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The association of excessive warfarin anticoagulation and postoperative ileus after total joint replacement surgery
The Journal of Arthroplasty Vol. 15 No. 2 2000
The Association of Excessive Warfarin Anticoagulation and Postoperative Ileus After Total Joint R e p l a c e m e n t Surgery Richard Iorio, MD, William L. Healy, MD, and David Appleby, BS
Abstract: Patients undergoing joint replacement who show signs of ileus in the postoperative period that require insertion of a nasogastric tube (NGT) must be monitored closely to avoid bleeding complications. The diagnosis of postoperative ileus was documented in 40 of 2,526 (1.6%) consecutive joint replacement operations between January 1, 1990, and March 1, 1998, at 1 hospital. Of the 40 patients with postoperative ileus, 34 received warfarin postoperatively. Of these 34 patients, 19 required a NGT for >48 hours, and 15 patients required a NGT for <48 hours or did not require a NGT. Of the 19 patients who required a NGT for >48 hours and who received warfarin anticoagulation, 17 had a prothrombin time of >20 seconds or an international normalized ratio (INR) of >2.0. None of the 15 patients who required a NGT for <48 hours and who received warfarin anticoagulation had a prothrombin time of >20 seconds or an INR of >2.0. This difference was highly statistically significant (P < .001). Key words: colonic pseudo-obstruction, ileus, nasogastric intubation, Ogilvie's syndrome, total joint replacement, warfarin anticoagulation.
The prevalence of postoperative ileus associated with total joint arthroplasty has been reported as high as 3% [1,2]. Postoperative ileus can be associated with peritoneal manipulation, electrolyte imbalances (such as potassium depletion), lengthy surgery, and trauma. As an ileus progresses, the large and small intestine b e c o m e distended, and gas and fluid a c c u m u l a t e in the lumen. An ileus leads to abdominal distention, and vomiting m a y result if decompression by nasogastric suction is not initiated [2,3]. Ileus is usually not a c c o m p a n i e d by mechanical obstruction. Acute colonic pseudo-obstruction, or
Ogilvie's syndrome, is a form of ileus that presents with e x t r e m e dilation of the c e c u m and the transverse colon, with a relative paucity of bowel gas in the distal segment. If untreated, Ogilvie's s y n d r o m e can lead to perforation of the cecum, which m a y be life-threatening. The incidence of Ogilvie's synd r o m e has b e e n reported to be 0.29% after total hip arthroplasty (THA) [4-71. Warfarin is frequently used for p h a r m a c e u t i c a l t h r o m b o e m b o l i c prophylaxis after joint replacem e n t surgery. The dose response to warfarin can be difficult to predict. Intestinal bacterial flora, medications, diet, level of activity, gastrointestinal function, liver disease, and several o t h e r lesser factors can affect the dose response to warfarin [8]. The present study evaluated the incidence and associated factors of ileus as a postoperative complication of lower e x t r e m i t y joint r e p l a c e m e n t surgery. The effect of ileus on the dose response of warfarin used as a t h r o m b o e m b o l i c prophylactic agent after joint r e p l a c e m e n t surgery was also analyzed.
From the Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts. Submitted July 8, 1999; accepted August 31, 1999. No benefits or funds were received in support of this study. Reprint requests: Richard lorio, MD, Department of Orthopaedic Surgery, Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA 01805.
