A prospective observational pilot study of synchronized nasal intermittent positive pressure ventilation (SNIPPV) as a primary mode of ventilation in infants > or = 28 weeks with respiratory distress syndrome (RDS)

OBJECTIVE

To compare the outcome of infants with respiratory distress syndrome (RDS) in the neonatal intensive care unit (NICU) who were extubated to synchronized nasal intermittent positive pressure ventilation (SNIPPV) or continued on conventional ventilation (CV), immediately postsurfactant.

STUDY DESIGN

Prospective observational study of postsurfactant ventilatory management of consecutive infants (born between 10/99 and 12/02) of 28 to 34 weeks gestation. Extubation to SNIPPV was at the attending neonatologists' discretion. Babies in the CV group remained intubated, postsurfactant.

RESULTS

There were no significant differences in the maternal demographics, antenatal steroid use, mode of delivery, birth weight (BW), gestational age (GA), gender, Apgar at 5 minutes, age at surfactant instillation, or oxygenation index (OI) prior to surfactant administration, between infants continued on CV (n=35) and those extubated to SNIPPV (n=24). The total duration of endotracheal intubation (mean+/-SEM; CV versus SNIPPV; 2.4+/-0.4 versus 0.3+/-0.0 days, p=0.001) and duration of supplemental oxygen exposure (15+/-3.2 versus 8.2+/-3.3 days, p=0.04) were significantly shorter in the SNIPPV group. Furthermore, the duration of parenteral nutrition (12.1+/-1.6 versus 8.4+/-0.8 days, p=0.02) and length of stay (37.5+/-3.0 versus 29.1+/-3.3 days, p=0.04) were also significantly shorter in the SNIPPV group. There were no differences between the two groups in blood gas or OI values postsurfactant (up to 48 hours). There was no statistical difference in the incidence of intraventricular hemorrhage grade I (three (9%) in the CV group and two infants (8%) in the SNIPPV group). No infant died in either group or had patent ductus arteriosus, air leaks, necrotizing enterocolitis, periventricular leukomalacia, retinopathy of prematurity or bronchopulmonary dysplasia.

CONCLUSIONS

Infants of 28 to 34 weeks GA with RDS requiring surfactant with early extubation to SNIPPV had a shorter duration of intubation, and decreased need for oxygen as compared to CV. There was also a significant decrease in the duration of parenteral nutrition and hospitalization. SNIPPV is a safe and effective primary mode of ventilation in larger premature infants.

Ventilación no invasiva en pacientes con enfermedad pulmonar obstructiva crónica e insuficiencia respiratoria aguda hipercápnica en una sala de hospitalización convencional

OBJECTIVE

To analyze chronic obstructive lung disease (COPD) subjects in acute hypercapnic failure who were treated with non-invasive mechanical ventilation in a general respiratory ward.

METHODS

This was a two-year prospective study of 35 patients with acute exacerbation of COPD and mean FEV1/FVC relation in stable condition of 55.3 +/- 14.8% of predicted that were treated with positive pressure respiration using a facemask in a general respiratory ward. 17 (48.5%) receive long-term oxygen therapy. Analysis was made of blood gases, before and after treatment of non-invasive ventilation, complications, and failure during treatment.

RESULTS

A significant improvement in blood gases was observed 24 hours after non-invasive ventilation treatment. The mean hospital stay was of 15.0 +/- 9.1 days and failures were registered in 3 cases (8.5%). Facial scares were the most common complication (13 patients) but it was possible to continue treatment.

CONCLUSIONS

Non-invasive ventilation is a viable treatment for patients with chronic obstructive lung disease and acute hypercapnic failure being treated in a general respiratory ward.

Airway pressure release ventilation as a primary ventilatory mode in acute respiratory distress syndrome

BACKGROUND

Airway pressure release ventilation (APRV) is a ventilatory mode, which allows unsupported spontaneous breathing at any phase of the ventilatory cycle. Airway pressure release ventilation as compared with pressure support (PS), another partial ventilatory mode, has been shown to improve gas exchange and cardiac output. We hypothesized whether the use of APRV with maintained unsupported spontaneous breathing as an initial mode of ventilatory support promotes faster recovery from respiratory failure in patients with acute respiratory distress syndrome (ARDS) than PS combined with synchronized intermittent ventilation (SIMV-group).

METHODS

In a randomized trial 58 patients were randomized to receive either APRV or SIMV after a predefined stabilization period. Both groups shared common physiological targets, and uniform principles of general care were followed.

RESULTS

Inspiratory pressure was significantly lower in the APRV-group (25.9 +/- 0.6 vs. 28.6 +/- 0.7 cmH2O) within the first week of the study (P = 0.007). PEEP-levels and physiological variables (PaO2/FiO2-ratio, PaCO2, pH, minute ventilation, mean arterial pressure, cardiac output) were comparable between the groups. At day 28, the number of ventilator-free days was similar (13.4 +/- 1.7 in the APRV-group and 12.2 +/- 1.5 in the SIMV-group), as was the mortality (17% and 18%, respectively).

CONCLUSION

We conclude that when used as a primary ventilatory mode in patients with ARDS, APRV did not differ from SIMV with PS in clinically relevant outcome.

Anaesthesia for cholecystectomy in two non-parturients with Eisenmenger's syndrome

Eisenmenger's syndrome consists of high pulmonary vascular resistance with reversed or bidirectional shunt at aortopulmonary, ventricular or atrial level. We describe the anaesthetic management of two adult females with Eisenmenger's syndrome admitted for laparoscopic cholecystectomy. One patient suffered post-operative complications, but the other case was uncomplicated. We used sevoflurane and total intravenous anaesthesia to provide general anaesthesia. Both techniques were tolerated.

Response to exogenous surfactant is different during open lung and conventional ventilation

OBJECTIVE

Previous studies have shown that the efficacy of exogenous surfactant is dose-dependent during conventional positive pressure ventilation (PPVCON). The present study aimed to determine whether this dose-dependent relationship is also present during open lung (OLC) ventilation. We also explored the effect of exogenous surfactant on the ventilation pressures applied during ventilation.

DESIGN

Animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Seventy-two newborn piglets.

INTERVENTIONS

After repeated whole lung lavage, animals were randomly allocated to two surfactant groups receiving either 100 mg/kg surfactant (S100) or 25 mg/kg surfactant (S25) or to a control group receiving a bolus of air. Within each group, animals were randomly assigned to either PPVCON, open lung PPV (PPVOLC), or open lung high-frequency oscillatory ventilation (HFOVOLC) and ventilated for 5 hrs.

MEASUREMENTS AND MAIN RESULTS

The ventilation pressures decreased in a dose-dependent way, showing the largest reduction in the S100 group. In both OLC groups, oxygenation, lung mechanics, and polymorphonuclear neutrophils analyzed in bronchoalveolar lavage were independent of the surfactant dose. In the PPVCON group, however, there was a clear dose-dependency, resulting in a deterioration of oxygenation and lung mechanics and an increase in polymorphonuclear neutrophils as the surfactant dose decreased. Although comparable between the three ventilation groups, bronchoalveolar lavage interleukin-8 concentrations significantly increased in all ventilation groups as the surfactant dose increased. Alveolar protein influx and conversion of large to small aggregate surfactant were higher during PPVCON compared with both OLC groups. There were no differences in the surfactant treatment response between PPVOLC and HFOVOLC.

