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Biomedical subjects

J M Torrance

Publications and source records attributed to J M Torrance.

9 recordsLinked to original sources
PubMed2002

Extreme value theory applied to postoperative breathing patterns.

BACKGROUND: There has been little published work on the statistical features of breath times in postoperative patients. We applied extreme value theory (a statistical method) to the variation in the timing of postoperative breathing. METHODS: We observed 49 patients 3-6 h after a variety of surgical procedures, once they had achieved a stable breathing pattern. The breathing patterns could be one of the three types predicted by the extreme value model. 'Finite' breathing patterns (n=30) have a finite upper limit of duration for any apnoea. Patients that displayed one of the other two patterns ('standard' and 'extended') have, potentially, no limit in duration of apnoea. RESULTS: The type of breathing pattern observed in each patient was not reliably identified by most of the commonly used risk factors (age, type of surgery, opioid type, dose, and route of administration). A finite pattern was observed in 13 of 26 patients receiving epidural (vs 17 of 23 parenteral analgesia: P=0.15), and 15 of 19 receiving morphine (vs 15 of 30 other opioids: P=0.05). The patients with 'finite' patterns were also significantly less drowsy (score 1.04 (0.92) vs 1.62 (0.62), P<0.05). CONCLUSIONS: The breathing pattern was not related to mean breath times, suggesting that the prevalence of apnoeas cannot be reliably predicted by measurement of the respiratory rate alone.

Adult↗
PubMed2001

The effect of closed system suction on airway pressures when using the Servo 300 ventilator.

OBJECTIVES: To measure airway pressures during closed system suctioning with the ventilator set to three differing modes of ventilation. METHODS: Closed system suctioning was conducted in 16 patients following cardiac surgery. Suctioning was performed using a 14 French catheter with a vacuum level of -500 cmH2O through an 8.0 mm internal diameter endotracheal tube. The lungs were mechanically ventilated with a Servo 300 ventilator set to one of three ventilation modes: volume-control, pressure-control or CPAP/pressure support. Airway pressures were measured via a 4 French electronic pressure transducer in both proximal and distal airways. RESULTS: Following insertion of the suction catheter, end-expiratory pressure increased significantly (p < 0.001) in both pressure-control and volume-control ventilation. This increase was greatest (p = 0.018) in volume-control mode (2.7 +/- 1.7 cmH2O). On performing a five second suction, airway pressure decreased in all modes, however the lowest airway pressure in volume-control mode (-4.9 +/- 4.0 cmH2O) was significantly (p = 0.001) less than the lowest airway pressure recorded in either pressure-control (0.8 +/- 1.9 cmH2O) or CPAP/pressure support (0.4 +/- 2.8 cmH2O) modes. In CPAP/pressure support mode, 13 of the 16 patients experienced a positive pressure 'breath' at the end of suctioning with airway pressures rising to 21 +/- 1.6 cmH2O. CONCLUSIONS: Closed system suctioning in volume control ventilation may result in elevations of end-expiratory pressure following catheter insertion and subatmospheric airway pressures during suctioning. Pressure control ventilation produces less elevation of end-expiratory pressure following catheter insertion and is less likely to be associated with subatmospheric airway pressures during suctioning. CPAP/pressure support has no effect on end-expiratory pressure following catheter insertion and subatmospheric airway pressures are largely avoided during suctioning.

Journal Article↗
PubMed1998

Artefactual episodic hypoxaemia during postoperative respiratory monitoring.

PURPOSE: To determine the reliability of continuous pulse oximetry in the detection of episodic hypoxaemia in total hip joint replacement patients. Episodic hypoxaemia has been described in postoperative patients and is associated with analgesic technique. This study compared the incidence of hypoxaemic episodes identified solely by pulse oximetry and then subsequently where additional monitoring, as indicated for sleep-related breathing disorders, was also utilised. METHODS: Eight patients were studied on the night before and for three nights after surgery. Pulse oximetry, ECG, chest impedance, nasal and oral airflow and transcutaneous CO2 were recorded. Sudden episodic hypoxaemia was defined as a decrease in oxygen saturation of > or = 5% within two minutes, for > five seconds and with a nadir of < 90%. Artefacts were identified by noise signals on the ECG and impedance recordings and by a motion annotation wave superimposed on the oximetry trace. RESULTS: Using these criteria 172 (79%) of 219 desaturation events were classified as artefactual. The median duration of genuine events was greater (P < 0.001 Mann Whitney U test) than artefactual events; 21 sec (range, 6-443) vs 11 sec (5-63). Genuine desaturations reached a median nadir of SpO2 87% (range 83-89%) compared with 81% (61-88%) for the artefactual. These differences were statistically significant (P < 0.001). CONCLUSION: Previous studies utilising unobserved pulse oximetry data alone may have overestimated the incidence of episodic hypoxaemic events in postoperative patients.

Aged↗
PubMed1997

Low-dose mivacurium supplementation of prilocaine i.v. regional anaesthesia.

We have compared in two groups of five healthy volunteers, the motor effect of prilocaine i.v. regional anaesthesia of the forearm with and without addition of mivacurium 0.6 mg. Although addition of mivacurium might, theoretically, provide the benefit of increased neuromuscular block with rapid plasma cholinesterase degradation in the isolated limb, we observed prolonged forearm weakness in the mivacurium group using tests of grip strength (median recovery to 90% of control, 80 min (range 60 min to > 8 h) vs control median recovery to 90% of 16 (8-24) min) and bead transfer (median recovery to 90% of control 36 (24-48) min vs control median recovery to 90% of 12 (8-16) min). This weakness was considerably in excess of that predicted by rapid systemic degradation of mivacurium. The mivacurium group experienced symptoms of local anaesthetic toxicity which did not occur in the control group and which could not be replicated by administration of mivacurium alone.

Anesthesia, Conduction↗
PubMed1987

Glucocorticoid receptors in murine erythroleukaemic cells.

Glucocorticoid receptors in murine erythroleukaemic cells were studied in relation to hexamethylene bisacetamide (HMBA) induced differentiation. Specific binding of dexamethasone was measured. A single class of saturable, high affinity binding sites was demonstrated in intact cells; with cell homogenates or fractions binding was low and could not be reliably quantified. Receptor binding in whole cell suspensions was lower in cells which had been treated with HMBA (36.5 +/- 8.2 pmol/g protein) than in untreated controls (87.9 +/- 23.6 pmol/g protein); dissociation constants were similar in treated (2.7 nM) and untreated cells (2.5 nM). Dexamethasone, hydrocortisone, corticosterone and progesterone competed with tritium-labelled dexamethasone for receptor binding sites; cortisone, deoxycorticosterone and oestradiol had little effect.

Acetamides↗