- Email: [email protected]
The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near-Infrared Spectroscopy Study in Humans
Accepted Manuscript The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared Spectroscopy Study in Humans Ariel Palanca, BS, MD, Arthur Yang, BS, MS, Julius A. Bishop, BS, MD PII:
S1934-1482(15)00924-7
DOI:
10.1016/j.pmrj.2015.07.015
Reference:
PMRJ 1555
To appear in:
PM&R
Received Date: 29 January 2015 Revised Date:
9 July 2015
Accepted Date: 13 July 2015
Please cite this article as: Palanca A, Yang A, Bishop JA, The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared Spectroscopy Study in Humans, PM&R (2015), doi: 10.1016/ j.pmrj.2015.07.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared Spectroscopy Study in Humans
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*Ariel Palanca, BS, MD – Corresponding Author – Foot and Ankle Fellow at Oakland Bone & Joint Specialists Arthur Yang, BS, MS
SC
Julius A. Bishop, BS, MD – Assistant Professor of Orthopaedic Surgery at the Stanford
Address for correspondence:
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University Medical Center
Dr. Ariel Palanca c/o Dr. Julius A. Bishop 450 Broadway Street, Pavilion A
Phone: 415-527-7500 Fax: 650-721-3470
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Redwood City, CA 94063
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Email: [email protected]
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The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared
2
Spectroscopy Study in Humans
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ABSTRACT
5
Background: Orthopaedic and rehabilitation physicians often instruct patients to elevate
6
a traumatized or postoperative lower extremity. Elevation is thought to improve patient
7
comfort, as well as decrease swelling, wound complications, and the risk of compartment
8
syndrome. However, elevating a limb with increased compartment pressures has been
9
shown to reduce perfusion pressure and contribute to tissue ischemia. This investigation
10
aims to advance our understanding of the tissue effects of limb elevation using a healthy
11
patient model.
12
Objective: To quantify the effects of elevation, experimentally induced ischemia and
13
immobilization on muscle oxygen saturation in the human leg using near infrared
14
spectroscopy (NIRS).
15
Design: Experimental crossover study
16
Setting: Orthopaedic Surgery research laboratory, Stanford Hospitals & Clinics
17
Patients for Participation: Twenty six healthy volunteers
18
Methods: Using transcutaneous sensors, muscle oxygen saturation of the anterior
19
compartment of the left (control) leg was measured at 0, 15, and 30 cm of elevation
20
relative to the heart using NIRS. A standardized short leg splint and a thigh tourniquet
21
inflated to 50 mmHg were then applied to the right (experimental) leg to simulate a
22
traumatized state. NIRS measurements were then repeated, again at 0, 15, and 30 cm of
23
elevation. Muscle oxygen saturation values at various degrees of elevation of the control
24
and experimental limb were then compared and analyzed using a crossover study design
25
and mixed effects regression.
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Main Outcome Measurements: Muscle oxygen saturation at varying levels of elevation
27
in both the a) control leg and b) experimental leg in a simulated traumatic state
28
Results: 18 males and 8 females between 22 and 62 years of age (mean 29.8 years) were
29
enrolled. Mean regional muscle oxygen saturation (rSO2) of the control limbs at 0, 15
30
and, 30 cm of elevation were 74.2%, 72.5%, and 70.6%, respectively, while mean rSO2
31
of the experimental limbs were 66.3%, 65.0%, and 63.3%. A statistically significant
32
decrease of rSO2 was observed (mean 7.65%) in the experimental limbs compared to the
33
control limbs. As elevation increased, there was a statistically significant decrease in
34
rSO2 of 0.12% per centimeter of elevation. Elevation did not decrease the rSO2 in the
35
experimental limb to a greater degree than in the control limb.
36
Conclusion: Increasing levels of elevation in a human limb results in progressively
37
compromised muscle oxygen saturation as measured by near infrared spectroscopy.
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INTRODUCTION
40
A common orthopaedic practice is to elevate a traumatized or postoperative lower
41
extremity with the goals of improving venous outflow and preventing the stasis of blood
42
associated with a dependent position. Elevation is also thought to decrease swelling,
43
patient discomfort, wound complications, as well as the risk of compartment syndrome.1
44
However, elevating a limb with increased compartment pressures has been shown to
45
reduce perfusion pressure and contribute to tissue ischemia.2,3 Therefore, the ideal degree
46
of elevation for a traumatized lower extremity remains controversial.
