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© 2001 International Anesthesia Research Society
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Abstract |
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The first aim of this prospective clinical study was to characterize the relationship between embolic events observed during cemented total hip arthroplasty using transesophageal echocardiography (TEE), and changes in cardiopulmonary function. The second aim was to assess the efficiency of a modified cementing technique that was developed to reduce the risk of embolism. The modification consists in a vacuum drainage placed in the proximal femur to reduce the increase of intramedullary pressure during insertion of the prosthesis. One hundred twenty patients were randomized into two groups. Group 1 received a total hip arthroplasty cemented conventionally, whereas Group 2 was cemented with the modified technique. Continuous TEE, hemodynamic monitoring, and blood gas analysis were done during the perioperative period. Severe embolic events were imaged during the insertion of the femoral component and the reduction of the hip joint. Embolism occurred in 93.3% of patients operated on with the conventional cementing technique, compared with 13.3% of patients operated on with the modified technique (P < 0.05). Intraoperative shunt values during insertion of the femoral component increased from 8.2% to 10.3% (P < 0.05) in Group 1 patients, whereas there was no significant change in Group 2 patients. We observed no clinical signs of fat embolism syndrome in any study patient. The results of the study indicate that embolic events observed using TEE can cause increased pulmonary shunt values during hip arthroplasty, especially in patients with systemic disease (ASA physical status III). The modified surgical technique effectively reduced the incidence of embolization during cemented hip arthroplasty.
Implications: Use of conventional cementing techniques is associated with echocardiographic evidence of embolism in 93% of patients and with a significant increase in pulmonary shunting. The incidence of embolism and change in shunting are reduced with a modified cementing technique that limits increases in intramedullary pressure.
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Introduction |
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Total hip arthroplasty is associated with hypotension (1), hypoxemia (1–3), pulmonary hypertension (4–7), cardiac arrest (6,8), and death (8,9). In a review of several studies ranging in size from 400 to 2012 patients (10), intraoperative cardiac arrest occurred in 0.6% to 10%, with a mortality rate of 0.02% to 0.5%.
Several hypotheses have been proposed to explain the pathophysiology of these intraoperative complications. A likely cause is pulmonary microembolism, with the degree of embolism determined by the intramedullary pressure generated at the time of insertion of the prosthesis (1,11–13). Fat, bone marrow, and air are extruded into the femoral venous channels and eventually embolize to the heart and lungs. Intraoperative embolism was detected with transesophageal echocardiography (TEE) in 90% to 98% of total hip arthroplasty patients (14–16). Nevertheless, the clinical relevance of intraoperative embolic events remains controversial (2,6,15,17).
The present study had two goals. The first goal was to find correlations between the embolic events observed while using TEE and the cardiopulmonary function of the patients during the intraoperative and postoperative periods. The second goal was to determine the efficacy of a modified surgical technique (12,16) designed to limit the intramedullary pressure during insertion of the stem and to reduce intraoperative embolic events.
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Methods |
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One hundred twenty total hip arthroplasty patients were enrolled in this randomized controlled trial. Inclusion criteria of the patient population were degenerative hip disease and hip fracture. Exclusion criteria were rheumatoid arthritis and history of deep vein thrombosis, pulmonary embolism, or esophageal disease. The study was approved by the institutional investigation committee of the hospital, and written informed consent was obtained from all patients. The patients were randomized into two groups. Randomization was at operation day using random number sheets. Sixty patients (Group 1) received a femoral component inserted with a conventional cementing technique, whereas the other 60 patients (Group 2) were operated on with a modified cementing technique developed to prevent the increase of intramedullary pressure during the insertion of the femoral component (12). The modification is in the drainage of the proximal femur. A cannula with a diameter of 4.5 mm was positioned along the prolongation of the linea aspera into the cancellous bone of the intertrochanteric region. Care was taken to avoid intramedullary placement of the 20-mm-long cannula. The cannula was connected to a vacuum pump (-800 milli-bar) ( Vacumix ; Braun, Melsungen, Germany) with a suction tube. The drainage system was checked thoroughly for adequate functioning. The cannula drained the femoral canal during application of the cement and the insertion of the stem, avoiding an increase of intramedullary pressure and migration of fat and bone marrow into the veins of the thigh. In contrast to the technique used in a previous study (16), in which a second drainage cannula was placed underneath the tip of the stem, in this series of patients we used only a proximal drainage cannula.
