Assessment of respiratory drive and muscle function in the pediatric intensive care unit and prediction of extubation failure

Pleural and transpulmonary pressures to tailor protective ventilation in children

This review aims to: (1) describe the rationale of pleural (P_PL) and transpulmonary (P_L) pressure measurements in children during mechanical ventilation (MV); (2) discuss its usefulness and limitations as a guide for protective MV; (3) propose future directions for paediatric research. We conducted a scoping review on P_L in critically ill children using PubMed and Embase search engines. We included peer-reviewed studies using oesophageal (P_ES) and P_L measurements in the paediatric intensive care unit (PICU) published until September 2021, and excluded studies in neonates and patients treated with non-invasive ventilation. P_L corresponds to the difference between airway pressure and P_PL Oesophageal manometry allows measurement of P_ES, a good surrogate of P_PL, to estimate P_L directly at the bedside. Lung stress is the P_L, while strain corresponds to the lung deformation induced by the changing volume during insufflation. Lung stress and strain are the main determinants of MV-related injuries with P_L and P_PL being key components. P_L-targeted therapies allow tailoring of MV: (1) Positive end-expiratory pressure (PEEP) titration based on end-expiratory P_L (direct measurement) may be used to avoid lung collapse in the lung surrounding the oesophagus. The clinical benefit of such strategy has not been demonstrated yet. This approach should consider the degree of recruitable lung, and may be limited to patients in which PEEP is set to achieve an end-expiratory P_L value close to zero; (2) Protective ventilation based on end-inspiratory P_L (derived from the ratio of lung and respiratory system elastances), might be used to limit overdistention and volutrauma by targeting lung stress values < 20-25 cmH₂O; (3) P_PL may be set to target a physiological respiratory effort in order to avoid both self-induced lung injury and ventilator-induced diaphragm dysfunction; (4) P_PL or P_L measurements may contribute to a better understanding of cardiopulmonary interactions. The growing cardiorespiratory system makes children theoretically more susceptible to atelectrauma, myotrauma and right ventricle failure. In children with acute respiratory distress, P_PL and P_L measurements may help to characterise how changes in PEEP affect P_PL and potentially haemodynamics. In the PICU, P_PL measurement to estimate respiratory effort is useful during weaning and ventilator liberation. Finally, the use of P_PL tracings may improve the detection of patient ventilator asynchronies, which are frequent in children. Despite these numerous theoritcal benefits in children, P_ES measurement is rarely performed in routine paediatric practice. While the lack of robust clincal data partially explains this observation, important limitations of the existing methods to estimate P_PL in children, such as their invasiveness and technical limitations, associated with the lack of reference values for lung and chest wall elastances may also play a role. P_PL and P_L monitoring have numerous potential clinical applications in the PICU to tailor protective MV, but its usefulness is counterbalanced by technical limitations. Paediatric evidence seems currently too weak to consider oesophageal manometry as a routine respiratory monitoring. The development and validation of a noninvasive estimation of P_L and multimodal respiratory monitoring may be worth to be evaluated in the future.

Predictive parameters and model for extubation outcome in pediatric patients

Background

Prolonged mechanical ventilation is associated with significant morbidity in critically ill pediatric patients. In addition, extubation failure and deteriorating respiratory status after extubation contribute to increased morbidity. Well-prepared weaning procedures and accurate identification of at-risk patients using multimodal ventilator parameters are warranted to improve patient outcomes. This study aimed to identify and assess the diagnostic accuracy of single parameters and to develop a model that can help predict extubation outcomes.

Materials and methods

This prospective observational study was conducted at a university hospital between January 2021 and April 2022. Patients aged 1 month to 15 years who were intubated for more than 12 h and deemed clinically ready for extubation were enrolled. A weaning process with a spontaneous breathing trial (SBT), with or without minimal setting, was employed. The ventilator and patient parameters during the weaning period at 0, 30, and 120 min and right before extubation were recorded and analyzed.

Results

A total of 188 eligible patients were extubated during the study. Of them, 45 (23.9%) patients required respiratory support escalation within 48 h. Of 45, 13 (6.9%) were reintubated. The predictors of respiratory support escalation consisted of a nonminimal-setting SBT [odds ratio (OR) 2.2 (1.1, 4.6), P = 0.03], >3 ventilator days [OR 2.4 (1.2, 4.9), P = 0.02], occlusion pressure (P0.1) at 30 min ≥0.9 cmH₂O [OR 2.3 (1.1, 4.9), P = 0.03], and exhaled tidal volume per kg at 120 min ≤8 ml/kg [OR 2.2 (1.1, 4.6), P = 0.03]; all of these predictors had an area under the curve (AUC) of 0.72. A predictive scoring system to determine the probability of respiratory support escalation was developed using a nomogram.

