Positive pressure ventilation through small cricothyroidotomy tubes in a model lung
Cricothyroidotomy is performed to maintain oxygenation and ventilation in cases of a critical ‘can’t intubate, can’t oxygenate (CICO)’ situation.1–3 Many anaesthesiologists prefer to perform a cricothyroidotomy using a percutaneous cannula technique2,4 rather than a surgical technique with large cuffed tubes, which may be more efficient.1,2 However, the efficacy of positive pressure ventilation through small uncuffed percutaneous cricothyroidotomy tubes in kits remains controversial.1–3,5,6 We evaluated the effectiveness of positive pressure ventilation applied by a common anaesthesia ventilator through small cricothyroidotomy tubes using an experimental lung model.
Following approval by the institutional ethics committee (Ethical Committee of Steel Memorial Yawata Hospital, Kitakyushu, Japan; no. 14-08), three uncuffed cricothyroidotomy tubes, a 3.5 mm internal diameter Melker (3.8 cm in length; Cook Medical, Bloomington, IN, USA), a 4.0 mm internal diameter Minitrach II Seldinger (9.2 cm in length; Smiths Medical, Hythe, Kent, UK) and a 4.0 mm internal diameter Quicktrach (4.0 cm in length; VBM, Sulz am Neckar, Germany), were compared with a standard 7.5 mm internal diameter tracheal tube. Each of the four tubes was connected to a standard anaesthesia circuit and a lung model (Ingmar Medical, Pittsburgh, PN, USA) with a compliance of 40 ml cm–1 (Fig. 1). The distal end of each cricothyroidotomy tube was attached to a fibreoptic swivel connector with a small port to prevent a leak. The side arm of the fibreoptic connector was blocked with tape. The distal cuff of the 7.5 mm standard tube was inflated and the leak was prevented.
Mechanical ventilation was performed using a common anaesthesia ventilator (GE/Datex-Ohmeda 7900 Smartvent, Wauwatosa, WI, USA) in pressure control mode with 100% oxygen. A ventilation pressure of 20, 25 or 30 cmH2O was applied to each tube, and a respiratory rate of 15 and an inspiratory: expiratory ratio of 1 : 2 were used. Positive end-expiratory pressure (PEEP) was set to 0 cm H2O. Two pneumotachographs (FlowAnalyser, PF-300; Imtmedical, Buchs, Switzerland) were attached to the distal and proximal sides of the tubes (Fig. 1), and the expiratory tidal volume (Vt), peak inspiratory pressure (PIP) and PEEP at each side of the tube were measured at each ventilation pressure setting. Measurements for each setting (four tubes and three ventilation pressures) were randomly taken 10 times. A one-way analysis of variance (ANOVA) followed by the Tukey–Kramer test were used to compare the values.
The mean Vt, PEEP and PIP values at the proximal and/or distal side of the tube at each ventilation pressure setting are presented in Table 1. For each tube, the mean distal Vt increased as the ventilator pressure increased (P < 0.001). The distal Vts with small tubes ranged from 300.7 to 607.7 ml and minute volumes from 4.5 to 9.1 l min–1. The mean Vt was lowest with the 3.5 mm Melker tube and largest with the 4.0 mm Quicktrach tube among kit tubes (P < 0.001). The pressure drop was more pronounced with the smaller internal diameter tubes (Table 1). The highest PEEP value was 6.7 cm H2O with the 3.5 mm Melker tube at 30 cmH2O ventilation pressure (P < 0.001).
Tidal volumes provided via small cricothyroidotomy tubes depended on the size, length and ventilation pressure. The minute volume measured with small tubes (>4.5 l min–1) seems almost satisfactory. Thus, oxygenation and ventilation with these tubes may be possible for a short time in the CICO situation on condition that the air does not escape to the upper airway and/or there is a lack of leakage at the puncture site.
In this event, additional techniques may be applied to prevent the leakage such as closing the patient's mouth and nose or packing gauze into the pharynx.5,6 Simultaneous positive pressure ventilation or the application of continuous positive airway pressure using a facemask or a supraglottic airway device have also been considered to overcome this backflow.