Copyright © 2000 by Churchill Livingstone® 0883-5403/00/1502-0014510.00/0
220
Excessive Warfarin and IleusAfterTJA
Materials and Methods Between J a n u a r y 1, 1990, and March 1, 1998, 2,526 consecutive lower extremity joint replacem e n t operations ( 1,142 primary THAs, 288 revision THAs, 996 primary total knee arthroplasty [TKA], and 140 revision TI(As) performed at 1 hospital were reviewed. A computerized total joint arthroplasty database [9], hospital records, and the Departm e n t of Orthopaedic Surgery m o n t h l y morbidity and mortality reviews were used to identify patients in w h o m an ileus developed after joint replacement surgery. Forty patients with a diagnosis of postoperative ileus after total joint arthroplasty surgery were identified and were included in the study. The diagnosis of postoperative ileus was made by physical examination; radiography; and consultation with gastrointestinal, general surgical, and colorectal specialists. If a diagnosis of ileus was made, patients were not permitted to ingest anything by m o u t h . If nausea or vomiting ensued, a nasogastric tube (NGT) was inserted and was connected to low intermittent wall suction. W h e n gastrointestinal peristalsis and bowel function returned, the NGT was clamped for several hours before its removal. Patients in w h o m ileus developed were characterized according to type of surgery, m e t h o d of anesthesia, type of postoperative analgesia, previous abdominal surgery, medical comorbidities, duration of NGT placement, and complications associated with the ileus. Patients receiving warfarin postoperatively for t h r o m b o e m b o l i c prophylaxis were given 5 mg on the evening of surgery. The p r o t h r o m b i n time (PT), partial thromboplastin time (PTE), and international normalized ratio (INR) were checked daily, and the dose was adjusted to achieve a PT of 15 to 18 seconds or an INR of 1.5 to 1.8. The relationship of postoperative ileus to warfarin administration was e x a m i n e d by analyzing total warfarin dosage, daily PT and PTF, and INR. Statistical analysis was performed to identify relationships b e t w e e n patient characteristics and the incidence of ileus. The incidence of elevated PT PTT, and INR in conjunction with postoperative ileus was also noted. Contingency table analysis was performed using chi-square and Fisher's exact test w h e n appropriate. Odds ratios and other relevant coefficients were recorded. Variables were coded into dichotomies to facilitate this type of analysis.
Results The prevalence of postoperative ileus in patients after joint replacement surgery at our institution
•
Iorio et al.
221
during an 8-year period from J a n u a r y 1, 1990, to March 1, 1998, was 1.6% (40 of 2,526). Postoperative ileus was diagnosed in 22 m e n (55%) and 18 (45%) w o m e n . Ileus occurred after 16 primary THAs, 6 revision THAs, 13 primary TKAs, and 5 bilateral TKAs. General anesthesia was given to 25 patients in w h o m an ileus developed, and 13 of these patients received regional anesthesia (spinal or epidural). Two patients received regional and general anesthesia. Postoperatively, 15 patients used patient-controlled intravenous analgesia; 25 patients did not use this m e t h o d of analgesia. Previous abdominal surgery, type of anesthesia (spinal, epidural, or general), type of surgical procedure (primary THA, primary TKA, revision THA, or revision TKA), and type of postoperative analgesia (intramuscular, parenteral, or patient-controlled intravenous analgesia) were not associated with the development of postoperative ileus. A m o n g 40 patients in w h o m a postoperative ileus developed, 34 received warfarin postoperatively for pharmacologic thromboembolic prophylaxis. A NGT was generally placed by postoperative day 3 (average, 2.6; range, 1-4). Administration of warfarin was discontinued on placement of the NGT. A NGT was required in 19 of these 34 patients for > 4 8 hours. The other 15 patients required a NGT for < 4 8 hours or did not require a NGT. Of the 19 patients w h o required a NGT for > 4 8 hours and w h o received warfarin anticoagulation, 17 (89%) had a PT of > 2 0 seconds or an INR of >2.0. The 17 patients w h o required a NGT for > 4 8 hours and w h o had a PT of > 2 0 seconds or an INR of >2.0 were given an average total warfarin dose of 12.8 mg (range, 7.5-20 mg). The 2 patients w h o did not have abnormally high PT and INR levels received only 5 mg of warfarin on the night of surgery. None of the 15 patients w h o required a NGT for < 4 8 hours had a PT of > 2 0 seconds or an INR of >2.0. This difference was highly statistically significant (P < .001) (Table 1).
Table 1. Postoperative Patients After Total Joint
Arthroplasty With Ileus Receiving Warfarin*
PT <20 s INR <2.0 PT >20 s INR 2.0 Total
NGT >48 h
NGT <48 h
Total
2
15
17
17
0
17
19
15
34
PT, prothrombin time; INR, international normalized ratio. *P < .001.
