory ventilation (SIMV). We studied spontaneously breathing infants with an endotracheal tube in place. The infants were < 12 hours of age, had a diagnosis of respiratory distress syndrome, and had an arterial/alveolar oxygen ratio of < 0.25. The infants had a mean birth weight of 1077 gm and gestational age of 28 weeks. The mean rate of asynchrony on intermittent mandatory ventilation (IMV) was 52% (range, 36% to 76%), and on SIMV was < 1%. Infants were randomly assigned to IMV or SIMV as their initial ventilator mode and underwent ventilation for four 15-minute periods, and crossed over to the alternate mode after each period. Ventilator settings and the fraction of inspired oxygen were not changed between modes. At the end of each period, arterial blood gas measurements were obtained; 26 paired comparisons were made between modes. The mean arterial partial pressure of oxygen was significantly higher during SIMV than during IMV (mean, 61.5 vs 53.3 mmHg; p < 0.01). The mean arterial partial pressure of carbon dioxide was slightly lower during SIMV than during IMV (mean, 42.7 vs 41.3 mm Hg; p < 0.05). The improvement in oxygenation demonstrated with SIMV may allow a reduction in ventilator pressure or oxygen exposure in this group of infants, who are at risk of having complications of ventilation.

Respiratory distress in newborn: treated with ventilation in a level II nursery

Fifty consecutive neonates with respiratory distress persisting beyond 6 h of age were studied during a 18 month period (total deliveries 2000/y). Twenty two neonates were managed with oxygen hood with increasing oxygen concentration, 28 with continuous positive airway pressure (CPAP) ventilation using a nasal cannula. Of these babies on CPAP, 10 were shifted to intermittent positive pressure ventilation (IPPV) on a pressure limited, time cycled ventilator (Neovent, Vickers). Babies were monitored with continuous hemoglobin oxygen saturation (SaO2), hourly blood pressure and vital charting. Radial arterial blood gas analysis (ABG) was done when feasible and especially on clinical deterioration. Oxygen (FiO2 0.95) from an oxygen concentrator was used as a source of continuous supply of oxygen. Commonest cause of respiratory distress was hyaline membrane disease (18%), followed by wet lung syndromes (14%), meconium aspiration (12%), asphyxia (12%) and septicemia (8%). In 8 babies, a lung biopsy (postmortem) was done to confirm the diagnosis. Nineteen of the 50 babies with respiratory distress died, there was a survival of 50% on CPAP and 30% on IPPV. No case of oxygen toxicity or other major complications was encountered. Even with moderate resources, neonatal ventilation in a Level II nursery is a challenging task. Babies less than 1000g require aggressive measures which is not very economical in a special care baby unit (SCBU).

Adult onset of nemaline myopathy presenting as respiratory insufficiency

A 49-year-old woman was admitted to the hospital for hypercapnia. Pulmonary function testing showed small lung volumes without parenchymal lung disease. Muscle enzyme levels were normal and the EMG was nonspecific. Finally, muscle biopsy revealed abundant nemaline bodies characteristic of nemaline myopathy. Nasal intermittent pressure ventilation was started with a preset pressure ventilator during sleeping hours with a good response.

Patient-ventilator interaction during synchronized intermittent mandatory ventilation. Effects of flow triggering

Synchronized intermittent mandatory ventilation (SIMV) intermixes assisted and spontaneous breaths. Its ability as a weaning technique has been questioned on the basis that patients show little adaptation to ventilator assistance. We studied inspiratory effort and patient-ventilator interaction at different levels (SIMV, 100, 50, and 0%) of flow-triggered SIMV versus pressure-triggered SIMV in patients during the weaning period. The two triggering systems were evaluated during constant flow and constant pressure mandatory SIMV breaths. Inspiratory effort was estimated as the esophageal pressure time product (PTP) per breath (PTP/b) and per minute (PTP/min). The PTP/b and PTP/min of both mandatory and spontaneous breaths were significantly lower during flow triggering than during pressure triggering SIMV, irrespective of the ventilatory mode. During pressure-triggered SIMV PTP/b and PTP/min were identical for mandatory and spontaneous breaths, whereas during flow-triggered SIMV PTP/b and PTP/min were significantly lower for mandatory than for spontaneous breaths. This difference was greatest when flow triggering and constant pressure ventilation were associated. These data show that flow triggering reduces inspiratory effort during both mandatory and spontaneous SIMV breaths and obtains a better patient-ventilator interaction.

