George Go

Changes in circulatory indices of thrombosis and fibrinolysis during total knee arthroplasty performed under tourniquet

Deep vein thrombosis may begin during surgery with the tourniquet inflated. Arterial levels of fibrinopeptide A, thrombin-antithrombin complexes, D-dimer, tissue plasminogen activator (t-PA) activity, and t-PA antigen were measured before surgery, during surgery with the tourniquet inflated, and following deflation of the tourniquet in 12 patients undergoing total knee arthroplasty. Minimal increases in fibrinopeptide A, thrombin-antithrombin complexes, and D-dimer were noted during surgery with the tourniquet inflated, but significant increases occurred immediately following deflation of the tourniquet. In 10 patients, intravenous heparin administration significantly suppressed the rise in fibrinopeptide A, but did not significantly alter the increases in either thrombin-antithrombin complexes, D-dimer, t-PA antigen, or t-PA activity. This study provides further evidence that deep vein thrombosis begins during surgery.

The John Charnley Award. Thrombogenesis during total hip arthroplasty.

The activation of the clotting cascade leading to deep venous thrombosis begins during total hip arthroplasty, but few studies have assessed changes in coagulation during surgery. A better understanding of thrombogenesis during total hip arthroplasty may provide a more rational basis for treatment. In 3 separate studies, the following observations were made. Circulating indices of thrombosis and fibrinolysis: prothrombin F1.2, thrombin-antithrombin complexes, fibrinopeptide A, and D-dimer, did not increase during osteotomy of the neck of the femur or during insertion of the acetabular component, but rose significantly during insertion of the femoral component. Thrombin-antithrombin complexes, fibrinopeptide A, and D-dimer were higher after insertion of a cemented component than insertion of a noncemented femoral component. A significant decline in central venous oxygen tension was observed after relocation of the hip joint and after insertions of cemented and noncemented femoral components, providing evidence of femoral venous occlusion during insertion of the femoral component. In patients receiving a cemented femoral component, mean pulmonary artery pressure increased after relocation of the hip joint, indicating intraoperative pulmonary embolism. No changes in mean pulmonary artery pressure were noted with noncemented total hip arthroplasty. Administration of 1000 units of unfractionated heparin before insertion of a cemented femoral component blunted the rise of fibrinopeptide A. The results of these studies suggest that (1) the greatest risk of activation of the clotting cascade during total hip arthroplasty occurs during insertion of the femoral component; (2) femoral venous occlusion and use of cemented components are factors in thrombogenesis during total hip arthroplasty; and (3) measures to prevent deep venous thrombosis during total hip arthroplasty (such as intraoperative anticoagulation) should begin during surgery rather than during the postoperative period and be applied during insertion of the femoral component.

Dose response of intravenous heparin on markers of thrombosis during primary total hip replacement.

BACKGROUND Thrombogenesis in total hip replacement (THR) begins during surgery on the femur. This study assesses the effect of two doses of unfractionated intravenous heparin administered before femoral preparation during THR on circulating markers of thrombosis. METHODS Seventy-five patients undergoing hybrid primary THR were randomly assigned to receive blinded intravenous injection of either saline or 10 or 20 U/kg of unfractionated heparin after insertion of the acetabular component. Central venous blood samples were assayed for prothrombin F1+2 (F1+2), thrombin-antithrombin complexes (TAT), fibrinopeptide A (FPA), and D-dimer. RESULTS No changes in the markers of thrombosis were noted after insertion of the acetabular component. During surgery on the femur, significant increases in all markers were noted in the saline group (P < 0.0001). Heparin did not affect D-dimer or TAT. Twenty units per kilogram of heparin significantly reduced the increase of F1+2 after relocation of the hip joint (P < 0.001). Administration of both 10 and 20 U/kg significantly reduced the increase in FPA during implantation of the femoral component (P < 0.0001). A fourfold increase in FPA was noted in 6 of 25 patients receiving 10 U/kg of heparin but in none receiving 20 U/kg (P = 0.03). Intraoperative heparin did not affect intra- or postoperative blood loss, postoperative hematocrit, or surgeons subjective assessments of bleeding. No bleeding complications were noted. CONCLUSIONS This study demonstrates that 20 U/kg of heparin administered before surgery on the femur suppresses fibrin formation during primary THR. This finding provides the pathophysiologic basis for the clinical use of intraoperative heparin during THR.

Perioperative pulmonary circulatory changes during bilateral total hip arthroplasty under regional anesthesia.

