Download Obesity, obstructive sleep apnoea, and diabetes

British Journal of Anaesthesia 103 (BJA/PGA Supplement): i23–i30 (2009)
doi:10.1093/bja/aep294
Obesity, obstructive sleep apnoea, and diabetes
mellitus: anaesthetic implications
K. Candiotti*, S. Sharma and R. Shankar
Department of Anesthesiology, Pain Management and Perioperative Medicine, University of Miami, Miller
School of Medicine, PO Box 016370 (R-370), Miami, FL 33136, USA
*Corresponding author. E-mail: [email protected]
Obesity is an epidemic in much of the Western World. The extent of this problem, combined
with the increasing preference for ambulatory surgical procedures, has produced a difficult situation for many anaesthesiologists. Even the simplest anaesthetic procedures can become very
complicated and potentially difficult in this population. Although there are numerous complications associated with obesity, perhaps obstructive sleep apnoea (OSA) and diabetes mellitus
are among the more significant. Patients with OSA are often not ideal candidates for certain
day-case procedures, but many outpatient procedures can be performed on patients with OSA
as long as attention is paid to anaesthetic technique. Diabetic patients are prone to numerous
complications in the perioperative period, including cardiac problems, but with careful management, they are able to undergo day-case surgical procedures safely.
Br J Anaesth 2009; 103 (Suppl. 1): i23–i30
Keywords: anaesthesia, day-case; complications, obesity; diabetes; sleep apnoea
Obesity
In the USA, more than one-third of the adult population
suffers from obesity. There is a higher prevalence in
certain ethnic populations, including African-, Asian-, and
Mexican-Americans.2 20 While definitions vary, obesity is
defined as a BMI of 30 kg m22 or greater and morbid
obesity as a BMI .35 kg m22.2 53 Super morbid obesity is
often categorized as patients with a BMI .50 kg m22 and
ultra obese patients as those with a BMI .70 kg m22.14
Obese patients, especially those with a central distribution
of fat, have an increased risk of various medical disorders
such as cardiovascular disease, stroke, and diabetes.2 53
Obesity can be classified as primary obesity resulting
from increased caloric intake and secondary obesity,
which is often a result of medications (e.g. corticosteroids)
or medical disorders such as Cushing’s disease or
hypothyroidism.2 This review focuses on primary obesity,
the associated diseases of diabetes and obstructive sleep
apnoea (OSA), and their implications for anaesthetic management focusing on the ambulatory care setting. The secondary form of obesity is associated with numerous other
complications beyond the scope of this review.
Pathophysiology
Obesity can present significant problems for anaesthesiologists, including difficult airway management, intravascular
access, pulmonary aspiration, monitoring, and choosing
appropriate medications.2 Although numerous organ systems
are affected in obese patients, the burden placed on the cardiovascular and respiratory system is especially concerning to
the anaesthesiologist. Because of the restrictive ventilatory
effects of obesity, these patients often show a decreased
functional residual capacity and a decreased expiratory
reserve volume, all leading to an overall decrease in total
lung capacity. These decreases lead to arterial hypoxaemia,
ventilation– perfusion mismatch, and right-to-left shunting.
Obese patients require increased cardiac output to maintain
pulmonary and systemic circulations. Since increased left
ventricular blood volume and systemic hypertension are
common in these patients, complications of chronic, increased
afterload, which translates into increased cardiac work and
increased oxygen demands, are often encountered.2 53
Apart from cardiovascular and pulmonary issues, morbidly obese patients suffer from higher perioperative complication rates including renal problems, atelectasis,
pneumonia, wound infections, sleep apnoea-related problems, and thromboembolic events.2 3 Thromboembolic problems, such as deep vein thrombosis, most likely arise from
polycythemia, high abdominal pressures, and reduced mobility, all leading to venous stasis.52 Prophylactic techniques
can reduce the occurrence of deep vein thrombosis and
include early ambulation, compression devices, and sometimes preoperative inferior vena cava filter placement.2 52
Anaesthetic considerations
Mask ventilation and intubation can pose a challenge in an
obese patient as a result of the excessive fat and
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Candiotti et al.
