Preoxygenation in children using expired oxygraphy

We performed preoxygenation on 25 patients, aged 1-12 yr. End-tidal oxygen sampling was used to find the duration of preoxygenation required to reach an end-tidal oxygen fraction of 0.9. All children reached this end-point within 80 s, which was markedly more rapid than that observed in adult subjects. The clinical applications of this form of monitoring in children are discussed.      

CONTINUOUS EXTRADURAL ANALGESIA IN LABOUR: Comparison Between "On Demand" and Regular "Top-up" Injections

In a prospective comparative study 240 patients received extraduralbupivacaine, either by regular timed injections or "on demand",for pain relief during the first stage of labour. Three concentrationsof bupivacaine were used (0.5%, 0.375% and 0.25%). Quality andcontinuity of analgesia, motor blockade, spread of sensory blockade,cardiovascular changes, fetal outcome and maternal sequelaewere recorded. Overall, the analgesia provided by regular top-upinjections was superior to the on demand technique, especiallywhen 0.375% bupivacaine was used. This improved analgesia wasachieved without causing an increased incidence of operativedeliveries or deleterious sequelae, with respect to the motheror the neonate.     

AUTORADIOGRAPHIC DISTRIBUTION STUDY OF "SHORT ACTING" AND "LONG ACTING" BARBITURATES: 35S-THIOPENTONE AND 14C-PHENOBARBITONE

The distribution of ³⁵S-thiopentone and ¹⁴C-phenobarbitone hasbeen studied after intravenous injection in the mouse wholebody and in the cat brain, using an auto-radiographic technique.Thirty seconds after injection ³⁵S-thiopentone reached the highestconcentration in the brain and liver of the mice, leaving theblood very rapidly. The adipose tissue built up increasing levelsof radioactivity up to 20 minutes after the injection of ³⁵S-thiopentone.¹⁴C-phenobarbitone showed a more even distribution in parenchymatousand lean tissues. A rather constant level of radioactivity waspresent in the blood during 4 hours after the administrationof ¹⁴C-phenobarbitone. ¹⁴C-pheno-barbitone penetrated the bloodbrain barrier at a much slower rate than ³⁵S-thiopentone. Thebrain distribution of both compounds was studied in furtherdetail in the cat brain. Experiments with pregnant mice revealedsome differences in the placental passage and foetal distributionof these two barbiturates.     

Unrecognized "crack" cocaine abuse in pregnancy

We report a case of "crack" cocaine abuse in a pregnant patient associated with haematuria, proteinuria, haemolytic anaemia, renal impairment, thrombocytopenia and pulmonary oedema. The case illustrates the problems for clinicians where unrecognized cocaine abuse interferes with the diagnosis and management of a complicated pregnancy. In addition, we discuss the principles for the safe conduct of anaesthesia in the pregnant cocaine abuser.      

THE "STOVE-IN" CHEST: ANOTHER APPROACH TO TREATMENT

A case of "stove-in" chest is described in which the drug R1406(phenoperidine), a powerful analgesic and respiratory depressant,was used to allow the easy application of a mechanical ventilatorafter initial surgical fixation of the flail segment. It wasnoted that, under the influence of the drug, ventilation inparticular was adequate, and management in general relativelyeasy compared with previous cases. Undesirable side effectssuch as emesis and hypotension were not observed.     

Evaluation of a humidified nasal high-flow oxygen system, using oxygraphy, capnography and measurement of upper airway pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow, Fisher and Paykel Healthcare) by measuring delivered FiO, and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order FiO2, F(E)O2, F(E)CO2 and airway pressures were measured. Calculation of FiO2 from F(E)O2 and F(E)CO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cm H20. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.     

A Brief History of the "Feature Detector"

The feature detector hypothesis, and its subsequent developmentinto the doctrine that single neurons code for perceptuallysignificant events, has been the leitmotiv of most work on sensorysystems. In the face of strong competition from the alternativetheories of neural networks and oscillating ensembles of neurons,the single neuron doctrine retains its grip on the imaginationof those working on the neural mechanisms of perception.     

