The effect of changes in inspiratory time on neonatal triggered ventilation

Synchronized mechanical ventilation for respiratory support in newborn infants

BACKGROUND

During synchronised mechanical ventilation, positive airway pressure and spontaneous inspiration coincide. If synchronous ventilation is provoked, adequate gas exchange should be achieved at lower peak airway pressures, potentially reducing baro/volutrauma, air leak and bronchopulmonary dysplasia. Synchronous ventilation can potentially be achieved by manipulation of rate and inspiratory time during conventional ventilation and employment of patient-triggered ventilation.

OBJECTIVES

To compare the efficacy of:(i) synchronised mechanical ventilation, delivered as high-frequency positive pressure ventilation (HFPPV) or patient-triggered ventilation (assist control ventilation (ACV) and synchronous intermittent mandatory ventilation (SIMV)), with conventional ventilation or high-frequency oscillation (HFO);(ii) different types of triggered ventilation (ACV, SIMV, pressure-regulated volume control ventilation (PRVCV), SIMV with pressure support (PS) and pressure support ventilation (PSV)).

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 5), MEDLINE via PubMed (1966 to June 5 2016), EMBASE (1980 to June 5 2016), and CINAHL (1982 to June 5 2016). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Randomised or quasi-randomised clinical trials comparing synchronised ventilation delivered as HFPPV to CMV, or ACV/SIMV to CMV or HFO in neonates. Randomised trials comparing different triggered ventilation modes (ACV, SIMV, SIMV plus PS, PRVCV and PSV) in neonates.

DATA COLLECTION AND ANALYSIS

Data were collected regarding clinical outcomes including mortality, air leaks (pneumothorax or pulmonary interstitial emphysema (PIE)), severe intraventricular haemorrhage (grades 3 and 4), bronchopulmonary dysplasia (BPD) (oxygen dependency beyond 28 days), moderate/severe BPD (oxygen/respiratory support dependency beyond 36 weeks' postmenstrual age (PMA) and duration of weaning/ventilation.Eight comparisons were made: (i) HFPPV versus CMV; (ii) ACV/SIMV versus CMV; (iii) SIMV or SIMV + PS versus HFO; iv) ACV versus SIMV; (v) SIMV plus PS versus SIMV; vi) SIMV versus PRVCV; vii) SIMV vs PSV; viii) ACV versus PSV. Data analysis was conducted using relative risk for categorical outcomes, mean difference for outcomes measured on a continuous scale.

MAIN RESULTS

Twenty-two studies are included in this review. The meta-analysis demonstrates that HFPPV compared to CMV was associated with a reduction in the risk of air leak (typical relative risk (RR) for pneumothorax was 0.69, 95% confidence interval (CI) 0.51 to 0.93). ACV/SIMV compared to CMV was associated with a shorter duration of ventilation (mean difference (MD) -38.3 hours, 95% CI -53.90 to -22.69). SIMV or SIMV + PS was associated with a greater risk of moderate/severe BPD compared to HFO (RR 1.33, 95% CI 1.07 to 1.65) and a longer duration of mechanical ventilation compared to HFO (MD 1.89 days, 95% CI 1.04 to 2.74).ACV compared to SIMV was associated with a trend to a shorter duration of weaning (MD -42.38 hours, 95% CI -94.35 to 9.60). Neither HFPPV nor triggered ventilation was associated with a significant reduction in the incidence of BPD. There was a non-significant trend towards a lower mortality rate using HFPPV versus CMV and a non-significant trend towards a higher mortality rate using triggered ventilation versus CMV. No disadvantage of HFPPV or triggered ventilation was noted regarding other outcomes.

AUTHORS' CONCLUSIONS

Compared to conventional ventilation, benefit is demonstrated for both HFPPV and triggered ventilation with regard to a reduction in air leak and a shorter duration of ventilation, respectively. In none of the trials was complex respiratory monitoring undertaken and thus it is not possible to conclude that the mechanism of producing those benefits is by provocation of synchronised ventilation. Triggered ventilation in the form of SIMV ± PS resulted in a greater risk of BPD and duration of ventilation compared to HFO. Optimisation of trigger and ventilator design with respect to respiratory diagnosis is encouraged before embarking on further trials. It is essential that newer forms of triggered ventilation are tested in randomised trials that are adequately powered to assess long-term outcomes before they are incorporated into routine clinical practice.

Synchronized mechanical ventilation for respiratory support in newborn infants

BACKGROUND

During synchronised mechanical ventilation, positive airway pressure and spontaneous inspiration coincide. If synchronous ventilation is provoked, adequate gas exchange should be achieved at lower peak airway pressures, potentially reducing baro/volutrauma, air leak and bronchopulmonary dysplasia. Synchronous ventilation can potentially be achieved by manipulation of rate and inspiratory time during conventional ventilation and employment of patient-triggered ventilation.

