Abstract
Background and Purpose Respiratory muscle training promotes weaning in patients who are dependent on mechanical ventilation. Respiratory muscles can be trained using linear inspiratory-resistive loads to improve their strength and endurance. The purpose of this case report is to demonstrate that a therapeutic intervention consisting of a linear pressure load device facilitates ventilator weaning in an infant who is chronically ventilated.
Case Description The patient was a newborn with a weight of 4,725 g and an Apgar score of 0 to 1 who had been on mechanical ventilation for 8 months. Respiratory muscle training with a linear pressure load was performed twice a day. The number of series and repetitions was increased progressively while maintaining the pressure load, with 3-minute intervals between series, until reaching a peak of 8 series with 70 repetitions and a pressure load of 13 cm H2O. During the intervention, the patient was maintained in the supine position at an elevation of 30 degrees.
Outcomes The infant required mechanical ventilation for 8 months (32 weeks of life), with 4,450 hours (26.5 weeks) of mechanical ventilation and 230 cumulative hours (1.4 weeks) of spontaneous breathing, without obtaining any weaning success. At 10 months of age (40 weeks) and after 2 months (8 weeks) of respiratory muscle training, the results were 490 hours (3 weeks) of mechanical ventilation and 854 hours (5 weeks) of spontaneous breathing. Complete independence of the infant from mechanical ventilation was achieved thereafter.
Discussion This case report describes respiratory muscle training using a linear pressure load device to successfully wean an infant from mechanical ventilation. However, well-controlled clinical trials are necessary to better understand the effects of this intervention on neonatal respiratory muscles.
Inspiratory muscle training has been shown to be beneficial for the weaning of patients from mechanical ventilation.1,2 The degree of respiratory muscle weakness has been associated with the duration of mechanical ventilation3,4 and might be a possible cause of difficulties with weaning from ventilation.5,6 Difficult weaning is defined as long-term mechanical ventilation (more than 2 or 3 weeks) associated with weaning attempts that are repeatedly unsuccessful.
A systematic review conducted by Choi et al7 on respiratory muscle training in adults requiring prolonged mechanical ventilation, including 10 relevant articles published between 1990 and 2007, reported the benefits of the intervention in these patients, but the best program still needs to be established in randomized controlled trials. Interventions promoting respiratory muscle training have shown some benefits, such as an increase in inspiratory muscle strength and tidal volume and eventual ventilator weaning.2,8–11 In this respect, studies on adult patients in intensive care units have demonstrated that inspiratory muscle training using a linear inspiratory resistive load facilitates ventilator weaning by increasing muscle contractility and causing desirable effects on muscle metabolism in patients who are critically ill.2,12,13
Different respiratory training devices are available, such as linear, nonlinear, and flow-resistive load devices. The technique most widely accepted for inspiratory muscle training uses linear resistive loads provided by a pressure threshold device, which permits a constant, sustained air flow-independent pressure throughout inspiration. When inspiring through this device, which possesses a linear pressure load valve, the patient must generate a minimum inspiratory muscle force to overcome the threshold load by generating a negative inspiratory pressure sufficient to open the spring-loaded valve and must sustain this pressure level throughout inspiration (isotonic load).2
Tan et al14 reported positive results of muscle training using an inspiratory flow-resistive load in premature infants, improving inspiratory muscle endurance and preventing the occurrence of muscle fatigue. We believe that the established and accepted models of respiratory muscle training can be applied to infants because this training has been reported to result in the successful weaning of adults on mechanical ventilation, with no reports of injury to the respiratory system.8–10
Therefore, the present case report describes the use of linear pressure inspiratory muscle training using a pressure-dependent and flow-independent device that provides constant and specific inspiratory resistance (Threshold Inspiratory Muscle Trainer [IMT], Cedar Grove, New Jersey).15 The purpose of this case report is to demonstrate that a therapeutic intervention with a linear pressure load device facilitated ventilator weaning in a newborn who was chronically ventilated.
