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Biomedical subjects

J R Mackenzie

Publications and source records attributed to J R Mackenzie.

At least 37 records · Page 2Linked to original sources
PubMed1984

Clinical scoring does not accurately assess hypoxemia in pediatric asthma patients.

Management of acute asthma in the pediatric population is based almost entirely on clinical evidence of severity. Although pulmonary function testing has been advocated to improve evaluation, it is difficult in the pediatric patient and not routinely practiced. A clinical scoring system has been devised to help standardize evaluation, but has not been validated by comparison of the results of clinical scoring with those of arterial blood oxygen levels as determined by blood gas analysis. This study was undertaken to compare clinical scoring of pediatric asthma patients with the results of arterial blood gas analysis. Thirty-eight children between the ages of 2 and 13 having 42 episodes of acute asthma were evaluated. The average age was 5.4 years. The average clinical score was 2.62; arterial blood for analysis was obtained in 37 (88%), with an average PaO2 of 81.7 mm Hg. None of the children had CO2 retention. There was no correlation between the clinical score of the children on presentation and the severity of hypoxia (correlation coefficient = -0.149). Comparison of age and arterial oxygen tension revealed a trend toward worsening hypoxemia with diminishing age from 6 to 2 years, which was not identified by clinical scoring. We conclude that clinical scoring is inaccurate for the assessment of hypoxemia in the pediatric age group. Arterial blood gas determination should be used to assess the severity of hypoxemia in the emergency treatment of pediatric asthma patients.

Acute Disease↗
PubMed1984

Predicting the utilization of helicopter emergency medical services: an approach based on need.

Accurately predicting the utilization of helicopter emergency medical services is critical to both resource allocation and fiscal integrity, and health planning agencies may insist that the need for such services be demonstrated before the system can become operational. Most utilization predictions have been based solely on the experience of other services despite wide variation in need and use. This kind of prediction has the serious disadvantage of not considering local demographics and individual system variations. A better method uses needs analysis to predict utilization and to calculate demand. This method is based on a systematic identification of conditions that will benefit significantly from helicopter transport to a referral center, the incidence of those conditions, and the population to be served. The need for service is estimated by multiplying the population by the incidence. The fraction of patients with demonstrated need who will actually use the service is estimated on the basis of the interaction between local characteristics and condition variables.

Accidents↗
PubMed1984

Disappearance of dimethoate, methamidophos and pirimicarb in lettuce.

Foliar sprays of dimethoate at 150 or 300 g a.i./ha, methamidophos at 450 or 900 g a.i./ha and pirimicarb at 140 or 280 g a.i./ha were applied for control of the green peach aphid, Myzus pericae (Sulzer), and the lettuce aphid, Nasonovia ribisnigri ( Mosley ), about 2 weeks before the lettuce started heading, and again about 1 week from harvest. In lettuce, dimethoate partially oxidized to its oxon and pirimicarb converted to its methylamino- and/or formyl methylamino-analogues. Most residues were present in the outer leaves which were exposed directly to the sprays; only traces of residues were detected in samples of the inner head leaves. Total residues disappeared rapidly. Pirimicarb was the least persistent and only traces of residues (less than 0.01 ppm) were detected in marketable heads. Concentrations of dimethoate, including the oxon and of methamidophos were well below their respective tolerances of 2 and 1 ppm respectively.

Carbamates↗
PubMed1984

Chest roentgenograms in diagnosis of traumatic rupture of the aorta. Observer variation in interpretation.

A significant p value is not always a good measure of the clinical value of a diagnostic test. By examining interobserver agreement with respect to chest roentgenogram interpretation, we determined which of seven roentgenographic signs statistically associated with traumatic rupture of the aorta (TRA) are most likely to be useful in clinical practice. Four surgeons and two radiologists were asked to interpret individually, in blinded fashion, the initial chest films of 149 trauma patients who had undergone aortography to rule out TRA. Agreement between all observers, as well as between specialty groups, was examined by chi-square and by calculation of Cohen's kappa statistic, which estimates the extent of agreement. Statistically significant agreement (p = .0000) was found between all observers with regard to mediastinal widening and obscuration of the aortic knob, but other comparisons showed no better than random agreement. Of the seven roentgenographic signs associated with TRA, identification of mediastinal widening and obscuration of the aortic knob show the most consistent interobserver agreement and are the most likely to be useful in clinical practice.