A comparison of the effects of assist-control, SIMV, and SIMV with pressure support on ventilation, oxygen consumption, and ventilatory equivalent

OBJECTIVE

To quantify the ventilatory efficiency of different modes of mechanical ventilation used to achieve full ventilatory support in normal subjects. Modes compared were assist-control, synchronized intermittent mandatory ventilation (SIMV), and SIMV with 10 cm H2O (0.98 kPA) of pressure support.

DESIGN

Prospective, randomized blocks repeated measures design. Subjects served as their own controls.

SETTING

A university affiliated pulmonary laboratory.

SUBJECTS

Ten healthy volunteers, aged 31-54 years.

OUTCOME MEASURES

Minute volume, respiratory rate, average tidal volume, oxygen consumption, and ventilatory equivalent.

INTERVENTION

Baseline spontaneous ventilation data collection was followed by mechanical ventilation by mouthpiece in each of three modes in a random sequence. All modes used a machine set rate of 12 breaths per minute, VT of 10 cc/kg of ideal body weight, inspiratory time of 1 second, square wave flow pattern and a sensitivity of -1 cm H2O (-0.09806 kPa) to achieve full ventilatory support. Data were collected continuously for 5 minutes and the mean values were reported. Ventilatory equivalent for oxygen is a measure of the efficiency of the ventilatory pump at various work loads and was calculated by dividing VE (BTPS) by the VO2 (STPD).

RESULTS

There were significant differences by mode of mechanical ventilation in average tidal volume (p = 0.02), minute volume (p = 0.02), oxygen consumption (p = 0.04), and ventilatory equivalent (p = 0.01) using ANOVA. There was no significant difference (p = 0.66) by mode of ventilation in respiratory rate. Pairwise follow-up comparisons for these variables found that SIMV with pressure support produced a significantly greater average tidal volume, minute volume, oxygen consumption, and ventilatory equivalent than SIMV alone. SIMV with pressure support also produced a significantly greater minute volume and ventilatory equivalent than assist-control. There were no significant differences between assist-control and SIMV. All three modes produced a lower ventilatory equivalent and higher oxygen consumption than spontaneous breathing.

CONCLUSIONS

SIMV with pressure support significantly increased minute volume and ventilatory equivalent when compared with assist-control or SIMV alone, and thus was the most efficient mode of full ventilatory support for our subjects. We found no difference in ventilatory efficiency between assist-control and SIMV. All three mechanical modes were less efficient for our subjects than spontaneous breathing. The inspiratory time of 1 second used in this study, although common in clinical practice, may be inadequate for some patients.

Haemodynamic consequences of immediate intra-anaesthesia application of intermittent positive pressure breathing in horses

Prolonged operation or a current need to improve intraoperative conditions, while anaesthesia is still on, may require applying controlled ventilation (CV). The purpose of this study was to evaluate cardiovascular effects of such a decision. Seven halothane-anaesthetized horses were the subject of our investigation, at first kept spontaneous ventilation (SV), then they were connected to respirator. After 30' CV, SV was restored and anaesthesia was continued. In those three stages of experiment haemodynamic parameters and gasometry were measured. It was found that during CV period both optimal gas exchange as well as the lowering of cardiac output actually took place. The authors suggest that equalization of circulation blood volume, which leads to the ventricular proload increase, will enable the veterinarians to apply CV not only because of life-rescular indications, but also to assure safe anaesthesia course.

[Artificial respiration in patients with acute severe asthma. Mode of ventilation and survival]

The purpose of the study was to register the treatment, mode of ventilation and mortality of patients with acute severe asthma treated with intermittent positive pressure ventilation (IPPV) in a Danish intensive care unit (ICU) during a ten-year period. Fifty-seven patients underwent ventilation on 78 occasions. Fifty-three patients were ventilated with controlled hypoventilation and low PEEP, while four patients were treated with high PEEP. One of the 53 patients receiving controlled hypoventilation and two of the four patients who received high PEEP developed a pneumothorax. All the patients were treated with intravenous steroid and infusion of a beta 2-agonist. Eighty-eight point three per cent received an infusion of theophylline whereas only 16.9% were treated with inhalation of a beta 2-agonist. Eight patients already had irreversible brain damage due to cardiac arrest before arrival to the ICU. Seven of these patients died due to brain damage. All the patients who reached the ICU without brain damage survived. After discharge from the hospital increased mortality was observed among these patients. Some of the patients died due to underestimation from doctors as well as patients of the severity of the asthma. Patients with acute severe asthma requiring IPPV should be ventilated with controlled hypoventilation. A high PEEP is associated with an increased risk of barotrauma. Continuing education of doctors and patients is necessary to increase the use of objective airflow measurement.

