Laryngeal Mask Airway

Laryngeal Mask Airway (LMA)

1-The LMA-Classic™:

-It is a reusable LMA™ airway for general anesthesia.
-The LMA-Classic™ is available in eight sizes: (1, 1½, 2, 2½, 3, 4, 5, and 6).

Advantages:

-A safe and effective alternative to the endotracheal tube and the facemask.

-Over 100 million uses worldwide.

-Leaves the anesthetist's hands free to attend, to monitoring and record keeping.

-Latex-free and exceptionally well tolerated.

-A reusable device that can be cleaned and steam sterilized up to 40 times before being discarded.

2-LMA-Unique™ (Single-use):

-The LMA-Unique™ is a convenient, single-use LMA™ airway suitable for general anesthesia procedures.

-The LMA-Unique™ is available in sizes: (1, 1½, 2, 2½, 3, 4, and 5).

-The LMA-Unique™ is a disposable, single-use device, made to the same design specifications as the LMA-Classic™.

Advantages:

-Packaged sterile - ready for use.

-Suitable for use on emergency vehicles.

-Suitable where access to sterilization facilities is limited.

-Made of medical-grade PVC.

3-LMA-Flexible™:

-The LMA-Flexible™ is a reinforced LMA™ airway with a flexible airway tube.

-The LMA-Flexible™ is available in sizes: (2, 2½, 3, 4, 5, and 6).

-The LMA-Flexible™ is a re-usable device that can be cleaned and steam sterilized up to 40 times before being discarded.

Advantages:

-Designed for ENT, dental, and head surgery.

-Allows extreme flexion.

-Guaranteed kink and crush-proof.

-Latex-free.

4-LMA Flexible (Single-use):

-The LMA Flexible™ Single Use is ideal for use in ENT, ophthalmic, dental, and other head and neck cases and extends the LMA™ Airway benefits of hemodynamic stability and smoother emergence to more procedures.

5-LMA-ProSeal™:

-The LMA-ProSeal™ is an advanced LMA™ airway suitable for general anesthesia.

-It has a unique double cuff arrangement that provides an exceptionally effective, 'hands-free' airway seal, at low intracuff pressures.

-The LMA-Proseal™ is available in sizes: (1½, 2, 2½, 3, 4, and 5).

-The LMA-Proseal™ is a re-usable device that can be cleaned and steam sterilized up to 40 times before being discarded.

Advantages:

-A new double tube design separates the respiratory and alimentary tracts, providing a safe escape channel for regurgitated fluids in the event of unexpected regurgitation.

-The mask is designed to be a minimally stimulating airway device, whose cuff tip presses against the upper oesophageal sphincter when it is correctly positioned. The sides of the mask face the pyriform fossae and the upper border rests against the base of the tongue.

-Latex-free.

6-LMA Supreme™ (Single-use):

-The first and only single-use laryngeal mask with a built-in drain tube.
-The integrated drain tube is designed to channel fluid and gas safely away from the airway. Several simple and quick tests help verify accurate positioning.
-An improved curve for easy insertion. Subtle refinements in the mask make correct placement easier.

7-LMA Fastrach™ & LMA Fastrach™ ETT:

-The design of the LMA-Fastrach™ facilitates rapid insertion from any position, even if space is limited, and moving the patient is a possible hazard.

-The device is self-positioning with the rigid tube designed to fit the curvature of the palatopharyngeal arch, enabling a firm seal to be achieved.

-The LMA-Fastrach™ is available in sizes: (3, 4, and 5).

-The LMA-Fastrach™ is a reusable device that can be cleaned and steam sterilized up to 40 times before being discarded.

Advantages:

The LMA-Fastrach™ has additional features to those of the LMA-Classic™:

-Designed specifically for the anatomically difficult airway.

-Ideal in emergency situations.

-Can be used as an intubating tool, with no interruption of patient oxygenation.

-Allows insertion in the neutral position, in limited space.

-No need to move the patient.

-No need to insert fingers into the patient's mouth.

8-LMA Fastrach™ & LMA Fastrach™ ETT (Single-use):

9-LMA CTrach™:

-The only difficult airway device that allows ventilation, visualization, and intubation.

-The LMA CTrach™ is designed to increase intubation success rates in difficult airways. The LMA CTrach™ mask enables ventilation during intubation attempts while built-in fiber optics provide a direct view of the larynx and real-time visualization of the ET tube passing through the vocal cords.

