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Biomedical subjects

D G McDowall

Publications and source records attributed to D G McDowall.

At least 19 recordsLinked to original sources
PubMed1986

Effect of high-dose dexamethasone on outcome from severe head injury.

The conflicting evidence concerning the influence of high-dose steroids on intracranial pressure (ICP) and outcome following severe head injury has led to the institution of the prospective double-blind controlled trial reported here. Severely head-injured patients admitted to intensive care during a 3-year period were randomly allocated to a dexamethasone- or placebo-treated group. Adults in the steroid group received dexamethasone, 50 mg intravenously, as a bolus on admission to the neurosurgical unit, then 100 mg on Days 1, 2, and 3, 50 mg on Day 4, and 25 mg on Day 5 on continuous intravenous infusion. Children received proportionate intravenous dosages calculated on a weight basis. Severity of head injury was assessed from admission Glasgow Coma Scale (GCS) scores and the appearance of the admission computerized tomography scan. Intracranial pressure (ICP) was monitored in all patients from the surface subarachnoid space. Outcome at 6 months was assessed using the Glasgow Outcome Scale. Steroid and placebo groups were similar in terms of admission GCS score, intracranial pathology, incidence of associated injuries, and time interval from injury to admission to intensive care. The ICP generally increased during the first 48 hours of intensive therapy; there was no difference in this trend between the steroid and placebo groups. A poorer outcome was observed in patients with elevated ICP who received steroids. No increase in the incidence of pulmonary, gastrointestinal, or other extracranial complications was seen in the steroid group. The 6-month outcome did not differ between the steroid and placebo groups. No advantage of high-dose dexamethasone on ICP trends or clinical outcome in the treatment of severe head injury has emerged from this study.

Adolescent↗
PubMed1985

Comparison of etomidate and althesin in the reduction of increased intracranial pressure after head injury.

The increasing use of shorter-acting hypnotic agents to control intracranial pressure (ICP) following severe head injury has prompted a prospective double-blind controlled trial comparing the efficacy of etomidate and Althesin, given by i.v. infusion. Over the dose ranges used, the two drugs appeared equipotent in decreasing ICP whilst preserving cerebral perfusion pressure. However, in two patients (one in each group) ICP did not respond to hypnotic infusion, a feature noted in other studies to occur in a minority of patients. With the cessation of Althesin manufacture and the discussion about the use of etomidate infusions, it is timely to document the effectiveness of etomidate in decreasing ICP.

Adolescent↗
PubMed1984

Assessment of Leeds device for monitoring intracranial pressure.

In Leeds a screw device is used to monitor surface subarachnoid pressure following severe head injury. The possibility that such measurements may under-read true intracranial pressure (ICP) has led to the development of an infusion test to confirm free communication with the surface subarachnoid space. The results of 69 infusion tests using 18 devices reveal that the device was reading accurately on 33 of 69 occasions. In 31 of the remaining 36, correction of the problem was possible. Particularly at ICP values exceeding 20 mm Hg the Leeds device may under-read, and possible causes for this are discussed. Reliable readings can usually be obtained using the infusion sequence described.

Brain Injuries↗
PubMed1983

Effects of 2% enflurane on intracranial pressure and cerebral perfusion pressure.

Ten patients with cerebral tumours were anaesthetized with thiopentone, 70% nitrous oxide in oxygen and fentanyl. Ventilation was controlled to give mean PaCO2 4.8 (range 3.6-6.7) kPa. Enflurane 2% was administered and ICP and MAP were recorded continuously for 10-15 min. The changes in ICP were not significant and ranged from -18.5 to 5.5 mm Hg. There were significant decreases in MAP (P less than 0.001) and CPP (P less than 0.001) during the administration of enflurane. In four patients the administration of enflurane had to be terminated prematurely because of a low CPP. Thus, enflurane has very little effect on ICP in patients with cerebral tumours and low concentrations of enflurane can safely be used during anaesthesia for intracranial operations, provided that the arterial pressure is monitored carefully.

Anesthesia, Inhalation↗
PubMed1983

Cerebral cortical extracellular fluid H+ and K+ activities during hypotension in cats.

