A Tidal volume calculator to improve lung protective ventilation in COVID-19 related Acute Respiratory Distress Syndrome (ARDS) (2020)

Type of publication:
Conference abstract

*Blair J.; *Hester S.; Baldwin A.; Ali T.

Intensive Care Medicine Experimental; 2020; vol. 8

Introduction: Routine use of lower tidal volumes (TVs) for the mechanical ventilation of patients with ARDS results in decreased mortality and increases the number of days without ventilator use [1]. Severe COVID-19 pneumonia has been associated with the development of ARDS as characterised by the Berlin definition [2]. A multi-centre preliminary audit was undertaken to identify whether ventilated COVID-19 related ARDS patients were receiving optimal TVs, as recommended by the Faculty of Intensive Care Medicine (FICM) and Intensive Care Society (ICS) ARDS management guidelines [3]. Objective(s): As a result of the audit, three main areas for improvement were identified. 1. To achieve accurate calculations for ideal body weight (IBW) and target TV 2. To improve documentation of IBW and target TV 3. To achieve TVs no greater than 6 ml/kg Methods: A 'tidal volume calculator' tool was developed using Microsoft Excel, which was simple, colour coded and kept on all Intensive Care Unit (ICU) computer desktops. This tool was designed to use height to calculate IBW and, if the patient's height was unavailable, could also be utilised to calculate height from ulna length. IBW was subsequently used to calculate a target TV. Staff received training on how to apply the tool. Two snapshot audits were carried out in April and May 2020 at two ICUs. The first was conducted prior to the tool's introduction with the second two weeks after its implementation. All patients receiving mechanical ventilation, except those spontaneously breathing, were included. Data was extracted from patient notes, charts and ventilator settings. Result(s): The initial audit included 14 patients. Six patients did not have an IBW documented. Three patients had documented IBWs that were 12 kg, 15 kg and 23 kg greater than the weight calculated using the tool, leading to increased tidal volume targets. Only three patients were achieving TVs of 4-6 ml/kg. Eleven patients were achieving a TV greater than 6 ml/kg, with two of these achieving a TV of greater than 8 ml/kg. The follow-up audit included ten patients. This revealed that all patients had an IBW clearly documented. Moreover, nine patients were achieving TVs within 4-6 ml/kg, with only one patient found to be achieving a TV greater than 6 ml/kg. Conclusion(s): This audit cycle revealed that initially adherence to lung protective ventilation and documentation of IBW was poor. In some instances, documented IBW was vastly different to the calculated IBW, suggesting that in these situations actual body weight may have been used. In a time when clinicians were being redeployed to support ICU, this simple tool was shown to support staff by clearly calculating and displaying IBW and target TV for reference. This directly led to improved adherence to lung protective ventilation and optimisation of patient care. Limitations include that no consideration was made for overall patient outcome, and only a snapshot of achieved TVs from ventilators were recorded; daily/weekly trends were not studied.

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