Standing With the Assistance of a Tilt Table Improves Minute Ventilation in Chronic Critically Ill Patients

Transcription

1 1972 Standing With the Assistance of a Tilt Table Improves Minute Ventilation in Chronic Critically Ill Patients Angela T. Chang, BPhty, Robert J. Boots, MBBS, MMedSci, FRACP, FJFICM, Paul W. Hodges, PhD, MedDr, Peter J. Thomas, BPhty, Jennifer D. Paratz, PhD, FACP ABSTRACT. Chang AT, Boots RJ, Hodges PW, Thomas PJ, Paratz JD. Standing with the assistance of a tilt table improves minute ventilation in chronic critically ill patients. Arch Phys Med Rehabil 2004;85: Objective: To investigate the effect of standing with assistance of the tilt table on ventilatory parameters and arterial blood gases in intensive care patients. Design: Consecutive sample. Setting: Tertiary referral hospital. Participants: Fifteen adult patients who had been intubated and mechanically ventilated for more than 5 days (3 subjects successfully weaned, 12 subjects being weaned). Intervention: Passive tilting to 70 from the horizontal for 5 minutes using a tilt table. Main Outcome Measures: Minute ventilation (V E), tidal volume (V T), respiratory rate, and arterial partial pressure of oxygen (PaO 2 ) and carbon dioxide (PaCO 2 ). Results: Standing in the tilted position for 5 minutes produced significant increases in V E (P.001) and produced both increases in respiratory rate (P.001) and VT (P.016) compared with baseline levels. These changes were maintained during the tilt intervention and immediately posttilt. Twenty minutes after the tilt, there were no significant changes in ventilatory measures of V E, VT, or arterial blood gases PaO 2 and PaCO 2 compared with initial values. Conclusions: Standing for 5 minutes with assistance of a tilt table significantly increased ventilation in critical care patients during and immediately after the intervention. There were no improvements in gas exchange posttilt. Using a tilt table provided an effective method to increase ventilation in the short term. Key Words: Intensive care; Physiotherapy; Rehabilitation by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation SUBGROUPS OF PATIENTS admitted to intensive care are characterized by periods of prolonged mechanical ventilation. 1 These chronic critically ill patients account for 5.8% of intensive care unit (ICU) admissions but use 37% of ICU From the Department of Physiotherapy, University of Queensland, St Lucia (Chang, Hodges); Intensive Care Facility, Royal Brisbane Hospital, Brisbane (Boots, Thomas); and Cardiopulmonary Research Centre, Alfred Hospital/La Trobe University, Melbourne (Paratz), Australia. Supported by the Australian Physiotherapy Association (Dorothy Hopkins Award), the Australian Federation of University Women (Daphne Elliot Bursary), the National Health and Medical Research Council of Australia, and a Sir Robert Menzies Allied Health Scholarship. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Angela T. Chang, BPhty, Dept of Physiotherapy, University of Queensland, St Lucia, QLD 4072, Australia, a.chang@shrs.uq.edu.au /04/ $30.00/0 doi: /j.apmr resources. 2 In addition to increased financial cost to the community, prolonged ICU stays have been associated with greater mortality and reduced function. 3-5 Early rehabilitation is encouraged in this population to optimize functional outcome after prolonged critical illness and ICU admission. 6 Physiotherapy (PT) rehabilitation techniques used in the management of this patient group include positioning, standing with the use of a tilt table, and mobilization. 7-9 Standing using the tilt table allows a patient to be passively tilted to varying angles to the horizontal and is hypothesized to increase ventilation, increase arousal, improve weight bearing of the lower limbs, and facilitate antigravity exercise of the limbs. 10 This technique is used as a precursor to standing when a patient has lower-limb weakness; it facilitates strengthening exercises of the upper and lower limbs. Despite use of tilting in this population, 7,9 its effects on respiration have not been investigated. Dean and Ross 11 in 1992 reported a case in which a woman admitted to intensive care after a motor vehicle crash was progressively tilted during her stay. Although Dean and Ross reported that her chest radiograph on the following day showed an increase in lung volumes, no measurements of ventilatory parameters or blood gases were recorded. In the clinical setting, tilting is often combined with other PT practices that are known to increase ventilation. 