This service evaluation is the first national study of its kind at the time of publication. It included patients admitted with respiratory failure during the COVID-19 pandemic from 12 different UK trusts. Patient demographics from this cohort closely matched ICNARC data21, indicating that we studied a generalizable sample.
In our evaluation, combined LUS and FUSIC Heart were performed in 89.5% of total patients enrolled. This indicates that, even in severely critically ill COVID-19 patients, combined LUS and FUSIC Heart were deliverable alongside the high intensity ICU clinical workload across the trusts.
However, there was a mean time to scan of 2 days from ICU admission, and only 39.5% of patients received two or more scans. Serial scan data in our study and other papers have shown increased mortality with worsening lung scores22. It could be argued, therefore, that there remains suboptimal provision for serial ICU PoCUS services across the trusts involved and potentially nationwide.
The correlation between 12-point and 6-point scores supports the role of the 6-point LUS protocol in ICU patients23,24. The PosteroLateral Alveolar and/or Pleural Syndrome (PLAPS) is easily achievable and provides good discrimination from the anterior views25,26,27,28. Clearly this is beneficial as movement of COVID-19 patients for posterior views requires additional manpower, can be time-consuming and can cause instability.
Typical LUS findings have a good correlation with COVID-19 PCR positivity. This has been well studied and published previously29,30,31,32,33,34. Preserved A-lines in all 6 zones made the diagnosis of COVID-19 related respiratory failure extremely unlikely35. Alveolar-interstitial syndrome associated with a normal LV function indicates a non-cardiogenic cause for respiratory failure.
LUS was able to identify those who had a higher 30-day mortality, particularly if the total score was >8 or there was a high score in the PLAPS zones36. The incidence of RV dysfunction was more prevalent in our study in those with higher LUS scores (indicating more extensive COVID lung involvement)37,38. This study has demonstrated worse outcomes in patients with RV dysfunction. This association has been extensively shown in ICU patients with RV dysfunction in the context of ARDS and COVID-19 9,39,40,41,42,43 . Lazzeri et al noted LUS score and right:left ventricle ratio (representing RV dilatation) were both independent predictors of ICU mortality in their observational study of 47 ICU patients17.
Most clinical guidelines used fraction of inspired oxygen concentration (FiO2), oxygen saturations and respiratory rate as parameters to identify patients who would benefit from critical care referral44. This study suggests that combined LUS score and RV assessment may aid in identifying those patients in a worse prognostic group. Patients with high LUS scores and RV dysfunction may benefit from earlier ICU admission and closer monitoring. However, as this was a service evaluation study, formal research studies will need to be done to assess this further.
65% of patients who had POCUS scans had a subsequent change in ICU management. Management strategies were adapted from literature45 and utilised on a recommendation basis from clinical advisory groups. Many of these guidelines included the need for LUS and FUSIC Heart to aid decision making46. These included optimal PEEP strategies based on lung compliance and right heart function, decision to prone and haemodynamic management strategies aimed at reducing pulmonary hypertension or augmenting the systolic RV function.
A systematic review of PoCUS use in patients with undifferentiated shock47 documented two ICU based studies where focused echocardiography resulted in a change in patient management in 41-51% of patients48,49. These studies focused primarily on shock management as an end point. COVID-19 pathophysiology is complex, multi-system, and the potential interventions are numerous and interdependent. This may explain why our percentage of intervention was higher. However, this study did not measure whether interventions led to changes in outcome. There is inherent bias due to this study being performed by enthusiastic PoCUS practitioners and so caution must be taken when interpreting this observation.
Given the association between LUS score > 8, RV dysfunction and outcome, acquiring this information becomes important. The utility of this information is clear: triaging to a clinical area of higher monitoring, instigating pre-emptive management strategies or altering existing therapies are all possible.
The combination of these two imaging modalities, LUS and FUSIC Heart, in COVID-19 patients at ICU admission (or ideally before) provides dynamic clinical information and informs the complex interactions between the heart and lungs and the effects, if any, of therapeutic intervention. It is therefore crucial to the overall management of this condition.
Limitations
Service evaluation methodology provides insight into how LUS and FUSIC Heart are utilised in the delivery of routine care at the expense of a defined study protocol which ensures consistency in approach. Based on the observational methodology, the results should be interpreted within the constraints and limitations of a service evaluation study.
There was significant variation in the time to first imaging study and intervals between studies. Including scans performed in the initial 7 days from ICU admission introduces a degree of survivor bias. The use of a semi-quantitative score may be an oversimplification of a fundamentally subjective assessment. The salient information which dictated changes may not have been captured within the ordinal scale used.
This is an evaluation of a service that for most was set up de novo to meet the needs of the pandemic. This may explain some of the discrepancies in the results. It seems less likely that a patient admitted to the ICU with severe respiratory failure due to COVID-19 pneumonitis had a lung score of zero, which may reflect issues with PoCUS sonographers' training or reporting.
It is important to note that RV assessment is more challenging than first appreciated. If the left ventricle is hyperdynamic, one may expect the right to be in a similar state. The fact that the right merely appeared to be ‘normally’ functioning may actually represent dysfunction at this stage in context. The basic level of training has enabled a larger number of patients to have an assessment scan. However, the trade-off is that subtle echo signs such as apical RV dilatation or early systolic dysfunction may have not been appreciated as this would have required an advanced skill set not reliably available on ICUs.
This raises questions around ‘quantity versus quality’ - is it better to provide a screening service where most patients have a scan or is it desirable to have a detailed analysis in a few, sicker patients? This question is beyond the scope of this study and requires further investigation to understand the optimum way to organise a PoCUS service.