[Yao's Anesthesiology] Obesity Management (2)

Click the blue word to follow our patient with morbid obesity and obstructive sleep apnea, female, 46 years old, planning to undergo elective laparoscopic gastric sleeve resection
.

She has a significant past medical history, including morbid obesity (height 1.
62 m; weight 176 kg; BMI, 66.
6 kg/m2), Pickwick appearance, mild rheumatoid arthritis, osteoarthritis, mild Asthma, hypertension, type II diabetes, peptic ulcer with severe gastroesophageal reflux, and obstructive sleep apnea
.

She was sleepy during the day, snored heavily at night, and had been sleeping in a seated position for the past two years
.

She can walk around the house on crutches, but cannot go up stairs
.

She had a diagnostic polysomnography test preoperatively and had an apnea-hypopnea index of 42
.

Two weeks before the operation, the patient received oxygen therapy with bi-directional positive pressure ventilation (BiPAP) at home, and the symptoms were significantly improved.
The design parameters of the oxygen therapy were: EQ0.
35, respiratory rate 10 times/min, inspiratory gas Positive airway pressure (IPAP) +11 cm H2O, expiratory positive airway pressure (EPAP) 4 cm H2O, spontaneous
.

Cardiac examination revealed that the patient was a high-risk patient, and echocardiography showed mild right heart enlargement and mild pulmonary hypertension
.

The patient's blood pressure was 155/82 mmHg, the pulse rate was 60 beats/min, and the respiratory rate was 20 beats/min
.

C Intraoperative management 1.
How to implement intraoperative monitoring of this patient? 2.
How to perform anesthesia induction? Describe the intubation method
.

3.
Why is preoxygenation important for obese patients? How to do this? Comparing the effects of four maximal spirometric oxygen and three-minute continuous oxygen techniques
.

4.
How to maintain general anesthesia during surgery? In what way to maintain? 5.
Which muscle relaxant should be used? 6.
Can local anesthesia be added to reduce the dosage of opioids during and after surgery? What are the advantages and disadvantages of local anesthesia? What newer technologies are available? 7.
What effect do narcotic drugs have on the sphincter of Oddi? Do you need medication? 8.
During the operation, arterial blood gas showed: pH 7.
35; PaO2 57mmHg; PaCO2 52mmHg; FiO2 0.
6; mechanical ventilation tidal volume IL; respiratory rate 15 times/min
.

Then the following ventilation indicators were adjusted: positive end-expiratory pressure was 10 cmH2O, and tidal volume was adjusted to 1.
2
L.

After 20 minutes, arterial blood gas showed: pH 7.
32; PaO2 55mmHg; PaCO2 55mmHg
.

How to explain these changes? 9.
What is apnea oxygen? 10.
What is diffuse hypoxia? How to avoid it? D Postoperative Management 1.
When should this patient be extubated? What are the criteria for extubation? 2.
What are the common early postoperative complications in patients with morbid obesity? How are health-related factors associated with obesity? Which factors are statistically associated with perioperative mortality? 3.
For obese patients, how does the surgical position affect respiratory function? 4.
How to avoid postoperative atelectasis? 5.
How long after surgery is supplemental oxygen required? 6.
How to perform postoperative analgesia? Partial Answers C Intraoperative Management C1.
How can intraoperative monitoring be performed on this patient? In addition to routine necessary monitoring, including electrocardiogram, non-invasive blood pressure, pulse oximetry, end-tidal carbon dioxide, and body temperature, the patient also underwent arterial cannulation for blood gas detection at any time and continuous intraoperative blood pressure monitoring
.

Take your temperature
.

Hourly urine output was recorded to assess total fluid intake
.

Peripheral nerve stimulators were used to monitor the effects of muscle relaxation
.

The bispectral index (BIS) was used to monitor the depth of anesthesia
.

Laparoscopic bariatric surgery is a procedure with low blood loss (typically less than 100-200 ml) and low fluid requirements
.

Invasive arterial blood pressure monitoring is mainly used in super-obese patients with cardiopulmonary disease, or those who cannot provide non-invasive blood pressure monitoring because of the conical upper extremity or the absence of a suitable blood pressure cuff
.

When peripheral venous catheterization is difficult, central venous catheterization is generally performed
.