SC
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39
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Near infrared spectroscopy (NIRS) is an emerging technology that provides a direct
49
measure of regional muscle oxygen saturation (rSO2). It has been previously verified as
50
an adequate tool to monitor muscle oxygen saturation in an orthopaedic setting.4,5 The
51
purpose of this study was to use NIRS to evaluate the effects of elevation and simulated
52
injury on muscle oxygen saturation of the lower extremity.
53
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48
METHODS
55
Twenty six healthy volunteers were enrolled. Institutional review board (IRB) approval
56
was obtained, and all volunteers gave informed consent. Inclusion criteria included age
57
between 18 and 65, no history of peripheral vascular pathology or major surgery on either
58
lower limb, and palpable pedal pulses. Participant information including age, gender and
59
tobacco use was documented. All perfusion measurements were obtained using the
60
INVOS™ 5100C Regional Saturation Monitor (Covidien, Mansfield, MA, USA). Two
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61
custom foam ramps were manufactured for limb elevation, the short ramp measuring 15
62
cm in height, and the tall ramp measuring 30 cm in height.
63 Each subject was initially positioned supine on an examination table. The INVOS sensor
65
was then placed on the anterior compartment of the control limb (see Figure 1).6 The
66
limb was positioned with no ramp (0 cm), the short ramp (15 cm), or the tall ramp (30
67
cm) for 5-minute intervals. At the end of each interval, the mean regional oxygen
68
saturation (rSO2) of the muscle was recorded.
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The experimental limb was then immobilized in a short leg splint with a pneumatic
71
tourniquet applied to the thigh (See Figure 2). The sensor was then placed on the anterior
72
compartment of the experimental leg. The tourniquet was elevated to 50 mmHg for 5
73
minutes before measurements were obtained. While the tourniquet remained inflated,
74
rSO2 measurements were performed at 0, 15, and 30 cm of elevation (See Figure 3). The
75
tourniquet was not deflated between measurements. Total tourniquet time never exceeded
76
30 minutes.
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77
An experimental crossover design was utilized. Mixed effects regression was used to
79
estimate the effects of ischemia, elevation, and immobilization both within the groups
80
and between the simulated injury and control groups, with a random effect for patient
81
identification to account for the non-dependence of repeated observations in the same
82
person.
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RESULTS
85
Eighteen males and 8 females between 22 and 62 years of age (mean 29.8 years) were
86
enrolled. Participant age had no significant effect on baseline or change in rSO2 in either
87
group. Mean rSO2 of the control limb at 0, 15 and 30 cm of elevation was 74.2%,
88
72.5%, and 70.6% respectively. Mean rSO2 of the experimental limb at 0, 15 and 30 cm
89
of elevation was 66.3%, 65.0%, and 63.3% respectively. In the experimental limb, there
90
was a statistically significant decrease in mean rSO2 of 7.65% (p < .001). In both groups,
91
a statistically significant decrease in 02 saturation of 0.12% per centimeter of elevation
92
was observed as elevation increased (p < .005). There was no significant difference in
93
effect of elevation on rSO2 between the experimental and the control groups. Changes in
94
limb perfusion with elevation are summarized in Figure 4.
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95 DISCUSSION
97
This study demonstrated progressively compromised muscle oxygen saturation in the
98
anterior compartment of the leg with increasing elevation. Muscle oxygen saturation was
99
also compromised by a simulated injury state induced by a pneumatic thigh tourniquet
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and short leg splint immobilization. As expected, oxygenation was most compromised in
101
subjects in the simulated injury state at the highest elevation, although the response to
102
elevation was the same in both limbs with and without simulated injury.