problematic chest and lung biomechanics. Predictors of
difficult mask ventilation include: age .55 yr, BMI
.26 kg m22, the presence of a beard, lack of teeth, and a
history of snoring.37 Tracheal intubation and positive
pressure ventilation are still considered the best options for
securing the airway in obese patients, but at times can be
difficult as well. Awake fibreoptic intubation has traditionally been the safest method of securing an airway in a
morbidly obese patient but can be difficult in obtunded or
uncooperative patients. A recent study comparing postoperative lung function and oxygen saturation in moderately obese patients concluded that a laryngeal mask
airway (LMA) can easily replace an orotracheal intubation
for patients posted for most peripheral surgeries. This
observation was based on the fact that oxygen saturation
decreased more in the intubated group at 30 min, 2, and
24 h after operation than in the LMA group. Even inspiratory and expiratory spirometric values were better in the
LMA group up to 24 h after operation.58 Another recent
report demonstrated the use of other devices to secure a
difficult airway such as the Aintree intubation catheter.
The Aintree stylet was placed over a fibreoptic bronchoscope and both were introduced through an LMA. A tracheal tube was then inserted over the stylet after removing
the fibreoptic scope and LMA.22 Another study assessed
the impact of obesity on emergency intubations in trauma
patients. The study included 9980 patients, with 46% lean,
37% overweight, 15% obese, and 2% morbidly obese
patients and concluded that emergency intubation of obese
trauma patients was not different from non-obese trauma
patients and can be safely and successfully performed at a
high volume level 1 trauma centre.50
Even with successful intubation, ventilation can present
difficulties in morbidly obese patients. These difficulties can
be attributed to the restrictive nature of the chest wall and the
altered pulmonary mechanics. A recent study compared
pressure-control ventilation with volume-control ventilation
in a group of 36 patients undergoing laparoscopic bariatric
surgery. The study demonstrated a higher PaO2, SaO2, and
0
PaO2/FIO2 ratio along with a lower ECO
–PaCO2 gradient and a
2
comparatively normal pH and PaCO2 with pressure-control
ventilation compared with volume-control ventilation. The
improved oxygenation with pressure-control was explained
by a better ventilation–perfusion ratio.17
Appropriate drug dosage and drug selection are critical
in morbidly obese patients. In general, opioids and sedatives should be used judiciously for induction, maintenance of anaesthesia and for postoperative analgesia
because of the risk of respiratory depression in morbidly
obese patients. Obese patients require different dosing
compared with average weight patients. For instance,
Shibutani and colleagues concluded that fentanyl should
be dosed based on pharmacokinetic mass, which has a
non-linear relationship to total body weight (TBW), in
order to avoid overdosing. With this approach, the relative
dosing of fentanyl in mg kg21 decreased as TBW
increased.48 Reduced opioid-induced complications can
also be achieved by multimodal analgesic therapy. A
number of studies have shown reduced fentanyl-induced
respiratory depression by using adjuvant drugs. One
showed that the preinduction use of ketamine and clonidine in morbidly obese patients posted for bariatric
surgery reduced total doses of intraoperative fentanyl and
sevoflurane, time to extubation, postoperative tramadol use
for analgesia, and visual analogue scale pain scores.52
Recently, the use of dexmedetomidine, a selective a2
adrenergic receptor agonist, has gained popularity in obese
patients because of its sedative/hypnotic, anaestheticsparing, analgesic, and sympatholytic properties. The use
of dexmedetomidine reduces opioid-induced respiratory
depression in morbidly obese patients with OSA and pulmonary hypertension undergoing bariatric surgery.30 The
drug has also proven advantageous in patients who are
undergoing laparoscopic gastric bypass procedures by
reducing the amount of opioids required, thus giving the
added advantage of reduced emesis and decreased duration
of post-anaesthesia care unit stay.30 51 Yet another study
demonstrated the use of dexmedetomidine as the sole
sedative agent for awake fibreoptic intubations in a series
of obese patients.1
The altered physiology in an obese individual, when
compared with a non-obese patient, affects the pharmacokinetics of many drugs including volatile anaesthetics.