-The LMA CTrach™ can be inserted exactly the same as the LMA Fastrach™, however, unlike the LMA Fastrach™, once the airway is secured and the patient is being ventilated, the viewer is switched on, placed in the magnetic connector, and a clear image of the larynx is displayed in real-time. The ET tube can be viewed as it enters the trachea. Once the patient is intubated, the viewer is removed and the mask is removed leaving the ET tube in place.

10-i-gel™:

-The i-gel supraglottic airway device accurately and naturally positions itself over the laryngeal framework to provide a reliable peri-laryngeal seal without the need for an inflatable cuff.

-i-gel is made from a medical-grade thermoplastic elastomer, i-gel has been designed to create a non-inflatable, anatomical seal of the pharyngeal, laryngeal, and peri-laryngeal structures whilst avoiding compression trauma.

-i-gel is currently available in sizes: (1, 1½, 2, 2½, 3, 4, and 5), and is supplied in an innovative, color-coded polypropylene ‘cage pack’.

Advantages:

-No inflatable cuff offers easy, rapid insertion.

-An integral bite block reduces the possibility of airway occlusion.

-A buccal cavity stabilizer aids rapid insertion and eliminates potential rotation.

-Made from a unique, soft, gel-like material to allow ease of insertion and reduced trauma.

-Gastric channel designed to improve and enhance patient safety.

-Reduces the possibility of epiglottis downfolding and obstructing the airway.

-Unique packaging protects the i-gel in transit and ensures that it maintains its anatomical shape.

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 Ventilators

-Early ventilators consisted of the generation of negative pressure around the whole of the patient’s body except the head and neck; these were called Cabinet or Iron lung ventilators.

-A negative pressure could also be applied over the thorax and abdomen: Cuirass Ventilators.

Classification:

1. Pattern of gas flow during inspiration:

a) Pressure generators:

Constant pressure is produced by bellows or a moderate weight which produces a decreasing inspiratory flow which alters with changes in lung compliance

b) Flow generators:

Constant flow is produced by a piston, heavyweight, or compressed gas. Flow is unaltered by changes in lung compliance although pressures will vary. These ventilators have a high internal resistance to protect the patient from high working pressures.

2. Power:

Pressure generators are low powered whereas flow generators are high powered.

3. Cycling:

Change from inspiration to expiration may be determined by:

a) Time:

Most common method. The duration of inspiration is predetermined, with the constant flow it may be necessary to preset a Tv; when this has been delivered there is an inspiratory pause (improves distribution) before the inspiratory cycle ends.

b) Pressure:

Used as a pressure limit on other modes. Ventilator cycles into expiration when preset airway pressure is reached (delivers a different Tv if compliance or resistance changes). Inspiratory time varies according to compliance and resistance.

c) Volume:

Usually used with an inspiratory flow restrictor. Cycles into expiration whenever a preset Tv is reached.

d) Flow:

Older ventilators.

4. Sophistication:

Newer ventilators can function in many of the above modes, and also have weaning modes such as SIMV, PS, and CPAP.

5. Function:

a) Minute volume dividers:

Fresh gas flow powers the ventilator. Minute volume equals the FGF divided into pre-set tidal volumes, thus determining the frequency.

b) Bag squeezers:

Replaces the hand ventilation of a Mapleson D or circle system. It needs an external power source.

c) Lightweight portable:

Powered by compressed gas and consists of the control unit and patient valve.

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Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth Disease (CMT)

-Charcot-Marie-Tooth disease (CMT) is a neuromuscular disorder characterized by length-dependent degeneration of the motor and sensory nerve fibers, with a prevalence of 1 in 2,500 (about 200,000 patients in the European Union).

-Anesthesia is administered to this population more frequently than to normal people, as CMT patients often need orthopedic surgery to correct muscle imbalance and limb deformities, and for osteosynthesis of bone fractures as they are prone to falls.

Anesthetic Management Complications:

1-Malignant hyperthermia.

2-Prolonged responses to neuromuscular blocking drugs.

3-Drug toxicity is caused by inappropriate doses in case of severe muscle wasting.

4-Medication-induced exacerbation of neuropathy.

5-Associated deformities such as scoliosis.

