9.6 Case 25

Acid-Base Physiology - Examples for 9.6
Case History 25 : An Old Lady with Abdominal Pain & Vomiting

Clinical Details
A 78 year old lady presented with at least a weeks history of abdominal pain and vomiting. She was mildly confused and may have been unwell for longer. She lived alone and was on no medication. General health was good and there was no history of cardiac, renal or chest disease. Free gas under the diaphragm was visible on an xray. She was thin and frail and was only mildly distressed. ECG showed sinus rhythm. Amylase level was low. Clinical assessment was perforated viscus with dehydration.

Initial blood results at 1000hrs in the Emergency Department:

Na⁺ 137 mmol/l
K⁺ 2.2 mmol/l
Cl^- 91 mmol/l
HCO3^- 38 mmol/l
urea 9.8 mmol/l
creatinine 0.07 mmol/l
albumin 21 g/l.
[Hb] 91 g/l

Resuscitation with normal saline with potassium was commenced. At operation, a dense pelvic abscess due to a perforated pelvic appendicitis was found.

Serial Blood Gas Results
Number:	1	2	3
Date:	29th	29th	30th
Time:	1200hrs	1730hrs	0600rs
Place:	Emerg Dept	Operating Theatre	ICU
F_IO2	21%	100%	30%
pH	7.52	7.43	7.32
pCO2	44.6	42	45
[HCO3]	35.8	27	22
pO2	59	94	81
Na+	137	141
K+	2.6	5.4	3.6

Assessment
The history and initial blood results strongly suggest an acute metabolic alkalosis (elevated HCO3) due to vomiting (loss of acid gastric contents) with typical findings of hypochloraemia and hypokalaemia. The hypochloraemia prevents the kidneys from excreting bicarbonate and maintains the alkalosis. The hypokalaemia is potentially life threatening but significant muscle weakness was not a complaint and there were no ECG abnormalities. The urea and creatinine were not elevated despite significant dehydration. The patient was maintaining some fluid intake.

Analysis of the initial blood gases collected after resuscitation was underway confirm the metabolic alkalosis (ie significant alkalaemia with elevated HCO3).

Is the respiratory compensation appropriate? The expected pCO2 by rule 6 is about 45mmHg [ie (0.7 x 36) + 20 ]. Respiratory compensation can be variable in metabolic alkalosis but is almost exactly at the expected level in this case. There is no respiratory acid-base disorder present.

The intraoperative gases later in the day are interesting. Hyperventilation has been avoided as this can lead to an acute respiratory alkalosis and cardiovascular deterioration. This is not particularly important in this case though as the metabolic alkalosis has been significantly corrected by this time. Blood gases in ICU the next morning show complete resolution of the alkalosis and a slight respiratory acidosis due to hypoventilation.

Other points:

The low albumin indicates chronic poor nutrition. A low albumin level is also a cause of metabolic alkalosis (see section 10.6) and this is relevant in this case. The albumin level fell further with fluid loading.

bullet Initial [Hb] fell with fluid loading and the patient was transfused. The patient had a significant anaemia and the haemoconcentration partly disguished its severity.

A lactate level was not measured in this patient. Hypovolaemia and poor perfusion especially if associated with sepsis can cause lactic acidosis and a lactate level will indicate the presence of a mixed metabolic disorder.

(Case 226042-98)

Firstly, initial clinical assessment (on the first gas results):

TO BE COMPLETED

Secondly, the acid-base diagnosis:
1. pH:
2. Pattern:
3. Clues:
4. Compensation:
5. Formulation:
6. Confirmation:

Finally, the Clinical Diagnosis:

Comment