One model, several results: the paradox of the Hosmer-Lemeshow goodness-of-fit test for the logistic regression model

BACKGROUND

The Hosmer-Lemeshow test, used extensively to assess the fit of the logistic regression model, is performed by several statistical packages. Recent studies have shown some problems in the use of this test when ties are present. These problems were attributed merely to the test implementation.

METHODS

We analysed the order of the observations as an alternative explanation of the problem of ties. Using a data-set of 1393 intensive care unit (ICU) patients we performed the Hosmer-Lemeshow test with all possible subjects dispositions.

RESULTS

We obtained about one million different P values, ranging from 0.01 to 0.95.

DISCUSSION

It is already known that when the Hosmer-Lemeshow goodness-of-fit test is performed with a number of covariate patterns lower than the number of subjects, its result may be inaccurate. We showed that the extent of this problem could be relevant under particular conditions. We also suggest a strategy for estimating the extent of the problem and subsequent interpretation.

Can airway complications following multilevel anterior cervical surgery be avoided?

OBJECT

The authors conducted a study to determine how to avoid emergency postoperative reintubation and its associated morbidity in patients who have undergone multilevel anterior-posterior cervical spine surgery.

METHODS

In a group effort between the departments of anesthesia and neurosurgery, a protocol was developed to avoid having to reintubate patients postoperatively. As a preventative measure, patients remained intubated overnight; on the 1st postoperative day or thereafter, based on direct fiberoptic visualization of reactive tracheal swelling, an anesthesiologist extubated the patients. Fifty-eight patients underwent multilevel anterior corpectomy with fusion (ACF; with 41 receiving plates and 17 not receiving plates), posterior wiring and fusion (PWF), and application of a halo. On average, ACF involved three levels, whereas PWF included 6.5 levels. Surgery typically lasted 10 hours, and an average 2.6 U of blood was required. Forty patients were successfully extubated on the 1st, five on the 2nd, three on the 3rd, two on the 4th, two on the 5th, and three on the 7th postoperative day. Three elective tracheostomies were performed on the 7th postoperative day. Risk factors associated with delayed extubation or tracheostomy in 18 patients included: operative time longer than 10 hours (12 patients), obesity greater than 220 lbs (12 patients), transfusion of more than 4 U of blood (10 patients), ACF reoperations (nine patients), ACF including C-2 (seven patients), four-level ACF (five patients), and asthma (five patients). In the only case in which emergency reintubation was required, three risk factors were present.

CONCLUSIONS

Emergency reintubation following anterior-posterior cervical surgery and fusion can be avoided by maintaining intubation overnight and subsequently having an anesthesiologist remove the tube after healing is fiberoptically confirmed. Familiarity with major risk factors contributing to airway compromise, combined with this protocol, should minimize the significant morbidity associated with reintubation following multilevel anterior-posterior cervical fusion.

Role of vagus nerve signaling in CNI-1493-mediated suppression of acute inflammation

CNI-1493 is a potent anti-inflammatory agent, which deactivates macrophages and inhibits the synthesis of proinflammatory mediators. The objective of the present study was to identify the role of the central nervous system (CNS) and efferent vagus nerve signaling in CNI-1493-mediated modulation of acute inflammation in the periphery. CNI-1493 was administered either intracerebroventricularly (i.c.v., 0.1-1,000 ng/kg) or intravenously (i.v., 5 mg/kg) in anesthetized rats subjected to a standard model of acute inflammation (subcutaneous (s.c.) injection of carrageenan). I.c.v. CNI-1493 significantly suppressed carrageenan-induced paw edema, even in doses at least 6-logs lower than those required for a systemic effect. Bilateral cervical vagotomy or atropine blockade (1 mg/kg/h) abrogated the anti-inflammatory effects of CNI-1493 (1 microg/kg, i.c.v. or 5 mg/kg, i.v.), indicating that the intact vagus nerve is required for CNI-1493 activity. Recording of the efferent vagus nerve activity revealed an increase in discharge rate starting at 3-4 min after CNI-1493 administration (5 mg/kg, i.v.) and lasting for 10-14 min (control activity=87+/-5.4 impulses/s versus CNI-1493-induced activity= 229+/-6.7 impulses/s). Modulation of efferent vagus nerve activity by electrical stimulation (5 V, 2 ms, 1 Hz) of the transected peripheral vagus nerve for 20 min (10 min before carrageenan administration and 10 min after) also prevented the development of acute inflammation. Local administration of the vagus nerve neurotransmitter, acetylcholine (4 microg/kg, s.c.), or cholinergic agonists into the site of carrageenan-injection also inhibited acute inflammation. These results now identify a previously unrecognized role of efferent vagus nerve activity in mediating the central action of an anti-inflammatory agent.