Conclusion

The proposed predictive model, which integrated both patient and ventilator parameters, showed a modest performance level (AUC 0.72); however, it could facilitate the process of patient care.

Ventilation Weaning and Extubation Readiness in Children in Pediatric Intensive Care Unit: A Review

Ventilation is one of the most common procedures in critically ill children admitted to the pediatric intensive care units (PICUs) and is associated with potential severe side effects. The longer the mechanical ventilation, the higher the risk of infections, mortality, morbidity and length of stay. Protocol-based approaches to ventilation weaning could have potential benefit in assisting the physicians in the weaning process but, in pediatrics, clear significant outcome difference related to their use has yet to be shown. Extubation failure occurs in up to 20% of patients in PICU with evidences demonstrating its occurrence related to a worse patient outcome including higher mortality. Various clinical approaches have been described to decide the best timing for extubation which can usually be achieved by performing a spontaneous breathing trial before the extubation. No clear evidence is available over which technique best predicts extubation failure. Within this review we summarize the current strategies of ventilation weaning and extubation readiness evaluation employed in the pediatric setting in order to provide an updated view on the topic to guide intensive care physicians in daily clinical practice. We performed a thorough literature search of main online scientific databases to identify principal studies evaluating different strategies of ventilation weaning and extubation readiness including pediatric patients receiving mechanical ventilation. Various strategies are available in the literature both for ventilation weaning and extubation readiness assessment with unclear clear data supporting the superiority of any approach over the others.

Diaphragm Activity Pre and Post Extubation in Ventilated Critically Ill Infants and Children Measured With Transcutaneous Electromyography

OBJECTIVES

Swift extubation is important to prevent detrimental effects of invasive mechanical ventilation but carries the risk of extubation failure. Accurate tools to assess extubation readiness are lacking. This study aimed to describe the effect of extubation on diaphragm activity in ventilated infants and children. Our secondary aim was to compare diaphragm activity between failed and successfully extubated patients.

DESIGN

Prospective, observational study.

SETTING

Single-center tertiary neonatal ICU and PICU.

PATIENTS

Infants and children receiving invasive mechanical ventilation longer than 24 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Diaphragm activity was measured with transcutaneous electromyography, from 15 minutes before extubation till 180 minutes thereafter. Peak and tonic activity, inspiratory amplitude, inspiratory area under the curve, and respiratory rate were calculated from the diaphragm activity waveform. One hundred forty-seven infants and children were included (median postnatal age, 1.9; interquartile range, 0.9-6.7 wk). Twenty patients (13.6%) failed extubation within 72 hours. Diaphragm activity increased rapidly after extubation and remained higher throughout the measurement period. Pre extubation, peak (end-inspiratory) diaphragm activity and tonic (end-inspiratory) diaphragm activity were significantly higher in failure, compared with success cases (5.6 vs 7.0 μV; p = 0.04 and 2.8 vs 4.1 μV; p = 0.04, respectively). Receiver operator curve analysis showed the highest area under the curve for tonic (end-inspiratory) diaphragm activity (0.65), with a tonic (end-inspiratory) diaphragm activity greater than 3.4 μV having a combined sensitivity and specificity of 55% and 77%, respectively, to predict extubation outcome. After extubation, diaphragm activity remained higher in patients failing extubation.

CONCLUSIONS

Diaphragm activity rapidly increased after extubation. Patients failing extubation had a higher level of diaphragm activity, both pre and post extubation. The predictive value of the diaphragm activity variables alone was limited. Future studies are warranted to assess the additional value of electromyography of the diaphragm in combined extubation readiness assessment.

Evolution of inspiratory muscle function in children during mechanical ventilation

BACKGROUND

There is no universally accepted method to assess the pressure-generating capacity of inspiratory muscles in children on mechanical ventilation (MV), and no study describing its evolution over time in this population.

