Ultrasound in Perioperative Setting

Objectives

• Familiarize yourself with the uses of ultrasound in the perioperative setting
• Discuss how ultrasound enhances patient care and safety
• List the uses of ultrasound in the perioperative setting
• Explain how ultrasound enhances patient care

History of Ultrasound

• Early 21st century: Ultrasound equipment became more compact and portable
• Exploration of other uses of ultrasound in perioperative setting began
  • Lung
  • Gastric
  • Spine
  • Trauma
  • ICU
  • Airway evaluation

Artifacts

• Speed of sound in tissues is assumed to be 1540 m/s
• Sound waves are assumed to travel in a straight line
• Tissue at different angles and echogenic properties change the angle of return
• Refractive and reflective properties of tissue generate shadows

Equipment

• Several machines and transducers are available for perioperative use
• Point-of-Care-UltraSound (POCUS) equipment provides basic images and advanced capabilities (e.g. 3D imaging, pulse doppler)
• Three basic types of transducers:
  • Linear: Shallow structures, high frequency, high definition
  • Phased array: Lower frequencies, better at spatial depth, good for thoracic organs
  • Curvilinear: More depth of field, used for deeper structures in abdomen

Trans-Thoracic Echocardiography (TTE) and Focused Cardiac Ultrasound (FOCUS)

• FOCUS is a qualitative exam
• Used to evaluate heart, valves, and vessels
• Used in conjunction with physical exam
• Limited in scope
• Can be used to narrow down list of possible diagnoses

FOCUS Information

• Global biventricular systolic function
• Atrial and Ventricular chamber size
• Valvular abnormalities
• Pericardial effusion or tamponade
• Volume response

Emergency Use of Ultrasound

• Uses of POCUS include FOCUS for multi-organ system evaluation
• Rapid Ultrasound in Shock (RUSH) for rapid diagnosis of problems and management of intraoperative shock

Lung Ultrasound

• Uses linear transducer
• Can diagnose:
  • Pneumothorax
  • Pleural effusion
  • Pneumonia
  • Pulmonary edema
  • Esophageal or endobronchial intubation
• Detection of pneumothorax is equal to or superior to CXR

Vascular Access

• Ultrasound can be used for cannulation of peripheral and central venous access
• Can also be used for intra-arterial blood pressure monitoring
• Techniques used are similar to those used for nerve blocks

Advantages and Disadvantages of Perioperative Ultrasound

• Advantages:
  • Versatility
  • Rapid acquisition of images
  • Ability to perform repeated examinations
  • Portability of ultrasound machines and probes
  • Absence of ionizing radiation risks
• Disadvantages:
  • Costs of initial purchase and maintenance of equipment
  • Training and availability of skilled clinicians

Objectives

• Familiarize yourself with the uses of ultrasound in the perioperative setting
• Discuss how ultrasound enhances patient care and safety
• List the uses of ultrasound in the perioperative setting
• Explain how ultrasound enhances patient care

History of Ultrasound

• Early 21st century: Ultrasound equipment became more compact and portable
• Exploration of other uses of ultrasound in perioperative setting began
  • Lung
  • Gastric
  • Spine
  • Trauma
  • ICU
  • Airway evaluation

Artifacts

• Speed of sound in tissues is assumed to be 1540 m/s
• Sound waves are assumed to travel in a straight line
• Tissue at different angles and echogenic properties change the angle of return
• Refractive and reflective properties of tissue generate shadows

Equipment

• Several machines and transducers are available for perioperative use
• Point-of-Care-UltraSound (POCUS) equipment provides basic images and advanced capabilities (e.g. 3D imaging, pulse doppler)
• Three basic types of transducers:
  • Linear: Shallow structures, high frequency, high definition
  • Phased array: Lower frequencies, better at spatial depth, good for thoracic organs
  • Curvilinear: More depth of field, used for deeper structures in abdomen

Trans-Thoracic Echocardiography (TTE) and Focused Cardiac Ultrasound (FOCUS)

• FOCUS is a qualitative exam
• Used to evaluate heart, valves, and vessels
• Used in conjunction with physical exam
• Limited in scope
• Can be used to narrow down list of possible diagnoses

FOCUS Information

• Global biventricular systolic function
• Atrial and Ventricular chamber size
• Valvular abnormalities
• Pericardial effusion or tamponade
• Volume response

Emergency Use of Ultrasound

• Uses of POCUS include FOCUS for multi-organ system evaluation
• Rapid Ultrasound in Shock (RUSH) for rapid diagnosis of problems and management of intraoperative shock

Lung Ultrasound

• Uses linear transducer
• Can diagnose:
  • Pneumothorax
  • Pleural effusion
  • Pneumonia
  • Pulmonary edema
  • Esophageal or endobronchial intubation
• Detection of pneumothorax is equal to or superior to CXR

Vascular Access

• Ultrasound can be used for cannulation of peripheral and central venous access
• Can also be used for intra-arterial blood pressure monitoring
• Techniques used are similar to those used for nerve blocks

Advantages and Disadvantages of Perioperative Ultrasound

• Advantages:
  • Versatility
  • Rapid acquisition of images
  • Ability to perform repeated examinations
  • Portability of ultrasound machines and probes
  • Absence of ionizing radiation risks
• Disadvantages:
  • Costs of initial purchase and maintenance of equipment
  • Training and availability of skilled clinicians

Strong Acids

• Very determined to donate protons to a base
• Essentially 100% ionized when dissolved in water
• Strong acids are relatively rare

Strong Bases

• In water, the strongest possible base is the hydroxide ion (OH−)
• A strong base ionizes essentially 100% to produce the OH− ion
• A strong base is a soluble ionic hydroxide

Weak Acids

• Able to donate hydrogen ions to bases, but are less determined to do so than strong acids
• Establish a dynamic equilibrium between the molecular form and the ionized form when dissolved in water

Weak Bases

• Able to accept hydrogen ions from acids, but are less determined to do so than strong bases
• Do not completely ionize in water to produce an equivalent concentration of the hydroxide ion
• Establish a dynamic equilibrium between the molecular form and the ionized form when dissolved in water

Acid-Base Reactions

• Involve a transfer of a hydrogen ion from the acid to the base
• To predict the products of an acid-base reaction, identify the acid and base, move an H+ ion from the acid to the base, and convert the acid into its conjugate base and the base into its conjugate acid
• Any acid-base reaction has two acids and two bases: one acid and one base on the reactant side, and the conjugate acid and conjugate base on the product side
• The base almost always has a lower (more negative) charge than the acid
• Hydrogen is almost always the first atom listed in the formula of an acid
• The reaction equilibrium always favors the formation of the weaker acid

Ionization of Weak Acids/Strong Base

• A drug with a low pKa (e.g. 3.5) is more non-ionized, while a drug with a high pKa (e.g. 8.5) is more ionized
• pH affects ionization: at pH 1.0, the drug is more acidic and non-ionized, while at pH 14, the drug is more basic and ionized
• Lipid solubility and ability to cross the blood-brain barrier (BBB) depend on ionization state

Drugs and Acids/Bases

• Most drugs are weak acids or weak bases
• Weak acids are usually paired with a positive ion (e.g. Na+, Ca+, Magnesium), while weak bases are paired with a negative ion (e.g. chloride, sulfate)
• Drug ionization affects its behavior and effects in the body

Become familiar with the uses of ultrasound in the perioperative setting, discuss its benefits, and list its uses in enhancing patient care and safety.