Neuromuscular Blockers in Cardiac Anesthesia

In  patient on β-blockers, the choice of neuromuscular blockers (NMBs) is critical due to their potential cardiovascular effects. Here’s a detailed analysis of the implications of using fentanyl and various NMBs, particularly focusing on vecuronium and its effects.

Key Points on Fentanyl and β-Blockers

• Fentanyl:

  • Fentanyl is an opioid analgesic that can cause bradycardia due to its vagolytic activity. While it has minimal hemodynamic effects, the bradycardia it induces can be problematic, especially in patients already on β-blockers, which reduce heart rate and blood pressure.

• β-Blockers:

  • These medications reduce heart rate and blood pressure, which can compound the bradycardic effects of fentanyl. Therefore, careful consideration must be given to the choice of additional medications that may further depress cardiac function.

Vecuronium

• Effects:

  • Vecuronium is a non-depolarizing neuromuscular blocker that has minimal cardiovascular side effects when used alone. However, it can potentiate decreases in heart rate and cardiac index when administered after fentanyl.
  • The absence of positive chronotropic effects (unlike pancuronium) means that vecuronium does not counteract the bradycardia induced by fentanyl, leading to a higher risk of significant bradycardia and hypotension.

• Vagal Tone:

  • Vecuronium may enhance vagal tone, further predisposing patients to bradycardia. This is particularly concerning in patients on β-blockers, as the combination can lead to compounded cardiac depression.

Comparison with Other Neuromuscular Blockers

1. Pancuronium:

   • Vagolytic Action: Pancuronium has vagolytic properties that can help attenuate bradycardia and support blood pressure. It is often preferred in cardiac anesthesia for its more favorable hemodynamic profile compared to vecuronium.
   • Tachycardia: While it can induce tachycardia, this effect may be mitigated in patients on β-blockers, which can blunt the tachycardic response.

2. Atracurium:

   • Histamine Release: Atracurium can release histamine, leading to hemodynamic changes such as increased heart rate and decreased blood pressure. These effects can be minimized by slow administration of small doses.

3. Rocuronium:

   • Minimal Hemodynamic Effects: Rocuronium is generally associated with a lack of significant cardiovascular side effects, although occasional increases in heart rate have been noted.

4. Cis-Atracurium:

   • Cardiovascular Stability: Cis-atracurium does not have cardiovascular effects and does not release histamine, making it a safer option in terms of hemodynamic stability.

SHOCK

Shock  is  defined  as  a  pathological  state  causing  inadequate  oxygen  delivery  to  the peripheral tissues and resulting in lactic acidosis, cellular hypoxia and disruption of normal metabolic condition.

CLASSIFICATION

Shock is generally classified into three major categories:

1.    Hypovolemic shock

2.    Cardiogenic shock

3.    Distributive shock

Distributive shock is further subdivided into three subgroups:

a.    Septic shock

b.    Neurogenic shock

c.    Anaphylactic shock

Hypovolemic  shock  is  present  when  marked  reduction  in  oxygen  delivery results from diminished cardiac output secondary to inadequate vascular volume. In general, it results from loss of fluid from circulation, either directly or indirectly.
e.g.    ▪    Hemorrhage
    •    Loss of plasma due to burns
    •    Loss of water and electrolytes in diarrhea
    •    Third space loss (Internal fluid shift into inflammatory exudates in
        the peritoneum, such as in pancreatitis.)

Cardiogenic shock is present when there is severe reduction in oxygen delivery secondary to impaired cardiac function. Usually it is due to myocardial infarction or pericardial tamponade.

Septic Shock (vasogenic shock) develops as a result of the systemic effect of infection. It is the result of a septicemia with endotoxin and exotoxin release by gram-negative and gram-positive bacteria. Despite normal or increased cardiac output and oxygen delivery, cellular oxygen consumption is less than normal due to impaired extraction as a result of impaired metabolism.