Nasal ventilation in acute exacerbations of chronic obstructive pulmonary disease: effect of ventilator mode on arterial blood gas tensions

BACKGROUND

There are no controlled trials of the use of different modes of nasal intermittent positive pressure ventilation (NIPPV) in patients with exacerbations of chronic obstructive pulmonary disease (COPD). This study describes the effect on blood gas tensions of four different modes of nasal ventilation.

METHODS

Twelve patients with acute exacerbations of COPD were studied (mean (SD) FEV1 0.59 (0.13) l, PaO2 (air) 5.10 (1.12) kPa, PaCO2 9.28 (1.97) kPa, pH 7.32 (0.03)). Each patient underwent four one-hour periods of nasal ventilation in randomised order: (a) inspiratory pressure support 18 cm H2O; (b) pressure support 18 cm H2O+positive end expiratory pressure (PEEP) 6 cm H2O (IPAP+EPAP); (c) continuous positive airway pressure (CPAP) 8 cm H2O; and (d) volume cycled NIPPV. Arterial blood samples were obtained before each period of ventilation and at one hour.

RESULTS

Pressure support, CPAP, and volume cycled NIPPV all produced significant improvements in PaO2; there was no difference between these three modes. The change in PaO2 with IPAP+EPAP did not reach statistical significance. None of the modes produced significant changes in mean PaCO2; patients with higher baseline levels tended to show a rise in PaCO2 whereas those with lower baseline levels tended to show a fall.

CONCLUSIONS

Although PaO2 improved in all patients there are differences in efficacy between the modes, while the changes in PaCO2 were variable. The addition of EPAP conferred no advantage in terms of blood gas tensions.

Different modes of noninvasive intermittent positive pressure ventilation (IPPV) in acute exacerbations of COLD patients

Patients with chronic obstructive lung disease may suffer from acute exacerbations of their disease, which may lead to acute respiratory failure necessitating endotracheal intubation and mechanical ventilation. We have compared retrospectively the results obtained with nasal positive pressure ventilation and those of standard medical therapy in acute relapses of severe COLD. The study showed that nasal IPPV (NIPPV) in control mode delivered for approximately 1 h, four times daily, six days a week over a 21 day period, does not result in independent improvement of acute exacerbation of COLD. In the next study the data seem to indicate, in apparent contrast, a marked reduction in the need for endotracheal intubation using noninvasive ventilation, both with assist-control and pressure support noninvasive modes, in comparison with an historical control group. We did not find a significant difference in the success rate of the two modes, but compliance to noninvasive ventilation was better with pressure support. In the former study patients showing neurological signs and requiring mechanical ventilation were excluded, while in the last study patients were selected on the basis of necessity of mechanical ventilation. The fact that in the last study, ventilation was applied by face mask instead of nasal mask may have influenced results. Further efforts are required to determine whether non-invasive ventilation is more a preventive measure to avoid endotracheal intubation, or is another means of delivering ventilatory support.

Comparative evaluation of diaphragmatic activity during pressure support ventilation and intermittent mandatory ventilation in animal model

The aim of the present study is a comparative evaluation of the effects of pressure support ventilation (PSV) and intermittent mandatory ventilation (IMV) on diaphragmatic activity in rabbit model of neonate. The animals were divided into a PSV group and an IMV group. In the IMV group, spontaneous breathing and four kinds of IMV rate (5, 10, 15, and 20/min) were applied (Ventilator: Bear BP200, peak inspiratory pressure [PIP]: 12 cm H2O, inspiratory time: 0.6 s). In the PSV group, spontaneous breathing and four levels of PSV (3, 6, 9, and 12 cm H2O) were applied (Ventilator: VIP Bird, flow triggering). Airway pressure (Paw), flow (V), esophageal pressure (Pes), integrated diaphragmatic electromyogram (Edi), and arterial gas data were measured. Amplitudes of Pes and Edi were expressed as percentages (% Edi and % Pes) of the control value during spontaneous breathing to evaluate diaphragmatic activity. Lower IMV rates did not reduce diaphragmatic activity. Approximately half of diaphragmatic activity of control remained even at IMV 15/min. Diaphragmatic activity disappeared at IMV20/min. In contrast, PSV reduced Edi and Pes linearly according to support level. In conclusion, diaphragmatic activity could be reduced more gradually with PSV than IMV by altering ventilatory support level.