Ventilatory assistance and respiratory muscle activity. 2: Simulation with an adaptive active ("aa" or "a-squared") model lung

The aim of this study was to develop a lung model which adapted its active simulation of spontaneous breathing to the ventilatory assistance it received--an "aa" or "a-squared" lung model. The active element required was the waveform of negative pressure (pmus), which is equivalent to respiratory muscle activity. This had been determined previously in 12 healthy volunteers and comprised a contraction phase, relaxation phase and expiratory pause. Ventilatory assistance had shortened the contraction and relaxation phases without changing their shape, and lengthened the pause phase to compensate. In this study, the contraction and relaxation phases could be adequately represented by two quadratic equations, in addition to a third to provide a smooth transition. Therefore, the adaptive element required was the prediction of the duration of the contraction phase. The best predictive variables were flow at the end of contraction or peak mouth pressure. Determination of either of these allowed adjustment of the "standard" waveform to the level of assistance produced by an "average" ventilator, in a manner that matched the mean response of 12 healthy conscious subjects.      

Safety of patient-maintained propofol sedation using a target-controlled system in healthy volunteers

We investigated the safety of a patient-maintained system that allows individuals to operate a target-controlled infusion of propofol to achieve sedation. Ten healthy volunteers were recruited and instructed to try to anaesthetize themselves with the system. A target-controlled infusion of propofol was set to deliver a target propofol concentration of 1 microgram ml-1, and the subjects allowed to increase the target in increments of 0.2 microgram ml-1 by pressing a control button twice in 1 s. There was a lockout time of 2 min and a maximum permitted target concentration of 3 micrograms ml-1. Heart rate and pulse oximetry oxygen saturation (SpO2) were monitored continuously, and non-invasive arterial pressure, ventilatory frequencies and sedation scores were measured every 5 min. Sedation was continued until the subject stopped pressing the button. A keyword was then read for the individual to remember and sedation discontinued. There were no instances of significant decrease of SpO2 or loss of airway control. Maximum target blood concentration of propofol recorded ranged from 1.4 to 3 micrograms ml-1. Two subjects became oversedated, one of whom was unrousable with loss of eyelash reflex. No subject could recall the keyword, although one recognized it from a list of 10 words. We conclude that the patient-maintained sedation system described could not be guaranteed to produce only conscious sedation in all patients, and that close clinical supervision by an anaesthetist would still be required for safe operation.     

Noninvasive estimation of cerebral perfusion pressure and zero flow pressure in healthy volunteers: the effects of changes in end-tidal carbon dioxide

Zero flow pressure (ZFP) in the cerebral circulation is defined as the arterial pressure at which flow ceases. Noninvasive methods of estimating cerebral perfusion pressure (CPP) and ZFP using transcranial Doppler ultrasonography have been described. There is a paucity of normal physiological data related to changes in estimated CPP (eCPP) and ZFP induced by changes in carbon dioxide (CO(2)). We studied the effects of CO(2) on eCPP and ZFP in 17 healthy volunteers. After baseline measurements of middle cerebral artery blood-flow velocity and blood pressure, subjects voluntarily hyperventilated to decrease their end-tidal CO(2) (PE'CO(2)) by approximately 7.5 mm Hg, and then they increased their PE'CO(2) by approximately 7.5 mm Hg by breathing through a Mapleson D circuit. Blood-flow velocity and blood pressure were recorded at each stage. The eCPP and ZFP were calculated by using established formulas, and the results were analyzed with analysis of variance. With increasing PE'CO(2), eCPP increased from 50.67 mm Hg (8.33 mm Hg) (mean [SD]) to 60.87 mm Hg (9.28 mm Hg) (20% increase; P < 0.001), with a corresponding decrease in ZFP (P = 0.017); hypocapnia resulted in the opposite effects on eCPP and ZFP. These results indicate physiological changes in eCPP and ZFP that can be expected from changes in CO(2) in subjects without any neurological disorder. IMPLICATIONS: Increasing end-tidal CO(2) increases the estimated cerebral perfusion pressure and vice versa. These results are opposite to those expected from the known effects of CO(2) on intracranial pressure. Thus, we support the suggestion that, in the absence of intracranial hypertension, vascular tone remains a major determinant of effective downstream pressure and cerebral perfusion.     