OBJECTIVES

To compare the efficacy of:(i) synchronised mechanical ventilation, delivered as high-frequency positive pressure ventilation (HFPPV) or patient-triggered ventilation (assist control ventilation (ACV) and synchronous intermittent mandatory ventilation (SIMV)), with conventional ventilation or high-frequency oscillation (HFO);(ii) different types of triggered ventilation (ACV, SIMV, pressure-regulated volume control ventilation (PRVCV), SIMV with pressure support (PS) and pressure support ventilation (PSV)).

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 5), MEDLINE via PubMed (1966 to June 5 2016), EMBASE (1980 to June 5 2016), and CINAHL (1982 to June 5 2016). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Randomised or quasi-randomised clinical trials comparing synchronised ventilation delivered as HFPPV to CMV, or ACV/SIMV to CMV or HFO in neonates. Randomised trials comparing different triggered ventilation modes (ACV, SIMV, SIMV plus PS, PRVCV and PSV) in neonates.

DATA COLLECTION AND ANALYSIS

Data were collected regarding clinical outcomes including mortality, air leaks (pneumothorax or pulmonary interstitial emphysema (PIE)), severe intraventricular haemorrhage (grades 3 and 4), bronchopulmonary dysplasia (BPD) (oxygen dependency beyond 28 days), moderate/severe BPD (oxygen/respiratory support dependency beyond 36 weeks' postmenstrual age (PMA) and duration of weaning/ventilation.Eight comparisons were made: (i) HFPPV versus CMV; (ii) ACV/SIMV versus CMV; (iii) SIMV or SIMV + PS versus HFO; iv) ACV versus SIMV; (v) SIMV plus PS versus SIMV; vi) SIMV versus PRVCV; vii) SIMV vs PSV; viii) ACV versus PSV. Data analysis was conducted using relative risk for categorical outcomes, mean difference for outcomes measured on a continuous scale.

MAIN RESULTS

Twenty-two studies are included in this review. The meta-analysis demonstrates that HFPPV compared to CMV was associated with a reduction in the risk of air leak (typical relative risk (RR) for pneumothorax was 0.69, 95% confidence interval (CI) 0.51 to 0.93). ACV/SIMV compared to CMV was associated with a shorter duration of ventilation (mean difference (MD) -38.3 hours, 95% CI -53.90 to -22.69). SIMV or SIMV + PS was associated with a greater risk of moderate/severe BPD compared to HFO (RR 1.33, 95% CI 1.07 to 1.65) and a longer duration of mechanical ventilation compared to HFO (MD 1.89 days, 95% CI 1.04 to 2.74).ACV compared to SIMV was associated with a trend to a shorter duration of weaning (MD -42.38 hours, 95% CI -94.35 to 9.60). Neither HFPPV nor triggered ventilation was associated with a significant reduction in the incidence of BPD. There was a non-significant trend towards a lower mortality rate using HFPPV versus CMV and a non-significant trend towards a higher mortality rate using triggered ventilation versus CMV. No disadvantage of HFPPV or triggered ventilation was noted regarding other outcomes.

AUTHORS' CONCLUSIONS

Compared to conventional ventilation, benefit is demonstrated for both HFPPV and triggered ventilation with regard to a reduction in air leak and a shorter duration of ventilation, respectively. In none of the trials was complex respiratory monitoring undertaken and thus it is not possible to conclude that the mechanism of producing those benefits is by provocation of synchronised ventilation. Triggered ventilation in the form of SIMV ± PS resulted in a greater risk of BPD and duration of ventilation compared to HFO. Optimisation of trigger and ventilator design with respect to respiratory diagnosis is encouraged before embarking on further trials. It is essential that newer forms of triggered ventilation are tested in randomised trials that are adequately powered to assess long-term outcomes before they are incorporated into routine clinical practice.

Synchronized mechanical ventilation for respiratory support in newborn infants

BACKGROUND

During synchronized mechanical ventilation, positive airway pressure and spontaneous inspiration coincide. If synchronous ventilation is provoked, adequate gas exchange should be achieved at lower peak airway pressures, potentially reducing baro/volutrauma, air leak and bronchopulmonary dysplasia. Synchronous ventilation can potentially be achieved by manipulation of rate and inspiratory time during conventional ventilation and employment of patient triggered ventilation.