12 In the present study, our aim was to investigate the effect of the passive tilting component alone on short-term ventilatory parameters and gas exchange in a chronic critically ill population and to determine whether any changes were maintained after the intervention was completed. METHODS Participants A consecutive sample of 16 subjects who met the clinical criteria to begin using tilting as part of PT management was recruited over a period of 8 months. One recruited subject did not complete the study protocol because of clinical deterioration; thus, a total of 15 subjects (11 men, 4 women), who were recruited from the ICU of a tertiary referral hospital, completed the study. The clinical criteria to commence tilting were subjects breathing spontaneously with supplemental oxygen (n 8) or with continuous positive airway pressure (CPAP) via a mechanical ventilator (n 7), 5 or more days on mechanical ventilation, an arterial oxygenation level above 70mmHg or oxygen saturation (SpO 2 ) greater than 90% in the absence of an arterial cannular (on a fraction of inspired oxygen [FIO 2 ] 0.4), and being deemed by the treating physiotherapist to be able to tolerate standing on a tilt table for 5 minutes by the treating physiotherapist. Subjects were excluded if they had frank bleeding, hemoglobin level less than 10g/dL, or platelet level less than / L; had an inotrope-dependent blood pressure; showed ischemic changes or arrhythmias on electrocardiograms (ECGs), a suspected or confirmed deep vein thrombosis, or any other condition where weight bearing was contraindicated; body temperature above 37.8 C and/or resting heart rate

2 VENTILATORY CHANGES WITH TILTING, Chang 1973 above 140 beats per minute except in systemic inflammatory response syndrome; had taken sedatives in the past 24 hours; had an intracranial pressure monitor in situ; or required manual hyperinflation during the intervention. Written informed consent was obtained from subjects relatives, with permission from the Guardianship and Administration Tribunal of Queensland and ethics clearance from the institutional Human Medical Research Ethics Committee, in accordance with the Declaration of Helsinki. Ventilatory Parameters Ventilatory parameters were recorded by a portable respiratory mechanics monitor (Ventrak, model 1550) a via a flow sensor into the subject s airway or a face mask. In intubated subjects (n 12), the sensor was placed at the end of the tracheostomy or endotracheal tube and the ventilator or humidification circuitry reattached. In subjects without a definitive airway (n 3), the sensor was attached to a tightly fitting face mask. b If subjects required additional oxygenation, an airoxygen blender c was attached via a T-piece to the mask at the same fractional concentration as before the intervention. The flow signal was exported and analyzed (Analysis Plus, version 5) a and measurements of tidal volume (VT), respiratory rate, and minute volume (V E) were recorded. Arterial Blood Gases When an arterial line was in situ (n 12), arterial blood gases were taken for arterial oxygenation (PaO 2 ) and arterial carbon dioxide (PaCO 2 ) analysis d before and after the tilting intervention. Additional Recordings Measurements of the duration of mechanical ventilation in days and weaning duration in hours, defined as the time from the initiation of the first CPAP or T-piece weaning trial until successful extubation, were recorded from medical records. In addition, demographic information was noted, including cause of ICU admission, sepsis-related organ failure assessment (SOFA) score, and medical history. Procedure Subjects were positioned supine and the flow sensor applied. Ventilated subjects were suctioned without additional oxygenation via closed suction circuit, and all subjects were rested for 20 minutes without intervention. An arterial blood sample was taken and initial measurements of respiratory mechanics were recorded for 2 minutes. The subject was transferred with assistance to the tilt table by using a sliding board and straps fastened at the level of the knees, hip, and chest for support. Respiratory mechanics were recorded as the tilt table was lifted from 0 to 70 from the horizontal for an average of 1 minute (transition to tilt) and for the 5 minutes during which the subject