Evaluation of five oxygen delivery devices in spontaneously breathing subjects by oxygraphy

Oxygen supply systems may be divided into constant and variable performance systems. As the variable performance systems are widely used, it is relevant to investigate the variation in performance between devices and the influence of oxygen supply on the inspired oxygen fraction. Data were collected from 10 healthy volunteers during the use of one constant performance system and four variable performance systems at different gas flows and inspired oxygen fractions. A thin sampling catheter was placed in the nasopharynx to allow the measurement of the end-tidal oxygen fraction. When oxygen was supplied to variable performance systems, end-tidal oxygen fraction values measured in this way varied less and were more easily quantifiable than inspired oxygen fraction. End-tidal oxygen fraction was used to calculate inspired oxygen fraction. With the variable performance systems, inspired oxygen fraction varied considerably between subjects whereas a constant and equal rise was found for each subject with the fixed performance system. A large nasal catheter was capable of delivering the highest inspired oxygen fraction, whereas the Venturi mask delivered the most precise inspired oxygen fraction. We found oxygraphy useful in the interpretation of measurements made in patients receiving unknown inspired fractions of oxygen.     

Clinical presentation of "silent" meningiomas after general anaesthesia

We present two patients who became unrousable within 48 h aftergeneral anaesthesia for non-neurosurgical operations; both werefound to have frontal meningiomas. Analysis of these and previousreports suggest that several anaesthetic and peri-operativefactors probably combine to contribute to the accelerated presentationof these previously "silent" tumours, and we recommend thatdexamethasone should be administered early in the course ofunexplained neurological deterioration after operation. (Br.J. Anaesth. 1995; 74: 335–337) Present address: Department of Anaesthesia, Charing Cross Hospital,Fulham Palace Road, London W6 8RF.     

Subcutaneous perfusion and oxygen during acute severe isovolemic hemodilution in healthy volunteers

HYPOTHESIS: Acute severe isovolemic anemia (to a hemoglobin [Hb] concentration of 50 g/L) does not decrease subcutaneous wound tissue oxygen tension (PsqO(2)). SETTING: University hospital operating room and inpatient general clinical research center ward. SUBJECTS: Twenty-five healthy, paid volunteers. METHODS: Subcutaneous oxygen tension and subcutaneous temperature (Tsq) were measured continuously during isovolemic hemodilution to an Hb level of 50 g/L. In 14 volunteers (initially well-perfused), "normal" perfusion (Tsq >34.4 degrees C) was achieved by hydration and systemic warming prior to starting isovolemic hemodilution, while in 11 volunteers (perfusion not controlled [PNC]), no attempt was made to control perfusion prior to hemodilution. MAIN OUTCOME MEASURES: Measurements of PsqO(2), Tsq, and relative subcutaneous blood flow (flow index). RESULTS: While PsqO(2), Tsq, and flow index were significantly lower in PNC vs well-perfused subjects at baseline, there was no significant difference between them at the Hb of 50 g/L (nadir). Subcutaneous PO(2) did not decrease significantly in either group. Arterial PO(2) was not different between the groups, and did not change significantly over time; Tsq and flow index increased significantly from baseline to nadir Hb in both groups. CONCLUSIONS: The level of PsqO(2) was maintained at baseline levels during hemodilution to Hb 50 g/L in healthy volunteers, whether they were initially well-perfused or mildly underperfused peripherally. Given the significant increase in Tsq and flow index, this resulted from a compensatory increase in subcutaneous blood flow sufficient to maintain oxygen delivery. Wound healing depends to a large extent on tissue oxygen delivery, and these data suggest that even severe anemia by itself would not be sufficient to impair wound healing. Thus, transfusion of autologous packed red blood cells solely to improve healing in surgical patients with no other indication for transfusion is not supported by these results.     

