Total-Knee Replacement
Background
Patients who need total-knee replacement frequently have severe
rheumatoid arthritis, degenerative osteoarthritis, obesity, and other significant
comorbidities that compound the difficulties of the operation. The average duration
of the procedure is 1 to 3 hours (see Table
61-5
).
Anesthetic Management
Unilateral versus Bilateral Total-Knee Replacement
There is considerable debate in the orthopedic literature about
the wisdom of performing one-stage bilateral total-knee replacement.[98]
[99]
Knee arthritis is frequently bilateral, and
patients appreciate the opportunity to have both replacements performed at the same
time so they have only one period of rehabilitation. However, patients undergoing
bilateral total-knee replacement have a higher rate of postoperative complications,
such as postoperative confusion, cardiopulmonary complications, and increased need
for banked blood.[100]
These patients require a
more rigorous selection process, especially if they have a history of preexisting
coronary artery disease. The outcome is usually excellent if patients have appropriate
hemodynamic monitoring, postoperative epidural analgesia, and a 24- to 48-hour period
of more intensive surveillance.[100]
Cement
When acrylic cement is applied to the cavities of the tibia, femur,
and patella, acute hemodynamic responses seldom follow. Such responses do occur,
however, when long-stem femoral prostheses are inserted after extensive femoral reaming.
[101]
[102]
Lesser
degrees of femoral reaming may reduce the incidence of embolic events, but the significance
of these events is unclear. Pressures in the femoral canal of 300 mm Hg or more
have been recorded during impaction of the femoral component,[103]
although this does not appear to adversely affect arterial oxygen or pulmonary artery
pressures.[104]
On release of the tourniquet after insertion of a cemented total-knee
replacement, showers of fine emboli are detectable in the right side of the heart.
Embolic events can occur even when the tourniquet is inflated during total-knee
arthroplasty.[105]
This has been associated with
an increase in pulmonary vascular resistance during general anesthesia.[106]
The use of a tourniquet appears to increase the likelihood of developing a pulmonary
embolus or DVT postoperatively.[107]
The severity
of metabolic injury[104]
and the echogenic material
[106]
were similar to that of intramedullary and
extramedullary fixation, suggesting that the emboli are thrombi rather than bone
marrow.[106]
Reducing marrow invasion during surgery
does not decrease the release of large emboli.[108]
Echogenic material has also been observed during total-shoulder replacement.[109]
Blood Loss
The intraoperative use of tourniquets makes intraoperative blood
loss negligible, but postoperative drainage averages 500 to 1000 mL per knee.[110]
Postoperative monitoring, possibly in the postanesthetic care unit, for 24 hours
or more may be necessary for high-risk patients until wound drainage slows. Patients
undergoing bilateral procedures are at additional risk for becoming hypovolemic during
the first few hours after the operation. Preoperative autologous blood donation
and intervention with drugs such as erythropoietin should be considered
before surgery. This can minimize the need for allogeneic blood transfusion, which
is associated with an increased incidence of complications such as fluid overload,
infection, and increased duration of hospitalization.[111]
Fibrinolytic activity increases when the tourniquet is inflated.
[112]
This observation provided the rationale for
the use of antifibrinolytic agents to minimize blood loss after total-knee replacement.
Although aprotinin has not been clinically proved to be useful in this setting,
[113]
tranexamic acid is cost effective in unilateral
total-knee replacement.[53]
[114]
[115]
[116]
Hypotensive
epidural anesthesia in total-knee replacement without a tourniquet has revealed decreased
total blood loss and need for transfusion.[117]
Postoperative Pain Management
Total-knee replacement is associated with significantly more pain
than total-hip replacement, and the use of continuous passive motion devices or early
mobilization of the knee increases the pain (see Chapter
72
). Regional analgesic techniques of continuous epidural or continuous
femoral block improve early rehabilitation by effectively controlling pain.[118]
[119]
These regional techniques provide better
pain
relief and faster rehabilitation than intravenous patient-controlled analgesia.[120]
A single-injection femoral nerve block provides effective analgesia, facilitates
early ambulation, and reduces length of hospital stay.[121]
Femoral or sciatic blocks or intrathecal morphine can be used to provide analgesia
for 8 to 24 hours.