222
The Journal of Arthroplasty Vol. 15 No. 2 February 2000
Six (35%) of the 17 patients w h o had a NGT for > 4 8 hours had an INR of > 3 . 0 or PT of > 3 0 seconds, which placed t h e m at great risk for bleeding complications. The average total warfarin dose in these at-risk patients was 10.4 mg (range, 7.5-15 rag). Of the 17 patients w h o s e ileus was treated with a NGT for > 4 8 hours and w h o had elevated PT and INR values, 3 (18%) required subsequent surgical intervention as a result of the ileus (2 laparotomies and 1 colonoscopic decompression). Two of these 3 patients had a diagnosis of Ogilvie's s y n d r o m e . One was successfully treated with colonoscopic d e c o m pression. In the other patient, cecal perforation required laparotomy. In a third patient, lower gastrointestinal tract bleeding occurred, with bright red blood per rectum. The elevated PT and INR levels were treated with fresh-frozen plasma and vitamin K. A superior mesenteric artery thrombosis resulted after this treatment, which required laparotomy.
Discussion Postoperative ileus after joint r e p l a c e m e n t surgery has been reported to occur in 3% of patients undergoing joint r e p l a c e m e n t procedures [ 1,2]. The incidence of postoperative ileus in this series of 2,526 joint r e p l a c e m e n t operations was 1.6%. Prior abdominal surgery, m e t h o d of anesthesia, type of joint replacement surgery, and m e t h o d of postoperative analgesia w e r e not specifically associated with the d e v e l o p m e n t of ileus in this series. The most interesting findings in the present series were the consequence of the t r e a t m e n t of the ileus with a NGT for > 4 8 hours and the administration of warfarin for t h r o m b o e m b o l i c prophylaxis. We docum e n t e d that the elevation of the PT to > 2 0 seconds or an increase of the INR to > 2 . 0 was significantly associated (P < .001) with the t r e a t m e n t of postoperative ileus with a NGT for > 4 8 hours. These increased PT and INR levels can lead to further complications because the clotting m e c h a n i s m is altered, and the o p p o r t u n i t y to offer surgical treatm e n t m a y be c o m p r o m i s e d . Attempts to correct the elevated PT and INR values quickly m a y lead to t h r o m b o e m b o l i c complications. To the best of o u r knowledge, this interaction of ileus, t r e a t m e n t of ileus with a NGT, and administration of warfarin has not been reported previously. Of the 17 patients in w h o m an ileus developed and w h o required NGT suction for > 4 8 hours, the average warfarin cumulative dose was 12.4 mg (range, 7.5-20 mg), which produced a PT of > 2 0 seconds or an INR of >2.0. In the 6 patients w h o s e PT was > 3 0 seconds or the INR was :>3.0, the
average warfarin c u m u l a t i v e dose was 10.4 mg (range, 7.5-15 mg). We believe that the m e c h a n i s m of excessive anticoagulation is the result of factors o t h e r t h a n warfarin overdose. Gastrointestinal disturbance, such as ileus, m a y potentiate warfarin anticoagulation. As ileus develops, oral intake of fluids and nutrients declines, and absorption of vitamin K declines. Production of vitamin K from bacterial flora decreases. As the dehydration secondary to ileus progresses, the relative concentration of warfarin in the s e r u m m a y increase [10,111. A cycle could result that causes increasing INR and PT levels out of proportion to the cumulatively administered dose of warfarin. A significant association exists b e t w e e n the develo p m e n t of postoperative ileus in patients undergoing total joint arthroplasty and elevation of the PT or INR to dangerous levels in patients w h o are given warfarin postoperatively for t h r o m b o e m b o l i c prophylaxis. Patients w h o s h o w signs of ileus in the postoperative period severe e n o u g h to warrant insertion of a NGT m u s t be m o n i t o r e d closely to avoid bleeding complications w h e n warfarin has been administered. An alternative form of anticoagulation m a y be w a r r a n t e d in patients at risk for postoperative ileus.