METHODS

In this prospective observational study, we have assessed the function of the inspiratory muscles in children on various modes of MV. During brief airway occlusion maneuvers, we simultaneously recorded airway pressure depression at the endotracheal tube (ΔPaw, force generation) and electrical activity of the diaphragm (EAdi, central respiratory drive) over five consecutive inspiratory efforts. The neuro-mechanical efficiency ratio (NME, ΔPaw/EAdimax) was also computed. The evolution over time of these indices in a group of children in the pediatric intensive care unit (PICU) was primarily described. As a secondary objective, we compared these values to those measured in a group of children in the operating room (OR).

RESULTS

In the PICU group, although median NMEoccl decreased over time during MV (regression coefficient - 0.016, p = 0.03), maximum ΔPawmax remained unchanged (regression coefficient 0.109, p = 0.50). Median NMEoccl at the first measurement in the PICU group (after 21 h of MV) was significantly lower than at the only measurement in the OR group (1.8 cmH2O/µV, Q1-Q3 1.3-2.4 vs. 3.7 cmH2O/µV, Q1-Q3 3.5-4.2; p = 0.015). Maximum ΔPawmax in the PICU group was, however, not significantly different from the OR group (35.1 cmH2O, Q1-Q3 21-58 vs. 31.3 cmH2O, Q1-Q3 28.5-35.5; p = 0.982).

CONCLUSIONS

The function of inspiratory muscles can be monitored at the bedside of children on MV using brief airway occlusions. Inspiratory muscle efficiency was significantly lower in critically ill children than in children undergoing elective surgery, and it decreased over time during MV in critically ill children. This suggests that both critical illness and MV may have an impact on inspiratory muscle efficiency.

Prolonged Weaning: S2k Guideline Published by the German Respiratory Society

Mechanical ventilation (MV) is an essential part of modern intensive care medicine. MV is performed in patients with severe respiratory failure caused by respiratory muscle insufficiency and/or lung parenchymal disease; that is, when other treatments such as medication, oxygen administration, secretion management, continuous positive airway pressure (CPAP), or nasal high-flow therapy have failed. MV is required for maintaining gas exchange and allows more time to curatively treat the underlying cause of respiratory failure. In the majority of ventilated patients, liberation or "weaning" from MV is routine, without the occurrence of any major problems. However, approximately 20% of patients require ongoing MV, despite amelioration of the conditions that precipitated the need for it in the first place. Approximately 40-50% of the time spent on MV is required to liberate the patient from the ventilator, a process called "weaning". In addition to acute respiratory failure, numerous factors can influence the duration and success rate of the weaning process; these include age, comorbidities, and conditions and complications acquired during the ICU stay. According to international consensus, "prolonged weaning" is defined as the weaning process in patients who have failed at least 3 weaning attempts, or require more than 7 days of weaning after the first spontaneous breathing trial (SBT). Given that prolonged weaning is a complex process, an interdisciplinary approach is essential for it to be successful. In specialised weaning centres, approximately 50% of patients with initial weaning failure can be liberated from MV after prolonged weaning. However, the heterogeneity of patients undergoing prolonged weaning precludes the direct comparison of individual centres. Patients with persistent weaning failure either die during the weaning process, or are discharged back to their home or to a long-term care facility with ongoing MV. Urged by the growing importance of prolonged weaning, this Sk2 Guideline was first published in 2014 as an initiative of the German Respiratory Society (DGP), in conjunction with other scientific societies involved in prolonged weaning. The emergence of new research, clinical study findings and registry data, as well as the accumulation of experience in daily practice, have made the revision of this guideline necessary. The following topics are dealt with in the present guideline: Definitions, epidemiology, weaning categories, underlying pathophysiology, prevention of prolonged weaning, treatment strategies in prolonged weaning, the weaning unit, discharge from hospital on MV, and recommendations for end-of-life decisions. Special emphasis was placed on the following themes: (1) A new classification of patient sub-groups in prolonged weaning. (2) Important aspects of pulmonary rehabilitation and neurorehabilitation in prolonged weaning. (3) Infrastructure and process organisation in the care of patients in prolonged weaning based on a continuous treatment concept. (4) Changes in therapeutic goals and communication with relatives. Aspects of paediatric weaning are addressed separately within individual chapters. The main aim of the revised guideline was to summarize both current evidence and expert-based knowledge on the topic of "prolonged weaning", and to use this information as a foundation for formulating recommendations related to "prolonged weaning", not only in acute medicine but also in the field of chronic intensive care medicine. The following professionals served as important addressees for this guideline: intensivists, pulmonary medicine specialists, anaesthesiologists, internists, cardiologists, surgeons, neurologists, paediatricians, geriatricians, palliative care clinicians, rehabilitation physicians, intensive/chronic care nurses, physiotherapists, respiratory therapists, speech therapists, medical service of health insurance, and associated ventilator manufacturers.

