Page 1 of Articles
34
in PresS. Am J Physiol Heart Circ Physiol (May 4, 2007). doi:10.1152/ajpheart.01237.2006
Impairments in microvascular reactivity are related to organ failure in
human sepsis
Kevin C. Doerschug,1 Angela S. Delsing,1 Gregory A. Schmidt,1 William G.
Haynes1,2
Department of Internal Medicine1 and General Clinical Research Center2
University of Iowa Carver College of Medicine
Iowa City, Iowa
Corresponding Author:
Kevin C. Doerschug, MD, MS
200 Hawkins Drive
Iowa City, IA 52242
319-384-6482 (P)
319-353-6406 (F)
[email protected]
Running title: Microvascular reactivity and organ failure in sepsis
Copyright Information
Copyright © 2007 by the American Physiological Society.
Page 2 of 34
-0Abstract
Severe sepsis is a systemic inflammatory response to infection resulting in acute
organ dysfunction. Vascular perfusion abnormalities are implicated in the
pathology of organ failure, but studies of microvascular function in human sepsis
are limited. We hypothesized that impaired microvascular responses to reactive
hyperemia lead to impaired oxygen delivery relative to the needs of tissue, and
that these impairments would be associated with organ failure in sepsis. We
studied 24 severe sepsis subjects 24 hours after recognition of organ
dysfunction; 15 healthy subjects served as controls. Near-InfraRed
Spectroscopy (NIRS) was used to measure tissue:1) microvascular hemoglobin
signal strength; and 2) oxygen saturation of microvascular hemoglobin (StO2).
Both values were measured in thenar skeletal muscle before and after 5 minutes
of forearm stagnant ischemia. At baseline, skeletal muscle microvascular
hemoglobin was lower in septic than control subjects. Microvascular hemoglobin
increased during reactive hyperemia in both groups, but less so in sepsis. StO2
at baseline and throughout ischemia was similar between the two groups,
however the rate of tissue oxygen consumption was significantly slower in septic
subjects than in controls. The rate of increase in StO2 during reactive hyperemia
was significantly slower in septic subjects than in controls; this impairment was
accentuated in those with more organ failure. We conclude that organ
dysfunction in severe sepsis is associated with dysregulation of microvascular
oxygen balance. NIRS measurements of skeletal muscle microvascular
perfusion and reactivity may provide important information about sepsis, and
Copyright Information
Page 3 of 34
-1serve as endpoints in future therapeutic interventions aimed at improving the
microcirculation.
Abstract: 250 words
Key Words: Sepsis; Microcirculation; Shock; Spectroscopy, Near-Infrared
Copyright Information
Page 4 of 34
-2Introduction
Severe sepsis is an inflammatory response to infection that results in
acute organ dysfunction.(5) Despite hyperdynamic systemic blood flow and
elevated mixed venous oxygen saturations, elevated blood lactate concentrations
are common in sepsis and suggest that a maldistribution of oxygen delivery
within the tissues may contribute to organ failure and death. Impaired
microvascular perfusion was first identified in animal models,(28) and direct
visualization of vessels recently demonstrated heterogeneous flow in the
sublingual microcirculation of patients with severe sepsis,(11, 38) providing
human data to substantiate the models.
Normal capillary beds maintain homogenous flow (i.e. matching supply to
demand) through signaling from endothelium to precapillary arterioles. Sepsis
disrupts this signaling(40) and also mechanically disrupts flow by activating
endothelium, leukocytes, and platelets. Models of flow heterogeneity
quantitatively predict observed abnormalities in oxygen delivery and critical
oxygen extraction in porcine models of sepsis.(42) Accordingly, impaired
microvascular function is recognized as a key to organ failure in sepsis,(3) and
urges us to investigate the regulation of tissue bloodflow.
Tissue ischemia is followed normally by arteriolar dilation and a temporary
rise in local blood flow, a phenomenon termed reactive hyperemia (RH), which is
mediated through myogenic and endothelial-derived factors. Prior studies have
shown impaired RH in humans with severe sepsis.(1, 27, 35) We hypothesized
that impaired microvascular responses to RH lead to impaired oxygen delivery
Copyright Information
Page 5 of 34
-3relative to the needs of tissue, and that these impairments would be associated
with organ failure. To test this hypothesis, we used near infra-red spectrometry
(NIRS) to measure skeletal muscle tissue hemoglobin concentration and oxygen
saturation before and after stagnant ischemia in septic patients.
Copyright Information
Page 6 of 34
-4-
Methods
We studied 24 consecutive patients in our Medical Intensive Care Unit that
fulfilled enrollment criteria, including 1) severe sepsis defined by consensus
statement(5); 2) organ failure for no more than 24 hours; 3) signed informed
consent, including from surrogate decision-makers. Patients were excluded for
the following reasons: 1) recent chemotherapy; 2) recent steroid or
immunosuppressive agents; 3) severe peripheral vascular disease, dialysis
fistulas, or mastectomies that would preclude safe forearm occlusion; 4) “Do Not
Resuscitate” order at time of enrollment. In addition to sepsis subjects, we
studied 15 healthy volunteers. This study was approved by the University of
Iowa Institutional Review Board.
