The single-breath vital capacity technique of inhalation induction was first described for use in adults in 1954 . It consists firstly of exhaling to residual volume and then, with the anaesthetic system and the mask gently applied to the face, inhaling to vital capacity followed by a breath hold. This technique has become increasingly popular in adults since the introduction of sevoflurane [2–4]. Sevoflurane has widely replaced halothane for the induction and maintenance of anaesthesia , but relatively few studies report the use of the vital capacity technique in children [6–8]. We have previously demonstrated that the vital capacity technique is effective and well tolerated in children. The success rate varies with age and ranges between 10% in 4- and 5-year-olds to 75% at 11 years and 95% by 14 years . The purpose of the present study was, firstly, to determine whether the vital capacity technique achieved more rapid induction of anaesthesia in children compared to the conventional tidal volume technique and, secondly, to compare the incidence of adverse events and satisfaction scores of the children using these techniques.
The single-breath vital capacity technique is suitable for inhalation induction of anaesthesia, using sevoflurane in children aged > 5 years. The purpose of this randomised trial was to compare the single breath vital capacity technique with the conventional tidal volume technique. Seventy- three ASA 1 or 2 children were instructed during the pre-operative visit in the vital capacity technique. The main criterion measured was time to loss of the eyelash reflex. Induction was performed using a circle-absorber breathing circuit primed with sevoflurane 7% in 50% nitrous oxide/oxygen with 6 l.min−1 fresh gas flow. Time required for induction, haemodynamic changes, airway tolerance and side-effects were recorded. The children's opinion on the technique used was scored using a visual analogue scale (0–100) and a Smiley scale (0–10). The time to loss of the eyelash reflex was found to be reduced in the vital capacity group compared to the tidal volume group. The time to central myosis, to achieve bispectral index values 60 and 40, haemodynamic changes, respiratory events and side-effect incidences were similar in both groups. However, we found that the vital capacity technique was preferred by the children to the tidal volume technique.
We obtained institutional human investigation committee approval and written informed consent. Following this, we enrolled ASA physical status 1 or 2 children aged between 5 and 15 years, scheduled to undergo elective urological, orthopaedic or visceral surgery using inhalational induction of anaesthesia with sevoflurane, into this prospective randomised study. Children with contra-indications to inhalation induction of anaesthesia (gastro-oesophageal reflux, vomiting, myopathy or familial history of malignant hyperthermia) and those with an history of impaired cardiac function, epilepsy, neurological disease, asthma, severe or acute respiratory illness/infection during the previous week were not included in this study. During the pre-operative anaesthetic visit (at least 48 h prior to surgery), all children were instructed in the vital capacity technique in a playful manner: ‘to blow out birthday candles’ and then ‘to inflate the lung and stop to breathing for as long as possible as if you had to dive into a swimming-pool’. Instructions were repeated until the child had mastered the three steps of the technique without exceeding five tests, to avoid stressing the child.
On the day of surgery, all children received oral or rectal midazolam premedication (Table 1). Immediately following the arrival of the child in the anaesthetic room, the children were asked to verify that they remembered the three steps of the vital capacity technique. Once verified, they were included in the study, and randomisation was performed using an envelope technique. Monitoring included non-invasive arterial pressure, heart rate, percutaneous oxygen saturation (Spo2), inspired and end-tidal sevoflurane and carbon dioxide measurements (KionTM, Siemens, Solna, Sweden). The bispectral index (BIS)TM was also recorded (Aspect Medical Systems, KG Leiden, Netherlands). According to local practice, a venous cannula was placed prior to induction of anaesthesia in children weighing > 30 kg. To minimise the pain of venepuncture, the children inhaled a mixture of 50% oxygen/nitrous oxide for 3 min; inhalation of this mixture ceased at least 5 min before the start of the study.
