Nociceptive and anaesthetic-induced changes in pulse transit time during general anaesthesia.
BACKGROUND
Pulse transit time (rPTT), the interval between ventricular electrical activity and arrival of a peripheral pulse waveform, has been used to detect changes in autonomic tone. The aim of this observational pilot study was to measure changes in rPTT in response to general anaesthesia and noxious stimuli.


METHODS
Thirty-one healthy women undergoing gynaecological surgery were allocated to groups depending on the need for airway management with tracheal intubation (n=9), a laryngeal mask (LMA, n=17) or a facemask (n=5). During general anaesthesia, we measured changes in RR interval (RR-int) and rPTT after (i) induction of anaesthesia, (ii) airway manipulation and (iii) surgical stimulus. rPTT was estimated as the interval from the peak in the R-wave to detection of the pulse oximeter waveform in the periphery.


RESULTS
Mean baseline rPTT was 245 (SD 27) ms. Upon induction of anaesthesia, rPTT increased (by 28.2 (20.4) ms, P<0.001) in all but two patients. rPTT decreased in response to endotracheal intubation (by 43.1 (24.6) ms, P=0.001) but did not vary in response to insertion of LMA or surgical stimulus. Mean baseline RR-int was 865 (141) ms. A mean reduction in RR-int after tracheal intubation did not reach statistical significance. RR-int was unchanged with induction of anaesthesia, LMA insertion or surgical stimulus.


CONCLUSIONS
Variation in rPTT reflects autonomic responses to nociceptive stimulation and fluctuations in anaesthetic depth independently of heart rate.
Department of Anaesthesia and Intensive Care, Waikato Hospital, Private Bag 3200, Hamilton, New Zealand.
S
S
Singham
L
L
Voss
J
J
Barnard
J
J
Sleigh
D000328:Adult; D018681:Anesthetics, General / Q000494:pharmacology*; D005260:Female; D013509:Gynecologic Surgical Procedures; D006801:Humans; D007442:Intubation, Intratracheal; D017214:Laryngeal Masks; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009619:Nociceptors / Q000502:physiology*; D010092:Oximetry / Q000379:methods; D010865:Pilot Projects; D011673:Pulsatile Flow / Q000187:drug effects* / Q000502:physiology
D018681:Anesthetics, General