Aorta, Thoracic↗
PubMed1983

Diagnosis of isolated small bowel injury following blunt abdominal trauma.

A review of the case histories of 29 patients with isolated rupture of the small bowel was undertaken to determine which diagnostic tests were most sensitive in the early diagnosis of this notoriously occult injury. Results indicate that peritoneal lavage was the most useful test for this purpose, clearly more sensitive than standard clinical or radiographic signs. All patients in this series had indications for peritoneal lavage, and 85% of the patients who underwent peritoneal lavage in the emergency department had positive results and prompt operation. Reliance on the development of clinical peritonitis or the detection of pneumoperitoneum leads to long delays before operation.

Abdominal Injuries↗
PubMed1983

Comparison of mediastinal width, mediastinal-thoracic and -cardiac ratios, and "mediastinal widening" in detection of traumatic aortic rupture.

This study was undertaken to determine whether direct measurement of mediastinal width or computation of ratios of measurements of easily detectable mediastinal structures is more effective than the subjective impression of "mediastinal widening" in selecting trauma patients for aortography. A group of five surgeons and radiologists individually read in blinded fashion 149 chest films of trauma victims who had undergone aortography to rule out traumatic rupture of the aorta (TRA). Each made a subjective interpretation of "mediastinal widening," as well as direct measurement of mediastinal width (MW), thoracic width at the level of the mediastinum, cardiac width, and maximum thoracic width. Mediastinal-cardiac (MC), mediastinal-thoracic (MT), and mediastinal-mediastinothoracic (MMT) ratios were calculated. Statistically significant differences were found in all parameters of direct measurement between cases with and without TRA (P from .0001 for MT to .01 for MMT). The critical measurement for mediastinal width separating positive from negative cases was 8.0 cm; the critical ratios were MT = 0.275, MC = 0.555, and MMT = 0.36. Application of these parameters to detect TRA yielded sensitivities of .75 for MW, .68 for MC, .66 for MMT, and .62 for MT. Statistically significant differences between observers' measurements were seen. None of these measurements was as effective as subjective interpretation of mediastinal widening, which had a sensitivity of .91 (P = .0000). We conclude that the subjective impression of mediastinal widening is superior to "objective" direct measurement of mediastinal structures for identification of trauma patients with aortic rupture.

Aorta↗
PubMed1983

Evaluation of experimental blunt and penetrating hepatobiliary trauma by sequential peritoneal lavage.

Peritoneal lavage, when used in the standard way to detect hemoperitoneum, gives no information regarding site or nature of injury. We think that it would be useful for the surgeon to be more able to characterize intraabdominal injuries preoperatively, and that this may be possible by extending the scope and duration of the technique of peritoneal lavage. To test this hypothesis, we investigated the use of sequential peritoneal lavage with extended chemical analysis to precisely define the nature and extent of hepatobiliary trauma in an animal model. Thirty-six dogs were divided randomly among one control and four experimental groups in which sham laparotomy, blunt thoracoabdominal trauma, direct laceration of the liver, liver laceration plus bowel perforation, and gallbladder perforation were carried out. Sequential peritoneal lavage was performed over a six-hour experimental period with simultaneous serum and lavage samples analyzed for red and white blood cells, bile, and enzyme activity (GOT, GPT, and alkaline phosphatase) at four test intervals up to six hours post injury. Our results demonstrate that enzyme activity is easily detectable in lavage effluent after blunt hepatic injury but not after penetrating trauma, and seems to correlate with the extent of hepatocellular disruption. Lavage white cell counts in excess of those anticipated for hemorrhage alone are present only in association with an inflammatory stimulus other than blood or bile. A lavage-to-serum-bilirubin ratio of one or more can be expected after gallbladder or extrahepatic biliary perforation. This information may be valuable in the emergency assessment of the trauma patient.