Use of Dexamethasone to Prevent Extubation Failure in Pediatric Intensive Care Unit: A Randomized Controlled Clinical Trial

Extubation failure is a common event in intensive care units. Corticosteroids are effective in preventing failure in adults, but no consensus has been reached on this matter in pediatrics. We assessed the efficacy of intravenous dexamethasone in mechanically ventilated children and adolescents for more than 48 hours, with at least one risk factor for failure. Extubations were scheduled 24 hours in advance when possible, and patients were randomly assigned into two groups: one group received a loading dose followed by up to four doses of dexamethasone, and the other group received no corticosteroids. Need for reintubation and length of stay in the pediatric intensive care unit were similar in both groups, and frequency of reintubation was 12.9%.

High Breath-by-Breath Variability Is Associated With Extubation Failure in Children

OBJECTIVES

Extubation failure is multifactorial, and most tools to assess extubation readiness only evaluate snapshots of patient physiology. Understanding variability in respiratory variables may provide additional information to inform extubation readiness assessments.

DESIGN

Secondary analysis of prospectively collected physiologic data of children just prior to extubation during a spontaneous breathing trial. Physiologic data were cleaned to provide 40 consecutive breaths and calculate variability terms, coefficient of variation and autocorrelation, in commonly used respiratory variables (i.e., tidal volume, minute ventilation, and respiratory rate). Other clinical variables included diagnostic and demographic data, median values of respiratory variables during spontaneous breathing trials, and the change in airway pressure during an occlusion maneuver to measure respiratory muscle strength (maximal change in airway pressure generated during airway occlusion [PiMax]). Multivariable models evaluated independent associations with reintubation and prolonged use of noninvasive respiratory support after extubation.

SETTING

Acute care, children's hospital.

PATIENTS

Children were included from the pediatric and cardiothoracic ICUs who were greater than 37 weeks gestational age up to and including 18 years who were intubated greater than or equal to 12 hours with planned extubation. We excluded children who had a contraindication to an esophageal catheter or respiratory inductance plethysmography bands.

INTERVENTIONS

Noninterventional study.

MEASUREMENTS AND MAIN RESULTS

A total of 371 children were included, 32 of them were reintubated. Many variability terms were associated with reintubation, including coefficient of variation and autocorrelation of the respiratory rate. After controlling for confounding variables such as age and neurologic diagnosis, both coefficient of variation of respiratory rate(p < 0.001) and low PiMax (p = 0.002) retained an independent association with reintubation. Children with either low PiMax or high coefficient of variation of respiratory rate had a nearly three-fold higher risk of extubation failure, and when these children developed postextubation upper airway obstruction, reintubation rates were greater than 30%.

CONCLUSIONS

High respiratory variability during spontaneous breathing trials is independently associated with extubation failure in children, with very high rates of extubation failure when these children develop postextubation upper airway obstruction.

Monitoring of Respiratory Muscle Function in Critically Ill Children

OBJECTIVES

This review discusses the different techniques used at the bedside to assess respiratory muscle function in critically ill children and their clinical applications.

DATA SOURCES

A scoping review of the medical literature on respiratory muscle function assessment in critically ill children was conducted using the PubMed search engine.

STUDY SELECTION

We included all scientific, peer-reviewed studies about respiratory muscle function assessment in critically ill children, as well as some key adult studies.

DATA EXTRACTION

Data extracted included findings or comments about techniques used to assess respiratory muscle function.

DATA SYNTHESIS

Various promising physiologic techniques are available to assess respiratory muscle function at the bedside of critically ill children throughout the disease process. During the acute phase, this assessment allows a better understanding of the pathophysiological mechanisms of the disease and an optimization of the ventilatory support to increase its effectiveness and limit its potential complications. During the weaning process, these physiologic techniques may help predict extubation success and therefore optimize ventilator weaning.

CONCLUSIONS

Physiologic techniques are useful to precisely assess respiratory muscle function and to individualize and optimize the management of mechanical ventilation in children. Among all the available techniques, the measurements of esophageal pressure and electrical activity of the diaphragm appear particularly helpful in the era of individualized ventilatory management.

