Lung recruitment and lung volume maintenance: a strategy for improving oxygenation and preventing lung injury during both conventional mechanical ventilation and high-frequency oscillation

OBJECTIVE

To determine whether using a small tidal volume (5 ml/kg) ventilation following sustained inflation with positive endexpiratory pressure (PEEP) set above the critical closing pressure (CCP) allows oxygenation equally well and induces as little lung damage as high-frequency oscillation following sustained inflation with a continuous distending pressure (CDP) slightly above the CCP of the lung.

MATERIAL AND METHODS

Twelve surfactant-depleted adult New Zealand rabbits were ventilated for 4 h after being randomly assigned to one of two groups: group 1, conventional mechanical ventilation, tidal volume 5 ml/kg, sustained inflation followed by PEEP > CCP; group 2, high-frequency oscillation, sustained inflation followed by CDP > CCP.

RESULTS

In both groups oxygenation improved substantially after sustained inflation (P < 0.05) and remained stable over 4 h of ventilation without any differences between the groups. Histologically, both groups showed only little airway injury to bronchioles, alveolar ducts, and alveolar airspace, with no difference between the two groups. Myeloperoxidase content in homogenized lung tissue, as a marker of leukocyte infiltration, was equivalent in the two groups.

CONCLUSIONS

We conclude that a volume recruitment strategy during small tidal volume ventilation and maintaining lung volumes above lung closing is as protective as that of high-frequency oscillation at similar lung volumes in this model of lung injury

[Airway pressure release in postoperative cardiac surgery in pediatric patients]

OBJECTIVE

Comparison of three modes of MV: intermittent mandatory ventilation with positive end expiratory pressure (IMV + PEEP), APRV and continuous positive airway pressure (CPAP) in children during cardiac surgery post operative with pulmonary hypertension and mild or moderate pulmonary lesion.

METHODS

Ten patients were studied with respiratory monitoring (Bear Neonatal Volume Monitor-1) in MV with a continuous flow, time cycled and pressure limited ventilator. The cardiocirculatory variables analyzed were central venous pressure (CVP), oxygen extraction ratio, cardiac rate, systolic arterial pressure, and arterial-mixed venous CO2 difference. Friedman's test (nonparametric) was used to compare the variables in three modalities of ventilation and the Wilcoxon test was used for the variables obtained in two of the modalities.

RESULTS

The mean airway pressure (MAP) showed a significant increasing during APRV compared to IMV + PEEP (p = 0.012). The positive inspiratory pressure (PIP), the minute volume and the ratio of oxygen arterial pressure to oxygen inspired fraction (PaO2/FiO2) didn't show statistical difference. During APRV there was a significant decrease in respiratory rate (p = 0.004) and an increase in tidal volume (p = 0.045) when compared to CPAP and IMV + PEEP. In the cardiocirculatory system only CVP showed a significant increased (p = 0.019) during APRV.

CONCLUSION

Due to the methodology utilized MAP was higher with APRV resulting in an increased tidal volume without respiratory or cardiocirculatory adverse effects when the three modes were compared. Our results suggest that APRV is a simple and safe method of ventilation.

Non invasive ventilation in COPD

Non invasive ventilation refers to the technique of providing ventilatory support without a direct conduit to the airway. It is a promising new technique, which is particularly useful in patients with COPD. Patients with COPD are prone to develop acute exacerbations, which pushes them into acute respiratory failure. Under these circumstances, tracheal intubation and mechanical ventilation is associated with significant morbidity and mortality. A number of well conducted studies support the fact that non invasive positive pressure ventilation (NIPPV) in these circumstances reduces rates of intubation, mortality, complications and duration of hospital stay. The biggest advantage of these techniques is their simplicity, ease of implementation and improved patient comfort allowing them to retain important functions like speech, cough and swallowing. NIPPV should be instituted early in the course of acute respiratory failure due to COPD before irreversible fatigue sets in. The current thinking is that NIPPV rests the respiratory muscles allowing other therapies time to be effective. Facilities for NIPPV should be available in all hospitals admitting patients with respiratory failure. Patients with severe, stable COPD who are hypercapnic and are deteriorating despite maximal conventional treatment should definitely be offered a trial of NIPPV. In such patients NIPPV has been shown to improve quality of life, reverse blood gas abnormalities, improve exercise tolerance and reduce hospital admissions. Physicians must familiarize themselves with this promising new ventilatory technique.

[The applied value of BiPAP mechanical ventilation via facial of nasal mask before or after ordinary mechanical ventilation]

To expore the applied value of BiPAP ventilator before or after regular ventilation, 44 patients who had indicators of regular mechanical ventilation and 4 patients who had difficulty of getting free from endotracheal intubation mechanical ventilation were ventilated with BiPAP ventilator via facial or nasal mask. The results showed that 13/44 patients had good responses and avoided receiving regular mechanical ventilation with endotracheal intubation or incision. BiPAP ventilation was also effective in patients who were dependent on regular mechanical ventilatin.

[Impact of acute respiratory failure on survival of COPD patients managed with long-term non-invasive ventilation and oxygen therapy]

Our study aimed to assess the impact of acute respiratory failure (ARF) on survival of patients with chronic obstructive pulmonary disease (COPD) receiving long-term oxygen therapy (LTOT) plus nasal intermittent positive pressure ventilation (NIPPV). Survival was analysed retrospectively in 24 patients with severe COPD initiated to NIPPV in addition to LTOT. Fourteen patients were established on NIPPV following exacerbation of acute respiratory failure which has required mechanical ventilation (group 1). Ten patients (group 2) have never been hospitalized for ARF. Comparison of clinical details at baseline, 6 months, 1, 2, and 3 years for the two groups failed to reveal any difference with the exception of prior episodes of ARF. The probability of survival at 3 years was 65% (95% confidence interval [CI] 43-86) for the overall population, 46% (95% CI 15-77) in group 1, and 74% (95% CI 42-105) in group 2. The difference between the two groups was statistically significant. We show that ARF requiring mechanical ventilation appears to be a factor that is negatively correlated with survival for patients treated by LTOT plus NIPPV. This data suggests that NIPPV should be tried before ARF arising in COPD patients who present a deterioration in chronic respiratory failure with hypercapnia.

