Physiological Changes in Laparoscopy

Pneumoperitoneum: Basics & Gas - The Big Blow-Up

• Artificial abdominal distension using gas for laparoscopic surgery.
• Creates operative space & improves visualization.
• Gases:
  • Carbon Dioxide (CO2): Most common.

    ⭐ CO2 is preferred for insufflation due to high solubility, minimizing embolism risk if intravascular entry occurs, and rapid excretion via lungs.

  • Others: N2O, Air (rarely used due to combustion/embolism risks).
• CO2 Benefits: Non-flammable, high blood solubility (↓ embolism risk), rapidly cleared via respiration.
• CO2 Drawbacks: Hypercapnia, respiratory acidosis, peritoneal & diaphragmatic irritation (shoulder pain).
• Pressure: Adults 12-15 mmHg; Children 6-10 mmHg. Max 20 mmHg (briefly).
• Creation: Veress needle (closed), Hasson (open). oka

Cardiovascular Impact - Heart Under Pressure

• ↑Intra-Abdominal Pressure (IAP): Due to pneumoperitoneum.
  • Mechanical compression (vessels, diaphragm).
  • Neurohormonal activation (catecholamines, vasopressin, RAAS).
• Hemodynamics:
  • Systemic Vascular Resistance (SVR) & Mean Arterial Pressure (MAP): Consistently ↑ (direct compression, humoral factors).
  • Venous Return (VR): Initial ↑ (splanchnic autotransfusion), then ↓ with ↑IAP (IVC compression, esp. >15 mmHg).
  • Cardiac Output (CO): Variable; often ↓ at IAP >15-20 mmHg or in hypovolemia/cardiac dysfunction.
  • Heart Rate (HR): Variable; vagal bradycardia (esp. during initial insufflation) or tachycardia (pain, hypercarbia, ↓CO).
  • Myocardial O₂ Demand: ↑ (due to ↑afterload, ↑HR).
• Arrhythmias: Common (bradycardia from vagal stimulation, ectopics, tachycardia).
• Positioning Effects:
  • Trendelenburg: Transient ↑VR, ↑MAP; may ↓CO (impaired diastolic filling, ↑afterload).
  • Reverse Trendelenburg: ↓VR, ↓MAP, ↓CO; risk of hypotension.
• ⚠️ Risks: CO₂ embolism (rare), severe hypotension/bradycardia, myocardial ischemia in susceptible patients.

⭐ Increased IAP primarily ↑SVR & ↑MAP. CO changes depend on IAP level, patient's volume status, cardiac function, & positioning (Trendelenburg may worsen CO despite initial ↑VR).

Respiratory Dynamics - Breathing Challenges

• Mechanical Effects (Pneumoperitoneum & ↑IAP):
  • Diaphragm elevation/splinting → ↓ Lung volumes (Total Lung Capacity - TLC, Vital Capacity - VC).
  • ↓ Lung & chest wall compliance.
  • ↑ Airway pressures (Peak & Plateau).
  • Basal atelectasis common → V/Q mismatch.
• Gas Exchange (CO2 Insufflation):
  • CO2 absorption → Hypercapnia ($↑PaCO_2$), respiratory acidosis.
  • ↑ End-tidal CO2 ($ETCO_2$) monitors this.
• Ventilation Strategy:
  • Controlled ventilation mandatory.
  • Consider ↑Respiratory Rate (RR), Positive End-Expiratory Pressure (PEEP).
  • Monitor $ETCO_2$, $PaCO_2$.
• Key Risks:
  • Barotrauma.
  • Subcutaneous emphysema, pneumothorax (rare).
  • CO2 embolism (rare).

⭐ A significant decrease in Functional Residual Capacity (FRC) by up to 30-50% is common due to diaphragmatic splinting and cephalad displacement, predisposing to atelectasis and V/Q mismatch.

Renal & Other Systemic Effects - The Wider Impact

• Renal Effects:

  ⭐ Oliguria during laparoscopy is common and usually transient (resolves post-desufflation), resulting from a combination of increased IAP causing renal parenchymal compression, renal vein compression, decreased renal blood flow, and hormonal changes (ADH, RAAS activation).

  • ↓ GFR & urine output (transient).
  • Minimal long-term renal risk in healthy; caution if pre-existing disease.
• Neuroendocrine Stress Response:
  • ↑ Catecholamines, cortisol, ADH, RAAS.
  • Transient hyperglycemia.
• Immunological Benefits:
  • Less immunosuppression vs open.
  • ↓ Pro-inflammatory cytokines (IL-6).
• Splanchnic Circulation:
  • ↓ Splanchnic blood flow (↑IAP); monitor high-risk.
• Other Considerations:
  • ↑ IOP (esp. Trendelenburg).
  • ↑ ICP (CO2 absorption, ↑CVP).
  • Shoulder-tip pain (phrenic irritation).

High‑Yield Points - ⚡ Biggest Takeaways

• Pneumoperitoneum (CO2) ↑ IAP, leading to multi-system effects.
• CV: ↑ MAP, ↑ SVR, ↓ CO (esp. IAP > 15 mmHg); risk of arrhythmias.
• Resp: ↓ FRC, ↓ compliance, ↑ airway pressure; hypercapnia from CO2 absorption.
• Renal: ↓ RBF, ↓ GFR, ↓ urine output (transient).
• Splanchnic: ↓ perfusion, potential ischemia with high/prolonged IAP.
• Neuroendocrine: Stress response with ↑ catecholamines, ↑ cortisol.
• Vagal reflexes can cause bradycardia/hypotension.