Diaphragmatic dysfunction in mechanical ventilation

Macronutrient and Micronutrient Intake in Children with Lung Disease

This review article aims to summarize the literature findings regarding the role of micronutrients in children with lung disease. The nutritional and respiratory statuses of critically ill children are interrelated, and malnutrition is commonly associated with respiratory failure. The most recent nutrition support guidelines for critically ill children have recommended an adequate macronutrient intake in the first week of admission due to its association with good outcomes. In children with lung disease, it is important not to exceed the proportion of carbohydrates in the diet to avoid increased carbon dioxide production and increased work of breathing, which potentially could delay the weaning of the ventilator. Indirect calorimetry can guide the process of estimating adequate caloric intake and adjusting the proportion of carbohydrates in the diet based on the results of the respiratory quotient. Micronutrients, including vitamins, trace elements, and others, have been shown to play a role in the structure and function of the immune system, antioxidant properties, and the production of antimicrobial proteins supporting the defense mechanisms against infections. Sufficient levels of micronutrients and adequate supplementation have been associated with better outcomes in children with lung diseases, including pneumonia, cystic fibrosis, asthma, bronchiolitis, and acute respiratory failure.

Is autonomic dysreflexia a cause of respiratory dysfunction after spinal cord injury?

INTRODUCTION

Spinal cord injury (SCI) often leads to impairment of the respiratory system. In fact, respiratory insufficiency is a significant cause of mortality and morbidity following SCI, related to the extent and level of the neurologic injury and its effects on the respiratory muscles (reduction in respiratory muscle strength and fatigue due to a reduction in inspiratory capacity, atelectasis and ineffective coughing). Less commonly recalled is the fact that autonomic dysreflexia (AD) is the result of parasympathetic imbalance. However, AD results from a massive, unrestrained outpouring of norepinephrine from the peripheral sympathetic ganglia. More accurately, the vagal (parasympathetic) response to this sympathetic discharge may have been responsible for the respiratory changes reported. This is not described in medical literature, although breathing difficulty is named as a common symptom and sign. The objective of this report is to describe a clinical case for the first time, that of T4 AIS (American spinal injury association impairment scale) A in which AD leads to acute respiratory insufficiency.

CASE REPORT

A patient with prior history of spinal cord injury, T4 AIS A, was admitted to the Inpatient Unit to improve her respiratory function and autonomy and to discontinue the ventilation maintained after an episode of pneumonia. The patient developed AD during the rehabilitation programme, namely during hamstring stretching exercises. Besides persistent hypertension, cutaneous rash, hyperhidrosis and light-headedness, the patient was diagnosed with acute respiratory insufficiency, with desaturation and hypercapnia. The patient fully recovered, in terms of the signs and symptoms of AD, with the cessation of noxious stimulation and oxygen administration.

DISCUSSION

To date, the association between AD and acute respiratory insufficiency has not been described in spinal cord injury or rehabilitation literature. This case draws attention for the first time to the possibility that respiratory insufficiency is one of the signs associated with episodes of AD and highlights the need to look at this possibility.

Does heart rate variability improve prediction of failed extubation in preterm infants?

Background Prematurity and its respective comorbidities may result in longer periods of mechanical ventilation in intensive care units (ICU). A method for the assessment of organic maturity would be useful for this population. Heart rate variability (HRV), as an indicator of homeostasis, is a well-established tool for this approach. The objective of the study was to assess HRV in intubated preterm infants in ICU immediately prior to extubation and correlate HRV with clinical evaluation outcomes. Methods A total of 46 preterm infants, 13 (28.2%) males, were prospectively studied and divided into a group with failed extubation (FEG: n=11) and a group with successful extubation (SEG: n=35). HRV was evaluated in time, frequency and nonlinear domains with a Polar RS800 device. HRV measurements were assessed with Kubios HRV Premium Software and statistically analyzed with the StatsDirect Statistical Software, version 1.9.2015 (2002). P<0.05 values were considered as statistically significant. Results There were no significant differences between heart rate variables of failed and successful extubation when analyzing the total group. However, the analysis of the sub-group of preterm infants weighing less than 1000 g showed a clear differentiation between the groups, when the nonlinear variables (approximate entropy, sample entropy and multiscale entropy 1, 2 and 3) were used, demonstrating that the group with successful extubation shows greater complexity and, therefore, relatively greater autonomic stability. Conclusion HRV was effective in predicting failed extubation in preterm infants when evaluated in a nonlinear domain and in preterm infants weighing less than 1000 g.