OBJECTIVES

To compare the efficacy of: (i) synchronized mechanical ventilation, delivered as high frequency positive pressure ventilation (HFPPV) or patient triggered ventilation - assist control ventilation (ACV) or synchronous intermittent mandatory ventilation (SIMV)) with conventional ventilation (CMV) (ii) different types of triggered ventilation (ACV, SIMV, pressure regulated volume control ventilation (PRVCV) and SIMV plus pressure support (PS) SEARCH STRATEGY: Searches from 1985-2007 of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2007),Oxford Database of Perinatal Trials, MEDLINE, previous reviews, abstracts and symposia proceedings; hand searches of journals in the English language and contact with expert informants.

SELECTION CRITERIA

Randomised or quasi-randomised clinical trials comparing synchronized ventilation delivered as high frequency positive pressure ventilation (HFPPV) or triggered ventilation (ACV/SIMV) to conventional mechanical ventilation (CMV) in neonates. Randomised trials comparing different triggered ventilation modes (ACV, SIMV, SIMV plus PS and PRVCV) in neonates.

DATA COLLECTION AND ANALYSIS

Data regarding clinical outcomes including mortality, air leaks (pneumothorax or pulmonary interstitial emphysema (PIE)), severe intraventricular haemorrhage (grades 3 and 4), bronchopulmonary dysplasia (BPD) (oxygen dependency beyond 28 days), moderate/severe BPD (oxygen/respiratory support dependency beyond 36 weeks postmenstrual age (PMA) and duration of weaning/ventilation. Four comparisons were made: (i) HFPPV vs. CMV; (ii) ACV/SIMV vs. CMV; (iii) ACV vs. SIMV or PRVCV vs. SIMV (iv) SIMV plus PS vs. SIMV. Data analysis was conducted using relative risk for categorical outcomes, weighted mean difference for outcomes measured on a continuous scale.

MAIN RESULTS

Fourteen studies were eligible for inclusion. The meta-analysis demonstrates that HFPPV compared to CMV was associated with a reduction in the risk of air leak (typical relative risk for pneumothorax was 0.69, 95% CI 0.51, 0.93). ACV/SIMV compared to CMV was associated with a shorter duration of ventilation (weighted mean difference -34.8 hours, 95% CI -62.1, -7.4). ACV compared to SIMV was associated with a trend to a shorter duration of weaning (weighted mean difference -42.4 hours, 95% CI -94.4, 9.6). Neither HFPPV nor triggered ventilation was associated with a significant reduction in the incidence of BPD. There was a non-significant trend towards a lower mortality rate using HFPPV vs. CMV and a non-significant trend towards a higher mortality rate using triggered ventilation vs. CMV. No disadvantage of HFPPV or triggered ventilation was noted regarding other outcomes. Since the last review, two new patient triggered modes have been included: pressure regulated volume control ventilation (PRVCV) and SIMV plus pressure support. Each of these methods of ventilation has only been tested in single randomised trials with no significant advantages in important outcomes.

AUTHORS' CONCLUSIONS

Compared to conventional ventilation, benefit is demonstrated for both HFPPV and triggered ventilation with regard to a reduction in air leak and a shorter duration of ventilation, respectively. In none of the trials was complex respiratory monitoring undertaken and thus it is not possible to conclude that the mechanism of producing those benefits is by provocation of synchronized ventilation. Further trials are needed to determine whether synchronized ventilation is associated with other benefits, but optimisation of trigger and ventilator design with respect to respiratory diagnosis is encouraged before embarking on further trials. It is essential newer forms of triggered ventilation are tested in adequately powered randomised trials with long-term outcomes before they are incorporated into routine clinical practice.

Synchronized mechanical ventilation for respiratory support in newborn infants

BACKGROUND

During synchronized mechanical ventilation, positive airway pressure and spontaneous inspiration coincide. Thus, if synchronous ventilation is provoked, adequate gas exchange should be achieved at lower peak airway pressures, potentially reducing barotrauma and hence airleak and chronic lung disease. Synchronous ventilation can be achieved by manipulation of rate and inspiratory time during conventional ventilation and employment of patient assisted ventilation.

OBJECTIVES

To compare (i) the efficacy of synchronized mechanical ventilation, delivered as high frequency positive pressure ventilation or triggered ventilation (patient triggered ventilation (PTV) or synchronous intermittent mandatory ventilation (SIMV)) with conventional ventilation(ii) different types of triggered ventilation

SEARCH STRATEGY

Searches from 1985-2004 of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2004), Oxford Database of Perinatal Trials, MEDLINE, previous reviews, abstracts and symposia proceedings; hand searches of journals in the English language and contact with expert informants.

SELECTION CRITERIA

Randomized or quasi randomized clinical trials comparing synchronized ventilation delivered as high frequency positive pressure ventilation (HFPPV) or triggered ventilation (PTV/SIMV) to conventional mechanical ventilation (CMV) in neonates. Randomized trials comparing different triggered ventilation modes (PTV and SIMV) in neonates.

