Abstract
Background and Purpose The Six-Minute Walk Test (6MWT) is a requirement for lung transplantation evaluation by the United Network for Organ Sharing. A subset of patients being evaluated for a lung transplantation require mechanical ventilation (MV) because of respiratory failure. The 6MWT has not been validated as an outcome measure for patients dependent on MV. Literature supports alternative forms of the 6MWT, including those with an oval track or treadmill, as valid for accommodating other populations. This case report describes the use of the 6MWT for 2 patients who had cystic fibrosis and required MV before a lung transplant.
Case Description A 34-year-old woman and a 37-year-old woman were admitted to a medical intensive care unit for exacerbation of cystic fibrosis requiring prolonged intubation and a subsequent tracheostomy. Their hospital courses were characterized by participation in early rehabilitation and variable dependence on MV. Both patients performed the 6MWT for a lung transplantation workup while dependent on MV.
Outcomes Both patients performed the 6MWT while using portable MV and achieved a distance greater than that required for transplantation consideration and approximately 50% of the reference-based expected distance for adults who are healthy. Confounding factors included external pacing and the use of an oval track.
Discussion The use of the 6MWT for 2 patients receiving MV appeared to be feasible. Research regarding the validity of this outcome is warranted.
Cystic fibrosis (CF) is a multisystem genetic disorder affecting sodium transport channels in all organ systems, most notably, the lungs. The production of thick mucus results in recurrent bacterial and fungal infections. Progressive pulmonary failure occurs because of chronic obstruction and inflammation within the airways. Treatments for this condition include airway clearance techniques, mucolytic agents, and antibiotics.1–3 Physical training, including aerobic and anaerobic activities, is recommended for airway clearance and functional maintenance for people with CF.1,3
At this time, approximately 50% of people with CF are 18 years of age or older; this fact indicates an increase in life expectancy for this population. The current average life expectancy is approximately 40.7 years.4 The number of lung transplantations performed in this population has increased because of the increase in average life expectancy. Two hundred forty-five people with CF received a lung transplant in the United States in 2013 because of the severity of their lung disease.4 Because of progressive pulmonary decline, mechanical ventilation (MV) may be required before or during lung transplant evaluation in people with CF.
Lung transplantation may be considered for patients with CF under the following 5 conditions: forced expiratory volume in the first second (FEV1) of less than 30% of the predicted value or a rapid decline in FEV1, exacerbation of pulmonary disease requiring an intensive care unit stay, increasing frequency of exacerbations requiring antibiotic therapy, refractory or recurrent pneumothorax, and recurrent hemoptysis not controlled by embolization.5 Until recently, many programs did not consider patients requiring MV for lung transplantation. However, research has shown that patients who have CF and require MV may have better survival after transplantation than patients with other end-stage lung diseases.5
Although there are other methods for assessing activity or endurance, the Six-Minute Walk Test (6MWT) is a reliable and valid outcome measure that evaluates the global and integrated responses of all systems during exercise. As a result, it is indicated as a one-time measure of functional status in patients awaiting a lung transplant.6 The 6MWT has been used in people with CF, has been found to be a useful indicator of oxygen desaturation and dyspnea during demanding physical activity, and has been found to provide a good assessment of global exercise capacity.6–9
Adults with CF were shown to have poorer performance on the 6MWT than adults who were of an equivalent age and healthy.8 This poorer performance was evidenced by shorter distances ambulated by people with CF than by people who were of a similar age and healthy.8 The poorer performance was not due to cardiac dysfunction but was related to oxygenation/oxygen diffusion and a sense of breathlessness. Even with pulmonary support by MV, such impairments are still likely to exist.8 The 6MWT has been shown to have validity in other populations, including people with chronic obstructive pulmonary disease and people who have had cardiac surgery.10–13
Because of its ability to measure functional endurance, the 6MWT is required by the United Network for Organ Sharing as an outcome measure for calculating the lung allocation score in patients being evaluated for a lung transplant.14 The score is created from medical information, such as laboratory test values, test results, functional status, and diagnosis, about each lung transplant candidate. The FEV1 has been used most frequently for assessing early mortality in people with CF. An FEV1 that was 30% of the predicted value was associated with 2-year mortality rates of approximately 40% in men with CF and 55% in women with CF.5 The lung allocation score was designed to represent the severity of illness and the chance of success after a lung transplant for each candidate.14 All patients awaiting a lung transplant receive a score from 0 to 100, with higher scores indicating a higher priority when compatible lungs become available.14 The median wait time for lung transplantation at the Johns Hopkins Transplant Center is 60 days.15 Comparatively, the national median wait time for lung transplantation is 918 days, according to the United Network for Organ Sharing.14 Factors that affect the wait time include blood type, immunologic matches, body size, and lung allocation score.15
The 6MWT has been implemented outside the guidelines provided by the American Thoracic Society (ATS) to accommodate other populations; however, there is no research to support the use of the 6MWT in patients with MV.10–13 The lack of research and the increasing need to perform the 6MWT in patients requiring MV warrant the need to examine the feasibility of using this test in patients who have CF and require MV before a lung transplant. This case report describes the use of the 6MWT in 2 patients who had CF and required MV before a lung transplant.