was in the tilted position. A 5-minute period was used because it was the subject s first tilt, and, in the absence of guidelines, our clinical experience suggested it was a duration that would be tolerated by patients who had clinical characteristics similar to those outlined by our inclusion and exclusion criteria. In addition, ECGs, blood pressure, and SpO 2 were monitored during the intervention. If, at any time during the testing, SpO 2 fell more than 10% of initial values, heart rate changed by greater than 30 beats per minute, cardiac arrhythmias developed, or any other clinical deterioration occurred, the tilting would have been stopped and supplemental oxygen given. This was not required for any subjects during the study protocol. The tilt table was returned to the horizontal position, and the respiratory measurements were repeated. After 20 minutes in this supine position, a second arterial blood sample was collected and all respiratory measurements were repeated. Two investigators collated all data; one collected ventilatory data and the other analyzed the arterial blood gas samples. Statistical Analysis The VT, respiratory rate, and V E were measured at 5 increments (initial, transition to the tilt, during standing with the tilt table, immediately posttilt, 20min after the tilt) and analyzed with a linear mixed model. The significance level was.05, and planned contrasts were used to compare the effect of time on each variable with baseline values. The duration of ventilation and weaning were included as covariates in the analysis. Measures of the pre- and posttilt PaO 2 and PaCO 2 were analyzed with repeated-measures analysis of variance. Power calculations indicated that a sample size of 15 subjects was sufficient to detect a 2.2L/min change in V E, a 20% difference from initial levels, with a power of 0.8 and significance level of.05. RESULTS Each subject s admitting conditions and comorbidities are outlined in table 1. Blood gas measurements were recorded in only 11 subjects because of equipment complications (n 1) and lack of arterial cannular (n 3). Ventilatory measurements at 20 minutes after the tilting intervention were recorded only in 7 subjects because of time constraints placed by clinical staff. No adverse events occurred during the study, and all 15 subjects completed the 5-minute tilt intervention without deterioration of their clinical condition. The tilting intervention was the subjects first exposure to the treatment modality. All interventions were during the weaning period (n 7) or during the postwean period before a subject could maintain spontaneous ventilation via oxygen support for 24 hours (n 8). Ventilatory Parameters When subjects stood with the assistance of the tilt table, there was a significant change in V E (P.001), respiratory rate (P.001), and VT (P.016) over time. Further analysis with planned contrasts showed the effects of tilting on VT, respiratory rate, and V E at each time period (fig 1). Minute ventilation increased by 26% during the transition to the tilt (n 15, P.002), by 27% during the tilt intervention (n 15, P.001), and by 26% posttilt (n 15, P.001) compared with baseline levels. At 20 minutes postintervention, there was a small but not significant 2.1% fall in V E (n 7, P.322). Similarly, respiratory rate increased by 11% in the transition to tilt (n 15, P.007), by 19% during the tilt (n 15, P.001), by 18% posttilt (n 15, P.001), and remained 13% higher than baseline levels at 20 minutes after the tilt (n 7, P.016). There was a small but nonsignificant increase in VT of 13% in the transition to tilt (n 15, P.083), but VT was increased by 17% during the tilt (n 15, P.015), and remained 11% above baseline levels posttilt (n 15, P.027). There was a trend for VT to decrease by 23% at 20 minutes posttilt, but this was not significant (n 7, P.369). Arterial Blood Gases Despite the increases in ventilatory parameters, there were no significant changes in PaO 2 or PaCO 2 after standing using the tilt table. There was a nonsignificant decrease in PaO 2 (82.0mmHg vs 79mmHg, P.24, n 12), and PaCO 2 was un-

