Dysfibrinogenemia: discrepant results following infusion of purified fibrinogen

Inherited dysfibrinogenemias are molecular disorders of fibrinogen that affect fibrin polymerization. The majority of cases are asymptomatic, but a significant proportion suffer from increased bleeding or thrombosis. We present two unrelated cases of dysfibrinogenemia, both of whom showed a characteristic discrepancy between fibrinogen activity and the immunologic fibrinogen. In one patient, the dysfibrinogenemia was confirmed by molecular analysis; in the other case, the diagnosis was presumptive based upon laboratory studies. Both patients underwent elective surgery. Both received a highly purified fibrinogen concentrate preoperatively and demonstrated a suboptimal laboratory response to the infusion. Three methods for determining fibrinogen concentration (Clauss fibrinogen, prothrombin-derived fibrinogen, and the viscoelastic functional fibrinogen) were utilized in the case of one patient, and these techniques showed discrepant results with the classic Clauss method giving the lowest concentration. Neither patient experienced excessive bleeding during surgery. Although these discrepancies have been previously described in untreated patients, their manifestation after infusion of purified fibrinogen is less well appreciated.

Photoplethysmography and Heart Rate Variability for the Diagnosis of Preeclampsia

BACKGROUND

The goal of this study was to determine a set of timing, shape, and statistical features available through noninvasive monitoring of maternal electrocardiogram and photoplethysmography that identifies preeclamptic patients.

METHODS

Pregnant women admitted to Labor and Delivery were monitored with pulse oximetry and electrocardiogram for 30 minutes. Photoplethysmogram features and heart rate variability were extracted from each data set and applied to a sequential feature selection algorithm to discriminate women with preeclampsia with severe features, from normotensive and hypertensive controls. The classification boundary was chosen to minimize the expected misclassification cost. The prior probabilities of the misclassification costs were assumed to be equal.

RESULTS

Thirty-seven patients with clinically diagnosed preeclampsia with severe features were compared with 43 normotensive controls; all were in early labor or beginning induction. Six variables were used in the final model. The area under the receiver operating characteristic curve was 0.907 (standard error [SE] = 0.004) (sensitivity 78.2% [SE = 0.3%], specificity 89.9% [SE = 0.1%]) with a positive predictive value of 0.883 (SE = 0.001). Twenty-eight subjects with chronic or gestational hypertension were compared with the same preeclampsia group, generating a model with 5 features with an area under the curve of 0.795 (SE = 0.007; sensitivity 79.0% [SE = 0.2%], specificity 68.7% [SE = 0.4%]), and a positive predictive value of 0.799 (SE = 0.002).

CONCLUSIONS

Vascular parameters, as assessed noninvasively by photoplethysmography and heart rate variability, may have a role in screening women suspected of having preeclampsia, particularly in areas with limited resources.

Monitoring Uterine Activity during Labor: Clinician Interpretation of Electrohysterography versus Intrauterine Pressure Catheter and Tocodynamometry

Objective The aim of this article was to compare clinical interpretation of uterine activity tracings acquired by tocodynamometry and electrohysterography with the gold standard, intrauterine pressure. Study Design Using data from a previous study, subjects who had simultaneous monitoring with all three uterine activity devices were included in this study. These were parturients who required intrauterine pressure catheter (IUPC) placement for obstetric indication. A Web-based application displayed scrolling 30-minute segments of uterine activity. Two blinded obstetricians and two blinded obstetric nurses independently reviewed the segments, marking uninterpretable segments and the peak of each contraction. Interpretability was compared using positive percent agreement. False positives are contractions marked in the noninvasive strip that have no corresponding contraction in the IUPC strip. False negatives are the reverse. Results A total of 135 segments, acquired during either Stage 1 (active labor) or Stage 2 (pushing), from 105 women, were included in this analysis. For all four observers, both interpretability and sensitivity of electrohysterography exceeded that of tocodynamometry (p < 0.0001). This remained true for the obese population (96 segments). Conclusion Compared with the IUPC, electrohysterography is more sensitive and provides tracings that are more often interpretable than tocodynamometry for intrapartum monitoring; electrohysterography is also less affected by increasing maternal body mass index.

Monitoring uterine activity during labor: a comparison of 3 methods

OBJECTIVE

Tocodynamometry (Toco; strain gauge technology) provides contraction frequency and approximate duration of labor contractions but suffers frequent signal dropout, necessitating repositioning by a nurse, and may fail in obese patients. The alternative invasive intrauterine pressure catheter (IUPC) is more reliable and adds contraction pressure information but requires ruptured membranes and introduces small risks of infection and abruption. Electrohysterography (EHG) reports the electrical activity of the uterus through electrodes placed on the maternal abdomen. This study compared all 3 methods of contraction detection simultaneously in laboring women.