Patient History and Review of Systems
A boy weighing 4,725 g was born at 40 weeks of gestation by cesarean section after prolonged expulsion and went into cardiorespiratory arrest. His 1-minute Apgar score was 0. The newborn underwent cardiorespiratory resuscitation maneuvers and received atropine, which resulted in the recovery of vital functions. The patient showed no spontaneous respiratory movements during the first 24 hours of life, and ventilatory support was maintained by orotracheal intubation. He was transferred to our pediatric intensive care unit at 3 days of life with a diagnosis of neonatal anoxia, bilateral pneumothorax, and cardiorespiratory arrest.
Computed tomography led to the diagnosis of diffuse cerebral edema. Upon physical examination, the patient was unresponsive to painful stimuli and presented anisocoria, generalized edema with a positive Godet sign, and superficial and irregular spontaneous respiratory movements. Lung auscultation revealed good bilateral expansion and no foreign noises. The newborn received a bilateral chest drain. Thus, positive pressure ventilation was established using pressure-limited control mode ventilation. The following ventilatory parameters were used to maintain oxygen saturation at 94% and desired blood gas parameters: a flow rate of 8 L/min, a controlled respiratory rate of 38 breaths per minute, an inspiratory time of 0.55 second, an inspiratory pressure of 22 cm H2O, a positive end-expiratory pressure of 5 cm H2O, and a fraction of inspired oxygen of 40%.
In the first week of hospitalization (10 days of life), the chest drain could be removed with good response. The newborn opened his eyes spontaneously and started to cry. Diuresis was obtained after bladder massage. Mechanical ventilation continued to be necessary for lung ventilation. The patient presented generalized edema, good peripheral perfusion, and generalized hypotonia; was unresponsive to painful stimuli; and was tolerant of a free diet.
In the third week of hospitalization (24 days of life), the patient presented superficial and irregular respiratory movements, discrete withdrawal movements of the lower limbs upon stimulation, and constant masticatory movements, and his pupils were reactive to light.
In the sixth week of hospitalization (45 days of life), the infant continued to show spontaneous eye opening and lower-limb clonus and was responsive to tactile stimuli. Laboratory analysis and radiological imaging examinations showed no anomalies. Ventilation weaning was initiated with a progressive reduction of ventilatory parameters. The following weaning techniques were used from the second month (8 weeks of life) to the eighth month (32 weeks of life) of mechanical ventilation: reduction of controlled respiratory rate, permitting the modality of intermittent mandatory ventilation (IMV); continuous positive airway pressure (CPAP) intercalated with IMV; and nasal CPAP using a nasal clip. However, none of the weaning techniques used was successful. The failure to wean was demonstrated by rapid oxygen desaturation (≤90%), perioral cyanosis, generalized paleness, increased respiratory effort accompanied by subdiaphragmatic retractions, and intercostal pulling. Time-controlled IMV, therefore, was reinstated.
After weaning failure, the patient was returned to IMV. Oxygen saturation was reestablished at ≥90%, and the ventilatory parameters returned to the values observed before weaning (positive inspiratory pressure of 16 cm H2O, positive end-expiratory pressure of 5 cm H2O, flow rate of 8 L/min, inspiratory time of 0.55 second, respiratory rate of 12 breaths per minute, and fraction of inspired oxygen of 30%). However, after 10 unsuccessful weaning attempts over 6 months of mechanical ventilation, respiratory muscle recruitment using a linear pressure load device was chosen as a therapeutic option.
Clinical Impression
Positive results have been reported in the literature for patients on long-term mechanical ventilation using a linear pressure load device (IMT valve) for respiratory muscle training. Adult patients with different clinical diagnoses and unsuccessful weaning using conventional methods have been weaned successfully from the ventilator after undergoing muscle training.2,8–10 The authors of these studies reported an increase in tidal volume and muscle strength and improvement in the duration of spontaneous breathing, which eventually led to weaning from the mechanical ventilator.2,8–10 However, there are no reports of the use of respiratory muscle training in full-term infants and few reports in premature infants. In this respect, Tan et al14 reported positive outcomes of respiratory muscle training in premature infants using flow training.