Point of care diaphragm ultrasound in infants with bronchiolitis: A prospective study

BACKGROUND

Bronchiolitis is the most common reason for hospitalization of children worldwide. Many scoring systems have been developed to quantify respiratory distress and predict outcome, but none of them have been validated. We hypothesized that the ultrasound evaluation of the diaphragm could quantify respiratory distress and therefore we correlated the ultrasound diaphragm parameters with outcome.

METHODS

Prospective study of infants with bronchiolitis (1-12 months) evaluated in a pediatric emergency department. Ultrasonography examinations of the diaphragm was performed (diaphragm excursion [DE], inspiratory excursion [IS], inspiratory/expiratory relationship [I/E], and thickness at end-expiration [TEE] and at end-inspiration [TEI]; thickening fraction [TF]).

RESULTS

We evaluated 61 infants, 50.8 % males. Mean TF was 47% (IQR 28.6-64.7), mean I/E 0.47 (± 0.15), mean DE 10.39 ± 4 mm. There was a linear correlation between TF and oxygen saturation at first evaluation (P = 0.006, r = 0.392). All children with lower values of TF required HFNC and one of them required CPAP. A higher IS was associated with the future need of respiratory support during admission (P = 0.007). IS correlated with the hours of oxygen delivery needed (P = 0.032, r = 0.422). TEI (t = 3.701, P = 0.002) was found to be main predictor of hours of oxygen delivery needed.

CONCLUSION

This study described ultrasound diaphragmatic values of previously healthy infants with bronchiolitis. DE, IS, and TEI correlated with outcome. If confirmed in larger studies, bedside ultrasound semiology of the diaphragm can be a new objective tool for the evaluation and outcome prediction of infants with bronchiolitis.

Progressive Diaphragm Atrophy in Pediatric Acute Respiratory Failure

OBJECTIVES

Diaphragm atrophy is associated with delayed weaning from mechanical ventilation and increased mortality in critically ill adults. We sought to test for the presence of diaphragm atrophy in children with acute respiratory failure.

DESIGN

Prospective, observational study.

SETTING

Single-center tertiary noncardiac PICU in a children's hospital.

PATIENTS

Invasively ventilated children with acute respiratory failure.

MEASUREMENTS AND MAIN RESULTS

Diaphragm thickness at end-expiration and end-inspiration were serially measured by ultrasound in 56 patients (median age, 17 mo; interquartile range, 5.5-52), first within 36 hours of intubation and last preceding extubation. The median duration of mechanical ventilation was 140 hours (interquartile range, 83-201). At initial measurement, thickness at end-expiration was 2.0 mm (interquartile range, 1.8-2.5) and thickness at end-inspiration was 2.5 mm (interquartile range, 2-2.8). The change in thickness at end-expiration during mechanical ventilation between first and last measurement was -13.8% (interquartile range, -27.4% to 0%), with a -3.4% daily atrophy rate (interquartile range, -5.6 to 0%). Thickening fraction = ([thickness at end-inspiration - thickness at end-expiration]/thickness at end-inspiration) throughout the course of mechanical ventilation was linearly correlated with spontaneous breathing fraction (beta coefficient, 9.4; 95% CI, 4.2-14.7; p = 0.001). For children with a period of spontaneous breathing fraction less than 0.5 during mechanical ventilation, those with exposure to a continuous neuromuscular blockade infusion (n = 15) had a significantly larger decrease in thickness at end-expiration compared with children with low spontaneous breathing fraction who were not exposed to a neuromuscular blockade infusion (n = 18) (-16.4%, [interquartile range, -28.4% to -7.0%] vs -7.3%; [interquartile range, -10.9% to -0%]; p = 0.036).

CONCLUSIONS

Diaphragm atrophy is present in children on mechanical ventilation for acute respiratory failure. Diaphragm contractility, measured as thickening fraction, is strongly correlated with spontaneous breathing fraction. The combination of exposure to neuromuscular blockade infusion with low overall spontaneous breathing fraction is associated with a greater degree of atrophy.

Using M-mode ultrasonography to assess diaphragm dysfunction and predict the success of mechanical ventilation weaning in elderly patients

Background

Ultrasonography (US) is a non-invasive and commonly available bedside diagnostic tool. The aim of this study was to assess the utility of M-mode US on ventilator weaning outcomes in elderly patients.