A study by Mantouvalou and colleagues41 showed that
there was no significant difference in the emergence and
recovery characteristics of desflurane or sevoflurane in
obese patients. In contrast, another study conducted by La
Colla and colleagues36 did show a significant difference in
the recovery profiles between desflurane and sevoflurane
with desflurane leading to significantly faster wash-in and
wash-out and a shorter recovery room stay compared with
sevoflurane.
The use of regional anaesthesia has been less explored
for morbidly obese patients. Challenges in performing
regional anaesthesia in obese patients often lie in finding
correct landmarks, selecting the right equipment and
positioning, all of which can be improved through obesespecific anaesthetic techniques.15 42 For example, fluoroscopic or ultrasonographic guidance can be used to
improve the success rate and ease of regional anaesthesia
procedures in obese patients.42 While obese patients are
increasingly being treated in ambulatory care centres with
regional anaesthesia, they have a higher rate of block failures and complications. For example, phrenic nerve palsy
after brachial plexus block in a morbidly obese patient led
to unanticipated hospitalization as a result of dyspnoea,
flank pain, chest discomfort, and anxiety.24 Overall, obese
patients are 1.62 times more likely to have an unsuccessful
block in an ambulatory setting. Despite these difficulties,
regional anaesthesia can still be an excellent option for
obese patients in an outpatient setting, particularly in
patients with OSA.42
i24
Obesity, sleep apnoea, and diabetes mellitus
Ambulatory patients
Candidacy for surgery, clinical outcomes, and likelihood
of being able to leave the hospital are factors often considered when assessing the obese patient for ambulatory
and other procedures.48 Morbid obesity does not appear to
be a significant independent risk factor for unanticipated
admissions after operation, and ambulatory surgeries
should not be avoided solely on the basis of weight.
However, morbidly obese patients have an increased likelihood of bronchospasm and need for supplemental oxygen
after surgery.31 Obese patients with a mean BMI of 44.5
kg m22 undergoing gastric banding were successfully
treated as outpatients with only nine of 343 patients
having significant complications, the most common being
stoma occlusion.56 The study included ASA I and II
patients; however, patients with severe sleep apnoea were
also enrolled, provided they were treated with appropriately titrated CPAP and were compliant with their
machines.
In contrast to these findings, other studies indicate that
obese patients experience frequent perioperative complications including postoperative oxygen desaturation, even
with supplemental oxygen, necessitating increased preventative measures for hypoxaemia.31 51 Even minor ambulatory procedures, such as dental surgeries, demonstrate
obesity-related complications. In a closed-claim study
based on office-based dental anaesthetic procedures,
obesity was cited as one of the most frequent risk factors
associated with increased morbidity and mortality.33
intra-airway pressure that can narrow the collapsible
segments of the pharynx as a result of the lack of bony
support. In REM sleep, the tone of the upper airway
muscles decreases, increasing upper airway resistance.
Any further diaphragmatic contraction during inspiration
produces additional negative pharyngeal pressure, collapsing the pharynx even more.13 The relationship between
OSA and obesity is emphasized by the observations that
obesity has an inverse relationship with pharyngeal area,
and the patency of the collapsible pharynx is determined
by the difference between the extraluminal and the intraluminal pressures and by wall compliance, both of which
are adversely affected by the fat mass in obese people.
The effect of obesity on OSA is simply demonstrated by
the fact that dietary and surgical weight reduction strategies reduce its severity.13
The systemic effects of OSA are primarily the result of
hypoxaemia and hypercapnia occurring during apnoeic episodes. These changes can not only cause arousal and disturbed sleep but also lead to cardiac arrhythmias and
ischaemia, pulmonary hypertension and right ventricular
hypertrophy, and systemic hypertension and left ventricular
hypertrophy.13 Fat distribution is not uniform in obese
patients, and recent studies indicate that abdominal circumference is a better predictor of OSA than neck circumference or BMI.49 Leptin, an adipose tissue-derived hormone,
regulates caloric intake, body weight, and fat distribution.