Case Description
Two women, 34 and 37 years of age, admitted to the medical intensive care unit (MICU) at Johns Hopkins Hospital consented to publication of the case report. The Johns Hopkins Medicine Internal Review Board determined that a review was not required for publication of the case report. Both patients were admitted from the Johns Hopkins Cystic Fibrosis Clinic because of concern about exacerbation of CF. In both cases, the patient's pulmonary status declined, and intubation, MV, and—eventually—a tracheostomy were required. Medical history, pertinent medications, course of admission by hospital day, and results of FEV1 tests for both patients are shown in Table 1 and Appendix 1.
Patient Demographicsa
Patient 1
Hospital course.
Patient 1 was a 34-year-old woman with CF (genotype: homozygous F508 deletion), a baseline FEV1 of 40.2% of the predicted value, and a body mass index of 15.8 kg/m2. Before admission, she was working full time as an endoscopy nurse and enjoyed running long-distance races and spending time with her family and dogs. She was initially admitted to the medical progressive care unit for management of the exacerbation of CF, and physical therapy intervention began on hospital day 1. Seven days after her initial admission, she was transferred to the MICU because of hypercarbic respiratory failure requiring intubation upon admission to the unit. At this time, the medical team began a workup for lung transplantation because of the severity of the patient's pulmonary decline. Five days after intubation, the patient underwent a tracheostomy to improve participation in early rehabilitation and progress with ventilator weaning. After consultation with the medical team and the respiratory therapist, the 6MWT was performed as part of the lung transplantation workup while the patient was using a portable mechanical ventilator on hospital day 19.
During her initial admission, the patient participated in daily weaning screens and spontaneous breathing trials (SBTs) performed by a respiratory therapist as part of the ventilator weaning process. For assessment of tolerance of weaning, subjective data (patient-reported comfort) and objective data (such as changes in respiration rate, tidal volume, and venous blood gasses [VBGs]) were used after changes to MV support at rest or in association with physical activity. Although VBGs were used to assess oxygen consumption, they are not documented consistently in patient charts or in coordination with the times when the 6MWT was administered and so cannot be reported here. The patient was able to progress with ventilator weaning to a tracheostomy collar and was transferred back to the medical progressive care unit. After passing a 24-hour capping trial on hospital day 47, she underwent decannulation and was discharged to home on hospital day 48 to await a transplant.
Unfortunately, the patient was readmitted within 2 weeks of discharge with an FEV1 of 21% of the predicted value. Intubation was performed on arrival to the emergency department, and she was readmitted to the MICU. She remained orally intubated until the time of bilateral orthotopic lung transplantation. A second 6MWT was not performed because of the severity of exacerbation and desaturation with minimal mobility on high ventilator settings. The patient underwent bilateral orthotopic lung transplantation on hospital day 8 of the second admission and was discharged to home 12 days later.
Physical therapist examination.
