Annual Scientific Meeting - 2001

LARYNGOSCOPY CONDITIONS IN SPONTANEOUSLY BREATHING PATIENTS: AN INCREMENTAL STEP-UP REGIMEN USING PROPOFOL BY TARGET CONTROLLED INFUSION.

S G Clarke^* & M F Dunsire^†

*Department of Anaesthesics, Charing Cross Hospital, Fulham Palace Rd, London, W6 8RF,UK,  †Department of Anaesthetics, Bromley Hospital, Cromwell Ave, Bromley, UK

Introduction. Inhalational induction of anaesthesia using halothane or sevoflurane has traditionally been the method of choice for attaining adequate depth of anaesthesia in those patients where it is imperative to maintain spontaneous respiration i.e. potentially difficult airways¹. However a significant proportion of patients find inhalational induction unpleasant, even with Sevoflurane². The increasing use of Target Controlled Infusion (TCI) systems has provided the ability to control the rate of induction & depth of anaesthesia using propofol³. The purpose of this interventional study was to induce anaesthesia in incremental steps to determine the stage at which satisfactory conditions for laryngoscopy could be achieved in spontaneously breathing patients, using propofol TCI.

Methods. After obtaining Ethics Committee approval and written informed consent we studied 31 ASA I & II patients undergoing elective surgery. Patients known or predicted to be difficult intubations (modified Mallampati score 3 or 4) or with a history of gastric reflux were excluded. Intravenous access was established and baseline measurements of heart rate (HR), blood pressure (MAP), & oxygen saturation (SpO₂) were recorded and at 1-minute intervals thereafter. Capnography confirmed spontaneous respiration throughout. After preoxygenation, propofol TCI was commenced at 1 μg.ml^-1 and the target was increased by 0.5μg.ml^-1 every 30 seconds until anaesthesia was induced as assessed by loss of verbal contact and eyelash reflex. Laryngoscopy was attempted 1 minute after loss of consciousness and intubating conditions assessed using a standard scoring system based on jaw relaxation, exposure/position of vocal cords, coughing and limb movement (graded 1-4). The target level was increased by 0.5μg.ml^-1 if conditions were deemed unfavourable (any score ≥3) and further laryngoscopy attempted 1 minute later. This pattern was followed until successful laryngoscopy was achieved (all scores ≤2). Statistical analysis was performed using paired t-tests.

Results. Over half (17/31) had favourable laryngoscopy conditions on the 1^st attempt, and almost 90% (27/31) by two further increments after loss of consciousness i.e. on the 3^rd attempt  (Table 1). Unsuccessful laryngoscopy was most commonly due to moderate limb movement (16/27 total failures), with the rest split between stiff jaw and coughing (5/27 & 6/27). There was a decrease in MAP after induction and post laryngoscopy (statistically but not clinically significant) but no difference in HR. SpO₂ did not fall below 95% at any stage and there were no episodes of apnoea. All patients were satisfied. No one had any recall of instrumentation. All rated the technique as pleasant and would be willing to undergo the same again.

Table 1.Outcome of laryngoscopy in 31 patients receiving propofol TCI step-up regimen. Values are number or median (range).

 Conclusions. This incremental step-up technique offers a safe alternative method to inhalational induction in assessing laryngoscopy in spontaneously breathing patients. Increasing blood concentration target levels of propofol slowly via TCI allows sufficient depth of anaesthesia to be attained to allow good conditions for laryngoscopy whilst allowing patients to breathe spontaneously. This technique may have a future role in the management of the difficult airway.

References.

1.MacIntyre PA & Ansari KA (1998) European Journal of Anaesthesiology 15: 462-466

2.Thwaites A, Edmends S & Smith I (1997) British Journal of Anaesthesia 78: 356-361

3.Chaudhri S, White M & Kenny GNC (1992) Anaesthesia 47: 551-553