Risk Factors for Pediatric Extubation Failure: The Importance of Respiratory Muscle Strength

OBJECTIVE

Respiratory muscle weakness frequently develops during mechanical ventilation, although in children there are limited data about its prevalence and whether it is associated with extubation outcomes. We sought to identify risk factors for pediatric extubation failure, with specific attention to respiratory muscle strength.

DESIGN

Secondary analysis of prospectively collected data.

SETTING

Tertiary care PICU.

PATIENTS

Four hundred nine mechanically ventilated children.

INTERVENTIONS

Respiratory measurements using esophageal manometry and respiratory inductance plethysmography were made preextubation during airway occlusion and on continuous positive airway pressure of 5 and pressure support of 10 above positive end-expiratory pressure 5 cm H2O, as well as 5 and 60 minutes postextubation.

MEASUREMENTS AND MAIN RESULTS

Thirty-four patients (8.3%) were reintubated within 48 hours of extubation. Reintubation risk factors included lower maximum airway pressure during airway occlusion (aPiMax) preextubation, longer length of ventilation, postextubation upper airway obstruction, high respiratory effort postextubation (pressure rate product, pressure time product, tension time index), and high postextubation phase angle. Nearly 35% of children had diminished respiratory muscle strength (aPiMax ≤ 30 cm H2O) at the time of extubation, and were nearly three times more likely to be reintubated than those with preserved strength (aPiMax > 30 cm H2O; 14% vs 5.5%; p = 0.006). Reintubation rates exceeded 20% when children with low aPiMax had moderately elevated effort after extubation (pressure rate product > 500), whereas children with preserved aPiMax had reintubation rates greater than 20% only when postextubation effort was very high (pressure rate product > 1,000). When children developed postextubation upper airway obstruction, reintubation rates were 47.4% for those with low aPiMax compared to 15.4% for those with preserved aPiMax (p = 0.02). Multivariable risk factors for reintubation included acute neurologic disease, lower aPiMax, postextubation upper airway obstruction, higher preextubation positive end-expiratory pressure, higher postextubation pressure rate product, and lower height.

CONCLUSIONS

Neuromuscular weakness at the time of extubation was common in children and was independently associated with reintubation, particularly when postextubation effort was high.

Post-extubation stridor in Respiratory Syncytial Virus bronchiolitis: Is there a role for prophylactic dexamethasone?

Aim

The purpose of this study was to determine the incidence of reintubation due to upper airway obstruction in a homogeneous group of ventilated infants with Respiratory Syncytial Virus bronchiolitis. Our secondary objective was to determine whether prophylactic administration of dexamethasone prior to extubation was associated with decreased risk of reintubation.

Methods

This retrospective observational study in two Pediatric Intensive Care Units in 2 university hospitals in The Netherlands included two hundred patients younger than 13 months admitted with respiratory insufficiency caused by Respiratory Syncytial Virus bronchiolitis, requiring invasive mechanical ventilation. A logistic regression analysis with propensity score method was used to adjust for possible confounding.

Results

Reintubation due to post-extubation stridor occurred in 17 (8.5%) of 200 patients. After propensity score matching, administration of dexamethasone prior to extubation was associated with a significantly (p = 0.0011) decreased risk of reintubation due to post-extubation stridor compared to patients not receiving prophylactic dexamethasone (absolute risk reduction 13%, 95% CI 5.3–21%).

Conclusion

Reintubation due to post-extubation stridor is an important complication of ventilation for Respiratory Syncytial Virus bronchiolitis. Dexamethasone administered prior to extubation probably reduces the risk of post-extubation stridor necessitating reintubation in these infants. The results of this study support initiation of a placebo-controlled trial to confirm the beneficial effect of prophylactic dexamethasone.

Monitoring of children with pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference

OBJECTIVE

To critically review the potential role of monitoring technologies in the management of pediatric acute respiratory distress syndrome, and specifically regarding monitoring of the general condition, respiratory system mechanics, severity scoring parameters, imaging, hemodynamic status, and specific weaning considerations.

DESIGN

Consensus conference of experts in pediatric acute lung injury.

METHODS

A panel of 27 experts met over the course of 2 years to develop a taxonomy to define pediatric acute respiratory distress syndrome and to make recommendations regarding treatment and research priorities. The monitoring subgroup comprised two experts. When published data were lacking a modified Delphi approach, emphasizing strong professional agreement was used.