STUDY DESIGN

Upon consent, laboring women were monitored simultaneously with Toco, EHG, and IUPC. Contraction curves were generated in real-time for the EHG, and all 3 curves were stored electronically. A contraction detection algorithm was used to compare frequency and timing between methods. Seventy-three subjects were enrolled in the study; 14 were excluded due to hardware failure of 1 or more of the devices (n = 12) or inadequate data collection duration (n = 2).

RESULTS

In comparison with the gold-standard IUPC, EHG performed significantly better than Toco with regard to the Contractions Consistency Index (CCI). The mean CCI for EHG was 0.88 ± 0.17 compared with 0.69 ± 0.27 for Toco (P < .0001). In contrast to Toco, EHG was not significantly affected by obesity.

CONCLUSION

Toco does not correlate well with the gold-standard IUPC and fails more frequently in obese patients. EHG provides a reliable noninvasive alternative, regardless of body habitus.

Labor and delivery in a patient with hemophilia B

Hemophilia B is a rare X-linked disorder that may cause dramatic bleeding. Women account for only 3.2% of those clinically affected. The X-linked inheritance frequently delays the diagnosis in women and may expose the patient to an increased risk of adverse events. There is limited experience with these patients during labor and delivery. A 28-year-old primiparous woman with hemophilia B (bleeding phenotype) delivered a male infant by an unplanned cesarean delivery under general anesthesia following treatment with factor IX and normalization of her coagulation parameters, guided by thromboelastography. Postpartum vaginal bleeding required transfusion of two units of packed red blood cells. Factor IX supplementation continued for one week. Once diagnosed with hemophilia B, a multidisciplinary approach and advanced antenatal planning can increase the likelihood of a safe delivery. Neuraxial approaches and cesarean delivery are recommended only after normalization of the coagulation profile. The male fetus of a hemophilia A or B patient requires special attention. Operative vaginal delivery and invasive fetal monitoring should be avoided. Thromboelastography is an excellent technique to assess parturients with bleeding disorders or peripartum hemorrhage and may be underused.

The Value of Anesthesiology in Undergraduate Medical Education as Assessed by Medical School Faculty

BACKGROUND

Unlike Europe and Canada, the majority of American medical schools do not require an anesthesiology rotation. Yet the skill set and knowledge base of anesthesiologists includes many topics of importance to all physicians. Furthermore, the clinical environment offers more procedural experience and real-time physiology and pharmacology for teaching than that available elsewhere. Medical schools, however, often focus on "general medical education" and discount the value of a required anesthesiology clerkship. This begs the question, of the topics anesthesiologists excel at teaching, which are considered important by faculty across the spectrum of medical specialties?

METHODS

Two-hundred-three senior medical students rated the importance to their career of 14 topics currently taught by lecture, simulation or reading assignment in the required anesthesiology curriculum at the University of Florida. Specialty faculty in each of the major specialties similarly rated the topics. The authors compared these with the opinion of 20 anesthesiology faculty who rated the importance of each topic for each major specialty.

RESULTS

Overall, acute pain management and acute decompensation management were rated "somewhat" or "very important" by the highest proportion of respondents; followed closely by vascular access and fluid management, non-invasive monitoring and conscious sedation. The topics of interest to surgeons most closely aligned with those offered (12/14 rated somewhat or very important by >75% of faculty polled, 14/14: students), followed by emergency medicine physicians (10/14: faculty, 11/14: students). Significant differences of opinion existed between all three groups on several topics.

CONCLUSIONS

Anesthesiologists excel in topics important to all future physicians; as many schools enter a new phase of curricular redesign, a rotation in anesthesiology should receive serious consideration. The input of students and physicians in major medical specialties may help define an appropriate curriculum. Including the flexibility for students to adapt that curriculum to individual goals may increase the rotation's value.

Spatiotemporal electrohysterography patterns in normal and arrested labor

OBJECTIVE

The purpose of this study was to investigate the spatiotemporal patterns of uterine electrical activity in normal and arrested labors.

STUDY DESIGN

From a database of electrohysterograms, 12 subjects who underwent cesarean delivery for active-phase arrest were each matched with 2 vaginally delivered controls. Using 30-minute segments of the electrohysterogram during the arrest, or the same dilation in controls, the center of uterine electrical activity was derived. The vertical motion of this center of uterine activity was determined for each contraction and the frequencies of movement patterns analyzed.

