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Anaesthesia for laparoscopic surgery
Peter Dzendrowski, MBBS, FRCA
Intraoperative problems
Anaesthetic management
Post-operative care
Further reading
Laparoscopic surgery requires the creation of a pneumoperitoneum.
CO2 is used for gas insufflation via a Veress needle, at a rate of
1-6 litre/min, to a pressure of 14-20mmHg. Constant CO2 flow of about
200-400mls/min maintains pneumoperitoneum perioperatively, thus creating the
"tension pneumoperitoneum".
Intraoperative problems
Most important:
Cardiovascular
Haemodynamic
Creation of tension pneumoperitoneum causes initial increase, followed by
decrease, in venous return, due to rise in intra-abdominal pressure (IAP).
Leads to fall in SV and CO, however this is offset by increase
in SVR due to raised IAP.
May lead to reflex tachycardia
BP generally remains relatively constant
Arryhthmias
Gas insufflation – may cause arrhythmias.
Include AV
dissociation, nodal
rhythm, sinus bradycardia and asystole.
Response more pronounced with rapid stretching of peritoneum at the
beginning of
insufflation. Probably vagally mediated reflex initiated by stretching of
peritoneum. Incidence
increased by hypercarbia and use of halothane
HINT: always have anticholinergic drug readily available
Gas embolus has been reported as cause of cardiac arrest during laparoscopy.
Respiratory
Pneumoperitoneum increases pressure on diaphragm, leading to cephalad
displacement of diaphragm
This leads to:
- reduction in lung volumes
, including:
- Tidal volume
- Minute volume
- Functional residual capacity
- decreased pulmonary compliance, increased airway resistance and increase
in pulmonary vascular resisistance, resulting in increased airway pressure
for any given tidal volume. Leads to increased haemodynamic changes and risk
of barotrauma during IPPV.
- restriction in diaphragmatic mobility promotes uneven distribution of
ventilation to the non-dependent part of the lung. Results in ventilation
perfusion mismatch with hypoxaemia and hypercarbia (CO2
absorption form pneumoperitoneum may also cause hypercarbia).
- ventilatory impairment is more severe if there is associated airway and
alveolar collapse, predisposing to post-op chest infections.
- increased intra-abdominal pressure may predispose to regurgitation and
aspiration in those susceptible patients – however much research has
suggested that SV via LMA is acceptable in properly assessed patients
- cephalad movement of diaphragm, combined with Trendelenberg position may
cause displacement of ETT tip and endobronchial intubation
Gastrointestinal
Pneumoperitoenum leads to increase in IAP, but also increase in
barrier pressure as well.
Barrier pressure = lower oesophageal pressure – intra-gastric pressure.
Therefore previous risks of aspiration and regurgitation may have been
overestimated and are now being re-assessed.
Increased incidence of nausea and vomiting associated with laparoscopic
surgery, so regular antiemetic prescription is vital
Trochar insertion can damage viscera, particularly a stomach distended
by hand ventilation. Therefore N-G aspiration may occasionally be necessary
prior to trochar insertion.
Renal and metabolic
IAP > 20 mmHg adversely affects renal function and urine output.
RBF and GFR decrease because of increase in renal vascular resistance,
reduction in glomerular filtration gradient and decrease in cardiac output
massive elevation in IAP produces lactic acidosis, probably by severely
lowering cardiac output and by impairing hepatic clearance of blood lactate
as with all surgery, there is an associated stress response with elevated
cortisol and circulating catecholamines
Complications of gas insufflation
- arrhythmias, as mentioned above.
- subcutaneous emphysema
- pneumomediastinum
- pneumopericardium
- pneumothorax
- venous gas embolus:
- potentially fatal
- gas may enter circulation if Verres needle or trochar directly punctures
blood vessel. However, in some cases of gas embolus no evidence of vascular
injury is found
- consequences depend on rate, amount and nature of gas
- magnitude of physiological disturbances caused by CO2 is 6.5 times less
than that of air because of its higher blood solubility
- slow infusion of gas is absorbed across pulmonary capillary-alveolar
membrane without causing any clinical effect. At higher infusion rates,
gas bubbles lodge in peripheral pulmonary circulation. Provoke neutrophil
clumping, activation of coagulation cascade and platelet aggregation.
Release of chemical mediators produces pulmonary vasoconstriction,
bronchospasm, pulmonary oedema and occasionally delayed pulmonary
haemorrhage
- gas bubbles attached to fibrin deposits and platelet aggregates also
mechanically obstruct the pulmonary vasculature, further increasing
pulmonary vascular resistance
- increase in right heart afterload leads to right ventricular failure
- large bolus of gas leads to complete mechanical obstruction of right
atrium and ventricle
- paradoxical emboli can occur
- portal venous gas embolism causes an initial trapping of gas in hepatic
portal circulation. This can subsequently lead to delayed manifestations
in the post-operative period
Hypercarbia
due mainly to absorption of peritoneal CO2 from pnemumoperitoneum, but also
to surgical positioning
In spontaneously ventilating patients, may promote tachypnoea, in IPPV, may
need to increase minute volume
Patient positioning
head down, or lithotomy, for lower abdominal procedures.
