Safer central venous access.
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Catheterization, Central Venous↗
Biomedical subjects
A J McShane
Publications and source records attributed to A J McShane.
Assessment of a simple artificial neural network for predicting residual neuromuscular block.
BACKGROUND: Postoperative residual curarization (PORC) after surgery is common and its detection has a high error rate. Artificial neural networks are being used increasingly to examine complex data. We hypothesized that a neural network would enhance prediction of PORC. METHODS: In 40 previously reported patients, neuromuscular function, neuromuscular block/antagonist usage and time intervals were recorded throughout anaesthesia until tracheal extubation by an observer uninvolved in patient care. PORC was defined as significant 'fade' (train of four <0.7) at extubation. Neuromuscular function was classified as PORC (value=1) or no PORC (value=0). A back-propagation neural network was trained to assign similar values (0, 1) for prediction of PORC, by examining the impact of (i) the degree of spontaneous recovery at reversal, and (ii) the time since pharmacological reversal, using the jackknife method. Successful prediction was defined as attainment of a predicted value within 0.2 of the target value. RESULTS: Twenty-six patients (65%) had PORC at tracheal extubation. Clinical detection of PORC had a sensitivity of 0 and specificity of 1, with an indeterminate positive predictive value and a negative predictive value of 0.35. Using the artificial neural network, one patient with residual block and one with adequate neuromuscular function were incorrectly classified during the test phase, with no indeterminate predictions, giving an artificial neural network sensitivity of 0.96 (chi(2)=44, P<0.001) and specificity of 0.92 (P=1), with a positive predictive value of 0.96 and a negative predictive value of 0.93 (chi(2)=12, P<0.001). CONCLUSIONS: Neural network-based prediction, using readily available clinical measurements, is significantly better than human judgement in predicting recovery of neuromuscular function.
Adult↗
Atracurium is associated with postoperative residual curarization.
BACKGROUND: Residual paralysis following the use of neuromuscular blocking drugs remains a clinical problem. As part of departmental quality assurance, we examined the degree of postoperative residual curarization (PORC) following atracurium. METHODS: Forty patients undergoing general anaesthesia involving atracurium were studied. Quantitative neuromuscular monitoring (mechanomyography, Myograph 2000, Biometer, Denmark) was performed by assessing the response to supramaximal train-of-four (TOF) stimulation of the ulnar nerve. Anaesthesia was provided by non-participating clinicians who were blinded to the study data. A TOF ratio </=0.7 at extubation was classified as PORC. RESULTS: At antagonism of neuromuscular block, 70% (28/40) of patients had a TOF ratio </=0.7, and 65% (26/40) of patients had a TOF ratio </=0.7 at extubation. Peripheral nerve stimulator use was associated with a longer interval from antagonism of block to extubation (P=0.01), but was not associated with differences in atracurium dosage or a reduction in PORC at extubation. Patients with TOF ratio </=0.7 at extubation had surgery of shorter duration [59 (SEM 6) vs 103 (9) min, P<0.001], greater doses of atracurium relative to the duration of surgery [6 (1) vs 11 (1) micro g kg(-1) min(-1), P<0.005], and shorter intervals from administration of last dose of atracurium to antagonism of neuromuscular block [29 (2) vs 53 (9) min, P<0.005] and from antagonism to extubation [6 (1) vs 15 (4) min, P<0.01]. Duration of surgical procedure was the sole multivariate predictor of PORC [odds ratio 0.94 (95% confidence intervals 0.91-0.98), P<0.01]. CONCLUSIONS: PORC remains a clinical problem despite use of intermediate-duration neuromuscular blocking drugs and peripheral nerve stimulators. Patients undergoing procedures of short duration may be at risk of inappropriately early tracheal extubation, possibly due to work pressures. The association between suboptimal antagonism of neuromuscular blockade and short procedures needs reinforcement during postgraduate training and departmental quality assurance.
Adult↗
Gastroesophageal reflux during spontaneous respiration with the laryngeal mask airway.
PURPOSE: To determine the incidence of gastroesophageal reflux during general anesthesia with the Laryngeal Mask Airway (LMA). METHODS: Twenty unpremedicated patients with no risk factors for reflux having day case anesthesia were included. Type of surgery was Orthopedic (n=8), General (n=7) and Gynecological (n=5). The average duration of anesthesia was 38.1 min, range 12 - 71 min. Anesthesia was induced with 1-2 microg x kg(-1) fentanyl and 2-3 mg x kg(-1) propofol and maintained with oxygen 33%, nitrous oxide 66% and isoflurane 1% (end-tidal). Ventilation by hand was performed until spontaneous respiration resumed. To facilitate surgery, 13 patients were placed in the supine and seven in the lithotomy positions. Two pH-sensitive electrodes were used to identify reflux. One was placed in the oesophagus 20 cm from the anterior nares to detect esophageal reflux and the other was placed through the bars of the LMA to detect refluxing material around the LMA. RESULTS: Esophageal reflux occurred in 12 patients (60%), in five of the 13 in the supine position and in all patients in the lithotomy position. The LMA electrode detected a decrease in pH in four cases (20%), all in the lithotomy position. The incidence reflux in the lithotomy and supine positions was different (Exact Probability test; P = 0.01). CONCLUSION: This study suggests that the lithotomy position predisposes patients to a higher risk of aspiration than the supine position when using a LMA.