Sepsis subjects were studied 24 hours after the clinical recognition of
organ dysfunction. All resuscitation goals were left to the ICU team. Patient
clinical data were collected prospectively. Organ failure was assessed using the
Sequential Organ Failure Assessment (SOFA) scoring system,(41) and severe
organ failure was defined as SOFA >10, a predictor of 50% mortality.(18)
Vasoconstrictor use was defined as SOFA cardiovascular component > 3.
NIRS measurements of perfusion and reactivity
We utilized NIRS as a non-invasive technique that detects differential
absorption of oxy- and de-oxyhemoglobin within arterioles, capillaries, and
venules of skeletal muscle with little influence from bloodflow to skin or other
tissues.(31) Because NIRS is limited to monitoring of only small vessels
Copyright Information
Page 7 of 34
-5(according to Beer’s law) (31), and because it monitors pre- and post-capillary
vessels (i.e. before and after oxygen extraction) NIRS has previously been used
to assess the oxygen balance in the microcirculation of skeletal muscles of septic
individuals.(21) In addition to microvascular oxy- and deoxy-hemoglobin, NIRS
detects oxy-and deoxy myoglobin in the muscle, although the latter chromophore
has little influence on the total signal.(6, 31) Nonetheless, nomenclature has
evolved such that some literature and device manufacturers refer to tissue
measurements, and we will utilize this nomenclature for the purpose of
consistency.
A commercially available, clinical spectrometer (InSpectra Tissue
Spectrometer Model 325, Hutchinson Technology Inc., Minnesota) was applied
to the thenar eminence throughout the study. This monitor utilizes 15 mm
spacing between emission and detection points, and provides tissue attenuation
measurements at four discreet wavelengths (680, 720, 760, and 800 nm).
Details of this wide-gap second derivative spectroscopic method have been
described previously.(34) The monitor provides the total hemoglobin signal
strength (TH) in the volume of tissue sensed by the probe, as well as fractions of
oxy- and de-oxyhemoglobin through a tissue depth approximating the probe
length.(34) Values were recorded directly to computer every 3.5 seconds. The
positioning of the probe on the thenar eminence was chosen due to relatively low
adiposity, consistency with other studies, and because of its amenability to
forearm manipulation.
Copyright Information
Page 8 of 34
-6A vascular cuff (Hokanson Inc., Washington) was inflated to 250 mm Hg
on the forearm to achieve stagnant ischemia for five minutes, then rapidly
deflated. For each subject we assessed the following:
1) Total hemoglobin signal, an indicator of blood volume in the region of
microvasculature sensed by the probe (referred to as total tissue
hemoglobin index (TH) by the manufacturer) expressed in arbitrary units
(au). TH was measured at baseline and recorded as the average of 5
values immediately prior to ischemia;
2) Microvascular hemoglobin during reactive hyperemia (TH-RH), defined as
the average of 5 TH values obtained during the interval 18-32 seconds
following the release of occlusion. This prospectively defined interval
depicts a plateau that follows a rapid increase during the initial 14 seconds
of flow, and precedes decline toward baseline values;
3) Change in TH ( TH), defined as the difference of TH-RH minus TH, and
percent change in TH (% TH), defined as TH * 100 / TH;
4) Oxygen saturation of hemoglobin in the microvasculature, referred to as
tissue oxygen saturation (StO2) by the device manufacturer, expressed as
percent;
5) Oxygen consumption of skeletal muscle tissue during ischemia (VO2tis),
defined as the difference in microvascular O2 content (TH * StO2 * 1.39) at
beginning and end ischemia divided by the duration of ischemia; and
Copyright Information
Page 9 of 34
-76) Rate of reoxygenation (RR), the average rate of StO2 increase in the first
14 seconds following the release of arterial occlusion (StO2 at 14 seconds
minus StO2 at end ischemia, divided by 14 seconds), expressed as
percent per second.
The timing and duration of intervals were defined prospectively based upon
previous data. Pulse rates and blood pressures were specifically recorded
during testing to exclude the possibility that systemic hemodynamic changes
were responsible for local perfusion changes.
Data were analyzed with GraphPad Prism software v4.0 (San Diego, CA).
Three groups were compared using one-way Analysis of Variance (ANOVA).
Significant differences (alpha <0.05) were evaluated with Tukey’s Multiple
Comparison Test. Two sepsis subjects had ischemia for less than five minutes
(one mechanical malfunction, one human error); for these subjects we analyzed
pre-ischemia data, but excluded post-ischemia data.
Copyright Information
Page 10 of 34
-8Results
Clinical Data
Twenty four subjects with severe sepsis were enrolled during the study
period. Demographic and clinical data are listed in Table 1.
The mortality of
sepsis subjects was 33%, consistent with a group at high risk of death. Taken as
a whole, these data describe a heterogeneous, critically ill population typical of
severe sepsis.