Pulmonary artery catheterization is generally used in patients with pulmonary hypertension, cor pulmonale, or left ventricular heart failure
.

C2.
How to perform anesthesia induction? Describe the intubation method
.

The patient should be visited before entering the operating room to confirm his fasting status, and a thicker-bore trocar should be selected for intravenous cannulation, and anticholinergic drugs should be used to reduce upper respiratory secretions.
Metoclopramide, a drug that boosts gastric motility to help the stomach empty
.

A complete set of airway preparation equipment, non-invasive and invasive (such as cricothyroidotomy device and surgical tracheostomy device, etc.
) should be prepared properly
.

When the patient enters the operating room, various monitoring devices are connected and pre-oxygenated
.

Sedation with a very low dose of midazolam (4 mg), dexmedeto at the usual dose [1 ug/kg for 10 minutes, then 0.
2-0.
7 ug/(kg·h), total body weight] Pyrimidine, a central alpha-receptor agonist; ketamine (10 mg/dose) can be added if needed
.

Keep the patient awake, calm, and cooperative
.

The physician decided to perform transnasal bronchoscopy-guided tracheal intubation for this patient
.

Cocaine (4%, 160 mg) was administered nasally for local anesthesia and local dilation of the muzzle and terminal airway was performed
.

4% lidocaine was used for local anesthesia of the oropharynx and anterior part of the uvula
.

After successful transnasal bronchoscopy, a topical spray of 4% lidocaine was also applied to the vocal cords prior to entry into the trachea
.

The endotracheal tube was carefully passed through the vocal cords, followed by pulmonary auscultation and capnography to confirm the placement of the tube, after which the patient was inhaled with sevoflurane for maintenance of anesthesia
.

When it was confirmed that the motor mechanism of the chest wall was normal, cisatracurium (0.
2 mg/kg TBW) was applied, and mechanical ventilation was performed
.

Endotracheal intubation under the guidance of fiberoptic bronchoscope can also be performed through the mouth in the case of unsatisfactory patient anatomy (small nostrils)
.

In this case, local anesthesia of the oropharynx with benzocaine, anesthesia of the lower pharynx with lidocaine nebulizer, and airway closure (glossopharynx, upper larynx, and larynx) were provided for nasal intubation.
in very good condition
.

When the external anatomical structure is not ideal, lidocaine gel is applied to the end of the peroral tracheal intubation.
When it passes through the larynx, it will contact the mucosa and then the peripheral nerves in the upper part of the larynx, and produce a certain peripheral nerve block effect on it
.

When the patient can tolerate the stimulation of the endotracheal tube without coughing, the patient is proved ready for bronchoscopy
.

If physical examination and previous anesthesia history confirm ease of oral intubation, rapid sequential tracheal intubation with thiopental (3-5 mg /kgTBW) or propofol (2mg/kg TBW), plus succinylcholine (1-1.
5mg/kgTBW)
.

If intubation conditions are not ideal, non-invasive airway management tools can be used for operational management
.

Tracheo-esophageal combined intubation is a beneficial tracheal intubation rescue product for morbidly obese patients
.

The most critical part of success lies in having skilled operation experience, adequate preparation, a profitable assistant, and the initiative to switch to direct laryngoscopy when necessary
.

C3.
Why is preoxygenation important for obese patients? How to do this? Comparing the effects of four maximal spirometric oxygen and three-minute continuous oxygen techniques
.

First, morbidly obese patients may spend longer intubation than non-obese patients; second, obese patients have less oxygen storage in the lungs (lower functional residual capacity) and faster oxygen consumption (in high oxygen consumption state), so they are a high-risk group for hypoxemia
.

The maximum pre-oxygenation of the whole body, or nitrogen excretion, requires the patient to inhale 100% pure oxygen for at least 3 minutes in a well-closed system, fully supply the alveoli, arteries, veins and various tissues of the body, and at the same time make the pulse oxygen saturation reach 99%-100%, this method is superior to the fast-track pre-oxygenation method, which is four times of maximum vital capacity oxygen
.

Generally speaking, patients with morbid obesity have the fastest effect of hemoglobin desaturation
.

Hemoglobin desaturation in children is second, and again, in adults who are generally sick
.

