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Biomedical subjects

B J Pollard

Publications and source records attributed to B J Pollard.

At least 37 records · Page 2Linked to original sources
PubMed1996

Anaesthesia and the QT interval in humans. The effects of isoflurane and halothane.

Prolongation of the QT interval may cause potentially hazardous arrhythmias. The effects on the QT interval (QTc, corrected for heart rate) of isoflurane and halothane followed by vecuronium have been investigated during induction of anaesthesia in 51 patients. All patients were ASA 1 or 2, without cardiovascular problems or electrolyte abnormalities and were not receiving medication. Midazolam 0.08 mg.kg-1 was administered intramuscularly for premedication. Anaesthesia was induced with either isoflurane (n = 26) or halothane (n = 25), and the inspired concentration increased to reach an end-tidal concentration of 2.5% to 3%. Recordings of ECG, heart rate, systolic and diastolic arterial pressure were obtained at the following times: prior to induction of anaesthesia; 1 min and 3 min after a stable end-tidal concentration had been reached; 1 min and 3 min following vecuronium administration, at the time of tracheal intubation and 1 min and 3 min later. Halothane significantly shortened QTc (p < 0.05 to p < 0.001), in contrast to isoflurane which prolonged it (p < 0.01). The heart rate decreased (p < 0.01 to p < 0.001) after induction of anaesthesia with halothane and returned to pre-induction values after tracheal intubation. In contrast, heart rate increased after induction with isoflurane and increased further after laryngoscopy and tracheal intubation (p < 0.001). In the isoflurane group, ST depression was noticed in seven patients and nodal rhythm in two, while in the halothane group seven patients developed nodal rhythm and, in two patients, ventricular ectopics were recorded. There were no sequelae. In both groups, systolic and diastolic arterial pressure decreased after induction of anaesthesia (p < 0.01 to p < 0.001), increasing again after intubation.

Adolescent↗
PubMed1995

The use of propofol for sedation of critically ill patients undergoing haemodiafiltration.

OBJECTIVE: To assess the requirement for propofol to provide sedation in critically ill patients in established renal failure during the commencement of haemodiafiltration. DESIGN: Prospective clinical study. SETTING: ICU, University Hospital. PATIENTS: 10 adult patients. All were mechanically ventilated, had acute oliguric renal failure which necessitated continuous veno-venous haemodiafiltration and were receiving a continuous intravenous infusion of propofol for sedation. Sedation was assessed using a scoring system. INTERVENTION: Veno-venous haemodiafiltration. MEASUREMENTS AND RESULTS: Connection of the extracorporeal circuit produced a reduction in plasma propofol concentration in 7 out of 9 patients (one sample misplaced) with subsequent awakening in 3 of these 7 patients. The commencement of haemodiafiltration itself did not significantly influence the requirement for propofol (8 out of 10 patients). CONCLUSION: Haemodiafiltration does not substantially influence the requirement for propofol but the initial introduction of the extracorporeal circuit will reduce plasma concentrations in the majority of patients. This may be due to haemodilution alone or absorption of plasma albumin (with propofol) onto the membrane.

APACHE↗
PubMed1995

Molecular mechanisms of neuromuscular blocking agents: is the increased understanding of importance to the practising anaesthetist?

A neuromuscular blocking agent is an essential component of many general anaesthetics. Although a great deal is known about the neuromuscular junction, the site of action of these agents, their precise mode of action remains unclear. This article reviews our present knowledge of the anatomy and physiology of neuromuscular transmission and the ways in which clinically useful drugs may modify this system. The decisions involved in clinical choice of which agent to use are described with particular respect to basic physiology and pharmacology and also to potential interactions with other drugs.

Adjuvants, Anesthesia↗
PubMed1995

Pulmonary function and head lift during spontaneous recovery from pipecuronium neuromuscular block.

We have studied in seven healthy conscious volunteers the correlation between the electromyographic (EMG) and clinical criteria used to identify adequate recovery from sub-paralysing doses of pipecuronium. Pipecuronium (mean dose 1.88 (range 0.92-3.16) mg) was administered to reach a T4/T1 ratio of 0.5; full recovery to 1.0 was produced in a mean time of 25.3 (14-39) min. During recovery from neuromuscular block, we measured tidal volume, forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) negative inspiratory pressure (NIP), peak expiratory flow rate (PEFR), mid-expiratory flow rate (MEFR) and 5-s head lift. The assessments were started when the train-of-four (TOF) ratio reached 0.5 +/- 0.001 and repeated at each 0.1 +/- 0.001 increase up to a ratio of 1.0. All volunteers showed ptosis and diplopia after the first dose and difficulty in swallowing with subsequent doses. They also experienced a pleasant, relaxing sedative sensation. All could sustain head lift for 5 s at a TOF ratio of 0.5 and higher, except for one subject who could not lift his head only at a ratio of 0.5. There was a statistically significant decrease in FVC, FEV1 and PEFR with a nonsignificant decrease in other pulmonary measurements, except for NIP which only decreased significantly at a ratio of 0.5. These changes are probably of no clinical importance. All the measured respiratory variables returned to control values at a TOF ratio of 0.9.