The clinical decision for the use of respiratory muscle training in this case report was based on the evidence found in studies on adult patients who were ventilation dependent, in which training with an IMT valve was used for ventilation weaning. Training with the linear pressure load device was selected for this case report because this training is used by other groups, according to reports in the literature,2,7,12 and we found no restrictions on the use of the IMT valve in children in the literature.
The choice of respiratory muscle training was based on established and accepted models for strength and endurance training of skeletal muscle. Bellemare and Grassino16 demonstrated an exponential relationship between the diaphragmatic tension-time index and how long loaded breathing could be tolerated. This relationship suggests that inspiratory muscle strength is predictive of the ability to sustain spontaneous breathing when breathing requires a significant portion of the pressure-generating capacity of inspiratory muscles. When the external inspiratory load or diaphragmatic tension-time index is decreased, or the inspiratory pressure-generating capacity is increased, the ability to sustain a spontaneous breathing effort moves from a gradual increase to an abrupt increase and approaches infinity. Thus, this condition may contribute to sustaining the respiratory muscle during spontaneous breathing and consequently favors ventilator weaning.
Examination
Before the beginning of respiratory muscle training, the patient was in good general health at 8 months of life (32 weeks), showing daily weight gain (height=67 cm and weight=8.5 kg). However, his motor and cognitive development was delayed, with the patient being unable to position his upper limbs in the midline and to control his head and trunk. As a consequence, the infant presented difficulties in rolling over and performing crawling movements, tasks that he should have been able to perform at this age. At 6 months (24 weeks), the patient was tracheostomized with a 4.5-cm cannula without a cuff and adapted well to the tracheostomy cannula.
Conventional weaning methods were unsuccessful over the 6 months of mechanical ventilation. The patient had neurological sequelae resulting from anoxia at birth; thus, success of ventilator weaning was necessary to facilitate neuromotor stimulation, to permit family integration, and to reduce the risk of respiratory infection.
Clinical Impression
We believe that the neurological sequelae, together with the prolonged duration of mechanical ventilation (32 weeks), reduced respiratory muscle strength and endurance, as demonstrated by the inability of the patient to maintain spontaneous breathing during the weaning attempts. Linear pressure respiratory muscle training, therefore, may be an option for neuromotor adaptation of the respiratory musculature, permitting independence from the mechanical ventilator. The respiratory muscle training program used was designed to improve strength and endurance12,17 by increasing the number of low-intensity repetitions to obtain an adaptive response of the muscle and to increase oxidative capacity as well as resistance to fatigue.13,18
Intervention
Resistive respiratory muscle training was started when the patient was 8 months old in an attempt to restore muscle strength and endurance and to permit weaning from the mechanical ventilator. Muscle training was performed with an inspiratory muscle trainer (Threshold IMT) connected to a system that offered supplemental oxygen at 2 L/min. A resting interval of 3 minutes between series was allowed. The load imposed was defined by the opening of the valve membrane generated by the inspiratory movement of the newborn because the prescription of respiratory muscle training for children who are dependent on mechanical ventilation is limited by the small number of scientific studies published to date.
The IMT valve was connected to the tracheostomy cannula, and oxygen saturation was maintained at ≥90%. However, in the case of a drop in saturation below the acceptable baseline level of 90%, mechanical ventilation support was reinitiated and training was interrupted temporarily. Vital signs were monitored continuously with a Dixtal (DX2010) monitor (Dixtal Medical USA, Wallingford, Connecticut), and there was no indication for the interruption of respiratory muscle training.
The training prescribed in the first week consisted of an initial load of 7 cm H2O, with the lowest load provided by the valve being used as the criterion of choice, and 4 series of 30 repetitions, with an interval of 3 minutes between series, twice a day, except for Sundays. The number of repetitions and series was progressively increased in the second week (34 weeks of life of the patient) until reaching a total of 8 series of 70 repetitions performed at a pressure load of 13 cm H2O from Monday to Saturday, twice a day.
