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Biomedical subjects

W A Tweed

Publications and source records attributed to W A Tweed.

At least 55 records · Page 3Linked to original sources
PubMed1983

The effect of halothane anaesthesia on the asphyxiated foetal lamb in utero.

In a previous study, we examined the effects of halothane on the normal foetal lamb in utero. The most significant finding was a 33 per cent fall in foetal mean arterial blood pressure (MABP). Cardiac output and placental blood flow were not affected. To determine if the asphyxiated foetus would respond similarly, the following study was performed. Seven pregnant ewes were surgically prepared two days prior to study with maternal and foetal indwelling arterial and venous cannulas. An inflatable occlusion loop was secured around the umbilical cord. On the day of study, a tracheostomy was performed on each ewe. Microspheres were injected into the foetal circulation during the control period. The occlusion loop was inflated to produce foetal asphyxia and microspheres were again injected. The ewe was then anesthetized with halothane; and after 15 minutes, microspheres were injected into the asphyxiated foetus and halothane levels were measured. The asphyxiated foetuses showed a significant rise in MABP, fall in heart rate and fall in cardiac output from control. Blood flow to the brain was significantly increased and flow to the placenta and gut decreased. Exposure of the asphyxiated foetus to halothane resulted in a fall of MABP to control but no significant change in cardiac output or brain blood flow. The mean halothane level in the foetus was 46.0 mg X l-1 or 0.32 vol%. Exposure of the asphyxiated foetus to halothane for 15 minutes does not produce significant further deterioration of the foetal lamb in utero.

Acid-Base Equilibrium↗
PubMed1983

The esophageal obturator airway: an appraisal.

The use of the Esophageal Obturator Airway (EOA) was prospectively studied in 300 cases of prehospital cardiac arrests. Seventy-seven complications were documented in 72 patients. Inadvertent tracheal intubation occurred in 72 patients. Inadvertent tracheal intubation occurred in 13 patients, five unrecognized. No differences were found when initial emergency room rhythm and resuscitation outcome were compared to a previous study using the oral airway (OA). A subgroup of 124 EOA and 55 OA patients were compared. The EOA was effective in reducing the frequency of aspiration (17 vs 34 per cent). Arterial oxygenation was similar, and rose in both groups following tracheal intubation. Esophageal trauma was found in 10 per cent of the EOA patients who underwent autopsy. Although the EOA is useful in prehospital emergency care, the only advantage for this technique in comparison to the OA is the prevention of aspiration of gastric contents. It also appears that other techniques of advanced cardiac life support, i.e. defibrillation, drug therapy, etc. are necessary to improve survival statistics.

Emergency Medical Services↗
PubMed1983

Prehospital cardiac rhythm deterioration in a system providing only basic life support.

Access to an ambulance service trained to provide only basic cardiac life support (BCLS) and adjunctive ventilation with oxygen provided the opportunity to study cardiac rhythms during BCLS in patients with circulatory arrest. Holter monitoring was attempted in 43 patients. Technically adequate traces throughout transport to hospital were obtained in 21. The average monitored time was 11.9 minutes. A tachydysrhythmia (mainly VF/VT) was initially found in 10, heart block or bradycardia in 9, and asystole in 2 persons. During BCLS, six patients with bradycardic rhythms converted temporarily to VF. The first ECG tracing obtained in the hospital revealed, however, that only five were still in a tachydysrhythmia and 15 were asystolic. These data demonstrate that important rhythm changes occur when BCLS is continued for several minutes during circulatory arrest. Although some bradycardic rhythms convert to VF, the VF is not sustained. After an average of 12 minutes, 90% of those initially in bradycardic rhythm and 50% of those initially in VF/VT were asystolic. This study provides further evidence that BCLS does not prevent cardiac deterioration.

Ambulances↗
PubMed1983

CPR skills retention of lay basic rescuers.

