Comparison of the Single Breath Vital Capacity Technique with the Tidal Volume Technique

Introduction: The single breath vital capacity (VC) induction and the tidal volume (TV) breathing induction are currently administered for inhalation of anaesthesia with sevoflurane in children. The aim of this study was to determine whether the vital capacity technique achieves more rapid induction of anaesthesia in children compared to the conventional tidal volume technique. Material and Methods: Sixty ASA physical status 1 or 2 children aged between 5 and 15 years, scheduled to undergo elective urological, orthopaedic or visceral surgery under general anaesthesia using inhalational induction with sevoflurane were recruited and randomized to receive either vital capacity induction or tidal volume induction with 8% sevoflurane at 6L/min of O2 followed by laryngeal mask airway insertion or endotracheal intubation with endotracheal tube. Time required for induction, hemodynamic changes, airway tolerance, side-effects, level of satisfaction using a visual analogue scale (0-100) and Smiley scale (0-10) were documented. Results: Induction time was significantly shorter with the vital capacity induction technique than with the tidal volume breathing induction technique (43.8 ± 13.4 seconds vs 70.8 ± 16.4 seconds; P<0.01). The time to central myosis, haemodynamic changes and respiratory events incidences were similar in both the group. Fewer complications occurred with vital capacity group. More than 94% of the children choose the single Breath Vital Capacity method of induction to the tidal volume technique. Conclusion: For inhalation induction of anaesthesia, the vital capacity induction was faster and produced less complication than that of tidal volume breathing technique.


Introduction
Sevofl urane's low blood gas solubility and sweet smelling means it is able to produce an acceptable induction in children 1 .Rapid induction and emergence from anaesthesia also makes it suitable agent for ambulatory anaesthesia and short surgical procedures.The need for a rapid recovery has become more important in day care surgeries are increasing in the children.Rapid and smooth induction of anaesthesia is frequently desirable in children, as long as cardiovascular stability is not compromised 2,3,4 .A slow inhalational induction may be upsetting for a child and excitability is not uncommon during gaseous induction 5,6,7.Traditional stepwise incremental increases in inspired concentration of sevofl urane as well as single breath vital capacity rapid inhalation induction using immediate high inspired concentration of sevofl urane have been well tolerated in paediatric patients 8 .
Vital capacity induction has advantages over the traditional method, as induction is more rapid and the transition from induction to the maintenance phase is smooth with a lower incidence of excitatory phenomena.Inhalation induction avoids the "hangover" associated with intravenous agents and it can be achieved without intravenous access 9 .
The single breath vital capacity technique is suitable for inhalation of anaesthesia, using sevofl urane in children aged more than fi ve years.It consists fi rstly 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 been widely popular in adults since the introduction of sevofl urane 10,11,12 .However, it remains a less practiced technique.
Therefore, this study was designed 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 of the children using these techniques.

Material and Methods
After institutional ethical approval and having written informed parenteral consent, 60 children, ASA physical status I or II, aged >5 and < 16 years, who were scheduled to undergo anesthesia by inhalational of sevofl urane to undergo elective urological, orthopaedic or visceral surgery were enrolled into this prospective open randomized clinical trial.
Children with contra-indication to inhalation induction of anaesthesia (gastro-oesophageal refl ux, vomiting, myopathy or familial history of malignant hyperthermia) and those with a history of cardiac function, epilepsy, neurological disease, and asthma, severe or acute respiratory illness/infection during the previous week were not included in this study.
Monitoring included pulse oximetry for haemoglobin oxygen saturation, electrocardiography for heart rate (HR) and non-invasive blood pressure (NIBP), inspired end tidal sevofl urane and carbon dioxide measurement.All instructions were carried out in the supine position by a single anaesthesiologist.The children were instructed the vital capacity technique in a playful manner: "to blow out birthday candles" and then "to infl ate the lung and stop breathing as possible as if you had to dive into a swimming-pool".
The paediatric circle-absorber breathing circuit of an anaesthesia machine was primed in standardized conditions with sevofl urane 8% in 6 litres/minutes fresh gas Oxygen fl ow.The 2 litre reservoir bag were then evacuated and refi lled.After forced exhalation, the child took a single vital capacity breath via a transparent mask connected to the breathing circuit.When the pupils were central, the fresh gas fl ow will be decreased to 2 litres/ minute and inspired sevofl urane was reduced to 4%.
A successful vital capacity is defi ned as complete expiration followed by complete inspiration and an immediate period of apnoea with infl ated lungs.Apnoea is defi ned as breath holding for at least 15s.
Any involuntary movements such as dystonic reactions were characterized by involuntary contractions in opposing fl exor and extensor muscles that produce sustained and fi xed abnormal postures, such as oculogyric crisis, tongue protrusion, trismus, laryngealpharyngeal constriction, torticollis, or bizarre positions of the limbs and the trunk.
A dedicated observer will review children's opinion using a visual analogue blinded scale graded from 0 to 100 and a modifi ed six-scale scored 0, 2, 4, 6, 8, and 10 where the child pointed the face that shows how much he has liked his induction 13 .Time for "Loss of Eye Lash refl ex" and central pupil was determined as time of putting facemask on patients until the loss of eye lash refl ex and constricted pupil respectively.
All results are expressed as mean ± standard deviation.Student's t test was used for analysis of time to loss of consciousness.ANOVA and Bonferroni tests were used to assess patients' variables and hemodynamic changes.A value of p<0.05 was considered to be statistically signifi cant.

