Magnetic phrenic nerve stimulation to assess diaphragm function in children following liver transplantation

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.

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.

Respiratory muscle assessment in acute exacerbation of chronic obstructive pulmonary disease and its role as a potential biomarker

BACKGROUND

AECOPD is a life threatening condition for patients with chronic obstructive pulmonary disease (COPD) and lack of specific biomarker hinders effective management. Sputum, blood, breath and urinary biomarkers have all been investigated. We measured maximum respiratory pressure post exacerbation once the patient was compliant with the test and after 6 weeks, to assess any correlations.

METHODS AND RESULTS

The maximum pressures were measured using a closed circuit spirometer with a clean rubber mouthpiece properly placed with the patients lips sealed around it. Patients were properly instructed to exhale slowly and completely, then inspire with maximum possible effort and advised to keep it for nearly 1.5 s for maximum inspiratory pressure (MIP). For maximum expiratory pressures (MEP) patients were instructed to inspire slowly and completely, then expire forcefully with maximum effort. With the recorded values TTI (time tension index) was calculated. This was repeated again after 6 weeks. Using Pearsons correlation coefficient we found that MIP had a negative correlation with TTI and a positive correlation with FEV1. FEV1 had a positive correlation with FVC. MEP showed no significant correlation with TTI, but a positive correlation with FEV1.

CONCLUSION

Acute exacerbations of COPD has a profound effect on the respiratory musculature especially the expiratory muscles but the maximum pressures are not specific enough to be prognostic markers. It might be worthwhile studying transformations of the respiratory musculature at the molecular level. More studies must be conducted to find a specific marker to aid in the management of the condition.

Paralysis in the left phrenic nerve after living-donor liver transplantation for biliary atresia with situs inversus

A 7-month-old boy with biliary atresia accompanied by situs inversus and absent inferior vena cava (IVC) underwent living-donor liver transplantation (LDLT). Because a constriction in the recipient hepatic vein (HV) was detected during the preparation of the HV in LDLT, a dissection in the cranial direction and a total clamp of the suprahepatic IVC was performed, and the suprahepatic IVC and the graft HV were anastomosed end-to-end. Postoperatively, atelectasis in the left upper lobe and ventilator failure accompanied by an elevation of the left hemidiaphragm were observed and mechanical ventilation was repetitively required. Paralysis in the left phrenic nerve was diagnosed by chest radiograph and ultrasonography. In our patient, conservative treatment was administrated, because weaning him from mechanical ventilation was possible a few days after intubation and the ventilator function was expected to be improved with growth. The disease course was good, and he was discharged from the hospital at 78 days after LDLT. Complications of paralysis in the phrenic nerve after cadaveric liver transplantation have been reported to be high. Although using a conventional technique during the reconstruction of the HV may injure the phrenic nerve directly, use of the piggyback technique with preservation of the IVC is rare. Even if LDLT was undertaken, a dissection of the HV or a total clamp of the suprahepatic IVC as a conventional technique can directly injure the phrenic nerve. Therefore, a dissection of the HV or a total clamp of the suprahepatic IVC at the reconstruction of the HV in LDLT should be carefully performed, and the possibility of paralysis in the phrenic nerve should be considered in patients with a relapse of respiratory symptoms and an elevation of the hemidiaphragm after LDLT.

Weaning Strategies in Problem Patients

Weaning usually accounts for approximately 40–50% of the total duration of mechanical ventilation. Approximately two-thirds of patients can tolerate withdrawal of ventilation without the need for more gradual weaning, but there are a significant number of patients for whom weaning is difficult. Weaning failure is defined as the failure of a spontaneous breathing trial, or the need for re-intubation within 48 hours of extubation. This article reviews the causes of failure to wean, and outlines a practical approach to dealing with the difficult-to-wean patient. The key to successful weaning combines an approach which optimises ventilation at night, adopts a stepwise approach to reducing ventilatory dependence during the day, and uses non-invasive ventilation as a ‘bridge’ out of the ICU. Having a weaning protocol and ensuring it is initiated in a timely manner is likely to be as important as what is in the protocol.

Use of non-invasive-stimulated muscle force assessment in long-term critically ill patients: a future standard in the intensive care unit?

BACKGROUND

This study's main purpose was to test the feasibility of employing a non-invasive-stimulated muscle force assessment approach in long-term critically ill patients.

METHODS

A case series was performed over a 4-year period in the intensive care unit (ICU). Of the 25 patients initially recruited, eight patients required long-time mechanical ventilation for a median of 3.8 weeks (range 2-10 weeks) and were immobilized for 5 weeks (range 2-10 weeks). With a previously tested non-invasive measuring device, we weekly assessed peak torques and rates of force development and relaxation of patients' ankle dorsiflexor contractile responses, induced via peroneal nerve stimulation. Subsequently, we derived each patient's time course of observed progressive weakness and/or recovery.

