Page 521 - Cardiac Nursing

8 A
8 A
M
M
0
0
8:2
8:2
P
g
g
e 4
e 4
P
P
a
a
p46
10.
qxd
p46
0-5
10.
10.
0-5
qxd
9/2
9/2
009
009
0
0
9/0
9/0
K34
K34
L L LWB
LWB
K34
21_
21_
0-c
0-c
97
Apt
97
97
ara
LWBK340-c21_21_p460-510.qxd 09/09/2009 08:28 AM Page 497 Aptara
Apt
ara
C HAPTER 2 1 / Hemodynamic Monitoring 497
p .05). In a study of moderate to high-risk cardiac surgery pa- threshold of 75% within the first hour of traumatic shock resus-
tients, postoperative goal-directed therapy integrated standard he- citation has been identified as a critical predictor of organ dys-
#
modynamic indices, oxygenation indices ( , ) and Flo- function and mortality y 490 and the severity of outcomes increases
Trac indices (CI, SV, SVV) were compared with a standard care with a lower StO 2 . 491 However, there is wide individual variability
group (HR, MAP, Sp o2 , CVP). 482 In the goal-directed group if the in StO 2 . For example, in the study by Ikossi et al. 487 the StO 2 in
2
CI was 2.5 L/min/m , the CVP was less than 6 mm Hg or the patients deemed to be adequately resuscitated was 63% 27%,
SVV was 10% fluidboluses were administered to optimize these and the average StO 2 in patients who required massive transfu-
parameters. Vasoactive medications and redblood cells were sub- sions was 58% 22% in contrast to patients who did not re-
2
sequently added to increase the SVI 30 mL/min/m and to quired a massive transfusion (67% 19%). 491
70%. The goal-directed group hadfewer Recently, changes in StO 2 that are created using an arterial or
achieve an Scvo 2
hours of mechanical ventilation and shorter period of ICU andhos- venous occlusion test (forearm compression with a cuff to create
pital stay. Further research is needed to determine if this integrated transient venous obstruction or ischemia) have been used to de-
goal-directed approach works in different patient populations. scribe microcirculatory reactivity and local O 2 consumption. 492,493
When the cuff is released reactive hyperemia occurs, which reflects
the local response to hypoxia and microcirculatory function. In pa-
Regional Indicators
tients with sepsis, microvascular reactivity was impaired compared
Monitoring of regional indices of oxygenation (gut mucosa, sub- with other critically ill patients or normal control subjects. 494–496
cutaneous tissue, and muscle tissue) is based on the assumption In addition, microvascular reactivity was higher in survivors versus
that these areas serve as early markers of systemic hypoperfusion. nonsurvivors 496 and the impairment was worse in patients who de-
The next section summarizes the current use of regional indicators veloped more severe organ failure. 497 In patients who are septic,
to detect and guide therapy to treat hypoperfusion. muscle O 2 consumption is also decreased, which may reflect cyto-
pathic hypoxia or impaired blood flow. 493,497
Tissue Perfusion Monitoring
Transcutaneous Tissue Monitoring
Tissue or peripheral perfusion monitoring may augment global Transcutaneous tissue O 2 (P tc O 2 ) reflects tissue oxygenation from
hemodynamic and oxygenation monitoring. In hypoperfusion the cell mitochondria to the venous capillary in contrast to pulse
and shock, blood is shunted away from less vital areas including oximetry, which reflects arterial oxygenation. In normal subjects,
the skin and muscle to vital organs and these areas regain normal the P tc O 2 is estimated to be approximately 80% of the Pa o2 and in
perfusion after restoration of circulation in other vital areas; thus, a recent study the P tc O 2 was 61% 15% in normal subjects and
monitoring of these areas may be useful in the early detection of 48% 13% in individuals who were morbidly obese. 498 In non-
hypoperfusion and evaluating the adequacy of resuscitation. The shock states the P tc O 2 varies with Pa o2 , but in shock states the
#
two most common technologies usedfor tissue perfusion moni- P tc O 2 mirrors changes in CO and with minimal response to
toring are NIRS and transcutaneous tissue monitoring. an increase in Fi o2 or Pa o2 . This lack of increase is thought to re-
flect increased O 2 consumption by ischemic cells; thus, the P tc O 2
Near-Infrared Spectroscopy provides insight into cellular oxygenation that may not be appar-
NIRS uses a probe placed on the thenar eminence or deltoid that ent from global hemodynamic indices.
emits near-infraredlight. NIRS monitoring is based on the finding The P tc O 2 and transcutaneous CO 2 (P tc CO 2 ) values may be
that hemoglobin, myoglobin, and cytochrome oxidase alter their early indicators of hypoperfusion and have prognostic implications.
absorption of near-infraredlight with changes in oxygenation, In trauma patients the P tc O 2 /Fi o2 was significantly higher in sur-
withhemoglobin providing the major contribution. The NIRS sig- vivors (220 132) than nonsurvivors (117 100) and the P tc CO 2
nal is a measure of tissue hemoglobin O 2 saturation (StO 2 ). was significantly lower (46 16 mm Hg versus 52 13 mm
In trauma patients and patients undergoing cardiac surgery Hg). 413,414 However, these results were not found in patients with
changes in StO 2 were found to mirror changes in global oxygena- severe sepsis and septic shock. 499,500
tion indices. 483,484 In contrast, in patients withleft ventricular In contrast to absolute values, in patients with sepsis and sep-
failure or sepsis the StO 2 and 2 were not correlated; 485 thus, tic shock the response to an oxygen challenge test (OCT), which
specific recommendations for the use of StO 2 as a surrogate for evaluates a change in P tc O 2 after 5 minutes of Fi o2 of 1.0, is asso-
under different shock conditions remain to be resolved. 486 ciated with morbidity and mortality. A positive OCT, which is
Svo 2
StO 2 or skeletal muscle oxygenation monitoring may be useful in defined as a baseline P tc O 2 of 30 mm Hg or more and the ability
identifying occult hypoperfusion. For example, during cardiac to achieve an increase in P tc O 2 of 25 to 40 mm Hg or more after
surgery the lowest StO 2 value preceded the highest lactate value by 5 minutes of Fi o2 of 1.0, is associated with decreased morbidity
90 minutes, 484 and in critically ill trauma victims who were con- and mortality. 499,500 The OCT has also been used as an endpoint
sidered adequately resuscitated the average StO 2 was 63% 27%, for resuscitation. Using a standardized protocol, patients with se-
#
which suggests incomplete resuscitation. 487 vere sepsis and septic shock were resuscitated to and Svo 2
The utility of NIRS to identify the severity of shock in trauma goals or an OCT response of 40 mm Hg or more. Mortality was
#
patients is equivocal. In trauma patients the StO 2 differentiated significantly lower in the OCT group (13%) versus the –Svo 2
between normals (83% 6%) and trauma patients without group (40%). Similar to earlier research related to achieving supra-
shock (83% 10%) and those with severe shock (45% 26%). normal oxygenation goals, patients who were unable to achieve
However, NIRS StO 2 did not differentiate patients with mild the OCT goal had increased mortality.
(83% 10%) or moderate shock(80% 12%), 488 which may Transcutaneous tissue monitoring uses an electrode placed on
limit its utility as an early indicator ofbloodloss 489 or to guide re- the anterior chest below the clavicle that heats the skin (44 C) and
suscitation. Another limitation is interpreting absolute StO 2 values changes the structures of the stratum corneum from the gel to the
and using StO 2 as an endpoint for resuscitation. 486 An StO 2 sol state, which allows rapid diffusion of O 2 and CO 2 from the