My opinion: you either need to keep looking, negotiate a way better deal, or at least negotiate dramatic increases based on a bonus structure, and/or dramatic increases in years 2, 3, and beyond.
Compare this offer to 2013 MGMA mean (2012 data) for anesthesia pain, total comp, including benefits, possibly ancillaries, etc:
25th percentile - $383,721yr
3702 wRVU
$101/wRVU
Mean- $545,259 / yr
6963 wRVU
$78/wRVU
Median- $443,447/ yr
5405wRvu
$82/wRVU
75th%ile- $680,652
10,013 wRVU
$68/wRVU
While I don't have the 2014 MGMA numbers, I'd bet they're a heck of a lot closer to the 2013 MGMA numbers than this lowball offer the hospital gave you. Get a copy of the 2014 MGMA and ask for 75th percentile MGMA numbers for anesthesia pain. Keep in mind, these are totals including benefits, which are part of your salary. The amount of money they'll make on facility fees, if you do a lot of procedures, is well over these yearly numbers. Bottom line: their offer of $38/wRVU is Family Practice numbers, actually worse, considering the wRVUs your going to putting in.
2013 MGMA family medicine (without ob work)
Mean- $225,701
5076 wRVU
$44/wRVU