Background and Objectives: The transient and rarely clinically relevant effect of bone and cement embolization during unilateral joint arthroplasty is a known phenomenon. However, available studies do not address events surrounding bilateral total hip arthroplasties, during which embolic load is presumably doubled. To elucidate events surrounding this increasingly used procedure and assess the effect on the pulmonary hemodynamics in the intraoperative and postoperative periods, we studied 24 subjects undergoing cemented bilateral total hip arthroplasty during the same anesthetic session. Materials: Twenty-four patients without previous pulmonary history undergoing cemented bilateral total hip arthroplasty under controlled epidural hypotension were enrolled. Pulmonary artery catheters were inserted and hemodynamic variables were recorded at baseline, 5 mins after the implantation of each hip joint, 1 hr and 1 day after surgery. Mixed venous blood gases and complete blood counts were analyzed at every time point. Results: An increase in pulmonary vascular resistance was observed after the second but not the first hip implantation when compared with values at incision. Pulmonary vascular resistance remained elevated 1 hr after surgery. Pulmonary artery pressures were significantly elevated on postoperative day 1 compared with those at baseline. The white blood cell count increased in response to the second hip implantation but not the first compared with incision. Conclusions: The embolization of material during bilateral total hip arthroplasty is associated with prolonged increases in pulmonary artery pressures and vascular resistance, particularly after completion of the second side. Performance of bilateral procedures should be cautiously considered in patients with diseases suggesting decreased right ventricular reserve.

The early recovery of cognitive function after total-hip replacement under hypotensive epidural anesthesia

Background and Objectives: Recovery of cognitive function immediately after major surgery has not been previously reported, partly because of residual drug effects and pain. Methods: Changes in cognitive function were assessed using the Stroop Color and Word Test (SCWT), which was performed preoperatively, and 1 and 2 hours after total-hip replacement performed under hypotensive epidural anesthesia. In this case series, patients were sedated with propofol alone and had a lumbar plexus block performed at the end of surgery. Results: The SCWT was completed in 52 of 55 patients at either 1 or 2 hours after surgery. A significant reduction in cognitive function was noted 1 hour after surgery but a return toward baseline occured 2 hours after surgery. Age older than 70 years adversely affected recovery of cognitive function, but neither the preoperative diagnosis of hypertension nor the degree or duration of intraoperative hypotension (mean arterial pressure less than 45 mmHg) influenced cognitive function. Conclusion: The Stroop Color and Word Test can be used to assess change in cognitive function immediately after surgery. Total-hip replacement performed under regional anesthesia with propofol sedation enables recovery of cognitive function (as assessed by SCWT) 2 hours after surgery.

Arterial and pulmonary arterial concentrations of the enantiomers of bupivacaine after epidural injection in elderly patients.

Bupivacaine HCl is a 50 50 racemic mixture of the levo [S(-)] and dex [R(+)] enantiomers. The R(+) enantiomer exhibits greater cardiac tissue binding and toxicity. To determine whether the lung exhibits selective uptake of one of the enantiomers of bupivacaine, we measured pulmonary artery and radial artery blood concentrations of the two enantiomers after a lumbar epidural injection of 20 mL of 0.75% bupivacaine in 10 elderly patients undergoing one-stage bilateral total knee arthroplasty. Significantly lower concentrations of R(+) than S(-) were noted in both pulmonary artery and arterial blood. Both enantiomers were absorbed by the lung to a similar extent within the first 5 min after epidural injection (extraction ratio approximately equal to 0.1 or 10%). Mean time of maximal concentration (Tmax) was 6 min. In 3 of the 10 patients, Tmax occurred in 1-3 min. We conclude that the lung absorbs both the R(+) and S(-) enantiomers of bupivacaine to a similar extent after epidural injection and that this is of doubtful clinical significance. This study also suggests that peak concentrations of bupivacaine may occur earlier after epidural injection in certain elderly patients than previously believed. Implications: In the first 5 min after epidural injection, approximately 10% of the local anesthetic bupivacaine was absorbed by the lung. Absorption of the two enantiomers (mirror images) of bupivacaine were similar. Lung absorption of bupivacaine is unlikely to influence local anesthetic toxicity. (Anesth Analg 1998;86:812-7)

Intraoperative adjusted-dose heparin thromboembolic prophylaxis in primary total hip arthroplasty.

Intraoperative, fixed, intermittent, low-dose intravenous heparin prophylaxis has been reported to significantly reduce the incidence of thromboembolic disease from 24.3% to 8.3% after primary total hip arthroplasty (THA). This study examined the potential efficacy of adjusted-dose intraoperative heparin administration, keeping the activated clotting time at 30%-50% greater than normal. It was hypothesized that prolongation of clotting parameters in a uniform manner would further decrease the incidence of thromboembolic disease postoperatively. Sixty-one patients completed the protocol. The overall incidence of thromboembolic disease was 9.8%. Five patients had a positive postoperative venogram: four in the calf and one in the proximal deep thigh vein. One patient had a symptomatic nonfatal pulmonary embolus diagnosed by ventilation-perfusion scan. There were no complications related to heparin administration. This approach was therefore equally as effective as the fixed-dose regimen, and it further confirmed the efficacy and safety of an intraoperative heparin prophylaxis regimen. The extra efforts required to maintain a constant intraoperative level of anticoagulation did not prove advantageous over the simpler, fixed-dose regimen in reducing the incidence of thromboembolic disease after primary THA.