RESULTS

Predominantly upward movement of the center of uterine activity (longer and/or stronger contraction at the fundus) was more common with normal dilation (P = .003). Receiver operating characteristic curve analysis gave an area under the curve of 0.91 for predicting outcome (vaginal vs cesarean delivery).

CONCLUSION

There is a significant correlation between upward movement of the center of uterine activity (fundal dominance) and current labor progress.

Monitoring Contractions in Obese Parturients

OBJECTIVE

To compare electrohysterogram-derived contractions with both tocodynamometry and intrauterine pressure monitoring in obese laboring women.

METHODS

From a large database of laboring patients with electrohysterogram monitoring, obese subjects were selected in whom data were recorded for at least 30 minutes before and after intrauterine pressure catheter placement for obstetric indication. Using a contraction detection algorithm, the relationship between the methods was determined with regard to both frequency and contraction duration.

RESULTS

Of the 25 subjects (median body mass index 39.6 [25th percentile 36.5, 75th percentile 46.3]), seven underwent amniotomy at the time of intrauterine pressure catheter placement. Tocodynamometry identified 248 contractions compared with 336 by electrohysterography, whereas intrauterine pressure catheter monitoring identified 319 contractions compared with 342 by electrohysterography. Using the Contractions Consistency Index, electrohysterogram contraction detection correlated better with the intrauterine pressure catheter (0.94+/-0.06) than with tocodynamometry (0.77+/-0.25), P=.004. Electrohysterogram-derived contraction lengths closely approximated those calculated from the intrauterine pressure catheter signal.

CONCLUSION

Contraction monitoring routinely is employed for managing labor, and tocodynamometry may be unreliable in obese parturients. In the obese women in this study, the electrohysterogram-derived contraction pattern correlated better with the intrauterine pressure catheter than tocodynamometry. Electrohysterography may provide another noninvasive means of monitoring labor, particularly for those women in whom tocodynamometry is inadequate.

A single dose of fentanyl and midazolam prior to Cesarean section have no adverse neontal effects

PURPOSE

Analgesia and sedation, routinely used as adjunct medications for regional anesthesia, are rarely used in the pregnant patient because of concerns about adverse neonatal effects. In an effort to obtain more information about maternal analgesia and sedation we studied neonatal and maternal effects of iv fentanyl and midazolam prior to spinal anesthesia for elective Cesarean section.

METHODS

In this double-blinded, randomized, placebo-controlled trial, 60 healthy women received either a combination of 1 microg x kg(-1) fentanyl and 0.02 mg x kg(-1) midazolam intravenously or an equal volume of iv saline at the time of their skin preparation for a bupivacaine spinal anesthetic. Sample size was based on a non-parametric power analysis (power > 0.80 and alpha = 0.05) for clinically important differences in Apgar scores. Fetal outcome measures included Apgar scores, continuous pulse oximetry for three hours, and neurobehavioural scores. Maternal outcomes included catecholamine levels, and recall of anesthesia and delivery.

RESULTS

There were no between-group differences of neonatal outcome variables (Apgar score, neurobehavioural scores, continuous oxygen saturation). Mothers in both groups showed no difference in their ability to recall the birth of their babies.

CONCLUSIONS

Maternal analgesia and sedation with fentanyl (1 microg x kg(-1)) and midazolam (0.02 mg x kg(-1)) immediately prior to spinal anesthesia is not associated with adverse neonatal effects.

Development and Evaluation of an Internet-Based Airway Evaluation Tutorial

Airway evaluation and basic management are essential skills for all physicians. Identifying patients for whom mask ventilation or endotracheal intubation will be difficult to impossible is vital for patient safety. Despite this, training in airway evaluation is minimal in the curricula of most medical schools. To ensure a thorough understanding of airway anatomy and evaluation, as well as exposure to various abnormal findings, we developed an Internet-based module including interactive components, graphics, animation, video, and a self-assessment tool. The site received more than 1800 visits in its first nine months of operation, with uniformly laudatory comments. Eighty subjects over a six-month period completed a pre- and post-test quiz structured to evaluate the utility of the site. Of those completing the on-line survey, more than 76% rated the site very useful. Most felt their knowledge of airway examination improved after completion of the site (p.

