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Postoperative venous thrombosis in gynecologic oncology surgery—Study design
870
Letters
ences cannot be explained by neonatal and surgical care provided to inborn versus outborn infants. The observations by Stringer et aI., that our study is uncontrolled, retrospective, and based on small numbers, are restatements of the limitations we have already described in our paper. We have reanalyzed our data, excluding the two neonates with intestinal atresia, and found the benefits to the elective cesarean group (fewer hospitalization days, shorter total parenteral nutrition days, and fewer days to enteral feedings) persist. This was true whether we used the parametric Student t test or the nonparametric Mann-Whitney U test. Stringer et ai. questioned our use of the simple X2 test to assess proportional differences. Kuzma,2 quoting Grizzle,' observed that because the Yates continuity correction for X2 values with 1 degree of freedom is too conservative, many practicing statisticians do not recommend its use. The recommendation by Stringer et ai. that maternal outcome be reported is a sound proposal for which we are gathering data. The lack of difference in birth-to-operation interval between the elective cesarean section and vaginal delivery groups reflects our practice of immediately enclosing all neonates after birth, from the thorax down,· in a "bowel bag" to minimize extrasensory fluid and temperature loss. Thus inborn infants need not be "rushed" off any more abruptly for surgery than outborn infants. The data on infectious morbidity are "soft" and await microbiologic confirmation. While we agree that antenatal bowel injury before labor is a significant cause of morbidity, it does not account for the enhanced outcome we found with the elective cesarean group. Although not proven, we believe the hypothesis that repetitive uterine contractions may jeopardize tenuous mesenteric blood supply, resulting in bowel injury and edema, is a plausible explanation of our study'S findings. Stringer et ai. provide no new evidence to challenge this thesis. The studies (cited by Stringer et aI., as well as by others we reviewed in our article) that show no apparent benefit to neonates with gastroschisis who are delivered by cesarean section have serious limitations: Labor and nonlabor groups were not described; the cesarean sections were emergency procedures performed for obstetric indications; the emergency cesarean sections included high numbers of fetal distress cases. Our study controlled for each of these drawbacks. We do concur with Stringer et ai. that the final answer to the optimal delivery management of the gastroschisis pregnancy awaits a randomized, prospective study. However, the significant morbidity differences we found between the vaginally delivered labor group and the cesarean section-delivered no-labor group, in spite of
September 1994 Am J Obstet Gynecol
our small number of subjects, may merit further investigation. Elmar P. Sakala, MD, MPH Division of Maternal-Fetal Medicine, Department of Gynecology and Obstetrics, Loma Linda University Medical Center, Loma Linda, CA 92350
REFERENCES 1. Sakala EP, Erhard LN, White]. Effect of elective cesarean section on neonatal outcome of gastroschisis. In: Proceedings of the District VIII Annual Meeting of the American College of Obstetricians and Gynecologists, Monterey, California, October 15, 1993. Washington: American College of Obstetricians and Gynecologists, 1993. 2. Kuzma ]W. Basic statistics for the health sciences. 2nd ed. Mountain View, California: Mayfield Publishing, 1992:185. 3. Grizzle ]E. Continuity correction in the x2 test for 2 X 2 tables. Statistician 1967;21:28-32. 6/8/56758
Postoperative venous thrombosis in gynecologic oncology surgery-Study design To the Editors: Venous thrombotic disease is the second most common cause of gynecologic deaths, being exceeded only by malignancy. I read with interest the recent article by Clarke-Pearson et al. (Clarke-Pearson DL, Synan IS, Dodge R, Soper JT, Berchuck A, Coleman RE. A randomized trial of low-dose heparin and intermittent pneumatic calf compression for the prevention of deep venous thrombosis after gynecologic oncology surgery. AMJ OBSTET GYNECOL 1993;168:114654). The study is potentially a very valuable contribution to this area of knowledge. However, it is a shame that such a good prospective randomized trial was methodologically flawed by failure to scan patients preoperatively to exclude those who had venous thrombosis before surgery. Alex J. Crandon, PhD Queensland Centre for Gynaecologic Cancer, Royal Women's Hospital Brisbane, Brisbane North Region, Bowen Bridge Road, Herston, Queensland 4029, Australia
6/8/58163
Reply
To the Editors: The presence of preoperative deep vein thrombosis is certainly a possibility, and the incidence may well be increased in gynecologic oncology surgical patients. In our initial studies evaluating low-dose heparin and external pneumatic calf compression as prophylactic measures to prevent postoperative deep vein thrombosis, we in fact screened all patients preoperatively with both fibrinogen iodine-125 leg scanning and impedance plethysmography.'-3 Of 516 patients entered into these three prospective trials, only four patients had evidence of preoperative deep vein thrombosis (0.8%). In addition, of 382 patients entered into a study of the natural history of postoperative deep vein
