Marc van Heerde

Imposed work of breathing during high-frequency oscillatory ventilation: a bench study

IntroductionThe ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators.MethodsA computer-controlled piston-driven test lung was used to simulate a spontaneously breathing patient. The test lung was connected to a high-frequency oscillatory ventilation (HFOV) ventilator by an endotracheal tube. The inspiratory and expiratory airway flows and pressures at various places were sampled. The spontaneous breath rate and volume, tube size and ventilator settings were simulated as representative of the newborn to adult range. The fresh gas flow rate was set at a low and a high level. The imposed WOB was calculated using the Campbell diagram.ResultsIn the simulations for newborns (assumed body weight 3.5 kg) and infants (assumed body weight 10 kg) the imposed WOB (mean ± standard deviation) was 0.22 ± 0.07 and 0.87 ± 0.25 J/l, respectively. Comparison of the imposed WOB in low and high fresh gas flow rate measurements yielded values of 1.63 ± 0.32 and 0.96 ± 0.24 J/l (P = 0.01) in small children (assumed body weight 25 kg), of 1.81 ± 0.30 and 1.10 ± 0.27 J/l (P < 0.001) in large children (assumed body weight 40 kg), and of 1.95 ± 0.31 and 1.12 ± 0.34 J/l (P < 0.01) in adults (assumed body weight 70 kg). High peak inspiratory flow and low fresh gas flow rate significantly increased the imposed WOB. Mean airway pressure in the breathing circuit decreased dramatically during spontaneous breathing, most markedly at the low fresh gas flow rate. This led to ventilator shut-off when the inspiratory flow exceeded the fresh gas flow.ConclusionSpontaneous breathing during HFOV resulted in considerable imposed WOB in pediatric and adult simulations, explaining the discomfort seen in those patients breathing spontaneously during HFOV. The level of imposed WOB was lower in the newborn and infant simulations, explaining why these patients tolerate spontaneous breathing during HFOV well. A high fresh gas flow rate reduced the imposed WOB. These findings suggest the need for a demand flow system based on patient need allowing spontaneous breathing during HFOV.

Talking With Parents About End-of-Life Decisions for Their Children

BACKGROUND AND OBJECTIVE: Retrospective studies show that most parents prefer to share in decisions to forgo life-sustaining treatment (LST) from their children. We do not yet know how physicians and parents communicate about these decisions and to what extent parents share in the decision-making process. METHODS: We conducted a prospective exploratory study in 2 Dutch University Medical Centers. RESULTS: Overall, 27 physicians participated, along with 37 parents of 19 children for whom a decision to withhold or withdraw LST was being considered. Forty-seven conversations were audio recorded, ranging from 1 to 8 meetings per patient. By means of a coding instrument we quantitatively and qualitatively analyzed physicians’ and parents’ communicative behaviors. On average, physicians spoke 67% of the time, parents 30%, and nurses 3%. All physicians focused primarily on providing medical information, explaining their preferred course of action, and informing parents about the decision being reached by the team. Only in 2 cases were parents asked to share in the decision-making. Despite their intense emotions, most parents made great effort to actively participate in the conversation. They did this by asking for clarifications, offering their preferences, and reacting to the decision being proposed (mostly by expressing their assent). In the few cases where parents strongly preferred LST to be continued, the physicians either gave parents more time or revised the decision. CONCLUSIONS: We conclude that parents are able to handle a more active role than they are currently being given. Parents’ greatest concern is that their child might suffer.

Perceptions of parents on satisfaction with care in the pediatric intensive care unit: the EMPATHIC study

PurposeTo identify parental perceptions on pediatric intensive care-related satisfaction items within the framework of developing a Dutch pediatric intensive care unit (PICU) satisfaction instrument.MethodsProspective cohort study in tertiary PICUs at seven university medical centers in The Netherlands.ParticipantsParents of 1,042 children discharged from a PICU.ResultsA 78-item questionnaire was sent to 1,042 parents and completed by 559 (54%). Seventeen satisfaction items were rated with mean scores <8.0 (1, completely unimportant, to 10, very important) with standard deviations ≥1.65, and thus considered of limited value. The empirical structure of the items was in agreement with the theoretically formulated domains: Information, Care and Cure, Organization, Parental Participation, and Professional Attitude. The Cronbach’s α of the domains ranged between 0.87 and 0.94.ConclusionsParental perceptions on satisfaction with care measures were identified and prioritized. Reliabilities of the items and domains were of high level.