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IV Fluids

A) Crystalloid solutions (< 30 000 Dalton):

1-Hypotonic solutions:

- D₅W, ½ NS, D5 ¼ NS, D5 ½ NS.

2-Isotonic solutions:

- NS, Ringer’s, Lactated Ringer’s (Hartmann’s), Ringer’s acetate.

3-Hypertonic solutions:

- NaCl (3%, 7.5%), Mannitol (10%, 20%), NaHCO₃ (5%, 7.5%, 8.4%).

B) Colloid solutions (> 30 000 Dalton):

1-Blood derived:

- Human albumin (5%, 25%).

- Plasma protein fraction 5%.

2-Synthetic:

a) Dextrose Starches:

- They are D-glucose polymers linked by alpha bonds into linear macromolecules prepared from sucrose.

- Their half-life is 12 hours.

- 6% Dextran-70 (Macrodex) MW = 70 000 Dalton

- 10% Dextran-40 (Rheomacrodex) MW = 40 000 Dalton

- Dextran-1 (Promit).

- Dose: 20 ml/kg/d., Max.: 1.5 L/d.

Disadvantages:

- Interfere with blood typing.

- Antiplatelet effect.

- Antigenic effect with anaphylactoid and anaphylactic reactions.

- Affect renal functions and can be associated with renal failure.

b) Gelatins:

- Their M.W. 30 000-35 000 Dalton.

- Their half-life is 4-5 hours.

- Succinylated Gelatin (Gelofusine 3.5%, 4%).

- Polygelline (Hemaccel 3.5%, Hemagel 4%).

- Dose: 20 ml/kg/d., Max.: 1.5 L/d.

Advantages:

- Does not interfere with blood grouping.

- Does not affect renal function.

Disadvantages:

- Histamine-mediated allergic reaction.

c) Hydroxy-Ethyl Starch (HES) (Etherified Starch):

Synthetic colloids resemble glycogen structurally, synthesized from amylopectin.

- Heta-starch (Hexa-starch) (e.g. HAES-Steril, Hespan): M.W. 450 000 Dalton, half-life 48 hours.

- Hextend: M.W. is higher, and the half-life is longer.

- Penta-starch: M.W. 200 000, half-life less than 24 hours.

- Tetra-starch: (e.g. Tetraspan, Voluven): M.W. 130 000, half-life less than 6 hours.

- Dose: 20-50 ml/kg/d.

Advantages:

- Do not affect the coagulation study.

- Not antigenic but can cause anaphylactoid reactions.

- Less expensive than human albumin.

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Ovarian Hyperstimulation Syndrome (OHSS)

- It is a complication of some forms of fertility medication. Most cases are mild, but small proportions are severe.

Causative Medications:

- Associated with the injection of a hormone called human chorionic gonadotropin (hCG) which is used for inducing final oocyte maturation and/or triggering oocyte release.

- The risk is further increased by multiple doses of hCG after ovulation and if the procedure results in pregnancy.

- Using a gonadotropin-releasing hormone (GnRH) agonist instead of hCG for inducing final oocyte maturation and/or release results in an elimination of the risk of OHSS, but a slight decrease of the delivery rate of approximately 6%.

Epidemiology:

- Sporadic OHSS is very rare and may have a genetic component.

- Clomifene citrate therapy can occasionally lead to OHSS, but the vast majority of cases develop after the use of gonadotropin therapy (with the administration of FSH), (Menopur, Pergonal, Repronex) and administration of hCG to induce final oocyte maturation and/or trigger oocyte release, often in conjunction with in vitro fertilization (IVF).

- The frequency varies and depends on patient factors, management, and methods of surveillance. About 5% of treated patients may encounter moderate to severe OHSS.

- Mortality is low, but several fatal cases have been reported.

Risk Factors:

- Risk factors include young age, the development of many ovarian follicles under-stimulation, extremely elevated serum estradiol concentrations, the use of hCG for final oocyte maturation and/or release, the continued use of hCG for luteal support, and the occurrence of a pregnancy (resulting in hCG production).

Pathophysiology:

- OHSS has been characterized by the presence of multiple luteinized cysts within the ovaries leading to ovarian enlargement and secondary complications.

- The central feature of clinically significant OHSS is the development of vascular hyperpermeability and the resulting shift of fluids into the third space.