In 1979-1980, 950 telephone company personnel were trained and tested at the basic rescuer level on recording manikins. In October 1981, a random group of 40 were retested without warning on the recording manikin. Skills retention was measured by comparing the tapes from training and retesting. Sixteen (40%) of those retested were able to perform effective ventilations and compressions of the manikin with 60% to 70% average retention compared to their training scores. The remaining 24 (60%) had ineffective ventilations or compressions or both. The two groups did not differ in the performance level achieved during training, or in the time interval between training and retesting. Eleven individuals retested at 13 to 14 months did not perform better than those retested later, suggesting the maximum skills deterioration had occurred within the first year. However, the effective performance group on the average were younger, and the majority had first aid training in addition to their CPR training. Only one had CPR retraining. This study supports the following recommendations: 1) lay basic rescuers should be retrained within the first year; 2) further studies of the factors influencing retention are advisable; 3) the younger age groups should be the first priority for citizen CPR training; and 4) because first aid training appears to improve CPR retention, training in both should be encouraged.

Adult↗
PubMed1983

Arterial oxygenation determines autoregulation of cerebral blood flow in the fetal lamb.

We examined autoregulation of cerebral blood flow (CBF) over the range of oxygen tension commonly observed in the chronic fetal lamb preparation. Seventeen animals were surgically prepared under general anesthesia for chronic in utero studies. Based on measured resting arterial PO2 and calculated % saturation 24-48 h after surgery, two groups were defined: a normoxic group of eight with saturation of 57% or higher (our laboratory normal for physiologically stable preparations) and an hypoxic group of nine with saturation less than 57%. Regional CBF was measured with radiolabeled 15-microns microspheres. Autoregulation of CBF was assessed by measuring the change in CBF when fetal mean arterial blood pressure (MABP) was acutely decreased and increased by withdrawal and reinfusion of fetal blood. In normoxic animals CBF was constant over an MABP range of 42-61 torr in all four areas of the brain examined: cerebral hemispheres, basal ganglia, cerebellum, and brain stem. In hypoxic animals CBF was pressure dependent in all areas over an MABP range of 46-73 torr, i.e., autoregulation was abolished. These studies demonstrate that the mechanism of autoregulation is functionally developed in the mature fetal lamb, but operationally dependent upon arterial oxygen concentration. Below a saturation of approximately 50-60% CBF varies directly with perfusion pressure.

Animals↗
PubMed1983

Cerebral circulation after head injury. Part 4: Functional anatomy and boundary-zone flow deprivation in the first week of traumatic coma.

A considerable body of evidence suggests that posttraumatic disturbances of the cerebral circulation contribute to poor neurological outcome after blunt head injury, especially when regional cerebral blood flow (rCBF) falls to the ischemic range (below 17 ml/100 gm/min). Cerebral infarction concentrated in the arterial boundary regions has been described in patients who died. Since arterial boundary zones are the cortical areas most susceptible to cerebral ischemia, the authors have investigated the relationship between neurological outcome and the anatomic pattern of rCBF values in the acute phase. The bolus-injection xenon-133 washout technique was used to measure rCBF in 35 regions of the hemisphere during the 1st week after head injury. Eighty-eight hemispheres were studied in 80 patients whose Glasgow Coma Scale (GCS) score was less than 8 on admission to the neurosurgical department. A characteristic pattern of rCBF was found in patients who later died of neurological complications, or who survived in a persistent vegetative state, with low flows in regions conforming to the arterial boundary zones. These patients also had lower average global cerebral blood flow (CBF), GCS scores, and cerebral perfusion pressure compared with those who recovered, with or without neurological deficits; the latter group had an rCBF pattern similar to that of normal individuals. There was little change in the GCS score between the time of hospital admission and CBF measurement, suggesting that the major neurological injury had occurred prior to admission. It was not possible to determine whether boundary-zone ischemia preceded neurological deterioration, but the rCBF pattern of boundary-zone flow deprivation was clearly related to poor neurological outcome. These observations suggest that elevated intracranial pressure and arterial hypotension were important etiological factors. Measures to protect regional cerebral perfusion should be instituted as early as possible after injury, preferably before the patient reaches the hospital.

Arteries↗
PubMed1983

Effect of halothane on cardiac output and regional flow in the fetal lamb in utero.