|TV group (n = 36)||VC group (n = 37)|
|Sex ratio (F/M); n||13/23||17/20|
|ASA 1/2; n||34/2||33/4|
|Age; months||101 (85–123) [60–176]||104 (84–131) [63–177]|
|Weight; kg||26 (22–30) [19–60]||29 (23–34) [15–45]|
|oral||180 (165–205) [80–250]||170 (130–200) [110–330]|
|rectal||300 (290–310) [290–320]||285 (190–300) [170–320]|
|Premedication to induction; min||34 (29–47) [12–164]||37 (27–57) [20–104]|
Induction of anaesthesia in all children was performed by one of three paediatric anaesthetists. The child was told that the anaesthetic had a definite ‘paint like’ smell but would not be unpleasant to breathe. The paediatric circle-absorber breathing circuit of a Kion anaesthesia machine was primed with sevoflurane 7% in 6 l.min−1 50% nitrous oxide/oxygen fresh gas flow. The 2-litre reservoir bag was then evacuated and refilled. Respiratory gases were sampled from the mask elbow connection at a rate of 150 ml.min−1 into a multigas SC 9000 monitor (Siemens) to monitor end-tidal and inspired concentrations of sevoflurane. In the vital capacity group, following a forced exhalation, the child took a single vital capacity breath via a transparent perfumed mask connected to the breathing circuit. In the tidal volume group, the child was instructed to breath normally using the mask. Inspired sevoflurane concentration was reduced to 4% when the pupils were divergent and to 2% when the pupils were central. At this point, the fresh gas flow was reduced to 2 l.min−1.
Sedation on arrival in the anaesthetic room was assessed using the Ramsay score  on a 6-point scale (1 = anxious and agitated patient; 2 = co-operative patient, orientated and tranquil; 3 = patient responding to command only; 4 = asleep patient, brisk response to loud voice or a light glabellar tap; 5 = sluggish response to loud voice or light glabellar tap; 6 = no response to pain). Co-operation prior to induction was evaluated using a continuous visual scale graded from 0 (none) to 100 (maximum) and the number of explanations required prior to induction of anaesthesia was recorded. The quality of the vital capacity breath was assessed clinically by an observer as there was no objective assessment of how complete the inspiration actually was. A successful vital capacity breath was defined as a complete expiration followed by a complete inspiration and an immediate period of apnoea with inflated lungs. Apnoea was defined as breath holding lasting at least 10 s. If any of these three steps was not completed successfully, the technique was recorded as a failure. However, the child was included in the statistical analysis on an intention to treat basis in the vital capacity group.
The speed of induction of anaesthesia was judged clinically (time for loss of eyelash reflex and central pupil myosis) and objectively using the BIS measurement (time to obtain 60 and 40 values). Baseline heart rate, arterial pressure, percutaneous O2 saturation (Spo2), respiratory rate and BIS measurements were obtained prior to induction of anaesthesia and measured at 1-min intervals for 10 min after placing the mask over the child's face. The occurrence of airway problems (stridor, cough, laryngospasm) was recorded. Dystonic reactions were characterised as involuntary contractions in opposing flexor and extensor muscles that produced sustained and fixed abnormal postures, such as oculogyric crises, tongue protrusion, trismus, laryngeal-pharyngeal constriction, torticollis, or bizarre positions of the limbs and the trunk. If present, dystonia was scored on a 4-point scale (1 = minor, 2 = mild, 3 = moderate, more movement but no significant interference with induction; 4 = severe, excessive movements interfering with induction and requiring restraint of the child). Occurrence of minor excitement was noted as well as intensity (graded from 1 to 4) and duration.
All children were reviewed by one of the investigators on the surgical ward postoperatively once the child had fully recovered (defined by the ability to eat and to walk, the absence of nausea, vomiting or excessive pain and the understanding of the explanations about the satisfaction scales). The children were asked about the acceptability of the induction of anaesthesia. The children's opinions were assessed using a visual analogue blinded scale graded from 0 to 100 and a modified six-face scale scored 0, 2, 4, 6, 8 and 10 where the child pointed to the face that reflected ‘how much he liked his inhalation induction’.
The sample size calculation was based on the results of Fernandez et al. . The primary endpoint was time to loss of the eyelash reflex. To keep to a minimum the number of patients required and to allow earlier termination of the study, we carried out the study as a sequential trial using the triangular test . A reduction of 25% from 46 (17.5) s to 37 (17.5) s was expected in the experimental group (vital capacity group). Results were analysed after every 10 patients treated. A working significance level of 0.05 against the one-sided alternative was required, together with a power of 0.80. Statistical analysis was performed using Statview® 5 (Abacus Concepts Inc., Berkeley, CA), Splus 6.2 Professional and PEST 3 software. Continuous data were expressed as (median (interquartile range 25–75%) [range]), except for heart rate, arterial pressure and BIS, which were expressed as mean (SD). Data, expressed by percentage of children, were analysed using the Chi-squared and Fisher's exact test as appropriate. Non-parametric data were analysed using the Mann–Whitney U-test. Haemodynamic data and BIS were analysed using anova for repeated measures followed by Tukey's tests. p-values < 0.05 were considered significant. Randomisation was undertaken by the statistical staff and balanced every 10 inclusions. The set of sealed envelopes, identified by a sequential number, was provided to the investigation site.