Only healthy adults with the slowest desaturation developed hypoxemia just when the effects of succinylcholine wore off
.

Studies have shown that the rate of oxyhemoglobin desaturation during apnea after induction of anesthesia correlates with BMI
.

They recommend that the patient perform 3 breaths of maximum vital capacity at 100% oxygen concentration, which allows the patient to tolerate 3 minutes of apnea before hypoxemia occurs
.

In their study, people without preoxygenation experienced hemoglobin desaturation in just 1 minute
.

Valentine et al.
, compared the effects of four maximal spirometry with three minutes of continuous oxygen in elderly patients
.

They found that the peak oxygen saturation after preoxygenation was essentially similar for both methods
.

However, when the patient was continuously apnea and exposed to room air, the duration of oxygen saturation at all levels of four maximal spirometry was shorter
.

The average time to 90% oxygen saturation was 3.
5 minutes for the four maximal spirometric doses and 6.
5 minutes for the three-minute continuous oxygen technique
.

When the SpO2 value of morbidly obese patients was maintained at 99%-100% during intubation, a period of apnea (159±60 seconds) could be safely tolerated
.

C4.
How to maintain general anesthesia during surgery? In what way to maintain? The literature supports the use of non-soluble anesthetic gases that are not easily metabolized or have no intra-fat accumulation effect, which is beneficial to the rapid recovery of airway responsiveness.
At the same time, intravenous drugs can be added, which can be hydrophilic and can be automatically decomposed in the body, or have an effect.
extremely short
.

As a potent inhaled drug, desflurane has many advantages; it is insoluble, enables rapid patient recovery, restores airway responsiveness quickly, and has low hepatic metabolism
.

The higher biotransformation rate of inhaled anesthetics in obese patients may lead to an increase in serum metabolic toxic products
.

Since abnormal liver function is often combined in morbidly obese patients (75% have fatty liver, 25% have severe liver function abnormality), and there is no exact correlation between liver function test results and liver function abnormalities, it is necessary to apply The drug with the least hepatic metabolism rate is 0.
02% for desflurane, 0.
2% for isoflurane, and 4%-5% for sevoflurane
.

The drug should preferably have a lower blood-gas dissolution rate, which can reduce the catabolism that may occur due to accumulation in the body, thereby making it stable in the target organ (brain) more quickly
.

Among the powerful inhalational anesthetic gases, desflurane wakes the patient the fastest, followed by sevoflurane, and finally isoflurane
.

Desflurane also has the effect of the fastest recovery of respiratory responsiveness, followed by sevoflurane
.

Although as a weaker inhalation anesthetic, nitrous oxide has certain advantages, such as a lower blood gas solubility (0.
46), it is not recommended for maintenance of anesthesia because of the nitrous oxide Nitrogen can cause flatulence and can cause vomiting
.

Nitrous oxide should not be used when there may be severe pulmonary hypertension, which is more common than severe obesity
.

Short-term application of nitrous oxide, especially during the end of surgery, can compensate for the effects of some fat-soluble drugs
.

Remifentanil is an option for intraoperative anesthesia and analgesia maintenance drugs because of its rapid onset, stable effect, and rapid recovery
.

Although remifentanil is a lipophilic drug, its half-life is 5 minutes, so it does not enter fat and accumulate
.

The volume of distribution of remifentanil can be calculated from lean body mass and is similar to that of normal weight individuals
.

Lipophilic opioids, such as fentanyl and sufentanil, are most often dosed by total body weight and, in high-risk patients, may cause regressive respiratory depression, especially with obstructive sleep apnea and hypopnea syndrome, so these drugs are not ideal
.

C5.
Which muscle relaxant should be used? During tracheal intubation, fast-acting muscle relaxants should be selected
.

In this case, both succinylcholine and rocuronium can be used
.

The succinylcholine dose was calculated based on total body weight because plasma cholinesterase activity increased proportionally with increasing BMI
.

Rocuronium is also an option that can be used in the minority of patients for whom succinylcholine is contraindicated
.

The dose calculation is based on lean body mass
.

During the maintenance of anesthesia, cisatracurium is generally preferred
.

Its dose calculation is based on total body weight
.

