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Biomedical subjects

N M Gibbs

Publications and source records attributed to N M Gibbs.

At least 37 records · Page 2Linked to original sources
PubMed1996

Sensitivity and specificity of the Hemochron, Hemotec and APTT for the detection of low concentrations of heparin.

This study compared two bedside methods recommended for the detection of low concentrations of heparin and the activated partial thromboplastin time (APTT), with reference to a laboratory measure of heparin concentration. Patients undergoing cardiopulmonary bypass had blood drawn at four stages when low levels of heparin could be expected. At each stage four tests were performed: whole blood clotting time using a Hemochron analyser with a Saline-Rinsed test cartridge, whole blood clotting time using a Hemotec analyser with a High Range Heparinase test cartridge, APTT, and heparin concentration by polybrene neutralization. Thirty patients were studied. The sensitivity of the Saline-Rinsed Hemochron, Hemotec High Range Heparinase, and APTT in detecting concentrations of heparin less than 1 U/ml was 38%, 40% and 97%, respectively, while specificities were 87%, 90%, and 30%, respectively. Neither the Saline Rinsed Hemochron, nor the Hemotec Heparinase cartridge reliably detected concentrations of heparin less than 1 U/ml.

Anticoagulants↗
PubMed1996

The effect of aprotinin on thrombelastography in vitro.

The effect of low dose (50 KIU/ml) and high dose (200 KIU/ml) aprotinin on standard thrombelastographic variables (r, K, alpha, MA) was examined in vitro using blood from forty ASA Class 1 patients. Both concentrations of aprotinin resulted in minor increases in r time above the normal range (P < 0.05). Aprotinin did not alter other thrombelastographic variables. The results indicate that aprotinin is a mild direct anticoagulant in vitro as assessed by thrombelastography.

Adolescent↗
PubMed1995

Effect of ketorolac, bupivacaine and low-dose heparin on thrombelastographic variables in vitro.

We have studied the effects of ketorolac, bupivacaine and low-dose heparin on three thrombelastographic (TEG) variables (r, alpha, MA) in vitro. Blood samples were obtained from 12 healthy volunteers and 88 ASA I-II elective surgical patients. Clinically relevant concentrations of ketorolac (4.1 micrograms ml-1) and bupivacaine (2.7 micrograms ml-1) had little or no effect on the TEG variables. However, low concentrations of heparin (0.07-0.28 u. ml-1) had marked effects on all three TEG variables. Thus the interpretation of TEG abnormalities during anaesthesia and surgery may be confounded by the presence of heparin, but not by clinical concentrations of ketorolac or bupivacaine.

Adult↗
PubMed1994

Thrombelastographic patterns following abdominal aortic surgery.

Postoperative changes in thrombelastographic patterns were studied in thirty patients undergoing elective abdominal aortic bypass surgery. Native whole blood thrombelastography was performed preoperatively and on days 1, 2, and 3 postoperatively. The thrombelastographic changes included a decrease in r on day one (P < 0.0001), with concurrent increases in alpha (P < 0.0001) and MA (P < 0.001). On days 2 and 3 there were further increases in MA (P < 0.0001). These changes indicate enhanced procoagulant activity and progressive increases in maximum clot strength. The results confirm that hypercoagulability occurs in whole blood following abdominal aortic bypass surgery. Further studies are warranted to determine whether modification of postoperative hypercoagulability reduces the incidence of thrombotic complications in this group of patients.

Aged↗
PubMed1993

Lymph node metastases in early rectal cancer.

Local excision of early rectal tumours is an attractive proposition, avoiding the morbidity and mortality of major resection and possible permanent stoma. This study was designed to investigate the incidence of lymph node metastases associated with tumours that are locally confined to the bowel wall. A total of 454 rectal excision specimens were reviewed. Twenty-two (20 per cent) of 109 patients with tumours locally confined to the bowel wall had metastases in local lymph nodes, although 14 of these had only one or two involved nodes. Three of 27 patients with tumours that did not penetrate through the submucosa had lymph node metastases. Less well differentiated tumours were more likely to have metastasized but there was no significant difference in the height or size of tumours or in the depth of invasion between patients with or without lymph node metastases.