Methods

This was a single center, prospective, observational study in patients aged 80 years or older who were in the medical intensive care unit, had undergone mechanical ventilation for >48 hours, and met the criteria for a spontaneous breathing trial (SBT). For 30 minutes at the start of SBT, each hemi-diaphragmatic movement and the velocity of contraction were evaluated by M-mode US. The the area under the receiver operating characteristic curve (AUROC) was calculated to determine the ability for measured variables to predict successful ventilator weaning.

Results

Forty patients were enrolled and assessed, grouped by those who had US-diagnosed diaphragm dysfunction (DD; 30/40; 75%) and those who did not (10/40; 25%). Patients with DD had a significantly longer total mechanical ventilation duration (536.4±377.05 vs. 250±109.02 hours, P=0.02) and weaning time (425.9±268.31 vs. 216.0±134.22 hours, P=0.002) than patients without DD. Patients with DD also had a higher incidence of weaning failure than patients without DD (24/30 vs. 4/10, P=0.017). Analysis of the receiver operating characteristic (ROC) curve (ROC) curve showed that the optimal cut-off values to predict weaning success were >10.7 mm for the right diaphragmatic movement, and >21.32 mm/s for the right diaphragmatic velocity of contraction; AUROC were 0.839 (95% CI, 0.689-0.936) and 0.833 (95% CI, 0.682-0.932), respectively. The sensitivity, specificity, positive and negative likelihood ratios for predicting weaning success were 83.33% vs. 66.67%, 75.00% vs. 92.86%, 3.33 vs. 9.33, and 0.22 vs. 0.36, for right diaphragmatic movement and diaphragmatic contraction velocity, respectively.

Conclusions

When assessed by M-mode US, DD appeared to be common in ventilated patients aged 80 years or older and was associated with a higher incidence of weaning failure. Larger right diaphragmatic movements or faster right diaphragmatic contraction velocity appeared to be good predictors of mechanical ventilation weaning success in elderly patients.

Diaphragm Activation in Ventilated Patients Using a Novel Transvenous Phrenic Nerve Pacing Catheter

OBJECTIVES

Over 30% of critically ill patients on positive-pressure mechanical ventilation have difficulty weaning from the ventilator, many of whom acquire ventilator-induced diaphragm dysfunction. Temporary transvenous phrenic nerve pacing using a novel electrode-bearing catheter may provide a means to prevent diaphragm atrophy, to strengthen an atrophied diaphragm, and mitigate the harms of mechanical ventilation. We tested the initial safety, feasibility, and impact on ventilation of this novel approach.

DESIGN

First-in-Humans case series.

SETTING

Angiogram suite.

PATIENTS

Twenty-four sedated, mechanically ventilated patients immediately prior to an elective atrial septal defect repair procedure.

INTERVENTIONS

A 9.5-Fr central venous catheter with 19 embedded electrodes was placed via Seldinger technique into the left subclavian vein and superior vena cava and evaluated for up to 90 minutes. The electrode combinations determined to provide best transvenous stimulation of the right and left phrenic nerves were activated in synchrony with mechanically ventilated breaths.

MEASUREMENTS AND MAIN RESULTS

One patient could not be tested for reasons unrelated to the device. In the 23 patients who underwent the full protocol, transvenous stimulation activated the diaphragm in 22 of 23 (96%) left phrenic capture attempts and 20 of 23 (87%) right phrenic capture attempts. In one subject, a congenital left-sided superior vena cava precluded right-sided capture. Significant reductions in ventilator pressure-time-product were achieved during stimulation assisted breaths in all 22 paced subjects (range, 9.9-48.6%; p < 0.001). There were no adverse events either immediately or at 2-week follow-up.

CONCLUSIONS

In this First-in-Human series, diaphragm pacing with a temporary catheter was safe and effectively contributed to ventilation in conjunction with a mechanical ventilator.

Mitigation of Ventilator-induced Diaphragm Atrophy by Transvenous Phrenic Nerve Stimulation

RATIONALE

Ventilator-induced diaphragm dysfunction is a significant contributor to weaning difficulty in ventilated critically ill patients. It has been hypothesized that electrically pacing the diaphragm during mechanical ventilation could reduce diaphragm dysfunction.

OBJECTIVES

We tested a novel, central line catheter-based, transvenous phrenic nerve pacing therapy for protecting the diaphragm in sedated and ventilated pigs.

METHODS

Eighteen Yorkshire pigs were studied. Six pigs were sedated and mechanically ventilated for 2.5 days with pacing on alternate breaths at intensities that reduced the ventilator pressure-time product by 20-30%. Six matched subjects were similarly sedated and ventilated but were not paced. Six pigs served as never-ventilated, never-paced control animals.

