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Biomedical subjects

L C Jenkins

Publications and source records attributed to L C Jenkins.

At least 37 records · Page 2Linked to original sources
PubMed1986

Perioperative transcutaneous oxygen monitoring in thoracic anaesthesia.

Transcutaneous oxygen tension (PtcO2) was measured in 30 patients scheduled for elective pulmonary resection requiring one-lung ventilation during anaesthesia. Simultaneous PtcO2 and arterial oxygen tension (PaO2) measurements were taken preoperatively (preop), intraoperatively during two-lung endotracheal (ET) and one-lung endobronchial ventilation (EB), and postoperatively (postop). There was a significant correlation (r) between PtcO2 and PaO2 at all time periods: 0.97 (preop); 0.91 (ET); 0.83 (EB); 0.81 (postop). There were no significant differences among the transcutaneous oxygen indices (tcO2 index = PtcO2/PaO2) in the preop (0.69 +/- 0.09), ET (0.68 +/- 0.10) and postop (0.71 +/- 0.12) time period. The tcO2 index was significantly lower during one-lung anaesthesia (0.61 +/- 0.14). The PtcO2 was consistently lower than the corresponding PaO2 measurement, thus providing a continuous estimation of the "minimum" PaO2 level throughout anaesthesia and recovery. In four patients a marked drop in PtcO2 occurred just after the initiation of one-lung ventilation. In three, this was associated with arterial hypoxaemia and in one, haemodynamic compromise. In all four cases the PtcO2 was the first monitored parameter to change. As there is a substantial risk of developing hypoxaemia during thoracic anaesthesia, PtcO2 monitoring provides valuable early warning of impending hypoxaemia or haemodynamic compromise, thereby facilitating early therapeutic intervention.

Adult↗
PubMed1985

Anaesthetic implications of calcium channel blockers.

Clinical uses of calcium channel blockers are expanding. In addition to the established uses in patients with arrhythmias, angina pectoris or hypertension, newer and to some extent investigational uses indicate widespread application. For instance, their use has been reported in hypertrophic cardiomyopathy and cold cardioplegia, as well as in pulmonary hypertension, antiplatelet therapy, asthma, achalasia and oesophageal spasm, increased intraocular pressure and in cerebral vasospasm. Their use in obstetrical practice has been proposed. Thus, the presentation of a patient who is treated with calcium channel blockers and who requires anaesthesia will become more common. Calcium channel blockers may, under certain circumstances, potentiate haemodynamic and MAC depressive effects of inhalation agents. There is also evidence that the effects of neuromuscular blocking agents may be potentiated. The anaesthetist should be aware that the potential for interactions exists with digoxin, propranolol, quinidine, theophylline or dantrolene. Of interest and some significance are the anaesthetic implications of pathophysiological alterations that can be induced by calcium channel blockers, by affecting lower oesophageal tone, intracranial hypertension, bronchomotor tone (asthma), muscular dystrophy, neuromuscular function, hypoxic pulmonary vasoconstriction, malignant hyperthermia, inhibition of platelet aggregation and hyperkalemia. Despite these significant potential anaesthetic implications and because, at this time, in some instances withdrawal has clearly demonstrated increase in the signs of myocardial ischaemia, it would not seem necessary to recommend preoperative discontinuation of calcium channel blocker medication in patients presenting for anaesthesia. It is, however, appropriate that there is a high index of awareness of potential problems, unless there is some modification in inhalation anaesthetic concentrations and neuromuscular blocker dosage. Monitoring of cardiovascular and neuromuscular functions is essential. Calcium channel blockers would appear to be currently the drugs of choice for angina pectoris, arrhythmias or hypertension in patients with associated chronic obstructive pulmonary disease.

Adrenergic beta-Antagonists↗
PubMed1983

Modification by preoperative beta-blockade of the renin response to infrarenal aortic cross-clamping.

The activity of the renin-angiotensin system was measured before, during, and after infrarenal aortic cross-clamping in 13 patients. Five of the patients studied were taking propranolol preoperatively and formed a subgroup. Intraoperative blood loss, volume of crystalloid and colloid infused, haemodynamic parameters and urine output were similar for the two groups. In eight patients who were not taking propranolol mean plasma renin activity was 2.24 ng . ml-1 . hr-1 prior to induction, 3.78 ng . ml-1 . hr-1 during surgery prior to cross-clamping and 4.42 ng X ml-1 X hr-1 15 minutes after the aorta was cross-clamped (increases not statistically significant). Mean plasma renin activity measured ten minutes prior to release of the cross-clamp (5.02 ng X ml-1 . hr-1), 15 minutes after clamp release (5.47 ng X ml-1 X hr-1), and 30 minutes after reaching the recovery room (5.84 ng X ml-1 X hr-1) were significantly greater than preinduction levels. Four patients developed postoperative hypertension (mean blood pressure greater than 120 mmHg); there was not a correlation between the elevated plasma renin activity observed postoperatively and the occurrence of postoperative hypertension. The five patients taking propranolol had a markedly attenuated renin activity response during and after surgery; the mean plasma renin activity was less than 1.5 ng X ml-1 X hr-1 at all sampling times. Two of these five patients did develop postoperative hypertension. It is concluded that surgery involving infrarenal aortic cross-clamping is associated with increased plasma renin activity with peak levels occurring postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

Prediction of the need for postoperative mechanical ventilation in myasthenia gravis: thymectomy compared to other surgical procedures.