Tissue hemoglobin
TH was significantly reduced in severe sepsis subjects at baseline (see
Figure 1). There was no correlation between TH and blood hemoglobin
concentration. Pre-ischemic TH did not differ between septic subjects with
severe organ failure and those with only modest dysfunction, however it was
lower in those subjects receiving vasoconstrictor infusions than in those who did
not receive these medications (13.4 au, SD 3.5, versus 18.4 au, SD 5.7, p =
0.01). Among subjects with severe sepsis, there was no relationship between
TH and age (linear regression r2 =0.005, p=0.74).
Tissue hemoglobin during reactive hyperemia
During and after the period of stagnant ischemia, there were no observed
changes in systemic pulse rate or blood pressure. Following the release of the
forearm vascular cuff and the subsequent return of blood flow, TH increased
rapidly (within 30 seconds) to baseline levels or higher and remained elevated for
approximately two minutes in both severe sepsis and control subjects. TH-RH
Copyright Information
Page 11 of 34
-9was significantly lower in septic subjects with both extensive and modest organ
dysfunction compared to control subjects (p= 0.0002, see Table 2) but there was
no significant difference between the two septic subgroups. When we examined
the incremental change in TH from baseline to reactive hyperemia ( TH),
subjects with severe sepsis culminating in extensive organ dysfunction tended to
have less increase in TH compared to either those with modest organ failure or
control subjects. Because TH was lower in severe sepsis subjects, however,
when TH was expressed as a percent of baseline (% TH), the values were
similar in all three groups. We examined the effect of vasoconstrictor infusions
on TH-RH and found this measure to be somewhat lower in subjects receiving
these medications (16.8 au [SD 6.0]) compared to those that did not receive
these medications (22.3 au [SD 6.5]; Student’s t-test p = 0.05). However, we
found virtually no effect of vasoconstrictor use on TH (p = 0.7) and % TH (p =
0.91).
Tissue oxygenation before, during, and after stagnant ischemia
Baseline, or resting, StO2 in control subjects was 84% [SD10], consistent
with a vascular bed that includes pre-and post-capillary vessels, and with
previous reports.(34) Resting StO2 was similar in severe sepsis subjects (82%
[SD13], see Figure 2),. In parallel, resting StO2 measured 24 hours after the
onset of organ dysfunction was not associated with organ failure or survival at 7,
14, or 30 days.
Copyright Information
Page 12 of 34
- 10 During stagnant ischemia, StO2 decreased in both control and severe
sepsis subjects. StO2 was similar in both groups at 30 and 60 seconds of
ischemia, as well as at the end of ischemia (Figure 2). Neither the absolute StO2
nadir nor change in StO2 during ischemia was associated with the degree of
organ failure in septic subjects. However, VO2tis was significantly lower in
severe sepsis (233 au [SD 156]) compared to control subjects (382 au [SD120];
p = 0.003)
With the return of bloodflow, StO2 increased rapidly and remained
elevated above baseline values for approximately two minutes in both severe
sepsis subjects and normal controls. Representative StO2 curves of two
individual subjects during reactive hyperemia are shown in Figure 3. In severe
sepsis subjects with only modest organ dysfunction, the rate of reoxygenation
(RR) tended to be slower (3.6 % / sec [SD 1.2]) than in normal controls (4.7 % /
sec [SD1.1]). Severe sepsis subjects with severe organ failure (SOFA >10) had
significant and pronounced impairments in RR (2.3 % / sec [SD1.5]) when
compared to septic subjects with less organ dysfunction as well as normal
controls (see Figure 4). RR tended to be slower in those that did not survive
hospitalization (2.5 % / sec [SD1.5]) than in those who survived (3.3 % / sec
[SD1.4]) although this fell short of statistical significance (p=0.20). RR was not
associated with mean arterial pressure (r2 = 0.01; p = 0.62) nor serum glucose
concentration. Because exogenous norepinephrine and other vasoconstrictors
may affect vasodilation and reactive hyperemia, we compared RR values in
severe sepsis subjects receiving vasoconstrictors (2.5 % / sec [SD1.7]) to sepsis
Copyright Information
Page 13 of 34
- 11 subjects not receiving vasoconstrictors (3.7 % / sec [SD1.3]) and found no
significant differences (Student t-test p = 0.11). There was no relationship
between RR and age in septic subjects as investigated by linear regression (r2 =
0.001; p = 0.85).
To further investigate the microvascular milieu resulting in impaired tissue
oxygen balance during reactive hyperemia in septic subjects, we analyzed the
relationships of RR with both tissue hemoglobin and tissue oxygen consumption.
In septic subjects, RR correlated significantly with TH-RH (r2 = 0.47, p = 0.0006;
see Figure 5) such that those with pronounced impairments in RR also had less
total microvascular hemoglobin during reactive hyperemia. Interestingly, we
also found a linear relationship between VO2tis and RR in severe sepsis subjects
(r2 = 0.38; p = 0.002; see Figure 6).