The modern, hybrid total hip arthroplasty for primary osteoarthritis at the Hospital for Special Surgery

We describe our technique and rationale using hybrid fixation for primary total hip arthroplasty (THA) at the Hospital for Special Surgery. Modern uncemented acetabular components have few screw holes, or no holes, polished inner surfaces, improved locking mechanisms, and maximised thickness and shell-liner conformity. Uncemented sockets can be combined with highly cross-linked polyethylene liners, which have demonstrated very low wear and osteolysis rates after ten to 15 years of implantation. The results of cement fixation with a smooth or polished surface finished stem have been excellent, virtually eliminating complications seen with cementless fixation like peri-operative femoral fractures and thigh pain. Although mid-term results of modern cementless stems are encouraging, the long-term data do not show reduced revision rates for cementless stems compared with cemented smooth stems. In this paper we review the conduct of a hybrid THA, with emphasis on pre-operative planning, surgical technique, hypotensive epidural anaesthesia, and intra-operative physiology.

An Observational Study of Cerebral Blood Flow Velocity During Hypotensive Epidural Anesthesia.

BACKGROUND:Hypotensive epidural anesthesia (HEA), as practiced at our institution, uses sympathetic blockade to achieve mean arterial blood pressure (MAP) of ⩽50 mm Hg while administering epinephrine by infusion to support the circulation. HEA has not been associated with gross adverse effects on neurologic outcome or cognitive function in the postoperative period, suggesting adequate cerebral blood flow (CBF). However, the use of MAPs well below the commonly accepted lower limit of CBF autoregulation suggests that CBF should be significantly reduced below normal levels. To examine these conflicting hypotheses, we performed a prospective investigation of the effects of HEA on CBF velocity (CBFV), an accepted index of cerebral perfusion. METHODS:Fifty-two hip replacement patients were studied. HEA was induced by lumbar epidural injection of local anesthetic and infusion of epinephrine to achieve an MAP of ⩽50 mm Hg. Propofol/midazolam sedation was administered. Baseline CBFV was recorded pre-HEA (after sedation and before local anesthetic injection) and continuously thereafter. RESULTS:During HEA, MAP decreased by 40% and was stable throughout. The CBFVmean at baseline and at 3 HEA intervals during surgery was 46 ± 12 (SD), 45 ± 12, 47 ± 14, and 47 ± 14 cm·s−1, respectively. Although mean CBFVmean did not vary, there was considerable heterogeneity among patients. Twelve patients (23%) experienced reductions of CBFVmean of >20% during HEA intervals (99% lower confidence limit: 9%) and 6 (12%) reductions of >30% (99% lower confidence limit: 1%). There was no correlation between CBFVmean and MAP for MAPs between 100 and 40 mm Hg (R2 = 0.0015, P = 0.44). There were no instances of gross postoperative neurologic injury. CONCLUSIONS:Both hypotheses proved partially correct. CBFV was sometimes well maintained during HEA, despite MAPs well below the commonly accepted lower limit of autoregulation. However, there was considerable interindividual heterogeneity with 23% of subjects having CBFV reductions >20% (99% lower confidence limit: 9%), with some reductions approaching the threshold for ischemic injury. The present data do not allow us to determine whether hypotension would be similarly tolerated in other circumstances.

Pulmonary circulatory changes after bilateral total knee arthroplasty during regional anesthesia

STUDY OBJECTIVE To monitor the pulmonary hemodynamics of patients undergoing bilateral total knee arthroplasty (BTKA) intraoperatively and up to 24 hours following surgery. DESIGN Prospective observational study. SETTING University-affiliated teaching hospital. PATIENTS 30 ASA physical status 2 and 3 patients scheduled for single-stage, cemented BTKA during epidural anesthesia. INTERVENTIONS Pulmonary artery catheters were in all patients. MEASUREMENTS Systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), the ratio of PVR to SVR at baseline, at the beginning of surgery, and after each knee implantation were recorded and compared with measurements taken one day postoperatively (POD 1). MAIN RESULTS On POD 1, PVR/SVR was increased by 30% compared with baseline (P < 0.0001) and by 20% versus the end of surgery (P < 0.0001). Systemic vascular resistance decreased during surgery and was significantly lower than baseline at 24 hours after surgery (P < 0.0001). No significant change in PVR was noted during surgery. CONCLUSION The PVR/SVR ratio on the day following BTKA was increased. This change may represent the different effects of inflammatory perioperative stresses on the pulmonary and systemic vasculature.