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Minute ventilation (VE) (mlmin−1), respiratory frequency (f), mixed expired carbon dioxide fraction (FĒCO2 and end-tidal carbon dioxide concentration E′CO2) (%) were measured, and alveolar ventilation (VA), deadspace (VD), deadspace/tidal volume ratio (VD/VT) and carbon dioxide output (VCO2) calculated in 58 anaesthetized, spontaneously breathing infants and children weighing 2.8−20.5kg. Although minute volumes varied, tidal volume correlated well with weight (r = 0.83), with a mean tidal volume (± ISD) of 5.2±1.2mlkg−1. It was concluded that, by the use of mean VT + ISD (approximated to 6 ml kg−1) the fresh gas flow in mlmin−1 should be set at 2.5×6×kg×f(15×kg×f) to avoid rebreathing in various T-piece systems in anaesthetized, intubated and spontaneously breathing infants up to a body weight of 20 kg. End-tidal carbon dioxide concentration was lower in younger patients who were premedicated with atropine alone than in the older ones who received opioid premedication also. Respiratory frequency, VD/VT and total VD per minute were higher in the younger age group, which explained the finding of a high VE in relation to VCO2 for these patients. This inefficiency of ventilation emphasizes the need to minimize apparatus deadspace in breathing systems used for small infants.

Measurements of minute and alveolar ventilation (VE and VA), respiratory frequency, end-tidal carbon dioxide concentration (E′CO2), deadspace (VD) and carbon dioxide output (VCO2) were made in 22 anaesthetized infants and young children during spontaneous (SV) and intermittent positive pressure ventilation (IPPV). In the children who had been given an opioid premedication, E′CO2 concentrations were significantly greater during SV than the predetermined value set for IPPV. In infants premedicated with atropine alone, E′CO2 during SV was only slightly greater than during IPPV, and VA was not changed. A mean tidal volume (VT) of 9.8 ± 2.5 ml kg−1, and a mean VE of between 225 and 250 ml min kg−1, were required to produce (E′CO2) 4.5% during IPPV. Despite a decrease in respiratory frequency, VD/VT and VD per minute were both decreased by IPPV in infants. VCO2 was unchanged in both groups. The decrease in wasted ventilation seen during IPPV in infants supports its use in clinical practice.

In 38 paediatric surgical patients given atracurium by infusion, the degree of neuromuscular blockade was monitored using the post-tetanic twitch response. This was assessed by counting the number of visible responses when single twitch stimulation was applied at 1 Hz for 30 s after a 5-s tetanic stimulation at 50 Hz. A post-tetanic count of less than 10 correlated with a single twitch height of less than 5% of control, and ensured adequate paralysis. Once the count was greater than 15, the blockade could be antagonized readily.

The performance of the Haloscale “Infanta” respirometer has been assessed in vitro using ISO test compliances and resistances, and in vivo by comparison with pneumotachograph volumes in 13 spontaneously breathing children and 13 children during intermittent positive pressure ventilation. The Infanta was shown to be capable of registering volumes between 15 and 200 ml with an accuracy of ±5%. The registered volume decreased rapidly below 15 ml, whilst above 200 ml over-registration developed.

The dimensions of tracheal tubes and connectors in common use were measured together with the resistance to breathing at flow rates occurring in babies breathing quietly. The outside diameters of rubber tubes varied more than those of plastic tubes. The main factors influencing resistance were the internal diameter and a sudden change in diameter or direction of flow. These are of particular importance in tubes of 2.5 mm i.d. and less and may cause an increase in the work of breathing during spontaneous ventilation. The resistance of small Cole pattern tubes was greater than that of plain tubes of similar o.d.

