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Biomedical subjects

A Holdcroft

Publications and source records attributed to A Holdcroft.

At least 19 recordsLinked to original sources
PubMed1992

Density of intrathecal agents.

The density of a drug in solution cannot be determined from a simple formula or from physicochemical tables, because it depends on the physical state of that substance in solution. The densities of agents which have been reported to be administered by the intrathecal route were measured at room and body temperatures. The results were compared with the density of cerebrospinal fluid. At room temperature, most drugs were isobaric with respect to cerebrospinal fluid, but as drugs warmed to body temperature they became relatively hypobaric.

Analgesics, Opioid↗
PubMed1992

Use of adrenaline in obstetric analgesia.

A questionnaire on the use of adrenaline in obstetric analgesia was completed by 87 obstetric anaesthetists: 71% of consultants in teaching hospitals were prepared to use adrenaline mixed with local anaesthetics compared with 33% of consultants in district hospitals; they had a similar duration of obstetric anaesthetic experience. Test doses containing adrenaline were not commonly used in labour, but were more often used prior to elective Caesarean section. Adrenaline was used with either lignocaine or bupivacaine; few consultants used both solutions. Contraindications to the use of adrenaline in the nonuser group were in decreasing order of rank: neurological damage, pregnancy-induced hypertension, stenotic valvular heart disease, sickle cell disease or trait of fetal distress. Overall, the contraindications related to the systemic absorption of adrenaline were most common.

Analgesia, Obstetrical↗
PubMed1991

The Alton Dean pressure infusor: an evaluation.

An automatically pressurised infusor system, the Alton Dean infusor, has been compared with two types (cloth and plastic) of commonly used pneumatically pressurised bags. All the infusors had reasonably accurate pressure gauges but pressure could only be consistently maintained with the cloth infusors or with the Alton Dean infusors when connected to a compressed air supply. Sequential fast infusions were possible with all infusors, but simultaneous infusions could be limited in number when the pressure infusor was connected directly to pipeline gas. One of the Alton Dean pressure infusors tested had a leak in the pressurisation system, and the pressure adjustment valves were difficult to manipulate. These may require modification.

Evaluation Studies as Topic↗
PubMed1990

A new infant oscillatory ventilator.

A new, simple and inexpensive oscillatory ventilator is described in which a rotating jet mounted in the breathing duct generates cyclically positive and negative pressures in the airway with a sinusoidal flow waveform. Unlike conventional oscillatory ventilators it is free from restrictions to inspiratory or expiratory gas flows and open to atmosphere at all times, making it intrinsically a safe system for ventilation. A prototype rotating jet oscillatory ventilator designed for application in infants was evaluated in rabbits (mean weight 3.8 kg). The positive peak and mean airway pressures were significantly less during oscillatory ventilation at 300 and 420 b.p.m. compared with normal and high frequency positive pressure ventilation at 30 and 300 b.p.m., respectively, while maintaining blood-gas tensions within the normal range. An increase in the oscillatory frequency from 300 to 420 b.p.m. provided no further benefit in terms of airway pressure, tidal volume or blood-gas tensions.

Animals↗
PubMed1990

Epidural anaesthesia and von Willebrand's disease.

A case is described of a primiparous patient with Von Willebrand's type 1 disease and diabetes who presented at 36 weeks' gestation for Caesarean section. This was performed under epidural anaesthesia in the absence of any coagulation disorder. The effects of pregnancy on coagulation factors in this disorder are discussed.

Anesthesia, Epidural↗
PubMed1990

A low flow open circle system for anaesthesia. Part I: Laboratory evaluation at normal and high frequencies.

A circle breathing system was connected by deadspace tubing to an open system valveless ventilator. The minimum volume of this tubing, required to prevent dilution of anaesthetic gas in the breathing system by the driving gas of the ventilator, was determined at frequencies of 15, 30, 60, 100 and 150 breaths/minute, with tidal volumes that ranged from 100 to 1100 ml and a fresh gas supply to the circle system of 1, 2 and 4 litres/minute. At 15 breaths/minute, tidal volumes equal to or less than the deadspace volume could be used safely without any mixing with the ventilator driving gas, when a fresh gas flow of 2 litres/minute or above is supplied to the circle system. At 1 litre/minute of fresh gas flow, mixing occurred at tidal volumes less than the deadspace volume. Mixing of gas occurred in the system at frequencies greater than 30 breaths/minute even when the tidal volume was much less than the deadspace volume. However, at high frequencies of ventilation, since the tidal volume requirement decreases, deadspace tubing with a safe internal volume, that is greater than 600 ml, may be used up to 100 breaths/minute.

Anesthesia, Closed-Circuit↗
PubMed1990

A low flow open circle system for anaesthesia. Part 2: Clinical evaluation.