103
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Wiger et al. studied the effects of limb elevation in the anterior compartment of the casted
105
legs under tourniquet using a Myopress catheter. Limb elevation produced a 40%
106
reduction in intramuscular pressure, but reduced blood perfusion pressure by 53%.3
6
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Zhang et al. studied the effects of limb elevation on perfusion and neuromuscular
108
function using photoplethysmography, finding that elevation led to reduced perfusion
109
pressure and mean blood flow.7 This study both corroborates and expands upon previous
110
research exploring the relationship between elevation and perfusion. In keeping with
111
these previous studies, we found that elevation is deleterious to muscle oxygenation, and
112
oxygenation is most compromised in the simulated injury state. While these previous
113
studies used invasive means to indirectly monitor perfusion, NIRS allowed us to directly
114
and noninvasively quantify muscle oxygen saturation. NIRS measurements have
115
previously been demonstrated to correlate directly with muscle perfusion pressures.8
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107
116
Lower limb elevation can help with both edema control and pain in the acute
118
posttraumatic period, but there is evidence that excessive degrees of elevation can
119
increase the risk of compartment syndrome. 1 Reisman et. al. obtained near-infrared
120
spectroscopy values in acute compartment syndrome cases diagnosed by
121
intracompartmental pressure readings.8 Among the ischemic compartments, NIRS values
122
in the anterior, lateral, deep posterior, and superficial posterior compartments of the
123
injured limbs were decreased by an average 10.1%, 10.1%, 9.4%, and 16.3% in
124
comparison with the corresponding compartments of the uninjured leg. Although there is
125
not a current accepted NIRS value which is diagnostic for compartment syndrome,
126
utilizing the contralateral leg as a control can provide a baseline normal value for the
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patient. This technology may provide utility particularly in cases where physical exam
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and symptoms are not diagnostic, if the patient has a brain or spinal cord injury, is
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neuropathic, or is noncommunicative, which can happen more frequently for the physical
130
medicine and rehabilitation specialist.
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131 The optimal amount of elevation for a traumatized extremity remains unknown. While
133
elevation may help with swelling, our study reveals that it is also associated with
134
decreased tissue perfusion. These findings are likely relevant during the acute and sub-
135
acute periods surrounding injury as well as to patients with chronic vascular disease as
136
claudication is characteristically worse in bed at night and is relieved by hanging
137
the leg off the bed. 9 While there aren’t any known elevation cut-offs, the treating
138
physician needs to be aware that every increase in elevation leads to a decrease in this
139
perfusion and the degree of elevation should therefore be individualized to the particular
140
patient and circumstances.
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Noninvasive tissue perfusion monitoring may also serve as a key resource for physiatrists
143
in helping to design rehabilitation protocols. Henton et. al. utilized photospectroscopy
144
and laser Doppler to monitor the success of postoperative regimes designed to
145
acclimatize lower limb free flaps.10 They found that prior to flap training, lower
146
limb dependency for 5 minutes caused reduced oxygenation, increased venous pooling
147
and decreased flow. However, following a three day training regime, flap perfusion
148
accommodated for these changes, proving that it may be a useful tool in postoperative
149
rehabilitation.
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There are several limitations to this study. NIRS is a new technology that is not currently
151
in widespread use, and the threshold for clinically relevant limb ischemia as measured by
152
NIRS is unknown. However, previous animal studies have validated NIRS to have
153
accuracy acceptable to support clinically relevant decision making for the assessment of
154
impaired tissue perfusion and acidosis.4 Stranc et al. used NIRS to monitor viability of
155
pedicled flaps raised in rats and identified a hemoglobin oxygen saturation threshold
156
below which tissues became visibly necrotic.11 Two previous human trials have also
157
utilized NIRS to measure perfusion in lower limbs with diagnosed compartment
158
syndrome, documenting decreased perfusion with increased compartment pressures.11
159
Despite being a relatively new technique, we believe that previous basic science and
160
clinical evidence identifies NIRS as the optimal modality for understanding and
161
quantifying elevation ischemia.
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There are also limitations related to subject selection and experimental design. Most
164
subjects in this study were young and healthy, and their results may not be transferrable
165
to the general population. However, we would expect patients with relevant underlying
166
comorbidities such as peripheral vascular pathology or systemic hypotension to be more
167
vulnerable to the changes that come with elevation. Also, we used a simulated injury
168
model that has been previously published but not validated, and the relationship between
169
elevation and ischemia in actual traumatized or posttraumatic limbs remains unknown.
170
One previous study investigated the effect of limb elevation on hand swelling after
171
surgery using a volumetric method, finding no differences in swelling or complications
172
between elevated and non-elevated groups.12 Furthermore, the investigators were not
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blinded to which limb was experimental and which limb served as a control during the
174
measurements; however, the readings of the NIRS monitor are automated and remain an
175
objective parameter. Finally, we cannot isolate the effects of hip or knee flexion on
176
muscle perfusion, although even at the highest elevation, hip and knee flexion were only
177
50 and 55 degrees respectively.