RESULTS

The Pediatric Acute Lung Injury Consensus Conference experts developed and voted on a total of 151 recommendations addressing the topics related to pediatric acute respiratory distress syndrome, 21 of which related to monitoring of a child with pediatric acute respiratory distress syndrome. All 21 recommendations had agreement, with 19 (90%) reaching strong agreement.

CONCLUSIONS

The Consensus Conference developed pediatric-specific recommendations related to monitoring children with pediatric acute respiratory distress syndrome. These include interpreting monitored values such as tidal volume using predicted body weight, monitoring tidal volume at the end of the endotracheal tube in small children, and continuous monitoring of exhaled carbon dioxide in intubated children with pediatric acute respiratory distress syndrome, among others. These recommendations for monitoring in pediatric acute respiratory distress syndrome are intended to promote optimization and consistency of care for children with pediatric acute respiratory distress syndrome and identify areas of uncertainty requiring further investigation.

Weaning from mechanical ventilation in paediatrics. State of the art

Weaning from mechanical ventilation is one of the greatest volume and strength issues in evidence-based medicine in critically ill adults. In these patients, weaning protocols and daily interruption of sedation have been implemented, reducing the duration of mechanical ventilation and associated morbidity. In paediatrics, the information reported is less consistent, so that as yet there are no reliable criteria for weaning and extubation in this patient group. Several indices have been developed to predict the outcome of weaning. However, these have failed to replace clinical judgement, although some additional measurements could facilitate this decision.

Predictive value of bronchoscopy after infant cardiac surgery: a prospective study

BACKGROUND AND AIMS

Airway evaluation following infant cardiac surgery often reveals evidence of tracheobronchial narrowing. We studied the association between airway narrowing and extubation failure (EF) in this population.

METHODS

Prospective cohort study of infants (age ≤6 months) from March-September 2009. Flexible bronchoscopy (FB) evaluations were obtained using a standardised protocol after operative intervention. The primary endpoint was the development of extubation failure (EF; defined as the need for invasive mechanical ventilation ≤48 h after primary extubation) and several secondary endpoints.

RESULTS

Fifty-three patients were evaluated at a median age of 81 [interquartile range (IQR) 13-164] days and weight of 4.2 (IQR 3.2-6.0) kg; 13 (25 %) of the patients had single ventricle palliations and two subsequently underwent heart transplantation. Significant airway narrowing was noted in 15 of 30 [50 %, 95 % confidence interval (CI) 31-69 %] patients who underwent FB; ten of the 53 patients (19 %, 95 %CI 10-32 %) subsequently developed EF. Narrowed airway calibre on bronchoscopy had a sensitivity and specificity of 50 % (95 %CI 28-71 %) and 50 % (95 %CI 28-71 %), respectively, for EF. The single greatest predictor of EF by univariate analysis was the need for preoperative ventilation [odds ratio (OR) 6.5, 95 %CI 1.3-33.2, p = 0.03]. Patients with EF had a greater likelihood of intensive care readmission (OR 4.8, 95 %CI 1.1-21, p < 0.04) during the same hospital admission.

CONCLUSIONS

Airway narrowing on FB is noted frequently after infant cardiac surgery. Overall assessment and presence of narrowing on bronchoscopy had poor sensitivity and specificity for EF in our cohort. Expert assessment of tracheobronchial narrowing on FB has poor to moderate inter-rater reliability.

[Weaning from invasive mechanical ventilation in pediatric patients (excluding premature neonates)]

The process of weaning from mechanical ventilation (WMV) is the same in children as in adults. In the pediatric literature, weaning failure rate ranges from 1.4 to 34%. So far, no indices of weaning success have been demonstrated to be sufficiently accurate. The criteria for assessing readiness to wean, which must be screened daily, have neither been validated nor adapted to the pediatric population. The spontaneous breathing test (SBT), the reference screening test for weaning, precedes extubation; it can be achieved with pressure support ventilation or spontaneous breathing (T piece or canopy or flow-inflating bag). A standardized weaning protocol (which can be computer driven) was used in only three pediatric studies and the impact on shortening the duration of mechanical ventilation has not yet been demonstrated. It should be paired with a sedative interruption protocol. Weaning criteria, SBT criteria, and/or protocol tolerance are guides, but clinicians must individualize decisions to use these criteria. The use of noninvasive ventilation is increasing and its place in weaning protocols for children needs to be determined; it might modify the definitions of weaning failure and weaning success in the future.

Tension-time index as a predictor of extubation outcome in ventilated children

RATIONALE

Indices that assess the load on the respiratory muscles, such as the tension-time index (TTI), may predict extubation outcome.

