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Biomedical subjects

G B Drummond

Publications and source records attributed to G B Drummond.

At least 19 recordsLinked to original sources
PubMed2006

Respiratory muscle activity and respiratory obstruction after abdominal surgery.

BACKGROUND: Respiratory movements in patients after abdominal surgery are frequently abnormal, with associated disturbances in the pattern of inspiratory pressure generation. The reasons for these abnormalities are not clear and have been attributed to impaired action of the diaphragm. However, an alternative is that partial airway obstruction could trigger reflex activation of the inspiratory ribcage muscles, which would cause a similar pattern of inspiratory pressure change. Direct measurement of electrical activity can indicate if reflex activation of inspiratory muscles occurs when partial airway obstruction is present. METHODS: In an open study, we implanted electrodes to measure the EMG of scalene, intercostal and external oblique abdominal muscles in patients after lower abdominal surgery. Analgesia was with morphine i.v. by patient control. We used nasal cannulae to measure nasal airflow and compared EMG activity when airway obstruction was present with activity when breathing was not obstructed. RESULTS: The pattern of activity of the different muscles was distinct. Intercostal activity reached a maximum during inspiration, before the scalene muscles, whereas scalene activity increased in phase with increasing lung volume. Abdominal muscle activity commenced when expiratory flow had ceased and continued until the next inspiration. In all three muscle groups, partial airway obstruction did not alter muscle activity. CONCLUSIONS: Partial airway obstruction does not activate inspiratory ribcage muscles, in patients receiving morphine for postoperative analgesia after lower abdominal surgery. Changes in respiratory pressures and abnormalities of chest wall movement described in previous studies cannot be attributed to reflex responses and probably result from increased airway resistance and abdominal muscle action.

Abdomen↗
PubMed2006

Acute effects of fentanyl on breathing pattern in anaesthetized subjects.

BACKGROUND: The predominant effect of opioids on respiratory pattern during anaesthesia is an increase in the duration of expiration (an effect on 'timing'), but there may also be changes in tidal volume (an effect on 'drive'). Timing and drive are controlled by separate neuronal systems, but are infrequently considered individually. The effects of opioids on breathing are not well characterized clinically because changes in carbon dioxide and anaesthetic levels usually occur at the same time, and can obscure the effects of the opioid. METHODS: To study these effects in isolation, we established stable mild hypercapnia in female patients breathing spontaneously during sevoflurane anaesthesia, and then gave fentanyl 0.5 microg kg(-1) i.v. End-tidal carbon dioxide and sevoflurane concentrations were maintained constant, and the changes in timing of inspiration, expiration and tidal volume were measured. RESULTS: The duration of inspiration increased by 30%, and the duration of expiration increased by 95%. Tidal volume increased in proportion to inspiratory duration, and the pattern of flow during the breath was recognizably changed, with a reduction in the rate of increase of flow at the onset of inspiration. CONCLUSIONS: Small doses of opioid given when anaesthesia and carbon dioxide are stable affect respiratory timing predominantly, but in addition changes in the pattern of motor output can be detected.

Adult↗
PubMed2005

Randomized comparison of three methods of induction of anaesthesia with sevoflurane.

BACKGROUND: Rebreathing will occur if a low gas flow and a Mapleson D circuit are used to induce anaesthesia with a volatile anaesthetic agent. This has the advantage that it allows ventilation to be sustained when consciousness is lost, and specific manoeuvres such as breath-holding or vital capacity breaths are not needed to facilitate induction of anaesthesia. However, if the fresh gas flow were too small, this would slow induction by limiting the rate of delivery of the anaesthetic agent. To assess the impact of fresh gas flow and rebreathing, we compared induction using sevoflurane 8% given by three different methods. METHODS: We randomly allocated 65 patients to receive induction of anaesthesia from either a Mapleson A breathing system with a fresh gas flow of 9 litre min(-1) (group A9), a Mapleson D system with a fresh flow of 6 litre min(-1) (group D6) or a Mapleson D system with a fresh flow of 3 litre min(-1) (group D3). We measured times for induction, end-tidal sevoflurane and end-tidal carbon dioxide. RESULTS: The median (quartiles) induction times were 58 (45, 72), 50 (42, 65) and 64 (52, 92) s in the groups A9, D6 and D3 respectively. Induction of anaesthesia took longer (P<0.01) and was more variable in group D3. In this group, end-tidal sevoflurane concentration at the time of induction of anaesthesia was lower (P<0.05). In group A9, end-tidal carbon dioxide was less (P<0.05). CONCLUSIONS: In adult patients allowed to breathe normally, prompt and consistent inhalation induction of anaesthesia with sevoflurane is obtained when fresh gas flow is limited to 6 litre min(-1) from a Mapleson D circuit, but smaller flows are impractical.

Adolescent↗
PubMed2005

Effect of partial liquid ventilation and nebulized perfluorocarbon on CT lung density distribution: randomized controlled study of experimental lung injury.

