Accuracy of the Lifebox pulse oximeter during hypoxia in healthy volunteers

Pulse oximetry is a standard of care during anaesthesia in high-income countries. However, 70% of operating environments in low- and middle-income countries have no pulse oximeter. The 'Lifebox' oximetry project set out to bridge this gap with an inexpensive oximeter meeting CE (European Conformity) and ISO (International Organization for Standardization) standards. To date, there are no performance-specific accuracy data on this instrument. The aim of this study was to establish whether the Lifebox pulse oximeter provides clinically reliable haemoglobin oxygen saturation (Sp O2 ) readings meeting USA Food and Drug Administration 510(k) standards. Using healthy volunteers, inspired oxygen fraction was adjusted to produce arterial haemoglobin oxygen saturation (Sa O2 ) readings between 71% and 100% measured with a multi-wavelength oximeter. Lifebox accuracy was expressed using bias (Sp O2 - Sa O2 ), precision (SD of the bias) and the root mean square error (Arms). Simultaneous readings of Sa O2 and Sp O2 in 57 subjects showed a mean (SD) bias of -0.41% (2.28%) and Arms 2.31%. The Lifebox pulse oximeter meets current USA Food and Drug Administration standards for accuracy, thus representing an inexpensive solution for patient monitoring without compromising standards.

The desaturation response time of finger pulse oximeters during mild hypothermia

Pulse oximeters may delay displaying the correct oxygen saturation during the onset of hypoxia. We investigated the desaturation response times of pulse oximeter sensors (forehead, ear and finger) during vasoconstriction due to mild hypothermia and vasodilation caused by glyceryl trinitrate. Ten healthy male volunteers were given three hypoxic challenges of 3 min duration under differing experimental conditions. Mild hypothermia increased the mean response time of finger oximeters from 130 to 215 s. Glyceryl trinitrate partly offset this effect by reducing the response time from 215 to 187 s. In contrast, the response times of the forehead and ear oximeters were unaffected by mild hypothermia, but the difference between head and finger oximeters was highly significant (p < 0.0001). The results suggest that the head oximeters provide a better monitoring site for pulse oximeters during mild hypothermia.

Variability in determination of point of needle insertion in peripheral nerve blocks: a comparison of experienced and inexperienced anaesthetists

Accurate identification of surface landmarks is essential for the successful performance of peripheral nerve blocks. The variability between experienced and inexperienced practitioners in identifying anatomical landmarks has not been studied previously. Anaesthetists were asked to identify the point of needle insertion for posterior lumbar plexus and sciatic nerve blocks on a volunteer using a standard textbook description. The chosen point for needle insertion was described in terms of X and Y co-ordinates, measured in millimetres, from a zero reference point marked on a volunteer's back. Fifteen experienced and 22 inexperienced anaesthetists took part in the study. The lumbar plexus block mean [range] values for the X, Y co-ordinates were 80 [62-108], 66 [46-86] and 92 [49-150], 62 [0-131] in the experienced and inexperienced groups, respectively. The sciatic nerve block X, Y co-ordinates were 77 [62-99], 70 [49-89] and 68 [29-116], 62 [26-93] in the experienced and inexperienced groups, respectively. The variance for the point of needle insertion was significantly greater in the inexperienced group (p <0.01) for both the lumbar plexus and sciatic nerve blocks. We conclude that with increasing experience, there is decreased variability in determining the point of needle insertion using anatomical landmarks.

A new approach to chronic pain in the ED

Patients presenting to emergency departments (EDs) for primary management of chronic or recurrent nonmalignant pain conditions and their physicians frequently report dissatisfaction, in part because of the impressions created by a small percentage of such patients that frequently visit EDs requesting opioids. Treating such patients with opioids is contrary to many published guidelines, but refusing them increases dissatisfaction. Narcotic registers serve to label patients who are suspected of seeking drugs, thus creating anxiety and often distrust in health care professionals treating them. The four Calgary adult EDs have developed a system that will attempt to remove labels associated with some of these patients, insure communication between patients, their family doctors, and ED staff, and facilitate optimal care of the patients' real problems, be they difficult home management of pain, drug dependence or addiction, or other social issues. Emphasis will be shifted to home management and the family doctor's office. If successful, the system will minimize ED visits by frequent attendees seeking medication for pain control, and should also decrease overall expenditure to the health care system.

Limitations of the prehospital index in identifying patients in need of a major trauma center

STUDY OBJECTIVE

To evaluate the usefulness of the prehospital index (PHI) as a triage tool in a population of trauma patients.

DESIGN

Retrospective analysis.

SETTING

The two adult trauma centers in Calgary, Alberta, Canada, serving a population of 1.2 million.

PARTICIPANTS

Six hundred forty-four consecutive patients admitted during an 18-month period with injury severity scores (ISSs) of 16 or more.

RESULTS

PHI of 4 or more was statistically related to death within 72 hours of emergency department presentation (P < .00001), emergency surgery within 24 hours (P < .039), emergency surgery within 4 hours (P < .00001), and emergency surgery within 4 hours or death within 72 hours (P < .0001). A more important statistic, however, in the evaluation of a screening tool is sensitivity. PHI of 4 or more had a sensitivity of 98% in identifying mortality but had sensitivity of only 59% for emergency surgery within 24 hours and 71% for emergency surgery within 4 hours.

CONCLUSION

PHI of 4 or more had limitations as a screening tool for triage in our study population because of the high number of patients it categorized as having minor trauma who required emergency surgery.

Response of a promethazine-induced coma to flumazenil

We report the first case of a patient in a promethazine-induced coma responding to treatment with flumazenil. A literature search conducted to determine the mechanism behind the antagonism of this overdose showed that promethazine interacts with receptors in the central nervous system. Sedative effects may, in fact, be mediated through the benzodiazepine receptor. We concluded that flumazenil can antagonize the sedative effects of promethazine at these receptors to return the patient to a wakeful state.

The effect of 25 grams i.v. glucose on serum inorganic phosphate levels

STUDY OBJECTIVE

To determine whether a 25-g IV glucose bolus will result in a fall in serum inorganic phosphate levels.

DESIGN

Single-blind, randomized, controlled trial.

PARTICIPANTS

Thirty-six healthy, nondiabetic, adult volunteers.

INTERVENTIONS

Random allocation to a control group receiving a 50-mL normal saline bolus followed by a normal saline infusion at 125 mL/hr for three hours; study group 1, receiving a 50-mL bolus of D50W followed by a normal saline infusion at 125 mL/hr for three hours; or study group 2, receiving a 50-mL bolus of D50W followed by an infusion of 2/3:1/3 dextrose:saline solution at 125 mL/hr for three hours.

MEASUREMENTS AND MAIN RESULTS

Serum inorganic phosphate levels were measured at time zero (baseline) and at 30-minute intervals for three hours. There was a statistically significant fall in serum inorganic phosphate levels in both groups receiving the glucose bolus. The group receiving the glucose infusion demonstrated a trend toward a further decline in serum phosphate levels.

CONCLUSION

A glucose bolus and infusion in the amounts compatible with what is given to patients with altered levels of consciousness produced a significant fall in serum inorganic phosphate levels in healthy, nondiabetic adults. Because hypophosphatemia may create a clinical picture of altered mental status very similar to that of hypoglycemia, consideration should be given to administering IV glucose only to patients with finger-stick-proven hypoglycemia. Consideration also should be given to monitoring phosphate levels after administration of IV glucose.