3 1974 VENTILATORY CHANGES WITH TILTING, Chang Subjects Table 1: Subject Demographics Age (y) Condition Past History ICU Stay (d) Wean (h) MV (d) SOFA Score 1 20 Closed head injury None Right Nephrectomy COPD, CCF, HT, obesity 3 67 Respiratory failure NIDDM HT Sepsis after colectomy AVR, HT Gastrointestinal bleed COPD, IHD Oesophagectomy COPD Community acquired COPD pneumonia 8 31 Lap salpingectomy None Subarachnoid None hemorrhage AAA repair, graft COPD, NIDDM infection Exacerbation of COPD COPD, CCF Exacerbation of COPD Asthma, HT Respiratory failure COPD, HT, smoker post Community acquired None pneumonia Aspiration after AAA repair CRF Abbreviations: AAA, abdominal aortic aneurysm; AVR, aortic valve repair; CCF, congestive cardiac failure; COPD, chronic obstructive pulmonary disease; CRF, chronic renal failure; HT, hypertension; IHD, ischemic heart disease; MV, mechanical ventilation; NIDDM, noninsulindependent diabetes mellitus. changed (41.7mmHg vs 40.8mmHg, P.12, n 12). When subjects were stratified according to a ratio of PaO 2 to FIO 2 (P/F ratio) below 200, 13 indicating poor gas exchange, subjects with initial P/F ratio less than 200 (n 4) all showed increases in PaO 2 20 minutes posttilt (mean, 2.3mmHg). DISCUSSION Our results show that standing using the assistance of the tilt table at 70 from the horizontal produced a transient increase in ventilation in critically ill patients. This increase was associated with increases in both VT and respiratory rate that were sustained immediately after the intervention. Ventilatory Increases With Tilting Despite the fact that tilting is used by physiotherapists to help ICU patients stand, few studies have investigated the clinical effects of tilting. 14 To our knowledge, there are no quantitative trials reporting the effects of tilting on ventilation. Only 1 case study 11 has been reported; a woman ventilated for more than 16 days began tilting on day 5 of her intensive care admission. The initial tilt angle was 15 for 5 minutes, increasing to 45 for 10 minutes. The study did not measure ventilatory parameters during or after tilt table treatments. Lung volumes on chest radiographs were improved posttilt intervention. From this single measure, it is difficult to determine the effect of tilting on ventilation. A systematic review 15 of positioning in ICU patients found no studies that investigated the effect of vertical positioning on ventilation of patients with acute respiratory failure. Therefore, our results are among the first to quantify the short-term effects on ventilation of standing using the tilt table in patients in intensive care. Mechanisms for Ventilatory Changes Several mechanisms may increase ventilation after a position change such as tilting. It is widely accepted that functional residual capacity (FRC) increases with standing with movement of the abdominal contents and greater descent of the diaphragm. 16,17 This change in FRC will also alter the point at which tidal breathing occurs on the pressure volume curve, resulting in improved compliance of the respiratory system. 18 As respiratory system resistance is decreased and compliance increased in the upright position 18,19 without a change in respiratory drive, 20 a larger change-inspired volume may occur in the tilted position. The effort required to sustain the position on the tilt table may also lead to increased energy expenditure and thus increase ventilation. In healthy subjects, increases in oxygen consumption (V O2 ) were shown with passive tilting 21,22 when subjects were not securely fastened to the table, which may result in increased muscle activity. In contrast, no changes in V O2 or carbon dioxide production were found when straps were used This suggests increased muscle activity in the tilted position may increase ventilation. We did not include limb exercises in our study, and it is possible that the contribution of muscle activity may be small. Because we did not measure energy expenditure or muscle activity, the effect of muscle contraction on ventilation cannot be determined. Alternatively, upright posture may promote increased ventilation by vestibular stimulation of the otolith organs. In the cat model, a head-up position to 50 produced a small increase in phrenic nerve activity, indicating some vestibular stimulation of respiration. 26 However, this was proposed as a strategy to increase intra-abdominal pressure and to facilitate venous return to the heart rather than as a mechanism to increase ventilation. 26 In the human model, there was no effect on ventilation with stimulation of the otolith organs. 27 Therefore, vestibular input from the effect of passive head-up or headdown tilting is unlikely to affect ventilation with head-up tilting to 70.