Teaching respiratory physiology: clinical correlation with a human patient simulator

In recent years students have increasingly objected to laboratory exercises involving animal subjects. We have replaced the valuable animal experiments with demonstrations using a full-scale human patient simulator. In small groups first-year medical students observe realistic clinical situations such as opioid-induced hypoventilation, pneumothorax, and pulmonary edema. Students obtain information through physical examination, arterial blood gas analysis and chest radiography. They practice interventions such as providing supplemental oxygen and mask ventilation, monitor the results, and develop a basic differential diagnosis and treatment plan. We utilize the clinical context to review fundamental concepts of respiratory physiology including the alveolar air equation and oxyhemoglobin dissociation curve. The students give these laboratory exercises uniformly superior evaluations.

Anesthesia for childbirth: controversy and change

First introduced to medical practice in 1847, anesthesia for childbirth has undergone constant changes. Current practice reflects evolving social values as well as new discoveries in science and medicine.

Vaginal birth after cesarean delivery: an historic cohort cost analysis

OBJECTIVE

The purpose of this study was to evaluate the relative cost-effectiveness of attempted vaginal birth after cesarean delivery compared with elective repeat cesarean delivery.

STUDY DESIGN

We performed an historic cohort analysis of women with a single prior cesarean delivery who were delivered at our institution during 1999. Inclusion criteria were > or =36 weeks' gestation and carrying a live, singleton fetus with no antenatally diagnosed anomalies. The primary outcome variable was mean cost of hospital care for mother-infant pairs, as obtained from the hospital's Clinical Resources Department.

RESULTS

The cohort consisted of 204 mother-infant pairs, 65 in the elective repeat cesarean group and 139 in the attempted vaginal birth group. Mean cost of care was higher for mothers ($4155 vs $3675;P <.001), neonates ($1794 vs $1187; P =.03), and mother-infant pairs ($5949 vs $4863; P =.001) for the elective repeat cesarean group compared with the attempted vaginal delivery group.

CONCLUSION

In women with a single prior cesarean delivery, a trial of labor is more cost-effective than an elective repeat cesarean delivery.

Small group teaching: clinical correlation with a human patient simulator

The popularity of the problem-based learning paradigm has stimulated new interest in small group, interactive teaching techniques. Medical educators of physiology have long recognized the value of such methods, using animal-based laboratories to demonstrate difficult physiological principles. Due to ethical and other concerns, a replacement of this teaching tool has been sought. Here, the author describes the use of a full-scale human patient simulator for such a workshop. The simulator is a life-size mannequin with physical findings (palpable pulses, breath/heart sounds, blinking eyes, etc.) and sophisticated mechanical and software models of the cardiovascular and pulmonary systems. It can be connected to standard physiological monitors to reproduce a realistic clinical environment. In groups of 10, first-year medical students explore Starling's law of the heart, the physiology of the Valsalva maneuver, and the function of the baroreceptor in a clinically realistic context using the simulator. With the use of a novel pre-/postworkshop assessment instrument that included student confidence in their answers, student confidence improved for all questions and survey items following the simulator session (P < 0.0001). The students give these laboratory exercises uniformly superior evaluations with > 85% of the students rating the workshop "very good" or "excellent".

Cesarean section combined with splenectomy in a parturient with immune thrombocytopenic purpura

The case of a 25-year-old parturient with immune thrombocytopenic purpura is discussed. The patient was first seen at 20 weeks' gestation because of a history of thrombocytopenia after delivery of a child six years previously. The patient was not compliant with prednisone therapy or return follow-up visits; a combined cesarean section with splenectomy was planned for this patient. The report discusses the multidisciplinary management of this patient during her pregnancy and delivery.

Waste gas monitor reduces wasted volatile anesthetic

OBJECTIVE

The increasing focus on health care costs requires that all physicians evaluate practice behaviors. The primary emphasis in anesthesia has been limiting the use of expensive medications and interventions. Reducing waste is another approach, and volatile anesthetics are an appropriate target in that simple reduction of fresh gas-flow (FGF) rates is effective. A monitor that measures and displays the cost of wasted volatile anesthetic was developed and used to determine if real-time display of the cost would result in decreased FGF rates, which, in turn, would decrease wasted anesthetic.

METHODS

The waste gas monitor (WGM) measures flow rate at the anesthesia machine's scavenger port, integrates this with agent concentration, and displays the calculated cost, real-time, on a portable computer screen. The WGM equipment was attached to the anesthesia machine in the gynecologic surgery operating room (OR) and those cases performed under general endotracheal anesthesia and lasting longer than one hour were eligible for inclusion. First year anesthesiology residents assigned to the study OR as part of a non-specialty rotation, were the subjects of the study. For each resident, after data were collected from at least two eligible baseline cases (Baseline Phase, WGM not visible and resident unaware of its presence), the monitor was introduced and data collection continued for at least three more eligible cases (Visible Phase).

