Two different methods to assess sympathetic tone during general anesthesia lead to different findings

End of year summary 2019: anaesthesia and airway management

This end of the year summary reviews anesthesia related manuscripts that have been published in the Journal of Clinical Monitoring and Computing in 2019. Anesthesia is currently defined as being composed of unconsciousness, immobility, and autonomic nervous system (ANS) control (Br J Anaesth;122:e127-e135135, Egan 2019). Pain is a postoperative issue, because by definition unconsciousness implies pain cannot be experienced. We first review work related to these aspect of the profession: unconsciousness (EEG, target control), immobility (muscle relaxants), and ANS control. Regaining consciousness has to be accompanied by pain control, and it is important to ensure that the patient regains baseline cognitive function. Anesthesia machine equipment, drug administration, and airway related topics make up the rest of published manuscripts.

Effects of anesthetic and sedative agents on sympathetic nerve activity

BACKGROUND

The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood.

OBJECTIVE

The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans.

METHODS

We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 μg/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 ± 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 ± 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study.

RESULTS

SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P <.001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 ± 0.25 μV to 0.77 ± 0.15 μV; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 ± 0.45 μV to 1.22 ± 0.58 μV (P = .000) and arm SKNA from 0.76 ± 0.43 μV to 0.55 ± 0.07 μV (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock.

CONCLUSION

Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA.

Pediatric blood pressures during anesthesia assessed using normalization and principal component analysis techniques

Expected values for blood pressure are known for both unanesthetized and anesthetized children. The statistics of changes in blood pressure during anesthesia, which may have important diagnostic significance, have not been reported. The purpose of this study was to report the variation in changes in blood pressure in four pediatric age groups, undergoing both cardiac and non-cardiac surgery. An analysis of the changes in blood pressure using normalization and principal component analysis techniques was performed using an existing electronic dataset of intra-arterial pediatric blood pressure values during anesthesia. Cardiac and noncardiac cases were analyzed separately. For 1361 non-cardiac cases, the average systolic blood pressure increased from 55.2 (17.6) mmHg in the first month of life to 85.4 (17.7) mmHg at 5-6 years. For 912 cardiac cases, the average systolic blood pressure increased from 55.7 (16.7) to 71.8 (24.8) mmHg in these cohorts. For non-cardiac cases in the first month, the mean (SD) for change in blood pressure over a 30 s period was 0.00 (8.8), for 5-6 year olds 0.0 (7.4); for cardiac cases, 0.1 (9.2) to - 0.1 (9.2). Variations in systolic blood pressure over a 5-min period were wider: in non-cardiac from 0.1 (12.2) mmHg (first month) to 0.4 (11.5) mmHg (5-6 year old) and from 0.2 (12.5) to 0.4 (14.2) mmHg in cardiac cases. Absolute blood pressures and changes in blood pressure during anesthesia in pediatric cardiac and non-cardiac surgical cases have been analyzed from a population database. Using these values, the quantitative methods of normalization and principal component analysis allow the identification of statistically significant changes.