Results
Anaesthesia was induced successfully in all patients.The two groups were similar in terms of age, sex and weight (Table 1) Induction of anaesthesia with both the techniques was associated with an increase of approximately 20mmHg in MAP which occurred within two minutes and persisted for at least the fi rst fi ve minutes of anaesthesia (Fig: 1).Heart rate increased slightly compared with baseline after induction of anaesthesia with both the techniques.However HR did not diff er signifi cantly between the groups at any time during induction (Fig: 2).There was also no diff erence in SP02 between the two groups at any time.The median visual score was 9.1 (8.8-9.4) and correlated (p<0.001) with modifi ed scale results (0 = 0.5%, 2 = 3%, 4 = 5%, 6 = 10%, 8 = 25%, 10 = 56.5% of the responses).

Discussion
The Study demonstrated statistically and clinically signifi cant lower incidences of adverse airway events in the single breath vital capacity technique using 8% sevofl urane when compared with the conventional tidal volume inhalational technique in the initial phases of anaesthesia.These adverse airway events, although benign and self-limiting have the potential to lead laryngospasm, and thereby produce clinically signifi cant hypoxia.
The single breath vital capacity technique is tolerated well than the more conventional tidal volume inhalational technique.The vital capacity technique produce a more rapid induction of anaesthesia, as assessed by the loss of the eyelash refl ex, and was also better tolerated by the children.Although the single breath vital capacity technique produced a more rapid loss of the eyelash refl ex, this benefi t remains small and the time to produce deep anaesthesia with central myosis was not reduced.Tolerance with single-breath vital capacity was good and side eff ects were less in comparison to tidal volume breath.Our study showed no hypoxia related to apnoea.
In our study, all patients were able to perform single breaths properly.Exhalation to residual volume minimizes the amount of alveolar air and maximizes the quality of sevofl urane entering the lungs and reaching the alveoli in one breath.Dilution of sevofl urane is reduced and the highest possible alveolar concentration of sevofl urane is maintained.A high-inspired sevofl urane concentration ensures that the alveolar partial pressure of sevofl urane approaches the inspired partial pressure and off sets uptake of sevofl urane by arterial blood in the lungs(concentration eff ect) 14 .
This study confi rms a high rate of success associated with 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 etal 15 to propose a double-breath vital capacity inhalation induction as a faster alternative.
Haemodynamic data were similar to those found in previous studies 16 .The inhibition of parasympathetic control of heart rate by sevofl urane may be responsible for the transitory tachycardia 17 .Smoothness of induction was signifi cantly improved with VC group.In this study, excitation during induction was low (assessed by quality of induction acceptance score) and this may be an eff ect of high concentration of sevofl urane.VC induction has been recently compared with TV induction, where VC induction produces signifi cantly more rapid attainment of central pupils, although time to loss of eyelash was not signifi cantly faster with TV induction.
Dystonias were the most frequent complications.They occurred at the beginning of deep anesthesia and were mostly limited to peripheral muscles.Rarely, when localized to cervical muscles 18 , dystonic movements caused spastic torticollis and rotation of the head and could favour airways obstruction as described in one of our patients.
A total of 50% of the patients who underwent a TV induction technique had one or more complications.On the contrary, induction of anaesthesia with VC technique was associated with a lower complication rate (16.5%)The incidence of purposeful and involuntary movements during induction was higher with TV technique 3 (10%) and 1(3.3%) respectively compared with a VC technique 1(3.3%) and 0(0%) respectively (p<0.05).Although not statistically, we noted four patients who held breath during induction while performing the TV technique whereas only two in the VC technique.

Conclusion
The Single breath vital capacity breathing technique is possible in young children.Induction of anaesthesia is signifi cantly faster with single breath vital capacity technique and is well tolerated in comparison to Conventional Tidal volume technique.Although the single-breath capacity technique with high sevofl urane concentrations seems to accelerate anaesthetic induction compared with tidal volume, further comparative studies with randomization of tidal volume vs vital capacity inhalation technique, are needed in large scale.

Table 1 :
Demographic data of subjects Induction of anaesthesia was signifi cafaster in the Vital capacity group in time to loss of eyelash refl ex, although the mean diff erence between the two groups was only 8 seconds.

Table 2 :
Characteristics of the induction

Table 3 :
Satisfaction with inhalational technique

Table 4 :
Incidence of complication during induction of anesthesia