Wojciech Płazak, Tomasz Muszyński, Alicja Macheta, Henryk Podziorny, Jacek Łach, Piotr Podolec, Krystyna Potocka-Płazak, Janusz Andres
Effect of oro- and nasotracheal intubation on the autonomous nervous system activity- analysis of the heart rate variability
Chair of Anaesthesiology and Intensive Therapy, Collegium Medicum, Jagiellonian University;
Head: J. Andres M.D., Ph.D.; 3rd Department of Cardiology, Institute of Cardiology, Collegium Medicum, Jagiellonian University; 2nd Dept of Internal Medicine, G. Narutowicz Memorial Regional Hospital Cracow, Poland
Monitoring of the heart rate variability (HRV) is a new, non-invasive method of assessing of the autonomic nervous system activity. LF (low freguency) reflexes adrenergic activation, HF (high freguency) - cholinergic activation and TP (total power) can be regarded as an index of the total autonomic activity.
We have assessed adrenergic and cholinergic activity during orotracheal and nasal intubation and extubation in 21, 17-72 yr old (mean 40,5) ASA I patients, undergoing craniofacial tumour surgery under nitrous oxide-fentanyl anaesthesia. HRV indexes were calculated from 5-minutes fragments of the ECG. We have observed the decrease of LF, HF and TP values after induction and intubation, and marked increases of LF and TP values during extubation. We have also noted a strong, short lasting stimulation during removal of the orotracheal tube. Those, who were intubated nasally, revealed weaker stimulation that was lasting longer.
We conclude that depression of the autonomic system activity during induction of anaesthesia and intubation may reflect effects of anaesthetic agents. Subsequently, the HRV index increase during extubation is caused by mechanical stimulation and neostygmine.
Heart rate variability (HRV) analysis has been adopted, for several years, as a useful method of assessing autonomous nervous system activity. It is also of prognostic value, especially in patients with cardiac diseases (history of myocardial infarction, cardiac insufficiency) . HRV assessment by spectral analysis may be useful in monitoring changes in adrenergic and cholinergic activities during general anaesthesia . The degree of HRV is calculated mathematically by power spectral analysis (PSA). HRV increase in the range of breathing rate (0.1-0.4 Hz), denoted as high frequency (HF) depicts the increase of cholinergic stimulation. Low frequency (LF) HRV (0.055-0.09 Hz) correlates with the degree of adrenergic stimulation. Total power (TP) index represents the overall activation of the autonomic system of the heart.
The present study aimed at assessing the HRV analysis in monitoring autonomic nervous activity during tracheal intubation, general anaesthesia and extubation. Possible differences between the degrees of adrenergic and cholinergic stimulation in patients intubated via oral and nasal routes were also investigated.
The study was performed in 21 ASA I patients, 9 women and 12 men aged from 17 to 72 years (mean: 40.5), scheduled for craniofacial tumor surgery under general anaesthesia. All patients gave their informed consent to participate in the study and agreed to use a Holter device in the perioperative period. All of them had a normal ECG tracing and no history of cardiovascular problems; their blood pressure values did not exceed 140/90 mmHg (18.7/12 kPa). In 14 patients orotracheal and in 7- nasotracheal intubation was performed. Surgical procedures lasted on average 2 hours. Anaesthesia was induced and maintained according to the scheme presented in table I.
Table I. Drugs used in successive phases of anaesthesia
|Phase of anaesthesia||Drugs employed|
|premedication||pethidine 75-100 mg i.m., promethazine 25-50 mg i.m. |
|preoxygenation||100% oxygen, atropine 0.5 mg i.v., fentanyl 0.1 mg i.v. |
|induction||pancuronium 1 mg i.v., thiopental 5 mg/kg i.v., suxamethonium 1 mg/kg i.v.|
|post-intubation||fentanyl 0.2 mg i.v., pancuronium 4-5 mg i.v.|
|maintenance||oxygen 2L/min., nitrous oxide 3 L/min., fentanyl 0.1 mg i.v. every 20 min, pancuronium 1 mg i.v. every 30 min|
|emergence||atropine 0.5 mg i.v., neostigmine 1-2 mg i.v., naloxone 0.1-0.2 mg i.v.|
EKG tracing, by Holter method, was registered with a Rosen - Margot Medical device from 30 min before premeditation to 60 min after extubation. Power spectral analysis of HRV was carried out using software manufactured by Del Mar® Holter Analysis Systems. Indices were calculated from 5-min fragments of tracing in the ranges best correlating with autonomic system activity  (Table II).
Table II. Spectral ranges used to calculate HRV index
Descriptions of the phases of general anaesthesia (used on X-axes of figures) are presented in table III.
Table III. Analyzed phases of anaesthesia
|Numbers on Fig. 1-3||Phases of anaesthesia|
|1.||before premedication |
|2.||during induction and intubation|
|4.||during surgical procedure |
|5.||before the end of the anaesthesia|
|6.||recovery from anaesthesia|
|8. ||5 min post-extubation|
|9.||10 min post-extubation|
|10.||15 min post-extubation|
|11.||20 min post-extubation|
|12.||25 min post-extubation|
|13.||30 min post-extubation|
The analysis was performed on those fragments of ECG tracing, which did not demonstrate arrhythmia nor artifacts which might interfere with values of HRV indices. The statistical significance of differences between the baseline level and each phase of anaesthesia and between patients intubated via oral and nasal routes during corresponding phases was calculated using Student's T-test.