Cerebral cortical blood flow, electrical activity, and extracellular fluid (ECF) pH and K+ ion activities were measured in anesthetized cats (0.7% halothane 65% N2O in O2) subjected to hypotension (mean BP 30-32 and 26-28 mmHg), induced by either practolol and trimetaphan (TMP) or practolol and nitroprusside (NTP). Limited blood withdrawal was also necessary to achieve these blood pressure (BP) levels. Cerebral cortical blood flow during hypotension was greater with NTP than with TMP, and hyperemia occurred in the recovery phase after NTP but not TMP. Electrical activity also was maintained better with NTP. ECF K+ increased in five of six TMP experiments but in only one of six NTP experiments. Values of K+ greater than 15 mM were only seen in the TMP group. Release of K+ into the ECF space occurred at values of cerebral cortical oxygen delivery below 3 ml 100 g-1 min-1. ECF K+ partially recovered after the end of hypotension in all except the experiment with the highest value. A progressive and severe cerebral acidosis was seen in all experiments during induced hypotension, and values below pH 6.50 were present at the stage of K+ increase in the ECF space. It is concluded that the ability of cell membranes in the cat's cortex to maintain normal ionic gradients is depressed by hypotension to these levels with TMP, but not with NTP, and that this difference is related to better-maintained oxygen supply values during NTP hypotension.

Animals↗
PubMed1983

Blood-brain barrier function following drug-induced hypotension in the dog.

To examine the effects of hypotension induced either with trimethaphan (TMP) or nitroprusside (NTP) on blood-brain barrier (BBB), penetration of Evans blue (EB) was observed in dogs anesthetized with halothane. Dogs given TMP were divided into two groups: Group 1, seven dogs rendered hypotensive to mean cerebral perfusion pressure (CPP) of 45 mmHg for 45 min and then of 30 mmHg for 45 min; Group 2, three dogs examined 3 days after arterial hypotension identical to that in Group 1. Dogs given NTP were divided into four groups: Group 1, seven dogs rendered hypotensive with NTP (at dose less than 1 mg/kg) identical to the TMP-Group 1; Group 2, three dogs examined as the TMP-Group 2; Group 3, seven dogs rendered hypotensive to CPP 45 mmHg for 45 min; Group 4, seven dogs rendered hypotensive with NTP (at dose greater than 1 mg/kg) identical to the NTP-Group 1. In all dogs, the dorsal cortical surface and standardized serial coronal sections were examined for evidence of EB penetration. The mean EB penetration score (+/- SEM) for TMP-Groups 1 and 2 was 12 +/- 6, 0 +/- 0, respectively, and for NTP-Groups 1, 2, 3, and 4 was 105 +/- 14, 30 +/- 7, 6 +/- 6, and 125 +/- 26, respectively. These results suggest that dysfunction of the BBB in the NTP group was more pronounced than in the TMP group.

Anesthesia↗
PubMed1983

Intensive management of severe head injuries. A scheme of intensive management of severe head injuries.

Seventy-six severely head-injured patients, 67% of whom had Glasgow Coma scores of five or less on admission, were managed according to an intensive treatment regime which included controlled hyperventilation (under full muscular paralysis), high-dose steroids, dehydrating agents, diuretics and hypnotics (Althesin and thiopentone). Intracranial pressure (ICP) was measured throughout the period of controlled ventilation. Treatment was directed to keeping the mean ICP below 25-30 mmHg and to the prevention of increases in ICP during chest physiotherapy and other noxious stimulation. Six months after injury 46% of patients had died and 4% were vegetative survivors, whilst 43% had made a good recovery or were only moderately disabled. Features associated with worse than average prognosis were: low coma score, pupillary abnormalities, respiratory dysrhythmia and ICP greater than 30 mmHg. Spontaneous hyperventilation was a relatively good initial feature. These results support the employment of intensive care in severely head-injured patients, particularly those with diffuse brain injury.

Adolescent↗
PubMed1982

Cerebral and systemic effects of hypotension induced by trimetaphan or nitroprusside in dogs.

The effects of hypotension induced by trimetaphan (TMP) or nitroprusside (NTP) together with controlled haemorrhage on cerebral electrical activity, cerebrospinal fluid pressure (CSFP) and systemic circulatory and metabolic variables were measured in 10 mongrel dogs anaesthetized with halothane (end-tidal, 0.88 +/- 0.03%). Induced hypotension was maintained at cerebral perfusion pressure (CPP) of 45 mmHg for 45 min and then at 30 mmHg for 45 min. In five TMP dogs, there were significant decreases in EEG-power and slowing of peak power frequency from the frontal area, but not from the occipital area. The CSFP did not change significantly except for an increase during the induction stage of hypotension. In five NTP dogs, there were no significant changes in EEG-power and peak power frequency throughout the study from either frontal or occipital areas, but CSFP increased significantly. With both drugs, an increase in glucose, lactate and lactate pyruvate ratio (L/P), and a decrease in PaO2 were more pronounced at 30 mmHg than 45 mmHg. With NTP, there were sustained increases in lactate and L/P, even after restoration of arterial pressure. The same magnitude and duration of the decrease in CPP induced by either TMP or NTP produced different effects on cerebral and systemic function.

