employment agency fees of approximately $102,000 related to the hiring of senior level personnel, an increase in legal fees of approximately $80,000 related certain corporate initiatives and an increase in accounting fees of approximately $57,000. These increases were offset by a decrease in consulting fees of approximately $28,000.
Selling, General and Administrative Expenses:
Selling, general and administrative expenses were approximately $12,908,000 for the six months ended June 30, 2020, as compared to $9,265,000 for the six months ended June 30, 2019, an increase of $3,643,000. This increase is related to an increase in salaries, commissions and related costs of approximately $2,373,000, an increase in royalty expenses of approximately $569,000 due to the increase in product sales, and an increase in non-cash restricted stock expense of approximately $295,000 related to restricted stock units granted to the Company’s executive officers, an increase in non-cash stock compensation expense of approximately $1,403,000. These increases were offset by a decrease in travel and entertainment expenses of approximately $238,000, a decrease in sales and marketing expenses, which include advertising and conference attendance of approximately $437,000 and a decrease in office supplies and other general and administrative costs of approximately $322,000.
Interest Expense, net:
For the six months ended June 30, 2020, interest expense was approximately $579,000, as compared to interest expense of approximately $420,000 for the six months ended June 30, 2019. This increase in interest expense of approximately $159,000 was primarily a result of the additional interest incurred related to the draw down of the $5,000,000 Term B Loan with Bridge Bank on July 31, 2019.
History of Operating Losses:
We have experienced substantial operating losses since inception. As of June 30, 2020, we had an accumulated deficit of approximately $195,109,000, which included losses of approximately $6,320,000 and $8,431,000 for the six-month periods ended June 30, 2020 and 2019, respectively. Historically, losses have resulted principally from costs incurred in the research and development of our polymer technology, clinical studies, and general and administrative expenses.
Liquidity and Capital Resources
Since inception, our operations have been primarily financed through the issuance of debt and equity securities. At June 30, 2020, we had current assets of approximately $41,948,000 including cash on hand of approximately $35,114,000 and current liabilities of approximately $15,664,000. On July 24, 2020, the Company closed the sale of approximately 6,052,631 shares of its Common Stock and received gross proceeds of approximately $57.5 million and, after deducting the underwriting discounts and commissions and expenses related to the offering, received total net proceeds of approximately $54,000,000. In early July 2020, the Company received approximately $2,414,000 in proceeds related to the sale of shares pursuant to the Open Market Sale Agreement with Jefferies LLC and B. Riley FBR, Inc.
On July 31, 2019, the Company executed an Amendment to its Loan Agreement with Bridge Bank and, simultaneous with this Amendment, received $5 million in proceeds from an additional term loan. In addition, the Amendment extended the interest-only period of the loan through October 2020. Monthly principal payments of approximately $833,000 commence in November 2020.
We believe that we have sufficient cash to fund our operations well into the future.
COVID-19 Impact on Financial Results
First half 2020 product revenues were positively impacted by underlying strength in our critical care and cardiac surgery business, and the use of CytoSorb to treat critically-ill COVID-19 patients in the ICU. Though difficult to quantitate, we estimate that approximately $2.4 million to $2.6 million of our second quarter 2020 revenues and $3.9 million to $4.3 million of our year-to-date revenues were related to COVID-19. Given the order patterns we are currently experiencing, we expect that the COVID-19 pandemic will continue to have a positive impact on product revenues in the third quarter of 2020. This may change with containment of the pandemic.
In addition, as a result of the EUA granted by the FDA on April 11, 2020, we began shipping CytoSorb to hospitals in the United States. Sales to hospitals in the United States under the EUA amounted to approximately $667,000 for the three months ended June 30, 2020.