In the midst of a global pandemic, emergency rooms across the US have fallen strangely quiet as patients with other illnesses have stayed away for fear of contracting Covid-19. As a result, one of the surprising corporate casualties of the coronavirus crisis could be some of the companies that provide staff for hospitals.

Envision, one of the largest medical staffing companies, completed a restructuring of its roughly $7bn of debt this month as it moved to stave off bankruptcy. This comes less than 18 months after KKR — one of the oldest and largest US private equity firms with more than $200bn of assets — bought the Nashville-based company for nearly $10bn.

The Envision deal highlights one of the stress points in a financial system that is creaking under the pressure of the coronavirus-induced recession. To fund around two-thirds of the acquisition, KKR loaded the company’s balance sheet with junk-rated loans and bonds — a familiar private equity tactic. Those securities provided fuel for one of Wall Street’s least known but most important debt machines: collateralised loan obligations.