Neurogenic shock results primarily from the disruption of the sympathetic nervous system which may be due to pain or loss of sympathetic tone, as in spinal cord injuries.

PATHO PHYSIOLOGY OF SHOCK

Shock stimulates a physiologic response. This circulatory response to hypotension is to conserve perfusion to the vital organs (heart and brain) at the expense of other tissues. Progressive vasoconstriction of skin, splanchnic and renal vessels leads to renal cortical necrosis and acute renal failure. If not corrected in time, shock leads to organ failure and sets up a vicious circle with hypoxia and acidosis.

CLINICAL FEATURES

The clinical presentation varies according to the cause. But in general patients with hypotension and reduced tissue perfusion presents with:
•    Tachycardia
•    Feeble pulse
•    Narrow pulse pressure
•    Cold extremities (except septic shock)
•    Sweating, anxiety
•    Breathlessness / Hyperventilation
•    Confusion leading to unconscious state

PATHO PHYSIOLOGY OF SHOCK

Shock stimulates a physiologic response. This circulatory response to hypotension is to conserve perfusion to the vital organs (heart and brain) at the expense of other tissues. Progressive vasoconstriction of skin, splanchnic and renal vessels leads to renal cortical necrosis and acute renal failure. If not corrected in time, shock leads to organ failure and sets up a vicious circle with hypoxia and acidosis.

CLINICAL FEATURES

The clinical presentation varies according to the cause. But in general patients with hypotension and reduced tissue perfusion presents with:
•    Tachycardia
•    Feeble pulse
•    Narrow pulse pressure
•    Cold extremities (except septic shock)
•    Sweating, anxiety
•    Breathlessness / Hyperventilation
•    Confusion leading to unconscious state

Intubation

Intubation is a critical procedure in airway management, and the choice of technique—oral intubation, nasal intubation, or tracheostomy—depends on the clinical situation, patient anatomy, and specific indications or contraindications. 

Indications for Each Intubation Technique

1. Oral Intubation

Oral intubation is often the preferred method in emergency situations and when nasal intubation is contraindicated. Indications include:

• Emergent Intubation: Situations such as cardiopulmonary resuscitation (CPR), unconsciousness, or apnea.
• Oral or Mandibular Trauma: When there is significant trauma to the oral cavity or mandible that may complicate nasal access.
• Cervical Spine Conditions: Conditions such as ankylosis, arthritis, or trauma that may limit neck movement.
• Gagging and Vomiting: In patients who are unable to protect their airway due to these conditions.
• Agitation: In cases where the patient is agitated and requires sedation and airway protection.

2. Nasal Intubation

Nasal intubation is indicated in specific situations where oral intubation may be difficult or impossible. Indications include:

• Nasal Obstruction: When there is a blockage in the oral route.
• Paranasal Disease: Conditions affecting the nasal passages that may necessitate nasal access.
• Awake Intubation: In cases where the patient is cooperative and can tolerate the procedure.
• Short (Bull) Neck: In patients with anatomical challenges that make oral intubation difficult.

3. Tracheostomy

Tracheostomy is indicated for long-term airway management or when other methods are not feasible. Indications include:

• Inability to Insert Translational Tube: When oral or nasal intubation fails or is not possible.
• Need for Long-Term Definitive Airway: In patients requiring prolonged mechanical ventilation or airway support.
• Obstruction Above Cricoid Cartilage: Conditions that obstruct the airway at or above the cricoid level.
• Complications of Translational Intubation: Such as glottic incompetence or inability to clear tracheobronchial secretions.
• Sleep Apnea Unresponsive to CPAP: In patients with severe obstructive sleep apnea who do not respond to continuous positive airway pressure (CPAP) therapy.
• Facial or Laryngeal Trauma: Structural contraindications to translaryngeal intubation.

Contraindications for Nasal Intubation

• Severe Fractures of the Midface: Nasal intubation is contraindicated due to the risk of further injury and complications.
• Nasal Fractures: Similar to midface fractures, nasal fractures can complicate nasal intubation and increase the risk of injury.
• Basilar Skull Fractures: The risk of entering the cranial cavity or causing cerebrospinal fluid (CSF) leaks makes nasal intubation unsafe in these cases.