Helium-oxygen mixture does not improve gas exchange in mechanically ventilated children with bronchiolitis

STATEMENT OF FINDINGS: Varying concentrations of helium-oxygen (heliox) mixtures were evaluated in mechanically ventilated children with bronchiolitis. We hypothesized that, with an increase in the helium:oxygen ratio, and therefore a decrease in gas density, ventilation and oxygenation would improve in children with bronchiolitis. Ten patients, aged 1-9 months, were mechanically ventilated in synchronized intermittent mandatory ventilation (SIMV) mode with the following gas mixtures delivered at 15-min intervals: 50%/50% nitrogen/oxygen, 50%/50% heliox, 60%/40% heliox, 70%/30% heliox, and return to 50%/50% nitrogen/oxygen. The use of different heliox mixtures compared with 50%/50% nitrogen/oxygen in mechanically ventilated children with bronchiolitis did not result in a significant or noticeable decrease in ventilation or oxygenation.

Effect of mouth leak on effectiveness of nasal bilevel ventilatory assistance and sleep architecture

Mouth leak is common during nasal ventilatory assistance, but its effects on ventilatory support and on sleep architecture are unknown. The acute effect of sealing the mouth on sleep architecture and transcutaneous carbon dioxide tension (Ptc,CO2) was tested in 9 patients (7 hypercapnic) on longterm nasal bilevel ventilation with symptomatic mouth leak. Patients slept with nasal bilevel ventilation at their usual settings on two nights in random order. On one night, the mouth was taped closed. Leak was measured with a pneumotachograph. Median leak fell from 0.35+/-0.07 (mean +/- SEM) L x s(-1) untaped to 0.06+/-0.03 L x s(-1) taped. Ptc,CO2 fell in 8/9, including all hypercapnic patients. Across all patients, the mean Ptc,CO2 fell by 1.02+/-0.28 kPa (7.7+/-2.1 mm Hg) with taping (p = 0.007). Arousal index fell in every patient. Mean arousal index fell from 35.0+/-3.0 to 13.9+/-1.2 h(-1) (p<0.0001), and rapid eye movement (REM) sleep increased from 12.9+/-1.5% to 21.1+/-1.8% sleep time (p = 0.0016). Slow wave sleep changed inconsistently, from a mean of 13.1+/-1.6% to 19.5+/-2.2% of sleep (p = 0.09). Sleep latency and efficiency were unchanged. In four healthy volunteers ventilator-induced awake hypopharyngeal pressure swing during timed bilevel ventilation fell by 35+/-5% L(-1) x s(-1) of voluntary mouth leak (p<0.0001). Mouth leak reduces effective nasal bilevel ventilatory support, increases transcutaneous carbon dioxide tension, and disrupts sleep architecture.

Is there a preferred technique for weaning the difficult-to-wean patient? A systematic review of the literature

OBJECTIVE

To answer the following question: In difficult-to-wean patients, which of the three commonly used techniques of weaning (T-piece, synchronized intermittent mandatory ventilation, or pressure support ventilation) leads to the highest proportion of successfully weaned patients and the shortest weaning time?

DATA SOURCES

Computerized literature searches in MEDLINE (1975-1996), Cinahl (1982-1996), and Healthplan (1985-1996), exploding all Mesh headings pertaining to Mechanical Ventilation and Weaning. Searches were restricted to the English language, adults, and humans. Personal files were hand searched, and references of selected articles were reviewed.

STUDY SELECTION

a)

POPULATION

Patients requiring a gradual weaning process from the ventilator (either requiring prolonged initial ventilation of >72 hrs or a failed trial of spontaneous breathing after >24 hrs of ventilation); b)

INTERVENTIONS

At least two of the following three modes of weaning from mechanical ventilation must have been compared: T-piece, synchronized intermittent mandatory ventilation, or pressure support ventilation; c)

OUTCOMES

At least one of the following: weaning time (time from initiation of weaning to extubation) or successful weaning rate (successfully off the ventilator for >48 hrs); and d)

STUDY DESIGN

Controlled trial.

DATA EXTRACTION

Two reviewers independently reviewed the articles and graded them according to their methodologic rigor. Data on the success of weaning and the time to wean were summarized for each study.

DATA SYNTHESIS

The search strategy identified 667 potentially relevant studies; of these, 228 had weaning as their primary focus, and of these, 48 addressed modes of ventilation during weaning. Only 16 of these 48 studies had one of the specified outcomes, and only ten of these were controlled trials. Of the ten trials, only four fulfilled all our selection criteria. The results of the trials were conflicting, and there was heterogeneity among studies that precluded meaningful pooling of the results.

CONCLUSIONS

There are few trials designed to determine the most effective mode of ventilation for weaning, and more work is required in this area. From the trials reviewed, we could not identify a superior weaning technique among the three most popular modes, T-piece, pressure support ventilation, or synchronized intermittent mandatory ventilation. However, it appears that synchronized intermittent mandatory ventilation may lead to a longer duration of the weaning process than either T-piece or pressure support ventilation. Finally, the manner in which the mode of weaning is applied may have a greater effect on the likelihood of weaning than the mode itself.

Lung recruitment during small tidal volume ventilation allows minimal positive end-expiratory pressure without augmenting lung injury

OBJECTIVES

Ventilation with positive end-expiratory pressure (PEEP) above the inflection point (P(inf)) has been shown to reduce lung injury by recruiting previously closed alveolar regions; however, it carries the risk of hyperinflating the lungs. The present study examined the hypothesis that a new strategy of recruiting the lung with a sustained inflation (SI), followed by ventilation with small tidal volumes, would allow the maintenance of low PEEP levels (<P(inf)) without inducing additional lung injury.

DESIGN

Prospective, randomized, controlled ex vivo study.

SETTING

An animal laboratory in a university setting.

SUBJECTS

Isolated nonperfused lungs of adult Sprague-Dawley rats.

INTERVENTIONS

We studied the effect on compliance and lung injury in four groups (n = 10 per group) of lavaged rat lungs. One group (group 1) served as a control; their lungs were inflated at PEEP < P(inf) but not ventilated. The other three groups were ventilated with small tidal volumes (5 to 6 mL/kg) for 2 hrs with the following interventions: group 2, PEEP < P(inf) without SI; group 3, PEEP < P(inf) after a SI to 30 cm H2O for 30 secs; and group 4, PEEP > P(inf).

