Tissue oxygen available as a criterion for the effectiveness of continuous positive pressure breathing.

As little as 3-5 cm H2O increase in proximal airway pressure applied to normal lung reduces cardiac output. It is postulated that decreased pulmonary compliance in respiratory distress syndrome (RDS) acts as a barrier thus offsetting this effect. Since cardiac output is not routinely measured, severe reduction in it could accompany regression of disease while maintaining the same airway pressure. This study was undertaken to determine whether tissue oxygen available (O2a) could be used to detect changes in perfusion during continuous positive pressure breating (CPPB). CPPB was evaluated in 10 normal rabbits (CL = 9.5 +/- 1.8 cc/g at 25 cm H2O) and in 10 pulmonary-damaged rabbits (CL = 5.5 +/- 1.4 cc/g at 25 cm H2O) produced by subjecting them to 100% O2. Airway pressure was increased from 0-15 cm H2O in 3 cm H2O increments at 10-min intervals. O2a and PaO2 were monitored continuously. In the normal group, O2a decreased at 3 cm H2O airway pressure, reaching 22% of control at 12 cm H2O, at which pressure PaO2 decreased. Breathing 100% O2 at this airway pressure increased PaO2 to 408 mm Hg, whereas O2a returned to 45% of control. In the experimental group, O2a decreased at 9 cm H2O airway pressure, at 12 cm H2O it was 36% of control at which pressure PaO2 decreased slightly. Breathing 100% O2 at this airway pressure increased PaO2 to 316 mm Hg, and increased O2a to 200% of control. These data indicate that with excessive airway pressure, muscle hypoxia may exist during systemic hyperoxemia and that a low compliance lung exerts a protective effect on O2a. Since changes in cardiac output during CPPB are compliance dependent, and since O2a is perfusion dependent, tissue oxygen available could provide a means of selecting optimal airway pressure during CPPB.     

Multispectral analysis of magnetic resonance images

Magnetic resonance (MR) imaging systems produce spatial distribution estimates of proton density, relaxation time, and flow, in a two dimensional matrix form that is analogous to that of the image data obtained from multispectral imaging satellites. Advanced NASA satellite image processing offers sophisticated multispectral analysis of MR images. Spin echo and inversion recovery pulse sequence images were entered in a digital format compatible with satellite images and accurately registered pixel by pixel. Signatures of each tissue class were automatically determined using both supervised and unsupervised classification. Overall tissue classification was obtained in the form of a theme map. In MR images of the brain, for example, the classes included CSF, gray matter, white matter, subcutaneous fat, muscle, and bone. These methods provide an efficient means of identifying subtle relationships in a multi-image MR study.     

Analysis and overview of the guidelines for assessing fitness to drive for commercial and private vehicle drivers

Guidelines on fitness to drive were released by AUSTROADS and the National Road Transport Commission in September 2003. No recognised legal medical authority was cited. There are three parts in the document: (i) background information, (ii) specific medical conditions and (iii) appendices of relevant documents and contacts. This paper analyses the relevance of the guidelines for physicians and notes that the disclaimer exonerates its authors from potential repercussions. Guidelines for both private and commercial drivers are combined in the document and the basis for such delineation is defined. A lack of universal Australian standards with no State indicating the driver's responsibility to report changes in health standards on the issued licences is confirmed by the guidelines. Not all States indemnify physicians for reporting contrary to patients' wishes, while South Australia and the Northern Territory mandate reporting those at risk. Much of the language is patronizing, expecting '... conciliatory and supportive ...' behaviour even with recalcitrant patients. No allowance is made for patients who may not fulfil the guidelines but whom the doctor may consider fit to drive. Ambiguity regarding responsibility to report, as identified in the background section, may leave the doctor vulnerable for not reporting a patient who subsequently may cause injury. Attempt is made to differentiate the role of the specialist from the family general practitioner (GP), advocating specialists for commercial drivers, although this is largely left to the discretion of the GP. There is an implied onus on doctors to report all patients with the conditions under review. Some diagnoses, such as syncope, are discussed in different sections with application of conflicting limitations. Inappropriate language, such as reference to a seizure being '... an isolated non-epileptiform event ...', or withdrawal of medications failing to be restricted to anti-epileptic medications confounds interpretation. Some sections, such as that on sleep and epilepsy, are effectively analysed, while illnesses such as dementia are considered superficially. The guidelines are an attempt to assess fitness to drive, but contain serious flaws and provide limited information upon which to base decisions. Ambiguous language complicates application of the guidelines and places the health care professional at risk, despite a disclaimer protecting its authors.     

