UBP 1.5 (Long Form): Orthopedics – Spinal Surgery Flashcards
Secondary Subject -- COPD/PFTs/DM/Tobacco Use/HTN/Chronic Alcohol Abuse/Perioperative Glucose Management/Spinal Cord Monitoring (SSEPs and MEPs)/Autonomic Neuropathy/Delayed Emergence/Metabolic Acidosis/Post-operative Vision Loss
Intra-Operative Management:
Are there any special monitors you would place for this case?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
Given the risk of unrecognized cardiac disease, and understanding the potential for significant blood loss and spinal cord ischemia during this procedure, in addition to the ASA standard monitors,
I would place –
- a 5-lead EKG to monitor for signs of cardiac ischemia,
- an arterial line to closely monitor hemodynamic changes,
- SSEPs and/or MEPs to monitor for intra-operative spinal cord ischemia, and
- a Foley catheter.
Intra-Operative Management:
Do you need to monitor MEPs when you are already monitoring SSEPs?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
While SSEPs are a fairly good indirect monitor of anterior spinal cord function, there have been multiple case series reporting significant changes in MEPs and subsequent postoperative neurologic deficits despite normal intra-operative SSEPs.
Therefore, given the risk of possible false negatives with SSEP monitoring and the apparent increased sensitivity of MEPs for detecting motor injury, many practitioners consider MEP monitoring a useful adjunct to SSEP monitoring during procedures that place the spinal cord at risk.
Monitoring MEPs, however, is not yet considered the standard of care and a decision to utilize this modality should include consideration of the associated risks, such as –
- scalp burns,
- bite injury (use a bite block to prevent this complication),
- seizures,
- cardiac arrhythmias,
- cost, and
- anesthetic restrictions.
Moreover, MEP monitoring should not be used for patients with –
- cochlear implants,
- active seizures, or
- vascular clips in the brain.
- *Xtra Q – Are there any potential complications with MEPs?*
- *Xtra Q – Are there any contraindications to MEPs?*
Intra-Operative Management:
How are you going to intubate this patient?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
- *per UBP online – set the stage by stating your goals/concerns. Then.. mention what you will do…**
- —*
My primary goals during intubation are to safely secure the airway while avoiding further cervical spinal injury and aspiration in a patient who may have the delayed gastric emptying that can be associated with diabetes mellitus and/or alcohol abuse.
Therefore, I would –
- administer metoclopramide, an H2-receptor antagonist, and a nonparticulate antacid;
- ensure adequate airway analgesia (avoiding transtracheal injection and superior laryngeal nerve blockade, since they may compromise protective laryngeal reflexes);
- place the patient in reverse-trendelenburg position (improve respiratory mechanics, facilitate rapid intubation, and reduce the risk of passive regurgitation);
- apply manual in-line stabilization (best performed with two operators); and
- perform an awake fiberoptic intubation, recognizing that this method of intubation results in the least distraction of the cervical spine and would reduce the risk for aspiration.
Moreover, an awake intubation allows for an assessment of neurologic function after final patient positioning.
Intra-Operative Management:
What is your plan for maintenance of anesthesia?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
My plan for maintenance of anesthesia is dependent on the availability and type of neuromonitoring.
My goal would be to provide adequate anesthesia with minimal depression of SSEPs or MEPs, while facilitating rapid emergence at the end of the case to allow immediate assessment of neurological function.
If MEPs were to be used, I would utilize a total intravenous technique with an infusion of propofol, remifentanil, and ketamine
(MEPs are the least affected by ketamine, narcotics, and midazolam;
the depressant effects of propofol are attenuated by the use of ketamine),
recognizing that this type of neuromonitoring is more sensitive to volatile agents than SSEPs.
If I believed that the use of volatile agents was desirable, I would limit the agent to 0.5 MAC and attempt to avoid variations in concentration that might complicate the interpretation of his MEPs.
*Note in online UBP how Dr. George answers this – he says “my goals would be.. then says what he would do.” – “My goal is to provide adequate anesthesia and analgesia.”
Intra-Operative Management:
How do anesthestic agents affect MEPs?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
**see how Dr. George answers this on Online UBP**
Motor evoked potentials (MEPs), which monitor the functional integrity of the descending motor pathways in the anterior spinal cord, may show decreased amplitude and increased latency with administration of opioids, sedative hypnotic drugs, and volatile agents.