The effect of the drug follows a certain dose-effect curve, and its metabolism in the body has nothing to do with organ metabolism, that is, the Hoffman phenomenon, so it will not prolong its recovery time
.

Laparoscopic bariatric surgery requires sufficient muscle relaxation to allow for easy inflation of the abdominal cavity, thereby maintaining surgical space and field of view, and allowing instrumentation and removal of excess tissue
.

Peripheral nerve stimulators should be used to monitor muscle relaxation effects
.

The extubation operation for tracheal intubation should be performed only after the four series of stimulation tests satisfy all baseline values ​​(T4/T1) > 0.
9 and the extubation criteria are met
.

At this time, a certain dose of muscle relaxant antagonists should be used
.

C8.
During the operation, arterial blood gas showed: pH 7.
35; PaO2 57mmHg; PaCO2 52mmHg; FiO2 0.
6; mechanical ventilation tidal volume IL; respiratory rate 15 times/min
.

Then the following ventilation indicators were adjusted: positive end-expiratory pressure was 10 cmH2O, and tidal volume was adjusted to 1.
2
L.

After 20 minutes, arterial blood gas showed: pH 7.
32; PaO2 55mmHg; PaCO2 55mmHg
.

How to explain these changes? Both blood gas results were suggestive of respiratory acidosis and hypoxemia
.

At this time, it is necessary to observe the surgical operation range, examine the patient, and perform chest auscultation to confirm whether the position of the tracheal intubation is too deep
.

When diagnosing the cause, the flow of inspired oxygen should be increased, the pneumoperitoneum pressure should be confirmed to remain below 20 cmHg, the peak airway pressure should be noted, manual ventilation, and the use of bronchodilators may be considered
.

There are a variety of pathophysiological changes that could explain these blood gas results without being life-threatening
.

In general, positive end-expiratory pressure ventilation causes PaO2 to increase, while tidal volume increases cause PaCO2 to decrease
.

However, in rare cases, especially in patients with morbid obesity, positive end-expiratory pressure and increased tidal volume may lead to a decrease in PaO2 and an increase in PaCO2
.

There are several reasons for this result: ① High airway pressure may interrupt the capillary blood flow in the lung during peak inspiration
.

Since these sites already have high ventilation/perfusion ratios, further reductions in perfusion result in an increase in the physiologic dead space (Vd/Vt) and an increase in PaCO2
.

Blocked blood flow is redistributed to areas unaffected by high airway pressures, resulting in increased intrapulmonary shunt (Qs/Qt) and decreased PaO2
.

②High airway pressure will reduce venous return and cardiac output, which will also reduce PaO2 and increase PaCO2
.

③ High tidal volume and high airway pressure may lead to volume and pressure injury, resulting in pulmonary edema
.

④ Hyperventilation may cause excessive expansion of the chest wall and produce turbulent flow, which can lead to bronchospasm in sensitive patients, such as asthma patients, especially under mild anesthesia
.

⑤ Excessive airway pressure may lead to the rupture of the originally existing pulmonary bullae
.

C10.
What is diffuse hypoxia? How to avoid it? When mixed anesthesia with nitrous oxide and oxygen was applied during the operation, and after breathing room air postoperatively, the patient developed mild hypoxemia for more than 10 minutes
.

Arterial oxygen saturation may drop by 5%-10%, and often reach below 90% (PaO2 is less than 60mmHg).
This phenomenon has repeatedly occurred in the process of rapid excretion of nitrous oxide from the lungs
.

Nitrous oxide is 35 times more soluble in blood than nitrogen
.

Therefore, the total amount of nitrous oxide diffused from the blood to the alveoli is much greater than the total amount of nitrogen diffused from the alveoli to the blood
.

The oxygen in the alveoli is thus diluted by nitrous oxide
.

Disseminated hypoxia can be avoided if patients can be ventilated with high-concentration oxygen for a few minutes before breathing room air after surgery
.

D Postoperative Management D1.
When should this patient be extubated? What are the criteria for extubation? The indications for extubation are: ▷ Nervous system recovery, fully awake and alert, can lift up and hold for more than 5 seconds
.

▷ Hemodynamically stable
.

▷ Body temperature is normal
.

The central body temperature is above 36°C
.

