INTRODUCTION:
General anesthesia is a drug-induced, reversible
condition that includes specific behavioral and physiological traits —
unconsciousness, amnesia, analgesia, and akinesia — with concomitant stability
of the autonomic, cardiovascular, respiratory, and thermoregulatory systems
(1,2). During general anesthesia, a myriad of
events occur in the body, from being
anxious, to unconscious and immobile and back to awake. Under conditions of optimal monitoring,
sedation and anesthesia, it is possible for a patient to undergo surgery and
have no recall of intra-operative events (3).
Although it is increasingly safe, general anesthesia
is not without risks and complications. Cardiovascular and respiratory
complications are the most common. Myocardial infarction, interference with
lung mechanics, and exacerbation of pre-existing co morbidities can all occur.
Other serious complications include acute renal impairment and the development
of long-term postoperative cognitive dysfunction. Minor but important
complications of general anesthesia include postoperative nausea and vomiting,
sore throat, and dental damage. All these complications can have a significant
impact on patients and may result in prolonged hospital stay and expense. By
being aware of potential complications related to general anesthesia, many can
be predicted and prevented. Thorough preoperative assessment is the key to
identifying risk factors and stratifying patients so that optimization and
planning can occur preoperatively.(4)
General Anesthetics:
There are inhalational and
intravenous anesthetics used to induce or maintain general anesthesia:
Inhalational: Nitrous Oxide,
Isoflurane, Sevoflurane, Desflurane and Xenon.
Intravenous: Propofol, Etomidate,
Ketamine, Methohexital and Thiopental.
These general anesthetic drugs are
often accompanied by sedative benzodiazepines: midazolam, diazepam and
lorazepam.(3)
General Mechanism of Action;
General
anesthetics are much more selective than is usually appreciated and may act by
binding to only a small number of targets in the central nervous system. At surgical
concentrations their principal effects are on ligand-gated (rather than
voltage-gated) ion channels, with potentiation of postsynaptic inhibitory
channel activity (5). General
anesthetics primarily act by either enhancing inhibitory signals or by blocking
excitatory signals. They all enhance the function of GABAARs,
the most abundant fast inhibitory neurotransmitter receptor in the CNS. General
anesthetics also have a spectrum of modest to strong effects on other ion
channels, including glycine receptors, neuronal nicotinic receptors, 5-HT3 receptors, glutamate receptors and the two
pore potassium channels [6], with each drug differing in its array of effects. Ketamine,
nitrous oxide and xenon inhibit ionotropic glutamate receptors, with the strongest
effects being seen on the NMDA receptor subtype.
Various Complications of General Anesthesia;
Any
anesthetic technique, either regional or general, has potential for
complications. A common side effect of general anesthesia is nausea and vomiting after
surgery. Some people may also have a sore throat and very occasionally damage
to teeth, lips, gums, or vocal cords from insertion of breathing tubes and
airway devices. Less common and more serious complications include malignant hyperthermia, heart attack,
stroke, or death; these are more likely in patients who have heart problems,
high blood pressure, diabetes, kidney disease, or lung diseases. Very rarely,
persons may become aware of events when they are thought to be unconscious from
general anesthesia; this is more likely during emergency surgery if the patient
is in shock, during open heart surgery with the heart bypass machine, or
because of medication error or malfunction of the anesthesia equipment.(7) A few other complications
are;
ON IMMUNE SYSTEM:
Anesthetic agents are believed to have an adverse effect on human immune
defense mechanisms. During general anesthesia with fentanyl, thiopental, and
isoflurane, there was a significant decrease of circulating NK cells in the
peripheral blood accompanied by a significant increase of B cells and CD8+T
lymphocytes. A significant anesthesia-associated increase of interferon
(IFN)-γ, IFN-α, tumor necrosis factor-α, and soluble
interleukin-2 receptor (sIL-2R) synthesis was also detected. These findings
suggest that general anesthesia interferes with immune cell number and immune
cell response (8).
Intraoperative allergic reactions occur, the most common life-threatening
manifestation of an allergic reaction is circulatory collapse, reflecting
vasodilatation with resulting decreased venous return. Airway maintenance, 100%
oxygen administration, intravascular volume expansion, and adrenaline are
essential to manage the hypotension and hypoxia that result from
vasodilatation, increased capillary permeability, bronchospasm and profound
ventilation- perfusion abnormality.(9)
IN OBSTETRIC
PRACTICE:
General anesthesia may lead to loss
of airway control, with anoxia and aspiration of gastric contents. The major
concerns regarding the use of general anesthesia for the obstetric population
are difficulty in airway management (failed intubation) and acid aspiration.
Awareness and drug toxicity are few other complications associated with general
anesthesia. When general anesthesia is to be used in obstetrics, the method of
airway management will depend on the urgency of the procedure and the
anticipated ease or difficulty of intubation and ventilation. All equipment for
routine and emergency airway management should be immediately available.