CONCLUSION

Exogenous surfactant enables a reduction in ventilation pressures. Compared with PPVCON, the efficacy of surfactant treatment is less dose-dependent during open lung ventilation. Surfactant conversion during open lung ventilation is reduced compared with PPVCON. Exogenous surfactant seems to up-regulate bronchoalveolar lavage interleukin-8 concentrations, independent of the ventilation strategy.

Standardized lung recruitment during high frequency and conventional ventilation: similar pathophysiologic and inflammatory responses in an animal model of respiratory distress syndrome

OBJECTIVE

To evaluate standardized lung recruitment strategy during both high frequency oscillation (HFO) and volume-targeted conventional ventilation (CV+V) in spontaneously breathing piglets with surfactant washout on pathophysiologic and inflammatory responses.

DESIGN

Prospective animal study.

SETTING

Research laboratory.

SUBJECTS

Twenty-four newborn piglets.

INTERVENTIONS

We compared pressure support and synchronized intermittent mandatory ventilation, both with targeted tidal volumes, (PSV+V, SIMV+V) to HFO. Animals underwent saline lavage to produce lung injury, received artificial surfactant and were randomized to one of the three treatment groups (each n=8). After injury and surfactant replacement, lung volumes were recruited in all groups using a standard protocol. Ventilation continued for 6 h.

MEASUREMENTS AND MAIN RESULTS

Arterial and central venous pressures, heart rates, blood pressure and arterial blood gases were continuously monitored. At baseline, post lung injury and 6 h we collected serum and bronchoalveolar lavage samples for proinflammatory cytokines: IL 6, IL 8 and TNF-alpha, and performed static pressure-volume (P/V) curves. Lungs were fixed for morphometrics and histopathologic analysis. No physiologic differences were found. Analysis of P/V curves showed higher opening pressures after lung injury in the HFO group compared to the SIMV+V group ( p<0.05); no differences persisted after treatment. We saw no differences in change in proinflammatory cytokine levels. Histopathology and morphometrics were similar. Mean airway pressure (P(aw)) was highest in the HFO group compared to SIMV+V ( p<0.002).

CONCLUSIONS

Using a standardized lung recruitment strategy in spontaneously breathing animals, CV+V produced equivalent pathophysiologic outcomes without an increase in proinflammatory cytokines when compared to HFO.

Removal of the tracheostomy tube in the aspirating spinal cord-injured patient

STUDY DESIGN

Four related case reports, occurring within a 10-month time frame during 2001.

OBJECTIVES

Aspiration is commonly reported in the literature as a contraindication to decannulation. We report four examples of successful removal of the tracheostomy tube in the presence of aspiration by an experienced team, utilising a risk management approach.

SETTING

Victorian Spinal Cord Service (VSCS), Austin Hospital, Melbourne, Australia.

METHODS

Four individuals in our unit with traumatic spinal cord injury, three quadriplegic and one paraplegic, presented with aspiration identified by a positive modified Evan's blue dye test or constant coughing, gagging and oxygen desaturation during cuff deflation trials. In three of the four cases, the tracheostomy tube had been in situ for a prolonged period and the patients had failed to progress towards decannulation. A decision was made to decannulate these four patients in spite of the presence of traditionally held contraindications for decannulation. The multidisciplinary team carefully compared the inherent risks of premature decannulation against those of prolonged tracheostomisation. Given the risk associated with this procedure, a closely monitored decannulation protocol was instituted.

RESULTS

All four patients were successfully decannulated with improved quality of life, eating between 1 and 4 days and communicating immediately after decannulation. None experienced respiratory deterioration.

CONCLUSION

It is possible to safely decannulate aspirating spinal cord injured individuals in some instances, using a risk management approach.

[Long-term outcome of patients treated by home mechanical ventilation]

To investigate the long-term survival of 95 patients treated by home mechanical ventilation, we prospectively analyzed the outcomes of their cases (treatments: 34, tracheostomy; 61, non-invasive methods) using the database of the local registration system in Aichi Prefecture. The annual actuarial probability of continuing home mechanical ventilation for the tracheostomized patients was 97.0% in the first year, 79.0% in the second year, 79.0% in the third year, and 69.2% in the fourth year, and those for the patients treated by non-invasive ventilation were 85.6%, 67.9%, 56.8%, and 46.4%, respectively. In comparison with patients with neuromuscular disease, patients with respiratory disease (both tracheostomized and non-tracheostomized) tended to show a lower continuation ratio, but the difference was not statistically significant. These data were comparable to those of previous reports, suggesting that home respiratory care in Aichi Prefecture satisfied the normal standards of quality.

Nocturnal mechanical ventilation improves exercise capacity in kyphoscoliotic patients with respiratory impairment

BACKGROUND

Patients with severe kyphoscoliosis, with or without stable respiratory failure, frequently experience oxyhaemoglobin desaturation during sleep, exercise, or both. Nasal Intermittent Positive Pressure Ventilation (NIPPV) applied during sleep has been demonstrated to be able to control nocturnal desaturations and also improve diurnal respiratory failure, if this is present, in this group of patients. The aim of this study was to evaluate the effect of a seven-day treatment with nocturnal NIPPV on exercise tolerance in a group of 6 patients with severe kyphoscoliosis and significant nocturnal and exercise-induced oxyhaemoglobin desaturation.

METHODS

NIPPV was applied each night for a week by means of a volume cycled pressure ventilator set in assisted/controlled mode. In each patient lung function, daytime arterial blood gas analysis, overnight non invasive recording of arterial saturation, and 6-minutes walking test were carried out initially and at the end of the NIPPV course.

RESULTS

During nocturnal NIPPV, as compared to baseline, the percent of night time spent below 90% of oxyhaemoglobin saturation significantly fell from 20 +/- 12.8 to 2.3 +/- 1.9 (Student t-test: p = 0.017). The 6-minute walking distance significantly increased from 244.7 +/- 132.2 to 340 +/- 122.3 m (p = 0.0097). Spirometry, daytime arterial blood gas analysis, and exercise-induced oxyhaemoglobin desaturation were unaffected by treatment.

CONCLUSION

A one-week course of treatment with nocturnal NIPPV improves exercise capacity in patients with severe kyphoscoliosis.

Effect of intrapulmonary percussive ventilation on mucus clearance in duchenne muscular dystrophy patients: a preliminary report

OBJECTIVE

To determine the effects of intrapulmonary percussive ventilation (IPV) on mucus clearance in tracheostomized Duchenne muscular dystrophy patients.

METHODS

We studied 8 patients, 5 of whom had mucus hypersecretion (> 30 mL/d). In a randomized, cross-over study we compared assisted mucus clearance techniques with and without IPV. There were 2 treatment sequences and each patient received 5 consecutive days of each treatment sequence, delivered 3 times a day. One sequence consisted of (1) assisted mucus clearance technique (AMCT, which involves forced expiratory technique and manual assisted cough), (2) endotracheal suctioning, (3) nebulizer administration of 5 mL of 0.9% sodium chloride solution for 5 min, (4) a second AMCT session, (5) endotracheal suctioning, (6) 45 min after the end of the nebulizer treatment a third AMCT session, (7) endotracheal suctioning. The other treatment sequence was the same except that it included IPV during the 5-min nebulizer treatment. The collected secretions were weighed. Vital capacity was measured once, before the treatments. Heart rate, respiratory rate, oxyhemoglobin saturation, end-tidal carbon dioxide, airway resistance, and peak expiratory flow were measured before and at 45 min after the treatments. Mean values were compared using analysis of variance with repeated measures.