Adult↗
PubMed1995

Prediction of infusion rates of vecuronium using the bolus test dose technique.

Fifty neurosurgical patients were given loading doses of vecuronium 0.1 mg kg-1 followed by boluses of 1, 2 or 4 mg after return of T1 of the train-of-four. Neuromuscular function was assessed simultaneously by palpation of the great toe after peripheral nerve stimulation of the lateral popliteal nerve using a handheld nerve stimulator and also using a Relaxograph attached to one arm. The time taken for the return of T1 after the bolus dose was recorded and an infusion of vecuronium was begun and subsequently adjusted to maintain steady state neuromuscular block. It was possible to predict the infusion rate of vecuronium from the duration of action of a 2-mg or 4-mg but not a 1-mg bolus dose using the handheld stimulator. The infusion rate could also be predicted from the duration of action of the initial loading dose.

Anesthesia, General↗
PubMed1995

The role of muscle relaxants in total intravenous anaesthesia.

For total intravenous anaesthesia (TIVA), all drugs that are required as part of the anaesthetic method are administered intravenously. This is usually taken to imply the use of intravenous infusions. It is normal practice to administer muscle relaxants intravenously, although other routes have been used. A muscle relaxant is required firstly to secure paralysis and secondly to maintain paralysis. The rate of onset of all the nondepolarizing neuromuscular blocking agents which are routinely available at present is similar; it takes about 3-6 min for a normal clinical dose to reach maximum effect. Maintenance of an adequate level of block is necessary, and it is usually helpful to the surgeon for the level of block to be relatively constant. The choice of drug is important. It should cause negligible side-effects. For administration by infusion, an agent with an intermediate (e.g., atracurium) or short (e.g., mivacurium) duration of action is essential to ensure a rapid recovery of effect on termination of the infusion. The routine use of neuromuscular monitoring is recommended when a continuous infusion of a relaxant is used.

Ambulatory Surgical Procedures↗
PubMed1995

Intubation conditions and time-course of action of low-dose rocuronium bromide in day-case dental surgery.

A relatively small dose of rocuronium (0.45 mg kg-1) was compared with equipotent doses of atracurium (0.35 mg kg-1) and vecuronium (0.075 mg kg-1) for ease of intubation at 60 s. All patients could be intubated but the proportion with excellent or good conditions was much greater with rocuronium. Mean clinical duration of effect of this dose was 22.2 min. There was no correlation between intubating conditions and the degree of block of the adductor policis.

Adult↗
PubMed1994

Recovery after oral surgery with halothane, enflurane, isoflurane or propofol anaesthesia.

We have compared the recovery characteristics of four different techniques for maintenance of anaesthesia in 99 day-case patients admitted for oral surgery. All patients received propofol for induction of anaesthesia followed by halothane, enflurane, isoflurane or propofol infusion for maintenance of anaesthesia. Each patient was subjected to a battery of psychometric tests which included Spielberger state, trait, mood stress and mood arousal questionnaires, Maddox-Wing test and five-choice serial reaction time. All tests were performed before operation and at 0.5, 1, 2, 4, 24 and 48 h after operation. Performance in the reaction time test decreased significantly in the immediate postoperative period, returning almost to preoperative values by 4 h. However, only those patients who received enflurane or propofol had returned to their performance level before surgery by 4 h, although all four groups had achieved this target by 24 h. There was a further improvement in performance at 48 h. Anxiety and stress were high before surgery and decreased rapidly in the postoperative period. The Maddox-Wing test demonstrated a significant impairment in performance in the first 1 h after surgery, which returned to normal by discharge at 4 h. There were no significant differences between the four groups in these latter tests.

Adult↗
PubMed1993

Haemodynamic effects of the position chosen for the insertion of an epidural catheter.

An epidural catheter may be inserted with the patient either in the flexed left lateral or the sitting position. We have studied, non-invasively, the haemodynamic changes associated with these positions, using the thoracic bio-impedance method (BOMED NCCOM3 Monitor). Maternal arterial pressure and fetal heart rate were monitored simultaneously. Twenty healthy pregnant patients at term and 20 non-pregnant healthy controls, matched for age and height, were studied. The pregnant patients were scheduled for elective caesarean section and had singleton healthy fetuses. A significant reduction in stroke index (SI) occurred when the pregnant patients were repositioned from supine 15degrees wedged position to either flexed left lateral (P < 0.01) or sitting positions (P < 0.05). Similar reductions in SI with positioning were observed in the non-pregnant patients: flexed left lateral (P < 0.01); and sitting (P < 0.01). These changes in SI produced significant reductions in cardiac index (CI) in both groups. In the pregnant patients the CI was significantly lower in the flexed left lateral than in the sitting position (P < 0.01). Consequently maternal systolic blood pressure was lower in the flexed left lateral position (P < 0.01).