MEASUREMENTS AND MAIN RESULTS

In groups 2 and 4, static compliance decreased after ventilation (p < .01). Histologically, group 2 (PEEP < P(inf) without SI) showed significantly greater injury of small airways, but not of terminal respiratory units, compared with group 1. Group 3 (PEEP < P(inf) after a SI), but not group 4, showed significantly less injury of small airways and terminal respiratory units compared with group 2.

CONCLUSIONS

We conclude that small tidal volume ventilation after a recruitment maneuver allows ventilation on the deflation limb of the pressure/volume curve of the lungs at a PEEP < P(inf). This strategy a) minimizes lung injury as well as, or better than, use of PEEP > P(inf), and b) ensures a lower PEEP, which may minimize the detrimental consequences of high lung volume ventilation.

The open lung during small tidal volume ventilation: concepts of recruitment and "optimal" positive end-expiratory pressure

OBJECTIVES

To test the hypotheses that during small tidal volume ventilation (5 mL/kg) deliberate volume recruitment maneuvers allow expansion of atelectatic lung units and that a high positive end-expiratory pressure (PEEP) above the lower inflection point of the pressure/volume (PV) curve is not necessarily required to maintain recruited lung volume in acute lung injury.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

An animal laboratory in a university setting.

SUBJECTS

Adult New-Zealand rabbits.

INTERVENTIONS

We studied a) the relationship of dynamic loops during intermittent positive pressure ventilation to the quasi-static PV curve, and b) the effect of lung recruitment on oxygenation, end-expiratory lung volume (EELV), and dynamic compliance in two groups (n = 4 per group) of lung-injured animals (lung lavage model): 1) the sustained inflation group, which received ventilation after a recruitment maneuver (sustained inflation); and 2) the control group, which received ventilation without any lung recruitment.

MEASUREMENTS AND MAIN RESULTS

In the presence of PV hysteresis, a single sustained inflation to 30 cm H2O boosted the ventilatory cycle onto the deflation limb of the PV curve. This resulted in a significant increase in EELV, oxygenation, and dynamic compliance despite equal PEEP levels used before and after the recruitment maneuver. Furthermore, after a single sustained inflation, oxygenation remained high over 4 hrs of ventilation when a PEEP above the critical closing pressure of the lungs, defined as "optimal" PEEP, was used and was significantly higher compared with that in the control group ventilated at equal PEEP without preceding lung recruitment.

CONCLUSIONS

The observation that ventilation occurs on the deflation limb of the tidal cycle-specific PV curve allows placement of the ventilatory cycle, by means of a recruitment maneuver, onto the deflation limb of the PV envelope of the optimally recruited lung. This strategy ensures sufficient lung volume recruitment to maintain the lungs during the tidal cycle while using relatively low airway pressures.

Proportional assist ventilation in low birth weight infants with acute respiratory disease: A comparison to assist/control and conventional mechanical ventilation

OBJECTIVES

To compare the physiologic efficacy and safety aspects of proportional assist (PA), assist/control (A/C), and intermittent mandatory ventilation (IMV) in very low birth weight infants with acute respiratory illness and to test the hypothesis that ventilatory pressure requirements are lower and arterial oxygenation is improved during PA when compared with IMV or A/C at an equivalent inspired oxygen fraction.

STUDY DESIGN

Randomized, 3-period, crossover design.

METHODS

Thirty-six infants were stratified by birth weight (600 to 750, 751 to 900, and 901 to 1200 g) and exposed to consecutive 45-minute epochs of the 3 modalities in a sequence chosen at random. Tidal volumes of 4 to 6 mL/kg were targeted during A/C and IMV. The IMV rate was matched to the rate during an A/C test period. PA was adjusted to unload the resistance of the endotracheal tube and the disease-related increase in lung elastic recoil.

RESULTS

Compared with A/C and IMV, PA maintained similar arterial oxygenation with lower airway and transpulmonary pressures (15% to 44% reduction depending on the index variable). The oxygenation index decreased by 28% during PA. No adverse events were observed. The number and severity of apneic episodes and periods of arterial oxygen desaturations were similar with the 3 modes. Similar results were obtained within each birth weight subgroup.

CONCLUSIONS

PA safely maintains gas exchange with smaller transpulmonary pressure changes compared with A/C and IMV. It may therefore offer a way of reducing the incidence of chronic lung disease in low birth weight infants.

Effect of early application of biphasic positive airway pressure on the outcome of extubation in ventilator weaning

Extubation failure is significantly associated with increased morbidity and mortality in mechanically ventilated patients. In respiratory distress after extubation, non-invasive positive pressure ventilation (NIPPV) has been suggested to avoid the complications of invasive mechanical ventilation. The purpose of this study was to evaluate the effect of early application of NIPPV on extubation outcome. We conducted a prospective study in 93 extubated patients with a mean age of 72.7 +/- 14.7 years (range, 24-93). Elective extubation was performed in 56 patients and unplanned extubation occurred in 37 patients. After extubation, patients randomly received either biphasic positive airway pressure (BIPAP) therapy (n = 47) or unassisted oxygen therapy (n = 46). Non-invasive positive pressure ventilation was delivered via face mask in BIPAP group. Of the 93 extubated patients, 73 (78.5%) were successfully extubated, and 20 (21.5%) had to be re-intubated. There were no significant differences in age, sex, pre-extubation blood gas data between re-intubated patients and those who were not re-intubated. While seven of the 46 patients in the unassisted oxygen therapy group required re-intubation, 13 of the 47 BIPAP-treated patients also required re-intubation. This difference was not statistically significant. The postextubation respiratory management, BIPAP or unassisted oxygen therapy, did not correlate with the extubation outcome, but the elective extubation had significantly better outcome than unplanned extubation. Patients with excessive bronchial secretions and intolerance to the equipment are poor candidates for NIPPV. We conclude that early application of BIPAP support did not predict a favourable extubation outcome. Our experience did not support the indiscriminate use of NIPPV to facilitate ventilator weaning.

[Pharmacological stress echocardiography--a new non-invasive follow-up examination of intermittent ventilation]

BACKGROUND

Patients with chronic respiratory insufficiency frequently develop pulmonary hypertension. Non-invasive intermittent ventilation is usually very successful in these patients to improve blood gas exchange and clinical symptoms. Alterations of pulmonary hemodynamics during non-invasive intermittent ventilation are rarely described. Pharmacological stress echocardiography of the right heart is a new method to examine pulmonary hemodynamics. Aim of this study was to answer the question whether non-invasive intermittent ventilation improves pulmonary hemodynamics.