Unifying Class-Based Representation Formalisms

The notion of class is ubiquitous in computer science and is central in many formalisms for the representation of structured knowledge used both in knowledge representation and in databases. In this paper we study the basic issues underlying such representation formalisms and single out both their common characteristics and their distinguishing features. Such investigation leads us to propose a unifying framework in which we are able to capture the fundamental aspects of several representation languages used in different contexts. The proposed formalism is expressed in the style of description logics, which have been introduced in knowledge representation as a means to provide a semantically well-founded basis for the structural aspects of knowledge representation systems. The description logic considered in this paper is a subset of first order logic with nice computational characteristics. It is quite expressive and features a novel combination of constructs that has not been studied before. The distinguishing constructs are number restrictions, which generalize existence and functional dependencies, inverse roles, which allow one to refer to the inverse of a relationship, and possibly cyclic assertions, which are necessary for capturing real world domains. We are able to show that it is precisely such combination of constructs that makes our logic powerful enough to model the essential set of features for defining class structures that are common to frame systems, object-oriented database languages, and semantic data models. As a consequence of the established correspondences, several significant extensions of each of the above formalisms become available. The high expressiveness of the logic we propose and the need for capturing the reasoning in different contexts forces us to distinguish between unrestricted and finite model reasoning. A notable feature of our proposal is that reasoning in both cases is decidable. We argue that, by virtue of the high expressive power and of the associated reasoning capabilities on both unrestricted and finite models, our logic provides a common core for class-based representation formalisms.

The importance of statistics in documentation on hip prostheses

The authors illustrate the possibilities and the limits of instruments that statistics currently make available in the analysis of a medical series involving hip prosthesis surgery. An analysis of the survival rate constitutes one of the most important tools with regard to data in the study of the effectiveness of implants, but its correct application is influenced by the assumption that so-called censored cases have no differences in survival in relation to those that remain under observation even in periods that follow. Simulation reveals the need to process series with a high number of cases, in order to obtain reliable estimates. Finally, only multivaried techniques allow for a correct evaluation of the incidence that single factors have in causing failure of implants.

Addiction recovery for low-income pregnant and parenting women: a process of becoming

A naturalistic field study of low-income women (N = 17) in an intensive outpatient addiction recovery program addressed the question: What is the nature of addiction recovery for pregnant and parenting-women in an addiction treatment program? Grounded theory methodology was used to determine the nature of the interpersonal and social processes that define addiction recovery for women in this study. Over 2 years, audiotaped semi-structured interviews, document reviews of medical records, treatment progress and group therapy notes, and participant observation notes were collected and analyzed. The constant comparison method of analysis involved an ongoing process of theoretical sampling, memoing, and open and then axial coding to identify, group, link, and reduce the categories produced. A developmental model of addiction recovery in pregnant and parenting women emerged that consisted of the dimensions of becoming drug and alcohol free, a partner in a relationship, a person, and a parent. These four dimensions parallel and transform each other, yielding different outcomes but similar patterns over time. This model of addiction recovery provides a beginning framework for understanding the transactional nature of addiction recovery for low-income women who are adapting to a drug and alcohol-free lifestyle and the task and role of parenting a newborn.

Metal-UHWMPE (Ultra High Molecular Weight Polyethylene) wear: experimental testing

Testing conducted on a hip joint simulator verified the Charnley hypothesis that the diameter of the prosthetic head is proportional to wear. The study was conducted by pairing heads in Ortinox TM with acetabular cups in polyethylene at high molecular weight (UHMWPE). A comparison between the different sizes of the heads (26 and 30 mm in diameter) showed a different trend in the wear rate; in particular, the head with a smaller diameter behaves better tribologically than the head with a larger diameter.