Leptin resistance, causing increased serum leptin levels, is a
contributing cause of obesity. Interestingly, OSA patients
on continuous positive airway pressure (CPAP) demonstrate
a decrease in serum leptin levels, suggesting a possible
association with OSA.49
Obstructive sleep apnoea
OSA can be a problem with serious implications for
anaesthetic management. It is a syndrome characterized by
some form of upper airway obstruction during sleep, often
leading to respiratory interruptions and excessive daytime
somnolence.9 Two separate entities have been documented: OSA, a complete cessation of airflow for more than
10 s (apnoea), and obstructive sleep hypopnoea (OSH)
characterized by an airflow reduction of more than 50%,
despite continuing breathing efforts resulting in hypoxaemia and hypercapnia.13 The accepted minimal clinical
diagnostic criteria for OSA is an apnoea – hypopnoea index
(AHI) of 10 plus symptoms of excessive daytime somnolence; AHI is the number of episodes of apnoea or hypopnoea per hour during sleep.20 Overt OSA has been
reported in 2% of women and 4% of men; however, these
numbers are expected to increase as the population grows
older and more obese.9
Pathophysiology
The pathophysiology of OSA depends on pharyngeal
anatomy and the stage of sleep. Normally during inspiration, the contraction of the diaphragm creates a negative
Anaesthetic considerations
Polysomnography (an overnight sleep study) is the best
method for diagnosis of sleep apnoea; however, it is
expensive, time-consuming, and clearly unsuitable for
general screening purposes. Therefore, questionnaire-based
tools have been developed to identify symptoms of
OSA.19 The ASA has published a set of guidelines that
help diagnose OSA based on elevated BMI, neck circumference, craniofacial alterations that obstruct the airway,
snoring, airway exam anomalies, and hypersomnolence.9
The ASA has also developed a scoring system to assess
the perioperative risk of complications from OSA
(Table 1).13 37 The Berlin questionnaire is another aid to
diagnose OSA before operation and uses three categories:
(i) snoring, (ii) sleep and fatigue, and (iii) arterial pressure,
weight, and height. A patient is at increased risk of OSA if
significant symptoms are present in two out of the three
categories.19 Recently, Chung and colleagues20 formulated
an excellent tool for the screening of OSA. The STOP
questionnaire includes four questions with yes/no answers:
Snoring, Tiredness during daytime, Observed apnoea, and
high arterial Pressure. To further improve its sensitivity,
i25
Candiotti et al.
Table 1 OSA scoring system
Points
A
B
C
D
Severity of sleep apnoea based on sleep study (or clinical
indicators if sleep study not available)
None
Mild
Moderate
Severe
Invasiveness of surgery and anaesthesia
Superficial under local or peripheral nerve block without
sedation
Superficial with moderate sedation and general anaesthesia
Peripheral with spinal or epidural anaesthesia and moderate
or greater sedation
Peripheral with general anaesthesia
Airway surgery with moderate sedation
Major surgery with general anaesthesia
Airway surgery with general anaesthesia
Postoperative opioids
None
Low dose oral
High dose oral, parenteral, neuraxial
Estimation of perioperative risk is calculated by adding A to
either B or C whichever is greater. The greater the score, the
greater the risk of perioperative complications
0
1
2
3
0
1
1
2
2
3
3
0
1
3
(0 –6)
they incorporated questions concerning: BMI, Age, Neck
circumference, and Gender to make the STOP-BANG
questionnaire. Clinical prediction formulas can help evaluate an obese patient’s risk for OSA which is often underdiagnosed. Sleep apnoea scoring systems, similar to that
developed by the ASA, have been published which help
predict the likelihood of OSA. For example, in one
scoring system, patients with a score of 15 or higher have
an 81% chance of having OSA.25 This category of patients
can also experience increased adverse events in the postanaesthesia care unit (PACU) and increased frequency of
unplanned intensive care unit (ICU) admissions. Patients
with high scores experience notably fewer adverse PACU
events, if regional anaesthesia is used.25 Since a diagnosis
of OSA in an obese patient affects anaesthetic care, the
presence of a history consistent with OSA (i.e. hypertension, a neck circumference .40 –42 cm, and snoring) is
valuable. The ASA practice guidelines recommend a sleep
study in patients with a probability of sleep apnoea in
order to assess severity.9
Despite advances in the pathophysiology of OSA and
the release of practice guidelines by the ASA, no standard
anaesthetic management strategy has been validated.
