J Goldstone

Medication errors: a prospective cohort study of hand-written and computerised physician order entry in the intensive care unit

IntroductionThe study aimed to compare the impact of computerised physician order entry (CPOE) without decision support with hand-written prescribing (HWP) on the frequency, type and outcome of medication errors (MEs) in the intensive care unit.MethodsDetails of MEs were collected before, and at several time points after, the change from HWP to CPOE. The study was conducted in a London teaching hospitals 22-bedded general ICU. The sampling periods were 28 weeks before and 2, 10, 25 and 37 weeks after introduction of CPOE. The unit pharmacist prospectively recorded details of MEs and the total number of drugs prescribed daily during the data collection periods, during the course of his normal chart review.ResultsThe total proportion of MEs was significantly lower with CPOE (117 errors from 2429 prescriptions, 4.8%) than with HWP (69 errors from 1036 prescriptions, 6.7%) (p < 0.04). The proportion of errors reduced with time following the introduction of CPOE (p < 0.001). Two errors with CPOE led to patient harm requiring an increase in length of stay and, if administered, three prescriptions with CPOE could potentially have led to permanent harm or death. Differences in the types of error between systems were noted. There was a reduction in major/moderate patient outcomes with CPOE when non-intercepted and intercepted errors were combined (p = 0.01). The mean baseline APACHE II score did not differ significantly between the HWP and the CPOE periods (19.4 versus 20.0, respectively, p = 0.71).ConclusionIntroduction of CPOE was associated with a reduction in the proportion of MEs and an improvement in the overall patient outcome score (if intercepted errors were included). Moderate and major errors, however, remain a significant concern with CPOE.

Continuous measurement of cerebral oxygenation by near infrared spectroscopy during induction of anesthesia.

UNLABELLED Near infrared spectroscopy (NIRS) measures tissue oxygenation continuously at the bedside. Major disturbances of cerebral oxygenation can be detected by using NIRS, but the ability to observe smaller changes is poorly documented. Although anesthetics generally depress cerebral metabolism and enhance oxygen delivery, the administration of etomidate has been associated with cerebral desaturation. We used this difference to study the ability of NIRS to detect the small changes associated with the onset of anesthesia. Thirty-six healthy patients were randomly allocated to have anesthesia induced with either etomidate, propofol, or thiopental. We found that there was a temporal association between the onset of anesthesia and NIRS-derived indices of cerebral oxygenation. Etomidate was associated with a decrease in cerebral oxygenation, whereas propofol and thiopental were associated with an increase in cerebral oxygenation. We conclude that NIRS is capable of detecting the small changes in cerebral oxygenation associated with the induction of general anesthesia and shows promise as a bedside investigational tool for the noninvasive assessment of cerebral oxygenation. IMPLICATIONS We conclude that near infrared spectroscopy is capable of detecting the small changes in cerebral oxygenation associated with the induction of general anesthesia and shows promise as a bedside investigational tool for the noninvasive assessment of cerebral oxygenation.

Maximum relaxation rate of the diaphragm during weaning from mechanical ventilation.

BACKGROUND--The maximum relaxation rate (MRR; percentage fall in pressure/10 ms) of oesophageal (POES) and transdiaphragmatic (PDI) pressure slows under conditions of loaded breathing, and has been measured previously in normal subjects. MRR has not been measured in intubated patients weaning from mechanical ventilation. METHODS--Five postoperative patients who were expected to wean and nine patients who had previously failed were studied. POES and PDI MRR, peak oesophageal pressure during spontaneous breathing, maximum oesophageal pressure, and the inspiratory duty cycle were measured at rest during mechanical ventilation, in the first two minutes of spontaneous breathing, and after reventilation in those patients who failed, or before extubation in those patients who succeeded. RESULTS--At rest POES MRR in intubated patients had a range of 5.6-11 and PDI MRR 6.9-10.0, with a coefficient of variation of 9.9% and 7.3% respectively. POES and PDI MRR were similar before and after extubation in five postoperative patients, and POES MRR was reflected by endotracheal MRR measured at the airway. In five patients who failed to wean POES and PDI MRR slowed by 47% and 44%, and fully recovered after 10 minutes reventilation. In four patients who were successfully weaned MRR was unchanged during spontaneous breathing. At the time when MRR decreased, the respiratory muscles were heavily loaded in relation to their strength. CONCLUSIONS--Weaning failure occurs when the applied load exceeds the capacity of the respiratory muscles, and this is associated with a slowing of respiratory muscle MRR.