OBJECTIVES

To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children.

METHODS

Eighty children (median [range] age 2.1 yr [0.15-16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied.

MEASUREMENTS AND MAIN RESULTS

TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n = 80) and TTdi greater than 0.15 (n = 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well.

CONCLUSIONS

Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.

Does taking endurance into account improve the prediction of weaning outcome in mechanically ventilated children?

INTRODUCTION

We conducted the present study to determine whether a combination of the mechanical ventilation weaning predictors proposed by the collective Task Force of the American College of Chest Physicians (TF) and weaning endurance indices enhance prediction of weaning success.

METHOD

Conducted in a tertiary paediatric intensive care unit at a university hospital, this prospective study included 54 children receiving mechanical ventilation (> or = 6 hours) who underwent 57 episodes of weaning. We calculated the indices proposed by the TF (spontaneous respiratory rate, paediatric rapid shallow breathing, rapid shallow breathing occlusion pressure [ROP] and maximal inspiratory pressure during an occlusion test [Pimax]) and weaning endurance indices (pressure-time index, tension-time index obtained from P(0.1) [TTI1] and from airway pressure [TTI2]) during spontaneous breathing. Performances of each TF index and combinations of them were calculated, and the best single index and combination were identified. Weaning endurance parameters (TTI1 and TTI2) were calculated and the best index was determined using a logistic regression model. Regression coefficients were estimated using the maximum likelihood ratio (LR) method. Hosmer-Lemeshow test was used to estimate goodness-of-fit of the model. An equation was constructed to predict weaning success. Finally, we calculated the performances of combinations of best TF indices and best endurance index.

RESULTS

The best single TF index was ROP, the best TF combination was represented by the expression (0.66 x ROP) + (0.34 x Pimax), and the best endurance index was the TTI2, although their performance was poor. The best model resulting from the combination of these indices was defined by the following expression: (0.6 x ROP) - (0.1 x Pimax) + (0.5 x TTI2). This integrated index was a good weaning predictor (P < 0.01), with a LR+ of 6.4 and LR+/LR- ratio of 12.5. However, at a threshold value < 1.3 it was only predictive of weaning success (LR- = 0.5).

CONCLUSION

The proposed combined index, incorporating endurance, was of modest value in predicting weaning outcome. This is the first report of the value of endurance parameters in predicting weaning success in children. Currently, clinical judgement associated with spontaneous breathing trials apparently remain superior.

Twitch airway pressure elicited by magnetic phrenic nerve stimulation in anesthetized healthy children

Children with diaphragm dysfunction may be unable to maintain adequate ventilation. Accurate diagnosis is important, but can only be achieved using an appropriate test and reference range. The aim of this study, therefore, was to measure diaphragm contractility and examine the influence of age and maturation, using magnetic phrenic nerve stimulation in healthy children. Anterolateral magnetic stimulation (MS) of the phrenic nerves was performed using a 43-mm figure-eight coil in 23 children (14 male; mean age, 7.8 years; range, 1.8-15.7) anesthetized for minor surgery with sevoflurane gas. The airway was maintained with a cuffed laryngeal mask airway (LMA) which was briefly occluded during MS. Diaphragm contractility was assessed by measuring the airway pressure (TwPaw) elicited by MS. TwPaw responses were obtained in all subjects, with mean (SD) TwPaw 18.2 (6.8) cm H2O bilateral, 7.3 (3.2) cm H2O left unilateral, and 8.6 (3.1) cm H2O right unilateral. Subgroup analysis was performed in 17 of the children who were prepubertal. Their mean (SD) TwPaw was 17.3 (6.8) cm H2O bilateral, 7.1 (3.7) cm H2O left unilateral, and 8.3 (3.3) right unilateral. The mean (SD) intrapatient coefficients of variation for bilateral and left and right unilateral TwPaw were 8.4% (5.2), 6.7% (3.5), and 11.7% (10.3), respectively. Bilateral and left and right unilateral TwPaw were significantly related to age (P < 0.05). In healthy prepubertal children, diaphragm contractility is primarily influenced by age.

Extubation failure in pediatric intensive care incidence and outcomes

OBJECTIVES

To evaluate the hypotheses that children requiring reintubation are at an increased risk of prolonged hospitalizations, congenital heart disease, and death compared with age- and disease-severity-matched control patients.