Influence of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work

OBJECTIVE

To determine the effect of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work.

DESIGN

Consecutive clinical, prospective, randomized trial.

SETTING

Medical intensive care unit (ICU) of a U.S. Veterans Affairs Medical Center.

PATIENTS

Eight patients recovering from acute respiratory failure of various etiologies.

INTERVENTIONS

Assist control, followed by randomized application of pressure- and flow-triggered synchronous intermittent mandatory ventilation at 60%, 40%, 20% of the assist-control rate, and flow-triggered continuous positive airway pressure. A total of eight settings were maintained for 10 mins each.

MEASUREMENTS AND MAIN RESULTS

Total work rate (joules/min), inspiratory muscle work (joules/L), and pressure time-product per breath (cm H2O-sec) were measured. During pressure- or flow-triggered synchronous intermittent mandatory ventilation, total work rate increased as the mandatory rate was decreased. The method of ventilator triggering had a significant effect on the total work rate. With pressure-triggered synchronous intermittent mandatory ventilation, the total work rate at 60% of the assist-control rate was similar to that with assist-control; whereas with flow-triggered synchronous intermittent mandatory ventilation, this result was achieved at 40% of the assist-control rate. At a machine support level of 20%, total work rate with pressure-triggered synchronous intermittent mandatory ventilation was significantly greater than with flow-triggered synchronous intermittent mandatory ventilation. The method of ventilator triggering had no significant effect on the inspiratory muscle work of the mandatory breaths. This finding was in contrast to the effect on inspiratory muscle work of spontaneous breaths. With pressure-triggered synchronous intermittent mandatory ventilation, inspiratory muscle work of the spontaneous breaths was greater than with the flow-triggered at machine support of 40% and 20%. With either pressure- or flow-triggered synchronous intermittent mandatory ventilation, inspiratory muscle work of the mandatory breaths was not significantly different from that of the corresponding spontaneous breaths, except at the lower machine support levels with the pressure-triggered synchronous intermittent mandatory ventilation. Pressure-time product followed a trend similar to that of inspiratory muscle work.

CONCLUSIONS

During synchronous intermittent mandatory ventilation, the method of ventilator triggering has a significant effect on the total work rate and inspiratory muscle work of the spontaneous breaths, particularly at lower machine support levels. Conversely, the method of ventilator triggering has no significant effect on inspiratory muscle work of the mandatory breaths.

Normalization of blood carbon dioxide levels by transition from conventional ventilatory support to noninvasive inspiratory aids

Chronic hypocapnia seems to be common in long-term ventilator assisted individuals (VAIs) with paralytic/restrictive respiratory conditions. It has predominantly been reported for VAIs using intermittent positive pressure ventilation (IPPV) delivered via tracheostomy tubes. Chronic hypocapnia decreases ventilator-free breathing time (VFBT) and may be associated with increased bone resorption. Attempts to reverse chronic hypocapnia by decreasing minute ventilation and providing supplemental carbon dioxide have failed because of air hunger and patient resistance. We maintained normocapnia in 22 24-hour-a-day VAIs by using noninvasive IPPV. Chronic hypocapnia was corrected in three VAIs and hypercapnia in two VAIs by switching from conventional ventilatory support to the use of noninvasive inspiratory muscle aids. The other 17 VAIs remained normocapneic by being managed by noninvasive ventilatory support from onset of ventilatory failure. Eleven of these VAIs had been intubated or tracheostomized for brief periods but were successfully returned to noninvasive support. We conclude that alveolar ventilation can be maintained within normal range for VAIs who use noninvasive IPPV and can be normalized by transition from conventional tracheostomy IPPV to noninvasive IPPV.