Tidal Volume and Mortality in Mechanically Ventilated Children: A Systematic Review and Meta-Analysis of Observational Studies

Objective:To determine whether tidal volume is associated with mortality in critically ill, mechanically ventilated children. Data Sources:MEDLINE, EMBASE, and CINAHL databases from inception until July 2013 and bibliographies of included studies without language restrictions. Study Selection:Randomized clinical trials and observational studies reporting mortality in mechanically ventilated PICU patients. Data Extraction:Two authors independently selected studies and extracted data on study methodology, quality, and patient outcomes. Meta-analyses were performed using the Mantel-Haenszel random-effects model. Heterogeneity was quantified using I2. Study quality was assessed using the Newcastle-Ottawa Score for cohort studies. Data Synthesis:Out of 142 citations, seven studies met the inclusion criteria, and additional two articles were identified from references of the found articles. One was excluded. These eight studies included 1,756 patients. Mortality rates ranged from 13% to 42%. There was no association between tidal volume and mortality when tidal volume was dichotomized at 7, 8, 10, or 12 mL/kg. Comparing patients ventilated with tidal volume less than 7 mL/kg and greater than 10 mL/kg or greater than 12 mL/kg and tidal volume less than 8 mL/kg and greater than 10 mL/kg or greater than 12 mL/kg also showed no association between tidal volume and mortality. Limiting the analysis to patients with acute lung injury/acute respiratory distress syndrome did not change these results. Heterogeneity was observed in all pooled analyses. Conclusions:A relationship between tidal volume and mortality in mechanically ventilated children could not be identified, irrespective of the severity of disease. The significant heterogeneity observed in the pooled analyses necessitates future studies in well-defined patient populations to understand the effects of tidal volume on patient outcome.

Heliox reduces respiratory system resistance in respiratory syncytial virus induced respiratory failure

IntroductionRespiratory syncytial virus (RSV) lower respiratory tract disease is characterised by narrowing of the airways resulting in increased airway resistance, air-trapping and respiratory acidosis. These problems might be overcome using helium-oxygen gas mixture. However, the effect of mechanical ventilation with heliox in these patients is unclear. The objective of this prospective cross-over study was to determine the effects of mechanical ventilation with heliox 60/40 versus conventional gas on respiratory system resistance, air-trapping and CO2 removal.MethodsMechanically ventilated, sedated and paralyzed infants with proven RSV were enrolled within 24 hours after paediatric intensive care unit (PICU)admission. At T = 0, respiratory system mechanics including respiratory system compliance and resistance, and peak expiratory flow rate were measured with the AVEA ventilator. The measurements were repeated at each interval (after 30 minutes of ventilation with heliox, after 30 minutes of ventilation with nitrox and again after 30 minutes of ventilation with heliox). Indices of gas exchange (ventilation and oxygenation index) were calculated at each interval. Air-trapping (defined by relative change in end-expiratory lung volume) was determined by electrical impedance tomography (EIT) at each interval.ResultsThirteen infants were enrolled. In nine, EIT measurements were performed. Mechanical ventilation with heliox significantly decreased respiratory system resistance. This was not accompanied by an improved CO2 elimination, decreased peak expiratory flow rate or decreased end-expiratory lung volume. Importantly, oxygenation remained unaltered throughout the experimental protocol.ConclusionsRespiratory system resistance is significantly decreased by mechanical ventilation with heliox (ISCRTN98152468).

Reflections on Pediatric High-Frequency Oscillatory Ventilation From a Physiologic Perspective

Mechanical ventilation using low tidal volumes has become universally accepted to prevent ventilator-induced lung injury. High-frequency oscillatory ventilation (HFOV) allows pulmonary gas exchange using very small tidal volume (1–2 mL/kg) with concomitant decreased risk of atelectrauma. However, its use in pediatric critical care varies between only 3% and 30% of all ventilated children. This might be explained by the fact that the beneficial effect of HFOV on patient outcome has not been ascertained. Alternatively, in contrast with present recommendations, one can ask if HFOV has been employed in its most optimal fashion related especially to the indications for and timing of HFOV, as well as to using the best oscillator settings. The first was addressed in one small randomized study showing that early use of HFOV, instead of rescue use, was associated with improved survival. From a physiologic perspective, the oscillator settings could be refined. Lung volume is the main determinant of oxygenation in diffuse alveolar disease, suggesting using an open-lung strategy by recruitment maneuvers, although this is in practice not custom. Using such an approach, the patient can be oscillated on the deflation limb of the pressure-volume (P-V) curve, allowing less pressure required to maintain a certain amount of lung volume. Gas exchange is determined by the frequency and the oscillatory power setting, controlling the magnitude of the membrane displacement. Experimental work as well as preliminary human data have shown that it is possible to achieve the smallest tidal volume with concomitant adequate gas exchange when oscillating at high frequency and high fixed power setting. Future studies are needed to validate these novel approaches and to evaluate their effect on patient outcome.

