Lab case 223 Interpretation

A 30 year old man is brought to your emergency department at 06:30 am on a winter morning by SJA after his partner rang the ambulance.

His partner left him in normal state the night before when she went to work on night shift. On coming back at 0600 she found him semiconcious in bed , confused, complaining of headache intermittently. There was no evidence of overdose , trauma , deliberate self harm at scene. The windows of room were closed and there was heater in lounge room left working overnight because of cold weather.

 

On arrival to ED patients GCS was fluctuating 13 -14 , RR 14, sats 95 % RA, HR 115, BP 100/70, ECG sinus tachycardia, Temp 37, There was no evidence of head trauma, BSL 15, ketones 0.2, Patients CT head did not show any acute intracranial event. Patients VBG results were as followed.

PH 7.27 BSL 15

HCO3 16 Cl 95

PCO2 44 Lactate 10

Na 135 BAL 0

K 4.4 COHB 38 %

Q1: What are the main metabolic abnormalities on this VBG?

Answer: Acidemia , predominantly metabolic as HCO3 is low, HAGMA as AG = 135 – 95 + 16 = 24.

Expected CO2 = 1.5 X 16 +8 = 32 meaning there is component of mild respiratory acidosis likley secondary to reduced GCS.

Delta Ratio = 24-12 / 24-16 = 12/8 = 1.5 ( Consistent with HAGMA).

Significantly high lactate which is the main cause of High anion gap.

Significantly high COHB levels , normal levels less than 5 % , background levels in smokers are up to 10 %.

Q2: What is the most likley diagnosis?

Answer: Although altered state of consciouss state in young male has broad differential diagnosis , above is case of carbon mono oxide poisoning given history, clinical presentation and VBG strongly point towards it.

CO Poisoning: CO poisoning is a common cause of poisoning death. It can be obvious if fire has occurred or patient admits to suicide attempt, otherwise symptoms can be subtle and exposure could be chronic . Acute deliberate exposure leads to exposure to high levels over short period of time and low risk of longterm neuropsychiatric sequelae. Accidental or domestic exposure involves exposure to low concentrations of CO for longer duration and high risk of long term sequelae. CO is odourless, colourless gas which has very high affinity to bind to O2 and leads to tissue hypoxia. It also initiates endothelial damage, lipid per oxidation and inflammatory cascade.

CO poisoning deaths almost always occur prehosiptal. For those who arrive at hospital usually survive and risk assessment is aimed at identifying those at risk of long term neuropsychological sequelae.

Q3: How will you manage this patient?

Main stay of resuscitation in CO poisoning is application of O2 , Those with Low GCS will need intubation but overall aim is the same i.e Provision of O2. All patients should recieve 100 % O2 or O2 via NRM . Duration of O2 is controversial , one recommendation is 8 hours of high flow to adults, 24 hours to pregnant patient.

Treatment with hyperbaric oxygen has been a controversial , but any patient with suspected / confirmed COHB poisoning should be discussed with hyperbaric unit as it has shown benefit in certain group of patients. examples include all pregnant patients, metabolic acidosis, significant LOC, signs of ischemia.

Risk assessment depends on duration and levels of COHB exposure i.e deliberate Vs domestic ( chronic) . Significant LOC, elderly age, persistent confusion, metabolic acidosis, myocardial ischemia are high risk features.

Bedside Investigations include VBG, ECG , BSL. Others FBC, UE. CK, troponin, CXR are indicated if complications i.e non cardiogenic pulmonary oedema or myocardial ischemia are suspected. are suspected. CT head / MRI may show cerebral oedema, demylenation in severe cases. Neuropsychiatric testing at 3-12 months to investigate persistent or delayed neurological symptoms.

Correlation Of COHB levels and clinical features: It has been used as diagnostic tool to confirm CO poisoning, But mildly increased levels do not exclude serious poisoning especially in chronic exposure. Upto 10 percent can be seen in smokers, at 50 % CVS, resp collapse , arrhythmias, and seizure can occur. between 20-30 is headache, nausea, vertigo, ataxia, dyspnea.

Disposition is HDU, ICU or hyperbaric unit.