The Journal of Arthroplasty Vol. 23 No. 7 2008

Hypoxemia After Total Joint Arthroplasty

A Problem on the Rise

Luke Austin, MD, Luis Pulido, MD, Raymond Ropiak, MD, Manny Porat, MD,Javad Parvizi, MD, FRCS, and Richard H. Rothman, MD, PhD

Abstract: Total joint arthroplasty (TJA) is categorized as a major risk factor forthromboembolic complications. The importance of hypoxemia during the post-operative period is subject of controversy. This prospective study elucidates theincidence and etiology of hypoxemia after TJA. Furthermore, we intended to assessthe predictive value of clinical findings in identifying the etiology of hypoxemia afterTJA. Of 1971 patients, 78 (4.0%) experienced an acute episode of hypoxemia duringtheir hospitalization after TJA. Hypoxemia as the initial presenting sign, predictedmajor complications, defined as life-threatening if left untreated, in 32% of thehypoxic population. These diagnoses included pulmonary embolism, pulmonaryedema, and pneumonia. Tachypnea was the only independent factor associated withpulmonary embolism. Our study presents the incidence and etiology of hypoxemiaafter TJA, and we recommend a heightened appreciation for the hypoxemic patient.Key words: arthroplasty, hip, knee, postoperative complications, hypoxemia.© 2008 Published by Elsevier Inc.

Total hip and knee arthroplasties are successfulprocedures providing pain relief and function topatients with arthritis [1-3]. Although rare, cardio-vascular complications, including pulmonary embo-lism, myocardial infarction, and even death, mayoccur in joint arthroplasty [4-9]. Early detection andtreatment is ideal in the pursuit for a betterprognosis. However, the evaluation of thromboem-

From the Rothman Institute of Orthopedics at Thomas JeffersonUniversity, Philadelphia, Pennsylvania.

Submitted October 25, 2007; accepted May 2, 2008.Each author certifies that their institution has approved the

human protocol for this investigation and that all investigationswere conducted in conformity with ethical principles of research.

Benefits or funds were received in partial or total support ofthe research material described in this article. These benefits orsupport were received from Stryker Orthopedics, Mahwah, NewJersey (Dr J Parvizi and Dr R Rothman).

Reprint requests: Javad Parvizi, MD, Rothman Institute ofOrthopedics at Thomas Jefferson Hospital, 925 Chestnut St,Philadelphia, PA 19107.

© 2008 Published by Elsevier Inc.0883-5403/08/2307-0012$34.00/0doi:10.1016/j.arth.2008.05.006

1016

bolic and cardiovascular complications after jointarthroplasty is a difficult challenge [10].

Hypoxia after total hip arthroplasty has beenreported as a common postoperative complication[11-13]. One previous study, reported a 42%incidence of hypoxemia on postoperative day 1after total hip arthroplasty [12]. Although, hypox-emia postarthroplasty could be secondary to multi-ple conditions such as hypoventilation, narcoticeffect, fluids overload, and postoperative atelectasis.The lack of a validated algorithm or test todifferentiate between the relatively “benign” condi-tions frommore dangerous complications, representa burden for the patients, the caring physician, andto the health system, as patients usually requireextensive diagnostic workup. Because of the highrisk of venous thromboembolism in the postarthro-plasty patient and the consequences of missing thediagnosis, it becomes a difficult clinical decision onthe course of action for the hypoxemic patient.

This prospective observational studywas designed toelucidate the incidence and the etiology of hypoxemiaafter total joint arthroplasty (TJA). Furthermore, we

Hypoxemia After Total Joint Arthroplasty � Austin et al 1017

intended to assess the predictive value of clinicalfindings in identifying the etiology of hypoxemiaafter TJA.