Incidence and risk factors of prolonged mechanical ventilation in neuromuscular scoliosis surgery.

Patients with neuromuscular scoliosis (NMS) are frequently considered at high risk for postoperative complications based on their underlying disease and comorbidities. Postoperative complications include prolonged mechanical ventilation (MV), defined longer than 72 h, at the paediatric intensive care unit. The objectives of this retrospective study were to assess the incidence of prolonged MV in patients with NMS following scoliosis surgery and to identify predictive risk factors. A total of 46 consecutive patients underwent surgical spinal fusion and instrumentation for progressive NMS. Prolonged MV was required in seven of 46 patients (15%). The only risk factor for prolonged MV was a decreased preoperative pulmonary function. Forced expired volume in 1 s and vital capacity were significantly decreased in patients with MV >72 h compared with patients with MV <72 h. Routine preoperative pulmonary function testing may reveal important information with regard to restrictive lung disease in the preoperative assessment of patients with NMS and predict the early postoperative clinical course.

Severe pulmonary hypertension secondary to a parachute-like mitral valve, with the left superior caval vein draining into the coronary sinus, in a girl with Turner's syndrome

A 17-year-old girl with Turners syndrome underwent two cardiac operations due to severe mitral stenosis with pulmonary hypertension, caused by a parachute-like mitral valve. The anomaly was associated with persistence of the left superior caval vein, which drained to the coronary sinus, and non-compaction of the left ventricular myocardium. The association of these lesions is rare in patients with Turners syndrome.

Demand flow facilitates spontaneous breathing during high-frequency oscillatory ventilation in a pig model.

Objective:Maintenance breathing is advocated in mechanical ventilation, which is difficult for the high-frequency oscillatory (HFO) ventilation. To facilitate spontaneous breathing during HFO ventilation, a demand flow system (DFS) was designed. The aim of the present study was to evaluate the system. Design:Animal experiment. Setting:University animal laboratory. Subjects:Eight pigs (47–64 kg). Interventions:Lung injury was induced by lung lavage with normal saline. After spontaneous breathing was restored HFO ventilation was applied, in runs of 30 minutes, with continuous fresh gas flow (CF) or the DFS operated in two different setups. Pressure to regulate the DFS was sampled directly at the Y-piece of the ventilator circuit (DFS) or between the endotracheal tube and measurement equipment at the proximal end of the endotracheal tube. In the end, animals were paralyzed. Breathing pattern, work of breathing, and gas exchange were evaluated. Measurements and Main Results:HFO ventilation with demand flow decreased breathing frequency and increased tidal volume compared with CF. Comparing HFO modes CF, DFS, and DFSPROX, total pressure–time product (PTP) was 66 cm H2O·sec·min−1 (interquartile range 59–74), 64 cm H2O·sec·min−1 (50–72), and 51 cm H2O·sec·min−1 (41–63). Ventilator PTP was 36 cm H2O·sec·min−1 (32–42), 8.6 cm H2O·sec·min−1 (7.4–10), and 1 cm H2O·sec·min−1 (−1.0 to 2.8). Oxygenation, evaluated by Pao2, was preserved when spontaneous breathing was maintained and deteriorated when pigs were paralyzed. Ventilation, evaluated by Paco2, improved with demand flow. Paco2 increased when using continuous flow and during muscular paralysis. Conclusions:In moderately lung-injured anesthetized pigs during HFO ventilation, demand flow facilitated spontaneous breathing and augmented gas exchange. Demand flow decreased total breathing effort as quantified by PTP. Imposed work caused by the HFO ventilator appeared totally reduced by demand flow.

Mechanical ventilation with heliox decreases respiratory system resistance and facilitates CO2 removal in obstructive airway disease

Sir: Helium has a density that is one-seventh that of air, resulting in a decreased resistance to gas flow allowing for increased bulk and oxygen flow. Additionally, CO2 diffuses through helium much easier than through air [1, 2]. The beneficial effect of heliox on lowering the respiratory system resistance (Rrs) has been demonstrated in a pediatric porcine model of obstructive airway disease (OAD) [3]. However, the