RESULTS

In patients with hypersecretion the mean +/- SD weight of the collected secretions was significantly higher with IPV (6.53 +/- 4.77 g vs 4.57 +/- 3.50 g, p = 0.01). Heart rate, respiratory rate, oxyhemoglobin saturation, end-tidal carbon dioxide, airway resistance, and peak expiratory flow did not differ statistically between the 2 treatments.

CONCLUSIONS

IPV is a safe airway clearance method for tracheostomized Duchenne muscular dystrophy patients, and this preliminary study suggests that IPV increases the effectiveness of assisted mucus clearance techniques.

Safe Criteria and Procedure for Kangaroo Care With Intubated Preterm Infants

Kangaroo care (KC) was safely conducted with mechanically ventilated infants who weighed less than 600 grams and were less than 26 weeks gestation at birth. These infants, ventilated for at least 24 hours at the time of the first KC session, were considered stable on the ventilator at low settings (intermittent mandatory ventilation < 35 breaths per minute and FiO2 < 50%), had stable vital signs, and were not on vasopressors. A protocol for implementation of KC with ventilated infants that uses a standing transfer, with two staff members assisting to minimize the possibility of extubation, is presented. Also discussed is the positioning of the ventilator tubing during KC. This protocol was implemented without any accidental extubation throughout an experimental research study. The criteria and protocol were compared to those available in published reports and revealed many similar elements, providing additional support for the recommended protocol. No adverse events occurred with the criteria and protocol reported here, suggesting that they can be adopted for broader use.

Elimination of ventilator dead space during synchronized ventilation in premature infants

BACKGROUND

Mainstream airflow sensors used in neonatal ventilators to synchronize mechanical breaths with spontaneous inspiration and measure ventilation increase dead space and may impair carbon dioxide (CO(2)) elimination.

OBJECTIVE

To evaluate a technique consisting of a continuous gas leakage at the endotracheal tube (ETT) adapter to wash out the airflow sensor for synchronization and ventilation monitoring without CO(2) rebreathing in preterm infants.

DESIGN

Minute ventilation (V'(E)) by respiratory inductance plethysmography, end-inspiratory and end-expiratory CO(2) by side-stream microcapnography, and transcutaneous CO(2) tension (TcPCO(2)) were measured in 10 infants (body weight, 835+/-244 g; gestational age, 26+/-2 weeks; age, 19+/-9 days; weight, 856+/-206 g; ventilator rate, 21+/-6 beats/min; PIP, 16+/-1 centimeters of water (cmH(2)O); PEEP, 4.2+/-0.4 cmH(2)O; fraction of inspired oxygen (FIo(2)), 0.26+/-0.6). The measurements were made during four 30-minute periods in random order: IMV (without airflow sensor), IMV+Sensor, SIMV (with airflow sensor), and SIMV+Leak (ETT adapter continuous leakage).

RESULTS

Airflow sensor presence during SIMV and IMV+Sensor periods resulted in higher end-inspiratory and end-expiratory CO(2), Tcpco(2), and spontaneous V'(E) compared with IMV. These effects were not observed during SIMV+Leak.

CONCLUSIONS

The significant physiologic effects of airflow sensor dead space during synchronized ventilation in preterm infants can be effectively prevented by the ETT adapter continuous leakage technique.

Respiratory muscle workload in intubated, spontaneously breathing patients without COPD: pressure support vs proportional assist ventilation

OBJECTIVE

To compare the respiratory muscle workload associated with pressure support ventilation (PSV) and proportional assist ventilation (PAV) in intubated and spontaneously breathing patients without COPD.

DESIGN AND SETTING

Prospective study, intensive care unit university hospital.

INTERVENTIONS

Twenty intubated patients, during early weaning, PSV settings made by clinician in charge of the patient, and two levels of PAV, set to counterbalance 80% (PAV 80) and 50% (PAV 50) of both elastic and resistive loads, respectively. The patients were ventilated in the following order: 1) PSV; 2) PAV 50 or PAV 80; 3) PSV; 4) PAV 80 or PAV 50; 5) PSV. PSV settings were kept constant.

MEASUREMENTS

Arterial blood gases, breathing pattern and respiratory effort parameters at the end of each of the five steps.

MAIN RESULTS

PSV and PAV 80 had the same effects on work of breathing (WOB). The pressure-time product (PTP) was significantly higher during PAV 80 than during PSV (90+/-76 and 61+/-56 cmH(2)O.s.min(-1), respectively, P <0.05). Tidal volume was comparable, albeit more variable with PAV 80 than with PSV (variation coefficient, 43% vs 25%, respectively, P <0.05). PAV 50 entailed a higher respiratory rate, lower tidal volume, and higher WOB and PTP than PSV and PAV 80. PaO(2)/FiO(2) and SaO(2) were lower with PAV 50 than with PSV and PAV 80.

CONCLUSION

In a group of intubated spontaneously breathing non-COPD patients, PAV 80 and PSV were associated with comparable levels WOB, whereas PTP was higher during PAV 80. PAV 50 provided insufficient respiratory assistance.

[Noninvasive positive pressure ventilation for acute respiratory failure in chronic obstructive pulmonary disease in a general respiratory ward]

BACKGROUND AND OBJECTIVE

In patients with acute exacerbations of chronic obstructive pulmonary disease (COPD), noninvasive ventilatory support (NPPV) with bilevel positive airway pressure (BiPAP) may improve clinical and physiological parameters. The present study used a randomized, prospective design to evaluate the possible benefits of NPPV plus standard therapy versus standard therapy alone in patients admitted with acute hypercapnic respiratory failure in a respiratory unit of a tertiary hospital.

PATIENTS AND METHOD

Forty-one patients were included in the study. Of them, 20 were randomly allocated to receive NPPV with a standard mask connected to a BiPAP ventilatory assist device (Respironics Inc, Murrysville, PA) and 21 to standard therapy. Both groups had similar characteristics upon their admission in the hospital.

RESULTS

The use of noninvasive ventilation significantly reduced the respiratory rates and improved the conscious level within the first 2 h (p < 0.001). There were significant differences in PaCO2 and pH (p < 0.05) at 6 h of treatment. The need for intubation was 5% in the NPPV group vs 14% in the control group. The length of hospital stay was significantly shorter in the NPPV group (7 vs 10 days; p < 0.01). Nasal NPPV was well tolerated and complications were uncommon and mild.

CONCLUSIONS

Early use of noninvasive ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease leads to a more rapid improvement of physiological variables. Moreover, it is possible to apply this treatment in a general respiratory ward.

Positive pressure mechanical ventilation

There have been numerous advances in the application of positive pressure mechanical ventilation in the last two decades. As knowledge of pulmonary physiology expands, the application of modes and parameters to maximize the efficacy and minimize the complications of ventilatory support continues to advance. As the use of noninvasive ventilation becomes more widespread, its usefulness in certain clinical entities such as COPD exacerbations and acute cardiogenic pulmonary edema will become more prominent. The role of specific modes and parameters of these devices likely will be further refined to maximize outcomes.

Successful pregnancies for ventilator users

This case series describes full-term pregnancies despite no autonomous ability to breathe due to poliomyelitis or ventilatory insufficiency due to severe kyphoscoliosis. Three women with postpoliomyelitis who were continuously dependent on noninvasive intermittent positive pressure ventilation and one woman who developed ventilatory insufficiency due to severe kyphoscoliosis became pregnant and delivered healthy, full-term babies. They had vital capacities of 240, 250, 280 (5% of normal), and 880 ml (14% of normal), respectively, when becoming pregnant. The up to continuous use of noninvasive intermittent positive pressure ventilation can permit the natural completion of pregnancies of women with little or no ability to breathe unaided.