References 1. Eftekhar NS: General and systemic complications. Part IX: Postoperative complications, p. 1449. In Eftekhar NS (ed): Total hip arthroplasty. St. Louis, Mosby-Year Book, ] 993 2. Eftekhar NS, Kiernan HA Jr, Stinchfield FE: Systemic and local complications following low-friction arthroplasty of the hip joint: a study of 800 consecutive operations. Arch Surg 111:150, 1976 3. Silen W: Acute and intestinal obstruction, p. 1765. In Piersdorf RG, Adams RD, Braunwald E, et al (eds): Harrison's principles of internal medicine. New York, McGraw-Hill, 1983 4. Ballaro A, Gibbons CL, Murray DM, et al: Acute colonic pseudo-obstruction after total hip replacement. J Bone Joint Surg Br 79:621, 1997 5. Chambers HG, Silver SM, Bucknell AL: Colonic pseudoobstruction associated with patient-controlled analgesia after total joint arthroplasty. Clin Orthop 254: 255, 1990 6. Clarke HD, Berry D~I, Larson DR: Acute pseudoobstruction of the colon as a postoperative complication of hip arthroplasty. J Bone Joint Surg Am 79:1642, 1997 7. Star M J, Colwell CW Jr, Johnson AC: Acute pseudoobstruction of the colon following total hip arthroplasty. Orthopedics 18:63, 1995 8. Paiemant GD, Green HG: Thromboembolic disease in hip and knee replacement patients, p. 5. In Callaghan J J, Dennis DA, Paprosky WG, Rosenberg AG (eds):
Excessive Warfarin and IleusAfterTJA
Orthopaedic knowledge update: hip and knee reconstruction. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995 9. Iorio R, Healy WL, Patch DA, Pfeifer BA: A computerized evaluation system for total hip arthroplasty: clinical, radiographic and o u t c o m e data assessment. American Academy of Orthopaedic Sur-
•
Iorio et al.
223
geons, Scientific Program, New Orleans, February 1994 10. Bell WR: Acetaminophen and warfarin: undesirable synergy (editorial). JAMA 279:702, 1998 11. Hylek EM, Heiman H, Skates SJ, et al: Acetaminophen and other risk factors for excessive warfarin anticoagulation. JAMA 279:657, 1998
The Association of Excessive Warfarin Anticoagulation and Postoperative Ileus After Total Joint R e p l a c e m e n t Surgery Richard Iorio, MD, William L. Healy, MD, and David Appleby, BS
Abstract: Patients undergoing joint replacement who show signs of ileus in the postoperative period that require insertion of a nasogastric tube (NGT) must be monitored closely to avoid bleeding complications. The diagnosis of postoperative ileus was documented in 40 of 2,526 (1.6%) consecutive joint replacement operations between January 1, 1990, and March 1, 1998, at 1 hospital. Of the 40 patients with postoperative ileus, 34 received warfarin postoperatively. Of these 34 patients, 19 required a NGT for >48 hours, and 15 patients required a NGT for <48 hours or did not require a NGT. Of the 19 patients who required a NGT for >48 hours and who received warfarin anticoagulation, 17 had a prothrombin time of >20 seconds or an international normalized ratio (INR) of >2.0. None of the 15 patients who required a NGT for <48 hours and who received warfarin anticoagulation had a prothrombin time of >20 seconds or an INR of >2.0. This difference was highly statistically significant (P < .001). Key words: colonic pseudo-obstruction, ileus, nasogastric intubation, Ogilvie's syndrome, total joint replacement, warfarin anticoagulation.
