Magnus Vegfors

Implementing a pre-operative checklist to increase patient safety : a 1-year follow-up of personnel attitudes.

Background: The operating room is a complex work environment with a high potential for adverse events. Protocols for perioperative verification processes have increasingly been recommended by professional organizations during the last few years. We assessed personnel attitudes to a pre‐operative checklist (‘time out’) immediately before start of the operative procedure.

Pulse oximetry ‐ clinical implications and recent technical developments

The pulse oximeter has been shown to be a reliable monitor of arterial oxygen saturation and has therefore been recommended as mandatory monitoring for patients during anaesthesia and intensive care. In 1989 two review articles on pulse oximetry were published (1, 2) and two years ago Severinghaus and Kelleher summarized the literature between 1989 and October 1991 (3). Our aim is to focus the discussion on technical aspects and applications of pulse oximetry with special attention centred on recent developments. This review is consequently an update on pulse oximetry since the end of 1991, and the first on technically‐based publications in the two last decades.

Presentation and evaluation of a new optical sensor for respiratory rate monitoring

A new optical sensor for respiratory rate monitoring was simultaneously compared with an acoustic sensor and a transthoracic impedance plethysmograph during normoventilation in the respiratory rate range of 9–17 breaths per minute. The response characteristics of the optical sensor were then measured during simulation of central apnoea and tachypnoea. Visual observation was chosen as the reference method for monitoring the respiratory rate. The measurements were performed in ten healthy volunteers and the respiratory signals recorded on an analogue tape and strip-chart recorder and analysed off-line. The response characteristics of the fibre optic sensor corresponded well with those of the acoustic sensor and impedance plethysmograph. All three methods responded rapidly to an apnoeic event.

High incidence of pruritus after large doses of hydroxyethyl starch (HES) infusions.

Background: There are several studies indicating a correlation between treatment with hydroxyethyl starch (HES) and pruritus. In order to see whether there is a possible dose–response relationship between HES and pruritus, we retrospectively studied 50 patients who had received HES in varying doses (cumulative dose 500–19500 ml) as hemodilution therapy after subarachnoid hemorrhage.

Hydroxyethyl starches and dextran during hip replacement surgery: effects on blood volume and coagulation

Background: Colloid fluids influence the coagulation system by diluting the plasma and, potentially, by exerting other effects that are unique for each fluid product. We hypothesised that changes in the coagulation measured at the end of surgery would be mainly governed by differences in half‐life between the colloid fluids.

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<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<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.

Accuracy of pulse oximetry at various haematocrits and during haemolysis in anin vitro model

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.

Non-invasive measurement of systolic blood pressure on the arm utilising photoplethysmography: development of the methodology

Photoplethysmography (PPG) can be used to measure systolic blood pressure at the brachial artery. With a specially designed probe, positioned in the most distal position beneath a pressure cuff on the upper arm, this is possible. The distance between the light source (880 nm) and the photodetector was 20 mm. A test was performed on neuro-intensive care patients by determining blood pressure from the PPG curves, and, when it was compared with systolic blood pressure obtained from inserted indwelling arterial catheters, a correlation factor of r=0.95 was achieved. The difference between blood pressure obtained using PPG and invasive blood pressure measurement was 3.9±9.1 mmHg (mean±SD), n=19. The depth to the brachial artery was 13.9±4.1 mm (mean±SD), n=18. A digital PPG system utilising pulsating light was also developed.

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 stepwise 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.

Alfentanil or fentanyl during isoflurane–based anaesthesia for day–care knee arthroscopy?

Forty patients agreed to participate in a study to compare whether fentanyl or alfentanil used as analgesic is associated with quicker recovery following anaesthesia for outpatient arthroscopy procedure. Psychomotor tests including choice reaction time (CRT), perceptive accuracy test (PAT) and finger tapping test (FTT) were done prior to induction of anaesthesia with propofol (2–3 mg–kg‐1). Patients were then divided into two groups: Group F (fentanyl) received 0.1 mg fentanyl prior to start of surgery and thereafter 0.05 mg every 30 min during the procedure. Group A (alfentanil) received 0.5 mg alfentanil prior to the onset of surgery and 0.25 mg every 15 min thereafter. Anaesthesia was then maintained using isoflurane (0.5–2%) in oxygen and air (Fio2 0.33) during spontaneous respiration with a face mask in a Bains system. Psychomotor tests were repeated every 45 min postoperatively. Clinical recovery, visual analogue pain intensity score (VAS) and time to discharge home were also assessed by a nurse blind to the method used. Patients in Group A returned to baseline values on the FTT after 90 min while those in Group F did not return to baseline values until 135 min after the end of the operation. Clinical recovery and time to discharge home (“home ready”) were also significantly longer in Group F. There was no difference in recovery as seen in the PAT and CRT between the groups. Also, there was no difference in the incidence of side effects and the pain intensity (VAS) scores were similar in the two groups at all time periods. We conclude that recovery following alfentanil is quicker compared to fentanyl when anaesthesia is based on isoflurane.