Respiratory mechanical unloading and proportional assist ventilation in infants

Conventional patient-triggered ventilation attempts to synchronize the upstroke in ventilator pressure with the onset of spontaneous inspiration. Other parameters of the mechanical cycle such as the peak inspiratory pressure are preset by the clinician. They will be imposed on the infant regardless of the actual spontaneous respiratory drive. Proportional assist ventilation (PAV) and respiratory mechanical unloading of spontaneous breathing (RMU, resistive and elastic unloading) are based on fundamentally different concepts. In contrast to the conventional perception of the ventilator being a pump, RMU/PAV servo-controls the applied ventilator pressure continuously throughout each inspiration. These modalities proportionally enhance the effect on ventilation of each respiratory effort. They rely on rather than interfere with the subject's respiratory control system. The patient controls all variables of the respiratory pattern while the ventilator works fully enslaved as a proportional amplifier. Back-up conventional mechanical ventilation is initiated during episodes of hypoventilation and apnoea. The clinician sets the degree of the assist during RMU/PAV in terms of "gains". Selecting specific gains for the elastic and resistive unloading components allows the ventilator pressure waveform to be tailored to the individual degree of restrictive and obstructive pulmonary disease. This results in a reduction in the transpulmonary pressure cost of ventilation compared with conventional modes.

CONCLUSION

Further studies on RMU/PAV are required to evaluate clinically important long-term outcome variables in infants and to determine whether the benefits outweigh potential drawbacks and the complexity involved in these new modes of mechanical ventilation.

Automatic control of arterial carbon dioxide tension in mechanically ventilated patients

This paper presents a method of controlling the arterial carbon dioxide tension of patients receiving mechanical ventilation. Controlling of the CO2 tension is achieved by regulating the ventilator initiated breath frequency and also volume per breath.

Traumatic tetraplegia: noninvasive respiratory management in the acute setting

A 15-yr-old patient with high-level spinal cord injury developed ventilatory failure 24 hr after hospital admission and required continuous ventilatory support. Although he lost all ventilator-free breathing tolerance, he was managed by receiving noninvasive intermittent positive-pressure ventilation rather than intermittent positive-pressure ventilation via an endotracheal intubation. Cooperative, uncomplicated, acutely injured patients with spinal cord injury who develop ventilatory failure are candidates to use noninvasive intermittent positive-pressure ventilation to avoid intubation.

An overnight comparison of two ventilators used in the treatment of chronic respiratory failure

Differences between bilevel ventilators used for noninvasive intermittent positive pressure ventilation (NIPPV) have been demonstrated during bench testing. However, there are no clinical studies comparing these machines. The authors have previously shown that the Quantum pressure support ventilator and Sullivan variable positive airway pressure II ST differ in performance during bench testing. To examine the clinical significance of this, these two machines were compared in the overnight treatment of subjects with chronic respiratory failure. Ten clinically-stable subjects with thoracic scoliosis were recruited. The subjects were already established on NIPPV, but none were using either of the ventilators to be tested. After familiarisation, the patients used the two ventilators in random order on consecutive nights. Peripheral oxygen saturation and transcutaneous carbon dioxide tension (Pt,CO2) were measured continuously, and sleep was recorded using polysomnography. There were no significant differences in arterial oxygen saturation, Pt,CO2 or sleep duration and quality between the two nights. Despite previously illustrated variation in laboratory performance, no differences were seen between the two ventilators when comparing overnight gas exchange and sleep in vivo. Further study is required to evaluate the significance of the differences found during bench testing in the clinical setting.

Effects of volume-guaranteed synchronized intermittent mandatory ventilation in preterm infants recovering from respiratory failure

OBJECTIVE

Volume guarantee (synchronized intermittent mandatory ventilation [SIMV]+VG) is a novel mode of SIMV for automatic adjustment of the peak inspiratory pressure to ensure a minimum set mechanical tidal volume (V(T mech)). The objective of this study was to compare the effects of SIMV+VG with conventional SIMV on ventilation and gas exchange in a group of very low birth weight infants recovering from acute respiratory failure.

METHODS

Nine infants were initially studied during 2 consecutive 60-minute ventilatory modalities of conventional SIMV (ventilator settings by clinical team) and SIMV+VG 4.5 (V(T mech) set at 4.5 mL/kg) in random order. Eight additional infants were studied during the same ventilatory modalities plus 1 additional epoch consisting of SIMV+VG 3.0 (V(T mech) set at 3.0 mL/kg).

RESULTS

Peak inspiratory pressure was significantly lower during SIMV+VG 3.0. Mean airway pressure, V(T mech), number of large V(T mech) (>7 mL/kg), and mechanical minute ventilation (V'(E)) were reduced during SIMV+VG 4.5 compared with SIMV and were further reduced during SIMV+VG 3.0. Spontaneous V'(E) increased during SIMV+VG 4.5 and was even higher during SIMV+VG 3.0. The resulting total V'(E) was higher during both SIMV+VG modes compared with SIMV. Arterial oxygen saturation by pulse oximetry, transcutaneous carbon dioxide tension, and fraction of inspired oxygen did not differ significantly, although transcutaneous carbon dioxide tension increased slightly during SIMV+VG 3.0.

CONCLUSIONS

The short-term use of SIMV+VG resulted in automatic weaning of the mechanical support and enhancement of the spontaneous respiratory effort while maintaining gas exchange relatively unchanged in comparison to conventional SIMV.

Crossover trial comparing pressure support with synchronized intermittent mandatory ventilation

OBJECTIVE

To compare pressure support ventilation (PSV) with volume guarantee (VG) to synchronized intermittent mandatory ventilation (SIMV) in infants with respiratory distress syndrome (RDS).

STUDY DESIGN

A randomized, crossover study design was used. We enrolled 14 infants [BW (mean+/-SD) 2.5+/-0.7 kg, GA 34+/-2 weeks, age 49+/-26 hours]. Subjects received 4 hours of each mode of ventilation, with the first mode selected randomly. End expiratory volume (EEV) was measured during both ventilatory modes.

RESULTS

Minute ventilation was greater with PSV+VG than with SIMV (p=0.012). This occurred despite no difference in p(a)CO(2). Mean airway pressure was higher during PSV+VG (p=0.023). There was no difference in the arterial/alveolar oxygen tension (a/A) ratio or in the specific dynamic compliance (sCdyn).

CONCLUSION

Because of an increase in V(E) with PSV+VG, and no difference in the a/A ratio or sCdyn, we do not recommend the routine use of PSV+VG for this population.