Patient 1 participated in a physical therapist examination on hospital day 2. She had no impairments in strength and had intact sensation in all dermatomes. The initial examination revealed intact integument; however, during the first admission, the patient developed a stage 2 sacral pressure ulcer, which was managed by wound care nurses. A review of other systems was significant for asymptomatic sinus tachycardia at rest and inspiratory discontinuous adventitious breath sounds throughout posterior lung fields on auscultation. The patient was independent with bed mobility and transfers. At the time of the initial examination, she ambulated 45.7 m (150 ft) with independence on 3 L of oxygen via a nasal cannula. Once intubated, she required contact guard assistance with the use of a rolling walker for ambulation. No learning barriers were identified. The patient reported that her home airway clearance program consisted mainly of self-directed physical exercise (primarily running) and intermittent use of a high-frequency chest wall oscillation vest.
Daily physical therapy intervention.
Patient 1 participated in physical therapist treatment sessions 3 times per day, including 2 airway clearance sessions and 1 activity session, in accordance with hospital protocol. Her goals were to increase independence with airway clearance techniques for productive and effective expectoration of secretions and to improve activity tolerance for normalized function in the hospital and upon discharge. Airway clearance sessions both before and after dependence on MV involved primarily manual chest physical therapy (including percussion, vibration, and postural drainage). When the patient was not dependent on MV, an oscillatory positive end pressure device was used intermittently for maximal expectoration of secretions. Before intubation, activity sessions involved primarily ambulation. When the patient was dependent on MV or the tracheostomy collar, ambulation and interval training on a stationary bike were used.
Patient 2
Hospital course.
Patient 2 was a 37-year-old woman with CF (genotype: homozygous F508 deletion), an FEV1 of 34.8% of the predicted value, and a body mass index of 17.3 kg/m2. Before admission, she was completely independent, working part time as a 911 dispatcher, and enjoyed spending time with friends and family. She was admitted to a general medicine floor from the Johns Hopkins Cystic Fibrosis Clinic because of concern about exacerbation of CF. On hospital day 3, she required intubation after experiencing a suspected seizure during a bronchoscopy, resulting in admission to the MICU. She underwent a tracheostomy on hospital day 17 because of prolonged intubation and inability to wean from the ventilator. After the tracheostomy, the medical team decided to proceed with a lung transplantation workup. The 6MWT was completed as part of this workup and was performed for the first time on hospital day 21. Weaning from the ventilator took longer than anticipated, resulting in a prolonged MICU admission. Because of the prolonged admission, a second 6MWT was performed while the patient was receiving MV approximately 1 month later, on hospital day 57. This second test was performed to ensure that the patient's physical condition and endurance had not deteriorated before transplantation, given the prolonged MICU admission.
The patient was screened daily for MV weaning with SBTs performed by the MICU respiratory therapist. Her medical history was significant for anxiety, which may have limited progress with weaning. She received lorazepam as needed to promote success with SBTs throughout the weaning process but was unable to wean to a tracheostomy collar. She played an active role in increasing the length of SBTs to prevent adverse events (such as an anxiety attack or desaturation). Subjective data (reported comfort on particular ventilator settings) and objective data (such as respiration rate, tidal volume, and VBGs) were used to assess tolerance of weaning. Although VBGs were used to assess oxygen consumption, they are not documented consistently in patient charts or in coordination with the times when the 6MWT was administered and so cannot be reported here. Data on VBGs also were difficult to obtain early in the weaning process given the short times that the patient participated in SBTs as a result of her anxiety.
The medical and transplantation teams determined that it was safest for the patient to remain in the MICU until transplantation rather than discharging her to a rehabilitation center for ventilator weaning. She underwent bilateral orthotopic lung transplantation and decannulation on hospital day 70. She was discharged to home 15 days later, on hospital day 85.
Physical therapist examination.
Patient 2 participated in a physical therapist evaluation on hospital day 2. She had no impairments in strength and had intact sensation in all dermatomes and intact integument. A review of other systems was significant for asymptomatic sinus tachycardia at rest and inspiratory discontinuous adventitious breath sounds throughout posterior lung fields on auscultation. The patient was independent with bed mobility and transfers. At the time of the evaluation, she was breathing room air but deferred ambulation. During a treatment session later on the same day, she ambulated approximately 137 m (450 ft) independently with 1 L of oxygen via a nasal cannula. After intubation, she required contact guard assistance with ambulation. Her medical history was significant for anxiety, which may have contributed to difficulty with weaning from the ventilator and which may have been a learning factor. Her home airway clearance program consisted of a high-frequency chest wall oscillation vest with huff coughing and intermittent manual chest physical therapy (including percussion, vibration, and postural drainage).