Table 1. Variables That Were Assessed as PotentialPredictors for Pulmonary Embolus

Preoperative Variables

ge Atrial fibrillation Chronic renal failureMI Congestive heart

failureHypothyroidism

ex Hypertension Rheumatoid arthritismoking status Coronary artery

diseaseSystemic sclerosis

SA History of VTE Cancerleep apnea Peripheral vascular

diseaseLeukemia

OPD Diabetes mellitus Mood disorderComorbidity index

Surgical Variables

ype ofanesthesia

Type of procedure Warfarinchemoprophylaxis

eneral Primary TJA Full dosepidural Revision TJA Regularpinal Hip Low doseepodur Kneeatient-controlledanesthesia

Unilateral

Bilateral

Associated Clinical Findings

Clinical symptoms Clinical signs

hest pain Apprehension Tachycardialeuritic pain Hemoptysis Tachypneacute dyspnea Fainting Feverough Timing of diagnosis

(POD)

BMI indicates body mass index; ASA, American Society ofnesthesiologist; VTE, venous thromboembolism; COPD, chronic

obstructive pulmonary disease; POD, postoperative days.

Material and Methods

After institutional review board approval, aprospective study was commenced that followed aconsecutive series of patients undergoing electiveTJA between January 1 and November 15, 2006, atour institution. The objective of the study was toelucidate the incidence and etiology of hypoxia inthe cohort.Patients undergoing hip or knee arthroplasty at

our institution are subjected to preoperative medicaloptimization by an internist. Hypotensive regionalanesthesia is used for all patients unless contra-indicated. All surgeries are performed by or underthe supervision of a fellowship-trained arthroplastysurgeon. Hip arthroplasty at our institution isperformed with the patient in the supine positionusing a modified anterolateral approach and unce-mented components. Total knee arthroplasty isperformed under tourniquet, using medial para-patellar arthrotomy and cemented fixation.During the study period, the postoperative proto-

col for joint arthroplasty patients included adminis-tration of warfarin chemoprophylaxis with a goalinternational normalized ratio of 2.0. Warfarin wasstarted on the evening of surgery and continued fora period of 6 weeks. Patients also received 1000 IU ofintravenous heparin at the time of hip dislocation orbefore inflation of the tourniquet for knee arthro-plasty. In the postoperative period, patients weremobilized early, and continuous passive-motiondevices were used for knee arthroplasty patients.All postoperative TJA patients were placed onoxygen during the immediate postoperative periodand were weaned over the course of 24 hours.Patients were monitored closely during the post-

operative period. Nursing surveillance includedrecording of pulse oximetry with routine vitalsigns every 6 hours after TJA. Hypoxemia wasdefined as a pulse oximetry reading lower than90%. An oxygen saturation (SO2) value equal orless than 90% was adopted because it correlateswith an arterial oxygen tension (PaO2) of 60 mm Hgor less, on the oxygen dissociation curve [14]. Ifpostoperative hypoxemia was detected, the patientwas evaluated by an internist. Vital signs wereassessed, the patient was stabilized, treated withoxygen, incentive spirometry, and continued obser-vation. Persistence of abnormal clinical signs, despitethe initial resuscitation, resulted in further evalua-

tion with an electrocardiogram, chest radiograph,cardiac enzymes (troponins), arterial blood gases,and other serological tests. Patients were askedabout specific symptoms including chest pain,pleuritic pain, acute dyspnea, cough, and hemopty-sis. Any patients with acute dyspnea or other signsand symptoms suspicious for pulmonary embolism(PE), such as persistent or refractory hypoxia, weresubjected to further workup that included the use ofmultidetector computed tomography (MDCT) or aventilation and perfusion scan (V/Q) if the patienthad a dye allergy or elevated creatinine level.

A detailed data sheet recording the exact circum-stances surrounding the hypoxic event, the findingsof the investigations, and the final outcome wascompleted for each patient (Table 1).

Statistic Analysis

Parametric and nonparametric analysis (T statis-tics and Wilcoxon) was performed for continuousvariables. χ2 and Fisher exact test was performed to

AB

SS

AS

C

T

GESDP

CPAC

A

1018 The Journal of Arthroplasty Vol. 23 No. 7 October 2008

compare the categorical variables. Descriptive ana-lysis was performed using univariate statistics for thecontinuous variables (age, body mass index, comor-bidity index, and postoperative days for medicaldiagnosis). All continuous variables were reportedusing means, SDs, and interquartile ranges. Descrip-tive analysis was performed using proportiondistribution for the categorical variables (sex, race,smoking history, types of anesthesia, type and sideof surgery, and anticoagulation categories). Catego-rical analysis was also performed using frequencydistribution in patients with/without symptomsincluding chest pain, pleuritic pain, cough, acutedyspnea, apprehension, hemoptysis, fainting, tachy-cardia, tachypnea, and fever. Multivariate analysiswas performed using forward logistic regressionanalysis to determine variables that were significantpredictors of the outcomes including pulmonaryembolism, pulmonary edema, pneumonia, chronicobstructive pulmonary disease (COPD), arrhythmia,atelectasis, and narcotics effect. All analysis per-formed were 2-tailed using SAS version 9.1 (SASInstitute, Cary, NC).

