Describe an anesthetic plan
for bariatric surgery.
Patient preparation begins well before entering
the operating room. Preoperative functional status of the upper airway, lower
airway, and cardiovascular system help predict perioperative outcome and should
be assessed. Although controversial, some form of aspiration prophy-laxis is
commonly administered. Often this is simply a non-particulate antacid by mouth,
just prior to entering the operating room. Most patients walk into the
operating room and lie down on the operating room table. Intravenous access is
frequently difficult, but rarely requires central venous cannulation. Large
blood pressure cuffs are useful for many patients, but for others large cuffs
slide distally and become unreliable. In such cases, normal-sized cuffs are
placed on the forearm. Infrequently, intra-arterial cannulation is required for
blood pressure measurements. Standard electrocardiogram electrodes and pulse
oximeter probes generally work well on MO patients.
Preoxygenation is achieved employing an
anesthesia facemask with an airtight seal. Three vital capacity breaths or 3
minutes of tidal breathing is rarely sufficient. Effective preoxygenation
requires varying amounts of time, depend-ing on several factors. A clinically
useful endpoint for pre-oxygenation is an expired oxygen concentration of 90%
or above.
Although some might argue it is unnecessary,
anesthesia is generally begun with a rapid sequence induction, utilizing
cricoid pressure. Any one of multiple induction agents can be administered.
Determining induction doses based on total body weight may result in
overdosing, while selecting induction doses predicated on ideal body weight can
result in underdosing. For most agents, dosing is predicated on lean body mass.
As a rule of thumb, lean body mass frequently approximates 100 kg in men and 80
kg in women. Actual doses of induction agents are modified based on myocardial
reserves. Succinylcholine is an excellent choice for laryngoscopy, although
nondepolarizing neuromuscu-lar blockers can be used as well. A Macintosh 3
blade or a Miller 2 blade provides adequate laryngoscopic views in most
patients and is a good way to start out. Tracheal tubes of various sizes are
prepared with one or more stylets.
Just about any anesthetic agent or adjuvant can
be used for bariatric patients. Since the goal is to have them awake and
extubated at the end of surgery, short-acting agents are preferable. The
duration of action of midazolam and its active metabolite often extends into
the emergence phase, thereby delaying awakening, and in combination with
opi-oids depresses respiration. For these reasons, midazolam seems to be
counterproductive as an anesthetic adjuvant during bariatric surgery. Muscle
relaxants are necessary for laparotomy and helpful for laparoscopy. Opioids are
useful as anesthetic adjuvants and required for postoperative analgesia. Even
laparoscopy patients suffer from significant abdominal wall soreness and
benefit from analgesia. Air is used instead of nitrous oxide to avoid bowel
distention. Potent inhalation agents are generally used.
MO patients are prone to soft tissue
infections, necessi-tating antibiotic prophylaxis. Two grams of cephalosporin
or equivalent is commonly administered intravenously prior to incision. The
stomach is decompressed before inserting trochars to help prevent gastric damage
by these sharp instruments. Additionally, the evacuated stomach takes up less
space in the abdomen, thereby providing improved surgical vision and
facilitates manipulations of the organ. Forced-air warming blankets help
prevent heat loss during laparotomy and laparoscopy.
For lean patients, intraoperative tidal volumes
are generally based on weight. To do so for MO patients results in excessive
tidal volumes and very high inspiratory pressures. In fact, selection of tidal
volume should be pred-icated on patient height. As a general rule of thumb,
short patients do well with tidal volumes approximating 500 ml and tall
patients do well with tidal volumes approximating 700 ml. Although these
starting points are adequate for many MO patients, they should be adjusted
depending upon the individual’s requirements. Selecting a tidal volume must
account for oxygenation, ventilation, and inspiratory pressures. Some authors
advocate larger tidal volumes as prophylaxis against intraoperative decreases
in FRC, that often result in hypoxemia. This was challenged by Sprung et al.
(2003), who showed that large tidal volumes did not improve oxygenation during
laparoscopy. An alternative to large tidal volumes is the use of positive end
expiratory pressure (PEEP). PEEP can improve oxygenation, but tends to increase
inspiratory pressures, predisposing to pneumothorax, and decreases venous
return to the heart, resulting in decreased blood pressures.
Emergence and extubation are critically
important. At the completion of surgery, bariatric patients still suffer from
the same preoperative problems with which they started, plus others. Residual
anesthetic agents depress respiratory drive and diminish upper airway dilator
muscle efficiency. Lingering muscle weakness impairs coughing and deep
breathing, as well as interfering with upper airway dilator muscle function.
Abdominal wall pain from laparotomy or abdominal wall soreness from laparoscopy
predispose to splinting and all its associated problems. Consequently, MO
patients are at risk for hypoxemia in the postoperative period. To prevent this
problem, those who do not meet extubation criteria remain intubated and
ventilated postoperatively. Those who satisfy extubation criteria are extubated
and given supplemental oxygen to breathe by nasal cannula or facemask. They are
nursed in the upright position to help restore FRC and ventila-tion/perfusion
matching.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.