- As hCG causes the ovary to undergo extensive luteinization, large amounts of estrogens, progesterone, and local cytokines are released. It is almost certain that vascular endothelial growth factor (VEGF) is a key substance that induces vascular hyperpermeability, making local capillaries "leaky", leading to a shift of fluids from the intravascular system to the abdominal and pleural cavity.

- Supraphysiologic production of VEGF from many follicles under the prolonged effect of hCG appears to be the specific key process underlying OHSS. Thus, while the patient accumulates fluid in the third space, primarily in the form of ascites, she actually becomes hypovolemic and is at risk for respiratory, circulatory, and renal problems. Patients who are pregnant sustain the ovarian luteinization process through the production of hCG.

- Avoiding OHSS typically requires interrupting the pathological sequence, such as avoiding the use of hCG. One alternative is to use a GnRH agonist instead of hCG.

Classification:

Mild OHSS:

- The ovaries are enlarged (5–12 cm), slight weight gain, mild abdominal distension, abdominal pain, nausea, diarrhea, and there may be an accumulation of ascites.

Moderate OHSS:

- Excessive weight gain (> 2 pounds/day or > 1 kg/day), increased abdominal girth, vomiting, darker urine and oliguria, excessive thirst, and dry skin and/or hair (in addition to mild symptoms).

Severe OHSS:

- Marked abdominal distention, lower abdominal pains, darker urine or anuria, pleural effusion, respiratory distress, calf and chest pains. There may be hemoconcentration, and thrombosis (in addition to mild and moderate symptoms).

- Symptoms generally resolve in 1 to 2 weeks but will be more severe and persist longer if pregnancy occurs. This is due to hCG from the pregnancy acting on the corpus luteum in the ovaries in sustaining the pregnancy before the placenta has fully developed. Typically, even in severe OHSS with a developing pregnancy, the duration does not exceed the first trimester.

- Early OHSS develops before pregnancy testing and late OHSS is seen in early pregnancy.

Criteria for Severe OHSS:

- Enlarged ovary, ascites.
- Hematocrit > 45%, WBC > 15,000/microliter.

- Oliguria, creatinine 1.0-1.5 mg/dL, creatinine clearance > 50 ml/min.

- Liver dysfunction, anasarca (extreme generalized edema).

Critical OHSS:

- Enlarged ovary, tense ascites with hydrothorax and pericardial effusion.

- Hematocrit > 55%, WBC > 25,000/microliter.

- Oligoanuria, creatinine > 1.6 mg/dL, creatinine clearance < 50 mL/min.

- Renal failure, thromboembolic phenomena (DVT, PE), ARDS.

Complications:

- Ovarian torsion, ovarian rupture, thrombophlebitis, and renal insufficiency.

Prevention:

- Physicians can reduce the risk of OHSS by monitoring FSH therapy, and by withholding hCG medication.

- Regarding dopamine agonists as prophylaxis, a systematic review and meta-analysis concluded that prophylactic treatment with Cabergoline (Dostinex) reduces the incidence, but not the severity of OHSS, without compromising pregnancy outcomes.

- OHSS may also be prevented by coasting, which is ovarian hyperstimulation in IVF without hCG administration for final maturation of follicles.

Treatment:

Mild OHSS:

- Can be treated conservatively with monitoring of abdominal girth, weight, and discomfort on an outpatient basis until either conception or menstruation occurs. Conception can cause mild OHSS to worsen in severity.

Moderate OHSS:

- Is treated with bed rest, fluids (IV hydration), and close monitoring of labs such as electrolytes (hyponatremia, hyperkalemia, acidosis), blood counts, and coagulation profile (PT, aPTT, INR). Ultrasound may be used to monitor the size of ovarian follicles. Depending on the situation, a physician may closely monitor a patient's fluid intake and output on an outpatient basis, looking for an increased discrepancy in fluid balance (over 1-liter discrepancy is cause for concern). Resolution of the syndrome is measured by decreasing the size of the follicular cysts on 2 consecutive ultrasounds.

Severe OHSS:

- Aspiration of accumulated fluid (ascites) from the abdominal (paracentesis) / pleural cavity may be necessary, intercostal tube, as well as opioids for the pain.

- If the OHSS develops within an IVF protocol, it can be prudent to postpone the transfer of the pre-embryos since the establishment of pregnancy can lengthen the recovery time or contribute to a more severe course. 

