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Biomedical subjects

W B Murray

Publications and source records attributed to W B Murray.

At least 37 records · Page 2Linked to original sources
PubMed1993

Effect of delay and storage on whole-blood clotting analysis as determined by thrombelastography.

The thrombelastogram (TEG) measures the viscoelastic properties of clotting blood, displaying a visual trace of all phases of coagulation and fibrinolysis. Thrombelastography can be performed on whole blood (WBTEG) or on citrated blood or plasma, citrated samples facilitating delayed analysis but requiring recalcification of the sample. The aim of this study was to investigate the effect of delay and storage method on WBTEG measurement. Thrombelastographic analysis of coagulation in whole blood was investigated after delays of 3 and 6 minutes in polystyrene syringes (PS3 and PS6) and 3 minutes in silicone-coated glass tubes (SG3). Thrombelastograms of the delayed samples were compared with those measured immediately. Silicone-coated glass tubes activated coagulation, as seen by shorter r times (p < 0.01), shorter r + k times (p < 0.01), and larger maximum amplitude (ma) values (p < 0.01) compared with TEG values determined immediately after sampling. In the SG3 group, 20% of samples had clotted by 3 minutes, and the use of SG tubes for this purpose cannot be recommended. A delay of 6 minutes in PS had less effect on the activation of clotting in the earlier stages in that the r time was prolonged (p < 0.01). However, there appeared to be some activation later in that k time was shorter (p < 0.01) and ma was wider (p < 0.05). Overall, a 3-minute delay in PS produced the best values.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Coagulation↗
PubMed1993

Construction and use of catheter-manometer systems.

The accuracy of invasive arterial blood pressure monitoring is dependent on an adequate damped natural frequency (DNF) and damping factor (DF) of the system. Several factors influencing the DNF and DF were investigated to determine requirements for optimal design of catheter-manometer systems. The frequency sweep method was used in a specially constructed chamber that included linearizing and compensation circuitry. The DNF of isolated 20-gauge cannulae varied from 35.1 to 47.7 Hz. The DNF of 24-gauge cannulae varied from 27.7 to 44.3 Hz. An arterial cannula was found to require a DNF above 40 Hz to prevent the DNF from decreasing to below 25 Hz with the addition of arterial pressure tubing. Arterial pressure tubings exceeding 300 mm in length had DNF values that were unacceptably low even before the addition of arterial cannulae (e.g., the DNF was 23.8 Hz for a 900-mm tubing length, 19.8 Hz for 1,000-mm length, and ranged from 12.9 to 21.4 Hz for 1,200-mm lengths). The 3-way stopcocks and continuous flush devices further decreased the DNF, especially when the diameters were not matched. The percentage decrease caused by 3-way stopcocks and flush devices ranged between 19.5 and 40.8% for 300-mm length tubings and between 2.3 and 25.8% for tubings of 1,200-mm lengths. The radius ratio (outside diameter divided by inside diameter) is introduced as a new method to express the stiffness of arterial pressure tubing.(ABSTRACT TRUNCATED AT 250 WORDS)

Amplifiers, Electronic↗
PubMed1993

Intubating conditions and haemodynamic changes following thiopentone or propofol for early tracheal intubation.

Intubating conditions and haemodynamic changes were studied 30 sec after a fixed induction dose of thiopentone or propofol in patients scheduled for elective surgery. The hypnotic agent was preceded by the administration of papaveretum 10 mg three minutes before induction and alcuronium 0.2 mg.kg-1 at induction. Ease of intubation was graded and the study conducted in a randomised double-blind fashion. In the thiopentone group (n = 30) intubation was very easy in 73% compared with 79% in the propofol group (n = 29). In two patients in the propofol group the tracheas were moderately difficult to intubate but there were no failed intubations in either group. No patients recalled the intubation period on subsequent postoperative questioning. The immediate post-induction average systolic pressure in the thiopentone group decreased by 0.7% (range 15.9% increase to 25.3% decrease) whilst the post-intubation systolic pressure increased by 6.3% (range - 31.5% increase to 24.2% decrease). In the propofol group there was a decrease in systolic pressure after induction (average 14.4%; range 15.5% increase to 41.4% decrease, P < 0.05) but the subsequent pressor response to intubation was markedly attenuated compared with baseline (average systolic pressure decreased 15.5% (range 22.4% increase to 42.7% decrease)). Following intubation and maintenance, ventilation with nitrous oxide 70% and halothane 1% the systolic pressure decreased markedly in both groups with a greater reduction in the propofol group (P < 0.05). Compared with baseline there were increases (P < 0.0001) in heart rate in both groups from induction of anaesthesia to the end of study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Calculating the protamine-heparin reversal ratio: a pilot study investigating a new method.

