HEMODYNAMIC MONITORING
The appropriate level of invasive hemodynamic monitoring (see
Chapter 32
) for the patient
undergoing vascular
Figure 52-8
Kaplan-Meier estimates of the cumulative percentages
of patients who died of cardiac causes or had a nonfatal myocardial infarction during
the perioperative period. I bars indicate the standard error, and the difference
between groups was significant (P < .001). (From
Poldermans D, Boersma E, Bax JJ, et al: The effect of bisoprolol on perioperative
mortality and myocardial infarction in high-risk patients undergoing vascular surgery.
Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography
Study Group. N Engl J Med 341:1789–1794, 1999.)
surgery is a controversial issue. Multiple considerations determine the need for
monitoring, and it is difficult to generalize for all vascular patients. Given the
frequency of coexisting disease, the potential for fluid shifts and blood loss, and
the physiologic changes associated with cross-clamping and unclamping, virtually
all patients undergoing major vascular surgery should be monitored with an intra-arterial
catheter. This allows beat-to-beat blood pressure monitoring, accurate determination
of diastolic pressure, and arterial blood sampling for diagnostic purposes. The
radial artery is most commonly selected for cannulation because of its superficial
location and the presence of collateral circulation. The need to verify collateral
blood flow is questionable. The Allen test[164]
can be used to assess collateral flow in the palmar arch, but there is evidence that
ischemic injury can occur in patients with a normal Allen test result[165]
and that no injury occurs in patients with an abnormal Allen test result
Figure 52-9
Kaplan-Meier curves of the cumulative percentage of patients
who survived vascular surgery and remained free of cardiac death and nonfatal myocardial
infarction during follow-up. The difference between groups was significant (P
= .004). (From Poldermans D, Boersma E, Bax JJ, et al: Bisoprolol reduces
cardiac death and myocardial infarction in high-risk patients as long as 2 years
after successful major vascular surgery. Eur Heart J 22:1353–1358, 2001.)
when the radial artery is cannulated.[166]
When
the radial artery is difficult to cannulate, the ulnar or axillary arteries are alternative
sites. The axillary artery can be cannulated by use of the Seldinger technique,
but care should be taken to avoid air injection when flushing an axillary catheter
because the tip may lie close to or inside the aortic arch, allowing air to enter
the cerebral circulation. Whenever possible, the femoral arteries should be avoided
in patients with peripheral vascular disease.
Vascular surgery patients often have a large discrepancy in arterial
blood pressure between the right and left arms as a result of atherosclerotic lesions
in the subclavian or axillary arteries, resulting in a falsely low pressure in the
ipsilateral arm.[167]
I have seen patients with
systolic differences as great as 100 mm Hg between arms, and 20 to 40 mm Hg differences
are common. Patients scheduled for carotid surgery have the greatest incidence of
right/left arm blood pressure differences.[167]
To avoid
Figure 52-10
Perioperative cardiac risk of death or myocardial infarction
as observed in subpopulations. Results are given according to the clinical risk
score, dobutamine stress echocardiography, and perioperative β-blocker therapy.
Percentages in parentheses represent the number of patients in the target category
as a proportion of the total number of 1351 patients. Numbers underneath the bars
represent the actual number of events (i.e., cardiac death and nonfatal myocardial
infarction) per the patients in the specific category. (From Boersma E,
Poldermans D, Bax JJ, et al: Predictors of cardiac events after major vascular surgery:
Role of clinical characteristics, dobutamine echocardiography, and beta-blocker
therapy. JAMA 285:1865–1873, 2001.)
"pseudohypotension," the blood pressure should be verified in both arms, and the
arm with the higher pressure should be monitored during surgery. It is possible
that both arms would have falsely low blood pressures as a result of bilateral disease.
In this case, the femoral artery may be the best option for monitoring.
There is significant controversy over the utility of central venous
and pulmonary artery catheters for monitoring patients during vascular surgery.
The surgical procedure determines the degree of fluid shifting and blood loss and
the usefulness of these monitors. The patient's underlying cardiac, pulmonary, and
renal status also needs to be considered. The indications for central venous pressure
and pulmonary artery catheter monitoring are discussed in further detail in the subsequent
sections.