In a recent report Leventhal, Orkin, and Hirsh described a scoring system felt to be of value in predicting the need for postoperative mechanical ventilation in patients with myasthenia gravis undergoing thymectomy. Leventhal, et al. identified four risk factors felt to have predictive value, namely: (1) duration of myasthenia gravis greater than or equal to 6 years, (2) chronic respiratory disease, (3) dose of pyridostigmine greater than or equal to 750 mg per day, and (4) vital capacity less than or equal to 2.9 litres. Forty-six patients with myasthenia gravis who received 68 general anaesthetics were studied retrospectively. They represented the past 10 years' anaesthetic experience with myasthenia gravis at the Vancouver General Hospital. The patients were divided into two groups: (1) those who underwent thymectomy, and (2) those who underwent procedures other than thymectomy. Using the risk factors of Leventhal, et al., a predictive score was assessed for each patient; the time of postoperative tracheal extubation was also noted for each patient. From this study it was concluded that the scoring system proposed by Leventhal, et al. may have been of some value in predicting whether or not a particular patient undergoing thymectomy was likely to need ventilation postoperatively. In 41 myasthenics who had procedures other than thymectomy, however, this scoring system was found to be of no value.

Adolescent↗
PubMed1981

A comparative evaluation of cimetidine and sodium citrate to decrease gastric acidity: effectiveness at the time of induction of anaesthesia.

Patients coming for elective surgery were randomly assigned to one of three treatment groups: control, cimetidine 300 mg orally two hours pre-operatively, or sodium citrate 0.3 M solution 30 ml orally, given as the patient was leaving the ward for the operating room. Each group consisted of 15 patients. This study reconfirms the average 26 per cent risk of significant aspiration in patients, coming for elective surgery, who have not received an agent intended to decrease gastric acidity or to decrease volume of gastric content. Sodium citrate is effective most of the time (87 per cent) in decreasing gastric acidity but is associated with a large mean volume (40.8 ml) of aspirate. From the results of this study cimetidine appears to be the preferable agent to use because it is completely effective in decreasing gastric acidity but does not increase the mean volume (17.0 ml) of the aspirate. Cimetidine appears to be an excellent agent to use as a preventative measure against aspiration during the induction of anaesthesia. Sodium citrate is a reasonable alternative if there is a contraindication to the use of cimetidine. However, these agents should be regarded only as adjuncts in the prevention of aspiration of gastric contents at the time of induction of anaesthesia.

Adult↗
PubMed1980

The absence of antagonism by naloxone during halothane/nitrous oxide anaesthesia in man.

Sixteen patients were studied to determine if naloxone could be shown to affect general anaesthesia with halothane and oxygen or nitrous oxide and oxygen with halothane. Changes in blood pressure, pulse rate, electroencephalogram and evidence of physical response were observed. The end-tidal halothane and carbon dioxide were controlled. The temperature and blood gases were held constant, as was the degree of neuromuscular blockade. Naloxone 1.2 mg was administered during general anaesthesia with either halothane in oxygen or halothane with nitrous oxide to 16 patients who were premedicated without a narcotic. No significant responses were recorded.

Adult↗
PubMed1980

Transcutaneous electrostimulation in the management of postoperative pain: initial report.

A study was undertaken to investigate recent reports concerning the use of transcutaneous electrostimulation (TES) for relief of postoperative pain. Thirty patients undergoing elective herniorrhaphy were subjected to a standard perianaesthetic protocol. The patients were divided into three groups of ten, designated control, sham TES and TES. Postoperative analgesic requirements for each group were compared. The number of intravenous doses of meperidine given to each group in the first three hours after operation was control group 46 doses; sham TES group 38 doses; TES group 10 doses (p less than 0.0005). The number of intramuscular doses of meperidine in the 3-24-hour period was control group 21 doses; sham TES 22 doses; TES group 17 doses (no statistical difference between groups). A subjectively beneficial effect of TES was also established. Despite a number of difficulties encountered during this study, primarily concerned with the subjective nature of pain and its assessment, a useful trend which warrants further investigation has been established in the use of transcutaneous electrostimulation (TES) for postoperative analgesia.

Adult↗
PubMed1979

Bacterial filters - are they necessary on anaesthetic machines?

At the Vancouver General Hospital the effectiveness of the system for decontamination of anaesthetic equipment was evaluated to determine the need for bacterial filters on anaesthetic machines. Two groups of patients were studied. Group I consisted of 33 patients, none of whom had clinical symptoms of respiratory tract disease. Group II consisted of 17 patients who had lower respiratory tract secretions. In the latter group 16 had chronic bronchitis and had cystic fibrosis. Of 550 bacterial cultures taken from the anaesthetic equipment immediately before and after anaesthesia in our 50 patients, only five yielded a growth of non-pathogenic bacteria. The results of this study indicate that bacterial colonization of anaesthetic equipment is of a low order and is adequately controlled by pasteurization even after use in patients with chronic lower respiratory tract disease. The use of bacterial filters does not appear justified if a strict regimen of cleaning and pasteurization is followed.

