Department of Anaesthesia, The Royal Hospital for Sick Children, Bristol BS2 8ET, UK*Corresponding author: Sir Humphry Davy Department of Anaesthesia, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW, UK
Accepted for publication: October 16, 2000
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Abstract |
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Br J Anaesth 2001; 86: 36671
Keywords: anaesthesia, paediatric; anaesthetics volatile, sevoflurane; anaesthetic techniques, subarachnoid
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Introduction |
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The introduction into paediatric practice in the UK of sevoflurane and desflurane with their properties of enhanced recovery characteristics may offer a more practical solution. In neonates undergoing pyloromyotomy, it has been observed that recovery after desflurane is twice as fast as isoflurane with less post-operative ventilatory disturbance.11 Sevoflurane has similar recovery characteristics but unlike desflurane provides excellent conditions for inhalation induction.12 13
We therefore designed a prospective, randomized pilot study that would reflect both clinical practice at our institution and explore the hypothesis that the recovery profile after sevoflurane anaesthesia is comparable with that after spinal anaesthesia. With neither group experiencing an increase in the number of episodes of apnoea, hypoxaemia or bradycardia relative to pre-operative levels.
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Patients and methods |
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In group 1, general anaesthesia was induced with a 2 MAC equivalent value for age of sevoflurane in 100% oxygen (1 MAC=3.2% in neonates).14 15 Atracurium 0.5 mg kg1 was used to provide muscle relaxation for tracheal intubation and the lungs were ventilated to normocapnia with an end-tidal sevoflurane concentration of 0.51.0 MAC in an airoxygen mixture until completion of skin closure.
In group 2, spinal anaesthesia was established with 0.5% bupivacaine 1 mg kg1. Patients were placed in the left lateral position and a 25-gauge short bevelled spinal needle inserted in the midline through either the fourth or fifth lumbar interspace until free flowing cerebrospinal fluid was obtained. To ensure that the groups were comparable to one another in terms of the duration and intensity of analgesia provided in the initial post-operative period, both patient groups received before skin incision a single injection of 0.25% bupivacaine 2 mg kg1 through a 22-gauge cannula inserted into the caudal epidural space.16 17 Induction to incision (group 1, start of gaseous induction to surgical incision; group 2, skin penetration with spinal needle to surgical incision) and incision to closure times were recorded for both patient groups (Table 1).
Upon completion of skin closure, sevoflurane administration in group 1 was discontinued and residual neuromuscular block antagonized with neostigmine 50 µg kg1 and glycopyrrolate 10 µg kg1.
All patients were monitored for a 12 h period pre- and post-operatively using a portable three channel continuous cardiorespiratory monitor (Nellcor Puritan-Bennett EdenTrace II Plus) with internal memory multi-channel recorder interfaced with an EdenTec 3310 Assurance monitor. This integrated monitoring system provided continuous contemporaneous recordings of respiratory effort and pattern (impedance pneumography/airflow thermistor), heart rate (ECG) and haemoglobin oxygen saturation (pulse oximeter) for each patient. In order to allow each patient to act as their own control, those infants presenting for surgery with an on-going oxygen requirement were prescribed a constant flow rate of supplemental nasal oxygen for the duration of the perioperative period of cardiorespiratory monitoring (Table 2).
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Clinical significance was defined as a bradycardia of less than 100 beat min1 for at least 5 s, a haemoglobin oxygen saturation (SpO2) of less than 90% for more than 10 s and apnoea as a sustained respiratory pause of 15 s or longer, or less than 15 s if accompanied by an SpO2 less than 90% or bradycardia. These manually validated reports, in which each subject acted as their own control, were then used to draw comparisons between the two groups in terms of the number of excess post-operative cardiorespiratory complications recorded. Excess in our study was defined as a 3-fold or more increase in the number of post-operative episodes of bradycardia or apnoea relative to pre-operative occurrence.
In accordance with departmental guidelines regarding the routine post-operative observation and care of infants potentially at risk of respiratory dysfunction, real-time apnoea monitoring (Graseby MR10 respiration monitor) in combination with nurse observation was undertaken for all study patients in the post-operative period.
In view of the small sample size, data are reported as median (range). Comparison of cardiorespiratory changes within and between groups (Table 3) was performed using the Mann-Whitney U test. A P<0.05 was considered statistically significant.
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Results |
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Spinal anaesthesia was attempted unsuccessfully in four patients in group 2 (28% failure rate). All had normal respiratory function and went on to have their surgery successfully completed under general anaesthesia but were excluded from further analysis.
Median pre- and post-operative values for heart rate, SpO2, relative duration of a decrease of SpO2 (per cent time SpO2 less than 90%) and number of episodes of desaturation (SpO2 less than 90% h1) in group 1 were comparable to values recorded in group 2 (Table 3).
In group 1, three out of the five patients with pre-existing abnormal respiratory function and two out of the nine patients with normal respiratory function experienced an excess of post-operative cardiorespiratory complications (Table 2). In contrast, none of the 10 patients in group 2 exhibited an excess of post-operative complications when compared with their respective pre-operative recordings (Fig. 1).
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The concurrent use post-operatively, as per hospital policy, of real-time apnoea monitoring in combination with nurse observation failed to detect any of the above recorded episodes of cardiorespiratory disturbance. All resolved spontaneously without intervention.