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178 Conclusion:
180
Increasing levels of elevation in a human limb results in progressively compromised
181
muscle perfusion as measured by near infrared spectroscopy. This suggests that the
182
clinical benefits of elevation such as edema control must be balanced against the
183
deleterious effects of compromised perfusion. Compromised perfusion can be limb-
184
threatening in the acute recovery stages, but may also play a role in subacute
185
rehabilitation stages, which is currently undefined. Ongoing research is indicated to
186
better characterize the relationships between elevation and ischemia in the setting of
187
lower extremity trauma, surgery and rehabilitation.
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ACKNOWLEDGEMENTS
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Covidien supplied the INVOS near infrared spectroscopy unit, which was returned to the
191
manufacturer upon completion of this study.
192 193
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The authors have no conflicts of interest to declare.
194 195
REFERENCES
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1. Browner BD, Levine AM, Jupiter JB, et al. 2008. Skeletal Trauma, 4th ed. Philadelphia: Saunders. 2. Matsen FA 3rd, Wyss CR, Krugmire RB Jr, et al. 1980. The effects of limb elevation and dependency on local arteriovenous gradients in normal human limbs
200
with particular reference to limbs with increased tissue pressure. Clin Orthop.
201
(150): 187-195.
3. Wiger P, Styf JR. 1998. Effects of limb elevation on abnormally increased
SC
202
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intramuscular pressure, blood perfusion pressure, and foot sensation: An
204
experimental study in humans. J Orthop Trauma. 12: 343-347.
205
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4. Ellerby GE, Smith CP, Zou F, Stoller BR. 2013. Validation of a spectroscopic
206
sensor for the continuous, noninvasive measurement of muscle oxygen saturation
207
and pH. Physiol Meas. 34: 859–871.
209 210
5. Stranc MF, Sowa MG, Abdulrauf B, Mantsch HH. 1998. Assessment of tissue
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viability using near-infrared spectroscopy. Br J Plast Surg. 51: 210-217. 6. Jackson K 2nd, Cole A, Potter BK, et al. 2013. Identification of optimal control compartments for serial near-infrared spectroscopy assessment of lower extremity
212
compartmental perfusion. J Surg Orthop Adv. 22: 2-9.
214 215 216
7. Zhang Q, Styf J, Lindberg LG. 2001. Effects of limb elevation and increased
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intramuscular pressure on human tibialis anterior muscle blood flow. Eur J Appl Physiol. 85: 567-571.
8. Reisman WM, Shuler MS, Kinsey TL, et al. 2013. Relationship between near
217
infrared spectroscopy and intra-compartmental pressures. J Emerg Med. 44: 292-
218
298.
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9. Beard, Jonathan D. Chronic lower limb ischemia. West J Med. 2000 Jul; 173(1): 60–63. 10. Henton JM, Simmons JM, Hettiaratchy S, Jain A. Perfusion dynamics in lower
222
limb reconstruction: Investigating postoperative recovery and training using
223
combined white light photospectroscopy and laser Doppler (O2C®). J Plast
224
Reconstr Aesthet Surg. 2015 May 21. [Epub ahead of print]
11. Giannotti G, Cohn SM, Brown M, et al. 2000. Utility of near-
SC
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infrared spectroscopy in diagnosis of lower extremity compartment syndrome. J
227
Trauma. 48: 396-401.
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reduce swelling? A randomized study. J Hand Surg Br 35: 192-194.
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12. Baker RP, Field J, Gozzard C, et al. 2010. Does postoperative hand elevation
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S1934-1482(15)00924-7
DOI:
10.1016/j.pmrj.2015.07.015
Reference:
PMRJ 1555
To appear in:
PM&R
Received Date: 29 January 2015 Revised Date:
9 July 2015
Accepted Date: 13 July 2015
Please cite this article as: Palanca A, Yang A, Bishop JA, The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared Spectroscopy Study in Humans, PM&R (2015), doi: 10.1016/ j.pmrj.2015.07.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared Spectroscopy Study in Humans
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*Ariel Palanca, BS, MD – Corresponding Author – Foot and Ankle Fellow at Oakland Bone & Joint Specialists Arthur Yang, BS, MS
SC
Julius A. Bishop, BS, MD – Assistant Professor of Orthopaedic Surgery at the Stanford
Address for correspondence:
M AN U
University Medical Center
Dr. Ariel Palanca c/o Dr. Julius A. Bishop 450 Broadway Street, Pavilion A
Phone: 415-527-7500 Fax: 650-721-3470
TE D
Redwood City, CA 94063
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Email: [email protected]
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1
The Effects of Limb Elevation on Muscle Oxygen Saturation: A Near Infrared
2
Spectroscopy Study in Humans
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1
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ABSTRACT
5
Background: Orthopaedic and rehabilitation physicians often instruct patients to elevate
6
a traumatized or postoperative lower extremity. Elevation is thought to improve patient
7
comfort, as well as decrease swelling, wound complications, and the risk of compartment
8
syndrome. However, elevating a limb with increased compartment pressures has been
9
shown to reduce perfusion pressure and contribute to tissue ischemia. This investigation
10
aims to advance our understanding of the tissue effects of limb elevation using a healthy
11
patient model.