• Contraindications for Oral Intubation

  1. Severe Facial or Oral Trauma:

     • Significant injuries to the face, jaw, or oral cavity may make oral intubation difficult or impossible and increase the risk of further injury.

  2. Obstruction of the Oral Cavity:

     • Conditions such as large tumors, severe swelling, or foreign bodies that obstruct the oral cavity can prevent successful intubation.

  3. Cervical Spine Instability:

     • Patients with unstable cervical spine injuries may be at risk of further injury if neck extension is required for intubation.

  4. Severe Maxillofacial Deformities:

     • Anatomical abnormalities that prevent proper visualization of the airway or access to the trachea.

  5. Inability to Open the Mouth:

     • Conditions such as trismus (lockjaw) or severe oral infections that limit mouth opening can hinder intubation.

  6. Severe Coagulopathy:

     • Patients with bleeding disorders may be at increased risk of bleeding during the procedure.

  7. Anticipated Difficult Airway:

     • In cases where the airway is expected to be difficult to manage, alternative methods may be preferred.

Contraindications for Tracheostomy

1. Severe Coagulopathy:

   • Patients with significant bleeding disorders may be at risk for excessive bleeding during the procedure.

2. Infection at the Site of Incision:

   • Active infections in the neck or tracheostomy site can increase the risk of complications and should be addressed before proceeding.

3. Anatomical Abnormalities:

   • Significant anatomical variations or deformities in the neck that may complicate the procedure or increase the risk of injury to surrounding structures.

4. Severe Respiratory Distress:

   • In some cases, if a patient is in severe respiratory distress, immediate intubation may be prioritized over tracheostomy.

5. Patient Refusal:

   • If the patient is conscious and refuses the procedure, it should not be performed unless there is an immediate life-threatening situation.

6. Inability to Maintain Ventilation:

   • If the patient cannot be adequately ventilated through other means, tracheostomy may be necessary, but it should be performed with caution.

7. Unstable Hemodynamics:

   • Patients with severe hemodynamic instability may not tolerate the procedure well, and alternative airway management strategies may be required.

Zygomatic Bone Reduction

When performing a reduction of the zygomatic bone, particularly in the context of maxillary arch fractures, several key checkpoints are used to assess the success of the procedure. Here’s a detailed overview of the important checkpoints for both zygomatic bone and zygomatic arch reduction.

Zygomatic Bone Reduction

1. Alignment at the Sphenozygomatic Suture:

   • While this is considered the best checkpoint for assessing the reduction of the zygomatic bone, it may not always be the most practical or available option in certain clinical scenarios.

2. Symmetry of the Zygomatic Arch:

   • Importance: This is the second-best checkpoint and serves multiple purposes:
     • Maintains Interzygomatic Distance: Ensures that the distance between the zygomatic bones is preserved, which is crucial for facial symmetry.
     • Maintains Facial Symmetry and Aesthetic Balance: A symmetrical zygomatic arch contributes to the overall aesthetic appearance of the face.
     • Preserves the Dome Effect: The prominence of the zygomatic arch creates a natural contour that is important for facial aesthetics.

3. Continuity of the Infraorbital Rim:

   • A critical checkpoint indicating that the reduction is complete. The infraorbital rim should show no step-off, indicating proper alignment and continuity.

4. Continuity at the Frontozygomatic Suture:

   • Ensures that the junction between the frontal bone and the zygomatic bone is intact and properly aligned.

5. Continuity at the Zygomatic Buttress Region:

   • The zygomatic buttress is an important structural component that provides support and stability to the zygomatic bone.

Zygomatic Arch Reduction

1. Click Sound:

   • The presence of a click sound during manipulation can indicate proper alignment and reduction of the zygomatic arch.