Letters
ences cannot be explained by neonatal and surgical care provided to inborn versus outborn infants. The observations by Stringer et aI., that our study is uncontrolled, retrospective, and based on small numbers, are restatements of the limitations we have already described in our paper. We have reanalyzed our data, excluding the two neonates with intestinal atresia, and found the benefits to the elective cesarean group (fewer hospitalization days, shorter total parenteral nutrition days, and fewer days to enteral feedings) persist. This was true whether we used the parametric Student t test or the nonparametric Mann-Whitney U test. Stringer et ai. questioned our use of the simple X2 test to assess proportional differences. Kuzma,2 quoting Grizzle,' observed that because the Yates continuity correction for X2 values with 1 degree of freedom is too conservative, many practicing statisticians do not recommend its use. The recommendation by Stringer et ai. that maternal outcome be reported is a sound proposal for which we are gathering data. The lack of difference in birth-to-operation interval between the elective cesarean section and vaginal delivery groups reflects our practice of immediately enclosing all neonates after birth, from the thorax down,· in a "bowel bag" to minimize extrasensory fluid and temperature loss. Thus inborn infants need not be "rushed" off any more abruptly for surgery than outborn infants. The data on infectious morbidity are "soft" and await microbiologic confirmation. While we agree that antenatal bowel injury before labor is a significant cause of morbidity, it does not account for the enhanced outcome we found with the elective cesarean group. Although not proven, we believe the hypothesis that repetitive uterine contractions may jeopardize tenuous mesenteric blood supply, resulting in bowel injury and edema, is a plausible explanation of our study'S findings. Stringer et ai. provide no new evidence to challenge this thesis. The studies (cited by Stringer et aI., as well as by others we reviewed in our article) that show no apparent benefit to neonates with gastroschisis who are delivered by cesarean section have serious limitations: Labor and nonlabor groups were not described; the cesarean sections were emergency procedures performed for obstetric indications; the emergency cesarean sections included high numbers of fetal distress cases. Our study controlled for each of these drawbacks. We do concur with Stringer et ai. that the final answer to the optimal delivery management of the gastroschisis pregnancy awaits a randomized, prospective study. However, the significant morbidity differences we found between the vaginally delivered labor group and the cesarean section-delivered no-labor group, in spite of
September 1994 Am J Obstet Gynecol
our small number of subjects, may merit further investigation. Elmar P. Sakala, MD, MPH Division of Maternal-Fetal Medicine, Department of Gynecology and Obstetrics, Loma Linda University Medical Center, Loma Linda, CA 92350
REFERENCES 1. Sakala EP, Erhard LN, White]. Effect of elective cesarean section on neonatal outcome of gastroschisis. In: Proceedings of the District VIII Annual Meeting of the American College of Obstetricians and Gynecologists, Monterey, California, October 15, 1993. Washington: American College of Obstetricians and Gynecologists, 1993. 2. Kuzma ]W. Basic statistics for the health sciences. 2nd ed. Mountain View, California: Mayfield Publishing, 1992:185. 3. Grizzle ]E. Continuity correction in the x2 test for 2 X 2 tables. Statistician 1967;21:28-32. 6/8/56758
Postoperative venous thrombosis in gynecologic oncology surgery-Study design To the Editors: Venous thrombotic disease is the second most common cause of gynecologic deaths, being exceeded only by malignancy. I read with interest the recent article by Clarke-Pearson et al. (Clarke-Pearson DL, Synan IS, Dodge R, Soper JT, Berchuck A, Coleman RE. A randomized trial of low-dose heparin and intermittent pneumatic calf compression for the prevention of deep venous thrombosis after gynecologic oncology surgery. AMJ OBSTET GYNECOL 1993;168:114654). The study is potentially a very valuable contribution to this area of knowledge. However, it is a shame that such a good prospective randomized trial was methodologically flawed by failure to scan patients preoperatively to exclude those who had venous thrombosis before surgery. Alex J. Crandon, PhD Queensland Centre for Gynaecologic Cancer, Royal Women's Hospital Brisbane, Brisbane North Region, Bowen Bridge Road, Herston, Queensland 4029, Australia
6/8/58163
Reply
To the Editors: The presence of preoperative deep vein thrombosis is certainly a possibility, and the incidence may well be increased in gynecologic oncology surgical patients. In our initial studies evaluating low-dose heparin and external pneumatic calf compression as prophylactic measures to prevent postoperative deep vein thrombosis, we in fact screened all patients preoperatively with both fibrinogen iodine-125 leg scanning and impedance plethysmography.'-3 Of 516 patients entered into these three prospective trials, only four patients had evidence of preoperative deep vein thrombosis (0.8%). In addition, of 382 patients entered into a study of the natural history of postoperative deep vein