PATIENTS AND METHOD

Five patients are examined prior to and during non-invasive intermittent ventilation by right ventricular stress echocardiography at rest and during exercise. Pulmonary arterial pressure was registered and compared. The effectiveness of intermittent ventilation was evaluated with respect to blood gas analytic values.

RESULTS

During non-invasive intermittent ventilation all 5 patients improved their pulmonary arterial mean (PAP mean) and systolic pressure, but no statistical significant changes could be observed during the 4.5-months follow-up.

CONCLUSION

Non-invasive intermittent ventilation improves the pulmonary hemodynamics at rest and during exercise the results not being significant.

Changes in airway resistance induced by nasal or oral intermittent positive pressure ventilation in normal individuals

Nasal intermittent positive-pressure ventilation (nIPPV) is used for the treatment of respiratory failure in patients with neuromuscular disease. The aim of the present study was to demonstrate that nIPPV may activate nose receptors, the consequence of which being reflex changes in lung resistance. The changes in interrupter resistances (Rint) in response to nIPPV were tested before and after local anaesthesia of the nasal mucosa in normal subjects. They were compared to the Rint changes induced by oral intermittent positive-pressure ventilation (oIPPV) in the same individuals. Rint was measured during 10-min periods of nIPPV or oIPPV at a constant rate (15 L x min(-1)), but at two different stroke volumes (0.8 and 1.2 L). Inspired temperature and relative humidity were held constant. nIPPV with 1.2 L (17 mL x kg(-1)) significantly increased the Rint value (+22%). This effect disappeared after nose anaesthesia or after inhalation of a cholinergic antagonist. oIPPV never changed Rint, even though the associated hypocapnia was present and more accentuated than during nIPPV. Adding CO2 to the inspired gas during nIPPV and oIPPV trials suppressed the Rint changes. The present study suggests the existence of a nasopulmonary bronchoconstrictor reflex elicited through the stimulation of nasal mechanoreceptors, their activity being markedly influenced by the changes in expired CO2 concentration.

[Long-term breathing via tracheostoma]

PATIENTS AND METHODS

From 1988 to 2/1997 we had introduced intermittent positive pressure ventilation (IPPV) in 298 patients. In most cases non-invasive nasal mask ventilation was possible, in 21 patients (7%) a tracheostoma was necessary. These 21 patients were analysed retrospectively due to age, sex, diagnose, ventilation mode, course of illness, home care and costs.

RESULTS

We had 13 male and 8 female patients, aged 49 years on average (min. 2, max. 84). 90% had neuromuscular diseases especially muscle dystrophies. Ventilation therapy was performed volume controlled with the cannula unblocked during daytime and blocked at night. Eighteen patients had industrial cannulas (72% Shiley, 28% Rüsch), 3 patients used silver cannulas. Daily ventilation amounted 24 hours in 7 patients, 6 to 14 hours in 14 patients. During the observed time 7 patients remained in stable health situation, in 9 patients the underlying disease was progressive and 5 of them died. IPPV was performed 50.7 months on an average, in living patients 68.8 months, in died 7.6 months. Fifteen patients lived at home, 5 were cared in nursing home, 1 patient stayed in hospital. Outside the hospital the bigger part of costs was paid by sick funds and care funds, the smaller part by social welfare offices. Often costs were divided. Total costs for caring about 24 hours ventilated patient at home amounted up to 21,000 German marks each month.

[The use of noninvasive positive pressure ventilation in the early postoperative period after cardiovascular surgery]

We used noninvasive positive pressure ventilation (NPPV) in 7 ICU patients after cardiovascular surgery. In 6 patients, we measured the variables of hemodynamics and arterial oxygenation by application of this nasal respiratory support (Companion 320 I/E, Puritan Bennett). Ventilator settings of expiratory positive airway pressure (EPAP) 3 cmH2O and inspiratory positive airway pressure (IPAP) 10 cmH2O were used and continued for 30 minutes. There were no significant changes in any hemodynamic variables during NPPV. Arterial oxygenation also remained unchanged at 30 min after discontinuation of NPPV. To conclude the efficacy of NPPV after cardiovascular surgery, higher level of IPAP and the combination with postural drainage should be studied further.

[Intermittent positive pressure ventilation after sternectomy]

BACKGROUND

The indication for intermittent positive pressure ventilation (IPPV) is the symptomatic hypercapnic ventilatory insufficiency. Beside the improvement of life quality and extension of life time the aim of IPPV is a reduction of the secondary effects of chronic hypoventilation in order to stabilize the symptoms.

PATIENTS AND METHODS

We examined 2 patients after sternectomy because of osteomyelitis who developed a symptomatic ventilatory insufficiency together with recurrent dys- and atelectasis and pneumonia, resistant against to antibiotic treatment. After initiation of IPPV the patients turned to a clinically stable condition. The nocturnal oxygen saturation improved as well as the daytime blood gas analysis. In these patients the indication for IPPV was not only the symptomatic hypercapnic ventilatory insufficiency but also the prophylaxis of recurrent dys- and atelectasis and pneumonia. Antibiotic therapy after sternectomy is often not successful, therefore in case of recurrent infections in patients with unstable thorax the early initiation of IPPV seems to be useful.

[Non-invasive positive pressure ventilation in cardiogenic pulmonary edema]

PATIENTS AND METHOD

30 patients being admitted to our intensive care unit with severe cardiogenic pulmonary edema received non-invasive positive pressure ventilation (NIPPV) via face mask.

RESULT

29 responded well, 1 patient had to be intubated. Within 30 minutes those who responded well showed a significant improvement of the following parameters: rise of peripheral saturation from 75.5 to 90.1% and of pH from 7.24 to 7.29, decrease of pCO2 from 60.7 to 48.8 mm Hg and of systolic blood pressure from 144 to 124 mm Hg. Mean duration of ventilation was 6 h 55 min. Mean stay in intensive care unit was 2 days. No patient required ventilator support within 24 hours after NIPPV. Four patients died during hospital stay as a result of their underlying disease but not due to pulmonary edema. Observed side effects were vomiting in 4 cases during NIPPV without aspiration and 3 cases of skin lesions which healed uneventfully.