Adult↗
Preoperative education and outcome of patient controlled analgesia.
PURPOSE: To determine the effect of intensive preoperative education on the outcome of Patient Controlled Analgesia (PCA) postoperatively. METHODS: This prospective randomised study was carried out in a single teaching hospital over three months. One group of patients (n = 42) received a 20 min standardised tutorial regarding PCA use from a single investigator and the other group (n = 43) received no additional education apart from the routine preoperative anaesthetic consultation. A blinded investigator assessed the patients following surgery. Pain scores and morphine consumption, patient satisfaction, side-effect profile and anti-emetic use were recorded at six, 24 and 48 hr postoperatively. RESULTS: Pain scores, satisfaction scores and morphine consumption were similar in both groups throughout the study period. Fewer patients in the tutored group complained of nausea from 6 to 24 hr than did untutored patients (28% vs 51%; P < 0.05). More tutored patients used antiemetic medication from 0 to 6 (28% vs 12%; P < 0.05) and 6 to 24 hr (37% vs 19%; P < 0.05). Side effect profile and requirement for rescue analgesia was otherwise similar in both groups. CONCLUSION: Our results suggest that specific preoperative education of patients using PCA does not alter pain scores, morphine consumption or patient satisfaction but may result in earlier and more effective use of anti-emetic medication.
Analgesia, Patient-Controlled↗
Gastroesophageal reflux and tracheal contamination during laparoscopic cholecystectomy and diagnostic gynecological laparoscopy.
UNLABELLED: Laparoscopy causes an increase in intraabdominal pressure and may lead to an increase in gastroesophageal reflux (GER). We designed this study to assess and compare the frequency of GER and tracheal contamination in patients undergoing laparoscopic cholecystectomy (LC) and gynecological laparoscopy (LG). We studied 20 LC and 17 LG patients. The pH was measured using monocrystalline antimony pH electrodes positioned in the middle to upper esophagus and on the posterior wall of the trachea distal to the tip of the endotracheal tube. Acid reflux was defined as a decrease in esophageal pH to 4.0 or less. Alkaline reflux was defined as an abrupt increase in esophageal pH of more than 1.0, not associated with previous acid reflux. More than 80% of all patients at baseline had a gastric pH < or = 2. Overall, acid GER alone occurred in 47% patients in the LG group and in 15% patients in the LC group. During recovery, a larger proportion of patients had acid reflux in the LG group (47%) than in the LC group (10%). In contrast, alkaline reflux occurred in 75% of LC patients and 11.7% of LG patients. After cholecystectomy, there is an acute increase in the incidence of alkaline reflux. This alkaline reflux may be due to duodenogastric reflux resulting in an alkaline gastric shift. IMPLICATIONS: We studied the incidence of reflux of stomach contents in patients undergoing laparoscopic (keyhole) surgery for cholecystectomy or gynecology, using pH probes in the esophagus (gullet) and the trachea (windpipe). Acid reflux was very common but did not pass into the trachea. After gallbladder removal, the refluxed material became alkaline.
Adult↗
An intravascular microdialysis sampling system suitable for application in continuous biochemical monitoring of glucose and lactate.
Direct sensor implantation for continuous biochemical monitoring has proved disappointing, but microdialysis sampling devices can serve as a biocompatible patient-sensor interface. We propose a novel "MiniShunt" extracorporeal microdialysis sampling circuit designed to sample core blood, and report the performance of different microdialysis probe membrane types and sizes with pumped and non-pumped blood flow in anaesthetised dogs. Discrete microdialysate and plasma samples collected during glucose and lactate monitoring were analysed with a YSI analyzer and showed microdialysis efficiency (% relative recovery) in excess of 95% for both analytes using fibres of greater than 70 mm2 internal surface area. Pumped veno-venous extracorporeal blood microdialysis sampling of this type could provide a suitable interface for future multi-analyte on-line biosensor applications in critically ill patients.
Animals↗
The incidence of gastroesophageal reflux with the laryngeal mask: a comparison with the face mask using esophageal lumen pH electrodes.