MEASUREMENTS AND MAIN RESULTS

Cumulative duration of pacing therapy ranged from 19.7 to 35.7 hours. Diaphragm thickness assessed by ultrasound and normalized to initial value showed a significant decline in ventilated-not paced but not in ventilated-paced subjects (0.84 [interquartile range (IQR), 0.78-0.89] vs. 1.10 [IQR, 1.02-1.24]; P = 0.001). Compared with control animals (24.6 μm²/kg; IQR, 21.6-26.0), median myofiber cross-sectional areas normalized to weight and sarcomere length were significantly smaller in the ventilated-not paced (17.9 μm²/kg; IQR, 15.3-23.7; P = 0.005) but not in the ventilated-paced group (24.9 μm²/kg; IQR, 16.6-27.3; P = 0.351). After 60 hours of mechanical ventilation all six ventilated-paced subjects tolerated 8 minutes of intense phrenic stimulation, whereas three of six ventilated-not paced subjects did not (P = 0.055). There was a nonsignificant decrease in diaphragm tetanic force production over the experiment in the ventilated-paced and ventilated-not paced groups.

CONCLUSIONS

These results suggest that early transvenous phrenic nerve pacing may mitigate ventilator-induced diaphragm dysfunction.

Targeting Heat Shock Proteins Mitigates Ventilator Induced Diaphragm Muscle Dysfunction in an Age-Dependent Manner

Intensive care unit (ICU) patients are often overtly subjected to mechanical ventilation and immobilization, which leads to impaired limb and respiratory muscle function. The latter, termed ventilator-induced diaphragm dysfunction (VIDD) has recently been related to compromised heat shock protein (Hsp) activation. The administration of a pharmacological drug BGP-15 acting as a Hsp chaperone co-inducer has been found to partially alleviate VIDD in young rats. Considering that the mean age in the ICU is increasing, we aimed to explore whether the beneficial functional effects are also present in old rats. For that, we exposed young (7–8 months) and old (28–32 months) rats to 5-day controlled mechanical ventilation and immobilization with or without systemic BGP-15 administration. We then dissected diaphragm muscles, membrane–permeabilized bundles and evaluated the contractile function at single fiber level. Results confirmed that administration of BGP-15 restored the force-generating capacity of isolated muscle cells from young rats in conjunction with an increased expression of Hsp72. On the other hand, our results highlighted that old rats did not positively respond to the BGP-15 treatment. Therefore, it is of crucial importance to comprehend in more depth the effect of VIDD on diaphragm function and ascertain any further age-related differences.

Interpreting diaphragmatic movement with bedside imaging, review article

The diaphragm is the most important muscle of respiration. At equilibrium, the load imposed on the diaphragmatic muscles from transdiaphragmatic pressure balances the force generated by diaphragmatic muscles. However, procedural and nonprocedural thoracic and abdominal conditions may disrupt this equilibrium and impair diaphragmatic function. Diaphragmatic dysfunction is associated with respiratory insufficiency and poor outcome. Therefore, rapid diagnosis and early intervention may be useful. Ultrasound imaging provides quick and accurate bedside assessment of the diaphragm. Various imaging techniques have been suggested, using 2-dimensional and M-mode technology. Diaphragm viewing depends on the degree of robe movement, determined by the angle of incidence of the ultrasound beam and by the direction of probe movement. In this review, we will discuss the function of the diaphragm focusing on clinically important anatomical and physiological properties of the diaphragm. We will review the literature regarding various sonographic techniques for diaphragm assessment. We will also explore the evidence for the role of the tidal displacement of subdiaphragmatic organs as a surrogate for diaphragm movement.

Respiratory management in the patient with spinal cord injury

Spinal cord injuries (SCIs) often lead to impairment of the respiratory system and, consequently, restrictive respiratory changes. Paresis or paralysis of the respiratory muscles can lead to respiratory insufficiency, which is dependent on the level and completeness of the injury. Respiratory complications include hypoventilation, a reduction in surfactant production, mucus plugging, atelectasis, and pneumonia. Vital capacity (VC) is an indicator of overall pulmonary function; patients with severely impaired VC may require assisted ventilation. It is best to proceed with intubation under controlled circumstances rather than waiting until the condition becomes an emergency. Mechanical ventilation can adversely affect the structure and function of the diaphragm. Early tracheostomy following short orotracheal intubation is probably beneficial in selected patients. Weaning should start as soon as possible, and the best modality is progressive ventilator-free breathing (PVFB). Appropriate candidates can sometimes be freed from mechanical ventilation by electrical stimulation. Respiratory muscle training regimens may improve patients' inspiratory function following a SCI.

