Criticare - A special feature on Anaesthesiology

Long hours of monitoring

Dr Smita Sharma

Any surgery related to neurosurgery takes anywhere from two to 24 hours, depending on the surgical lesion, patient’s condition and surgeon. It entails long hours of vigilance from the anaesthetist and a significant monitoring of the vital signs, physiology and biochemistry of the patient to provide safe and ideal conditions for the operation.

Other surgeries that can last for several hours are head and neck cancer surgery, cochlear implants, major abdominal surgery, liver transplants and occasionally peripheral vascular surgery. As the duration of anaesthesia increases, the effects on the various body systems starts showing up

Effect on respiratory system

With the induction of anaesthesia, the functional residual capacity (FRC) falls, alveolar gas exchange starts reducing, ciliary movement reduces, physiological dead space increases and ventilation/perfusion mismatch occurs. There is also the presence of the endotracheal tube and the pressure of its cuff on the mucosa of the trachea.

Effect on cardio vascular system

Several drugs are used in the course of anaesthesia and exert some effect on the heart contractility and filling.

Effect on CNS

The dynamics of pulse and blood pressure and effect of drugs and oxygenation play an important role in affecting cerebral perfusion, ICP and autoregulation. Brain cannot tolerate hypoxia for more than two minutes and is very sensitive to small alterations of carbon dioxide levels.

Effect on biochemical activities

Life is an acidogenic process and stress of prolonged surgery and anaesthesia can increase the systemic metabolic lactic acidosis. There is also constant derangement of glucose utilisation, increased resistance to insulin and electrolyte changes.

Effect on temperature

It is disturbed and combined with reduced OT temperatures, effects on inhalational agents and IV fluids, body temperature starts draping. If active care is not taken it after three to four hours, it drops by 0.5 degree C every hour.

General

There is always some increase is catecholamine release and peripheral vasoconstriction during a long operation. Hepatic and renal functions can get affected due to reduced blood flow and effect of drugs. There are some reports of delirium and cognitive function impairment in elderly.

Nausea and vomiting are commoner in prolonged anaesthesia. There is often positional edema, more so on face and tongue and sometimes pressure necrosis when a patient is lying in one position for several hours. There is also increased susceptibility to post operative infection as immune systems are also depressed with prolonged anaesthesia

The anaesthetist looking after the patient has to be constantly vigilant and look for warnings both in terms of monitoring and body biochemistry. If a patient is otherwise healthy, body compensatory mechanisms come into play. As everything looks normal, but a catastrophe can occur suddenly. However, it does not as the derangements take time to build up The trained and experienced anaesthetist can see and interpret far more from the same set of figures that the inexperienced eye and mind can miss. The key is to anticipate and prevent complications rather than treat them. The paediatric and geriatric age group has far less tolerance and reserves even in absence of a medical problem

Essential monitoring in long operations is ECG Arterial blood pressure . It is not a good idea to rely on the blood pressure cuff for prolonged operations, particularly if massive blood loss occurs.

SaO2 and ETCO2 CVP and cardiac filling pressures if indicated Urine output Core body temperature

Sensible and judicious use of the investigations helps to make early corrections. It is important to measure : Arterial blood gases, Blood sugar and electrolyes (tight control in diabetics ,otherwise every 4-6 hours is acceptable), Coagulation factors with the help of activated clotting time or thromboelastogram, Serum lactate levels after about 6-8 hours and Osmolarity and specific gravity of urine.

The anaesthetist is responsible for the safety of the patient and for providing the surgeon ideal operating conditions. He has to be prepared for a long operation, choose his drugs judiciously (avoid hepatotoxic and nephrotoxic drugs) and take very basic precautions like fixing the endotracheal tube securely (head and neck surgery and neurosurgery the endotracheal tube is under the drapes and can loosen with secretions), warming and humidification of anaesthetic gases, maintenance of body temperature and ensure cerebral protection.

There may be some role of incorporating biologically variable ventilation (BVV). Antibiotics should be given at their scheduled times and all aseptic precautions must be maintained throughout. In major abdominal surgery it is a good idea to combine epidural anesthesia with GA

The dilemma the anesthetist often faces is when to suggest a two stage operation if all is going well. The decision is a matter of experience, understanding between surgeon and anesthetist, facilities available and quality of post operative care. It is a good idea to continue mechanical ventilation after prolonged surgery.

Lastly, there is the fatigue factor. Anesthetists can get fatigued, lose concentration and sometimes be more hypothermic than the patient! It is always good to have a second colleague or an assistant. All said and done, medical science has come a long way from the days when anesthetists had to keep a hand on the pulse and take manual BP. With safe techniques and adequate skills, long operations are done routinely today without any significant complications.

The writer is consulatant anaesthesiologist with Bombay Hospital. Email: smitasharma29@hotmail.com