2019B11 Describe the respiratory and cardiovascular changes associated with a
carbon dioxide pneumoperitoneum for laparoscopic surgery.

 

List:

·       Intro

·       Effects of intra-abdominal hypertension

·       Effects of hypercapnoea

·       Effects of position change

·       Miscellaneous complications

 

Intro:

Capnoperitoneum

·     Steady state insufflation rate 200-400mL/min

·     Pressure 10-20mmHg

Cause of derangements

·     Raised intra-abdominal pressure (↑IAP)

·     Hypercapnoea

·     Positioning

Summary of effects

·     Respiratory:

o  Dose-dependent embarrassment

o  Worse if obese or Trendelenburg)

o  Can be offset by recruitment manoeuvres and PEEP, but at expense of CVS system

·     Cardiovascular:

o  Variable

o  Significantly worse if hypovolaemic

 

Intra-abdominal hypertension:

Respiratory

·     Cephalad diaphragm displacement -> ↓lung volumes

o  ↓FRC ± closing capacity

o  Small airway closure

o  Atelectasis

o  Shunt

o  Hypoxaemia

·     ↓Lung compliance

o  Restrictive deficit

o  ↑Peak airway pressure

o  ↑Risk of barotrauma

o  Hypoventilation

·     Changes worse if obese, pregnant, Trendelenburg

Cardiovascular

·     Biphasic effects on venous return

o  At first: autotransfusion of splanchnic blood -> ↑VR -> ↑CO (± initial ↑mAP)

o  Then: compression of IVC -> ↓VR -> ↓CO (more pronounced if hypovolaemic)

·     ↑SVR due to

o  ↑IAP

o  ↑PaCO2 -> ↑catecholamine release

·     Dose-dependent effects on steady-state blood pressure

o  IAP <~20mmHg -> ↑mAP (↑SVR outweighs ↓venous return/cardiac output)

o  IAP >~20mmHg -> ↓mAP (↓venous return/cardiac output outweighs ↑SVR)

·     Effect on myocardial oxygen supply and demand

o  ↑Demand: ↑HR, ↑contractility, ↑stroke work

o  ↑Supply: metabolic autoregulation (but impaired if coronary artery disease)

·     Oliguria

o  ↑IAP ->? renal venous obstruction -> ↓GFR

 

 

Hypercapnoea:

Mechanism

·     CO2 is rapidly absorbed into systemic circulation (30-50mL/min)

·     Diffuses into rapidly and slowly equilibrating compartments down partial pressure gradient (note large body stores ~120L)

·     CO2 + H2O <-> H2CO3 <-> HCO3- + H+

·     Hence ↑PaCO2 -> ↓pH (whole body including CNS)

·     Prolonged laparoscopy with ↑PaCO2 -> ↑accumulation -> ↑minute ventilation requirement

Respiratory effects

·     Respiratory acidosis

·     Potentiation of HPV

·     Distribution of blood away from poorly-ventilated dependent lung

·     ↑V/Q matching

·     ↑PaO2

·     Hence offsets V/Q inequality caused by small airway closure

Cardiovascular

·     If pH >7.2: ↑SNS output -> ↑inotropy

·     If pH <7.2: ↓pH -> ↓inotropy

·     ↓pH -> sensitisation of myocardium to arrhythmogenic effects of catecholamines

·     Pulmonary vasoconstriction

·     Systemic vasodilatation (offsets ↑IAP -> ↑SVR)

·     ↑Myocardial O2 demand (↑HR)

·     ↑Myocardial O2 supply (metabolic autoregulation – but impaired if coronary artery disease)

 

Position:

Trendelenburg

·     Respiratory

o  ± Endobronchial intubation -> massive shunt -> ↓PaO2

o  ↑Diaphragm compression

·     Cardiovascular

o  ↑Venous return: offsets venous compression

Reverse Trend.

·     Respiratory

o  ↓Diaphragm compression

·     Cardiovascular

o  ↓Venous return: compounds venous compression

 

Miscellaneous complications:

Gas in wrong place

·     Pneumomediastinum

·     Pneumothorax

·     Subcutaneous emphysema

·     Venous gas embolism -> cardiovascular collapse:

o  Either intravascular insufflation directly into vessel

o  Or Venturi effect

CVS collapse at insufflation

·     Peritoneal stretch -> vagal response

o  Sinus bradycardia, nodal rhythm, asystole)

·     Empty ventricle -> Bezold-Jarisch reflex

o  Contraction of underfilled LV

o  Stimulation of unmyelinated PSNS C fibres

o  ↑↑PSNS output -> ↓HR, ↓BP, coronary vasodilatation

Surgical misadventure

·     Damage to vessel by trochar

·     Difficult to control bleeding

·     Difficult to estimate blood loss