Copyright Information
Page 14 of 34
- 12 -
Discussion
We have shown that microvascular function is abnormal in septic subjects
studied within 24 hours of organ dysfunction. First we found that the skeletal
muscle tissue hemoglobin signal is reduced in sepsis. Most blood volume and
thus hemoglobin is likely to be contained within post-capillary venules in skeletal
muscle, and therefore these data imply impaired venous vessel capacitance.
However, this is in contrast to common descriptions of increased venous
capacitance in the macrovasculature during septic shock.(13) Catecholamine
infusions decrease venous capacitance(9) and hence could explain some of the
differences in tissue hemoglobin found in our septic subjects. However, septic
subjects not receiving these medications also had impaired tissue hemoglobin
compared to controls. Several characteristics of sepsis, such as anemia, and
abnormal microvascular perfusion due to vessel constriction, decreased
microvascular density, or venular leukostasis could also account for this reduced
signal. Because we could show no correlation between TH and blood
hemoglobin concentration, we suspect that microvascular perfusion
abnormalities underlie this finding.
In addition to deficits in tissue hemoglobin during sepsis, we demonstrated
abnormal tissue oxygen balance during and after stagnant ischemia. Baseline
StO2 was normal in resuscitated sepsis, a finding that parallels findings of normal
or high central venous oxygen saturations after resuscitation.(37) Despite
normal resting StO2, VO2tis was significantly reduced during ischemia in septic
subjects. Measurements of oxygen consumption in the absence of flow should
Copyright Information
Page 15 of 34
- 13 be interpreted carefully, as flow-induced vasomotion may increase oxygen
expenditures.(8) However, our finding is in line with several studies showing that
oxygen extraction and consumption are indeed low,(24, 25) in contrast to the
teaching of a decade ago.
Our most provocative finding is that the rate of tissue reoxygenation is
markedly impaired in sepsis and that the rate of reoxygenation is related to the
degree of organ dysfunction. While our method does not measure bloodflow per
se, an acute rise in StO2 can only reasonably be explained by an influx of oxygen
rich arterial blood. The NIRS method does not detect hemoglobin in a single
vessel, but rather the bulk of hemoglobin within the entire microvascular bed
within the probed region. It stands to reason that impaired RR may represent
either reduced (bulk) arterial influx to the tissue, or rapid desaturation of
hemoglobin within the capillaries; both explanations describe an imbalance of O2
delivery relative to the needs of the tissue. Furthermore, our findings of similar
rates of StO2 decrease during ischemia in sepsis, as well the relationship
between RR and TH-RH, argue against an increase in deoxyhemoglobin as a
cause for impaired RR.
These data suggest that the thenar microvasculature is unable to respond
appropriately to ischemia by augmenting blood flow, especially in the sickest
subjects. Microvascular perturbation due to abnormal vasoconstriction in sepsis
is evident in studies describing improved microvascular flow after administration
of vasodilators.(10, 39) Sepsis is associated with increased nitric oxide (NO)
Copyright Information
Page 16 of 34
- 14 synthesis via inducible nitric oxide synthase (iNOS) in many cells and tissues,
which down-regulates endothelial NOS,(17, 30) leading to impaired reactivity.(2)
Catecholamines will counteract NO and impair reactive hyperemia. It is
interesting that microvascular reoxygenation rates of subjects receiving
vasoconstrictor infusions were somewhat lower than of those subjects not
receiving these medications, but this difference did not exceed that which may
occur through statistical chance. Similarly, the total microvascular hemoglobin
during reactive hyperemia was statistically lower in subjects on vasoconstrictors
compared to the same measure in their counterparts. Yet neither the absolute
change nor relative change in microvascular hemoglobin was affected by
vasoconstrictors, suggesting this difference may reflect differences in baseline
microvascular hemoglobin (including both pre- and post-capillary vessels) more
than the hyperemic response. We suspect three factors contribute to a lack of
evidence of catecholamine effects on the microvascular hyperemic response in
severe sepsis: 1) adrenergic receptors have decreased binding affinity for
norepinephrine(20) and are down-regulated in sepsis,(7) thus diminishing the
response to norepinephrine and other catecholamines; 2) endogenous
vasoconstrictors are prevalent in the septic bloodstream,(43) and thus the
relative contribution of exogenous catecholamines to arteriolar constriction may
be small; and 3) additional patient factors beyond catecholamines likely
contribute to impaired microvascular bloodflow.
Tissue oxygen transport is exceedingly complex in sepsis as tissue
perfusion,(37) oxygen diffusion, and mitochondrial function,(19) are disturbed
Copyright Information
Page 17 of 34
- 15 and inter-dependent. Mathematical models from experimental sepsis predict that
vessel density, flow heterogeneity, and oxygen consumption all play a role in
tissue hypoxia in skeletal muscle.(22, 23) Specifically, the regulation of capillary
density in response to changes in oxygen delivery is impaired in septic
animals,(15) and may contribute to impaired oxygen extraction. Meanwhile, if
oxygen consumption is limited as we found in our subjects, reactive hyperemia
may be impaired as flow-mediated dilation has tremendous oxygen costs.(8) Our
data provide further insight into the myriad microvascular perturbations in severe
sepsis.