Changes in values of LF, HF and TP indexes during anaesthesia are illustrated by figures 1 to 3.
In patients with orotracheal intubation all HRV index values were statistically lower after intubation and during maintenance of anaesthesia as compared with the baseline levels (p<0.05). LF and TP index values were significantly higher during extubation.
Fig. 1. Changes in LF values as the result of adrenergic stimulation (for X-axis labels refer to Tab. III)
Fig. 2. Changes in HF values as the result of cholinergic stimulation (for X-axis labels refer to Tab. III)
Fig. 3. Changes in TP values as the result of the overall activ-ity of autonomous system (for X-axis labels refer to Tab. III)
In patients in whom nasotracheal intubation was performed all HRV index values diminished after intubation and during maintenance of anaesthesia. A significant rise in TP value was observed 5 min after extubation.
General anaesthesia provokes significant changes in the activity of the autonomic nervous system, reflected by changes of values of HRV indices. Of the observations presented in this paper two are worth to be stressed: lowering of all index values during induction, intubation and maintenance of anaesthesia, and marked rise of these values during and following extubation.
From the moment of administration of the drugs used for induction, gradual decrease of HRV indices (most prominent for HF) was observed, which can be attributed to the action of thiopental and fentanyl. Other authors observing decrease of HF [4,5], TP  or HF and TP  reported similar results after thiopental administration. Following intubation this trend persisted, most probably resulting from the continuous action of drugs administered at induction and beginning of nitrous oxide influence. A similar drop of HF has been described in studies on healthy volunteers breathing nitrous oxide . Schubert et al.  observed diminishing the LF value following intubation, although other authors  reported no influence of intubation on HF and LF. It is well recognised that tracheal intubation triggers activation of both adrenergic and cholinergic parts of the autonomic nervous system, as a result of stimulation of vagal fibres by the endotracheal tube. The influence of this stimulation on cardiovascular system is however limited by concomitantly administered drugs.
The maximum increase of all HRV index values occurred during extubation and recovery from anaesthesia. This is mainly due to cessation of nitrous oxide administration, gradual diminishing of fentanyl action and the depth of anaesthesia, administration of anticholinesterase drugs. Return of the patient's consciousness and mechanical irritation of the throat by suctioning and extubation play also an important role in this phenomenon. For safety reasons, extubation was always performed after obtaining good contact with the patient, return of laryngeal reflexes and preceded by careful suctioning of secretion accumulated proximally to the tube cuff. All these manoeuvres, as well as the pharmacological action of small doses of naloxone, predisposed to the increase of autonomic stimulation during this period. Similar observations have been reported also by other authors .
Removing the orotracheal tube resulted in an immediate but short-lasting increase of LF and HF values, reflecting marked autonomic activation provoked by extubation. These values returned to the baseline levels during the first 5min after extubation and dropped even lower in next few minutes. In the 20th-25th minute, another slight increase in LF and HF was observed, which is difficult to explain. One can speculate that it depended on psychologic factors (postoperative emotional stress) or nociceptive stimulation from the operative wound.
Changes of HRV index values following extubation in patients intubated with a nasotracheal tube demonstrated a different pattern. The increase was slower and reached its peak 10 min after extubation. The values returned to the baseline level 5 min later. This may suggest, that nasotracheal extubation provokes longer - lasting autonomic activation than orotracheal, although it seems to be less intense.
The degree of activation of the autonomic innervation of the cardiac muscle is reflected by increase in LF and HF, observed at the end of anaesthesia. This suggests that the phases of recovery from anaesthesia and extubation carry a relatively higher risk of cardiovascular complications. This can be especially true in patients with cardiovascular problems.
This is noteworthy, that in spite of marked changes of values of the HRV indices, observed during and following extubation, heart rate and blood pressure values were totally stable. Both systolic and diastolic pressures in this period were comparable to the baseline values. Heart rate, during 30 min after extubation averaged 60-67/min. ("oral" group) and 65-78/min. ("nasal" group).
Spectral analysis of HRV during general anaesthesia may provide useful information about the degree of autonomic stimulation. This information cannot be obtained by monitoring of blood pressure, heart rate or vegetative reflexes. Similar conclusions are expressed by Schubert et al. , who (on the basis of HRV monitoring) observed extensive disturbances of autonomic system homeostasis following induction of anaesthesia, despite perfectly stable blood pressure and heart rate values.
1. Extubation is the strongest stimulus of the autonomic nervous system during general anaesthesia
2. Orotracheal extubation results in a rapid, short-acting autonomic nerve system activation
3. Nasotracheal extubation stimulates autonomic system for a more prolonged period of time.
Originally published in Anestezjologia Intensywna Terapia 31; (1), 3-6, 1999.
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