Page 522 - Cardiac Nursing

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498 P A R T III / Assessment of Heart Disease
A B C
■ Figure 21-23 Representative examples of the sublingual microcirculation in (A) control patient (B) car-
diogenic shock, 512 and (C) septic shock. 513 Note the decrease in the density of small vessels in the patient with
severe cardiac failure and the decreased vascular density and increased heterogeneity of perfusion in the patient
with septic shock. (Reproduced from De Backer, D., Creteur, J., Dubois, M. J., et al. [2004]. Microvascular al-
terations in patients with acute severe HF and cardiogenic shock. American Heart Journal, 147, 95 and De
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Backer, D., Creteur, J., Preiser, J.-C., et al. [2002]. Microvascular flow is altered in patients in sepsis. American
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Journal of Respiratory and Critical Care Medicine, 166, 99.)
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subcutaneous tissue to the electrode. To avoid electrode-induced which may limits its utility for continuous bedside monitoring.
burns the probe must be moved every 4 hours. Of note in several Recent research using a buccal PCO 2 (PbuCO 2 ) probe in animal
studies there were no thermal burns if these safety guidelines were models of hemorrhagic shock have demonstrated similar re-
followed. 413,499,500 With each application of the electrode the sys- sults 509,510 and the buccal probe may be easier to use at the bed-
tem requires a 10- to 15-minute recalibration. side.
Sublingual Capnography Microcirculatory Monitoring
Perfusion to the gut is often considered the “canary of the body,” 501 Currently, two technologies (orthogonal polarization spectral imag-
providing an indicator of circulatory redistribution during hemody- ing and sidestream dark-field imaging) are being used to visualize
namic compromise. Gastric tonometry was used to study alterations and assess sublingual microcirculatory flow. 511 These techniques
in gut perfusion. However, this procedure was difficult to perform at use specialized light probes, with the sublingual mucosa as the pri-
the bedside and affected by factors such as the concurrent adminis- mary site of analysis. The probes emit light and the scattered light,
tration of H 2 -blockers, proton-pump inhibitors or antacids and the which is absorbed by hemoglobin of red blood cells in superficial
need to stop enteral feedings before obtaining the measurements. vessels, and allows for the direct visualization of the microcircula-
The sublingual mucosa was considered an alternative site for assess- tion and the qualitative evaluation of vascular density, capillary
ment and monitoring as the sublingual and mesenteric vascular perfusion, and perfusion heterogeneity, which reflects the distri-
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structures share a common embryonic origin and changes in sublin- bution of perfused and nonperfused capillaries (Fig. 21-23A and
gual PCO 2 and mirror those in splanchnic vessels. 502 Assessment of B). Sidestream dark-field imaging and orthogonal polarization
the microcirculation is important as persistent microvascular alter- spectral imaging, which have been used primarily under experi-
ations (despite normalization of global hemodynamics) are associ- mental conditions, are limited by motion artifact (requires the pa-
ated with increased morbidity and mortality. 503,504 tient be heavily sedated) and differences in data interpretation.
Sublingual capnography, which is performed with a disposable Further research is needed before this technology will be available
sensor that detects sublingual CO 2 , is used to measure for routine bedside clinical use.
PslCO 2 . 505,506 As described by the Fick equation, the two deter- Microcirculatory derangements vary depending on the cause
minants of tissue PCO 2 are CO 2 production and tissue blood flow of shock (e.g., distributive, hemorrhagic, cardiogenic). 514 For ex-
and there is an inverse relationship between perfusion and ample, in patients with severe sepsis and septic shock microcir-
PslCO 2 . 507,508 With acute perfusion failure there is an increase in culatory derangements are more severe in nonsurvivors and
O 2 extraction, hydrogen ion concentration, and tissue CO 2 , with those with more severe global cardiovascular dysfunction. 515 In
addition, during early goal-directed therapy, survivors demon-
a subsequent increase in venous PCO 2 and the venoarterial PCO 2
gradient. 503,505 In a recent study in patients with sepsis the dif- strate improvement in microcirculatory function in contrast to
ference between arterial PCO 2 and PslCO 2 (PslCO 2 gap) decreased nonsurvivors and improvement in microcirculatory flow was
as the proportion of well-perfused capillaries increased, and greater in patients who did not develop organ failure. 511 In an
changes in PslCO 2 mirrored changes in gastric CO 2 demonstrat- animal model, microcirculatory derangements were more severe
ing the relationship between sublingual perfusion and gut perfu- in septic animals compared with animals with hemorrhagic
sion 502 . Sublingual capnometry may provide a rapid, noninvasive shock, independent of BP and CI, and with fluid resuscitation
method to monitor microcirculatory status and provide an early there was normalization of microcirculation in the hemorrhagic
indication of tissue hypoperfusion and to assess the patient’s re- shock group but not the septic group. 516 Patients with severe
sponse to therapy. However, use of the sublingual probe requires HF and cardiogenic shock had a lower proportion of perfused
a specialized holder to maintain the probe in the correct position, small vessels than cardiac patients without HF independent of