## Tuesday, July 22, 2014

### Delta –Delta or corrected HCO3- where is this other disorder hiding?

Often when we have a severe gap acidosis, we are forced to calculate the “delta/delta” and look for either a non gap acidosis or met alkalosis. How does this work?
Let’s work an example:
Ph 7.1, AG is 22 and serum Hco3 is 10 with a premise of AG metabolic acidosis.

Method one:

Corrected bicarbonate = measured bicarbonate +( change in AG)
Corrected bicarbonate = 10 + (22-12) = 20
If corrected bicarbonate is <22, a non gap acidosis is present as well
If corrected bicarbonate is >26, a met alk is also present.
If 22-26, a pure gap acidosis remains.

Method two:
Think out loud,   “If the AG dropped increased from 12 to 22, there was a change of 10, hence bicarbonate should be roughly down by 10meq.  Normal bicarbonate is 24 and hence bicarbonate should be 14, but it’s 10, hence a non gap acidosis is present as well.”

Most online calculators use this method:

Problem with this method: Assumptions about all buffering occurring in the ECF and being totally by bicarbonate are not correct. Fifty to sixty percent of the buffering for a metabolic acidosis occurs intracellularly.

Method three: using the delta-delta ratio
delta ratio = (Increase in Anion Gap / Decrease in bicarbonate)
delta ratio = ( 10/14)=  <1 giving us the same diagnosis of combined gap and non gap acidosis.
See the below table

##### Assessment Guideline
0.4 - 0.8
Consider combined high AG & normal AG acidosis
1 to 2
Usual for uncomplicated high-AG acidosis
Lactic acidosis: average value 1.6
DKA more likely to have a ratio closer to 1
> 2
Suggests a pre-existing elevated HCO3 level so consider: concurrent metabolic alkalosis

As a general rule, in uncomplicated lactic acidosis, the rise in the AG should always exceed the fall in bicarbonate level.

The situation with a pure DKA  is a special case as the urinary loss of ketones decreases the anion gap and this returns the delta ratio downwards towards one. A further complication is that these patients are often fluid resuscitated with 'normal saline' solution which results in a increase in plasma chloride and a decrease in anion gap and development of a 'hyperchloraemic normal anion gap acidosis' superimposed on the ketoacidosis. The result is a further drop in the delta ratio.

Ref:
{"ft_lang_label":"__label__en","ft_lang_prob":0.8592803,"math_prob":0.8359063,"size":2851,"snap":"2023-40-2023-50","text_gpt3_token_len":742,"char_repetition_ratio":0.14506498,"word_repetition_ratio":0.25813448,"special_character_ratio":0.24061732,"punctuation_ratio":0.12477718,"nsfw_num_words":0,"has_unicode_error":false,"math_prob_llama3":0.9823192,"pos_list":[0],"im_url_duplicate_count":[null],"WARC_HEADER":"{\"WARC-Type\":\"response\",\"WARC-Date\":\"2023-12-02T02:41:29Z\",\"WARC-Record-ID\":\"<urn:uuid:fe5f6d45-cc7a-487a-8f8e-18bdf263fc06>\",\"Content-Length\":\"178538\",\"Content-Type\":\"application/http; msgtype=response\",\"WARC-Warcinfo-ID\":\"<urn:uuid:1b8070b1-baf3-44f5-a44c-a4e0b5429d07>\",\"WARC-Concurrent-To\":\"<urn:uuid:ed2467e5-233f-4435-8a3d-c55664a476cf>\",\"WARC-IP-Address\":\"172.253.62.121\",\"WARC-Target-URI\":\"http://www.nephronpower.com/2014/07/delta-delta-or-corrected-hco3-where-is.html\",\"WARC-Payload-Digest\":\"sha1:FYODQ4WUZH3WQSCFWU6ZE4J64DPGV4UD\",\"WARC-Block-Digest\":\"sha1:F7TOTLWWFVASTRMXK6ZGYVCFFH7HNW3N\",\"WARC-Identified-Payload-Type\":\"text/html\",\"warc_filename\":\"/cc_download/warc_2023/CC-MAIN-2023-50/CC-MAIN-2023-50_segments_1700679100309.57_warc_CC-MAIN-20231202010506-20231202040506-00644.warc.gz\"}"}