After 1 week of respiratory muscle training, withdrawal from the intermittent ventilatory support was started (1 hour of spontaneous breathing intercalated with 2 hours of mechanical ventilation until reaching 10 hours of spontaneous breathing and 2 hours of mechanical ventilation), which permitted the analysis of progressive tolerance to ventilator weaning.
Clinical Impression
In the first week of respiratory muscle training, the patient tolerated being off the ventilator for personal hygiene, such as bathing, and for transfer from the bed to the mother's lap and to the baby seat, without experiencing a drop in oxygen saturation. After the beginning of respiratory muscle training, the tolerance of the newborn to daily care improved. He could maintain the ventilation when he was off the ventilator, and he showed good tolerance to the progressive increase of repetitions and training series. Therefore, the respiratory muscle training program was continued.
Outcomes
Before muscle training, the patient spent 8 months of his life (32 weeks) on mechanical ventilation and all weaning attempts failed. Considering the number of weaning attempts and persistence on the ventilator, the patient remained 4,450 hours (26.5 weeks) on mechanical ventilation and 230 cumulative hours (1.4 weeks) of spontaneous breathing. In contrast, respiratory muscle training resulted in tolerance of the patient to spontaneous breathing and in a reduction of dependence on mechanical ventilatory support.
In the 33rd week of life, the patient started to use the linear load device as a weaning strategy, and the period of spontaneous breathing was increased gradually. After 2 months (8 weeks) of resistive muscle training, the sum of hours was 490 hours (3 weeks) of mechanical ventilation and 854 hours (5 weeks) of spontaneous breathing. At 11 months of life (44 weeks) and 9 weeks of muscle training, the patient did not return to the ventilatory support and was discharged to the ward (Figure).
Respiratory muscle training was started in the 33rd week of life (arrow) and led to a gradual increase in spontaneous breathing.
In the first week of training, the patient started intermittent weaning consisting of 1 hour of spontaneous breathing intercalated with 2 hours of mechanical ventilation. The time of spontaneous breathing was increased gradually until reaching 10 hours, as detailed below. The duration on mechanical ventilation was 2 hours during the respiratory muscle training period.
In the second week of respiratory muscle training, the patient remained 1 hour on spontaneous breathing and 2 hours on mechanical ventilation. After the third week, there was a progressive increase in the tolerance to spontaneous breathing. The patient achieved 2 hours of spontaneous breathing and 2 hours of mechanical ventilation in the third week, 4 hours of spontaneous breathing and 2 hours of mechanical ventilation in the fourth week, 6 hours of spontaneous breathing and 2 hours of mechanical ventilation in the fifth week, 8 hours of spontaneous breathing and 2 hours of mechanical ventilation in the sixth week, and 10 hours of spontaneous breathing in the seventh and eighth weeks. Thus, the patient was maintained only on spontaneous breathing in the following weeks (Figure).
The patient tolerated the linear pressure respiratory muscle training, maintaining stable vital signs. Before training, the mean heart rate was 113 bpm, the respiratory rate was 36 breaths per minute, and oxygen saturation was 93%. These variables were 111 bpm, 34 breaths per minute, and 94% after training.
After successful weaning from the ventilator using a linear pressure load device, the patient was discharged from the unit and was followed for 3 months on an outpatient basis. During this time, he required supplemental oxygen at 0.5 L/min. Daily prescription of the preestablished respiratory muscle training was maintained. The patient did not need to return to the ventilator.
Discussion
Respiratory muscle training is a technique used to facilitate ventilator weaning. Studies have shown the beneficial effect of respiratory muscle training programs in adult patients who were weaned successfully from mechanical ventilation.2,11,12
Weaning of the patient failed, and some weaning alternatives were tested, such as a reduction in the controlled respiratory rate during IMV, CPAP intercalated with IMV, and nasal CPAP using a nasal clip. Weaning failure was characterized by rapid oxygen desaturation (≤90%), generalized paleness, and increased respiratory effort, indicating paradoxical respiration. Thus, inspiratory muscle training using a linear pressure load was chosen in this case report to favor weaning from the ventilator.