Daily physical therapy intervention.
Patient 2 participated in physical therapist treatment sessions 3 times per day, including 2 airway clearance sessions and one activity session. Her goals were to return to her prior level of function and to be discharged to home as soon as possible. Airway clearance sessions both before and after dependence on MV involved primarily chest physical therapy. Activity sessions before and after dependence on MV involved primarily ambulation. The patient participated in ambulation while intubated with an endotracheal tube and after the tracheostomy. In addition, after the tracheostomy, interval training on a stationary bike was used in conjunction with ambulation to improve endurance before lung transplantation.
Clinical Impression 1
Ambulation has been shown to decrease the negative effects of bed rest, improve functional outcomes, and decrease ICU and hospital lengths of stay overall.16,17 The patients were deemed eligible for ambulation and interval training in accordance with current literature, meeting the criteria of a fraction of inspired oxygen (Fio2) of less than 60%, a saturation of peripheral oxygen (SpO2) of greater than 90%, a respiration rate of less than 30 breaths per minute, and a positive end-expiratory pressure of less than 10 cm of H2O.16 Both patients received MV for most of their hospital stays before lung transplantation and participated in early rehabilitation while admitted to the MICU. The patients were hemodynamically stable and participated in daily ambulation with a physical therapist throughout the pretransplantation period as well as traditional airway clearance in accordance with the CF protocol at Johns Hopkins Hospital. Airway clearance techniques varied by patient preference and observed efficacy. The techniques used included an oscillatory positive end pressure device, postural drainage, manual percussion and vibration, or a combination of these techniques.1,3 Activity sessions involved walking on level surfaces, stair climbing, and interval training.1,3
Patient 1 ambulated approximately 4 times before the 6MWT and ambulated only after the tracheostomy. Before administering the 6MWT, patient 2 ambulated approximately 18 times with MV and an endotracheal tube and after the tracheostomy. Variation in the timing of the 6MWT between patient 1 and patient 2 occurred for several reasons, including hemoptysis after intubation, a rapid pulmonary decline, and a subsequent tracheostomy—within 1 week of intubation—in patient 1. The 6MWT was performed by patient 1 at this time to allow for an expedited lung transplantation workup. Patient 2 had a much longer course of treatment before the tracheostomy because the team was hopeful that she would be weaned from the ventilator and that a lung transplantation workup would not be necessary. Therefore, the 6MWT was performed by patient 2 when a lung transplantation workup eventually was required. Both patients participated in in-room mobilization, including bed mobility and transfers with nursing staff, outside of directed physical therapist treatment sessions. Although the 6MWT is an outcome measure used in the acute care setting, it is not often used in the intensive care unit setting, except when activity tolerance data are needed for making significant clinical decisions.
Intervention
Neither patient had performed the 6MWT before administration of the test in the MICU. The 6MWT was performed in the MICU hallway, which consisted of a 90.2-m (296-ft) oval loop. During the test, both patients received MV from a VersaMed iVent portable ventilator (GE Healthcare, Little Chalfont, United Kingdom) through a tracheostomy tube; the MV was managed by a respiratory therapist. For both patients, tracheostomy sites were secured with tracheostomy ties to ensure safety with mobilization. Transfer to the portable ventilator and management of the ventilator during ambulation were coordinated with the respiratory therapist before administration of the 6MWT. In case of emergency, the assigned nurse and the medical team also were notified that the 6MWT was taking place.
The MICU guidelines for mobility and ambulation include stable vital signs (SpO2 of greater than 90%, blood pressure within the target range, resting heart rate of less than 120 beats per minute, and respiration rate of less than 30 breaths per minute) and no escalation of intervention parameters for at least 2 hours before the physical therapist intervention.16 Because neither patient was on any life-sustaining infusion of medication at the time of the 6MWT, each patient's assigned registered nurse disconnected lines to increase ease of mobility. A respiratory therapist was present throughout the test to manage the ventilator and ensure the security of the tracheostomy site. The physical therapist managed the MV tubing to prevent excessive pulling on the tracheostomy site. Although ATS guidelines indicate that patients should push their own oxygen supply, the respiratory therapist advanced the equipment because the mechanical ventilator was part of a wheeled tower created by Johns Hopkins University biomedical engineering students to allow for consolidated transport of the ventilator, oxygen tanks, and telemetry monitor.6 The Figure shows the setup of the equipment.