CONCLUSION

Key role for this highly effective method seems to be the rapid improvement of left ventricular function during NIPPV.

[The role of non-invasive positive pressure ventilation in lung volume reduction surgery of pulmonary emphysema--a survey of German hospitals]

BACKGROUND

Since the first publication by Cooper et. al. in 1994 of lung volume reduction surgery (LVRS) of emphysema a marked respiratory failure with hyperkapnia (PaCO2 > 55 Torr) has been regarded as an exclusion criterion for LVRS.

PATIENTS AND METHOD

In a survey in German hospitals the question was asked whether non-invasive nasal ventilation (NIPPV) has a role in the management of LVRS. Of 12 hospitals 6 had experience with NIPPV and LVRS in a total of 19 patients with a mean FEV1 of 0.64 +/- 0.101.

RESULTS

LVRS improved FEV1 by 0.20 +/- 0.181. Preoperative NIPPV was short (< 6 months) in 8 patients and resulted in improvement of physical condition and getting the patient used to NIPPV for better perioperative management. In 5 cases NIPPV was used on a long-term basis in order to allow the patient to be included in the LVRS program. In fact 7 of these 13 patients needed ventilation perioperatively, and 4 had to continue long-term NIPPV after surgery. In further 3 patients NIPPV was applied only perioperatively. One patient had to resume NIPPV after 15 months. Two patients started NIPPV 1 resp. 12 months after surgery. Two patients had bronchial cancer which was resected. Four patients died: 1 perioperatively after intubation, 2 after 3 resp. 13 months due to respiratory failure, 1 for cancer relapse after 20 months.

CONCLUSION

NIPPV may be helpful in the planning and management of LVRS in patients with ventilatory failure with hypercarbia.

[Different approaches to long-term O2 therapy (LTOT) in patients using intermittent positive pressure ventilation]

BACKGROUND

Until now there is no conclusion about a distinguished long-term O2 therapy in patients using IPPV.

PATIENTS AND METHODS

24 patients (6 women, 18 men, mean age 60 years, mean length of IPPV 15.6 months, mean length of long-term O2 therapy 16.7 months) with IPPV and long-term O2 therapy were studied by the topical and the past dose and the length of long-term O2 therapy.

RESULTS

1. Thirteen patients had the highest need for oxygen under strain with same need under IPPV and daytime. 2. The distribution among the others was different, 3 patients showed an elevated need for oxygen from IPPV to day-time to activity, 3 needed oxygen only under strain. 3. Changing the length was necessary in 4 patients. 4. The individual dose was changed in the course in 18 patients, reduced in 4, raised in 6 and both in 8 patients.

CONCLUSION

1. A distinguished long-term O2 therapy with testing the need in rest, under IPPV and in activity is convenient. 2. Regular controls are necessary because of the individual changings.

[Exercise tolerance of patients under nasal intermittent positive pressure ventilation (nIPPV)]

BACKGROUND

There are only a few papers concerning with exercise tolerance of patients under nasal intermittent positive pressure ventilation (nIPPV).

PATIENTS AND METHOD

Therefore since 1996 we routinely checked exercise tolerance of our nIPPV-patients when admitted to the hospital. Till March 1997 we had carried out 1386-minute walking tests (6-min WT) in 111 patients.

QUESTIONS

Is there an improvement of exercise tolerance in the course of nIPPV-therapy? Are hypoxemia or hypercapnia occurring during exercise-test?

METHODS

The 6-min WT was performed after one practice walk. The patients got oxygen in case of a preexisting oxygen therapy or in case of an oxygen saturation below 85% before starting. Blood gas analyses were carried out before and after stopping the test. Oxygen saturation and heart rate were registered continuously. The distance walked was measured. Twenty-one patients were tested before introducing nIPPV therapy and 3 months after home mechanical ventilation (HMV).

RESULTS

The average distance walked amounted only 283 +/- 82 m (norm in healthy persons: 800 m). pO2 decreased from 69 +/- 11 to 58 +/- 12 mm Hg, pCO2 increased from 47 +/- 8 to 49 +/- 8 mm Hg. Oxygen saturation (SaO2) fell from 92 +/- 5 to 80 +/- 10%, heart rate increased from 104 +/- 18 to 130 +/- 23 beats/min. The distance walked changed not significantly from 282 +/- 109 to 308 +/- 71 m. Six patients could be tested a 3rd time after 6 months HMV. The distance walked was 315 +/- 103 m (also no significant difference).

CONCLUSIONS

Everyday activity can cause severe hypoxemia in nIPPV patients. Ambulatory oxygen therapy should be considered in each case. A significant improvement of exercise tolerance under nIPPV therapy is not yet proven. Our data only show a tendency towards an increase.

Bipap improves survival and rate of pulmonary function decline in patients with ALS

Amyotrophic Lateral Sclerosis (ALS) is a progressive motor neuron disease that frequently causes death within five years of diagnosis. The majority of deaths are due to pulmonary complications resulting from respiratory muscle weakness and bulbar involvement. A promising respiratory intervention is the recently introduced bi-level intermittent positive pressure (Bipap), which is a noninvasive ventilator modality shown to reduce the work of breathing and improve not only gas exchange, but also exercise tolerance and sleep quality. The aim of this study was to assess the utility of Bipap in prolonging survival in ALS. We retrospectively analyzed the results of Bipap use in 122 patients followed at Hahnemann University. All patients in this study were offered Bipap when their forced vital capacity (FVC) dropped below 50% of predicted value. Group 1 (n=38) accepted Bipap and used it more than 4 h/day. Group 2 (n=32) did not tolerate Bipap well and used it less than 4 h/day. Group 3 (n=52) refused to try Bipap. There was a statistically significant improvement in survival from initiation of Bipap in Group 1 (14.2 months) compared to Group 2 (7.0 months, P=0.002) or 3 (4.6 months, P<0.001) respectively. Furthermore, when the slope of vital capacity decline was examined, the group that used Bipap more than 4 h/day had slower decline in vital capacity (-3.5% change/month) compared to Group 2 (-5.9% change/month, P=0.02) and Group 3 (-8.3% change/month, P<0.001). We conclude that Bipap can significantly prolong survival and slow the decline of FVC in ALS. Our results suggest that all patients with ALS be offered Bipap when their FVC drops below 50%, at the onset of dyspnea, or when a rapid drop in %FVC is noted.