Inspiratory muscle strength training using a linear pressure load is appropriate for patients who are dependent on mechanical ventilation because, like skeletal muscle, respiratory muscles weaken with the lack of use.19–21 Traditional weaning methods such as altering the modes of mechanical ventilation to promote resting periods for the inspiratory muscles, providing pressure support, increasing firing thresholds to start ventilator-supported respiration, and making attempts at spontaneous breathing are unlikely to provide a sufficient training stimulus to improve inspiratory muscle strength.7 Many patients fail at weaning attempts because of difficulties in maintaining spontaneous respiratory cycles despite the maintenance of adequate minute ventilation and adequate blood gas levels. Thus, respiratory effort is related inversely to respiratory muscle strength.12
In a nonrandomized prospective study, Sprague and Hopkins10 investigated the effect of respiratory muscle training with a linear load using a threshold valve in 6 adult patients with various diseases. All patients had been on mechanical ventilation for a period of 18 to 221 days. The patients were weaned successfully from the ventilator after 9 to 18 days of inspiratory muscle training. Martin et al2 also used linear load training with a threshold device and reported a 90% success rate for ventilator weaning. However, that study had some limitations, such as the lack of a control group, the small number of patients, and important differences in the number of days on mechanical ventilation. In contrast, Aldrich et al8 evaluated respiratory muscle training with a nonlinear load using the Pflex device (Health Scan Inc, Upper Montclair, New Jersey) in patients who had undergone tracheostomy. They reported a success rate of ventilator weaning of 63%, but the sample studied was heterogeneous and small, and no control group was included. In a randomized controlled study, Tan et al14 investigated the effects of respiratory muscle training with flow-resistive loads in premature infants. Respiratory muscle endurance had increased significantly by 137% in the trained group after 2 weeks of training. No significant difference in inspiratory muscle strength was observed between the control and trained groups.
In the present case report, the patient presented spontaneous breathing for 230 hours during the 8 months preceding the muscle training and for 854 hours during the 8 weeks of training, indicating an increase in the tolerance to spontaneous breathing. Thus, total independence from mechanical ventilation was achieved within 4 weeks of respiratory muscle training. A 50% increase in the tolerance to spontaneous breathing was observed between the second and third weeks of muscle training, whereas this increase was 33.3% between the third and fourth weeks, 12.5% between the fourth and fifth weeks, and 11% in the sixth week. No additional increase was observed in the seventh or eighth week. Taken together, these results show a growing response to respiratory muscle training, with a peak between the second and third weeks. Training prescription was maintained in the last week before weaning from the mechanical ventilator. These findings agree with the results reported by Tan et al,14 who observed improvement of the variables analyzed in premature infants after 2 weeks of respiratory muscle training. In a study by Pardy et al18 involving adults, the benefits of muscle training were observed within 4 weeks.
In the present case report, we followed a patient on long-term mechanical ventilation in whom respiratory muscle training resulted in the success of ventilator weaning, as also reported by other investigators.2,7,9,22 In contrast, Caruso et al,23 studying patients who were critically ill and mechanically ventilated who received inspiratory muscle training, observed no reduction in weaning duration or reintubation rate. In addition, there was no increase in inspiratory muscle strength. Caruso et al concluded that inspiratory muscle training is ineffective in patients who are acutely critically ill and mechanically ventilated. Thus, evidence in the literature indicates that respiratory muscle training has an influence only on patients undergoing long-term mechanical ventilation.
In conclusion, this case report showed that respiratory muscle training in an infant who was chronically ill and dependent on mechanical ventilation led to the gradual improvement in tolerance to spontaneous breathing and consequent successful weaning from the ventilator. Systematic clinical trials of respiratory muscle training in children are needed to better understand this type of intervention in this population.
Footnotes
-
Dr Brunherotti provided concept/idea/project design, writing, data collection, and fund procurement. Ms Bezerra, Ms Bachur, and Dr Jacometti provided clerical support. All authors provided data analysis, project management, patient, facilities/equipment, and consultation (including review of manuscript before submission).
- Received August 13, 2011.
- Accepted January 19, 2012.
- © 2012 American Physical Therapy Association
References
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