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"Can a PAC be inserted safely in patients with
pre-existing left bundle branch block (LBBB)?"
Yes, but additional measures to insure a stable
cardiac rhythm are necessary. During passage of the PAC, a temporary
right bundle branch block is often induced as the catheter impacts
the interventricular septum. Thus, in a patient with a pre-existing
LBBB, cardiac asystole may occur. The risk of asystole in this setting
is probably in the range of 1 - 2%. Therefore, during insertion
of the PAC in these patients, an alternative mechanism to pace the
heart must be immediately available. This could include an internal
temporary endocardial pacing wire, epicardial pacing wires, or placement
of transcutaneous pacing patches (Zoll? transcutaneous pacemakers).
"What dangers are associated with outpatient liposuction
procedures?"
Liposuction is now the most frequently performed
cosmetic surgical procedure in the United States, utilizing both
general anesthesia and MAC. The most common operative technique
today is called tumescent liposuction, where large volumes of saline,
epinephrine, and lidocaine are infused into the subcutaneous fat,
augmenting subsequent aspiration via operative cannulas. While the
content of the infusate varies, it typically contains 500 - 1,000
mg of lidocaine, and 0.25 - 1.0 mg epinephrine, per liter of saline.
Several case reports have noted patient deaths as a result of unheralded,
and precipitous intraoperative hypotension and bradycardia. Two
patient who arrested intraoperatively had received total lidocaine
doses of 10 and 14.3 mg/kg, with blood lidocaine concentrations
of 5.2 and 2.0 mg/liter (determined at autopsy). Other problems
associated with this procedure may include: peripheral nerve injury;
local infection and sepsis; overhydration, leading to pulmonary
edema and respiratory distress; congestive heart failure; pulmonary
embolism; fat embolization; and marked hemorrhage leading to severe
anemia.
"What risks are associated with mild hypothermia
of patients in the perioperative period?"
There are three major perioperative adverse outcomes
associated with a core temperature of < 35.0 to 35.5 degrees C.
These include increased risk of wound infection, increased bleeding,
and cardiac complications, especially in elderly or other vulnerable
patients. One study found a three-fold increase in the incidence
of postoperative wound infections in patients who develop hypothermia
during colon resection, despite antibiotics in all cases. It is
theorized these wound infections are due to decreased tissue oxygenation
secondary to thermoregulatory vasoconstriction. Hypothermic patients
having hip surgery had a 20% increase in intraoperative and postoperative
bleeding. Lastly, this degree of hypothermia increases the duration
of the PACU stay, and the thermal discomfort experienced by patients.
Thus, this issue also has economic and quality of care ramifications
as well.
"What factors should you consider in deciding
whether to attempt oral intubation or request a immediate surgical
airway when presented with a patient with massive facial trauma
from a motor vehicle crash?"
Factors to consider include hemodynamic stability
of the patient, immediate airway patency, mental status, rate of
blood loss, severity of facial injury, expertise of anesthesia and
surgical/ER personnel, the most likely next step in the management
of the patient, etc.
"How would you transfer a patient from the ICU
to the OR for a emergent procedure when that patient has ARDS and
is on pressure control ventilation with a pressure limit of 36,
with an FIO2 of 0.6, and 15 cm of PEEP?"
This is dependent on transfer ventilator equipment
available in individual hospitals. The need to maintain the complex
regimen and not just "go quickly" is key to the response.
"What circumstances would cause discrepant readings
between the pulse oximeter hemoglobin saturation value and those
measured by a laboratory cooximeter?"
This would most likely happen in situations where
there are greater than the usual (insignificant) amounts of carboxyhemoglobin
(CO-Hb) or methemoglobin (MetHb). The pulse oximeter reading (called
the functional saturation) will be falsely elevated compared to
a laboratory cooximeter measurement of Hb saturation (called functional
saturation). Why? The oximeter measures the percentage of 02Hb and
reduced Hb using the relative absorption of only two wavelengths
of light. Other hemoglobin types, such as carboxyhemoglobin and
methemoglobin are not measured by this method. Conversely, laboratory
cooximeters measure 02Hb, reduced Hb, CO-Hb, and MetHb by using
at least four wavelengths of light. As a theoretical example, if
a patient has 15 gm Hgb, of which 11gm are 02Hb, 3 gm are CO-Hb,
1 gm is reduced Hb, the pulse oximeter reading(fractional saturation)
will be the following: 02Hb/02Hb+ reduced Hb, 11/11 + 1 or 11/12,
92% but the Cooximeter (functional saturation) reading will be:
02Hb/02 Hb + reduced Hb + CO-Hb or 11/ 11 + 3 + 1 or 11/15, 73%.