Noninvasive measurement of cerebral blood flow in adults using near-infrared spectroscopy and indocyanine green: a pilot study.

This pilot study was designed to determine the feasibility of measuring cerebral blood flow noninvasively after an intravenous bolus of indocyanine green using near-infrared spectroscopy and pulse dye–densitometry. Feasibility aside, this study did not attempt to validate the measured values of cerebral blood flow against an established method of measurement. Twelve healthy volunteers were investigated after peripheral intravenous injection of indocyanine green. Arterial and cerebral changes in indocyanine green concentration were measured using pulse dye–densitometry and near-infrared spectroscopy, respectively. Two methods of calculating cerebral blood flow were used, and a blood flow index was also estimated. Absolute cerebral blood flow was calculated using a modification of the Fick principle and a deconvolution algorithm to derive the impulse residue function. Mean (range) estimated cerebral blood flow for the Fick method was 8.2 mL/100 g/min (4.2–16.2 mL/100 g/min) and 8.3 mL/100 g/min (4.7–15.3 mL/100 g/min) for the impulse residue function method. The impulse residue function method provided a more precise intrasubject estimation of cerebral blood flow compared with the modified Fick principle, with a coefficient of variation of 10.1% versus 25.5%. The blood flow index was 8.6 mg/sec (range: 5.6–17.3 mg/sec) with an intrasubject coefficient of variation of 12.0%. Estimation of cerebral blood flow using near-infrared spectroscopy and pulse dye–densitometry can be made at the bedside after intravenous injection of indocyanine green, and the precision can be improved using a deconvolution algorithm. Notwithstanding the low values obtained for absolute cerebral blood flow, further investigation and validation of this bedside technique is warranted.

Changes in cerebral blood volume with changes in position in awake and anesthetized subjects

UNLABELLED Changes in posture affect cerebral blood volume (CBV), and moderate head-up tilt is used as a therapeutic maneuver to reduce CBV and intracranial pressure. However, CBV is rarely measured in the clinical setting. Near-infrared spectroscopy allows real-time bedside monitoring of cerebral hemodynamics, and we have used this technique to measure changes in CBV with changes in posture in 10 normal subjects and 10 propofol-anesthetized patients. In the awake subjects, changes in CBV were correlated with the degree of table tilt. CBV decreased with 18 degrees head-up tilt and increased with 18 degrees head-down tilt (P < 0.0001, r = -0.924). In anesthetized patients, there were differences between head-up and head-down tilt. In the head-down position, CBV was also correlated with the degree of table tilt (P < 0.001, r = -0.782), whereas there was a clinically insignificant reduction in CBV in the head-up position. Near-infrared spectroscopy allows continuous, real time measurement of changes in CBV at the bedside. IMPLICATIONS Near-infrared spectroscopy, a bedside technique, has been used to measure changes in cerebral blood volume in normal subjects. We have used the same technique in anesthetized patients and have shown that, when a patient is placed in the head up position, the decrease in cerebral blood volume is attenuated, relative to normal subjects.

Investigation of the Effects of Hypocapnia upon Cerebral Haemodynamics in Normal Volunteers and Anaesthetised Subjects by near Infrared Spectroscopy (NIRS)

The effect of alterations in arterial carbon dioxide tension (PaCO2) upon the cerebral blood vessels was first described in 1930 by Wolff and Lennox and quantified in 1948 by Kety and Schmidt. Since then many studies have investigated this relationship in terms of cerebral blood flow (CBF) (Novack et al 1953, Severinghaus et al 1967, Grubb et al 1974.) and volume (CBV)(Greenberg et al 1978, Artru 1984). CBV has not been as closely studied as CBF because of the paucity of measurement techniques. Since arterial PCO2 is frequently maintained at an artificially low level during anaesthesia for neurosurgery, to reduce intracranial pressure, it is of interest to measure the changes in cerebral haemodynamics as well as to describe the time course. 133Xenon washout and positron emission tomography (PET) are relatively invasive and can only provide measurements intermittently. Near infrared spectroscopy (NIRS) has been used to quantify the response of CBV to altered PaCO2 (CBVR) in newborn infants and is capable of measuring changes in CBV at 0.5 second intervals. The purpose of this study was to quantify both the extent and the duration of the haemodynamic response to an alteration in PaCO2 in anaesthetised patients and healthy volunteers.