4 VENTILATORY CHANGES WITH TILTING, Chang 1975 Effects on Gas Exchange Despite the increases in ventilatory parameters, there were no changes in PaO 2 or PaCO 2 20 minutes after the tilt. This shows that passive tilting does not adversely affect gas exchange in long-term ICU patients as it does in subjects with compromised gas exchange (P/F ratio 200, n 4). All subjects showed an increase in PaO 2 minutes after the tilt, when there was no change in V E or VT. This suggests that tilting may benefit gas exchange in this patient group, which is at greater risk of respiratory compromise. Clinical Implications of Standing With a Tilt Table The increases in V E and VT may indicate that standing with a tilt table can help prevent pulmonary complications. For instance, increased V E and VT may help redistribute secretions and facilitate coughing or suctioning. 11 Because ventilation increases with tilting, it may be used in conjunction with other respiratory techniques such as breathing exercises, to further improve ventilation in debilitated patients. In addition, because tilting is passive, this technique may be used to increase ventilation in patients who cannot participate in active breathing exercises because of impaired ability to cooperate, such as patients with neurologic injuries. However, the effect of standing with assistance of a tilt table in the prevention of pulmonary complications cannot be determined through this preliminary study. Fig 1. Effect of standing with assistance of a tilt table on ventilatory parameters. (A) Tidal volume, (B) minute ventilation, and (C) respiratory rate. Note the increase in VT, V E, and respiratory rate during and posttilt. Error bars denote 1 standard deviation. *P<.05; **P<.01. The tilting intervention may increase a patient s anxiety levels, and thus elevated sympathetic nervous system (SNS) activity may have influenced respiration. It is widely accepted that ventilatory response to SNS stimulation involves airway dilation and rapid shallow breathing, that is, an increased respiratory rate and reduced VT. 28 These ventilatory changes also occur with induced anxiety in healthy subjects doing mental arithmetic 29 and while receiving electric stimulation. 30 Respiratory response to tilting in this study was characterized by an increase in VT during the tilt intervention and immediately posttilt, suggesting that other factors may influence ventilation because sympathetic activity alone would have induced a reduction in VT, as reported in healthy subjects. We showed an increase in ventilation with passive tilting; further studies are required to determine the mechanisms of changes in ventilation with standing with assistance of the tilt table because the mechanisms may have clinical implications when selecting techniques to improve ventilation. Study Limitations An unexpected finding of the study was the lack of significant change in V E and VT 20 minutes after the cessation of the tilt. However, ventilatory data at 20 minutes posttilt were only obtained in 7 of the 15 subjects. We were unable to record ventilatory parameters in 8 subjects because the equipment malfunctioned and because of time restraints placed on the clinical staff. The reduced sample for this time period may explain the lack of significant change in V E and VT; further investigation is needed to determine the carryover effect of passive tilting. Additionally, the lack of carryover effects may reflect the duration of tilting; longer periods may be required to produce sustained changes. Having the patient sit in a chair after a tilt intervention may also help maintain the ventilatory changes and could form the basis of further study. The clinical presentations of our subjects were varied (table 1). This variation was necessary to represent the clinical case mix of patients commonly seen in a general ICU. Two subjects continued on ventilation for longer periods to manage their intracranial hemodynamics rather than because of respiratory complications. However, tilting is a technique used by physiotherapists with a wide case mix of patients. Despite the varying presentations, our study showed increases in VT, V E, and respiratory rate after tilting. Safety Issues During the tilting intervention, there were no adverse events, as defined as a fall in SpO 2 greater than 10% of initial values, a change in heart rate greater than 30 beats per minute, development of cardiac arrhythmias, or other clinical deterioration, agitation, or disconnection of equipment. Despite a mean SOFA score of 5.3, all subjects tolerated the standing with the tilt table. CONCLUSIONS This study showed the physiologic responses in the ventilatory system with an increase in V E, VT, and respiratory rate after standing with the tilt table for 5 minutes without limb

5 1976 VENTILATORY CHANGES WITH TILTING, Chang exercise in patients who had been ventilated for more than 5 days. This shows that passive tilting alone may affect ventilation, with changes in respiratory mechanics and FRC, which may be more pronounced when combined with other exercise programs in the tilted position. Our results, however, show that the tilt table can be used as a treatment tool to improve short-term minute ventilation in stable intensive care patients without adverse effects on arterial blood gases. Further research is needed to determine the long-term effects of progressive tilting in preventing pulmonary complications in this patient population. References 1. Carson SS, Bach PB. The epidemiology and costs of chronic critical illness. Crit Care Clin 2002;18: Wagner DP. Economics of prolonged mechanical ventilation. Am Rev Respir Dis 1989;140(2 Pt 2):S Carson SS, Bach PB, Brzozowski L, Leff A. Outcomes after long-term acute care. 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