Triage assessment of cardiorespiratory risk status based on measurement of the anaerobic threshold, and estimation by activity limitation in patients with pulmonary arteriovenous malformations and hereditary haemorrhagic telangiectasia
Authors: Thurairatnam Saranya , Gawecki Filip , Strangeways Timothy , Perks Joseph , Santhirapala Vatshalan , Myers Jonathan , Tighe Hannah C , Howard Luke SGE , Shovlin Claire L. 
Published: March 2020

Background

Rapid triaging, as in the current COVID-19 pandemic, focuses on age and pre-existing medical conditions. In contrast, preoperative assessments use cardiopulmonary exercise testing (CPET) to categorise patients to higher and lower risk independent of diagnostic labels. Since CPET is not feasible in population-based settings, our aims included evaluation of a triage/screening tool for cardiorespiratory risk.

Methods

CPET-derived anaerobic thresholds were evaluated retrospectively in 26 patients with pulmonary arteriovenous malformations (AVMs) who represent a challenging group to risk-categorise. Pulmonary AVM-induced hypoxaemia secondary to intrapulmonary right-to-left shunts, anaemia from underlying hereditary haemorrhagic telangiectasia and metabolic equivalents derived from the 13-point Veterans Specific Activity Questionnaire (VSAQ) were evaluated as part of routine clinical care. Pre-planned analyses evaluated associations and modelling of the anaerobic threshold and patient-specific variables.

Results

In the 26 patients (aged 21-77, median 57 years), anaerobic threshold ranged from 7.6-24.5 (median 12.35) ml.min-1kg-1 and placed more than half of the patients (15, 57.7%) in the >11 ml.min-1kg-1 category suggested as “lower-risk” for intra-abdominal surgeries. Neither age nor baseline SpO2 predicted anaerobic threshold, or lower/higher risk categories, either alone or in multivariate analyses, despite baseline oxygen saturation (SpO2) ranging from 79 to 99 (median 92)%, haemoglobin from 108 to 183 (median 156)g.L-1. However, lower haemoglobin, and particularly, arterial oxygen content and oxygen pulse were associated with increased cardiorespiratory risk: Modelling a haemoglobin increase of 25g.L-1 placed a further 7/26 (26.9%) patients in a lower risk category. For patients completing the VSAQ, derived metabolic equivalents were strongly associated with anaerobic threshold enabling risk evaluations through a simple questionnaire.

Conclusions

Baseline exercise tolerance may override age and diagnostic labels in triage settings. These data support approaches to risk reduction by aerobic conditioning and attention to anaemia. The VSAQ is suggested as a rapid screening tool for cardiorespiratory risk assessment to implement during triage/screening.

Key Messages

What is already known

Alongside age, pre-existing medical conditions are perceived negatively during triage assessments, particularly if rare, and/or theoretically expected to influence cardiorespiratory risk;

Anaesthetists use cardiopulmonary exercise testing to categorise patients to higher and lower risk independently to diagnostic labels, but this is not feasible in acute settings;

Pulmonary arteriovenous malformations are an exemplar of a condition where, due to expected or measured abnormalities (hypoxaemia-low PaO2 SpO2), poor physiological capacity might be predicted.

What this study adds

Neither age nor usual SpO2 predicted lower/higher risk categories by anaerobic threshold, but haemoglobin-dependent indices of oxygen delivery to the tissues were associated with higher risk, offering opportunities for improvement by attention to anaemia and aerobic conditioning;

Baseline exercise tolerance may override age and diagnostic labels in triage settings: the 13-point VSAQ Veterans Specific Activity Questionnaire (VSAQ) is suggested as a rapid screening tool for cardiorespiratory risk assessment.