Modification of chronotropic response to anticholinergics by halogenated anaesthetics in children

Heart rate response to atropine in humans anaesthetized with five different techniques

Atropine, 0.01 mg.kg-1, was given intravenously before the start of surgery to 169 patients who were anaesthetized with one of five different techniques; halothane, enflurane, cervical epidural, lumbar epidural or narcotic anaesthesia in addition to nitrous oxide and oxygen. Atropine produced a significant increase in heart rate (HR) within 1 min in all patients studied; the HR increases in patients anaesthetized with halothane (37 +/- 11 beats.min-1, n = 37) or narcotic (34 +/- 12 beats.min-1, n = 30) were significantly greater than in those anaesthetized with enflurane (25 +/- 10 beats.min-1, n = 35; P less than 0.01) or epidural anaesthesia. Because of the presence of an acute cardiac sympathectomy, the patients who received cervical epidural anaesthesia were expected to have different responses to the atropine. However, there was no significant difference in the HR increases between the patient groups with cervical (19 +/- 12 beats.min-1, n = 32) and lumbar (22 +/- 8 beats.min-1, n = 35) epidural anaesthesia. Atropine also produced a small but significant increase in arterial pressure in all five groups of patients. These results suggest that the cardiac responses to atropine may differ depending on the individual anaesthetic agent used, and are likely dependent upon the agent's effect on autonomic nervous system activity.

The cardiovascular effects of anticholinergic agents administered during halothane anaesthesia in children

The cardiovascular effects of anticholinergic agents administered during halothane anaesthesia were studied in 31 children aged 1-12 years undergoing peripheral orthopaedic surgery. Either normal saline, glycopyrrolate (10 micrograms.kg-1) or atropine (20 micrograms.kg-1) was administered in randomized double-blind fashion during the induction of anaesthesia with halothane while the electrocardiogram was continuously recorded. After induction, the children were paralyzed with atracurium, intubated, and ventilated. Anaesthesia was maintained with N2O/O2 and halothane (up to 2.5% inspired). The concentrations of expired CO2 and halothane were measured continuously using mass spectrometry. Sixty-one percent (19/31) of the children developed one or more dysrhythmias. Junctional rhythm occurred in 74% (14/19) of the children with dysrhythmias, developed early during induction (mean +/- s.d. time = 2.29 +/- 2.0 min after commencement of induction), and usually resolved before the administration of the study drug (8/14). All dysrhythmias initially occurred before or during induction and none developed during intubation, during incision, during the maintenance of anaesthesia, or after the administration of anticholinergic agents. The data suggest that: 1) a combination of factors present during halothane induction is highly dysrhythmogenic especially for junctional rhythm; 2) junctional rhythm will resolve spontaneously; 3) the administration of an anticholinergic agent during halothane induction is safe but may be unnecessary in children greater than 1 year of age; and 4) the dysrhythmogenic factors present during induction are attenuated during the maintenance of halothane anaesthesia.

Ventilation and the oculocardiac reflex. Prevention of oculocardiac reflex during surgery for squints: role of controlled ventilation and anticholinergic drugs

A randomised prospective study was carried out in children undergoing surgery for squint correction, to determine the value of controlled ventilation as a prophylaxis against the occurrence of the oculocardiac reflex. One hundred patients anaesthetised with nitrous oxide/oxygen and halothane were randomly assigned to either ventilated or spontaneously breathing groups of 50 each. Half the patients in each group received glycopyrronium 7.5 micrograms/kg intravenously at the time of induction of anaesthesia. Heart rate, rhythm, blood pressure and end tidal CO2 concentration were monitored throughout. A positive oculocardiac reflex, defined as a fall in heart rate of 20% or more and/or the occurrence of dysrhythmias, was observed in 72% of spontaneously breathing patients and in 100% of ventilated patients not receiving prophylactic intravenous glycopyrronium. The incidence of a positive reflex in patients receiving glycopyrronium was 10% (4 and 16% respectively in spontaneously breathing and ventilated patients). It is concluded that controlled ventilation is of no value as a preventive measure against the occurrence of the oculocardiac reflex in patients undergoing squint surgery and that prophylaxis is safely achieved with the use of intravenous glycopyrronium.

