Biomedical subjects
Publications and source records attributed to M D Stoneham.
A patient with Eisenmenger's syndrome presented for removal of a carotid body tumour. Continuous cervical plexus blockade was successfully used to provide peri-operative and postoperative analgesia. The risks and benefits of regional and general anaesthesia in this high risk patient are discussed.
We describe the management of two patients undergoing awake carotid surgery who developed signs of cerebral ischaemia following cross-clamping of the internal carotid artery. Administration of oxygen 100% with a close-fitting anaesthetic facemask reversed the neurological deficit, avoiding the need for insertion of an internal carotid artery shunt. Thus, the incidence of shunt insertion, which is reduced by the use of regional rather than general anaesthesia, could be reduced further by supplementary oxygenation. The possible mechanism and implications are discussed.
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We describe the management of three patients undergoing awake carotid surgery who developed signs of cerebral ischaemia after carotid cross-clamping. Drug treatment to increase arterial blood pressure above baseline reversed the neurological deficit and an internal carotid artery shunt was not needed. Shunt insertion is less frequent with regional rather than general anaesthesia, and blood pressure control can reduce this even more. Coincidentally, one of the patients, who gave a history of angina of effort after walking 100 m, complained of chest pain after cross-clamp release. This was treated successfully with sublingual nitroglycerin before ST segment changes became apparent on the ECG. These reports suggest that regional anaesthesia for carotid surgery allows potential complications to be identified earlier than under general anaesthesia using reports from the patient, so that treatment may be modified to prevent morbidity and even mortality.
We conducted a postal questionnaire survey of the members of the Vascular Anasthesia Society of Great Britain and Ireland, asking questions about the provision of anasthesia for carotid endartectomy. Of 215 respondents, 187 were currently providing anasthesia for carotid endarterectomy. The majority of respondents (69%) always use general anasthesia for this operation but 99/215 (46%) had some experience of regional anasthesia for carotid endartectomy. Amongst those currently using regional anasthesia, combined deep and superficial cervical plexus block was the technique used by 71%. Other regional techniques used included local infiltration and superficial block alone. During regional anasthesia, most (66%) anasthetists used cerebral monitoring techniques such as stump pressure or transcranial Doppler as well as keeping the patient awake. However, in a significant proportion of cases (37%) under general anasthesia no cerebral monitoring was used. Reported surgical shunt insertion rates were lower in awake (mean 42%) patients than those receiving general anasthesia (61%). Respondents using regional anasthesia were more likely to feel that their technique was appropriate than those using general anasthesia.
A novel positioning technique was tested to see whether the unpredictability of block height and haemodynamic instability during spinal anaesthesia for caesarean section could be reduced. In this 'Oxford' position, the woman is placed left lateral with an inflated bag under the shoulder and pillows supporting the head. Following spinal injection the woman is turned to an identical right lateral position. This is maintained until just before incision to minimise aorto-caval compression, when she is placed in the wedged supine position. Sixty women undergoing elective caesarean section were randomised to receive spinal anaesthesia using hyperbaric bupivacaine in either the Oxford (group O), or the sitting position followed immediately by the wedged supine position (group S). Ephedrine 6 mg was given every minute that systolic blood pressure was less than 80% of baseline. In group S, 9/30 women lost pinprick sensation up to T4 at 5 minutes compared with 2/30 in group O (chi2 test, P = 0.04). Block height was more variable in group S than in group O (f test, P = 0.001). Blood pressure decreased by a greater amount initially: group S women required more ephedrine (15.5 +/- 12.9 versus 9.2 +/- 7.7 mg, t test, P = 0.03). Block height with spinal anaesthesia for caesarean section is more predictable and haemodynamically stable if the Oxford position is used whilst anaesthesia develops.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