To test the hypothesis that the laryngeal mask airway (LMA) predisposes patients to gastroesophageal reflux, we randomly assigned 55 patients having elective surgery to receive standardized anesthesia with the LMA or with conventional face mask (FM) plus airway. A pH-sensitive probe with two electrodes, 10 cm apart, was passed nasally into the esophagus 1 h before induction of anesthesia, and recordings were made continuously until 30 min after surgery. At the distal electrode, 30 cm from the anterior nares, there was a significant difference in the incidence of reflux: 53.6% with the LMA versus 22.2% with the FM (P < 0.05). At the level of the proximal electrode, 20 cm from the anterior nares, there was no difference between groups. Multiple reflux events, defined as two or more reflux events before, during, or after anesthesia, were significantly more frequent in the LMA group (P < 0.05). Reflux events continued in the postanesthesia care unit (PACU) in both groups with no significant difference between groups. There was no clinical evidence of aspiration of gastric contents in either group. Use of the LMA appears to result in increased reflux to the level of the mid to upper esophagus, and is associated with a more frequent incidence of multiple reflux events than use of the FM.
Adult↗
Bacteraemia following nasopharyngeal airway insertion.
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Bacteremia↗
Barbiturate anesthetics inhibit thromboxane-, potassium-, but not angiotensin-induced pulmonary vasoconstriction.
Administration of the oxidant lipid peroxide tertiary butyl hydroperoxide (t-bu-OOH) in the isolated rabbit lung leads to acute pulmonary vasoconstriction, which is caused by the synthesis of thromboxane. The inhalational anesthetics, halothane, nitrous oxide, and cyclopropane, markedly enhance t-bu-OOH-induced pulmonary vasoconstriction and thromboxane production. The effects of the intravenous (iv) barbiturates thiopental and pentobarbital on t-bu-OOH-induced vasoconstriction were studied. Thiopental completely and pentobarbital partially blocked t-bu-OOH-induced vasoconstriction. Thiopental inhibited t-bu-OOH-induced synthesis of thromboxane and prostacyclin but pentobarbital did not. This inhibitory action of thiopental may be due to its antioxidant properties because similar inhibition has been observed of t-bu-OOH-induced thromboxane production with the antioxidants, vitamin E, or butylated hydroxylanisole. Thiopental and pentobarbital also inhibited the vasoconstriction induced by a thromboxane analog, epoxymethano prostaglandin H2 (U46619). Finally, both barbiturates partially inhibited the pulmonary vasoconstriction caused by potassium chloride, which requires calcium entry, but they did not inhibit the constriction caused by angiotensin II, which does not require calcium entry. These results suggest that pentobarbital and thiopental may block pulmonary vasoconstriction by inhibiting calcium entry.
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
Mepacrine attenuates pulmonary vasoreactivity in rabbits.
The organic peroxide tert-butyl hydroperoxide (t-bu-OOH) induces pulmonary vasoconstriction by stimulating production of thromboxane in the rabbit lung, possibly by activating phospholipase A2. t-bu-OOH-induced vasoconstriction and thromboxane production is augmented by inhalational anesthetic agents, perhaps due to an effect of anesthetic agents on membrane lipids. To further investigate the mechanism of thromboxane generation, we studied the influence of the phospholipase A2 inhibitor, mepacrine, in a dose known to inhibit the enzyme in other systems, on t-bu-OOH-induced pulmonary arterial vasoconstriction. We found that 10(-4) M mepacrine completely inhibited t-bu-OOH-induced vasoconstriction. We also found that mepacrine inhibited arachidonic acid-induced pulmonary vasoconstriction but did not inhibit thromboxane productions. We also investigated the effect of mepacrine on two other pulmonary vasoconstrictors, angiotensin II (ANG II) and KCl, which do not act through arachidonic acid metabolites in the rabbit lung. Mepacrine inhibited both ANG-II and KCl-induced vasoconstriction. The inhibition by mepacrine of pulmonary vasoconstriction is reversible if the drug is washed out of the lung. This effect of mepacrine cannot be explained by phospholipase inhibition alone and is consistent with prevention of smooth muscle contraction.
Angiotensin II↗
Effect of PEEP and jugular venous compression on canine cerebral blood flow and oxygen consumption in the head elevated position.
