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Biomedical subjects

A Holdcroft

Publications and source records attributed to A Holdcroft.

At least 55 records · Page 3Linked to original sources
PubMed1994

Ventilation techniques to minimize circulatory depression in rabbits with surfactant deficient lungs.

Changes in aortic blood flow were measured in rabbits with both normal and surfactant depleted lungs in order to elucidate the effect of different modes of ventilation on the circulation while optimizing arterial oxygenation (PaO2). Conventional mechanical ventilation (CMV), reversed inspiratory to expiratory ratio of CMV (IRV), high frequency positive pressure ventilation (HFV), and high frequency oscillation (HFO) were used. Normocapnia was maintained throughout during different modes of ventilation. In normal lungs the aortic blood flow during IRV was significantly lower with similar levels of PaCO2 compared with CMV, HFV, and HFO. In lavaged lungs, without positive end-expiratory pressure (PEEP), the aortic blood flow during CMV was significantly higher than with other modes of ventilation. When 10 cm H2O of PEEP was applied, the PaO2 increased maximally to normal values at all modes of ventilation, but the aortic blood flow was significantly reduced (P < 0.05) during CMV and IRV compared to HFV and HFO. The aortic blood flows at 5 cm H2O of PEEP were very similar during CMV, HFV, and HFO but significantly reduced during IRV. This study showed that at an optimal arterial oxygenation with higher PEEP levels, maintenance of aortic blood flow was maximal during HFV and HFO.

Animals↗
PubMed1994

Acute tissue damage following epidural cannulation: a comparison between the midline and paramedian approach in obstetric patients.

Forty obstetric patients were randomly allocated to receive either a midline or paramedian approach to the epidural space using loss of resistance to air. Tissue trauma was assessed by blinded observers, clinically by the presence of pain and radiologically using magnetic resonance imaging (MRI). Technical difficulties with imaging reduced those who were scanned to 10 in the paramedian group and 8 in the midline group. Lateralizing signs of tissue oedema were not related to the method of epidural cannulation. There was no significant difference in localized back pain between the two groups, and this was not related to MRI findings. Pain did not persist for more than 4 days.

Journal Article↗
PubMed1993

Cardiorespiratory effects of conventional and high frequency ventilation in rabbits with bilateral pneumothoraces and surfactant depleted lungs.

We compared high frequency ventilation (HFV) to conventional mechanical ventilation (CMV) under normoxic and normocapnic condition in surfactant depleted rabbits with bilateral pneumothoraces. We hypothesized that lower airway pressures would be required with HFV under these conditions. We applied CMV and HFV in 8 anaesthetized rabbits with a prototype ventilator at frequencies of 30, 100, 200, and 300 cycles/min. A positive end-expiratory pressure (PEEP) just below the pressure sufficient to open the air leak from the pneumothoraces was applied at all frequencies. Airway pressures, gas exchange, heart rate, and mean arterial pressure were recorded. Peak airway pressure decreased significantly from 2.50 to 2.10 kPa when the frequency of ventilation was increased from 30 to 300 cycles/min. There were no significant changes in mean airway pressure, PaO2, arterial pH, heart rate, and mean arterial pressure when HFV was compared to CMV. In conclusion, during HFV peak airway pressures measured at the mouth were decreased. Our ability to maintain adequate gas exchange in the face of ongoing pulmonary air leaks may reflect lower alveolar pressures.

Animals↗
PubMed1993

Differential effects of alfentanil, fentanyl, pethidine and lignocaine administered intrathecally on nociceptive responses evoked by low and high frequency stimulation of somatic nerves.

We have studied in anaesthetized dogs the effects of alfentanil, fentanyl, pethidine and lignocaine administered intrathecally on nociceptive responses evoked by low and high frequency supramaximal electrical stimulation of the tibial and radial nerves. Doses were selected to abolish both A delta and C fibre somatosympathetic reflexes to single stimuli. Pethidine and lignocaine eliminated reflex pressor and heart rate responses to repeated single stimuli and almost completely abolished responses to train stimulation. The pressor response to single stimuli was abolished by fentanyl and reduced by alfentanil, but these drugs did not reduce significantly this response to train stimulation, suggesting a stimulation rate-dependent effect. Of the opioids, only pethidine had an effect comparable to that of lignocaine. The absence of sympathetic block and antagonism by naloxone imply a lack of significant local anaesthetic effect. We suggest that the greater analgesic efficacy of pethidine is a result of endogenous synergism between a minor local anaesthetic and a major opioid effect.

Alfentanil↗
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↗
PubMed1980

Methohexitone or etomidate for induction of dental anaesthesia.

Ninety-two patients who presented for outpatient dental extractions received methohexitone (1.5 mg . kg-1, 46 patients) or etomidate (0.3 mg . kg-1, 23 patients and 0.2 mg . kg-1, 23 patients). The induction characteristics of both drugs such as pain on injection, involuntary muscle movements and respiratory difficulties were comparable and the theoretical disadvantages of etomidate for dental anaesthetics did not prove troublesome in practice. Muscle movements did not interfere with the dentists' manipulations and pain on injection into veins of the antecubital fossa did not occur. The duration of operation for up to four extractions was three minutes and, following induction, anaesthesia was maintained with nitrous oxide, oxygen and halothane. Recovery was assessed by grading consciousness, airway control and motor activity. All the patients could maintain their airways one minute after the end of operation. The incidence of nausea and vomiting was significantly greater in the etomidate group.

Adolescent↗
PubMed1980

Comparison of thiopentone and methohexitone as induction agents for Caesarean section.

Anaesthesia was induced with equipotent doses of either thiopentone or methohexitone in 127 women undergoing Caesarean section. They divided into three groups: those having normal placental function, those with an undefinable degree of placental insufficiency, and emergencies. There was no clinical or biochemical difference in the neonates following induction of anaesthesia with either thiopentone or methohexitone. The clinical condition of neonates born of mothers with normal placental function was superior to the other two groups.

Anesthesia, Intravenous↗
PubMed1980

Outpatient preoperative assessment: the anaesthetist's view.

The functions of an outpatient anaesthetic clinic are discussed in relation to the first 100 patients who attended. Preoperative assessment excluded 11 patients who would have been refused anaesthesia for elective operations without further treatment. Six of these required preoperative physiotherapy, 4 antihypertensive therapy, and 1 hospital admission for incipient myocardial infarction. The clinic also played an important role with regard to advice and reassurance of the patient from an experienced anaesthetist, organising suitable admission dates, and detecting anaesthetic and surgical hazards, especially dental caries and obesity, which could be corrected before operation. Two patients developed postoperative complications which could not have been foreseen.

Anesthesiology↗
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↗