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.
The ability to deliver positive pressure ventilation depends on the ‘effective ventilation pressure’, which is defined as the difference between the PIP at the distal side of the tube and the PEEP values (Table 1). These important values have not been investigated with these smaller tubes. The ‘effective ventilation pressures’ through these tubes were enough to obtain adequate tidal volumes in our model with normal lung compliance. In the presence of decreased lung compliance or increased airway resistance, ventilation pressures >30 cm H2O may need to be applied.
With the use of the smaller tubes, anaesthesiologists worry about the risk of barotrauma due to air trapping (‘auto-PEEP’).1,2 In this study, the largest PEEP value was only 6.7 cm H2O measured with the 3.5 mm Melker tube at a ventilation pressure of 30 cm H2O. The GE/Datex-Ohmeda anaesthetic ventilator has ascending bellows that produce 2 to 3 cm H2O of PEEP within the breathing circuit.7 With these values, the level of ‘auto-PEEP’ and the risk of barotrauma may be low. However, caution should be taken in patients with chronic obstructive pulmonary disease who would have higher levels of auto-PEEP.
Using a lung model, we demonstrated that positive pressure ventilation is possible with small cricothyroidotomy tubes and a common anaesthesia ventilator at 20, 25 and 30 cm H2O ventilation pressure in the absence of leakage. If ventilation with these smaller tubes fails, the operator should be prepared to perform an immediate surgical cricothyroidotomy or tracheostomy.
Acknowledgements related to this article
Assistance with the study: we would like to thank Cook Japan, Japan, for lending Melker Emergency Cricothyrotomy Catheter Set. We thank IMI Co, Ltd, Japan, for their assistance with the use of the FlowAnalyser, PF-300.
Financial support and sponsorship: support was provided solely from institutional and/or departmental sources (Department of Anaesthesia, Steel Memorial Yawata Hospital).
Conflicts of interest: none.
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