Midazolam and cardioversion.
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Anesthesia↗
Biomedical subjects
M Vegfors
Publications and source records attributed to M Vegfors.
The influence of changes in blood flow on the accuracy of pulse oximetry in humans.
Oxygen saturation (SpO2) was measured with a pulse oximeter in ten healthy, young men breathing air. A pulse oximeter probe was attached to the second toe and a laser Doppler probe to the first toe of the same foot for measurement of changes in peripheral blood flow. The pulse oximeter and laser Doppler readings were simultaneously compared when the foot was positioned 40 cm (position 1) above heart level, elevated 10 cm (position 2) above heart level and horizontally at heart level (position 3). Using this experimental human model, we achieved various blood flows. The AC and DC optical signals used for determination of oxygen saturation were recorded from the pulse oximeter and analysed. There was a significant increase (P less than 0.05) between position 1 and 3 in blood flow as measured by the laser Doppler flow meter. The corresponding pulse oximeter readings of haemoglobin saturation also increased significantly (P less than 0.05) comparing these two leg positions. Analysing the AC- and DC optical signals, the AC value of infrared light increased considerably, while the AC value of the red light decreased slightly. The DC values of red and infrared light did not change significantly. In summary, when blood flow was decreased, the ratio of red to infrared transmitted light was changed, resulting in a low SpO2 reading.
Adult↗
The accuracy of pulse oximetry at two haematocrit levels.
The object of this study was to investigate the influence of haematocrit on the accuracy of pulse oximetry. Seven Swedish land race rabbits were studied. The oxygen saturation of haemoglobin was decreased step-wise using increasing fractions of nitrogen to the inspiratory gas. One pulse oximeter probe was attached on the front leg and another probe directly over the common carotid artery. The pulse oximeter readings (SpO2) were compared with simultaneous oxygen saturation analysis (SaO2) by a haemoximeter. The pulse oximeter measurements were performed at the haematocrit levels of approximately 40% and 11%, respectively. We found a good correlation between SpO2 and SaO2 in a wide range of the oxygen saturation, i.e. SaO2 26-100%. After haemodilution the correlation was improved in the range 86-100%, but not in the range 26-85%. No correlation between SpO2 and SaO2 was found when the sensor was attached directly over the artery during normal haematocrit levels. After haemodilution a better correlation was however obtained. These results indicate that the accuracy of pulse oximetry is dependent on the haematocrit level.
Animals↗
[Spinal blockade is a good alternative in elective cesarean section].
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Anesthesia, Epidural↗
Carboxyhaemoglobinaemia and pulse oximetry.
We compared measurements obtained with a pulse oximeter (SpO2) against values obtained from a CO-oximeter in a patient with carbon monoxide poisoning. SpO2 was equal to the sum of the oxyhaemoglobin (HbO) and carboxyhaemoglobin (HbCO) values over the range of HbCO from 30 to 1%. This confirms the experimental findings that pulse oximeters measure HbCO as HbO. The patient was treated with oxygen (FlO2 = 50%) and recovered without any sequelae. Under these circumstances, the half-life of HbCO was approximately 2 h.
Adult↗
Hypoxemia during induction of anaesthesia.
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Adult↗
Basic studies of pulse oximetry in a rabbit model.
We have developed an animal model for the evaluation of pulse oximetry during severe hypoxaemia. Twelve rabbits were anaesthetized and mechanically ventilated via a tracheostomy tube. Increasing fractions of nitrogen were added to the gas mixture they inhaled to obtain severe hypoxaemia (saturation range 26%-100%). On 412 occasions, simultaneous pulse oximeter (SpO2) and invasive haemoximeter (SaO2) measurements were compared. The regression analysis of the data gave the equation: y = 0.7 x + 26.7, r = 0.90. In the SaO2 range less than or equal to 85%, the bias (mean value of SaO2-SpO2) was higher when compared with SaO2 greater than 85%. In an in vitro study the light absorption characteristics of rabbit haemoglobin (Hb) were compared to human Hb. The millimolar extinction coefficients of both reduced and oxygenated Hb from rabbits were found to be similar to human Hb. We consider the animal model (rabbit) suitable for studies of pulse oximetry during physiological and pathophysiological conditions.
Animals↗
Assessment of peripheral blood flow using a pulse oximeter.