DATA COLLECTION AND ANALYSIS

Data regarding clinical outcomes including mortality, airleaks (pneumothorax or pulmonary interstitial emphysema (PIE)), severe intracerebral haemorrhage (grades 3 and 4), chronic lung disease (oxygen dependency beyond 28 days) and duration of weaning/ventilation. Three comparisons were made: (i) HFPPV vs CMV; (ii) PTV/SIMV vs CMV; (iii) PTV vs SIMV. Data analysis was conducted using relative risk for categorical outcomes, weighted mean difference for outcomes measured on a continuous scale.

MAIN RESULTS

Eleven studies were eligible for inclusion. The meta-analysis demonstrate that HFPPV compared to CMV was associated with a reduction in the risk of airleak (typical relative risk for pneumothorax was 0.69, 95% CI 0.51, 0.93). PTV/SIMV compared to CMV was associated with a shorter duration of ventilation (weighted mean difference -34.8 hours, 95% CI -62.1, -7.4). PTV compared to SIMV was associated with a trend to a shorter duration of weaning (weighted mean difference -42.4 hours, 95% CI -94.4, 9.6). Neither HFPPV nor triggered ventilation was associated with a significant reduction in the incidence of chronic lung disease. There was a non-significant trend towards a lower mortality rate using HFPPV versus CMV, but a non-significant trend towards a higher mortality rate using triggered ventilation versus CMV. No disadvantage of HFPPV or triggered ventilation was noted regarding other outcomes.

REVIEWERS' CONCLUSIONS

Compared to conventional ventilation, benefit is demonstrated for both HFPPV and triggered ventilation with regard to a reduction in airleak and a shorter duration of ventilation, respectively. In none of the trials was complex respiratory monitoring undertaken and thus it is not possible to conclude that the mechanism of producing those benefits is by provocation of synchronized ventilation. Further trials are needed to determine whether synchronized ventilation is associated with other benefits, but optimization of trigger and ventilator design with respect to respiratory diagnosis is encouraged before embarking on further trials.

Long versus short inspiratory times in neonates receiving mechanical ventilation

BACKGROUND

When intermittent positive pressure ventilation (IPPV) was introduced in newborn infants with hypoxic respiratory failure from hyaline membrane disease (HMD), mortality was high and air leaks problematic. This barotrauma was caused by the high peak inspiratory pressures (PIP) required to oxygenate stiff lungs. The primary determinants of mean airway pressure (and thus oxygenation) on a conventional ventilator are the inspiratory time (IT), PIP, positive end expiratory pressure and gas flow rates. In the 1970s uncontrolled studies on a small number of infants demonstrated a benefit in reducing barotrauma using a long IT and slow rates. This strategy was subsequently widely adopted. Current neonatal ventilators have been designed to minimise lung injury but rates of bronchopulmonary dysplasia (BPD) remain high. It is therefore important that the inspiratory time causing least harm is used.

OBJECTIVES

To determine in mechanically ventilated newborn infants whether the use of a long rather than a short IT reduces the rates of death, air leak and BPD.

SEARCH STRATEGY

The standard search strategy of the Cochrane Neonatal Review Group (CNRG) was used. Searches of electronic and other databases were performed. These included MEDLINE (1966 - April 2004) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2003). In order to detect trials that may not have been published, the abstracts of the Society for Pediatric Research, and the European Society for Pediatric Research were searched from 1998 - 2003.

SELECTION CRITERIA

All randomised and quasi-randomised controlled trials enrolling mechanically ventilated infants with or without respiratory pathology evaluating the use of long versus short IT (including randomised crossover studies with outcomes restricted to differences in oxygenation).

DATA COLLECTION AND ANALYSIS

The standard method of the Cochrane Collaboration and its Neonatal Review Group were used. Two authors independently assessed eligibility, and the methodological quality of each trial, and extracted the data. The data were analysed using relative risk (RR) and risk difference (RD) and their 95% confidence intervals. A fixed effect model was used for meta-analyses.

MAIN RESULTS

In five studies, recruiting a total of 694 infants, a long IT was associated with a significant increase in air leak [typical RR 1.56 (1.25, 1.94), RD 0.13 (0.07, 0.20), NNT 8 (5, 14)]. There was no significant difference in the incidence of BPD. Long IT was associated with an increase in mortality before hospital discharge that reached borderline statistical significance [typical RR 1.26 (1.00, 1.59), RD 0.07 (0.00, 0.13)].

REVIEWERS' CONCLUSIONS

Caution should be exercised in applying these results to modern neonatal intensive care, because the studies included in this review were conducted prior to the introduction of antenatal steroids, post natal surfactant and the use of synchronised modes of ventilatory support. Most of the participants had single pathology (HMD) and no studies examined the effects of IT on newborns ventilated for other reasons such as meconium aspiration and congenital heart disease (lungs with normal compliance). However, the increased rates of air leaks and deaths using long ITs are clinically important; thus, infants with poorly compliant lungs should be ventilated with a short IT.