The trial commenced in January 2003 and was stopped following the 7th sequential analysis in September 2004. At this time, 70 patients had been included and the difference between the groups for time to loss of the eyelash reflex had reached significance (Fig. 1). However, three additional patients were enrolled to confirm the crossing of the upper boundary (p = 0.017). At the end of the study, 37 children had been included in the vital capacity group and 36 in the tidal volume group. The demographic data of the two groups were similar (Table 1). Fifty percent of children in each group had previously experienced inhalation induction of anaesthesia.
Most of the patients (85%) required one explanation at the pre-operative visit; 14% and 1% of children required two and three explanations, respectively. Midazolam was administered orally in 89% and 79% of the children in the tidal volume and vital capacity groups, respectively; and in the rest of the cases, it was given rectally (Table 1). Sedation on arrival in the anaesthetic room was similar in both groups: 86% and 84% of the children in the tidal volume group and vital capacity group, respectively, were graded 2 on the Ramsay scale; 8% and 13% were graded 1; 6% and 3% were graded 3. An intravenous cannula was placed prior to induction of anaesthesia in 14% of children in the tidal volume group and in 27% of children in the vital capacity group. Induction was performed by three investigators with a similar distribution of both techniques.
Values are presented as median (interquartile range) [range]. Median co-operation score was 100 (100–100) [80–100] in the tidal volume group and 100 (100–100) [86–100] in the vital capacity group. Only three children scored < 80. Thirty children (81%) performed the vital capacity technique successfully. In the other seven cases, 82 (77–101) [75–134] months old, two children failed to perform any step of the technique due to anxiety. Lack of breath holding occurred in three cases of failure (alone in two cases or associated with an incomplete inspiration in one case). Incomplete inspiration occurred in two cases. Median time of apnoea was 29 (13–45) [0–95] s. Times for induction of anaesthesia are shown in Table 2. Only the time to loss of the eyelash reflex was shorter in the vital capacity group compared to the tidal volume group. Initial BIS values (mean (SD)) were 94 (4), with a rapid decrease in the BIS value to 22 (13) seen in both groups during the first 2 min of induction, followed by a small rise and then stabilisation to between 31 and 36 after 6 min (Fig. 2).
|TV group (n = 36)||VC group (n = 37)|
|Time to loss of the eyelash reflex*||35 (30–40) [20–57]||30 (25–34) [18–56]|
|Time to BIS 60||60 (44–67) [28–99]||55 (48–66) [25–97]|
|Time to BIS 40||65 (56–78) [38–120]||68 (52–75) [39–288]|
|Time to 4% inspired sevoflurane||90 (78–113) [57–180]||101 (80–118) [40–270]|
|Time to central myosis||193 (167–237) [110–356]||196 (168–215) [122–395]|
|Time to insertion of Guedel airway||200 (145–232) [104–420]||204 (177–228) [111–450]|
|Time to venous puncture||265 (218–319) [170–420]||249 (233–281) [170–658]|
We found no differences in the haemodynamic and respiratory parameters or in the incidence of side-effects between the groups. Heart rate (mean (SD)) increased from 90 (17) to 108 (25) beats per minute in the initial 2 min, returning to baseline values by 4 min (Fig. 3). Blood pressure decreased significantly from baseline values during induction of anaesthesia; however, this did not require any treatment (Fig. 4).
Median initial sevoflurane concentration in the circuit was 7.6% (6.7–8.1%). End tidal sevoflurane concentrations during induction were similar in both groups. Seven patients (19%) in the tidal volume group and three (8%) in the vital capacity group coughed when the mask was first placed on their face (p = NS). Two children (5%) in the tidal volume group and four in the vital capacity group (11%) tried to reject the mask (p = NS). No reaction was observed when the mask was applied in 75% and 81% of the children in the tidal volume and vital capacity group, respectively (p = NS). Respiratory rate increased by 45% from the baseline value (22 (5) breaths per minute) by the second minute and then remained stable until the end of the study period. Tachypnoea, defined as a respiratory rate > 40 breaths per minute, was seen in 55% (tidal volume group) and 57% (vital capacity group) of the children. Eight percent (tidal volume group) and 24% (vital capacity group) of the children required ventilatory assistance with positive airway pressure (Table 3) (p = NS). An episode of hypoxaemia occurred in one child in each group. In the vital capacity group, mild laryngospasm was associated with a reduction in the Spo2 value to 79% for 10 s. This was due to premature stimulation of the child and rapidly responded to intravenous propofol (2 mg.kg−1). In the tidal volume group, hypoxaemia (87% for 8 min) occurred due to the inadvertent use of a perforated reservoir bag. Spo2 remained > 97% in all other children (Table 3). A Guedel airway was used to improve the airway in 92% and 94% of the tidal volume and vital capacity groups, respectively (p = NS).