The same surgeon performed or directly supervised the operative procedures. Pulsatile high-volume lavage (1000 mL of saline solution) was performed in all patients before cementing of the stem to wash the bone surface. Clinical data of the patients were evaluated by chart review at admission and examination of the staff anesthesiologists. The preoperative physical status of the patients was assessed according to the criteria of the American Society of Anesthesiologists (ASA) (18). During surgery and in the recovery room, patients received routine perioperative care according to the direction of the attending anesthesiologist. This included administration of low-molecular-weight heparin (3800 IU, Fraxiparin ; Sanofi Winthrop, Munich, Germany). Clinical monitoring included a three-lead electrocardiogram, invasive measurement of arterial pressure with a radial artery catheter, and measurement of pulse oximetric oxygen saturation and end-tidal carbon dioxide tension. Patients with severe associated diseases (ASA III-IV) received a central venous catheter placed into the right internal jugular vein. Anesthesia was induced with propofol (1–2 mg/kg) or etomidate (0.1–0.2 mg/kg), combined with fentanyl (>3 µg/kg). Muscle relaxation was obtained before intubation with suxamethonium (1–1.5 mg/kg) and atracurium (0.3–0.6 mg/kg), cisatracurium (0.08–0.15 mg/kg), or pancuronium (0.08–0.1 mg/kg) during the operation. Anesthesia was maintained with nitrous oxide (FINO2 = 0.66) and one-third to one-half minimal alveolar concentration of isoflurane or desflurane. During the operation, all patients received repetitive doses of fentanyl (50–100 µg) and atracurium (5–10 mg) and cisatracurium (1–2 mg) or pancuronium (1 mg). Antiemetic prophylaxis was done with 1.25 to 2.5 mg dehydrobenzperidol. All patients were mechanically ventilated to maintain a constant end-tidal carbon dioxide level. Fractional inspiratory oxygen concentration was increased (FIO2 = 0.33) in the postoperative period by insufflating oxygen (3 L/min) through a nasal probe.
TEE was recorded continuously with a 5-mHz multiplanar probe ( Sonoline Versa-Plus ; Siemens, Erlangen, Germany) after anesthetic induction and tracheal intubation until skin closure in all patients. The ultrasound probe was positioned into the esophagus to obtain a four-chamber view to detect echogenic material in the right atrium and ventricle as well as a possible embolization through a patent foramen ovale. No IV fluids were administered during preparation of the femur, cementation of the stem, or relocation of the hip joint.
Rating of intraoperative embolic events was performed off-line by a blinded observer who used established criteria (6,16) ( Fig. 1): grade 0, no emboli or small echogenic particles; grade 1, a few fine emboli; grade 2, a cascade of fine emboli or embolic masses with a diameter of <5 mm, and the right atrium is opacified with echogenic material; and grade 3, fine emboli mixed with large embolic masses with a diameter of >5 mm or serpentine emboli.
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The duration of embolic phenomena graded 1 was determined by the first appearance (starting point) and disappearance (ending point) of fine emboli without opacification of the right atrium. The duration of embolic phenomena graded 2 was determined by the first appearance (starting point) and disappearance (ending point) of complete opacification of the right atrium. Echocardiographical findings were compared with the clinical and laboratory data. For this purpose, measurement of arterial CO2 tension, arterial oxygen tension, pH, and oxygen saturation were drawn at defined points of the operative period: (a) at the operative incision, (b) 5 min after insertion of the cup, (c) after preparation of the femur, (d) 5 min after insertion of the stem, (e) 5 min after relocation of the hip joint, (f) 15 min after relocation of the hip joint, and (g) 2 h after the end of operation.
For calculating the shunt values, we used the method suggested by Ries et al. (19) (Appendix). This calculation is an approximation derived from a previous study of 97 patients in whom the shunt value (Qs/Qt) was calculated by using the Fick principle with a mixed venous oxygen content (25). Shunt fraction then was plotted against the arterial blood gases that were drawn at the same time. The calculation with the formula Qs/Qt (shunt) = (5.8 x RI) + 6.7, where RI (respiratory index) = {[(PB - PH2O) x FIO2] - PaCO2- PaO2}/PaO2, where PB = barometric pressure and PH2O = partial pressure of water, was derived with a regression line, with r = 0.6, P < 0.0001, and 95% confidence limits.
The demographic data of the patients, as well as the severity and duration of the transatrial embolic events in the two groups of patients, were analyzed with a two-tailed, unpaired t-test. A repeated-measures analysis of variance and a Newman-Keuls test for intergroup comparisons were performed for all of the samples used for arterial blood gas determination, for the measurement of end-tidal carbon dioxide levels, and for each set of pulmonary shunt values. Differences were considered statistically significant with the values of P < 0.05.