Time course of diaphragm function recovery after controlled mechanical ventilation in rats

Controlled mechanical ventilation (CMV) is known to result in rapid and severe diaphragmatic dysfunction, but the recovery response of the diaphragm to normal function after CMV is unknown. Therefore, we examined the time course of diaphragm function recovery in an animal model of CMV. Healthy rats were submitted to CMV for 24-27 h (n = 16), or to 24-h CMV followed by either 1 h (CMV + 1 h SB, n = 9), 2 h (CMV + 2 h SB, n = 9), 3 h (CMV + 3 h SB, n = 9), or 4-7 h (CMV + 4-7 h SB, n = 9) of spontaneous breathing (SB). At the end of the experiment, the diaphragm muscle was excised for functional and biochemical analysis. The in vitro diaphragm force was significantly improved in the CMV + 3 h SB and CMV + 4-7 h SB groups compared with CMV (maximal tetanic force: +27%, P < 0.05, and +59%, P < 0.001, respectively). This was associated with an increase in the type IIx/b fiber dimensions (P < 0.05). Neutrophil influx was increased in the CMV + 4-7 h SB group (P < 0.05), while macrophage numbers remained unchanged. Markers of protein synthesis (phosphorylated Akt and eukaryotic initiation factor 4E binding protein 1) were significantly increased (±40%, P < 0.001, and ±52%, P < 0.01, respectively) in the CMV + 3 h SB and CMV + 4-7 h SB groups and were positively correlated with diaphragm force (P < 0.05). Finally, also the maximal specific force generation of skinned single diaphragm fibers was increased in the CMV + 4-7 h SB group compared with CMV (+45%, P < 0.05). In rats, reloading the diaphragm for 3 h after CMV is sufficient to improve diaphragm function, while complete recovery occurs after longer periods of reloading. Enhanced muscle fiber dimensions, increased protein synthesis, and improved intrinsic contractile properties of diaphragm muscle fibers may have contributed to diaphragm function recovery.

Moderate and prolonged hypercapnic acidosis may protect against ventilator-induced diaphragmatic dysfunction in healthy piglet: an in vivo study

Introduction

Protective ventilation by using limited airway pressures and ventilation may result in moderate and prolonged hypercapnic acidosis, as often observed in critically ill patients. Because allowing moderate and prolonged hypercapnia may be considered protective measure for the lungs, we hypothesized that moderate and prolonged hypercapnic acidosis may protect the diaphragm against ventilator-induced diaphragmatic dysfunction (VIDD). The aim of our study was to evaluate the effects of moderate and prolonged (72 hours of mechanical ventilation) hypercapnic acidosis on in vivo diaphragmatic function.

Methods

Two groups of anesthetized piglets were ventilated during a 72-hour period. Piglets were assigned to the Normocapnia group (n = 6), ventilated in normocapnia, or to the Hypercapnia group (n = 6), ventilated with moderate hypercapnic acidosis (PaCO₂ from 55 to 70 mm Hg) during the 72-hour period of the study. Every 12 hours, we measured transdiaphragmatic pressure (Pdi) after bilateral, supramaximal transjugular stimulation of the two phrenic nerves to assess in vivo diaphragmatic contractile force. Pressure/frequency curves were drawn after stimulation from 20 to 120 Hz of the phrenic nerves. The protocol was approved by our institutional animal-care committee.

Results

Moderate and prolonged hypercapnic acidosis was well tolerated during the study period. The baseline pressure/frequency curves of the two groups were not significantly different (Pdi at 20 Hz, 32.7 ± 8.7 cm H₂O, versus 34.4 ± 8.4 cm H₂O; and at 120 Hz, 56.8 ± 8.7 cm H₂O versus 60.8 ± 5.7 cm H₂O, for Normocapnia and Hypercapnia groups, respectively). After 72 hours of ventilation, Pdi decreased by 25% of its baseline value in the Normocapnia group, whereas Pdi did not decrease in the Hypercapnia group.

Conclusions

Moderate and prolonged hypercapnic acidosis limited the occurrence of VIDD during controlled mechanical ventilation in a healthy piglet model. Consequences of moderate and prolonged hypercapnic acidosis should be better explored with further studies before being tested on patients.