Update on patient-triggered ventilation

Physiologic studies have demonstrated short-term benefits of triggered ventilation over conventional ventilation. The results of the randomized trials are disappointing. Meta-analysis has highlighted that the only significant difference in outcomes on PTV compared with conventional ventilation is a shorter duration of weaning. A few of the trials included infants with meconium aspiration syndrome and congenital pneumonia, but most infants randomized had RDS. In addition, a high proportion of the infants included in the meta-analysis were from two trials in which the SLE 2000 and airway pressure triggering system were mainly used. We cannot confidently conclude that in a population of infants with another respiratory disorder or even in those with RDS supported by an alternative triggering system, a different result might have been achieved. In addition, the benefits of PTV demonstrated in physiologic studies are largely related to achieving synchronized ventilation. In none of the randomized trials was any attempt made to determine if the infants were breathing synchronously with their ventilators. Before dismissing PTV for use in the management of infants with acute respiratory distress, an appropriately designed trial needs to take place. Essential, before any such trial, is identification of optimum method of PTV delivery, which may be disease specific.

International randomised controlled trial of patient triggered ventilation in neonatal respiratory distress syndrome

AIM

To compare the effects of patient triggered ventilation (PTV) with conventional ventilation (IMV) in preterm infants ventilated for respiratory distress syndrome (RDS).

METHODS

Nine hundred and twenty four babies from 22 neonatal intensive care units were assessed. They were under 32 weeks of gestation and had been ventilated for respiratory distress syndrome (RDS) for less than 6 hours within 72 hours of birth. The infants were randomly allocated to receive either PTV or IMV. Analysis was on an "intention to treat" basis. Death before discharge home or oxygen therapy at 36 weeks of gestation; pneumothorax while ventilated; cerebral ultrasound abnormality nearest to 6 weeks; and duration of ventilation in survivors were the main outcome measures.

RESULTS

There was no significant difference in outcome between the two groups. Unadjusted rates for death or oxygen dependency at 36 weeks of gestation were 47.4% and 48.7%, for PTV and IMV, respectively; for pneumothorax these were 13.4% and 10.3%; and for cerebral ultrasound abnormality nearest to 6 weeks these were 35.4% and 36.9%. Median duration of ventilation for survivors in both groups was 6 days. Overall, 79% of babies received only their assigned ventilation. PTV babies were more likely to depart from their intended ventilation (27% vs 15%). The trend towards higher pneumothorax rates with PTV occurred only in infants below 28 weeks of gestation (18.8% vs 11.8%).

CONCLUSIONS

There was no observed benefit from the use of PTV, with a trend towards a higher rate of pneumothorax under 28 weeks of gestation. Although PTV has a similar outcome to IMV for treatment of RDS in infants of 28 weeks or more gestation, within 72 hours of birth, it was abandoned more often. It cannot be recommended for infants of less than 28 weeks' gestation with the ventilators used in this study.

The Hering-Breuer reflex in anesthetized infants: end-inspiratory vs. end-expiratory occlusion technique

Both end-inspiratory (EIO) and end-expiratory (EEO) occlusions have been used to measure the strength of the Hering-Breuer inflation reflex (HBIR) in infants. The purpose of this study was to compare both techniques in anesthetized infants. In each infant, HBIR activity was calculated as the relative prolongation of expiratory and inspiratory time during EIO and EEO, respectively. Respiratory drive was assessed from the change in airway pressure during inspiratory effort against the occlusion, both at a fixed time interval of 100 ms (P0.1) and a fixed proportion (10%) of the occluded inspiratory time (P10%). Twenty-two infants [age 14.3 +/- 6. 4 (SD) mo] were studied. No HBIR activity was present during EIO [-11.8 +/- 15.9 (SD) %]. By contrast, there was significant, albeit weak, reflex activity during EEO [HBIR: 27.2 +/- 17.4%]. A strong HBIR (up to 310%) was elicited in six of seven infants in whom EIO was repeated after lung inflation. P0.1 was similar during both types of occlusions, whereas mean +/- SD P10% was lower during EEO than during EIO: 0.198 +/- 0.09 vs. 0.367 +/- 0.15 kPa, respectively (P < 0.01). These data suggest a difference in the central integration of stretch receptor activity in infants during anesthesia compared with during sleep.