RESULTS

Nine residents were initially enrolled, but due to scheduling difficulties only five residents completed the protocol. Data from cases using the WGM demonstrated a 50% decrease (3.58 +/- 1.34 l/min vs. 1.78 +/- 0.51 l/min (p = 0.009)) in the scavenger flow rates, which resulted in a 48% ($5.28 +/- 0.68 vs. $2.72 +/- 0.80 (p = 0.002)) decrease in hourly cost of wasted volatile anesthetic. There was no difference between the Baseline and Visible phases with regard to use of nitrous oxide or intravenous anesthetic agents. CONCLUSIONS. The WGM decreased wasted volatile anesthetic by encouraging decreased FGF rates.

Problem-based learning in residency education: a novel implementation using a simulator

BACKGROUND

We developed a problem-based learning exercise with a full-scale human patient simulator to teach residents the emergency management and differential diagnosis of acute intraoperative hypotension.

METHODS

We developed the exercise through the following steps: clear definition of learning objectives, preparation of an appropriate case stem, development of clinically realistic scenarios to illustrate objectives, and an interactive instructor to stimulate discussion.

RESULTS

The exercise focused on the differential diagnosis of intraoperative hypotension, and the acute treatment of hypovolemia, cardiac tamponade, tension pneumothorax, and anaphylaxis.

CONCLUSIONS

Exercises on a full-scale patient simulator are a natural extension of problem-based learning. Recent research in learning theory provides the rationale for this teaching modality's potential as a learning tool.

Influence of pulse oximetry and capnography on time to diagnosis of critical incidents in anesthesia: a pilot study using a full-scale patient simulator

OBJECTIVE

Many studies (outcome, epidemiological) have tested the hypothesis that pulse oximetry and capnography affect the outcome of anesthetic care. Uncontrollable variables in clinical studies make it difficult to generate statistically conclusive data. In the present study, we eliminated the variability among patients and operative procedures by using a full-scale patient simulator. We tested the hypothesis that pulse oximetry and capnography shorten the time to diagnosis of critical incidents.

METHODS

A simulator was programmed to represent a patient undergoing medullary nailing of a fractured femur under general anesthesia and suffering either malignant hyperthermia, a pneumothorax, a pulmonary embolism or an anoxic oxygen supply. One hundred thirteen anesthesiologists were randomly assigned to one of two groups of equal size, one with access to pulse oximetry and capnography data and the other without. Each anesthesiologist was further randomized to one of the four critical incidents. Each anesthetic procedure was videotaped. The time to correct diagnosis was measured and analyzed.

RESULTS

Based on analysis of 91 of the subjects, time to diagnosis was significantly shorter (median of 432 s vs. >480 s) for the anoxic oxygen supply scenario (p = 0.019) with pulse oximetry and capnography than without. No statistical difference in time to diagnosis was obtained between groups for the other three critical incidents.

CONCLUSIONS

Simulation may offer new approaches to the study of monitoring technology. However, the limitations of current simulators and the resources required to perform simulator-based research are impediments to wide-spread use of this tool.

Modeling obstetric cardiovascular physiology on a full-scale patient simulator

To our knowledge, this is the first attempt at adapting an existing cardiovascular model to simulate the hemodynamics of a particular patient population. Despite attempts to define the physiologic alterations in advance, we discovered there were critical parameters not completely defined in the literature. These were discovered through the iterative process of testing, comparing resulting vital signs with targets, and literature review. A list of the parameters that should be sought for future modeling efforts is provided (Table 3), but this list is by no means exhaustive. As further work is performed in this area, additional independent and essential parameters will be identified (pressure characteristics of valvular anomalies, for example). To define a physiology that is less well described in the literature, empirical alterations and best-guess estimates of parameter changes will be required with significantly more iterations. Finally, we have described only modeling of cardiovascular physiology, modeling the respiratory system will require a similar process.

Sarcoidosis in a pregnant woman

Sarcoidosis, a rare multisystem disease, often occurs in women of childbearing age. The disease, which may be improved or exacerbated by pregnancy, presents unique considerations to the anesthesiologist. These considerations are illustrated by the case presented here of complicated sarcoidosis in a parturient who underwent cesarean section.