|TV group (n = 36)||VC group (n = 37)|
|Positive pressure ventilatory assistance||3||9|
|Tachypnoea (> 40 breaths per minute)||20||21|
Minor excitement was seen in four children in the tidal volume group and in three children in the vital capacity group. Dystonia occurred in 19% (tidal volume group) and 22% (vital capacity group) of children (p = NS). The dystonia was graded 1 in 11% and 8% of the children, and graded 2 in 8% and 11% of the children in the tidal volume and vital capacity groups, respectively. Only one dystonia was graded 3 in a child of the vital capacity group.
The satisfaction of seven children in the tidal volume group and two children in the vital capacity group could not be evaluated because of lack of recall of any event associated with the induction of anaesthesia. The Smiley score was not performed; however, the visual analogue score was obtained for one child in the tidal volume group and four children in the vital capacity group. The proportions of children who performed visual analogue and Smiley scores were not significantly different between the groups. Visual analogue scores were correlated with modified face scale results (p < 0.0001). Overall, children preferred the vital capacity technique of induction to the tidal volume technique (Table 4).
|TV group||VC group|
|Smiley score*||8 (6–10) [0–10] (n = 29)||10 (8–10) [0–10] (n = 35)|
|Visual analogue score**||86 (46–100) [0–100] (n = 28)||96 (87–100) [0–100] (n = 31)|
This study demonstrates that the single-breath vital capacity technique using 7% sevoflurane is tolerated as well as is the more conventional tidal volume inhalation technique. The vital capacity technique produced a more rapid induction of anaesthesia, as assessed by the loss of the eyelash reflex, and was also better tolerated by the children.
The time to loss of eyelash reflex in the vital capacity group is the shortest that has been reported in the literature for inhalation induction of anaesthesia in children [6–8]. This may be due to the use of midazolam premedication, the priming of the circuit with sevoflurane and the use of nitrous oxide . We found a reduction in the incidence of agitation occurring during induction of anaesthesia, which may have been due to the use of nitrous oxide. This was lower than that reported in our previous study where sevoflurane was administered in 100% oxygen .
Although the single-breath vital capacity technique produced a more rapid loss of the eyelash reflex, this benefit remains small and the time to produce deep anaesthesia with central myosis was not reduced.
In the absence of a clear superiority of one technique over the other, it is important to take into consideration the children's view. Unfortunately, anterograde amnesia due to midazolam affected the evaluation of the satisfaction of the children in some cases . The better memory associated with the single-breath vital capacity technique may be due to the active participation in the anaesthetic induction that is requested from the child. Recently, it has been demonstrated that an altered perception of smell facilitates inhalation induction of anaesthesia in children .
This study confirms a high rate of success associated with using the vital capacity technique and provides evidence that this technique can be used in children aged between 5 and 15 years . The inability of a few children to hold a vital capacity breath has prompted Ho et al.  to propose a double-breath vital capacity inhalation induction as a faster alternative. Nevertheless, as the result of the absence of a breath hold in most of their patients, the time to eyelash reflex was longer than that found in our study.
Haemodynamic data were similar to those found in previous studies . The inhibition of parasympathetic control of heart rate by sevoflurane may be responsible for the transitory tachycardia . Sevoflurane causes less reduction in cardiac output compared with halothane. However, there was a reduction in blood pressure and systemic vascular resistance compared to awake values at all concentrations .
In conclusion, the reduced time to loss of consciousness produced by using the single-breath vital capacity technique, with a circuit primed with a high sevoflurane concentration and nitrous oxide, is significant but small. However, as the technique seems to be better tolerated by children compared with the more conventional tidal volume technique, its use should be considered in selected paediatric patients.