We investigated the bar graph on a pulse oximeter as an indicator of peripheral blood flow. Because blood flow is known to increase in the lower extremities during spinal analgesia, we chose patients receiving spinal analgesia as the experimental model. Although they are indirect indicators, we used laser Doppler readings and skin temperature to reflect peripheral blood flow. These measurements were made from each patient's foot and hand before and after spinal analgesia and were compared with the deflection on the pulse oximeter bar graph. After subarachnoid injection of bupivacaine, laser Doppler readings from the foot increased to 620 +/- 120% (P less than 0.05) of the control reading. The pulse oximeter signal amplitude increased from 5.2 +/- 0.4 to 9.4 +/- 0.3 bars (P less than 0.05) and mean skin temperature increased from 24.6 +/- 0.5 to 31.2 +/- 0.8 degrees C (P less than 0.05). No changes were noted in readings obtained from the hand. A Nellcor N-200 pulse oximeter may be used to evaluate the effect of sympathetic nerve block as indicated by an increase in peripheral blood flow.
Adult↗
Anaesthesia for cardioversion. A comparison between propofol, thiopentone and midazolam.
This study compares the induction and recovery characteristics, haemodynamic changes and side effects of propofol, thiopentone and midazolam when used as the anaesthetic agents for cardioversion. Recovery after midazolam was significantly longer (p less than 0.05) than with either thiopentone or propofol. There was no difference in the recovery times between thiopentone and propofol. There was a significant decrease in mean arterial pressure 2 minutes after induction with propofol and midazolam. Three patients each in the thiopentone and propofol groups needed assisted ventilation because of apneoea, and four patients each in the propofol and midazolam groups had low Spo2 values (less than 95%). Flumazenil was used to reverse the effects of midazolam in eight patients and five of these were still drowsy 4 hours after the procedure. This study indicates that thiopentone is the most satisfactory agent for anaesthesia for cardioversion.
Aged↗
The clinical value of the haemoglobin concentration analysis (g/L) and the calculation of oxyhaemoglobin saturation (%) in an automatic blood gas analyser (ABL2, Radiometer A/S, Denmark).
This study was aimed to evaluate the accuracy and thereby the clinical value of the haemoglobin concentration (g/L) analysis and of the calculation of oxyhaemoglobin saturation (%) in a commonly used automatic blood gas analyser (ABL2, Radiometer A/S, Denmark). The measured and calculated values (ABL2) were compared to the readings obtained in a last generation haemoximeter (OSM3, Radiometer A/S, Denmark), which served as reference. The haemoglobin concentration measurements performed in the ABL2 apparatus showed an increasing underestimation of the true haemoglobin value at larger haemoglobin concentration values. This together with a poor correlation makes the analysis unsuitable for clinical use. The oxyhaemoglobin saturation values (%) obtained using the ABL2, however, had a good correlation to the corresponding values measured in the OSM3. It is suggested that the oxyhaemoglobin saturation value obtained in the ABL2 can be used clinically, e.g., for invasive control of pulsoximeters.
Arteries↗
Pulse oximetry during extradural analgesia for extracorporeal shock wave lithotripsy.
Exracorporeal shock wave lithotripsy (ESWL) may require immersion of the patient in water and extradural blockade for analgesia, which may both affect pulmonary and cardiovascular function and increase the likelihood of hypoxaemia. Twenty-four patients (ASA I-III) with extradural blockade and six healthy subjects were studied by pulse oximetry during immersion. Oxygen saturation (SaO2) tended to decrease after induction of extradural analgesia. Immersion decreased SaO2 further, by up to 2% in healthy volunteers (P less than 0.05) and 3% in patients (P less than 0.05). In two patients with arteriosclerosis, an SaO2 of 92% was accompanied by arrhythmias which resolved after administration of oxygen.
Adult↗
Should oxygen be administered after laparoscopy in healthy patients?
This study aimed to assess the oxygen flow necessary to maintain satisfactory oxygen saturation when administered via a nasopharyngeal catheter. Oxygen saturation was displayed by a pulse oximeter and/or measured in arterial blood samples. Thirty-six healthy women scheduled for elective diagnostic laparoscopy were anaesthetized using thiopentone, fentanyl and O2/N2O. Atracurium was used as relaxant which was reversed with atropine and neostigmine. Arterial samples were obtained prior to anaesthesia, on arrival in the postoperative ward and 1 h postoperatively. Oxygen saturation was monitored postoperatively using a pulse oximeter. The patients were randomly divided into three groups which received either no oxygen, 2 l O2/min or 4 l O2/min. On arrival in the postoperative ward 15% of the patients were below the normal limit of O2 saturation (94%). In patients receiving 2 l or 4 l O2, oxygen saturation was well above normal values. In patients receiving no oxygen, two had low oxygen saturation (92% and 93%). Comparing saturation values obtained in arterial samples with values measured with pulse oximetry gave r = 0.79. It is concluded that all patients should be given oxygen in the immediate postoperative period. Increasing oxygen flow from 2 to 4 l/min had no major effect on oxygen saturation. These results were obtained in healthy patients following minor abdominal surgery.
Adult↗