Animals↗
PubMed1981

CO2 responses of the cerebral circulation during drug-induced hypotension in the cat.

Concern has often been expressed that hypocapnia produced by controlled hyperventilation might further reduce cerebral perfusion during drug-induced hypotension. In the present studies, hypotension was induced in cats with either practolol/trimetaphan (five experiments) or practolol/nitroprusside (five experiments) together with controlled haemorrhage. Arterial PCO2 was altered between 17 and 51 mm Hg by varying inspired CO2 during constant-volume ventilation, first during control conditions of light halothane/nitrous oxide anaesthesia and then during hypotension to mean blood pressure of 36-37 mm Hg. Cerebral cortical perfusion was measured by the krypton clearance technique and pial artery diameter by the image-splitting method. Cerebral cortical blood flow did not alter with PaCO2 changes during trimetaphan hypotension, but some responsiveness to CO2 persisted during nitroprusside hypotension, though at less than half control levels. No changes in pial artery diameter were seen with CO2 during hypotension under either technique. It is postulated that CO2 responsiveness persisted with nitroprusside because cerebral blood flow (CBF) values were higher when hypotension was produced with this drug, as compared with trimetaphan. It would appear that hypocapnia does not further reduce CBF during trimetaphan hypotension but does do so with nitroprusside. However, the combination of hypocapnia and nitroprusside hypotension did not in any instance lower CBF below the values found during trimetaphan hypotension.

Animals↗
PubMed1981

Electrical activity of the cerebral cortex during induced hypotension with sodium nitroprusside and trimetaphan in the cat.

A comparison of the blood flow and electrical power and an area of parietal cortex has been made in cats subjected to controlled hypotension induced with either practolol and trimetaphan or practolol and nitroprusside. In both groups it was necessary also to remove blood to achieve the required low values of arterial pressure (AP). It was found that cerebral cortical blood flow was significantly greater at mean AP of 40, 35 and 30 mm Hg during nitroprusside (NTP) as compared with trimetaphan (TMP) hypotension. The total power in the e.e.g. as assessed by the cerebral function monitor (CFM) was less depressed at mean AP 35 and 30 mm Hg during NTP hypotension. Even at mean AP 26 mm Hg with NTP, electrical power, although significantly reduced, was still 66 +/- 3% of control values. Correlation of cortical blood flow with CFM activity indicated that electrical power tended towards zero at flow values of 20-25 ml min-1 per 100 g. It is concluded that, in the parietal cortex of the lightly-anaesthetized cat, cortical blood flow and electrical power are better-maintained when hypotension is induced with NTP than with TMP.

Animals↗
PubMed1980

Effect of low concentrations of halothane on the oxygen electrode.

The effect of low concentrations of halothane dissolved in saline (equivalent to 0.34% halothane) on the oxygen electrode was examined using a multi-wire Clark type electrode, consisting of eight platinum wires, each of 15 microns tip diameter. On the first exposure of the day to saline equilibrated with halothane in 10% oxygen or air, the output of the oxygen electrode increased by 40% over 56 min. On the second and subsequent exposures the increase in output was much less, but was still 10% greater than the correct values. After immersing the electrode overnight in saline without halothane the high sensitivity to halothane was present again next morning, even if neither membrane nor electrolyte was changed.

Blood Gas Analysis↗
PubMed1980

The use of anesthetic drugs to reduce ICP changes in head-injured patients.

Chest physiotherapy causes increases in intracranial pressure (ICP) in patients with severe head injuries. In mechanically hyperventilated severe head injuries (PaCO2 3.3 - 4 kPa) 50% nitrous oxide in 50% oxygen exacerbated ICP increases associated with chest physiotherapy, while thiopentone and Althesin reduced these changes in ICP.

Alfaxalone Alfadolone Mixture↗
PubMed1980

A comparison between sodium nitroprusside and trimetaphan-induced hypotension.

Hypotension induced with nitroprusside is compared with the same degree of hypotension produced by trimetaphan in terms of cerebral perfusion, oxygenation and brain electrical activity. It is concluded that in all these respects nitroprusside has advantages over trimetaphan. On the other hand, nitroprusside increases intracranial pressure whilst trimetaphan does not. Both these drugs have a place in hypotension for neurosurgery.

Animals↗