The new obstetrics: its integration into neonatal clinical practise, teaching and research

Most neonatologists have not yet incorporated into their teaching, clinical service and research the advances in high risk obstetrics particularly as it relates to fetal surveillance. This brief review emphasizes some of the "new obstetrics" from the viewpoint of perinatal medicine, particularly in terms of neonatal teaching and the design of future neonatal research. The information that can be obtained about an infant prenatally by the use of ultrasound. power doppler, computerized fetal heart rate monitoring, cordocentesis, etc is extensive and yet, has rarely been utilized in the design of neonatal research protocols. It is becoming imperative that the "new obstetrics" be recognized and utilized in modern neonatal thinking if a truly "perinatal medicine" is to be practised.

Comparison of body surface and airway triggered ventilation in extremely premature infants

Failure of patient triggered ventilation in very premature infants may reflect the use of inappropriate triggering systems. We have therefore compared the performance of an airway and a body surface trigger in 12 infants of median gestational age 26 weeks (range 24-27). Airway flow and oesophageal and ventilator pressure changes were recorded during two periods of patient triggered ventilation. From the traces, the degree of asynchrony (inflation extending beyond inspiration), triggering rate, sensitivity (proportion of the infant's breaths detected) and trigger delay (response time) were calculated. Although with both triggering systems there was a high rate of asynchrony, the triggering rate (p < 0.05), sensitivity (p < 0.05) and trigger delay (p < 0.01) were all better with the body surface trigger. These results suggest that the body surface trigger is the more appropriate system for very immature infants.

Patient-triggered ventilation: a comparison of tidal volume and chestwall and abdominal motion as trigger signals

Patient-triggered synchronized ventilation requires reliable and early detection of the infant's inspiratory effort. Several trigger methods have been developed that frequently lack the sensitivity to detect inspiration in small preterm infants (trigger failure), or show a high rate of breaths triggered by artifacts in the respiratory signal (autotrigger). The purpose of this study was to determine the effectiveness of the following trigger signals: abdominal movement sensed by a newly developed induction technique, chestwall motion detected by changes in transthoracic impedance, and tidal volume measured by anemometry at the endotracheal tube connector. Ten preterm infants (birth weight, 580-1,424 g; median weight, 943 g; study weight, 535-1,415 g; median weight, 838 g; gestation age, 26-32 weeks, median gestational age, 28 weeks, study age, 1-50 days, median study age, 11 days) were included in the study. A Sechrist SAVI ventilator was triggered by one of three signals: chestwall or abdominal movement, or tidal volume generated by the infants. Response time between beginning of inspiratory flow, the occurrence of the trigger signal (signal delay), and the onset of the triggered breath (trigger delay) were determined for each of the three signals. The signal response time was -13.5 msec (95% CI, -33 to -2 msec) for the abdominal movement signal, indicating that it started before inspiratory flow; 0.0 msec for the volume signal; and 44.0 msec (95% CI, 29-73 msec) for the chestwall signal (P < 0.002); this long delay was secondary to chestwall distortion and a subsequent delay in outward ribcage movement in many infants. The trigger delay for the abdominal signal was 90.0 msec (95% CI, 55-104 msec), 135.5 msec (95% CI: 82-186 msec) for the volume signal, and 176.5 msec (95% CI: 165-232 msec) for the chestwall signal, indicating that there was a difference in the rise time of signal voltage between the three methods (P < 0.01). The rate of autotriggered breaths was 3.2% (95% CI, 0.3-9.3%) when using the abdominal signal, 0.55% (95% CI, 0.0-2.1%) for the tidal volume signal, and 11.25% (95% CI, 0.5-27.8%) for the chestwall signal (P < 0.05). The incidence of trigger failure was low with all three signals and was not significantly different between the techniques. In summary, the chestwall signal had a long trigger delay and was highly susceptible to false triggering. It is, therefore, not a reliable trigger signal for synchronized mechanical ventilation in preterm infants. In contrast, tidal volume and abdominal movement signals had an acceptable trigger delay and a low rate of autotriggering, making them useful clinical trigger signals.

Randomized multicenter trial comparing synchronized and conventional intermittent mandatory ventilation in neonates

OBJECTIVE

To compare synchronized intermittent mandatory ventilation (SIMV) and conventional intermittent mandatory ventilation (IMV) in neonates.

STUDY DESIGN

Prospective, multicenter, randomized clinical trial.

SETTING

Level III neonatal intensive care units at six university or children's hospitals.

PATIENTS

Three hundred twenty-seven infants receiving conventional IMV for respiratory distress syndrome, pneumonia, or meconium aspiration pneumonitis were randomly assigned a 7.5 +/- 6 hours of age to either continue with IMV or change to SIMV. Infants assigned to each mode of ventilation had similar birth weight (BW), gestational age, and Apgar scores at birth, and similar oxygenation indexes at randomization. They received similar surfactant therapy and had similar incidence of sepsis, seizures, secondary pneumonia, and necrotizing enterocolitis. In the infants with BW less than 1000 gm, more infants receiving IMV had surgical ligation of their patent ductus arteriosus than did those receiving SIMV (27 vs. 7 %; p = 0.02).