Salmeterol inhaler using a non-chlorinated propellant, HFA134a: systemic pharmacodynamic activity in healthy volunteers.

BACKGROUND--Metered dose inhalers for the treatment of asthma use chlorofluorocarbons as propellants. These face an international ban due to their effect on the ozone layer. Salmeterol has been reformulated using the non-chlorinated propellant Glaxo inhalation grade HFA134a. METHODS--The safety, tolerability and systemic pharmacodynamic activity of the salmeterol/HFA134a inhaler, the current salmeterol inhaler, and placebo (HFA134a) were compared in 12 healthy volunteers in a double blind, randomised crossover study using a cumulative dosing design. RESULTS--Safety and tolerability were similar and the response was related to the dose over the range used (50-400 micrograms) with both salmeterol inhalers. The salmeterol/HFA134a inhaler showed no differences from the current inhaler for pulse rate, blood pressure, tremor, QTc interval, and plasma glucose levels. The salmeterol/HFA134a inhaler had significantly less effect on plasma potassium levels. CONCLUSIONS--In healthy volunteers the salmeterol/HFA134a inhaler is at least as safe and well tolerated as the current salmeterol inhaler, and has similar systemic pharmacodynamic activity.     

"As time goes by": Angiotensin II-mediated transactivation of the EGF-receptor comes of age

Nephrol Dial Transplant 2005; 20: 2050–2053 The incorrect version of Figure 1 was published, the correctversion of this figure is     

CONGENITAL FIBRO-OSSEOUS DYSPLASIA OF JAWS ("HIPPOPOTAMUS FACE"): An anaesthetic problem

Two brothers with "hippopotamus face" deformities presentedfor corrective surgery under general anaesthesia. In the firstpatient, blind nasal intubation was successful. In the secondpatient, trache otomy was avoided by the use of an intubatingbronchoscope.     

THE HALOSCALE "INFANTA" WRIGHT RESPIROMETER: An In Vitro and In Vivo Assessment

The performance of the Haloscale "Infanta" respirometer hasbeen assessed in vitro using ISO test compliances and resistances,and in vivo by comparison with pneumotachograph volumes in 13spontaneously breathing children and 13 children during intermittentpositive pressure ventilation. The Infanta was shown to be capableof registering volumes between 15 and 200 ml with an accuracyof ±5%. The registered volume decreased rapidly below15 ml, whilst above 200 ml over-registration developed.     

The effect of ketanserin on cerebral blood flow and oxygen metabolism in healthy volunteers

Summary The effect of the anti-hypertensive agent ketanserin on average global cerebral blood flow (CBF) and average global cerebral oxygen metabolism (CMRO₂) was examined in 8 healthy volunteers. CBF and CMRO₂ were measured with the Kety-Schmidt technique before ketanserin administration (baseline) and after administration of 2 different doses of ketanserin intravenously (dose I: 10 mg bolus and an infusion of 6 mg/h; dose II: 20 mg bolus and an ifusion of 20 mg/ h). Baseline CBF and CMRO₂ were 60 and 3.6 ml/100 g/min, respectively, and were not changed by administration of ketanserin dose I. During administration of dose II, however, CBF fell to 52 ml/ 100 g/min (p=0.05) and CMRO₂ was reduced to 3.2 ml/100 g/min (p < 0.05).We conclude that when administered in a high dose, ketanserin has the ability to depress cerebral oxygen metabolism, but when administered in a clinically relevant dose ketanserin does not influence average global CBF or average global CMRO₂. Ketanserin could be a safe antihypertensive drug in neuroanaesthesia or in the neuro-intesive care unit.