We studied the effect of halothane on the fetal cardiovascular system of six lambs in utero by measuring fetal heart rate and femoral arterial blood pressure and by injecting labeled microspheres during a control period and again after 60 and 90 min of halothane anesthesia administered to six pregnant ewes at an inspired concentration of 1.5%. There were no significant effects on maternal cardiovascular function or acid-base balance, but fetal blood pressure decreased significantly by 27% after 8 min of halothane anesthesia and remained at this level for the duration of the experiment. However, there were no significant changes either in fetal regional blood flow to the vital organs or in fetal cardiac output. Fetal oxygenation and acid-base status remained stable. We conclude that in normal fetal lamb in utero the decrease in mean fetal arterial blood pressure associated with maternal halothane anesthesia is due to a decrease in peripheral vascular resistance because regional blood flow and acid-base status are well maintained.

Anesthesia, Inhalation↗
PubMed1982

Appraisal of pediatric cardiopulmonary resuscitation.

Sixty-six patients more than 30 days and less thant 16 years of age suffering an unexpected cardiac arrest in an 18-month period were included in a study of resuscitative measures in children. Six children survived to be discharged from hospital. Respiratory disease accounted for most (29%) of the cardiac arrests, but it also had the most favourable prognosis, 21% of the 19 patients surviving. None of the patients survived whose cardiac arrest was secondary to sepsis or trauma, even when the resuscitative efforts were initially successful. Only 1 of the 41 patients who had a cardiac arrest outside of hospital survived, and only 1 of the 34 patients who presented with asystole survived, and then with considerable damage to the central nervous system. The interval between cardiac arrest and application of basic life support was substantially shorter among the survivors. Also, most of the survivors did not present with asystole. The results of this study suggest that survival among resuscitated children is no better than that among adults but can be improved with early recognition and monitoring of children at risk. earlier application of basic and advanced life support, improved education of medical and lay personnel, and further research into pediatric resuscitative techniques.

Adolescent↗
PubMed1982

Prognosis after cardiac arrest based on age and duration of coma.

In an attempt to determine the relation between duration of coma and neurologic recovery following cardiac resuscitation 163 survivors of cardiac arrest from Winnipeg, Manitoba and Aarhus, Denmark were studied. The age of the patients did not influence the outcome. Of the 153 patients who had awakened from the coma within 24 hours, only 11 suffered brain damage, compared with all of the 10 patients who wakened after 24 hours. The three who wakened after 72 hours had severe brain damage and required permanent care in an institution. It was concluded that recovery of communicative brain function is unlikely if coma persists longer than 72 hours after cardiac arrest and that full recovery cannot be expected after 24 hours of coma.

Adult↗
PubMed1982

Pre-hospital analgesia with Entonox.

Pre-hospital self-administered analgesia using a 50:50 mixture of nitrous oxide and oxygen (Entonox) was evaluated in 240 patients. Of these, 93.4 per cent experienced either complete or partial relief from traumatic, chest, abdominal or back pain. Drowsiness was the most common side effect noted. No complications occurred during delivery of the mixture. Attention is drawn to the effect of extreme temperatures on the Entonox mixture and recommendations are made with respect to its use below-freezing climates. Because of its ease of use and short duration of action, Entonox appears to be well suited for the treatment of pre-hospital pain by Emergency Medical Technicians.

Adolescent↗
PubMed1982

Preservation of fetal brain blood flow relative to other organs during hypovolemic hypotension.

The asphyxiated newborn is particularly vulnerable to hypotension, which contributes to hypoxic brain damage by reducing cerebral perfusion. During asphyxia, cerebral blood flow (CBF)( is pressure passive, that is, CBF autoregulation is abolished. It is important to know if the nonasphyxiated fetus and newborn are similarly vulnerable to hypotension. In the present study, we have measured acute responses of organ blood flow to a hypovolemic/hypotensive stress in the normoxic near term sheep fetus. Changes in brain flow were compared to changes in other organs. Eight chronically prepared fetal lambs were studied. Organ blood flows were measured by the microsphere technique during a control period, after a 20% blood volume reduction, and again after reinfusion of that volume. Hypovolemia was accompanied by a 21% decrease in blood pressure and a 4 torr increase in PCO2; after reinfusion blood pressure increased 16% above control. Control measurements of organ perfusion were similar to those reported by other investigators. Cardiac output and flow to all organs, with the exception of the brain, were reduced 30-56% during hypovolemia. Brain blood flow was insignificantly reduced by 9%. If a correction is applied for the increase in PCO2, CBF corrected to control PCO2 would have have been significantly reduced by 18%. After reinfusion, flow to all organs increased to near control levels. We conclude that the normoxic fetal lamb shows evidence of CBF autoregulation, and is able to preserve relative constancy of CBF within a blood pressure range of +/- 20% of normal. However, the evidence presented in this study suggests that autoregulation may be less effective in response to a hypotensive stress, even though CBF is better preserved than flow to most other organs.