ANALYSIS

Data was analyzed overall for all infants and also separately within three BW groups: less than 1000 gm, 1000 to 2000 gm, and more than 2000 gm. The 1000 to 2000 gm BW group was further analyzed in subgroups weighing 1000 to 1499 gm and 1500 to 2000 gm.

RESULTS

In all infants, at 1 hour after randomization, the infants receiving SIMV had a lower mean airway pressure than those receiving IMV (8.08 +/- 2.15 vs. 8.63 +/- 2.59; p<0.05), with similar fractions of inspired oxygen and oxygenation indexes. Infants whose BW was 1000 to 2000 gm at 0.5 hour required a lower fraction of inspired oxygen with SIMV than with IMV (0.52 +/- 0.20 vs. 0.62 +/- 0.27; p<0.05) and had better oxygenation at 1 hour, as shown by lower oxygenation indexes with SIMV than with IMV (6.14 +/- 4.17 vs. 9.42 +/- 8.41; p = 0.01). Infants whose BW was 1000 to 2000 gm received a lower number of unit doses of sedative/analgesic drugs per infant during the first 4 days of SIMV than did infants receiving IMV (3.8 +/- 3.4 vs 6.3 +/- 5.5 unit doses; p = 0.02). Infants whose BW was more than 2000 gm had a shorter duration of mechanical ventilation with SIMV than with IMV (median, 72 vs 93 hours; p = 0.02). Three of the forty-six infants receiving IMV but none of the 47 infants receiving SIMV required extracorporeal membrane oxygenation. In the infants with BW less than 1000 gm, fewer infants treated with SIMV required supplemental oxygen at 36 weeks of postconceptional age than did those treated with IMV (47 vs 72%; p<0.05). In 83 infants whose lungs were mechanically ventilated for 14 days or longer, all with BW less than 2000 gm, those treated with SIMV regained their BW earlier than those treated with IMV (median, 21.5 vs 29 days; p<0.01). There were no differences in the rates of death, intraventricular hemorrhage (grades III and IV), air leak, need for pharmacologic paralysis, or need for supplemental oxygen at 28 days.

CONCLUSIONS

We found that SIMV was at least as efficacious as conventional IMV, and may have improved certain outcomes in BW-specific groups.

Comparison of weaning by patient triggered ventilation or synchronous intermittent mandatory ventilation in preterm infants

Forty preterm infants were entered into a randomized controlled trial to compare the efficacy and duration of weaning by patient triggered ventilation (PTV) to that of synchronous intermittent mandatory ventilation (SIMV). Infants were randomized during recovery from respiratory distress once ventilator rate had been reduced to 40 breaths per minute; weaning during PTV was by reduction in ventilator pressure only, whereas infants randomized to SIMV were weaned by reduction in rate only. Weaning failed in 12 infants, 6 from each group, the 12 infants were more immature than those in whom weaning succeeded (p < 0.01). Overall, the duration of weaning did not differ significantly between the PTV and SIMV groups.

Response time and reliability of three neonatal patient-triggered ventilators

We studied the response time (RT) and reliability of three neonatal patient-triggered ventilator (PTV) systems: the Draeger Babylog 8000, the Bear Cub enhancement module (CEM), and the Infrasonics Star Sync. In 10 adult rabbits, airway flow and pressure recordings showed the RT of the Star Sync to be shorter than that of the Bear CEM (53 +/- 13 versus 65 +/- 15 ms, p < 0.05), and both were shorter than that of the Babylog (95 +/- 24 ms, p < 0.01) by ANOVA. The RT of the Bear CEM and the Babylog increased significantly at decreased trigger sensitivity settings. All ventilators triggered successfully on assist-control (A/C). However, the Babylog had a higher rate of asynchrony on SIMV (30 +/- 25%) than the Bear CEM (1.1 +/- 0.3%) and the Star Sync (1.2 +/- 0.4%), p < 0.01. In 10 infants with respiratory failure, recordings of airway flow and pressure were made at ventilator inspiratory time (Ti) settings of 0.3, 0.4, and 0.5 s on assist-control and on SIMV at rates of 15, 30, 45, and 60 breaths/min. The Star Sync and Bear CEM triggered successfully on A/C (100%) and had low rates of asynchrony on SIMV (1 to 3%). The Babylog had a lower success rate on A/C (70 +/- 12%) and a higher rate of asynchrony on SIMV (29 +/- 30%) than the other two ventilators; p < 0.01. The lower reliability of the Babylog was due to its variable refractory period (0.2 to 0.5 s, to equal the set Ti).(ABSTRACT TRUNCATED AT 250 WORDS)