Halothane anesthesia in infancy: identification and correlation of preoperative risk factors with intraoperative arterial hypotension and postoperative recovery

Infants are well known to be sensitive to the myocardial depressant effects of halothane. In this study of more than 300 infants, 0 to 24 weeks of age, who received halothane anesthesia, preoperative risk factors were correlated with intraoperative outcome and postoperative recovery. Possible risk factors considered were age, history of respiratory distress syndrome (RDS), preoperative fasting time, and anemia. Intraoperative morbidity was evaluated by occurrence of significant hypotension, slow heart rates, or serious bradycardias. Parameters of postoperative recovery included postanesthetic recovery room admission score, duration of recovery room stay, and time to first feeding. Arterial hypotension occurred with an unexpectedly high frequency of 49.2%. Infants younger than 8 weeks of age (particularly newborns), infants 9-16 weeks of age (fasting eight or more hours), and RDS survivors 0-16 weeks of age were found to be most susceptible to hypotension. Only age and history of RDS, however, proved to be statistically significant risk factors in predicting the probability of intraoperative circulatory depression. Though circulatory depression during halothane inhalation was common, it was not associated with significant intraoperative or postoperative morbidity in terms of cardiorespiratory arrests, serious dysrhythmias, prolonged postanesthetic recovery, or delayed feeding times.

Effect of halogenated anaesthetics on heart rate changes during reversal of neuromuscular block with glycopyrrolate and neostigmine

The effect of halothane and enflurane on changes in heart rate during reversal of neuromuscular blockade was compared in 48 patients. Premedication and anaesthetic technique was standardized. Either halothane or enflurane was used as the primary anaesthetic. Neuromuscular block was reversed by injection of glycopyrrolate and neostigmine, given either separately or simultaneously. Heart rate changes were significantly different between the halothane and enflurane subgroups. Patients anaesthetized with enflurane showed less fluctuations in heart rate. Simultaneous injection of glycopyrrolate and neostigmine minimized the tachycardia in the halothane subgroups only.

Glycopyrrolate: pharmacology and clinical use

This is a review of glycopyrrolate whose function in clinical practice is compared with that of atropine.

Modification by halogenated anaesthetics of chronotropic response during reversal of neuromuscular blockade

The effect of halothane and enflurane on changes in heart rate during reversal of neuromuscular block was compared in 48 adult patients. Premedication and anaesthetic technique were standardized. Either halothane or enflurane was the primary anaesthetic while pancuronium was used in all patients to achieve muscle relaxation. Ventilation was mechanically controlled and PaCO2 was between 30-40 mmHg. The neuromuscular block was reversed by an intravenous injection of atropine 1.2 mg and neostigmine 2.5 mg, given either separately or simultaneously, in different patient subgroups. Heart rate changes were significantly different between the halothane and enflurane groups. In general, reversal of neuromuscular block was accompanied by less fluctuations in heart rate after enflurane as compared to halothane anaesthesia. Simultaneous injection of atropine and neostigmine modified the tachycardiac response in the halothane sub-group only. Our observations suggest that use of enflurane offers an advantage over halothane in those patients in whom rapid fluctuations in heart rate during reversal of neuromuscular block may be dangerous.

Atropine and glycopyrrolate: changes in cardiac rate and rhythm in conscious and anaesthetised children

Heart rate and rhythm were studied in conscious children and children under nitrous oxide and halothane anaesthesia following intravenous administration of atropine or glycopyrrolate. Both drugs produced a similar increase in heart rate when the potency of glycopyrrolate is considered twice that of atropine. There is no difference in the response of anaesthetised and awake children. Junctional rhythm is the main dysrhythmia observed which appears to occur more frequently in anaesthetised children. The administration of both drugs is safe in paediatric patients.

Premedication with atropine or glycopyrrolate in children. Effects on heart rate and rhythm during induction and maintenance of anesthesia

Atropine 15 micrograms/kg and glycopyrrolate 5 or 10 microgram/kg were studied as anticholinergic premedicants in groups of 20 children each. A control group of 20 children did not receive anticholinergic premedication. Both atropine and the higher dose of glycopyrrolate produced significant increases in heart rate prior to induction of anaesthesia. The subsequent increase during the process of induction was less than in those who had not received an anticholinergic drug or glycopyrrolate 5 micrograms/kg. Dysrhythmias during induction of anaesthesia occurred slightly less frequently in the patients given atropine or the higher dose of glycopyrrolate. Although the incidence was similar in these two groups, ventricular ectopic beats occurred less frequently following the use of glycopyrrolate. The control of secretions was also superior with this anticholinergic premedicant.