Bolden and colleagues,14 in a limited study, concluded
that developing and following a perioperative anaesthesia
protocol is the best way to avoid an adverse outcome in
patients suffering from OSA. Preoperative preparation is
an important part in the management of OSA patients and
is intended to optimize their physical status. The ASA recommends (i) CPAP, or non-intermittent positive-pressure
ventilation (NIPPV) or bilevel positive airway pressure,
(ii) preoperative weight loss, (iii) preoperative medication,
and (iv) preoperative use of mandibular advancement or
oral appliances.9 Patients using CPAP should be instructed
to bring the machine with them if admitted to the hospital
for any reason.
As a result of the propensity for airway collapse and the
aforementioned pharyngeal pathophysiology, OSA predisposes to the respiratory depressant effects of sedatives,
opioids, and inhaled anaesthetics. These drugs should be
used judiciously in patients with a history of OSA.9 20
Short-acting drugs, such as remifentanil, and agents with
limited respiratory depression, such as dexmedetomidine,
should be favoured.20 Patients with OSA have an increased
incidence of difficult intubation. If a difficult airway is
suspected, the patient should be managed conservatively,
with an awake fibreoptic intubation considered optimal.9 If
induction before intubation is considered appropriate, a
rapid sequence induction is advisable as the risk of aspiration in obese and OSA patients is high as a result of poor
lower oesophageal sphincter tone.49 51 Because of these
airway issues, complete recovery from neuromuscular
block and awake extubation are considered appropriate.
A semi-upright or lateral position for extubation has also
been suggested to be of benefit irrespective of the patient
position during surgery.9
In patients with OSA, regional anaesthesia appears to
carry significant benefits over general anaesthesia.9 20 If
sedation for these patients is considered, it is appropriate
to utilize continuous capnography. CPAP can also prove
beneficial.32 The use of CPAP in moderate sedation might
allow more liberal use of sedatives to improve patient
comfort and prevent airway collapse.32 For simple peripheral procedures, local anaesthesia should be the preferred
choice.9
Postoperative complications for patients with OSA
include respiratory problems such as oxygen desaturation,
apnoea, respiratory arrest, and cardiovascular problems
such as hypertension, arrhythmias, and cardiac arrest.20 In
order to minimize such complications, the ASA guidelines
recommend supplemental oxygen until the patient is able
to maintain a baseline saturation on room air. CPAP or
NIPPV has been advised in patients who were receiving
treatment before operation but remains controversial in
those patients who were not. If frequent or severe obstruction or hypoxaemia occurs during postoperative monitoring, initiation of nasal CPAP or NIPPV should be
considered.9 Either a semi-upright or lateral position can
prove beneficial. Continuous oximetry monitoring in a
step-down unit, until room air oxygen saturation remains
above 90% during sleep, has been advised to reduce the
risk of respiratory complications. Additionally, the use of
regional anaesthesia and non-steroidal anti-inflammatory
drugs to minimize the use of opioids for postoperative
analgesia can also be beneficial.9 OSA was not an independent risk factor for postoperative hypoxaemia in the
first 24 h after laparoscopic bariatric surgery. However, all
obese patients with or without OSA experienced frequent
desaturations, despite supplemental oxygen.4 In view of
these findings, it has been suggested that perioperative
i26
Obesity, sleep apnoea, and diabetes mellitus
management of bariatric surgeries should include strategies
to detect and prevent postoperative hypoxaemia, but additional measures in OSA patients might not be required.4
Table 2 The American Diabetic Association diagnostic criteria for diabetes
1
2
Ambulatory patients
3
A number of factors must be considered before posting a
patient with OSA for an ambulatory (day-case) procedure.