The prevalence of postoperative ileus associated with total joint arthroplasty has been reported as high as 3% [1,2]. Postoperative ileus can be associated with peritoneal manipulation, electrolyte imbalances (such as potassium depletion), lengthy surgery, and trauma. As an ileus progresses, the large and small intestine b e c o m e distended, and gas and fluid a c c u m u l a t e in the lumen. An ileus leads to abdominal distention, and vomiting m a y result if decompression by nasogastric suction is not initiated [2,3]. Ileus is usually not a c c o m p a n i e d by mechanical obstruction. Acute colonic pseudo-obstruction, or
Ogilvie's syndrome, is a form of ileus that presents with e x t r e m e dilation of the c e c u m and the transverse colon, with a relative paucity of bowel gas in the distal segment. If untreated, Ogilvie's s y n d r o m e can lead to perforation of the cecum, which m a y be life-threatening. The incidence of Ogilvie's synd r o m e has b e e n reported to be 0.29% after total hip arthroplasty (THA) [4-71. Warfarin is frequently used for p h a r m a c e u t i c a l t h r o m b o e m b o l i c prophylaxis after joint replacem e n t surgery. The dose response to warfarin can be difficult to predict. Intestinal bacterial flora, medications, diet, level of activity, gastrointestinal function, liver disease, and several o t h e r lesser factors can affect the dose response to warfarin [8]. The present study evaluated the incidence and associated factors of ileus as a postoperative complication of lower e x t r e m i t y joint r e p l a c e m e n t surgery. The effect of ileus on the dose response of warfarin used as a t h r o m b o e m b o l i c prophylactic agent after joint r e p l a c e m e n t surgery was also analyzed.
From the Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts. Submitted July 8, 1999; accepted August 31, 1999. No benefits or funds were received in support of this study. Reprint requests: Richard lorio, MD, Department of Orthopaedic Surgery, Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA 01805.
Copyright © 2000 by Churchill Livingstone® 0883-5403/00/1502-0014510.00/0
220
Excessive Warfarin and IleusAfterTJA
Materials and Methods Between J a n u a r y 1, 1990, and March 1, 1998, 2,526 consecutive lower extremity joint replacem e n t operations ( 1,142 primary THAs, 288 revision THAs, 996 primary total knee arthroplasty [TKA], and 140 revision TI(As) performed at 1 hospital were reviewed. A computerized total joint arthroplasty database [9], hospital records, and the Departm e n t of Orthopaedic Surgery m o n t h l y morbidity and mortality reviews were used to identify patients in w h o m an ileus developed after joint replacement surgery. Forty patients with a diagnosis of postoperative ileus after total joint arthroplasty surgery were identified and were included in the study. The diagnosis of postoperative ileus was made by physical examination; radiography; and consultation with gastrointestinal, general surgical, and colorectal specialists. If a diagnosis of ileus was made, patients were not permitted to ingest anything by m o u t h . If nausea or vomiting ensued, a nasogastric tube (NGT) was inserted and was connected to low intermittent wall suction. W h e n gastrointestinal peristalsis and bowel function returned, the NGT was clamped for several hours before its removal. Patients in w h o m ileus developed were characterized according to type of surgery, m e t h o d of anesthesia, type of postoperative analgesia, previous abdominal surgery, medical comorbidities, duration of NGT placement, and complications associated with the ileus. Patients receiving warfarin postoperatively for t h r o m b o e m b o l i c prophylaxis were given 5 mg on the evening of surgery. The p r o t h r o m b i n time (PT), partial thromboplastin time (PTE), and international normalized ratio (INR) were checked daily, and the dose was adjusted to achieve a PT of 15 to 18 seconds or an INR of 1.5 to 1.8. The relationship of postoperative ileus to warfarin administration was e x a m i n e d by analyzing total warfarin dosage, daily PT and PTF, and INR. Statistical analysis was performed to identify relationships b e t w e e n patient characteristics and the incidence of ileus. The incidence of elevated PT PTT, and INR in conjunction with postoperative ileus was also noted. Contingency table analysis was performed using chi-square and Fisher's exact test w h e n appropriate. Odds ratios and other relevant coefficients were recorded. Variables were coded into dichotomies to facilitate this type of analysis.
Results The prevalence of postoperative ileus in patients after joint replacement surgery at our institution
•
Iorio et al.