RESULTS

During their critical illnesses, seven out of eight patients elicited significant decreases in measured peak torques. In survivors (n = 6) during their recovery periods, torques gradually recovered. In the two patients who died, their strengths decreased continuously until death. The rate of force development data elicited similar trends as peak torque responses, whereas relative relaxation rates differed more widely between individuals.

CONCLUSION

This approach of non-invasive-stimulated muscle force assessment can be used in long-term critically ill patients and may eventually become a standard in the intensive care unit, e.g. for assessing recovery. This method is easy to employ, reproducible, provides important phenotypic quantification of skeletal muscle contractile function, and can be used for long-term outcomes assessment.

Noninvasive positive pressure ventilation: five years of experience in a pediatric intensive care unit

OBJECTIVES

To evaluate the feasibility and outcome of noninvasive positive pressure ventilation (NPPV) in daily clinical practice.

DESIGN

Observational retrospective cohort study.

SETTING

Pediatric intensive care unit in a university hospital.

PATIENTS

: Patients treated by NPPV, regardless of the indication, during five consecutive years (2000-2004).

MEASUREMENTS AND RESULTS

A total of 114 patients were included, and 83 of the 114 patients (77%) were successfully treated by NPPV without intubation (NPPV success group). The success rate of NPPV was significantly lower (22%) in the patients with acute respiratory distress syndrome (p < .05) than in the other patients. The Pediatric Risk of Mortality II (p = .003) and Pediatric Logistic Organ Dysfunction scores (p = .002) at admission were significantly higher in patients who were unsuccessfully treated with NPPV (NPPV failure group). Baseline values of Pco2, pulse oximetry, and respiratory rate did not differ between the two groups. A significant decrease in Pco2 and respiratory rate within the first 2 hrs of NPPV was observed in the NPPV success group. Multivariate analysis showed that a diagnosis of acute respiratory distress syndrome (odds ratio, 76.8; 95% confidence interval, 4.4-1342; p = .003) and a high Pediatric Logistic Organ Dysfunction score (odds ratio, 1.09; 95% confidence interval, 1.01-1.17; p = .01) were independent predictive factors for NPPV failure. A total of 11 patients (9.6%), all belonging to the NPPV failure group, died during the study.

CONCLUSIONS

This study demonstrates the feasibility and efficacy of NPPV in the daily practice of a pediatric intensive care unit. This ventilatory support could be proposed as a first-line treatment in children with acute respiratory distress, except in those with a diagnosis of acute respiratory distress syndrome.

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.

Nutritional status is an important predictor of diaphragm strength in young patients with cystic fibrosis

BACKGROUND

The effect of nutritional status and lung disease progression on diaphragm strength in young patients with cystic fibrosis remains unclear.

OBJECTIVE

The aim of this study was to investigate the effect of nutritional status and airway obstruction on diaphragm strength.

DESIGN

Twitch transdiaphragmatic pressure (Tw Pdi) obtained by bilateral anterior magnetic phrenic nerve stimulation, body mass index (BMI) z score, fat mass, fat-free mass (FFM), arm muscle circumference (AMC), forced expiratory volume in 1 s (FEV(1)), and functional residual capacity (FRC) were measured in 20 patients aged 15.1 +/- 2.8 y (x +/- SD). Values were expressed as a percentage of predicted values.

RESULTS

Mean (+/-SD) Tw Pdi was 24.3 +/- 5.5 cm H(2)O. Univariate regression analysis showed positive correlations between Tw Pdi and nutrition scores (BMI z score: r = 0.63, P = 0.003; FFM: r = 0.47, P = 0.04; AMC: r = 0.45, P = 0.04), airway obstruction (FEV(1): r = 0.68, P = 0.001), and arterial oxygen partial pressure (r = 0.68, P = 0.001). Negative correlations were observed between Tw Pdi and dynamic hyperinflation (FRC: r = -0.65, P = 0.005) and arterial carbon dioxide pressure (r = -0.50, P = 0.03). Furthermore, stepwise regression analysis showed that Tw Pdi correlated with BMI z score (r = 0.75, P = 0.0002) and FEV(1) (r = 0.69, P = 0.001).

CONCLUSIONS

Diaphragm strength is relatively well preserved in young patients with cystic fibrosis. However, the strength of the diaphragm decreases with the progression of malnutrition and airway obstruction.

Respiratory muscle testing in children

The range of techniques available to assess respiratory muscles weakness has greatly expanded over recent years. Respiratory muscle tests can be divided into non-invasive tests, such as lung function parameters, maximal static pressures and sniff nasal pressure and invasive tests, such as transdiaphragmatic pressures during crying, maximal static pressures and magnetic stimulation of the phrenic nerves. Sniff nasal pressure and magnetic stimulation should have increasing relevance in children in the coming years. However, probably the most important message is to arrange for the evaluation of respiratory muscles in children with unexplained or disproportionate breathlessness such as in patients with neuromuscular diseases. Improvements are needed to evaluate respiratory muscle endurance in children, which is more difficult but complementary to the assessment of respiratory muscle strength.