These include sleep apnoea status, anatomical and physiological abnormalities, coexisting diseases, type of surgery,
type of anaesthesia, need for postoperative opioids, age,
adequacy of postoperative observation, and the capabilities
of the out-patient facility.9 There is general agreement that
superficial surgeries using local or regional anaesthesia,
minor orthopaedics procedures with local or regional
anaesthesia, and lithotripsy can be performed in outpatient
settings.9 20 The ASA guidelines do not recommend performance of airway procedures, including tonsillectomies,
in patients with OSA in an ambulatory setting. They do recommend ambulatory facilities for patients with OSA have
emergency difficult airway equipment, CPAP capabilities,
nebulizer and ventilator equipment, a radiology facility,
clinical laboratory access, and a transfer arrangement to a
nearby in-patient facility. Furthermore, monitoring for at
least 3 h more than non-OSA patients and for at least 7 h
after the last episode of apnoea or airway obstruction has
been recommended for all ambulatory OSA patients.9
Diabetes mellitus
Diabetes mellitus is a chronic disease characterized by a
decrease in insulin production (type 1) or impaired utilization of insulin as a result of peripheral insulin resistance
(type 2) causing hyperglycaemia.57 The current diagnostic
criteria for diabetes, as indicated by American Diabetic
Association, are listed in Table 2.54 According to WHO
statistics, 180 million people in the world suffer from
diabetes at present and this number is likely to double by
2030. The reason for this dramatic increase in diabetes is
thought to be the ageing of the population, increased
prevalence of obesity, sedentary lifestyle, and dietary
changes.54 The major risk factor for type 2 diabetes is
obesity with 90% of these patients being overweight.16 Of
note, it appears that the development of type 2 diabetes
can be delayed or sometimes prevented from manifesting
in individuals with obesity who are capable of losing sufficient weight.21
Pathophysiology
The relationship between obesity and diabetes is emphasized by the fact that they both are important components
of the metabolic syndrome,11 a syndrome characterized by
central obesity, atherogenic dyslipidaemia, elevated arterial pressure, insulin resistance, and prothrombotic and
proinflammatory states.6 38 Obesity is strongly associated
Symptoms of diabetes (polydypsia, polyuria, and unexplained weight
loss) plus a casual (non-fasting) glucose concentration of 200 mg dl21,
or
A fasting (.8 h) glucose concentration 126 mg dl21 (normal ,100 mg
dl21), or
A glucose concentration 200 mg dl21 2 h after ingestion of 75 g of
glucose (normal ,140 mg dl21)
with insulin resistance and diabetes. In a study of the
impact of intra-abdominal fat and age on insulin sensitivity, visceral fat was a strong determinant of insulin sensitivity and B-cell function.55 In a retrospective cohort
study of patients undergoing coronary artery bypass
surgery, obesity in non-diabetic patients was not independently associated with an increased risk of adverse postoperative outcomes. In contrast, obesity in diabetic
patients was independently associated with a significant
increased risk of postoperative respiratory failure, ventricular tachycardia, atrial fibrillation, atrial flutter, renal insufficiency, and leg wound infections.43 Another study of the
impact of bariatric surgery on type 2 diabetes concluded
that clinical and laboratory (fasting glucose and HbA1c)
parameters related to type 2 diabetes resolved or improved
after bariatric surgery with 78% of the study group showing
complete resolution of diabetes and 87% showing either
resolution or improvement. The same study also demonstrated that weight loss and improvement of diabetes were
related to the type of surgical procedure with a maximum
impact associated with a biliopancreatic diversion.16
Diabetes is not only associated with obesity but also
with OSA. A study of the association between OSA and
impaired glucose metabolism in normal weight and obese
individuals concluded that OSA is associated with occult
diabetes, impaired fasting glucose, and impaired fasting
glucose plus impaired glucose tolerance. The magnitude
of this association was similar for obese and non-obese
patients with OSA. Thus, OSA is an important risk factor
for diabetes irrespective of weight.47
Anaesthetic considerations
Diabetic patients suffer from an increased incidence of
perioperative adverse cardiac events, including unexplained hypotension, arrhythmias, hypoxaemia, electrocardiographic changes, and myocardial infarction, which have
a peak incidence at 48– 72 h after surgery.8 More severe
diabetics can suffer from autonomic dysfunction and these
patients often do not experience pain with myocardial
ischaemia. The presence of orthostasis (heart rate increase
.15 beats min21, or systolic arterial pressure decrease
.20 mm Hg 5 – 10 min after changing position from
supine to upright) is a sign of autonomic neuropathy and
indicates potential operative haemodynamic instability.7
Preoperative b-block has been shown to decrease the risk
of myocardial infarction and had been advised in diabetic
i27
Candiotti et al.