The effect of positive end expiratory pressure (PEEP) during mechanical ventilation of the lungs was measured in 10 young children, aged 3 weeks to 30 months, who were being ventilated artificially after cardiopulmonary bypass surgery. Changes in the end-tidal lung volume were measured directly using a jacket plethysmograph, and were assumed to indicate change in functional residual capacity (FRC). Simultaneous changes in compliance and blood-gases were measured also. FRC was increased in all subjects, and in most this increase was accompanied by an increase in arterial oxygenation. There was no significant alteration in the mean values of dynamic or static compliance in the group, although dynamic compliance increased during PEEP in six patients. PEEP may be of value after cardiopulmonary bypass in young children when oxygenation is poor despite high inspired oxygen fractions. The possible mechanisms by which it increases PaO2 are discussed.

The change in end-tidal position (ETP) after suxamethonium-induced paralysis was measured in 15 children during routine general anaesthesia. In all patients the onset of muscle paralysis was associated with an increase in lung volume from ETP. This increase may be the result of paralysis of the expiratory muscles which are active during anaesthesia.

Jarvis, S. C. and Hatch, D. J. 1985. The effects of aluminium on the growth of white clover dependent upon fixation of atmospheric nitrogen.−J. exp. Bot. 36: 1075–1086. The effects of aluminium (Al3 +) on the growth of white clover dependent upon symbiotic fixation of atmospheric nitrogen were examined at concentrations that may be encountered in solutions from soils of low pH. Well established plants were grown in flowing solution culture with carefully maintained concentrations of Al and of P and with pH held constant at a value (4.5) at which insoluble precipitates are unlikely to form. After 3 weeks of treatment, there were major visual differences between treatments in both shoots and roots. Although added Al at 25, 50 and 100 mmol m−3 reduced dry weight, the differences between the plants were not significant. There were, however, some considerable differences in P and Ca contents between the treatments. Much of the Al held by the roots was displaced when plants were transferred to solutions containing either scandium or gallium. As well as the effects on the plant, Al had a considerable influence on the fixation of atmospheric nitrogen. At concentrations of 50 and 100 mmol m−3 Al3+ nodule initiation was reduced and there was a much reduced nodule nitrogenase activity per unit of root. Even at 25 mmol m−3 Al3+, when nodule numbers were not reduced, nitrogenase activity was adversely affected.

In 12 spontaneously breathing intubated children (9.3–25 kg), ventilatory responses to rebreathing and to the inhalation of carbon dioxide (CO2) were investigated during halothane anaesthesia for minor surgical procedures. A T-piece (Mapleson F system) was used, modified by the insertion of a pneumotachograph and a paediatric airway adaptor of an in-line capnograph in the patient limb. Exhaled gas was collected for determination of expired CO2 content. Measurements were made when the fresh gas flow (FGF) was at the borderline for rebreathing (FGFr) and during 10 min with a mean FGF 44% lower, producing a maximal inspired CO2 (ICO2 max) (%) of 1.45±0.38% (mean± 1 SD). Measurements were repeated 5 min after returning to a flow exceeding FGFr and then during CO2 inhalation for 10 min after the addition of 1.24±0.32 % CO2 (mean±1 SD) to this flow. During both rebreathing and CO2 inhalation end-tidal CO2 (ECO2) was unchanged and $$\dot{\hbox{ V }}\hbox{ E }$$ did not increase significantly (18%), but during CO2 inhalation alveolar ventilation increased (P < 0.05), indicating an adequate and intact response to this level of CO2 inhalation. Estimations of ICO2 max could be made from the expression: lCO2 max(%) = −0.7 x FGF/$$\dot{\hbox{ V }}\hbox{ E }$$ +2.5 and FGF to minute ventilation ($$\dot{\hbox{ V }}\hbox{ E }$$) ratios lower than 1 were found to produce lCO2 max of 1.8% or higher. Such low FGF are likely to result in rebreathing within the alveolar ventilation and are thus of clinical importance. We believe that to increase the margin of safety in anaesthetized spontaneously breathing children, FGF of at least 1.5 to 2 times $$\dot{\hbox{ V }}\hbox{ E }$$ should be used.