Intraoperative fractures of the femur in prosthetic hip reimplantations

A total of 19 cases of intraoperative fractures of the femoral diaphysis occurring during prosthetic hip reimplantation are described. Incidence, predisposing factors, treatment, and influence on long-term results are discussed. The pre-existence of osteolysis or narrowing of the femoral cortex, often associated with primary cemented implantation with a metal-polyethylene combination, constitutes a factor that predisposes the patient to fracture. Fracture consolidation occurs in most cases with minimum treatment, at times without instrumentation; fracture, however, always means a delay in weight-bearing and a slowing down in recovery times. Long-term clinical evaluation shows functional results that are worse for reimplantations complicated by fracture as compared to those where there are no complications. The differences in the radiographic results instead do not reveal statistical significance.

Breaking ground: combining community service, critical thinking, and writing in a mental health clinical course

This article describes the experience of a team of nursing educators who, over the course of 2 years, redesigned the delivery of an undergraduate nursing clinical course to reflect the changing face of mental health care near the turn of this century. Case studies of student learning experiences show the value of nontraditional clinical settings such as homeless shelters to the professional growth and training of nursing students. Recommendations offer practical advice for combining nontraditional community-based clinical experiences with critical thinking exercises as key components of the mental health clinical course delivery.

[Primary hydatid cyst of the coracobrachial muscle. A clinical case]

Primary localization of hydatidosis in the musculoskeletal system is a quite rare occurrence. We report a case of a 67 year old man with an infestation of the coracobrachialis muscle. We discuss several instrumental and serologic diagnosis methods and the hypothesis of a primary muscular localization.

[Update on laparoscopic surgery: on the treatment of hydatid cyst of the liver and peritonitis caused by a perforated duodenal ulcer]

Laparoscopic surgery represents a real innovation with respect to the traditional laparotomic way of access, owing to its undeniable advantages, both intraoperative and postoperative. This new technique reduces the complications connected with the surgical wound and with forced allerement. Therefore it allows the patient's fast recovery. Laparoscopic surgery application ground get's wider and wider every day: in fact, the authors report two medical cases, one of elective surgery (treatment of a hidatid cyst of the liver) and the other in emergency surgery (peritonitis due to perforated duodenal ulcer), both obtaining a positive result about the clinical and the postoperative timing of recovery.

Evaluation of intraoperative somatosensory-evoked potential monitoring during 100 cervical operations

Continuous intraoperative somatosensory-evoked potential monitoring during scoliosis surgery, along with improved instrumentation techniques, has contributed to the reduction of neurologic injury from 4-6.9% to 0-0.7%. To assess whether somatosensory-evoked potential monitoring might play a similar role in cervical surgery, the authors compared the morbidity and mortality rates associated with 218 patients who were not monitored and were operated on between 1985-1989 with those found in 100 consecutive somatosensory-evoked potential monitored procedures done from 1989-1991. The cervical procedures were conducted for disc disease, stenosis, spondylosis, and ossification of the posterior longitudinal ligament. Eight of 218 unmonitored patients became quadriplegic (3.7%) and 1 died (0.5%); no instances of quadriplegia and no deaths were encountered among the 100 monitored patients. The reduction of neurologic deficit was attributed in part to early somatosensory-evoked potential detection of vascular or mechanical compromise of the spinal cord or nerve roots and to the immediate alteration of anesthetic or surgical technique in response to somatosensory-evoked potential changes, i.e., reversal of systemic or "relative" hypotension, adjustment of operative position, release of distraction, and cessation of manipulation. Continuous intraoperative somatosensory-evoked potential monitoring also was a practical tool in monitoring cervical surgery.

Structural characterization of terflavoxate

Data are reported on the structural characterization of 3-methyl-4-oxo-2-phenyl-4H-1-benzopyran-8-carboxylic acid 1,1-dimethyl-2-(N-piperidinyl)ethyl ester hydrochloride (terflavoxate-HCl, Rec 15/2053, CAS 86433-39-8), a new antispasmodic for the lower urinary tract. UV, IR, NMR and MS spectra fully confirmed the structure. The X-ray crystal structure determination revealed that the molecular structure consists of a rigid platform, formed by the chromone system, with two arms, the phenyl group at C(2) and the ester chain at C(8). The ester chain conformation generates a small hollow where two oxygen atoms face.