2. Symmetry of the Arches:

   • Assessing the symmetry of the zygomatic arches on both sides of the face is crucial for ensuring that the reduction has been successful and that the facial aesthetics are preserved.

Cricothyroidotomy

Cricothyroidotomy is a surgical procedure that involves making an incision through the skin over the cricothyroid membrane, which is located between the thyroid and cricoid cartilages in the neck. This procedure is performed to establish an emergency airway in situations where intubation is not possible or has failed, such as in cases of severe airway obstruction, facial trauma, or anaphylaxis.

Indications

Cricothyroidotomy is indicated in the following situations:

• Acute Airway Obstruction: When there is a complete blockage of the upper airway due to swelling, foreign body, or trauma.
• Failed Intubation: When attempts to secure an airway via endotracheal intubation have been unsuccessful.
• Facial or Neck Trauma: In cases where traditional airway management is compromised due to injury.
• Severe Anaphylaxis: When rapid airway access is needed and other methods are not feasible.

Anatomy

• Cricothyroid Membrane: The membrane lies between the thyroid and cricoid cartilages and is a key landmark for the procedure.
• Surrounding Structures: Important structures in the vicinity include the carotid arteries, jugular veins, and the recurrent laryngeal nerve, which must be avoided during the procedure.

Procedure

Preparation

1. Positioning: The patient should be in a supine position with the neck extended to improve access to the cricothyroid membrane.
2. Sterilization: The area should be cleaned and sterilized to reduce the risk of infection.
3. Anesthesia: Local anesthesia may be administered, but in emergency situations, this step may be skipped.

Steps

1. Identify the Cricothyroid Membrane: Palpate the thyroid and cricoid cartilages to locate the membrane, which is typically located about 1-2 cm below the thyroid notch.
2. Make the Incision: Using a scalpel, make a vertical incision through the skin over the cricothyroid membrane, approximately 2-3 cm in length.
3. Incise the Membrane: Carefully incise the cricothyroid membrane horizontally to create an opening into the airway.
4. Insert the Airway Device:
   • A tracheostomy tube or a large-bore cannula (e.g., a 14-gauge catheter) is inserted into the opening to establish an airway.
   • Ensure that the device is positioned correctly to allow for ventilation.
5. Secure the Airway: If using a tracheostomy tube, secure it in place to prevent dislodgment.

Post-Procedure Care

• Ventilation: Connect the airway device to a bag-valve-mask (BVM) or ventilator to provide oxygenation and ventilation.
• Monitoring: Continuously monitor the patient for signs of respiratory distress, oxygen saturation, and overall stability.
• Consider Further Intervention: Plan for definitive airway management, such as a formal tracheostomy or endotracheal intubation, once the immediate crisis is resolved.

Complications

While cricothyroidotomy is a life-saving procedure, it can be associated with several complications, including:

• Infection: Risk of infection at the incision site.
• Hemorrhage: Potential bleeding from surrounding vessels.
• Damage to Surrounding Structures: Injury to the recurrent laryngeal nerve, carotid arteries, or jugular veins.
• Subcutaneous Emphysema: Air escaping into the subcutaneous tissue.
• Tracheal Injury: If the incision is not made correctly, there is a risk of damaging the trachea.

An ulcer is a break in the continuity of the skin or the mucous membrane.

Mode of onset:  Traumatic ulcers heal when the traumatic agent is removed., If it persists it becomes chronic as in the case of dental ulcer of the tongue. Ulcers may develop spontaneously as in the case of gumma (syphilitic ulcer). It may develop with varicose veins called varicose ulcer, which develops in the lower third of the leg.

Sometimes a malignant ulcer develops in a scar called Marjolin’s ulcer. Special features are:

 No pain - as there are no nerves. It does not spread - as there is scar tissue. No metastases - as there are no lymphatics Treatment:- Wide excision.