Normocapnia during nIPPV in chronic hypercapnic COPD reduces subsequent spontaneous PaCO2

Hypercapnia has been accepted during nasal intermittent positive pressure ventilation (nIPPV) and during subsequent spontaneous breathing in patients with chronic hypercapnic respiratory failure (HRF) due to COPD. We tested the hypothesis that nIPPV aimed at normalizing PaCO2 will reduce PaCO2 during subsequent spontaneous breathing. For that purpose 14 consecutive inpatients (age 61.4 +/- 9.9 years) with chronic HRF due to COPD were established on passive pressure-controlled nIPPV in a stepwise approach. Assisted ventilation with supplemental oxygen to reach normoxemia was started followed by passive ventilation with a stepwise increment in the inspiratory pressure and finally by a stepwise increase in the respiratory rate to establish normocapnia. Baseline pulmonary function parameters were: FEV1 0.97 +/- 0.43 l, PaCO2 59.5 +/- 8.4 mmHg, PaO2 49.9 +/- 7.8 mmHg, HCO3- 35.6 +/- 5.2 mmol/l, pH 7.39 +/- 0.04. Normoxemia as well as normocapnia was thus established by decreasing PaCO2 by 19.5 +/- 7.0 mmHg during nIPPV within 8.8 +/- 3.8 days (P < 0.001) (inspiratory pressure 29.8 +/- 3.8 mmHg, respiratory rate 22.9 +/- 1.9 BPM). Spontaneous PaCO2 measured 4 h after cessation of nIPPV decreased to 46.0 +/- 5.5 mmHg (P < 0.001), and HCO3- decreased to 27.2 +/- 3.0 mmol/l (P < 0.001). At 6 months of follow-up, II patients continued nIPPV with stable blood gases and with a decrease of P0.1/Plmax from 9.4 +/- 4.3% to 5.9 +/- 2.0% (P < 0.005). In conclusion, normalization of PaCO2 by passive nIPPV in patients with HRF due to COPD is possible and leads to a significant reduction of PaCO2 during subsequent spontaneous breathing and is associated with improved parameters of respiratory muscle function.

Noninvasive ventilation in acute exacerbations of chronic obstructive pulmonary disease in patients with and without home noninvasive ventilation

OBJECTIVE

The frequency of home ventilation has increased greatly. The objective of the study was, first, to compare the outcome of episodes of acute exacerbation of chronic obstructive pulmonary disease treated with mask intermittent positive-pressure ventilation (MIPPV) in patients with home MIPPV and in patients without home ventilatory support and, second, for each category of patients, to compare patients successfully ventilated with MIPPV with those who failed with MIPPV.

DESIGN

Prospective, controlled, nonrandomized clinical study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

In the groups with and without home MIPPV, respectively, 31 and 78 episodes of acute exacerbations of chronic obstructive pulmonary disease were studied.

INTERVENTIONS

MIPPV was performed in a sequential mode and delivered through a full-face mask with a bilevel positive airway pressure system.

MEASUREMENTS AND MAIN RESULTS

The clinical and functional characteristics of the two groups, at admission, were similar. In groups with and without home ventilation, respectively, success rates were 68% and 72% (p =.68), length of intensive care unit stay was 8 +/- 6 and 10 +/- 4 days (p =.02), and intensive care unit deaths were 13% and 8% (p =.30). In survivors and in groups with and without home ventilation, respectively, the total time of ventilatory assistance in intensive care unit was 5 +/- 4 and 8 +/- 4 days (p =.004), and the length of intensive care unit stay was 7 +/- 5 and 10 +/- 4 days (p =.003). A greater correction of pH, after 45 mins of MIPPV with optimal settings, was recorded in the success patients than in the failure patients, respectively; in the group with home MIPPV, the pH after 45 mins was 7.34 +/- 0.04 vs. 7.31 +/- 0.04 (p =.06), and in the group without home MIPPV, pH was 7.34 +/- 0.04 vs. 7.30 +/- 0.04 (p =.001).

CONCLUSION

MIPPV may also be favorable during episodes of acute exacerbations in patients with chronic obstructive pulmonary disease. Experience with MIPPV could benefit selected patients in the management of acute respiratory failure.

Update on modalities of mechanical ventilators

Recent advances in ventilator technology have often not been confirmed by randomised trials and instead serious shortcomings have been highlighted. Ventilation modes should only be introduced into routine clinical practice when proved efficacious in appropriately designed studies and no adverse outcomes identified by long term follow up.

Controlled versus assisted mechanical ventilation

On the basis of currently available data, it can be suggested that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary dysfunction if no contraindications, such as increased intracranial pressure, are present. Improvements in pulmonary gas exchange, systemic blood flow, and oxygen supply to tissues, which have been observed when spontaneous breathing was allowed during ventilatory support, are reflected in the clinical improvement in the patient's condition, as indicated by significantly fewer days with ventilation, earlier extubation, and shorter stays in the intensive care unit. The positive effects of spontaneous breathing have been documented only for some of the available partial ventilatory support modalities. If ventilatory modalities are limited to those whose positive effects have been documented, then partial ventilatory support can be used as a primary modality even in patients with severe pulmonary dysfunction. Whereas controlled mechanical ventilation followed by weaning with partial ventilatory support modalities has been the earlier standard in ventilation therapy, this approach should be reconsidered in view of the available data.

Energy balance in the intubated human airway is an indicator of optimal gas conditioning

OBJECTIVE

The optimal level of inspired heat and humidity for patients receiving long-term mechanical ventilation is still the subject of debate. Many laboratory studies examining surrogate markers for optimal humidity suggest that inspired gas should be at body temperature and fully saturated. The aim of this study was to determine the inspired gas condition that was thermodynamically neutral to the airway of intubated patients, and also examine the contribution of the endotracheal tube to airway heat and water balance.

DESIGN

Prospective, block-randomized, observational study.

SETTING

General adult intensive care unit of a metropolitan teaching hospital.

PATIENTS

Ten adult patients requiring intermittent positive pressure ventilation for nonpulmonary reasons.

INTERVENTIONS

Each patient was given four different gas conditions--30 degrees C, 30 mg/L; 34 degrees C, 38 mg/L; 37 degrees C, 44 mg/L; and 40 degrees C, 50 mg/L--to breathe in random order.

MEASUREMENTS AND MAIN RESULTS

Inspired and expired gas temperature and humidity, and the temperature gradient down the endotracheal tube, were measured and the inspired gas condition that gave thermodynamic neutrality was determined. This was found to be gas at body temperature, saturated. Airway workload and airway water loss increased linearly as the inspired gas departed from this condition, at approximately 1.4 kJ/hr/ degrees C and 0.5 mL/hr/ degrees C, respectively. The endotracheal tube contributed very little to heat and water exchange.

CONCLUSIONS

Inspired gas at body temperature and saturated is thermodynamically neutral to the intubated airway, and thus may be considered the optimal condition for ventilation lasting more than a few hours.

Conventional ventilation in neonates: experience from Saudi Arabia

OBJECTIVE

To study the clinical profile and immediate outcome of inborn neonates receiving intermittent positive pressure ventilation (IPPV) at the neonatal intensive care unit of Civil Hospital, Khamis Mushayt, Saudi Arabia, a level II nursery.

METHODS

78 liveborn neonates who had received IPPV over a 20 months period from January 1999 to August 2000 were reviewed from their charts and nursery registers. The indications for IPPV and the immediate outcome including complications were studied with respect to various weight groups (1 kg or less, > 1-1.25 kg, > 1.25-1.5, > 1.5-2 kg and > 2 kg) and gestation groups (28 weeks or less, 29-32 weeks, 33-36 weeks and full term).

RESULT

Hyaline Membrane disease (n = 31, 39.7%) and perinatal asphyxia (n = 29, 37.2%) were the major indications for IPPV. 67.9% (53 of the 78) ventilated neonates survived. The chances for survival showed a statistically significant increase with increasing birthweight (P = 0.0006) and with increasing gestational age (P = 0.002). (80%) (44 of 55) of neonates weighing more than 1.25 kg survived vs 39.1% (9 of 23) of those 1.25 kg or less, P = 0.0011. Similarly, 79.3% (46 of 58) of neonates of 29 or more weeks of gestation survived vs 35% (7 of 20) of those 28 weeks or less, P = 0.0007. The complications seen in the study group included blood culture positive sepsis (n = 7), pulmonary hemorrhage (n = 6), air leak syndromes (n = 4), endotracheal tube related problems (n = 5), chronic lung disease (n = 3) and retinopathy of prematurity (n = 2).