The clinical characteristics at the onset of a severe asthma attack and the effects of high frequency jet ventilation for severe asthmatic patients

To clarify the relationship between the clinical characteristics and the effects of high frequency jet ventilation based on the differences in the speed of deterioration in severe asthmatic patients who required intubation and mechanical ventilation, we classified 37 severe asthmatics into two groups (acute onset group: n = 20, intubated within 24 hours; slow onset group: n = 17, intubated over 3 days) and measured the arterial blood gas values, the duration of mechanical ventilation, and the peak inspiratory pressure during synchronized intermittent mechanical ventilation with or without high frequency jet ventilation. The acute onset group showed a significantly higher incidence of cyanosis (75% vs. 41%, p < 0.05), an acute loss of consciousness (90% vs. 53%, p < 0.05), severe mixed acidosis with extreme hypercapnoea (pH 7.11 +/- 0.19, PaCO2 94.1 +/- 10.7 mmHg, BE -8.3 +/- 1.7 mEq/l), and a more elevated peak inspiratory pressure (59.7 +/- 1.8 mmHg vs. 41.1 +/- 1.8 mmHg, p < 0.05) during synchronized intermittent mechanical ventilation at admission, compared with the slow onset group (p < 0.05). The slow onset group required a more prolonged mechanical ventilation than the acute onset group (5.4 +/- 4.0 vs. 3.0 +/- 2.4 days, p < 0.05), in spite of a lower peak inspiratory pressure than that observed in the acute onset group, because of either a large amount of secretion or an infection in the airway. Both the high peak inspiratory pressure and the severe mixed acidosis with markedly elevated hypercapnoea were significantly reduced by the application of high frequency jet ventilation between the intra- and the inter-groups. These findings thus indicated the existence of significant differences in the clinical features and pathogenesis of airway hyperreactivity between these two groups, and the application of high frequency jet ventilation to the status asthmaticus was thus found to be effective.

Noninvasive management of pediatric neuromuscular ventilatory failure

OBJECTIVE

To evaluate the use of mouth piece/nasal intermittent positive-pressure ventilation (IPPV) as an alternative to intubation or to permit extubation for patients with primarily neuromuscular ventilatory impairment and no ventilator-free breathing ability.

DESIGN

A case control study.

INTERVENTIONS

Using a protocol in which oxyhemoglobin desaturation was prevented or reversed by the continuous use of noninvasive IPPV and manually and mechanically assisted coughing as needed, patients with neuromuscular ventilatory failure and no ventilator-free breathing ability were managed noninvasively or extubated to continuous use of noninvasive IPPV for ventilatory support on room air.

MEASUREMENTS AND MAIN RESULTS

Four of ten patients who presented in acute ventilatory failure were managed without intubation, despite becoming dependent on continuous ventilator use. The six intubated patients were extubated successfully to continuous noninvasive IPPV once normal arterial oxygen saturation levels could be maintained on room air, despite their having no ventilator-free breathing ability.

CONCLUSIONS

The use of inspiratory and expiratory aids can decrease the need for intubation for patients with neuromuscular ventilatory failure in the absence of significant lung disease. It can also permit extubation, despite the need for continuous ventilatory support and, thereby, decrease the need to resort to tracheostomy.

Efficacy of nasal intermittent positive pressure ventilation in treating apnea of prematurity

The efficacy of nasal intermittent positive pressure ventilation (NIPPV) in treating apnea of prematurity was evaluated. Apneic preterm infants were randomly assigned to receive either NIPPV or continuous positive airway pressure (NCPAP) for 4 hr when they failed to respond to conservative therapy. The amount of reduction in apneic spells and bradycardia in the two groups after treatment was compared. Thirty-four infants (18 with NIPPV, 16 with NCPAP) were enrolled. Their birth weights ranged from 590-1,880 g (mean, 1,021 g) and gestational ages from 25-32 weeks (mean, 27.6 weeks). The baseline characteristics were comparable in the two groups. Frequency of apnea and bradycardia was reduced during both forms of treatments. However, the infants receiving NIPPV had a greater reduction of apneic spells (P = 0.02) and a tendency to greater decrease in bradycardia (P = 0.09) than those receiving NCPAP. We conclude that NIPPV is more effective than NCPAP in reducing apnea in preterm infants. NIPPV may reduce bradycardia; however, this needs to be validated by a larger number of observations.

Assisted ventilation in cystic fibrosis: nursing care

In this article the author explains nasal intermittent positive pressure ventilation (NIPPV) for patients with cystic fibrosis (CF). Indications for use are noted before nursing care of the patient is described in detail.

Comparison of oxygen cost of breathing with pressure-support ventilation and biphasic intermittent positive airway pressure ventilation

OBJECTIVE

To assess the oxygen cost of breathing with either pressure-support ventilation (PSV) or biphasic intermittent positive airway pressure ventilation (BIPAP).

DESIGN

Prospective, randomized, crossover study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Twenty clinically stable and spontaneously breathing patients after long-term mechanical ventilation.

INTERVENTIONS

Patients were randomized to start on either PSV or BIPAP, and measurements were performed after an adaptation period of 30 mins. Immediately after, the ventilatory mode was changed and after another 30-min adaptation period, the same measurements were performed.

MEASUREMENTS AND MAIN RESULTS

Indirect calorimetry was performed during each ventilatory mode for a period of 30 mins. Oxygen consumption, energy expenditure, CO2 production, and respiratory quotient did not differ significantly between the two ventilatory modes, regardless of the patients' randomization. There were no statistically significant differences with regard to respiratory rate, minute volume, and blood gas analysis. All patients tolerated both ventilatory modes without any signs of discomfort.

CONCLUSIONS

Pressure support ventilation and BIPAP are both used for weaning patients gradually from the ventilator. BIPAP may be advantageous in patients not breathing sufficiently with PSV, since no patient effort is necessary with use of this ventilatory mode.

Nasal ventilation

Nasal intermittent positive pressure ventilation is likely to have an increasing role in the management of acute ventilatory failure, weaning, and chronic ventilatory problems. Further improvements in ventilator and mask design will be seen. Appropriate application is likely to reduce both mortality and admissions to intensive care, while domiciliary use can improve life expectancy and/or quality of life in chronic ventilatory disorders. As with any new technique, enthusiasm should not outweigh clear outcome information, and possible new indications should always be subject to careful assessment.

