In this study of 24 patients undergoing bilateral hybrid total hip replacement under regional anesthesia, we observed an increase in pulmonary vascular resistance that was pronounced after the implantation of the second hip. Interestingly, the increase in pulmonary vascular changes continued into the postoperative period. Pulmonary arterial pressures were significantly increased from baseline on postoperative day 1. Further, an increase in white blood cell count was associated with the second hip implantation but not with the first.
The impact of unilateral hip arthroplasty on the pulmonary vasculature has been described in the past.1–7
Most trials however, have found little clinical significance of events surrounding the so called “bone cement implantation syndrome” and have described changes in pulmonary pressures and right heart function as small and relatively short lived.12–14
While most studies have employed transesophageal monitoring for hemodynamic assessment, López-Durán et al. using Swan Ganz catheters showed that during elective unilateral total hip replacement under general anesthesia pulmonary arterial pressures and pulmonary vascular resistance remained virtually unchanged,14
supporting our findings that no major significant changes were seen in these parameters intraoperatively in response to the first hip implant.
While reassuring when taking care of patients for unilateral procedures, no extrapolation of findings of studies assessing one sided approaches can be made to bilateral surgeries in which the embolic load of intramedullary debris and cement to the lung is presumably doubled. Outcome studies evaluating the impact of bilateral joint arthroplasty provide controversial results but seem to suggest higher incidence of perioperative complications despite younger average age and lower overall comorbidity burden, including complications presumably attributable to lung injury, i.e. adult respiratory distress syndrome.15
Indeed, when studying the impact of bilateral procedures on pulmonary vascular parameters, the addition of the second side results in a significant increase in pulmonary circulatory parameters as compared to values at incision in our study. This effect occurs in the absence of changed fluid conditions as measured by pulmonary arterial occlusion pressure, supporting that our findings are irrespective of left ventricular events. In addition to adverse hemodynamic changes in response to a second hip implantation, we found evidence of an increase in the inflammatory response as shown by a 45% increase in the white blood cell count compared to the first arthroplasty. White blood cell counts have been previously described as a reliable and timely marker of acute inflammation secondary to injury and stress.16
While white blood cell counts are known to rise in response to increased plasma epinephrine levels, the exogenous administration of this drug used in conjunction with the controlled hypotension protocol as described previously,10
remained stable throughout the intraoperative period (range 1.7 to 1.9 mcg/min) (P>0.1 between all intraoperative comparisons).
We found that the induction of anesthesia and the use of a controlled hypotensive technique using a low thoracic epidural10
was accompanied by a reduction (although not significant in this study) in pulmonary arterial pressures and vascular resistance compared to baseline, while cardiac output was maintained. This approach may be viewed as beneficial when dealing with embolic phenomena to the lung. Animal studies have shown that the use of a thoracic epidural block improves hemodynamics by reducing mean pulmonary pressure and raising cardiac index in the setting of pulmonary embolism,17
a situation with similar hemodynamic consequences observed during intramedullary debris and cement embolization of the lung. The fact that thoracic but not lumbar epidural placement of the catheter has been associated with this beneficial effect seems to point to the role of a sympathetic blockade in this process.18
Thus, the anesthetic technique used in our study may have been beneficial in providing a “best possible scenario” to study the effects of intramedullary content embolization during hip surgery, leaving the question if the use of other forms of anesthesia may be associated with more significant changes in pulmonary hemodynamics.
To our knowledge, this study is the first to establish the prolonged adverse effect on pulmonary hemodynamics and inflammation after bilateral hybrid total hip replacement. This suggests that the stress on the right ventricle is sustained after implantation of the joint. Although speculative, this may expose particularly patients with pre-existing decreased reserve to perioperative problems. To ameliorate the impact of the debris load and its effects on the pulmonary vasculature a discussion with surgeons to thoroughly clean and dry the intramedullary canal prior to cementation and injection of cement in a retrograde fashion with a cement gun to minimize intramedullary pressure and venous extravasation during insertion of the femoral prosthesis should be encouraged as such approach may be associated with a decrease in debris load to the lung. Avoiding cemented prosthesis altogether in patients at risk poses another option to minimize adverse effects to the lung.4
However, the potential benefits of a low thoracic epidural with sympathetic blockade in the clinical setting remains speculative.
Our study is limited by a number of factors. First, we only included patients without pre-existing pulmonary pathology. Thus, we cannot predict what the effect of hip arthroplasty may be in the patient population in whom pulmonary vascular disease is present at baseline, although it is likely that these patients would be more susceptible to perioperative injury. However, our patient selection is in keeping with clinical practice in our hospital to pre-select candidates without significant cardiopulmonary disease for bilateral procedures under the assumption that a more complicated bilateral surgery may predispose patients with less reserve to more complications. Second, we did not collect data beyond the first postoperative day, as it would not have been feasible or necessary to leave the pulmonary artery catheter in situ beyond this time point. In addition, this study does not include a control group of unilateral total hip arthroplasty patients. The argument could be made that our findings of prolonged hemodynamic changes may at least in part reflect delayed effects of the first arthroplasty. However, anecdotal evidence from clinical experience and observations from previous studies suggest that pulmonary hemodynamic changes in response to unilateral procedures are small and transient.12–14
While conceptually results from a unilateral THA cohort would be interesting, performing pulmonary catheterization in healthy, elective unilateral hip arthroplasty recipients may further pose ethical limitations. Thus our data will have to be interpreted in the context of our study design, with the realization that the theoretical possibility exists that increases in pulmonary pressures and white cell count may partially be influenced by a timing effect related to the first hip implant.
Irrespective of these limitations, our study shows that in the setting of bilateral total hip arthroplasty pulmonary arterial pressures and vascular resistance remains increased beyond the immediate implantation phase.
In summary, our data suggests that cemented bilateral hybrid total hip arthroplasty is associated with increases in pulmonary artery pressures and vascular resistance, particularly after the second side. Keeping patient safety a priority, the performance of bilateral procedures should be cautiously considered and perhaps staged in patients with diseases suggesting decreased pulmonary reserve and increased right ventricular afterload, i.e. pre-existing pulmonary hypertension.