The Nuffield 200 ventilator was compared with a new valveless ventilator (CW 200) in 20 children undergoing general anaesthesia for paediatric surgery. The new ventilator incorporates design features which overcome the main disadvantages of the Nuffield 200 and make it an inherently safer machine. At identical ventilator settings it produced a significantly greater tidal volume with a reduction in end-tidal carbon dioxide partial pressure. This may have advantages in avoiding pulmonary barotrauma in children.

A system is described which uses a microcomputer to control pH in flowing solution culture and a brief account is given of its performance when intact perennial ryegrass (Lolium perenne L.) plants were grown in nutrient solutions with pH controlled at 5.0, 5.5, 6.0 and 7.0.

All 484 candidates for the 1988 Fellowship in Anaesthesia (Part Three) were surveyed to investigate any differences between successful and unsuccessful candidates in study techniques, work and domestic factors, and examination history that might lead to better guidance to those preparing for the examination and an improvement in the current success rate of less than 30%. Candidates' views were sought also on the examination process. The response rate was 67%. Forty-two percent of respondents passed the examination. Forty-seven percent of successful and 55% of unsuccessful candidates considered their clinical workload was excessive. Successful candidates reported better departmental support, more systematic and adequate preparation, and a better knowledge of the scope of the examination. Unsuccessful candidates were more likely to have had a personal or family crisis or change in job which impeded their preparation for the examination. Almost 50% of all respondents were unhappy with the method of announcing results.

The results of the ventilatory management of babies, obtained in the first 3 years of a neonatal surgical intensive care unit, are assessed. Overall mortality figures and detailed examination of the cause of death in individual diagnostic groups support a selective approach to intermittent positive pressure ventilation (IPPV) based mainly on clinical criteria. The adoption of a policy of prophylactic IPPV after operation would achieve virtually no improvement in mortality.

The onset characteristics of pancuronium, tubocurarine and a mixture of these two neuromuscular blocking drugs were studied during the induction of neuromuscular blockade, using a train-of-four pattern of stimulation. Four characteristics of onset were defined: train-of-four fade = a reduction in the height of the fourth twitch greater than a reduction in the height of the first twitch; latent onset time = time from injection of neuromuscular blocker to a greater than 5% reduction in the first twitch in the train-of-four; total onset time = time to 90% reduction in twitch height; manifest onset time = time from 5% to 90% reduction in twitch height. Tubocurarine was associated with significantly more fade than either pancuronium or the mixture. During the period of study the fade profile of the mixture was almost identical to that of pancuronium alone. The mixture had the most rapid total onset time (100.3 s), tubocurarine the slowest (135.1 s) and pancuronium was intermediate (124.0 s). The mixture and tubocurarine had similar latent onset times, while the mixture and pancuronium had similar manifest onset times.

The influence of fresh gas flow (FGF) setting on rebreathing was investigated in 15 infants and children (weight 3.5–21.8 kg) during balanced anaesthesia with mechanically controlled ventilation using a T-piece (Mapleson E) system and a Nuffield ventilator 200. Tidal volume (VT), minute volume (VE), maximal inspired (PlCO2) and end-tidal (PE′co2) carbon dioxide tensions and airway pressure were measured. VE, set to produce a PE′CO2 of about 4.5 kPa and measured at a high FGF (minimal rebreathing), was unchanged throughout the study and the regression equation for VE and weight was: VE (ml min−1) = 146× kg ³ 482, r = 0.92. Measurements were then repeated at FGF: VE ratios reduced to 1.5 and 1.0. To achieve minimal rebreathing (PlCO2 less than 0.5 kPa), FGF: VE ratios greater than 1.8 (range 1.8–4.9) had to be used. At FGF: VE ratios of 1.5, some alveolar rebreathing occurred, indicated by increased inspired (P < 0.001) and end-tidal (P < 0.001) carbon dioxide tensions. At FGF: VE ratios equal to 1.0, alveolar rebreathing was more pronounced and hypercapnoea occurred with a PE′CO2 (mean ± 1 SD) of 5.89±0.53 kPa. At this FGF setting, change in I: E ratio from 1: 2 to 1: 1 did not influence the level of alveolar rebreathing. A minimal FGF (ml min−1) setting of 1.5 × VE (that is, 1.5 (146 × kg ³ 482), approximated to the expression (200 × kg ³ 1000) is recommended for controlled ventilation to avoid hypercapnoea when using the T-piece system in children weighing less than 20 kg.