There is no consensus as to the dosage of protamine required to reverse a given dose of heparin. The amounts advised vary widely. The hypothesis was investigated that doses of protamine smaller than those usually recommended could be used following cardiac surgery to successfully reverse heparin activity as measured by the activated coagulation time (ACT). A group of 18 patients scheduled for cardiopulmonary bypass (CPB) were investigated with their informed consent. A baseline ACT was measured before anticoagulation with heparin. At the end of CPB, an initial neutralizing dose (IND) of protamine (2 mg/kg) was administered. The ACT was measured after 5 minutes and a further dose of protamine (2 mg/kg) was then administered to make up the full dose. The heparin activity (HA) before and after the IND of protamine reversal was calculated according to the method described by Bull. The IND of protamine (2 mg/kg) was expressed as a ratio of the change in HA (the latter also expressed as mg/kg). The average +/- standard deviation (SD) preoperative ACT was 155 +/- 21 seconds with a range of 130 to 199 seconds. Following heparin administration the ACT increased to 701 +/- 152 seconds. After the IND of protamine, the average ACT of 160 +/- 31 (range, 121 to 250) was not statistically (NS) significantly different from the starting value. A further dose of 2 mg/kg of protamine ("full-dose") decreased (NS) the ACT only minimally to an average of 151 +/- 18 (range, 128 to 206) seconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Standards of practice in anaesthesia--intra-operative monitoring.

Intra-operative monitoring practice during anaesthesia was studied in a randomised selection of hospitals in different categories. Questionnaires from 45 anaesthetists in 20 hospitals provided information on 973 cases. The study showed that in 11% of cases the patient was left at some stage during anaesthesia without the attention of a medical practitioner and that in 7% of cases no record was made of the anaesthetic or of the parameters monitored. Types of monitoring varied considerably between hospitals and often fell short of acceptable minimal standards. Pulse oximetry, which is considered essential, was used in only 53% of cases. One in 18 cases was associated with a peri-operative critical incident and in 7 cases a critical incident occurred where the monitoring was deemed to be inadequate. Pulse oximetry would have assisted the anaesthetist in 6 of these 7 cases. In 3% of cases the anaesthetist admitted to fatigue during the procedure. This study highlights deficits in anaesthetic practice and in available equipment, both of which require urgent attention.

Anesthesia↗
PubMed1992

Anaesthesia without tears.

Rectal induction of anaesthesia is a useful method but is not widely used in South Africa. We studied the onset of action and side-effects of 1% methohexitone administered rectally in a dose of 20 mg/kg to 110 preschool children. Ninety-one per cent were adequately sedated for inhalation induction by mask within 10 minutes, and all by 15 minutes, of drug administration. There was no evidence of significant cardiovascular or respiratory depression and only minor complications such as faecal soiling (11.8%) and hiccough (3.6%) were noted. The technique has been favourably received by parents, surgeons and nursing staff and has now become routine practice.

Anesthesia, Rectal↗
PubMed1992

Information yield from routine pre-operative chest radiography and electrocardiography.

Studies in First-World settings suggest that routine pre-operative investigations are of minimal usefulness. A retrospective study of 797 case records determined the yield of significant information from routine chest radiography and ECG in a provincial general hospital serving a broad socio-economic sector. The results were in agreement with those of other studies, viz. that routine investigation may be worthwhile only in older patients. Routine chest radiographs showed an overall positive yield of 6%; 17% in those over 60 years but only 2% in those under 60 years. Routine ECGs showed a positive yield of 7% overall; 7.4% in those older than 40 years and 4.5% in those under 40 years. Investigations indicated by history or physical examination had a significantly greater yield: 34% for chest radiography and 31% for ECGs. Positive results of indicated investigations were more evenly spread across the age groups. The pre-eminence of clinical skills in determining which patients require special investigations is reaffirmed.