CONCLUSION

Gestational age of less than 28 weeks and birth weight less than 1.25 kg can be recommended as the cut off weight and gestation criteria for in utero transfer in this centre and upgradation of existing facilities are urgently called for to improve the survival rates further.

Devices and pressure sources for administration of nasal continuous positive airway pressure (NCPAP) in preterm neonates

BACKGROUND

Nasal continuous positive airway pressure (NCPAP) is used to support preterm infants recently extubated, those experiencing significant apnoea of prematurity and those with respiratory distress soon after birth as an alternative to intubation and ventilation. This review will focus exclusively on identifying the most effective pressure source and interface for NCPAP delivery in preterm infants.

OBJECTIVES

In preterm infants extubated to NCPAP following intermittent positive pressure ventilation (IPPV) for respiratory distress syndrome (RDS) or in those treated with NCPAP soon after birth, which technique of pressure generation and which type of nasal interface for NCPAP delivery most effectively reduces the need for additional respiratory support?

SEARCH STRATEGY

The strategy included searches of MEDLINE (1966-2002), the Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2002), CINAHL, abstracts from conference proceedings, cross-referencing of previous reviews and the use of expert informants.

SELECTION CRITERIA

Randomised or quasi-randomised trials comparing different techniques of NCPAP pressure generation and/or nasal interfaces in preterm infants extubated to NCPAP following IPPV for RDS or treated with NCPAP soon after birth.

DATA COLLECTION AND ANALYSIS

Data was extracted and analysed by the first three authors. Dichotomous results were analysed using the relative risk (RR), risk difference (RD) and number needed to treat (NNT).

MAIN RESULTS

1. Preterm infants being extubated to NCPAP following a period of IPPV for RDS: Meta-analysis of the results from Davis 2001 and Roukema 1999a demonstrated that short binasal prongs are more effective at preventing re-intubation than single nasal or nasopharyngeal prongs [typical RR 0.59 (CI: 0.41, 0.85), typical RD -0.21 (CI: -0.35, -0.07), NNT 5 (CI: 3, 14)]. In the single study comparing short binasal prong devices (Sun 1999) the re-intubation rate was significantly lower with the Infant Flow Driver than with the Medicorp prong [RR 0.33 (CI: 0.17, 0.67), RD -0.32 (CI: -0.49, -0.15), NNT 3 (CI: 2, 7)]. 2. Preterm infants primarily treated with NCPAP soon after birth: The one trial identified, Mazzella 2001, found a significantly lower oxygen requirement and respiratory rate in those randomised to short binasal prongs when compared with CPAP delivered via nasopharyngeal prong. The requirement for intubation beyond 48 hours from randomisation was not assessed. No studies comparing different techniques of pressure generation were identified.

REVIEWER'S CONCLUSIONS

Short binasal prong devices are more effective than single prongs in reducing the rate of re-intubation. Although the Infant Flow Driver appears more effective than Medicorp prongs the most effective short binasal prong device remains to be determined. The improvement in respiratory parameters with short binasal prongs suggests they are more effective than nasopharyngeal CPAP in the treatment of early RDS. Further studies incorporating longer-term outcomes are required. Studies are also needed to determine the optimal pressure source for the delivery of NCPAP.

Speed of collapse of the non-ventilated lung during one-lung anaesthesia: the effects of the use of nitrous oxide in sheep

By enhancing gaseous uptake from the non-ventilated lung during procedures performed thoracoscopically, the rapid diffusion properties of nitrous oxide would be expected to speed lung collapse and so facilitate surgery. To assess the effect of nitrous oxide on the speed of absorptive lung collapse, a study was conducted using 11 anaesthetised sheep. Speed of collapse was assessed in an indirect manner by recording the time required in a closed-chest situation for the airway pressure distal to a single lung airway occlusion to decrease to - 1.0 kPa. The influence of nitrous oxide was assessed by comparing the time taken for this decrease in airway pressure when the animal was being mechanically ventilated with 50% nitrous oxide in oxygen with the time taken when using 100% oxygen. In all assessments, it was found that the decrease in airway pressure to - 1.0 kPa occurred in a shorter time when nitrous oxide was used. The findings lend support to the hypothesis that during thoracoscopic surgery, mechanical lung ventilation with an oxygen/nitrous oxide mixture will increase the rate of gaseous uptake from the non-ventilated lung and so hasten its absorptive collapse.

Feasibility of tidal volume-guided ventilation in newborn infants: a randomized, crossover trial using the volume guarantee modality

BACKGROUND AND AIM

Volume guarantee (VG) is a new composite mode of pressure-limited ventilation, available on the Dräger Babylog 8000 ventilator, which allows the clinician to set a target mean tidal volume to be delivered while still maintaining control over peak airway pressures. This study aimed to investigate the feasibility and efficacy of this mode of ventilation in premature newborn infants with respiratory distress syndrome (RDS).

METHODS

Two groups of infants were studied: those receiving synchronized intermittent positive pressure ventilation (SIPPV) in early phase of RDS (group 1) and those in recovery phase of RDS being weaned from artificial ventilation through synchronized intermittent mandatory ventilation (SIMV; group 2). Both groups of infants were studied over a 4-hour period. Before the start of the study, the infants were either receiving SIPPV (group 1) or SIMV (group 2). Infants in group 1 were randomized to either continue on SIPPV for the first hour of the study or to receive SIPPV plus VG for the first hour. Subsequently, the 2 modes were used alternately for the remaining three 1-hour periods. Similarly, infants in group 2 were randomized to either continue on SIMV for the first hour of the study or to receive SIMV plus VG for the first hour. Data on ventilation parameters and transcutaneous carbon dioxide and oxygen were collected continuously.

RESULTS

Forty infants were studied, 20 in each group. The mean (standard error) gestational age was 27.9 (0.3) weeks; birth weight was 1064 (60) g. No adverse events were observed during the study. Fractional inspired oxygen during SIMV plus VG was 0.31 (0.3); during SIMV, 0.31 (0.3); during SIPPV plus VG, 0.41 (0.4); and during SIPPV, 0.40 (0.4). Transcutaneous carbon dioxide pressure during SIMV plus VG was 6.0 (2.2) kPa; during SIMV, 5.9 (2.2) kPa; during SIPPV plus VG, 6.4 (2.9) kPa; and during SIPPV, 6.4 (2.8) kPa. Transcutaneous partial pressure of oxygen during SIMV plus VG was 8.4 (8.7) kPa; during SIMV, 8.6 (8.8) kPa; during SIPPV plus VG, 7.6 (4.0) kPa; and during SIPPV, 7.7 (4.2) kPa. None of these differences was statistically significant. The mean (standard error) peak inspiratory pressure used during SIMV was 17.1 (3.4) cm of water; during SIMV plus VG, 15.0 (7.5) cm of water; during SIPPV plus VG, 17.1 (9.3) cm of water; and during SIPPV, 18.7 (8.3) cm of water. The mean airway pressure during SIMV plus VG was 6.5 (3.1) cm of water; during SIMV, 6.9 (2.8) cm of water; during SIPPV plus VG, 9.6 (4.5) cm of water; and during SIPPV, 9.8 (4.6) cm of water.

