Physiology

Question 1

Why is CO2 preferred for Lap gases

Answer 1

Colourless
Noncombustible
Very soluble in blood (easily diffuses into bodily tissues)
-So less risk CO2 gas embolism
Inexpensive

Question 2

Physiological complications of using Lap CO2

Answer 2

CO2 gets absorbed
-Hypercapnia with associated cardiac arrhythmias

Nervous system = CO2 activates sympathetic nervous system
-Higher HR
-More cardiac contractility
-More vascular resistance

Question 3

What is preferred pneumoperitoneum pressure? and why?

Answer 3

Commonly was 15

But studies show 12 more optimal
-Reduces post op pain
-Less effect on cardiac factors like stroke volume

Question 4

Pneumoperitoneum effects on venous flow

Answer 4

Actually depends on atrial pressures

Normal/hypovolaemia states = Low atrial pressures
-pneumoperitoneum reduces venous return due to IVC compression

Hypervolaemic states = High atrial pressures
-IVC resists intrabdominal pressure, and actually increases venous return

These apply up to 20mmHg pneumoperitoneum

Question 5

Lap effects on arrhythmias

Answer 5

Can cause tachycarda and ventricular extrasystoles

As a result of hypercapnia
Also vagal irritation from vagal stimulation

Question 6

Can you use CVP during lap surgery?

Answer 6

No

The increased intrabdominal pressures may artificially elevate the CVP

Question 7

What are the respiratory effects of the pnuemoperitoneum?

Answer 7

Limits diaphragmatic motion

Pulmonary dead space unchanged
Reduces functional reserve capacity

Average peak pressure needed to keep constant tidal volume increases parallel to increases in intra-abdo pressure

Question 8

Anaesthetic complications/considerations from head down position?

Answer 8

Elevates the diaphragm = Decreases vital capacity

Can cause dislocation of ETT = Causing right main bronchus intubation

Head down position can cause pulmonary oedema in patients with increased left sided heart pressures

Limit fluids = Can cause facial swelling post op

Question 9

Renal effects of pneumoperitoneum

Answer 9

Causes reduced urine output (oliguria)

Decreased renal vein blood flow + Direct renal parenchymal compression

Question 10

What pressure should you use to avoid oliguria in lap surgery?

Answer 10

Using 10mmHr or less is recommended to avoid oliguric state

Can also use lasix, mannitol, or dopamine to help overcome oliguria.

Question 11

Pneumoperitoneum effects on bowel

Answer 11

Mesenteric vessels also have reduced blood flow

Lap causes less physiological ileus then open ops

But does cause some = Possibly from hypercapnia

Also there is more gastroesophageal reflux, and regurg in these patients

Question 12

Acid-Base effects of pneumoperitoneum

Answer 12

Hypercapnia
Respiratory acidosis

Question 13

Monitoring for COPD patients undergoing lap surgery

Answer 13

Should have intermittent ABGs for lap/robotic surgeries over 1 hour of CO2 insufflation

Should also continue post op after extubation

This risk also exists in retroperitoneal and extraperitoneal lap surgery

Question 14

Signs of CO2 embolism

Answer 14

Abrupt increase in end tidal CO2
O2 Desaturation
And then marked decrease in end tidal CO2

Question 15

Treatment of CO2 embolism

Answer 15

Stop CO2 insufflation
Release CO2 from abdomen
Turn to left lateral decubitus (right side up)
And head down position
-Aims to minimise RV outflow problems to force air embolus to go to apex of RV
Hyperventilate patient with 100% O2

Later = Hyperbaric O2 and cardiopulmonary bypass are options