▷ Four series of stimulation trials with peripheral nerve stimulators showed complete recovery of patients from neuromuscular blocking drugs
.

▷Respiration rate is greater than 10 and less than 30 breaths per minute
.

▷Peripheral blood oxygen saturation measured by pulse oximeter reaches the basic value: SpO2>95% when the inspired oxygen flow is 0.
4 ▷If there is an arterial catheter, the blood gas condition can be detected
.

Acceptable blood gas indicators are: when the inspired oxygen flow is 0.
4, the pH value is 7.
35-7.
45, PaO2>80mmHg, PaCO2<50mmHg
.

▷Acceptable respiratory system conditions: Negative force inhalation is greater than 25-30 cm H2O, lung capacity is greater than 10 ml/kg IBM, and tidal volume is greater than 5 ml/kg IBW
.

▷ Acceptable level of pain discomfort
.

▷No laboratory abnormalities
.

Indications for extubation should be systematically applied to obese patients
.

In all cases, an attending anesthesiologist skilled in airway control was required to be present at the time of extubation
.

Reintubation may be required in emergencies
.

Patients with a history of difficult intubation should be preplanned before extubation
.

Patients with obstructive sleep apnea and hypopnea syndrome, obesity-hypopnea syndrome, and Pickwick syndrome were more likely to develop postoperative respiratory disturbances
.

In these patients, extra attention is required before and after extubation, and sometimes further observation with a monitor in bed is required
.

D3.
For obese patients, how does the surgical position affect respiratory function? In the supine position, intra-abdominal contents can move up and compress the diaphragm, resulting in diaphragmatic dysfunction, decreased functional residual capacity, airway occlusion, increased mixed venous blood, decreased PaO2, and possible orthostatic ventilation disorders
.

For obese patients, both non-surgical and open, functional residual capacity was increased by 30% in the sitting position compared to the supine position
.

When the patient is recovering from surgery, once hemodynamically stable, the semi-Fowler position (with the head elevated at a 30- to 45-degree angle) should be used as soon as possible
.

Other benefits of the semi-sitting position include reduced pressure on the superior vena cava and a reduced chance of postural injury, which is more common in morbidly obese patients
.

The patient in the semi-sitting position provides a convenient condition for the laryngoscope operator if emergency mask ventilation or re-intubation is required
.

D4.
How to avoid postoperative atelectasis? Previously, bariatric surgery was often performed with an open laparotomy, which had a 45% chance of developing atelectasis after surgery
.

About 75% of bariatric surgeries are now performed laparoscopically, so the chances of developing atelectasis are reduced
.

Early post-operative movement, intentional thoracic breathing exercises, and effective coughing can all contribute to the recovery of postoperative pulmonary function
.

Prolonged semi-recumbent positions should be avoided as this position affects the ventilation/perfusion ratio
.

The dose of postoperative analgesics should be carefully controlled to ensure pain relief without hypoventilation due to excessive sedation
.

D6.
How to perform postoperative analgesia? More than 90% of bariatric surgery patients are treated with PCA by patient-controlled analgesia
.

For morbidly obese patients, the dose of opioids in patient-controlled analgesia was calculated based on ideal body weight
.

All basal settings were 10 minutes apart, no continuous background volume, and dose 80% of the calculated maximum
.

There are three main types of local anesthesia/analgesia: thoracic epidural/patient-controlled epidural analgesia, intrathecal opioids, and continuous subarachnoid anesthesia/patient-controlled analgesia Painful way
.

Their side effects are basically the same
.

Compared with parenteral patient-controlled analgesia, the use of small doses of drugs can produce fewer side effects and serious complications, and can provide effective analgesia, faster postoperative recovery, less Respiratory complications, lower systemic oxygen consumption, improved cardiac function (lower left ventricular beat index), and shorter hospital stay
.

In morbidly obese patients, the dose of patient-controlled epidural analgesia should be reduced by 75% to 80% due to the decrease in epidural space due to increased abdominal pressure
.

Side effects include drowsiness, postoperative nausea and vomiting, pruritus, and urinary retention
.

Respiratory depression occurs less frequently, but hydrophilic analgesics (eg, unadditive morphine) cause respiratory depression more often than lipophilic analgesics
.

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