Previous studies have evaluated vascular reactivity in sepsis. Two studies
have evaluated forearm bloodflow before and after stagnant ischemia using
venous plethysmography.(1, 27) These studies noted that the ratio of flow during
reactive hyperemia to that at baseline was lower in septic subjects than in
controls. Unfortunately, this ratio may be biased by the baseline high flow in the
forearms of septic patients. Additionally, these studies addressed regional
forearm bloodflow rather than specifically addressing the skeletal muscle
microcirculation. Other studies utilized laser-Doppler(35) or NIRS(12)
measurements of the skeletal muscle microcirculation and found impaired
microvascular perfusion and reactive hyperemia, but there was no assessment of
associated organ dysfunction. Several previous studies excluded patients
receiving vasopressors, thereby not representing the population seen commonly
in practice. Ours is the largest study to date to use NIRS to specifically measure
microvascular reactivity in patients at high risk of death, and the first to identify a
Copyright Information
Page 18 of 34
- 16 relationship between the degree of impaired reactivity with the degree of organ
failure.
NIRS monitors vary greatly in terms of wavelength selection, number of
wavelengths, optode spacing, and algorithms used to calculate data from the
absorption data.(6) Accordingly, great care should be used when comparing
reports generated from different spectrometers.
NIRS does not measure individual vessels, which may limit its use in
mechanistic studies of individual vessel responses during sepsis. However,
blood flow is variable between tissues,(32) as well as within the tissues of septic
humans.(4) Individual vessels therefore very likely have different impairments in
reactivity as hemostatic activation,(33) impaired red blood cell deformation,(36)
leukoadherence,(26) and perturbations of endothelial vasomotor function all
potentially affect microvascular perfusion and contribute to heterogeneous
bloodflow. The importance of this heterogeneous flow is demonstrated in studies
that show that the ratio of fast-flow to stop-flow capillaries relates to tissue
oxygenation in animal models of sepsis.(16) To this end, NIRS may be better
suited to measure bulk microvascular regulation in a heterogeneous tissue bed
than instruments that look at individual or select groups of vessels.
Our study is limited by the lack of systemic, macrovascular, hemodynamic
data other than blood pressure, reflecting the global trend away from the use of
invasive cardiac output monitoring.(14) It is noteworthy that mean arterial
pressure was not associated with RR just as mean arterial pressure greater than
65 has not been shown to affect organ perfusion or oxygen kinetics in other
Copyright Information
Page 19 of 34
- 17 studies.(29) Low cardiac output does occur in severe sepsis, and this would
certainly lead to decreased perfusion and reactive hyperemia. However, as the
incidence of low output states in resuscitated sepsis is low,(13, 37) decreased
systemic flows seems an unlikely explanation of our observations.
We have shown that microvascular perfusion and reactivity to ischemia
are impaired in humans with severe sepsis. Importantly, impaired microvascular
reactivity is related to tissue dysoxia as well as organ dysfunction. NIRS is an
effective tool to study these impairments, providing important information in
physiologic studies, and could measure relevant endpoints in therapeutic
interventions aimed at improving the microcirculation in severe sepsis.
Grants
American Heart Association 0660058Z (PI—KCD); National Institutes of Health
K23HL071246 (PI--KCD); NIH General Clinical Research Centers RR-59 (PI-WGH).
Copyright Information
Page 20 of 34
- 18 REFERENCES
1.
Astiz ME, DeGent GE, Lin RY, and Rackow EC. Microvascular function
and rheologic changes in hyperdynamic sepsis. Crit Care Med 23: 265-271,
1995.
2.
Avontuur JA, Bruining HA, and Ince C. Nitric oxide causes dysfunction
of coronary autoregulation in endotoxemic rats. Cardiovasc Res 35: 368-376,
1997.
3.
Bateman RM and Walley KR. Microvascular resuscitation as a
therapeutic goal in severe sepsis. Crit Care 9 Suppl 4: S27-32, 2005.
4.
Boerma EC, Mathura KR, van der Voort PH, Spronk PE, and Ince C.
Quantifying bedside-derived imaging of microcirculatory abnormalities in septic
patients: a prospective validation study. Crit Care 9: R601-606, 2005.
5.
Bone RC, Balk RA, Cerra FB, Dellinger RP, Fein AM, Knaus WA,
Schein RM, and Sibbald WJ. Definitions for sepsis and organ failure and
guidelines for the use of innovative therapies in sepsis. The ACCP/SCCM
Consensus Conference Committee. American College of Chest
Physicians/Society of Critical Care Medicine. Chest 101: 1644-1655, 1992.
6.
Boushel R and Piantadosi CA. Near-infrared spectroscopy for
monitoring muscle oxygenation. Acta Physiol Scand 168: 615-622, 2000.