Unfortunately, these signal changes are similar to those seen with spinal cord ischemia.
(Note: With MEPs, changes in latency are less reliable, and are not typically used in management decisions, but a 50% - 80% decrease in amplitude is considered significant.)
Since MEPs are more sensitive than SSEPs to signal suppression from volatile agents, total intravenous anesthesia is the preferred technique with this type of neuromonitoring.
And, while MEPs may still be monitored with partial neuromuscular blockade (maintain at least two twitches), most practitioners completely avoid the administration of muscle relaxants.
Finally, since MEPs may be altered by anesthesia, it is important to obtain baseline signals prior to induction, and to then maintain anesthesia at a constant level to avoid false positives.
Note: Monitoring techniques that employ rapid trains of transcranial electric or magnetic stimuli (rather than single pulse) are more resistant to the effects of anesthetic agents, making the use of volatile agents more acceptable.
Intra-Operative Management:
How do anesthetic agents affect SSEPs?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
In general, somatosensory evoked potentials (SSEPs), which monitor the functional integrity of the ascending sensory neural pathways in the posterior spinal cord, may show decreased amplitude and increased latency with anesthetic suppression (narcotics probably have the least effect on SSEPs).
Unfortunately, anesthetic suppression, hypothermia, hypercarbia, hypoxia, and hypotension all produce similar signal changes to those seen with spinal cord ischemia.
As with MEPs, it is important to obtain baseline SSEPs prior to induction, and to then maintain anesthesia at a constant level to avoid false positives.
Intra-Operative Management:
After induction and positioning in the prone position, the patient becomes hypotensive, with a blood pressure of 62/48 mmHg. Treatment with ephedrine is ineffective. What would you do?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
I would –
- quickly provide 100% oxygen,
- ensure adequate ventilation,
- confirm sinus rhythm on the EKG,
- give a fluid bolus, and
- ensure that patient positioning was not obstructing venous return.
Recognizing that this diabetic patient with resting tachycardia, orthostatic hypotension, hypertension, and a poor response to ephedrine may suffer from significant autonomic neuropathy, I would –
- administer a small bolus of a direct acting vasopressor such as phenylephrine.
Xtra Q – why is ephedrine ineffective?
Intra-Operative Management:
What is autonomic neuropathy?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
In patients with longstanding, poorly controlled diabetes, excessive glycosylation can result in neuropathy of the autonomic nervous system.
The clinical manifestations of this disorder include – gastroparesis, GERD, exercise intolerance, early satiety, bloating, lack of sweating, peripheral neuropathy, dysrhythmias, nocturnal diarrhea, nausea, vomiting, epigastric pain, impotence, HTN, resting tachycardia, orthostasis, painless myocardial ischemia, lack of reflex tachycardia with hypovolemia, and resistance to indirect acting agents such as ephedrine.
Diabetic autonomic neuropathy often affects the parasympathetic system first, which can be assessed by measuring the heart rate response to performing a valsalva maneuver, moving from the supine to standing position, and/or taking six deep breaths over 1 minute.
In more severe disease, the sympathetic system is affected, which can be assessed by measuring the patient’s blood pressure to sustained handgrip and moving from the supine to standing position.
Intra-Operative Management:
During instrumentation there is decreased amplitude and increased latency in the SSEP and MEP signals.
Is this significant?
What would you do?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
A 50% decrease in amplitude and/or a 10% increase in latency of the SSEP signal and/or a 50% decrease in amplitude of the MEP signal would be considered clinically significant (some sources suggest that a “significant” decrease in MEP amplitude requires a 75-80% change).
Therefore, assuming the changes were significant, I would:
- correct any hypoxemia, hypotension (return to normal levels or even 20% above normal), hypovolemia, anemia, and hypo/hypercarbia in order to optimize oxygen delivery to the spinal cord and reverse any conditions that may result in false-positives;
- make sure that the depth of anesthesia had remained stable and was not interfering with the evoked potential readings; and
- ask the surgeon to rule out surgical causes of spinal cord injury such as excessive distraction.