New basic esters of 2-phenyl-3-methyl-4-oxo-4H-1-benzopyran-8-carboxylic acid endowed with spasmolytic properties. Synthesis and pharmacological-pharmacokinetic evaluation

In order to obtain new analogs of flavoxate endowed with higher stability and possibly higher potency, a new series of basic esters of 2-phenyl-3-methyl-4-oxo-4H-1-benzopyran-8-carboxylic acid (MFCA) has been prepared and investigated. Derivatives in which the structure of flavoxate was modified by branching and lengthening of the estereal alkyl chain were synthesized, together with the conformationally restricted N-piperidinyl derivatives. Esters containing in their structure various alicyclic tertiary amines which are present in natural or synthetic drugs endowed with spasmolytic properties, mainly of anticholinergic nature, were also prepared. The stability in aqueous solution, acute toxicity in mouse, and in vitro spasmolytic properties of the new compounds were investigated in comparison with flavoxate. Based on the results obtained from this screening procedure, 3 compounds were selected for further investigation. In this phase, further pharmacological and stability testing as well as preliminary animal pharmacokinetic investigations were carried out. The obtained results suggested the choice of 1,1-dimethyl-2-(1-piperidinyl)ethyl 2-phenyl-3-methyl-4-oxo-4H-1-benzopyran-8-carboxylate HCl (Rec 151 2053, terflavoxate, CAS 86433-39-8) as a candidate for preclinical development. The deeper pharmacological characterization of this compound, carried out mainly in comparison with flavoxate, terodiline, and oxybutynin confirmed its good spasmolytic activity.

Hospital-based nursing response to perinatal drug exposure

This study examined hospital-based nursing interventions used for the problem of drug exposure in newborns and their mothers. Although there are few published reports of treatment services for this at-risk population, there is a consensus among health care providers on the need for treatment and the type of services that a treatment program should offer. A questionnaire measured use of assessment tools for newborn drug exposure and maternal drug use, patterns of referral, and use of aftercare and community treatment programs. The mean number of policies was 2.5, and the mean number of services offered was 1.042, consisting mostly of referral to community programs after discharge. Results can be used to develop quality assurance programs to address this issue and provide a more comprehensive response to the problem.

The relationship between umbilical artery Doppler velocimetry and fetal biometry

The relationship between peak-systolic/end-diastolic ratio of the umbilical artery waveform and fetal biometry was studied in 127 uncomplicated pregnancies with established dates between 20 and 40 weeks' gestation. At each ultrasonographic examination fetal biometry included measurement of the biparietal diameter, head circumference, abdominal circumference, and femur length. The peak-systolic/end-diastolic ratio was measured by either a continuous or a pulsed-wave method. There were significant linear negative correlations between all the biometric parameters, as well as between the ultrasonographically estimated fetal weight and peak-systolic/end-diastolic ratio. Of the individual ultrasonographic parameters the femur length (for gestations less than 30 weeks) and the abdominal circumference (for gestations greater than or equal to 30 weeks) were found to be best correlated with the peak-systolic/end-diastolic ratio. Regression curves, including the 10th and the 90th percentile, were developed between each biometric parameter (biparietal diameter, head circumference, abdominal circumference, and femur length), as well as between estimated fetal weight and peak-systolic/end-diastolic ratio. The estimated fetal weight nomogram had the best sensitivity (48%) in predicting intrauterine growth retardation. These nomograms should prove most useful in assessing downstream placental vascular resistance in high-risk patients with unknown dates.

Transverse cerebellar diameter/abdominal circumference ratio throughout pregnancy: a gestational age-independent method to assess fetal growth

In a prospective study of 162 patients, measurements of the transverse cerebellar diameter (TCD) and abdominal circumference (AC) were obtained between 15-38 weeks' gestation. A ratio between the TCD and AC was calculated after each examination. This ratio remained constant during gestation. The mean ratio was 13.7% (fifth and 95th percentiles of 11.9 and 15.9%, respectively); the median ratio was 13.6%. Forty-two patients had repeat measurements and the ratio did not change. This ratio is gestational age-independent; however, further investigation is needed to determine its application in the assessment of fetal growth abnormalities.