BACKGROUND: Carotid endarterectomy may be performed under cervical plexus block with local anesthetic supplementation by the surgeon as necessary during surgery. It is unclear, however, whether deep or superficial cervical plexus block offers the best operating conditions or patient satisfaction. Therefore, the authors compared the two in patients undergoing carotid endarterectomy. METHODS: Forty patients undergoing carotid endarterectomy were randomized to receive either a superficial or a deep cervical plexus block with 20 ml bupivacaine, 0.375%. Outcomes subjected to statistical analysis included supplemental anesthetic supplementation with lidocaine, 1%, by the surgeon, dermatomes affected by the block, paresthesia during block placement, postoperative pain scores, and analgesic requirements. RESULTS: Median supplemental lidocaine requirements were 6 ml (range, 0.5 to 20 ml) in the deep block group and 6 ml (range, 0 to 20 ml) in the superficial block group (P = 0.7323). Patients in the deep block group who reported paresthesia during block placement required less lidocaine supplementation (median, 2; range, 0.5 to 20 ml) than the 9.5 ml (range, 6 to 15.5 ml) required by those who did not experience paresthesia (P = 0.0113). Compared with patients in the superficial block group, those in the deep block group were less likely to need analgesia in the first 24 h after operation (P = 0.047), and those who required analgesia received it later (6.6 +/- 4.1 vs. 3.9 +/- 1.4 h after operation; Student's t test, P = 0.02). One patient in each group expressed dissatisfaction with the technique. CONCLUSIONS: Carotid endarterectomy may be performed satisfactorily during superficial or deep cervical plexus block placement with no differences in terms of supplemental local anesthetic requirements, although this is influenced by whether paresthesia is elicited during placement of the deep block. Therefore, the clinician's decision to use one block rather than another need not be based on any assumed superiority of one block based on intraoperative conditions or patient satisfaction.
PURPOSE: Protamine reversal of heparin anticoagulation during cardiovascular surgery may cause severe hypotension and pulmonary hypertension. A novel protamine variant, [+18RGD], has been developed that effectively reverses heparin anticoagulation without toxicity in canine experiments. Heretofore, human studies have not been undertaken. This investigation hypothesized that [+18RGD] would effectively reverse heparin anticoagulation of human blood in vitro. METHODS: Fifty patients who underwent anticoagulation therapy during vascular surgery had blood sampled at baseline and 30 minutes after receiving heparin (150 IU/kg). Activated clotting times were used to define specific quantities of [+18RGD] or protamine necessary to completely reverse heparin anticoagulation in the blood sample of each patient. These defined amounts of [+18RGD] or protamine were then administered to the heparinized blood samples, and percent reversals of activated partial thromboplastin time, thrombin clotting time, and antifactor Xa/IIa levels were determined. In addition, platelet aggregation assays, as well as platelet and white blood cell counts were performed. RESULTS: [+18RGD] and protamine were equivalent in reversing heparin as assessed by thrombin clotting time, antifactor Xa, antifactor IIa levels, and white blood cell changes. [+18RGD], when compared with protamine, was superior in this regard, as assessed by activated partial thromboplastin time (94.5 +/- 1.0 vs 86.5 +/- 1.3% delta, respectively; p < 0.001) and platelet declines (-3.9 +/- 2.9 vs -12.8 +/- 3.4 per mm3, respectively; p = 0.048). Platelet aggregation was also decreased for [+18RGD] compared with protamine (23.6 +/- 1.5 vs 28.5 +/- 1.9%, respectively; p = 0.048). CONCLUSIONS: [+18RGD] was as effective as protamine for in vitro reversal of heparin anticoagulation by most coagulation assays, was statistically more effective at reversal than protamine by aPTT assay, and was associated with lesser platelet reductions than protamine. [+18RGD], if less toxic than protamine in human beings, would allow for effective clinical reversal of heparin anticoagulation.