BACKGROUND: Perfluorocarbon (PFC) liquid can improve gas exchange in acute lung injury. How PFC aerosol is distributed in the lung is unknown. METHODS: We induced lung injury in rabbits with saline lavage, followed by mechanical ventilation in the supine position. The animals were divided into three groups: a control group, a group treated with partial liquid ventilation and a group given nebulized perfluorocarbon (PF 5080). We made CT image slices of the excised lungs. In the apical, middle and caudal slices we defined three regions of interest, from anterior to posterior, and noted the mean attenuation of each area. We also studied two rabbits which had not received lung injury or mechanical ventilation. RESULTS: Group means were different between the normal rabbits and all three study groups. There was a difference between the control and partial liquid ventilation groups, and between the partial liquid ventilation and nebulized groups, but no difference between the nebulized and control groups. Within each treatment group, there was no regional difference in the distribution of density. CONCLUSIONS: PF 5080 is not deposited in large amounts by aerosol. Less PFC was found in the lungs after partial liquid ventilation than expected. Within treatment groups, lung densities indicate less gravitational and regional differences than found in other studies.

Animals↗
PubMed2004

Abdominal muscle action during expiration can impair pressure controlled ventilation.

Pressure controlled ventilation, and pressure support for spontaneous breathing are often used in intensive care because coordination of the ventilator with patient efforts can improve comfort and possibly reduce sedation. However we report a series of 10 patients whose efforts did not synchronise with pressure controlled ventilation. This was incorrectly diagnosed as inadequate sedation, and treated with increased sedation or muscle paralysis. Better recognition of this condition showed that slow respiratory rates and increased abdominal muscle action during expiration can affect pressure-controlled ventilation and pressure assisted breathing. If the condition is not recognised, treatment for poor synchronisation may delay weaning or be inappropriate.

Abdominal Muscles↗
PubMed2003

The incidence of flushing on induction of anaesthesia in patients who blush easily.

Flushing (reddening and blotching of the skin) is seen frequently at induction of anaesthesia, is associated with anaesthetic agents such as thiopental and muscle relaxants, and is attributed to histamine release. The changes are generally confined to the neck and upper chest (the blush area). In conscious subjects, the mechanisms responsible for blushing in the same skin distribution are well defined and neurally mediated. We investigated the relationship between a history of blushing easily and flushing after intravenous induction o f anaesthesia. We interviewed 898 patients about to undergo general anaesthesia and asked them if they blushed easily. Anaesthesia was induced with thiopental followed by suxamethonium and/or alcuronium. We noted skin colour and the presence of a flush every 5 min for 20 min. Women reported blushing more than men (47% of women, compared with 33% of men, p < 0.001), and blushing was more common in young people (p < 0.001). In those women with a history of blushing, 32% flushed on induction of anaesthesia, compared with 6% of those who did not blush. In men, a flush was seen in 22% of those who blushed, and in 0.2% of those who did not. These differences in the frequency of flushing were significant (p < 0.001). In conclusion, flushing after induction of anaesthesia appears to be related to individual predisposition and may be neurally mediated.

Adolescent↗
PubMed2002

Effect of spinal anaesthesia on plasma concentrations of glutathione S-transferase.

BACKGROUND: Plasma glutathione S-transferase (GST) concentration measurement is a sensitive and specific index of hepatocellular injury. GST concentration increases after anaesthesia with most volatile anaesthetic agents, but not after propofol. Such increases are thought to result from reduced liver blood flow. The effect on GST concentration of spinal (subarachnoid) anaesthesia, which might also reduce liver blood flow, is not known. METHODS: We studied the effects of spinal anaesthesia on GST concentrations measured by specific radioimmunoassay in 33 patients undergoing intermediate orthopaedic, general or gynaecological surgery. GST concentrations were measured before anaesthesia and 3, 6 and 24 h after induction of anaesthesia. Hypotension (systolic blood pressure <70% of pre-induction value) was rapidly corrected with i.v. ephedrine. RESULTS: Mean duration of surgery was 41 min (range 11-80). No increase in GST concentration was observed at any time, but at 24 h GST concentration was significantly reduced (P<0.05). One patient in whom hypotension was not treated developed a greatly increased GST concentration at 3 h. CONCLUSION: We found no association between spinal anaesthesia and disturbance of hepatocellular integrity when hypotension does not occur or is rapidly corrected.

Adult↗
PubMed2002

Respiratory response to skin incision during anaesthesia with infusions of propofol and alfentanil.