CONCLUSION

VG seems to be a stable and feasible ventilation mode for neonatal patients and can achieve equivalent gas exchange using statistically significant lower peak airway pressures both during early and recovery stages of RDS.ventilation, airway pressure, volume guarantee, tidal volume.

Early high-frequency oscillatory ventilation versus synchronized intermittent mandatory ventilation in very low birth weight infants: a pilot study of two ventilation protocols

OBJECTIVE

To evaluate the feasibility of conducting a prospective, randomized trial comparing early high-frequency oscillatory ventilation (HFOV) to synchronized intermittent mandatory ventilation (SIMV) in very low birth weight (VLBW) premature infants. This pilot study evaluated two ventilator management protocols to determine how well they could be implemented in a multicenter clinical trial. Although this pilot study was not powered to detect differences in outcome, we also collected outcome data.

DESIGN

Prospective, multicenter, randomized pilot study.

SETTING

Seven tertiary-level intensive care nurseries with previous experience with both HFOV and flow-triggered SIMV.

PATIENTS

Fifty infants weighing 501 to 1200 g, less than 4 hours of age, who had received one dose of surfactant and required ventilation with mean airway pressure > or =6 cm H2O and F(I)O2 > or =0.25, and had an anticipated duration of ventilation greater than 24 hours.

INTERVENTIONS

Patients were stratified by birth weight and prenatal steroid status, then randomized to either HFOV or SIMV with tidal volume monitoring. Ventilator management for patients in both study arms was strictly governed by protocols that included optimizing lung inflation and blood gases, weaning strategies, and extubation criteria.

MEASUREMENTS

Data were collected using the tools planned for the larger collaborative study. Protocol compliance was closely monitored, with successive changes in the protocol made as necessary to improve clarity and increase compliance. The incidence of major neonatal adverse outcomes was recorded.

MAIN RESULTS

Data are presented for 24 HFOV and 24 SIMV infants (two infants, twins, were withdrawn from the study at parent's request). Nineteen of the 24 HFOV infants and 20 of the 24 SIMV infants survived to 36 weeks corrected age. Age at final extubation for survivors was 16+/-16 (mean+/-SD) days for HFOV infants and 24+/-24 days for SIMV infants. At 36 weeks corrected age, 14 of the 19 HFOV survivors were extubated and in room air, whereas 5 required supplemental oxygen. In comparison, 6 of the 20 SIMV survivors were extubated and in room air, whereas 14 required supplemental oxygen. Grade III/IV IVH and/or periventricular leukomalacia occurred in 2 HFOV and 2 SIMV patients. Overall compliance with the ventilator protocols was 82% for the SIMV protocol, and 88% for the HFOV protocol.

CONCLUSIONS

The preliminary outcome data supports conducting the large randomized trial, which began in July of 1998. The protocols for the ventilator management of VLBW infants, both with HFOV and with SIMV were easily implemented and consistently followed, and are presented here.

[A comparison of the effects of PAV, PSV and IPPV on cardiopulmonary function in patients with acute respiratory failure]

OBJECTIVE

Comparing the effects of proportional assist ventilation (PAV), pressure support ventilation (PSV), and intermittent positive pressure ventilation (IPPV) on cardiopulmonary function in patients with acute respiratory failure, in particular, evaluating the clinical significance of PAV.

METHODS

Ten patients with acute respiratory failure were firstly ventilated with IPPV. Elaslance (Ers) and Resistance (Rrs) were measured and calculated. Then PSV mode was adapted. Based on the parameters of IPPV, inspiratory positive airway pressure was adjusted to maintain the same tidal volume (V(T)) as that in IPPV. Finally PAV mode was used. According to the parameters of PSV, the assist ratio was adjusted to maintain the same V(T) and peak pressure peak, as those in PSV. Respiratory mechanics, arterial blood gas and hemodynamics were recorded during above three modes of ventilation.

RESULT

Comparing with PSV and IPPV mode, PAV created a significantly lower peak, less work of breathing of patients (WoBp) and work of breathing of ventilation (WoBv) under the similar V(T); Central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) were significantly lower in PAV mode as compared with those in IPPV; While comparing with PSV, V(T), mean blood pressure (mBP) and cardiac output (CO) were higher and mean pulmonary arterial pressure (mPAP), WoBp were lower in patients with PAV under similar peak. Among them the fall of WoBp was statistically significant.

CONCLUSION

In patients receiving three modes of ventilation, PAV presents with lower airway pressure, less WoBp and less effect on hemodynamics as compared with those with PSV or IPPV.

Randomized trial of nasal synchronized intermittent mandatory ventilation compared with continuous positive airway pressure after extubation of very low birth weight infants

OBJECTIVE

To determine whether noninvasive, nasal synchronized intermittent mandatory ventilation (nSIMV) improves the likelihood that very low birth weight infants will be successfully extubated.

METHODS

Infants of <1251-g birth weight who were due to be extubated before 6 weeks of age were eligible once they were receiving <35% oxygen and were on a ventilator rate of <18 breaths per minute (bpm). Extubation was performed following intravenous loading with aminophylline, after a successful trial of 12 hours of endotracheal synchronized intermittent mandatory ventilation at a rate of 8. Infants were randomized to either nasal continuous positive airway pressure (nCPAP) at 6 cm H(2)O or nSIMV after extubation. nSIMV was commenced at a rate of 12 bpm with pressure on the ventilator set to achieve a delivered pressure of at least 12 cm H(2)O and a peak end expiratory pressure of 6 cm H(2)O. Continuous recording for diagnosis of apnea was performed for 72 hours after extubation. Objective criteria for failure of extubation were as follows: a PaCO(2) >70; FIO(2) >0.7; or severe recurrent apnea (>2 apneas requiring intermittent positive-pressure ventilation in 24 hours or >6 apneas >20 seconds per day). The study ended after 72 hours postextubation or when infants satisfied failure criteria. A sample size of 54 was determined by power analysis.

RESULTS

Mean birth weight (831 standard deviation [SD]: 193 g) and gestation (26.3 SD: 1.8 weeks) did not differ between groups. Mean age at extubation was 7.6 (SD: 9.7) days, range 1 to 40 days. The nSIMV group had a lower incidence of failed extubation 4/27 compared with the continuous positive airway pressure group, 12/27. This was attributable to both a decreased incidence of apnea and a decreased incidence of hypercarbia. There was no increase in the incidence of abdominal distension or feeding intolerance.

DISCUSSION

nSIMV is effective in preventing extubation failure in very low birth weight infants in the first 72 hours after extubation. Noninvasive ventilation may have other roles in the care of the very low birth weight infant.

Noninvasive ventilation allows gastrostomy tube placement in patients with advanced ALS

The use of noninvasive positive pressure ventilation for ventilatory support during percutaneous endoscopic gastrostomy (PEG) tube placement is described in five patients with advanced ALS, four having significant bulbar symptoms. No respiratory complications occurred in any of these patients, who were considered to be at high risk for PEG placement because of severe ventilatory impairment and might not otherwise have been considered for this procedure.

A prospective randomized trial comparing the cuffed oropharyngeal airway (COPA) with the laryngeal mask for elective minor surgery in female patients

OBJECTIVE

The cuffed oropharyngeal airway (COPA), a modified Guedel-type airway with a cuff at the distal end, has recently been introduced into anesthetic practice. The aim of this study was to compare the COPA with the well established laryngeal mask airway (LMA). Special consideration was granted to the difficult airway.