If the SSEP and/or MEP signals remained abnormal despite these actions, I would perform a wake-up test to determine if further steps, such as removing surgical instrumens, were necessary.
*Per UBP Online – Note: This question did not have all the info %age of amplitude**/latency change… so answer as such “assuming that there is a 50% decrease, etc.. I would consider this significant.”
Intra-Operative Management:
Which part of the spinal cord is most vulnerable to ischemic injury?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
*Note – per UBP online, Mock examinee answers this well at 22:47*
–
In general, the anterior spinal cord is the most vulnerable, due to a relatively limited blood supply from the anterior spinal artery, which arises from the vertebral arteries and is augmented by blood flow from radicular arteries.
–
The anterior spinal artery supplies the anterior 2/3 of the spinal cord and receives 4-10 radicular arteries arising from the aorta, including the largest of these, the artery of Adamkiewicz, which supplies the majority of blood to the anterior, lower two-thirds of the spinal cord.
Post-Operative Management:
At the end of the case, the patient’s neuromuscular blockade has been fully reversed, he is taking adequate tidal volumes, and his expiratory concentration of volatile agent is reading zero.
Despite this, he remains unresponsive to verbal and tactile stimuli.
What do you think is going on?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
Delayed emergence in this patient is concerning and, given the surgical procedure and the patient’s medical history, I would consider the possibility of –
- neurologic deficit,
- hyper/hypoglycemia, or
- alcohol withdrawal.
Other potential etiologies include –
- hypoxia, hyper/hypocarbia,
- residual anesthetic,
- residual neuromuscular blockade, and
- metabolic derangements.
–
In this situation, I would assure adequate ventilation and oxygenation, review medications given during the case, confirm complete neuromuscular reversal with a twitch monitor, and check serum glucose and electrolytes.
If the cause of delayed emergence was still unknown, I would consult a neurologist, order an EEG, and order a CT of the head and neck.
Post-Operative Management:
Lab work returns showing the following: pH = 7.26, PaCo2 = 38, PaO2 = 314 on Fio2 of 100%, Na+ = 139 mEq/L, K+ = 3.0 mEq/L, HCO3- = 18 mEq/L, and Cl- = 99 mEq/L.
What is your interpretation?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
The patient has an increased anion gap metabolic acidosis (anion gap = [Na+ - (Cl- + HCO3-)]), which can occur by any process that increases unmeasured anions.
This patient with a history of poorly controlled diabetes, daily alcohol consumption, and recent surgery could have developed this metabolic derangement secondary to –
- progressive diabetic or alcoholic ketoacidosis;
- the accumulation of lactic acid due to poor tissue oxygenation or liver dysfunction (alcohol abuse may lead to impaired lactate metabolism); and/or
- intravascular dilution (dilutional acidosis may result secondary to the administration of hypotonic fluids, hyperglycemia, and/or an impairment of free water excretion due to stress-induced increases in antidiuretic hormone).
Other potential causes of increased anion gap metabolic acidosis include –
- renal failure,
- rhabdomyolysis (secondary to the release of phosphate, sulphate, uric acid, and lactic acid from the muscle cell),
- starvation, and
- the ingestion of certain toxins (methanol, ethylene glycol, salicylate, etc.).
–
- Note: The normal anion gap is 12 +/- 4. Some labs with more modern measurement techniques (providing more accurate measurements of chloride levels) will list the normal anion gap as 7 +/- 4. Also note that these “normal” anion gap ranges are based on the omission of K+ from the equation. Therefore, you should always consult your specific laboratory’s normal reference range when making clinical decisions.*
- —*
- Xtra Q: What does an increased gap mean? What is the normal Anion gap?*
Post-Operative Management:
Lab work returns showing the following: pH = 7.26, PaCo2 = 38, PaO2 = 314 on Fio2 of 100%, Na+ = 139 mEq/L, K+ = 3.0 mEq/L, HCO3- = 18 mEq/L, and Cl- = 99 mEq/L.
How would you treat his acidosis?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
My treatment plan would consist of adjusting ventilation to help compensate for the acidemia, and identifying and treating the underlying cause of the metabolic derangement.