Wheeled tower created for consolidated transport of the ventilator, oxygen tanks, and telemetry monitor.
Patient 1 used a rolling walker for stability while performing the 6MWT. Patient 2 did not require the use of an assistive device. The physical therapist read modified ATS 6MWT directions (Appendix 2) to the patients before the test and monitored vital signs before, during, and after the session. Directions were modified to describe the test with the use of an oval track rather than the 100-m straightaway described in the ATS guidelines and to ensure that if a rest break was needed for patient safety, the patients understood the means of communication. During each 6MWT, a physical therapy technician was present to follow a wheelchair, time the test, and measure the final distance with a rolling measuring wheel. The ATS guidelines for the termination of testing—chest pain, intolerable dyspnea, leg cramps, staggering, diaphoresis, and pale or ashen appearance—were used.6
Neither patient required a rest break during the 6MWT, nor did any adverse responses occur. Both patients received a 20% increase in the Fio2 at the time of transfer to the portable ventilator (before ambulation) for the 6MWT. In the MICU at Johns Hopkins Hospital, physical therapists have standing orders to titrate Fio2 as needed to increase tolerance of or participation in physical activity and maintain an SpO2 of greater than 90%.18 The increase in the Fio2 was determined by the respiratory therapist and the physical therapist with input from the patient regarding comfort level. During the second 6MWT for patient 2, no increase in Fio2 was required; however, ventilator settings were changed from “assist control” in the patient's room to “continuous positive airway pressure/pressure support ventilation with high-pressure support” in accordance with the patient's reported increase in comfort at these settings. Table 2 shows the relevant information and hemodynamic response for each 6MWT.
Six-Minute Walk Test Dataa
Clinical Impression 2
The 6MWT guidelines published by the ATS state that the recommendations written in the publication are not intended to limit the use of alternative protocols for research studies.6 The test has been amended to accommodate the needs of certain populations and thus has been performed on a treadmill and an oval track.10–12 Literature also has outlined the effects of changes in delivery on outcomes of the test with regard to the distance ambulated.10,11 These factors may be taken into consideration by a transplantation team because patients may ambulate greater distances with changes in track layout and administration. Safe ambulation by a patient dependent on MV requires multiple people and cumbersome equipment. Therefore, in accordance with the literature, an oval track was used in the MICU to prevent the loss of time associated with navigating the equipment around turns.10
Both patients participated in the 6MWT with tracheostomy tubes; however, patient 2 participated in ambulation with an endotracheal tube before the tracheostomy. According to current literature, intubation through an endotracheal tube is not a contraindication to early mobilization and ambulation.16 This information indicates that the 6MWT can be performed by patients requiring MV through an endotracheal tube or a tracheostomy.
No significant differences were noted between the patients despite the fact that patient 1 used a rolling walker. Both patients performed the test without adverse responses (SpO2 of >90%, blood pressure within the target range, resting heart rate of <120 beats per minute, and respiration rate of <30 breaths per minute), demonstrating the apparent feasibility of patients performing the 6MWT while receiving portable MV.
For patient 2, the process of weaning from the ventilator took longer than anticipated, and the patient remained dependent on MV throughout hospitalization before transplantation. Patient 1 was able to wean to a tracheostomy collar, undergo decannulation, and be discharged to home before readmission for transplantation. Given the drastically different weaning mechanics of the patients, it also seems feasible for patients to perform the 6MWT whether or not they are having difficulty weaning from MV.