Humans↗
PubMed1993

Dose-response relationship of atracurium besylate in the halothane-anaesthetised pig.

The dose response relationship for the intermediate-acting non-depolarising muscle relaxant, atracurium besylate in the pig was determined using evoked electromyography. An incremental dose technique was used in seven Large White/Landrace crossbred pigs anaesthetised with nitrous oxide and halothane. ED50 and ED95 were 510 +/- 87 micrograms kg-1 and 1150 +/- 270 micrograms kg-1, respectively. Although these values may represent an overestimate, they provide a reasonable guideline for the use of atracurium by veterinary anaesthetists.

Anesthesia, Inhalation↗
PubMed1992

Postoperative changes in coagulant and anticoagulant factors following abdominal aortic surgery.

The extent and time course of changes in selected procoagulant and anticoagulant factors were investigated in 19 patients undergoing elective abdominal aortic surgery. The coagulation factors were measured preoperatively, and on days two, four, and six postoperatively. It was found that there were no significant changes outside the normal range in prothrombin time, partial thromboplastin time, or thrombin clotting time. However, there were large increases in the procoagulants, fibrinogen, factor VIII coagulant, factor VIIIRag/von Willebrand factor, and in alpha 1-antitrypsin. Over the same time there were marked decreases in the naturally occurring anticoagulants, protein C and antithrombin III, and in alpha 2-macroglobulin. These changes implied that the patients were "hypercoagulable" in the postoperative period. The maximum changes in the procoagulants occurred on either postoperative day two or day four. The maximum changes in the natural anticoagulants occurred on postoperative day two. There were no significant changes in factor V, factor X, alpha 2-antiplasmin, or platelet aggregability. The timing of the changes coincided with a period of high risk of perioperative myocardial infarction in this group of patients. Thus, it is possible that postoperative hypercoagulability contributes to the development of coronary artery thrombosis and myocardial infarction following abdominal aortic surgery.

Aged↗
PubMed1992

The effect of epidural blockade on postoperative hypercoagulability following abdominal aortic bypass surgery.

The effect of epidural blockade on postoperative hypercoagulability was assessed in patients undergoing elective abdominal aortic bypass surgery. Twenty patients were randomised to receive general anaesthesia alone, or general anaesthesia plus thoracic epidural blockade with 0.5% bupivacaine. It was found that the addition of epidural blockade did not alter the postoperative increase in plasma fibrinogen, factor VIII coagulant, or alpha 1-antitrypsin. Similarly, epidural blockade did not affect the postoperative decrease in antithrombin III. The results suggest that epidural blockade with local anaesthetic agents does not prevent the postoperative hypercoagulability response following abdominal aortic bypass surgery.

Aged↗
PubMed1991

The accuracy of Finapres noninvasive mean arterial pressure measurements in anesthetized patients.

The Finapres (FIN) is a new noninvasive blood pressure monitor that provides continuous arterial waveform display with the use of a finger cuff. The authors assessed the accuracy of FIN mean arterial pressure (MAP) measurements relative to simultaneous direct radial arterial pressures in 20 patients undergoing general anesthesia for major elective surgery. Data were collected digitally with the use of RS-232 communications over a total of 16.2 h. The data were processed into 6012 interference-free time samples, each spanning 6 s. The authors determined the difference between FIN and direct MAPs during each time sample. The authors calculated not only the bias of FIN measurements, but also the frequency, magnitude, and duration of discrepancies between simultaneous FIN and direct MAPs. The overall bias of the FIN MAP was -0.5 +/- 1.0 mmHg, which was not significantly different from zero. However, 32.3 +/- 6.2% of all MAP comparisons differed by greater than +/- 10 mmHg, and 5.0 +/- 1.1% differed by greater than +/- 20 mmHg. Moreover, there was an average of one episode every 2 patient-hours when the FIN MAP differed by greater than +/- 20 mmHg for more than 1 min. Although the MAP measured by FIN accurately reflected direct MAPs most of the time, there were occasional discrepancies of different magnitude such that clinical usefulness may be limited in patients in whom continuous accurate blood pressure measurements are essential.