Aspiration is commonly associated with general anesthesia. (10) Leaving
the endotracheal tube in place till the patient is fully awake and completely
responsive to commands and has no sign of muscle weakness is mandatory to avoid
aspiration. Early recognition (anticipation) of
airway difficulty, proper planning and its execution is crucial to prevent
aspiration. A high incidence of awareness has been reported after GA in the
obstetric population. It is necessary to avoid awareness during anesthesia as
it may lead to long-lasting psychological symptoms. Use of inhalational
anesthetic agents (halothane 0.5%, isoflurane 0.6% and sevoflurane 1%) with 50%
nitrous oxide virtually prevents the awareness (11).
MORTALITY:
The role of anesthesia in
contributing to surgical mortality has been studied in 33,224 patients given
either spinal anesthesia or a general anesthetic to which muscle relaxants were
added(12). As the patients' physical
condition worsened, deaths related to anesthesia increased in incidence.
IN CHILDREN:
The child experiences dizziness or
headache, agitation on waking, sore throat. Pain relieving drugs are given.
There is mounting and convincing preclinical evidence that anesthetics in
common clinical use are neurotoxin to the developing brain in vitro and cause long-term neurobehavioral
abnormalities in vivo.
Ketamine induces neuronal apoptosis and neurodegeneration in both
rats and monkeys with high doses, prolonged exposure, or repeated doses
(13,14). Similar dose-dependent
effects have been documented for propofol and isoflurane (15,16). Neurotoxic
effects were more prominent when the exposure was to a combination of
anesthetic agents with both NMDAR and GABAR actions than from exposure to an
agent with either NMDAR or GABAR actions alone.
RESPIRATORY
COMPICATIONS:
In the most patients irregular breathing occurred.
Laryngeal spasm, Coughing, hiccup, Obstruction by the tongue and excessive
secretion occurred, Despite the premedication (atropine), excessive secretion
followed i.v. ketamine anesthesia occurred. (17)
In patients who have airway hyper reactivity (e.g.
acute respiratory infection, bronchial asthma) it is advocated that extubation
should be performed in deep inhalation anesthesia (18). Other methods of reducing aspiration pneumonitis associated with
anesthesia are the use of metoclopramide to enhance gastric emptying and ranitidine or proton pump inhibitors to increase the pH of
gastric contents.
HYPOTHERMIA:
Mild hypothermia is common during
deep sedation or general anesthesia and is frequently associated with patient
discomfort and shivering. Volatile anesthetics, propofol, and older opioids
such as morphine and meperidine promote heat loss through vasodilation. This
process is compounded further by the fact that these drugs, as well as fentanyl
and its derivatives, directly impair hypothalamic thermoregulation in a
dose-dependent manner. Opioids also depress overall sympathetic outflow, which
further inhibits any attempts at thermoregulation. The depressant effect on the
hypothalamus results in an elevated threshold for heat response, along with a
diminished threshold for cold response such as vasoconstriction and shivering.
Therefore, opioids widen the normal interthreshold range from ∼0.2°C to as much as 4°C, and patients are unable to adjust to
cold environments and heat loss resulting from vasodilation (19). The most
common complications associated with hypothermia are (20) a threefold increase
in morbid myocardial events, (21) a
threefold increase in the risk of surgical wound infection,(22)and an increase in blood loss and transfusion
requirements. Postoperative shivering should be treated with warming of the
patient, most effectively via forced-air systems. Treatment includes temperature
monitoring which is a standard for patients undergoing general anesthesia. The
operating room should be warmed to greater than 24°C (i.e., 76°F) during
induction and while the patient is prepped and draped. Warming of i.v fluids
can only help to minimize heat loss.(20)
IN
OBSTRUCTIVE SLEEP APNOEA:
Patients with obstructive sleep
apnoea are particularly vulnerable during anesthesia and sedation. They are at
high risk of developing postoperative complications when having surgery or
other invasive interventions under general anesthesia. Serious complications
include reintubations and cardiac events.(23,24) Preoperative sedation with
benzodiazepines 45 minutes before the induction of general anesthesia has
anticonvulsive and muscle relaxing effects on the upper airway musculature,
causing an appreciable reduction of the pharyngeal space. Consequently, a
higher risk of preoperative phases of hypopnoea and consecutive hypoxia and
hypercapnia arises after administration, and oxygen saturation needs to be monitored
adequately (23, 25) Tracheal extubation should be carried out only when the
patient is conscious, communicative, and breathing spontaneously with an
adequate tidal volume and oxygenation.
Respiratory depression and repetitive apnoeas often occur directly after
extubation in patients with obstructive sleep apnoea(26). Use of
opioids increases this risk, and intravenous administration may cause delayed
respiratory depression (27). Use of nasal continuous positive airway pressure
preoperatively and directly postoperatively reduces the risk of developing
respiratory depression.