Factors affecting flow through blood administration sets in vitro were assessed under gravity-fed and pressurized conditions including an assessment of the influence of the intravenous (i.v.) cannula and Luer lock fitting. The fastest gravity fed flow of 4.775 mL s-1 was obtained through the largest internal diameter (ID = 4.8 mm) blood administration set. Flow through blood administration sets with ID = 3 mm was approximately 50% of this. Flow increased over base-line through all the administration sets when the i.v. cannula was removed (range 18-50%) and increased further over base-line when the Luer lock fitting was removed from the distal end (range 26-129%), indicating that these are rate-limiting steps in the system. The Y-type trauma set with the largest diameter tubing facilitated the fastest flow, although flow through all the Y-type trauma sets produced lower flow rates than the corresponding blood administration sets, which may reflect their relative increased length. The ideal blood administration set should have an internal diameter at least 4 mm and be less than 170 cm in length.
A four-week retrospective survey of intravenous fluid and electrolyte prescriptions on post-operative surgical patients revealed wide variability in fluid and electrolyte prescription by medical staff. Median volume of intravenous fluid prescribed was 3000 ml (range 1667-5000). Total sodium prescribed varied from 0 to 770, median 242 mmol/day), with potassium infrequently added (range 0-81, median 0 mmol/day). Patients undergoing emergency surgery were prescribed more sodium than those undergoing routine procedures (p = 0.0403); 0.9% saline was the most common fluid prescribed overall. There was poor correlation between serum electrolyte values and the amounts of electrolytes prescribed. Intravenous fluid prescription should take into account the post-operative stress response which reduces sodium requirements (unless there are other concomitant losses) and increases urinary potassium losses. A suitable post-operative 'maintenance' fluid is 4% dextrose/0.18% saline with 1-2 g potassium chloride, particularly if serum electrolyte levels are not known. Other fluid losses should be replaced with equivalent fluids.
Cardioversion is a minor procedure requiring sedation and analgesia. However, it is often performed out-of-hours in remote sites by inexperienced anaesthetists. An understanding is required both of the pathophysiology underlying cardiac arrhythmias and of the technical side of defibrillation equipment, including electrical safety. Patients should have their coagulation status and electrolyte balance checked prior to the procedure to reduce the likelihood of complications. Almost all the available anaesthetic agents have been used for cardioversion in the past, with varying degrees of success. The anaesthetic agent chosen for patients undergoing cardioversion must provide analgesia and sedation, cause the least cardiovascular compromise possible and still enable rapid recovery. Propofol may be the closest anaesthetic agent to this ideal currently available, although careful titration of any agent chosen is also important. Cardioversion may be performed as an emergency, including in the pregnant patient, providing safe anaesthetic practice is followed.
We have performed a prospective randomised trial of 30 patients undergoing craniotomy to compare intramuscular codeine phosphate with patient-controlled analgesia using morphine 1 mg bolus with a 10-min lockout and no background infusion. For 24 h postoperatively, pain, nausea, Glasgow coma score, respiratory rate and sedation score were assessed. There was a wide variation in the amounts of morphine requested by the patients in the patient-controlled analgesia group in the first 24 h postoperatively (range 2-79 mg, median 17 mg). There was a small, but non-significant, reduction in pain scores in the patient-controlled analgesia group. There were no significant differences between the two groups in respect of nausea and vomiting, sedation score or respiratory rate. No major adverse effects were noted in either group. Patient-controlled analgesia with morphine is an alternative to intramuscular codeine phosphate in neurosurgical patients which merits further investigation.
I have evaluated in vitro methods of increasing the flow rate of clear fluids through an i.v. cannula at room temperature. These included, alone and in combination: increasing the height of a gravity-fed system; increasing the i.v. cannula diameter, manual compression of the lower drip chamber and the use of pressure bags. Flow rate was measured using a uroflowmeter, which was found to be reliable and reproducible. The most effective methods of increasing flow were the use of a 14-gauge cannula rather than a 16-gauge cannula, which resulted in a 50% increase, and the use of a 300-mm Hg pressure bag with automatic adjustable pressure regulator, which doubled the flow rate. The combination of these two tripled the overall flow to nearly 600 ml min-1. Manual compression of the drip chamber, despite producing peak pressures of more than 100 cm H2O, was an inefficient method of improving flow compared with an external pressure bag.