Results

During the period of this study, 2216 arthroplas-ties were performed in 1971 patients. Of these, 1158surgeries (1091 patients) were hip arthroplastiesand 1058 (880 patients) were knee arthroplasties.

Fig. 1.Differential diagnosis after hypoxemia after TJA. 1, PE; 2,6, atelectasis; 7, narcotic-related respiratory depression; 8, hypo

Of 1971 patients, 78 (4.0%) experienced an acuteepisode of hypoxemia during their hospitalizationafter TJA. Hypoxemia occurred more frequentlyduring the second postoperative day (mean, 2 days;range, 0-17 days). Hypoxemia during the evening ofjoint arthroplasty (postoperative day 0) occurred in13 patients (17%, 13/78). The oxygen desaturationseen in the cohort ranged from 65% to 89%.Further diagnostic studies were performed in 82%of the patients, including chest radiographs(19 patients), MDCT of thorax (44 patients), V/Qscan of the lungs (11 patients), and arterial bloodgases (10 patients). The etiology that predisposedpatients to hypoxemia was determined in most cases(Fig. 1). Six different etiologies (outcomes) werefound and confirmed by clinical and diagnosticstudies. The majority (70%, 55/78 patients) of thehypoxemic patients were evaluated for PE. Allpulmonary embolisms were diagnosed on MDCTscan (27%, 12 patients with PE, of 44 MDCTperformed). No pulmonary embolisms were inden-tified on V/Q scan. No etiology could be elicited for21 (27%) of the 78 patients with hypoxia.

After unadjusted analysis, we identified multipleperioperative variables associated with a clinicaldiagnosis in hypoxemic patients (Table 2). However,after adjusting for all variables using multivariateregression analysis, we were only able to identifytachypnea as a significant predictor of pulmonaryembolism (P = .008). Body mass index as a predictorfor pulmonary edema (P = .01) and the presence of

pulmonary edema; 3, pneumonia; 4, COPD; 5, arrhythmia;xemia with unknown etiology.

Table 2. Hypoxemia After Total Joint Arthroplasty:Positive Predictors of Outcomes After Univariate Analysis

Outcome Variable P

Pulmonary embolism Older age .04Female .05Coronary artery disease .03Leukemia .02Hemoptysis .02Tachypnea .0004

Pulmonary edema Higher BMI .04Revision surgery .03CHF .03

Pneumonia Sleep apnea .03VTE .05Systemic sclerosis .0006

Atelectasis Female .04White race .03Diabetes mellitus .02

COPD Epidural .09

CHF indicates congestive heart failure.

Hypoxemia After Total Joint Arthroplasty � Austin et al 1019

diabetes mellitus as a predictor for atelectasis (P =.02) (Table 3).

Table 3. Hypoxemia after Total Joint Arthroplasty:Independent Factors and Outcomes After Multivariate

Analysis

utcomesOddsRatio P

95%ConfidenceIntervalositive Variables

ulmonary embolismachypnea 11.93 .008 1.92; 75.01ulmonary edemaMI 1.14 .01 1.03; 1.28telectasisiabetes mellitus 3.85 .02 1.25; 11.80

Discussion

Total joint arthroplasty has been categorized as amajor risk factor for thromboembolic complications[7,8,15-18]. Physicians and patients should beaware of the challenges that represent the diagnosisof these cardiovascular complications in the perio-perative setting [10]. The lack of a validated screen-ing tool [10], the poor sensitivity of the clinical signsand symptoms of thromboembolic complications[19], and the possibility of a fatal outcome [8,15,20]are factors that increase the level of concern in thepostoperative care of these patients.A strict postoperative surveillance of patients

undergoing TJA, including monitoring of pulseoximetry readings every 6 hours with routine vitalsigns, are part of the current protocol of patient careat our institution. This strategy is performed toidentify possible cardiovascular complications in atimely manner. However, it is important to recog-nize that the value of pulse oximetry and bloodgases in the evaluation of pulmonary embolism isstill uncertain [21-23].The number of days a patient should be observed

in the hospital after TJA is a matter of debate. In2007 Parvizi et al [5] suggested that day-of-surgerydischarge would lead to a significant increase inmissed life-threatening complications. The findingspresented in the presented study support theirconclusion. In this study's cohort of patients, day-of-surgery discharge would have missed 11 PEs,8 cases of pulmonary edema, and 3 pneumonias.