12
Objective: To quantify the effects of elevation, experimentally induced ischemia and
13
immobilization on muscle oxygen saturation in the human leg using near infrared
14
spectroscopy (NIRS).
15
Design: Experimental crossover study
16
Setting: Orthopaedic Surgery research laboratory, Stanford Hospitals & Clinics
17
Patients for Participation: Twenty six healthy volunteers
18
Methods: Using transcutaneous sensors, muscle oxygen saturation of the anterior
19
compartment of the left (control) leg was measured at 0, 15, and 30 cm of elevation
20
relative to the heart using NIRS. A standardized short leg splint and a thigh tourniquet
21
inflated to 50 mmHg were then applied to the right (experimental) leg to simulate a
22
traumatized state. NIRS measurements were then repeated, again at 0, 15, and 30 cm of
23
elevation. Muscle oxygen saturation values at various degrees of elevation of the control
24
and experimental limb were then compared and analyzed using a crossover study design
25
and mixed effects regression.
AC C
EP
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M AN U
SC
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4
2
ACCEPTED MANUSCRIPT
Main Outcome Measurements: Muscle oxygen saturation at varying levels of elevation
27
in both the a) control leg and b) experimental leg in a simulated traumatic state
28
Results: 18 males and 8 females between 22 and 62 years of age (mean 29.8 years) were
29
enrolled. Mean regional muscle oxygen saturation (rSO2) of the control limbs at 0, 15
30
and, 30 cm of elevation were 74.2%, 72.5%, and 70.6%, respectively, while mean rSO2
31
of the experimental limbs were 66.3%, 65.0%, and 63.3%. A statistically significant
32
decrease of rSO2 was observed (mean 7.65%) in the experimental limbs compared to the
33
control limbs. As elevation increased, there was a statistically significant decrease in
34
rSO2 of 0.12% per centimeter of elevation. Elevation did not decrease the rSO2 in the
35
experimental limb to a greater degree than in the control limb.
36
Conclusion: Increasing levels of elevation in a human limb results in progressively
37
compromised muscle oxygen saturation as measured by near infrared spectroscopy.
M AN U
SC
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26
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38
3
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INTRODUCTION
40
A common orthopaedic practice is to elevate a traumatized or postoperative lower
41
extremity with the goals of improving venous outflow and preventing the stasis of blood
42
associated with a dependent position. Elevation is also thought to decrease swelling,
43
patient discomfort, wound complications, as well as the risk of compartment syndrome.1
44
However, elevating a limb with increased compartment pressures has been shown to
45
reduce perfusion pressure and contribute to tissue ischemia.2,3 Therefore, the ideal degree
46
of elevation for a traumatized lower extremity remains controversial.
SC
RI PT
39
M AN U
47
Near infrared spectroscopy (NIRS) is an emerging technology that provides a direct
49
measure of regional muscle oxygen saturation (rSO2). It has been previously verified as
50
an adequate tool to monitor muscle oxygen saturation in an orthopaedic setting.4,5 The
51
purpose of this study was to use NIRS to evaluate the effects of elevation and simulated
52
injury on muscle oxygen saturation of the lower extremity.
53
TE D
48
METHODS
55
Twenty six healthy volunteers were enrolled. Institutional review board (IRB) approval
56
was obtained, and all volunteers gave informed consent. Inclusion criteria included age
57
between 18 and 65, no history of peripheral vascular pathology or major surgery on either
58
lower limb, and palpable pedal pulses. Participant information including age, gender and
59
tobacco use was documented. All perfusion measurements were obtained using the
60
INVOS™ 5100C Regional Saturation Monitor (Covidien, Mansfield, MA, USA). Two
AC C
EP
54
4
ACCEPTED MANUSCRIPT
61
custom foam ramps were manufactured for limb elevation, the short ramp measuring 15
62
cm in height, and the tall ramp measuring 30 cm in height.