Copyright Information
Page 21 of 34
- 19 7.
Bucher M, Kees F, Taeger K, and Kurtz A. Cytokines down-regulate
alpha1-adrenergic receptor expression during endotoxemia. Crit Care Med 31:
566-571, 2003.
8.
Cabrales P, Tsai AG, Johnson PC, and Intaglietta M. Oxygen release
from arterioles with normal flow and no-flow conditions. J Appl Physiol 100: 15691576, 2006.
9.
Coffman JD. Alpha-adrenergic and serotonergic receptors and forearm
venous compliance in normal human subjects. J Cardiovasc Pharmacol 19: 996999, 1992.
10.
De Backer D, Creteur J, Dubois MJ, Sakr Y, Koch M, Verdant C, and
Vincent JL. The effects of dobutamine on microcirculatory alterations in patients
with septic shock are independent of its systemic effects. Crit Care Med 34: 403408, 2006.
11.
De Backer D, Creteur J, Preiser JC, Dubois MJ, and Vincent JL.
Microvascular blood flow is altered in patients with sepsis. Am J Respir Crit Care
Med 166: 98-104, 2002.
12.
De Blasi RA, Palmisani S, Alampi D, Mercieri M, Romano R, Collini S,
and Pinto G. Microvascular dysfunction and skeletal muscle oxygenation
assessed by phase-modulation near-infrared spectroscopy in patients with septic
shock. Intensive Care Med 31: 1661-1668, 2005.
Copyright Information
Page 22 of 34
- 20 13.
Dellinger RP. Cardiovascular management of septic shock. Crit Care Med
31: 946-955, 2003.
14.
Dellinger RP, Carlet JM, Masur H, Gerlach H, Calandra T, Cohen J,
Gea-Banacloche J, Keh D, Marshall JC, Parker MM, Ramsay G, Zimmerman
JL, Vincent JL, and Levy MM. Surviving Sepsis Campaign guidelines for
management of severe sepsis and septic shock. Crit Care Med 32: 858-873,
2004.
15.
Drazenovic R, Samsel RW, Wylam ME, Doerschuk CM, and
Schumacker PT. Regulation of perfused capillary density in canine intestinal
mucosa during endotoxemia. J Appl Physiol 72: 259-265, 1992.
16.
Ellis CG, Bateman RM, Sharpe MD, Sibbald WJ, and Gill R. Effect of a
maldistribution of microvascular blood flow on capillary O(2) extraction in sepsis.
Am J Physiol Heart Circ Physiol 282: H156-164, 2002.
17.
Ermert M, Ruppert C, Gunther A, Duncker HR, Seeger W, and Ermert
L. Cell-specific nitric oxide synthase-isoenzyme expression and regulation in
response to endotoxin in intact rat lungs. Lab Invest 82: 425-441, 2002.
18.
Ferreira FL, Bota DP, Bross A, Melot C, and Vincent JL. Serial
evaluation of the SOFA score to predict outcome in critically ill patients. Jama
286: 1754-1758, 2001.
19.
Fink MP. Bench-to-bedside review: Cytopathic hypoxia. Crit Care 6: 491-
499, 2002.
Copyright Information
Page 23 of 34
- 21 20.
Ghosh S and Liu MS. Changes in alpha-adrenergic receptors in dog
livers during endotoxic shock. J Surg Res 34: 239-245, 1983.
21.
Girardis M, Rinaldi L, Busani S, Flore I, Mauro S, and Pasetto A.
Muscle perfusion and oxygen consumption by near-infrared spectroscopy in
septic-shock and non-septic-shock patients. Intensive Care Med 29: 1173-1176,
2003.
22.
Goldman D, Bateman RM, and Ellis CG. Effect of decreased oxygen
supply on skeletal muscle oxygenation and oxygen consumption during sepsis:
Role of heterogeneous capillary spacing and blood flow. Am J Physiol Heart Circ
Physiol, 2006.
23.
Goldman D, Bateman RM, and Ellis CG. Effect of sepsis on skeletal
muscle oxygen consumption and tissue oxygenation: interpreting capillary
oxygen transport data using a mathematical model. Am J Physiol Heart Circ
Physiol 287: H2535-2544, 2004.
24.
Herbertson MJ, Werner HA, Russell JA, Iversen K, and Walley KR.
Myocardial oxygen extraction ratio is decreased during endotoxemia in pigs. J
Appl Physiol 79: 479-486, 1995.
25.
Jakob SM, Ruokonen E, and Takala J. Effects of dopamine on systemic
and regional blood flow and metabolism in septic and cardiac surgery patients.
Shock 18: 8-13, 2002.
Copyright Information
Page 24 of 34
- 22 26.
Kayal S, Jais JP, Aguini N, Chaudiere J, and Labrousse J. Elevated
circulating E-selectin, intercellular adhesion molecule 1, and von Willebrand
factor in patients with severe infection. Am J Respir Crit Care Med 157: 776-784,
1998.
27.