Cerebral blood flow (CBF) (radiolabelled microspheres) and oxygen consumption (CMRO2) were studied in nine dogs during 30 min of either neck vein compression or application of positive end-expiratory pressure (PEEP) ventilation. With the animal in the prone position, elevation of the head from horizontal to 30 cm above the heart markedly decreased cisterna magna (PCSF) and dorsal sagittal sinus pressure (PCV). With the head elevated, compression of neck veins using neck tourniquet (pressure 40 mmHg) increased PCSF and PCV from 3.6 +/- 2.2 to 6.8 +/- 4.8 and -2.5 +/- 2.7 to 2.3 +/- 2.3 mmHg (mean +/- SE, P less than 0.05), respectively, while total or regional CBF and CMRO2 remained unchanged. Application of PEEP (15 cm H2O) increased right atrial pressure (-4.7 +/- 1.7 to -0.1 +/- 3.4 mmHg, P less than 0.05), but did not affect PCSF or PCV (3.4 +/- 3.3 to 3.3 +/- 3.7 and -3.5 +/- 2.6 to -4.1 +/- 2.4 mmHg, respectively, P greater than 0.05). Total or regional CBF and CMRO2 were also unaffected. These data demonstrate that, although neither maneuver affects CBF or CMRO2, neck vein compression elevates PCV above atmospheric pressure, but PEEP does not. In patients at risk for cerebral venous embolism, intermittent neck vein compression should be used as a prophylactic measure to prevent air embolism.
Animals↗
Potential analgesic contribution from morphine-6-glucuronide in CSF.
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Analgesia↗
Autotransfusion: quality of blood prepared with a red cell processing device.
The quality of blood salvaged at operation and prepared with the Dideco Autotrans BT 795 autotransfusion device was compared with that of donor blood in 41 patients having cardiac surgery involving cardiopulmonary bypass. Saved blood had a higher haemoglobin concentration (17.3 v. 13.1 g dl-1; P less than 0.001), a higher 2,3-diphosphoglycerate concentration (5.3 v. 1.1 mmol litre-1; P less than 0.00001), higher white cell count (17.1 X 10(9) litre-1 v. 4.1; P less than 0.00001), higher pH (7.5 v. 6.6; P less than 0.00001) and a more physiological potassium concentration (5.4 v. 8.8 mmol litre-1; P less than 0.00001) than donor blood. Saved blood platelet count was 34.5 X 10(9) litre-1 compared with 146.24 X 10(9) litre-1 (P less than 0.00001) and its heparin concentration was 0.64 u. ml-1. We conclude that this autotransfusor is a useful aid to blood conservation, producing good quality red cells with relatively normal pH and potassium values. However, modification of the centrifugation and washing is required to lessen the high white cell count and heparin concentrations found in the saved blood.
Adolescent↗
Preoxygenation and pulse oximetry may delay detection of esophageal intubation.
A case of delayed detection of esophageal intubation is described. Preoxygenation and pulse oximetry were used, and the first indication of tube misplacement was arterial desaturation indicated by the pulse oximeter. The combination of preoxygenation and pulse oximetry may contribute to delays in early detection of endotracheal tube misplacement for the following reasons: (1) preoxygenation results in a pulmonary reservoir of oxygen sufficient to maintain arterial hemoglobin saturation for an extended period of time; and (2) the maintenance of normal arterial saturations for an extended period after inadvertent esophageal tube placement may lead the practitioner to initially seek other causes of declining oxygen saturations. Although pulse oximetry is an acknowledged advance in patient monitoring, it must not be utilized as an early indication of correct endotracheal tube placement.
Aged↗
Prevention of bacterial endocarditis: does nasal intubation warrant prophylaxis?
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Adolescent↗
Induction of anesthesia with isoflurane in children.
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Adolescent↗
Isoflurane in paediatric anaesthesia. Induction and recovery from anaesthesia.
The characteristics of induction with and recovery from isoflurane anaesthesia were studied in 248 children. The mean time to loss of consciousness was 1.5 min (SD 0.5). Tracheal intubation, without interruption of spontaneous ventilation, was accomplished in a mean time of 4.2 min (SD 54 seconds). Movement and excitement, of 20-30 seconds duration, occurred in 23.9% children and 22 patients coughed during induction; 15 (12.6%) during the first 124 inductions; 7 (5.6%) subsequently. The mean half-times of reduction of alveolar isoflurane concentrations in 28 children whose lungs were ventilated with isoflurane and in 13 children who breathed isoflurane spontaneously during anaesthesia were: 45 sec after exposure for one hour, 70 sec after exposure of 2-3 hours and 110 seconds following exposures of 4-8 hours. The mean recovery times of the three groups were 6.5, 9.5 and 11.5 min respectively. In two further groups of nine children the mean half times of elimination of halothane and isoflurane were 220 seconds and 54 seconds respectively; recovery from isoflurane was markedly faster. Isoflurane is well accepted by children; induction is more rapid than with halothane, and the marked flexibility in the control of its effects are due to its relative insolubility. It has wide application in paediatric anaesthesia.
Adolescent↗