Neither patient ambulated more than 73.4% of her age-predicted distance on the basis of the equations of Enright and Sherrill,19 in part because of baseline pulmonary impairment and deconditioning despite daily ambulation. The 6MWT was able to demonstrate an improvement in exercise capacity with ambulation in patients receiving MV. Patient 2 showed a 75.46-m improvement in ambulation distance; this value exceeds the 54 m that has been determined to be the minimal clinically important difference on the 6MWT for patients with chronic obstructive pulmonary disease.6 This information is significant because CF is categorized as an obstructive lung condition.2 Improvement in the 6MWT distance could not be attributed solely to daily ambulation because the training effect may have affected performance.6
Discussion
Feasibility
It appears feasible for patients using portable MV to perform the 6MWT in accordance with current recommendations from supporting literature and clinical judgment. Both patients were able to perform the test without rest breaks and with appropriate vital sign responses. Minimal modifications of ATS guidelines were required for implementation of the 6MWT. Patient 2 also showed an improvement in exercise capacity between the first and second administrations of the 6MWT, demonstrating that the requirement for MV did not threaten the validity of the 6MWT. Consideration must be given to having the necessary personnel and equipment to perform the test safely. Administration of the 6MWT in patients receiving MV appears to be safe because no adverse events occurred during administration. Generalizing the findings of this case report with regard to feasibility is difficult because only 2 patients and 3 tests were used.
Generalization of Findings
The findings of this case report cannot be generalized to all patients who are dependent on MV. Ambulation in people receiving MV has been shown to be safe and effective, but clinical judgment should be applied to determine whether the use of this outcome measure with a patient is appropriate.16 For determining the appropriateness of the 6MWT for patients receiving MV, the criteria described in the Clinical Impression 1 section can be used. Clinicians treating patients with pulmonary diagnoses that require MV can consider using the 6MWT as an outcome measure, but they must consider ambulatory status and prior level of function to ensure that the 6MWT is an appropriate outcome measure regardless of MV.
Limitations
A factor limiting the validity of the 6MWT for patients receiving MV was the potential for the distance walked being greater than that on a straight 100-m path.10 Another consideration was the external pacing that may have occurred because of the respiratory therapist advancing the tower with the ventilator or the physical therapist managing the ventilator tubing.6 The environment in which the 6MWT was performed also may be a limitation. The MICU at Johns Hopkins Hospital is an intensive care unit with a marked focus on early mobility; all team members regularly participate in mobilizing patients receiving MV, and appropriate equipment is available for safe ambulation.
To our knowledge, this is the first case report to describe the use of the 6MWT in people who have CF and are receiving MV before a lung transplant. With the increased survival of people who have CF and resulting respiratory failure, there will be an ongoing—if not growing—need for lung transplantation workup and validated measures (such as the 6MWT) of functional performance for patients requiring MV.6 For the 2 patients described in this case report—who had CF, were receiving MV, and were actively awaiting a lung transplant—the 6MWT appeared to be both safe and feasible. Both patients were able to perform the 6MWT with appropriate vital sign responses and ambulated distances greater than the approximately 150-m (500-ft) target for lung transplant consideration.14
Research regarding the validity of the 6MWT for people who have CF and are receiving MV is warranted to allow for modifications, such as modified instructions and normative data. The use of alternative outcome measures, such as the 2-Minute Walk Test, the standing step test, and the Physical Function in Independence Test Scored (timed marching component), to assess, prescribe, and monitor outcomes for endurance in patients in intensive care units should be considered. A larger number of patients requiring MV would be needed to formally assess the feasibility of the 6MWT for such patients, and investigating a broader population of patients with pulmonary diagnoses requiring MV would be needed to establish 6MWT norms for such patients.
Appendix 1.
Hospital Course by Daya
a Patients received physical therapist treatment sessions 3 times per day as 2 airway clearance sessions and 1 activity session (eg, walking or standing exercise) and 1 airway clearance session performed by a respiratory therapist in the evening.
Appendix 2.
Modified Six-Minute Walk Test Directionsa
a Modifications made to American Thoracic Society (ATS) guidelines are shown in italic type. All other directions read during the test were those indicated by ATS guidelines.
Footnotes
Both authors provided concept/idea/project design and writing. Dr Malamud provided data collection, data analysis, project management, patients, and consultation (including review of manuscript before submission).
- Received April 17, 2015.
- Accepted February 15, 2016.
- © 2016 American Physical Therapy Association
References
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