IN CATARACT SURGERY:
The incidence of
airway complications following general anesthesia using either a tracheal tube
or a laryngeal mask airway can lead to some disturbances. Coughing after
anesthesia for cataract surgery may cause a rise in intraocular tension and
increase the possibility of iris or vitreous prolapse (28). Intermittent
positive pressure ventilation (IPPV) is commonly used to control the arterial
pressure of carbon dioxide and thus reduce intraocular pressure in patients
undergoing general anesthesia for cataract surgery. Coughing, laryngospasm, and
breathholding all have the capacity to cause hypoxaemia, and a technique that
reduces their incidence must therefore be considered a potential advantage to
the patient. Laryngeal mask airway reduces the incidence of immediate
postoperative upper airway complications (29).
IN PSYCHIATRIC PATIENTS:
Psychiatric patients are at increased
risk for perioperative complications, as their biological response to stress is
impaired. Pancuronium, ketamine,
meperidine and epinephrine containing solutions should be avoided in patients
being treated with tricyclic antidepressant drugs. There are two hazardous drug
interaction risks to be avoided: The direct effect on the cardiac system and
the interactions with anesthetic drugs regulating the cardiovascular system. Ketamine should probably be avoided in
patients taking antipsychotic drugs as antipsychotics decrease the seizure
threshold (30,31). The use of tramadol in patients taking antipsychotic drugs
is of particular interest as tramadol may itself cause psychiatric symptoms.
Mood stabilizers and antipsychotic drugs should be continued throughout the
perioperative period to avoid the risk of relapse.
NEUROLOGICAL
COMPLICATIONS:
Premedicants like atropine and scopolamine have been
reported to cause central anticholinergic syndrome and hyperpyrexia in
paediatric patients.(32,33) Promethazine has often been blamed for producing
extra pyramidal symptoms. Ketamine, a popular induction agent with good
analgesic properties can cause hallucinations. The occurrence of myoclonic and
seizure like motor activity has been observed clinically in non-epileptic
patients after both intravenous and intramuscular ketamine.(32,34) Propofol,
causes incidence of neurological symptoms, which include twitching, myoclonic
movements, opisthotonus and seizures.(35) Enflurane has been shown to cause
epileptiform activity and grand mal seizure patterns. Meperidine neurotoxicity
is well known and is manifest clinically as shakiness, tremor, myoclonus and
seizures. There have been reports too of grandmal seizure activity in patients
after administration of fentanyl.(36) Isoflurane has also been implicated in
producing seizure activity when administered along with nitrous oxide.
Meticulous care during selection of drugs, dosages and anesthetic technique
with monitoring of core temperature, ventilatory and circulatory functions help
in averting these neurological complications. For mitigation of this
neurological complication the use of benzodiazepines and intermittent
administration of inhalational anesthetics has been recommended. It is also
imperative to avoid a light plane of anesthesia intraoperatively.
HYPERTENSION:
During induction of general
anesthesia, patients with hypertension may exhibit significant increases in
heart rate and blood pressure (37). Hypertensive subjects during general
anesthesia suffered more from hemodynamic instability. One preventive approach
is to substitute long-acting preparations of the patient’s long-term
antihypertensive regimen starting, if possible, several days before surgery and
to be given in the morning of the day of surgery. The patient’s BP elevation
should be considered.
HYPOTENSION:
Severe hypotension after induction of
anesthesia is quite common and is more prevalent during the late postinduction
period than at other times. The incidence of hypotension postinduction of
anesthesia is strongly predicted by age ≥50 years, hypotension before
induction, and propofol used at induction of anesthesia. Increasing fentanyl
dosage during the anesthetic induction also appears to have a significant
association with hypotension in patients with less systemic disease. (38) General anesthesia commonly results in mild
hypotension due to the effects of intravenous induction agents and inhalational
agents in reducing cardiac output and systemic vascular resistance. In the
elderly induction agents need to be given slowly and at reduced doses to avoid
severe hypotension. Optimise preload: administer an intravenous fluid bolus
e.g. 10 ml / kg crystalloid or colloid, and assess the response. Elevation of
legs or head down tilt also improves venous return • Increase contractility:
administer ephedrine • Systemic vasoconstriction: administer vasoconstrictor
e.g. metaraminol, ephedrine(39)
CONCLUSION:
General anesthesia enables a patient
to tolerate surgical procedures that would otherwise inflict unbearable pain,
potentiate extreme physiologic exacerbations, and result in unpleasant
memories. Though it has complications, it cannot be avoided in serious
operations where one needs to be totally unconscious and unaware of the
procedure. The focus of the anesthesiologist should be on risk management to
prevent such complications in patients undergoing surgery on general
anesthesia. Prompt detection
and immediate management of such adverse complications should be done.
Continuous monitoring of machine and patient, during the anesthesia is the
corner stone of success at all times. The
prevention of perioperative and post-operative complications is an important
task for the anesthesiologist. Thus this article aims at bringing awareness
about the various complications of general anesthesia and its importance of managing
it for the benefit of the patient undergoing anesthesia.
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