The incidence of hypoxemia after TJA in thisstudy was relatively low (4%) and dramatically lessthan previously reported incidence (42%) [12]. Webelieve the marked discrepancy may be related thedifferences in the definition and monitoring ofhypoxemia. The mechanism of hypoxemia can besummarized into 2 possible physiologic explanationsas follows: hypoventilation or abnormal gasexchange [24]. Hypoxemia as a postoperativecomplication varies according to patient's physicalstatus and cardiovascular reserve [12,24,25]. Theevaluation of hypoxemia is complex and multi-factorial and may differ from patient to patient [26].Although we could assume that episodes of hypox-emia are secondary to multiple reasons such aspatient's comorbidities, intravenous fluid overload,postoperative atelectasis, or hypoventilation sec-ondary to anesthesia-analgesia medications, wecould not exclude, on the basis of the clinicalpresentation, the possibility of a serious condition.

The etiologies of hypoxemia are equally impor-tant to consider in the evaluation of the arthroplastypatient. One important objective of this study was topresent the influence of patients' comorbidity profileand the clinical findings as possible predictors ofoutcomes of hypoxemia after TJA. Six differentetiologies or outcomes were identified as follows:pulmonary embolism, pulmonary edema, pneumo-nia, COPD, atelectasis, and narcotics side effects.Although no diagnosis was made in 27% of thepatients, we may hypothesize that central orobstructive apnea were the most likely causes. Ofthe diagnosed etiologies, atelectasis was the mostcommon finding. Pulmonary embolism, pulmonaryedema, and pneumonia were the most seriousconditions, which required further medical manage-ment. Within the hypoxemic group, 15% of patientswere diagnosed with pulmonary embolism.

Pulmonary embolism is the most common seriousmedical complication after TJA [5]. Because of theinconsistent clinical presentation, PE is frequently

O

P

PTPBAD

1020 The Journal of Arthroplasty Vol. 23 No. 7 October 2008

under diagnosed [27]. Joint arthroplasty surgerysets patients at a higher risk for venous thromboem-bolic disease [7,8,15-18]. Therefore, PE must becarefully considered in the differential diagnosis ofhypoxemia. Our unadjusted analysis presentedpatients with advanced age (N70 years old), females,history of malignancy, coronary artery disease,hemoptysis, and tachypnea, with a higher likelihoodof having PE. However, the only factor thatpresented a constant correlation after multivariateanalysis was tachypnea.Predictors for pulmonary edema included higher

body mass index, history of congestive heart failure,and revision surgery. Blood loss after revision surgeryrequires abundant blood transfusions and aggressivefluid resuscitation. Intravenous fluid overload, in aweak malfunctioning heart, predisposes to pulmon-ary edema, which could present with respiratoryfailure and hypoxemia. One important observation isthat hypoxemia was not associated with acutecoronary events during this study. Nonetheless,complete cardiovascular evaluation, including anelectrocardiogram and cardiac enzymes, were per-formed according to clinical acumen.In conclusion, we found pulse oximetry a useful

tool in the perioperative care of the arthroplastypatient. Hypoxemia could be found in 4% of thepatients. Most patients in this prospective study whohad further diagnostic workup were found to have amedical complication (Fig. 1). Overall, hypoxemiaas the initial presenting sign, predicted majorcomplications, defined as life-threatening if leftuntreated, in 32% of the hypoxic population.These diagnoses included pulmonary embolism,pulmonary edema, and pneumonia. Hypoxemiaalone or in correlation with other clinical variables(Table 1) was not found to be specific for a particularetiology and further diagnostic evaluation shouldbe considered.

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