RSI vs Modified RSI (Rapid-Sequence Induction)

Background: Why RSI Exists

Classical / Standard RSI

Definition

Steps (the "classic" technique)

Indications

• Full stomach (non-compliance with NPO guidelines)
• Bowel obstruction
• Pregnancy (from 2nd trimester onward - though this dogma has been questioned)
• Significant GERD, nasogastric tube in situ
• Morbid obesity, diabetic gastroparesis
• Predicted difficult mask ventilation with non-difficult intubation (e.g., edentulous/bearded patient)

Drug Choice for NMBD

• Succinylcholine (1-1.5 mg/kg): Gold standard for classical RSI due to ultra-rapid onset (~45 s) and brief duration; depolarizing mechanism
• Rocuronium (1.0-1.2 mg/kg): Used when succinylcholine is contraindicated; provides intubating conditions in <90 seconds; now favored because sugammadex (16 mg/kg) can immediately reverse blockade if intubation fails

Modified RSI

Definition

Key Difference from Classical RSI

Why Modified RSI Is Used

• Obese patients - reduced FRC, high O2 consumption
• Pregnant patients - elevated diaphragm, increased metabolic demand
• Critically ill patients - pre-existing hypoxemia
• Pediatric patients (especially neonates and infants) - low FRC + high O2 consumption = very short apneic oxygenation time
• Situations where preoxygenation could not be adequately completed (uncooperative or obtunded patient)
• Situations where longer time to intubating conditions is required (standard doses of non-depolarizing NMBDs)

Technique

• Gentle low-pressure mask ventilation (10-20 cm H2O) as muscle relaxant takes effect
• Cricoid pressure is maintained throughout ventilation
• Everything else mirrors classical RSI (preoxygenation, rapid induction bolus, NMBD, rapid intubation)
• Ultra-modified RSI: Uses transnasal humidified rapid insufflation ventilatory exchange (THRIVE) instead of mask ventilation - Barash 9e

Comparative Summary Table

Controversy: Cricoid Pressure

• Against: MRI studies show cricoid pressure displaces the esophagus laterally rather than compressing it; decreases lower esophageal sphincter tone; worsens laryngoscopic view; can occlude the subglottic airway
• For: Proper technique occludes the hypopharynx (position of esophagus argued to be irrelevant); low risk of harm when applied correctly
• Current practice: Used in both RSI and modified RSI due to low harm risk, but routinely released or reduced if it worsens laryngoscopy

Relative Contraindications to RSI

• Anticipated difficult airway where failed intubation risk is high (risk of cannot-intubate/cannot-ventilate)
• Raises intracranial pressure, arterial blood pressure, and heart rate - Morgan & Mikhail 7e
• In the pediatric patient: too-aggressive cricoid pressure can obstruct the trachea (soft, compressible cricoid ring) - Barash 9e

Key Points for Exam (10 marks)

1. RSI = bolus induction + immediate NMBD + no bag-mask ventilation + cricoid pressure
2. Modified RSI = same sequence but gentle mask ventilation (<20 cm H2O) allowed while awaiting paralysis
3. Succinylcholine remains the classic drug; rocuronium (with sugammadex reversal available) is a safe alternative
4. Modified RSI is indicated when rapid desaturation is expected (obesity, pregnancy, pediatrics, critical illness)
5. No standardized definition of modified RSI; practice variation is acknowledged in the literature
6. Cricoid pressure (Sellick maneuver): 10N awake, 30N post-LOC; controversial but widely used
7. Risk of classical RSI: hypoxia during apnea; risk of modified RSI: gastric insufflation/aspiration
8. Sugammadex has made high-dose rocuronium a viable alternative to succinylcholine, especially when succinylcholine is contraindicated (hyperkalemia risk, malignant hyperthermia susceptibility, myopathy)

Electrical Safety in the Operating Room

1. Basics of Electrical Hazard in the OR

• Abundant mission-critical electrical equipment drawing high currents
• Frequent spilling or pooling of electrolyte solutions (IV fluids, irrigation)
• Wet skin and conductive catheters reducing body resistance
• Staff distraction from patient-care tasks