63 Each subject was initially positioned supine on an examination table. The INVOS sensor
65
was then placed on the anterior compartment of the control limb (see Figure 1).6 The
66
limb was positioned with no ramp (0 cm), the short ramp (15 cm), or the tall ramp (30
67
cm) for 5-minute intervals. At the end of each interval, the mean regional oxygen
68
saturation (rSO2) of the muscle was recorded.
M AN U
69
SC
RI PT
64
The experimental limb was then immobilized in a short leg splint with a pneumatic
71
tourniquet applied to the thigh (See Figure 2). The sensor was then placed on the anterior
72
compartment of the experimental leg. The tourniquet was elevated to 50 mmHg for 5
73
minutes before measurements were obtained. While the tourniquet remained inflated,
74
rSO2 measurements were performed at 0, 15, and 30 cm of elevation (See Figure 3). The
75
tourniquet was not deflated between measurements. Total tourniquet time never exceeded
76
30 minutes.
EP
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70
77
An experimental crossover design was utilized. Mixed effects regression was used to
79
estimate the effects of ischemia, elevation, and immobilization both within the groups
80
and between the simulated injury and control groups, with a random effect for patient
81
identification to account for the non-dependence of repeated observations in the same
82
person.
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5
ACCEPTED MANUSCRIPT
RESULTS
85
Eighteen males and 8 females between 22 and 62 years of age (mean 29.8 years) were
86
enrolled. Participant age had no significant effect on baseline or change in rSO2 in either
87
group. Mean rSO2 of the control limb at 0, 15 and 30 cm of elevation was 74.2%,
88
72.5%, and 70.6% respectively. Mean rSO2 of the experimental limb at 0, 15 and 30 cm
89
of elevation was 66.3%, 65.0%, and 63.3% respectively. In the experimental limb, there
90
was a statistically significant decrease in mean rSO2 of 7.65% (p < .001). In both groups,
91
a statistically significant decrease in 02 saturation of 0.12% per centimeter of elevation
92
was observed as elevation increased (p < .005). There was no significant difference in
93
effect of elevation on rSO2 between the experimental and the control groups. Changes in
94
limb perfusion with elevation are summarized in Figure 4.
M AN U
SC
RI PT
84
95 DISCUSSION
97
This study demonstrated progressively compromised muscle oxygen saturation in the
98
anterior compartment of the leg with increasing elevation. Muscle oxygen saturation was
99
also compromised by a simulated injury state induced by a pneumatic thigh tourniquet
EP
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96
and short leg splint immobilization. As expected, oxygenation was most compromised in
101
subjects in the simulated injury state at the highest elevation, although the response to
102
elevation was the same in both limbs with and without simulated injury.
103
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100
104
Wiger et al. studied the effects of limb elevation in the anterior compartment of the casted
105
legs under tourniquet using a Myopress catheter. Limb elevation produced a 40%
106
reduction in intramuscular pressure, but reduced blood perfusion pressure by 53%.3
6
ACCEPTED MANUSCRIPT
Zhang et al. studied the effects of limb elevation on perfusion and neuromuscular
108
function using photoplethysmography, finding that elevation led to reduced perfusion
109
pressure and mean blood flow.7 This study both corroborates and expands upon previous
110
research exploring the relationship between elevation and perfusion. In keeping with
111
these previous studies, we found that elevation is deleterious to muscle oxygenation, and
112
oxygenation is most compromised in the simulated injury state. While these previous
113
studies used invasive means to indirectly monitor perfusion, NIRS allowed us to directly
114
and noninvasively quantify muscle oxygen saturation. NIRS measurements have
115
previously been demonstrated to correlate directly with muscle perfusion pressures.8
M AN U
SC
RI PT
107
116
Lower limb elevation can help with both edema control and pain in the acute
118
posttraumatic period, but there is evidence that excessive degrees of elevation can
119
increase the risk of compartment syndrome. 1 Reisman et. al. obtained near-infrared
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spectroscopy values in acute compartment syndrome cases diagnosed by
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intracompartmental pressure readings.8 Among the ischemic compartments, NIRS values
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in the anterior, lateral, deep posterior, and superficial posterior compartments of the
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injured limbs were decreased by an average 10.1%, 10.1%, 9.4%, and 16.3% in
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comparison with the corresponding compartments of the uninjured leg. Although there is
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not a current accepted NIRS value which is diagnostic for compartment syndrome,
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utilizing the contralateral leg as a control can provide a baseline normal value for the
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patient. This technology may provide utility particularly in cases where physical exam
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and symptoms are not diagnostic, if the patient has a brain or spinal cord injury, is
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neuropathic, or is noncommunicative, which can happen more frequently for the physical
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medicine and rehabilitation specialist.