Adolescent↗
PubMed1992

Oxygen masks.

Explore the source record for details and available documents.

Humans↗
PubMed1992

Early tracheal intubation with thiopentone in elective surgery.

We have studied tracheal intubating conditions within 30 s of administration of thiopentone in 24 patients and compared this with our usual method of tracheal intubation, which involves 3 min of manual ventilation in 29 patients. All patients received papaveretum 10 mg 3 min before induction and alcuronium at induction of anaesthesia. Satisfactory intubating conditions were observed in 83% of patients in both groups. There were no difficult or failed intubations and no patient had laryngospasm. The duration of laryngoscopy in the control group was 14.1 (SD 8.6) s (range 7-50 s), compared with 12.4 (3.1) s (range 6-20 s), in the early intubation group (ns). In the control group there was a significant decrease in systolic pressure before tracheal intubation and a significant increase in heart rate after intubation, compared with baseline values. The average systolic pressure in the early intubation group increased only minimally: from a pre-intubation value of 143.3 (21.2) mm Hg to 145.5 (25.1) mm Hg after intubation. Our results demonstrate that early tracheal intubation under thiopentone supplemented with an opioid and a non-depolarizing neuromuscular block is feasible, associated with minimal changes in arterial pressure and not accompanied by an increased incidence of side effects.

Adult↗
PubMed1992

Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia.

Difficult tracheal intubation, often unexpected, has been identified as the commonest contributory factor to anesthetic-related maternal death. The ability to predict such cases preoperatively would be of great value. Preoperative airway assessment and potential risk factors for difficult tracheal intubation were recorded in 1,500 patients undergoing emergency and elective cesarean section under general anesthesia. Airway assessment using a modified Mallampati test recorded oropharyngeal structures visible upon maximal mouth opening. Potential risk factors documented were obesity; short neck; missing, protruding, or single maxillary incisors; receding mandible; facial edema; and swollen tongue. Subsequent to induction of anesthesia, the view at laryngoscopy and difficulty at intubation were graded. There was a significant (P less than 0.001) correlation between the oropharyngeal structures seen and both the veiw at laryngoscopy and difficulty at intubation. Univariate analysis demonstrated a significant association between difficult intubation and short neck (P less than 0.001), obesity (P less than 0.0001), missing maxillary incisors (P less than 0.02), protruding maxillary incisors (P less than 0.001), single maxillary incisor (P less than 0.0001), and receding mandible (P less than 0.003). Neither facial edema (P = 0.414) nor swollen tongue (P = 0.141) were found to be associated with difficult intubation. Multivariate analysis removed obesity and missing and single maxillary incisors as risk factors. Obesity was eliminated because of its strong association with short neck. The probability of experiencing a difficult intubation for various combinations of risk factors was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Invasive v. non-invasive blood pressure measurements--the influence of the pressure contour.

A reasonable correlation exists between invasive and non-invasive methods of measuring systemic blood pressure. However, there are frequent individual differences between these methods and these variations have often caused the validity of the non-invasive measurement to be questioned. The hypothesis that certain invasive systolic blood pressures may represent a pressure impulse rather than a flow-generating pressure was used to classify the invasive pulse pressure contour into various types, and the invasive pressure measurement was then correlated with the non-invasive. There was a significantly greater difference between these two methods of measuring systolic blood pressure in patients exhibiting prominent inotropic pressure pulse phenomena compared with patients without such phenomena. Since non-invasive monitors measure blood pressure by volume displacement or flow detection and invasive ones measure pressure impulses rather than flow, it was concluded that the pressure measured by the non-invasive monitor more accurately reflects the propulsive pressure-causing flow when inotropic pressure pulse phenomena are present.

Adult↗