[Home mechanical ventilation with nasal intermittent positive pressure ventilation for a boy with congenital central hypoventilation syndrome]

We report a 4-year-old boy with congenital central hypoventilation syndrome (CCHS) successfully treated with home mechanical ventilation with nasal intermittent positive pressure ventilation (NIPPV) during sleep hours. He had had frequent severe apneic attacks from the neonatal period. At 8 months, he was treated with positive pressure ventilation following a tracheostomy. At 4 year and 2 months, NIPPV was attempted because of recurrent respiratory tract infections and cor pulmonale. The tracheostomy was successfully abandoned 6 months later. Adequate ventilation has been maintained for more than 3 years without troubles. NIPPV is an effective and non-invasive treatment of CCHS that it significantly improves the quality of life during daytime.

Using nasal intermittent positive pressure ventilation on a general respiratory ward

OBJECTIVES

To assess the use of nasal intermittent positive pressure ventilation (NIPPV) in treating acute-on-chronic respiratory failure in a general medical ward.

DESIGN

Retrospective analysis of clinical outcome.

SETTING

A general medical ward of a tertiary respiratory medicine referral centre.

SUBJECTS

Altogether 75 patients admitted with acute exacerbations of chronic respiratory failure and treated NIPPV.

MAIN OUTCOME MEASURES

Blood gas tensions determined at admission to hospital and during NIPPV, tolerance of NIPPV and mortality.

RESULTS

During treatment with NIPPV, the mean (SD) PaO2 increased rapidly by 2.31 (3.58) kPa (p < 0.0001), while the mean PaCO2 fell by 1.07 (1.74) kPa (p < 0.0001) and the mean pH increased by 0.03 (0.07) (p = 0.001). Altogether 57 (76%) of patients tolerated NIPPV, and (9.3%) died in hospital. Improvement in PaO2 was more noticeable in patients with chronic obstructive pulmonary disease (+3.13 (3.49) kPa, p < 0.0001) than in those with restrictive chest wall disease (+1.20 (3.07) kPa, p = 0.25) or obstructive sleep apnoea (+0.18 (3.64), p = 0.88). The reduction in PaCO2 was similar in all three groups.

CONCLUSIONS

In routine treatment of unselected patients with acute-on-chronic respiratory failure who are being cared for on a general ward, NIPPV rapidly improves hypoxaemia and hypercapnia, is well tolerated and is associated with low mortality.

Treatment of type I spinal muscular atrophy with noninvasive ventilation and gastrostomy feeding

Type I spinal muscular atrophy (SMA) is a rapidly progressive, degenerative neuromuscular disease of infancy. In severe SMA, weakness, hypotonia, and bulbar involvement lead to progressive respiratory insufficiency and swallowing dysfunction, which are frequently complicated by aspirations. There are few studies reported in the literature that address the respiratory management of type I SMA. This article reports the results of treating four patients with infantile SMA with noninvasive positive pressure ventilation and gastrostomy feeding. All patients had gastroesophageal reflux disease, which was managed medically. Despite these therapies, survival was only 1 to 3.5 months after presenting with severe aspirations. The treatment strategy, which can be effective in less rapidly progressive neuromuscular diseases, did not alter the very poor prognosis of type I SMA. The treatment options are reviewed, and a strategy designed to optimize quality of life for infants with this fatal disease is presented.

Mechanical ventilation: past and present

Emergency physicians commonly manage patients with acute respiratory failure who require assisted mechanical ventilation. Several different modes of positive pressure mechanical ventilation can be used to manage these patients when they present to the emergency department. These modes of ventilation have evolved over the last three decades. A comprehensive review of the most important historical moments in mechanical ventilation as well as the different modes commonly used in the emergency department are presented. In addition, new techniques in noninvasive mechanical ventilation are presented.

Influence of tidal volume and positive end-expiratory pressure on inspiratory gas distribution and gas exchange during mechanical ventilation in horses positioned in lateral recumbency

OBJECTIVE

To study effects of intermittent positive-pressure ventilation (IPPV) with large tidal volumes and addition of positive end-expiratory pressure (PEEP) on maldistribution of ventilation in anesthetized horses positioned in lateral recumbency.

ANIMALS

6 healthy adult horses.

PROCEDURE

Anesthesia was induced by i.v. infusion of thiopental sodium and guiafenesin and was maintained with supplemental doses of thiopental and i.v. infusion of chloral hydrate. Functional separation of the lungs was achieved, using a tube-in-tube intubation technique. Intermittent positive-pressure ventilation of both lungs with air was done by use of an anesthetic circle system and a ventilator. Data were collected during spontaneous respiration and during IPPV, using increasing tidal volumes with and without PEEP of 10 and 20 cm of H2O.

RESULTS

Uneven distribution of inspired gas between the lungs that existed during spontaneous respiration was not altered by IPPV and large tidal volumes. Addition of PEEP caused a significant and reversible shift of inspired gas to the dependent lung and preferentially increased functional residual capacity of the nondependent lung. This was accompanied by significant increase in PaO2. With IPPV, the combined effects of PEEP and large tidal volume caused an increase of the fractional distribution of inspired gas to the dependent lung from 34% to 50%, accompanied by an increase in PaO2 and alveolar dead space of both lungs.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of PEEP during IPPV changes distribution of inspired gas. Increased in PaO2 can be attributed to improved ventilation-perfusion, especially in the dependent lung, in which previously collapsed lung units might have been reopened and participated again in gas exchange after redistribution of inspired gas. The most pronounced effects of IPPV and PEEP were associated with high airway pressures, which are likely to offset the beneficial effects of the increase of PaO2 on total oxygen availability to the tissues because of the expected negative effects on cardiac output.

