B. It\'s a busy day in the ER, and Dr. Lawson is needed to help out, so he is de
ID: 3474330 • Letter: B
Question
B. It's a busy day in the ER, and Dr. Lawson is needed to help out, so he is detained from attending the tennis match as well. The next pt was a 21 year old, 65kg male in a coma who was breathing very slowly with episodes of apnea. The pts friends ditched him at the door and then sped off in a cobalt blue Maserati, Their erratic behavior was noted by the door guard. All signs pointed to a narcotic overdose. Dr. Lawson ordered CO, levels and blood pH. The results indicate that the pt has respiratory acidosis. Pt values: pH = 7.22 CO_2 = 2.0 mM Dr. Lawson was about give the order to inject the pt with bicarbonate when Dr. Divya Katdare popped in to save the day. What is the pt's HCO, level? What would be a better treatment for this patient?Explanation / Answer
1)
From the lab reports, we have 2 values, the patient's pH, and CO2 level. Using these 2 values and using the Henderson-Hasselbalch equation we can find out the patients HCO3 level.
Henderson-Hasselbalch equation is pH = pKa + log [HCO3-]/[CO2] where pKa is the negative logarithm of the acid dissociation constant for carbonic acid which is a constant value of 6.1.
So, substituting the values,
7.22 = 6.1 + log [x/2] where x is the value of HCO3
Rearranging,
X = CO2 * 10 (pH - 6.1)
X = 2 * 10 (7.22-6.1)
X = 2 * 10 (1.12) = 2 * 13.18 = 26.36
So, the patients HCO3 level is 26.36 mM
(Additional info: The question gave us CO2 level and not pCO2 level [which is the partial pressure value]. If that was given, then to calculate CO2 level, multiply pCO2 level with 0.03)
2)
The question says the patient had respiratory acidosis a condition in which acid-base balance disturbance is present. If the doctor had pumped in more bicarbonate into the patient thinking that it is a narcotic overdose, it would have complicated patients as in respiratory acidosis the bicarbonate level would already be at a higher level than normal. For this patient bronchodilator or respiratory stimulants could be given. Oxygen therapy can also be considered since the pO2 value for this patient is in the range recommended for oxygen therapy. Since the patient is in a coma, ventilator support also has to be initiated. Note: Bicarbonate is a treatment option only if the pH of the patient is very less (like <7 which is not in this case) and is rarely used in respiratory acidosis.
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