THA technique affects vein occlusion, pulmonary artery oxygen saturation

Venous obstruction can lead to venous stasis, a known factor influencing deep vein thrombosis risk.

Leg positioning during total hip arthroplasty influences the extent of venous occlusion and affects pulmonary artery oxygen saturation, according to a new study.

Nigel E. Sharrock, MB, ChB, and colleagues at the Hospital for Special Surgery in New York City, in reaching their findings, randomly assigned 19 patients to undergo THA involving one of two different leg and hip positioning techniques. They published their results in the Journal of Arthroplasty.

“The duration of the period the leg was held in flexion and internal rotation was related to the decline in [pulmonary artery oxygen saturation],” the authors said.

“This is consistent with the concept that venous obstruction leads to venous stasis. The static blood desaturates over time, and with the release of the venous obstruction, the desaturated blood passes centrally and can be detected as an acute reduction in [pulmonary artery oxygen saturation],” they said. Combinations of venous stasis, intimal injury and hypercoagulability have been known to cause the formation of venous thrombi, they noted.

“These data support the concept that prolonged periods of femoral venous occlusion favor deep vein thrombosis,” they said, adding that efforts to relieve it help reduce that risk.

Two leg positions

The first positioning technique — T1 — involved placing the thigh in a flexed, adducted and internally rotated position, which was maintained until the cement fixating the prosthesis polymerized. The second technique — T2 — involved femur extension and internal rotation after inserting the femoral component. The surgeon maintained this position until the cement hardened, avoiding any soft tissue contact or component movement, the authors said.

The researchers found reductions in pulmonary artery oxygen saturation in all patients following joint relocation, ranging from 2% to 21%. For both positioning techniques, trial repositioning caused similar oxygen saturation declines.

The first technique produced a significantly greater reduction following final relocation (P=.0003), however. After final hip relocation, mean oxygen saturation declined 12% for T1 patients compared with 4% for patients treated with the second technique (T2; P<.0001), according to the study.

The OR team maintained systolic blood pressure at between 45 and 55 mm Hg and monitored patients using pulse oximetry and electrocardiogram. To evaluate oxygen saturation, the researchers used a Swan-Ganz continuous cardiac output/oximetry thermodilution catheter (Baxter). They also used the Vigilance monitor (Baxter), according to the study.

Surgeons used a posterolateral surgical approach with the patient in the lateral position in all cases. Once sedated, all patients breathed nasal oxygen at a concentration of 3 L/min throughout the duration of surgery.

Patients undergoing both surgical techniques had similar mean surgical durations — 69 ± 15 minutes for T1 patients and 69 ± 21 minutes for T2 patients, according to the study. No patients received blood transfusions, the authors noted.

For more information:
Sharrock NE, Go G, Mayman D, Sculco TP. Decreases in pulmonary artery oxygen saturation during total hip arthroplasty. J Arthroplasty. 2005;20:499-502.