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Results |
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Of the 120 patients in this study, there were 76 women and 44 men with a mean age of 72 yr. Demographic characteristics were similar in the two groups of patients ( Table 1). A cascade of fine echogenic particles or embolic masses with a diameter as large as 5 mm (grade 2) were imaged during the insertion of the stem in 56 patients (93.4%) by using conventional cementing technique and in eight patients (13.4%) by using the modified technique ( Table 2). The difference in the intensity and the duration of the grade 2 embolic events between the two groups of patients was significant (P < 0.05). The prevalence of embolic masses with a diameter >5 mm (grade 3) imaged after the relocation of the joint in the two groups of patients was also significantly different (51.7% and 8.3%, respectively; P < 0.05).
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A nearly immediate cause and effect relationship was observed between embolic events graded 2 and 3 imaged during the operation and changes of hemodynamic and cardiorespiratory function. Pulse oxymetric oxygen saturation and end-tidal carbon dioxide tension changed significantly with time ( Fig. 2, A and B). A significant increase of pulmonary shunt values from 8.2% to 10.3% (P < 0.05) was observed after conventional insertion of the femoral component, indicat-ing intraoperative ventilation-perfusion mismatching (Fig. 3). In patients who received a stem inserted with the modified cementing technique, the mean pulmonary shunt values showed an insignificant increase from 8.1% to 8.7% during the operation. Baseline pulmonary shunt values of healthy patients or patients with mild systemic disease (ASA I-II) who sustained embolic events graded 2 or 3 were reestablished uneventfully at the end of the operation. In contrast, pulmonary shunt values of patients with severe systemic disease (ASA III-IV) remained abnormally increased, even in the postoperative period ( Fig. 4).
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Twenty-two of 64 patients (34.4%), who had a cascade of fine emboli (grade 2) during the insertion of the stem, reacted with a transient decrease of systolic blood pressure of >20 mm Hg. Hypotensive reactions were observed in the same set of patients after the relocation of the hip joint.
Heart rhythm and heart rate remained stable in all patients during the operation. No patient experienced a cardiac arrest or demonstrated evidence of postoperative fat embolism syndrome (11) (major symptoms include petechial rash, respiratory symptoms, bilateral positive radiographic changes, and cerebral signs unrelated to head injury or any other condition; mi-nor symptoms include tachycardia, pyrexia, retinal changes, urinary changes, a sudden decrease in hemoglobin level, sudden thrombocytopenia, high erythrocyte sedimentation rate, and fat globules in the sputum).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionAppendixReferences |
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The purpose of this randomized clinical trial was to investigate whether the severity and duration of embolic events observed by TEE during cemented total hip arthroplasty correlates with clinical cardiorespiratory impairment. A second goal was to determine whether patients with high anesthesiological risk can profit from a modified cementing technique designed to reduce intraoperative embolic phenomena. The application of a vacuum suction along the linea aspera can avoid the increase of intramedullary pressure and the embolization of fat and bone marrow during the insertion of the stem (12,16). A previous experimental study (21) showed a marked underpressure within the femoral canal (-224 millibars) by using the modified cementing technique. The physiological value of the intramedullary pressure is approximately 66 millibars (50 millimeters of mercury).
A large number of patients was allocated in the present study, and TEE was recorded during the entire surgical procedure, which was performed or supervised by the same surgeon. Embolic events were observed during the insertion of the femoral component and the reduction of the hip joint. This is a phenomenon that has been reproduced by other investigators (2–5,7,17) and confirms the observations of a previous study (16). We used a four-grade score for the quantification of the embolic events. This system is similar to scores used in other studies (2,3,6) and provides the same reproducibility and validation limits. In this study, a blinded, experienced observer performed the quantification of echocardiographic findings off-line. We did not perform intraobserver and interobserver tests. A computer-assisted analysis probably represents the more accurate method to assess the echogenic events (10), but in this setting, the reproducibility and validation have not yet been defined.
Echogenic findings are of multifactorial origin. They can be caused by fat and bone marrow, but also by artifacts of a high flow infusion. For this reason, all IV infusion was stopped at the observation points. Because TEE gives a two-dimensional view of the heart, we may have overlooked some emboli or a paradoxical embolization through a patent foramen ovale. Paradoxical embolism, strokes, and death may occur in patients undergoing total hip arthroplasty who have an undocumented patent foramen ovale (6,20). In a previous study (16), we observed a patent foramen ovale in 6 of 70 total hip arthroplasty patients (8.6%). Shortly after the operation, two of these six patients, who had severe transatrial embolism during the insertion of the stem, suffered transitory signs of neurological impairment.