Journal Article↗
PubMed1993

Extending a pipecuronium neuromuscular block. Increments of atracurium or vecuronium as an alternative to pipecuronium.

Ten patients received increasing doses of pipecuronium at induction of anaesthesia. A dose response relationship was then constructed from which ED90 and ED95 values were measured as 43.4 micrograms.kg-1 and 50.5 micrograms.kg-1 respectively. A further 30 patients received pipecuronium in a dose sufficient to produce greater than 90% neuromuscular block. When the first contraction of the train-of-four had returned to 10% of control, a small increment of atracurium (1.1 mg), vercuronium (0.25 mg) or pipecuronium (0.21 mg) was administered, and this was repeated subsequently using the same criterion of recovery on each occasion. The duration and intensity of the block with pipecuronium increments remained constant. The duration of the block following atracurium or vecuronium was progressively less with subsequent increments until steady state was reached. The final mean durations at steady state were pipecuronium 7.37 min, atracurium 6.99 min, and vecuronium 5.15 min.

Adolescent↗
PubMed1993

The onset of alcuronium and tubocurarine: alone and in combination.

The rates of onset of neuromuscular blockade have been measured following 0.25 mg.kg-1 alcuronium (ED95), 0.51 mg.kg-1 tubocurarine (ED95), a combination of 50% of the ED95 of each and a combination of 33% of the ED95 of each. Train-of-four stimulation of the ulnar nerve was used with recording of the amplitude of the evoked compound electromyogram from the thenar prominence. The rate of increase in blockade in patients receiving the 50% combination was significantly greater than for either agent given alone, or than for the 33% combination. The mean time to 75% block of the first contraction of the train (T1) with the 50% mixture was 90 s, significantly faster than alcuronium alone (132 s), tubocurarine alone (174 s) or the 33% mixture (127 s). These latter three groups did not differ significantly. In conclusion, the rate of onset of the 50% combination resulted in a more rapid onset of neuromuscular blockade, whereas the rate of onset of the 33% combination was no different to that of either drug alone. This small degree of acceleration with agents which are known to be markedly synergistic makes it unlikely that this technique will prove to be of clinical importance.

Adult↗
PubMed1993

The use of midazolam and flumazenil for invasive radiographic procedures.

This study has examined the use of flumazenil to improve recovery following sedation with midazolam in elderly patients undergoing invasive radiological procedures. Forty patients received either flumazenil or placebo in a randomized double-blind fashion following midazolam sedation. Nalbuphine 10-15 mg was given for premedication. All but one of the patients in the flumazenil group were fully awake immediately following the reversal agents compared to only one in the placebo group (P = 0.016). This statistically significant difference remained after 20 minutes (P = 0.029). There were no adverse effects on heart rate, blood pressure, forced expiratory volume in one second, vital capacity or oxygen saturation. The majority of patients (78% overall) could not recall their procedure. All patients said that they would be willing to undergo a similar technique in the future.

Aged↗
PubMed1992

Effect of physiotherapy on the auditory evoked response of paralysed, sedated patients in the intensive care unit.

Auditory evoked response (AER) was recorded before, during and after physiotherapy in 11 paralysed (atracurium 0.56 (SD) 0.13 mg kg-1 h-1), sedated (propofol 2.2 (1.0) mg kg-1 h-1; fentanyl 4.4 (2.3) micrograms kg-1 h-1) and critically ill patients undergoing ventilation in the intensive care unit (ICU). The latency of the negative wave, NB, was reduced by physiotherapy (mean 44.8 (SD) 7.9 ms before, 41.0 (6.8) ms during (P less than 0.01, non-parametric Friedman test) and 45.6 (6.3) ms after physiotherapy); NB amplitude showed no consistent change (-0.81 (1.4) microV, -0.81 (1.5) microV and -0.71 (1.3) microV, respectively). NB latency responded to patient arousal at constant levels of sedation and this requires further evaluation as a means of monitoring sedation in paralysed patients in the ICU.

Adult↗
PubMed1992

Effect of doxapram on neostigmine evoked antagonism of vecuronium neuromuscular block.

We have examined the effect of doxapram on neostigmine-evoked antagonism of vecuronium neuromuscular block in a double-blind study in anaesthetized patients. Neuromuscular transmission was measured with a Datex Relaxograph. The mean time to recovery of the first contraction of the train-of-four (T1) from 25% to 75% was significantly longer in the presence of doxapram (138 (SEM 21) s; n = 23) than in its absence (95 (13) s; n = 29) (P = 0.014). The recovery of the train-of-four ratio was prolonged also in the presence of doxapram, although this difference was not statistically significant.

Adult↗