patients, despite previous concerns regarding the masking
of symptoms of hypoglycaemia and worsening glucose
intolerance.26 However, the use of b-blockers in all at-risk
patients in the perioperative period was recently called
into question by the Peri Operative Ischemic Evaluation
(POISE) trial which showed an increased risk of death and
stroke in patients started on b-blockers in the perioperative
period.40 Although the exact handling of b-blockers is
controversial, it is clear that patients who are currently
taking these agents should have them continued in the
perioperative period.54 Microvascular changes, secondary
to diabetes, can make a diabetic patient more prone to cardiomyopathy with subsequent diastolic dysfunction. This
dysfunction can respond well to b-blockers and calcium
channel blockers that act by decreasing the heart rate and
increasing diastolic relaxation.27
Reviewing the medication history of diabetic patients is
an important part of the preoperative assessment. Poorly
controlled diabetes is associated with worsening organ
damage. For instance, long-term uncontrolled hyperglycaemia is an important risk factor for development of end-stage
renal disease. Angiotensin-converting enzyme (ACE) inhibitors are commonly prescribed for the prevention of renal
complications in diabetic patients; however, patients with a
creatinine concentration .3.0 mg dl21 or creatinine clearance of ,30 ml min21 should probably not receive ACE
inhibitors because of an increased risk for deterioration of
renal function.12 Biguanides, such as metformin, should also
be discontinued in patients with compromised renal function
or who will undergo large or extensive surgical procedures
because of their propensity to cause lactic acidosis.7
Diabetic patients are at increased risk for various other
perioperative complications.34 Hyperglycaemia decreases
leucocyte chemotaxis and function. Increased susceptibility
to delayed wound healing and wound infections, feared
complications in diabetics, can be reduced by keeping blood
glucose (BG) concentrations ,250 mg dl21. In addition to
the tendency to diabetic ketoacidosis and non-ketotic hyperosmotic state, hyperglycaemia produces hyperosmolarity
and hyperviscosity which can lead to thrombogenesis and
increased perioperative complications.34 As a result of the
frequent presence of microvascular disease, diabetic patients
have an increased susceptibility to soft tissue ischaemia in
addition to nerve injury, so pressure points must be well
padded during positioning. For similar reasons, epinephrine
should probably be avoided in diabetic patients when local
anaesthetics are injected into areas of marginal blood
supply.23 29 Diabetic patients are also at risk for pulmonary
aspiration secondary to delayed gastric emptying. While not
a first-line drug for postoperative nausea and vomiting,
metoclopramide can be effective for aspiration prophylaxis
in patients with gastroparesis.21 35 While several other
agents are effective for the prevention of postoperative
nausea and vomiting in diabetics, dexamethasone should be
used with caution due to its exaggerated effect on glucose
in diabetics compared to non-diabetics.28
Approaches to managing of insulin dosing in the perioperative period vary by institution. In general, patients
with type 1 diabetes and type 2 diabetes on chronic
insulin therapy are treated similarly, with half of the usual
long-acting insulin given the morning of surgery (basal
insulin), supplemented by a regular insulin sliding scale
titrated according to hourly glucose measurements.
Alternatively, a regular insulin infusion of 0.5– 2 U h21
can be used to meet basal metabolic needs. With
either method, a slow glucose infusion will prevent
hypoglycaemia while the patient is fasting. For type 2
diabetics undergoing short procedures, insulin is sometimes simply held the morning of surgery.5 46 No specific
intraoperative recommendations regarding drug or fluid
administration exist for diabetics. However, decisionmaking should rely on regular intraoperative blood sugar
monitoring. If an infusion is required for glucose control,
regular insulin in 5% dextrose with or without potassium
may be used to ensure a gradual decrease of the serum
glucose level.46
While the hallmark of diabetes is hyperglycaemia, diabetic patients can also suffer from hypoglycaemia, defined
as serum BG concentration ,50 mg dl21 in adults, usually
related to treatment with medications such as insulin.
Prolonged severe hypoglycaemia can cause seizures, focal
neurological deficits, coma, and death. Confusion, irritability, fatigue, headache, and somnolence are manifestations
of hypoglycaemia. An adrenergic response can result in
restlessness, diaphoresis, tachycardia, hypertension,
arrhythmias, and angina. Anaesthetic drugs, analgesics,
sedatives, and sympatholytic agents can interfere with
symptom presentation. Administration of dextrose 50%
(50 ml) is the initial therapy for significant hypoglycaemia.