Kirschenbaum LA, Astiz ME, Rackow EC, Saha DC, and Lin R.
Microvascular response in patients with cardiogenic shock. Crit Care Med 28:
1290-1294, 2000.
28.
Lam C, Tyml K, Martin C, and Sibbald W. Microvascular perfusion is
impaired in a rat model of normotensive sepsis. J Clin Invest 94: 2077-2083,
1994.
29.
LeDoux D, Astiz ME, Carpati CM, and Rackow EC. Effects of perfusion
pressure on tissue perfusion in septic shock. Crit Care Med 28: 2729-2732, 2000.
30.
Liu SF, Adcock IM, Old RW, Barnes PJ, and Evans TW. Differential
regulation of the constitutive and inducible nitric oxide synthase mRNA by
lipopolysaccharide treatment in vivo in the rat. Crit Care Med 24: 1219-1225,
1996.
31.
Mancini DM, Bolinger L, Li H, Kendrick K, Chance B, and Wilson JR.
Validation of near-infrared spectroscopy in humans. J Appl Physiol 77: 27402747, 1994.
32.
McCuskey RS, Urbaschek R, and Urbaschek B. The microcirculation
during endotoxemia. Cardiovasc Res 32: 752-763, 1996.
Copyright Information
Page 25 of 34
- 23 33.
McGill SN, Ahmed NA, and Christou NV. Increased plasma von
Willebrand factor in the systemic inflammatory response syndrome is derived
from generalized endothelial cell activation. Crit Care Med 26: 296-300, 1998.
34.
Myers DE, Anderson LD, Seifert RP, Ortner JP, Cooper CE, Beilman
GJ, and Mowlem JD. Noninvasive method for measuring local hemoglobin
oxygen saturation in tissue using wide gap second derivative near-infrared
spectroscopy. J Biomed Opt 10: 034017, 2005.
35.
Neviere R, Mathieu D, Chagnon JL, Lebleu N, Millien JP, and Wattel
F. Skeletal muscle microvascular blood flow and oxygen transport in patients with
severe sepsis. Am J Respir Crit Care Med 153: 191-195, 1996.
36.
Poschl JM, Leray C, Ruef P, Cazenave JP, and Linderkamp O.
Endotoxin binding to erythrocyte membrane and erythrocyte deformability in
human sepsis and in vitro. Crit Care Med 31: 924-928, 2003.
37.
Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B,
Peterson E, and Tomlanovich M. Early goal-directed therapy in the treatment of
severe sepsis and septic shock. N Engl J Med 345: 1368-1377, 2001.
38.
Sakr Y, Dubois MJ, De Backer D, Creteur J, and Vincent JL. Persistent
microcirculatory alterations are associated with organ failure and death in
patients with septic shock. Crit Care Med 32: 1825-1831, 2004.
Copyright Information
Page 26 of 34
- 24 39.
Spronk PE, Ince C, Gardien MJ, Mathura KR, Oudemans-van Straaten
HM, and Zandstra DF. Nitroglycerin in septic shock after intravascular volume
resuscitation. Lancet 360: 1395-1396, 2002.
40.
Tyml K, Yu J, and McCormack DG. Capillary and arteriolar responses to
local vasodilators are impaired in a rat model of sepsis. J Appl Physiol 84: 837844, 1998.
41.
Vincent JL, de Mendonca A, Cantraine F, Moreno R, Takala J, Suter
PM, Sprung CL, Colardyn F, and Blecher S. Use of the SOFA score to assess
the incidence of organ dysfunction/failure in intensive care units: results of a
multicenter, prospective study. Working group on "sepsis-related problems" of
the European Society of Intensive Care Medicine. Crit Care Med 26: 1793-1800,
1998.
42.
Walley KR. Heterogeneity of oxygen delivery impairs oxygen extraction by
peripheral tissues: theory. J Appl Physiol 81: 885-894, 1996.
43.
Wilson MF and Brackett DJ. Release of vasoactive hormones and
circulatory changes in shock. Circ Shock 11: 225-234, 1983.
