Anesthetic Monitoring

ANESTHETIC MONITORING NOTES

BEFORE ANESTHESIA

Patient Preparation

  • Physical Examination

  • Collection of Baseline Vital Signs: TPR (Temperature, Pulse, Respiratory rate)

  • Baseline Bloodwork:

    • PCV (Packed Cell Volume)

    • TP (Total Protein)

    • Glucose

    • BUN (Blood Urea Nitrogen)

    • CBC (Complete Blood Count) with differential

    • Chemistry Panel

  • Ensure Patient Comfort: Pre and Post-Operative

  • Medication Protocol: Pre, Intra and Post Operative

Machine and Supplies Preparation

  • Equipment Checks:

    • Check vaporizer levels

    • Conduct leak check on anesthesia machine

    • Check sodasorb (CO2 absorbent)

    • Leak check endotracheal (ET) tubes

    • Inspect monitors

  • Ensure all supplies are available

  • Prepare warming equipment

IMPORTANCE OF MONITORING

  • Main Purpose: To warn the anesthetist of changes in anesthetic depth and patient condition before reaching a dangerous level.

  • Key Objectives:

    • Recognize signs of changing depth in a timely manner to intervene.

    • Maintain patient safety and regulate anesthetic depth.

  • Consequences of Poor Monitoring:

    • Patient perception of pain

    • Slow recovery

    • Anesthetic overdose

    • Potential brain damage

    • Risk of death

IDEAL ANESTHETIC MONITOR

  • An attentive, well-trained technician.

  • Recommended monitoring frequency:

    • Every 5 minutes for vitals

    • Every 15 minutes for temperature

PARAMETERS WE MONITOR

Vital Signs

  • Indicators of Patient's Circulatory and Respiratory Function:

    • Heart Rate (HR) and Rhythm

    • Respiratory Rate (RR) and Depth

    • Blood Pressure (BP)

    • Mucous Membrane Color (MMC)

    • Capillary Refill Time (CRT)

    • Pulse Quality

    • Temperature

Reflexes

  • Involuntary responses to stimuli that help determine anesthetic depth:

    • Palpebral Reflex

    • Swallowing Reflex

    • Pedal Reflex

    • Pupillary Light Reflex (PLR)

    • Corneal Reflex +/-

ANESTHETIC STAGES

Stage I: Induction

  • Voluntary movement, gradual loss of consciousness.

Stage II: Excitement

  • Loss of voluntary control, irregular breathing.

  • Symptoms include paddling, vocalizing, struggling; all reflexes are present.

Stage III: Surgical Anesthesia

  • Progressive muscle relaxation, decreased HR and RR, loss of reflexes.

  • Planes of Stage III:

    • Plane 1 (Light Plane):

    • Regular respiratory pattern, eyeballs rotate ventromedially, PLR diminished, response to painful stimuli present.

    • Plane 2 (Surgical Plane):

    • Regular but may be shallow respiration, decreased HR, pulse strength, BP, ventromedial eyeball position, diminished pedal/palpebral reflexes, no response to painful stimuli.

    • Plane 3 (Deep Stage Anesthesia):

    • Significant respiratory/circulatory depression, reduction in BP/pulse strength, marked decrease in tidal volume, central eyeball position, pupils dilated, no reflexes.

Stage IV: Total Collapse

  • Complete cessation of respiration, dramatic drop in BP and HR, pale MMC, very prolonged CRT.

  • Immediate resuscitation required.

MONITORING GUIDELINES

ACVAA Guidelines

  • Parameters Assessed:

    • Circulation

    • Oxygenation

    • Ventilation

    • Temperature

  • Recordkeeping: Monitoring during recovery, sedated patients, and those under neuromuscular blockade.

REFLEXES

Characteristics

  • Reflexes diminish as anesthetic depth increases.

  • Reflexes to assess:

    • Swallowing: Response indicative of readiness for extubation; absent during surgical anesthesia.

    • Laryngeal Reflex: Closure of epiglottis/vocal cords; laryngospasm indicates a light state.

    • Palpebral Reflex: Blink response to stimuli; indicates inadequate depth if present.

    • Pedal Reflex: Withdrawal response to digit pinching; absent during deep anesthesia.

    • Corneal Reflex: Involuntary eyeball retraction or blink when stimulated, difficult to elicit in small animals.

OTHER INDICATORS OF ANESTHETIC DEPTH

  • Spontaneous Movement: Indicates potential need for intervention; sign of light anesthesia or pain.

  • Muscle Tone: Helps assess degree of skeletal muscle relaxation; noted as marked, moderate, or flaccid.

  • Eye Position and Pupil Size:

    • Ventromedial in surgical anesthesia; central in light/deep planes, varies with drugs.

FUNDAMENTALS OF ANESTHETIC MONITORING

Three Key Aspects

  • Oxygenation:

    • Ensure a patient’s arterial blood is adequately oxygenated.

    • Tools: Pulse oximetry, blood gas analysis.