Alanine Transaminase↗
PubMed1983

Assessment of mediastinal widening associated with traumatic rupture of the aorta.

In order to best determine the reliability and usefulness of widening of the mediastinum (WMED) and other radiographic abnormalities in the selection of trauma patients for aortography to detect traumatic rupture of the aorta (TRA), we designed a blind study in which a panel of radiologists and surgeons reviewed 149 chest films of trauma victims who subsequently underwent aortography to rule out TRA. Sixteen patients had TRA. Panelists identified mediastinal widening (WMED) in 83 of 93 observations on films in cases of TRA (89%). There was a significant association between WMED and TRA found both for the panel as a whole and for each panelist individually (p = 0.0000), making this an extremely reliable sign both in terms of detectability and in signalling the need for aortography. Significant associations with TRA were also found overall for six other radiographic abnormalities but none of these was reliable for all panelists or was as sensitive as WMED in the detection of TRA. Despite the reliability of these signs, panelists making decisions based on the chest film alone failed to recommend aortography in seven of 93 instances of TRA. Direct mediastinal measurements varied by at least 2 cm among panelists in one half of the cases of TRA, and 25% of these (4/16) had at least two measurements of mediastinal width of 7 cm or less. Of all the radiographic signs associated with TRA, widening of the mediastinum is the most reliable, but in this study all observers would not have detected all cases of ruptured aorta using radiographic signs alone. Clinical judgment and consideration of the forces involved in the injury must continue to play an important role in the selection of patients for aortography.

Aortic Rupture↗
PubMed1982

Indications for aortography in blunt thoracic trauma: a reassessment.

The indications for aortography in patients sustaining blunt chest trauma have increased as the number of radiographic and clinical findings associated with traumatic rupture of the thoracic aorta (TRA) proliferate. No studies, however, have demonstrated whether these findings are useful in selecting patients for aortography. In order to determine the predictive value of reported associations in TRA, the presence or absence of nine radiographic and nine clinical findings associated with TRA were tabulated and tested for correlation with the results of aortography in 173 consecutive patients who underwent arch aortography from 1975 to 1980 to rule out TRA following blunt trauma. Mediastinal widening was the most reliable indicator of TRA. All patients less than 65 years old with TRA presented with mediastinal widening. In patients under 65, the reliability of mediastinal widening to predict TRA was not enhanced by any other clinical or radiographic finding studied. On the other hand, only two of six TRA's in patients over 65 had mediastinal widening. Only in this group over 65 did other publicized indications for aortography, including pulmonary contusions or multiple rib fractures including ribs 1 and 2, have any association singly or in combination with TRA. We conclude that all trauma victims who have a widened mediastinum should undergo aortography. Other reported associations by themselves are not absolute indications for aortography except in patients 65 years old or older.

Adolescent↗
PubMed1981

Sequential peritoneal lavage and early diagnosis of colon perforation.

In order to determine the usefulness of the lavage white blood cell count as a diagnostic indicator of occult colon perforation, we subjected 20 mongrel dogs to sham laparotomy, isolated liver stab wound, or closed colon perforation and then performed sequential peritoneal lavage. The lavage white cell count rose steadily in those animals with colon perforations, and 100% of these animals had a positive lavage at six hours post-injury. After correction for the white cells shed intraperitoneally secondary to hemorrhage, the lavage white count of animals with liver wounds and of those with sham laparotomy failed to rise significantly during the period of observation. Gram stain of the lavage effluent as well as lavage amylase determination were not of diagnostic value. For solid viscus injury, lavage white cell count rises in proportion to organ hemorrhage; in hollow viscus perforation, lavage white cell count rises disproportionately and is higher than one would expect on the basis of the red cell count. We believe sequential peritoneal lavage white cell counts are of value in the diagnosis of occult colon perforation.

Animals↗