Copyright Information
Page 27 of 34
Table 1. Clinical Data of Severe Sepsis Subjects
Minimum Maximum
Age (years)
Mean arterial pressure (mm Hg)
Heart rate (beats/min)
SpO2 (%)
Hemoglobin (g/dL)
Blood Lactate*
SOFA Score
Total enrolled
Male gender
Severe organ failure†
Vasoconstrictor use‡
Mechanical Ventilation
Survived
40
55
72
94
7.9
1.1
2
85
90
121
100
14.7
10.3
18
n
%
24
12
12
15
12
16
100
50
50
63
50
67
*
n = 11 subjects
Severe organ failure defined as SOFA > 10
‡
Vasoconstrictor use defined as SOFA cardiovascular
component > 3
†
Copyright Information
Mean
Median
56
70
93
98
10.7
4
9.6
55
69
92
98
10
3
9
Page 28 of 34
Table 2. Total Tissue Hemoglobin Index in Reactive Hyperemia
Subject group
TH
TH-RH
TH
Control
Sepsis,
modest organ failure
Sepsis,
severe organ failure
22.7 ± 2.4
27.7 ± 5.1
5 ± 4.2
21.7 ± 17.6
15.8 ± 5.5**
19.7 ± 6.5*
4.5 ± 3.8
30.2 ± 28.4
15.2 ± 4.9**
16.9 ± 6.9**
2.4 ± 3.6
16.7 ± 23.9
All values are mean ± standard deviation. Definition of abbreviations: TH = Total Tissue
Hemoglobin Index, at baseline, expressed in arbitrary units; TH-RH = TH during reactive
hyperemia; TH = change in TH from baseline to reactive hyperemia; % TH = the ratio
TH * 100 / TH
*p < 0.01 vs control
**p < 0.001 vs control
Copyright Information
% TH
Page 29 of 34
Figure 1. Tissue hemoglobin concentration is impaired in severe sepsis. The total tissue
hemoglobin index (TH, arbitrary units) was measured in thenar muscle capillaries of
severe sepsis and controls subjects. Panel A: TH was impaired in both septic subjects
with modest organ dysfunction (SOFA < 10, light grey bar), and those with severe organ
failure (SOFA >10, dark grey), compared to control subjects (white bar, ** p<0.001
versus each septic sub-group). Panel B: TH had no relationship with blood hemoglobin
concentration in severe sepsis subjects. The horizontal line depicts the linear regression
line r2= 0, with 99% confidence interval (grey dashed lines).
Copyright Information
Page 30 of 34
Figure 2. Tissue oxygenation before and during ischemia. The oxygen saturation of tissue
hemoglobin (StO2) was measured in thenar skeletal muscles during stagnant ischemia.
Panel A: StO2 decreased in both severe sepsis (grey bars) as well as control (white bars)
subjects. There were no identifiable differences between the two groups at baseline, at
30 or 60 seconds of ischemia, nor at the end of five minutes of ischemia. The data shown
depict the mean and SD at each time point. Panel B: Tissue oxygen consumption (VO2tis)
was calculated as the difference between tissue oxygen contents (StO2 * tissue
hemoglobin) at beginning and end ischemia. VO2tis was significantly reduced in severe
sepsis subjects (p=0.003)
Copyright Information
Page 31 of 34
Figure 3. Tissue oxygen saturation during reactive hyperemia. The oxygen saturation of
tissue hemoglobin (StO2) was measured in thenar skeletal muscles following forearm
stagnant ischemia. StO2 increased rapidly during the initial period of reactive hyperemia,
to a level at or above baseline. Shown are representative two individual StO2 curves
during the initial seconds of reactive hyperemia in a septic subject with severe organ
failure (black) and control subject (grey). Reoxygenation rates (dashed diagonal lines)
represent the average rate of StO2 increase in the first 14 seconds of reactive hyperemia
(StO2 at 14 seconds minus StO2 at end ischemia, divided by 14 seconds). The
represented subjects were chosen by the reoxygenation rate that best approached the
mean for the represented group.
Copyright Information
Page 32 of 34
Figure 4. Reoxygenation rate is related to organ injury in sepsis. The rate of increase of
tissue oxygen saturation during the first 14 seconds of reactive hyperemia
(reoxygenation rate, RR) was measured in the thenar skeletal muscles of septic and
control subjects. Panel A. RR was significantly impaired in sepsis subjects with severe
organ failure (SOFA '10, dark grey bar), compared to septic subjects with modest organ
dysfunction (light grey bar, *p< 0.05) and control subjects (white bar, tp < 0.001; ANOVA
and Tukey's MCT). The data shown depict mean ± SD. Panel B. In sepsis subjects, RR
tended to be slower in those that did not survive hospitalization than in those who
survived although this fell short of statistical significance (p=0.20). The data shown
depict mean, interquartile range, and range for each group.
Copyright Information
Page 33 of 34
Figure 5. Reoxygenation rate is related to microvascular hemoglobin during reactive
hyperemia. The tissue hemoglobin index (TH-RH; arbitrary units) and the rate of increase
of tissue oxygen saturation (reoxygenation rate, RR; % per second) were measured in
the thenar muscles of severe sepsis subjects during reactive hyperemia. RR correlated
with TH-RH (r2 = 0.47, p = 0.0006), demonstrating that low RR is associated with
reduced influx of hemoglobin to the tissue bed.
Copyright Information
Page 34 of 34
Figure 6. Reoxygenation Rate is related to tissue oxygen consumption. Tissue oxygen
consumption (VO2tis) was calculated by the rate of decrease of oxygen content during
five minutes of ischemia in thenar skeletal muscles. Following ischemia, the rate of
increase of tissue oxygen saturation during the first 14 seconds of reactive hyperemia
(reoxygenation rate, RR) was measured in the thenar skeletal muscles of septic subjects.
RR had a significant linear relationship with VO2tis (r2 = 0.38; p = 0.002).
Copyright Information