Low tidal volume ventilation

We read with interest your article on protective mechanical ventilation in Severn and Essex Critical Care units. ¹ At Blackpool Teaching Hospital, we are currently participating in a local network quality improvement project called ‘Blow Low’, aimed at improving our unit compliance with low tidal volume lung protective ventilation methods.

Baseline data in our unit showed that approximately 50% of patients were receiving tidal volumes in excess of 7 ml/kg of predicted body weight. Although we have good evidence to suggest lung protective ventilation should perhaps be the best practice in all patients,^2–4 we were not unique in having problems translating this into standard practice over a decade after publication of the ARDSnet trial. ⁴ We would like to share our success following a regional level Quality Improvement project, the ‘Blow Low’ campaign, the catchy memorable title being key to raising awareness among staff in our unit. The aim of the campaign was to ensure patients without contraindications received low tidal volume ventilation of 6–7 ml/kg with a target to reduce breaches of this tidal volume to less than 20% of total ventilated hours per patient.

We used a continuous quality improvement methodology of plan-do-study-act (PDSA) cycles ⁵ to help drive the change in our unit. During the first cycle, our interventions involved:

1. The re-introduction of a straightforward ideal body weight calculator attached to the ventilator at each bedside allowing all staff to easily calculate the target tidal volume range for each patient (6–7 ml/kg) and ensuring staff measure patient height and input IBW at admission.

2. Publication of educational fact sheets to aid education of all members of the critical care team and one–one bedside teaching sessions.

3. Posters located around the unit to increase awareness of the project.

4. Regular feedback of data to staff to highlight progress made.

After six weeks of the above, we conducted our first data analysis. Initially, there seemed to be minimal impact of the campaign but when subgroups were analysed, there was evidence of big improvements. In patients with an ideal body weight of >60 kg, 88% reached the target of tidal volumes <7 ml/kg. However, there was only 24% compliance in those with an ideal body weight of <60 kg, highlighting what we suspected was a lack of awareness that the tidal volumes should be calculated on ideal not actual body weight.

Taking all this into account, we set about with the next PDSA cycle. Our interventions during this cycle were:

5. Focus and education around those patients with ideal body weights <60 kg.

6. Incorporation of tidal volume checks on to the ward round checklist.

7. Highlighting any deviations from the standard using a red pen on the observation chart.

8. Video to highlight and educate staff on the importance of identifying spontaneous breathing whilst on a pressure control mode.

At Blackpool, we use Drager Evita Infinity and XL ventilators with the predominant mode of ventilation being PC-BIPAP. This allows spontaneous breathing throughout the whole ventilatory cycle. The video demonstrated to nursing staff how to detect the contribution of spontaneous effort to mandatory tidal volumes and how to record this on the observation charts. The aim of this was to record data in a more refined and accurate way.

After 16 weeks of the project, the data collected showed that we had improved compliance with low tidal volume ventilation dramatically and nearly 80% of recorded tidal volumes were less than 7 ml/kg ideal body weight. This improvement has largely been sustained over the last eight months. As a result of this, we decided to change the target slightly and now aim for a lower tidal volume of 6–6.5 ml/kg. We have recently rolled out our third PDSA cycle and have introduced:

9. A ‘blow low sign’ attached to each patient’s ventilator which clearly displays their height, ideal body weight and target tidal volume.

10. Continued education amongst the critical care team including a thank you event where all the results to date were communicated.

We have yet to review any data since reducing the target but will continue to work through the quality improvement cycles and hopefully improve compliance rates further over the coming months. It was also interesting to read that in your cohort of patients those managed using volume control ventilation as opposed to the more traditional pressure-controlled methods had significantly lower tidal volumes. This may be something to consider for the future in our hospital and critical care network.