DESIGN

Prospective decision to evaluate all children undergoing extubation over a 5-yr time interval (1997-2001) with retrospective analysis of all failed extubation patients.

SETTING

A large multidisciplinary, dual-site, single-system pediatric intensive care unit caring for critically ill and injured children.

PATIENTS

All children intubated and ventilated during the study period (1997-2001).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Failed extubation was defined as the unanticipated requirement to replace an endotracheal tube within 48 hrs of extubation. One hundred thirty children of 3,193 pediatric intensive care unit patients failed extubation (4.1%). The median age of children who failed extubation was 6.5 months, compared with a median age of 21.3 months in the control population. The median age of failed extubation in children with cardiac disease was 9.3 months. Failed extubation patients had lengthier hospital and pediatric intensive care unit stays, longer duration of mechanical ventilation, and a higher rate of tracheostomy placement than nonfailed extubation patients (p < .001). Children with congenital heart disease who failed extubation had the longest duration of hospitalization (40.0 +/- 5.4 days). Conversely, cardiac patients who did not fail extubation had the shortest length of stay (11.2 +/- 0.4 days).

CONCLUSIONS

In the present trial, 4.1% of mechanically ventilated children failed extubation. Pediatric intensive care unit patients with failed extubation have longer hospital, pediatric intensive care unit, and ventilator courses but are not at increased risk of death relative to nonfailed extubation patients.

Extubation failure in pediatric intensive care: A multiple-center study of risk factors and outcomes

OBJECTIVE

To determine a contemporary failed extubation rate, risk factors, and consequences of extubation failure in pediatric intensive care units (PICUs). Three hypotheses were investigated: a) Extubation failure is in part disease specific; b) preexisting respiratory conditions predispose to extubation failure; and c) admission acuity scoring does not affect extubation failure.

DESIGN

Twelve-month prospective, observational, clinical study.

SETTING

Sixteen diverse PICUs in the United States.

PATIENTS

Patients were 2,794 patients from the newborn period to 18 yrs of age experiencing a planned extubation trial.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A descriptive statistical analysis was performed, and outcome differences of the failed extubation population were determined. The extubation failure rate was 6.2% (174 of 2,794; 95% confidence interval, 5.3-7.1). Patient features associated with extubation failure (p <.05) included age < or =24 months; dysgenetic condition; syndromic condition; chronic respiratory disorder; chronic neurologic condition; medical or surgical airway condition; chronic noninvasive positive pressure ventilation; the need to replace the endotracheal tube on admission to the PICU; and the use of racemic epinephrine, steroids, helium-oxygen therapy (heliox), or noninvasive positive pressure ventilation within 24 hrs of extubation. Patients failing extubation had longer pre-extubation intubation time (failed, 148.7 hrs, SD +/- 207.8 vs. success, 107.9 hrs, SD +/- 171.3; p <.001), longer PICU length of stay (17.5 days, SD +/- 15.6 vs. 7.6 days, SD +/- 11.1; p <.001), and a higher mortality rate than patients not failing extubation (4.0% vs. 0.8%; p <.001). Failure was found to be in part disease specific, and preexisting respiratory conditions were found to predispose to failure whereas admission acuity did not.

CONCLUSION

A variety of patient features are associated with an increase in extubation failure rate, and serious outcome consequences characterize the extubation failure population in PICUs.

Monitorización de la función respiratoria en el niño con ventilación mecánica (II): complianza, resistencia, hiperinsuflación dinámica, espacio muerto y trabajo respiratorio

Several parameters can be used to study respiratory mechanics in children on mechanical ventilation. Compliance is a measure of the distensibility of the respiratory system. In mechanical ventilation two measures of compliance can be used. Static compliance (pulmonary distensibility) can be measured in volume modes by the application of an inspiratory pause with the respiratory system at rest (sedated patients without inspiratory effort). Dynamic compliance does not require an inspiratory pause and the respiratory system need not be at rest. Compliance can be calculated numerically or expressed graphically in the volume-pressure curve. Many respirators can calculate inspiratory and expiratory airway resistance (including endotracheal tube resistance). Several measures can be used to detect dynamic hyperinflation (intrinsic PEEP, auto-PEEP, trapped air volume) after application of an expiratory pause. The latest respirators can perform these measurements almost automatically. Work of breathing and respiratory effort can also be analyzed by measuring several parameters (pressure-time product, imposed work of breathing, P 0.1, maximum inspiratory pressure). However, these measures have not yet been standardized in children.