Long-term nasal intermittent positive pressure ventilation in patients with cystic fibrosis and hypercapnic respiratory failure (1991-1996)

In patients with cystic fibrosis (CF), nasal intermittent positive pressure ventilation (NIPPV) is currently used as a short-term bridge to transplantation but its precise role has yet to be determined. Patients were offered a therapeutic trial of NIPPV when candidates for lung transplantation, with respiratory failure unresponsive to medical treatment. Twelve patients, six male of mean age of 26 +/- 1.4 years, had a trial of NIPPV. At recruitment the mean percentage predicted forced expired volume in one second (FEV1) was 15.1% +/- 1.2%, arterial carbon dioxide (PaCO2) 8.7 +/- 0.6 kPa, arterial oxygen (PaO2) with variable FiO2 7.4 +/- 0.6 kPa and arterial bicarbonate (HCO3-) 40.1 +/- 1.6 mmol l-1. Ten cases tolerated NIPPV for 1-15 months, mean 5.1 +/- 1.4 months, with subjective improvement in headache and quality of sleep. At 3 months, there was significant improvement in forced vital capacity, PaCO2 and arterial HCO3- and there was a reduction in the number of hospital inpatient days (P < 0.05). Subsequently three cases had lung transplantation, four died on the active list and three are awaiting organs. Two patients failed to tolerate NIPPV owing to abdominal bloating and increasing hypercapnia. In conclusion, NIPPV, if tolerated, was a useful adjunct in the treatment of CF patients with hypercapnic respiratory failure awaiting transplantation. Further prospective studies are required to determine the optimum time to commence NIPPV and to clarify its precise role.

Thoracoabdominal motion in newborns during ventilation delivered by endotracheal tube or nasal prongs

Preterm infants have asynchronous thoracoabdominal motion (TAM) secondary to a highly compliant chest wall and different lung mechanics compared to term infants. We compared TAM during continuous positive airway pressure (CPAP) administered through an endotracheal tube (ETT-CPAP) or nasal prongs (nasal-CPAP), and during synchronized intermittent mandatory ventilation administered by nasal prongs (nasal-SIMV) in 14 preterm newborn infants. Asynchrony of TAM was quantified by measuring relative motion of chest wall and abdomen with strain gauges and calculating phase angles (theta). Phase angles were lower during nasal-SIMV compared to nasal-CPAP or ETT-CPAP (P < 0.05), and lower during nasal-CPAP compared to ETT-CPAP (P < 0.05). The reduced TAM asynchrony during nasal-SIMV and nasal-CPAP may be due to elimination of resistance of the ETT and/or effective stabilization of the chest wall. These data suggest that nasal-SIMV may be an effective mode of respiratory support for preterm infants requiring minimal ventilatory support.

Improved oxygenation using the prone position in patients with ARDS

BACKGROUND

The prone position is known to increase oxygen uptake in patients with Adult Respiratory Distress Syndrome (ARDS).

METHODS

In this clinical study from 1995-96, 14 ARDS patients with severe respiratory failure were treated for at least 1 h in the prone position. Responders, defined as having more than 10% increase in PaO2/FiO2 ratio from baseline after 1 h, were treated at least 6 h in the prone position.

RESULTS

11 patients responded during the first period of the prone position (primary responders). Two of the 3 non-responders were turned prone a second time with increase in the PaO2/FiO2 ratio (secondary responders). Mean PaO2/FiO2 ratio (mean +/- SEM) in the supine position was 11.7 +/- 0.8 kPa, increasing to 16.6 +/- 1.8 kPa and 18.0 +/- 1.4 kPa after 1 and 6 h respectively (P = 0.009). Mean time spent in the prone position was 69 h (range 3-256 h), and mean ventilatory time was 17 d (3-52 d). The mortality in this subgroup of our patients with ARDS was 42%, compared to 58% in 19 patients not turned prone in the same period.

CONCLUSION

The prone position together with PEEP appears to improve ventilation-perfusion matching. The prone position is simple, effective and readily available and could be used early in most patients with ARDS.

Domiciliary nasal intermittent positive pressure ventilation in severe COPD: effects on lung function and quality of life

The aim of this study was to determine the effect of domiciliary nasal intermittent positive pressure ventilation (NIPPV) on lung function and quality of life in hypercapnic patients with chronic obstructive pulmonary disease (COPD). Fourteen hypercapnic COPD patients in a stable clinical condition were evaluated in a prospective study of domiciliary NIPPV plus long-term oxygen therapy. Baseline data obtained during a 4 week run-in period were compared with measurements at the end of the 6 month study period. Spirometric parameters, arterial blood gas tensions, and quality of life were assessed. Quality of life was measured using the St George's Respiratory Questionnaire (SGRQ) and the French version of the Nottingham Health Profile (FVNHP). All patients completed 6 months of domiciliary NIPPV. Gastro-intestinal inflation was reported by eight patients. Daytime arterial oxygen tension and arterial carbon dioxide tension, improved after therapy. During the NIPPV study period, the total SGRQ score and impacts score both improved significantly; significant improvements were also noted in the total FVNHP score and the physical mobility, emotional reactions, and energy component scores. Domiciliary nasal intermittent positive pressure ventilation combined with long-term oxygen therapy has been found to improve blood gases in spontaneous ventilation, as well as the quality of life of patients with chronic obstructive pulmonary disease.

Short-term effects of nasal proportional assist ventilation in patients with chronic hypercapnic respiratory insufficiency

Proportional assist ventilation (PAV) has recently been proposed as a mode of synchronized partial ventilatory support. This study evaluates the short-term effects of nasal PAV on arterial blood gases in stable patients with chronic hypercapnia. Forty two patients (30 with chronic obstructive pulmonary disease (COPD) and 12 with restrictive chest wall disease (RCWD) due to kyphoscoliosis) underwent a 1 h run of nasal PAV. Randomly, two levels of assistance were performed: 1) PAV was set at a level corresponding to volume assist (VA) and flow assist (FA) at 80% of the individual values of elastance (Ers) and resistance (Rrs) obtained with the "runaway" method; and 2) VA and FA were set at a value corresponding to the difference between the patients' individual Ers and Rrs and normal values of Ers and Rrs. Arterial blood gases and dyspnoea (by visual analogue scale (VAS)) were evaluated in all patients during unsupported ventilation and 60 min of PAV. PAV was well tolerated and resulted in significant improvement in arterial oxygen tension (Pa,O2), arterial carbon dioxide tension (Pa,CO2) (6.8+/-0.8 to 7.4+/-1.4 and 7.2/-0.9 to 6.8+/-0.9 kPa, respectively) and VAS (29+/-23 to 20+/-18%). The effects of PAV were not different in the two groups of diseases nor in the two groups of settings. Different settings of nasal proportional assist ventilation are well tolerated and may improve gas exchange and dyspnoea in patients with stable hypercapnic respiratory insufficiency.