"How is temperature monitoring different in the
neonate compared to the adult?"
Temperature regulation in the newborn is difficult
for a variety of reasons. Neonates have a large surfacearea to body
weight ratio, less subcutaneous fat and minimal ability to shiver.
Rectal temperature probes provide a reasonable measure of core temperature,
but placement of the well lubricated probe should be done carefully
since rectal perforation is a risk of using this site. Leak of inspired
gases around endotracheal tubes may cool probes placed into the
nasopharynx, resulting in inaccurate readings from nasopharyngeal
probes. Tympanic measurement has been advocated as a measure of
central temperature but it is uncertain whether or not tympanic
temperature reflects central temperature and there have been reports
of tympanic membrane perforation. Esophageal probes will accurately
reflect aortic root temperature if placed into the distal third
of the esophagus.
"Is it safe to place a lumber epidural catheter
in a 6 year old child after the induction of general anesthesia?"
Placement of lumbar epidural catheters in children
is regularly done after anesthesia, because placement in an anxious,
uncooperative child is not only painful and frightening but also
exposes the child to excessive risk. However, correct placement
of the catheter can be ascertained only through indirect means.
Test doses are still done in the usual fashion, while recognizing
the limitations. Numerous investigator have shown that IV administration
of the doses of epinephrine used in epidural test doses lead to
inconsistent increases in heart rate in the anesthetized child.
In studies which followed blood pressure increase and T wave changes
following IV injection of an epinephrine dose equal to that used
in epidural test doses, the results have also been inconsistent.
Certainly if the vital signs do change intravascular placement should
be assumed and the catheter replaced or the technique abandoned.
In cases where inadvertent intrathecal placement has occurred, in
young children administration of a test dose with a local anesthetic
will not lead to a significant lowering of blood pressure. Slight
lowering of blood pressure after intrathecal administration of local
anesthetics is seen in children older then 7 years of age. Teenagers
exhibit the degree of hypotension similar to that seen in adults.
Obtaining an Xray (epidurogram) after injection of a small amount
of contrast into the catheter may be used to confirm correct placement.
In cases where the epidural is crucial for intra and post operative
care, fluoroscopy may be used during placement to confirm correct
position of the catheter.
"How do the types of anesthesia errors differs
between children and adults?"
According to the American Society of Anesthesiologists
Closed Claims Data Base, a comparison of adult and pediatric closed
claims indicates a large prevalence of airwayrelated damaging events,
most frequently related to inadequate ventilation, occurring in
children. In particular, respiratory events were more common among
pediatric patients (43% in children versus 30% in adult claims).
In the opinion of the reviewers, 89% of the pediatric claims related
to inadequate ventilation could have been prevented with pulse oximetry
and/or end tidal CO2 measurement. However, pulse oximetry appeared
to prevent poor outcome in only one of seven claims in which pulse
oximetry was used and could possibly have done so. Moreover, in
pediatric (compared with adult inadequate ventilation claims), poor
medical condition and/or obesity (6% versus 41%; P < or = 0.01)
were uncommon factors.
"What types of nerve injuries occur most commonly
and what factors are associated with them?"
Again, according to the American Society of Anesthesiologists
Closed Claims Data Base, 16% of claims are for anesthesiarelated
nerve injury. The most frequent sites of injury are the ulnar nerve
(28%), brachial plexus (20%), lumbosacral nerve root (16%), and
spinal cord (13%). Ulnar nerve (85%) injuries are more likely to
have occurred in association with general anesthesia, whereas spinal
cord (58%) and lumbosacral nerve root (92%) injuries were more likely
to occur with regional techniques. Ulnar nerve injury occur predominately
in men (75%) and are also more apt to have a delayed onset of symptoms
(62%) than other nerve injuries. Spinal cord injuries are the leading
cause of claims for nerve injury that occurred in the 1990s. Advanced
age, thinness, obesity and the presence of diabetes increase the
incidence of perioperative neuropathy. The length of anesthesia
or the intraoperative positioning do not correlate with the incidence
of this neuropathy but the length of the hospital stay does. Bilateral
neuropathy has been reported in 9% of patients. Interestingly, asymptomatic
ulnar neuropathy as indicated by nerve conduction studies has been
found to be present in the contralateral extremity in almost all
patients who suffered from postoperative ulnar neuropathy.