Randomised controlled trial of weaning by patient triggered ventilation or conventional ventilation

A group of preterm infants (n = 40) were entered into a randomised controlled trial to compare the duration and efficacy of weaning by patient triggered ventilation (PTV) or conventional ventilation. Once recovery from respiratory distress had begun, enabling the ventilator rate to be reduced to 40 breaths/min, infants were randomised to either regime. Infants randomised to PTV were weaned by reduction in ventilator pressure only, whereas infants randomised to conventional ventilation were weaned by reduction in ventilator rate only. Only one infant required re-ventilation within 24 h of extubation; this infant had been weaned by conventional ventilation. Three infants, all of less than 28 weeks gestation, did not tolerate weaning by PTV and were subsequently weaned conventionally. The duration of weaning was analysed according to the original randomisation allocation and was significantly shorter in the PTV group, being a median of 30 h (mean 39, range 3-186) compared to a median of 61 h (mean 65, range 15-262) in the conventional group, P < 0.02. We conclude PTV is the more advantageous form of weaning in preterm infants of greater than 27 weeks gestational age.

Evaluation of triggering systems for patient triggered ventilation for neonates ventilator-dependent beyond 10 days of age

The performance of two triggering systems was compared during patient triggered ventilation (PTV) of infants ventilator-dependent beyond 10 days of age. Ten infants were studied who had a median gestational age of 26.5 weeks and a postnatal age of 15.5 days. PTV was administered via the SLE ventilator and the two triggering systems, an airway pressure monitor and the MR10 respiration monitor, were used in random order each for 30 min. The airway pressure trigger had a superior performance in that, although it did not differ significantly in delivered inflation volume or sensitivity to the MR10 respiration monitor, it had a shorter trigger delay (P < 0.01). Oxygenation improved in eight of the ten infants on the airway pressure trigger, but only in three on the MR10 respiration monitor. The reduction in PaCO2 was greater during PTV with the airway pressure trigger compared with the MR10 respiration monitor (P < 0.01). We conclude that the airway pressure trigger has a superior performance compared to the MR10 respiration monitor trigger in infants who are ventilator-dependent beyond 10 days of age.

Patient triggered ventilation using a flow triggered system

The role of patient triggered ventilation (PTV) for the newborn was assessed using a new patient triggered ventilator, the Draeger Bablylog 8000, which incorporates significant improvements in both ventilator performance and the triggering system. Thirty three infants, median gestational age 30 weeks and postnatal age 2.5 days, were entered into the study to compare blood gases obtained during conventional and patient triggered ventilation. Oxygenation did not improve with PTV in the group overall but increased significantly (median change 7%) in infants greater than 28 weeks' gestation. Arterial carbon dioxide tension (PaCO2) decreased during PTV in the majority of infants (median reduction 7%), this was not related to the gestational or postnatal age, but was greatest in infants previously on a low conventional ventilation rate. Blood gases (both PaO2 and PaCO2) deteriorated in infants requiring the highest inspired oxygen concentration. We conclude that patient triggered ventilation is most useful in infants with mild respiratory distress.

Airway pressure triggered ventilation for preterm neonates

The usefulness of airway pressure triggered ventilation for the preterm newborn has been assessed using a new patient triggered valveless ventilator, the SLE 2000 infant ventilator (SLE 2000). This ventilator performs well at fast rates with no inadvertent positive end expiratory pressure (PEEP) even at rates of 150 breaths per minute (bpm). The ventilator is triggered by a change in airway pressure equal to or exceeding 0.5 cmH2O. If the infant fails to achieve the change in airway pressure which will trigger the ventilator the infant is ventilated at the back-up rate which is predetermined in conventional mode prior to commencing PTV. Infants were ventilated for one hour on a conventional neonatal ventilator, then for one hour on the SLE 2000 in conventional mode without changing the ventilator settings and finally for one hour on the SLE 2000 in patient triggered mode. Arterial blood gases were checked at the end of each hour. During patient triggered ventilation (PTV) the peak pressure, inspiratory time and inspired oxygen concentration were the same as those used during conventional mode. Simultaneous recordings were made of flow, volume, ventilator and oesophageal pressure change, from this recording the trigger delay during PTV was calculated. The trigger delay, being the time lag from the start of spontaneous inspiration, indicated by the negative deflection in the oesophageal pressure trace, and the onset of the ventilator breath. Thirteen infants were included in the study, median gestational age 32 weeks (range 25-35) and birthweight 1640 g (range 838-3038). All were being ventilated for respiratory distress syndrome (RDS) and were 4 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)