PATIENTS AND METHODS

Two hundred and fifty-two women of ASA class I or II undergoing elective gynecological or breast surgery under general anesthesia were randomly assigned to either cuffed oropharyngeal or laryngeal mask airway management. Insertion and removal of the device, airway maintenance throughout the procedure, and postoperative course and complications were assessed.

RESULTS

A patent airway was obtained with either device in all patients. Global first-time success rates for insertion were similar in the two study groups. Initial failure of correct placement occurred more frequently in the COPA as compared to the LMA group if the interincisor gap was < 5 cm and mandibular protrusion impossible (p < 0.01). Neither thyromental distance nor Mallampati scores nor body mass index (BMI) were of relevance for insertion success. The incidence of postoperative complaints and of mucosal injuries was significantly higher with the LMA.

CONCLUSION

On the whole, high overall success and low complication rates render COPA and LMA equally suitable for routine anesthetic airway management.

The effect of breath termination criterion on breathing patterns and the work of breathing during pressure support ventilation

With pressure support ventilation (PSV), each PSV breath is flow-cycled, and the breath termination criterion (TC) is usually nonadjustable. When TC does not match the interaction between the patient's inspiratory-expiratory efforts to the opening and closing of the inspiratory and expiratory valves, patient-ventilator asynchrony may occur, and the work of breathing (WOB) may increase. Therefore, we studied the effect of TC on breathing patterns and WOB during PSV in eight patients with acute respiratory distress syndrome or acute lung injury. We studied five levels of TC during PSV-1%, 5%, 20%, 35%, and 45% of the peak inspiratory flow. With increasing levels of TC, the tidal volume decreased and respiratory frequency increased, along with a decrease in duty cycle. WOB markedly increased with increasing levels of TC from 0.31 +/- 0.12 J/L with TC 1% to 0.51 +/- 0.11 J/L with TC 45%. Premature termination with double breathing occurred in one patient with TC 35% and four patients with TC 45%. Delayed termination with a duty cycle of >0.5 occurred in two patients with TC 1%. In conclusion, the proper adjustment of TC improves patient-ventilator synchrony and decreases WOB during PSV.

IMPLICATIONS

Although termination criterion (TC) is usually nonadjustable, it influences the effectiveness of pressure support ventilation for mechanical ventilation. The proper adjustment of TC is crucial to improve patient-ventilator synchrony and decrease work of breathing. TC 5% of the peak inspiratory flow may be the optimal value for patients with acute respiratory distress syndrome or acute lung injury.

Ventilatory response to CO2 re-breathing before and after nocturnal nasal intermittent positive pressure ventilation in patients with chronic alveolar hypoventilation

Long-term nocturnal nasal intermittent positive pressure ventilation (NIPPV) has beneficial effects on daytime PaCO2 in patients with chronic alveolar hypoventilation. Our aim was to investigate if these beneficial effects are related to improved respiratory drive as measured by ventilatory response to CO2. In 17 hypoventilated patients (mean age 62 years) we obtained daytime arterial blood gases, nocturnal transcutaneous oxygen saturation, nocturnal transcutaneous PaCO2 ventilatory response to CO2 re-breathing, spirometry and indices of respiratory muscle strength before and after 9 months of NIPPV. Patients served as their own controls. After 9 months of NIPPV day-time PaCO2 decreased from 7.1 kPa to 6.3 kPa, (P<0.001) and PaO2 increased from 8.1 kPa to 9.3 kPa, (P<0.01). The changes in morning and daytime PaCO2 and in nocturnal transcutaneous oxygen saturation were significantly correlated to the changes in several variables derived from the ventilatory response to CO2 re-breathing. In patients with substantial improvement in daytime PaCO2 we found significant improvements in ventilatory response to CO2 re-breathing. The present study confirms the beneficial effect of long-term NIPPV on daytime arterial blood gases. The results are consistent with the hypothesis that the improvement of daytime PaCO2 is related to improved respiratory drive observed after NIPPV.

Do we need new indications for ECMO in neonates pretreated with high-frequency ventilation and/or inhaled nitric oxide?

OBJECTIVE

High-frequency ventilation (HFV) and/or inhaled nitric oxide (iNO) has reduced ECMO in neonates. But, frequently, improvement with HFV/iNO is temporary and only prolongs lung injury without preventing ECMO. We tried to identify a threshold oxygenation index (OI) that predicts temporary or persistent improvement with HFV/iNO in neonatal ECMO candidates as early as possible.

DESIGN

Cohort study of all neonates with OI > 40 during intermittent positive pressure ventilation between 1992 and 1997. The first treatment was HFV; at an OI > 40 during HFV, iNO was added; at an OI > 40 during HFV+iNO, ECMO was initiated. Temporary improvement was defined as secondary need for ECMO or fatal chronic lung disease without ECMO.

SETTING

University hospital level III neonatal intensive care unit.

MAIN RESULTS

Ten of the 34 neonates studied rapidly required ECMO despite HFV/iNO. Eleven neonates temporarily improved for 1-10 days before the OI was again > 40. Nine received ECMO, two were denied ECMO after mechanical ventilation > 14 days and died of chronic lung disease. Thirteen neonates persistently improved with HFV/iNO without ECMO. The OI before, at 24 h or 48 h of HFV/iNO did not predict temporary or persistent improvement. However, after 72 h of HFV/iNO, neonates with persistent improvement had lower OIs than those with temporary improvement [median OI 16 (4-24) vs 31 (20-40); P = 0.0004]. In all neonates with an OI > or = 25 after 72 h, HFV/iNO eventually failed (positive predictive value 100%, sensitivity 91 %, specificity 100%, positive likelihood ratio 91).

CONCLUSION

For neonates pretreated with HFV/iNO, an OI > 40 is an inadequate ECMO indication. Based on our data we hypothesize that an OI > or = 25 after 72 h of HFV/ iNO is a better ECMO indication that avoids prolonged barotrauma.

Hemodynamic effects of bilevel nasal positive airway pressure ventilation in patients with heart failure

AIMS

Benefits of nasal continuous positive airway pressure (CPAP) in patients presenting with chronic heart failure (CHF) are controversial. The purpose of this study was to compare the hemodynamic effects of CPAP and bilevel positive airway pressure (BiPAP) in patients with or without CHF.

METHODS AND RESULTS

Twenty patients with CHF and 7 with normal left ventricular function underwent cardiac catheterization. Measurements were made before and after three 20-min periods of BiPAP: expiratory positive airway pressure (EPAP) = 8 cm H2O and inspiratory positive airway pressure (IPAP) = 12 cm H2O, EPAP = 10 cm H2O and IPAP = 15 cm H2O, and CPAP = EPAP = IPAP = 10 cm H2O administered in random order. Positive pressure ventilation decreased cardiac output (CO) and stroke volume. No change was observed in either pulmonary or systemic arterial pressure. There was no difference in the hemodynamic effects of the three ventilation settings. Only mean pulmonary wedge pressure (MPWP) and heart rate were lower with CPAP than with BiPAP. CO decreased only in patients with low MPWP (</=12 mm Hg). BiPAP ventilation increased PaO2 and decreased PaCO2 more than CPAP.

CONCLUSIONS

In patients with cardiac failure, a decrease in CO occurs both during CPAP and BiPAP, when pulmonary wedge pressure is low (</=12 mm Hg).