  • Ventilation:

    • Ensure adequate ventilation is maintained.

    • Observe respiratory rate and effort, assess capnography.

  • Circulation:

    • Monitoring heart rate/rhythm, BP, and use of ECG for direct assessment.

MUCOS MEMBRANE COLOR (MMC)

Assessment

  • Normal Color: Pink, baseline varies by species.

  • Abnormal Colors Indicate:

    • Pale: Anemia, poor perfusion

    • Cyanosis: Low blood oxygen concentration, potential respiratory arrest.

OXYGEN TRANSPORT

Blood Oxygen Content

  • Total oxygen transported in blood is in two forms:

    • Unbound (1.5% dissolved in plasma).

    • Bound to hemoglobin (98.5%).

    • Each hemoglobin molecule can bind 4 oxygen molecules, saturation is 100% when all sites occupied.

PULSE OXIMETRY

  • Purpose: Non-invasive, continuous portable monitoring of oxygen saturation and pulse rate.

  • Normal Levels: 95%-100%.

  • Critical Levels:

    • SpO2 < 95%: hypoxemia investigated.

    • SpO2 < 85%: emergency action needed.

  • Sensor Types:

    • Transmission: clamp-like, used on tongue, toe, lip, etc.

    • Reflective: flat, used on tissue beds, probes for intra-oesophageal or rectal insertion.

TROUBLESHOOTING PULSE OXIMETER

  • Check the patient first for pulses and vitals.

  • If normal: Check the probe, assess for peripheral blood flow issues, hypothermia, or equipment malfunction.

BLOOD GAS ANALYSIS

  • Measures: pH, O2 (PaO2), and CO2 (PaCO2) in blood.

  • Appropriate use: In critical or high-risk patients post-anesthesia for monitoring.

  • PaO2 Normal Parameters:

    • Breathing room air: PaO2 ~ 100 mmHg

    • Breathing 100% O2: PaO2 ~ 500 mmHg

  • Hypoxemia Cut offs:

    • PaO2 < 80 mmHg indicates need for intervention.

HYPOXIA VERSUS HYPOXEMIA

  • Hypoxia Defined: Reduction of oxygen supply at the tissue level; not directly measured.

  • Hypoxemia Defined: Low arterial oxygen tension (PaO2) measured.

VENTILATION

Oxygen Supply Process

  • Lungs supply O2 during inspiration and remove CO2 during expiration.

  • Ventilation: Movement of gases in/out of alveoli; Respiration: O2 supply and CO2 removal in tissues.

RESPIRATORY RATE AND QUALITY

  • Normal RR during Anesthesia: 8-20 breaths/min.

  • Monitor through visual inspection of thorax, reservoir bag movement, and supplemental breaths if RR < 6.

CAPNOGRAPHY/CAPNOMETRY

  • Measures end-tidal carbon dioxide (ETCO2): Important for assessing ventilation adequacy.

  • Normal ETCO2 Range: 35-45 mmHg, increases in depth can raise ETCO2 levels.

CAPNOGRAPHY WAVEFORM

  • Normal Waveform Characteristics:

    • Square shape peaking at 35-45 mmHg during expiration.

    • Phases include baseline, expiratory upstroke, plateau, and inspiratory downstroke.

BLOOD PRESSURE MONITORING

Understanding BP

  • Blood Pressure Standards

    • Systolic Pressure: Contraction phase of the heart.

    • Diastolic Pressure: Relaxation phase of the heart.

    • MAP (Mean Arterial Pressure): Indicator of organ perfusion; optimal MAP is between 70-90 mmHg.

TYPES OF BLOOD PRESSURE MEASUREMENTS

  • Invasive (direct): Using an arterial catheter for real-time BP.

  • Noninvasive (indirect): Use of Doppler or oscillometric to gauge BP; systolic, diastolic, and MAP can be derived.

HYPOTENSION ACTIVE INTERVENTION

  • Thresholds for concerning hypotension: MAP < 60 mmHg, Systolic BP < 80 mmHg.

  • Address Hypotension by:

    • Reducing inhalant if depth is high.

    • Increasing fluids (10 ml/kg bolus recommended).

    • Administering vasopressors.

TEMPERATURE REGULATION

Normal Temperature Ranges

  • Normal Rectal Temperature = 100°F - 102°F.

  • Hypothermia: < 97°F; can reduce MAC, cause prolonged recovery.

  • Hyperthermia: > 103.5°F; treat immediately to avoid risks of brain/liver damage or death.

ANESTHETIC RECOVERY PROCESS

  • Turn off vaporizer; administer O2 for 5 minutes post-anesthesia.

  • Monitor for return of vital signs and reflexes; extubate when swallowing reflex returns (with caution for brachycephalic breeds).

POST-EXTUBATION CARE

  • Maintain patient warmth and comfort; monitor for abnormalities or signs of distress post-extubation.

  • Administer post-operative medications as appropriate.