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Discussion |
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Several studies to date have determined that the incidence of clinically significant post-operative apnoea falls exponentially with time from the completion of surgery.2 6 19 Proposed aetiological factors for this include the hang-over effect of residual anaesthetic agents combined with an elevated plasma level of circulating endorphins. The contribution of the latter is in turn related to the intensity and duration of the surgical insult.5 19 By attempting to ensure that both groups were comparable in terms of the duration and intensity of analgesia provided, we hoped to be able to detect in the initial post-operative period any excess cardiorespiratory complications attributable to residual anaesthesia alone.
The results of our pilot study suggest that despite the enhanced recovery characteristics of sevoflurane, the recovery profile in this vulnerable age group may not be comparable to that of awake spinal anaesthesia in all infants. However, balanced against this, was our inability to establish spinal anaesthesia in four subjects (28%), despite the technique being performed by experienced paediatric anaesthetists. This highlights the considerable expertise and practice required and is one of the primary reasons why the seemingly advantageous procedure of spinal anaesthesia has not gained universal acceptance in many paediatric institutions.3 7 These findings need to be interpreted within the context of the limited size of the study and, therefore, require further comment.
Viewed as a whole, the recovery profile of both groups appeared comparable with neither group experiencing a significant number of episodes of hypoxaemia (SpO2 less than 90% h1) relative to pre-operative levels (Table 3). It must, however, be appreciated that these results were based on computer generated recordings and are therefore susceptible to artefact.20 The addition of real-time video surveillance in a sleep study unit would have helped to limit the impact of the undefined noise-to-signal ratio of the recording system, but because of the unpredictable scheduling of surgery this was not a feasible option. An observer blinded to the anaesthetic technique used, therefore checked the validity of each recording manually.
Five out of the 14 patients (36%) in group 1 compared with none of the 10 patients in group 2 exhibited an excess of post-operative cardiorespiratory complications (Table 2). In patients with pre-existing abnormal respiratory function, three out of five patients in group 1 demonstrated an excess of post-operative cardiorespiratory complications compared with none of four in group 2 (Fig. 1). We propose a number of possible explanations to account for this difference between the groups.
First, with reference to a standard premature infant growth chart, we established that those patients in group 2 with pre-existing abnormal respiratory function were born small-for-gestational-age (less than 10th percentile) as opposed to appropriate-for-gestational-age (10th90th percentile) when compared with the birth weights of corresponding patients in group 1.21 Coté and colleagues have determined that when controlled for age, haematocrit (greater than 30%) and institution, small-for-gestational-age infants seem to have a somewhat lower risk of post-operative apnoea.19
Second, it is possible that the observed differences between the two subgroups are purely a function of the level of monitoring. In our study, the concurrent use of standard real-time post-operative apnoea monitoring in combination with nurse observation, as per hospital policy, failed to detect any of the subsequently computer identified adverse episodes (Tables 2 and 4). This raises the interesting question whether cardiorespiratory complications only detectable by sophisticated techniques are clinically important; particularly when they appear to resolve spontaneously without intervention.
Third, the study of relatively rare events requires a large patient population that is impossible to acquire at any one institution. Using a statistical approach recommended by Hanley and Lippman-Hand, Coté and colleagues determined that a sample size of at least 300 patients would be necessary to detect a 1% incidence of apnoea with 95% confidence in a particular age group.19 22 Therefore, considering the limited size of this pilot study, it is possible that we have rejected our hypothesis when it is, in fact, true. In other words, the observed difference between the two groups is not significant and our results are, at best, inconclusive.
Impedance pneumography is the most widely used form of respiratory monitoring but has limitations for detecting obstructive airway problems and a high incidence of false alarms.20 The importance of upper airway obstruction in the pathophysiology of apnoea and bradycardia is well described in infants with periodic breathing and low PCA.23 24 It is, therefore, reasonable to conclude that general anaesthesia, which can decrease upper airway muscle tone, may contribute to the development of cardiorespiratory complications in susceptible infants.9 Given the limitations of impedance pneumography for detecting obstructive airway problems, this may account for why the incidence of apnoea was comparable between the groups and may also, in part, explain the excess of temporally unrelated episodes of bradycardia in group 1 (Tables 2 and 4).
It is clear even from our limited study that post-operative cardiorespiratory complications occur frequently in former pre-term infants after relatively minor surgical procedures. Allowing for the high detection rate with sophisticated computer-assisted continuous recording devices, it is also apparent that general anaesthesia even with modern evanescent agents such as sevoflurane can induce or unmask abnormalities of cardiopulmonary function in predisposed infants. Recent work by OBrien and colleagues has been more encouraging.12 They suggest that desflurane, in terms of the quality of recovery that it offers, may be the most appropriate potent inhalational agent with which to maintain general anaesthesia in high risk infants.
In conclusion, spinal anaesthesia may be preferable to general anaesthesia for ex-premature infants undergoing lower abdominal surgery within the first weeks of life. But until this has been demonstrated in large prospective, controlled studies in comparison with modern low solubility potent inhalational agents, we will continue to have reservations about routinely subjecting our patients to an awake technique that is potentially stressful for the infant and associated with a clinically significant failure rate.
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References |
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