221
during an 8-year period from J a n u a r y 1, 1990, to March 1, 1998, was 1.6% (40 of 2,526). Postoperative ileus was diagnosed in 22 m e n (55%) and 18 (45%) w o m e n . Ileus occurred after 16 primary THAs, 6 revision THAs, 13 primary TKAs, and 5 bilateral TKAs. General anesthesia was given to 25 patients in w h o m an ileus developed, and 13 of these patients received regional anesthesia (spinal or epidural). Two patients received regional and general anesthesia. Postoperatively, 15 patients used patient-controlled intravenous analgesia; 25 patients did not use this m e t h o d of analgesia. Previous abdominal surgery, type of anesthesia (spinal, epidural, or general), type of surgical procedure (primary THA, primary TKA, revision THA, or revision TKA), and type of postoperative analgesia (intramuscular, parenteral, or patient-controlled intravenous analgesia) were not associated with the development of postoperative ileus. A m o n g 40 patients in w h o m a postoperative ileus developed, 34 received warfarin postoperatively for pharmacologic thromboembolic prophylaxis. A NGT was generally placed by postoperative day 3 (average, 2.6; range, 1-4). Administration of warfarin was discontinued on placement of the NGT. A NGT was required in 19 of these 34 patients for > 4 8 hours. The other 15 patients required a NGT for < 4 8 hours or did not require a NGT. Of the 19 patients w h o required a NGT for > 4 8 hours and w h o received warfarin anticoagulation, 17 (89%) had a PT of > 2 0 seconds or an INR of >2.0. The 17 patients w h o required a NGT for > 4 8 hours and w h o had a PT of > 2 0 seconds or an INR of >2.0 were given an average total warfarin dose of 12.8 mg (range, 7.5-20 mg). The 2 patients w h o did not have abnormally high PT and INR levels received only 5 mg of warfarin on the night of surgery. None of the 15 patients w h o required a NGT for < 4 8 hours had a PT of > 2 0 seconds or an INR of >2.0. This difference was highly statistically significant (P < .001) (Table 1).
Table 1. Postoperative Patients After Total Joint
Arthroplasty With Ileus Receiving Warfarin*
PT <20 s INR <2.0 PT >20 s INR 2.0 Total
NGT >48 h
NGT <48 h
Total
2
15
17
17
0
17
19
15
34
PT, prothrombin time; INR, international normalized ratio. *P < .001.
222
The Journal of Arthroplasty Vol. 15 No. 2 February 2000
Six (35%) of the 17 patients w h o had a NGT for > 4 8 hours had an INR of > 3 . 0 or PT of > 3 0 seconds, which placed t h e m at great risk for bleeding complications. The average total warfarin dose in these at-risk patients was 10.4 mg (range, 7.5-15 rag). Of the 17 patients w h o s e ileus was treated with a NGT for > 4 8 hours and w h o had elevated PT and INR values, 3 (18%) required subsequent surgical intervention as a result of the ileus (2 laparotomies and 1 colonoscopic decompression). Two of these 3 patients had a diagnosis of Ogilvie's s y n d r o m e . One was successfully treated with colonoscopic d e c o m pression. In the other patient, cecal perforation required laparotomy. In a third patient, lower gastrointestinal tract bleeding occurred, with bright red blood per rectum. The elevated PT and INR levels were treated with fresh-frozen plasma and vitamin K. A superior mesenteric artery thrombosis resulted after this treatment, which required laparotomy.