BACKGROUND: The ventilatory response to skin incision during anaesthesia with enflurane is an increase in tidal volume without a change in frequency. As opioids affect respiratory frequency and also affect the processing of pain, we investigated if the breathing response to a painful stimulus could be different during anaesthesia using opioids. METHODS: We studied 12 patients during anaesthesia with target-controlled infusions of propofol (plasma target concentration 4-6 microg ml(-1)) and alfentanil (plasma target concentration 40-60 ng ml(-1)), having varicose vein surgery. RESULTS: After the initial skin incision, tidal volume increased promptly by 17 (4, 81)% (median, quartile values) (P<0.01). Respiratory frequency changed variably with no significant change overall [median change 2 (-8, +50)%]. The duration of inspiration was virtually unaltered, and the duration of expiration decreased gradually by 5 (-7, 32)%. Patients who showed more response also showed more change in tidal volume, so that there was a significant relationship between increased inspiratory flow rate and reduced expiratory time (P<0.05). CONCLUSIONS: During opioid anaesthesia, the mechanism of ventilatory increase after stimulation involves changes in both drive and timing of breathing. This pattern of response does not resemble the changes seen during anaesthesia with potent volatile agents.

Adult↗
PubMed2002

Effect of ethanol on psychomotor performance and on risk taking behaviour.

Ethanol may increase the willingness to take risks, but this issue remains controversial. We used a risk-taking paradigm in which volunteers answered a series of general knowledge questions with numerical answers and were asked to judge the length of a line that would just fit into a given gap. A maximum score was given for an exactly correct answer. For answers that were less than the correct value, the score was reduced gradually to zero, while answers even slightly over the correct value were penalized considerably. Total points were rewarded by cash payments, so volunteers were taking real risks when making their responses. Performance was assessed in a two-period, double-blind crossover study, comparing ethanol (0.7 g/kg) with placebo in 20 female volunteers aged 19-20 years. Tests were carried out before and at 45 min after dosing. Mean (SD) ethanol blood alcohol concentrations were 65 (10.5) mg/100 ml. Ethanol impaired the skill/ability measure of the length estimation test (SD of difference between length of line and gap), which increased from 5.9 to 6.6 (p < 0.05), indicating a reduced accuracy of estimation. The risk measures in both tasks were not significantly affected. The skill/ability measure in the general knowledge task was not significantly affected. Other performance tests showed that ethanol produced the expected impairment of both speed and accuracy. These results suggest that risk-taking is not increased by ethanol at doses approaching the UK legal limit for driving.

Adult↗
PubMed2002

Abdominal pressure during laparoscopy: effects of fentanyl.

BACKGROUND: In patients breathing spontaneously during anaesthesia, expiration is active and opioids enhance this effect. The mechanical consequences are not well characterized. METHODS: We studied 14 patients undergoing laparoscopy for minor gynaecological procedures, anaesthetized with isoflurane in nitrous oxide, and breathing spontaneously through a laryngeal mask airway. We made direct recordings of intra-abdominal pressure and respiratory flow before and after giving fentanyl 25 microg i.v. RESULTS: Satisfactory records were obtained in 11 patients. Before fentanyl, the abdominal pressure changes were small and had an inconsistent pattern, increasing in inspiration in seven patients and during expiration in five. After fentanyl, an increase in pressure during inspiration was seen in only two patients, and the intra-abdominal pressure during expiration was increased. The mean value of maximum abdominal pressure (which always occurred during expiration) increased from 17 (SD 5) cm H2O before to 25 (9) cm H2O after fentanyl (P<0.01). CONCLUSIONS: Direct measurements support previous findings that opioids stimulate active phasic expiratory activity and can cause large increases in abdominal pressure.

Abdominal Muscles↗
PubMed2001

A comparison of the respiratory effects of high concentrations of halothane and sevoflurane.

We studied the respiratory effects of the administration of either 5% halothane or 8% sevoflurane in 70% nitrous oxide (N2O) for 5 min in 21 boys aged 1-5 years. A similar degree of ventilatory depression was noted with both agents. Minute volume fell by approximately 50% as a result of a reduction in tidal volume despite an increase in respiratory rate.

Anesthesia, Epidural↗
PubMed2001

A video-based optical system for rapid measurements of chest wall movement.

We tested apparatus developed to measure the movement of the surface of the chest and abdomen, during breathing in the supine subject. A line of light is projected onto the chest wall. The line image from a video camera is analysed to estimate of the height of the surface profile, so that the shape and volume of the object can be derived. The data can provide direct or inferential volume estimates. We compared this system with the widely used inferential system of inductance bands in supine volunteers who breathed using patterns designed to emphasize variability in movements: normal and large breaths, and breathing through an expiratory resistance. We calculated the differences between a spirometer signal and continuous volume estimates using the linear regression method, obtained using signals from the two methods. The volume estimate differences obtained by the optical system and induction bands were not significantly different, but the optical system was more precise. Using the optical device, an acceptable interquartile range of differences from spirometric volume (50 ml) was significantly likely when the optical device was used. During resistive loaded breathing (mean tidal volume 390 ml) direct optical measurements of volume, and inductance band estimates, were compared with tidal volume. The optical system showed distortion of the shape of the abdomen during this breathing pattern. Mean error with the optical system was 64 ml and with the inductance band system was 108 ml (p < 0.05). The optical system gives accurate reproducible results in supine human subjects and additional valuable information on shape changes.

Abdomen↗