Additional bolus doses might be necessary, and continuous
evaluations of BG should be performed.
Surgery and critical illness activate the metabolic
response to stress, which includes alterations in both
hormone and cytokine concentrations. These in turn lead to
both increased glucose production and a state of insulin
resistance that can be additive to the defects in carbohydrate metabolism already present in the diabetic
patient.54 Preoperative glucose control can be achieved by
oral hypoglycaemic drugs or insulin. The importance of
preoperative glucose control was noted in a prospective
study evaluating the impact of preinduction hyperglycaemia and BMI in the perioperative management of cardiac
surgical patients. A preinduction glucose above 110 mg
dl21 was associated with a higher perioperative insulin
consumption than in patients with a preinduction BG of
110 mg dl21 or less. When the glucose was above 110 mg
dl21, insulin requirements were not different between
patients with or without a history of diabetes.
Intraoperative insulin management was more difficult in
patients with a higher preinduction glucose, requiring more
adjustments in the rate of insulin infusion and more periods
of BG levels below 80 mg dl21 or above 200 mg dl21.18
i28
Obesity, sleep apnoea, and diabetes mellitus
Interventions other than medications have also been
reported to be useful in controlling blood sugar levels.
Studies have demonstrated the beneficial effects of CPAP
on hyperglycaemia in diabetic patients with OSA. After a
mean treatment period of 83 days, 1 h postprandial
glucose values and elevated levels of HbA1c were significantly reduced in patients using CPAP. Additionally,
patients who were noted to have elevated levels of HbA1c
(.7%) had a significant reduction in those levels as
well.10 In support of these findings, CPAP treatments
increased insulin sensitivity significantly in non-diabetic
patients with OSA after two nights of treatment and beneficial effects were preserved even after 3 months of
CPAP therapy.45 CPAP when used regularly and with
effective pressures improved insulin sensitivity over longer
time periods (mean 2.9 yr).45
Despite the knowledge of the adverse effects of hyperglycaemia, the question remains as to how tightly glucose
levels should be controlled in the perioperative period. In
this past decade, studies had been conducted to support
tight glucose control (TGC). In 2001, a landmark randomized controlled trial on 1500 surgical ICU patients showed
that intense insulin therapy (IIT) (target BG, 80– 110 mg
dl21) reduced in-hospital mortality by 34% compared with
standard therapy (target BG, 180– 200 mg dl21) and significantly decreased morbidity, including bloodstream infections, acute renal failure, red-cell transfusions, and
critical-illness polyneuropathy.40 Recently, however, an
evidence-based review on perioperative glucose control
reported that the current criteria for TGC should be interpreted with care, since the major studies in favour of TGC
were in surgical intensive care settings and might not apply
to other settings. In general, careful and stepwise implementation of IIT protocols to maintain BG ,150 mg dl21
and reduce BG variability can be both safe and effective in
reducing adverse events. There are subpopulations that
might benefit from TGC, but until those patients are identified IIT should be avoided in most surgical patients.39
Ambulatory patients
The pre- and perioperative anaesthetic considerations for
diabetic patients in day-case surgery do not differ significantly from inpatient procedures with the exception that in
almost all ambulatory procedures, food intake is resumed
fairly quickly after surgery. Importantly, this can allow for
the timely resumption of routine diabetic medications.
Medications should not, however, be resumed at normal
levels until the patient has recovered sufficiently to maintain
good oral intake and, while typically true for any patient,
special consideration for admission after surgery should be
given to patients who suffer from severe diabetes and have
difficulty eating. In general, however, with the exception of
patients who have significant autonomic dysfunction and
tend to manifest haemodynamic instability, outpatient
surgery can be safely considered for most diabetics.44
Conclusions
As the obese populations of many countries continue to
grow so will the frequency of their presentation for
surgery. With proper training and education, good care for
these patients, while perhaps more complex, is obtainable.
While many physicians in practice today see a large
number of obese patients, they often do not fully recognize
all the implications of obesity and its related disease
states, OSA and diabetes. It is through this increased
awareness that the care of obese patients can be improved.
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