Classification of Ulcer

A) Pathologically

I. Non-specific ulcers:

a. Due to infected wound after trauma, that is physical or chemical agents.

b. Due to local infection example dental ulcer, pressure sore

 Specific ulcers: Caused by specific infection

a. Syphilitic ulcers (Hunterian chancre)

b. Tubercular  ulcers, actinomycosis

Trophic ulcer:- Caused by two factors:

Diminished nutrition due to inadequate blood supply to the tissues

Eg. Ulcers in Buerger’s Disease, Artherosclerosis

b. Diminished or absence of sensation of the skin leading to perforating ulcer of the foot

iv. Malignant ulcer: Due to squamous cell carcinoma, rodent ulcers and melanoma.

B) Clinical classification of ulcers

1. Acute Ulcer:  The edge is inflamed oedematous and painful with slough in the floor and n o granulation tissue. Profuse purulent Discgarge seen

2. Healing ulcers: edge sloping with bluish margin The floor is covered with a red, healthy granulation tissue.

3. Chronic or callous ulcer (non- healing) There is no tendency to heal by itself, the base is jndurated  unhealthy granulation tissue is present in the floor The edge is rounded and thickened.

Chronic ulcer occur due to:

Chronic infection , Defective circulation , Foreign body, Persistent local oedema , Malignancy , Diabetes , Malnutrition (loss of proteins), Gout

Specific Ulcers

Tubeculous Ulcer

Edge Undermined, floor contains granulation tissue a watery discharge is present. Caseous material is found in the floor of the ulcer. It usually occurs in tubercular lymphadenitis in the neck, axilla or groin.

Syphilitic Ulcer

a) Huntarian Chancre or  primary sore or hard chancre: usuaIly occurs over the genitalia especially on penis. Occurs in the primary stage of syphilis Ulcer is round or oval, it is hard,indurated, elevated and painless It feels like a button, discharges serum containing spirochetes (cork screw) which is highly infective.

b) In the Secondary stage mucous patches and condylomata occurs The ulcers are shallow white patches, of sodden thickness which occur in the mouth and tongue. Condyloma are hypertrophied epithelium with serous discharge occurring in mucocutaneous junction around the anus. The regional lymphnod (inguinal transverse chain) are enlarged.

c) In tertiary stage of syphilis gummatous ulcers occur They have a punched  out edge and wash Ieather floor. They occur on the subcutaneous bones like sternum and tibia. They are painless and refuse to heal.

Soft Sore (chanchroid)

They are painful muitiple ulcers, with copious discharge. They are caused by Bacillus Ducrey  lncubation time is 3 to 4 days. located on glans penis and prepuce is due to venereal infection. They are associated with enlarged called bilateral inguinal lymphnodes

Tropical ulcer:

a) Oriental Sore - due to L. Tropica (lieshmaniasis)

b) Ulcers and sinuses are due to guinea worm abscess

c) Histoplasmosis with multiple ulcers on the tibia.

d) Chronic ulcers due to yaws

e) Amoebic ulcers occur in colon_and rectum , flask shaped ulcers , undermined edge , caused by  Entamoeba Histolytica

Varicose Ulcer:

Associated with varicose veins. Occurs on the inner aspect of the lower third of leg , chronic ulcer The surrounding area is pigmented and eczema is present. The sore is longitudinally oval It does not penetrate the deep fascia and is painless The base is adherent to the periosteum of the tibia

Rodent ulcer

Usually Occurs on the face above a line joining the lobule of the ear to the angle of the mouth. Usually occurs at the inner canthous of the eye . Edge is raised and rolled, Erodes the deeper structures and the bone, the lyrnph nodes are not involved.

Treatment: If small wide excision is done with skin grafting, If large, radiotherapy is given.

Malignant Ulcer

Occurs due to chronic irritation as in the case of malignant ulcer of the tongue. The edge is everted. The floor is covered with slough and tumor tissue The regional lymph nodes are hard.

Initially mobile later becomes hard

Treatment: Wide excision is done.

Marjolin ulcer: Malignant Ulcer occurring on scar of Burns