Predicting Oscillation in Arterial Saturation from Cardiorespiratory Variables

The potential of near infrared spectroscopy (NIRS) as a non invasive tissue oxygenation monitor was first outlined by J6bsis (J6bsis, 1977). Extension of the basic technique to measure tissue blood flow using a Fick technique was developed by Edwards and Reynolds (Edwards et aI., 1988; Edwards et aI., 1993). This uses a rapid change in arterial oxyhaemoglobin concentration to act as an intravascular tracer, avoiding the problem of recirculation of indicator.

Continuous Measurement of Cerebral Oxygenation by Nirs During Induction of Anaesthesia

Continuous intraoperative monitoring of cerebral oxygenation is not routine because existing techniques are either invasive, require a prolonged period of equilibration or involve the use of ionizing radiation. The potential of near infrared spectroscopy (NIRS) as a non invasive tissue oxygenation monitor was first outlined by Jobsis (Jobsis, 1977). NIRS enables the continuous measurement of oxyhaemoglobin (HbO2) and deoxyhaemoglobin (Hb). To date most of the studies that have used NIRS during anaesthesia have considered either the effects on cerebral dynamics of extreme manoeuvres, such as clamping of a carotid artery and induction of ventricular fibrillation (Kirkpatrick et al., 1995; Mason et al., 1994; Williams et al., 1995; Levy et al., 1995), or have been confined to measuring cerebral blood flow (CBF) or cerebral blood volume (CBV) (Owen-Reece et al., 1994; Owen-Reece et al., 1996).

Near infrared oximetry and near infrared spectroscopy

and subsequent formation of carbonic acid. This is a late change and only occurs some time after the soda lime has become clinically ineffective. In addition to the lateness of the colour change, further problems with ethyl violet are that it can become bleached by exposure to fluorescent light and also that it deteriorates with time once the container is opened, even if the soda lime is stored in the dark [l]. Either of these mechanisms might account for the lack of colour indication of soda lime exhaustion described by Dr Bell. Several years ago, in Zimbabwe, we experienced a similar problem to that described by Dr Liley in that we received a consignment of soda lime containing no indicator. Economic requirements made the use of low flow systems necessary and we did not have ready access to capnography. As a consequence, a simple but effective means of detecting the functioning of the soda lime was adopted. Gas flow through the soda lime canister is from the bottom upwards and because the absorption of carbon dioxide is an exothermic process a clear area of warmth can be felt in the portion of the canister in which carbon dioxide absorption is taking place. It is now my routine practice to feel the canister, at regular intervals throughout an anaesthetic, in order to ascertain the region of the canister in which soda lime absorption of carbon dioxide is occurring. A trial in which carbon dioxide was passed through the canister showed that no carbon dioxide emerged from the top of the canister until the band of warmth had reached at least two-thirds of the way up the canister. Monitoring the temperature band on the canister in this way is a more reliable method of ascertaining the functional capacity of the soda lime than looking for a colour change. A recent Japanese publication (of which I have only read the English abstract) suggested that the dynamic and functional state of soda lime can be more precisely assessed by measuring changes in wall temperatures of the absorption chambers using a liquid crystal thermometer rather than observing colour change of the soda lime granules[2]. Mounting a temperature-sensitive strip to the side of the soda lime canister would seem to be a simple and satisfactory answer to the problem.

Use of Near Infrared Spectroscopy to Estimate Cerebral Blood Flow in Conscious and Anaesthetized Adult Subjects

Near infrared spectroscopy (NIRS) can be used to quantify cerebral haemodynamic states non-invasively and to estimate cerebral blood flow (CBF). In the first part of this study we have compared CBF measurements in conscious and anaesthetized subjects. In the second part we have compared paired measurements made during anaesthesia, first on the scalp and then the dura after craniotomy. Mean CBF was 17 (SD 7) ml 100 g-1 min-1 in the conscious subjects compared with 21 (8) ml 100 g-1 min-1 on the scalp during anaesthesia (P > 0.1). Mean CBF on the dura was 68 (21) ml 100 g-1 min-1 (P < 0.0001). Computer modelling suggests that the difference in magnitude between scalp and dura measurements of CBF is likely to be caused by the optical effect of extracerebral tissue which powerfully scatters light passing through it but does not contribute significantly to the measured CBF because it has only a small blood content itself. The results lend support to this method of estimating CBF although formal validation by comparison with an established technique is needed.