2. Types of Electrical Shock

Macroshock

Microshock

• A patient with such a catheter is called electrically susceptible
• Ventricular fibrillation threshold by direct cardiac current: 100 µA (0.1 mA) - far below the 1 mA perception threshold
• This means a provider can deliver a lethal microshock to a patient without feeling anything themselves
• Reported fibrillation thresholds in humans: 80-200 µA

3. Grounded vs. Isolated (Ungrounded) Power System

Grounded Power (Domestic/Standard)

• Neutral line is connected to earth ground at the breaker box
• If a live wire touches a grounded patient, a complete circuit exists - shock occurs with a single-fault condition
• A ground-fault circuit interrupter (GFCI) can interrupt this, but it cuts power entirely - unacceptable for life-support equipment

Isolated Power System (IPS) - Standard in ORs

• The OR uses a line isolation transformer (LIT) to isolate the secondary circuit from earth ground
• The neutral line is not tied to earth ground - this is a "floating ground"
• A single fault (e.g., frayed wire touching a grounded patient) does NOT complete a circuit - the patient is safe
• A second fault is needed to create a shock hazard, greatly reducing risk
• This is why ORs continue operating during a single-line fault without interrupting patient care

4. Line Isolation Monitor (LIM)

• Continuously monitors the impedance between each line of the isolated power circuit and earth ground
• Alarm threshold: 2 mA or 5 mA (per NFPA 99 standard)
• When a first fault occurs (one line contacts ground), the LIM alarms, warning staff that the safety of the isolated system is compromised
• The LIM does NOT cut power - it only alerts
• Correct response: identify and remove the offending faulty equipment while continuing patient care; do not ignore the alarm
• "Line isolation monitors notify OR personnel about potentially unsafe equipment so that it can be serviced at a time safe for patient care" - Barash 9e

5. Microshock Prevention

• Use battery-powered equipment wherever possible near the patient
• Ensure all equipment is properly grounded - a functioning ground wire is the best protection against leakage current reaching the heart
• Do not use damaged plugs or equipment with broken ground pins
• Use hospital-grade plugs and receptacles (identified by a green dot, UL-listed) - these have longer ground pins (contact ground first on insertion) and reinforced construction
• Keep power strips and electrical equipment off the floor to avoid electrolyte contamination
• Never connect IV fluid administration sets to electrical connectors
• Intact ground wire provides a low-resistance alternate path that diverts leakage current away from the patient

6. Equipment Grounding and Hospital-Grade Standards

• Hospital-grade plugs (green dot, UL-listed): solid pins, thicker plug bodies, longer ground prong
• Ground pin connects to earth before hot/neutral pins on insertion
• OR circuits typically carry only 15-20 A - easily overloaded by multiple high-draw devices (fluid warmers, forced air warmers, rapid infusors) on a single circuit
• Ceiling-mounted outlet arms and wall-mounted power strips keep wiring off the floor
• Power strips with splash-resistant covers are required in modern ORs

7. Electrosurgery (ESU) - Special Electrical Hazard

• The ESU (Bovie) delivers high-frequency current (300 kHz-3 MHz) at high power; at these frequencies, current does not trigger neuromuscular stimulation
• The dispersive (return) electrode (grounding pad) must have full skin contact; partial contact concentrates current density, causing burns at the pad site
• Capacitive coupling and direct coupling can deliver stray current to unintended tissues
• Implanted pacemakers and defibrillators are susceptible to ESU interference

Quick Exam Summary (5-mark points)

1. Types of shock: Macroshock (skin contact, VF at 100-300 mA) vs. Microshock (direct cardiac, VF at 100 µA) - microshock is a risk with any intracardiac catheter/wire
2. Isolated power system (IPS): OR standard; floating ground via line isolation transformer; single fault does NOT cause shock - prevents macroshock from single-line faults
3. Line isolation monitor (LIM): Sounds alarm when isolated system is compromised by a first fault; does NOT cut power; suspect equipment must be identified and removed
4. Microshock prevention: Battery-powered devices, intact ground wires, hospital-grade outlets (green dot), no damaged plugs/cables near electrically susceptible patients
5. Electrosurgery safety: Full-contact return electrode essential; high-frequency current bypasses neuromuscular stimulation; EMI risk to pacemakers