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131 The optimal amount of elevation for a traumatized extremity remains unknown. While
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elevation may help with swelling, our study reveals that it is also associated with
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decreased tissue perfusion. These findings are likely relevant during the acute and sub-
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acute periods surrounding injury as well as to patients with chronic vascular disease as
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claudication is characteristically worse in bed at night and is relieved by hanging
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the leg off the bed. 9 While there aren’t any known elevation cut-offs, the treating
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physician needs to be aware that every increase in elevation leads to a decrease in this
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perfusion and the degree of elevation should therefore be individualized to the particular
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patient and circumstances.
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Noninvasive tissue perfusion monitoring may also serve as a key resource for physiatrists
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in helping to design rehabilitation protocols. Henton et. al. utilized photospectroscopy
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and laser Doppler to monitor the success of postoperative regimes designed to
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acclimatize lower limb free flaps.10 They found that prior to flap training, lower
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limb dependency for 5 minutes caused reduced oxygenation, increased venous pooling
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and decreased flow. However, following a three day training regime, flap perfusion
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accommodated for these changes, proving that it may be a useful tool in postoperative
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rehabilitation.
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There are several limitations to this study. NIRS is a new technology that is not currently
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in widespread use, and the threshold for clinically relevant limb ischemia as measured by
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NIRS is unknown. However, previous animal studies have validated NIRS to have
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accuracy acceptable to support clinically relevant decision making for the assessment of
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impaired tissue perfusion and acidosis.4 Stranc et al. used NIRS to monitor viability of
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pedicled flaps raised in rats and identified a hemoglobin oxygen saturation threshold
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below which tissues became visibly necrotic.11 Two previous human trials have also
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utilized NIRS to measure perfusion in lower limbs with diagnosed compartment
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syndrome, documenting decreased perfusion with increased compartment pressures.11
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Despite being a relatively new technique, we believe that previous basic science and
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clinical evidence identifies NIRS as the optimal modality for understanding and
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quantifying elevation ischemia.
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There are also limitations related to subject selection and experimental design. Most
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subjects in this study were young and healthy, and their results may not be transferrable
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to the general population. However, we would expect patients with relevant underlying
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comorbidities such as peripheral vascular pathology or systemic hypotension to be more
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vulnerable to the changes that come with elevation. Also, we used a simulated injury
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model that has been previously published but not validated, and the relationship between
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elevation and ischemia in actual traumatized or posttraumatic limbs remains unknown.
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One previous study investigated the effect of limb elevation on hand swelling after
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surgery using a volumetric method, finding no differences in swelling or complications
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between elevated and non-elevated groups.12 Furthermore, the investigators were not
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blinded to which limb was experimental and which limb served as a control during the
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measurements; however, the readings of the NIRS monitor are automated and remain an
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objective parameter. Finally, we cannot isolate the effects of hip or knee flexion on
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muscle perfusion, although even at the highest elevation, hip and knee flexion were only
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50 and 55 degrees respectively.
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178 Conclusion:
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Increasing levels of elevation in a human limb results in progressively compromised
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muscle perfusion as measured by near infrared spectroscopy. This suggests that the
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clinical benefits of elevation such as edema control must be balanced against the
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deleterious effects of compromised perfusion. Compromised perfusion can be limb-
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threatening in the acute recovery stages, but may also play a role in subacute
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rehabilitation stages, which is currently undefined. Ongoing research is indicated to
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better characterize the relationships between elevation and ischemia in the setting of
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lower extremity trauma, surgery and rehabilitation.
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ACKNOWLEDGEMENTS
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Covidien supplied the INVOS near infrared spectroscopy unit, which was returned to the
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manufacturer upon completion of this study.
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The authors have no conflicts of interest to declare.
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REFERENCES
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