The nearly immediate cause and effect relationship between the embolic events graded 2 and 3 with hypotension, hypoxemia, decrease of end-tidal CO2 levels, and increase of pulmonary shunt values found in the present study during operation confirm the observations of other investigators (14,15). In this study, a grade 1 embolism was never followed by changes in laboratory and clinical variables. Depending on the preoperative clinical conditions of the patient, the hemodynamic changes may remain subclinical for those with good reserve or may be clinically significant for those with poor reserve. The stratification of results in relation to preoperative physical status (18) showed that after embolization grade 2 or 3, patients with low preoperative anesthesiological risk (ASA I-II), even when signs of cardiorespiratory impairment were significant, returned to the baseline at the end of the surgical procedure. We agree with other investigators (2,3,6) that in these cases, the observations in the majority of patients are without clinical relevance. In the present study, patients with severe coexisting diseases (ASA III-IV) who sustained an embolization graded 2 or 3 showed marked changes in blood gas and shunt values that extended into the postoperative period. Other investigators describe a similar observation in regard to ventilation-perfusion values (19,22).
For ethical reasons, a right heart catheter was not placed in our patients. Thus, we were not able to measure changes in pulmonary arterial blood gas values, pulmonary artery pressure, pulmonary vascular resistance (5–7), cardiac output (6), right ventricular ejection fraction (7), or contractility (3), which can underline the severity of the embolic events observed with echocardiography. On the other hand, by using the method suggested by Ries et al. (19) (Appendix) we were able to compare changes in shunt values immediately after detection of embolism with TEE. The values of calculated pulmonary shunt are relative measurements, and a true mixed venous oxygen content can be performed only with a pulmonary artery catheter. In our opinion, the method suggested by Ries et al. is a reliable way to compare pulmonary shunting in different groups of patients. This is more likely true when a large number of patients are investigated. The calculation can also be performed in the postoperative period if inspiratory oxygen concentration is maintained at the same intraoperative levels with a nasal oxygen probe (19,23–25).
It should be mentioned that there are different reported results in regard to changes of pulmonary function during total hip arthroplasty. Ereth et al. (6) did not find a ventilation-perfusion mismatching after cementing. They explained that this result was probably altered by the inert gas technique, which required 30 minutes for equilibration.
Arterial pressure has been reported in previous studies to decrease (1) or to remain stable (2). Arterial hypotension is a result of a reduced left ventricular preload and the failure of the right ventricle to compensate for the increased pulmonary arterial pressure and the pulmonary vascular resistance (5–7,22). Changes in arterial pressure depend therefore on the grade of embolism. In this study, patients of Group 1 with grade 2 or 3 embolism showed hypotension, whereas patients of Group 2 who did not present severe embolic events had stable arterial pressure.
We conclude that TEE is a reliable method for detecting and quantifying pulmonary embolism during cemented total hip arthroplasty. Furthermore, it gives information on the effect of therapeutic strategies to prevent this embolization. The release of IV fat and bone marrow content depends on the cementing technique used during operation for the fixation of the femoral component. The results of this study show the efficacy of a modified surgical technique for reduction of severe embolization. A vacuum drainage of the proximal femur along the linea aspera is a logical and effective method to reduce high intramedullary pressure and the migration of fat and bone marrow into the venous system. Patients with preexisting diseases can profit from a reduction of intraoperative large emboli that result in cardiorespiratory impairment.
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Appendix |
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TopAbstractIntroductionMethodsResultsDiscussionAppendixReferences |
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Approximation of Qs/Qt according to Ries et al. (19) and Benumof (25):
Qs/Qt = (5.8 x RI) + 6.7,
where Qs = shunt flow and Qt = cardiac output.
Respiratory index (RI) according to Goldfab et al. (24):
RI = (PAO2 - PaO2)/PaO2,
where PAO2 = alveolar partial pressure of oxygen and PaO2 = arterial partial pressure of oxygen.
Alveolar partial pressure of oxygen:
PAO2 = {(PB - PH2O) x FIO2}- PaCO2,
where PB = barometric pressure; PH2O = partial pressure of water; FIO2 = fraction of inspired oxygen; and PaCO2 = arterial pressure of carbon dioxide.
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References |
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