In 14 intubated, spontaneously breathing children with body weight (bw) ranging from 8.3 to 25.6 kg, the influence of midazolam 0.1 mg kg−1 i.m. (group M0.1′, n = 7) and 0.2 mg kg−1 i.m. (group M0.2′ n = 7) as pre-medication, on sedation, ventilation, ventilatory response to carbon dioxide and hormonal stress response was studied in connection with minor surgical procedures during halothane anaesthesia. The concentrations of catecholamines, ACTH and cortisol were measured immediately after induction, during undisturbed anaesthesia, during surgery and 15 min after the end of the surgical procedure. Sedation was better and plasma catecholamine concentrations during undisturbed anaesthesia were less in children receiving the larger dose of midazolam. During surgery and in recovery there were no differences in hormone concentrations. In recovery, the concentrations of all hormones were significantly greater compared with during undisturbed anaesthesia. During surgery, VE and respiratory rate were somewhat lower in group M0.2 while E'CO2, was similar. A dose dependent depression of the response to carbon dioxide was found. However, clinically, the response to carbon dioxide after surgery was considered to be adequate in both groups.

The multiple occlusion technique was used to study the effects of paralysis on ventilatory mechanics during anaesthesia. Total respiratory compliance (Crs) was measured during spontaneous breathing and following neuromuscular block with controlled ventilation in 23 infants. There was marked variation in response to paralysis: some infants demonstrated no change in Crs between the two states; others had values of Crs which were significantly higher during paralysis with controlled ventilation than during spontaneous breathing. A possible cause of these differences may be the type of controlled ventilation given during paralysis, with tidal volume directly influencing values of Crs obtained. The results of this study suggest that values of Crs obtained during spontaneous breathing and paralysis should not be used interchangeably until further studies have been performed to assess factors influencing Crs during controlled ventilation.

A computerized database was set up to study the incidence and outcome of complications of nasotracheal intubation in a paediatric hospital. We studied 2953 intensive care admissions over a 4-yr period. The overall complication rate was 8%. Accidental extubation and tube blockage were the most frequent events, accounting for a mean of 3.5% and 2.6% of the complications per year, respectively. Complications were more common in smaller children and there were differences between fields of intensive care. None of the complications was fatal or resulted in serious sequelae. None of the children in the study showed clinical symptoms of acquired subglottic stenosis before discharge from hospital, and none has been readmitted for this condition subsequently.

Sixteen children with congenital cardiac malformations were divided into cyanotic (n = 9) and acyanotic (n = 7) groups, and pulmonary ventilation and gas exchange were assessed before surgery, after sternotomy, just after the completion of cardiopulmonary bypass (CPB), 30 min after CPB and after closure of sternostomy before transfer to ICU. Most patients in the cyanotic group had oligaemic, while all in the acyanotic group had overperfused, lungs before surgery. Total compliance was similar in the two groups. Alveolar ventilation was higher and the physiological deadspace to tidal volume ratio (Vd/Vt) lower in the acyanotic group compared with the cyanotic group (P < 0.05) before surgery. In the cyanotic group the preoperative large difference between arterial (PaCO2) and end-tidal (PE'CO2) carbon dioxide tension was smaller immediately after CPB and remained so after closure of the sternum. In the acyanotic children the small arterial to end-tidal carbon dioxide difference before CPB had increased Just after and 30 min after CPB, and Vo/Vr was significantly increased (P < 0.05) just after CPB. After closure of the sternum the arterial to end-tidal carbon dioxide difference and the Vo/Vr ratio had returned to baseline. The arterial to end-tidal carbon dioxide difference is a good indicator of ventilatory efficiency after open heart surgery.