Exacerbates pulmonary effects of pneumoperitoneum. However alveolar deadspace is
reduced because of the decrease in hydrostatic gradient in the lung and the
increase in cardiac output resultant on increased venous return. Venous
congestion of head and neck may compromise cerebral perfusion and produce
intracerebral and intraocular hypertension
head up for upper abdominal surgery.
Improved pulmonary function occurs at expense of decreased cardiac function
Accidental injuries of intra-abdominal structures
laceration of viscera and vessels – massive haemorrhage
injuries may not be noticed during surgery and present as GI sepsis after
Laparoscopic Equipment
restricts access to patient
electrical hazards
burns from end of light cable
Additional problems during thoracoscopic procedures
complete isolation of one lung mandatory to provide surgical access
application of CPAP to isolated lung not practicable as it causes partial
expansion of lung
pneumothorax best created by opening the taps of the cannulae to atmosphere
and allowing lung to collapse under own elastic recoil
pressure in pneumothorax must be carefully regulated to prevent excessive
mediastinal displacement and cardiovascular collapse
suctioning within enclosed thoracic cavity can lead to negative pressure
within the hemithorax and mediastinal displacement. Air entry vent should be
inserted
damage to heart potential complication
Anaesthetic management
Pre-anaesthetic assessment
medical contraindications are relative. Successful laparoscopic surgery
has been performed in anticoagulated, pregnant and morbidly obese patients
assess cardiac and respiratory function carefully. If ASA I or II with
no contraindiactions, then may be reasonable to allow spontaneous ventilation
via LMA
resuscitate if necessary
Anaesthetic technique
General anaesthesia
If appropropriate, GA with SV via LMA, otherwise, GA with muscle paralysis,
intubation and IPPV
adjust ventilatory pattern to respiratory and haemodynamic response of
patient
large tidal volumes (12-15 ml/kg) prevents progressive micro-atelectasis and
hypoxaemia and allows for more effective alveolar ventilation and CO2
elimination. However may cause excessive increase in intrathoracic pressure
and thus deleterious cardiovascular effects which will result in an increased
alveolar dead-space
N2O does not adversely affect surgical conditions during
laparoscopic cholecystectomy by causing bowel distension and does not increase
the incidence of post-operative nausea and vomiting. However does increase
incidence of PONV in by 32% in gynaecological procedures
isoflurane volatile of choice because it is less arrhythmogenic and causes
less myocardial depression
Epidural anaesthesia
- has been used for outpatient gynaecologic laparoscopy to reduce
complications and shorten recovery after anaesthesia
also has been used for laparoscopic cholecystectomy in a patient with severe
cystic fibrosis
- problems:
- shoulder tip pain
- shivering
- block as high as T2 required to abolish discomfort of surgical stimulation
of upper GI structures but this causes myocardial depression and reduced
venous return which aggravates the effects of tension pneumoperitoneum.
Vagally mediated arrhythmias are also exacerbated
Local anaesthesia
can be used for diagnostic laparoscopic procedures
supplemented with IV sedation
Monitoring
ECG
indirect BP
pulse oximeter
peripheral nerve stimulator
end-tidal CO2. In patients undergoing gynaecologic laparoscopy and in most
patients undergoing laparoscopic cholecystectomy Paco2
and PE'co2 are closely correlated. However in patients
with impaired cardiopulmonary function gradient between the two may become
large and unpredictable during laparoscopic surgery and direct estimation of Paco2
may be necessary. PE'co2 monitor also useful for early
detection of gas embolus
airway pressure monitor
Post-operative
- recovery usually very rapid
- minor complications (eg suxamethonium muscle pains, PONV) may produce
considerable morbidity and delay discharge
- PONV particularly troublesome after laparoscopic cholecystectomy and
gynaecological procedures
- pain consists of an early transient vague abdominal and shoulder
discomfort. Also experience a deep-seated pain relating to trauma at the
surgical site; this can be severe and may require opioids. Pain from trochar
puncture wounds usually mild.
- pulmonary function better preserved following laparoscopic surgery than
open surgery in patients with normal lungs. However there is some evidence
to suggest that patients with underlying pulmonary dysfunction develop more
severe ventilatory impairment that lasts longer after laparoscopic as
opposed to open cholecystectomy
- use of NSAIDS, opioids, PCA or epidural should all be accompanied by an
antiemetic
Further reading
Chui PT, Gin T and Oh TE, Anaesthesia for laparoscopic general
surgery. Anaesthesia and Intensive Care, 1993; 21:163-171
Verghese C, Brimacombe JR. Anaesth. Analg. 1996; 82: 129-33
© Peter Dzendrowski and Charles Gomersall September 1999
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