Effect of intravenous heparin administration on duration of hospitalization

OBJECTIVE: To determine how frequently hospital discharge is delayed to administer intravenous heparin to patients with diverse indications for oral anticoagulation (OAC) medications and how often these delays are potentially avoidable, as assessed by the prevalence of contraindications to outpatient use of low-molecular-weight heparin (LMWH). PATIENTS AND METHODS: Records were reviewed from a random sample of 309 patients who received at least 1 dose of OAC medication while hospitalized at the Mount Sinai Hospital in New York City between January 1 and December 31, 1997. Medical records were abstracted to determine admission diagnoses; patient demographics and comorbid conditions; indications for anticoagulation; laboratory data; and treatment and discharge medications, including whether LMWH was prescribed. A delay was defined as the continuation of hospitalization solely to administer intravenous heparin. Predefined criteria were used to classify the delay of discharge as appropriate or avoidable on the basis of the patient's potential eligibility for outpatient treatment with LMWH. RESULTS: Discharge was delayed for 75 of 309 patients (24%; 95% confidence interval [CI], 19%-29%); during analysis of the avoidability of delay, 67 of the 75 medical records were available and showed that 32 of 67 delays (48%; 95% CI, 35%-60%) were avoidable. Of patients taking long-term OAC medications who were admitted for reasons unrelated to thromboembolism or bleeding, discharge was delayed for 18 of 146 (12%; 95% CI, 7%-19%); during analysis of the avoidability of delay, 16 of the 18 medical records were available and showed that 9 of 16 delays (56%; 95% CI, 30%-80%) were avoidable. Of patients admitted for acute venous thromboembolism who were not taking long-term OAC medications, discharge was delayed for 24 of 38 (63%; 95% CI, 46%-78%); during analysis of the avoidability of delay, 22 of the 24 medical records were available and showed that 11 of 22 delays (50%; 95% CI, 28%-72%) were avoidable. CONCLUSIONS: For patients taking OAC medications, hospital discharge is frequently delayed so that intravenous heparin can be administered; approximately half of these delays could be avoided by outpatient use of LMWH. Studies of the safety, efficacy, and feasibility of outpatient use of LMWH for indications other than deep venous thrombosis are needed because timely discharge of these patients could substantially decrease health care costs.     

Percutaneous Interventions in Radiation-Associated Coronary In-Stent Restenosis

This study was performed to evaluate the outcome of percutaneous revascularization in edge restenoses developing after radioactive stent implantation in de novo and in-stent lesions. Twenty-one consecutive patients undergoing target lesion revascularization (TLR) at any follow-up after phosphorus-32 radioactive stent implantation were included in this study. We assessed the incidence of death, myocardial infarction, repeated TLR and recurrent angina over the following 18 months. After 6 months, TLR rate was 28.6%, and no stent thromboses, deaths or Q-wave myocardial infarctions occurred. Among the patients with TLR there were significantly more subjects who had received a radioactive stent in a previous in-stent restenosis (66.7% vs. 0% in patients without second restenosis; P < 0.001), or who had received two radioactive stents (83.3% vs. 33.3%; P = 0.038). After 18 months, TLR rate was 33.3%, and two patients (9.5%) had died. Restenosis after intravascular radiotherapy can be safely treated by percutaneous interventional techniques, yielding an acceptable clinical result within 18 months.