Therefore, after adjusting the ventilator settings to maintain his PaCo2 in the low 30s, I would check:
- a serum lactate (a level >2 suggests lactic acidosis);
- his urine output, creatinine, and blood urea nitrogen to identify acute renal failure, which could lead to the accumulation of renal acids;
- a blood glucose and urinary ketones to identify diabetic ketoacidosis; and
- a blood alcohol level, recognizing that binge drinking and minimal nutritional intake could lead to alcoholic ketoacidosis.
Then, I would –
- initiate the appropriate treatment to address the underlying cause of his metabolic derangement and
- consider administering bicarbonate if –
- his acidosis became severe (pH < 7.1),
- his bicarbonate dropped below 10 mEq/L, or
- if he developed life threatening hyperkalemia.
Post-Operative Management:
Do you have any concerns about treatment with sodium bicarbonate?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
Xtra Q – Would you treat with bicarbonate?
–
My concerns with the administration of bicarbonate would include:
- the generation of additional CO2 (bicarbonate reacts with hydrogen ions to form CO2), which then could diffuse into cells resulting in worsening intracellular acidosis;
- a leftward shifting of the oxyhemoglobin dissociation curve, with an increase in hemoglobin’s affinity for oxygen leading to decreased oxygen unloading and transient tissue hypoxia;
- the development of a hyperosmolar state secondary to excessive sodium; and
- the development of hypokalemia secondary to movement of K+ from the extracellular to the intracellular compartment.
Therefore, I would probably avoid treatment with bicarbonate unless the patient developed life threatening hyperkalemia or severe acidosis (pH < 7.1 and/or bicarbonate < 10 mEq/L), the latter of which can lead to dysrhythmias, hypotension, myocardial depression, and resistance to exogenous catecholamines.
Post-Operative Management:
After successful treatment and emergence, the patient states he cannot see out of either eye.
What would you do?
- (A 53-year-old 61 kg man presents to the OR for posterior cervical laminectomy with instrumentation. Three weeks prior, he was involved in a MVA and sustained a whiplash injury. He reports gait problems and increasing neck pain radiating to both arms.*
- PMHx: His past medical history includes type II diabetes and hypertension for the past eight years. Additionally, he has smoked two packs of cigarettes a day for the past 25 years and admits to daily alcohol consumption.*
- Meds: Ramipril. lopressor, furosemide, glyburide, and albuterol prn*
- Allergies: Morphine, Percocet, Lortab*
- PE: Vital Signs: P = 104, BP 132/60, RR = 20, T = 37.1 °C, SpO2 = 91% on room air.*
- Airway: poor dentition with multiple caries, mallampati II, decreased cervical ROM secondary to pain*
- Cardiovascular: orthostatic hypotension*
- Lungs: bilateral diffuse wheezing*
- Extremities: bilateral hyperreflexia and mild weakness*
- CXR: Hyperinflated lung fields*
- Lab: Na+ = 132 mEq/L, K+ = 3.2 mEq/L, Cl- = 91 mEq/L, CO2 = 35, Glucose = 220 mg/dL, Hgb = 11 gm/dL, HgbA1C = 11*
- MRI: Severe spinal stenosis with a spinal cord contusion at C4 and C5 levels)*
Recognizing that significant postoperative vision loss, such as occurs with anterior and posterior ischemic optic neuropathy, retinal artery occlusion, and cortical blindness, is likely the result of impaired oxygen delivery, I would –
- immediately assess the patient and seek to optimize physiologic conditions by correcting any metabolic disturbances;
- elevating the head of the bed (to facilitate venous drainage); and
- ensuring adequate blood pressure, hemoglobin, oxygenation, and cardiac function.
Ideally, the risk of postoperative blindness would have been discussed with the patient and his family preoperatively.
In any case, I would assure them that all precautions had been taken to minimize this risk, and that everything possible would be done to appropriately assess and treat the patient, including an urgent ophthalmology consult.
- Note: While MRI may be considered to rule out an intracranial cause of vision loss (i.e. cerebral infarction), the ASA practice advisory for perioperative vision loss associated with spinal surgery concludes that, “there is no role for antiplatelet agents, steroids, or intraocular pressure-lowering agents in the treatment of perioperative ION”.*
- —*
- Xtra Q – Would steroids be helpful?*