Anesthesia, General↗
PubMed1991

The effect of the depth of neuromuscular blockade on the haemodynamic response to tracheal intubation.

The effect of two different doses of vecuronium on the heart rate and mean arterial pressure response to tracheal intubation was compared in 32 adult ASA class I patients. It was found that the higher dose of vecuronium (2.5 X ED95) produced greater depression of the evoked electromyogram (P less than 0.01), and provided better intubating conditions (P less than 0.01) than the lower dose of vecuronium (1 X ED95). However, the heart rate and the mean arterial pressure response to tracheal intubation was similar with both doses. The results indicate that, within the range of neuromuscular blockade commonly used to facilitate tracheal intubation, the depth of neuromuscular blockade per se does not affect the haemodynamic response to intubation.

Adult↗
PubMed1991

The onset and duration of neuromuscular blockade using combinations of atracurium and vecuronium.

The effect of atracurium-vecuronium combinations on the onset and duration of neuromuscular blockade was investigated in 30 adult patients undergoing general anaesthesia for elective surgery. The patients were randomized to receive either atracurium 0.6 mg.kg-1, vecuronium 0.1 mg.kg-1, or quarter-dose, half-dose, or full-dose combinations of the two drugs. Neuromuscular blockade was assessed by measuring the evoked electromyographic response of the abductor digiti minimi to transcutaneous stimulation of the ulnar nerve. It was found that half-dose combinations of atracurium and vecuronium did not produce a shorter onset time, but did result in a longer duration of neuromuscular blockade than full-doses of either drug alone (P less than 0.01). The quarter-dose combinations did not reduce onset time or increase duration. The full-dose combinations produced both a shorter onset time (P less than 0.01) and a longer duration (P less than 0.001). The results indicate that atracurium-vecuronium combinations are supra-additive in terms of the duration of the neuromuscular blockade produced. However, the inability of atracurium-vecuronium combinations to reduce onset time without increasing duration suggests that there is little advantage in combining the two drugs in clinical practice.

Adult↗
PubMed1991

The effect of anaesthetic agents on platelet function.

This paper reviews studies which have investigated the effect of anaesthetic agents on platelet function. The results of these studies suggest that halothane is the only agent in current use which inhibits platelet function in concentrations used clinically. Nitrous oxide appears to cause only a modest inhibition, while enflurane and isoflurane appear to have minimal or negligible effects. There is no current evidence that intravenous induction agents, opiates, or muscle relaxants affect platelet function. Reports indicate that local anaesthetic agents inhibit platelet aggregation, but only at concentrations far greater than peak plasma concentrations found during clinical use. Epidural anaesthesia may be associated with a reduction in platelet aggregation through a mechanism unrelated to direct local anaesthetic inhibition. The clinical significance of the effect of halothane on platelet function is not known. However, it is possible that halothane may affect bleeding or thrombotic complications in a similar manner to other 'anti-platelet' drugs.

Anesthetics↗
PubMed1990

Extent of mesorectal spread and involvement of lateral resection margin as prognostic factors after surgery for rectal cancer.

The extent of tumour growth beyond the muscularis propria (mesorectal spread) was measured in specimens from 167 consecutive patients with rectal cancer. The 5-year survival was significantly greater in patients with slight mesorectal spread (4 mm or less) than in those with more extensive mesorectal spread (55% [95% confidence interval 42-66%] vs 25% [13-38%]). The prognostic value for survival of mesorectal spread was independent of the presence of lymphnode metastases. There were also significant differences in survival between patients with slight and extensive mesorectal spread among patients with Dukes' stage B tumours (66% [41-82%] vs 37% [14-60%]) and those with Dukes' stage C tumours (30% [12-52%] vs 18% [6-34%]). Thus mesorectal spread of rectal cancer is an important determinant of survival, and its accurate measurement may serve to subdivide Dukes' B and C cases. In this study tumour involvement of the lateral resection margin was not a useful predictor of local recurrence, but it did correlate with poor prognosis.

