Lean body weight local anaesthesia topicalisation charts for awake tracheal intubation

In our institution, we have been routinely following up all awake tracheal intubations (ATI) since November 2020, with service evaluation authorisation granted. During this time, we reviewed 106 cases (until June 2022), of which 87 (82%) had a documented patient height and weight, allowing lean body weight (LBW) to be calculated. The Difficult Airway Society (DAS) recommends a maximum local anaesthetic dose for airway topicalisation of 9 mg.kg⁻¹ LBW lidocaine [1]. Of these 87 cases, 61% received local anaesthesia doses exceeding the DAS recommendation [1]; 91% received a dose of lidocaine within 9 mg.kg⁻¹ actual body weight. This clearly demonstrates that there is a lack of awareness of the requirement to calculate and dose local anaesthesia for topicalisation according to LBW. While no cases of overt local anaesthetic toxicity were reported, it is possible that more subtle signs of toxicity may be obscured by the concurrent use of sedation and subsequent anaesthesia. Woodall et al. [2] found that, in a cohort of 200 healthy anaesthetists on a training course who underwent airway topicalisation with lidocaine up to 9 mg.kg⁻¹ and no sedation for airway endoscopy, a third (36%) experienced symptoms attributable to lidocaine toxicity, including agitation, drowsiness, dysphoria, nausea, circumoral tingling and paraesthesia. The article did not specify whether actual or lean body weight was used for lidocaine dosing.

Excessive local anaesthesia dosing clearly presents an ongoing patient safety issue. To address this, we produced quick reference LBW lidocaine calculation charts for airway topicalisation (Fig. 1). The charts allow clinicians to easily find the appropriate maximum safe dose of lidocaine adjusted to LBW, based on the patient's actual weight, height and gender. As the LBW calculation varies according to sex, we have produced charts for both male and female patients. The maximum doses are rounded down to the nearest 10 mg in order to facilitate simple calculations. These charts are displayed in all potential ATI locations in the Trust. Electronic copies have been distributed to all anaesthetists and ODPs in our institution, as well as all trainees in the region, to enable quick reference on a smartphone or tablet device. The charts have also been incorporated into our local DAS-approved Northwick Education in Oxygenation (NEO) airway course, delivered twice annually.

Figure 1

Female lean body weight (LBW) local anaesthesia dosing calculation chart for awake tracheal intubation topicalisation. Maximum safe lidocaine dose according to patient's actual body weight and height. There is a corresponding chart for male patients in a contrasting colour.

We anticipate these charts will aid safe drug dosing and patient care, by improving compliance with the maximum safe doses of lidocaine, but also by reducing the cognitive load associated with ATI and helping to mitigate drug calculation errors. We are currently evaluating the impact of these LBW calculation charts on safe local anaesthetic dosing and believe that other centres may also benefit from this resource.