Neuropathy can develop in patients who received
local anesthesia or light sedation and can occur during hospitalization
without surgery. This suggests mechanisms of nerve compression and
stretching may occur outside the operating room. Remember that the
findings of the Closed Claims analysis may differ from those experienced
in everyday clinical practice since this database includes only
closed ("settled") law suits.
"Can succinylcholine be safely used in children?"
Yes, however children with myopathic conditions
may be susceptible to both malignant hyperthermia and catastrophic
hyperkalemia when given succinylcholine. Young children, particularly
males under the age of 8, may present with undiagnosed myopathies,
such as Duchenne Muscular Dystrophy. Dangerous hyperkalemia can
occur and present with sudden onset of life threatening arrhythmias.
If this happens after the administration of succinylcholine, hyperkalemia
should be strongly suspected. The immediate treatment of life threatening
hyperkalemia is the administration of intravenous calcium chloride
or calcium gluconate. Calcium is an electrophysiologic antagonist
of hyperkalemia and should be the first line treatment. Subsequent
administration of glucose, insulin and sodium bicarbonate should
also be strongly considered, to facilitate the movement of potassium
to the intracellular space. Life threatening hyperkalemia can also
occur when in patients who have sustained upper motor neuron lesions,
burns, trauma, crush injuries, sustained period of bedrest or immobility,
sepsis, stroke, spinal cord injury and progressive degenerative
neurological states such as amyotrophic lateral sclerosis.
"What is the appropriate endpoint for reversal
of neuromuscular blockade?"
A train-of-four (TOF) ratio of 0.60 correlates with
a vital capacity of 55 ml/kg, a negative inspiratory force of 70
cm H2O, and a peak expiratory flow of 95% control values. This degree
of recovery allows most patients to cough adequately and maintain
a patent airway. Double burst stimulation (DBS) of the ulnar nerve
detects 40% fade between the first and the second response, thereby
improving the clinician's ability to detect more subtle degrees
of residual neuromuscular block.
The clinical implications of residual neuromuscular
block are important. Precurarization decreases the TOF ratio to
as low as 0.63, may cause difficulty breathing and swallowing, and
decreases inspiratory force and peak expiratory flow rate. Even
a decrease in the TOF ratio to 0.85 is associated with general discomfort,
malaise, ptosis and blurred vision.Other more recent studies with
volunteers have shown that TOF ratios of 0.6 to 0.7 are associated
with decreased upper esophageal tone and a decrease in the coordination
of the esophageal musculature during swallowing. Fluoroscopic study
of these individuals while swallowing demonstrated significant pharyngeal
dysfunction resulting in misdirected swallowing, leading to a four
to five-fold increase in the risk of aspiration. A TOF recovery
= 0.90 is required to return esophageal tone and pharyngeal coordination
to baseline. NMB drugs also interfere with hypoxic ventilatory control.
In vitro, while application of acetylcholine to the carotid body
results in hyperventilation, application of anticholinergics eliminated
the increase in neuronal activity of the carotid body sinus nerve
that otherwise occurs with hypoxia. In awake volunteers who have
received atracurium, vecuronium or pancuronium, with a train-of-four
ratio of 0.70, the hypoxic ventilatory drive is reduced by 30%.
"Does residual neuromuscular weakness affect clinical
outcomes?"
A recent prospective, randomized, blinded study
indicates that residual neuromuscular block after administration
of pancuronium is associated with an increased incidence of postoperative
pulmonary complications. Thus, an optimal level of neuromuscular
recovery may be TOF ratio of > 0.90. Only with this degree of recovery
do patients manifest normal swallowing, fully protect their airways,
and resume normal respiratory function. It may require this more
robust level of neuromuscular recovery to minimize the postoperative
risk of aspiration and pneumonia.
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