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Ebstein’s Anomaly

-A rare congenital cardiac abnormality.

-The septal and posterior cusps of the tricuspid valve are displaced downwards and are elongated, such that a varying amount of the right ventricle effectively forms part of the atrium. Its wall is thin and it contracts poorly. The remaining functional part of the right ventricle is therefore small.

-The foramen ovale is patent, or defective, in 80% of cases.

-The degree of abnormality of right ventricular function, and the size of the ASD, are probably the main determinants of the severity of the condition, which varies considerably.

-The right ventricular systolic pressure is low, and the RVEDP is elevated. Tricuspid incompetence can occur.

-There may be a right to left shunt, with cyanosis, on effort, and pulmonary hypertension and right heart failure may supervene.

-The natural history of the disease is very variable. Fifty percent of cases present in infancy with cyanosis, and 42% die in the first 6 weeks of life.

-In those who survive to adulthood, symptoms may be precipitated by the onset of arrhythmias, or by pregnancy. A few patients remain asymptomatic, even as adults, although once symptoms develop, the disability can increase rapidly.

-A cardiothoracic ratio of ≥ 0.65 is a better predictor of sudden death than the symptomatic state, and those who developed atrial fibrillation died within 5 years. It has therefore been suggested that tricuspid surgery should be undertaken before the cardiothoracic ratio reaches 0.65.

Preoperative Abnormalities:

1. There may be a right to left shunt, with dyspnea and cyanosis at rest, or on moderate exertion. Alternatively, the patient may be asymptomatic.

2. Episodes of tachyarrhythmias occur in 25% of patients. Some provoke syncopal attacks.

3. The ECG may show varying abnormalities, including large peaked P waves, a long P–R interval, Wolff–Parkinson–White syndrome, RBBB, and right heart strain. Paroxysmal supraventricular tachycardia occurs in 15%, usually because of the presence of WPW syndrome.

4. Chest X-ray may show cardiomegaly, with a prominent right heart border, and poorly perfused lung fields.

5. Paradoxical systemic embolism and bacterial endocarditis may occur.

6. Many other lesions of the tricuspid valve or right ventricle may mimic Ebstein’s anomaly, therefore the discriminating clinical and echocardiographic features for correct diagnosis have been enumerated.

Anesthetic Problems:

These will depend upon the anatomical abnormality, the degree of right to left shunt, and the presence or absence of right heart failure.

1. Induction time is prolonged, because of the pooling of drugs in the large atrial chamber.

2. Intracardiac catheter insertion may be hazardous because it can provoke serious cardiac arrhythmias.

3. Air entering peripheral venous lines or any open veins at subatmospheric pressure may cause paradoxical air emboli.

4. Tachycardia is poorly tolerated because of impaired filling of the functionally small right ventricle.

5. Hypotension may increase the right to left shunt if present.

6. Hypoxia causes pulmonary vasoconstriction, which also increases a right to left shunt.

7. There is a risk of bacterial endocarditis, especially if a CVP line is in place.

8. Deterioration may occur in pregnancy because of a decrease in right ventricular function, and an increase in blood volume and cardiac output, or with the onset of arrhythmias.

Management:

1. The severity of the lesion must be assessed. In the presence of maternal cyanosis or arrhythmias during pregnancy, there should be close monitoring of both mother and fetus. Deterioration may occur, despite previous successful pregnancies.

2. Treatment of heart failure and arrhythmias.

3. Antibiotic prophylaxis against bacterial endocarditis.

4. If a CVP is used for monitoring, its tip should be kept within the superior vena cava. The use of intracardiac catheters should probably be avoided.

5. Techniques should aim to minimize tachycardia and hypotension.

6. Oxygen therapy increases pulmonary vasodilatation. Long-term maternal therapy is required during pregnancy from 14 weeks, to treat fetal hypoxia that is demonstrated by umbilical venous blood gases.

7. Several anesthetic techniques have been described. A two-catheter epidural technique can be used for vaginal delivery to minimize hypotension. Bupivacaine doses must be fractionated and saline rather than air used to site the epidural, to avoid paradoxical air emboli. Cesarean section under general anesthesia, preceded by fentanyl, and a neurolept analgesic technique for hysterectomy, have been described.

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