Actuarial Analysis↗
PubMed1989

Management of screen detected ductal carcinoma in situ of the female breast.

Thirty eight ductal carcinomas in situ of the female breast detected during the first 7 years of screening by the Guildford Breast Screening Unit have been treated by one surgeon. Twenty-eight cases were treated conservatively and ten by mastectomy. In the group treated conservatively there have been five local recurrences: four as ductal carcinoma in situ and one as node negative microinvasive carcinoma. There were no clinical or pathological features that predicted local recurrence, which was detected only by follow-up mammography. Based on these early results, an initially conservative approach to screen detected ductal carcinoma in situ is advocated.

Aged↗
PubMed1989

Halothane induces depressor responses to noxious stimuli in the rat.

The effect of halothane on hemodynamic responses to noxious stimuli was investigated in anesthetized male Sprague-Dawley rats. It was found that increasing the end-tidal halothane concentration from sub-MAC to supra-MAC levels was frequently associated with a reversal of the mean arterial pressure response to a noxious stimulus from a pressor response to depressor response. The depressor responses could be produced by noxious stimuli at several sites but were of greatest frequency (100%) and magnitude (up to -80 mmHg) after clamp application at the base of the tail. The depressor responses were often, but not always, accompanied by decreases in heart rate. The correlation coefficient between the changes in heart rate and the changes in mean arterial pressure caused by noxious stimuli was +0.61 (n = 9). The authors further characterized the depressor responses in an additional 18 rats. The depressor responses were not influenced by vagotomy or muscarinic cholinergic blockade and were associated with concurrent decreases in both cardiac output and systemic vascular resistance. The hemodynamic changes associated with the depressor responses were consistent with a centrally mediated withdrawal of sympathetic tone. Knowledge of this effect of halothane on the arterial blood pressure and heart rate responses to noxious stimuli may be important for correctly interpreting animal responses to noxious stimuli in the presence of general anesthetic agents, particularly because animals are frequently used to characterize both the potency and the hemodynamic effects of anesthetic agents. The presence of depressor responses also indicates that mean arterial pressure responses to noxious stimuli cannot be used as a linear index of anesthetic depth in rats anesthetized with halothane.

Anesthesia, General↗
PubMed1989

The effect of neuromuscular blockade with vecuronium on hemodynamic responses to noxious stimuli in the rat.

The effect of neuromuscular blockade with vecuronium on the hemodynamic responses to a noxious stimulus was investigated in male Sprague-Dawley rats. The rats were anesthetized with either halothane (group 1, n = 10), or isoflurane (group 2, n = 10). The maximum values for heart rate and mean arterial pressure during the noxious stimulus (base-tail clamp) were measured, and the maximum changes in these values (maximum minus prestimulation) were calculated. The responses were measured at two different anesthetic concentrations (0.6 X MAC, 0.75 X MAC), before and after vecuronium 1.0 mg.kg-1 iv. It was found that neuromuscular blockade with vecuronium did not reduce any of the hemodynamic responses measured, at either anesthetic concentration, in either the halothane or the isoflurane group. However, increasing the anesthetic concentration from 0.6 X MAC to 0.75 X MAC produced statistically significant (P less than 0.01) reductions in several of the responses measured. The inability of vecuronium to reduce hemodynamic responses to noxious stimuli in this study suggests that neuromuscular blockade does not alter anesthetic depth in the rat. A knowledge of this "absence of effect" may be important for investigators who need to induce muscle relaxation in laboratory animals prior to examining the effect of anesthetic agents on hemodynamic responses to noxious stimuli. The results also question the ability of neuromuscular blockade to reduce anesthetic requirement, and support the view that neuromuscular blockade does not contribute to the anesthetic state.

Anesthesia, Inhalation↗