A prototype valveless ventilator was attached by open deadspace tubing to a circle system and used to ventilate the lungs of 12 patients with low flows of anaesthetic gases for periods between 60 and 120 minutes during intra-abdominal surgery. Anaesthesia was induced with thiopentone and maintained with nitrous oxide 50% in oxygen and enflurane. This was reduced to 2 litres/minute after a 10-minute period of nitrogen wash out and stabilisation of anaesthetic gas concentration, with an initial anaesthetic gas flow of 6 litres/minute. The concentration of oxygen, carbon dioxide, nitrous oxide and enflurane were measured in the outflow from both the anaesthetic machine and the inspiratory limb of the circle system. The measured mean inspired oxygen and nitrous oxide concentrations showed no significant variation throughout the low flow period of the study. This new low flow open circle ventilation system appears to offer some advantages in terms of safety and versatility over other systems which are discussed.

Adult↗
PubMed1989

Circulatory depression with high peep in the surfactant-deficient rabbit.

Surfactant depletion was induced by lung lavage in 10 rabbits. Ascending aortic blood flow was measured at normocapnia at 0, 5 and 10 cm H2O PEEP before and after lavage. Aortic blood flow was reduced by PEEP, by a maximum of 24% before lavage and 60% after lavage. It was concluded that, although adequate arterial oxygenation can be maintained with 10 cm H2O PEEP in surfactant-depleted rabbit's lungs, the circulatory impairment may result in inadequate oxygen delivery.

Animals↗
PubMed1979

Epidural analgesia and the metabolic response to surgery.

The effect of epidural blockade on the metabolic and hormonal responses to pelvic surgery was investigated in 14 female patients. Central venous blood samples were collected every 30 minutes and analysed for free fatty acids, glycerol, beta-hydroxybutyrate, acetoacetate, glucose, lactate, pyruvate, cortisol and growth hormone concentrations. There was no change in fat and glucose metabolism except for a transient decrease in lipolysis after 30 minutes of surgery. Cortisol and growth hormone values were significantly increased (p less than 0.01) after 60 minutes. A small but statistically significant increase in blood lactate concentration was observed (p less than 0.01) and the concept of a "metabolic V/Q" abnormality is postulated to explain the lacticacidaemia.

Adult↗
PubMed1979

The ocular effects of etomidate.

Etomidate, a new intravenous hypnotic agent, significantly lowered the mean intraocular pressure (IOP) of fifty patients within 30 s of an intravenous injection from 15.7 to 9.5 mmHg. This effect was present even during the administration (to twenty patients) of low doses (0.25 mg/kg) when the mean reduction was from 15.6 to 7.6 mmHg. The reduction in IOP was unaffected by the presence of muscle movement. Low frequency pendular nystagmus was observed in five patients.

Adolescent↗
PubMed1979

Redistribution of body heat during anaesthesia. A comparison of halothane, fentanyl and epidural anaesthesia.

Epidural anaesthesia and high dose fentanyl (50 micrograms/kg) when used to supplement nitrous oxide and oxygen anaesthesia for a standard lower abdominal operation were associated with a mean fall in deep body temperature, as measured in the external auditory meatus, of 0.46 degrees C and 0.6 degrees C/hr respectively. This is significantly different from the mean values of 0.14 degrees C and 0.2 degrees C/hr which were recorded when moderate dose fentanyl (10 micrograms/kg) or 0.5% halothane were used to supplement anaesthesia. When mean skin temperature is combined with the core temperature to provide an estimate for total body heat, there is no difference between the groups. Redistribution of body heat occurs and this may be related to reduced adrenergic stimulation and altered regional blood flow. Where the facilities and environments are inadequate for the maintenance of normothermia, care should be taken in the choice of anaesthetic technique. In the recovery period mean body heat gain showed a wide scatter of results but those patients receiving epidural anaesthesia were slow to rewarm despite a high incidence of shivering in this group. The implications of this are discussed.

Adult↗
PubMed1978

Heat loss during anaesthesia.

The superficial and deep body temperatures of 23 patients were studied during prolonged anaesthesia for microscopic surgery of the fallopian tubes. The patients were divided randomly into three groups, receiving either halothane 0.5%, halothane 1% or low-dose fentanyl as a supplement to nitrous oxide, oxygen and myoneural block. Other variables were kept constant, and the theatre temperature was maintained at 24 degrees C. Temperature changes were unrelated to both the type of anaesthesia and the percentage of subcutaneous fat to body weight. Halothane 1% decreased the rate of heat loss in the 3rd hour. Large heat losses occurred on transfer to the recovery room, where the total heat produced increased rapidly and was unrelated to shivering.

Adult↗
PubMed1977

Airway closure and pregnancy.

During pregnancy there is a fall in functional residual capacity and expiratory reserve volume. The point of airway closure in relation to vital capacity and the expiratory reserve volume was determined in 11 post-partum patients who had previously been studied during pregnancy. The lung volume at which airway closure occurred in pregnancy and the post-partum period did not change in relation to the vital capacity whereas the expiratory reserve volume did, so that airway closure became imminent in the pregnant women during tidal ventilation, especially whilst in the suping position. The significance of this alteration in pulmonary function to obstetric anaesthesia is discussed.

Adult↗