Discussion Postoperative ileus after joint r e p l a c e m e n t surgery has been reported to occur in 3% of patients undergoing joint r e p l a c e m e n t procedures [ 1,2]. The incidence of postoperative ileus in this series of 2,526 joint r e p l a c e m e n t operations was 1.6%. Prior abdominal surgery, m e t h o d of anesthesia, type of joint replacement surgery, and m e t h o d of postoperative analgesia w e r e not specifically associated with the d e v e l o p m e n t of ileus in this series. The most interesting findings in the present series were the consequence of the t r e a t m e n t of the ileus with a NGT for > 4 8 hours and the administration of warfarin for t h r o m b o e m b o l i c prophylaxis. We docum e n t e d that the elevation of the PT to > 2 0 seconds or an increase of the INR to > 2 . 0 was significantly associated (P < .001) with the t r e a t m e n t of postoperative ileus with a NGT for > 4 8 hours. These increased PT and INR levels can lead to further complications because the clotting m e c h a n i s m is altered, and the o p p o r t u n i t y to offer surgical treatm e n t m a y be c o m p r o m i s e d . Attempts to correct the elevated PT and INR values quickly m a y lead to t h r o m b o e m b o l i c complications. To the best of o u r knowledge, this interaction of ileus, t r e a t m e n t of ileus with a NGT, and administration of warfarin has not been reported previously. Of the 17 patients in w h o m an ileus developed and w h o required NGT suction for > 4 8 hours, the average warfarin cumulative dose was 12.4 mg (range, 7.5-20 mg), which produced a PT of > 2 0 seconds or an INR of >2.0. In the 6 patients w h o s e PT was > 3 0 seconds or the INR was :>3.0, the
average warfarin c u m u l a t i v e dose was 10.4 mg (range, 7.5-15 mg). We believe that the m e c h a n i s m of excessive anticoagulation is the result of factors o t h e r t h a n warfarin overdose. Gastrointestinal disturbance, such as ileus, m a y potentiate warfarin anticoagulation. As ileus develops, oral intake of fluids and nutrients declines, and absorption of vitamin K declines. Production of vitamin K from bacterial flora decreases. As the dehydration secondary to ileus progresses, the relative concentration of warfarin in the s e r u m m a y increase [10,111. A cycle could result that causes increasing INR and PT levels out of proportion to the cumulatively administered dose of warfarin. A significant association exists b e t w e e n the develo p m e n t of postoperative ileus in patients undergoing total joint arthroplasty and elevation of the PT or INR to dangerous levels in patients w h o are given warfarin postoperatively for t h r o m b o e m b o l i c prophylaxis. Patients w h o s h o w signs of ileus in the postoperative period severe e n o u g h to warrant insertion of a NGT m u s t be m o n i t o r e d closely to avoid bleeding complications w h e n warfarin has been administered. An alternative form of anticoagulation m a y be w a r r a n t e d in patients at risk for postoperative ileus.
References 1. Eftekhar NS: General and systemic complications. Part IX: Postoperative complications, p. 1449. In Eftekhar NS (ed): Total hip arthroplasty. St. Louis, Mosby-Year Book, ] 993 2. Eftekhar NS, Kiernan HA Jr, Stinchfield FE: Systemic and local complications following low-friction arthroplasty of the hip joint: a study of 800 consecutive operations. Arch Surg 111:150, 1976 3. Silen W: Acute and intestinal obstruction, p. 1765. In Piersdorf RG, Adams RD, Braunwald E, et al (eds): Harrison's principles of internal medicine. New York, McGraw-Hill, 1983 4. Ballaro A, Gibbons CL, Murray DM, et al: Acute colonic pseudo-obstruction after total hip replacement. J Bone Joint Surg Br 79:621, 1997 5. Chambers HG, Silver SM, Bucknell AL: Colonic pseudoobstruction associated with patient-controlled analgesia after total joint arthroplasty. Clin Orthop 254: 255, 1990 6. Clarke HD, Berry D~I, Larson DR: Acute pseudoobstruction of the colon as a postoperative complication of hip arthroplasty. J Bone Joint Surg Am 79:1642, 1997 7. Star M J, Colwell CW Jr, Johnson AC: Acute pseudoobstruction of the colon following total hip arthroplasty. Orthopedics 18:63, 1995 8. Paiemant GD, Green HG: Thromboembolic disease in hip and knee replacement patients, p. 5. In Callaghan J J, Dennis DA, Paprosky WG, Rosenberg AG (eds):
Excessive Warfarin and IleusAfterTJA
Orthopaedic knowledge update: hip and knee reconstruction. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995 9. Iorio R, Healy WL, Patch DA, Pfeifer BA: A computerized evaluation system for total hip arthroplasty: clinical, radiographic and o u t c o m e data assessment. American Academy of Orthopaedic Sur-
•
Iorio et al.
223
geons, Scientific Program, New Orleans, February 1994 10. Bell WR: Acetaminophen and warfarin: undesirable synergy (editorial). JAMA 279:702, 1998 11. Hylek EM, Heiman H, Skates SJ, et al: Acetaminophen and other risk factors for excessive warfarin anticoagulation. JAMA 279:657, 1998