Animals↗
PubMed1981

Cerebrovascular mechanisms in perinatal asphyxia: the role of vasogenic brain edema.

Previous studies from our laboratory have demonstrated penetration of Evan's blue dye into the brain in profound fetal asphyxia, suggesting that vasogenic brain edema (BE) might be an immediate contributing factor in asphyxial brain injury. We modified the 125I-labeled albumin method of Pappius and McCann to quantitate vasogenic BE after acute fetal asphyxia. With 51Cr-labeled red cells to measure intravascular volume, and 125I-labeled albumin to measure total tissue plasma, the equivalent extra vascular plasma volume, i.e., vasogenic BE, was calculated. Twenty chronically prepared animals were studied, six nonasphyxiated controls and 14 asphyxiated (of which sex term animals were normotensive and five term and three premature animals were hypertensive during asphyxia). No difference in extra vascular plasma volume was found between asphyxiated and control animals in any of four brain regions. We conclude that, although blood brain barrier function might be impaired, vasogenic BE is not quantitatively significant immediately after severe fetal asphyxia.

Animals↗
PubMed1980

Resuscitation from cardiac arrest: assessment of a system providing only basic life support outside of hospital.

Resuscitation outside of hospital of victims of cardiac arrest is a major challenge to our emergency care system. Most cities in Canada do not have a mobile advanced life support service; instead they rely on basic life support outside of hospital. The outcome in such cases and the factors affecting the outcome are largely unknown. Thus, it is difficult to estimate the lifesaving potential of adding advanced life support to the existing measures available for care outside of hospital.A prospective study of all resuscitation attempts begun outside of hospital was conducted during 18 consecutive months in 1977-78 in Winnipeg; at that time only basic life support was available outside of hospital. Resuscitation was attempted 849 times, and 33 patients (4%) survived to be discharged from hospital. Data analysis revealed that: (a) none of the 58% of patients in asystole at the time of arrival at a hospital survived to be discharged, but 11% of the patients with ventricular fibrillation or tachycardia (27% of the entire group) survived; (b) the survival rate was lower when the interval from the emergency telephone call to the patient's arrival at the hospital exceeded 10 minutes; and (c) basic life support was begun immediately in 29% of the patients with ventricular fibrillation or tachycardia, and increased the survival rate fivefold.The training of private citizens in basic life support is a vital component of total emergency cardiac care. A mobile advanced life support service will be effective in saving lives if it reduces the delay before definitive care is instituted, preferably to less than 10 minutes.

Ambulances↗
PubMed1980

Evaluation of hospital-based cardiac resuscitation, 1973--77.

The resuscitation experience of a large teaching hospital during 1973-77 was reviewed. Resuscitation was attempted on 2091 victims of cardiac arrest; 261 patients (12.5%) survived to be discharged from hospital.Coronary heart disease caused about one half of all the cardiac arrests, but was associated with a better survival rate (14.4%) than the other causes. Cardiac arrest following multiple trauma had the worst prognosis; only 3% of the patients survived to be discharged from hospital. However, the main factor influencing outcome was the site of arrest. The survival rates of patients on whom resuscitation was initiated in the emergency room or an intensive care area were triple and double the rate for patients in hospital wards, although one third of all the cardiac arrests induced by a coronary event and occurring in hospital were on the wards. Patients whose arrest occurred outside hospital, where only basic life support was available, had a survival rate of just 6.3%, whereas those whose arrest occurred in the emergency room had a survival rate of 31.9%. Since these two patient groups were similar in terms of age and diagnosis, we believe that the potential survival rate for victims of cardiac arrest outside of hospital that are optimally treated is close to 30%.These data suggest that increased survival from cardiac arrest can be expected with extension of the resuscitation services both inside and outside of hospital, but particularly with increased emphasis on emergency cardiac care outside of hospital.

Adolescent↗