Adolescent↗
PubMed1978

Intermittent mandatory ventilation and controlled mechanical ventrilation without positive end-expiratory pressure following cardio-pulmonary bypass.

In a group of 18 male patients undergoing coronary artery bypass grafting with cardiopulmonary bypass, the overall incidence of post-operative atelectasis was 60%. Nearly three-quarters occurred during anaesthesia. After operation there was no difference whether CMV or IMV without PEEP was provided overnight. Atelectasis already present did not improve and further atelectasis occurred. A role for IMV is not excluded, since it facilitates the use of PEEP. Many factors operate and interact to provoke atelectasis during anaesthesia, which increases post-operative morbidity. Many of these factors are prevertible or reversible if their physiological basis is understood. Optimal post-operative ventilation should be tailored to the needs of the individual patient and demands close co-operation between anaesthetist and surgeon.

Anesthesia↗
PubMed1978

Protection of the brain from hypoxia: a review.

A functional classification of hypoxia of the brain has been presented and some of its significant aspects have been discussed. Mechanisms of protection from hypoxia of the brain were reviewed under the headings of prevention, hyperventilation, hypothermia and protection by barbiturates. In prevention of hypoxia of the brain, avoidance of factors producing a fall in cerebral perfusing pressure was emphasized. Hyperventilation is not advised unless one can readily measure regional cerebral blood flow. In the operating room, normocarbia or slight hypocarbia is recommended. Animal studies indicate a protective role of barbiturates in ischaemic hypoxia of the brain. However, it should be emphasized that, at present, hypothermia is the only established means of protection against hypoxia of the brain in man, when it is induced prior to the hypoxic insult. The evidence for protection by barbiturates has been found only in experimental animals. If one can extrapolate the results of studies in animals to man, then potential benefits would be expected in clinical stroke, cardiac arrest, in operations on the carotid artery and in head injury.

Anesthesia↗
PubMed1977

The influence of intravenous anaesthetics on enflurane-induced central nervous system seizure activity.

This study assesses the effects of agents commonly used in anaesthesia on enflurane-induced seizure threshold and on established seizure activity, during steady state enflurane anaesthesia. EEG seizure activity was monitored in cats from chronic cortical and subcortical recording sites. Diazepam, thiopentone, methohexitone and ketamine all enhanced established EEG seizure challenge. This latter effect was most evident under conditions of lowered PaCO2. The effects of these intravenous agents on established enflurane seizure patterns exceeded in duration the expected EEG effect of the agent when used alone. The limited number of experiments, however, precluded statistical verification of our findings. The similarities between centrencephalic minor motor seizures and enflurane seizure pattern in terms of EEG and convulsive expression, including drug response, are noted.

Anesthesia, Inhalation↗
PubMed1976

A study of anaesthesia depth by power spectral analysis of the electroencephalogram (EEG).

The feasibility of using computer-based EEG spectral analysis to monitor the level of anaesthesia during nitrous oxide-alphaprodine anaesthesia has been established by this study. At present, this system is capable of estimating the level of anaesthesia correctly from 55 per cent to 80 per cent of the time. There are several possible clinical applications of such a monitoring system during anaesthesia. It provides a continuous estimation of the depth of anaesthesia, without requiring any special EEG training on the part of the anaesthetist. This system can also be of particular benefit during anaesthesia for critically ill patients, or in specific cases, as in neurosurgery and caesarian section when there may be periods of time when the gross clinical evaluation of depth of anaesthesia may not be precise or reliable and yet it is imperative not to deepen the anaesthesia unnecessarily. In such instances it appears that a monitoring system such as we have developed could provide valuable indication of the depth of anaesthesia. Other potential applications might be in the training of students in the clinical assessment of patients during anaesthesia and in the study of new anaesthetic agents.

Adult↗
PubMed1975

The cardiovascular effects of ketamine in hypotensive states.

Ketamine was found to raise the systemic arterial blood pressure but not necessarily the perfusion in hypovolaemic states. However, in hypotensive states of short duration from endotoxin treatment, it improved the haemodynamics with increase in both the perfusion and the systemic pressure. The implications of these observations for clinical situations were discussed.

Animals↗
PubMed1975

Central nervous system effects of bupivacaine.

The central nervous system and concurrent cardiovascular effects of bupivacaine infusion were studied in cats. It was possible to block cortical E.E.G. desynchronization resulting from a sensory stimulus with bupivacaine. The earliest subcortical change that occurred was rhythmic activity in the amygdala and later in the hippocampus. Occasionally, this activity appeared simultaneously in both these sites. Diazepam pretreatment raised the seizure threshold of bupivacaine. Diazepam was also effective in terminating established seizure activity resulting from bupivacaine. All animals pretreated with diazepam (Valium) or diazepam solvent developed cardiac dysrhythmias durind bupivacaine infusion. The possible clinical significance of the interaction of bupivacaine and diazepam solvent is considered.

Amygdala↗